Solvent-induced crystallization of spherical micelles formed by copolymer blends

We have followed the morphological evolution and crystallization process of spherical micelles formed by the mixture of polystyrene-b-poly(acrylic acid) (PS-b-PAA) and polystyrene-b-poly(2-vinylpyridine)b-poly(ethylene oxide) (PS-b-P2VP-b-PEO) (the core of the spherical micelles was made of P2VP and PAA blocks through hydrogen bonding in neutral solvent N,N-dimethylformamide, DMF) via DMF vapor treatment. Different phenomena, such as rupture of the film, formation of cylinder aggregates and regular square lamellae, were observed when the micelle film was treated in DMF for different times. At the early stage of annealing in DMF vapor, the micelle film became unstable and ruptured. Cylinder aggregates, within which the PEO blocks achieved the association and primary chain folding, formed as the mesophases before the nucleation of the PEO single crystals at this stage. Further treatment in DMF vapor resulted in the nucleation of the PEO blocks at the corners of quasi-square lamellae. Then a quite regular "sandwich" lamellar structure, constructed by a PEO single-crystal layer covered by two tethered layers of other amorphous blocks on the top and bottom crystal basal surfaces, formed when the film of micelles was annealed in DMF vapor for sufficient times.

Biodegradable amphiphilic triblock copolymer bearing pendant glucose residues: Preparation and specific interaction with Concanavalin A molecules

A novel biodegradable amphiphilic block copolymer PLGG-PEG-PLGG bearing pendant glucose residues is successfully prepared by the coupling reaction of 3-(2-aminoethylthio) propyl-R-D-glucopyranoside with the pendant carboxyl groups of PLGG-PEG-PLGG in the presence of N,N'-carbonyldiimidazole. The polymer PLGG-PEG-PLGG, i.e., poly {(lactic acid)-co-[(glycolic acid)-alt-(L-glutamic acid)]}-block-poly(ethylene glycol)-block-poly{( lactic acid)-co-[( glycolic acid)-alt-(L-glutamic acid)]}, is prepared by ring-opening copolymerization of L-lactide (LLA) with (3s)-benzoxylcarbonylethylmorpholine-2,5-dione (BEMD) in the presence of dihydroxyl PEG with molecular weight of 2000 as macroinitiator and Sn(Oct)(2) as catalyst, and then by catalytic hydrogenation. The glucose-grafted copolymer shows a lower degree of cytotoxicity to ECV-304 cells and improved specific recognition and binding with Concanavalin A (Con A). Therefore, this kind of glucose-grafted copolymer may find biomedical applications.

Preparation and properties of polyimide films codoped with barium and titanium oxides

Polyimide hybrid films containing bimetalic compounds were obtained by codoping poly(amic acid) with a barium and titanium precursor prepared from BaCO3, Ti(OBu)(4), and lactic acid followed by casting and thermal curing. FTIR, WAXD, and XPS measurements showed that barium and titanium precursor could be transformed to BaTiO3 at a temperature above 650 degreesC, while the mixed oxides were only found in hybrid films. The measurements of TEM and AFM indicated a homogeneous distribution of inorganic phase with particle sizes less than 50 nm. The hybrid films exhibited fairly high thermal stability, good optical transparency, and promising mechanical properties. The incorporation of 10 wt % barium and titanium oxide lowered surface and volume electrical resistivity by 2 and 5 orders, respectively, increasing dielectric constant from 3.5 to 4.2 and piezoelectric constant from 3.8 to 5.2 x 10(-12) c/N, relative to the nondoped polyimide film.

Preparation of polyimide-BaTiO3 hybrid films by a dispersion process and their microstructure

Barium titanate (BaTiO3) powders with particle sizes of 30 similar to 50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wit % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.

Synthesis and characterization of polypyrrole-polyurethane cationomer composites

Poly(ether urethane) cationomers based on poly(oxytetramethylene), 4,4'-bibenzyldiisocyanate, N-methyldiethanolamine as chain extender, and acrylic acid/poly(acrylic acid) as quaternization agent were synthesized. Pyrrole (15 wt.-%) was polymerized in films of the ionomer containing CuCl2. The films were characterized by dynamic mechanical analysis, thermogravimetry and differential scanning calorimetry. The electric conductivity of the film without polypyrrole is 7.5 . 10(-12) Omega(-1)cm(-1), while incorporation of polypyrrole increases the conductivity to 4.5 . 10(-6) Omega(-1) cm(-1).

