饱和ATP为原料合成多级孔ZSM-5沸石分子筛的制备与表征

研究以饱和ATP吸附材料为合成沸石分子筛的硅源,采用双模板法,用四丙基氢氧化铵(TPAOH)为微孔模板剂和十六烷基三甲基溴化烷(CTAB)为介孔模板剂直接合成多级孔ZSM-5沸石分子筛,通过XRD、SEM、比表面积及孔径分析仪进行N2吸附-脱附等手段对多级孔ZSM-5沸石分子筛表征测试分析。结果表明,饱和ATP吸附材料在180℃下,水热提纯12 h获得硅源,再加入TPAOH和CTAB进行初始凝胶反应,后移入水热反应釜中,控温180℃,水热晶化反应15 h,即得多级孔ZSM-5沸石分子筛。     

饱和ATP为原料合成多级孔ZSM-5沸石分子筛的制备与表征

研究以饱和ATP吸附材料为合成沸石分子筛的硅源,采用双模板法,用四丙基氢氧化铵(TPAOH)为微孔模板剂和十六烷基三甲基溴化烷(CTAB)为介孔模板剂直接合成多级孔ZSM-5沸石分子筛,通过XRD、SEM、比表面积及孔径分析仪进行N2吸附-脱附等手段对多级孔ZSM-5沸石分子筛表征测试分析。结果表明,饱和ATP吸附材料在180℃下,水热提纯12 h获得硅源,再加入TPAOH和CTAB进行初始凝胶反应,后移入水热反应釜中,控温180℃,水热晶化反应15 h,即得多级孔ZSM-5沸石分子筛。     

Physicochemical characterization of some fully aromatic polyamides

The characterization of eight fully aromatic polyamides are described with the procedures required to yield film- and fiber-forming materials. Solutions of these aromatic polyamides in dimethylacetamide were characterized by NMR and the effects of dissolved lithium chloride on these spectra investigated. The NMR resonances for specific protons in these polymers are assigned. The IR spectra of thin films and fibers of these polyamides are also reported, together with glass transition temperatures as measured by differential scanning calorimetry (DSC). The value of NMR and IR to identify specific polyamide homopolymers and copolymers is discussed.     

Conversion of human 15-lipoxygenase to an efficient 12-lipoxygenase: the side-chain geometry of amino acids 417 and 418 determine positional specificity

Positional specificity determinants of human 15-lipoxygenasewere examined by site-directed mutagenesis and by kinetic analysisof the wild-type and variant enzymes. By comparing conserveddifferences among sequences of 12- and 15-lipoxygenases, a smallregion responsible for functional differences between 12- and15-lipoxygenases has been identified. Furthermore, the replacementof only two amino acids in 15-lipoxygenase (at 417 and 418 inthe primary sequence) by those found in certain 12-lipoxygenasesresults in an enzyme that has activity similar to 12-lipoxygenase.An examination of the activity of nine variants of lipoxygenasedemonstrated that the amino acid side-chain bulk and geometryof residues 417 and 418 are the key components of the positionalspecificity determinant of 15-lipoxygenase. Overexpression ofa variant (containing valines at positions 417 and 418) thatperforms predominantly 12-lipoxygenation was achieved in a baculovirus-insectcell culture system. This variant was purified to >90% homogeneityand its kinetics were compared with the wild-type 15-lipoxygenase.The variant enzyme has no change in its apparent K_M for arachidonicacid and a minor(3-fold) change in its V_max. For linoleic acid,the variant has no change in its K_M and a 10-fold reductionin its V_max, as expected for an enzyme performing predominantly12-lipoxygenation. The results are consistent with a model inwhich two amino acids of 15-lipoxygenase (isoleucine 417 andmethionine 418) constitute a structural element which contributesto the regiospecificity of the enzyme. Replacement of theseamino acids with those found in certain 12-lipoxygenases resultsin an enzyme which can bind arachidonic acid in a catalyticregister that prefers 12-lipoxygenation.     

