Electrocatalyst

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Electrocatalyst 

 

A platinum cathode electrocatalyst's stability is measured.

An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.

Practical Electrocatalysts

Chloralkali Process

The chloralkali process is a large scale application that uses electrocatalysts. This technology supplies most of the chlorine and sodium hydroxide required by many industries. The cathode is a mixed metal oxide clad titanium anode (also called a dimensionally stable anode).

Basic membrane cell used in the electrolysis of brine. At the anode (A), chloride (Cl⁻) is oxidized to chlorine. The ion-selective membrane (B) allows the counterion Na+ to freely flow across, but prevents anions such as hydroxide (OH⁻) and chloride from diffusing across. At the cathode (C), water is reduced to hydroxide and hydrogen gas. The net process is the electrolysis of an aqueous solution of NaCl into industrially useful products sodium hydroxide (NaOH) and chlorine gas.

Electrofluorination

Many organofluorine compounds are produced by electrofluorination. One manifestation of this technology is the Simons process, which can be described as:

R₃C–H + HF → R₃C–F + H₂

In the course of a typical synthesis, this reaction occurs once for each C–H bond in the precursor. The cell potential is maintained near 5–6 V. The anode, the electrocatalyst, is nickel-plated.

Hydrodimerization of acrylonitrile

Acrylonitrile is converted to adiponitrile on an industrial scale via electrocatalysis.

Background and Theory

In general, a catalyst is an agent that increases the speed of a chemical reaction without being consumed by a reaction. Thermodynamically, a catalyst lowers the activation energy required for a chemical reaction to take place. An electrocatalyst is a catalyst that affects the activation energy of an electrochemical reaction. Shown below is the activation energy of chemical reactions as it relates to the energies of products and reactants. The activation energy in electrochemical processes is related to the potential, i.e. voltage, at which a reaction occurs. Thus, electrocatalysts frequently change the potential at which oxidation and reduction processes are observed. Alternatively, an electrocatalyst can be thought of as an agent that facilitates a specific chemical interaction at an electrode surface. Given that electrochemical reactions occur when electrons are passed from one chemical species to another, favorable interactions at an electrode surface increase the likelihood of electrochemical transformations occurring, thus reducing the potential required to achieve these transformations.

Potential energy diagram for a reaction with and without a catalyst. A catalyst increases the rate of a reaction by lowering the activation energy of a reaction without being consumed in the reaction. An electrocatalyst lowers the activation energy of an electrochemical reaction, often lowering the electric potential at which the reaction occurs.

Electrocatalysts can be evaluated according to three figures of merit: activity, stability, and selectivity. The activity of electrocatalysts can be assessed quantitatively by understanding how much current density is generated, and therefore how fast a reaction is taking place, for a given applied potential. This relationship is described with the Tafel equation. In assessing the stability of electrocatalysts, the ability of catalysts to withstand the potentials at which transformations are occurring is crucial. The selectivity of electrocatalysts refers to their preferential interaction with particular substrates, and their generation of a single product. Selectivity can be quantitatively assessed through a selectivity coefficient, which compares the response of the material to the desired analyte or substrate with the response to other interferents.

In many electrochemical systems, including galvanic cells, fuel cells and various forms of electrolytic cells, a drawback is that they can suffer from high activation barriers. The energy diverted to overcome these activation barriers is transformed into heat. In most exothermic combustion reactions this heat would simply propagate the reaction catalytically. In a redox reaction, this heat is a useless byproduct lost to the system. The extra energy required to overcome kinetic barriers is usually described in terms of low faradaic efficiency and high overpotentials. In these systems, each of the two electrodes and its associated half-cell would require its own specialized electrocatalyst.

Half-reactions involving multiple steps, multiple electron transfers, and the evolution or consumption of gases in their overall chemical transformations, will often have considerable kinetic barriers. Furthermore, there is often more than one possible reaction at the surface of an electrode. For example, during the electrolysis of water, the anode can oxidize water through a two electron process to hydrogen peroxide or a four electron process to oxygen. The presence of an electrocatalyst could facilitate either of the reaction pathways.

 

Types of electrocatalyst materials, including homogeneous and heterogeneous electrocatalysts.

Homogeneous Electrocatalysts

A homogeneous electrocatalyst is one that is present in the same phase of matter as the reactants, for example, a water-soluble coordination complex catalyzing an electrochemical conversion in solution. This technology is not practiced commercially, but is of research interest.

Synthetic Coordination Complexes

Many complexes catalyze electrochemical reactions. For example, cobalt porphyrins and cobalt polypyridines show high (>80%) Faradaic yields for the hydrogen evolution reaction.

Examples of transition metal complexes that serve as homogeneous electrocatalysts.

Enzymes

Some enzymes can function as electrocatalysts. Nitrogenase, an enzyme that contains a MoFe cluster, can be leveraged to fix atmospheric nitrogen, i.e. convert nitrogen gas into molecules such as ammonia. Immobilizing the protein onto an electrode surface and employing an electron mediator greatly improves the efficiency of this process. The effectiveness of bioelectrocatalysts generally depends on the ease of electron transport between the active site of the enzyme and the electrode surface. Other enzymes provide insight for the development of synthetic catalysts. For example, formate dehydrogenase, a nickel-containing enzyme, has inspired the development of synthetic complexes with similar molecular structures for use in CO₂ reduction. Microbial fuel cells are another way that biological systems can be leveraged for electrocatalytic applications. Microbial-based systems leverage the metabolic pathways of an entire organism, rather than the activity of a specific enzyme, meaning that they can catalyze a broad range of chemical reactions. Microbial fuel cells can derive current from the oxidation of substrates such as glucose, and be leveraged for processes such as CO₂ reduction.

