S-S Bond Research Articles

Thermodynamic calculations and dynamics simulation on thermal-decomposition reaction of MoS2 and Mo2S3 under vacuum

In this paper, thermal decomposition process of molybdenum concentrate in vacuum was thermodynamically analyzed, and decomposition mechanism of MoS system in molybdenum was mainly studied. To further investigate and analyze the electronic properties in different temperature, the simulation calculations of MoS2(0 0 1) surface and Mo2S3(0 0 1) surface density of states, electron density difference, electronic orbital and Mulliken overlap population were carried out by density functional theory(DFT) formalism. The dynamics simulations results of MoS2(0 0 1) surface and Mo2S3(0 0 1) surface were obtained the temperature range of phase transforming are 1573 K–1673 K and from 1473 K to 1573 K at 20Pa, respectively. The interaction of MoS2 and Mo2S3 shows that thermal-decomposition of MoS2 and Mo2S3 does react, when new SS bonds and MoMo bond are formed instead of MoS bond fracture. The experimental results of the thermal decomposition of MoS2 and Mo2S3 were in accordance with the thermodynamics theoretical calculation results and ab-initio molecular dynamics simulation results.

Exploration on the removal mechanism of sulfur ether model compounds for coal by microwave irradiation with peroxyacetic acid

The removal mechanism of sulfoether in coal by microwave with peroxyacetic acid, was determined by evaluating changes in sulfur containing compounds after desulfurization by XANES and GC/MS. The highest occupied molecular orbital composition, the electrostatic potential distribution, and the sulfur containing bond dissociation energy (BDE) of model compounds molecules were also determined to support the experimental results. Results showed that sulfoether was easily oxidized to corresponding sulfoxide or sulfone in treated samples. Although benzyl sulfides were more readily oxidized than disulfides, the latter was easier to remove due to the higher breaking probability of the SS bond. The sulfur atoms within sulfur ether in coal are the active sites for electrophilic reaction. As sulfur atoms were oxidized, the sulfur containing BDEs decreased considerably and the dipole moments of sulfoether molecules increased. These findings suggest that the removal efficiency of sulfoether in coal may be improved by moderate and selective oxidation under microwave treatment.

Influence of hydrolysis behaviour and microfluidisation on the functionality and structural properties of collagen hydrolysates.

The functionality and structural properties of pig skin hydrolysates with different degrees of hydrolysis (DH, 10% and 20%) and microfluidisation (120MPa), prepared by pepsin and Alcalase® have been investigated in this study. Extensive hydrolysis can significantly improve the absolute value of the zeta potential and surface hydrophobicity. The particle distribution of hydrolysates decreased with increasing DH. The numbers of free sulfhydryl (SH) and disulfide bonds (SS) were significantly increased with increasing DH (p<0.05). Hydrolysates with a lower DH showed a better emulsifying property than those with a higher DH. Microfluidisation led to the transformation of structural and interfacial properties of the hydrolysates and increased the value of the zeta potential, S0, and gel strength. Microfluidisation results in limited breakage of chemical bonds, the number of SS and SH bonds unchanged in the treatment. These results reflect the functionality and structural properties of collagen-rich pig skin hydrolysates.

Doxorubicin Delivery Using pH and Redox Dual-Responsive Hollow Nanocapsules with a Cationic Electrostatic Barrier.

For the delivery of doxorubicin (DOX), pH and redox dual responsive hollow nanocapsules were prepared through the stabilization of polymer vesicles, which spontaneously formed from polyamidoamine dendron-poly(l-lysine) (PAMAM dendron-PLL), by the introduction of disulfide (SS) bonds between PLLs. The SS-bonded nanocapsules exhibited a very slow release of DOX under an extracellular environment because the cationic PLL membrane acted as an electrostatic barrier against the protonated DOX molecules. However, increasing the glutathione concentration to the intracellular level facilitated the immediate release of DOX through the collapse of nanocapsules by the spontaneous cleavage of SS bonds. SS-bonded nanocapsules also escaped from the endosome by the buffering effect of PAMAM dendrons, and DOX delivery into the cytoplasm was achieved. Furthermore, DOX molecules delivered by SS-bonded nanocapsules exhibited an effective in vitro anticancer effect to HeLa cells.

