Determination of tributyrin and its metabolite butyrate in Wistar rat plasma samples by gas chromatography/mass spectrometry

A gas chromatographic (GC) method with mass spectrometric (MS) detection was developed for the determination of tributyrin and its metabolite butyrate in rat plasma. Following precipitation of plasma protein with acetonitrile, the analytes in the samples were separated on a DB-5ms capillary column with helium as carrier gas. Phenylmethylsulfonyl fluoride (PMSF), an inhibitor for serine proteases, papain and acetylcholinesterase, was found to be essential to inhibit the activity of enzyme(s) responsible for the hydrolysis of tributyrin in both rat and human blood samples. The enzyme inhibitor in 5 mM (final concentration) was added immediately into the blood samples after collection to prevent the hydrolysis. The linear concentration ranges for tributyrin and butyrate were 0.1-2.0 and 1-20 microM, respectively. The coefficients of variation for intra-day and inter-day assays for tributyrin were all <10%, and those for butyrate were also <10%, except for the lowest concentration (1 microM), which was less than 20%. The accuracy of all concentration determinations ranged from 96.0-110.0%. The limit of quantification (LOQ) was 0.1 microM for tributyrin and 1.0 microM for butyrate. This method could detect tributyrin and butyrate simultaneously, and represents an improvement in sensitivity for the detection of tributyrin compared with the previous gas chromatography-flame ionization detection (GC-FID) method.     

Aptamer-based electrochemical sensors that are not based on the target binding-induced conformational change of aptamers

This study describes a new kind of aptamer-based electrochemical sensor that is not based on the target binding-induced conformational change of the aptamers by using a 15-mer thrombin-binding aptamer (5'-GGTTGGTGTGGTTGG-3') as the model oligonucleotide. The sensors are developed by first self-assembling the aptamer (i.e. a thrombin-binding aptamer) onto an Au electrode and then hybridizing the assembled aptamer with a ferrocene (Fc)-labeled short aptamer-complementary DNA oligonucleotide to form an electroactive double-stranded DNA (ds-DNA) oligonucleotide onto the Au electrode. The binding of the target (i.e. thrombin) towards the aptamer essentially destroys the Watson-Crick helix structure of the ds-DNA oligonucleotide assembled onto the electrode and leads to the dissociation of the Fc-labeled short complementary DNA oligonucleotide from the electrode surface to the solution, resulting in a decrease in the current signal obtained at the electrode, which can be used for the determination of the target. With the thrombin-binding aptamer as the model oligonucleotide, the current decrease obtained with the aptamer-based electrochemical sensors is linear with the concentration of thrombin within the concentration range from 0 to 10 nM (DeltaI/nA = 6.7C(thrombin)/nM + 2.8, gamma = 0.975). Unlike most kinds of existing aptamer-based electrochemical sensor, the electrochemical aptasensors demonstrated here are not based on the conformational change of the aptamers induced by the specific target binding. Moreover, the aptasensors are essentially label-free and are very responsive toward the targets. This study may pave a facile and general way to the development of aptamer-based electrochemical sensors.     

Stereoselective total synthesis of cis- and trans-3-hydroxypipecolic acid

[reaction: see text] 3-Hydroxypipecolic acid, a nonproteinogenic cyclic alpha-amino acid, is a common structural moiety found in a large number of natural and synthetic compounds of medicinal significance. Utilizing D-serine as a chiral template, the present research describes efficient and straightforward routes to cis- and trans-3-hydroxypipecolic acids in enantiopure form. The key steps in the syntheses involve chelation-controlled addition of a homoallyl Grignard reagent to a protected serinal derivative toward stereoselective formation of the corresponding syn-amino alcohol adduct 3. On the other hand, zinc borohydride-mediated chelation-controlled reduction of a serine-derived alpha-aminoketone precursor leads to the formation of the corresponding anti-amino alcohol adduct 4 with high stereoselectivity. Following an efficient sequence of reactions, the above amino alcohol derivatives were subsequently transformed to the corresponding cis- and trans- title compounds, respectively.     

Pressure-induced semiconductor–metal phase transition in Mg2Si

In situ electrical resistivity measurement of powdered Mg₂Si has been performed in a diamond anvil cell up to 25.4 GPa. At about 22.2 GPa, Mg₂Si underwent a pressure-induced semiconductor–metal phase transition that took place in the Ni₂In-type structure rather than the anti-fluorite structure predicted theoretically. The other phases (anti-fluorite and anti-cotunnite) belong to the semiconductor phase.     

Weibull 分布等分位数数据填充算法及其应用

基于作者曾提出的处理非随机删失数据的迭代算法,针对weibull分布相同定时截尾型试验数据,通过改变数据的填补方式,在保证由算法所得的参数估计的相合性和不变性的前提下,使得改进后的算法所得的虚拟完全数据更接近于真实的完全数据.模拟研究表明,对于删失数据情形下可靠度的区间估计问题,改进后的算法更加精确.     

First‐principle investigations of the peculiar magnetic behavior of Sr2FeOsO6

Structural, electronic and magnetic properties of Sr₂FeOsO₆ have been revisited by using the first‐principle calculations. Semiconducting behavior is reproduced. The band gap is 0.09 eV from generalized gradient approximation (GGA) and 0.30 eV by considering both SOC and U, a bit larger than the experimental observed 0.125 eV. In the C‐type antiferromagnetic configuration, spin frustration is found by analysing the magnetic exchange parameters, explaining the experimental observed magnetic complexity.

     

Local discontinuous galerkin approximation of convection‐dominated diffusion optimal control problems with control constraints

In this article, we investigate local discontinuous Galerkin approximation of stationary convection‐dominated diffusion optimal control problems with distributed control constraints. The state variable and adjoint state variable are approximated by piecewise linear polynomials without continuity requirement, whereas the control variable is discretized by variational discretization concept. The discrete first‐order optimality condition is derived. We show that optimization and discretization are commutative for the local discontinuous Galerkin approximation. Because the solutions to convection‐dominated diffusion equations often admit interior or boundary layers, residual type a posteriori error estimate in L² norm is proved, which can be used to guide mesh refinement. Finally, numerical examples are presented to illustrate the theoretical findings. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 339–360, 2014     

Preparation of a mixed stir bar for sorptive extraction based on monolithic material for the extraction of quinolones from wastewater

In this study, a novel mixed mode monolithic material was prepared and acted as the SBSE coating. The monolithic material was prepared by in situ copolymerization of methacrylic acid-3-sulfopropyl ester potassium salt (MASE) and divinylbenzene (DB) in the presence of a porogen solvent containing cyclohexanol, 1-dodecanol, and water with azobisisobutyronitrile as initiator. The influences of the contents of the porogen solvent and monomer in the polymerization mixture on the extraction performance were investigated thoroughly. Several characteristic techniques, such as elemental analysis, scanning electron microscopy and infrared spectroscopy were used to characterize the monolithic material. To achieve optimum extraction performance for quinolones, several parameters, including pH value, desorption solvent, ionic strength in sample matrix, extraction and desorption time were investigated. The results show that under the optimized experimental conditions, the method has good sensitivity, linearity, simplicity and low cost. The extraction performance of present method to the target compounds was compared with commercial SBSE which using polydimethylsiloxane as coating and other SBSEs which based on monolithic materials. The comparative results indicate that present SBSE can extract the analytes more effectively than other SBSEs because both ion-exchange and hydrophobic interactions contribute to the extraction of quinolones.