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Sulfur Atom (sulfur + atom)

Distribution by Scientific Domains

Chemistry	90%
Life Sciences	4%
Polymers and Materials Science	3%

Distribution within Chemistry

Organic Chemistry	23%
General & Introductory Chemistry	20%
Computational Chemistry & Molecular Modeling	16%
Biochemistry (Chemical Biology)	3%
9 Other Subdomains	35%

Selected Abstracts

First Example of the Mislow,Braverman,Evans Rearrangement Retaining the Sulfur Atom on the Original Carbon.

CHEMINFORM, Issue 26 2006
Tsuyoshi Satoh
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

ChemInform Abstract: Crown Ethers with Azo or Azoxy Unit and Sulfur Atom(s) in 16-Membered Macrocycle.

CHEMINFORM, Issue 44 2001
J. Szczygelska-Tao
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Electronic structure and reactivity of guanylthiourea: A quantum chemical study

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2010
Ahmed Mehdi
Abstract Electronic structure analysis of guanylthiourea (GTU) and its isomers has been carried out using quantum chemical methods. Two major tautomeric classes (thione and thiol) have been identified on the potential energy (PE) surface. In both the cases conjugation of pi-electrons and intramolecular H-bonds have been found to play a stabilizing role. Various isomers of GTU on its PE surface have been analyzed in two different groups (thione and thiol). The interconversion from the most stable thione conformer (GTU-1) to the most stable thiol conformer (GTU-t1) was found to take place via bimolecular process which involves protonation at sulfur atom of GTU-1 followed by subsequent CN bond rotation and deprotonation. The detailed analysis of the protonation has been carried out in gas phase and aqueous phase (using CPMC model). Sulfur atom (S1) was found to be the preferred protonation site (over N4) in GTU-1 in gas phase whereas N4 was found to be the preferred site of protonation in aqueous medium. The mechanism of S-alkylation reaction in GTU has also been studied. The formation of alkylated analogs of thiol isomers (alkylated guanylthiourea) is believed to take place via bimolecular process which involves alkyl cation attack at S atom followed by CN bond rotation and deprotonation. The reactive intermediate RS(NH2)CNC(NH2)2+ belongs to the newly identified ,N(,L)2 class of species and provides the necessary dynamism for easy conversion of thione to thiol. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

Synthesis and Characterization of Semiconductive Dichloridobis(thianthrene)gold(1+) Tetrachloridoaurate(1,)

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2009
Rachmat Triandi Tjahjanto
Abstract A new (thianthrene)gold(III) complex has been synthesized in liquid SO2 as the solvent from thianthrene (TA) andAuCl3. [AuCl2(TA)2][AuCl4] [triclinic, P, a = 9.9832(2) Å, b = 10.3404(2) Å, c = 15.0798(4) Å, , = 75.038(1)°, , = 81.610(1)°, , = 68.409(1)°, V = 1396.15(5) Å3, Z = 2] has a salt-like structure consisting of [AuCl2(TA)2]+ and [AuCl4], ions, both with square-planar coordinated gold atoms of oxidation state +3. In the cation, two bent TA molecules are coordinated to Au each through one sulfur atom. The title compound is thermally stable up to 425 K and is semiconducting with a conductivity reaching 25 mSm,1 at 380 K and a low activation energy of 0.43 eV. A model for the charge transport along the stacked cationic complexes is discussed. When dissolved in chloroform [AuCl2(TA)2][AuCl4] is converted into the already known uncharged, mononuclear complex [AuCl3(TA)], which shows that a polymerization isomerism exists between the two forms.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Dynamic Stereochemical Behaviour of Congested Ruthenium(II) Complexes Containing Asymmetric Thioether Ligands Based on Pyridine and Pyrimidine

