Effect of substrate (ZnO) morphology on enzyme immobilization and its catalytic activity

In this study, zinc oxide (ZnO) nanocrystals with different morphologies were synthesized and used as substrates for enzyme immobilization. The effects of morphology of ZnO nanocrystals on enzyme immobilization and their catalytic activities were investigated. The ZnO nanocrystals were prepared through a hydrothermal procedure using tetramethylammonium hydroxide as a mineralizing agent. The control on the morphology of ZnO nanocrystals was achieved by varying the ratio of CH₃OH to H₂O, which were used as solvents in the hydrothermal reaction system. The surface of as-prepared ZnO nanoparticles was functionalized with amino groups using 3-aminopropyltriethoxysilane and tetraethyl orthosilicate, and the amino groups on the surface were identified and calculated by FT-IR and the Kaiser assay. Horseradish peroxidase was immobilized on as-modified ZnO nanostructures with glutaraldehyde as a crosslinker. The results showed that three-dimensional nanomultipod is more appropriate for the immobilization of enzyme used further in catalytic reaction.     

Conformational and dynamo-optical properties of fluorinated poly(p-phenylene-1,3,4-oxadiazole-imide-amide) molecules in solutions

Conformational parameters of the fluorinated poly(p-phenylene-1,3,4-oxadiazole-imide-amide) molecules in dilute solutions in N,N′-dimethylacetamide, N,N′-dimethylformamide and 96% sulphuric acid were evaluated by using the data of hydrodynamic and dynamo-optical investigations. Optical anisotropy of the statistical Kuhn segment was found to be about half of that for poly(amide-benzimidazole) and close to that previously obtained for poly(p-phenylene-1,3,4-oxadiazole) molecules. The observed effect is referred to the higher equilibrium flexibility of the polymer chain attributed to the hexafluoroisopropylidene units incorporated into the molecule backbone. Noticeable degradation of the polymer molecules in solution in 96% H₂SO₄ at ambient temperature was detected and characterised.     

底物特异性的生物催化与酶设计改造

随着生物产业的发展,生物酶催化发挥着越来越重要的作用。然而,部分酶在应用过程中仍然存在诸多问题,影响了生物催化的进一步发展。本文以酶的底物特异性为切入点,回顾了酶的专一性、高效性和环保性;介绍了酶在药物合成和天然产物改性领域的应用以及所遇到的问题;综述了酶的底物特异性改造过程中各种方法的应用,包括化学修饰、非理性和理性设计。化学修饰作为一种直观的修饰方法,通过化学反应对酶分子进行改造;非理性设计是利用易错PCR和DNA Shuffling等手段获得底物特异性提高的突变体;理性设计是基于序列和结构信息对酶分子进行改造。本文从重塑活性口袋提高酶的底物特异性和重塑活性口袋改变酶促反应类型两个方面出发,详述了理性设计改变酶的底物特异性的方法,为酶的特异性改造提供借鉴。     

Influence of mustelid semiochemicals on population dynamics of the deer mouse (Peromyscus maniculatus)

The influence of mustelid anal-gland compounds on population dynamics of the deer mouse (Peromyscus maniculatus) was investigated. Densities of deer mice were not found to be significantly different between treated and control areas. However, on average, numbers of deer mice were lower on treated areas following the July treatments of 1991 and 1992. Survival rates appeared to be lower and more erratic on treated than control areas in 1991; however, there were no statistically significant differences. Reproduction appeared to be unaffected by the odors. We concluded that deer mice did not display a behavioral response to weasel odors. We speculated that decreases in densities were owing to predation by weasels, which were attracted to the odors on treated sites. We also concluded that the use of weasel odors as a biological control method for voles (Microtus spp.) would likely have little impact on deer mice (a nontarget species).     

The influence of substrate absorbency on coating surface chemistry

The composition of the top surface of a coating layer can influence its functional properties or subsequent processing steps. The effect of the substrate absorbency on the coating surface chemistry is reported. Different coating systems containing a kaolin clay pigment, fine or coarse precipitated calcium carbonates, and a common latex binder were examined. The influence of a soluble polymer added into the coating was characterized. The surface chemistry was measured with attenuated total internal reflectance (ATR) and X-ray photoelectron spectroscopy (XPS).

