Electronic structure of functionalized thia- and calix[4]arenes

The electronic structure of calix[4]arene phosphine oxides (CPO) and thiacalix[4]arene phosphine oxides (TCPO) is studied by X-ray photoelectron and emission spectroscopy and quantum chemical methods. The electron density distribution over atoms contained in CPO and TCPO is analyzed. The structure of higher occupied molecular orbitals (HOMO) is examined. It is shown that HOMOs of these compounds mainly consist of contributions of oxygen 2p atomic orbitals (AOs) of phosphoryl and hydroxyl moieties and also bridging sulfur 3p AOs, which indicates the bifunctionality of the considered extractant molecules. The mutual effect of the lower and upper rims of CPOs and TCPOs as well as the effect of their structures on the electron density distribution over calixarene molecules is investigated.     

On the effect of d orbitals on relativistic bond-length contractions

5d AOs are found to diminish the usual relativistic bond-length contraction in some hydrides. This is shown to be a first-order effect, unrelated to the relativistic expansion of 5d AOs, by both the perturbative Dirac-Fock one-center expansion and Hartree-Fock-Slater methods. The latter method is used to investigate the chemical similarity of Zr and Hf.     

Development of Novel Indole-Based Bifunctional Aldose Reductase Inhibitors/Antioxidants as Promising Drugs for the Treatment of Diabetic Complications

Aldose reductase (AR, ALR2), the first enzyme of the polyol pathway, is implicated in the pathophysiology of diabetic complications. Aldose reductase inhibitors (ARIs) thus present a promising therapeutic approach to treat a wide array of diabetic complications. Moreover, a therapeutic potential of ARIs in the treatment of chronic inflammation-related pathologies and several genetic metabolic disorders has been recently indicated. Substituted indoles are an interesting group of compounds with a plethora of biological activities. This article reviews a series of indole-based bifunctional aldose reductase inhibitors/antioxidants (ARIs/AOs) developed during recent years. Experimental results obtained in in vitro, ex vivo, and in vivo models of diabetic complications are presented. Structure–activity relationships with respect to carboxymethyl pharmacophore regioisomerization and core scaffold modification are discussed along with the criteria of ‘drug-likeness”. Novel promising structures of putative multifunctional ARIs/AOs are designed.     

The use of comet assay data with a simple reaction mechanism to evaluate the relative effectiveness of free radical scavenging by quercetin, epigallocatechin gallate and N-acetylcysteine in UV-irradiated MRC5 lung fibroblasts

Comet assay data (tail DNA %) have been gathered for the concentration dependent role of three antioxidants (AOs); quercetin (Q), epigallocatechin gallate (EGCG) and N-acetylcysteine (NAC) in reducing UV-induced damage to DNA in normal fetal lung fibroblasts (MRC5). All three compounds demonstrate a concentration dependent reduction maximum with a pro-oxidant effect at higher (though not cytotoxic) concentrations. Manipulation of a simple 4-step reaction mechanism for free radical (FR) scavenging by AOs produced rate constant ratios which allowed the relative effectiveness (Q > EGCG > NAC) of the AOs to be evaluated.     

Intermetallic compounds of the heaviest elements and their homologs: the electronic structure and bonding of MM', where M=Ge, Sn, Pb, and element 114, and M'=Ni, Pd, Pt, Cu, Ag, Au, Sn, Pb, and element 114