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2008
Giuseppe Tresoldi
Abstract The asymmetric thioethers L [L = 2-pyridylmethyl 2,-pyrimidyl sulfide (pps) and 2-(4-methylpyrimidyl) 2,-pyridylmethyl sulfide (mps)] reacted with cis -[RuCl2(N,N -L,)2] [L, = di-2-pyridyl sulfide (dps); 2,2,-bis(4-methylpyridyl) sulfide (4mdps); 2,2,-bis(5-methylpyridyl) sulfide (5mdps)] to give the five-membered-ring chelate complexes [Ru(N,N -L,)2(Npyridine,S -L)]++ as the major products (92,95,%). Because the sulfur and ruthenium atoms are stereogenic centres, with (R) and (S) and , and , configurations, respectively, four isomers, including the enantiomers were obtained. At low temperature and in the methylene region of the 1H NMR spectra, two AB systems due to the enantiomer couples ,S ,R (a) and ,R ,S (b) were observed with abundances of 77,89 and 6,18,%, respectively. Furthermore, NMR spectroscopic investigations showed that the hybrid polydentate ligands L change their coordination mode. Thus, although a and b largely predominate, a mixture of species containing L and the Ru(N,N -L,)2 unit in the ratio 1:1 are present. The four-membered-ring chelate complexes [Ru(N,N -L,)2(Npyrimidine,S -L)]++ (c), as minor species (abundance 1,8,%), are always observed, whereas the dinuclear species [{Ru(N,N -L,)2}2(,-L)2]+4 (d, e) are observed when L, = dps or 5mdps. In these cases, four AB systems are assigned to dinuclear species d and e containing two bridging L that act as Npyridine,S- or Npyridine,Npyrimidine -donor ligands. The 1H NMR spectra are temperature dependent in that at low temperature the complexes undergo inversion of the chiral centre of the coordinated sulfur atom (a [rlhar2] b) and the dimer (d, e) and monomer (c) are in equilibrium; at higher temperatures the complexes undergo a structural dynamic rearrangement, which involves exchange between the coordinated and uncoordinated N atoms (b [rlhar2] c). One-dimensional band-shape analysis of the exchanging methylene and methyl proton signals showed that the energy barriers for inversion of the sulfur centre are in the 50,53 kJ,mol,1 range, whereas those for the higher-temperatures process are in the 62,68 kJ,mol,1 range. The possible mechanisms of the processes are discussed. NMR spectroscopic findings suggest that inversion at the sulfur centre occurs without any bond rupture, whereas the exchange, at higher temperatures (b [rlhar2] c), is a dissociative process involving the breaking of a Ru,Npyridine bond.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Variable Coordination Modes of Benzaldehyde Thiosemicarbazones , Synthesis, Structure, and Electrochemical Properties of Some Ruthenium Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2008
Swati Dutta
Abstract Reaction of benzaldehyde thiosemicarbazones [H2LR, where H2 stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH3, CH3, H, Cl, and NO2) for the para substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S-donor ligand forming a four-membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru2(PPh3)2(CO)2(LR)2] were obtained. The crystal structure of [Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S-donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. 1H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low-spin d6, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes show the ruthenium(II),ruthenium(III) oxidation within 0.48,0.73 V vs. SCE followed by a ruthenium(III),ruthenium(IV) oxidation within 1.09,1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron-withdrawing character of the substituent R. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

An Investigation of the Reactivity of [(diimine)(dithiolato)M] Complexes Using the Fukui Functions Concept

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2006
Christodoulos Makedonas
Abstract Fukui functions are widely used when investigating the reactivity of organic molecules, but rarely with metal complexes. Here, we investigate the reactivity of [(diimine)(dithiolato)M] complexes with different types of reagents and upon oxidation employing this concept. Mixed-ligand complexes of this type have a peculiar electronic description due to the mixed-metal-ligand-to-ligand charge-transfer band, which is why they are considered as very promising candidates for non-linear optical (NLO) materials and molecular photochemical devices (MPD). As a result, their reactivity is of crucial importance for their potential applications. The obtained results of f+ and f, for the neutral [(diimine)(dithiolato)M] complexes (M = Pd, Ni and Pt) not only predict that the sulfur atom is the preferable active site for electrophilic attack but also reveal the different tunability of these complexes when they are subjected to an oxidation process, in agreement with experimental results. Under the framework of the Fukui indices we also provide an alternative explanation for crystal packing that could find widespread application. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Synthesis, Characterization and in Vitro Study of the Cytostatic and Antiviral Activity of New Polymeric Silver(I) Complexes with Ribbon Structures Derived from the Conjugated Heterocyclic Thioamide 2-Mercapto-3,4,5,6-tetra- hydropyrimidine

