CS Fragments Research Articles

Ultrafast Extreme Ultraviolet Photoelectron Spectroscopy of Nonadiabatic Photodissociation of CS2 from 1B2 (1Σu+) State: Product Formation via an Intermediate Electronic State.

We studied nonadiabatic dissociation of CS2 from the 1B2 (1Σu+) state using ultrafast extreme ultraviolet photoelectron spectroscopy. A deep UV (200 nm) laser using the filamentation four-wave mixing method and an extreme UV (21.7 eV) laser using the high-order harmonic generation method were employed to achieve the pump-probe laser cross-correlation time of 48 fs. Spectra measured with a high signal-to-noise ratio revealed clear dynamical features of vibrational wave packet motion in the 1B2 state; its electronic decay to lower electronic state(s) within 630 fs; and dissociation into S(1D2), S(3PJ), and CS fragments within 300 fs. The results suggest that both singlet and triplet dissociation occur via intermediate electronic state(s) produced by electronic relaxation from the 1B2 (1Σu+) state.

Theoretical investigation of the CS + OH → Products reaction on an interpolated potential energy surface: reaction dynamic and chemical kinetic insights

An interpolated potential energy surface to describe the gas phase CS+OH reaction has been constructed by quantum chemical ab-initio data. Quasi-classical trajectory simulations are applied to calculate the probability of reaction. To obtain the physical observable parameters such as thermal rate constant and cross-section, the reaction probability is used. These calculations upon this interpolated surface illustrate that the total rate coefficient is close to that reported by Loison et al. The total reaction cross-section and corresponding reaction probability with respect to the relative translation energy of all species over a range of 2.63 to 170.66 kJ mol−1 are investigated as well. In addition, the effect of the impact parameter and relative translational energy of fragments on the reaction probability, average angular momentum, and scattering angle was studied. Depending on the orientation of reactant molecules, for the title reaction, two different channels were found. First, the OH radical comes close to the CS fragments and leads to formation of trans-HOCS with − 198.68 kJ mol−1 energy relative to the reactants’ total energy. Next, the C atom abstracts the oxygen of OH radical through a saddle point to generate the carbonyl sulfide with 45.31 kJ mol−1 barrier energy.

Unusual chemical transformations of acetone thiosemicarbazone mediated by ruthenium: C–H bond activation, thiolation, and C–N bond cleavage

Upon reaction with Ru(PPh3)3Cl2 in ethanol in the presence of triethylamine, acetone thiosemicarbazone undergoes several interesting chemical transformations, such as thiolation via methyl C–H bond activation, C–N bond cleavage, and conversion of the CS fragment to CO. Two complexes (1 and 2) were obtained from this reaction, both of which contained a modified thiosemicarbazone coordinated in SNS- or SNO-mode, two triphenylphosphines and a N-bound thiocyanate. The crystal structures of both the complexes have been determined. Theoretical and mass spectral studies have been carried out to probe the transformations. These complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on both the complexes show a reversible oxidation near 0.6 V vs. SCE, followed by an irreversible oxidation near 1.2 V vs. SCE. DFT calculations have been carried out to explain the electronic spectra, as well as the electrochemical observations.

Silk fibroin derived polypeptide-induced biomineralization of collagen

Silk fibroin (SF) is extensively investigated in osteoregenerative therapy as it combines extraordinary mechanical properties and directs calcium-phosphate formation. However, the role of the peptidic fractions in inducing the protein mineralization has not been previously decoded. In this study, we investigated the mineralization of fibroin-derived polypeptides (FDPs), which were obtained through the chymotryptic separation of the hydrophobic crystalline (Cp) fractions and of the hydrophilic electronegative amorphous (Cs) fractions. When immersed in simulated body fluid (SBF), only Cs fragments demonstrated the formation of carbonated apatite, providing experimental evidence that the mineralization of SF is dictated exclusively by its electronegative amino-acidic sequences. The potential of Cs to conceptually mimic the role of anionic non-collagenous proteins in biomineralization processes was investigated via their incorporation (up to 10% by weight) in bulk osteoid-like dense collagen (DC) gels. Within 6 h in SBF, apatite was formed in DC-Cs hybrid gels, and by day 7, carbonated hydroxylapatite crystals were extensively formed. This accelerated 3-D mineralization resulted in a nine-fold increase in the compressive modulus of the hydrogel. The tailoring of the mineralization and mechanical properties of hydrogels through hybridization with FDPs could potentially have a significant impact on cell delivery and bone regenerative medicine.

