SC Bonds Research Articles

Heteroatoms doped graphene for catalytic ozonation of sulfamethoxazole by metal-free catalysis: Performances and mechanisms

In this study, reductive graphene oxides (rGO) and heteroatoms (N and P) doped graphene oxides (NGO, PGO) were synthesized and firstly applied in catalytic ozonation of sulfamethoxazole (SMX). As metal-free materials, NGO and PGO were found to exhibit significant abilities in catalytic ozonation of SMX, of which the efficiency were both more than 2.5 times to ozonation system and 1.5 times to the undoped rGO, respectively. Materials characterization showed the doping of heteroatoms into graphene oxides layers would modulate the configuration and properties of graphene oxides meanwhile create new active sites to enhance the catalytic performance. Density functional theory (DFT) calculations were then employed to give an in-depth probe of the degradation mechanism. The theoretical calculations were in good correspondence with the experimental results, indicating that the S atom was the most susceptible attacking site, which resulted in the cleavage of SN and SC bond of SMX during the catalytic ozonation processes. This study proposes a new insight into catalytic ozonation of SMX by NGO and PGO materials.

Thermal and Chemical Stability of n-Hexadecanethiol Monolayers on Au(111) in O2 Environments

Understanding the mechanisms of degradation of self-assembled monolayers (SAM) is required for their use in molecular devices and in general in long term applications. In this context, we investigated the thermal and chemical stability of n-hexadecanethiolate (C16T) monolayers on Au(111) exposed to O2. The degradation of the monolayers was followed by electrochemical (EC) techniques, surface enhancement Raman spectroscopy (SERS) and high resolution photoemission spectra (HR-XPS). The C16T monolayers were heated both under N2 and O2 flux up to 480K for different times. The degradation of the SAM in the presence of O2 is characterized by the appearance of oxidized sulfur species and sulfur atoms on the surface. The formation time in the dipping solution also affects the thermal stability of the monolayer. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations were performed to elucidate the possible degradation mechanisms. MD shows that O2 molecules easily penetrate the monolayer reaching the Au surface. The DFT calculations identified two oxidation mechanisms which involve the S atom and the alpha carbon of the alkylthiolate. Both mechanisms are very exothermic. The oxidation of the sulfur atom produces a sulfinate which does not alter the monolayer structure. On the contrary, the oxidation of the alpha carbon induces the breakage of the SC bond, the adsorption of atomic S and the desorption of the alkyl chain as an aldehyde.

Gas and crystal structures of CCl2FSCN

Dichlorofluoromethyl thiocyanate, CCl2FSCN, was structurally studied in the solid and in the gas phase by means of single-crystal X-ray (XRD) and gas electron diffraction (GED), respectively. In the gas phase the title molecule adopts two stable conformers, described by the FC–SC dihedral angle. The gauche-conformer (FC bond with respect to the SC bond) is more stable than the anti-conformer. In this work we present the first experimental evidence for the existence of the anti-CF2ClSCN form. In the solid state only the most stable gauche-conformer was found. Intermolecular interactions were detected in the crystal structure and analyzed. A structural comparison of the results with those of related species as CCl2FSCN, CCl3SCN and CH2ClSCN is presented.

Insight into the loading temperature of sulfur on sulfur/carbon cathode in lithium-sulfur batteries

Lithium–sulfur batteries are highly desired because of their characteristics such as high energy density. However, the applications of Li-S batteries are limited because they exist dissolution of polysulfides into electrolytes. This study reports the preparation of sulfur cathodes by using bimodal microporous (0.5nm and 0.8nm to 2.0nm) carbon spheres with high specific area (1992m2g−1) and large micropore volume (1.2gcm−1), as well as the encapsulation of polysulfides via formation of carbon–sulfur bonds in a sealed vacuum glass tube at high temperature. Given that sulfur and polysulfides are well confined by the SC bond, the shuttle effect is effectively suppressed. The prepared S/C cathodes with a sulfur loading of up to 75% demonstrate high sulfur activity with reversible capacity of 1000mAhg−1 at the current density of 0.1Ag−1 and good cycling stability (667mAhg−1 after 100 cycles).

