Multiphilic Descriptor for Chemical Reactivity and Selectivity

In line with the local philicity concept proposed by Chattaraj et al. (Chattaraj, P. K.; Maiti, B.; Sarkar, U. J. Phys. Chem. A. 2003, 107, 4973) and a dual descriptor derived by Morell, Grand and Toro-Labbé, (J. Phys. Chem. A 2005, 109, 205), we propose a multiphilic descriptor. It is defined as the difference between nucleophilic (omega(k)+) and electrophilic (omega(k)-) condensed philicity functions. This descriptor is capable of simultaneously explaining the nucleophilicity and electrophilicity of the given atomic sites in the molecule. Variation of these quantities along the path of a soft reaction is also analyzed. Predictive ability of this descriptor has been successfully tested on the selected systems and reactions. Corresponding force profiles are also analyzed in some representative cases. Also, to study the intra- and intermolecular reactivities another related descriptor, namely, the nucleophilicity excess (Deltaomega(g)-/+) for a nucleophile over the electrophilicity in it, has been defined and tested on all-metal aromatic compounds.

Bowls, balls and sheets of boric acid clusters: the role of pentagon and hexagon motifs

Ab initio calculations suggest the possibility of forming boric acid clusters in the laboratory. The most stable form of the boric acid dimer contains two hydrogen bonds, similar to the carboxylic acid dimers. Though the trimer and the tetramer form extensions of this geometry, the pentamer prefers a bowl shape. Any addition of boric acid molecules to this geometry leads to bowl-shaped structures with the 15-mer forming a (3/4)buckyball and the 20-mer a full-fledged buckyball. The hexamer, on the other hand, prefers to stay planar as a hexagon-centered rosette. Any further extension of this geometry leads to planar structures as long as a pentagon is not included.

Bader's Electron Density Analysis of Hydrogen Bonding in Secondary Structural Elements of Protein

The hydrogen-bonding (H-bonding) interactions in alpha-helical and beta-sheet model peptides have been studied by using the atoms-in-molecule (AIM) approach. The relative importance of NH...O and CH...O H-bonding interactions in the different secondary elements such as alpha-helix, parallel, and antiparallel beta-sheets have been assessed. The electron density values at the NH...O bond are higher than those of the CH...O bonds in the alpha-helical conformation. The electron density values at the H-bonded critical points (HBCPs) corresponding to NH...O and CH...O interactions are nearly equal in the parallel beta-sheet of the order of 10(-3) au, whereas in the case of antiparallel beta-sheets, rho(rc) values for NH...O and CH...O interactions are of the order of 10(-2) and 10(-3) au, respectively. It is interesting to point out here that the weakening of NH...O interactions in the parallel beta-sheet arrangement is evident from the AIM analysis. This is concomitant with the increase in the NH...O distance in the parallel beta-sheet conformation. In addition to the clear description of H-bonding by electron density at the HBCP, possible good linear relationships between the electron density at ring critical points (RCP) and stabilization energy (SE) have been observed corresponding to the various beta-sheet conformations.

Hydrogen bonding without borders: an atoms-in-molecules perspective

It is shown that the electron density at the hydrogen bond critical point increases approximately linearly with increasing stabilization energy in going from weak hydrogen bonds to moderate and strong hydrogen bonds, thus serving as an indicator of the nature and gradual change of strength of the hydrogen bond for a large number of test intermolecular complexes.

Preparation and characterization of polystyrene-multiwalled carbon nanotube composite fibers by electrospinning

Electrospinning is a simple technique to prepare polymer fibers in nanometer diameters using very high electrostatic fields. These nanofibers are useful in many applications since the surface area to volume ratio in these fibers is very high. Here we have prepared nanofibers of composites of Polystyrene (PS) with different concentrations (0.05% to 2% w/w) of multi-walled carbon nanotubes (MWCNT) by electrospinning. The fibers are characterized by SEM, TEM, Raman spectra, and TGA. The room temperature electrical conductivity of single fibers of these composites are measured and found to show dramatic improvement in the conductivity due to the addition of MWCNT to the polymer matrix compared to the pure PS.

Determining the proximal extent of ulcerative colitis: white cell scan correlates well with histological assessment

BACKGROUND

Assessing the extent of ulcerative colitis determines therapeutic strategies and provides prognostic information. Colonoscopy with mucosal biopsy is considered unsafe in patients with severe disease.

