			Home About us Contact

Sulfur Bonds (sulfur + bond)

Distribution by Scientific Domains

Chemistry	87%

Selected Abstracts

Two Distinct Mechanisms of Alkyne Insertion into the Metal,Sulfur Bond: Combined Experimental and Theoretical Study and Application in Catalysis

CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2010
Valentine
Abstract The present study reports the evidence for the multiple carbon,carbon bond insertion into the metal,heteroatom bond via a five-coordinate metal complex. Detailed analysis of the model catalytic reaction of the carbon,sulfur (CS) bond formation unveiled the mechanism of metal-mediated alkyne insertion: a new pathway of CS bond formation without preliminary ligand dissociation was revealed based on experimental and theoretical investigations. According to this pathway alkyne insertion into the metal,sulfur bond led to the formation of intermediate metal complex capable of direct CS reductive elimination. In contrast, an intermediate metal complex formed through alkyne insertion through the traditional pathway involving preliminary ligand dissociation suffered from "improper" geometry configuration, which may block the whole catalytic cycle. A new catalytic system was developed to solve the problem of stereoselective SS bond addition to internal alkynes and a cost-efficient Ni-catalyzed synthetic procedure is reported to furnish formation of target vinyl sulfides with high yields (up to 99,%) and excellent Z/E selectivity (>99:1). [source]

ChemInform Abstract: Phosphine-Catalyzed Formation of Carbon,Sulfur Bonds: Catalytic Asymmetric Synthesis of ,-Thioesters.

CHEMINFORM, Issue 30 2010
Jianwei Sun
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]

Electrophilic Attack on Sulfur,Sulfur Bonds.

CHEMINFORM, Issue 43 2004
Part 1.
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Electrophilic Attack on Sulfur,Sulfur Bonds: Coordination of Lithium Cations to Sulfur-Rich Molecules Studied by Ab Initio MO Methods

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005
Yana Steudel Dr.
Abstract Complex formation between gaseous Li+ ions and sulfur-containing neutral ligands, such as H2S, Me2Sn (n = 1,5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiSn heterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from ,88 kJ,mol,1 for [H2SLi]+ to ,189 kJ,mol,1 for the most stable isomer of [Me2S5Li]+ which contains three-coordinate Li+. Of the various S6 ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5S ligand have the highest binding energies (,163±1 kJ,mol,1). However, the global minimum structure of [LiS6]+ is of C3v symmetry with the six-membered S6 homocycle in the well-known chair conformation and three LiS bonds with a length of 256 pm (binding energy: ,134 kJ,mol,1). Relatively unstable isomers of S6 are stabilized by complex formation with Li+. The interaction between the cation and the S6 ligands is mainly attributed to ion,dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4 units, as in [Li(S3)2]+ and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+ complexes, the number of SS bonds is at maximum and the coordination number of Li+ is either 3 or 4. A topological analysis of all investigated complexes revealed that the LiS bonds of lengths below 280 pm are characterized by a maximum electron-density path and closed-shell interaction. [source]

Two Distinct Mechanisms of Alkyne Insertion into the Metal,Sulfur Bond: Combined Experimental and Theoretical Study and Application in Catalysis

The Alternative Oxidase: in vivo Regulation and Function

PLANT BIOLOGY, Issue 1 2003
F. F. Millenaar
Abstract: This review focuses on the biochemical regulation and function of the alternative oxidase in vivo. About 10 years ago, two activation mechanisms were discovered in isolated mitochondria, namely activation by reducing sulfur bonds in the protein and activation by an allosteric effect of pyruvate. It was proposed that plants would have a regulatory mechanism to modify alternative oxidase activity in vivo. However, more recent studies have shown that these two activation mechanisms may not play such an important role in regulation of alternative oxidase activity in vivo after all. Pyruvate and reduction of the sulfide bonds in the protein are definitely required for alternative oxidase activity, but they do not appear to be regulating the activity in vivo. Despite the energy wasting nature of the alternative oxidase, there was no obvious physiological function for the pathway for many years. It is now more clear that the alternative oxidase can prevent the production of excess reactive oxygen species radicals by stabilizing the redox state of the mitochondrial ubiquinone pool, while allowing continued activity of the citric acid cycle. This may be important under conditions when the NADH supply is relatively high (reductant overflow), or when the cytochrome pathway is restrained. The cytochrome pathway might be inhibited by naturally occurring cyanide, nitric oxide, sulfide, high concentrations of CO2, low temperatures, or by limited phosphate supply. [source]

A Targeted Releasable Affinity Probe (TRAP) for In Vivo Photocrosslinking

CHEMBIOCHEM, Issue 9 2009
Ping Yan Dr.
Abstract A protein TRAP: The in vivo photocrosslinking of TRAP after its intracellular targeting to a binding sequence on the bait protein stabilizes protein interactions. Because the crosslinker is releasable, simple mass spectrometry can be used to identify the protein binding sites after purification. Protein crosslinking, especially coupled to mass-spectrometric identification, is increasingly used to determine protein binding partners and protein,protein interfaces for isolated protein complexes. The modification of crosslinkers to permit their targeted use in living cells is of considerable importance for studying protein-interaction networks, which are commonly modulated through weak interactions that are formed transiently to permit rapid cellular response to environmental changes. We have therefore synthesized a targeted and releasable affinity probe (TRAP) consisting of a biarsenical fluorescein linked to benzophenone that binds to a tetracysteine sequence in a protein engineered for specific labeling. Here, the utility of TRAP for capturing protein binding partners upon photoactivation of the benzophenone moiety has been demonstrated in living bacteria and mammalian cells. In addition, ligand exchange of the arsenic,sulfur bonds between TRAP and the tetracysteine sequence to added dithiols results in fluorophore transfer to the crosslinked binding partner. In isolated protein complexes, this release from the original binding site permits the identification of the proximal binding interface through mass spectrometric fragmentation and computational sequence identification. [source]

Description of the Ground-State Covalencies of the Bis(dithiolato) Transition-Metal Complexes from X-ray Absorption Spectroscopy and Time-Dependent Density-Functional Calculations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2007
Kallol Ray Dr.
Abstract The electronic structures of [M(LBu)2], (LBu=3,5-di- tert -butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(,) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(LBu)2], (M=Ni, Pd, Pt) and [Au(LBu)2] are best described as delocalized class,III mixed-valence ligand radicals bound to low-spin d8 central metal ions while [M(LBu)2], (M=Cu, Au) and [M(LBu)2]2, (M=Ni, Pd, Pt) contain completely reduced dithiolato(2,) ligands. The case of [Co(LBu)2], remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S1s,valence-, versus S1s,valence-, transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal,sulfur bonds from ligand K-edge absorption spectroscopy. [source]