Fully relativistic (four-component) density-functional theory calculations were performed for intermetallic dimers MM', where M=Ge, Sn, Pb, and element 114, and MM'=group 10 elements (Ni, Pd, and Pt) and group 11 elements (Cu, Ag, and Au). PbM and 114M, where M are group 14 elements, were also considered. The results have shown that trends in spectroscopic properties-atomization energies D(e), vibrational frequencies omega(e), and bond lengths R(e), as a function of MM', are similar for compounds of Ge, Sn, Pb, and element 114, except for D(e) of PbNi and 114Ni. They were shown to be determined by trends in the energies and space distribution of the valence ns(MM')atomic orbitals (AOs). According to the results, element 114 should form the weakest bonding with Ni and Ag, while the strongest with Pt due to the largest involvement of the 5d(Pt) AOs. In turn, trends in the spectroscopic properties of MM' as a function of M were shown to be determined by the behavior of the np(1/2)(M) AOs. Overall, D(e) of the element 114 dimers are about 1 eV smaller and R(e) are about 0.2 a.u. larger than those of the corresponding Pb compounds. Such a decrease in bonding of the element 114 dimers is caused by the large SO splitting of the 7p orbitals and a decreasing contribution of the relativistically stabilized 7p(1/2)(114) AO. On the basis of the calculated D(e) for the dimers, adsorption enthalpies of element 114 on the corresponding metal surfaces were estimated: They were shown to be about 100-150 kJ/mol smaller than those of Pb.     

Determination of polycyclic aromatic sulfur heterocycles in diesel particulate matter and diesel fuel by gas chromatography with atomic emission detection

The sulfur content of diesel fuel is of environmental concern because sulfur can facilitate the formation of diesel particulate matter (DPM) and sulfur dioxide (SO2) in the exhaust can poison catalytic converters. The US Environmental Protection Agency (EPA) has established more stringent regulations to reduce the sulfur content of diesel fuels in the near future. In this study, various types of organosulfur compounds in DPM extracts and the corresponding fuels have been determined by gas chromatography with atomic emission detection. The diesel fuels used have sulfur contents of 2284 and 433 ppm, respectively, and are labeled as high-sulfur and low-sulfur diesel fuels. The compounds identified are mainly polycyclic aromatic sulfur heterocycles (PASHs). In the fuels tested, trimethylbenzothiophenes (TMBTs), dibenzothiophenes (DBTs), and 4-methyldibenzothiophene (4-MDBT) were the most abundant sulfur compounds, while larger PASH compounds were more abundant in DPM extracts. The high-sulfur diesel fuel contained a larger proportion of PASHs with one or two rings (lighter PASHs). In DPM, the concentrations of total organic sulfur and individual PASHs are higher for the high-sulfur diesel fuel, and the relative percentage of one or two-ring PASHs is higher as well. The influence of engine load on the DPM composition was also examined. With increasing load, the PASH concentration in DPM decreased for lighter PASHs, increased for heavier PASHs, and had a bell-shaped distribution for PASHs in between.     

Electronic structure of calix[4]arene thioethers and their complexes with palladium,as studied by X-ray emission spectroscopy,X-ray photoelectron spectroscopy,and quantum chemistry

The charge state of calix[4]arene thioethers and their complexes with palladium was studied by X-ray emission spectroscopy and X-ray photoelectron spectroscopy. Experimental data were compared with the results of quantumchemical calculations. The involvement of the sulfur lone electron pairs in the coordination to Pd atoms causes a decrease in the energies of the corresponding MOs having contributions from the sulfur 3p AOs and, consequently, a decrease in the intensity of the maximum A on going from the S(Kβ) spectra of free ligands to the spectra of complexes. The binuclear nature of the complexes does not lead to the onset of significant additional interactions between two metal centers.     

Liquid chromatographic properties of aromatic sulfur heterocycles on a Pd(II)-containing stationary phase for petroleum analysis

