非等温单分子化学反应体系中温度场的时空对称破缺及温度波

从线性稳定性分析和计算机数值模拟两个方面研究了小尺度空间展布、伴有扩散和热传导的Lindemann单分子化学反应体系的温度场时空对称破缺. 研究结果表明, 在一定参数值和固定边界条件下, 反应体系经由时间-空间对称破缺分支能够产生温度波.     

空间展布体系中由化学反应-扩散-热传导耦合导致的温度场对称破缺

分析了由于化学反应-扩散-热传导耦合而导致的非等温非均匀体系中温度场对称破缺.研究结果表明,在一定的边界条件下,甚至是单组分化学反应-扩散-热传导体系,温度场的这种自组织进程也不可避免.作为温度场结构的一个范例,进一步从解析解及计算机模拟两个方面研究了小展布非等温的Lindeman模型;结果表明,温度场出现时空自组织的阈值不仅与本征参数有关,而且与体系的边界条件及外控约束相关,揭示出了诱发或避免这种温度场时空自组织之途径.     

Electrical conduction in a nonconjugated polymer doped with SnCl4 and SbCl5

The electrical and optical properties of 1,4-cis-polyisoprene before and after doping with SnCl₄ and SbCl₅ were investigated. The material becomes reddish brown and black upon doping with SnCl₄ and SbCl₅, respectively, and the conductivity increases by about 11 orders of magnitude. The optical absorption, infrared spectra, elemental analyses, and the studies of reversibility upon compensation indicate that radical cation formation is the most likely mechanism for electrical conduction in these complexes. The results are consistent with previously published articles involving iodine doping. © 1994 © John Wiley & Sons, Inc.     

A comparative study on chemical conversion of cellulose between the batch-type and flow-type systems in supercritical water

Microcrystalline cellulose (avicel) was treated in supercritical waterusing batch-type and flow-type systems. The flow-type system made it possibletoshorten the heating, treating and cooling times, compared with the batch-typesystem. As a result, the flow-type system was able to liquefy avicel withoutproducing any supercritical water-insoluble residue. Although hydrolyzedproducts such as glucose and fructose, and pyrolyzed products such aslevoglucosan, 5-hydroxymethyl furfural, erythrose, methylglyoxal,glycolaldehydeand dihydroxyacetone were found in common from the water-soluble portiontreatedby both systems, the flow-type system gave a water-soluble portion with morehydrolyzed and less pyrolyzed products, together with water-solubleoligosaccharides consisting of cellobiose to cellododecaose and theirdecomposedproducts at their reducing end of glucose, such as[–glucopyranosyl]_1–11 –levoglucosan,[–glucopyranosyl]_1–11 –erythrose and[–glucopyranosyl]_1–11 –glycolaldehyde. Inaddition, the precipitates of polysaccharides were recovered after 12h setting of the water-soluble portion. These results indicatedthat the flow-type system can hydrolyze cellulose with minimizing pyrolyzedproducts. On the other hand, the batch-type system resulted in a higher yieldof the pyrolyzed products due to the longer treatment, but a higher yield ofglucose due possibly to the higher pressure and concomitantly higher ionicproduct of water. Based on these lines of evidence, the process to increase theyield of the sugar is discussed under supercritical water treatment.     

Loss of stability by migration and chemical reaction of Santonox R in branched polyethylene under anaerobic and aerobic conditions

Plaques of branched polyethylene stabilized with 0.1 wt.% 4,4′-thiobis(6-tert-butyl-3-methylphenol) [Santonox^® R] were aged at different temperatures between 75 and 95 °C in anaerobic (nitrogen or water) and aerobic (air or water saturated with air) media. Antioxidant concentration profiles were obtained by oxidation induction time (OIT) measurements using differential scanning calorimetry. Results obtained by high performance liquid chromatography of extracts confirmed that the gradual decrease in OIT with increasing ageing time was due to migration of antioxidant to the surrounding medium. The antioxidant concentration profiles along the plaque thickness direction were flat in the plaques aged in the non-aqueous media indicating that the migration of antioxidant to the surrounding medium was controlled by the low evaporation rate at the material boundary. Crystals of antioxidant were detected by optical microscopy on the samples exposed to nitrogen. The similarity of the antioxidant concentration profiles obtained after ageing in nitrogen and in air suggested that the fraction of the antioxidant oxidized is negligible in comparison with the loss of antioxidant by migration to the surrounding media. The antioxidant concentration profiles along the plaque thickness direction obtained after ageing in water were less flat, suggesting faster dissolution in the water phase than evaporation in the case of non-aqueous ageing. The antioxidant diffusivity could be determined from the aqueous experiments and was in reasonable agreement with data reported by Moisan. For the samples exposed to water, the loss of antioxidant was faster from the samples exposed to water saturated with air. This difference is attributed to a faster degradation of the antioxidant in the oxygen-containing water phase increasing the mass transport from the polymer phase boundary to the water phase.     