The crystal structure and drawing induced polymorphism in poly(aryl ether ketone)s .3. Crystallization during hot-drawing of poly(ether ether ketone ketone)

The evolution of crystallinity and polymorphism during hot-drawing of amorphous poly(ether ether ketone ketone) (PEEKK) as a function of strain rate, draw ratio, and temperature was investigated. In modification I, the competition of chain extension and molecular alignment is responsible for the strain rate and temperature dependence. Modification II crystallization is basically controlled by chain extension during stretching. The former can be transformed into the latter via relaxation during stretching or annealing at elevated temperature.

STUDY OF THE ELECTRODE PROCESS OF HEMOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode is reported. The resulting film on a platinum electrode surface was analyzed with electron spectroscopy for chemical analysis (ESCA). The heterogeneous electron transfer processes of hemoglobin at the polymerized azure A film electrode have been investigated using in situ UV-visible spectroelectrochemistry. The formal potential (E-degrees') and electron transfer number (n) of hemoglobin were calculated as E = 0.088 V versus NHE (standard deviation +/- 0.5, N = 4) and n = 1.8 (standard deviation +/- 0.5, N = 4). Exhaustive reduction and oxidation electrolysis are achieved in 80 and 380 seconds, respectively, during a potential step between -0.3 and +0.3 V. A formal heterogeneous electron-transfer rate constant (k(sh)) of 3.54(+/- 0.12) X 10(-6) cm/s and a transfer coefficient (alpha) of 0.28(+/- 0.01) were obtained by cyclic voltabsorptometry, which indicated that the poly-azure A film electrode is able to catalyze the direct reduction and oxidation of hemoglobin.

Simultaneous determination of monoamine and amino acid neurotransmitters in rat endbrain tissues by pre-column derivatization with high-performance liquid chromatographic fluorescence detection and mass spectrometric identification

A sensitive and efficient method for simultaneous determination of glutamic acid (Glu), gamma-amino-butyric acid (GABA), dopamine (DA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) in rat endbrains was developed by high-performance liquid chromatography (HPLC) with fluorescence detection and on-line mass spectrometric identification following derivatization with 1,2-benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC). Different parameters which influenced derivatization and separation were optimized. The complete separation of five neurotransmitter (NT) derivatives was performed on a reversed-phase Hypersil BDS-C-18 column with a gradient elution. The rapid structure identification of five neurotransmitter derivatives was carried out by on-line mass spectrometry with electrospray ionization (ESI) source in positive ion mode, and the BCEOC-labeled derivatives were characterized by easy-to-interpret mass spectra. Stability of derivatives, repeatability, precision and accuracy were evaluated and the results were excellent for efficient HPLC analysis. The quantitative linear range of five neurotransmitters were 2.441-2 x 10(4) nM, and limits of detection were in the range of 0.398-1.258 nM (S/N = 3:1). The changes of their concentrations in endbrains of three rat groups were also studied using this HPLC fluorescence detection method. The results indicated that exhausting exercise could obviously influence the concentrations of neurotransmitters in rat endbrains. The established method exhibited excellent validity, high sensitivity and convenience, and provided a new technique for simultaneous analysis of monoamine and amino acid neurotransmitters in rat brain. (C) 2008 Elsevier B.V. All rights reserved.

Chiral separation of enantiomers of amino acid derivatives by high-performance liquid chromatography on a norvancomycin-bonded chiral stationary phase