Lactose-hydrolyzed milk powder: Physicochemical and technofunctional characterization

The objective of this work is to demonstrate the effect of operational drying parameters on the physicochemical and techno-functional properties of lactose-hydrolyzed milk powder (LHMP). LHMP showed water content superior to the control regardless of drying conditions, which is a direct result of the difficulties encountered in drying the product. For a lab-scale spray dryer, the LHMP produced at θ_air,in?=?145°C and m_CM?=?1.0?kg?·?h^?1 was the only sample that met all stipulated quality parameters: water content <5% (w/w), a_w?93, particle sizes similar to control, and complete rehydration.     

Physicochemical characterization of carrageenans—A critical reinvestigation

Kappa‐, iota‐, and lambda‐carrageenan (food grade) were analyzed by static light scattering (MALS in batch mode) in 0.1M NaNO₃ at 25 and 60°C, earlier heated up to 90°C or not. At 25°C, there was a strong tendency for a concentration‐dependent aggregation in the order lambda < kappa < iota. At 60°C, all samples were molecularly dispersed. The strongly temperature‐dependent refractive index increments (equilibrium dialysis) differ. Data interpretation in terms of the wormlike chain model using the Skolnik‐Odijk‐Fixman approach led to an intrinsic persistence length around 3 to 4 nm and expansion factors as high as 1.5 and above in a thermodynamically good solvent for all three types. Triple‐detector HPSEC (DRI, MALS, viscometry) on the three commercial samples plus a degraded (by acidic hydrolysis) kappa‐carrageenan in the same solvent/eluant at 60°C yielded a uniform and slightly curved [η]‐M relationship for 5 × 10³ ≤ M/(g mol) ≤ 3 × 10⁶ and a nearly identical molar mass dependence of the radius of gyration. HPSEC at 25°C on kappa‐carrageenan confirmed formation of soluble aggregates. Special emphasis was put on analytical and methodological aspects. The reliability of the experimental data was demonstrated by analogous measurements on dextran calibration standards. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Purification and characterization of a fatty acid binding protein from human prostatic tissue

Epidemiological studies suggest the existence of a strong relationship between the incidence of prostatic cancer and the intake of dietary lipids in humans. However, very little information is available on intracellular fatty acid metabolism in human prostatic tissue. The objective of this study was to identify and subsequently characterize a fatty acid binding protein of human prostatic tissue. A fatty acid binding protein (FABP) was purified and characterized from human prostatic tissue. The purified FABP had an apparent molecular mass of 15.0±1.0 kDa as averaged from three different methods, sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), gel filtration and amino acid analysis. The pI value of the protein was determined to be 6.8. Scatchard analysis of fatty acid binding to the purified FABP from malignant prostatic tissue showed a Kd value of 0.53±0.02 μM for arachidonic acid (n=5). The Kd values of FABP purified from benign prostatic tissue were 0.57±0.02 μM for oleic acid and 0.51±0.04 μM for arachidonic acid (n=5). Fatty acid analysis revealed that the level of endogenously bound arachidonic acid was about 2.5-fold higher in FABP from malignant than from benign tissue. In addition, both malignant and benign tissues contained the same concentration of FABP. The concentrations of FABP in malignant and benign tissues were 19.2±1.8 and 21.4±2.1 μg per mg of total cytosolic protein, respectively. Characterization based on amino acid composition, isoelectric point and fluorescence with dansyl undecanoic acid suggests that the FABP may not be of the heart type, but is rather more closely related to the liver type. As malignant prostatic tissue produces more PGE₂ compared to benign tissue, our data suggest that FABP may help enhancing the synthesis of the prostaglandin in malignant tissue by facilitating arachidonic acid transport. A preliminary account of this work was presented at the Biochemical Society Meeting, London, December 16–18, 1991, and published as an abstract (Ref. 1).     