Heterogeneous Electrocatalysts

A heterogeneous electrocatalyst is one that is present in a different phase of matter from the reactants, for example, a solid surface catalyzing a reaction in solution. Different types of heterogeneous electrocatalyst materials are shown above in green. Since heterogeneous electrocatalytic reactions need an electron transfer between the solid catalyst (typically a metal) and the electrolyte, which can be a liquid solution but also a polymer or a ceramic capable of ionic conduction, the reaction kinetics depend on both the catalyst and the electrolyte as well as on the interface between them. The nature of the electrocatalyst surface determines some properties of the reaction including rate and selectivity.

Bulk Materials

Electrocatalysis can occur at the surface of some bulk materials, such as platinum metal. Bulk metal surfaces of gold have been employed for the decomposition methanol for hydrogen production. Water electrolysis is conventionally conducted at inert bulk metal electrodes such as platinum or iridium. The activity of an electrocatalyst can be tuned with a chemical modification, commonly obtained by alloying two or more metals. This is due to a change in the electronic structure, especially in the d band which is considered to be responsible for the catalytic properties of noble metals.

Nanomaterials

Nanoparticles

A variety of nanoparticle materials have been demonstrated to promote various electrochemical reactions, although none have been commercialized. These catalysts can be tuned with respect to their size and shape, as well as the surface strain.

Electronic density difference of a Cl atom adsorbed on a Cu(111) surface obtained with a DFT simulation.

Also, higher reaction rates can be achieved by precisely controlling the arrangement of surface atoms: indeed, in nanometric systems, the number of available reaction sites is a better parameter than the exposed surface area in order to estimate electrocatalytic activity. Sites are the positions where the reaction could take place; the likelihood of a reaction to occur in a certain site depends on the electronic structure of the catalyst, which determines the adsorption energy of the reactants together with many other variables not yet fully clarified.

According to the TSK model, the catalyst surface atoms can be classified as terrace, step or kink atoms according to their position, each characterized by a different coordination number. In principle, atoms with lower coordination number (kinks and defects) tend to be more reactive and therefore adsorb the reactants more easily: this may promote kinetics but could also depress it if the adsorbing species isn't the reactant, thus inactivating the catalyst. Advances in nanotechnology make it possible to surface engineer the catalyst so that just some desired crystal planes are exposed to reactants, maximizing the number of effective reaction sites for the desired reaction.

To date, a generalized surface dependence mechanism cannot be formulated since every surface effect is strongly reaction-specific. A few classifications of reactions based on their surface dependence have been proposed but there are still many exceptions that do not fall into them.

Particle Size Effect

An example of a particle-size effect: the number of reaction sites of different kinds depends on the size of the particle. In this four FCC nanoparticles model, the kink site between (111) and (100) planes (coordination number 6, represented by golden spheres) is 24 for all of the four different nanoparticles, while the number of other surface sites varies.

The interest in reducing as much as possible the costs of the catalyst for electrochemical processes led to the use of fine catalyst powders since the specific surface area increases as the average particle size decreases. For instance, most common PEM fuel cells and electrolyzers design is based on a polymeric membrane charged in platinum nanoparticles as an electrocatalyst (the so-called platinum black).

Although the surface area to volume ratio is commonly considered to be the main parameter relating electrocatalyst size with its activity, to understand the particle-size effect, several more phenomena need to be taken into account:

• Equilibrium shape: for any given size of a nanoparticle there is an equilibrium shape which exactly determines its crystal planes
• Reaction sites relative number: a given size for a nanoparticle corresponds to a certain number of surface atoms and only some of them host a reaction site
• Electronic structure: below a certain size, the work function of a nanoparticle changes and its band structure fades away
• Defects: the crystal lattice of a small nanoparticle is perfect; thus, reactions enhanced by defects as reaction sites get slowed down as the particle size decreases
• Stability: small nanoparticles have the tendency to lose mass due to the diffusion of their atoms towards bigger particles, according to the Ostwald ripening phenomenon
• Capping agents: in order to stabilize nanoparticles it is necessary a capping layer, therefore part of their surface is unavailable for reactants
• Support: nanoparticles are often fixed onto a support in order to stay in place, therefore part of their surface is unavailable for reactants

Carbon-Based Materials

Carbon nanotubes and graphene-based materials can be used as electrocatalysts. The carbon surfaces of graphene and carbon nanotubes are well suited to the adsorption of many chemical species, which can promote certain electrocatalytic reactions. In addition, their conductivity means they are good electrode materials. Carbon nanotubes have a very high surface area, maximizing surface sites at which electrochemical transformations can occur. Graphene can also serve as a platform for constructing composites with other kinds of nanomaterials such as single atom catalysts. Because of their conductivity, carbon-based materials can potentially replace metal electrodes to perform metal-free electrocatalysis.

Framework Materials

Metal—organic frameworks (MOFs), especially conductive frameworks, can be used as electrocatalysts for processes such as CO₂ reduction and water splitting. MOFs provide potential active sites at both metal centers and organic ligand sites. They can also be functionalized, or encapsulate other materials such as nanoparticles. MOFs can also be combined with carbon-based materials to form electrocatalysts. Covalent organic frameworks (COFs), particularly those that contain metals, can also serve as electrocatalysts. COFs constructed from cobalt porphyrins demonstrated the ability to reduce carbon dioxide to carbon monoxide.

However, many MOFs are known unstable in chemical and electrochemical conditions, making it difficult to tell if MOFs are actually catalysts or precatalysts. The real active sites of MOFs during electrocatalysis need to be analyzed comprehensively.

Research on Electrocatalysis

Water Splitting/ Hydrogen Evolution

A schematic of a hydrogen fuel cell. To supply hydrogen, electrocatalytic water splitting is commonly employed.

 

Main article: Electrolysis of water

Hydrogen and oxygen can be combined through by the use of a fuel cell. In this process, the reaction is broken into two half reactions which occur at separate electrodes. In this situation the reactant's energy is directly converted to electricity. Useful energy can be obtained from the thermal heat of this reaction through an internal combustion engine with an upper efficiency of 60% (for compression ratio of 10 and specific heat ratio of 1.4) based on the Otto thermodynamic cycle. It is also possible to combine the hydrogen and oxygen through redox mechanism as in the case of a fuel cell. In this process, the reaction is broken into two half-reactions which occur at separate electrodes. In this situation the reactant's energy is directly converted to electricity.

