SH Fragments Research Articles

Effect of SH/SBA‐15 Molar Ratio on Pb(II) and Cd(II) Ions Adsorption from Aqueous Solution by Mercaptopropyl‐grafted SBA‐15 Mesoporous Material as Adsorbent

AbstractThe purposes of the current study were to investigate the adsorption of Pb(II) and Cd(II) from aqueous solution by thiol‐functionalized SBA‐15 materials designed by SBA‐15‐SH (x) where x is the SH/SBA‐15 molar ratio, which corresponds to the introduced moles number of Mercapto moieties to that of siliceous of the SBA‐15 materials. Furthermore, these materials were synthesized using 3‐Mercaptopropyltrimethoxysilane (MPTMS) via post‐grafting approach. SBA‐15‐SH(x) materials were characterized by XRD, N2 adsorption‐desorption and FT‐IR. The incorporation of SH fragments was proved by FT‐IR Spectroscopy, thermogravimetric analysis (TGA) and solid state 13C and 29Si NMR Spectroscopy.The removal of lead ions is more important than that of cadmium ions. Furthermore, the lead removal on SBA‐15‐SH(x) increased with the increase of SH/SBA‐15 molar ratio (removal rate of 28.5, 71.3, and 96.8 % for SH/SBA‐15 molar ratio=0.35, 0.7 and 1.4, respectively) while the removal of cadmium was not affected (around 57 % removal rate for all molar ratios).

Theoretical study on photodissociation dynamics of vibrational excited states of H2S in the first absorption band

The photodissociation quantum dynamics for the first absorption band of H2S in different initial vibrational states have been investigated using Chebyshev real wave packet method. Because of the difference of the wave functions for the initial vibrational states, the calculated absorption spectra and the distributions of vibrational and rotational state of the products display different dynamic characteristics. The width and peak position of the absorption spectra for initial stretching excited states (1,0,0) and (0,0,1) are different from that of the vibrational ground state, while the (0,1,0) vibrational state has two almost equally high peaks in its absorption spectrum because of the change of wave function in angular coordinate. The product vibrational state distribution for (0,1,0) initial state weakly depends on the excitation energy and is dominated by the products of v=0, but SH(v=1) fragment is dominant at lower energy for (1,0,0) and (0,0,1) vibrational states. The rotational state distributions of products are very cold with the peak at j=l for these four states and weakly depend on the total energy. Besides, the rotational state distribution from (0,1,0) vibrational state displays strong oscillation, and its anisotropic parameter with rotational quantum numbers is also different from that of the other three vibrational states.

New accurate diabatic potential energy surfaces for the two lowest 1A'' states of H2S and photodissociation dynamics in its first absorption band.

In this work, state-to-state photodissociation dynamics of H2S in its first absorption band has been studied quantum mechanically with a new set of coupled potential energy surfaces (PESs) for the first two 1A'' excited states, which were developed at the explicitly correlated internally contracted multi-reference configuration interaction level with the cc-pVQZ-F12 basis set and a large active space. The calculated absorption spectrum, product state distributions, and angular distributions are in excellent agreement with available experimental data, validating the accuracy of the PESs and the non-adiabatic couplings. Detailed analysis of the dynamics reveals that there are strong non-adiabatic couplings between the bound 11B1 and dissociative 11A2 states around the Franck-Condon region, leading to very fast predissociation to ro-vibrationally cold SH(X̃) fragments, during which marginal angular anisotropy of the PESs is involved. This study provides quantitatively accurate characterization of the electronic structure and detailed fragmentation dynamics of this prototypical photodissociation system, which is desirable for improving astrochemical modelling.

Elucidating the stabilities and properties of the thiolate-protected Au nanoclusters with detaching the staple motifs.

