Evaluation of Binding Between Electroactive Biotin Derivative and Streptavidin Immobilized on Chitin Film

Evaluation of the streptavidin‐biotin binding at the surface of chitin film was carried out with voltammetry. Immobilization of streptavidin was attempted to the protonated chitin film, based on an electrostatic interaction that hardly causes any change in the protein structure. The streptavidin‐biotin binding was estimated from changes in the electrode response of biotin labeled with an electroactive compound. Although the response of daunomycin as an electroactive compound did not change at an electrode covered with streptavidin/chitin film, the response of the labeled biotin decreased. This observation shows that streptavidin is immobilized on the chitin film and the biotin binds with immobilized streptavidin. Consequently, it was clear that the chitin film is useful as a reaction field for protein‐ligand binding. Generally, a binding event between protein and its ligand in the living body occurs on the cell surface. The electrochemical evaluation of protein‐ligand binding on a natural polysaccharide like chitin membrane surface is important.     

Selective Synthesis of Oligosaccharides by Mechanochemical Hydrolysis of Chitin over a Carbon-Based Catalyst

Oligosaccharides possess fascinating functions that are applicable in a variety of fields, such as agriculture. However, the selective synthesis of oligosaccharides, especially chitin-oligosaccharides, has remained a challenge. Chitin-oligosaccharides activate the plant immune system, enabling crops to withstand pathogens without harmful agrichemicals. Here, we demonstrate the conversion of chitin to chitin-oligosaccharides using a carbon catalyst with weak acid sites and mechanical milling. The catalyst produces chitin-oligosaccharides with up to 94 % selectivity in good yields. Monte-Carlo simulations indicate that our system preferentially hydrolyzes larger chitin molecules over oligomers, thus providing the desired high selectivity. This unique kinetics is in contrast to the fact that typical catalytic systems rapidly hydrolyze oligomers to monomers. Unlike other materials carbons more strongly adsorb large polysaccharides than small oligomers, which is suitable for the selective synthesis of small oligosaccharides.     

UV-vis-infrared optical and AFM study of spin-cast chitosan films

Optical properties of spin-cast chitosan films have been determined in the infrared, visible, and ultraviolet region of the spectrum using spectroscopic ellipsometry. Optical constants for the UV–vis–near IR spectra from 130 to 1700 nm were determined using Cauchy dispersion forms combined with Lorentzian oscillator models in the absorptive shorter wavelength regions. Infrared index of refraction and extinction coefficients from 750 to 4000 cm⁻¹ were determined using ellipsometric data fits to dispersion models based on harmonic oscillators. This modeling determined that optical anisotropy was present and measurable over all wavelength regions of ellipsometric data.

To obtain information on the micro- and nano-scale surface structure, tapping mode atomic force microscopy (AFM) imaging was employed to determine morphology and roughness information of dry spin-cast chitosan films.     

Chitin Extraction and Synthesis of Chitin-Based Polymer Films from Philippine Blue Swimming Crab (Portunus pelagicus) Shells

Chitin has been extracted from Philippine blue swimming crab. The extracted chitin was subjected to thermo gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis The degree of acetylation of the extracted chitin, derived from the X-ray diffraction intensity values of chitin characteristic peaks, revealed that the extracted chitin is purer than the commercially acquired high purity chitin. The extracted chitin was used to form polymer films at different formation conditions. Polymer films were also formed from commercially acquired chitin for comparison. It was shown that films prepared from the extracted chitin at different conditions have greater ultimate tensile strengths as compared to the commercially-available plastic film. Morphologies of the material surface and the fracture surface were investigated using the scanning electron microscope to identify stress concentration sites that contributed to the weakening of material under tensile loading.     

A3B5 nanowhiskers: MBE growth and properties

The structural properties of GaAs nanowhiskers (NWs) grown by molecular beam epitaxy (MBE) are investigated. Under optimal growth conditions, the aspect ratio of MBE grown GaAs NWs is higher than 100. The maximum length of NWs is several times (up to 10) larger than the effective thickness of deposited GaAs. A kinetic model of the diffusion-induced NW rowth is used to predict the dependence of NW length on the technologically controlled MBE growth conditions. The obtained results demonstrate that the NW growth is controlled by the adatom diffusion towards their tip rather than by the conventional vapor-liquid-solid mechanism. The growth conditions influence on the NW morphology may be used for the controlled fabrication of NWs by MBE for different applications. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.     