Polycyclic aromatic sulfur heterocycles (PASHs) can show very poor reactivities in catalytic hydrodesulfurization processes in refineries, especially those in high-boiling fractions and distillation residues. An insight into the structural features of the most recalcitrant PASHs is essential for developing more efficient catalysts and improving refinery processes. The very high complexities of such mixtures necessitate fractionation of the samples into smaller subsets according to defined criteria. A stationary phase containing a palladium(II)-complex was previously shown to be efficient for separating PASHs in lighter petroleum fractions. Here we characterize this ligand exchange chromatographic phase using a large number of sulfur aromatic model compounds that were synthesized for the purpose. In general, compounds containing thiophene rings that are not condensed with other aromatic systems are weakly retained and elute in a first fraction with the polycyclic aromatic hydrocarbons. Thiophene rings condensed with other aromatic rings are more strongly retained and elute in a later fraction with a more polar eluent. If the sulfur is in a non-aromatic ring, the compound is irreversibly retained by the Pd(II) ions. Some steric effects are seen in compounds with alkyl or aryl substituents close to the sulfur atom but in general they do not interfere strongly with the complexation. Thus it seems possible to separate groups of aromatic sulfur compounds according to their complexation properties. For instance, such fractionated samples can be studied much more easily by mass spectrometric techniques.     

Fast analysis of oxygen and sulfur compounds in gasoline by GC-AED

This paper describes a method for determining both the total sulfur content and the concentration of oxygenated additives in gasoline by gas chromatography with atomic emission detection (GC-AED). The AED provides selective detection of oxygen and sulfur compounds. Because the response factors for sulfur and oxygen are largely independent of the type of compound, calibration and determination of total element content are simplified. The use of a 0.1 mm i.d. capillary column enables complete elution of the components of the gasoline in under 10 minutes.     

Electrochemical antioxidant detection technique based on guanine-bonded graphene and magnetic nanoparticles composite materials

An antioxidant (AO) amperometric technique based on guanine attached to graphene and Fe(3)O(4) nanoparticles (NPs) magnetic materials was developed. Guanine molecules acted as an antioxidant competitor were bonded with graphene nanosheets, onto which magnetic Fe(3)O(4) NPs were attached and the as-prepared magnetic composite can be attracted to the electrode surface by an external magnetic field. When applied with negative potentials, the dissolved oxygen was reduced to H(2)O(2) at the electrode surface, and then reacted with the EDTA-Fe(ii) complex via a Fenton-like reaction to produce OH radicals. After oxidation damage by OH radicals, the electrochemical oxidation of guanine gave a decreased current. In the presence of AOs, the reactive oxygen species (ROS, e.g. OH radicals and H(2)O(2)) were scavenged by AOs and fewer guanine probe molecules were oxidized, thus inducing a higher electrochemical oxidation current of guanine. So AOs competed with the guanine probe molecules toward oxidation by ROS. The current signals of the guanine probe molecules were proportional to the concentrations of AOs. A kinetic model was proposed to quantify the ROS scavenging capacities of the AOs. Using guanine as an oxidizable probe and OH radicals and H(2)O(2) as endogenous ROS, this kind of AO detection technique mimicks the antioxidant protection mechanism by small AO molecules in the human body.     

加拿大合成原油减压馏分油及其催化裂化液体产物中含硫化合物分析

应用GC PFPD和GC MS技术对加拿大油砂合成原油（Synthetic Crude Oil,简称SCO）减压馏分油（350 ℃~500 ℃）中的含硫化合物进行定性定量分析。结果表明,所含硫化物主要是C3~7二苯并噻吩,而催化裂化反应后则以短侧链二苯并噻吩为主,还含少量烷基苯并噻吩和烷基噻吩,三者的质量分数分别为82.04%、13.42%和0.56%,均属于难以加氢脱除的含硫化合物。SCO减压馏分油和大港减压馏分油按不同比例混合后进行催化裂化反应,随着加拿大合成原油减压馏分油搀兑比增加,所得液相产物中烷基噻吩和烷基苯并噻吩质量分数逐渐降低,烷基二苯并噻吩相对质量分数增加,4-MDBT是丰度最高的含硫化合物,显示加氢油的特征。随掺兑比的提高,液相产物中总硫质量分数和柴油馏分中硫质量分数逐渐增高,而汽油馏分中硫质量分数逐渐降低。     