Transformations of 5-HETE by activated keratinocyte 15-lipoxygenase and the activation mechanism

There is convincing evidence that normal cultured human keratinocytes possess a 15-lipoxygenase activity which, however, does not appear to manifest itself without cell membrane damage. When “activated”, this enzyme transforms arachidonic acid into 15-hydroxyeicosatetraenoic acid (15-HETE), and linoleic acid into 13-hydroxyoctadecadienoic acid, presumably by peroxidase action on their respective hydroperoxy intermediates. Normal but notmembrane-damaged keratinocytes metabolize exogenous 5-HETE, principally by esterifying the eicosanoid intact, primarily in the triacylglycerol fraction. In the present study, membrane-damaged keratinocytes were found to transform 5-HETE to 5,15-diHETE and also to a lipoxin-like group of tetraenes. Similar, if not identical, tetraenes were produced by action of the keratinocyte enzyme on 5(S),15(S)-diHETE, which points to the role of the latter as an intermediate between 5-HETE and the tetraenes. A direction for further study of the mechanism of the “activation” step is presented.     

Physicochemical characterization of lignins from rice straw by hydrogen peroxide treatment

Extraction of the dewaxed rice straw with 1% NaOH at 55°C for 2 h and following treatment without and with 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0% hydrogen peroxide (H₂O₂) at 45°C for 12 h at pH 11.5 resulted in a dissolution of 68.3, 85.4, 89.4, 92.3, 92.3, 94.3, and 95.1% of the original lignin, respectively. Meanwhile, the two‐stage treatment together solubilized 67.2, 77.2, 78.7, 83.7, 85.5, 87.3, and 88.5% of the original hemicelluloses and degraded 2.5, 9.8, 11.8, 12.1, 15.6, 16.4, and 17.8% of the original cellulose under the conditions given, respectively. Analyses of these lignins revealed that alkali‐soluble lignin fractions did not suffer sever oxidation, but nearly 60% of the original lignin was dissolved out during the first stage of alkali treatment. In the second stage of alkaline peroxide treatment, the residual lignins were substantially released and enriched in oxidized carbonyl and carboxyl groups. In comparison, the isolated eight pure lignin samples were further characterized by both destructive methods such as alkaline nitrobenzene oxidation and nondestructive techniques such as ultraviolet (UV), Fourier transform infrared (FTIR), and carbon‐13 magnetic resonance spectroscopy (¹³C‐NMR) as well as gel permeation chromatography (GPC), and the results are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 719–732, 2001     

Physicochemical characterization and dissolution enhancement of loratadine by solid dispersion technique

The purpose of this investigation was to enhance the dissolution rate of loratadine using polyethylene glycol 6000 (PEG) solid dispersions (SDs). The solubility behavior of loratadine in the presence of polyethylene glycol 4000 and polyethylene glycol 6000 in water showed linear increase with increasing concentrations of PEG, indicating A _L type solubility diagrams. SDs of loratadine with PEG 6000 were prepared at 1: 1, 1: 3, 1: 5, 1: 7 and 1: 9 ratios by the solvent evaporation method. Solid dispersions were characterized for drug content, dissolution behavior and for physicochemical characteristics. The dissolution rate of loratadine was enhanced rapidly with increasing concentrations of PEG 6000 in SDs. Fourier transform infrared (FTIR) studies showed the stability of loratadine and the absence of a well-defined loratadine — PEG 6000 interaction. Differential scanning calorimetry (DSC) and X-ray powder diffractometry (XRD) studies revealed the amorphous state of loratadine in SDs of loratadine with PEG 6000 which was further confirmed from scanning electron microscopy (SEM) studies. The flow properties of the blend, physical characteristics and disintegration time of the tablets formulated indicated that PEG 6000 SD can be used to formulate fast release loratadine tablets.     