Absorbent substrates generate bulky coatings with high voids and low gloss. Rapid dewatering by the absorbent substrate pulls the small particles, like latex binder, away from the top layers causing a low latex concentration at the surface. On non-absorbent substrates, the addition of the soluble polymer generates coating layers with higher void volume, lower gloss, and lower latex concentrations at the coating surface. However, on absorbent substrates, polymer addition causes coatings with lower void volumes and higher gloss. In this case, the rapid dewatering and mobility of particles is reduced by the polymer, which helps to retain the small particles at the surface. As a result, latex concentration at the surface increases with polymer addition on absorbent substrates.     

Influence of substrate dideuteration on the reaction of the bifunctional heme enzyme psi factor producing oxygenase A (PpoA)

PpoA is a bifunctional enzyme that catalyzes the dioxygenation of unsaturated C18 fatty acids. The products of this reaction are termed psi factors and have been shown to play a crucial role in conferring a balance between sexual and asexual spore development as well as production of secondary metabolites in the fungus Aspergillus nidulans. Studies on the reaction mechanism revealed that PpoA uses two different heme domains to catalyze two subsequent reactions. Initially, the fatty acid substrate is dioxygenated at C8, yielding an 8‐hydroperoxy fatty acid at the N‐terminal domain. This reaction is catalyzed by a peroxidase/dioxygenase‐type domain that exhibits many similarities to prostaglandin H2 synthases and involves a stereospecific homolytic hydrogen abstraction from C8 of the substrate. The C terminus harbors a heme thiolate P450 domain in which rearrangement of the 8‐hydroperoxide to the final product, a 5,8‐dihydroxy fatty acid, takes place. To obtain further information about the intrinsic kinetics and reaction mechanism of PpoA, we synthesized C5‐dideutero‐ and C8‐dideutero‐oleic acid by a novel protocol that offers a straightforward synthesis without employing the toxic additive hexamethylphosphoramide (HMPA) during C? C coupling reactions or mercury salts upon thioketal deprotection. These deuterated fatty acids were then employed for kinetic analysis under multiple‐turnover conditions. The results indicate that the hydrogen abstraction at C8 is the rate‐determining step of the overall reaction because we observed a KIE (V_H/V_D) of ～33 at substrate saturation that suggests extensive nuclear tunneling contributions for hydrogen transfer. Deuteration of the substrate at C5, however, had little effect on V_H/V_D but resulted in a different product pattern presumably due to an altered lifetime and partitioning of a reaction intermediate.     

Adsorbate (substrate)-induced restructuring of active transition metal sites of heterogeneous and enzyme catalysts

Adsorbate-induced restructuring of transition metal surfaces and those of transition metal clusters embedded in metalloproteins has been shown to be a dominant phenomenon by LEED surface crystallography and X-ray crystallography studies, respectively. The restructuring is thermodynamically driven and is more facile for low-coordination metal sites (surface defects, steps and kinks, and nanoclusters). Dynamic restructuring of catalytically active transition metal sites may occur on the time scale of catalytic turnover or faster. The structural flexibility of transition metal surfaces and clusters embedded in enzymes could provide for seamless evolutionary changes of catalytic chemistry from inorganic to more complex and selective bio-organic systems.     

UV-cured fluorinated coatings for plastics: effect of the photoinitiator and of the substrate filler on adhesion

A high-performance fluorinated acrylic coating, containing perfluoropolyether chains, was applied to polyethylene and polypropylene by means of the UV-curing technique. The conditions for a good adhesion onto the plastic substrates were studied. A chemical bonding between the cured network and both the substrates was achieved when the photopolymerization was performed in the presence of benzophenone as a photoinitiator: by hydrogen abstraction from the substrate, polymer radicals were formed and could then initiate the polymerization of the acrylic species; grafting experiments of hydroxyethylacrylate confirmed this mechanism. However, the grafting reaction did not take place when the plastic substrates contained carbon black as a filler, which acted as a radical scavenger. In this case, in fact the adhesion results are not good, similar to those obtained in presence of a cleavage-type photoinitiator.     

