Guoxin Sun

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.

Extraction of U(VI) with N,N′-dimethyl-N,N′-dioctylmalonamide from nitrate media

The extraction of uranyl nitrate with the novel extractant N,N′-dimethyl-N,N′-dioctylmalonamide (DMDOMA) from aqueous sodium nitrate (and nitric acid) was investigated. The extraction mechanism was established and the stoichiometry of the main extracted species confirms to UO2(NO3)2 · DMDOMA. The IR spectral study was also made of the extracted species. Methyl substituent improves the extraction ability of malonamide for U(VI) compared with that of N,N,N′,N′-tertrabutylmalonamide (TBMA).

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.

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).

N,N′-Dimethyl-N,N′-diphenyl-3-oxa­penta­nediamide

In the title compound, C18H20N2O3, the two phenyl rings, adopt opposite orientations in the backbone and are oriented at a dihedral angle of 36.66 (3)°. In the crystal, intermolecular C—H⋯O interactions link the molecules into a three-dimensional network.