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For the scientific journal named Science, see Science (journal).

The scope of this article is limited to empirical sciences. For mathematical sciences, see mathematics.

Science (from Latin scientia - knowledge) refers to the system of acquiring knowledge – based on empiricism, experimentation, and methodological naturalism. The term science also refers to the organized body of knowledge humans have gained by such research.

Most scientists maintain that scientific investigation must adhere to the scientific method, a process for evaluating empirical knowledge under the working assumption of methodological materialism, which explains observable events in nature as a result of natural causes, rejecting supernatural notions. Less formally, the word science often describes any systematic field of study or the knowledge gained from it. Particular specialized studies that make use of empirical methods are often referred to as sciences as well. This article concentrates on the more specific definition.

Fields of science are commonly classified along two major lines:

• Natural sciences, the study of the natural phenomena including biology;
• Social sciences, the systematic study of human behaviour and society.

Mathematics has both similarities and differences compared to other fields of science, and is sometimes included within a third, separate classification, called formal science. Mathematics is similar to other sciences because it is a rigorous, structured study, (of topics such as quantity, structure, space, and change). It is different because of its method of arriving at its results. Mathematics as a whole is vital to the sciences — indeed major advances in mathematics have often led to major advances in other sciences. Certain aspects of mathematics are indispensable for the formation of hypotheses, theories and laws in discovering and describing how things work (natural sciences) and how people think and act (social sciences).

Science as defined above is sometimes termed pure science to differentiate it from applied science, the application of research to human needs.

The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation.

Etymology

The word science comes from the Latin word, scientia, which means knowledge; thus the phrase scientia potentia est: knowledge is power.

Until the “Age of Enlightenment,” the word science (or its Latin cognate) meant any systematic or exact, recorded knowledge. Science therefore had the same sort of very broad meaning that philosophy had at that time. It should be noted that in some languages, the word corresponding to “science” still carries this meaning.

Centuries ago there was a distinction between “natural philosophy” (a term originally coined by Aristotle and put into use during the period from about 1600-1800 CE), and “moral philosophy” (at that time referring to the studies of human behavior and interaction). In the 1800’s “natural philosophy” gradually gave way to the term “natural science.” “Natural science” was gradually narrowed down to its current use, which typically includes physical sciences and biological sciences. The social sciences, originally “moral philosophy,” are today typically included in under the auspices of science as well, to the extent that these disciplines also use empirical methods. “Moral philosophy” today refers specifically to the branch of philosophy called “ethics.”

Scientific method

Main article: Scientific method

The terms model, hypothesis, theory, and law have different, more specific meanings in science than in colloquial speech. Scientists use model to refer to a description of something, specifically one which can be used to make predictions that can be tested by experiment or observation. A hypothesis is a contention that has been neither well supported nor ruled out by experiment yet. A theory, in the context of science, is a logically self-consistent model or framework for describing the behavior of a certain natural phenomena. A physical law or law of nature is a scientific generalization based on a sufficiently large number of empirical observations that it is taken as fully verified.

The scientific method provides an objective process to find solutions to problems in a number of scientific and technological fields. Often scientists have a preference for one outcome over another, and it is important that this preference does not bias their interpretation. The scientific method attempts to minimize the influence of a scientist’s bias on the outcome of an experiment. This can be achieved by correct experimental design, and thorough peer review of experimental design as well as conclusions of a study.

Scientists never claim absolute knowledge. Unlike a mathematical proof, a proven scientific theory is always open to falsification, if new evidence is presented. Even the most basic and fundamental theories may turn out to be imperfect if new observations are inconsistent with them. Critical to this process is making every relevant aspect of research publicly available, which permits peer review of published results, and also allows ongoing review and repeating of experiments and observations by multiple researchers operating independently of one another. Only by fulfilling these expectations can it be determined how reliable the experimental results are for potential use by others.

Newton’s law of gravitation is a famous example of an established law that was later found not to be universal - it does not hold in experiments involving motion at speeds close to the speed of light or in close proximity of strong gravitational fields. Outside these conditions, Newton’s Laws remain an excellent model of motion and gravity. Since general relativity accounts for all the same phenomena that Newton’s Laws do and more, general relativity is now regarded as a better theory.

Philosophy of science

Main article: Philosophy of science

The philosophy of science seeks to understand the nature and justification of scientific knowledge, and its ethical implications. It has proven difficult to provide a definitive account of the scientific method that can decisively serve to distinguish science from non-science. Thus there are legitimate arguments about exactly where the borders are. There is nonetheless a set of core precepts that have broad consensus among published philosophers of science and within the scientific community at large. (see: Problem of demarcation)

Science is reasoned-based analysis of sensation upon our awareness. As such, the scientific method cannot deduce anything about the realm of reality that is beyond what is observable by existing or theoretical means. When a manifestation of our reality previously considered supernatural is understood in the terms of causes and consequences, it acquires a scientific explanation. For example, God may choose to be hidden from this reality, hence making discussion over God’s existence non-scientific.

Resting on reason and logic, such as the principle of Occam’s Razor, which states a principle of parsimony, scientific theories are formulated and the most promising theory is selected after analysing the collected evidence. Some of the findings of science can be very counter-intuitive. Atomic theory, for example, implies that a granite boulder which appears a heavy, hard, solid, grey object is actually a combination of subatomic particles with none of these properties, moving very rapidly in space where the mass is concentrated in a very small fraction of the total volume. Many of humanity’s preconceived notions about the workings of the universe have been challenged by new scientific discoveries. Quantum mechanics, particularly, examines phenomena that seem to defy our most basic postulates about causality and fundamental understanding of the world around us.

Mathematics and the scientific method

Mathematics is essential to many sciences. The most important function of mathematics in science is the role it plays in the expression of scientific models. Observing and collecting measurements, as well as hypothesizing and predicting, often require mathematical models and extensive use of mathematics. Mathematical branches most often used in science include calculus and statistics, although virtually every branch of mathematics has applications, even “pure” areas such as number theory and topology. Mathematics is most prevalent in physics, but less so in chemistry, biology, and some social sciences.

Some thinkers see mathematicians as scientists, regarding physical experiments as inessential or mathematical proofs as equivalent to experiments. Others do not see mathematics as a science, since it does not require experimental test of its theories and hypotheses, although some theorems can be disproved by contradiction through finding exceptions. (More specifically, mathematical theorems and formulas are obtained by logical derivations which presume axiomatic systems, rather than a combination of empirical observation and method of reasoning that has come to be known as scientific method.) In either case, the fact that mathematics is such a useful tool in describing the universe is a central issue in the philosophy of mathematics.

Further information: Eugene Wigner, and The Unreasonable Effectiveness of Mathematics in the Natural Sciences, and [[]], and [[]], and [[]], and [[]], and [[]], and [[]], and [[]]

Richard Feynman said “Mathematics is not real, but it feels real. Where is this place?”, while Bertrand Russell’s favourite definition of mathematics was “the subject in which we never know what we are talking about nor whether what we are saying is right.”

Goals of science

Science continually seeks to gain increased understanding and, where appropriate, the possibility for control of many specific aspects of the physical world. Its successes in achieving this goal stem directly from its ability to shed light on the foundational mechanisms which underlie nature’s processes. Here, an image of “artificial” bioluminescence which has been induced in a tobacco plant by the use of genetic engineering.

The underlying goal or purpose of science to society and individuals is to produce useful models of reality. It has been said that it is virtually impossible to make inferences from human senses which actually describe what “is.” On the other hand, people can form hypotheses based on observations that they make in the world. By analyzing a number of related hypotheses, scientists can form general theories. These theories benefit society or human individuals who make use of them. For example, Newton’s theories of physics allow us to predict various physical interactions, from the collision of one moving billiard ball with another, to trajectories of space shuttles and satellites. Relativity can be used to calculate the effects of our sun’s gravity on a mass light-years away. The social sciences allow us to predict (with limited accuracy for now) things like economic turbulence and also to better understand human behavior and to produce useful models of society and to work more empirically with government policies. Chemistry and biology together have transformed our ability to use and predict chemical and biological reactions and scenarios. In modern times though, these segregated scientific disciplines (notably the latter two) are more often being used together in conjunction to produce more complete models and tools. One goal of science is to explain and utilize multiple known phenomenon with one theory or set of theories.