Pheromone specificity inEriocrania semipurpurella (Stephens) andE. sangii (Wood) (Lepidoptera: Eriocraniidae) based on chirality of semiochemicals

The fifth abdominal segment of femaleEriocrania semipurpurella (Stephens) andE. sangii (Wood) contains a pair of exocrine glands. Hexane extracts of this segment were prepared from both species and analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). For both species, the EAD active peaks were identified as nonan-2-one, (Z)-6-nonen-2-one, and (Z)-6-nonen-2-ol by means of mass spectrometry and comparison of retention indices with those of synthetic standards. Enantiomeric separation of chiral alcohols from the female extracts was achieved by gas chromatographic analysis on a cyclodextrin column. InE. semipurpurella, a mixture of (2S,6Z)-nonen-2-ol and (2R,6Z)-nonen-2-ol (2: I) was found, whereas inE. sangii (2S,6Z)-nonen-2-ol was the predominant enantiomer and only traces of theR enantiomer were indicated by the antennal response. In field tests, a blend of the three compounds was not attractive to conspecific males. A subtractive assay showed that the alcohol in various enantiomeric mixtures was the only attractive compound, whereas addition of (Z)-6-nonen-2-one to the alcohol completely inhibited the attraction of both species. A trapping experiment including a wide range of ratios between theR andS enantiomers showed that baits containing 95–100% of theS enantiomer were attractive to maleE. sangii, whereas males ofE. semipurpurella were attracted to all tested ratios of the enantiomers. However, the response profiles of maleE. semipurpurella differed between populations from southern Sweden, south Finland, and the Kola Peninsula in Russia. In south Sweden males were maximally attracted to a racemic mixture of the alcohols. At the Kola PeninsulaE. semipurpurella was attracted to baits containing 95–100% of theR enantiomer. In south Finland all tested ratios between 0 and 100%R enantiomer trappedE. semipurpurella, but the trap catches appeared to be bimodally distributed with peaks around 15 and 70%R enantiomer. The trapping results suggest the existence of pheromone races or sibling species among the specimens identified asE. semipurpurella.Dedicated to Prof. H. J. Bestmann on the occasion of his 70th birthday.     

The influence of filler particles and polymer structure on the mobility of polymer molecules

The presence of carbon filler has been shown to cause a change in the glass transition temperature of polymers. For poly(vinyl chloride) and two of its copolymers with 10 and 15% vinyl acetate an increase in T_g was observed when Graphon C Carbon was added. The increase was greater when the proportion of vinyl acetate was greater. Polar vinyl acetate units allow stronger adsorption of polymer onto the carbon. Brittle polymers such as polystyrene and poly(methyl methacrylate) showed scattered T_g's when filled with carbon. The changes were not a function of concentration. It is postulated that the thermal stress of these polymers is increased in the presence of filler.     

含氟聚醚醚酮增韧环氧树脂相形貌与性能研究

采用SEM观察了热塑性含氟结构聚醚醚酮(6FPEEK)共混增韧环氧树脂的浇铸体脆断断口相形貌,测试了浇铸体的力学性能及动态机械性能,通过统计和数学分析建立了冲击韧性(αk)、热塑颗粒粒径(d)和粒间距(D)间的半定量关系。结果表明,该体系可得到连续相为环氧树脂而分散相为热塑颗粒的相结构,热塑相颗粒尺寸较为统一,且随热塑性树脂含量的增加而增大;6FPEEK含量增加对拉伸强度的影响不大,环氧树脂和热塑性塑料的结合界面差导致了冲击韧性在6FPEEK质量分数达到9.09%时出现峰值而后下降;该增韧体系的增韧机理可能为刚性粒子增韧。     

纳米颗粒对环氧树脂胶粘剂／钢铁附着强度的影响

采用纳米Al2O3、纳米CaCO3、纳米SiO2三种纳米颗粒,机械混合对环氧树脂胶粘剂进行改性,并对纳米颗粒改性的环氧树脂胶粘试样进行了附着强度的检测。结果发现,通过改变纳米颗粒的种类和含量,环氧胶粘剂／钢铁基体之间的附着强度得到不同程度的提高,其中添加2％纳米Al2O3颗粒的环氧胶粘剂与钢铁基体的附着强度提高了4倍左右。通过断面形貌特征和不同基体粗糙度下对添加纳米颗粒环氧胶与钢铁基体之间附着强度的检测,对此现象产生的原因进行了分析和讨论。     