Note: Single-ultraviolet-photon dissociation dynamics of ${\rm CS}_{\rm 2}^ + (\tilde X{}^2\Pi _g)$ CS 2+(X̃2Πg) in 227–243 nm revealed by time-sliced velocity map imaging

The single-UV-photon (227–243 nm) dissociation of ${\rm CS}_2^ + (\tilde X{}^2\Pi _{g,3/2,1/2})$ CS 2+(X̃2Πg,3/2,1/2) into the S+(4S)CS(X1)Σ+ channel was investigated by means of time-sliced velocity map imaging technique. In the high-energy region of the $\tilde B{}^2\Sigma _u^ +$B̃2Σu+ state, a rather subtle photodissociation dynamics was observed, i.e., a slight variation in the excitation photon energy may lead to a drastic change in the vibronic distributions of the CS(X1Σ+) fragments originating from the two spin-orbit $\tilde X{}^{\rm 2}\Pi _g$X̃2Πg states. The photodissociation mechanisms involved here may be interpreted as being due to the complex interplay among various vibronic and spin-orbit interactions in this energy region of ${\rm CS}_{\rm 2}^ +$ CS 2+. It is quite impressive that, for such a simple triatomic cation species, ${\rm CS}_{\rm 2}^ +$ CS 2+, there exhibits such complexity and subtlety in its photodissociation dynamics.

(1+1) Resonance‐Enhanced Multiphoton Ionization and Photodissociation Study of CS2 via the 1B2 State

(1+1) Resonance-enhanced multiphoton ionization (REMPI) spectra of CS(2) and molecular dissociation dynamics are investigated using a time-of-flight mass spectrometer equipped with velocity imaging detection. The REMPI spectra via a linear-bent 1Sigma(g)+-->(1)B(2)(1Sigma(u)+) transition are acquired in the wavelength range of 208-217 nm. Each ro-vibrational band profile of the (1)B(2)(1Sigma(u)+) state is deconvoluted to yield the corresponding predissociative lifetime from 0.3 to 3 ps. Upon excitation at 210.25 and 212.54 nm, the resulting images of S(+) and CS(+) fragments are analyzed to give individual translational energy distributions, which are resolved into two components corresponding to the CS+S((3)P) and CS+S((1)D) channels. The product branching ratios of S((3)P)/S((1)D) are evaluated to be 5.7+/-1.0 and 9.6+/-2.5 at 210.25 and 212.54 nm, respectively. Despite the difficulty avoiding the effect of multiphoton absorption, the molecular dissociation channel is verified to prevail over the dissociative ionization channel of CS(2). The anisotropy parameters for the triplet and singlet channels are determined to be approximately 0.8 and 1.1-1.3, respectively, suggesting that the predissociative state should have a bent configuration with a short lifetime.

K-Dependent Predissociation Dynamics of CS2 in the 210−216 nm Region

The dependence of CS2 predissociation upon rotational quantum number K at vibrational levels below the barrier to linearity of the 1B2(1Sigmau+) state has been investigated in detail with laser spectroscopy, by using a heated supersonic source to increase the intensities of hot band transitions. Predissociation lifetimes were determined from rotational contour simulations of 13 vibronic bands in the CS photofragment excitation (PHOFEX) spectrum, each terminating at the same upper vibrational level but via transitions with different K number (K = 0, 1, 2, respectively). The rovibrational populations of CS fragment at these excitation bands were derived from the laser-induced fluorescence (LIF) spectrum, and were used further to obtain the dissociation branching ratios S(1D)/S(3P) as well as the excess energy partitionings after dissociation. The lifetimes and the branching ratios were found to be sensitively dependent on quantum number K; the lifetime decreases with the increase of K, and the branching ratio increases with K. Analysis shows that quantum number K influences the S(1D) channel more effectively than the S(3P) channel. About 28 and 15% of the total available energy is taken up by the CS vibrational and rotational degrees of freedom, respectively. Systematic analysis indicates that the two electronic states interacting with 1B2(1Sigmau+) state should be bent, and the state correlating with S(1D) channel should be more bent.