Thiolate-protected Au nanoclusters (AuNCs) have been widely studied in areas of catalysis, biosensors, and bioengineering. In real applications, e.g., catalytic reactions, the thiolate groups are normally partially detached. However, which of the thiolate groups are easily detached and how the detachment of the ligands affects the geometries and electronic structures of the Au nanoclusters have been rarely studied. In this work, we employed the density functional theory calculations as well as the molecular orbital analysis to explore the detachment effect of the ligands using nine thiolate-protected AuNCs as examples. Our results showed that there existed a nearly linear relationship between the averaged detachment energies and the numbers of Au atoms in the motifs. Detaching longer motifs normally required more energies owing to the stronger aurophilic effects. For detaching a full motif, based on the structure decomposition via the grand unified model, analysis on the inner Au core indicated that the change in Au-Au bond length was more sensitive for the inter-block compared to the intra-block. The detachment of the -SH fragment generally needs less energy and brings less structural deformations when compared to the removal of a full motif. Molecular orbital analysis showed that the relative energies of the HOMO orbitals were elevated, which led to the narrow down of the HOMO-LUMO gap. This work provides a primary description of the correlation of the ligands' detachment with the relative stabilities and structures of the AuNCs, which would be beneficial for establishing the structure-property relationship of AuNCs in real applications.

Quantum chemical DFT study of molecular adsorption of H2S on clean and chemically modified Au(1 1 0) surfaces

The non-dissociative adsorption of H2S on Au(110) and the coadsorption with SH, S and H have been examined by periodic density functional theory (DFT) to indirectly give useful information about the associated surface reactivity. For bare surfaces, the enthalpy calculations indicate that energetically favored adsorption structures are generated at low to medium coverage. Each coadsorbate does not appreciably perturb the binding configuration but does promote the adsorption. With the aid of the calculated electron density differences, the trends can be rationalized in the context that the surface H2S constitutes hydrogen bonding only with the preadsorbed SH and S species. Unexpectedly, there is a net charge transfer from the seemingly electronegative H2S towards the metal surface, which is far from chemical intuition. As for the experimental adsorption enthalpy, comparatively strong values of it are here affirmed to be related to the case in which some molecules have decomposed at Au(110). Furthermore, only on the S-modified surface do the predicted vibrational frequencies of H2S agree with the published HREELS spectra, suggesting that the dissociation leaves, instead of the previously proposed SH fragment, atomic sulfur on Au(110) at low temperatures.

Resonant electron capture by Captopril molecules

The modified dipeptide, Captopril, was studied to determine the effect of lateral functional groups on the decay of biomolecules in resonant reactions of electrons with molecules. The main channels of fragmentation of negative molecular ions were determined, and the characteristic fragment ions were identified. The SH fragment of the lateral substituent of cysteine plays an important role similarly as does the carboxyl fragment of aspartic acid in oligopeptides.

Understanding the Lack of Reactivity of 2,4-Dihydroxybenzaldehyde Towards the Biginelli Adduct Using Density Functional Theory Molecular Modeling

The Biginelli reaction is a multicomponent reaction for obtaining dihydropyrimidinthiones quickly, with multiple substitution patterns. The reaction mechanism remains unclear. Three possible pathways proposed for the reaction are the iminium route, an enamine intermediate, and the Knoevenagel pathway. However, when thiourea was used, no theoretical calculations were reported. Thus, based on the literature, the iminium pathway was used to obtain evidence explaining the lack of reactivity of 2,4-dihydroxybenzaldehyde towards the Biginelli adduct, compared with 4-hydroxybenzaldehyde. This computational study, carried out using the B3LYP/6-31++G(d,p) level of theory, showed an increment of 150 kJ/mol in the activation energy of the slowest pathway, due to the presence of a hydroxyl group in position 2 (ortho) of the aromatic aldehyde, decreasing its reactivity. Natural bond orbital (NBO) calculations suggest that the determinant steps are simultaneous, i.e., the polarization of the carbonyl group and its corresponding protonation by the hydrogen of the SH fragment of the thiourea tautomer. The activation enthalpy values suggest that the nucleophile attack takes place later on the compound 2,4-dihydroxybenzaldehyde compared to 4-hydroxybenzaldehyde-TS, confirming that the OH group in position 2 hinders the condensation reaction.

ZnO Nanocluster as a Potential Catalyst for Dissociation of H2S Molecule

Adsorption of hydrogen sulfide (H2S) on the external and internal surface of Zn12O12 nanocluster was studied by using density functional calculations. The results indicate that the H2S molecule is physically adsorbed or chemically dissociated by the nanocluster. It was found that the H2S molecule can dissociate into –H and–SH fragments, suggesting that the nanocluster might be a potential catalyst for dissociation of the H2S molecule. Also, dissociation of H2S to S species in internal surface of the Zn12O12 nanocluster is energetically impossible. The HOMO–LUMO energy gap of H2S dissociation configuration is changed about 27.68 %, indicating that the electronic properties of the nanocluster by dissociation process have strongly changed.

