Aromatic Thiols Research Articles

Linkage Dependence of Interfacial Charge-Transfer Transitions in ZnO: Carboxylate versus Sulfur Linker.

Interfacial charge-transfer transitions (ICTTs) between organic compounds and inorganic semiconductors have recently attracted much attention due to the unique features of a wide range of visible light absorption with colorless organic molecules and direct interfacial charge separation for their potential applications in photoenergy conversions and chemical sensing. As the research on ICTT has almost been limited to titanium oxide semiconductors such as TiO2, the exploration of ICTT in other inorganic semiconductors is a high-priority issue. Recently, we demonstrated that ICTT is strongly induced by chemisorption of aromatic thiols on ZnO nanoparticles via the sulfur atom. Here, we report on ICTT in ZnO nanoparticles adsorbed with benzoic acid derivatives and the linkage dependence of ICTT in ZnO. We observed ICTT bands in the visible region upon adsorption of 4-(dimethylamino)benzoic acid (4-DMABA) and 3,4-dimethoxybenzoic acid (3,4-DMOBA) on ZnO nanoparticles via the carboxylate group. Notably, the ICTT absorption intensities are about 1 order of magnitude lower than those in the ZnO surface complexes with aromatic thiol compounds. Time-dependence density functional theory (TD-DFT) calculations well reproduce the linkage dependence of ICTT. This characteristic linkage dependence of ICTT in ZnO is attributed to the difference in the valence orbital of bridging atoms. The sulfur bridging atom with the larger 3p valence orbitals gives rise to strong electronic couplings between ZnO and adsorbates for ICTT, in contrast to very weak electronic couplings via the smaller 2p valence orbitals of the oxygen bridging atoms in the carboxylate linkage. Our research reveals the important linkage dependence of ICTT in ZnO and elucidates the mechanism.

An efficient and simple strategy toward the synthesis of highly functionalized compounds

The expedient syntheses of small libraries of ((β-ethoxycarbonyl, -cyano and -acetyl)propyloxy) methylphosphonate scaffolds bearing olefin, sulfanyl, or amine functions are described. All these new derivatives are readily produced from easily available starting reagents (aldehydes, electron-poor olefins, and dialkylphosphites) following a three steps reaction sequence of condensations, SN2′-type reaction and a conjugated thia- or aza-Michael 1,4-addition with aromatic and aliphatic thiol or amine nucleophiles.

Diphenyl Diselenide-Catalyzed Synthesis of Triaryl Phosphites and Triaryl Phosphates from White Phosphorus.

Industrially important triaryl phosphites, traditionally prepared from PCl3, have been synthesized by a diphenyl diselenide-catalyzed one-step procedure involving white phosphorus and phenols, which provides a halogen- and transition metal-free way to these compounds. Subsequent oxidation of triaryl phosphites produces triaryl phosphates and triaryl thiophosphates. Phosphorotrithioates are also prepared efficiently from aromatic thiols and aliphatic thiols.

Definitive assignment and mechanistic study of interfacial charge-transfer transitions between ZnO and benzenethiol

Interfacial charge-transfer transitions (ICTTs) between organic compounds and inorganic semiconductors have recently attracted increasing interest for their potential applications in solar energy conversions and biosensing due to the key features of visible-light absorption with colourless organic molecules and direct photoinduced charge separation. Recently, we first reported ICTT between ZnO nanoparticles and aromatic thiols such as benzene thiol (BT). Here, we computationally examine ICTT between ZnO and BT with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Our research provides the definitive assignment of ICTT in the ZnO-BT surface coordination complex and clarifies the mechanism of the ICTT.

Bis(μ-thiolato)-dicopper Containing Fully Spin Delocalized Mixed Valence Copper-Sulfur Clusters and Their Electronic Structural Properties with Relevance to the CuA Site.

