Capillary electrochromatography of caffeine and its metabolites in rat brain microdialysate

A capillary electrochromatography (CEC) method has been developed for the separation of caffeine and its two metabolites 1-methylxanthine (1-MX) and 1,7-dimethylxanthine (1,7-DX). The stationary phase was 3-(1,8-naphthalimido) propyl-modified silyl silica gel (NAIP) and the best separations were achieved with 4.0 mM citrate buffer (pH 5.0) containing 80% methanol at an applied voltage of 25 kV. The compounds were completely separated in less than 3.5 min with good repeatability, which was approximately 3-times less than that in high-performance liquid chromatography (HPLC) with NAIP. The proposed method coupled with microdialysis was successfully applied to the monitoring of caffeine concentration in rat brain with detection limits of 1.11 microg/mL.     

新型螺吡喃化合物的合成及应用研究

设计合成了几种新型螺吡喃化合物(SP), 采用¹H NMR, IR 和MS 对其结构进行表征. 研究了目标产物的光致变色性能及其影响因素, 并对SP1 在高分子材料领域的应用作了初步研究. 结果表明: 苯并吡喃环连有强吸电子基时, 最大吸收峰红移; 1 位N原子上连有柔性长链基团时, 热褪色速率较慢; 采用紫外光照射目标产物不同时间, SP1 表现出较好的抗光疲劳性. 分别以SP1 为接枝组分和共混组分制备两种高分子材料SP-g-hPMMA 和SP-m-PMMA, 通过紫外光辐照动力学研究表明, SP-g-hPMMA 和SP-m-PMMA 均表现出比SP1 优异的光致变色性能, 且不影响PMMA 的机械性能. SP1 有望用于高分子光致变色材料领域.     

Preparation and characterization of modified 3-aminopropylsilyl silica phases with 1,8-naphthalic anhydrides in HPLC

Modified 3-aminopropylsilyl silica stationary phases with 1,8-naphthalic anhydrides [3-(1,8-naphthalimido)propyl (NAIP), 3-(4-amino-1,8-naphthalimido)propyl (4A-NAIP), 3-(3-nitro-1,8-naphthalimido)propyl (3N-NAIP), and 3-(4-nitro-1,8-naphthalimido)propyl modified silyl silica gel (4N-NAIP)] are prepared in a single reaction. Chromatographic properties of these phases are characterized using various solutes including monosubstituted benzenes, alkyl benzenes, and polycyclic aromatic hydrocarbons (PAHs) in high-performance liquid chromatography. Even though the retention in these NAIPs is mainly based on the reversed-phase mode, 3N- and 4N-NAIP show a remarkable recognition toward aromatic hydrocarbons, which is attributed to their strong pi-pi interaction. Furthermore, the recognition ability is according to the molecular planarity and non-linearity of PAHs. Subsequently, 3N- and 4N-NAIP has a distinct selectivity from octadecyl silica and, therefore, will be a valuable alternative for a separation or a solid-phase extraction of aromatic compounds.     

Toward a stable α-cycloalkyl amino acid with a photoswitchable cationic side chain

The N-alkylated indanylidenepyrroline (NAIP) Schiff base 3 is an unnatural α-amino acid precursor potentially useful for the preparation of semisynthetic peptides and proteins incorporating charged side chains whose structure can be modulated via Z/E photoisomerization. Here we report that the heteroallylic protons of 3 led to partial loss of ethanol accompanied by formation of the novel heterocyclic system 4 during attempted deprotection. We also show that the same protons catalyze the thermal isomerization of 3, making the light-driven conformational control concept ineffective for times longer than a few hours. These problems are not present in the previously unreported compound 5 where the acidic methyl group is replaced by an H atom. Therefore, 5, rather than 3, constitutes a promising prototype for the design of building blocks capable to modulate the electrostatic potential of a protein in specific locations via light irradiation.     

Complex DNA binding kinetics resolved by combined circular dichroism and luminescence analysis

We recently reported that ruthenium complexes, with general structure [mu-bidppz(bipy)4Ru2](4+) (B) or [mu-bidppz(phen)4Ru2](4+) (P) (bidppz=11,11'-bi(dipyrido[3,2- a:2',3'-c]phenazinyl)), show extreme kinetic selectivity for long AT tracts over mixed-sequence calf thymus DNA (ct-DNA), a selectivity that also varies markedly with the size (between B and P) and sense of chirality of the complex. Earlier studies, exploiting the great increase in luminescence intensity when the compound intercalates, have yielded complex kinetics indicating the presence of both first- and second-order processes. Even with a homogeneous DNA sequence, such as poly(dAdT)2, the luminescence kinetics generally requires more than a single exponential for a satisfactory fit. We here reveal that at least part of the complexity is a result of the extreme sensitivity of the effective quantum yield of the complexes, so that the luminescence trajectories also reflect subtle variations in the environment and binding geometry that the complex is sampling on its path to its final binding site. By monitoring the rearrangement process using circular dichroism (CD), we show that threading of both enantiomers of B and P into poly(dAdT)2 is effectively a monoexponential process, as expected if the compounds are not affecting each other during the intercalation process. Thus, the complex luminescence trajectories may be explained by slow relaxations in the binding geometry (DNA conformation) and associated changes in the environment of the entering complexes. To further disentangle the intriguing features of the threading intercalation kinetics, and how they may depend on the flexibility and size of the ruthenium complexes, we have also designed and studied two new ruthenium complexes, [mu-dtpf(phen)4Ru2](4+) (F) (dtpf=4,5,9,12,16,17,21,25-octaaza-23 H-ditriphenyleno[2,3-b:2,3-h]fluorene), in which the bridging ligand is made totally rigid, and [mu-bidppz([12]aneS4) 2Ru2](4+) (S), which has less bulky, nonaromatic ancillary ligands. The threading of F into poly(dAdT)2, also found to be a monoexponential process, is about 3 times slower than for P, indicating that the flexibility of the bridging ligand is an important factor for the intercalation rate. Surprisingly, in contrast to all other compounds, S requires two exponentials to fit its binding kinetics as monitored by CD. Also surprisingly, in view of the smaller steric bulk, even the fastest phase is roughly 2 times slower for S than for B and P. Thus, not only the size of the ancillary ligand but also other properties that can influence the energy landscape of the threading path are rate-determining factors. With mixed-sequence ct-DNA, threading of B and that of P are both multiphasic processes when monitored with CD as well as with luminescence. The rate constants for threading into ct-DNA show much larger variations between complexes than for poly(dAdT)2, confirming earlier results based on luminescence data.     

Rapid separation of barbiturates and benzodiazepines by capillary electrochromatography with 3-(1,8-naphthalimido)propyl-modified silyl silica gel

A capillary electrochromatographic (CEC) method was applied to the simultaneous separation of barbiturates (barbital, phenobarbital, secobarbital and thiopental) and benzodiazepines (nitrazepam, diazepam and triazolam). The separation was performed in a 75 microm i.d. capillary, packed with 3-(1,8-naphthalimido)propyl-modified silyl silica gel (NAIP), studying the effects of buffer pH and mobile phase composition. Using an applied voltage of 20 kV and the short-end injection method (9 cm capillary effective length), the mobile phase of 1.0 mM citrate buffer (pH 5.0) containing 45% methanol provided the baseline separation of seven toxic drugs in less than 9 min. In CEC with NAIP, the benzodiazepines were separated by the combination of hydrophobic and pi-pi interactions, whereas the separation of the barbiturates was based on the hydrophobic interaction.     

Dynamics of a droplet imbibing on a rough surface

We consider the imbibition of a liquid droplet of finite size on a rough surface and theoretically show that the imbibition dynamics is significantly slower than the familiar Washburn diffusive dynamics, ～t(0.5). The imbibition does not follow a simple power law. The droplet starts to imbibe with ～t(0.5) dynamics but progressively becomes slower with time. The slower imbibition is mainly attributed to the finite size of the droplet, resulting in a limited capillary driving force as compared to a steady capillary driving force in the case of imbibition from a steady source.     

