Synthesis and ferroelectric properties of laterally substituted fluoro liquid crystals derived from 4-mercaptobenzoic acid

Several new ferroelectric liquid crystals with thiobenzoate mesogenic cores have been synthesized and the influence of a single fluorine atom ortho to the alkyloxy tail on the mesomorphic properties of some two and three benzene ring core compounds has been studied. The two benzene ring derivatives do not display the ferroelectric smectic C phase but the three phenyl ring compounds exhibit a wide temperature range S_c* phase. The transition temperatures and enthalpies of transition for these compounds have been determined; the spontaneous polarization, response time and tilt angle have also been measured and are discussed as a function of the structure near to the chiral centre.     

4-Mercaptophenylboronic acid functionalized graphene oxide composites: Preparation,characterization and selective enrichment of glycopeptides

Selective enrichment and isolation of glycopeptides from complex biological samples was indispensable for mass spectrometry (MS)-based glycoproteomics, however, it remained a great challenge due to the low abundance of glycoproteins and the ion suppression of non-glycopeptides. In this work, 4-mercaptophenylboronic acid functionalized graphene oxide composites were synthesized via loading gold nanoparticles on polyethylenimine modified graphene oxide surface, followed by 4-mercaptophenylboronic acid immobilization by the formation of Au–S bonding (denoted as GO/PEI/Au/4-MPB composites). The composites showed highly specific and efficient capture of glycopeptides due to their excellent hydrophilicity and abundant boronic acid groups. The composites could selectively capture the glycopeptides from the mixture of glycopeptides and nonglycopeptides, even when the amounts of non-glycopeptides were 100 times more than glycopeptides. Compared with commercial meta-amino phenylboronic acid agarose, the composites showed better selectivity when the sample was decreased to 10 ng. These results clearly verified that the GO/PEI/Au/4-MPB composites might be a promising material for glycoproteomics analysis.     

New dialkyldithiophosphinic acid self-assembled monolayers (SAMs): influence of gold substrate morphology on adsorbate binding and SAM structure

We report the fabrication and characterization of new self-assembled monolayers (SAMs) formed from dihexadecyldithiophosphinic acid [(C(16))(2)DTPA] molecules on gold substrates. In these SAMs, the ability of the (C(16))(2)DTPA headgroup to chelate to the gold surface depends on the morphology of the gold substrate. Gold substrates fabricated by electron-beam evaporation (As-Dep gold) consist of ～50-nm grains separated by deep grain boundaries (～10 nm). These grain boundaries inhibit the chelation of (C(16))(2)DTPA adsorbates to the surface, producing SAMs in which there is a mixture of monodentate and bidentate adsorbates. In contrast, gold substrates produced by template stripping (TS gold) consist of larger grains (～200-500 nm) with shallower grain boundaries (<2 nm). On these substrates, the low density of shallow grain boundaries allows (C(16))(2)DTPA molecules to chelate to the surface, producing SAMs in which all molecules are bidentate. The content of bidentate adsorbates in (C(16))(2)DTPA SAMs formed on As-Dep and TS gold substrates strongly affects the SAM properties: Alkyl chain organization, wettability, frictional response, barrier properties, thickness, and thermal stability all depend on whether a SAM has been formed on As-Dep or TS gold. This study demonstrates that substrate morphology has an important influence on the structure of SAMs formed from these chelating adsorbates.     

UPS, XPS, and NEXAFS study of self-assembly of standing 1,4-benzenedimethanethiol SAMs on gold

We report a study of the self-assembly of 1,4-benzenedimethanethiol monolayers on gold formed in n-hexane solution held at 60 °C for 30 min and in dark conditions. The valence band characteristics, the thickness of the layer, and the orientation of the molecules were analyzed at a synchrotron using high resolution photoelectron spectroscopy and near edge X-ray adsorption spectroscopy. These measurements unambiguously attest the formation of a single layer with molecules arranged in the upright position and presenting a free -SH group at the outer interface. Near edge X-ray absorption fine structure (NEXAFS) measurements suggest that the molecular axis is oriented at 24° with respect to the surface normal. In addition, valence band features could be successfully associated to specific molecular orbital contributions thanks to the comparison with theoretically calculated density of states projected on the different molecular units.     

4-Nitrophenyl sulfenyl chloride as a new precursor for the formation of aromatic SAMs on gold surfaces

4-Nitrophenyl sulfenyl chloride was used as a new precursor for the formation of densely packed aromatic SAMs on gold. The adsorption involves the reductive dissociation of the S-Cl bond. A well-ordered row structure corresponding to a √3 × 4 phase with a molecular area of 27.8 ?(2) is obtained.     

