Biosilicification takes place at or very close pH 7.0 and under ambient conditions of temperature and pressure in vivo. The silicic acid transporters and the proteins facilitating biosilicification in diatoms have been identified. Silica synthesis under mild conditions in vitro has been demonstrated using synthetic polymers with control over the resulting silica morphology. The results presented herein show that the silica synthesis in vitro is not specific to particular enzymes/polypeptides due to their particular chemical structure and activity but that many other synthetic macromolecules are also capable of facilitating silica formation at neutral pH. We also report the synthesis of organic-inorganic hybrid materials that have potential in optoelectronic applications. 相似文献
We report herein the synthesis of well-defined silica structures atneutral pH and ambient conditions using poly(allylamine hydrochloride)(PAH), a cationically charged synthetic polymer, as a catalyst/template.Tetramethoxysilane (TMOS) was used as the precursor and the synthesisprocess parameters varied include TMOS pre-hydrolysis time(tP), reaction time (tR), buffer, molecular weightof the polymer, TMOS concentration, polymer concentration andperturbation of the reaction mixture. It was found that the TMOSpre-hydrolysis time was an important parameter governing the resultingsilica morphology along with the reaction time and the TMOSconcentration. Characterization of the silica was performed using SEM,FTIR, EDS and XRD. The poly(allylamine hydrochloride), which was thecatalyst/template, was found to be incorporated into the silicaparticles. These findings are of importance for understanding the roleof polypeptides, in nature, and macromolecules, in general, that arecapable of forming similar silica structures. 相似文献
The present work describes the preparation and characterization of polyelectrolyte coatings of poly-l-lysine (PLL) to modify a glassy carbon electrode and its application to the pre-accumulation of nitroprusside (NP). The effects
of the coating on the electrochemical reduction of NP were investigated. The performance of the modified electrode indicates
that the drug can be immobilized by electrostatic interaction and the voltammetric signal monitored at all pH values in the
range of 2–12. The strong interaction between NP and PLL stabilizes the complex on the electrode surface and minimizes the
chemical reaction of lost CN− ions as a subsequent reaction of electron transfer, which could improve the action mechanism of NP. 相似文献
Numerous microcapsule systems have been developed for a wide range of applications, including the sustained release of drugs,
cell transplantation for therapy, cell immobilization, and other biotechnological applications. Despite the fact that microcapsule
membrane is a dominant factor governing overall microcapsule performance, its characterization is challenging. We report a
new method for characterizing microcapsule membranes, using the most common alginate-poly-l-lysine-alginate (APA) microcapsule as an example. Our data demonstrate that genipin, a naturally derived reagent extracted
from gardenia fruits, interacts with poly-l-lysine (PLL) and generates fluorescence. This fluorescence allows clear visualization and easy analysis of the PLL membrane
in the APA microcapsules using confocal laser scanning microscopy. The results also show that PLL binding correlates to the
reaction variables during PLL coating such as PLL concentration and coating time. In addition, five other different microcapsule
formulations consisting of PLL and/or chitosan membranes were examined, and the results imply that this method can be extended
to characterize a variety of microcapsule membranes. These findings suggest that genipin can serve as a fluorogenic marker
for rapid characterization of microcapsule membranes, a superior method that would have important implications for microcapsule
research and potential in many other applications. 相似文献
The conformation of poly(l-lysine) (PLL) was investigated in sodium alkanesulfonate CnSO3Na (n=8, 7) at various temperatures by circular dichroism spectrum measurements. C8SO3Na induced a double-step conformational change from a coil, to a β-sheet, and then to an α-helix, in which C7SO3Na induced a single-step coil-to-helix conformational change. Binding isotherms of C8SO3Na by PLL were constructed from the potentiometry of equilibrium concentration of the surfactant using a surfactant ion-selective electrode. The curves indicated the cooperative binding characteristic and were analyzed by a linear lattice model using the Bethe approximation. The thermodynamic parameters obtained from the model revealed that the binding of C8SO3Na by PLL was an entropy-driven process. The conformational change was observed at nearly full binding, presumably due to the surfactant clustering of the ordered conformation. 相似文献