A first-principles study of H2S adsorption and dissociation on the AlN nanotube

Adsorption of hydrogen sulfide (H2S) onto AlN nanotube surface was investigated using density functional theory. It was found that the molecule is either physically adsorbed on the surface of the tube or chemically dissociated into –H or –SH fragments. The physical adsorptions are barrierless, while the dissociations have to overcome small activation energies of 2.2–3.1kcal/mol, suggesting that the tube might be a potential catalyst for dehydrogenation of the H2S molecule. All the adsorptions are electronically harmless processes and have negligible effects on the electronic properties especially on the HOMO/LUMO energy gap of the AlN nanotube.

Imaging CH3SH photodissociation at 204 nm: the SH + CH3 channel

The SH + CH(3) product channel for the photodissociation of CH(3)SH at 204 nm was investigated using the sliced velocity map ion imaging technique with the detection of CH(3) products using state selective (2+1) resonance enhanced multiphoton ionization (REMPI). Images were measured for CH(3) formed in the ground and excited vibrational states (v(2) = 0, 1, and 2) of the umbrella mode from which the correlated SH vibrational state distributions were determined. The vibrational distribution of the SH fragment in the SH + CH(3) channel at 204 nm is clearly inverted and peaks at v = 1. The highly negative anisotropy parameter of the CH(3) (v(2) = 0, 1, and 2) products is indicative of a fast dissociation process for C-S bond cleavage. Two kinds of slower CH(3) products were also observed (one of which was partly vibrationally resolved) that are assigned to a two-step photodissociation processes, in which the first step is the production of the CH(3)S (X(2)E) radical via cleavage of the S-H bond in CH(3)SH, followed by probe laser photodissociation of nascent CH(3)S radicals yielding CH(3)(X(2)A(1), v(2) = 0-2) + S((3)P(j)/(1)D) products.

Imaging the photodissociation of CH3SH in the first and second absorption bands: The CH3(X̃A12)+SH(XΠ2) channel

The CH3(X2A1)+SH(X2Pi) channel of the photodissociation of CH3SH has been investigated at several wavelengths in the first 1 1A"<--X 1A' and second 2 1A"<--X1A' absorption bands by means of velocity map imaging of the CH3 fragment. A fast highly anisotropic (beta=-1+/-0.1) CH3(X2A1) signal has been observed in the images at all the photolysis wavelengths studied, which is consistent with a direct dissociation process from an electronically excited state by cleavage of the C-S bond in the parent molecule. From the analysis of the CH3 images, vibrational populations of the SH(X2Pi) counterfragment have been extracted. In the second absorption band, the SH fragment is formed with an inverted vibrational distribution as a consequence of the forces acting in the crossing from the bound 2 1A" second excited state to the unbound 1 1A" first excited state. The internal energy of the SH radical increases as the photolysis wavelength decreases. In the case of photodissociation via the first excited state, the direct production of CH3 leaves the SH counterfragment with little internal excitation. Moreover, at the longer photolysis wavelengths corresponding to excitation to the 1 1A" state, a slower anisotropic CH3 channel has been observed (beta=-0.8+/-0.1) consistent with a two step photodissociation process, where the first step corresponds to the production of CH3S(X2E) radicals via cleavage of the S-H bond in CH3SH, followed by photodissociation of the nascent CH3S radicals yielding CH3(X2A1)+S(X3P0,1,2).

Velocity Map Imaging Study of the Photodissociation of CH3SH: Internal Energy Distribution of the SH Fragment

Energy breakdown: Photodissociation of mercaptan in the second absorption band has been studied by velocity map imaging. CH3 fragment images (see figure) show a structure directly related to the vibrational population of the SH counterfragment. An inverted SH vibrational population has been measured suggesting a non-adiabatic fast photodissociation.