The C-terminal Domain of Escherichia coli Trigger Factor Represents the Central Module of Its Chaperone Activity

The C-terminal Domain of Escherichia coli Trigger Factor Represents the Central Module of Its Chaperone Activity

Enzyme Isoselective Inhibitors: A Tool for Binding‐Trend Analysis

A transition-state analogue inhibitor that covalently reversibly binds to an enzyme formally consists of two parts: the chemical site, CS and the recognition site, RS. We have experimentally and theoretically demonstrated that the trend of binding affinity in a series of isoselective inhibitors (with identical RS and different CS fragments) depends mainly on their CS fragments. Isoselective inhibitors have the same affinity trend toward different enzymes of the same family with a common catalytic mechanism. Thus, very good correlation between experimentally determined and theoretically calculated Ki values was demonstrated. A practical outcome is the application of the described method as a tool for an expert analysis in virtual screening of inhibitor libraries and in the design of new enzyme inhibitors.

Photoionization dynamics in CS fragmented from CS2 studied by high-resolution photoelectron spectroscopy

The photoionization dynamics of CS have been studied using high-resolution laser photoelectron spectroscopy. The photodissociation of CS2 at ~308 nm results in highly rotationally excited CS in its X1Σ+ singlet ground state, as well as in rotationally cold CS in the excited a3Π triplet state. The ground-state CS fragments are formed together with sulfur in its 3P, 1D, and 1S electronic states; triplet CS is produced in coincidence with ground-state sulfur (3P). In both channels the photoelectron spectra are dominated by Δv = 0 propensity, but transitions involving Δv = 1 and 2 are also observed. Key words: photoelectron spectroscopy, photoionization, photodissociation, excited states, reactive intermediates.