Listen to the chemical and histological information in biological tissue

Photoacoustic imaging (PAI), as an emerging biomedicine diagnostic technique that has been developed quickly in the past decade, inherits the high spatial resolution of ultrasonography in imaging deep tissue and the high sensitivity of optical imaging in evaluating tissue chemical and physiological information. In this paper, after introducing the basic principles of PAI including both photoacoustic tomography and photoacoustic microscopy, we will review some recent progress of PAI in biomedicine and demonstrate the capability of PAI in detecting the chemical compositions and in evaluating the histological microstructures in biological tissue.     

Multi-stimulus Room Temperature Phosphorescent Polymers Sensitive to Light and Acid cyclically with Energy Transfer

The stimulus-responsive room temperature phosphorescent (RTP) materials have endowed wide potential applications. In this work, by introducing naphthalene and spiropyran (SP) into polyacrylamide as the energy donor and acceptor respectively, a new kind of brilliant dynamic color-tunable amorphous copolymers were prepared with good stability and processibility, and afterglow emissions from green to orange in response to the stimulus of photo or acid, thanks to multi-responsibility of SP and the energy transfer between naphthalene and SP. In addition to the deeply exploring of the inherent mechanism, these copolymers have been successfully applied in dynamically controllable applications in information protection and delivery.     

A comparative study of proton conduction between two new Cd(II) and Co(II) complexes and in vitro antibacterial study of the Cd(II) complex

Two new complexes based on 4,4′-[1,3-phenylenebis(oxy)]diphthalic acid (H₄L) ligands were synthesized, namely, [Cd₂(L)(1,10-phen)₂(H₂O)]_n( 1 ) and [Co₂(L)(1,10-phen)₂(H₂O)]_n( 2 ), in which 2D structures transform into 3D supramolecular structures by C H···π interaction. The proton conductivity of complexes 1 and 2 at low temperature is close (σ₁ = 3.12 × 10⁻⁸ S cm⁻¹ and σ₂ = 3.81 × 10⁻⁸ S cm⁻¹ at 30°C), but these two complexes show different conduction mechanisms. The Vehicular mechanism in 1 is caused by the O···H/H···O contact in 1 , which is stronger than 2 , and the Grotthuss mechanism in 2 is caused by the N···H/H···N contact in 2 , which is stronger than 1 . At the same time, complex 1 showed excellent antibacterial properties in vitro, mainly reflected in that five kinds of bacteria (Escherichia coli, Bacillus amyloliquefaciens, Pantoea agglomerans, Pseudomonas putida, and Pectobacterium carotovora) could play an obvious inhibitory effect in the concentration range of 20 μg·ml⁻¹.     

Temperature selectivity effects in reversed-phase liquid chromatography due to conformation differences between helical and non-helical peptides

