Sulfur Bond Research Articles

Probing the Role of Connecting Bonds and Modifying Chains in the Rational Design of Prodrug Nanoassemblies.

Prodrug-based self-assembled nanoparticles combined with the merits of nanotechnology and prodrugs strategies have gradually become a research trending topic in the field of drug delivery. These prodrugs usually consist of parent drugs, connecting bonds, and modifying chains. The influences of the connecting bonds and modifying chains on the pharmaceutical characteristics, in vivo delivery fate, and antitumor activity of prodrug nanoassemblies remain elusive. Herein, three docetaxel (DTX) prodrugs were designed using sulfur bonds (thioether bond or disulfide bond) as connecting bonds and fatty alcohols (straight chain or branched chain) as modifying chains. Interestingly, the difference between connecting bonds and modifying chains deeply influenced the colloidal stability, redox responsive drug release, cytotoxicity, pharmacokinetic properties, tumor accumulation, and antitumor effect of prodrug nanoassemblies. DTX conjugated with branched chain fatty alcohols via disulfide bonds (HUA-SS-DTX) significantly improved the antitumor efficiency of DTX and reduced the systematic toxicity. Our study elaborates on the vital role of connecting bonds and modifying chains in the rational design of prodrug nanoassemblies.

Comparative homology of Pleurotus ostreatus laccase enzyme: Swiss model or Modeller?

Laccases stand out in the industrial context due to their versatile biotechnological applications. Although these enzymes are frequently investigated, currently, Pleurotus ostreatus laccase structural model is unknown. Therefore, this research aims to predict and validate a P. ostreatus laccase theoretical model by means of comparative homology. The laccase target’s primary structure (AOM73725.1) was obtained from the NCBI database, the model was predicted from homologous structures obtained from the PDB (PDB-ID: 5A7E, 2HRG, 4JHU, 1GYC) using the Swiss-Model and Modeller, and was refined in GalaxyRefine. The models were validated using PROCHECK, VERIFY 3D, ERRAT, PROVE and QMEAN Z-score servers. Moreover, molecular docking between the laccase model (Lacc4MN) and ABTS was performed on AutoDock Vina. The models that were generated by the Modeller showed superior stereochemical and structural characteristics to those predicted by the Swiss Model. The refinement made it difficult to stabilize the copper atoms which are typical of laccases. The Lacc4MN model showed the interactions between the amino acids in the active site of the laccase and the copper atoms, thereby hinting the stabilization of the metal through electrostatic interactions with histidine and cysteine. The molecular docking between Lacc4MN and ABTS showed negative free energy and the formation of two hydrogen bonds involving the amino acids ASP 208 and GLY 268, and a Pi–sulfur bond between residue HIS 458 and ABTS, which demonstrates the typical catalytic functionality of laccases. Furthermore, the theoretical model Lacc4MN presented stereochemical and structural characteristics that allow its use in silico tests. Communicated by Ramaswamy H. Sarma

Recent Advances in Inverted Perovskite Solar Cells: Designing and Fabrication.

Inverted perovskite solar cells (PSCs) have been extensively studied by reason of their negligible hysteresis effect, easy fabrication, flexible PSCs and good stability. The certified photoelectric conversion efficiency (PCE) achieved 23.5% owing to the formed lead−sulfur (Pb−S) bonds through the surface sulfidation process of perovskite film, which gradually approaches the performance of traditional upright structure PSCs and indicates their industrial application potential. However, the fabricated devices are severely affected by moisture, high temperature and ultraviolet light due to the application of organic materials. Depending on nitrogen, cost of protection may increase, especially for the industrial production in the future. In addition, the inverted PSCs are found with a series of issues compared with the traditional upright PSCs, such as nonradiative recombination of carriers, inferior stability and costly charge transport materials. Thus, the development of inverted PSCs is systematically reviewed in this paper. The design and fabrication of charge transport materials and perovskite materials, enhancement strategies (e.g., interface modification and doping) and the development of all−inorganic inverted devices are discussed to present the indicator for development of efficient and stable inverted PSCs.