Mo-theoretical characterization of organic reaction mechanisms—VI : Outer 3d orbital participation in the reactions of sulfur-containing compounds

Participation of 3d orbitals in reactions of sulfur-containing compounds are studied in terms of the triplet stability-instability criterion for the restricted Hartree-Fock molecular orbitals. The criterion seems to permit infallible judgment as to whether or not the introduction of d orbitals would really possess any chemical significance for the reacting systems. It is shown that sulfur d orbitals should play an important role in the Hofmann elimination of sulfonium salts as well as the thermal decomposition of thiirane 1,1-dioxide. In the addition of sulfenyl cations to olefin and the thermal allylic rearrangement of allyl sulfides, however, the d orbital participation is found to be of little significance. The conclusions find support in the results of analytic studies of the sulfur bondings involved.     

Analysis of sulfur compounds from the in-oven roast beef aroma by comprehensive two-dimensional gas chromatography

After a previous investigation of carbonyl compounds in the in-oven top note of roast beef [S. Rochat, A. Chaintreau, J. Agric. Food Chem. 53 (2005) 9578], this paper focuses on the role of sulfur compounds. Because of the complexity of the roast beef headspace where sulfur compounds occur in trace amounts, a high resolution and sensitive technique, comprehensive two-dimensional gas chromatography (GC x GC), was chosen, that allowed the detection of thousands of compounds in the oven headspace. As identifying all of them would be too time consuming, a strategy had to be developed to extract the pertinent information. More than 70 sulfur compounds were found by GC x GC hyphenated to time-of-flight mass spectrometry (TOF-MS), and the identity of 50 of them was confirmed. To overcome the absence of many retention indices in databanks, the missing values were simulated using a multiple linear regression to help the peak identification. The selection of the most important sulfur odorants from this list was achieved by GC-olfactometry, using the GC-"SNIF" technique. Seven compounds have been found for the first time in beef aroma, of which only one has been previously found in nature.     

Mulliken集居数的基本关系

Mulliken的集居数分析就是将MO的正交归一化关系向AO、AO重迭区或原子进行分解。本文即基于这一认识,对它作了统一详细的讨论,并以甲烷为例,对EHMO程序,FORTICON的主要输出结果给予了计算说明。     

The antioxidant profile of 2,3-dihydrobenzo[b]furan-5-ol and its 1-thio, 1-seleno, and 1-telluro analogues