In order to characterize the effect of temperature on the retention behaviour and selectivity of separation of polypeptides and proteins in reversed-phase high-performance liquid chromatography (RP-HPLC), the chromatographic properties of four series of peptides, with different peptide conformations, have been studied as a function of temperature (5-80 degrees C). The secondary structure of model peptides was based on either the amphipathic alpha-helical peptide sequence Ac-EAEKAAKEX(D/L)EKAAKEAEK-amide, (position X being in the centre of the hydrophobic face of the alpha-helix), or the random coil peptide sequence Ac-X(D/L)LGAKGAGVG-amide, where position X is substituted by the 19 L- or D-amino acids and glycine. We have shown that the helical peptide analogues exhibited a greater effect of varying temperature on elution behaviour compared to the random coil peptide analogues, due to the unfolding of alpha-helical structure with the increase of temperature during RP-HPLC. In addition, temperature generally produced different effects on the separations of peptides with different L- or D-amino acid substitutions within the groups of helical or non-helical peptides. The results demonstrate that variations in temperature can be used to effect significant changes in selectivity among the peptide analogues despite their very high degree of sequence homology. Our results also suggest that a temperature-based approach to RP-HPLC can be used to distinguish varying amino acid substitutions at the same site of the peptide sequence. We believe that the peptide mixtures presented here provide a good model for studying temperature effects on selectivity due to conformational differences of peptides, both for the rational development of peptide separation optimization protocols and a probe to distinguish between peptide conformations.     

A systems chemical biology study of malate synthase and isocitrate lyase inhibition in Mycobacterium tuberculosis during active and NRP growth

The ability of Mycobacterium tuberculosis (Mtb) to survive in low oxygen environments enables the bacterium to persist in a latent state within host tissues. In vitro studies of Mtb growth have identified changes in isocitrate lyase (ICL) and malate synthase (MS) that enable bacterial persistence under low oxygen and other environmentally limiting conditions. Systems chemical biology (SCB) enables us to evaluate the effects of small molecule inhibitors not only on the reaction catalyzed by malate synthase and isocitrate lyase, but the effect on the complete tricarboxylic acid cycle (TCA) by taking into account complex network relationships within that system.To study the kinetic consequences of inhibition on persistent bacilli, we implement a systems-chemical biology (SCB) platform and perform a chemistry-centric analysis of key metabolic pathways believed to impact Mtb latency. We explore consequences of disrupting the function of malate synthase (MS) and isocitrate lyase (ICL) during aerobic and hypoxic non-replicating persistence (NRP) growth by using the SCB method to identify small molecules that inhibit the function of MS and ICL, and simulating the metabolic consequence of the disruption.Results indicate variations in target and non-target reaction steps, clear differences in the normal and low oxygen models, as well as dosage dependent response. Simulation results from singular and combined enzyme inhibition strategies suggest ICL may be the more effective target for chemotherapeutic treatment against Mtb growing in a microenvironment where oxygen is slowly depleted, which may favor persistence.     

Quantum theory of chemical bond formation processes in condensed systems: studies towards exploration of electrochemical dark and photoprocesses on semiconductors

Quantum theoretical models of chemical bond formation and partial charge transfer processes in condensed systems, and their extension to processes in electronic non-equilibrium are investigated in this paper with a view to further exploration of electrochemical and photoelectrochemical kinetics on semiconductors. Electrochemical dark and photocurrents on n-III-V-semiconductors are correlated with calculated transition probabilities for atom-group transfer over larger distances (80 to 240 pm), leading to a first estimate of potential surface shapes compatible with experiment. Some specific problems connected with transition probability calculations for heavy-particle transfer in strong anharmonic potentials are considered in detail, including approximation of Franck-Condon transitions in arbitrary potentials by their classical limit.     

Separation of two overlapping redox waves by cyclic-voltammo-thermometry: Applications to Cu/CuCl and Ag/AgCl systems in chloride solutions

When two reactions take place at a given potential, other information is necessary, in addition to the relation between the applied potential and electric current, in order to evaluate the individual contribution of the reactions. Information about the heat evolved at the electrode during cyclic voltammetry enables the reaction components to be separated. It is concluded that the Cu/Cu^I redox system in chloride solution (0.1 < [Cl^?] < 0.45 M) giving a simple CV curve, can be divided into two reactions: Cu/CuCl_ad and Cu/CuCl^?₂. A similar overlap of the Ag/AgCl_ad and Ag/AgCl^?₂ reactions is also observed for the Ag/Ag^I redox system in 7 < [Cl^?] < 9 M solutions.     

