Ditopic receptors based on cyclodextrins bearing a metal binding site were used as enantioselective fluorescence sensors,
which were able to generate different responses in the presence of d- or l-amino acids. The performances of the selectors as a function of their structure were evaluated, and the same analysis was
extended to other analytes. In this work, this approach is used for the enantiomers of a series of amino acid derivatives
and in particular of 2-aminocaprolactam. The results showed that the ability of these sensors to perform enantiomeric analysis
can be extended to other analytes of interest in organic synthesis such as amino acid amides and α-aminolactams. 相似文献
The physicochemical properties of hydrophobically modified polyacrylamide (HAPAM) containing a small amount of hydrophobic groups (3,5,5-trimethylhexane methacrylate) and its partially hydrolyzed derivative (HAPAM-10N500) were investigated. The 13C spectrum was used to establish the degree of hydrolysis of HAPAM-10N500. Small-angle X-ray scattering (SAXS) was employed to highlight the polyelectrolyte character of HAPAM-10N500, estimate the chain conformation in the semidilute regime, and evaluate the influence of the ionic strength and the type of salt. The weight average molecular weight, the second virial coefficient, and radius of gyration were determined by static light scattering (SLS). The polymers showed different rheological properties in aqueous solution, with significant increase in viscosity due to partial hydrolysis of HAPAM, however, with strong dependence on ionic strength of the medium. Results showed that the polymers HAPAM and HAPAM-10N500 are suitable for application in processes of moderate temperatures and salinities. 相似文献
Two Streptomyces strains, M7a and M23, from a Brazilian forest soil were evaluated for the cellulase production of their superna tants after growth in a microcrystalline cellulose medium, using carboxy methylcellulose and filter paper as substrates at different temperatures and pH values. Endoglucanase and exoglucanase activities were compared to a commercial Trichoderma reesei cellulase using fluorogenic conjugated substrates Similar specific activities were observed for the enzyme preparations of strain M23 and T. reesei. For M7a the activities were about seven times higher than those obtained for T. reesei. Extracellular or cell-associated cellobiase activities were not detected in both strains.
The influence of small amounts of bovine serum albumin (BSA) (nM concentration) on the lateral organization of phospholipid monolayers at the air-water interface and transferred onto solid substrates as one-layer Langmuir-Blodgett (LB) films was investigated. The kinetics of adsorption of BSA onto the phospholipid monolayers was monitored with surface pressure isotherms in a Langmuir trough, for the zwitterionic dipalmitoylphosphatidyl ethanolamine (N,N-dimethyl-PE) and the anionic dimyristoylphosphatidic acid (DMPA). A monolayer of N,N-dimethyl-PE or DMPA incorporating BSA was transferred onto a solid substrate using the Langmuir-Blodgett technique. Atomic force microscopy (AFM) images of one-layer LB films displayed protein-phospholipid domains, whose morphology was characterized using dynamic scaling theories to calculate roughness exponents. For DMPA-BSA films the surface is characteristic of self-affine fractals, which may be described with the Kardar-Parisi-Zhang (KPZ) equation. On the other hand, for N,N-dimethyl-PE-BSA films, the results indicate a relatively flat surface within the globule. The height profile and the number and size of globules varied with the type of phospholipid. The overall results, from kinetics of adsorption on Langmuir monolayers and surface morphology in LB films, could be interpreted in terms of the higher affinity of BSA to the anionic DMPA than to the zwitterionic N,N-dimethyl-PE. Furthermore, the effects from such small amounts of BSA in the monolayer point to a cooperative response of DMPA and N,N-dimethyl-PE monolayers to the protein. 相似文献
Two selectors based on modified cyclodextrins containing a metal binding site and a dansyl fluorophore-6-deoxy-6-N-(N(alpha)-[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]phenylalanylamino-beta-cyclodextrin-containing D-Phe (3) and L-Phe (4) moieties were synthesized. The conformations of the two selectors were studied by circular dichroism, two-dimensional NMR spectroscopy and time-resolved fluorescence spectroscopy. Cyclodextrin 4 was found to have a predominant conformation in which the dansyl group is self-included in the cyclodextrin cavity, while 3 showed a larger proportion of the conformation with the dansyl group outside the cavity. As a consequence, the two cyclodextrins were found to bind copper(II) with different affinities, as revealed by fluorescence quenching in competitive binding measurements. Addition of D- or L-amino acids induced increases in fluorescence intensity, which were dependent on the amino acid used and in some cases on its absolute configuration. The cyclodextrin 4 was found to be more enantioselective than 3, suggesting that the self-inclusion in the cyclodextrin cavity strongly increases the chiral discrimination ability of the copper(II) complex. Accordingly, a linear fluorescent ligand N(alpha)-[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]-N(1)-propyl-phenylalaninamide, which has the same binding site and absolute configuration as 4, showed very low chiral discrimination ability. The enantioselectivity in fluorescence response was found to be due to the formation of diastereomeric ternary complexes, which were detected by ESI-MS and by circular dichroism. Time-resolved fluorescence studies showed that the fluorescence of the dansyl group was completely quenched in the ternary complexes formed, and that the residual fluorescence was due to uncomplexed ligand. 相似文献