Infrared Spectra of Planar and Agostic-Like Bridged Scandium Methylidene Complexes Prepared in Reactions of Laser-Ablated Sc Atoms with Di-, Tri-, and Tetrahalomethanes

Reactions of laser-ablated Sc metal atoms with di-, tri-, and tetrahalomethanes were carried out in excess argon during condensation, and the matrix infrared spectra of products were investigated. Scandium methylidenes are the primary products, and they have planar or bridged structures depending on the degree of halogen substitution in the precursor, whereas neither insertion nor methylidyne complexes were observed. Although these Sc methylidene complexes are not agostic as far as any C–H bonds are concerned, numerous bridged halogen agostic-like structures arise through electron donation from the halogen atom bonded to carbon to the scandium metal center. This bridged methylidene is in fact an intermediate between the methylidene and methylidyne complexes. The 3d14s2 electronic structure prevents scandium from generating higher oxidation state products, and the bond order of the methylidene C–Sc bond is approximately 1.5 or 1.0 for planar or bridged structures, respectively.

First-principle investigation of thiophene adsorption on TM (Ni/Co/Mn)-doped (ZnO)15 nanotube

The adsorption of thiophene on transition metal (Ni/Co/Mn)-doped (ZnO)15 nanotube is investigated using density functional theory calculation. Different adsorption possibilities have been investigated. It is found that the stability of the nanotube increases with the doping of the transition metal (Ni/Co/Mn) atom, and the doping of transition metal (Ni/Co/Mn) atom should be mainly responsible for the reduction of the energy gap. We also observed an elongation of the SC bond in adsorbed thiophene in Ni/Co/Mn-doped (ZnO)15 adsorption systems, compared with those of adsorbed thiophene in pristine (ZnO)15 adsorption systems, illustrating the SC bonds in adsorbed thiophene are active by transition metal atom in Ni/Co/Mn-doped (ZnO)15 nanotubes. Molecular orbital results show that π-backdonation is found in η2 bonding mode. Moreover, compared with the vibrational frequencies of free thiophene, the ν(CC)sym and ν(CS)as bands of η2 bonding mode are shifted to lower wavenumber.

Synthesis and characterization of palladium (II) complex of Schiff base ligand: C[sbnd]S bond cleavage and catalytic activity

Reaction of ligand, L-CH2Ph with Pd(CH3CN)2Cl2 in acetonitrile in presence of PPh3 and subsequent addition of NaClO4 yielded Pd(II) complex, [Pd(L)(PPh3)](ClO4) 1 due to the SC (CH2Ph) bond cleavage during complexation. Complex 1 was characterized by spectral analysis and the structure was authenticated by single crystal X-ray diffraction. The diffraction analysis revealed that the monoanionic ligand binds with palladium (II) in (N, N, S) fashion in a distorted square planar geometry where the fourth position is occupied by one tri phenyl phosphine group. One ClO4− ion satisfies the charge of the former aggregate, [Pd(L)(PPh3)]+. The complex [Pd(L)(PPh3)](ClO4), 1 exhibits a very good catalytic activity towards CC bond formation.

A metal–metal bond passing through the arene ligand: a theoretical study on inverse sandwiches X[Sc–C8H8–Sc]nX (X = F, Cl, Br; n = 1, 2)

In X[Sc–C8H8–Sc]2X (X = F–Br), Sc–Sc bonds between two [Sc–C8H8–Sc] units and the Sc–Sc bond through C8H8form the uninterrupted Sc–Sc–Sc–Sc bond-chain.

Water and ionic liquid synergy: A novel approach for the synthesis of benzothiazole-2(3H)-one

Synergy between water, a green reaction medium and ionic liquid, a green catalyst has opened new vistas in the field of organic transformation. The developed methodology has emerged as an interesting combination for an environmentally benign, facile and efficient synthesis of benzothiazole-2(3H)-one. Product was achieved in excellent yield by the reaction of structurally diverse 2-iodoanilines with potassium thiocyanate. The strategy involves nucleophilic substitution forming NC and SC bonds resulting in the desired heterocyclic scaffold. This novel approach is also helpful for the synthesis of other related heterocycles for the development of an important drug like library. The reaction proceeded smoothly at an ambient temperature.

Structures and stability of SCBO+/− and SBCO+/−: prediction of very short yet classical triple bonding of sulfur

Compounds containing the sulfur triple bonding have continued to attract chemists’ attention. In this article, with an attempt to predict intrinsically stable species with sulfur-related triple bonding, we report a thorough computational study of two charged systems [B,C,O,S]+ and [B,C,O,S]− at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(3df,2p)+ZPVE level for singlet and triplet potential energy surfaces, aug-cc-pVTZ-B3LYP, M06-2X, and CCSD(T) levels for critical structures, as well as the CCSD(T)/aug-cc-pVQZ and G4 levels for adiabatic bond dissociation energy (ABDE). A total of 26 isomers and 25 transition states were located. The cationic and anionic [B,C,O,S] have the singlet and triplet ground states, respectively. For both systems, the former low-lying isomers are the linear SCBO+/− 01 and SBCO+/− 02, both of which contain the S≡X (X = C, B) bonding and are kinetically very stable against interconversion and fragmentation. With the increased valence electron number in the order of SCBO/SBCO+ < SCBO/SBCO < SCBO/SBCO−, the SX bond distance elongates as 1.5653 < 1.6126 < 1.6924 A for X = B and 1.4715 < 1.5319 < 1.6100 A for X = C at the M06-2X/aug-cc-pVTZ level. Notably, SBCO+ bears the shortest S≡B bond known to date, while SCBO+ bears the shortest S≡C bond among the known classical and non-protonated compounds (the well-known F3SCCF3 and F3SCSF5 have been termed as “nonclassical” because of their unusually low ABDE of SC bond). Future mass spectroscopic studies are greatly appealed for the characterization of the cationic and anionic SCBO+/− 01 as well as SBCO+/− 02.

First-principles investigation of thiophene adsorption on Ni13 and Zn@Ni12 nanoclusters

The adsorption of thiophene on icosahedral Ni13 and Zn doped Ni13 clusters is investigated using density functional theory calculations. Different adsorption possibilities have been studied. The results indicate that thiophene is preferentially adsorbed on Ni13 and Zn@Ni12 clusters with the whole ring π-bond to the hollow site (η5 bonding model). For Ni13C4H4S with η5 bonding model, the strong interaction between thiophene and Ni13 cluster results in the elongation of the SC bonds (1.78–1.83Å) and the quite large adsorption energies (2.21–2.57eV). However, the adsorption of thiophene with η1(S) bonding model is relatively weak based on the small value of adsorption energies (0.89eV) and Bader charge transfer (0.07 |e|). Compared with the Ni13C4H4S clusters with η5 bonding model, the Zn@Ni12C4H4S clusters have a larger adsorption energy. When Zn atom is on the shell (Ni@Ni11Zn1), thiophene is more likely to be adsorbed on the Ni site rather on the Zn site.

Mechanical and optical properties of inverse-perovskites Sc3InX (X = B, C, N)

We present first-principles density functional theory (DFT) investigations of mechanical, thermodynamic and optical properties of synthesized inverse-perovskites Sc3InX (X=B, C and N). The elastic constants at zero pressure and temperature are calculated and the anisotropic behavior of the compounds is illustrated. All the three materials are shown to be brittle in nature. The computed Peierls stress, approximately 3–5 times larger than in a selection of MAX phases, show that movement may follow but with much reduced occurrences compared to these MAX phases. The Mulliken dislocation bonding population and charge density maps show stronger covalency between Sc and X atoms compared with Sc–Sc bond. The Vickers hardness values of Sc3InX are predicted to be between 3.03 and 3.88GPa. The Fermi surfaces of Sc3InX contain both hole- and electron-like topology which changes as one replaces B with C or N. The bulk modulus, specific heats, thermal expansion coefficient, and Debye temperature are calculated as a function both temperature and pressure using the quasi-harmonic Debye model with phononic effects. The results so obtained are analyzed in comparison to the characteristics of other related compounds. Moreover optical functions are calculated and discussed for the first time. The reflectivity is found to be high in the IR-UV regions up to ∼10.7eV (Sc3InB and Sc3InC) and 12.3eV (Sc3InN), which would predict these to be good coating materials.