A novel norvancomycin-bonded chiral stationary phase (NVC-CSP) was synthesized by using the chiral selector of norvancomycin. The chiral separation of enantiomers of several dansyl-amino acids by high-performance liquid chromatography (HPLC) in the reversed-phase mode is described. The effects of some parameters, such as organic modifier concentration, column temperature, pH and flow rate of the mobile phase, on the retention and enantioselectivity were investigated. The study showed that ionic, as well as hydrophobic interactions were engaged between the analyte and macrocycle in this chromatographic system. Increasing pH of buffers usually improved the chiral resolution for dansyl-alpha-amino-n-butyric acid (Dns-But), dansyl-methionine (Dns-Met) and dansyl-threonine (Dns-Thr), but not for dansyl-glutamic acid (Dns-Glu) which contains two carboxylic groups in its molecular structure. The natural logarithms of selectivity factors (In alpha) of all the investigated compounds depended linearly on the reciprocal of temperature (1/T), most processes of enantioseparation were controlled enthalpically. Interestingly, the process of enantioseparation for dansyl-threonine was enthalpy-controlled at pH of 3.5, while at pH of 7.0, it was entropy-controlled according to thermodynamic parameters Delta(R,S)DeltaHdegrees and Delta(R,S)DeltaSdegrees afforded by Van't Hoff plots. In order to get baseline separation for all the solutes researched, norvancomycin was also used as a chiral mobile phase additive. In combination with the NVC-CSP remarkable increases in enanselectivity were observed for all the compounds, as the result of a "synergistic" effect. (C) 2003 Elsevier B.V. All rights reserved.

Molecular modeling on some human interleukins sharing gamma c of interleukin-2 receptor, and structure-function relationships

Five models for human interleukin-7 (HIL-7), HIL-9, HIL-13, HIL-15 and HIL-17 have been generated by SYBYL software package. The primary models were optimized using molecular dynamics and molecular mechanics methods. The final models were optimized using a steepest descent algorithm and a subsequent conjugate gradient method. The complexes with these interleukins and the common gamma chain of interleukin-2 receptor (IL-2R) were constructed and subjected to energy minimization. We found residues, such as Gln127 and Tyr103, of the common gamma chain of IL-2R are very important. Other residues, e.g. Lys70, Asn128 and Glu162, are also significant. Four hydrophobic grooves and two hydrophilic sites converge at the active site triad of the gamma chain. The binding sites of these interleukins interaction with the common gamma chain exist in the first helical and/or the fourth helical domains. Therefore, we conclude that these interleukins binds to the common gamma chain of IL-2R by the first and the fourth helix domain. Especially at the binding sites of some residues (lysine, arginine, asparagine, glutamic acid and aspartic acid), with a discontinuous region of the common gamma chain of IL-2R, termed the interleukins binding sites (103-210). The study of these sites can be important for the development of new drugs. (C) 2000 Elsevier Science B.V. All rights reserved.

Determination of sexual hormones in liquid cosmetics by polymer monolith microextraction coupled with high performance liquid chromatography

A method was presented for the determination of testosterone, methyltestosterone and progesterone in liquid cosmetics by coupling polymer monolith microextraction (PMME) to high performance liquid chromatography with UV detection. A poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column was selected as the extraction medium, which showed high extraction capacity towards these compounds. To achieve optimum extraction performance, several parameters relating to PMME were investigated, including extraction flow rate and pH value, inorganic salt and organic phase concentration of the sample matrix. By simple dilution with phosphate solution and filtering, the sample solution then could be directly injected into the device for extraction. The limits of detection of testosterone, methyltestosterone and progesterone were calculated to be 2, 3, 2, 8 and 4.6 mu g/L. Good linearity was achieved in the range of 10 to 1000 mu g/L with a linear coefficient. r value above 0. 996. Excellent method reproducibility was found by intra- and inter-day precisions, yielding the relative standard deviations of < 7. 7 % and < 7. 5 %, respectively. Recovery for them in the real samples was between 83% and 119%.

Measurement of 5-day biochemical oxygen demand without sample dilution or bacterial and nutrient enhancement

A direct method for measuring the 5-day biochemical oxygen demand (BODS) of aquaculture samples that does not require sample dilution or bacterial and nutrient enrichment was evaluated. The regression coefficient (R-2) between the direct method and the standard method for the analyses of 32 samples from catfish ponds was 0.996. The slope of the regression line did not differ from 1.0 or the Y-intercept from 0.0 at P = 0.05. Thus, there was almost perfect agreement between the two methods. The control limits (three standard deviations of the mean) for a standard solution containing 15 mg/L each of glutamic acid and glucose were 17.4 and 20.4 mg/L. The precision of the two methods, based on eight replicate analyses of four pond water samples did not differ at P = 0.05. (c) 2005 Elsevier B.V All rights reserved.