AIM

To assess the correlation between proximal extent of ulcerative colitis as determined by Technitium-99-m hexamethylpropylene amine oxime labelled leucocyte scan (white cell scan) with that determined by histological assessment.

METHODS

One hundred and thirty-five patients, with histologically-confirmed ulcerative colitis, who had a white cell scan and histological assessment of colonic inflammation within 6 months of each other, during the years 1991-2004, were included. Overall agreement, quadratic-weighted kappa (kappa) and polychoric correlations (rho) were calculated to estimate the inter-rater reliability.

RESULTS

The correlation between white cell scan and histological extent was excellent (kappa = 0.7 rho = 0.8). Macroscopic appearance on colonoscopy did not correlate as well with histological extent (kappa = 0.62 and rho = 0.67). White cell scans correlated significantly better in patients with extensive disease (P = 0.02). Colonoscopy predicted disease extent more accurately in patients with limited colitis (P = 0.002).

CONCLUSIONS

Proximal extent of ulcerative colitis determined by white cell scans correlates well with histological assessment especially in patients with more extensive disease. White cell scans offer a reasonable alternative to colonoscopy with mucosal biopsies in determining the proximal extent of colitis.

Electrophilicity-Based Charge Transfer Descriptor

In line with the charge transfer (DeltaNmax = -mu/eta) proposed by Parr et al. (Parr, R. G.; Szentpály, L. V.; Liu, S. J. Am. Chem. Soc. 1999, 121, 1922), we propose an electrophilicity-based charge transfer (ECT) descriptor in this paper and validate it through the interaction between a series of chlorophenols and DNA bases. Application of ECT can be extended to the interaction of any toxin with the biosystem.

Solvation of H3O+ by Phenol: Hydrogen Bonding vs π Complexation

Ab initio calculations at the second-order Møller-Plesset perturbation theoretic level have been carried out to study the solvation of protonated water by phenol molecules. The results show that in addition to classical O-H...O hydrogen bonds, C-H...O, pi...H-O, and pi...H-C bonds are also formed, thus stabilizing the H3O+(C(6)H(5)OH)3 complex.

P450ome of the white rot fungus Phanerochaete chrysosporium: structure, evolution and regulation of expression of genomic P450 clusters

The model white rot fungus Phanerochaete chrysosporium has the extraordinary ability to degrade (to CO2) lignin and detoxify a variety of chemical pollutants. Whole genome sequencing of this fungus has revealed the presence of the largest P450ome in fungi comprising approx. 150 P450 genes, most of which have unknown function. On the basis of our genome-wide structural and evolutionary analysis, these P450 genes could be classified into 12 families and 23 subfamilies and under 11 fungal P450 clans. The analysis further revealed an extensive gene clustering with a total of 16 P450 clusters constituted of up to 11 members per cluster. In particular, evidence and role of gene duplications and horizontal gene transfer in the evolution of these P450 clusters have been discussed using two of the P450 families [CYP63 and CYP505 (where CYP is cytochrome P450)] as examples. In addition, the observed differential transcriptional induction of the clustered members of the CYP63 gene family, in response to different xenobiotic chemicals and carbon sources, indicated functional divergence within the P450 clusters, of this basidiomycete fungus.

Role of Aspartic Acid in Collagen Structure and Stability: A Molecular Dynamics Investigation

A molecular dynamics (MD) simulation study has been carried out to understand the stability of the triple helical collagen models. The calculations show that the presence of the aspartic acid residue in different positions leads to the local variation in the structure. Analyses of root-mean-square deviation (RMSD), radial distribution function (RDF), puckering effect, dihedral angle variation, hydrogen bond (H-bond), and conformational changes during molecular dynamics simulation reveal that the local perturbation in the sequences, increase in chain flexibility due to removal of five membered rings in the collagen by aspartic acid, change of intermolecular H-bonding pattern, and differences in the association of water are mainly influencing the nature of stabilization of collagen by aspartic acid.