Exploring the charge density distribution and the electrical characteristics of Oligo phenylene ethylene molecular nanowire using quantum chemical and charge density analysis

To understand the charge density distribution and the electrical characteristics of Au and thiol substituted Oligo phenylene ethylene (OPE) molecular nanowire, a quantum chemical calculation has been carried out using high level Density Functional Theory (DFT) with the basis set LANL2DZ coupled with the Bader’s theory of atoms in molecules. The applied electric field (0.05–0.26VÅ−1) altered the geometrical conformation, charge density distribution and the electronic energy levels of molecular wire. The bond topological analysis characterizes the terminal AuS, SC bonds as well as the bonds of central OPE molecule for zero and the applied fields. The field polarizes the molecule, in consequence of that the dipole moment of the molecule abruptly increases from 3.23 to 39.73D. For the zero bias, the HOMO–LUMO gap is 2.17eV, as the field increases this gap rapidly decreases to 0.4eV; presumably, this small energy gap at higher field may enhance the conductivity. The I–V characteristics of the molecule have been studied for various applied fields.

Mass spectrometric and theoretical studies on dissociation of the S[sbnd]S bond in the allicin: Homolytic cleavage vs heterolytic cleavage

On the basis of the tandem mass spectrometry (ESI-MS/MS) technique and DFT calculations, an experimental and theoretical investigation has been conducted into the gas-phase dissociation of the S1S1′ bond in the allicin as well as that of the SC (S1C2, S1′C2′) bond. Meanwhile, the influence of protonation, alkali metal ion and electron transfer on the dissociation of the S1S1′ bond has been taken into account. ESI-MS/MS experiments and DFT calculations show that in the neutral allicin, [allicin+Li]+ and [allicin+Na]+, the S1S1′ bond favors homolytic cleavage, while in the allicin radical cation and protonated allicin, the S1S1′ bond prefers heterolytic cleavage. In addition, alkali metal ions can strengthen the S1S1′ bond in the allicin, while protonation or the loss of an electron will weaken the S1S1′ bond.

Mapping Disulfide Bonds in Insulin with the Route 66 Method: Selective Cleavage of S [sbnd]C Bonds Using Alkali and Alkaline Earth Metal Enolate Complexes

Simple and fast identification of disulfide linkages in insulin is demonstrated with a peptic digest using the Route 66 method. This is accomplished by collisional activation of singly and doubly charged cationic Na(+) and Ca(2+) complexes generated using electrospray ionization mass spectrometry (ESI-MS). Collisional activation of doubly charged metal complexes of peptides with intermolecular disulfide linkages yields two sets of singly charged paired products separated by 66 mass units resulting from selective SC bond cleavages. Highly selective elimination of 66 mass units, which corresponds to the molecular weight of hydrogen disulfide (H(2)S(2)), is observed from singly charged metal complexes of peptides with disulfide linkages. The mechanism proposed for these processes is initiated by formation of a metal-stabilized enolate at Cys, followed by cleavage of the S-C bond. Further activation of the products yields sequence information that facilitates locating the position of the disulfide linkages in the peptic digest fragments. For example, the doubly charged Ca(2+) complex of the peptic digest product GIVEQCCASVCSL/FVNQHLCGSHL yields paired products separated by 66 mass units resulting from selective SC bond cleavages at an intermolecular disulfide linkage under low-energy collision-induced dissociation. Further activation of the product comprising the A chain reveals the presence of a second disulfide bridge, an intramolecular linkage. Experimental and theoretical studies of the disulfide linked model peptides provide mechanistic details for the selective cleavage of the S-C bond.

Methane and methyl halide activation by Sc atoms: Infrared spectra and DFT calculations for the CH 3–ScX and CH 2–ScHX complexes

Reactions of laser-ablated scandium atoms with methane and methyl halides have been done during condensation in excess argon, and matrix infrared spectra were recorded for the products. Scandium is as effective as titanium in producing insertion products (CH 3–ScX, X = H, F, Cl, Br) and higher oxidation-state methylidene complexes (CH 2–ScHX) following α-hydrogen migration. However, unlike the Group 4–6 metal complexes, the Group 3 methylidene complexes do not show agostic distortion, and the computed C–Sc bond lengths of the methylidene complexes are slightly shorter than those for the insertion products. This shows that carbon–transition metal bond lengths in the double bond range are needed to support the agostic interaction. The computed spin densities are consistent with weak C(p)–Sc(d) π-bonding in the methylidene complexes.