Despite popular impressions of science, it is not the goal of science to answer all questions. The goal of the sciences is to answer only those that pertain to perceived reality. Also, science cannot possibly address nonsensical, or untestable questions, so the choice of which questions to answer becomes important. Science does not and can not produce absolute and unquestionable truth. Rather, science tests some aspect of the world and provides a reasonable theory to explain it.

Science is not a source of subjective value judgements, though it can certainly speak to matters of ethics and public policy by pointing to the likely consequences of actions. What one projects from the currently most reasonable scientific hypothesis onto other realms of interest is not a scientific issue, and the scientific method offers no assistance for those who wish to do so. Scientific justification (or refutation) for many things is, nevertheless, often claimed. Of course, value judgements are intrinsic to science itself. For example, scientists value relative truth and knowledge.

In short, science produces useful models which allow us to make often useful predictions. Science attempts to describe what is, but avoids trying to determine what is (which is for practical reasons impossible). Science is a useful tool. . . it is a growing body of understanding that allows us to contend more effectively with our surroundings and to better adapt and evolve as a social whole as well as independently.

Individualism is a tacit assumption underlying most empiricist accounts of science which treat science as if it were purely a matter of a single individual confronting nature, testing and predicting hypotheses. In fact, science is always a collective activity conducted by a scientific community. This can be demonstrated many ways, perhaps the most fundamental and trivial of which is that scientific results must be communicated with language. Thus the values of scientific communities permeate the science they produce.

Where science is practiced

Science is practiced in universities and other scientific institutes as well as in the field; as such it is a solid vocation in academia, but is also practiced by amateurs, who typically engage in the observational part of science.

Workers in corporate research laboratories also practice science, although their results are often deemed trade secrets and not published in public journals. Corporate and university scientists often cooperate, with the university scientists focusing on basic research and the corporate scientists applying their findings to a specific technology of interest to the company. Although generally this method of co-operation has benefited both the advancement of science and the corporations, it has also in some cases lead to ethical problems, when the results arrived at in the course of research have had a negative aspect for the financing corporation. A classical example is the history of health research related to smoking.

Individuals involved in the field of science education argue that the process of science is performed by all individuals as they learn about their world.

The methods of science are also practiced in many places to achieve specific goals. For example:

• Quality control in manufacturing facilities (for example, a microbiologist in a cheese factory ensures that cultures contain the proper species of bacteria)
• Obtaining and processing crime scene evidence (forensics)
• Monitoring compliance with environmental laws
• Performing medical tests to help physicians evaluate the health of their patients
• Investigating the causes of a disaster (such as a bridge collapse or airline crash)

Science and social concerns

A basic understanding of science and technology has become indispensable for anyone living in a city or town, because technology - a product of science - has become an important part of peoples’ lives. Science education aims at increasing common knowledge about science and widening social awareness. The process of learning science begins early in life for many people; school students start learning about science as soon as they acquire basic language skills, and science is always an essential part of curriculum. Science education is also a very vibrant field of study and research. Learning science requires learning its language, which often differs from colloquial language. For example, the terminology of the physical sciences is rich in mathematical jargon, and that of biological studies is rich in Latin names. The language used to communicate science is rich in words pertaining to concepts, phenomena, and processes, which are initally alien to children.