The standard reduction potential of hydrogen is defined as 0V, and frequently referred to as the standard hydrogen electrode (SHE).

Half Reaction	Reduction Potential Eored (V)
2H+ + 2e− → H2 (g)	≡ 0
O2(g) + 4H+ + 4e− → 2H2O(l)	+1.23

HER can be promoted by many catalysts.

Carbon Dioxide Reduction

Main article: Electrochemical reduction of carbon dioxide

Electrocatalysis for CO₂ reduction is not practiced commercially but remains a topic of research. The reduction of CO₂ into useable products is a potential way to combat climate change. Electrocatalysts can promote the reduction of carbon dioxide into methanol and other useful fuel and stock chemicals. The most valuable reduction products of CO₂ are those that have a higher energy content, meaning that they can be reused as fuels. Thus, catalyst development focuses on the production of products such as methane and methanol. Homogeneous catalysts, such as enzymes and synthetic coordination complexes have been employed for this purpose. A variety of nanomaterials have also been studied for CO₂ reduction, including carbon-based materials and framework materials.

Ethanol-Powered Fuel Cells

Aqueous solutions of methanol can decompose into CO₂ hydrogen gas, and water. Although this process is thermodynamically favored, the activation barrier is extremely high, so in practice this reaction is not typically observed. However, electrocatalysts can speed up this reaction greatly, making methanol a possible route to hydrogen storage for fuel cells. Electrocatalysts such as gold, platinum, and various carbon-based materials have been shown to effectively catalyze this process. An electrocatalyst of platinum and rhodium on carbon backed tin-dioxide nanoparticles can break carbon bonds at room temperature with only carbon dioxide as a by-product, so that ethanol can be oxidized into the necessary hydrogen ions and electrons required to create electricity.

Chemical synthesis

Electrocatalysts are used to promote certain chemical reactions to obtain synthetic products. Graphene and graphene oxides have shown promise as electrocatalytic materials for synthesis. Electrocatalytic methods also have potential for polymer synthesis. Electrocatalytic synthesis reactions can be performed under a constant current, constant potential, or constant cell-voltage conditions, depending on the scale and purpose of the reaction.

Viral vector

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Viral_vector

Viral vectors are tools commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism (in vivo) or in cell culture (in vitro). Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect. Delivery of genes or other genetic material by a vector is termed transduction and the infected cells are described as transduced. Molecular biologists first harnessed this machinery in the 1970s. Paul Berg used a modified SV40 virus containing DNA from the bacteriophage λ to infect monkey kidney cells maintained in culture.

In addition to their use in molecular biology research, viral vectors are used for gene therapy and the development of vaccines.

Key properties of a viral vector

Viral vectors are tailored to their specific applications but generally share a few key properties.

• Safety: Although viral vectors are occasionally created from pathogenic viruses, they are modified in such a way as to minimize the risk of handling them. This usually involves the deletion of a part of the viral genome critical for viral replication. Such a virus can efficiently infect cells but, once the infection has taken place, requires a helper virus to provide the missing proteins for production of new virions.
• Low toxicity: The viral vector should have a minimal effect on the physiology of the cell it infects.
• Stability: Some viruses are genetically unstable and can rapidly rearrange their genomes. This is detrimental to predictability and reproducibility of the work conducted using a viral vector and is avoided in their design.
• Cell type specificity: Most viral vectors are engineered to infect as wide a range of cell types as possible. However, sometimes the opposite is preferred. The viral receptor can be modified to target the virus to a specific kind of cell. Viruses modified in this manner are said to be pseudotyped.
• Identification: Viral vectors are often given certain genes that help identify which cells took up the viral genes. These genes are called markers. A common marker is resistance to a certain antibiotic. The cells can then be isolated easily, as those that have not taken up the viral vector genes do not have antibiotic resistance, and so cannot grow in a culture with the relevant antibiotic present.

Applications

Basic research

Viral vectors were originally developed as an alternative to transfection of naked DNA for molecular genetics experiments. Compared to traditional methods of transfection (like calcium phosphate precipitation), transduction can ensure that nearly 100% of cells are infected without severely affecting cell viability. Furthermore, some viruses integrate into the cell genome facilitating stable expression.

Protein coding genes can be expressed using viral vectors, commonly to study the function of the particular protein. Viral vectors, especially retroviruses, stably expressing marker genes such as GFP are widely used to permanently label cells to track them and their progeny, for example in xenotransplantation experiments, when cells infected in vitro are implanted into a host animal.

Gene insertion, which can be done with viral vectors, is cheaper to carry out than gene knockout. But as gene silencing, an effect that may be intended with gene insertion, is sometimes non-specific and has off-target effects on other genes, it hence provides less reliable results. Animal host vectors also play an important role.

Gene therapy

Main article: Gene therapy

Gene therapy is a technique for correcting defective genes responsible for disease development. In the future, gene therapy may provide a way to cure genetic disorders, such as severe combined immunodeficiency, cystic fibrosis or even haemophilia A. Because these diseases result from mutations in the DNA sequence for specific genes, gene therapy trials have used viruses to deliver unmutated copies of these genes to the cells of the patient's body. There have been a huge number of laboratory successes with gene therapy. However, several problems of viral gene therapy must be overcome before it gains widespread use. Immune response to viruses not only impedes the delivery of genes to target cells but can cause severe complications for the patient. In one of the early gene therapy trials in 1999 this led to the death of Jesse Gelsinger, who was treated using an adenoviral vector.

Some viral vectors, for instance gamma-retroviruses, insert their genomes at a seemingly random location on one of the host chromosomes, which can disturb the function of cellular genes and lead to cancer. In a severe combined immunodeficiency retroviral gene therapy trial conducted in 2002, four of the patients developed leukemia as a consequence of the treatment; three of the patients recovered after chemotherapy. Adeno-associated virus-based vectors are much safer in this respect as they always integrate at the same site in the human genome, with applications in various disorders, such as Alzheimer's disease.