With aromatic and aliphatic thiol-S donor Schiff base ligands, the copper-sulfur clusters, [(L1)8CuI6CuII2](ClO4)2·DMF·0.5CH3OH (1) and [(L2)12CuI5CuII11(μ4-S)(μ4-O)6](ClO4)·4H2O, respectively, have been reported ( Chem. Commun. 2017, 53, 3334); HL1/HL2 are 2-(((3-methylthiophen-2-yl)methylene)amino)benzene/ethanethiol). Complex 1 comprises a wheel shaped Cu8S8 framework, made up of interlinked Cu2{μ-S(R)}2 units. To understand the properties with relevance to the CuA site and to check whether self-assembly generates similar type clusters to 1, three complexes, [(L3)8CuI6CuII2](ClO4)2·(C2H5)2O·2.5H2O (2), [(L3Cl)8CuI6CuII2](ClO4)2·1.25(C2H5)2O·1.25CH3OH·2H2O (3), and [(L3CF3)8CuI6CuII2](ClO4)2·2(C2H5)2O·H2O (4) have been synthesized with supporting ligands HL3X (HL3 = 2-((furan-2-ylmethylene)amino)benzenethiol when X = -H; X = -Cl or -CF3 para to thiol-S are HL3Cl and HL3CF3 ligands, respectively). The X-ray structures of 3 and 4 feature a similar Cu8S8 architecture to 1. The spectroscopic properties and the X-ray structures revealed that 2-4 are fully spin delocalized mixed valence (MV) of class-III type clusters. The structural parameters of the N2Cu2{μ-S(R)}2 units of 3 and 4 closely resemble those of the MV binuclear CuA site. With the aid of UV-vis-NIR, EPR, and spectroelectrochemical studies, the electronic properties of these complexes have been described in comparison with the MV model complexes and CuA site.

Comparative study of structural order, thermal desorption behavior, and work function change of self-assembled monolayers of pentafluorobenzenethiols and tetrafluorobenzenethiols on Au(1 1 1)

The surface and interface structures, thermal desorption behaviors, and electronic properties of pentafluorobenzenethiol (PFBT) and tetrafluorobenzenethiol (TFBT) self-assembled monolayers (SAMs) on Au(111) formed at different vapor deposition temperatures (298, 323, and 348 K) were examined to understand the effect of dipole directions in fluorinated aromatic thiol SAMs using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), and Kelvin probe (KP) measurements. Molecular-scale STM observations revealed that PFBT SAMs on Au(111) had a well-ordered phase with a c(2 × √3) structure at 348 K, whereas TFBT SAMs showed a well-ordered phase with a (2√3 × 8√2)R30° structure at 323 K.TDS and XPS measurements also demonstrated thatPFBT and TFBT SAMs showed significantly different thermal desorption behaviorsand interface structures due toopposite directions of molecular dipole moments. The KP measurements showed that the extent of the work function change of SAM-modified Au substrates was lowest in most highly-ordered PFBT and TFBT SAMs formed at 348 K and 323 K, respectively, regardless of chemisorbed surface coverage. These findings revealed that the degree of structural order of SAMs is a more significant factor in causing the depolarization effect rather than chemisorbed surface coverage.

A green methodology for thioether formation reaction and synthesis of symmetrical disulfides over new heterogeneous Cu attached to bifunctionalized mesoporous MCM-41

Abstract Bifunctional porous nanomaterials are in high demand for heterogeneous catalysis. In this exploration, a new recyclable Cu attached bifunctionalized mesoporous MCM-41 (MCM-41-quinoline-2-4-dicarboxylic acid-Cu) has been developed through post-functionalization modification of silica MCM-41. This catalyst was demonstrated to be a novel, effective, and greener catalyst for the thioether formation reaction between aryl halides and S8, instead of thiol, and synthesis of disulfides by coupling of aromatic thiols with molecular O2 (air). This protocol is a greener way toward the thioether formation reaction and the synthesis of disulfides and shows a 100% atom economy. In this system, thioether is produced as the only product. One way that chemists evaluate a synthetic route is to focus on its atom economy, the proportion of reactant atoms that end up in the desired product. The efficiency of synthesis is quantified in terms of the percent atom economy: The catalytic system exhibits high chemo-selectivity, as shown by high yields. The catalyst can be easily separated using simple recovery and reused several times with consistent activity.

