Showing papers in "Studies in Inorganic Chemistry in 1984"

Sulfur in Artwork: Lapis Lazuli and Ultramarine Pigments

Abstract: The sulfur containing aluminosilicate mineral lazurite, called lapis lazuli, prized as a valuable semi-precious gem since the classical era, and as the raw material for the production of the brilliant blue pigment ultramarine in the Middle Age, represents one of the most fascinating objects of structural inorganic chemistry. In this essay, after a short outline of the history of the lapis lazuli and the artificial ultramarines, some of the pathways are described which led to the solutions of the problem of the constitution of these substances. Their chromophores are small sulfur molecules, S 3 (yellow), S 4 (red), and, preferably, radical ions S 2 - (yellow), S 3 - (blue), S 4 - (red), which are imbedded in the cavities of the sodalite lattice.

Phototrophic Bacteria and their Sulfur Metabolism

Abstract: Phototrophic bacteria derive energy from light. The classical anaerobic phototrophic bacteria, the “purple” and “green bacteria” cannot use water as the photosynthetic electron donor and thus do not produce oxygen in the light. Instead, most of them use sulfide, thiosulfate or elemental sulfur as electron donors, others hydrogen gas or simple carbon compounds. The dissimilatory sulfur metabolism of whole cells of phototrophic bacteria may be described in three essential sequences: (1) Formation of elemental sulfur that appears as globules inside or outside the bacteria during oxidation of sulfide or thiosulfate. (2) Formation of sulfite, thiosulfate or tetrathionate, which may or may not appear as intermediates in the nutrient solution. (3) Formation of sulfate as the final product. Enzymological studies have revealed that at least ten enzymes and two non-enzymatic steps may be involved in these processes. Other important aspects of sulfur metabolism in phototrophic bacteria are the assimilation of sulfate and sulfide for the biosynthesis of cystein and other organic sulfur compounds, the use of sulfur compounds as electron acceptors during dark fermentative maintenance metabolism, and the supply of electrons for aerobic dark chemolithotrophic growth. These capacities do not occur equally in all phototrophic bacteria.

Elemental Sulfur and Related Homocyclic Compounds and Ions

Abstract: Sulfur is the element with the largest number of allotropes of which those consisting of cyclic molecules Sn (n = 6 − 20) are discussed in this chapter - their preparation, molecular and crystal structures, molecular spectra (IR, Raman, MS, UV) and thermodynamic properties (melting points, enthalpies of formation, entropies and heat capacities). In addition, the chromatographic separation of Sn molecules (n = 6 − 26) by high-pressure liquid chromatography (HPLC) is discussed and the detection of Sn as components of various reaction mixtures (liquid sulfur, irradiated sulfur solutions, synthetic sulfurs from acidified thiosulfate or from the thermal decomposition of unstable iodosulfanes) by HPLC or Raman spectroscopy is reviewed. The homocyclic cations Sn+ (observed in the vapor phase only) and Sn2+ (isolated as cations in crystalline solids) are related to elemental sulfur not only by their structures but also by their preparation. The synthesis, spectra, structures and some reactions of salts containing the species Sn2+ (n = 4, 8, 19) are discussed in some detail. The homocyclic sulfur oxides Sn0 (n = 6 − 10) and S702 are also derivatives of sulfur rings Sn and their preparation, structures, bonding, molecular spectra and chemical reactions are reviewed. Finally the homocyclic sulfur iodide cations S7I+ and S14I3+ as components of salt-like solids are briefly discussed. The literature is covered up to spring 1983.

Microorganisms and the Sulfur Cycle

Abstract: The biogeochemical sulfur cycle consists of an assimilatory and a dissimilatory side. On the assimilatory side inorganic sulfur in reduced or oxidized form is taken up into microbes, plants and animals (via plants) and transformed there into amino acids, proteins, and coenzymes that function there until they are excreted or the organisms die and are decomposed. The turnover rates during these processes are low as compared with those in dissimilatory processes, during which inorganic sulfur compounds serve as electron donors or acceptors in microbial metabolism. The different metabolic types involved are dissimilatory sulfate reduction (anaerobic; sulfate as electron acceptor), dissimilatory sulfur reduction (anaerobic; elemental sulfur as electron acceptor), phototrophic sulfur oxidation (anaerobic; reduced sulfur compounds as electron donors for photosynthesis), chemotrophic sulfur oxidation (anaerobic and aerobic; reduced sulfur compounds as electron donors for respiration). Communities of sulfur-oxidizing and -reducing bacteria form natural sulfur cycles, so-called sulfureta. Microbial mass transformations of inorganic sulfur compounds occured already very early in the geological record and are traceable by their kinetic isotope effects.