Vaccines

Main article: Viral vector vaccine

A live vector vaccine is a vaccine that uses an organism (typically virus or bacterium) that does not cause disease to transport the pathogen genes into the body in order to stimulate an immune response. Viruses expressing pathogen proteins are currently being developed as vaccines against these pathogens, based on the same rationale as DNA vaccines. The genes used in such vaccines are usually antigen coding surface proteins from the pathogenic organism. They are then inserted into the genome of a non-pathogenic organism, where they are expressed on the organism's surface and can elicit an immune response.

Unlike attenuated vaccines, viral vector vaccines lack other pathogen genes required for replication, so infection by the pathogen is impossible. Adenoviruses are being actively developed as vaccine vectors.

Medicine delivery

A strain of canarypox virus modified to carry feline interleukin-2 is used to treat cats with fibrosarcoma.

Types

Retroviruses

Main article: Retroviruses

Retroviruses are one of the mainstays of current gene therapy approaches. The recombinant retroviruses such as the Moloney murine leukemia virus have the ability to integrate into the host genome in a stable fashion. They contain a reverse transcriptase to make a DNA copy of the RNA genome, and an integrase that allows integration into the host genome. They have been used in a number of FDA-approved clinical trials such as the SCID-X1 trial.

Retroviral vectors can either be replication-competent or replication-defective. Replication-defective vectors are the most common choice in studies because the viruses have had the coding regions for the genes necessary for additional rounds of virion replication and packaging replaced with other genes, or deleted. These virus are capable of infecting their target cells and delivering their viral payload, but then fail to continue the typical lytic pathway that leads to cell lysis and death.

Conversely, replication-competent viral vectors contain all necessary genes for virion synthesis, and continue to propagate themselves once infection occurs. Because the viral genome for these vectors is much lengthier, the length of the actual inserted gene of interest is limited compared to the possible length of the insert for replication-defective vectors. Depending on the viral vector, the typical maximum length of an allowable DNA insert in a replication-defective viral vector is usually about 8–10 kB. While this limits the introduction of many genomic sequences, most cDNA sequences can still be accommodated.

The primary drawback to use of retroviruses such as the Moloney retrovirus involves the requirement for cells to be actively dividing for transduction. As a result, cells such as neurons are very resistant to infection and transduction by retroviruses.

There is concern that insertional mutagenesis due to integration into the host genome might lead to cancer or leukemia. This concern remained theoretical until gene therapy for ten SCID-X1 patients using Moloney murine leukemia virus resulted in two cases of leukemia caused by activation of the LMO2 oncogene due to nearby integration of the vector.

Lentiviruses

Main article: Lentivirus

 

Packaging and transduction by a lentiviral vector.

Lentiviruses are a subclass of Retroviruses. They are sometimes used as vectors for gene therapy thanks to their ability to integrate into the genome of non-dividing cells, which is the unique feature of Lentiviruses as other Retroviruses can infect only dividing cells. The viral genome in the form of RNA is reverse-transcribed when the virus enters the cell to produce DNA, which is then inserted into the genome at a random position (recent findings actually suggest that the insertion of viral DNA is not random but directed to specific active genes and related to genome organisation) by the viral integrase enzyme. The vector, now called a provirus, remains in the genome and is passed on to the progeny of the cell when it divides. There are, as yet, no techniques for determining the site of integration, which can pose a problem. The provirus can disturb the function of cellular genes and lead to activation of oncogenes promoting the development of cancer, which raises concerns for possible applications of lentiviruses in gene therapy. However, studies have shown that lentivirus vectors have a lower tendency to integrate in places that potentially cause cancer than gamma-retroviral vectors. More specifically, one study found that lentiviral vectors did not cause either an increase in tumor incidence or an earlier onset of tumors in a mouse strain with a much higher incidence of tumors. Moreover, clinical trials that utilized lentiviral vectors to deliver gene therapy for the treatment of HIV experienced no increase in mutagenic or oncologic events.

For safety reasons lentiviral vectors never carry the genes required for their replication. To produce a lentivirus, several plasmids are transfected into a so-called packaging cell line, commonly HEK 293. One or more plasmids, generally referred to as packaging plasmids, encode the virion proteins, such as the capsid and the reverse transcriptase. Another plasmid contains the genetic material to be delivered by the vector. It is transcribed to produce the single-stranded RNA viral genome and is marked by the presence of the ψ (psi) sequence. This sequence is used to package the genome into the virion.

Adenoviruses

Main article: Adenovirus

As opposed to lentiviruses, adenoviral DNA does not integrate into the genome and is not replicated during cell division. This limits their use in basic research, although adenoviral vectors are still used in in vitro and also in vivo experiments. Their primary applications are in gene therapy and vaccination. Since humans commonly come in contact with adenoviruses, which cause respiratory, gastrointestinal and eye infections, majority of patients have already developed neutralizing antibodies which can inactivate the virus before it can reach the target cell. To overcome this problem scientists are currently investigating adenoviruses that infect different species to which humans do not have immunity, for example, the chimpanzee adenovirus used as a vector to transport SARS-CoV-2 spike gene in Oxford AstraZeneca COVID vaccine. PEGylation of adenoviruses for gene therapy can help prevent adverse reactions due to pre-existing adenovirus immunity.

Adeno-associated viruses

Main article: Adeno-associated virus

Adeno-associated virus (AAV) is a small virus that infects humans and some other primate species. AAV is not currently known to cause disease, and causes a very mild immune response. AAV can infect both dividing and non-dividing cells and may incorporate its genome into that of the host cell. Moreover, AAV mostly stays as episomal (replicating without incorporation into the chromosome); performing long and stable expression. These features make AAV a very attractive candidate for creating viral vectors for gene therapy. However, AAV can only bring up to 5kb which is considerably small compared to AAV's original capacity.