Design Criteria for Star Polymer Formation Processes via Living Free Radical Polymerization

The kinetics of reversible addition−fragmentation chain transfer (RAFT), R-group approach star polymerizations have been studied via a combined experimental and theoretical approach. From the improved understanding herein developed, design criteria have been suggested to aid in future syntheses of RAFT, R-group approach star polymer. The suggested criteria are as follows. To minimize the quantity of linear polymer in the system, it is important to have a high rate of monomer propagation but a small delivery of radicals to the system. Crucial to the prevention of star−star coupling and resulting molecular weight distribution (MWD) broadening is the minimization of radical termination events between star molecules. Noting that the number of termination events is directly correlated to the number of decomposed initiator molecules, this might be achieved via several methods. A slow rate of initiator decomposition, a fast rate of propagation, or use of a rate-retarding RAFT agent can all lead to a reduction in star−star coupling events. Additionally, simulations reported herein demonstrate that the use of a star-forming RAFT agent substrate which has a fewer number of arms will lead to a reduction in the concentration of star−star coupled products. Ab initio calculations have been used to study intramolecular RAFT equilibria occurring early in the preequilibrium. These calculations have shown that highly stable intramolecular adduct radicals might be formed due to the close proximity of radicals and SC bonds. The effect of these on the kinetics is studied.

Hyperfine structure of Sc@C82 from ESR and DFT

The electron spin g- and hyperfine tensors of the endohedral metallofullereneSc@C82 are anisotropic. Using electron spin resonance (ESR) and density functional theory (DFT),we can relate their principal axes to the coordinate frame of the molecule, finding that theg-tensor is not axially symmetric. The Sc bond with the cage is partlycovalent and partly ionic. Most of the electron spin density is distributedaround the carbon cage, but 5% is associated with the scandiumdyz orbital, and this drives the observed anisotropy.

Interaction of Sc and O on W

The surface chemistry on top of scandate cathodes plays a fundamental role in the performance and reliability of the cathodes. The surface chemical reaction is a complex dynamical process that involves Sc, Ba, O, W and noble metals at elevated temperatures. An initial approach is to investigate the interaction among the elements in subsets separately. In this study we investigate the interaction of Sc and O on W substrates, combining temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES).There are three distinct states of Sc adsorption on W that originate from the first-layer, second-layer and multiple-layer states in a decreasing order of binding energy. The first layer grows to about 2/3 completion when the second layer begins to form, but the second layer is unstable. Agglomeration into multiple layers occurs when the second layer exceeds 1/3 layer. Sc bonds to W more strongly than Ba to W. The desorption maximum of the first-layer Sc occurs at 1575±22K, in comparison with the desorption maximum of Ba from W at 1250±4K. The addition of O strengthens the Sc-to-W bonds. There are also three distinct binding states that emerge simultaneously during the growth of oxidized Sc. The weakest binding state has a desorption maximum at 1732±29K, which is about 300K higher than the desorption maximum of the oxygen-enhanced Ba adsorption on W.Evaporation rates as a function of temperature are determined from TPD spectra of thick films. The results suggest that during activation of a scandate cathode the loss of metallic Sc can be substantial while the loss of oxidized Sc is minimal. It implies also that thermal evaporation from oxidized Sc may not be an effective method to replenish the Sc, the loss of which could occur from ion sputtering during operation in a vacuum electron device.

Electronic and Geometrical Structure of the Sc[BO]+ Cation. An Ab Initio Investigation

The Sc[BO]+ molecular cation has been investigated theoretically by multireference CI methods. We have examined the potential energy surfaces of all states that correlate to the ground-state Sc+(3D) + BO(X2Σ+) fragments. Three kinds of minima were discovered corresponding to the linear Sc−BO+ and BOSc+ and to the bent BOSc+ configurations, with the bent structure being the global minimum for all states. Full potential energy curves are reported for all symmetries examined, i.e., 2A‘(3), 2A‘ ‘(2) for the bent and 2Δ, 2Π, 2Σ+, 4Δ, 4Π, and 4Σ+ for the linear geometries. The ground state is of 2A‘ ‘ symmetry with a BO−Sc binding energy De = 63.9 kcal/mol at an equilibrium geometry with B−OSc and BO−Sc bond lengths of 1.260 and 2.046 Å, respectively, and a BOSc angle of 90.7°.