SO 2−· Electron Transfer Ion/Ion Reactions with Disulfide Linked Polypeptide Ions

Multiply-charged peptide cations comprised of two polypeptide chains (designated A and B) bound via a disulfide linkage have been reacted with SO2-* in an electrodynamic ion trap mass spectrometer. These reactions proceed through both proton transfer (without dissociation) and electron transfer (with and without dissociation). Electron transfer reactions are shown to give rise to cleavage along the peptide backbone, loss of neutral molecules, and cleavage of the cystine bond. Disulfide bond cleavage is the preferred dissociation channel and both Chain A (or B)-S* and Chain A (or B)-SH fragment ions are observed, similar to those observed with electron capture dissociation (ECD) of disulfide-bound peptides. Electron transfer without dissociation produces [M + 2H]+* ions, which appear to be less kinetically stable than the proton transfer [M + H]+ product. When subjected to collision-induced dissociation (CID), the [M + 2H]+* ions fragment to give products that were also observed as dissociation products during the electron transfer reaction. However, not all dissociation channels noted in the electron transfer reaction were observed in the CID of the [M + 2H]+* ions. The charge state of the peptide has a significant effect on both the extent of electron transfer dissociation observed and the variety of dissociation products, with higher charge states giving more of each.

Immunophenotyping of acute leukemia using an integrated piezoelectric immunosensor array.

Immunophenotyping evaluation is of particular importance for the clinical diagnosis, therapy, and prognosis of acute leukemia. In this paper, an integrated piezoelectric immunosensor array has been developed for the first time to detect the differentiated leukocyte antigens for immunophenotyping of acute leukemia. The probes (crystals) of the array were fabricated with plasma-polymerized n-butylamine film and nanometer-sized gold particles on which the Fab'-SH fragments obtained by the reduction of leukemic lineage-associated monoclonal antibodies (markers) were subsequently immobilized. Investigation results showed that the developed immunosensor array could rapidly identify normal cells from leukemic blasts and define the leukemic blasts within certain phenotypic groups (lineages) by only one analysis of the sample purified or unpurified. It permits the detection of unpurified leukocytes in the dynamic concentration range of 2 orders of magnitude (10(4)-10(6) cells mL(-1)). Up to 17 successive assay cycles with retentive sensitivity were achieved for the probes regenerated with 8 M urea. Moreover, the piezoelectric immunoassay system was applied to evaluate a number of practical specimens with immunophenotyping results in acceptable agreement with those clinically classified. The newly proposed multiparameter analysis technique provides a rapid, simple, and direct alternative tool for clinical immunophenotyping of acute leukemia.

Antibody immobilisation on fibre optic TIRF sensors

A study of antibody immobilisation techniques on quartz and fibre optic surfaces for immunosensors has been carried out. Methods of covalent antibody immobilisation which have not previously been applied to optical fibres were investigated, and compared with classical methods found in the literature. Preliminary experiments on covalent immobilisation methods on planar quartz surfaces were conducted to enable us to choose the most suitable protein immobilisation technique for sensor applications. The immobilisation studies were directed in particular towards obtaining a high density of binding sites for the analyte of interest. Two of the most promising methods, antibody immobilisation on surfaces coated with dextran based hydrogel and F(ab′)-SH fragments bound to silanised glass, which resulted in surface densities of active sites of above 0.45 pmol/cm 2, were selected for further experiments on a fibre optic total internal reflection fluorescence immunosensor and gave satisfactory responses to changes in analyte concentrations of the order of 10 −8 M. The efficiency of polar organic solvents, such as dimethylsulfoxide, in dissociating the antigen–antibody complex and hence to regenerate the immunosensor surface was also evaluated.

Immunosensing platforms using spontaneously adsorbed antibody fragments on gold.

This paper describes the construction and characterization of miniaturized antigenic immunosurfaces composed of spontaneously adsorbed Fab'-SH fragments on gold. Rabbit Fab'-SH fragments contain a free sulfhydryl group that forms a thiolate bond with a gold substrate as detailed by X-ray photoelectron spectroscopy. This approach creates surfaces of higher epitope density, a factor critical to the early detection of disease, than surfaces composed of adsorbed whole molecule IgG on gold. The viability and specificity of antigenic Fab'-SH immunosurfaces is demonstrated using atomic force microscopy and confocal fluorescence microscopy, and possible explanations for the larger epitope density are discussed.