Innovative Technologies in Nanomedicines: From Passive Targeting to Active Targeting/From Controlled Pharmacokinetics to Controlled Intracellular Pharmacokinetics.

Nanomedicines promise to extend drug therapy from small molecular compounds to proteins/nucleic acids/genes. Multifunctional envelope-type nanodevices (MENDs) have been developed for delivering such molecules to the site of action. The YSK-MEND contains new types of pH-responsive cationic lipids to efficiently deliver siRNA to hepatocytes via receptor-mediated endocytosis and use in treating hepatitis C and B in model mice. The RGD ligand is introduced to target tumor endothelial cells (TEC) and RGD-MEND is able to send siRNA to TEC to regulate the function of tumor microenvironments. The MITO-Porter is also developed to target mitochondria via membrane fusion. Antisense oligo RNA in the MITO-Porter permits the knock down of mitochondrial function. Finally, the ssPalms is designed based on a new concept of pH-dependent protonation in endosomes and cleavage of SS bonds in the reducing conditions in cytosol. These new technologies promise to stimulate the use of Nanomedicines in the future.

Spectroscopic study on biological mackinawite (FeS) synthesized by ferric reducing bacteria (FRB) and sulfate reducing bacteria (SRB): Implications for in-situ remediation of acid mine drainage

Mackinawite (FeS), widespread in low temperature aquatic environments, is generally considered to be the first Fe sulfide formed in sedimentary environments which has shown effective immobilization of heavy metals and toxic oxyanions through various sorption reactions. The spectroscopic study researches on mackinawite formed by FRB and SRB and its environmental implication for in-situ remediation of acid mine drainage where contains large amounts of Fe3+ and SO42−. The XRD result of biologically synthetic particles shows that these particles are mainly composed of mackinawite (FeS0.9). The Raman peaks observed at 208, 256, 282, 298cm−1 are attributed to FeS stretching vibrations of mackinawite. The Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) reveals that the diagnostic bands of low intensity for these FeS particles occur at 412–425cm−1 and 607–622cm−1, which are assigned to the stretching vibrations of SS and FeS bonds. The Raman and IR vibrations from organic components both confirm that these particles are biogenic origin. The IR spectra of biologically synthesized mackinawite for different aging times show that the nano-sized particles mackinwate will be completely oxidized within 10h. All these findings have good implications for in-situ remediation of acid mine drainage.

Photoinduced formation of thiols in human hair

Raman, scanning electron, and optical microscopy of hair and spectrophotometry of soluble hair proteins are used to study the effect of UV-vis radiation on white hair. The samples of a healthy subject are irradiated using a mercury lamp and compared with non-irradiated (control) hair. The cuticle damage with partial exfoliation is revealed with the aid of SEM and optical microscopy of semifine sections. Gel filtration chromatography shows that the molecular weight of soluble proteins ranges from 5 to 7kDa. Absorption spectroscopy proves an increase in amount of thiols in a heavier fraction of the soluble proteins of irradiated samples under study. Raman data indicate a decrease in the amount of SS and CS bonds in cystines and an increase in the amount of SH bonds due to irradiation. Such changes are more pronounced in peripheral regions of hair. Conformational changes of hair keratins presumably related to the cleavage of disulfide bonds, follow from variations in amide I and low-frequency Raman bands. An increase in the content of thiols in proteins revealed by both photometric data on soluble proteins and Raman microspectroscopy of hair cuts can be used to develop a protocol of the analysis of photoinduced hair modification.

Radical Cations of the Monomer and van der Waals Dimer of a Methionine Residue as Prototypes of (2 Center-3 Electron) SN and SS Bonds. Molecular Simulations of Their Absorption Spectra in Water.

Oxidation of peptides or proteins by the OH(•) radicals produced by pulse radiolysis yields species identified by their absorption spectra in the UV-visible domain. However, the case of methionine (Met) in peptides is complex because its oxidation can lead to various free radicals with 2 center-3 electron (2c-3e) bonds. We have performed Monte Carlo/density functional theory molecular simulations of the radical cation of the methylated methionine aminoacid, Met(•+), taken as a model of the methonine residue of peptides, and of the radical cation of its van der Waals dimer, Met2(•+). The cation of the methionine residue displays a 2c-3e SN bond. The cation of dimer Met2(•+) displays three quasidegenerate conformers, one stabilized by a 2c-3e SS bond and the other two stabilized by ion-molecule interactions and made up of a neutral and a cationic unit. These conformers are characterized by their charge and spin density localization and their UV-visible absorption spectra. These spectra enable a discussion of the absorption spectra of the literature; in particular, we emphasize the role of dimers before and after the oxidation process.