A novel keratanase‐generated keratan sulphate antibody and its applications

Introduction The sequencing of the genome has provided us with important information regarding the primary structure of many matrix proteins. This in turn has lead to advances in studies of the functions of post‐translational modifications on connective tissue proteoglycans (PGs). Changes in GAG structure with ageing and disease have been well documented (Thonar et al. 1986; Brown et al. 1998). However, little is known about the exact sites of and differential substitution of GAGs on the aggrecan core protein and how these substitutions facilitate normal function or the changes seen with disease. The CS : KS ratio of substitution change significantly, with KS levels increasing with age and decreasing with the onset of disease. Objective was to produce monoclonal antibody (MAb) reagents to keratanase (k'ase) generated stub epitopes, that could be used to help identify, characterize and quantify sites of KS substitution on PGs, providing the potential to determine how the arrangement of such substitutions change with development, ageing and pathology.Methods Bovine Nasal Cartilage aggrecan (BNC A1D1) was trypsin digested, generating a range of glycosaminoglycan (GAG) fragments. The sample was then subjected to anion‐exchange and size exclusion chromatography to separate KS from CS fragments. Fractions collected were analysed by SDS‐PAGE and Western blotting. Fractions positive for KS were pooled and kinase digested to expose the KS stub antigens. Immunization and fusions were carried out as previously described (Nieduszynski et al. 1990). Initial screenings were carried out using ELISA. Briefly, 96‐well microtitre plates were coated with the immunizing antigen overnight at 37 °C. The plates were then blocked prior to the addition of hybridoma media for 1–2 h at 37 °C. Binding was detected using an alkaline phosphatase‐conjugated secondary antibody for 1 h at 37 °C prior to the addition of the substrate. Positive wells were further screened by ELISA and SDS‐PAGE using the immunizing antigen, chondroitinase‐digested BNC and an A1D1 BNC preparation to establish the kinase stub specificity of the hybridomas. Further screenings by Western blotting was carried out on positive hybridomas selected. Antigens used included keratanase‐digested bovine corneal KS‐PGs, keratanase‐II‐digested KS‐PGs and a nonkeratanase‐digested corneal KS‐PG sample.Results Screening: Screening identified two positive hybridomas, B‐KS‐I and B‐KS‐II, which were specific for kinase‐generated KS stub. On screening, these antigens showed reactivity specifically for kinase‐digested BNC abc core, with no reactivity to the nonkinased linear KS GAG epitopes. Reactivity to kinase‐digested corneal KS‐PGs indicated that the MAbs generated were indeed to a stub structure in the KS chain and not to some linkage region epitope, amino acid sequence or oligosaccharide present on the core protein.Application: Immunohistochemistry utilizing B‐KS‐I was used to localize KS in a range of tissues along side anti‐KS 5D4. In human articular cartilage engineered grafts, labelling showed B‐KS‐I and 5D4 to have broadly overlapping labelling patterns for KS; however, label for B‐KS‐I had a much more restricted and subtle tissue distribution than that of antibody 5D4.Discussion These new KS stub MAbs have potential to be used in many different areas of research. They may be used in analysis of trypsin‐digested purified aggrecan from cattle joints of different ages to determine sites of KS substitution, which remain common or change with development and ageing. They may also be used in analysis of cartilage explant culture metabolites to assess KS substitution on the aggrecan fragments generated after stimulation of these cultures with cytokines such as IL‐1 or TNF‐α. Collectively it will provide important new information on the changing pattern of KS substitution in connective tissue PGs with development, ageing and the onset of pathology.

Dissociative excitation of carbon disulfide by electron impact

Dissociative excitation of carbon disulfide (CS 2) producing CS fragments in the A 1Π excited state has been studied by optical excitation method in the electron energy range from threshold to 30 eV. The threshold energy for the dissociative excitation has been determined to be 9.33±0.06 eV. It has been also verified that the vibrational population of the CS radicals is inverted for v=0 and 1 levels.

The structure of [Co 3(η 5-C 5H 5) 3(μ 3-S)(μ 3-CSMe)] +, and the reactions of the metal cluster cations [{Co(η 5-C 5H 5)} 2{Fe(CO) 2(PPh 3)}(μ 3-S)(μ 3-CSR)] + and [{Co(η 5-C 5H 5)} 3(μ 3-S)(μ 3-CSR)] + (R=Me, Et) with nucleophiles

[Co 3(η 5-C 5H 5) 3(μ 3-S)(μ 3-CSR)][I], [ 5]I (R=Me), [ 6]I (R=Et) are not dealkylated by treatment with [PhCH 2NMe 3]OH, NaOH, NaOMe or NaOEt in either CH 2Cl 2 or MeOH–EtOH solutions. [{Co(η 5-C 5H 5)} 2{Fe(CO) 2(PPh 3)}(μ 3-S)(μ 3-CSMe)][X], [ 3]X (X −=I − or [SO 3CF 3] −), is similarly not dealkylated but instead undergoes nucleophilic attack at coordinated CO to give zwitterionic [{Co(η 5-C 5H 5)} 2{Fe(CO)(CONu)(PPh 3)}(μ 3-S)(μ 3-CSMe)] derivatives ( 7) (Nu −=(a) OH −, (b) MeO −, or (c) EtO −). Although they may be identified unambiguously by spectroscopy, they could not be isolated in the pure state as their formation is reversible and made completely so by addition of aqueous acids. [{Co(η 5-C 5H 5)} 2{Fe(CO) 2(PPh 3)}(μ 3-S)(μ 3-CSEt)][X], [ 4]X, undergoes partial dealkylation (ca. 20%) to [{Co(η 5-C 5H 5)} 2{Fe(CO) 2(PPh 3)}(μ 3-S)(μ 3-CS)] ( 1), but the principal reaction is CO attack to give [{Co(η 5-C 5H 5)} 2{Fe(CO)(CONu)(PPh 3)}(μ 3-S)(μ 3-CSEt)] derivatives ( 8) (Nu −=(a) OH −, (b) MeO −, or (c) EtO −). The structure of [Co 3(η 5-C 5H 5) 3(μ 3-S)(μ 3-CSMe)][BPh 4] has been determined by X-ray diffraction. It is concluded that the conversion of μ 3-CS in [Co 3(η 5-C 5H 5) 3(μ 3-S)(μ 3-CS)] ( 2) to μ 3-CSMe in [ 5] + greatly modifies the bonding between Co 3S and CS fragments. The Co 3 triangle is distorted from equilateral to isosceles and the C–S bond is lengthened to 1.714(5)/1.719(5) Å (c.f. 1.638(3) Å in 1 and 1.728(7) Å in [ 3a] +). This suggests that the positive charge is not localised on the μ 3-CSMe moiety but has been delocalised into the cluster by backbonding which, consequently, renders the Me group less susceptible to nucleophilic attack. The μ 3-CSEt ligand is more susceptible to nucleophilic attack, perhaps due to the possibility of elimination-type reaction pathways.