Adeno-associated viral vectors have been engineered to evade virus recognition by TLR9 receptors by incorporating TLR9-inhibiting genes into the vector.

Furthermore, because of its potential use as a gene therapy vector, researchers have created an altered AAV called self-complementary adeno-associated virus (scAAV). Whereas AAV packages a single strand of DNA and requires the process of second-strand synthesis, scAAV packages both strands which anneal together to form double stranded DNA. By skipping second strand synthesis scAAV allows for rapid expression in the cell. Otherwise, scAAV carries many characteristics of its AAV counterpart.

Plant viruses

Main article: Plant virus

Plant viruses can be used to engineer viral vectors, tools commonly used to deliver genetic material into plant cells; they are also sources of biomaterials and nanotechnology devices. Tobacco mosaic virus (TMV) is the first virus to be discovered. Viral vectors based on tobacco mosaic virus include those of the magnICON and TRBO plant expression technologies.

Hybrids

Hybrid vectors are vector viruses that are genetically engineered to have qualities of more than one vector. Viruses are altered to avoid the shortcomings of typical viral vectors, which may have limited loading capacity, immunogenicity, genotoxicity, and fail to support long-term adequate transgenic expression. Through the replacement of undesirable elements with desired abilities, hybrid vectors may in the future outperform standard transfection vectors in terms of safety and therapeutic efficiency.

Challenges in application

The choice of a viral vector to deliver genetic material to cells comes with some logistical problems. There are a limited number of viral vectors available for therapeutic use. Any of these few viral vectors can cause the body to develop an immune response if the vector is seen as a foreign invader. Once used, the viral vector cannot be effectively used in the patient again because it will be recognized by the body. If the vaccine or gene therapy fails in clinical trials, the virus can't be used again in the patient for a different vaccine or gene therapy in the future.

Pre-existing immunity against the viral vector could also be present in the patient, rendering the therapy ineffective for that patient. Because priming with a naked DNA vaccine and boosting with a viral vector results in a robust immune response via yet indefinite mechanism(s), despite pre-existing viral vector immunity, this vaccination strategy can counteract this problem. However, this method may present another expense and obstacle in the vaccine distribution process. Pre-existing immunity may also be challenged by increasing vaccine dose or changing the vaccination route.

Some shortcomings of viral vectors (such as genotoxicity and low transgenic expression) can be overcome through the use of hybrid vectors.

Uncontacted peoples

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Uncontacted_peoples 

Members of an uncontacted tribe photographed in 2012 near Feijó in Acre, Brazil

 

A map of uncontacted peoples, around the start of the 21st century

Uncontacted peoples are communities or groups of indigenous peoples living without sustained contact to neighbouring communities and the world community; groups who decide to remain uncontacted are referred to as indigenous peoples in voluntary isolation. Legal protections make estimating the total number of uncontacted tribes challenging, but estimates from the Inter-American Commission on Human Rights in the UN and the non-profit group Survival International point to between 100 and 200 tribes numbering up to 10,000 individuals. A majority of tribes live in South America, particularly Brazil, where the Brazilian government and National Geographic estimate between 77 and 84 tribes reside.

Knowledge of uncontacted peoples comes mostly from encounters with neighbouring indigenous communities and from aerial footage.

Definition

Most groups of indigenous peoples have had contact with other peoples, particularly since the Colonial era with early colonial settlers and explorers arriving, and as such have not been truly "uncontacted".

However some have remained largely isolated, therefore international organizations, including the United Nations, have defined such indigenous peoples in isolation, sharing several key characteristics:

• They are self-sufficient and highly integrated with their environment.
• They are unfamiliar with mainstream society and how to function in it.
• They are highly vulnerable and in most cases at risk of extinction.

International organizations have focused on these characteristics because they highlight the importance of protecting indigenous peoples' environment and lands, the importance of protecting them from exploitation or abuse, and the importance of no contact to prevent the spread of modern diseases.

A 2009 UN report also classified "peoples in initial contact" as sharing the same characteristics, but beginning to regularly communicate with and integrate into mainstream society.

To highlight their agency in staying uncontacted or isolated, international organizations emphasize calling them "indigenous peoples in isolation" or "in voluntary isolation". Otherwise they have also been called "hidden peoples", "uncontacted tribes", or, incorrectly, "lost tribes".

Relations with outsiders

Opinions differ between anthropologists, national governments and the medical community on how to interact with uncontacted peoples.

However, historic exploration and abuse at the hands of the majority group have led many governments to give uncontacted people, along with their lands, legal protection. Many indigenous groups live on national forests or protected grounds, such as the Vale do Javari in Brazil or the North Sentinel Island in India.

Uncontacted peoples in the Acre region of Brazil

Much of the contention over uncontacted peoples has stemmed from governments' desires to extract natural resources. In the 1960s and 1970s Brazil's federal government attempted to assimilate and integrate native groups living in the Amazon jungle in order to use their lands for farming. Their efforts were met with mixed success and criticism, until in 1987 Brazil created the Department of Isolated Indians inside of FUNAI (Fundação Nacional do Índio), Brazil's Indian Agency. FUNAI was successful in securing protected lands which have allowed certain groups to remain relatively uncontacted until the present day.

A different outcome occurred in Colombia when the Nukak tribe of indigenous people was contacted by an evangelical group. The tribe was receptive to trade, and eventually moved in order to have closer contact with settlers. This led to an outbreak of respiratory infections, violent clashes with narco-traffickers, and the death of hundreds of the Nukak, more than half of the tribe. Eventually the Colombian government forcibly relocated the tribe to a nearby town where they received food and government support, but were reported as living in poverty.

The threats to the Nukak tribe are generally shared by all peoples in isolation, such as the outside world's desire to exploit their lands. This can include lumbering, ranching and farming, land speculation, oil prospecting and mining, and poaching. For example, Peruvian President Alan García claimed in 2007 that uncontacted groups were only a "fabrication of environmentalists bent on halting oil and gas exploration". As recently as 2016 a Chinese subsidiary mining company in Bolivia ignored signs that they were encroaching on uncontacted tribes, and attempted to cover it up. In addition to commercial pursuits, missionaries can also pose a threat.