Due to the growing economic value of technology and industrial research, the economy of any modern country depends on its state of science and technology. The governments of most developed and developing countries therefore designate a significant part of their annual budget to science and technology research and communication and often have a science policy and there are some large-scale science projects - often termed as big science. The practice of science by scientists has undergone remarkable changes in the past few centuries. Most scientific research is currently funded by government or corporate bodies. These relatively recent economic factors appear to increase the incentive for some to engage in fraud in reporting results of scientific research [1],[2] often termed scientific misconduct. Occasional instances of verified scientific misconduct, however, are by no means solely modern occurences. (see also: Junk science)

Scientific literature

Main article: Scientific literature

Science has become so pervasive in modern societies that it is generally perceived a necessity to communicate the achievements, news, and dreams of scientists to a wider populace. This need is fulfilled by an enormous range of scientific literature. While scientific journals communicate and document the results of research carried out in universities and various other institutions, and new discoveries in various fields of science, science magazines cater to the needs of a wider readership. Besides these, science books and magazines on science fiction ignite the interest of many more people. A significant fraction of literature in science is also available on the World Wide Web; most reputed journals and newsmagazines have their own websites. Also, a growing number of people are being attracted towards the vocation of science popularization and science journalism.

Fields of science

Natural sciences

See also: #Social sciences

Physics

Chemistry

Earth sciences

Biology

Social sciences

See also: #Natural sciences

Interdisciplinary and applied sciences

Environmental sciences

See also

• Organization and practice of science: International Council of Science (ICSU).
• For an understanding of how these fields came to be: History of science.
• See also scientists for catalogs of people active in each of these fields.

External articles and references

Wikiquote has a collection of quotations related to:

Science

Textbooks

• “GSCE science textbook“. Wikibooks.org
• National Center for Biotechnology Information Bookshelf
• Science & Engineering books for free download

News and articles

News

• Hypography - Science for everyone
• The Science Site a New Zealand-based zine with realtime news feeds (very popular site, with the world’s first Squidcam).
• Daily Science News (German)
• Strange Science and Technology News (Alternative and under-reported video and audio streams with an analysis-ready news network with Online Analytical Processing and embedded Extract, Transform, and Load Data Mining capabilities.)

Articles

• Science-advisor, Online Review of Scientific Articles (Writings of short comments on scientific articles, reviews and letters with a scientific litterature search engine.)
• Popperian Science Henning von Weber
• Most scientific papers are probably wrong - Kurt Kleiner - New Scientist - August 2005
• How NOT to produce Scientific Graphs and Figures - For Science students - Markus Weichselbaum, July 1997

Resources

• “Current Events“. New Scientist Magazine, Reed Business Information Ltd.
• “United States Science Initiative“. Authoritative selected science information provided by U.S. Government agencies, including research and development results.
• “NEWTON BBS Ask A Scientist“. The purpose is to provide a means to have questions answered that are not going to be easily found on the web or within common references.

Further reading

• “Classification of the Sciences“. Dictionary of the History of Ideas.
• Mendoza, Martha, “Allegations of Fake Scientific Research Hit New High; U.S. Fielded Record 274 Scientific Misconduct Complaints Last Year, 50 Percent More Than in 2003“. ABC News (Associated Press), July 10, 2005. (source: spinwatch.org)
• Cole, K. C., “Things your teacher never told you about science (Nine shocking revelations!); Maybe you think that science is devoted to gathering and cataloging facts, and that scientists are a dull, deary lot who don’t know how to have fun. Maybe you should think again.“. Newsday, Long Island, New York, March 23, 1986, pg 21+
• Bauer, Henry H., “Ethics in Science“. Chemistry Department, Virginia Polytechnic Institute and State University, Blacksburg, VA.

Wikimedia Commons has media related to:

Science

Scavenger (chemistry)

A scavenger is a substance added to a mixture in order to remove or inactivate impurities or unwanted reaction products.

In atmospheric chemistry, the most common scavenger is the hydroxyl radical, a short-lived radical produced photolytically in the atmosphere. It is the most important oxidant for carbon dioxide, methane and other hydrocarbons, sulfur dioxide, hydrogen sulfide, and most of other contaminants, removing them from the atmosphere.