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2004
Panagiotis C. Zachariadis
Abstract Silver(I) bromide reacts with 2-mercapto-3,4,5,6-tetrahydropyrimidine (StpmH2, C4H8N2S) in DMSO with an excess of triethylamine to give a water-insoluble complex of formula [Ag6(,2 -Br)6(,2 -StpmH2)4(,3 -StpmH2)2]n (1), while the reaction of silver(I) nitrate with StpmH2 under the same conditions gives a water-insoluble complex of formula [{Ag4(,2 -StpmH2)6}(NO3)4]n (2). The products were characterized by elemental analyses, and FT-IR far-IR, UV/Vis, 1H and 13C NMR spectroscopy. Crystal structures of complexes 1 and 2 were determined by X-ray diffraction. Complex 1, C24H48Ag6N12S6, crystallizes in the triclinic system space group P , a = 8.041(1) Å, b = 12.838(4) Å, c = 13.281(2) Å, , = 68.40(1)°, , = 72.97(1)°, , = 87.80(2), Z = 2, forming a one-dimensional infinite ribbon structure by strong interatomic interactions of two ,2 -Br bonds with Ag(1). Complex 2, C24H48Ag4N16O12S6, crystallizes in the orthorhombic system, space group Cmc21, and a = 32.148(3) Å, b = 9.461(2) Å, c = 7.234(1) Å, , = , = , = 90°, Z = 8, forming infinite Ag,S,Ag chains which are bridged to each other by a sulfur atom of ,2 -StpmH2 ligands. Complexes 1 and 2 were studied for their cytostatic activity against murine leukemia (L1210) and human T-lymphocyte (Molt4/C8 and CEM) cells and for their antiviral activity against a wide variety of viruses. They are markedly cytostatic at 50% inhibitory concentration (IC50) values ranging from 3 to 17 ,g/mL. None of the compounds showed appreciable antiviral activity at subtoxic concentrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

First (Peroxo)vanadium(V) Complex with Heteroligand Formed in Reaction System , Synthesis, Structure and Reactivity of K[VO(O2)(omeida)]·H2O {omeida = N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetato(2,)}

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003
Michal Sivák
Abstract The crystalline peroxo complex of vanadium(V), K[VO(O2)(omeida)]·H2O, where omeida is a ,-lactone derivative, N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetate(2,), has been obtained by reaction of vanadate with H2O2 and N -(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) in acidic aqueous solution at pH = 3 and 278 K. X-ray analysis revealed a distorted pentagonal-bipyramidal coordination around the vanadium atom, with a typical cis arrangement of oxo and peroxo ligands in apical and equatorial positions, respectively. Two amino nitrogen atoms of the tetradentate omeida(2,)-N1,N2,O1,O2 ligand occupy the neighbouring equatorial positions of the pentagonal plane, and two oxygen atoms of carboxymethyl groups bound to the same N1 nitrogen atom are in equatorial and apical positions. The six-membered lactone ring in omeida was formed in the reaction solution from carboxy and hydroxy groups not involved in coordination with the vanadium atom. The 51V NMR spectra of K[VO(O2)(omeida)]·H2O, and of peroxovanadate/HEDTA/H2O and vanadate/HEDTA/H2O solutions, as well as the 1H NMR spectrum of HEDTA, proved that lactone ring closure proceeds only in peroxovanadate but not vanadate solutions. Spectroscopic investigation of the oxygen transfer reaction from the peroxo ligand in [VO(O2)(omeida)], to the thiolato sulfur atom in [Co(en)2{S(CH2)2NH2}]2+ or [Co(en)2(cyst)]+, and of the oxidation of N -acetyl- L -cysteine by K[VO(O2)(omeida)]·H2O, revealed much more complicated reaction mechanisms than those of other (amino-polycarboxylato)monoperoxo complexes of vanadium(V). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Alternative Mechanistic Paths in the Hetero-Diels,Alder Reaction of ,-Oxothiones: A Theoretical Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2007
Laura Legnani
Abstract DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels,Alder reactions between several ,-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated ,-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Utilization of the Versatility of Sulfur in C,C Bond Formation and Cleavage: Synthesis of ABC Taxoid Skeletons

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2007
Subhash P. Chavan
Abstract A practical and convenient five-step protocol is described to access the ABC ring system of Taxol by utilizing the versatility of the sulfur atom in its various oxidation states viz., condensation/Pummerer cyclization/coupling/annulation/fragmentation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

4- and 4,5-Substituted N -Methoxythiazole-2(3H)-thiones , Preparation,UV/Vis Spectra, and Assignment of Electronic Transitions in Comparison to N -Methoxypyridine-2(1H)-thione Using Time-Dependent Density Functional Theory Calculations