It was those threats, combined with attacks on their tribe by illegal cocaine traffickers, that led a group of Acre Indians to make contact with a village in Brazil, and subsequently with the Brazilian government in 2014. This behaviour suggests that many tribes are aware of the outside world, and choose not to make contact unless motivated by fear or self-interest. Satellite images suggest that some tribes intentionally migrate away from roads or logging operations in order to remain secluded.

Indigenous rights activists have often advocated indigenous peoples in isolation to be left alone, saying that contact will interfere with their right to self-determination as peoples. On the other hand, experience in Brazil suggests isolating peoples might even want to have trading relationships and positive social connections with others, but choose isolation out of fear of conflict or exploitation. The Brazilian state organization National Indian Foundation (FUNAI) in collaboration with anthropological experts has chosen to make controlled contact with tribes in initial contact. The organization operates 15 trading posts throughout protected territory at which tribes can trade for metal tools and cooking instruments. The organization also steps in to prevent some conflicts and deliver vaccinations. However, FUNAI has been critical of political will in Brazil, reporting that it only got 15% of its requested budget in 2017. In 2018, after consensus among field agents, FUNAI released videos and images of several tribes under their protection. Although the decision was criticized, the director of the isolated Indian department, Bruno Pereira, responded that “The more the public knows and the more debate around the issue, the greater the chance of protecting [isolated Indians] and their lands”. He shared that the organization has been facing mounting political pressure to open up lands to commercial companies. He also justified the photography by explaining that FUNAI was investigating a possible massacre against the Flechieros tribe.

Right to self-isolation

Recognizing the myriad problems with contact, the United Nations Human Rights Council in 2009 and the Inter-American Commission on Human Rights in 2013 introduced guidelines and recommendations that included a right to choose self-isolation.

India

Aerial photograph of North Sentinel Island

India is home to two uncontacted tribes, both living on islands in the Andaman Island chain.

The Sentinelese

The Sentinelese people of North Sentinel Island, which lies near South Andaman Island in the Bay of Bengal, reject contact. Attempts to contact them have usually been rebuffed, sometimes with lethal force. Their language is markedly different from other languages on the Andamans, which suggests that they have been isolated for thousands of years. They have been called by experts the most isolated people in the world, and they are likely to remain so.

During the 2001 Census of India, a joint expedition conducted during 23–24 February 2001 identified at least a few dozen individuals, but it was not exhaustive. Helicopter surveys after the 2004 Indian Ocean tsunami confirmed the Sentinelese had survived, and there have been a few limited interactions with them since. The local Andaman and Nicobar administration has adopted an "eyes-on and hands-off" policy to ensure that no poachers enter the island. A protocol of circumnavigation of North Sentinel Island has been made and notified in consultation with the Indian government.

However, individuals have occasionally attempted to intrude upon them, although such attempts are against the law. In November 2018, a violent contact made international headlines. American missionary John Allen Chau was killed by the Sentinelese during an illegal expedition to the island, where Chau had intended to convert the tribe to Christianity.

The Andamanese

Another Andamanese tribe, the Jarawas, live on the main islands, largely isolated from other peoples. They are thought to number a few hundred people.

South America

Bolivia

The Toromona are an uncontacted people living near the upper Madidi River and the Heath Rivers in northwestern Bolivia. The government has created an "exclusive, reserved, and inviolable" portion of the Madidi National Park to protect the Toromona. It was this group which faced encroachment from a Chinese mining company in 2016.

Among the Ayoreo people of the Gran Chaco are a small number of uncontacted nomadic hunter-gatherers in the Kaa-Iya del Gran Chaco National Park and Integrated Management Natural Area.

Pacahuaras are believed to be living in voluntary isolation in Pando Department.

Brazil

Members of an uncontacted tribe in Acre, Brazil, in 2009

Until the 1970s Brazil attempted unsuccessfully to move anyone on lands that could be commercially cultivated. Then, in 1987, it set up the Department of Isolated Indians inside FUNAI, facilitating the work of Sydney Possuelo and José Carlos Meirelles, and declared the Vale do Javari perpetually sealed off, encompassing an area of 85,444.82 km ² (32,990 mi ²). In 2007, FUNAI reported the presence of 67 uncontacted indigenous peoples in Brazil, up from 40 in 2005.

The Awá are people living in the eastern Amazon rainforest. There are approximately 350 members, and 100 of them have no contact with the outside world. They are considered highly endangered because of conflicts with logging interests in their territory.

The Kawahiva live in the north of Mato Grosso. They are constantly on the move and have little contact with outsiders. Thus, they are known primarily from physical evidence they have left behind: arrows, baskets, hammocks, and communal houses.

The Korubu live in the lower Vale do Javari in the western Amazon Basin. Other tribes may include the Uru-Eu-Wau-Wau, and the Himarimã. There may be uncontacted peoples in Uru-Eu-Uaw-Uaw Indigenous Territory and Kampa Indigenous Territory and Envira River Isolated Peoples.

Recently in 2019 some isolated groups of one to two people came into the media's attention. Two brothers of the Piripkura tribe continue to live alone in the jungle, but initiated contact with FUNAI after a fire they had kept burning for 18 years went out. They were the subsequent focus of the documentary Piripkura. Another man, colloquially called "the man of the holes" lives alone on 8,000 hectares where he has dug hundreds of holes for farming and trapping.

As of 2021, uncontacted peoples in Brazil are threatened by illegal land grabbers, loggers and gold miners, as the government of Jair Bolsonaro has signalled its intention to develop the Amazon and reduce the size of indigenous reservations.

Colombia

With the creation of gigantic tribal reserves and strict patrolling, Colombia is now regarded as one of the countries where uncontacted indigenous people are offered maximum protection.