Theoretical Investigation of the Reactivity of Copper Atoms with Carbon Disulfide

The mechanism of the Cu + CS2 reaction has been investigated using density functional and coupled cluster calculations. The lowest energy route on the potential energy surface corresponds to the insertion product SCuCS via the formation of intermediate coordination complexes: η1S and η2CS, which all lie below the energy of the reactants. Another path corresponding to the formation of a cyclic C2v compound η2SS leads to the same insertion product, but it involves a higher energy barrier (34.7 kcal/mol vs 26.9 kcal/mol with respect to the reactants at the CCSD(T) level). The dissociation of the insertion product SCuCS into the CuS and CS fragments is found to be endothermic by 43 kcal/mol (CCSD(T) level). Our results are related to experimental data obtained in low-temperature rare gas matrixes and in the gas phase.

Tandem mass spectra of ammonium ion, metal ion and ligated metal ion adducts of acyclic sugar derivatives.

The tandem mass (MS/MS) spectra of ammonium ion, metal ion and ligated metal ion adducts of chain-extended acyclic nitro-containing deoxyglucose and deoxygalactose derivatives have been studied. The ammonium adducts fragment primarily by elimination of ammonia followed by acetic acid, thus not giving much structural information. In contrast, cationization of these compounds by metal ions and ligated metal ions gave structurally informative and useful fragment ions on MS/MS. The metal ions and ligated metal ions play an important role in controlling and directing fragmentation. Retro-aldol fragmentation is facilitated by metal ions such as Li(+), Na(+), Ag(+) and Cu(+), whereas the adducts with higher alkali metal ions such as Rb(+) and Cs(+) fragment to give only the corresponding metal ions. The divalent metal ions such as Cu(2+) and Ba(2+) also induce retro-aldol fragmentation. However, the charge is carried by the aldehyde fragment in the case of Cu(2+) adducts, whereas the nitroalkane fragment carries the charge in the case of Ba(2+) adducts. Ligated metal ions such as ZnCl(+), CuCl(+), InCl(2) (+) and BaCl(+) also behave similarly and induce retro-aldol fragmentation in these acyclic sugars. Both the metal ion and ligated metal ion adducts can fragment by elimination of metal-containing neutral molecules.