Cytochromes and iron sulfur proteins in sulfur metabolism of phototrophic bacteria

Abstract: Dissimilatory sulfur metabolism in phototrophic sulfur bacteria provides the bacteria with electrons for photosynthetic electron transport chain and, with energy. Assimilatory sulfate reduction is necessary for the biosynthesis of sulfur-containing cell components. Sulfide, thiosulfate, and elemental sulfur are the sulfur compounds most commonly used by phototrophic bacteria as electron donors for anoxygenic photosynthesis. Cytochromes or other electron transfer proteins, like high-potential-iron-sulfur protein (HIPIP) function as electron acceptors or donors for most enzymatic steps during the oxidation pathways of sulfide or thiosulfate. Yet, heme- or siroheme-containing proteins themselves undergo enzymatic activities in sulfur metabolism. Sirohemes comprise a porphyrin-like prosthetic group of sulfate reductase. eenzymatic reactions involve electron transfer. Electron donors or acceptors are necessary for each reaction. Cytochromes and iron sulfur problems, are able to transfer electrons.

Sulfide and Other Sulfur Containing Ligands in Metalloproteins and Enzymes

Abstract: Sulfur is an essential constituent of living matter. It occurs as an integral component of the metal-containing prosthetic groups of many metalloproteins in either an organic form, as the amino acids cysteine and methionine, or as the inorganic entity, sulfide. Examples of sulfur-ligated prosthetic groups occur in proteins concerned with storage and transport, electron-transfer proteins and enzymes of the oxido-reductase type. Metalloproteins containing cysteine or methionine as their only sulfur-based donors are most often found with copper and iron, with well-documented examples occuring for zinc, manganese, molybdenum and tungsten also. The occurence of sulfide (S 2- ) as a ligand in proteins and enzymes is known for only iron and molybdenum where, with just one known exception in xanthine oxidase/dehydrogenase, it acts as a bridging ligand between two metals.

Biodegradation of Sulfur Minerals and its Application for Metal Recovery

Abstract: Bacteria of the genus Thiobacillus are capable of changing water-insoluble metal sulfides to water-soluble metal sulfates by a set of interacting biochemical and geochemical reactions. These reactions can be utilized for the mobilization of metals from low-grade ores. Biodegradation of sulfide minerals - bacterial leaching - is already being used on a large scale in cases where conditions are appropriate. An enlargement of its possibilities, both with regard to the particular microorganisms used as well as to the ore-type to be leached, is of great economic interest.

Sulfur in the Earth's Crust, its Origin and Natural Cycle

Abstract: The outer volume of the earth (mantle and crust) contains distinctly less sulfur than primary cosmic matter represented by carbonaceous and common chondritic meteorites (5.9 % and 2.1 % S). Sediments (4250 ppm S) have accumulated a large proportion of the total sulfur of the earth's crust (43 %). Metamorphic and magmatic rocks as the other typical crustal materials contain distinctly less sulfur (~600 ppm S). They originate to a large extent from former sediments. At higher pT conditions the precursor sediments have lost more than three quarters of their original sulfur concentration. Pyrite (FeS 2 ) is the common sulfur mineral of sediments. It forms from bacterially reduced sea water sulfate and sedimentary iron oxides. This abundant process in the interstitial volume of sediments produces isotopically light sulfur. Sea water (1.4 × 10 15 t S) preferentially accumulates the isotopically heavy sulfur from residual solutions of the bacterial reduction etc. The storage of sulfur in crustal sinks (sediments, ocean crust), which partly remove materials from the crust to the mantle by subduction, is compensated by degassing of volcanic rocks (10 5 to 10 6 t S per year).

Chemical Problems of Flue- Gas Desulfurisation

Abstract: Flue-gas desulfurisation plays a very important role in connection with antropogenic acid-base chemistry in the atmosphere and the corresponding fallouts (e.g. “acid rain”). This paper does not deal with the legal aspects and environmental problems as such nor does it deal with presently used waste-producing processes (e.g. Ca(OH)2 or CaCO3, resulting in CaSO3-slurries). The fundamental chemistry of product-producing aqueous scrubbing-stripping processes, however, is discussed in some detail. It is much more complicated than had hitherto been assumed as a basis for economically as well as technically feasible processes. Finally a process is proposed which, by a combination of already known chemical steps, allows the desulfurisation of flue-gas together with the production of a valuable product: elemental sulfur.

Sulfur in History: The Role of Sulfur in “Black Powder”

Abstract: After a short outline of the history of black powder the subject of this article is a discussion of the concerted mechanism of the reactions in exploding gunpowder. Evidently, the first step of the powder reaction is the reduction of potassium nitrate to nitrite by charcoal and/or hydrogen sulfide, which originates from the reaction of sulfur with the minor hydrogen content of charcoal. Sulfur is then inserted into the nitrite to yield potassium thionitrate, KSNO2. The latter causes a rapid ignition of the charcoal/nitrate mixture through its strongly exothermic decomposition into thiosulfate and dinitrogen oxide, which is totally consumed by its explosive reaction with carbon monoxide to yield nitrogen and carbon dioxide.