Expanding the Structural Diversity of Protein Building Blocks with Noncanonical Amino Acids Biosynthesized from Aromatic Thiols

AbstractIncorporation of structurally novel noncanonical amino acids (ncAAs) into proteins is valuable for both scientific and biomedical applications. To expand the structural diversity of available ncAAs and to reduce the burden of chemically synthesizing them, we have developed a general and simple biosynthetic method for genetically encoding novel ncAAs into recombinant proteins by feeding cells with economical commercially available or synthetically accessible aromatic thiols. We demonstrate that nearly 50 ncAAs with a diverse array of structures can be biosynthesized from these simple small‐molecule precursors by hijacking the cysteine biosynthetic enzymes, and the resulting ncAAs can subsequently be incorporated into proteins via an expanded genetic code. Moreover, we demonstrate that bioorthogonal reactive groups such as aromatic azides and aromatic ketones can be incorporated into green fluorescent protein or a therapeutic antibody with high yields, allowing for subsequent chemical conjugation.

Expanding the Structural Diversity of Protein Building Blocks with Noncanonical Amino Acids Biosynthesized from Aromatic Thiols.

Incorporation of structurally novel noncanonical amino acids (ncAAs) into proteins is valuable for both scientific and biomedical applications. To expand the structural diversity of available ncAAs and to reduce the burden of chemically synthesizing them, we have developed a general and simple biosynthetic method for genetically encoding novel ncAAs into recombinant proteins by feeding cells with economical commercially available or synthetically accessible aromatic thiols. We demonstrate that nearly 50 ncAAs with a diverse array of structures can be biosynthesized from these simple small-molecule precursors by hijacking the cysteine biosynthetic enzymes, and the resulting ncAAs can subsequently be incorporated into proteins via an expanded genetic code. Moreover, we demonstrate that bioorthogonal reactive groups such as aromatic azides and aromatic ketones can be incorporated into green fluorescent protein or a therapeutic antibody with high yields, allowing for subsequent chemical conjugation.

Template-Assisted Plasmonic Nanogap Shells for Highly Enhanced Detection of Cancer Biomarkers.

We present a template-assisted method for synthesizing nanogap shell structures for biomolecular detections based on surface-enhanced Raman scattering. The interior nanogap-containing a silver shell structure, referred to as a silver nanogap shell (Ag NGS), was fabricated on silver nanoparticles (Ag NPs)-coated silica, by adsorbing small aromatic thiol molecules on the Ag NPs. The Ag NGSs showed a high enhancement factor and good signal uniformity, using 785-nm excitation. We performed in vitro immunoassays using a prostate-specific antigen as a model cancer biomarker with a detection limit of 2 pg/mL. To demonstrate the versatility of Ag NGS nanoprobes, extracellular duplex surface-enhanced Raman scattering (SERS) imaging was also performed to evaluate the co-expression of cancer biomarkers, human epidermal growth factor-2 (HER2) and epidermal growth factor receptor (EGFR), in a non-small cell lung cancer cell line (H522). Developing highly sensitive Ag NGS nanoprobes that enable multiplex biomolecular detection and imaging can open up new possibilities for point-of-care diagnostics and provide appropriate treatment options and prognosis.

Cobalt catalysed aminocarbonylation of thiols in batch and flow for the preparation of amides.

The synthesis of amides from thiols through a cobalt-catalyzed aminocarbonylation is shown. After optimizing all the reaction parameters, the methodology makes possible the obtention of amides with variable yields, while competing reactions such as the formation of disulfides and ureas can be limited. The process works well with aromatic thiols with electron donating groups (EDG) whereas other thiols give reaction with lower yields. The previous process has been transferred and optimized into flow equipment, thus allowing using less CO in a safer way, and permitting the scaling up of the synthesis. Two drugs, moclobemide and itopride were prepared with this methodology, albeit only in the second case with good results. A mechanistic pathway is proposed.