Preemptive, but not reactive, spinal cord stimulation mitigates transient ischemia-induced myocardial infarction via cardiac adrenergic neurons

Our objective was to determine whether electrical neuromodulation using spinal cord stimulation (SCS) mitigates transient ischemia-induced ventricular infarction and, if so, whether adrenergic neurons are involved in such cardioprotection. The hearts of anesthetized rabbits, subjected to 30 min of left anterior descending coronary arterial occlusion (CAO) followed by 3 h of reperfusion (control), were compared with those with preemptive SCS (starting 15 min before and continuing throughout the 30-min CAO) or reactive SCS (started at 1 or 28 min of CAO). For SCS, the dorsal C8-T2 segments of the spinal cord were stimulated electrically (50 Hz, 0.2 ms, 90% of motor threshold). For preemptive SCS, separate groups of animals were pretreated 15 min before SCS onset with 1) vehicle, 2) prazosin (alpha(1)-adrenoceptor blockade), or 3) timolol (beta-adrenoceptor blockade). Infarct size (IS), measured with tetrazolium, was expressed as a percentage of risk zone. In controls exposed to 30 min of CAO, IS was 36.4 +/- 9.5% (SD). Preemptive SCS reduced IS to 21.8 +/- 6.8% (P < 0.001). Preemptive SCS-mediated infarct reduction was eliminated by prazosin (36.6 +/- 8.8%) and blunted by timolol (29.4 +/- 7.5%). Reactive SCS did not reduce IS. SCS increased phosphorylation of cardiac PKC. SCS did not alter blood pressure or heart rate. We conclude that preemptive SCS reduces the size of infarcts induced by transient CAO; such cardioprotection involves cardiac adrenergic neurons.

Theoretical Study on the Complete Series of Chloroanilines

The environmental effects of chloroanilines depend on their physical and chemical properties, and it is therefore important to know their structure-property relationships that allow a complete understanding of their environmental consequences. The chemical reactivity profiles of all 19 chloroanilines have been investigated using the density functional theory for the first time. Global reactivity descriptors, such as hardness, chemical potential, electrophilicity index, and polarizability, and local reactivity descriptors, namely, local philicities, have been calculated in order to gain insights into the reactive nature and the reactive sites of the selected systems. Using AIM theory, the presence of hydrogen bond critical points (HBCPs) and the values of electron density and Laplacian of electron density at the HBCPs have been analyzed to appreciate the presence of intramolecular hydrogen bonding in the selected systems. Structure-toxicity analysis of the selected set of chloroanilines demonstrates the importance of the electrophilicity index in the prediction of reactivity/toxicity.

Molecular Orbital Calculations on Polythiophenes Containing Heterocyclic Substituents: Effect of Structure on Electronic Transitions

Molecular orbital calculations have been performed on thiophene oligomers bearing heterocyclic substituents at the third position in order to understand the interplay of effects such as the nature of substituent, skeletal substitution pattern, heteroatom identity, etc. on electronic transitions. The geometry optimization was carried out using the semiempirical AM1 method, and the electronic transitions predicted for the oligomers were extrapolated for polymers using an oligomeric approach. The experimentally determined optical transitions were found to follow the predicted trend of electronic transitions of monomers and polymers.

Group philicity and electrophilicity as possible descriptors for modeling ecotoxicity applied to chlorophenols

The search for the best quantitative structure-activity relationship (QSAR) models in ecotoxicology is an ever-topical research activity. Hence, the development of new descriptors and applying them successfully in QSAR studies seems demanding in ecotoxicology. In the present work, group philicities are utilized for the first time in QSAR analysis for ecotoxicological studies on chlorophenols (CPs). It is important to point out that group philicities are capable of providing the best QSAR model for the toxicity of CPs against Daphnia magna. Furthermore, global electrophilicity and group philicities together give the best QSAR models for Brachydanio rerio and Bacillus with the maximum value of coefficient of determination and high internal predictive ability. The developed QSAR models clearly show the importance of the selected density functional reactivity indices as descriptors in ecotoxicological studies.