Organized assemblies of thiol-terpyridine and thiophenol on gold surfaces: preferential composition of mixed species evidenced

Mixed self-assembled monolayers based on thiol-terpyridine and thiophenol molecules on gold surfaces show a tendency to form films whose composition is almost independent of the molar fraction of the components in the starting solution, and this indicates the formation of particularly stable assemblies.     

Electrochemical desorption of n-alkylthiol SAMs on polycrystalline gold: studies using a ferrocenylalkylthiol probe

The reductive voltammetric desorption of n-alkylthiol self-assembled monolayers (SAMs) was studied using ferrocenyldodecanethiol (FcC12SH) as a probe. A short (10 s) incubation in a 2 mM FcC12SH solution labels the pre-existing defect sites present in a tetradecanethiol (C14S-Au) SAM. Additional defects in a C14S-Au SAM are then created by voltammetric cycling to reductive potentials. The effects of changing the desorption potential and the hold time at the desorption potential were investigated by monitoring the change in the two characteristic FcC12S-Au peaks. These two peaks are associated with FcC12S-Au filling individual single site defects (peak I at 260 mV) and pinhole defects (peak II at 380 mV). The reductive desorption potential applied to a binary (FcC12S-/C14S-Au) SAM results in a partial desorption and a potential "remixing" of the phase-separated state.     

Catalytic reduction of 4-nitrophenol using biogenic gold and silver nanoparticles derived from Breynia rhamnoides

A simple, green method is described for the synthesis of Gold (Au) and Silver (Ag) nanoparticles (NPs) from the stem extract of Breynia rhamnoides. Unlike other biological methods for NP synthesis, the uniqueness of our method lies in its fast synthesis rates (~7 min for AuNPs) and the ability to tune the nanoparticle size (and subsequently their catalytic activity) via the extract concentration used in the experiment. The phenolic glycosides and reducing sugars present in the extract are largely responsible for the rapid reduction rates of Au(3+) ions to AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs (or AgNPs) and NaBH(4) was observed and was found to depend upon the nanoparticle size or the stem extract concentration used for synthesis.     

Quantitative determination of SH groups using 19F NMR spectroscopy and disulfide of 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid

A new method of measurement of thiol concentration by 19F NMR spectroscopy is developed. The method is based on the detection of products of the exchange reaction of thiols with a newly synthesized fluorinated disulfide, 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid (BSSB). A significant broadening of the 19F NMR signal of BSSB in the presence of thiols was observed and attributed to the exchange reaction between the parent disulfide and 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid. The rate constant for this reaction was found to be equal to (63 +/- 11) x 10(3) M(-1) s(-1) at pH 7.0. The method was applied for the measurement of concentration of glutathione and albumin in rat blood.     

Ethynylbenzene monolayers on gold: a metal-molecule binding motif derived from a hydrocarbon

Exposure of a Au(111) surface to ethynylbenzene in solution leads to the formation of a bound monolayer. A chemisorption process occurs to give a stable layer consisting of oxygen-containing hydrocarbon species. Ethynylbenzene itself does not oxidize under the deposition conditions indicating that the gold surface facilitates the oxidation process. Calculations show that ethynylbenzene and its oxidation products phenylacetic acid and phenyloxirane have positive binding energies to the gold surface. 1,4-Diethynylbenzene also binds to Au(111) and anchors gold nanoparticles deposited from solution to form dense, semiregular arrays.     

Some 2-fluoroethylamines derived from hydrocinnamic acid, phenylpyruvic acid and DL-phenylalanine

Fluorine-containing nitrogen mustards attached to hydrocinnamic acid, phenylpyruvic acid and -phenylalanine as carrier groups have been synthesized. The N-(2-chloroethyl)-N-(2′-fluoroethyl)amines are obtained by alkylation of the sodium salts of N-(benzyloxycarbonyl)amines with 2-fluoroethyl p-toluenesulfonate or 2-bromofluorethane, removal of the benzyloxycarbonyl group, followed by hydroxyethylation and chlorination. The bis(2-fluoroethyl)amines are obtained by heating the bis(2-p-toluenesulfonyloxyethyl)amines with potassium fluoride in a suitable solvent. By these reactions, methyl m-aminohydrocinnamate was converted to the chlorofluoro mustard XIX and the bis-fluoro mustard XX. Starting with aniline, the above reactions, in conjunction with the Vilsmeier-Haack reaction, afforded the benzaldehyde mustards VII and VIII. These are converted to the corresponding azlactones. A two-step hydrolysis of the azlactones afforded the chlorofluoro mustard IXA and the bisfluoro mustard IXB of phenylpyruvic acid. Reduction of the azlactone with zinc and acid, followed by hydrolysis, afforded the corresponding -phenylalanine mustards XIIIA and XIIIB.     