CYCLIC PEPTIDE HEPATOTOXINS FROM FRESH-WATER CYANOBACTERIAL (BLUE-GREEN-ALGAE) WATERBLOOMS COLLECTED IN CENTRAL CHINA

Toxic cyanobacteria (blue-green algae) waterblooms have been found in several Chinese water bodies since studies began there in 1984. Waterbloom samples for this study contained Anabaena circinalis, Microcystis aeruginosa and Oscillatoria sp. Only those waterblooms dominated by Microcystis aeruginosa were toxic by the intraperitoneal (i.p.) mouse bioassay. Signs of poisoning were the same as with known hepatotoxic cyclic peptide microcystins. One toxic fraction was isolated from each Microcystis aeruginosa sample. Two hepatotoxic peptides were purified from each of the fractions by high-performance liquid chromatography and identified by amino acid analysis followed by low and high resolution fast-atom bombardment mass spectrometry (FAB-MS). LD50 i.p. mouse values for the two toxins were 245-mu-g/kg (Toxin A) and 53-mu-g/g (Toxin B). Toxin content in the cells was 0.03 to 3.95 mg/g (Toxin A) and 0.18 to 3.33 mg/kg (Toxin B). The amino acid composition of Toxin A was alanine [1], arginine [2], glutamic acid [1] and beta-methylaspartic acid [1]; for Toxin B it was the same, except one of the arginines was replaced with a leucine. Low- and high-resolution FAB-MS showed that the molecular weights were 1,037 m/z (Toxin A) and 994 m/z (Toxin B), with formulas of C49H76O12N13 (Toxin A) and C49H75O12N10 (Toxin B). It was concluded that Toxin A is microcystin-RR and Toxin B is microcystin-LR, both known cyclic heptapeptide hepatotoxins isolated from cyanobacteria in other parts of the world. Sodium borohydride reduction of microcystin-RR yielded dihydro-microcystin-RR (m/z = 1,039), an important intermediate in the preparation of tritium-labeled toxin for metabolism and fate studies.

Fabrication of Novel Superhydrophobic Surfaces and Water Droplet Bouncing Behavior - Part 1: Stable ZnO-PDMS Superhydrophobic Surface with Low Hysteresis Constructed Using ZnO Nanoparticles

A superhydrophobic surface has many advantages in micro/nanomechanical applications, such as low adhesion, low friction and high restitution coefficient, etc. In this paper, we introduce a novel and simple route to fabricate superhydrophobic surfaces using ZnO nanocrystals. First, tetrapod-like ZnO nanocrystals were prepared via a one-step, direct chemical vapor deposition (CVD) approach. The nanostructured ZnO material was characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) and the surface functionalized by aminopropyltriethoxysilane (APS) was found to be hydrophobic. Then the superhydrophobic surface was constructed by depositing uniformly ZnO hydrophobic nanoparticles (HNPs) on the Poly(dimethylsiloxane) (PDMS) film substrate. Water wettability study revealed a contact angle of 155.4 +/- 2 degrees for the superhydrophobic surface while about 110 degrees for pure smooth PDMS films. The hysteresis was quite low, only 3.1 +/- 0.3 degrees. Microscopic observations showed that the surface was covered by micro- and nano-scale ZnO particles. Compared to other approaches, this method is rather convenient and can be used to obtain a large area superhydrophobic surface. The high contact angle and low hysteresis could be attributed to the micro/nano structures of ZnO material; besides, the superhydrophobic property of the as-constructed ZnO-PDMS surface could be maintained for at least 6 months. (C) Koninklijke Brill NV, Leiden, 2010