Origins of the photoinitiation capacity of aromatic thiols as photoinitiatiors: a computational study.

In this work, we report the photophysical properties of three thiol derivatives, commonly used as photoinitiators in thiol-ene free radical polymerization, the ultimate goal being to rationalize the main reason behind the photoinitiation efficiency. For this aim, time dependent density functional theory is used to simulate the absorption spectra of alkyl thiol (R-SH), thiophenol (PhSH) and p-(trifluoromethyl) thiophenol (p-CF3PhSH), describe their excited state topologies, and explore their potential energy surfaces along the S-H dissociation. Excited state calculations have shown that the S-H photolysis is achieved through the triplet excited states following intersystem crossing from the originally populated singlet manifolds. More specifically, while in aromatic thiol derivatives dissociation is mainly triplet-state mediated, the first excited singlet state and first triplet state of alkyl thiol are both dissociative and hence potentially capable of generating the photoinduced radical species. We have also justified the experimental findings concerning the photoinitiator efficiency considering both their potential energy surface topologies and the absorption intensity, in the lowest energy region.

Functional Group-Directed Photochemical Reactions of Aromatic Alcohols, Amines, and Thiols Triggered by Excited-State Hydrogen Detachment: Additive-free Oligomerization, Disulfidation, and C(sp2)-H Carboxylation with CO2.

Exploring new types of photochemical reactions is of great interest in the field of synthetic chemistry. Although excited-state hydrogen detachment (ESHD) represents a promising prospective template for additive-free photochemical reactions, applications of ESHD in a synthetic context remains scarce. Herein, we demonstrate the expansion of this photochemical reaction toward oligomerization, disulfidation, and regioselective C(sp2)-H carboxylation of aromatic alcohols, thiols, and amines. In the absence of any radical initiators in tetrahydrofuran upon irradiation with UV light (λ = 280 or 300 nm) under an atmosphere of N2 or CO2, thiols and catechol afforded disulfides and oligomers, respectively, as main products. Especially, the photochemical disulfidation proceeded highly selectively with the NMR and quantum yields of up to 69 and 0.46%, respectively. In stark contrast, the photolysis of phenylenediamines and aminophenols results in photocarboxylation in the presence of CO2 (1 atm). p-Aminophenol was quantitatively carboxylated by photolysis for 17 h with a quantum yield of 0.45%. Furthermore, the photocarboxylation of phenylenediamines and aminophenols proceeds in a highly selective fashion on the aromatic C(sp2)-H bond next to a functional group, which is directed by the site-selective ESHD of the functional groups for the formation of aminyl and hydroxyl radicals.

WEB (water extract of banana): An efficient natural base for one-pot multi-component synthesis of 2-amino-3,5-dicarbonitrile-6-thio-pyridines

One-pot multi-component synthesis of 2-amino-3,5-dicarbonitrile-6-thio-pyridines derivatives using WEB (water extract of banana peels ash) as a green catalyst is described. A variety of aromatic aldehydes (with electron-donating and electron-withdrawing groups) in conjunction with aromatic and aliphatic thiols are known to tolerate this reaction condition using WEB. The reaction has simple work up procedure without using toxic solvents.

Iodine‐Promoted One‐Pot Multicomponent Chemoselective Reaction for C‐C/C‐N and C‐C/C‐S Bond Formation Using Thiols

A simple approach for a C–N bond‐forming reaction is developed using a multicomponent strategy. Iodine promoted multicomponent reaction of heterocyclic thiols, aromatic aldehydes, and trimethoxybenzene proceeds at the ambient temperature in TFE in a short period. The reaction is also compatible with aromatic thiols leading to C–S bond formation. Heterocyclic thiols undergo a chemoselective reaction affording the corresponding C–N products over C–S products. To the best of our knowledge, this is the first report for C–N bond formation using heterocyclic thiols, trimethoxybenzene, and aromatic aldehydes, where the solvent is playing a significant role and iodine is acting as a promoter.