Applications of Alternating Current/Alternating Potential Electro­lysis in Organic Synthesis

AbstractThis review summarises the rarely used method of alternating current electrolysis for the synthesis of organic products. Different waveforms have been investigated which opens the possibility for further influence the outcome of the electrolysis by variation of the frequency as well as the highest peak current. In recent years alternating current electrolysis has been applied in increasingly more complex transformations. Especially the functionalisation of (hetero)arenes, functional group manipulation, metathesis reactions, and transition-metal-catalysed cross-coupling reactions were reported in recent years and the results of these and some other investigations are summarized in this review article.1 Introduction1.1 Waveforms1.2 Objectives1.3 Early Examples of the Optimisation of Alternating Current Electrolysis2 Recent Applications of Alternating Current Electrolysis for Organic Synthesis2.1 Substitution Reaction on Arenes2.2 Nitrogen–Sulfur Bond Formation and Sulfur–Sulfur Bond Metathesis2.3 Oxidation and Reduction2.4 Cross-Coupling Reactions2.5 Frequency Optimisation3 Conclusion

Synthesis of nano-oxides by preparing metal complexes based on dithiocarbamate derivatives

Metal oxide nanoparticles are a branch of nanoparticles that have high optical properties. Dithiocarbamites are organic sulfur bonds that form stable complexes with metals. There are two types of dithiocarbamate: mono- and di-alkyl dithiocarbamate. In this study, two Schiff bases were prepared, the first Schiff base: [(E)-N-(2-ethylhexyl)-1-Phenyl methanimine] and the second Schiff base: [(E)-N-benzyl-1-Phenyl methanimine ]. From these two bases, the first secondary amine was prepared: N-Benzyl-2-ethylhexyl-1-amine, and the second secondary amine, Di Benzylamine. This was followed by the preparation of ligands from the two prepared secondary amines, which are Potasium benzyl(2-ethyl) Carbamadithioate, and the second ligand: Potasium di benzyl Carbamodithioate. These two ligands were employed in the interaction with the ions: Mn, Cu, Zn. each separately to form the macrocyclic complexes.

Intrinsic electron transport in monolayer MoSi2N4 and WSi2N4

We systematically studied the intrinsic electron transport of the recently fabricated two-dimensional (2D) monolayer MoSi2N4 and WSi2N4 (belong to the MA2Z4 family, where M is a transition metal; A is Si or Ge; and Z is N, P, or As) by using the Boltzmann transport theory with the scattering rates calculated from first-principles calculations. It is found that both materials have moderate room temperature electron mobility of 87 cm2/V s for MoSi2N4 and 119 cm2/V s for WSi2N4. Our detailed analysis shows that their electron mobility difference is attributed to the different average effective mass. Moreover, by comparing studies with monolayer MoS2 and WS2, we reveal that the polar optical phonon pattern of MoSi2N4 and WSi2N4 is governed by the antiparallel silicon–nitrogen bond oscillation, different from MoS2 and WS2, in which is governed by the antiparallel transition metal–sulfur bond oscillation. This feature is arising from the large electronegativity difference between N and Si. Nitrogen has the fourth largest electronegativity, so it always tends to attract plenty of electrons from Si and thus Si has a large Born effective charge, thereby resulting in strong Fröhlich interaction. We further found that all the 2D semiconducting MA2Z4 have large Born effective charges, thereby indicating a generally strong electron–phonon coupling strength.

Selective CO2-to-Formate Conversion Driven by Visible Light over a Precious-Metal-Free Nonporous Coordination Polymer

Metal–organic frameworks (MOFs) and coordination polymers (CPs) are potential candidates for high-performance photocatalysts because of their high tunability of electronic and structural properties. For example, MOFs and CPs having a high specific surface area (∼1000 m2 g–1) have been applied as visible-light-driven photocatalysts for CO2 reduction and water splitting. Herein, we show a unique CP possessing a metal–sulfur bond with Pb2+, an earth-abundant metal ion. Different from ordinary high-surface-area MOFs and CPs, this CP is nonporous and has just 0.7 m2 g–1 surface area. Nevertheless, owing to its capability of absorbing visible light up to ∼500 nm, it efficiently photocatalyzes CO2 reduction to formate (HCOO–) under visible-light irradiation with >99% selectivity and an apparent quantum yield of 2.6% at 400 nm, even without postmodification treatment such as cocatalyst loading. These values are the highest yet reported for a precious-metal-free single-component photocatalyst for the visible-light-driven reduction of CO2 to HCOO–. This work may thus shed light on the great potential of nonporous CPs as building units of photocatalytic CO2 conversion systems.