Cryogenic relaxations of polystyrene and poly(fluorinated styrenes)

The effect of structural and morphologic modifications of styrene and fluorinated styrene polymers on their internal friction was studied by means of a free-oscillating torsional pendulum at temperatures from 300° to 4.2°K and frequencies of 1 to 2 Hz. Atactic and isotactic polystyrene gave the previously observed δ and β′ loss peaks at 38° and 100°K, respectively. These losses decrease in intensity with crystallinity in isotactic polystyrene but remain relatively unchanged in uniaxially drawn atactic polymer. Atactic polypentafluorostyrene showed an intense δ loss peak at 52°K and a broad shoulder around 100°K, which extends toward the β′ relaxation. In poly-α,β,β-trifluorostyrene, the δ loss peak is largely suppressed, the logarithmic decrement showing only broad maxima at 22° and 100°K. Plasticization of atactic polystyrene with 2% mineral oil gives rise to a sharp loss maximum at 100°K, which does not occur in the pure atactic polymer.     

The influence of the double layer field on the absorption spectrum of adsorbed molecules

The electrostatic interaction of the double layer field with optically absorbing admolecules can cause modulation reflectance spectra owing to the Stark effect and the dissociation field effect, respectively. The spectra depend on the state of polarization of incident light, the stationary electrode potential, the pH value and other parameters. From the results it could be concluded to the admolecular orientation, the field strength in the double layer and interfacial protonation. This is illustrated for some organic substances.     

Electroantennogram responses of the southern pine beetle parasitoidDinotiscus dendroctoni (Ashmead) (Hymenoptera: Pteromalidae) to potential semiochemicals

In two studies using the electroantennogram (EAG) technique, bark beetle- and tree-produced semiochemicals were presented toDinotiscus dendroctoni (Ashmead), a larval parasitoid ofDendroctonus frontalis Zimm. In the first study, 20 test compounds and a standard mixture of oxygenated monoterpenes were presented individually at one concentration to the parasitoids. In the second study, the nine compounds that elicited the greatest EAGs in study 1 were then tested as serial dilutions of 10 to 0.0001g/ul. The individual compounds did not elicit responses greater than the standard mixture of oxygenated monoterpenes. Males and females exhibited similar dose responses, although females showed lower thresholds of response than males to frontalin, terpinen-4-ol,E,Z-chalcogran, andexo-brevicomin. In both studies, pino-/isopinocamphone elicited the greatest responses at high concentrations. Tests of different ratios of the camphone mixture indicated that pinocamphone elicited the greatest response. Most of the test compounds elicited similar responses which suggests that several of the compounds may be used together byD. dendroctoni in habitat and/or host community location.     

Synthesis and properties of fluorinated polyimides and fluorinated poly(imide amide)s containing pendent cyano groups

A series of fluorinated polyimides and fluorinated poly(imide amide)s containing pendent cyano groups were prepared and investigated to determine their dielectric constants as a function of relative humidity and thermal characteristics. The fluorinated polymides and fluorinated poly(imide amide)s containing pendent cyano groups were prepared by reaction of bis(4-aminophenoxy) benzonitriles with a fluorinated dianhydride and with a fluorinated di(acid chloride) containing preformed imide rings. The properties of the fluorinated polyimides and fluorinated poly(imide amide)s containing pendent cyano groups were compared with those of fluorinated polyimides and fluorinated poly(imide amide)s prepared from 1,3-bis(4-aminophenoxy)benzene. The introduction of the pendent cyano groups caused an increase in the dielectric constant and an increase in the glass transition temperature of the polymers compared with the polymers prepared without pendent cyano groups.     

The influence of chromate quenching and chloride contamination level on the performance of the painted hot-dipped galvanized steel (duplex system)

The influences of the chromate quenching step and the surface chloride contamination levels of galvanized steel on the performance of duplex systems were studied. Steel panels were galvanized in a commercial steel bath adopting three different postdipping procedures. A comparative study of the galvanized steel, both painted and nonpainted, was performed by electrochemical techniques. It was verified that the chloride contamination level of the galvanized steel surfaces is the main cause of duplex system failures. An explanation for the influence of the chromate quenching on the performance of duplex systems was presented.     

