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alpha-Glycylglycine in its actual crystalline phase is studied by ab initio calculated nuclear quadrupole coupling constants. These physical quantities are computed for 2H and 14N in the hydrogen bonds. The type of hydrogen bond is the N-H...O type. The computations are performed with the RHF and B3LYP methods and 6-31++G** and 6-311++G** basis sets using the Gaussian 98 program. Values of the calculated nuclear quadrupole coupling constants are shown in Tables 1-3. The aim of this work is the study of 2H and 14N quadrupole coupling constants which contribute in the CON2H...O=CN2H type of hydrogen bond. The computed nuclear quadrupole coupling constants of 2H nuclei meet the related experimental values. In addition, the computed chi value of 14N belonging to the -CO-14NH- group agrees well with values obtained experimentally. However, there are some discrepancies between calculated 14N chi values of the N+H3 residue and experiments. Also, the values of these physical parameters are calculated for >C2H2 of alpha-glycylglycine in its crystalline phase. Calculations for these parameters are carried out in a single molecule using X-ray diffraction coordinates, too.

Nanotechnology holds great potential in advanced water and wastewater treatment to improve treatment efficiency. Zinc oxide nanoparticles (ZnO NPs) have received considerable attention due to their unique antibacterial activities toward various microorganisms that are commonly found in the environment. In the present study, ZnO NPs were synthesized through both mechano-chemical and sol-gel methods. The synthesized ZnO NPs were characterized through X-ray diffraction and transmission electron microscopy techniques. Then, their antibacterial activities against separated wastewater bacteria were evaluated by determining the zone inhibitor, the minimum inhibitory concentration, and the minimum bactericidal concentration. The results were compared with those obtained from wastewater after chlorine disinfection and ultraviolet (UV) disinfection. These studies demonstrated that the antibacterial activity of ZnO NPs depends on the type and the strain of bacteria. They have also demonstrated that the activity increases as the concentration of ZnO NPs increases. Overall, the experimental results suggest that ZnO NPs can potentially be an antibacterial reagent to treat wastewater. They can particularly be applied as a complementary method with UV disinfection. Thus, they can be developed as antibacterial agents to improve wastewater quality.

Esterase (EST) from Pseudomonas putida IFO12996 catalyzes the stereoselective hydrolysis of methyl DL-␤-acetylthioisobutyrate (DL-MATI) to produce D-␤-acetylthioisobutyric acid (DAT), serving as a key intermediate for the synthesis of angiotensin-converting enzyme inhibitors. The EST gene was cloned and expressed in Escherichia coli; the recombinant protein is a non-disulfide-linked homotrimer with a monomer molecular weight of 33,000 in both solution and crystalline states, indicating that these ESTs function as trimers. EST hydrolyzed DL-MATI to produce DAT with a degree of conversion of 49.5% and an enantiomeric excess value of 97.2% at an optimum pH of about 8 to 10 and an optimum temperature of about 57 to 67°C. The crystal structure of EST has been determined by X-ray diffraction to a resolution of 1.6 Å, confirming that EST is a member of the ␣/␤ hydrolase fold superfamily of enzymes and includes a catalytic triad of Ser97, Asp227, and His256. The active site is located approximately in the middle of the molecule at the end of a pocket ϳ12 Å deep. EST can hydrolyze the methyl ester group without affecting the acetylthiol ester moiety in DL-MATI. The examination of substrate specificity of EST toward other linear esters revealed that the enzyme showed specific activity toward methyl esters and that it recognized the configuration at C-2.Esterases belong to the hydrolase family and are ubiquitous enzymes identified in various species (24). These enzymes exist as either monomers or oligomers with subunit molecular weights (MW) that range from 25,000 to 60,000 (13), with a conserved pentapeptide (Gly-X 1 -Ser-X 2 -Gly) sequence around the catalytic serine residue (3), despite sharing a low sequence homology. Unlike lipases, esterases preferentially hydrolyze water-soluble esters or short-chain fatty acid triglycerides. The proposed mechanism of catalysis for esterases is similar to the serine protease mechanism, which involves nucleophilic attack by the catalytic serine hydroxyl on the carbonyl carbon of the scissile bond. This hydroxyl group becomes more nucleophilic and the reaction is stabilized through hydrogen bonding to the imidazole group of the catalytic histidine that is stabilized by the carboxyl group of the acidic member of the catalytic triad (9, 12). The importance of esterases for application in pharmaceutical and agrochemical industries is increasing because their properties as stereo-selective catalysts in the synthesis of optically pure molecules are diverse. On the basis of their protein structures, the ␣/␤ hydrolase architecture of lipases possesses an additional movable helical lid that controls access to the active site, providing a molecular explanation for lipase-enhanced activity upon contact with a lipase-water interface (41).D-␤-acetylthioisobutyric acid (DAT), also known as S-␤-acetylthio-2-methylpropionic acid, is a key intermediate for the synthesis of angiotensin-converting enzyme inhibitors, such as captopril and alacepril, which are used to treat hypertension and congestive he...

A systematic computational study was carried out to characterize the 17O, 14N, and 2H nuclear quadrupole resonance (NQR) parameters in the anhydrous and monohydrated cytosine crystalline structures. To include the hydrogen-bonding effects in the calculations, the most probable interacting molecules with the central molecule in the crystalline phase were considered in the pentameric clusters of both structures. To calculate the parameters, couples of the methods B3LYP and B3PW91 and the basis sets 6-311++G** and CC-pVTZ were employed. The mentioned methods calculated reliable values of 17O, 14N, and 2H NQR tensors in the pentameric clusters, which are in good agreements with the experiment. The different influences of various hydrogen-bonding interactions types, N-H...N, N-H...O, and O-H...O, were observed on the 17O, 14N, and 2H NQR tensors. Lower values of quadrupole coupling constants and higher values of asymmetry parameters in the crystalline monohydrated cytosine indicate the presence of stronger hydrogen-bonding interactions in the monohydrated form rather than that of crystalline anhydrous cytosine.