葡萄糖氧化酶介体电极稳定性的研究

本文阐述了介体行丢失速率与电极基线电流大小的关系，以此为依据，讨论了介体液态石蜡中的溶解度对介体丢失的影响，通过向电极表面添加ＤＥＡＥ－葡萄糖来减小带正电荷的介体丢失速率，研究了ＤＥＡＥ－葡萄糖对葡萄糖氧化酶介体电极测试性能的影响。     

Unusual selectivity in the oxidative functionalization of gem-dibromocyclopropanes

Oxidation of gem-dibromocyclopropanes with chromium trioxide in acetic acid or a number of other reagents is generally slower than that of the corresponding cyclopropane; in a number of cases moderate yields of products are obtained but these show unexpected oxidation patterns.     

Cooperativity and selectivity in chemomechanical polyethylenimine gels

Gel particles obtained from polyethylenimine (PEI) cross-linked with 10% ethylene glycol diglycidyl ether show considerable selectivity in size changes if exposed to solutions of different effector compounds. Monocarboxylic acids induce contractions of, e.g., -9% for benzoate and -40% for 2-naphthoate (all values in one dimension such as length). With diacids, the contractions increase to -29% for 1,4-benzene and -68% for 2,6-naphthalene disulfonate, indicating the significant contributions of noncovalent ionic cross-linking and of interactions with aromatic residues. A striking cooperativity is observed if aromatic compounds such as naphthoic acid are used simultaneously with amino acids as effectors. The combination with, e.g., 2-naphthoic acid and phenylalanine induces, e.g., 69% contraction, whereas the single effector compounds induce only 40% and 8%, respectively. As expected with contraction of chemomechanical polymers, the kinetics of effector absorption is significantly slower than that of the size changes, which take, e.g., 5 min to reach one-half of the final contraction; with smaller gel particles, the rates are significantly increased. Gravimetric determinations show that release of solvation water is largely responsible for the observed volume contractions. Copper or zinc ions induce small contractions, also in experiments with PEI solutions, but show no evidence of cooperativity in combination with amino acids or peptides. MAS NMR spectra of the gels induced by aromatic effector compounds exhibited moderate upfield shifts of the polymer backbone signals, as a result of ring current effects.     

Genotype-phenotype correlation of SMN locus genes in spinal muscular atrophy patients from India

Spinal muscular atrophy has been classified into four groups based on the age of onset and clinical severity of the disease. Homozygous deletion in SMN1 gene causes the disease but the clinical severity may be modified by copy number of homologous gene SMN2 as well as the extent of deletion at SMN locus. In the view of scarcity of genotype and phenotype correlation data from India, this study has been undertaken to determine that correlation in SMA patients by using the SMN and NAIP genes and two polymorphic markers C212 and C272 located in this region. Two to four alleles of the markers C212 and C272 were observed in normal individuals. However, majority of Type I patients showed only one allele from both markers whereas in Type II and III patients, 2-3 alleles were observed. The SMN2 copy number in our type III patients showed that patients carry 3-5 copies of SMN2 gene. Our results suggest that extent of deletions encompassing H4F5, SMN1, NAIP and copy number of SMN2 gene can modify the SMA phenotype, thus accounting for the different clinical subtypes of the disease.     

The true Johari-Goldstein beta-relaxation of monosaccharides

Broadband isothermal dielectric relaxation measurements of anhydrous fructose, glucose, galactose, sorbose, and ribose were made at ambient pressure in their liquidus and glassy states. We found a new secondary relaxation in fructose and glucose that is slower than those seen before by others. This new secondary relaxation also appears in the dielectric spectra of galactose, sorbose, and ribose, and hence it is a general feature of the relaxation dynamics of the monosaccharides. Dielectric measurements at elevated pressure of fructose and ribose show that the new secondary relaxation shifts to lower frequencies with applied pressures, mimicking the behavior of the alpha-relaxation. In contrast, the faster secondary relaxation remains stationary on applying pressure. These results together with other inferences indicate that the slower secondary relaxation bears relations to the alpha-relaxation, and hence, it is the true Johari-Goldstein secondary relaxation of the monosaccharides.     

