Free vibration analysis of Timoshenko pipes with fixed boundary conditions conveying high velocity fluid.

Sever vibration will be induced due to the high flow velocity in the pipe. When the flow velocity exceeds the critical value, the static equilibrium configuration of the pipe loses its stability, and the vibration properties change accordingly. In this paper, the free vibration characteristics of the pipe with fixed-fixed ends are revealed in the supercritical regime. Based on the Timoshenko beam theory, the governing equations of the nonlinear vibration near the non-trivial static equilibrium configuration are established. The influences of system parameters on equilibrium configuration, critical velocity, and free vibration frequency is analyzed. The effects of supercritical velocity in different ranges on the natural frequencies are revealed. In addition, the comparison with the Euler-Bernoulli pipe model shows that the differences in critical velocity, equilibrium configuration, and frequency are still significant even the length-diameter ratio is large. The increase of the flow velocity reduces the difference of non-trivial static equilibrium configurations, but eventually aggravates the difference of natural frequencies. Within a certain supercritical velocity range, the vibration difference between the two pipe models is small, beyond this range, the vibration difference increases significantly.

Determination methods for the anticancer drug dicycloplatin, a supramolecule assembled through hydrogen bonding.

Dicycloplatin is a new generation supramolecular platinum-containing anti-cancer drug. Due to its structure, it is difficult to differentiate dicycloplatin from physical mixtures of carboplatin and cyclobutane dicarboxylate, and confounding results may arise during drug characterization. To solve this problem, this study aims to provide a reliable and reproducible standard for the determination of dicycloplatin. A simple method for dicycloplatin quality control has been developed using X-ray powder diffraction (XRPD) and high performance liquid chromatography (HPLC). XRPD allowed the control of impurities and dissociation of the dicycloplatin active ingredient to less than 1%, and HPLC allowed the monitoring and control of the relative molar ratio of carboplatin and cyclobutane dicarboxylate within the purity range. The study proved for the first time that the dicycloplatin supramolecule is substantially different from a physical mixture of carboplatin and cyclobutane dicarboxylate.

Crystal structure analysis of a recombinant predicted acetamidase/formamidase from the thermophile Thermoanaerobacter tengcongensis.

The structure of acetamidase/formamidase (Amds/Fmds) from the archaeon Thermoanaerobacter tengcongensis has been determined by X-ray diffraction analysis using MAD data in a crystal of space group P21, with unit-cell parameters a = 41.23 (3), b = 152.88 (6), c = 100.26 (7) Å, ß = 99.49 (3) ° and been refined to a crystallographic R-factor of 17.4% and R-free of 23.7%. It contains two dimers in one asymmetric unit, in which native Amds/Fmds (TE19) contains of the 32 kDa native protein. The final model consists of 4 monomer (299 amino acids residues with additional 2 expression tag amino acids residues), 5 Ca²âº, 4 Zn²âº and 853 water molecules. The monomer is composed by the following: an N-domain which is featuring by three-layers ß/ß/ß; a prominent excursion between N-terminal end of strand ß7 and ß11, which contains four-stranded antiparallel ß sheet; an C-domain which is formed by the last 82 amino acid residues with the feature of mixed α/ß structure. The protein contains ion-pair Ca²âº-Zn²âº. The portion of three-layer ß/ß/ß along with the loops provides four protein ligands to the tightly bound Ca²âº, three water molecules complete the coordination; and provides five protein ligands to the tightly bound Zn²âº, one water molecule complete the coordination.

Expression, purification, crystallization and preliminary crystallographic study of a potential metal-dependent hydrolase with cyclase activity from Thermoanaerobacter tengcongensis.

The putative metal-dependent hydrolase gene TTE1006 from Thermoanaerobacter tengcongensis strain MB4T (T = type strain; Genbank accession No. AE008691) was heterologously expressed in Escherichia coli. The 205-amino-acid gene product was purified and crystallized. The crystal used for data collection belongs to space group P2(1), with unit-cell parameters a = 85.2, b = 62.1, c = 172.4 A, beta = 104.2 degrees. Using a synchrotron-radiation source, the resolution limit of the data reached 1.87 A. Eight molecules were estimated to be present in the asymmetric unit, with a solvent content of 48%. Structure determination is ongoing using the multiple-wavelength anomalous diffraction (MAD) method and also the molecular-replacement (MR) method.

Crystallization and preliminary crystallographic study of a recombinant predicted acetamidase/formamidase from the thermophile Thermoanaerobacter tengcongensis.

No crystal structures are yet available for homologues of a predicted acetamidase/formamidase (Amds/Fmds) from the archaeon Thermoanaerobacter tengcongensis. The Amds/Fmds gene was cloned and expressed as a soluble protein in Escherichia coli. Native Amds/Fmds and its SeMet-substituted form were purified and crystallized by vapour diffusion in hanging drops at 296 K. The native crystals, which were grown in PEG 8000, belong to the monoclinic space group P2(1), with unit-cell parameters a = 41.23 (3), b = 152.88 (6), c = 100.26 (7) A, beta = 99.49 (3) degrees. The diffraction data were collected to 2.00 A resolution using synchrotron radiation. Based on a predicted solvent content of 50%, a Matthews coefficient of 2.44 A3 Da(-1) and two main peaks in the self-rotation function, the asymmetric unit is predicted to contain two dimers of the 32 kDa native protein. MAD data were collected for the SeMet protein, but the corresponding crystals display different unit-cell parameters and appear to contain four dimers in the asymmetric unit.

Crystallization and preliminary crystallographic study of rBmKalphaIT1, a recombinant alpha-insect toxin from the scorpion Buthus martensii Karsch.

Alpha-insect scorpion toxins are a distinct group of scorpion neurotoxins for which no crystal structures are yet available. A novel alpha-insect toxin named BmKalphaIT1 from the scorpion Buthus martensii Karsch (BmK) has been expressed as an inclusion body in Escherichia coli and purified by chromatography after renaturation. Recombinant BmKalphaIT1 (rBmKaIT1) was crystallized using the vapour-diffusion technique in hanging drops at 296 K. The crystals, which were grown in sodium phosphate, belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 30.24 (1), b = 36.51 (3), c = 57.08 (2) A. Diffraction data were collected to 2.1 A resolution using synchrotron radiation. There appears to be one rBmKalphaIT1 molecule in the asymmetric unit.

Linear correlation between thermal stability and folding kinetics of lysozyme.

We have studied the refolding and thermal denaturation of hen egg white lysozyme in a wide range of pH values (from 1.5 to 9.4) using stopped-flow circular dichroism (CD) and differential scanning calorimetry (DSC). A linear correlation was found between the thermal denaturation temperature (T(m)) and the logarithm of the refolding rate of the slow folding phase of hen egg white lysozyme (lnk(2)).