Converting the sacrificial DNA repair protein N-ada into a catalytic methyl phosphotriester repair enzyme

Mutation of the active-site residue Cys38 of N-Ada converts it from a sacrificial DNA repair protein to an enzyme that uses methanethiol as an external sacrificial reagent to repair DNA methyl phosphotriesters catalytically.     

Self-assembled biotinylated disulfide derivative monolayer on gold electrode for immobilizing enzymes

Based on self-assembled biotinylated disulfide derivative monolayer on gold electrode, the sensors immobilized monolayer or multilayer membranes composed of avidin and biotinlabeled glucose oxidase (B.GOD) or of avidin-B.GOD complex (ABC) and B.COD were prepared. The present technique may be useful for controlling the enzyme content of the sensors in molecular level by repeating the deposition of enzyme layers. The sensors have the characteristics of shorter response time, higher sensitivity. The linear range is from 6.0 x 10(-6) - 5.0 x 10(-3) M. The sensor can be used for more than 1 month and can be reactivated. The sensor was used to determine glucose in human blood serum, and the results are satisfactory.     

Detection of a biomarker for Alzheimer's disease from synthetic and clinical samples using a nanoscale optical biosensor

A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-beta derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 x 10(12) M(-1) and 9.5 x 10(8) M(-1). The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new information relevant to the understanding and possible diagnosis of Alzheimer's disease.     

Adsorption of 1,10-phenanthroline within a dodecanethiol monolayer: an approach to a switchable electrode surface

A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer.     

LC-ESI-MS Determination of Bilobalide and Ginkgolides in Canine Plasma

A sensitive and selective method using liquid chromatography with electrospray ionization mass spectrometric detection was developed for the quantification of bilobalide and ginkgolides in canine plasma. The analytes were extracted with diethyl ether-dichloromethane-isopropanol (6:3:1, v/v) after spiking the samples with daidzein (internal standard). The lower limit of quantification (LLOQ) of the method was 2.5 μg L⁻¹ for ginkgolide B and 10.0 μg L⁻¹ for bilabolide, ginkgolide A and ginkgolide C. The accuracy of the method was within 15% of the actual values over a wide range of plasma concentrations. The intra-day and inter-day precision was better than 15% (R.S.D.). Finally, the LC-ESI-MS method was successfully applied to study the pharmacokinetics of ginkgolides and bilabolide after administration of Ginkgo biloba extracts to dogs.     

A New Approach to α—Bromochalcones

α-Bromo benzolymethylene triphenylphosphorane 3 has been synthesized by the reaction of benzoylmethylene triphenylphosphorane 1 with N-bromosuccinimide in the yield of 87% and can react with aromatic aldehydes 4 to give α-bromochalcones 5 in good yields.     

Characteristic sequences for DNA primary sequence

A DNA sequence can be identified with a word over an alphabet N = [A, C, G, T]. Characteristic sequences of a DNA sequence are given in term of classifications of bases of nucleic acids. Using the characteristic sequences, we construct a set of 2 x 2 matrices to represent DNA primary sequences, which are based on counting of the frequency of occurrence of all (0,1) triplets of characteristic sequences. Furthermore, the leading eigenvalues of these matrices are computed and considered as invariants for the DNA primary sequences. Similarity and dissimilarity analysis based on the characteristic sequences are given for eight exon-1 genes of beta-globin about eight species.     

An efficient procedure for protection of carbonyls in Brønsted acidic ionic liquid [Hmim]BF4

Protection of carbonyls as acetals or ketals using Brønsted acidic ionic liquid [Hmim]BF₄ as catalyst as well as solvent was investigated. Satisfactory results were obtained for the protection of carbonyls as cycloacetals or ketals with diols. The product can be separated conveniently from the reaction system, and the ionic liquid can be reused after removal of water.     

Remote substituent effects on bond dissociation energies of para-substituted aromatic silanes

UB3LYP/6-31G(d) and ROMP2/6-311++G(d,2p) methods were used to calculate the Si-X bond dissociation energies (BDEs) of a number of para-substituted aromatic silanes (4-Y-C(6)H(4)-SiH(2)X, where X = H, F, Cl, or Li). It was found that the substituent effect on the Si-H BDE of 4-Y-C(6)H(4)-SiH(3) was small, as the slope (rho(+)()) of the BDE- regression was only 0.09 kJ/mol. In comparison, the substituent effect on the Si-F BDE of 4-Y-C(6)H(4)-SiH(2)F was much stronger, whose rho(+ )()value was -2.34 kJ/mol. The substituent effect on the Si-Cl BDE of 4-Y-C(6)H(4)-SiH(2)Cl was also found to be strong with a rho(+)() value of -1.70 kJ/mol. However, the substituent effect on the Si-Li BDE of 4-Y-C(6)H(4)-SiH(2)Li was found to have a large and positive slope (+9.12 kJ/mol) against. The origin of the above remarkably different substituent effects on the Si-X BDEs was found to be associated with the ability of the substituent to stabilize or destabilize the starting material (4-Y-C(6)H(4)-SiH(2)X) as well as the product (4-Y-C(6)H(4)-SiH(2)* radical) of the homolysis. Therefore, the direction and magnitude of the effects of Y-substituents on the Z-X BDEs in compounds such as 4-YC(6)H(4)Z-X should have some important dependence on the polarity of the Z-X bond undergoing homolysis. This conclusion was in agreement with that from earlier studies (for example, J. Am. Chem. Soc. 1991, 113, 9363). However, it indicated that the proposal from a recent work (J. Am. Chem. Soc. 2001, 123, 5518) was unfortunately not justified.     

Racemization of chiral amino alcohols III: Effect of Mg or Ca addition on the activity and stability of the Co/γ-Al2O3 catalyst

The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al₂O₃ catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield of over 83% at using the Mg modified Co/γ-Al₂O₃ catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H₂. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous for dispersing and stabilizing the active species of the Co/γ-Al₂O₃ catalyst, protecting from sintering, significantly improving its catalytic activity and stability.