Guangming Xia

Surface modification of magnetite nanoparticles using gluconic acid and their application in immobilized lipase.

Superparamagnetic magnetite nanoparticles (SMN) were surface-modified with gluconic acid (GLA) to improve their hydrophilicity and bio-affinity. Gluconic acid was successfully coated on the surface of magnetite nanoparticles and characterized using Fourier transform infrared spectroscopy (FT-IR). With water-soluble carbodiimide (EDC) as the coupling reagent, lipase was successfully immobilized onto the hydroxyl-functionalized magnetic nanoparticles. The immobilized lipase had better resistance to temperature and pH inactivation in comparison to the free form and hence widened the reaction pH and temperature range. Thermostability and storage stability of the enzyme improved upon covalent immobilization. Immobilized lipase showed higher activity after recycling when compared to the free one and could be recovered by magnetic separation.

5-(Methoxy­carbon­yl)thio­phene-2-carboxylic acid

In the title compound, C7H6O4S, a monoester derivative of 2,5-thiophenedicarboxylic acid, the carboxylic acid and the carboxylic acid ester groups are approximately coplanar with thiophene ring, making a dihedral angle of 3.1 (4) and 3.6 (4)°, respectively. In the crystal structure, molecules are connected by classical intermolecular O—H⋯O hydrogen bonds, forming centrosymmetric dimers.

Bis(tetra­butyl­ammonium) bis­(3,4,5-trioxocyclo­pent-1-ene-1,2-dithiol­ato-κ2S,S′)cadmate(II) 0.25-hydrate

The title compound, (C16H36N)2[Cd(C5O3S2)2]·0.25H2O, contains two disordered tetrabutylammonium cations, a complex [Cd(C5O3S2)2]2− anion and a 0.25-hydrate water. The anion is composed of a bidentate coordinated 3,4,5-trioxocyclopent-1-ene-1,2-dithiolate (dtcroc) group forming a distorted tetrahedral configuration around the CdII ion. The dihedral angle between the least-squares planes of the ten-atom sulfur-substituted croconate groups in the anion is 84.10 (8)°. The crystal packing is stabilized by weak C—H⋯O and C—H⋯S cation–anion hydrogen-bond interactions. In each of the two cations one butyl group is disordered over two positions in the ratios 0.589 (11):0.411 (11) and 0.796 (12):0.204 (12).

Dimethyl 3,3'-diphenyl-2,2'-[(S)-thio-phene-2,5-diylbis(carbonyl-aza-nedi-yl)]dipropano-ate tetra-hydro-furan monosolvate.

The title compound, C26H26N2O6S·C4H8O, a solvated bis-amide derivative, is also a chiral amino acid ester with l-phenylalanine methyl ester groups as amine substituents. The thiophene-2,5-dicarboxamide core approximates C 2 point symmetry. The tetrahydrofuran solvent molecule is linked to the main molecule through an intermolecular N—H⋯O hydrogen bond. The central ring makes dihedral angles of 90.0 (2) and 76.5 (2)° with the pendant rings.

Dimethyl 3,3'-diphenyl-2,2'-[(S)-thio-phene-2,5-diylbis(carbonyl-aza-nedi-yl)]dipropano-ate.

The asymmetric unit of the title compound, C26H26N2O6S, contains two independent molecules; each has twofold symmetry with the S atom and the mid-point of the C—C bond of the thiophene ring located on a twofold rotation axis. In the two molecules, the terminal benzene rings are oriented at dihedral angles of 65.8 (3) and 63.5 (3)° with respect to the central thiophene rings. The methoxycarbonyl group of one molecule is disordered over two positions with site-occupancy factors of 0.277 (12) and 0.723 (12). Intermolecular N—H⋯O hydrogen bonding is present in the crystal structure.

1-Bromo-2,7-di-tert-butyl­pyrene

In the title molecule, C24H25Br, one of two tert-butyl groups is rotationally disordered between two orientations in a 0.59 (3):0.41 (3) ratio. The crystal packing exhibits no π–π interactions; however, relatively short intermolecular Br⋯Br contacts of 3.654 (1) Å are observed.

(−)-Dimethyl 3,3′-diphenyl-2,2′-[pyridine-2,6-diylbis(carbonyl­imino)]dipropanoate

The title compound, C27H27N3O6, a bis-amide derivative, is also a chiral amino acid ester with l-phenylalanine methyl ester groups as amine substituents. The pyridine ring is oriented at dihedral angles of 89.69 (3) and 62.95 (3)° with respect to the phenyl rings, while the dihedral angle between the phenyl rings is 60.76 (3)°. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into chains. One of the carbonyl O atoms and one of the methoxy CH3 groups are disordered over two positions. The O atom was refined with occupancies of 0.69 (13) and 0.31 (13), while C and H atoms were refined with occupancies of 0.69 (8) and 0.31 (8).