Site-directed mutagenesis of aspartic acid 372 at the ATP binding site of yeast phosphoglycerate kinase: over-expression and characterization of the mutant enzyme

A new phosphoglycerate kinase over-expression vector, pYE-PGK,has been constructed which greatly facilitates the insertionand removal of mutant enzyme genes by cleavage at newly introducedBamtHI sites. This vector has been used to prepare mutant proteinin appreciable (100 mg) quantities for use in kinetic, crystaUographicand NMR experiments. Aspartate 372 is an invariant amino acidresidue in genes known to code for a functionally active PGK.The function of this acidic residue appears to be to help desolvatethe magnesium ion compfexed with either ADP or ATP when thissubstrate binds to the enzyme. Both crystallographk and nuclearmagnetic resonance experiments show that the replacement ofthe residue with asparagine has only minimal effects on theoverall structure. The substitution of the charged carboxylgroup with that of the neutral amide affects the binding ofthe nucleotide substrate as predicted but not, as might havebeen expected, the binding of 3-phospho-glycerate. The overallvelocity of the enzymic reaction (V_max) is reduced 10-fold bythe substitution of aspartic acid 372 by an asparagine residue(D372N). This reduction in V_max is considerably less than onewould expect from its known position within the structure ofthe enzyme. This result therefore poses questions about ourunderstanding of charged groups at the active centres of enzymesand of the reason for their apparent conservation.     

磷改性ZSM-5分子筛物化性质和裂解制乙烯性能的研究

The physicochemical features of phosphorus-modified ZSM-5 zeolites (SiO2/Al2O3 molar ratio is 25) were characterized by XRD(X-ray diffraction), BET(Brunauer, Emmett and Teller spcific surface area measurement), NH3-TPD(ammonia temperature-programmed desorption) and MASNMR(magic angle spinning nuclear magnetic resonance), and the performance on catalytic pyrolysis to produce ethylene was investigated with a light hydrocarbon fixed bed micro-reactor with n-octane as feed. The results show that the acid site density, acid intensity and hydrothermal stability of ZSM-5 zeolite were improved by phosphorus modification. When P205 content in ZSM-5 zeolite is higher than 2.5%, phosphorus modification can prevent ZSM-5 zeolite crystal structure transformation from orthorhombic to monoclinic. In addition, the dealumination of ZSM-5 zeolite framework was moderated by phosphorus modification under high temperature hydrothermal treatment. The results of n-octane pyrolysis on phosphorus-modified ZSM-5 zeolites show that ethylene yields of zeolites with different phosphorus content are almost the same under the same n-octane conversion. However, the modified zeolites with higher pyrolysis activity give lower yield of propene, butene and total olefin than lower pyrolysis activity under the same n-octane conversion.     

Physicochemical approach to nanobubble solutions

Small bubbles of nitrogen, methane, or argon with an average radius of 50 nm, as measured by scanning electron microscopy, were prepared under atmospheric conditions. The lifetime of the nanobubbles extended to more than two weeks. The total amount of gases in the nanobubble solutions reached 600 cm³ per 1 dm³ of water, and the liquid density was about 0.988 g/cm³. The internal pressure of the nanobubbles was estimated to be 6 MPa. The number of nanobubbles was 1.9×10¹⁶ bubbles per 1 dm³ of water. These findings show that almost no gas samples are dissolved homogeneously in the aqueous solution and that the vast majority is present in the form of nanobubbles, that is, nanobubbles should be thermodynamically unstable. Attenuated total reflectance infrared spectroscopy showed that the surfaces of the nanobubbles contain hard hydrogen bonds that may reduce the diffusivity of gases through the interfacial film.     

Physicochemical characterization and antioxidant activity of quercetin‐loaded chitosan nanoparticles

Quercetin is an abundant flavonoid in food plants with numerous biological activities and widely used as a potent antioxidant. Being sparingly soluble in water and subject to degradation in aqueous intestinal fluids, the absorption of quercetin is limited upon oral administration. In the present study, chitosan nanoparticles and quercetin‐loaded nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. The encapsulation of quercetin in the chitosan nanoparticles were confirmed by differential scanning calorimetry, X‐ray powder diffractometry, Fourier transformed infrared spectroscopy, ultraviolet‐visible spectrum, and fluorescence spectrum. The morphology of the nanoparticles was characterized by atomic force microscopy. The antioxidant activity of the quercetin‐nanoparticles was also evaluated in vitro by two different methods (free radical scavenging activity test and reducing power test), which indicates that inclusion of quercetin in chitosan nanopaticles may be useful in improving the bioavailabilty of quercetin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Physicochemical characterization of alloy of polyimide with varying degree of crosslinking through diisocyanates

Polyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components and followed by thermal imidization. The blend components can be synthesized by the reaction of polyamic acid with the varying concentration of crosslinker [here methylene bis (4-phenyl isocyanate or MDI)] from 1.54 × 10^?2 mol/L (i.e. hypothetically calculated critical crosslinker concentration or CCC) to 1.54 × 10^?6 mol/L. This communication discusses the synthesis and characterization of polyimide (PI) blends and alloys prepared by varying degrees of crosslinking introduced via isocyanate-amic acid reaction. The polyimides were prepared by thermally imidizing the polyamic acid blends at different curing temperatures from 50°C to 350°C. The degree of imidization and residual solvent content for blends having varying mole fractions of crosslinked (or branched) and uncrosslinked components and two extreme conditions and at specified temperature-time profiles have been studied. The resultant PI-MDI blends have exhibited synergism on mechanical properties. The improvement in mechanical properties, however, was significantly higher at the lower imidization temperature (i.e. 50°C to 150°C). The feasibility of preparing polyimide alloys with synergistic combinations of crosslinked and uncrosslinked polyimide components was inferred.     

Physicochemical characterization of actinomycetes isolated from decayed cedar wood: contact angle measurement

Physicochemical characterization of microorganism is very important in a wide range of scientific and technological fields. In this study, we reported the isolation and the molecular identification of actinomycetes recovered from cedar wood decay. The isolates named H5 and H8 were identified by 16S rDNA sequencing and were shown to belong to the genus Nocardia and Streptomyces, respectively. Furthermore, physicochemical proprieties including hydrophobicity, electron donor/acceptor, and the Lifshitz–van der Waals (γ^LW) of these strains were evaluated using contact angle measurements. The results showed that Nocardia sp. (H5) had a hydrophobic (ΔGiwi?=??78.56?mJ/m²) and a weak electron donor/acceptor character. In contrast, results from contact angle measurements showed that the surface free energy of Streptomyces strains (H2, H3, and H8) were ΔGiwi?=?20.71?mJ/m², ΔGiwi?=?30.63?mJ/m², and ΔGiwi?=?15.35?mJ/m², respectively, classifying these microorganisms as hydrophilic bacterium. Moreover, the three strains were predominantly electron donating (γ^–?) and exhibit a weak electron-accepting (γ⁺) character.     

Physicochemical characterization of hydrogels based on polyvinyl alcohol–vinyl acetate blends

Hydrogels made of polyvinyl alcohol–vinyl acetate and its blends with water soluble polymer were studied in terms of swelling behavior, microstructure, and dynamic mechanical properties. Hydrogels prepared by blending polyvinyl alcohol–vinyl acetate with either polyacrylic acid or poly(4‐vinyl pyridine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was used for blending, an unusual pH dependency was observed. An increase in the equilibrium water content in all systems resulted in an increase in the freezable water as determined by DSC. Critical point drying led to a striated surface on polyacrylic acid–polyvinyl alcohol–vinyl acetate hydrogels, whereas a porous structure was observed on the freeze‐dried poly(vinyl pyrrolidone)–polyvinyl alcohol–vinyl acetate gels. Hydrogels with elevated storage modulus were obtained when either polyvinyl alcohol–vinyl acetate alone or polyacrylic acid–polyvinyl alcohol–vinyl acetate blends were thermally treated at high temperatures (i.e., 150°C). Low storage modulus was observed for both poly(vinyl pyrrolidone) and poly(4‐vinyl pyridine)‐containing hydrogels. Temperature dependency of storage modulus from 20 to 60°C was observed only for poly(4‐vinyl pyridine)–polyvinyl alcohol–vinyl acetate hydrogels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3578–3590, 2001