Protein Engineering of a Pyridoxal-5'-Phosphate-Dependent l-Aspartate-α-Decarboxylase from Tribolium castaneum for ß-Alanine Production.

In the present study, a pyridoxal-5'-phosphate (PLP)-dependent L-aspartate-α-decarboxylase from Tribolium castaneum (TcPanD) was selected for protein engineering to efficiently produce ß-alanine. A mutant TcPanD-R98H/K305S with a 2.45-fold higher activity than the wide type was selected through error-prone PCR, site-saturation mutagenesis, and 96-well plate screening technologies. The characterization of purified enzyme TcPanD-R98H/K305S showed that the optimal cofactor PLP concentration, temperature, and pH were 0.04% (m/v), 50 °C, and 7.0, respectively. The 1mM of Na+, Ni2+, Co2+, K+, and Ca2+ stimulated the activity of TcPanD-R98H/K305S, while only 5 mM of Ni2+ and Na+ could increase its activity. The kinetic analysis indicated that TcPanD-R98H/K305S had a higher substrate affinity and enzymatic reaction rate than the wild enzyme. A total of 267 g/L substrate l-aspartic acid was consumed and 170.5 g/L of ß-alanine with a molar conversion of 95.5% was obtained under the optimal condition and 5-L reactor fermentation.

[Molecular structure and luminescent property of bis(2-(4-methyl-2-hydroxyphenyl)benzothiazolate) zinc].

Bis(2-(4-methyl-2-hydroxyphenyl)benzothiazolate) zinc(Zn(4-MeBTZ)2) was synthesized. Its molecular structure was confirmed by single-crystal x-ray diffraction. Single-crystal data are as follows: space group triclinic, P-1; a = 8.989 9(11) angstroms, b =12.161 7 (15) angstroms, c = 12.871 9 (16) angstroms, alpha = 63.492 (2) degrees, beta = 84.825 (2) degrees, gamma =71.187 (2) degrees. The steric hindrance provided by introduction methyl groups on phenoxide ring prohibited effectively the formation of pentacoordinate complex. There is distinct intermolecular pi-pi interaction between molecules. The dihedral angle between the phenol and benzothiazolate rings of Zn(4-MeBTZ)2 is 2.166 degrees. The HOMO energy, LUMO energy and optical gap are -5.84, -3.46 and 2.37 eV, respectively. The maximum wavelength peak of PL spectra located at 470 nm. The double-layer devices were employed using Zn(4-MeBTZ)2 as emitter and NPB as hole-transport material. The EL spectra split into two peaks located at 501 and 544 nm respectively. The broadened EL spectra were demonstrated to be originated from the exciplexes formed at the interface between NPB and Zn(4-MeBTZ)2.

[Mechanism of advanced glycation end-products in the inducement of apoptosis of human gingival fibroblast and related effect of puerarin in the process].

OBJECTIVE: To observe the effect of synthesized advanced glycation end-products (AGE) on reactive oxygen species formation and apoptosis of the cultured human gingival fibroblast and investigate the potential mechanisms of AGE in the modification of periodontal impairment. METHODS: AGE products with different concentrations [0, 50, 150 mg/L AGE-human serum albumin (AGE-HSA)] were incubated with human gingival fibroblast for 48 h, respestively. Flow cytometry was used to detect intracellular reactive oxygen species and cell apoptosis. The culture media with 50 mg/L AGE-HSA was exposed to 0.24 mmol/L puerarin for 48 h and then cell apoptosis was measured. RESULTS: The values of cellular apoptotic rate in 0, 50, 150 mg/L AGE-HSA groups were (1.60 ± 0.30)%, (29.43 ± 1.45)%, (49.20 ± 4.43)%, respectively. The differences between each AGE-HSA group and control were statistically significant (P < 0.05). AGE-HSA increased cell apoptosis in a dose-dependent manner (150 mg/L > 50 mg/L > 0 mg/L, P < 0.05). The cellular fluorescence intensity value was elevated as the concentration of AGE-HSA increased (P < 0.05). After incubation of human gingival fibroblast with AGE-HSA for 48 h, there was a significant decrease in apoptotic rate in puerarin group [(6.37 ± 3.02)%], compared with the control [(29.43 ± 1.45)%, P < 0.05]. CONCLUSIONS: AGE can stimulate apoptosis of human gingival fibroblast, which may be mediated by oxidative stress. Puerarin may protect periodontal tissues by inhibiting the apoptosis.