可控相转变温度热敏高分子的制备及其在免疫分析中的应用

合成了一种新型的快速响应热敏高分子聚N－异丙基丙烯酰胺－丙烯酰胺[P(NIP-co-AA)]，通过改变丙烯酰胺的含量可以改变高分子的临界溶解温度（LCST），使之用于不同用途。其中，将相转变温度（Ttr)在37℃的热敏高分子用于免疫分析的载体，建立了夹心型荧光免疫分析兔IgG的新方法。与聚N－异丙基丙烯酰胺（PNIP）作载体相比，两灵敏度相当，但由于相转变温度的提高，使得免疫反应的温度更接近于生物体的生理环境，并使免疫反应速率得到提高。该方法线性范围为0-1000μg/L；检出限为10μg/L。用于兔血清中兔IgG的测量，结果令人满意。     

A solid-liquid extraction approach to elucidate the chemical availability of metals in soil and sediment assuming Langmuir isotherm behaviour

In an earlier paper (Anal. Chim. Acta 514 (2004) 137) we claimed that the maximal extractability of a metal from soil or sediment for a user-defined extractant, i.e. the chemical availability in that particular extractant, may be biased as a result of inadequate volume to mass (V/m) ratios. Correcting for that artifact using an implementation of the simple linear isotherm model gave good results although we cautioned the general applicability. In this paper we will theoretically derive the limitations of that approach based on the more general assumption that sorption processes are described by a Langmuir isotherm.NIST reference material 8704 was extracted with 1 mol l⁻¹ NaOAc (adjusted to pH 5) to experimentally verify the applicability of the Langmuir isotherm approach and illustrate the deviations obtained for some metals using the linear isotherm approach. Of the seven metals measured (Cr, Co, Ni, Cu, Zn, Cd, and Ba) only for Cr and Cu severe discrepancies between both approaches were found, which could be traced back to non-linear isotherm behaviour. Moreover, the Langmuir isotherm approach showed that the above mentioned extractability artifact is even more serious than earlier assumed applying the linear isotherm approach.     

An HPLC method forin vivo quantitation of oxygen free radicals using spin and chemical traps in biological systems

Summary We describe here anin vivo method for direct and simultaneous determination and quantitation of the oxygen free radicals (OFR) superoxide (O₂ ^–) and hydroxy (OH) radicals in biological tissue and blood of 2 week-old swine. Our method utilizes OFR trapping techniques, a spin trap 5,5-dimethyl-1-pyrroline-n-oxide (DMPO), 50 mg/kg, for O₂ ^– and a chemical trap, Na salicylate, (SA, 100 mg/kg) for OH, was infused into the right atrium or pulmonary artery of two-week old swine (n=12). The OFR contents of coronary sinus (CS) blood and left ventricular (LV) tissue (quick frozen at 77°K) were measured by an HPLC method developed by us (Waters 590 solvent delivery system, using Waters electrochemical 460 EC detector, and 740 data module) at +0.6V. The DMPO-O₂ ^– (measured as DMPO-OH) adduct assay was performed with a mobile phase consisting of 0.03 M citric acid, 0.05 M NaOH and 8.5% acetonitrile (Ph 5.1) at a flow rate of 1 ml/min through a Waters Resolve 5 C₁₈ column. The salicylate-OH products (2,5 and 2,3 dihydroxy benzoic acids, DHBA) were assayed using mobile phase of 0.03 M Na citrate, 0.03 M Na acetate, with N₂ bubbled (pH 3.6) at a flow rate of 0.8 ml/min through a 5 Resolve C₁₈ column. The detected peak for DMPO-O₂ ^– adduct (9.5 min) was standardized with a hypoxanthine (HX) and xanthine oxidase (XO) mixture and the salicylate-OH products (11.5 min) were standardized with HX, XO and FeCl₃. Forin vitro experiments, the blood/tissue samples were immediately (<30 sec) incubated directly with 100 mM DMPO and/or 200 mM salicylate for 1 min, vortexed and injected for HPLC analysis. Superoxide dismutase (1 M) and DMSO (10 mM) scavenged O₂ ^– and OH adduct peaks by 77 and 80% respectively. The coefficient of variation for DMPO-O₂ ^– adduct was ±12.6% and for salicylate-OH adduct was ±10.9% (n=12). The normal LV tissue levels determined for O₂ ^– and OH were 0.41 and 0.32 nm/g wet weight, respectively. (In blood, the OFR contents were very small: 0.09 and 0.06 nm/ml, respectively.) This method is very specific and sensitive, 50 pm for O₂ ^– and 0.2 pm for OH radicals.Presented at the 39th National Meeting, American Association of Clinical Chemistry, New Orleans, 1988.     