固定化红酵母细胞合成L-苯丙氨酸研究

In this paper, bioconversion of trans-cinnamic acid(t-Ca)to L-phenylalanine (L-phe) has been investigated by using immobilized yeast cells with induced L-phe Ammonia-lyase(PAL, EC.4.3.1.5) as biocatalysts. The contents are the following. (1) Thirty strains of yeasts, including two genera (Rhodotorula, Sporobolomyces), six species (R. glutinis R. minuta,R.rubra,R.sineses,R.roseus and S.salmonicolor)were screened for their ability to converse the substrates, t-Ca and ammonia, to the product, L-phe, by using yeast cells as biocatalyst, and primary evaluation for PAL activity of the selected strains was investigated. From the results of the screening experiments, it was found that 22 strains were able to produce L-phe from t-Ca with the range of conversion yield from 2% to 67%. Studies on PAL formation time course during cultivation show that the maximum PAL activity of several different strains ranges from 2.3 to 14.4×10-3U/mg cell dry weight. The biomass of tested strains at their maximum enzyme activity is also greatly varied. (2)One of the selected strains, R. rubra as 2.166, was used for immobilized cells as biocatalysts to produce L-phe. The optimum conversion conditions and effective stablization agents were investigated. The results shown that polyacrylamide gel was chosen as a suitable matrix for immobilization of the yeast cells, and it can retain 88% of the PAL activity in the reverse direction at the following reactive conditions: [t-Ca]: 34mM. [NH4OH]: 6.OM.PH10.00, temperature: 30℃. (3) The effects of various kinds of effectors on the production of L-phe were also examined. Membrane permeabilizing agents can stimulate L-phe synthesis, but make the stability of PAL decline greatly. Polyalchoholic agents and glutamic acid were very effective for the stabilization of PAL. At the presence of glutamic acid (5%), the half life of L-phe productivity with the immobilized cells was extended to 192 hours, which was much higher than most of that having been reproted, while the half life of resting cells was only about 15 hours. (4) Use of initial velocity studies on the kinetics of enzyme-catalized reaction indicated that the apparent Km value was 13.0mM for the immobilized cells, and 4.8mM for the resting cells. Thermostability of the immobilized cells was better than the resting cells. Fluid bed bioreactor is more effective than batch bioreator in prolonging the thermostability of the biocatalysts. (5) CGA- 688 resin column chromatographic procedure was employed in the isolation and purification of L-phe, t-Ca and other substances from the reactire mixture. (6) Preparative-scale production of L-phe on a level of gram amount by immobilized cells from the culture broth of R. rubra AS2.166 allowed for the conversion yield with 30%. The characteristic physico-chemical criteria (including melting point, optical activity, elements analysis, IR, NMR) are the same with the standard L-phe. 本文报告了利用诱导的苯丙氨酸解氨酶 (PAL.EC.4.3.1.5)催化反式肉桂酸(t-Ca)氨加 成制备L-苯丙氨酸(L-phe)的研究，主要内容为：(1) 我们搜集了三十株酵母菌株，利用全细胞转化t-Ca生成L-phe的能力进行了直 接筛选，并对其PAL活性水平进行了初步评估研究。研究结果表明，其中22株酵母具有转化t-Ca生产L-phe的能力，它们包括 Rhodotorula glutinis,R.rubra, R.sineses 和Sporobolomyces roseus 的菌株，转化率在2-67%。细胞生长和PAL形成过程的研究 表明，不同菌株PAL最大活力在2.3-14.4×10-3U/mg 细胞干重，达到最大PAL活性时各株酵母的生长情况也极不一致。(2) 利用筛 选出的一株深红酵母R.rubra AS2.166 作为供试菌株，研究了细胞固定化条件下生物转化的最适条件及PAL在固定化条件下的稳定 性。结果表明以聚丙烯酰胺凝胶包埋法较为理想，能使细胞合成L-phe活力保持88%，最适t-Ca浓度为34mM，最适NH4OH浓度为6M,最 适PH10.0，最适温度45℃。(3) 多种效应物对L-phe 合成的影响研究表明：表面活性剂能刺激L-phe的合成，但使PAL稳定性下降。 多羟基化合物及Glu对PAL的稳定十分有效在有Glu存在下，能使固定化细胞合成L-phe的半寿期达192小时左右，高于大部分现已报 导的固定化结果。(4) 用初速度法研究了深红酵母AS2.166中PAL的酶促反应特征，测得固定化细胞对t-Ca的表观米氏常数Km为 13.0mM，全细胞为4.8mM，细胞固定后热稳定性提高。(5) 建立了适合低浓度分离纯化产物与底物的聚苯乙烯大孔树脂柱层析技术 ，能使L-phe与t-Ca及产物混合物中其它成分有效分开。(6) 利用固定化的R.rubra AS2.166细胞所做的制备实验能够使L-phe的产 率达到30%左右，其主要的理化指标(包括熔点、比旋光度、元素分析、IR、NMR等)与标准L-phe一致。