New Developments in the Field of Organic Sulfur Chemistry

Abstract: Organosulfur chemistry has developed very rapidly during the last decades: Previously a topic of interest only for specialists, it may be considered nowadays as an integral and important part of general organic chemistry. New structural types found recently, characteristic for organosulfur compounds, enlarge our knowledge of bonding and electron distribution in molecules in general; many new reaction types possible for compounds with sulfur functionalities are widely applicable in organic syntheses. They have brought about almost a new area of synthetic chemistry. This is especially true for natural product synthesis. On the other hand, many new types of biologically important organosulfur compounds have been detected in recent years, their molecular structure, their chemistry as well as their biochemical role have been investigated.

Sulfido-Complexes of Molybdenum and Tungsten: Synthetic Aspects

Abstract: The physics, inorganic chemistry, industrial chemistry and biochemistry of the interaction between sulfide and the group VI transition metals, molybdenum and tungsten, have been studied intensively recently. The present contribution surveys the synthesis of discrete mono- and poly-nuclear sulfido-complexes of molybdenum and tungsten and concentrates particularly on the interplay between the metal and sulfur formal oxidation states. Such interactions primarily determine the structure and reactivity of the synthetic species.

Metal Sulfides in Photovoltaic, Photoelectrochemical and Solar Biological Energy Conversion

Abstract: Crystallized metal compounds of sulfur are gaining increasing importance in various rapidly developing areas of solar energy conversion. One reason is that many metal sulfides form semiconductors with energy gaps well suited for the capture of solar energy. Several photovoltaic and photoelectrochemical solar cells with good energy conversion efficiencies have already been tested using CdS, Cu 2 S, CuInS 2 , MoS 2 and other sulfides. For the photoelectrolysis of water into hydrogen and oxygen semiconducting materials are being developed which permit light-induced hole reactions via valence energy bands derived from transition metal d-states. Sulfur compounds of transition metals (PtS 2 , RuS 2 , Ru 1-x Fe x S 2 ) constitute the first useful materials for oxygen evolution from water using low energy photons. In this case advantage is taken of the favourable property of sulfur as a metal ligand which permits efficient d-d interaction resulting in adequate d-d splitting and reasonably broad d-state energy bands. A third property of metal sulfides interesting for solar energy conversion is their ability to store chemical energy and to serve as an energy source for autotrophic bacteria (Thiobacilli). When metal sulfides are generated from their oxidation products (metal sulfates) by means of solar power using high pressure thermal and photoelectrochemical techniques, they can be used to grow bacterial biomass. Experimental and theoretical studies suggest that such an artificial solar biomass production could be far more energy-efficient than natural photosynthesis, besides of permitting the use of infertile and arid land on which compact and largely automatic installations would generate proteins, carbohydrates and lipids for energy and food with a remarkable economy of water consumption. Several aspects of sulfur chemistry with respect to mechanism of solar energy conversion are still unexplored and deserve detailed investigations.

Inorganic Chemistry Related to Rubber Vulcanisation

Abstract: The vulcanisation of natural and related diene rubbers can be achieved by heating the rubber with a mixture of S 8 , ZnO, organosulfur accelerators, eg (R 2 NCS) 2 or C 7 H 4 NS 2 R (benzothiazole-2-thiolato derivatives), and stearic acid A mechanism is proposed to account in part for the involvement of zinc in the activation of sulfur in the early stages of vulcanisation This mechanism is thought to involve anionic zinc species derived from the organosulfur accelerators, viz [Zn(S 2 CNR 2 ) 3 ] - , [Zn(C 7 H 4 NS 2 ) 3 ˙H 2 O] - , etc, and these compounds, and cadmium analogues, are characterised spectroscopically and crystallographically The mechanistic arguments are supported by studies of dithiophosphato and phosphinato complexes of zinc and cadmium, and the use of 31 P NMR spectroscopy

Thiolates — Intriguing and Versatile Ligands for Transition Metals

Abstract: Thiolates are capable of forming a wide diversity of complexes with transition metals. The presence of additional lone pairs of electrons on co-ordinated thiolate sulfur permits the formation of clusters with single, double or triple thiolate-bridges. Facile C-S bond cleavage occurs with aliphatic thiols to give sulfido-bridged clusters. A wide variety of stereochemistries are possible with polydentate thiolate ligands and S-S interactions are important for stabilising the observed geometries. Co-ordinated thiolates also readily undergo disulfide elimination with formal reduction of the metal. The use of sterically-hindered aryl thiols prevents both thiolate-bridging and C-S bond cleavage and produces co-ordinatively unsaturated monomeric species.