A novel synthesis of 2,3-dihydrobenzo[b]thiophene-5-ol based on intramolecular homolytic substitution on sulfur was reported. The "antioxidant profile" of the series of 2,3-dihydrobenzo[b]furan-5-ol (2a) its 1-thio (2b), 1-seleno (2c) and 1-telluro (2d) analogues was determined by studies of redox properties, the capacity to inhibit stimulated lipid peroxidation, the reactivity toward tert-butoxyl radicals, the ability to catalyze decomposition of hydrogen peroxide in the presence of glutathione, and the inhibiting effect on stimulated peroxidation in liver microsomes. The one-electron reduction potentials of the aroxyl radicals corresponding to compounds 2a-2d, E degrees (ArO(*)/ArO(-)) were 0.49, 0.49, 0.49, and 0.52 V vs NHE, respectively, as determined by pulse radiolysis. With increasing chalcogen substitution the compounds become slightly more acidic (pK(a) = 10.6, 10.0, 9.9, and 9.5, respectively, for compounds 2a-2d). By using Hess' law, the homolytic O-H bond dissociation enthalpies of compounds 2a-2d (340, 337, 336, and 337 kJ mol(-)(1), respectively) were calculated. The reduction potentials for the proton coupled oxidation of compounds 2a-2d (ArOH --> ArO(*) + H(+)) as determined by cyclic voltammetry in acetonitrile were 1.35 (irreversible), 1.35 (quasireversible) 1.13 (reversible), and 0.74 (reversible) V vs NHE, respectively. As judged by the inhibited rates of peroxidation, R(inh), in a water/chlorobenzene two-phase lipid peroxidation system containing N-acetylcysteine as a thiol-reducing agent in the aqueous phase, the antioxidant capacity increases (2d > 2c = 2b > 2a) as one traverses the group of chalcogens. Whereas the times of inhibition, T(inh), were slightly reduced for the oxygen (2a) and sulfur (2b) derivatives in the absence of the thiol-reducing agent, they were drastically reduced for the selenium (2c) and tellurium (2d) derivatives. This seems to indicate that the organochalcogen compounds are continuously regenerated at the lipid aqueous interphase and that regeneration is much more efficient for the selenium and tellurium compounds. The absolute rate constants for the oxidation of compounds 2a-2b by the tert-butoxyl radical in acetonitrile/di-tert-butyl peroxide (10/1) were the same-2 x 10(8) M(-)(1) s(-)(1). Whereas the oxygen, sulfur, and selenium derivatives 2a-2c were essentially void of any glutathione peroxidase-like activity, the organotellurium compound 2d accelerated the initial reduction of hydrogen peroxide, tert-butyl hydroperoxide, and cumene hydroperoxide in the presence of glutathione 100, 333, and 213 times, respectively, as compared to the spontaneous reaction. Compounds 2a-2d were assessed for their capacity to inhibit lipid peroxidation in liver microsomes stimulated by Fe(II)/ADP/ascorbate. Whereas the oxygen, sulfur, and selenium compounds showed weak inhibiting activity (IC(50) values of approximately 250, 25, and 13 microM, respectively), the organotellurium compound 2d was a potent inhibitor with an IC(50) value of 0.13 microM.     

Headspace solid‐phase microextraction and gas chromatographic analysis of low‐molecular‐weight sulfur volatiles with pulsed flame photometric detection and quantification by a stable isotope dilution assay

Low‐molecular‐weight volatile sulfur compounds such as thiols, sulfides, disulfides as well as thioacetates cause a sulfidic off‐flavor in wines even at low concentration levels. The proposed analytical method for quantification of these compounds in wine is based on headspace solid‐phase microextraction, followed by gas chromatographic analysis with sulfur‐specific detection using a pulsed flame photometric detector. Robust quantification was achieved via a stable isotope dilution assay using commercial and synthesized deuterated isotopic standards. The necessary chromatographic separation of analytes and isotopic standards benefits from the inverse isotope effect realized on an apolar polydimethylsiloxane stationary phase of increased film thickness. Interferences with sulfur‐specific detection in wine caused by sulfur dioxide were minimized by addition of propanal. The method provides adequate validation data, with good repeatability and limits of detection and quantification. It suits the requirements of wine quality management, allowing the control of oenological treatments to counteract an eventual formation of excessively high concentration of such malodorous compounds.     

Transition‐Metal Chemistry of Alkaline‐Earth Elements: The Trisbenzene Complexes M(Bz)3 (M=Sr,Ba)

We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)₃ (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D₃ symmetric structure involving three equivalent η⁶‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n?1)d AOs of M and strong backdonation from the occupied (n?1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals.     

AB initio study of the regular polyhedral molecules N4, P4, As4, N8, P8 and As8

Ab initio pseudopotential SCF calculations were performed on tetrahedral X₄ molecules using double-zeta basis sets with and without d functions. The inclusion of d orbitals shortens the bond lengths, stabilizes the X₄ structures and intensifies the electron density inside the tetrahedron. The cubic X₈ molecules, calculated without d AOs, are not predicted to be more stable than 2X₄. Repulsions between parallel bonds in X₈ may compensate the lack of ring strain.     

Transition‐Metal Chemistry of Alkaline‐Earth Elements: The Trisbenzene Complexes M(Bz)3 (M=Sr,Ba)

We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)₃ (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D₃ symmetric structure involving three equivalent η⁶‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n?1)d AOs of M and strong backdonation from the occupied (n?1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals.