Effects of arbitrarily directed field on spin phase oscillations in biaxial molecular magnets

Quantum phase interference and spin-parity effects are studied in biaxial molecular magnets in a magnetic field at an arbitrarily directed angle. The calculations of the ground-state tunnel splitting are performed on the basis of the instanton technique in the spin-coherent-state path-integral representation, and complemented by exactly numerical diagonalization. Both the Wentzel-Kramers-Brillouin exponent and the preexponential factor are obtained for the entire region of the direction of the field. Our results show that the tunnel splitting oscillates with the field for the small field angle, while for the large field angle the oscillation is completely suppressed. This distinct angular dependence, together with the dependence of the tunnel splitting on the field strengh, provide an independent test for spin-parity effects in biaxial molecular magnets. The analytical results for the molecular Fe$_{8}$ magnet, are found to be in good areement with the numerical simulations, which suggests that even the molecular magnet with total spin S=10 is large enough to be treated as a giant spin system.Comment: 19 pages, 5 figure

Surface Science Studies of Graphene Film and Nanoislands

Ph.DDOCTOR OF PHILOSOPH

Molecular cloning and characteristic analysis of a thioredoxin from Neobenedenia melleni

Thioredoxin (Trx) can regulate disulfide bond reduction of target proteins to maintain the reduced intracellular state in various organisms. Here, we cloned a cDNA sequence of thioredoxin from Neobenedenia melleni, which is a kind of platyhelminth parasite infecting many fishes of great economic value. The deduced N. melleni Trx (NmTrx) contained 170 amino acid residues with an active site consisting of four amino acid motif CPGC. Sequence comparison and phylogenetic tree analysis confirmed NmTrx as a distinct member of thioredoxin. Real-time quantitative polymerase chain reaction (PCR) revealed a significantly higher expression of NmTrx transcript in the adult stage compared with the egg and oncomiracidium stages. In the egg and adult stages, the NmTrx transcript level in the 32°C group was higher than those in the 18 and 25°C groups. NmTrx was expressed and purified from Escherichia coli, and antiserum against NmTrx was prepared. Western blot confirmed the higher NmTrx expression of the egg and adult stages in the 32°C group with respect to the other temperature groups. Recombinant NmTrx was able to reduce the disulfide bond in insulin, and its antioxidant capacity was determined to be 5.12 U/mg protein, similar to the classic thioredoxins. Trx activity was lower in the oncomiracidium stage and higher in the adult stage compared with the egg stage. These results indicate that NmTrx could function as an important antioxidant molecule under physiological conditions.Keywords: Thioredoxin, Neobenedenia melleni, redox regulation, mRNA expression, prokaryotic expressio

Two-Dimensional Controlled Syntheses of Polypeptide Molecular Brushes via N-Carboxyanhydride Ring-Opening Polymerization and Ring-Opening Metathesis Polymerization.

Well-defined molecular brushes bearing polypeptides as side chains were prepared by a "grafting through" synthetic strategy with two-dimensional control over the brush molecular architectures. By integrating N-carboxyanhydride ring-opening polymerizations (NCA ROPs) and ring-opening metathesis polymerizations (ROMPs), desirable segment lengths of polypeptide side chains and polynorbornene brush backbones were independently constructed in controlled manners. The N2 flow accelerated NCA ROP was utilized to prepare polypeptide macromonomers with different lengths initiated from a norbornene-based primary amine, and those macromonomers were then polymerized via ROMP. It was found that a mixture of dichloromethane and an ionic liquid were required as the solvent system to allow for construction of molecular brush polymers having densely-grafted peptide chains emanating from a polynorbornene backbone, poly(norbornene-graft-poly(β-benzyl-l-aspartate)) (P(NB-g-PBLA)). Highly efficient postpolymerization modification was achieved by aminolysis of PBLA side chains for facile installment of functional moieties onto the molecular brushes