English

β-galactosidase (EC.3.2.1.23) is an important enzyme, mainly used in the preparation of lactose hydrolyzed milk suitable for people with lactose intolerance. It is essential to understand the structural and functional aspects of various β-galactosidase produced from different sources. The present work deals with the use of bioinformatics to describe the physiochemical, functional and structural properties of β-galactosidase enzymes on Bacillus sp. selected from the gene bank of NCBI. The grand average hydropathy (GRAVY) and low range of AFY63015.1 value indicates the possibility of better interaction with water and instability index were computed to characterise YP_004205251.1, ZP_10511829.1, BAL72724.1, AFY63015.1, NP_242888.1 stating that they are stable and disulfide bridges, CYS_REC recognizes the presence of 38 cysteine residues in β-galactosidase sequences and predicted most probable SS bond patterns of pairs in YP_004981461 and 1AFY63015.1. The self- optimized prediction method (SOPM) was used to predict the secondary structure. The SOPM results indicated the presence of alpha helix is more dominated in sequences AFY63015.1 and YP_004981461.1. Overall this represents in silico analysis of sequence, structural and functional information of β-galactosidase of Bacillus species. Key words: Bacillus sp., β-galactosidase, in silico analysis, physico-chemical characterization, proteomics tools.

Trends in the Structural and Vibrational Properties of the Disulfanes S2X2 (X = H, Halogen, CH3, CF3)

AbstractThe geometrical parameters and associated force constants for the molecules XSSX (X = H, halogen, CH3, CF3) were studied using DFT quantum chemistry calculations. The study showed rather monotonic trends in these properties related to the SS bonds, although an anomalous behavior is noted when the substituent is CF3. The calculated vibrational frequencies allowed a confirmation of published band assignments, but corrections were necessary for S2F2 and S2H2.

A flame retardant synergism of organic disulfides and phosphorous compounds

A highly efficient halogen-free flame retardant system for polystyrene foams consisting of phosphororganic compounds and synergists of the general structure RSSR is described here and mechanistic details of its mode of action are given. Compared to the corresponding individual components, the flame retarding effect is enhanced or actually imparted by the use of various combinations of those compounds. Among the disulfides investigated bis(benzothiazolyl)disulfide showed the best synergistic effect. Bis(diphenylphosphinothiolyl)disulfide as a one-component flame retardant combining phosphorous entities and a disulfide bridge in one molecule exhibits a similar flame retardant efficiency. Polystyrene samples containing these additives were analyzed by thermal desorption mass spectrometry (TD-MS), whereby the release of S2-fragments during the thermal decomposition of the disulfides could be detected even in the case of systems for which a cleavage of SS bonds would rather be expected. Based on these experiments and extensive quantum chemical calculations a conclusive mechanism is derived, which can help to design future flame retardant additives.

A QTAIM and stress tensor perspective of large-amplitude motions of the tetrasulfur tetranitride S4N4molecular graph

The nature of the bonding interactions including the intramolecular SS interactions in tetrasulfur tetranitride, S4N4 are probed by performing very large amplitude vibrations of all of the 18 normal modes of vibration. The QTAIM and stress tensor point properties are -then investigated and found to be highly dependent on the mode of vibration. A considerable degree of metallicity ξ(rb) is found for the SS and SN bonding interactions. A unique bonding feature is found for a small amplitude vibration of the most anharmonic mode of this investigation, mode 2, where the SS bond critical point (BCP) transforms from a closed-shell SS BCP to a shared-shell SS BCP. We find 17 new unique QTAIM topologies for the molecular graphs corresponding to the 18 modes of vibration along with seven “missing” topologies that are mapped onto a spanning 2-D Quantum topology Phase Diagram (QTPD). In addition, eleven unique topologies existing on 3-D QTPDs are found due to the presence of non-nuclear attractors (NNAs). We use the stress tensor eigenvalues to explain the invariance of the numbers and types of QTAIM critical points. The applicability of both the stiffness S and stress tensor stiffness Sσ are also explored. Two new bond measures are introduced, a polarizability P and the stress tensor polarizability Pσ which are derived from the stiffness S and stress tensor stiffness Sσ, respectively. © 2016 Wiley Periodicals, Inc.