Temperature coefficient of NH chemical shifts of thioamides and amides in relation to structure

NH chemical shift temperature coefficients have been measured in a large series of N-substituted-3-piperidinethiopropionamides in which the NN distances are short but of varied length, as well as in a couple of the corresponding amides and in some simpler amides and thioamides. Geometries are calculated by means of ab initio DFT methods. The N-substituted-3-piperidinethiopropionamides show in most cases strong intramolecular N–HN hydrogen bonds according to IR spectra and ab initio calculations. For compounds with rather short NN distances the S=C–N–H moiety is non-planar. Dihedral angles as small as 160° are found. The NH chemical shift coefficients measured in non-polar solvents in all the N-substituted-3-piperidinethiopropionamides are more negative (−8 to −17 ppb/K) than in non-hydrogen bonded thioamides. For the latter in non-polar solvents like CDCl₃ and toluene the temperature coefficients are as small as −1 to −4 ppb/K. The large negative effects can be related not only to the non-planarity of the thioamide group in a way that the more pronounced the non-planarity the more negative the temperature coefficients, but also to strong hydrogen bonding and the fact that the acceptor is a nitrogen. For similar amides with non-planar amide groups and nitrogen acceptor large negative temperature coefficients are likewise seen. In polar solvents like DMF the effects in simple thioamides are uniform and close to −6 ppb/K, whereas in the more complex compound like 4p(t) the temperature coefficient is close to 0. An essential feature of measuring temperature coefficients of compounds without strong intramolecular hydrogen bonds in non-polar solvents and at low temperatures is to keep the concentration low enough to avoid dimerisation.     

Hydrogen-bonding interactions in crown-(thio)urea complexes with anions,chemical warfare agents and simulants

ABSTRACT

Benzocrown ethers incorporating phenyl and nitrophenyl urea and thiourea moieties were synthesised. Both the nitrophenyl urea and thiourea derivative gave a fluoride-specific colorimetric response but only the urea derivative bound the organophosphonate nerve agent simulants dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP). This suggested an application as sensors for the nerve agents sarin, soman and cyclosarin which release fluoride upon hydrolysis. Although no fluoride-induced response was observed in the UV-visible spectrum, binding to soman was determined by ¹H NMR. DFT computational simulations suggested that the two crowns adopt different conformations in which both can bind fluoride but only the urea derivative can bind DMMP, DIMP and soman. The results show that, for this system, simulant- and soman-binding behaviours are in good agreement.     

Determination of chemical warfare agents and related compounds in environmental samples by solid-phase microextraction with gas chromatography

Solid phase microextraction (SPME) is an increasingly common method of sample isolation and enhancement. SPME is a convenient and simple sample preparation technique for chromatographic analysis and a useful alternative to liquid-liquid extraction and solid phase extraction. SPME is speed and simply method, which has been widely used in environmental analysis because it is a rather safe method when dealing with highly toxic chemicals. A combination of SPME and gas chromatography (GC) permits both the qualitative and quantitative analysis of toxic industrial compounds, pesticides and chemical warfare agents (CWAs), including their degradation products, in air, water and soil samples. This work presents a combination of SPME and GC methods with various types of detectors in the analysis of CWAs and their degradation products in air, water, soil and other matrices. The combination of SPME and GC methods allows for low detection limits depending on the analyte, matrix and detection system. Commercially available fibers have been mainly used to extract CWAs in headspace analysis. However, attempts have been made to introduce new fiber coatings that are characterized by higher selectivities towards different analytes of interest. Environmental decomposition of CWAs leads to the formation of more hydrophilic products. These compounds may be isolated from samples using SPME and analyzed using GC however, they must often be derivatized first to produce good chromatography. In these cases, one must ensure that the SPME method also meets the same needs. Otherwise, it is helpful to use derivatization methods. SPME may also be used with fieldportable mass spectrometry (MS) and GC-MS instruments for chemical defense applications, including field sampling and analysis. SPME fibers can be taken into contaminated areas to directly sample air, headspaces above solutions, soils and water.