Phosphine-Mediated Cleavage of Sulfur–Sulfur Bonds

Phosphine-Mediated Cleavage of Sulfur–Sulfur Bonds

One‐pot sulfa‐Michael addition reactions of disulfides using a pyridine‐borane complex under blue light irradiation

AbstractWe report a one‐pot sulfa‐Michael addition reaction using a disulfide and a pyridine‐borane complex under blue light irradiation. This novel synthetic approach has a broad substrate scope and a high functional group tolerance. Mechanistic studies suggest that sequential radical and ionic processes provide a practical solution for constructing carbon–sulfur bonds.

Commonly Used Alkylating Agents Limit Persulfide Detection by Converting Protein Persulfides into Thioethers

AbstractProtein persulfides (R‐S‐SH) have emerged as a common post‐translational modification. Detection and quantitation of protein persulfides requires trapping with alkylating agents. Here we show that alkylating agents differ dramatically in their ability to conserve the persulfide's sulfur–sulfur bond for subsequent detection by mass spectrometry. The two alkylating agents most commonly used in cell biology and biochemistry, N‐ethylmaleimide and iodoacetamide, are found to be unsuitable for the purpose of conserving persulfides under biologically relevant conditions. The resulting persulfide adducts (R‐S‐S‐Alk) rapidly convert into the corresponding thioethers (R‐S‐Alk) by donating sulfur to ambient nucleophilic acceptors. In contrast, certain other alkylating agents, in particular monobromobimane and N‐t‐butyl‐iodoacetamide, generate stable alkylated persulfides. We propose that the nature of the alkylating agent determines the ability of the disulfide bond (R‐S‐S‐Alk) to tautomerize into the thiosulfoxide (R‐(S=S)‐Alk), and/or the ability of nucleophiles to remove the sulfane sulfur atom from the thiosulfoxide.

Synthesis and Characterization of Dihydrouracil Analogs Utilizing Biginelli Hybrids.

Dihydrouracil presents a crucial intermediate in the catabolism of uracil. The vital importance of uracil and its nucleoside, uridine, encourages scientists to synthesize novel dihydrouracils. In this paper, we present an innovative, fast, and effective method for the synthesis of dihydrouracils. Hence, under mild conditions, 3-chloroperbenzoic acid was used to cleave the carbon–sulfur bond of the Biginelli hybrids 5,6-dihydropyrimidin-4(3H)-ones. This approach led to thirteen novel dihydrouracils synthesized in moderate-to-high yields (32–99%).

Atomic modulation of Fe-Co pentlandite coupled with nitrogen-doped carbon sphere for boosting oxygen catalysis

Reversible oxygen reaction plays a crucial role in rechargeable battery systems, but it is limited by the slow reaction kinetics. Herein, the ionic modulation of cobalt pentlandite coupled with nitrogen-doped bowl-like hollow carbon sphere is well designed on octahedral and tetrahedral sites. The robust FexCo9–xS8-NHCS-V with iron replacing at the octahedron possesses prolonged metal sulfur bond and exhibits excellent bifunctional electrocatalytic performance towards oxygen reduction reaction (ORR, E1/2 = 0.80 V vs. RHE) and excellent oxygen evolution reaction (OER, Ej= 10 = 1.53 V vs. RHE) in 0.1 mol/L KOH. Accordingly, a rechargeable Zn-air battery of FexCo9–xS8-NHCS-V cathode endows high energy efficiency (102 mW cm−2), and a microbial fuel cell achieves a high-power density (791 ± 42 mW m−2), outperforming the benchmark Pt/C catalyst.