Biodesulfurization of vulcanized rubber by enzymes induced from Gordonia amicalisa

In this work, Gordonia amicalisa was used to treat two kinds of vulcanized synthetic rubbers, vulcanized isoprene rubber (v-IR) and vulcanized styrene butadiene rubber (v-SBR). The effects of microbial treatment on vulcanized rubbers were evaluated by changes of crosslinking density, sol fraction, morphology, element content and chemical group of treated rubber samples. The results showed that G. amicalisa can break CC bond mainly on v-IR and SS bonds mainly on v-SBR. After microbial treatment of 20 days, the crosslink densities of v-IR and v-SBR decreased by 13.7% and 22.1%, respectively. The carbon content on v-IR surface was decreased by 9.1%. FTIR analysis showed that CC bonds transferred into CO bonds, indicating the main chain scission. Regarding to the v-SBR, sulfur content on its surface was decreased by 22.9%, SS bonds were broken and SO producing, indicating the sulfur crosslink scission. Furthermore, the inducing mechanism of desulfurizing enzyme produce from G. amicalisa was investigated. v-SBR and v-IR were used as enzyme inducers, and dibenzothiophene was used as substrate reacting with desulfurizing-enzyme. The liquid chromatography and ultraviolet spectrum analysis showed that v-SBR was the specific substrates that can induce G. amicalisa to secret desulfurizing enzyme, making desulfurizing reaction happen.

Role of Disulfide Bonds in Stabilizing the Conformation of Selected Enzymes—An Approach Based on Divergence Entropy Applied to the Structure of Hydrophobic Core in Proteins

One of the factors responsible for tertiary structural stabilization in proteins is the presence of the hydrophobic core—a result of hydrophobic interactions within the protein body. In some proteins (especially extracellular ones) additional stabilization is provided by covalent bonds between selected Cys residues, commonly referred to as disulfide bonds. The mutual interplay of both factors and their respective contributions to stabilization are the focus of this work. The assessment of the effects of disulfide bonds isinterpreted by Fuzzy Oil Drop (FOD) model in which individual polypeptide chain fragments (including fragments which participate in SS bonds) can be evaluated in the context of their influence upon tertiary structural stabilization by comparing their corresponding theoretical and idealized hydrophobicity density distributions. The proteins were identified with both factors reinforcing each other, as well as proteins where they seem to counteract each other. The analysis presents a number of enzymes, including ribonuclease, lysozyme, disulfide isomerase and phospholipase.

A computational study of ion current modulation in hVDAC3 induced by disulfide bonds

The human VDAC channel exists in three isoforms characterized by high sequence homology and structural similarity. Yet the function and mode of action of hVDAC3 are still elusive. The presence of six surface cysteines exposed to the oxidizing environment of the mitochondrial inter-membrane space suggests the possible establishment of intramolecular disulfide bonds. Two natural candidates for disulfide bridge formation are Cys2 and Cys8 that, located on the flexible N-terminal domain, can easily come in contact. A third potentially important residue is Cys122 that is close to Cys2 in the homology model of VDAC3. Here we analyzed the impact of SS bonds through molecular dynamics simulations of derivatives of hVDAC3 (dubbed SS-2-8, SS-2-122, SS-8-122) including a single disulfide bond. Simulations showed that in SS-8-122, the fragment 1-7 crosses the top part of the barrel partially occluding the pore and causing a 20% drop of conductance. In order to identify other potential channel-occluding disulfide bonds, we used a set of neural networks and structural bioinformatics algorithms, after filtering with the steric constraints imposed by the 3D-structure. We identified other three species, namely SS-8-65, SS-2-36 and SS-8-36. While the conductance of SS-8-65 and SS-2-36 is about 30% lower than that of the species without disulfide bonds, the conductance of SS-8-36 was 40–50% lower. The results show how VDAC3 is able to modulate its pore size and current by exploiting the mobility of the N-terminal and forming, upon external stimuli, disulfide bridges with cysteine residues located on the barrel and exposed to the inter-membrane space.