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2005
Jens Hartung
Abstract Experimentally observed absorptions in UV/Vis spectra of N -methoxy-4-methylthiazole-2(3H)-thione, N -methoxy-5-(p -methoxyphenyl)-4-methylthiazole-2(3H)-thione, N -methoxypyridine-2(1H)-thione, and selected N -hydroxy derivatives thereof have been assigned to ,,,*-type transitions as dominating character, using the results from ab initio calculations [time-dependent density functional theory (TD)RI-BLYP/TZVPP]. Theory further predicts that electronic excitations in N -methoxythiazole-2(3H)-thiones on one side and N -meth-oxypyridine-2(1H)-thione on the other side differ significantly with respect to character and statistical weight of contributing transitions. These effects originate predominantly from contributions of the endocyclic sulfur atom onto orbital energies and shapes in thiazole-2(3H)-thiones, and may be intensified by substituents such as a p -methoxyphenyl group located in position 5. Since the majority of the calculated spectral differences between thiazole- and pyridinethiones refers to excitations of low intensity, the findings from the present study correlate with two important experimental facts: (i) Apart from minor shifts in the exact spectral location of UV/Vis absorptions, electronic spectra of N -hydroxy- or N -methoxy-substituted pyridine-2(1H)-thiones and thiazole-2(3H)-thiones are surprisingly similar in shape. (ii) N -alkoxypyridine-2(1H)-thiones and N -alkoxythiazole-2(3H)-thiones liberate upon UV/Vis excitation oxygen-centered radicals with a comparable efficiency. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Structures and properties of two diastereomeric cyclic sulfites derived from cis -3,4-di- tert -butylthiolane-3,4-diol and thionyl chloride

HETEROATOM CHEMISTRY, Issue 7 2003
Sanae Tanaka
cis-3,4-Di-tert-butylthiolane-3,4-diol (1) was treated with an equimolar amount of thionyl chloride in the presence of triethylamine or pyridine in several solvents of different polarity to furnish two diastereomeric sulfites 2a and 2b generally in excellent combined yields. Although 2a was consistently formed as the major diastereomer when pyridine was used as the base, 2a and 2b were formed in approximately equal amounts when triethylamine was used as the base in polar solvents. X-ray crystallographic analyses revealed that the SO group of 2a is anti to the thiolane ring and that of 2b syn to the thiolane ring. Density functional theory calculations (B3LYP/6-31G* level) revealed that 2a is less stable than 2b by 1.28 kcal mol,1, although 2a was formed generally as the predominant diastereomer. Spectroscopic data of 2a and 2b are discussed with emphasis on comparison with those obtained by calculations. Treatment of 2a and 2b with m-chloroperbenzoic acid resulted in the oxidation of the divalent sulfur atom of the thiolane ring and not the sulfite sulfur atom. The above oxidations took place exclusively at the syn-side with respect to the tert-butyl groups.© 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:587,595, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10192 [source]

A temperature-dependent kinetics study of the reaction of O(3PJ) with (CH3)2SO

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002
F. D. Pope
A laser flash photolysis,resonance fluorescence technique has been employed to investigate the kinetics of the reaction of ground state oxygen atoms, O(3PJ), with (CH3)2SO (dimethylsulfoxide) as a function of temperature (266,383 K) and pressure (20,100 Torr N2). The rate coefficient (kR1) for the O(3PJ) + (CH3)2SO reaction is found to be independent of pressure and to increase with decreasing temperature. The following Arrhenius expression adequately describes the observed temperature dependence: kR1(T) = (1.68 ± 0.76) × 10,12 exp[(445 ± 141)/T] cm3 molecule,1 s,1, where the uncertainties in Arrhenius parameters are 2, and represent precision only. The absolute accuracy of each measured rate coefficient is estimated to be ±30%, and is limited predominantly by the uncertainties in measured (CH3)2SO concentrations. The observed temperature and pressure dependencies suggest that, as in the case of O(3PJ) reactions with CH3SH and (CH3)2S, reaction occurs by addition of O(3PJ) to the sulfur atom followed by rapid fragmentation of the energized adduct to products. The O(3PJ) + (CH3)2SO reaction is fast enough so that it could be a useful laboratory source of the CH3SO2 radical if this species is produced in significant yield. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 156,161, 2002; DOI 10.1002/kin.10040 [source]