Prodrug nanoassemblies bridged by Mono-/Di-/Tri-sulfide bonds: Exploration is for going further

Sulfur bonds, including thioether bond and disulfide bond, have been widely used to develop tumor redox-responsive drug delivery systems. Recently, trisulfide bond was also introduced into the construction of prodrug nanoassemblies. However, the integrated effects of these sulfur bonds on prodrug nanoassemblies remain elusive. Here, three paclitaxel homodimeric prodrugs are synthesized using thioether bond, disulfide bond or trisulfide bond as linkages. Interestingly, the sulfur bonds significantly changed the molecular assembly of prodrugs, thereby influencing the colloidal stability and in vivo destiny of prodrug nanoassemblies. More importantly, the trisulfide bond is found to be a novel redox dual-sensitive linkage, and the responsive mechanism is illustrated. The differences of thioether/disulfide/trisulfide bond are investigated in-depth, and their effect on the antitumor efficacy of prodrug nanoassemblies is also clarified. Our findings provide deep insights into the impacts of sulfur bonds on prodrug nanoassemblies, and highlight the potential of trisulfide bond for the development of redox dual-responsive nanomedicines.

Sulfonyl Chlorides as Thiol Surrogates for Carbon-Sulfur Bond Formation: One-Pot Synthesis of Thioethers and Thioesters.

A method to synthesize thioethers and thioesters directly from readily available sulfonyl chlorides is reported. We demonstrate that a transient intermediate formed during phosphine-mediated deoxygenation of sulfonyl chlorides can be trapped in situ by activated alcohols or carboxylic acids to effect carbon-sulfur bond formation. The method is operationally simple and tolerates a broad range of functional groups. Special attention has been focused on the late-stage diversification of densely functionalized natural products and pharmaceuticals.

RaS-RiPPs in Streptococci and the Human Microbiome.

Radical S-adenosylmethionine (RaS) enzymes have quickly advanced to one of the most abundant and versatile enzyme superfamilies known. Their chemistry is predicated upon reductive homolytic cleavage of a carbon–sulfur bond in cofactor S-adenosylmethionine forming an oxidizing carbon-based radical, which can initiate myriad radical transformations. An emerging role for RaS enzymes is their involvement in the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs), a natural product family that has become known as RaS-RiPPs. These metabolites are especially prevalent in human and mammalian microbiomes because the complex chemistry of RaS enzymes gives rise to correspondingly complex natural products with minimal cellular energy and genomic fingerprint, a feature that is advantageous in microbes with small, host-adapted genomes in competitive environments. Herein, we review the discovery and characterization of RaS-RiPPs from the human microbiome with a focus on streptococcal bacteria. We discuss the varied chemical modifications that RaS enzymes introduce onto their peptide substrates and the diverse natural products that they give rise to. The majority of RaS-RiPPs remain to be discovered, providing an intriguing avenue for future investigations at the intersection of metalloenzymology, chemical ecology, and the human microbiome.

High Purity Single Wall Carbon Nanotube by Oxygen-Containing Functional Group of Ferrocene-Derived Catalyst Precursor by Floating Catalyst Chemical Vapor Deposition.

Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst’s exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (–OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate () than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal–sulfur bonds (such as S2− and ). The hydroxyl group (–OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.

Molybdenum-Sulfur Bond: Electronic Structure of Low-Lying States of MoS.

The molybdenum-sulfur bond plays an important role in many processes such as nitrogen-fixation, and it is found as a building block in layered materials such as MoS2, known for its various shapes and morphologies. Here, we present an accurate theoretical and experimental investigation of the chemical bonding and the electronic structure of 20 low-lying states of the MoS molecule. Multireference and coupled cluster methodologies, namely, MRCISD, MRCISD + Q, RCCSD(T), and RCCSD[T], were employed in conjunction with basis sets up to aug-cc-pwCV5Z-PP/aug-cc-pwCV5Z for the study of these states. We note the significance of including the inner 4s24p6 electrons of Mo and 2s22p6 of S in the correlated space to obtain accurate results. Experimentally, the predissociation threshold of MoS was measured using resonant two-photon ionization spectroscopy, allowing for a precise measurement of the bond dissociation energy. Our extrapolated computational D0 value for the ground state is 3.936 eV, in excellent agreement with our experimental measurement of 3.932 ± 0.004 eV. The largest calculated adiabatic D0 (5.74 eV) and the largest dipole moment (6.50 D) were found for the 5Σ+ state, where a triple bond is formed. Finally, the connection of the chemical bonding of the isolated MoS species to the relevant solid, MoS2, is emphasized. The low-lying septet states of the diatomic molecule are involved in the material as a building block, explaining the stability and the variety of the shapes and morphologies of the material.