Enzymatic thiol Michael addition using laccases: Multiple C[sbnd]S bond formation between p-hydroquinones and aromatic thiols

Laccases create CC, CO or CN bonds and have been investigated intensively as catalysts for green chemistry and white biotechnology. However, little is known about CS bond formation in laccase-catalyzed reactions. We have used the laccases from Pycnoporus cinnabarinus and Myceliophthora thermophila to create heteromolecular reaction products from p-hydroquinones and aromatic thiols via CS bond formation. We discovered a broad assortment of different thiolated products, ranging from dimers to tetramers. During laccase-catalysis of the aromatic thiols without p-hydroquinones homomolecular dimers were formed and these were always linked by SS bonds. The use of laccase is a convenient way to form heteromolecular thiolated products and homomolecular SS bonds under eco-friendly environments.

小麦グリアジン（グリアA）の生地形成および製パン性に及ぼすPDI-ERO1によるS-S結合形成の作用

小麦グリアジン（グリアA）の生地形成および製パン性に及ぼすPDI-ERO1によるS-S結合形成の作用

Theoretical studies on the molecular structure, conformational preferences, topological and vibrational analysis of allicin

The molecular structure, conformational preferences, topological and vibrational analysis of allicin has been investigated at two different approaches. Calculations have been carried out on static (DFT and MP2) levels with an assortment of Dunning's basis sets and dynamic CPMD simulations. In this both case within the isolated molecule approximation. The results point out that at least twenty different conformers coexist on the PES as confirmed by the flexible character of this molecule. The topological analysis of ELF showed very similar nature of the SS and SO bonds. The infrared spectrum has been calculated, and a comparative vibrational analysis has been performed.

Hydrophobic core structure of macromomycin – the apoprotein of the antitumor antibiotic auromomycin – fuzzy oil drop model applied

Abstract The fuzzy oil drop model was applied to analyze the structure of macromomycin, the apoprotein of the antitumor antibiotic auromomycin, revealing the differentiation of β-structural fragments present in β-sandwich. The seven-stranded antiparallel β-barrel and two antiparallel β-sheet ribbons represent the highly ordered geometry of the structure. However, participation in hydrophobic core formation appears different. The structure of the complete domain represents the status of the irregular hydrophobic core; however, some β-structural fragments appear to represent the hydrophobicity density distribution accordant with the idealized distribution of hydrophobicity as expected using the fuzzy oil drop model. Four β-structural fragments generating one common layer appear to be unstable in respect to the general structure of the hydrophobic core. This area is expected to be more flexible than other parts of the molecule. The protein binds the ligand – chromophore, two 2-methyl-2,4-pentanediol – in a well-defined cleft. The presence of this cleft makes the general structure of the hydrophobic core irregular (as it may be interpreted using the fuzzy oil drop model). Two short loops generated by two SS bonds fit very well to the general distribution of hydrophobicity density as expected for the model. No information about the potential amyloidogenic character of this protein is given in the literature; however, the specificity of the hydrophobicity distribution profile is found to be highly similar to the one observed in transthyretin (Banach M, Konieczny L, Roterman I. The fuzzy oil drop model, based on hydrophobicity density distribution, generalizes the influence of water environment on protein structure and function. J Theor Biol 2014;359:6–17), suggesting a possible tendency to turn to the amyloid form. A detailed analysis of macromomycin will be given, and a comparable analysis with other proteins of β-sandwich or β-barrel will be presented.

Mechanism of the dissolution of As–S chalcogenide glass in n-butylamine and its influence on the structure of spin coated layers

Chalcogenide glass thin layers are useful to many practical applications especially for the fabrication of infrared (IR) optical elements. In comparison to the conventional vacuum deposition methods of their preparation, recently chemical methods such as spin coating are gaining attention. They involve dissolution of the source bulk glass in appropriate solvent and then depositing its thin layer. Chemical processes occurring during the glass dissolution and thin layer deposition determine the physico-chemical properties of deposited thin layers. The structure of chalcogenide bulk glasses (AsxS100−x, where 30≤×≤40) and their solutions in n-butylamine have been studied in this work by Raman spectroscopy. From the composition and time dependence of Raman spectra of solutions the mechanism of arsenic–sulfur glass dissolution involving the reaction of aliphatic amine solvent with homopolar SS bonds is proposed and the presence of alkyl ammonium arsenic sulfide salts in thin layers is established.