Organometallic Sulfur Compounds

Abstract: The organometallic chemistry of S 2- and SH - ligands is outlined. The ability of substituent free sulfur to act as a two, four, or six electron donor and of the SH unit to act as a one, three, or five electron donor is the reason for structural diversity and the preference for polynuclear complexes. Lack of inertness due to unshared electron pairs on the sulfur ligands limits the number of accessible compounds. The reactivity of organometal-SH complexes is not comparable to that of simple R-SH compounds. Due to their extremely low acidity derivatizations require special pathways. The most typical S 2- complexes contain M 3 S units which have characteristic electron reservoir properties. These properties are of structural, chemical, electrochemical, and biochemical significance. Sulfur bridged organometallic clusters have made possible several new basic metal cluster reactions.

Interaction Between Metal Centers Through Sulfur Containing Ligands

Abstract: This contribution is devoted to the magnetic properties of the binuclear complexes with sulfur-containing bridging ligands. The theoretical background is presented in the first section, then the possibility to achieve a strong antiferromagnetic interaction between metal ions far away from each other through sulfur containing extended bridging ligands is discussed. The dithiooxamidato copper(II) binuclear complexes are presented as typical examples of this kind of compounds. The first results in the new field of the ordered bimetallic magnetic chains with sulfur containing bridges are mentioned. Finally, the magnetic properties of the iron-sulfur complexes are discussed.

Metal Complexes of Sulfur and Sulfur-Nitrogen Compounds and their Catalytic Properties

Abstract: This report summarizes a study of reactions with metal cations and sulfur containing compounds Especially the coordination chemistry of Ag + with these ligands is discussed The catalytic behaviour of metal cations for the preparation of S(CN) 4 from (CN) 2 and sulfur is reported From these investigations the conclusion can be drawn that metal cations play an important role in synthetic and biological systems where sulfur compounds are involved

Sulfuric Acid — An Important Basic Product in Chemistry. Problems and Recent Developments in Production

Abstract: The large increase in the production of sulfuric acid and its function as an auxiliary in chemical reactions has raised a number of problems which had to be solved. Four main subjects are dealt with in this article: (1) Reduction of emissions: The emissions of SO 2 could be reduced substantially by introduction of the double contact process develeoped by the BAYER AG. The principle of the process is decribed. (2) Raw materials: There is a world-wide tendency towards the use of elementary sulfur. The resulting technical consequences are discussed. (3) Energy recovery: During the manufacture of sulfuric acid large quantities of heat are produced. Regarding the present energy situation the recovery of this energy is an important necessity. The heat from the formation of SO 2 and from the reaction from SO 2 to SO 3 is recovered to a large extent and is converted to high pressure steam. Presently, large efforts are made in order to use also the heat from the reaction with water. A number of technical possibilities together with some material problems are discussed. (4) Recycling of spent acids and by-products: The re-use or recycling of spent acids plays an increasing role. Technical solutions are possible for the recovery of spent acids with organic as well as inorganic load by concentration and cleavage processes.

Genetic Diseases of Sulfur Metabolism in Humans

Abstract: The known hereditarily determined inborn errors of metabolism in humans affecting the transport or transformation of sulfur-containing compounds are listed. For each condition, the impaired enzyme or transport process is specified. It is emphasized that a given chemical abnormality may result from different genetic lesions, and that many genetic lesions, differing in detail, may each produce abnormalities of a given enzyme or transport factor. Homocystinuria due to cystathionine s-synthase deficiency is reviewed in some detail. This disease produces mental retardation, dislocation of the optic lenses, bony abnormalities, and early (often life-threatening) thromoembolic episodes. Studies using antibody to cystathionine s-synthase and an in vitro system capable of translating messenger RNAs have recently permitted detailed analyses of the genetic abnormalities in a number of lines of fibroblasts derived from small skin biopsies taken from patients with cystathionine s-synthase deficiency or their relatives and grown in tissue culture.

Spectroscopic Aspects of Sulfur Chemistry: Electronic and Resonance Raman Spectroscopy of Sulfur Containing Complexes, Ions and Radicals

Abstract: The electronic and resonance Raman spectroscopy of complexes containing sulfur-donor ligands and of sulfur radicals is reviewed. Particular attention is paid to Raman spectra obtained at resonance with charge-transfer bands, to the information which this provides on the degree of valence-electron delocalisation, and to the determination of excited state geometries. The spectroscopy of radical cations (e.g. S 4 2+ ) and radical anions (e.g. S 3 - , S 2 - in ultramarines etc.) is also discussed.