Analyzing Toxicity Through Electrophilicity

The toxicological structure-activity relationships are investigated using conceptual DFT based descriptors like global and local electrophilicities. In the present work the usefulness of electrophilicity in predicting toxicity of several polyaromatic hydrocarbons (PAH) is assessed. The toxicity is expressed through biological activity data (pIC50) defined as molar concentration of those chemicals necessary to displace 50% of radiolabeled tetrachlorodibenzo-p-dioxin (TCDD) from the arylhydrocarbon (Ah) receptor. The experimental toxicity values (pIC50) for the electron acceptor toxin like polychlorinated dibenzofurans (PCDF) are taken as dependent variables and the DFT based global descriptor electrophilicity index (omega) is taken as independent variable in the training set. The same model is then tested on a test set of polychlorinated biphenyls (PCB). A good correlation is obtained which vindicates the importance of these descriptors in the QSAR studies on toxins. These toxins act as electron acceptors in the presence of biomolecules whereas aliphatic amines behave as electron donors some of which are also taken into account for the present work. The toxicity values of the aliphatic amines in terms of the 50% inhibitory growth concentration (IGC50) towards ciliate fresh-water protozoa Tetrahymena pyriformis are considered. Since there is no global nucleophilicity we apply local nucleophilicity (omegamax+) as the descriptor in this case of training set. The same regression model is then applied to a test set of amino alcohols. Although the correlation is very good the statistical analysis reflects some cross validation problem. As a further check the amines and amino alcohols are used together to form both the training and the test sets to provide good correlation. It is demonstrated that the toxicity of several toxins (both electron donors and acceptors) in the gas and solution phases can be adequately explained in terms of global and local electrophilicities. Amount of charge transfer between the toxin and the biosystem, simulated as nucleic acid bases and DNA base pairs, indicates the importance of charge transfer in the observed toxicity. The major strength of the present analysis vis-à-vis the existing ones rests on the fact that it requires only one descriptor having a direct relationship with toxicity to provide a better correlation. Importance of using the information from both the toxin and the biosystem is also analyzed.

Probing photochemical transformations at TiO2∕Pt and TiO2∕Ir interfaces using x-ray absorption spectroscopy

Structural transformations at the TiO2Pt and TiO2Ir interfaces during UV-irradiation have been probed by X-ray absorption spectroscopy. Oxidation by the photogenerated holes results in the intercalation of Pt and Ir into the Titania matrix. The structural transformations observed with Pt and Ir nanoparticles anchored on TiO2 is different than the clustering of gold atoms observed in the TiO2/Au system. Implications of such structural transformations on the photocatalytic activity of semiconductor photocatalyts are discussed.

Systematic review of postoperative complications in patients with inflammatory bowel disease treated with immunomodulators

Background

This systematic review examined the use of immunomodulators and the risk of postoperative complications after abdominal surgery in patients with inflammatory bowel disease.

Methods

Electronic databases (PubMed, Embase, Ingenta, Zetoc and Ovid) were searched and the reference lists in all articles identified were hand-searched for further relevant papers. Studies were included if they evaluated postoperative complications and defined exposure to individual immunomodulators.

Results

All 11 studies that met the inclusion criteria were observational studies; two were reported only in abstract form. Five studies reported risks associated with azathioprine, five reported risks associated with cyclosporin and three reported risks associated with infliximab. None showed an increased risk of either total or infectious complications associated with immunomodulator use. However, subgroup analysis in one study, published as an abstract, suggested increased rates of anastomotic complications and reoperation associated with azathioprine.

Conclusion

Available evidence does not suggest an increased rate of postoperative complications associated with immunomodulator use.

pKa Prediction Using Group Philicity

Acid-base dissociation constants (pK(a) values) are important in understanding the chemical, environmental and toxicological properties of molecules. Though various methods have been developed to predict pK(a) by experimental and theoretical models, prediction of pK(a) is still complicated. Hence, a new approach for predicting pK(a) using the group philicity concept has been attempted. Presence of known functional groups in a molecule is utilized as the most important indicator to predict pK(a). The power of this descriptor in describing pK(a) for the series of carboxylic acids, various substituted phenols, anilines, phosphoric acids, and alcohols is probed. Results reveal that the group electrophilicity is suitable for effectively predicting the pK(a) values.

Hydrogen Peroxide Clusters: The Role of Open Book Motif in Cage and Helical Structures

Hartree-Fock (HF) calculations using 6-31G*, 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ basis sets show that hydrogen peroxide molecular clusters tend to form hydrogen-bonded cyclic and cage structures along the lines expected of a molecule which can act as a proton donor as well as an acceptor. These results are reiterated by density functional theoretic (DFT) calculations with B3LYP parametrization and also by second-order Møller-Plesset perturbation (MP2) theory using 6-31G* and 6-311++G(d,p) basis sets. Trends in stabilization energies and geometrical parameters obtained at the HF level using 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ basis sets are similar to those obtained from HF/6-31G* calculation. In addition, the HF calculations suggest the formation of stable helical structures for larger clusters, provided the neighbors form an open book structure.

Deficiency of beta1 integrins results in increased myocardial dysfunction after myocardial infarction

OBJECTIVE

To study the role of beta1 integrins in left ventricular (LV) remodelling after myocardial infarction (MI).