Zwitterionic dithiocarboxylates derived from N-heterocyclic carbenes: coordination to gold surfaces

The zwitterionic dithiocarboxylates 1(+)-CS(2)(-)-4(+)-CS(2)(-) were prepared by reacting the corresponding N-heterocyclic carbenes 1,3-bis(2,6-diisoproylphenyl)imidazol-2-ylidene (1), 1,3-diisopropylimidazol-2-ylidene (2), 1,3-dibenzylimidazol-2-ylidene (3) and 1,3-diethylbenzimidazol-2-ylidene (4) with CS(2). In the latter two cases, the corresponding N-heterocylic carbene was generated in situ. Compounds 2(+)-CS(2)(-)-4(+)-CS(2)(-) were structurally characterised by single-crystal X-ray diffraction studies. The chemisorption of these zwitterionic dithiocarboxylates on solid gold substrates was investigated in situ and in real time by optical second harmonic generation (SHG). The resulting thin films were exemplarily characterised by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) in the case of 1(+)-CS(2)(-) and 2(+)-CS(2)(-), revealing the formation of almost contamination-free self-assembled monolayers, which exhibit a remarkable degree of orientational order.     

A comparison of selected force constants derived from ab initioSCF calculations on β-hydroxyacrolein. Acrolein,performic acid,and formic acid

Harmonic force fields have been calculated for the planar hydrogen-bonded ring conformer of β-hydroxyacrolein, cCc, which is the most stable, and the chain conformer, cCt, generated by 180° rotation of O? H about the C? O bond axis. The equilibrium structure obtained using the 4-31 G basis set with full geometry optimization was employed in each case. Selected force constants for the bonds directly concerned in the formation of the ring from the chain structure, and the increments in going from the one to the other, are compared with the values for the corresponding conformers of performic and formic acids. As the ring size increases from four in trans-formic acid, to five in cis–cis-performic acid and to six in the cCc conformer of β-hydroxyacrolein there is a successive increase in the mechanical strength of the hydrogen-bridging unit. The energy changes for the chain → ring conversion do not follow this progression: performic acid is out of order. But, since a force constant is a localized bond property, whereas the energy changes are determined not only by interactions specific to the hydrogendonor and hydrogen-acceptor groups but also by interactions involving more distant parts of the molecule, the force constants for the bonds directly concerned in the formation of the hydrogen bridge provide a less ambiguous basis for comparing the strength of the intramolecular hydrogen bonding.     

Electrochemical enzymatic biosensor for tyramine based on polymeric matrix derived from 4-mercaptophenylacetic acid

Journal of Solid State Electrochemistry - In this paper, we investigated a novel functionalized polymeric film derived from 4-mercaptophenylacetic acid (MPAA). The polymerization was carried out...     

Raman mapping and in situ SERS spectroelectrochemical studies of 6-mercaptopurine SAMs on the gold electrode

The self-assembled monolayers (SAMs) of 6-mercaptopurine (6MP) were formed at the roughened polycrystalline gold surfaces in acid and alkaline media. The time-dependent Raman mapping spectral analysis in conjunction with the quantum calculations for the vibrational modes using ab initio BLYP/6-31G method suggested that both of the resulted 6MP SAMs adopted the same adsorption mode through the S atom of pyrimidine moiety and the N7 atom of the imidazole moiety anchoring the gold surface in a vertical way. The in situ surface-enhanced Raman scattering spectroelectrochemical experiment was conducted to examine the stability of the SAMs at various bias potentials. It was found that the detaching process of the 6MP SAMs from the surface involved one electron reduction as the voltage was applied at ca. 0.7 V vs a standard calomel electrode.     

Synthesis and characterization of gold(III) complexes with dithiocarbimates derived from sulfonamides

This work describes the syntheses of four new gold(III) complexes with the general formula: K[Au(RSO₂N = CS₂)₂] (R = Ph, 2-MeC₆H₄, 4-MeC₆H₄, 4-ClC₆H₄) from the reaction of hydrogen tetrachloroaurate tetrahydrate with the corresponding potassium dithiocarbimate salts dihydrate in water. The characterization of the complexes has been carried out by elemental analyses, conductance measurements, and IR, UV–VIS, ¹H- and ¹³C-NMR spectroscopies. Elemental analyses were consistent with the proposed formulae. The molar conductance data are consistent with the complexes being monoanions complexes. Electronic spectra, vibrational spectra, ¹H- NMR and ¹³C-NMR data are consistent with formulation as AuS₄ diamagnetic square planar complexes.     

Pyrrolidinones derived from (S)-pyroglutamic acid: penmacric acid and analogues

Alkylation reactions using alpha-halolactams or lactam enolates derived from bicyclic lactam templates can proceed with high endo- or exo- diastereoselectivity respectively. In the latter case, stereochemical correction by means of enolate generation and hindered phenol quench is possible with moderate efficiency. This protocol has been applied to the synthesis of protected penmacric acid and its analogues.