[Synthesis and luminescence properties of europium (III) complexes].

Three types of europium complexes were synthesized by introducing benzoylacetone as the first ligand and 1, 10-phenanthroline, triphenylphosphine oxide, 2,2'-bipyridyl as the second ligand, respectively. The properties of above materials were characterized by infrared absorption spectra, UV-Vis absorption spectra and fluorescence spectra. Then, it was discussed that the different second ligands of europium complexes can affect their luminescence properties, and their intramolecular energy transfer models had been set up. The results indicated that ligands and complexes have a strong absorption of UV light and the three types of europium complexes exhibit characteristic luminescence of europium ion when excited by UV light. In addition, it is suggested that the fluorescence yield of europium complexes mostly depend on both the energy difference between the second ligand and the Eu3+ ion and the energy difference between the second ligand and the first ligand.

[A new type of iridium (III) phenylpyrazole complexes: synthesis, photophysical characterization].

New heteroleptic iridium(III) complexes (ppz)2Ir(LX), which consist of two cyclometalated ligands ppz(1-phenylpyrazole) together with an ancillary ligand LX (LX= 2-(2'-hydroxylphenyl)benzothiazole (BTZ), 2-(3'-methyl-2'-hydroxylphenyl) benzothiazole (3-MeBTZ), 2-(4'-methyl-2'-hydroxylphenyl) benzothiazole (4-MeBTZ) and 2-(4'-Trifluoromethyl-2'hydroxylphenyl) benzothiazole (4-tfmBTZ)), were synthesized and characterized. The molecular structures and photophysical properties were characterized and analyzed comparatively. The results show that the four complexes have basically similar UV-Vis absorption spectra, fluorescence excitation and emission spectra. Their maximum emission peaks are located at 583-615 nm, and accompanied by a lower intensity emission band around 400 nm. The weak emissions around 400 nm are ascribed to the radi ation transition of single state excition from ancillary ligand BTZ perturbed by metallic ion, and light emission around long-wave-length to the radiation transition of 3MLCT of Ir(BTZ) fragment. While the triplet state 3 MLCT of Ir(ppz)2 fragment might be quenched at room temperature. For all complexes, the excitations with maximum efficiency are located at 250-310 nm, which indicates that main contributor to light emitting is ligand-centered absorption (1pi-pi*) of ppz and BTZ rather than 3MLCT transitions, and thus provides a striking evidence that there is intersystem crossing from 1pi-pi* state to 3MLCT state in these complexes. Compared with Ir(ppz)3, these complexes not only have stronger phosphorescence at room temperature but also their emission color can be tuned by modifying ancillary ligand.

[Characterization and photoluminescence properties of a blue-light-emitting material].

Tris (2-methyl-8-hydroxyquinoline) aluminum (AlMeq3) was synthesized and purified by vacuum sublimation. The structure of the complex was characterized by 1H NMR, FTIR spectra and elemental analysis techniques. AlMeq3 consists of three 2-methyl-8-hydroxyquinoline ligands and one aluminum atom. Its thermal stability was studied by TG and DSC analysis and the result shows that AlMeq3 is a thermally stable material, with decomposition and crystalline transition temperature being 357 and 158 degrees C, respectively. Energy band structure was investigated by UV-Vis absorption spectra and fluorescence emission spectra. Experimental results show that its UV absorption bands were at about 246 and 390 nm, and the absorption band at about 246 nm can be assigned to pi--pi* of phenyl ring. AlMeq2 displays 8-hydroxyquinoline-oriented photophysical properties. The optical gap of AlMeq3: was about 2.85 eV, as determined by intrinsic absorption band edge of the complex in ethanol solution. Under UV excitation at 365 nm, the complex in ethanol solution emitted intensive blue fluorescence with the maximum emission peak at 479 nm, while the effective energy-transfer from the ligand to the central AlP+ ion occurred in the complex. AlMeq3 with bright blue photoluminescence can be applied as luminescent material in OLEDs.