METHODS AND RESULTS

LV structural and functional alterations were determined in wild-type (WT) and beta1 integrin heterozygous knockout (hKO) mice one month after MI. MI increased beta1 integrin expression in both groups; however, the increase was lower in hKO. Infarct size was similar in WT and hKO mice, whereas lung wet weight to dry weight ratio was increased in the hKO-MI mice (5.17 (SE 0.13) v 4.60 (0.15) in WT-MI, p < 0.01). LV end systolic and end diastolic diameters were significantly higher and percentage fractional shortening was significantly lower in hKO-MI. The ratio of peak velocity of early LV filling (E wave) to that of the late LV filling (A wave) and the isovolumic relaxation time (IVRT) were increased in both MI groups but the increase in IVRT was significantly higher in hKO-MI group than in WT-MI mice. Langendorff perfusion analysis indicated reduced peak LV developed pressure and increased LV end diastolic pressure in both MI groups. The reduction in peak LV developed pressure (36.7 (2.2) v 53.4 (1.9) mm Hg, p < 0.05) and increase in LV end diastolic pressure was higher in hKO-MI than in WT-MI. Increase in fibrosis was not different between the two MI groups. The increase in myocyte circumference was higher in the hKO-MI group (p < 0.001 v WT-MI). The number of apoptotic myocytes was significantly higher in hKO-MI than in WT-MI mice (p < 0.005) three days after MI. The number of necrotic myocytes was not different between the two MI groups.

CONCLUSION

beta1 integrins are crucial in post-MI remodelling with effects on LV function, hypertrophy and apoptosis.

High Rate Reversibility Anode Materials of Lithium Batteries from Vapor-Grown Carbon Nanofibers

We demonstrate the high-rate capability of lithium ion insertion-deinsertion reactions in carbon nanofibers (CNFs). The morphology of CNFs with structural and surface defects, due to the mixed features of disordered and graphitic carbon, plays an important role in both the enhancement of the lithium ion storage and the rate-determining reactions during the topotactic process. The reversible specific capacity of the CNFs at a 0.1 C rate was 461 mA x h/g. The most promising property, which is expected to overcome the hurdles of lithium batteries for high-power applications, is that they deliver considerably high specific capacity even at a very high charge-discharge current, i.e., at a cycling rate of 10 C the reversible capacity is around 170 mA x h/g with a 95% Coulombic efficiency.

Chemical Reactivity Indices for the Complete Series of Chlorinated Benzenes: Solvent Effect

We present a comprehensive analysis to probe the effect of solvation on the reactivity of the complete series of chlorobenzenes through the conceptual density functional theory (DFT)-based global and local descriptors. We propose a multiphilic descriptor in this study to explore the nature of attack at a particular site in a molecule. It is defined as the difference between nucleophilic and electrophilic condensed philicity functions. This descriptor is capable of explaining both the nucleophilicity and electrophilicity of the given atomic sites in the molecule simultaneously. The predictive ability of this descriptor is tested on the complete series of chlorobenzenes in gas and solvent media. A structure-toxicity analysis of these entire sets of chlorobenzenes toward aquatic organisms demonstrates the importance of the electrophilicity index in the prediction of the reactivity/toxicity.

QSPR models for polychlorinated biphenyls: n-Octanol/water partition coefficient

The logarithmic n-octanol/water partition coefficient (logK(ow)) is an important property for pharmacology, toxicology and medicinal chemistry. Quantitative structure-property relationship (QSPR) model for the lipophilic behaviour (logK(ow)) of the data set containing 133 polychlorinated biphenyl (PCB) congeners is analyzed using the conceptual density functional theory based global reactivity parameter such as electrophilicity index (omega) along with energy of lowest unoccupied molecular orbital (E(LUMO)) and number of chlorine substituents (N(Cl)) as descriptors. A reasonably good coefficient of determination (r(2) = 0.914) and the internal predictive ability (r(cv)(2) = 0.909) values are obtained indicating the significance of the considered descriptors in the property analysis of PCBs. Further, the developed method has widespread applicability from chemical reactivity to toxicity analysis and in studies related to various physicochemical properties in the series of dioxins and other polyaromatic hydrocarbons.