Resonance enhanced multiphoton ionization spectroscopy of carbon disulphide

Rydberg excited states of the CS2 molecule in the energy range 56 000–81 000 cm−1 have been further investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization (MPI) spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been aided by parallel measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. Thus we have been able to extend, and clarify, previous analyses of the tangled spin–orbit split vibronic structure associated with the 3Πu and 1Πu states derived from the configuration [2Πg]4pσu and the 3Δu, 1Δu, and 1Σ+u states resulting from the configuration [2Πg]4pπu, and to deduce an approximate wave number for the origin of the hitherto unidentified 3Σ+u state derived from this same configuration. Moving to higher energies we are able to locate, unambiguously, the origins of the next (n=5) members of four of these [2Πg]np Rydberg series, and to identify extensive series based on the presumed Rydberg configurations [2Πg]nsσg and [2Πg]nfλu with, in both cases, n≤10. We also identify MPI resonances attributable to CS(a 3Π) fragments, to ground state C atoms, and to S atoms in both their ground (3P) and excited (1S) electronic states. Analysis of the former resonances indicates that the CS(a 3Π) fragments resulting from two photon dissociation of CS2 at excitation wavelengths around 300 nm are formed with substantial rovibrational excitation.

Photodissociation of CS2 at 193 nm investigated by polarised photofragment translational spectroscopy

The predissociation dynamics of CS2 in the (B- 1(2)) state have been investigated by means of high resolution photofragment translational spectroscopy at 193 nm. The photofragment translational energy distributions derived from the time-of-night (TOF) distributions of the CS fragment are qualitatively similar to the ones obtained in previous investigations. Detailed measurements carried out with a linearly polarised photolysis laser reveal a pronounced anisotropy of the fragment recoil which is dependent on the translational energy and on the molecular beam carrier gas. It is possible to partition each TOF distribution of the CS fragment into two components corresponding to the formation of S(P-3) and S(D-1) partner fragments, respectively, in a manner consistent with recent branching ratio determinations. In the case of the Ne beam this partitioning leads to the anisotropy parameters beta(S D-1)approximate to 0.2 and beta(S 3P)approximate to 1.0. These results indicate that the overall photodissociation process occurs on a time scale of similar to 1.5 ps and that the formation of CS + S(D-1) proceeds through a strongly bent transition state.

Are the C 4v complexes of cyclobutadiene with CO, NO +, and CS minima?

While the C 4v pyramidal structures of the cyclobutadiene-CO and cyclobutadiene-NO + complexes are second-order saddle points rather than minima, the pyramidal C 4v cyclobutadiene-CS complex is a minimum due to stronger interactions of the e π * orbitals of the CS fragment with the cyclobutadiene e g π-orbitals. However, the isomerization barrier of this complex into bicyclo[2.1.0]pententhione, only 0.5 kcal/mol at MP2/6–31G *//MP2/6–31G *+ZPE(HF/6–31G *), disappears at higher levels. This C 4v C 4H 4CS complex is unlikely to be a viable candidate for experimental observation as an isolated entity.

Product energy disposal in the nonadiabatic reaction S(1D)+CS2→S2 (X 3Σ−g)+CS (X 1Σ+)

The product energy disposal in the reaction S(1D)+CS2→S2+CS is measured via laser-induced fluorescence. Molecular sulphur is produced exclusively in its electronic ground state (3Σ−g) with up to 3 quanta of vibrational excitation and rotational excitation that roughly approximates a 1000 K Boltzmann distribution. The CS produced from the reaction is formed predominantly in its vibrationless state. The total internal energy content of the product molecular sulphur is only about 12% of the total available energy of the reaction; the CS fragment also has minimal internal energy, implying that most of the reaction energy resides in product translation. These results are different from those observed in the isovalent S+OCS reaction and suggest that a different detailed mechanism is operative.

Photofragment spectroscopy of CS2 at 193 nm: Direct resolution of singlet and triplet channels

The 193 nm dissociation of CS2 has been studied under supersonic molecular beam conditions, with the atomic S products detected by vacuum ultraviolet laser-induced fluorescence. These experiments measure the branching ratio between singlet and triplet channels to be S(3P)/S(1D) =2.8±0.3. Doppler spectroscopy on the S(3P2) and S(1D2) products was used to study the dynamics of each channel separately. The energy release in each channel was similar, with the CS fragments formed vibrationally inverted with about 50% of the available energy in CS rotation and vibration. The recoil velocity anisotropy in each channel was also measured, found to be the same for both, and was consistent with a 2 ps lifetime for the 1Σ+u(1B2) excited state of CS2.