First principles density functional study of the adsorption and dissociation of carbonyl compounds on magnesium oxide nanosurfaces

The adsorption and dissociation of three carbonyl compounds, formaldehyde, acetaldehyde, and acetone, on the magnesium oxide nanosurface, consisting of four stacked (MgO)3 hexagons, is investigated by first principles density functional theory (DFT). In the case of formaldehyde, strongly chemisorbed species, with carboxylate-like structures, are initially formed. These may subsequently undergo heterolytic cleavage of an aldehyde C-H bond to form formate ions involving a surface oxide ion and a hydride ion adsorbed over the magnesium dication [(MgH+)(HCOO-)]. For acetaldehyde, besides this reaction leading to the formation of acetate, the methyl hydrogen of the adsorbed species also tends to attach itself to a surface oxide ion, yielding surface hydroxyl ions and adsorbed [CH2=C(H)OMg]+. These results are in accord with our previous experimental and theoretical results. In particular, the shift of the aldehyde C-H vibration band to higher frequency and the appearance of OH bands in the infrared spectrum are clearly accounted for. For acetone, the mechanism is found to be similar, i.e., a methyl hydrogen shift to yield surface enolate. Again, this is in agreement with experimental studies.     

Lysozyme-imprinted polymer synthesized using UV free-radical polymerization

Molecular imprinting is a method to fabricate a polymeric material (molecularly imprinted polymer or MIP) capable of selectively recognizing template molecules. Molecular imprinting of small molecules has been studied widely. Less common, however, is the imprinting of biological macromolecules, including proteins, among which lysozyme is an important molecule in the food, pharmaceutical, and diagnostic sciences. In this study, lysozyme MIP was fabricated in two steps. First, lysozyme, PEG600DMA, and methacrylic acid were used as the template molecule, cross-linking monomer, and the functional monomer, respectively, in a UV free-radical polymerization process to synthesize a polymeric gel. Second, lysozyme was removed by enzymatic digestion. Non-imprinted polymer (NIP) was synthesized without lysozyme addition. To evaluate the preferential binding capability of MIP, lysozyme, RNase A, or a 50:50 mixture of lysozyme and RNase A was added to MIP and NIP and then released by digestion. It was found that when more lysozyme was added to the reaction mixture, the quantity of protein released from the polymer increased, reflecting more potential binding sites. Tests of MIP with a competitive binding mixture of lysozyme and RNase A showed the MIP preferentially bound a greater amount of lysozyme, up to 20 times more than RNase A. NIP bound only small amounts of both proteins and did not show a preference for binding either lysozyme or RNase A. These results demonstrate that lysozyme was successfully imprinted into the MIP by UV free-radical polymerization, and the fabricated MIP was able to preferentially bind its template protein.     

Kinetic and mechanistic significance of the chemical activation of ciprofloxacin for conjugation chemistry

Ciprofloxacin is an important category of fluroquinolones that has versatile applications in imaging when conjugated with different ligands. For conjugation chemistry, chemical activation of the carboxylic group at the third position is an important step. Here, we study the kinetics for the activation of the acidic group of ciprofloxacin by N‐hydroxysuccinimide (NHS) and dicyclohexylcarbodiimide (DCC). The extent of the reaction was followed by registering a decrease in absorbance at 332, 412, and 423 nm by monitoring the consumption of ciprofloxacin as a function of [NHS], [DCC], pH, ionic strength, and temperature by varying only one parameter at a time while keeping all other parameters constant. The reaction between ciprofloxacin and NHS, in the presence of DCC, exhibits a 1:1:1 stoichiometry. The reaction is found to show first‐order dependence on the concentration of ciprofloxacin to the order of 10³ s^?1(k_obs) and zero order with respect to the concentrations of NHS and DCC, respectively. The activation parameters and thermodynamic quantities vis‐à‐vis E_a, ΔH^≠, and ΔS^≠ have been computed with respect to the forward reaction as 12.024, 131.43, and 27.31 J K^?1 mol^?1, respectively, which provided additional support to the proposed kinetic pathway. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 349–356, 2009     

Adsorption of methyl isocyanate on M4 (M=Fe,Ni, and Cu) cluster-decorated graphene and vacancy graphene: a DFT-D2 study

Structural Chemistry - Adsorption of a toxic gas, methyl isocyanate (MIC), has been studied on different metal (Fe, Ni, and Cu) cluster-decorated graphene and vacancy graphene. The binding of M4...     

Solid state multinuclear NMR study of sigma-acetylide complexes of platinum, trans-[ClPt(PnBu3)2-C=C-p-C6H4-C=C-Pt(PnBu3)2Cl] and trans-[-Pt(PnBu3)2-C=C-p-C6H4-C=C-]n.

Solid state 13C, 31P and 195Pt NMR has been employed to study the electronic and geometric structure of the dimeric and polymeric sigma-acetylide complexes of platinum, trans-[ClPt(PnBu3)2-C identical to C-p-C6H4-C identical to C-Pt(PnBu3)2Cl] and trans-[-Pt(PnBu3)2-C identical to C-p-C6H4-C identical to C-]n. The 195Pt shielding tensor has been measured and analysed to reveal details about the electronic properties of the Pt-ligand bonds.     

Global Dynamics of a Multi-group SEIR Epidemic Model with Infection Age

National Natural Science Foundation of China (No. 12022113),Henry Fok Foundation for Young Teachers, China (No. 171002), Outstanding Young Talents Support Plan of Shanxi Province, Science and Engineering Research Board (SERB for short), India(No. ECR/2017/002786), UGC-BSR Research Start-Up-Grant, India (No. F.30-356/2017(BSR)), and Senior Research Fellowship from the Council of Scientific and Industrial Research (CSIR for short),India (No. 09/1131(0006)/2017-EMR-I).     

Syntheses of chiral β- and γ-amino ethers, morpholines, and their homologues via nucleophilic ring-opening of chiral activated aziridines and azetidines

Lewis acid catalyzed quaternary ammonium salt mediated highly regioselective ring-opening of chiral activated aziridines and azetidines with alcohols to nonracemic β- and γ-amino ethers has been developed. The reaction mainly proceeds via an S(N)2 pathway, and the partial racemization of the starting substrate was effectively controlled by using quaternary ammonium salts. β- and γ-amino ethers are obtained with high enantio- and diastereospecificity (ee up to >99%, de up to 99%). The methodology was further extended to synthesize morpholines and their homologues with high enantiospecificity (ee up to 90%) when halo alcohols were employed as the nucleophiles.     

Effect of aqueous solvation on the structures of pyruvic acid isomers and their reactions in solution: a computational study

The pyruvic acid molecule and its various isomers have been studied in aqueous solution in order to understand the mechanism of decarboxylation. The tautomeric equilibrium remains in favor of the keto form in aqueous solution, but the energy difference between the two tautomers decreases. The anion also exists in the keto form in aqueous solution. Good agreement between the calculated and observed gas phase protonation and basicity values is obtained, and the calculated pK_a value is also in reasonable agreement with the literature value. The importance of the catalytic mechanism may be gauged from the fact that, in the absence of an enzymatic pathway, the reaction has high activation barrier and may not occur at all. Copyright © 2007 John Wiley & Sons, Ltd.