Mechanism of the Asymmetric Sulfoxidation in the Esomeprazole Process: Effects of the Imidazole Backbone for the Enantioselection

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009
Muthu Seenivasaperumal
Abstract The asymmetric sulfoxidation reaction of imidazole-based prochiral sulfides was studied to explore the mechanistic details of the highly efficient esomeprazole process, which is one of the few industrial scale catalytic asymmetric procedures. The synthetic studies revealed that the smallest subunit governing the selectivity in the esomeprazole process is an imidazole ring. Thus, by using the esomeprazole procedure methyl imidazole sulfide could be oxidized as efficiently as its several functionalized derivatives, including pyrmetazol. However, alkylation of the imidazole nitrogen led to a major drop of the enantioselectivity. Our atmospheric pressure chemical ionization-mass spectrometry (APCI/MS) studies indicate that addition of small amounts of water to the reaction mixture facilitates the formation of mononuclear titanium species, which are the active catalytic intermediates of the selective oxidation reaction. One of the most important features of the esomeprazole procedure is that amine additives increase the enantioselectivity of the oxidation process. The NMR studies of the presumed reaction intermediates show that under catalytic conditions the amines are able to coordinate to titanium and dissociate the coordinated imidazole substrate. The density functional theory (DFT) modelling studies provided new insights in the mechanism of the asymmetric induction. It was found that the oxidation requires a lower activation energy if the imidazole sulfide precursor does not coordinate to titanium. Two possible reaction paths were explored for this out of sphere oxidation mechanism. The most important interaction governing the enantioselection is hydrogen bonding between the NH of the imidazole ring and the chiral tartrate ligand on titanium. Furthermore, the oxidation reaction imposes an important structural constraint to the TS structure involving a linear arrangement of the peroxide oxygens and the sulfur atom. This constraint and the N coordination of imidazole leads to a very strained structure for the inner sphere mechanism of the oxidation, which leads to a much higher activation barrier than the corresponding out of sphere process, and therefore it is unlikely. [source]

A family of thioxanthato ruthenium and osmium aryls

ISRAEL JOURNAL OF CHEMISTRY, Issue 3 2001
Swarup Chattopadhyay
The title complexes of type M(RL2)(PPh3)2(CO)(S2CSEt) (2a: M = Ru; 2b: M = Os) have been synthesized in excellent yields by reacting M(RL1)(PPh3)2(CO)X (1a: M = Ru, × = Cl; 1b: M = Os, × = Br) with potassium ethyl thioxanthate and have been characterized with the help of spectral and electrochemical data. The RL2 ligand in 2 is the imine-phenol tautomer of N-C6H4R(p)-4-methylsalicylaldimine (R = Me, MeO, Cl) coordinated at the carbanionic-C2 atom only while RL1 in 1 is the iminium-phenolato tautomer chelated via carbanionic-C2 and phenolato-O atoms. The synthetic reaction is thus attended with tautomerization of the Schiff base ligand. It is also associated with a rotation of the ligand by ,180° around the M,C bond in order to exclude steric repulsion. These features have been revealed by structure determination of 2a (R = Me). The metallated aldimine ring is found to be highly noncoplanar (dihedral angle ,40°) with the thioxanthate chelate ring due to steric repulsion originating from the relatively large size of the sulfur atom. This phenomenon, which is absent in both the precursor 1 (R = Me) and in the carboxylate analogue Ru(MeL2)(PPh3)2(CO)(O2CMe), 7, has distinctive effects on bond parameters of 2a (R = Me). Thus the two Ru,P bonds in 2a (R = Me) differ in length by as much as 0.06 Å. The thioxanthate 2 is thermodynamically more stable than the precursor 1 as well as the carboxylate 7. Accordingly, both of these are irreversibly transformed to 2a (R = Me) upon treatment with thioxanthate. [source]

Novel Palladium-on-Carbon/Diphenyl Sulfide Complex for Chemoselective Hydrogenation: Preparation, Characterization, and Application