Elastomers typically require the incorporation of reinforcing fillers in order to improve their mechanical properties. For commercial silicone systems silica and titania are typically used as fillers. Fumed and precipitated silica are made on an industrial scale for many applications; however, we have shown recently that biological and synthetic macromolecules can generate new silica structures using a bioinspired route. Herein we have incorporated bioinspired silica fillers into poly(dimethylsiloxane) (PDMS) elastomers and investigated their mechanical, morphological and thermal properties as a function of filler loading. The equilibrium stress-strain characteristics of the PDMS-bioinspired silica hybrids were determined as a function of bioinspired filler loading and the Mooney-Rivlin constants (2C1 and 2C2) were calculated. The thermal characteristics, in particular glass transition temperatures (Tg) and melting points (Tm), of the PDMS-bioinspired silica hybrids were characterized using differential scanning calorimetry (DSC). The thermal stability of these hybrid materials were investigated using thermogravimetric analysis (TGA). The morphology of the samples was characterized using scanning electron microscopy (SEM), and the filler dispersion was characterized using ultra small angle X-ray scattering (USAXS) and scanning electron microscopy (SEM). Although spherical silica particles were used here, we have demonstrated elsewhere that this bioinspired synthetic route also enables highly asymmetric silica structures to be prepared such as fibres and sheets. This methodology therefore offers the interesting possibility of preparing new hybrid systems where the properties are highly anisotropic. 相似文献
The polymerization of o-phenylenediamine (OPD) on l-tyrosine (Tyr) functionalized glassy carbon electrode (GCE) and its electro-catalytic oxidation towards ascorbic acid (AA)
had been studied in this report. l-Tyrosine was first covalently grafted on GCE surface via electrochemical oxidation, which was followed by the electrochemical
polymerization of OPD on the l-tyrosine functionalized GCE. Then, the poly(o-phenylenediamine)/l-tyrosine composite film modified GCE (POPD-Tyr/GCE) was obtained. X-ray photo-electron spectroscopy (XPS), field emission
scanning electron microscope (SEM), and electrochemical techniques have been used to characterize the grafting of l-tyrosine and the polymerization and morphology of OPD film on GCE surface. Due to the doping of the carboxylic functionalities
in l-tyrosine molecules, the POPD film showed good redox activity in neutral medium, and thus, the POPD-Tyr/GCE exhibited excellent
electrocatalytic response to AA in 0.1 mol l−1 phosphate buffer solution (PBS, pH 6.8). The anode peak potential of AA shifted from 0.58 V at GCE to 0.35 V at POPD-Tyr/GCE
with a greatly enhanced current response. A linear calibration graph was obtained over the AA concentration range of 2.5 × 10−4–1.5 × 10–3 mol l−1 with a correlation coefficient of 0.9998. The detection limit (3δ) for AA was 9.2 × 10−5 mol l−1. The modified electrode showed good stability and reproducibility and had been used for the determination of AA content in
vitamin C tablet with satisfactory results. 相似文献
DNA complexes with cationic polymers (polyvinylamine (PVA), polyallylamine (PAA), polydimethylaminoethylmethacrylate (PDMAEM),
poly-(N,N,N-trimethylammonio)ethyl methacrylate chloride (PTMAEM), poly-l-lysine (PLL)) were investigated. It was shown that volume and persistent length of DNA do not change essentially at low cationic
polymer concentration in a solution. DNA packaging in 0.005 M NaCl was observed at charge ratio N/P ≈ 1. Secondary DNA structure
in complexes was not disrupted, and DNA was protected from protonation. The comparison between DNA packaging in complexes
with polycations and DNA condensation induced by trivalent ions was made. 相似文献
Summary In recent decades several methods have been developed for determination of the proportion of nitrogen-containing substances
passed from the rumen into the abomasum, or small intestine, which are of microbial origin. Recently, when examining thed-amino acid content of foodstuffs, particularly milk and milk products, it was observed that, in addition tod-alanine (d-Ala,d-glutamic acid (d-Glu) andd-aspartic acid (d-Asp) can also be detected in similar quantities, primarily in products which have links with bacterial activity. This gave
rise to the idea of examining the diaminopimelic acid (DAPA),d-Glu, andd-Asp content of bacteria extracted from the rumen of cattle, and that of chyme from the same cattle, to establish whetherd-Asp andd-Glu can be used to estimate protein of bacterial origin.