Careful Scrutiny of the Philicity Concept

The philicity concept [J. Phys. Chem. A 2003, 107, 4973] is put in proper perspective. In the present work we analyze different physicochemical problems using philicity. It provides satisfactory results in all such cases. We also compare the relative electro(nucleo)philicity with philicity to show that philicity is better than relative electro(nucleo)philicity when the intermolecular reactivity trends are considered and there is hardly any preference of one above the other as far as the intramolecular reactivities are concerned. On the contrary, the philicity concept has some advantages over the other concept.

Density Functional Theoretical Investigation on Influence of Heterosubstitution and Benzannelation on the Thermal 6π Electrocyclization of cis-Cyclononatetraene

Thermal 6pi electrocyclization of cyclononatetraene (CNT), its hetero-substituted analogues, and its benzannelated derivatives have been investigated by using the B3LYP method employing 6-31G* and 6-311+G** basis sets. The results indicate that heterosubstitution and benzannelation influence the rate of cyclization. Nucleus independent chemical shifts (NICS), conceptual density functional theory (DFT) based reactivity descriptors, group electronegativity values, and barriers to planarity provide complementary evidence for the predicted rate of cyclization. The available experimental data are in good agreement with the computed values.

Molecular Structure, Reactivity, and Toxicity of the Complete Series of Chlorinated Benzenes

The structure and chemical reactivity profiles of all 12 chlorobenzenes have been investigated using the density functional theory and ab initio molecular orbital calculations. Global and local reactivity descriptors such as electrophilicity index and local philicity, respectively, of the selected systems have been calculated in order to gain insights into the reactive nature and the reactive sites of these compounds. Also, the effects of chlorine substitution on the aromaticity of the compounds have been analyzed by calculating the nucleus-independent chemical shift. Interaction through charge transfer between chlorobenzenes and nucleic acid bases/selected base pairs are determined using Parr's formula. The results revealed that the chlorobenzenes act as electron acceptors in their interaction with biomolecules. Structure-toxicity analysis of this entire set of chlorobenzenes demonstrates the importance of the electrophilicity index in the prediction of reactivity/toxicity.

Hydrothermal Synthesis and Pseudocapacitance Properties of MnO2Nanostructures

The effect of varying the hydrothermal time to synthesize manganese oxide (MnO(2)) nanostructures was investigated along with their influence on structural, morphological, compositional, and electrochemical properties in supercapacitor electrode materials. XRD and TEM studies showed that the MnO(2) prepared in shorter hydrothermal dwell time was a mixture of amorphous and nanocrystalline particles, and there was an evolution of crystallinity of the nanostructures as the dwell time increased from 1 to 18 h. Interestingly, SEM, TEM, and HRTEM revealed a variety of structures ranging from nanostructured surface with a distinct platelike morphology to nanorods depending upon the hydrothermal reaction time employed during the preparation of the manganese oxide: increasing the amount of individual nanorods in the materials prepared with longer hydrothermal reaction time. The surface area of the synthesized nanomaterials varied from 100 to 150 m(2)/g. Electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge studies, and the capacitance values were in the range 72-168 F/g depending upon synthesis conditions. The formation mechanism of the nanorods and their impact on the specific capacitance were discussed in detail.

Quantum chemical studies on polythiophenes containing heterocyclic substituents: Effect of structure on the band gap

Color tuning by the tailoring of substituents at the 3-position of thiophene is very encouraging, and comparative experimental and theoretical studies proved to be powerful in the search for a suitable design for the above. Since the novel polythiophene-based materials substituted with five-membered/six-membered ring containing sulphur and nitrogen at different positions are proven to be potential candidates for electron-transporting hole blocking functions, the structure-property relationship of these systems have been focused in the present study. Molecular-orbital calculations are applied to obtain the optimized geometries and band gaps of the thiophene oligomers. An oligomeric approach has been implemented for calculating the band gaps, and the theoretically obtained band gaps for the different model compounds are compared. Density-functional theory B3LYP6-31G* predicted band-gap values are compared with the experimental band gaps obtained from optical-absorption edge. The predicted values show little deviations from experimental band gaps, but the trend in band gap is found to be the same in experimental and theoretical results in most of the cases. Hence, this study illustrates the usefulness of quantum-mechanical calculations in understanding the effects of various structural parameters on optical band gap.