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2008
Akinori Mori
Abstract A diphenyl sulfide immobilized on palladium-on-carbon system, Pd/C[Ph2S], was developed to achieve the highly chemoselective hydrogenation of alkenes, acetylenes, azides, and nitro groups in the presence of aromatic ketones, halides, benzyl esters, and N-Cbz protective groups. Instrumental analyses of the heterogeneous catalyst demonstrated that diphenyl sulfide was embedded on Pd/C via coordination of its sulfur atom to palladium metal or physical interaction with graphite layers of the activated carbon. The catalyst could be recovered and reused at least five times without any significant loss of the reactivity. [source]

Phosphonic acid functionalized polyethylene glycol and derivatives

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
Mohamed Essahli
Abstract This article describes the functionalization of polyethylene glycol, mono or bifunctional, and a nonionic surfactant by phosphonic acids without the need for protection of the functional group. The functionalization is performed in two steps, first an esterification by thioglycolic acid, secondly a radical addition of vinyl phosphonic acid on the thiol group. All products were obtained quantitatively and characterized by 1H-, 13C-, 31P-NMR spectroscopy techniques, MALDI, and step-by-step chemical titrations. Enhanced thermal properties were found while phosphonylating polyethylene glycol, particularly when the sulfur atom was oxidized into a sulfone group. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Arylsulfonates as sole source of sulfur for Clostridium pasteurianum DSM 12136

JOURNAL OF BASIC MICROBIOLOGY, Issue 4 2005
Chih-Ching Chien Prof.
A variety of arylsulfonates were examined for their ability to support growth of Clostridium pasteurianum as sole source of sulfur. Among the eleven different arylsulfonates tested, six of them (benzenesulfonate, 4-toluenesulfonate, 4-xylene-2-sulfonate, 4-aminobenzenesulfonate, 4-sulfobenzoic acid, 1,3-benzenedisulfonate) could serve as sole sulfur source for C. pasteurianum DSM 12136. None of the sulfonates tested could serve as sole sulfur source for C. pasteurianum ATCC 6013. The two C. pasteurianum in this study could not utilize any of these sulfonates as sole carbon and energy source. We demonstrated that desulfonation of arylsulfonates could take place under anoxic conditions and the sulfur atom of these compounds could be utilized as sole source of sulfur by anaerobic bacteria. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electronic structure and reactivity of guanylthiourea: A quantum chemical study

Force-field parameters of the , and , around glycosidic bonds to oxygen and sulfur atoms

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2009
Minoru Saito
Abstract The , and , torsion angles around glycosidic bonds in a glycoside chain are the most important determinants of the conformation of a glycoside chain. We determined force-field parameters for , and , torsion angles around a glycosidic bond bridged by a sulfur atom, as well as a bond bridged by an oxygen atom as a preparation for the next study, i.e., molecular dynamics free energy calculations for protein-sugar and protein-inhibitor complexes. First, we extracted the , or , torsion energy component from a quantum mechanics (QM) total energy by subtracting all the molecular mechanics (MM) force-field components except for the , or , torsion angle. The , and , energy components extracted (hereafter called "the remaining energy components") were calculated for simple sugar models and plotted as functions of the , and , angles. The remaining energy component curves of , and , were well represented by the torsion force-field functions consisting of four and three cosine functions, respectively. To confirm the reliability of the force-field parameters and to confirm its compatibility with other force-fields, we calculated adiabatic potential curves as functions of , and , for the model glycosides by adopting the , and , force-field parameters obtained and by energetically optimizing other degrees of freedom. The MM potential energy curves obtained for , and , well represented the QM adiabatic curves and also these curves' differences with regard to the glycosidic oxygen and sulfur atoms. Our , and , force-fields of glycosidic oxygen gave MM potential energy curves that more closely represented the respective QM curves than did those of the recently developed GLYCAM force-field. © 2009 Wiley Periodicals, Inc., J Comput Chem, 2009 [source]

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2009
N. M. F. S. A. Cerqueira
Abstract The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton-electron transfer stage, where the MoV species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo-dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with MoVI ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl-dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur-based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of MoV species. MoVI intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the MoVI species allow water molecule dissociation, and, the concomitant enzymatic turnover. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source]

Conformational analysis of thiopeptides: derivation of sp2 sulfur parameters for the CFF91 force field