The investigations performed have provided evidence that bothd-Asp andd-Glu might be appropriate for determination of protein of bacterial origin. The results obtained using these two bacterial
markers (d-Asp andd-Glu) proved to the approximately 10% lower than those obtained using DAPA; this was not because of to error attributable
to the new markers but rather to the unreliability of determination using DAPA Analyses performed on samples of known bacterial
protein content indicate thatd-Asp andd-Glu gave almost identical results for bacterial protein content which were very close to the theoretical (calculated) values.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001. 相似文献
An enzymatic method for determining L-malic acid in wine based on an L-malate sensing layer with nicotinamide adenine dinucleotide (NAD+), L-malate dehydrogenase (L-MDH) and diaphorase (DI), immobilized by sol-gel technology, was constructed and evaluated. The sol-gel glass was prepared
with tetramethoxysilane (TMOS), water and HCl. L-MDH catalyzes the reaction between L-malate and NAD+, producing NADH, whose fluorescence (λexc = 340 nm, λem = 430 nm) could be directly related to the amount of L-malate. NADH is converted to NAD+ by applying hexacyanoferrate(III) as oxidant in the presence of DI. Some parameters affecting sol-gel encapsulation and the
pH of the enzymatic reaction were studied. The sensing layer has a dynamic range of 0.1–1.0 g/L of L-malate and a long-term storage stability of 25 days. It exhibits acceptable reproducibility [sr(%)≈10] and allows six regenerations. The content of L-malic acid was determined for different types of wine, and polyvinylpolypyrrolidone (PVPP) was used as a bleaching agent
with red wine. The results obtained for the wine samples using the sensing layer are comparable to those obtained from a reference
method based on UV-vis molecular absorption spectrometry, if the matrix effect is corrected for. 相似文献
A modified synthetic boundary experiment of analytical ultracentrifugation has been employed to examine, on-line, polyelectrolyte complex formation at flat interfaces yielding highly swollen membranes/networks. Systematic experiments with sodium alginate as a polyanion and chitosan and poly(l-lysine) as polycations identified the influence of concentration, pH, molar mass, and polycation type on the membrane characteristics and the formation process. The membranes have been evaluated by five characteristics defined herein: total thickness, compactness, heterogeneity, symmetry, and growth. The results confirm the sensitivity of the method suited to elaborate general relationships for polyelectrolyte membrane design. 相似文献
A facile method for the shape-selective synthesis of silica nanostructures using a reversemicroemulsion -mediated template(RMMT) technique is reported.In this method,positive poly-Llysine (PLL) is selected as template due to its configuration diversity.By adjusting pH and concentration, PLL demonstrates various secondary structures containing random coil,α-helix andβ-sheet,which result in the formation of silica nanorods,silica nanospheres and silica nanotubes in the reversemicroemulsion system,respectively.Thus,the shape-selective synthesis of silica nanostructures might be achieved by using PLL as structural template in the reverse-microemulsion system. 相似文献
This work represents a continuation of our investigation into environmental conditions that promote lactic acid synthesis
by Zymomonas mobilis. The characteristic near theoretical yield of ethanol from glucose by Z. mobilis can be compromised by the synthesis of d- and l-lactic acid. The production of lactic acid is exacerbated by the following conditions: pH 6.0, yeast extract, and reduced
growth rate. At a specific growth rate of 0.048/h, the average yield of dl-lactate from glucose in a yeast extract-based medium at pH 6.0 was 0.15 g/g. This represents a reduction in ethanol yield
of about 10% relative to the yield at a growth rate of 0.15/h. Very little lactic acid was produced at pH 5.0 or using a defined
salts medium (without yeast extract) Under permissive and comparable culture conditions, a tetracycline-resistant, d-ldh negative mutant produced about 50% less lactic acid than its parent strain Zm ATCC 39676. d-lactic acid was detected in the cell-free spent fermentation medium of the mutant, but this could be owing to the presence
of a racemase enzyme. Under the steady-state growth conditions provided by the chemostat, the specific rate of glucose consumption
was altered at a constant growth rate of 0.075/h. Shifting from glucose-limited to nitrogen-limited growth, or increasing
the temperature, caused an increase in the specific rate of glucose catabolism. There was good correlation between an increase
in glycolytic flux and a decrease in lactic acid yield from glucose. This study points to a mechanistic link between the glycolytic
flux and the control of end-product glucose metabolism. Implications of reduced glycolytic flux in pentose-fermenting recombinant
Z. mobilis strains, relative to increased byproduct synthesis, is discussed. 相似文献
Our recent work concerning the synthesis, characterisation and testing of bioinspired electron transfer catalysts is described
in this contribution. The catalysts were various Cu(II) complexes having mixed C- or N-protected amino acids (l-histidine and l-tyrosine) as ligands covalently grafted onto surface-modified silica gel. The resulting materials were structurally characterised
by FT-IR spectroscopy, and their superoxide dismutase activities were tested. The covalently anchored Cu(II) complexes displayed
appreciable activities in the test reaction; thus, they may be considered as promising candidates as durable electron transfer