The structural,mechanical, and thermodynamic properties of B2-type TMZr (TM = Ru,Mo, Rh,Os, and Re) compounds from first-principles calculations

The B2-type cubic Zr-based compounds are attractive advanced high-temperature materials because of the strong and symmetrical bonds. However, the mechanical and thermodynamic properties of the B2-type cubic Zr-based compounds are not well understood. Here, we use the first-principles calculations to investigate the structural, elastic modulus, ductility, and thermodynamic properties of TMZr (TM = Ru, Mo, Rh, Os, and Re) compounds. Two novel TMZr compounds, MoZr and ReZr, are first predicted by using the phonon dispersion and formation enthalpy, respectively. The results show that the B2-type TMZr compounds not only exhibit high elastic modulus but also show better ductility due to the symmetrical TM-Zr metallic bonds. In particular, the calculated elastic modulus of OsZr is larger than that of the other four TMZr compounds, indicating that the OsZr shows the strongest deformation resistance in five TMZr compounds. The calculated Θ _D of RuZr is 328 K, which is larger than that of the other four TMZr compounds. The calculated phonon density of state shows that the high-temperature thermodynamic properties of TMZr derive from the vibration of Zr atom. Therefore, our work predicts that the B2-type OsZr is an attractive high-temperature structural material.     

Influence of filler type and content on properties of styrene‐butadiene rubber (SBR) compound reinforced with carbon black or silica

Rubber compounds are filled with reinforcing fillers to improve their physical properties. Carbon black and silica have different surface chemistries to each other. Differences in properties of carbon black‐ and silica‐reinforced styrene‐butadiene rubber (SBR) compounds were studied. Variation of properties of carbon black‐ or silica‐filled compounds with the filler content was also investigated. The silica‐filled compounds without any coupling agent and dispering agent were prepared to investigate the influence of polar materials‐adsorption on the silica surface. Viscosity and crosslink density increased with increase of the filler content. Hardness, modulus, tensile strength, and wear property were improved more and more by increasing the filler content. Viscosity of the silica‐filled compound was higher than that of the carbon black‐filled one. Cure rate of the silica‐filled compound became slower as the filler content increased, while that of the carbon black‐filled one became faster. Difference in properties between the carbon black‐ and silica‐filled compounds were explained by the poor silica dispersion and the adsorption of cure accelerator on the silica surface. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of active acidic compounds on storage stability of coker naphtha

Coker naphtha was separated into ten distillation fractions equal in volume via Engler distillation. It was found that the mercaptan sulphur compounds were mainly concentrated in the lighter fractions, whereas the basic nitrogen compounds were concentrated in the heavier fractions. The gum content increased gradually with increasing the boiling point of each fraction after storage for 21 days under ambient conditions (25°C, 101 kPa). The active organic acidic compounds in coker naphtha extracted with aqueous solution of 20 mass % NaOH represented 0.26 mass %. The GC-MS analysis of the active organic acidic compounds showed the amounts of small molecule thiols, thiophenols (including benzyl mercaptan) and phenolic compounds to be 2.6%, 4.4% and 90.0%, respectively. After removal of the active acidic compounds by caustic scrubbing, the increase in the rate of gum formation was much slower than that of the blank coker naphtha after 27 days of storage under ambient conditions, indicating that the effect of these acidic compounds on the gum formation is more significant than with basic nitrogen compounds. It is demonstrated that the storage stability of coker naphtha was decreased in the presence of large amounts of phenolic compounds, which may accelerate the acid-catalysed polymerisation of olefins.     

Folding kinetics of a naturally occurring helical peptide: implication of the folding speed limit of helical proteins