In molecular laser isotope separation, methane is used as a scavenger gas for fluorine atoms.

Hydrazine and ascorbic acid are used as oxygen scavenger corrosion inhibitors.

Tocopherol, naringenin, and DEHA are free radical scavengers.

Organotin compounds are used in polymer manufacture as hydrochloric acid scavengers.

See also:

• Synthetic catalytic scavenger

This chemistry article is a stub. You can help Wikipedia by expanding it.

Saturation vapor pressure

The saturation vapor pressure is the static pressure of a vapor when the vapor phase of some material is in equilibrium with the liquid phase of that same material. Frequently vapor pressure and saturated vapor pressure are used synonymously. The saturation vapor pressure of any material is solely dependent on the temperature of that material. As the absolute temperature rises the saturation vapor pressure rises by the same ratio.

An example is water vapor when air is saturated with water vapor. It is the vapor pressure usually found over liquid water, and is a dynamic equilibrium where the rate of condensation of water equals the rate of evaporation of water. In general, the higher the temperature, the higher the vapor pressure. When air is at the saturation vapor pressure, it is said to be at the dew point. Thus, at saturation vapor pressure, air has a relative humidity of 100% and condensation occurs with any increase of water vapor content or a reduction in temperature.

The international standard for saturation vapor pressure over water is given by the Goff-Gratch equation.

Assuming absolutely clean air, if water droplets have a high curvature, which is the case when they are smaller, they require relative humidities in excess of 100% (known as supersaturation) to be at an equilibrium vapor pressure. As droplets approach approximately 20 micrometers, they can survive at 100% relative humidity. As the droplet grows larger by collision and coalescence, it can survive longer because its curvature becomes smoother as the droplet grows. Of course, in actual practice in the Earth’s atmosphere, the ability of water to condense into droplets is generally affected by the presence of hygroscopic dust particles. The relative humidity required for droplets to actually form can be significantly below the real saturation vapor pressure due to the solute effect. Finally, if the temperature becomes low enough in a cloud, as it does in nimbostratus and cumulonimbus clouds, microscopic ice crystals may also serve as condensation nuclei for the cloud in a process known as the Bergeron process.

This climatology/meteorology-related article is a stub. You can help Wikipedia by expanding it.

Saturation (chemistry)

In chemistry, saturation has four different meanings:

1. In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance. This point, the saturation point, depends on the temperature of the liquid as well as the chemical nature of the substances involved. This can be used in the process of recrystallisation to purify a chemical: it is dissolved to the point of saturation in hot solvent, then as the solvent cools and the solubility decreases, excess solute precipitates. Impurities, being present in much lower concentration, do not saturate the solvent and so remain dissolved in the liquid. If a change in conditions (e.g. cooling) mean that the concentration is actually higher than the saturation point, the solution has become supersaturated.
2. In physical chemistry when referring to surface processes, saturation denotes the degree of which a surface is full of something, e.g. base saturation means the fraction of exchangeable cations that are base cations. Similarly, in soil chemistry soil moisture saturation means that all voids are filled with water and thus all surfaces wetted, and nitrogen saturation means that an ecosystem, e.g. a soil, can not store any more nitrogen
3. In organic chemistry, a saturated compound has the maximum amount of hydrogens possible: i.e., no double bonds or, in a hydrocarbon chain, every carbon atom is attached to two hydrogen atoms. Of simple hydrocarbons, alkanes are saturated, and alkenes are unsaturated. In the modern treatment of electronic structure, unsaturated compounds are characterized by pi electron systems. The term is applied similarly to the fatty acid constituents of lipids, where the fat is described as saturated or unsaturated, depending on whether the constituent fatty acids contain carbon-carbon double bonds. Unsaturated is used when any carbon structure contains double or occasionally triple bonds. Many vegetable oils contain fatty acids with one (monounsaturated) or more (polyunsaturated) double bonds in them.
4. In biochemistry the term saturation refers to the fraction of total protein binding sites that are occupied at any given time.