The Nukak people are nomadic hunter-gatherers living between the Guaviare and Inírida rivers in south-east Colombia at the headwaters of the northwest Amazon basin. There are groups, including the Carabayo, Yuri and the Passé, in Río Puré National Park.

Ecuador

Two isolated indigenous peoples of Ecuador live in the Amazon region: the Tagaeri and the Taromenane. Both are eastern Huaorani peoples living in Yasuni National Park. These semi-nomadic people live in small groups, subsisting on hunting, gathering, and some crops. They are organized into extended families. Since 2007 there is a national policy which mandates: untouchability, self-determination, equality, and no contact. In 2013, more than 20 Taromenane were killed by other Huaorani.

Paraguay

Approximately 100 Ayoreo people, some of whom are in the Totobiegosode tribe, live uncontacted in the forest. They are nomadic, and they hunt, forage, and conduct limited agriculture. They are the last uncontacted peoples south of the Amazon basin, and are in Amotocodie. Threats to them include rampant illegal deforestation. According to Survival International, Brazilian company Yaguarete Porá S.A. is converting thousands of hectares of the Ayoreo-Totobiegosode tribe's ancestral territory into cattle ranching land. The Union of Ayoreo Natives of Paraguay is working for their protection, with support from the Iniciativa Amotocodie.

Peru

The Mashco-Piro are nomadic Arawak hunter-gatherers who inhabit Manú National Park in Peru. In 1998, the International Work Group for Indigenous Affairs estimated their number to be around 100 to 250. They speak a dialect of the Piro languages. Amid incursions on their land, the tribe has made it clear they do not wish to be contacted. As of 2013, all the bands seem to be surviving. Other groups include the Machiguenga, Nanti, Asháninka, Mayoruna, Isconahua, Kapanawa, Yora, Murunahua, Chitonahua, Mastanahua, Kakataibo, and Pananujuri. Many of them speak dialects of Panoan languages. There are five reserves for uncontacted peoples. However, the law designed to protect those peoples does not prevent economic operations there.

Venezuela

In Venezuela some groups from the Hoti, Yanomami, and Piaroa tribes live in relative isolation. The Ministry of Indigenous Peoples has no policies designed to protect these people specifically.

New Guinea

There are over 40 uncontacted tribes living in West Papua region in Indonesia although contact is usually established upon their initial encounter. While it is illegal for journalists and other organizations to enter West Papua, there is no dedicated government agency for the protection of isolated indigenous groups. Human rights organizations including Survival International have argued that there is a need to raise awareness of the existence of uncontacted tribes, for example to prevent the development of infrastructure near their lands. On the other hand, remaining vague about the exact location and size of the tribe may help to avoid encouraging contact.

Uncontacted peoples in modern culture

Uncontacted peoples have been objectified and used to satisfy modern fascinations with claiming first contact and accessing the indigenous peoples' projected state of nature, historically by colonial endeavours and contemporarily by people paying tour operators who offer adventure tours to search isolated peoples out. As such indigenous peoples and their lands have been the object of the search for Prester John, king of a wealthy Christian realm in isolation, and for the Ten Lost Tribes of Israel. Furthermore indigenous peoples in isolation have been identified altogether as part of modernity and how they shape their lives in it as one way of life in the modern world.

Why global warming is good for us

Climate change is creating a greener, safer planet.

Original link:  https://www.spiked-online.com/2022/02/15/why-global-warming-is-good-for-us/?fbclid=IwAR1mE1NII-29ILIqZtXRNp6yZ3KmYKBu-Uz3v_9lE2nSAmTGcut-TEfIyRA

Matt Ridley

15th February 2022

Topics Long-reads Politics Science & Tech

Global warming is real. It is also – so far – mostly beneficial. This startling fact is kept from the public by a determined effort on the part of alarmists and their media allies who are determined to use the language of crisis and emergency. The goal of Net Zero emissions in the UK by 2050 is controversial enough as a policy because of the pain it is causing. But what if that pain is all to prevent something that is not doing net harm?

The biggest benefit of emissions is global greening, the increase year after year of green vegetation on the land surface of the planet. Forests grow more thickly, grasslands more richly and scrub more rapidly. This has been measured using satellites and on-the-ground recording of plant-growth rates. It is happening in all habitats, from tundra to rainforest. In the four decades since 1982, as Bjorn Lomborg points out, NASA data show that global greening has added 618,000 square kilometres of extra green leaves each year, equivalent to three Great Britains. You read that right: every year there’s more greenery on the planet to the extent of three Britains. I bet Greta Thunberg did not tell you that.

The cause of this greening? Although tree planting, natural reforestation, slightly longer growing seasons and a bit more rain all contribute, the big cause is something else. All studies agree that by far the largest contributor to global greening – responsible for roughly half the effect – is the extra carbon dioxide in the air. In 40 years, the proportion of the atmosphere that is CO2 has gone from 0.034 per cent to 0.041 per cent. That may seem a small change but, with more ‘food’ in the air, plants don’t need to lose as much water through their pores (‘stomata’) to acquire a given amount of carbon. So dry areas, like the Sahel region of Africa, are seeing some of the biggest improvements in greenery. Since this is one of the poorest places on the planet, it is good news that there is more food for people, goats and wildlife.

But because good news is no news, green pressure groups and environmental correspondents in the media prefer to ignore global greening. Astonishingly, it merited no mentions on the BBC’s recent Green Planet series, despite the name. Or, if it is mentioned, the media point to studies suggesting greening may soon cease. These studies are based on questionable models, not data (because data show the effect continuing at the same pace). On the very few occasions when the BBC has mentioned global greening it is always accompanied by a health warning in case any viewer might glimpse a silver lining to climate change – for example, ‘extra foliage helps slow climate change, but researchers warn this will be offset by rising temperatures’.