Ultraviolet photoelectron spectroscopic study on the interface electronic structure of the L‐cysteine on Pd surface

L‐cysteine is one of the most versatile biomolecules with a unique metal‐binding ability. L‐cysteine has an outstanding role in the bioelectronics field as a linker between proteins of biomolecules and metal electrodes of the inorganic metals through multiple functional groups. The interface electronic structures between L‐cysteine with metals deserve further investigation for applications in bioelectronics. However, the interface electronic structures of L‐cysteine and metals have not been well understood. We have previously reported the existence of a new state between the highest occupied molecular orbital (HOMO) of L‐cysteine and the Fermi level of the metals for L‐cysteine/Au(111), L‐cysteine/Ag(111), and L‐cysteine/Cu(111) using photoemission spectroscopy and attributed the formation of the new state to an interaction of the d band with HOMO of L‐cysteine. In this study, the electronic structure at the interfaces of L‐cysteine on a Palladium (Pd) surface is investigated by ultraviolet photoemission spectroscopy (UPS) using synchrotron radiation including work function, secondary electron cutoff (SECO), and HOMO onset; the position of an interface state, charge injection barrier, and ionization energy are estimated. It is observed that thin‐film spectra of L‐cysteine on Pd surfaces in the valance top region are different from the L‐cysteine thick films, and this can be attributed to an interaction between a sulfur‐originated state of L‐cysteine HOMO with Pd d orbitals. Also, a 0.6‐eV SECO shift is estimated due to the charge transferring between L‐cysteine and Pd. The results of SECO further confirm the weakening of the Pd–sulfur bond with increasing L‐cysteine coverage on Pd.

Photochemical carbon-sulfur bond cleavage in thioethers mediated via excited state Rydberg-to-valence evolution.

Time-resolved photoelectron imaging and supporting ab initio quantum chemistry calculations were used to investigate non-adiabatic excess energy redistribution dynamics operating in the saturated thioethers diethylsulfide, tetrahydrothiophene and thietane. In all cases, 200 nm excitation leads to molecular fragmentation on an ultrafast (<100 fs) timescale, driven by the evolution of Rydberg-to-valence orbital character along the S-C stretching coordinate. The C-S-C bending angle was also found to be a key coordinate driving initial internal conversion through the excited state Rydberg manifold, although only small angular displacements away from the ground state equilibrium geometry are required. Conformational constraints imposed by the cyclic ring structures of tetrahydrothiophene and thietane do not therefore influence dynamical timescales to any significant extent. Through use of a high-intensity 267 nm probe, we were also able to detect the presence of some transient (bi)radical species. These are extremely short lived, but they appear to confirm the presence of two competing excited state fragmentation channels - one proceeding directly from the initially prepared 4p manifold, and one involving non-adiabatic population of the 4s state. This is in addition to a decay pathway leading back to the S0 electronic ground state, which shows an enhanced propensity in the 5-membered ring system tetrahydrothiophene over the other two species investigated.

Carbon-Sulfur Bond Formation: Tandem Process for the Synthesis of Functionalized Isothiazoles.

In this paper, we report a new process for the construction of 3,4,5-substituted isothiazoles via reaction cascades including Pummerer-like rearrangement, nucleophilic condensation, and sulfenamide cyclization followed by concomitant elimination and dehydration under mild reaction conditions. This process provides isothiazoles bearing fluorine and other functional groups in good to excellent yields from readily available starting materials.