See also

• Saturated fat
• Unsaturated fat

Saturated calomel electrode

The Saturated calomel electrode (SCE) is a reference electrode which uses the reaction between mercury metal and mercury(I) chloride, to fix its potential. The aqueous phase in contact with the mercury and the mercury(I) chloride (Hg₂Cl₂ calomel) is a saturated solution of potassium chloride in water. The electrode is normally linked via a porous frit to the solution in which the other electrode is immersed. This porous frit is a salt bridge.

The Nernst equation is

As the mercury concentration can be worked out from the solubility product

K = [Cl − ]2[Hg2 + + ]

Then as [Cl-] is fixed by the solubility of the potassium chloride then

[Hg2 + + ] = K / [Cl − ]2

As the activity of a solid or liquid which is imissible is 1, also two electrons are transferred per Hg₂ dication the Nernst equation becomes

E = E_Hg2++/Hg - (RT/2F) ln (K / [Cl-]2)

This electrode and the silver/silver chloride reference electrode work in the same way, for both electrodes the redox active metal chloride has a very low solubility and is fixed by the chloride solution.

The SCE is commonly used in pH measurement, cyclic voltammetry and general aqueous electrochemistry.

Rydberg states

Rydberg states are electronically excited states with energies that follow the Rydberg formula as they converge on an an ionic state with an ionization energy. Although the Rydberg formula was developed to describe atomic energy levels, it has been used to describe many other systems that have electronic structure roughly similar to atomic hydrogen. In general, at sufficiently high principle quantum numbers, an excited electron - ionic core system will have the general character of a hydrogenic system and the energy levels will follow the Rydberg formula. Rydberg states have energies converging on the energy of the ion. The ionization threshold energy is the energy required to completely liberate an electron from the ionic core of an atom or molecule.

Rydberg series describe the energy levels associated with partially removing an electron from the ionic core. Each Rydberg series converges on an ionization energy threshold associated with a particular ionic core configuration. These quantized Rydberg energy levels can be associated with the quasiclassical Bohr atomic picture. The closer you get to the ionization threshold energy, the higher the principal quantum number, and the smaller the energy difference between “near threshold Rydberg states.” As the electron is promoted to higher energy levels, the spacial excursion of the electron from the ionic core increases and the system is more like the Bohr quasiclassical picture.

The energy of Rydberg states can be refined by including a correction called the quantum defect in the Rydberg formula. The “quantum defect” correction is associated with the presence of a distributed ionic core. Even for many electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the proton and the electron in the hydrogen atom. The spectroscopic assignment of these states follows the Rydberg formula and they are called Rydberg states of molecules.

References

ATOMIC SPECTRA AND ATOMIC STRUCTURE, Gerhard Herzberg, Prentice-Hall, 1937.

ATOMS & MOLECULES, Martin Karplus and Richard N. Porter, Benjamin & Company, Inc., 1970.

External links

Rydberg molecules

Rydberg molecules are electronically excited species. Electronically excited molecular states are generally quite different in character from electronically excited atomic states. However, particularly for highly electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the proton and the electron in the hydrogen atom. The spectroscopic assignment of these states follows the Rydberg formula and they are called Rydberg states of molecules. Rydberg series are associated with partially removing an electron from the ionic core.

Each Rydberg series of energies converges on an ionization energy threshold associated with a particular ionic core configuration. These quantized Rydberg energy levels can be associated with the quasiclassical Bohr atomic picture. The closer you get to the ionization threshold energy, the higher the principal quantum number, and the smaller the energy difference between near threshold Rydberg states. As the electron is promoted to higher energy levels in a Rydberg series, the spacial excursion of the electron from the ionic core increases and the system is more like the Bohr quasiclassical picture.

The Rydberg states of molecules with low principal quantum numbers can interact with the other excited electronic states of the molecule. This can cause shifts in energy. The assignment of molecular Rydberg states often involves following a Rydberg series from intermediate to high principal quantum numbers. The energy of Rydberg states can be refined by including a correction called the quantum defect in the Rydberg formula. The quantum defect correction can be associated with the presence of a distributed ionic core.