Chlorophyll Catalysed Ultrafast Oxidation of Thiols in Water

AbstractWe have developed an efficient and eco‐friendly method of disulfides synthesis in water using surfactant (DODAB). This reaction is catalysed by chlorophyll and fluorescent lamp is used as source of energy. This, one pot, ultra fast reaction, which involve a photo‐induced electron transfer (PET) mechanism, affords a green and efficient strategy for the conversion of commercially available aromatic thiols into diversified disulfides. This rapid synthesis allows the formation of various disulphides in the range of 80–94% yield at room temperature.

Curing behavior, chain dynamics, and microstructure of high Tg thiol-acrylate networks with systematically varied network heterogeneity

A series of networks is introduced with systematically varied network heterogeneity and high overall values of average glass transition temperature (Tg), based on polymerization of rigid acrylate and aromatic thiol monomers. The curing behavior, chain dynamics, and microstructure of these networks were investigated through a combination of dynamic mechanical analysis and infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and x-ray scattering, respectively. The maximum Tg achieved during cure can be related to the breadth of the mechanical loss tangent, as others have previously suggested, as well as the temperature dependence of the chain dynamics in the network as monitored by 1H NMR. In addition, the microstructures of the networks are characterized by periodic, fractal microgels with characteristic length scales of ca. 20–40 nm. Intriguingly, this structural motif persists in the more homogeneous networks exhibiting comparatively narrow glass transitions and chain dynamics, indicating that dynamically homogeneous networks can still exhibit significant compositional heterogeneity at the mesoscale.

Crystal Structure of Au30-xAgx(S-tBu)18 and Effect of the Ligand on Ag Alloying in Gold Nanomolecules.

We report the X-ray crystal structure of the Au30-xAgx(S-tBu)18 alloy and the effect of the ligand on alloying site preferences. Gold-silver nanoalloys prepared by co-reduction of metal salts are known to have only partial Ag occupancies. Interestingly, Au30-xAgx(S-tBu)18 has 100% Ag occupancy at two sites on the core surface as well as partial Ag occupancies on the surface, capping, and staples sites. The Au30-xAgx(S-tBu)18 (x = 1-5) composition was confirmed by X-ray diffraction and electrospray ionization mass spectrometry studies. Thiolate ligands can be categorized into three classes on the basis of the groups at the α-position as aliphatic, aromatic, and bulky thiols. The effect of the ligand on Ag doping can be clearly seen in the crystal structures of Au36-xAgx(SPh-tBu)24 and Au38-xAgx(SCH2CH2Ph)24 when compared with that of Au30-xAgx(S-tBu)18. Ag is preferentially doped onto the core surface when the ligand is aliphatic, and Ag is doped in both core surface and staple metal sites when the ligand is aromatic or bulky.

Evaluation of Aromatic Thiols as Photoinitiators

The unique photodynamics of aromatic thiols (relative to alkyl thiols) allowed their employment as effective ultraviolet and visible light photoinitiators (PIs) for acrylate photopolymerizations, r...

Electrophilic Vinylation of Thiols under Mild and Transition Metal‐Free Conditions

AbstractThe iodine(III) reagents vinylbenziodoxolones (VBX) were employed to vinylate a series of aliphatic and aromatic thiols, providing E‐alkenyl sulfides with complete chemo‐ and regioselectivity, as well as excellent stereoselectivity. The methodology displays high functional group tolerance and proceeds under mild and transition metal‐free conditions without the need for excess substrate or reagents. Mercaptothiazoles could be vinylated under modified conditions, resulting in opposite stereoselectivity compared to previous reactions with vinyliodonium salts. Novel VBX reagents with substituted benziodoxolone cores were prepared, and improved reactivity was discovered with a dimethyl‐substituted core.