Dynamics of the Reaction O(3P) + H2S → OH + SH. 2. State-Resolved Differential Cross Sections and Angular Momentum Correlations

Measurements are reported of Doppler resolved polarized laser-induced fluorescence of the OH product of the O(3P) + H2S reaction, leading to estimates of the differential cross sections and angular momentum correlations in the system. O(3P) was produced with translational energy above the barrier to reaction by the polarized 355 nm photolysis of NO2. Three quantum states were studied in detail. For the most populated OH level, v‘ ‘ = 1, N‘ ‘ = 6, the scattering for the A‘ ‘ Λ doublet was found to be largely sideways/backward, with the remaining energy appearing as product translation, and measurements of average Λ doublet scattering showed similar behavior for the A‘ Λ doublet. The same scattering dynamics were observed for the v‘ ‘ = 0, N‘ ‘ = 13 state. For the rotationless v‘ ‘ = 1, N‘ ‘ = 1 state the results were more ambiguous, but if the same distribution of available energy appeared in the SH fragment as deduced for the measurements on rotationally excited OH, then the scattering was seen to be clea...

Photodissociation dynamics of H 2S at 266 nm via the degenerate four-wave mixing spectroscopy

Photodissociation dynamics of H 2S has been studied using the degenerate four-wave mixing (DFWM) technique at 266 nm and room temperature. The DFWM spectra of SH A 2Σ−X 2Π i (0,0) transitions have been observed and the nascent rotational distributions, spin-orbit state ratio, and Λ-doublet population ratio of the SH fragments have been extracted. The rotational distributions are cold and characterized by a Boltzmann temperature of 348±20 K for the SH( 2 Π 3 2 ) state. The Λ-doublet population ratio has been found to be close to unity. The SH( 2 Π 3 2 )/ SH( 2 Π 1 2 ) ratio has been observed to be 3.50±0.18.

On the near ultraviolet photodissociation of hydrogen sulphide

The near ultraviolet photolysis of H2S has been investigated further, at nine different excitation wavelengths in the range 244-198 nm and at yet higher resolution than hitherto, using the technique of H (Rydberg) atom photo-fragment translational spectroscopy. Analyses of the total kinetic energy release spectra of the primary H + SH fragments has allowed further refinement of the parent bond dissociation energy, D00(HS-H) = 31440 ± 20 cm-1, and revealed a marked correlation between the wavelength dependence of , the fraction of the available energy partitioned into SH(X) product vibration, and the first of the diffuse vibronic structures evident in the UV absorption spectrum of the H2S parent. Secondary photolysis of the primary SH(X) fragments has also been investigated further. 2 + 1 Resonance enhanced multiphoton ionization spectroscopy has been used to confirm that the S(3P) atoms resulting from 218⋅2 nm photolysis of the primary SH(X) fragments are formed in all three spin-orbit states, with...

Near ultraviolet photolysis of methanethiol studied by H atom photofragment translational spectroscopy

The technique of H Rydberg atom photofragment translational spectroscopy has been applied to a high resolution study of the primary photochemistry of methanethiol (CH3SH) following excitation at a wide range of wavelengths in the near ultraviolet. In accord with previous studies of this molecule, excitation within its first (1 1A″−X̃ 1A′) absorption continuum is shown to result in S–H bond fission. Spectral analysis yields a refined value for the bond dissociation energy: D00(CH3S–H)=30 250±100 cm−1. The resulting CH3S(X̃) fragments are deduced to carry only modest vibrational excitation, distributed specifically in the ν3 (C–S stretching) mode and in one other mode having a wave number of ∼1040 cm−1. We associate this latter mode with bending of the CH3 moiety in the plane containing the C and S nuclei and the lobe of the unpaired electron which was originally involved in the S–H bond. Decreasing the excitation wavelength (while remaining within the first absorption continuum) results in an increase in both the vibrational and rotational excitation of the CH3S(X̃) fragments, but a decrease in the relative yield of the upper (2E1/2) spin–orbit component. Excitation at still shorter excitation wavelengths accesses the second (2 1A″−X̃ 1A′) absorption band of CH3SH. The CH3S fragments resulting from S–H bond fission at these excitation wavelengths are observed to carry very much higher levels of vibrational excitation in the above two modes. The observation of H atoms attributable to secondary photolysis of SH(X) fragments indicates increased competition from the alternative C–S bond fission channel at these shorter excitation wavelengths. Additional peaks in the H atom time-of-flight spectrum, most clearly evident following excitation at wavelengths in the range 213–220 nm, are interpretable in terms of secondary photolysis of the primary CH3S(X̃) fragments yielding thioformaldehyde (H2CS), primarily in its à 1A2 excited electronic state. Symmetry arguments provide an explanation for this specific electronic branching in the near ultraviolet photolysis of CH3S fragments.