多糖类生物医用材料—甲壳素和壳聚糖的研究及应用

对甲壳素和壳聚糖的制备工艺,结构与性质以人在固定化酶、药物控释载体、絮凝剂、吸附剂、医用敷料等方面的应用进行了综述。     

家蚕蛹皮制取壳聚糖的最佳工艺条件

以蛹皮为原料制取了壳聚糖,并采用正交试验法研究了氢氧化钠处理浓度、处理时间、温度及甲壳质与氢氧化钠溶液配比这四个因素对壳聚糖脱乙酰度的影响,结果表明,氢氧化钠浓度是影响甲壳质脱乙酰基的最主要因素,处理温度次之,处理时间和甲壳质与氢氧化钠溶液配比对壳聚糖脱乙酰度没有影响。通过方差分析,得到甲壳质脱乙酰基的最佳工艺条件是氢氧化钠处理浓度为50％,时间为16h,温度为95℃,甲壳质与氢氧化钠溶液配比为1：10。     

Insight into the adsorption of dyes onto chitin in aqueous solution: An experimental and computational study

This study aimed to get an insight into the adsorption of three synthetic dyes onto chitin using experimental and computational approaches. The successful preparation of α-chitin was confirmed using the Fourier Transform Infrared (FTIR) and X-ray Diffraction (XRD). In addition, the presence of porous and fiber on the surface of the extracted chitin was revealed by the Scanning Electron Microscopy (SEM) analysis. The extracted α-chitin was then used as an adsorbent to remove synthetic dyes, namely Malachite green, Basic red 18, and Alizarin yellow R. The kinetic study showed that the adsorption of dyes was well-described using a pseudo-second-order model, whereas the isotherm adsorption obeyed the Freundlich model. The Frontier Molecular Orbital (FMO) revealed several locations of dyes and chitin molecules that are potentially active sites for adsorption. The adsorption trend could be related to the Highest Occupied Molecular Orbital (HOMO) – Lowest Unoccupied Molecular Orbital (LUMO) energy gap and electrophilicity index of the dyes. The Conductor-like Model for Real Solvent (COSMO-RS) model demonstrated, for the first time, that several interactions occurred during the adsorption of dyes onto α-chitin. For the Malachite green and Basic Red 18, the Van der Waals forces of the dyes controlled its adsorption behavior. In contrast, the hydrogen bonding interaction governed the adsorption behavior of Alizarin yellow R dye onto α-chitin. The gathered insight from this work might guide us better to understand the molecular level of dyes–chitin interactions and, ultimately, to design adsorbents to remove synthetic dyes from wastewater.     

Chitin- and Streptavidin-Mediated Affinity Purification Systems: A Screening Platform for Enzyme Discovery

Affinity purification of recombinant proteins is an essential technique in biotechnology. However, current affinity purification methods are very cost-intensive, and this imposes limits on versatile use of affinity purification for obtaining purified proteins for a variety of applications. To overcome this problem, we developed a new affinity purification system which we call CSAP (chitin- and streptavidin-mediated affinity purification) for low-cost purification of Strep-tag II fusion proteins. The CSAP system is designed to utilize commercially available chitin powder as a chromatography matrix, thereby significantly improving the cost-efficiency of protein affinity purification. We investigated the CSAP system for protein screening in 96-well format as a demonstration. Through the screening of 96 types of purified hemoproteins, several proteins capable of the catalytic diastereodivergent synthesis of cyclopropanes were identified as candidates for an abiotic carbene transfer reaction.     

Molecular characterization of selected dermatophytes and their identification by electrophoretic mutation scanning

Dermatophytes are fungi that can be contagious and cause infections in the keratinized skin of mammals, including humans. The etiological diagnosis of dermatophytosis relies on a combination of in vitro‐culture and microscopic methods. Effective molecular tools could overcome the limitations of conventional methods of identification. In the present study, following phenetic identification as M. canis, M. fulvum, M. gypseum, T. mentagrophytes and T. terrestre, we genetically characterized key dermatophytes, employing the sequences of the first and second internal transcribed spacers of nuclear ribosomal DNA as well as part of the chitin synthase‐1 gene, and assessed the utility of these DNA regions (based on levels of nucleotide variation within and among species/taxa) as markers for the classification of species and genotypes. Employing partial chitin synthase‐1 gene as the marker, we also established a PCR‐coupled SSCP approach as a diagnostic/analytical mutation‐scanning tool. This tool should facilitate fundamental investigations of the ecology, epidemiology and population genetics of dermatophytes and, importantly, should assist in allowing a more rapid diagnosis of dermatophytoses in humans and other animals, thus overcoming the significant delays in targeted chemotherapy following diagnosis using conventional methods. (Nucleotide sequence data reported in this paper are available in the EMBL, GenBank and DDJB datadases under accession numbers FJ897707–FJ897713 (ITS‐1), FJ897714–FJ897720 (ITS‐2) and FJ897700–FJ897706 (pchs‐1)).