The experimental study of molecular Rydberg states has been conducted with traditional methods for generations. However, the development of laser-based techniques such as Resonance Ionization Spectroscopy has allowed relatively easy access to these Rydberg molecules as intermediates. This is particularly true for Resonance Enhanced Multiphoton Ionization (REMPI) spectroscopy, since multiphoton processes involve different selection rules from single photon processes. The study of high principal quantum number Rydberg states has spawned a number of spectroscopic techniques. These “near threshold Rydberg states” can have long lifetimes, particularly for the higher orbital angular momentum states that do not interact strongly with the ionic core.

References

Molecular Spectra and Molecular Structure, Vol. I, II and III, Gerhard Herzberg, Krieger Pub. Co, revised ed. 1991.

ATOMS & MOLECULES, Martin Karplus and Richard N. Porter, Benjamin & Company, Inc., 1970.

External links

Rubredoxin

Rubredoxins are a class of low-molecular-weight iron-containing proteins found in sulfur-metabolizing bacteria and archaea. Sometimes rubredoxins are classified as iron-sulfur proteins; however, in contrast to iron-sulfur proteins, rubredoxins do not contain inorganic sulfide. Like cytochromes, ferredoxins and Rieske proteins, rubredoxins participate in electron transfer in biological systems.

Structure

The 3-D structures of a number of rubredoxins have been solved. The fold belongs to the α+β class, with 2 α-helices and 2-3 β-strands. Rubredoxin active site contains an iron ion which is coordinated by the sulfurs of four conserved cysteine residues forming an almost regular tetrahedron. This is sometimes denoted as a [1Fe-0S] or an Fe₁S₀ system, in analogy to the nomenclature for iron-sulfur proteins.

Rubredoxins perform one-electron transfer processes. The central iron atom changes between the +2 and +3 oxidation states. In both oxidation states, the metal remains high spin, which helps to minimize structural changes. The reduction potential of a rubredoxin is typically in the range +50 mV to -50 mV.

Structural representation of a rubredoxin active site.

Rubredoxin in some biochemical reactions

EC 1.14.15.2 camphor 1,2-monooxygenase [(+)-camphor,reduced-rubredoxin:oxygen oxidoreductase (1,2-lactonizing)]

(+)-bornane-2,5-dione + reduced rubredoxin + O₂ = 5-oxo-1,2-campholide + oxidized rubredoxin + H₂O

EC 1.14.15.3 alkane 1-monooxygenase (alkane,reduced-rubredoxin:oxygen 1-oxidoreductase)

octane + reduced rubredoxin + O₂ = 1-octanol + oxidized rubredoxin + H₂O

EC 1.15.1.2 superoxide reductase (rubredoxin:superoxide oxidoreductase)

reduced rubredoxin + superoxide + 2 H⁺ = rubredoxin + H₂O₂

EC 1.18.1.1 rubredoxin—NAD⁺ reductase (rubredoxin:NAD⁺ oxidoreductase)

reduced rubredoxin + NAD⁺ = oxidized rubredoxin + NADH + H⁺

EC 1.18.1.4 rubredoxin—NAD(P)⁺ reductase (rubredoxin:NAD(P)⁺ oxidoreductase)

reduced rubredoxin + NAD(P)⁺ = oxidized rubredoxin + NAD(P)H + H⁺

See also

• Bioinorganic chemistry
• Iron-sulfur proteins
• Ferredoxin
• Cytochrome
• Rieske protein

References

• Stephen J. Lippard, Jeremy M. Berg, Principles of Bioinorganic Chemistry, University Science Books, 1994, ISBN 0-935-70272-5
• J.J.R. Fraústo da Silva and R.J.P. Williams, The biological chemistry of the elements: The inorganic chemistry of life, 2nd Edition, Oxford University Press, 2001, ISBN 0-19-850848-4

External links

• PDB 1IRO - X-ray structure of rubredoxin from Clostridium pasteurianum
• PDB 1VCX - neutron diffraction structure of rubredoxin from Pyrococcus furiosus
• InterPro IPR001052 - InterPro entry for rubredoxin

This biochemistry article is a stub. You can help Wikipedia by expanding it.