The influence of a polymer substrate on the light fastness and isomerisation of some azo dyes

Poly(ethylene terephthalate) films having different morphologies have been coloured with some azo dyes. Isotropic and anisotropic films showed an inversion in dyeing behaviour as well as in light fastness, always at crystallinity β=0.5. We have interpreted the phenomenon in terms of a different localisation of the dye in going from a structure of PET corresponding to a free-volume model to a structure corresponding to a pore model. It was found that polymer morphology strongly affected dye photofading whilst the thermal cis-trans isomerisation of azo dyes in the PET matrix depended only on the amorphous region; below the glass transition temperature isomerisation proceeded in a way that was determined by the effects of restrictions in the mobility of the photochrome itself.     

Species discrimination in five species of winter-flying geometrids (Lepidoptera) based on chirality of semiochemicals and flight season

Enantiomer separation of (6Z,9Z)-cis-3,4-epoxynonadecadiene and (3Z,9Z)-cis-6,7-epoxynonadecadiene could be achieved using chiral high-resolution gas chromatography and a cyclodextrin-bond column. (3Z,9Z)-(6R,7S)-Epoxynonadecadiene was identified from ovipositor extracts ofColotois pen-Naria, while inErannis defoliaria the 6S,7R-enantiomer was found. In field trapping tests pure synthetic enantiomers caught only conspecific males of these species. (3Z,6Z,9Z)-Nonadecatriene was found in both species, while the presence of (3Z,6Z,9Z)-heneicosatriene was indicated inC. Pennaria only. A 10103 blend of (3Z,9Z)-(6R,7S)-epoxynonadecadiene, (3Z,6Z,9Z)-heneicosatriene, and (3Z,6Z,9Z)-nonadecatriene was found to be optimal for catchingC. Pennaria, whileE. Defoliaria males were optimally caught by a 11 mixture of (3Z,9Z)-(6S,7R)-epoxynonadecadiene and (3Z,6Z,9Z)-nona-decatriene. (6Z,9Z)-(3S,4R)-Epoxynonadecadiene was identified from ovipositor extracts ofAgriopis (Erannis) aurantiaria. In field tests the pure enantiomer proved to be a highly specific sex attractant for both the late autumn/early winter flyingA. Aurantiaria and the late winter/early spring flyingA. Leucophearia. Males ofAgriopis marginaria, which fly in late winter/early spring, were attracted to (3Z,9Z)-(6S,7R)-epoxynonadecadiene. The addition of (3Z,6Z,9Z)-nonadecatriene to theS,R-enantiomer increased captures. Optimal catches were recorded with a 103 epoxide-hydrocarbon blend. Enantiomer specificity in all species was confirmed in EAG measurements.     

Synthesis of 2'-aminoalkyl-substituted fluorinated nucleobases and their influence on the kinetic properties of hammerhead ribozymes

Hammerhead ribozymes are ribonucleic acids that catalyse the hydrolytic cleavage of RNA. They interfere with gene expression in a highly specific manner and recognize the mRNA target through Watson-Crick base pairing. To overcome the problem of point mutations (Watson-Crick "mismatches") occurring in viral genomes, we developed 2'-aminoethyl-substituted fluorinated nucleosides, which are universal nucleobases. The highly efficient synthetic pathway, which features a direct phthaloylamination of a primary alcohol under Mitsunobu conditions, leads to modified phosphoroamidites. The 1'-deoxy-1'-(4,6-difluoro-1H-benzimidazol-1-yl)-2'-(beta-aminoethyl)-beta-D-ribofuranose nucleoside analogue does not differentiate between the four natural nucleosides and leads to a RNA duplex that is as stable as the unmodified parent duplex. Upon incorporation into a ribozyme, the analogue's catalytic activity is equal for all four possible substrates, and the cleavage rates for the modified ribozymes are significantly higher (up to a factor of 13) than for the natural Watson-Crick "mismatch" base pairs. In agreement with the thermodynamic data obtained by measurement of the T(m) values of the RNA 12-mers, the cleavage rates for the 2'-substituted fluorinated benzimidazole derivative 4 are slightly higher than for the corresponding fluorinated benzene derivative 3.