Stability and Reactivity of All-Metal Aromatic and Antiaromatic Systems in Light of the Principles of Maximum Hardness and Minimum Polarizability

It is demonstrated that among various possible isomers of all-metal aromatic compounds such as Al(4)(2-) and their complexes the most stable isomer with the minimum energy is the hardest and the least polarizable. A similar situation is observed for different isomers of all-metal antiaromatic compounds such as Al(4)(4-) and their complexes. It is shown that linear Al(4)(4-) is energetically more stable than its cyclic isomer. The reaction energies associated with the complexation processes highlight the stability of those complexes. The difference in energy, hardness, and polarizability between a cyclic molecule and its linear counterpart convincingly shows that an aromatic molecule exhibits negative changes in energy and polarizability but positive changes in hardness as expected from the principles of minimum energy, minimum polarizability, and maximum hardness. Although the aromaticity of Al(4)(2-) is unequivocally established through this study, the antiaromaticity picture in the case of Al(4)(4-) is shown to be poorly understood;however, the present analysis sheds light on this controversy.

Stabilization of collagen using plant polyphenol: Role of catechin

Collagen, a unique connective tissue protein finds extensive application as biocompatible biomaterial in wound healing, as drug carriers, cosmetics, etc. A work has been undertaken to study the stabilization of type I collagen using the plant polyphenol catechin. Catechin treated collagen fibres showed a shrinkage temperature around 70 degrees C implying that catechin is able to impart thermal stability to collagen. Catechin treated collagen fibres has been found to be stable even after treatment with high concentration of the secondary structural destabilizer, urea. Circular dichroism studies revealed that there is no major alteration in the structure of collagen on treatment with catechin. The study has demonstrated the involvement of hydrogen bonding and hydrophobic interactions as the major forces involved in the stabilization of collagen by the plant polyphenol, catechin.

Electrophilicity as a possible descriptor for toxicity prediction

Electrophilicity is one of the cardinal chemical reactivity descriptors successfully employed in various molecular reactivity studies within a structure-activity relationship parlance. The applications of this quantity in the modeling of toxicological properties have inspired us to perform a more exhaustive study in order to test and/or to validate the application of electrophilicity in assessing its chemical and toxicological potential. For this reason the toxicity of a large data set of molecules comprising 252 aliphatic compounds on the Tetrahymena pyriformis is studied. A quantitative structure-activity relationship analysis enabled us to model toxicity in terms of global and local electrophilicities, which provide a reasonably good prediction of aliphatic toxicity. It is heartening to note that the global and local electrophilicity values together can explain the toxicity of a large variety of aliphatic compounds nicely without resorting to any other descriptor or other microscopic/macroscopic physicochemical properties as is the situation in all other QSAR studies.

Asbestos problem in India

Primary exposure to asbestos in India can be encountered in the form of asbestos mining, asbestos cement industries, asbestos processing unit and during renovation and demolition of old asbestos cemented roof or other structures as well as modern electrical as well as mechanical appliances in which asbestos is still found. Ultimately construction workers, electricians, vehicle mechanics and other workers in the building trades who are exposed to asbestos inhale hundreds and thousands of amphiboles, which causes lung damage. It is being mined in India at places such as Andhra Pradesh (Pulivendla), Jharkand (Roro), Rajasthan (Ajmer, Bhilwara, Udaipur, Rajsamand) and the common problem faced by the locals are asbestosis through air and fluorosis through drinking water. The problem continues to be in India as well as other developing countries. Also, India import and re-export asbestos to other countries and workers at shipyard, transport of the hazardous material on road and roadside residents all are vulnerable to this uncommon disease. The signs and symptoms generally found with the workers are shortness of breath, persistent and productive cough due to pulmonary fibrosis can show up many years after the asbestos exposure.

Distribution and partitioning of phosphorus in solid waste and sediments from drainage canals in the industrial belt of Delhi, India

Phosphorus is an essential and often limiting nutrient in both marine and freshwater ecosystems. However, its oversupply is of great concern in many environments due to its role in eutrophication. The concentration and distribution of sediment bound phosphorus species not only record its input into the environment, but also suggest their possible sources. It is recognized that the features of phosphorus behaviour have not been extensively studied in urban environments. In this study, phosphorus in solid waste and sediments from drainage canals within the industrial belt of Delhi were fractionated into five operationally defined forms, i.e., exchangeable or loosely sorbed phosphorus (Exch-P), Fe-bound phosphorus (Fe-P), authigenic apatite, CaCO3-bound phosphorus and biogenic apatite (Acet-P), detrital apatite (Det-P) and organic-bound phosphorus (Org-P), in order to assess the potential bioavailability status in these systems.