Rieske protein

Rieske iron-sulfur center

The iron-sulfur protein (ISP) component of cytochrome bc₁ complex was first discovered and isolated by John S. Rieske and co-workers in 1964. The homologues of the Rieske proteins include ISP components of cytochrome b₆f complex), aromatic-ring-hydroxylating dioxygenases (phthalate dioxygenase, benzene, napthalene and toluene 1,2-dioxygenases) and arsenite oxidase (EC 1.20.98.1). Comparison of amino acid sequences has revealed the following consensus sequence:

Cys-Xaa-His-(Xaa)_15–17-Cys-Xaa-Xaa-His

The crystal structures of a number of Rieske proteins are known. The overall fold, comprising two subdomains, is dominated by antiparallel β-structure and contains the only α-helix. The smaller “cluster-binding” subdomains in mitochondrial and chloroplast proteins are virtually identical, whereas the large subdomains are substantially different in spite of a common folding topology. The [Fe₂S₂] cluster-binding subdomains have the topology of an incomplete antiparallel β-barrel. One iron atom of the Rieske [Fe₂S₂] cluster is coordinated by two cysteine residues and the other is coordinated by two histidine residues through the N^δ atoms. The ligands coordinating the cluster originate from two loops; each loop contributes one Cys and one His.

References

• Ferraro, D.J., Gakhar, L. and Ramaswamy, S. (2005). “Rieske business: structure-function of Rieske non-heme oxygenases”. Biochem. Biophys. Res. Commun. 338: 175–190. PMID 16168954.
• Link, T.A. (1997). “The role of the ‘Rieske’ iron sulfur protein in the hydroquinone oxidation (Q_P) site of the cytochrome bc₁ complex. The ‘proton-gated affinity change’ mechanism”. FEBS Lett. 412: 257–264. PMID 9256231.
• Mason, J.R. and Cammack, R. (1992). “The electron-transport proteins of hydroxylating bacterial dioxygenases”. Annu. Rev. Microbiol. 46: 277–305. PMID 1444257.
• Rieske, J.S., Maclennan, D.H. and Coleman, R. (1964). “Isolation and properties of an iron-protein from the (reduced coenzyme Q)-cytochrome C reductase complex of the respiratory chain”. Biochem. Biophys. Res. Commun. 15: 338–344.
• Schmidt, C.L. (2004). “Rieske iron-sulfur proteins from extremophilic organisms”. J. Bioenerg. Biomembr. 36: 107–113. PMID 15168614.
• Schneider, D. and Schmidt, C.L. (2005). “Multiple Rieske proteins in prokaryotes: where and why?”. Biochim. Biophys. Acta 1710: 1–12. PMID 16271700.

External links

• PDB 1RIE - X-ray structure of Rieske protein (water-soluble fragment) of the bovine mitochondrial cytochrome bc₁ complex
• PDB 1RFS - X-ray structure of Rieske protein (water-soluble fragment) of the spinach chloroplast cytochrome b₆ fcomplex
• PDB 1FQT - X-ray structure of Rieske-type ferredoxin associated with biphenyl dioxygenase from Burkholderia cepacia
• PDB 1G8J - X-ray structure of Rieske subunit of arsenite oxidase from Alcaligenes faecalis
• InterPro IPR005806 - InterPro entry for Rieske [2Fe-2S] region

Retarder (chemistry)

A retarder is a chemical agent that slows down a chemical reaction. For example, retarders are used to slow the chemical hardening of plastic materials such as concrete, and adhesives.

Sugar water acts as a retarder for the curing of concrete. It can be used to retard the chemical hardening of the surface, so that the top layer can be washed off to expose the underlying aggregate.

See also

• Accelerator (chemistry)

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