catalysts approaching the efficiency of the enzyme mimicked. 相似文献
Substrate selectivity of Gluconobacter oxydans (ATCC 9937) for 2,5-diketo-d-gluconic acid (2,5-DKG) production was investigated with glucose, gluconic acid, and gluconolactone in different concentrations
using a resting-cell system. The results show that gluconic acid was utilized favorably by G. oxydans as substrate to produce 2,5-DKG. The strain was coupled with glucose dehydrogenase (GDH) and 2,5-DKG reductase for synthesis
of 2-keto-l-gulonic acid (2-KLG), a direct precursor of l-ascorbic acid, from glucose. NADP and NADPH were regenerated between GDH and 2,5-DKG reductase. The mole yield of 2-KLG of
this multienzyme system was 16.8%. There are three advantages for using the resting cells of G. oxydans to connect GDH with 2,5-DKG reductase for production of 2-KLG: gluconate produced by GDH may immediately be transformed into
2,5-DKG so that a series of problems generally caused by the accumulation of gluconate would be avoided; 2,5-DKG is supplied
directly and continuously for 2,5-DKG reductase, so it is unnecessary to take special measures to deal with this unstable
substrate as it was in Sonoyama’s tandem fermentation process; and NADP(H) was regenerated within the system without any other
components or systems. 相似文献
Anionic polypeptide, the poly(sodium L-glutamate), was applied to fabricate microporous silica hollow nanospheres templated by the secondary structures of the polypeptide as porogens. In the synthesis, 3-aminopropyltrimethoxysilane (APMS) and tetraethyl orthosilicate (TEOS) were used as the silica sources, and the coassembly followed the mechanism of the anionic surfactant-templated mesoporous silica (AMS) through a S-N+-I- pathway, where S indicates the anionic polypeptide, I indicates inorganic precursors (TEOS), and N indicates costructure-directing agent (APMS), which interacted with the negatively charged anionic polypeptide secondary structures electrostatically and cocondensed with silica source to form the silica framework. The product was subjected to characterizations of X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetric (TG) analysis, scanning electron microscopy (SEM), transmitted electron microscopy (TEM), and nitrogen adsorption-desorption measurement. It was found that the pH value of the synthesis solution was an important factor to the morphological control of the silica products. Besides the microporous hollow nanospheres, microporous submicron silica solid and hollow spheres were also obtained facilely by changing the synthesis parameters. Our study further implied that anionic polypeptides, which were able to control mineralization of calcium carbonate and calcium phosphate, could also induce silica condensation in the presence of proper silica precursors. It was also expected that functional calcium carbonate (phosphate)/silica-nanocomposite materials would be fabricated under the control of the anionic polypeptide. 相似文献
Mushroom tyrosinase was immobilized on modified polystyrene—polyaminostyrene (PSNH) and polymethylchloridestyrene (PSCL)—to
produce l-DOPA from l-tyrosine. Glutaraldehyde was used as an activating agent for the PSNH to immobilize the tyrosinase and 10% (w/v) glutaraldehyde
was optimal in conferring the highest specific activity (11.96 U/g) to the PSNH. Methylchloride on the PSCL was directly linked
with the tyrosinase, and 1.5 mmol of Cl/g was optimal in attaining the specific activity of 17.0 U/g. The temperature and
optimal acidity were, respectively, 60°C and pH 5.5 for the PSNH, and 70°C and pH 3.0 for the PSCL. In a 50-mL batch reactor
working over 36 h, the l-DOPA production rate at 30°C was 1.44 mg/(L·h) for the PSNH and 2.33 mg/(L·h) for the PSCL. The production rate over 36 h
was 3.86 mg/(L·h) for the PSNH at 60°C and 5.54 mg/(L·h) for the PSCL at 70°C. Both of the immobilized enzymes showed a remarkable
stability with almost no change in activity after being stored wet. The operational stability study indicated a 22.4% reduction
in l-DOPA production for the PSNH and an 8.63% reduction for the PSCL over seven runs (each run was for 144h at 30°C) when the
immobilized enzymes were used under turnover conditions. The immobilized tyrosinase was more stable on the PSCL than on the
PSNH. 相似文献
Polyelectrolyte multilayer (PEM) coatings on biomaterials are applied to tailor adhesion, growth, and function of cells on biomedical implants. Here, biogenic and synthetic polyelectrolytes (PEL) are used for layer‐by‐layer assembly to study the osteogenic activity of PEM with human osteosarcoma MG‐63 cells in a comparative manner. Formation of PEM is achieved with biogenic PEL fibrinogen (FBG) and poly‐l ‐lysine (PLL) as well as biotinylated chondroitin sulfate (BCS) and avidin (AVI), while poly(allylamine hydrochloride) (PAH) and polystyrene sulfonate (PSS) represent a fully synthetic PEM used as a reference system here. Surface plasmon resonance measurements show highest layer mass for FBG/PLL and similar for PSS/PAH and BCS/AVI systems, while water contact angle and zeta potential measurements indicate larger differences for PSS/PAH and FBG/PLL but not for BCS/AVI multilayers. All PEM systems support cell adhesion and growth and promote osteogenic differentiation as well. However, FBG/PLL layers are superior regarding MG‐63 cell adhesion during short‐term culture, while the BCS/AVI system increases alkaline phosphatase activity in long‐term culture. Particularly, a multilayer system based on affinity interaction like BCS/AVI may be useful for controlled presentation of biotinylated growth factors to promote growth and differentiation of cells for biomedical applications.