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2001
Tran Trung Tran
Abstract When a sulfur atom is used to substitute for the oxygen in peptide bonds, its bulkiness should restrict the conformational space available to an amino acid. This conformational restriction as well as the ability to confer resistance to enzymatic degradation in the body means that thio-substituted amino acids are potentially useful building blocks for drug design. To simulate the effects of thio substitution, force field parameters for sp2 sulfur are required. In this article, parameters for the thioamide group have been derived for the molecular mechanics CFF91 force field (available at http://www.ludwig.edu.au/archive/tran). The bond increment charges were obtained by fitting to ab initio charges and dipoles. The van der Waals parameters were obtained by fitting to high-resolution crystallographic data, and the nonbonded parameters were verified by comparing with experimentally derived lattice energy. The bonded parameters were derived by least-square fits to the ab initio calculated energy surfaces, i.e., conformational energy as well as their first and second derivatives of seven model thioamide molecules. When the sp2 sulfur parameters were tested on a set of seven X-ray crystallographic structures from the Cambridge Structural Database, they satisfactorily reproduced the bond lengths, bond angles, torsional angles, and nonbonded distances of all the crystal structures. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1010,1025, 2001 [source]

Modeling excitation properties of iridium complexes

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2009
Katarzyna, widerek
Abstract Five iridium Ir(III) complexes have been studied using B3P86, B3LYP, M05, M06, M05-2X, and M06-2X functionals within configuration interaction singles (CIS) and time dependent density functional theory (TDDFT) formalisms with the aim of finding theory level that would allow for reliable prediction of emission properties. Knowledge of these properties prior to synthesis may significantly facilitate rational design of organic light-emitting diodes (OLEDs). Our results indicate that the M05-2X functional gives excellent results in this respect for the class of complexes studied here with the exception of the (bsn)2Ir(acac) complex. We have shown that the discrepancy between the theoretical and experimental values for this complex is due to the presence of the sulfur atom. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Mechanism of 4-methyl-1,2,4-triazol-3-thione reaction with formaldehyde

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2008
Monika Wujec
Abstract We have recently described theoretically the mechanism of the reaction between 4-methyl-1,2,4-triazol-3-thiol and formaldehyde that leads to the N- substituted product, N1 -hydroxymethyl-4-methyl-1,2,4-triazol-3-thione. New experimental findings indicate that the thione tautomeric form in reaction with formaldehyde also yields this product. This observation could not be explained on the basis of previous calculations, which predicted that the thione tautomer undergoes nucleophilic substitution at the sulfur atom, leading to the S- substituted product. We present theoretical explanation of the observed reactivity. We show that under experimental conditions this reaction proceeds with the intervention of the anionic form of the triazole with the Gibbs free energy of activation of only 1.8,kcal/mol. Copyright © 2008 John Wiley & Sons, Ltd. [source]

QSAR of Progestogens: Use of a Priori and Computed Molecular Descriptors and Molecular Graphics

MOLECULAR INFORMATICS, Issue 4 2003
Rudolf Kiralj
Abstract Quantitative Structure-Activity Relationship (QSAR) study of two sets of oral progestogens was carried out by using Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA) and Partial Least Squares (PLS). A priori, computed (at DFT 6-31G** level) and molecular graphics and modeling descriptors were employed. Molecular graphics and modeling studies of crystal structures of complexes progesterone receptor (PR)-progesterone, Fab,-progesterone and PR-metribolone have been performed. QSAR of progestogens is a three-dimensional phenomenon (over 96% of information is explained by the first three Principal Components), which can be, although it exhibits significant non-linearity, treated well with linear methods such as PLS. Progestogen activity depends primarily on double bond contents and resonance effects which define the skeletal conformation, and also on substituent characteristics (size, conformational and electronic properties). Sterical relationships between a substituent at C6(sp2) or C6(sp3)-, and sulfur atom from Met 801 residue of PR are important for progesterone binding to the protein and can be quantified. Basically the same was observed for substituents at ,-C10 with respect to residue Met759. [source]

Prediction of reversibly oxidized protein cysteine thiols using protein structure properties