Another bit of good news is on deaths. We’re against them, right? A recent study shows that rising temperatures have resulted in half a million fewer deaths in Britain over the past two decades. That is because cold weather kills about ’20 times as many people as hot weather’, according to the study, which analyses ‘over 74million deaths in 384 locations across 13 countries’. This is especially true in a temperate place like Britain, where summer days are rarely hot enough to kill. So global warming and the unrelated phenomenon of urban warming relative to rural areas, caused by the retention of heat by buildings plus energy use, are both preventing premature deaths on a huge scale.

Surely this will change in the future? Probably not. Britain would have to get much, much hotter for summer mortality to start exceeding winter deaths. Not even Greece manages that. And the statistics show that – as greenhouse-gas theory predicts – on the whole more warming is happening in cold places, in cold seasons and at cold times of day. So winter nighttime temperatures in the global north are rising much faster than summer daytime temperatures in the tropics.

Summer temperatures in the US are changing at half the rate of winter temperatures and daytimes are warming 20 per cent slower than nighttimes. A similar pattern is seen in most countries. Tropical nations are mostly experiencing very slow, almost undetectable daytime warming (outside cities), while Arctic nations are seeing quite rapid change, especially in winter and at night. Alarmists love to talk about polar amplification of average climate change, but they usually omit its inevitable flip side: that tropical temperatures (where most poor people live) are changing more slowly than the average.

A farm worker labours in a field near the town of Arvin, southeast of Bakersfield, California.

But are we not told to expect more volatile weather as a result of climate change? It is certainly assumed that we should. Yet there’s no evidence to suggest weather volatility is increasing and no good theory to suggest it will. The decreasing temperature differential between the tropics and the Arctic may actually diminish the volatility of weather a little.

Indeed, as the Intergovernmental Panel on Climate Change (IPCC) repeatedly confirms, there is no clear pattern of storms growing in either frequency or ferocity, droughts are decreasing slightly and floods are getting worse only where land-use changes (like deforestation or building houses on flood plains) create a problem. Globally, deaths from droughts, floods and storms are down by about 98 per cent over the past 100 years – not because weather is less dangerous but because shelter, transport and communication (which are mostly the products of the fossil-fuel economy) have dramatically improved people’s ability to survive such natural disasters.

The geological record shows greater climatic volatility in cold periods of the Earth’s history than in hot periods. At the peak of recent ice ages, the temperature fluctuated dramatically between years and decades, while decade-long mega-droughts ravaged Africa, drying up Lake Victoria at least twice. Those mega droughts happened 17,000 years ago and 15,000 years ago respectively, when the world was much colder than today and cooler oceans meant failed monsoons. One theory about the invention of farming argues that it was impossible until the climate settled down in the post-glacial warmth of around 10,000 years ago: ‘Recent data from ice- and ocean-core climate proxies show that the last glacial climates were extremely hostile to agriculture – dry, low in atmospheric CO2, and extremely variable on quite short time scales.’ It then became calmer as it became significantly warmer than today between 9,000 and 6,000 years ago, when human civilisation emerged.

The effect of today’s warming (and greening) on farming is, on average, positive: crops can be grown farther north and for longer seasons and rainfall is slightly heavier in dry regions. We are feeding over seven billion people today much more easily than we fed three billion in the 1960s, and from a similar acreage of farmland. Global cereal production is on course to break its record this year, for the sixth time in 10 years.

Nature, too, will do generally better in a warming world. There are more species in warmer climates, so more new birds and insects are arriving to breed in southern England than are disappearing from northern Scotland. Warmer means wetter, too: 9,000 years ago, when the climate was warmer than today, the Sahara was green. Alarmists like to imply that concern about climate change goes hand in hand with concern about nature generally. But this is belied by the evidence. Climate policies often harm wildlife: biofuels compete for land with agriculture, eroding the benefits of improved agricultural productivity and increasing pressure on wild land; wind farms kill birds and bats; and the reckless planting of alien sitka spruce trees turns diverse moorland into dark monoculture.

Meanwhile, real environmental issues are ignored or neglected because of the obsession with climate. With the help of local volunteers I have been fighting to protect the red squirrel in Northumberland for years. The government does literally nothing to help us, while it pours money into grants for studying the most far-fetched and minuscule possible climate-change impacts. Invasive alien species are the main cause of species extinction worldwide (like grey squirrels driving the red to the margins), whereas climate change has yet to be shown to have caused a single species to die out altogether anywhere.

Of course, climate change does and will bring problems as well as benefits. Rapid sea-level rise could be catastrophic. But whereas the sea level shot up between 10,000 and 8,000 years ago, rising by about 60 metres in two millennia, or roughly three metres per century, today the change is nine times slower: three millimetres a year, or a foot per century, and with not much sign of acceleration. Countries like the Netherlands and Vietnam show that it is possible to gain land from the sea even in a world where sea levels are rising. The land area of the planet is actually increasing, not shrinking, thanks to siltation and reclamation.

In January 2020, the UK’s chief scientific adviser organised for some slides to be shown to Boris Johnson to convert him to climate alarmism. Thanks to a freedom of information request, we now know that these slides showed the likely acceleration in sea-level rise under a scenario known as RCP 8.5. This is shocking because RCP 8.5 has long been discredited as a highly implausible future. It was created by piling unrealistic assumptions on to each other in models: coal use increasing tenfold by 2100, population growth accelerating to 12 billion people, innovation drying up and an implausibly high sensitivity of temperature to carbon dioxide. No serious scientist thinks RCP 8.5 represents a likely outcome from ‘business as usual’. Yet those who want to grab media attention by making alarming predictions use it all the time.

Environmentalists don’t get donations or invitations to appear on the telly if they say moderate things. To stand up and pronounce that ‘climate change is real and needs to be tackled, but it’s not happening very fast and other environmental issues are more urgent’ would be about as popular as an MP in Oliver Cromwell’s parliament declaring, ‘The evidence for God is looking a bit weak, and I’m not so very sure that fornication really is a sin’. And I speak as someone who has made several speeches on climate in parliament.

No wonder we don’t hear about the good news on climate change.

Matt Ridley is co-author of Viral: The Search for the Origin of Covid-19, with Alina Chan.