The folding mechanism and dynamics of a helical protein may strongly depend on how quickly its constituent alpha-helices can fold independently. Thus, our understanding of the protein folding problem may be greatly enhanced by a systematic survey of the folding rates of individual alpha-helical segments derived from their parent proteins. As a first step, we have studied the relaxation kinetics of the central helix (L9:41-74) of the ribosomal protein L9 from the bacterium Bacillus stearothermophilus , in response to a temperature-jump ( T-jump) using infrared spectroscopy. L9:41-74 has been shown to exhibit unusually high helicity in aqueous solution due to a series of side chain-side chain interactions, most of which are electrostatic in nature, while still remaining monomeric over a wide concentration range. Thus, this peptide represents an excellent model system not only for examining how the folding rate of naturally occurring helices differs from that of the widely studied alanine-based peptides, but also for estimating the folding speed limit of (small) helical proteins. Our results show that the T-jump induced relaxation rate of L9:41-74 is significantly slower than that of alanine-based peptides. For example, at 11 degrees C its relaxation time constant is about 2 micros, roughly seven times slower than that of SPE(5), an alanine-rich peptide of similar chain length. In addition, our results show that the folding rate of a truncated version of L9:41-74 is even slower. Taken together, these results suggest that individual alpha-helical segments in proteins may fold on a time scale that is significantly slower than the folding time of alanine-based peptides. Furthermore, we argue that the relaxation rate of L9:41-74 measured between 8 and 45 degrees C provides a realistic estimate of the ultimate folding rate of (small) helical proteins over this temperature range.     

两种偶氮分子玻璃材料的光致取向特性

利用光诱导双折射和偏振红外光谱法研究了2种无定形树枝状偶氮分子材料G1-AZ-CN和G2-AZ-CN的光致取向行为, 对其偶氮生色团及非光响应性星形核的光致取向速度、 取向松弛速度和饱和取向程度进行了系统研究. 结果表明, G2-AZ-CN中偶氮生色团和星形核的光致取向速度快于G1-AZ-CN, 但其取向松弛速度慢于G1-AZ-CN, 这与G2-AZ-CN具有更高的偶氮生色团密度有关. G1-AZ-CN具有较高的饱和取向程度及较好的取向稳定性. 与具有相同类型偶氮生色团的偶氮聚合物BP-AZ-CN相比, G1-AZ-CN和G2-AZ-CN中偶氮生色团表现出较慢的取向速度. 其取向行为与其特殊的星形分子结构有关.     

Infrared spectra of Li2SeO4.H2O,Li2SO4.H2O and Li2(S,Se)O4.H2O

On of the hydrogen bonds formed by water molecules in lithium selenate monohydrate is evidently stronger than in the corresponding sulfate, whereas the other one is weaker. The temperature dependence of the stretching and bending modes of water is similar in both compounds, their frequencies decreasing on lowering the temperature. The study of mixed sulfate—selenate compounds made it possible to clearly show that the effective symmetry of the tetrahedral ions is higher than their local crystallographic one.     

Design of Energetic Materials Based on Asymmetric Oxadiazole

A new family of asymmetric oxadiazole based energetic compounds were designed. Their electronic structures, heats of formation, detonation properties and stabilities were investigated by density functional theory. The results show that all the designed compounds have high positive heats of formation ranging from 115.4 to 2122.2 kJ mol⁻¹. −N− bridge/−N₃ groups played an important role in improving heats of formation while −O− bridge/−NF₂ group made more contributions to the densities of the designed compounds. Detonation properties show that some compounds have equal or higher detonation velocities than RDX, while some other have higher detonation pressures than RDX. All the designed compounds have better impact sensitivities than those of RDX and HMX and meet the criterion of thermal stability. Finally, some of the compounds were screened as the candidates of high energy density compounds with superior detonation properties and stabilities to that of HMX and their electronic properties were investigated.     

污水污泥流化床气化焦油的化学组成分析

以空气为气化剂、并通过GC-MS分析,研究了污水污泥流化床气化时气化温度（650、750和850 ℃）和污泥性质对污泥气化焦油产率及其化学组成的影响。结果表明,污泥气化焦油产率随气化温度的升高而降低,且厌氧消化污泥气化焦油的产率比未消化污泥的低。污泥气化焦油中的化学组成可分为五类：脂肪族化合物、脂环化合物、芳香烃、芳香烃衍生物和杂环化合物。随气化温度的升高,A²/O工艺的未消化污泥气化生成的焦油中脂肪族化合物和脂环化合物的产率均明显降低,芳香烃衍生物的产率则有显著地提高,而芳香烃和杂环化合物的产率均先增加后减少。气化温度为650 ℃时,活性污泥法消化污泥气化焦油中五类有机物的产率均低于未消化污泥的,而A²/O工艺消化污泥气化焦油中芳香烃产率高于未消化污泥的,其他四种有机物的产率则均低于未消化污泥的。