PROTEIN SCIENCE, Issue 3 2008
Ricardo Sanchez
Abstract Protein cysteine thiols can be divided into four groups based on their reactivities: those that form permanent structural disulfide bonds, those that coordinate with metals, those that remain in the reduced state, and those that are susceptible to reversible oxidation. Physicochemical parameters of oxidation-susceptible protein thiols were organized into a database named the Balanced Oxidation Susceptible Cysteine Thiol Database (BALOSCTdb). BALOSCTdb contains 161 cysteine thiols that undergo reversible oxidation and 161 cysteine thiols that are not susceptible to oxidation. Each cysteine was represented by a set of 12 parameters, one of which was a label (1/0) to indicate whether its thiol moiety is susceptible to oxidation. A computer program (the C4.5 decision tree classifier re-implemented as the J48 classifier) segregated cysteines into oxidation-susceptible and oxidation-non-susceptible classes. The classifier selected three parameters critical for prediction of thiol oxidation susceptibility: (1) distance to the nearest cysteine sulfur atom, (2) solvent accessibility, and (3) pKa. The classifier was optimized to correctly predict 136 of the 161 cysteine thiols susceptible to oxidation. Leave-one-out cross-validation analysis showed that the percent of correctly classified cysteines was 80.1% and that 16.1% of the oxidation-susceptible cysteine thiols were incorrectly classified. The algorithm developed from these parameters, named the Cysteine Oxidation Prediction Algorithm (COPA), is presented here. COPA prediction of oxidation-susceptible sites can be utilized to locate protein cysteines susceptible to redox-mediated regulation and identify possible enzyme catalytic sites with reactive cysteine thiols. [source]

Role of 2-oxo and 2-thioxo modifications on the proton affinity of histidine and fragmentation reactions of protonated histidine,

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2010
Adrian K. Y. Lam
A combination of electrospray ionisation (ESI), multistage and high-resolution mass spectrometry experiments was used to compare the gas-phase chemistry of the amino acids histidine (1), 2-oxo-histidine (2), and 2-thioxo-histidine (3). Collision-induced dissociation (CID) of all three different proton-bound heterodimers of these amino acids led to the relative gas-phase proton affinity order of: histidine >2-thioxo-histidine >2-oxo-histidine. Density functional theory (DFT) calculations confirm this order, with the lower proton affinities of the oxidised histidine derivatives arising from their ability to adopt the more stable keto/thioketo tautomeric forms. All protonated amino acids predominately fragment via the combined loss of H2O and CO to yield a1 ions. Protonated 2 and 3 also undergo other small molecule losses including NH3 and the imine HN=CHCO2H. The observed differences in the fragmentation pathways are rationalised through DFT calculations, which reveal that while modification of histidine via the introduction of the oxygen atom in 2 or the sulfur atom in 3 does not affect the barriers against the loss of H2O+CO, barriers against the losses of NH3 and HN=CHCO2H are lowered relative to protonated histidine. Copyright © 2010 John Wiley & Sons, Ltd. [source]

The factors that influence the elution order for the resolution of amino acids on vancomycin phase using the polar-organic mobile phases after their pre-column derivatization with electrophilic reagents

BIOMEDICAL CHROMATOGRAPHY, Issue 6 2005
S. Chen
Abstract A variety of amino acids were enantioresolved on a vancomycin bonded chiral phase using the polar-organic mobile phases after their pre-column derivatization with electrophilic reagents in alkaline medium. The resolution was highly dependent on the analyte's structure and was enhanced as the aromatic side-chain group on the skeleton of analyte for ,,, interaction with the chiral selector became available. The steric hindrance resulting from the bulky side-chain group on the analyte also affected the resolution. Elution reversal, not found on the teicoplanin phase under the same chromatographic conditions, was possible through altering the type of reagent used in the derivatizing reaction (e.g. 2,4-difluorophenylisothiocyanate to 2,4-difluorophenylisocyanate). It is believed that the steric hindrance, as a result of the bulky sulfur atom in reagents such as methylisothiocyanate and others examined in this study, was responsible for the reversed elution order. The bulkiness of the substituent on the aromatic ring of derivatizing reagents (i.e. 2,3- and 3,5-dichlorophenylisothiocyanate) was observed to affect the resolution and alter the elution order as well. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Conformational Consequences of Regio- and Stereoselective Disulfide Bridge Oxidation in a Cyclic Peptide

CHEMBIOCHEM, Issue 1 2008
Miroslav Male
Synthesis of thiosulfinates. A thiosulfinate moiety was introduced into a cyclic peptide by regio- and stereoselective disulfide-bridge oxidation of S2,S6 -cyclo(H-Gly-Cys-Ser-Pro-Ala-Cys-Gly-OH). The CD, FTIR and NMR spectroscopic data demonstrated drastic changes in the peptide secondary structure upon oxidation of the Cys6 sulfur atom, while oxidation of the Cys2 sulfur atom caused only minor structure perturbations. [source]