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11.
Optical imaging fibers with micrometer-sized wells were used as a sensing platform for the development of microarray optical ion sensors based on selective bulk extraction principles established earlier for optodes. Uniform 10 μm sized microspheres based on plasticized poly(vinyl chloride) containing various combinations of ionophores, fluoroionophores and lipophilic ion-exchangers were prepared for the detection of sodium, potassium, calcium and chloride, and deposited onto the wells of etched fiber bundles. Specifically, sodium sensing particles were based on tert-butylcalix[4]arene tetraacetic acid tetraethylester, potassium particles on 2-dodecyl-2-methyl-1,3-propanediyl bis[N-[5′-nitro(benzo-15-crown-5)-4′-yl]carbamate] (BME-44), calcium particles on an acrylic derivative of ETH 129 (AU-1) covalently attached to a methacrylic polymer, and chloride particles based on the anticrown ionophore [9]mercuracarborand-3 (MC-3). The fluorescence emission characteristics of individual microspheres were observed from the backside of the fibers and were found to selectively and rapidly change as a function of the sample composition. The optical characteristics of the particles were found to be comparable to that of corresponding thin optode films and particles deposited onto microscope glass slides. The measuring ranges (logarithmic molar concentrations) at pH 7.0 were found as −3 to 0 for sodium, −3.5 to −0.5 for potassium, −7 to −2 for calcium, and −5 to 0.5 for chloride. Selectivities were determined over other common electrolytes and found to be sufficient for physiological applications. The simultaneous deposition of sodium and chloride sensing particles was successfully performed, demonstrating that such microarray sensors are capable of simultaneously sensing multiple analytes. This technology is compatible with other microsphere-based fluorescent sensing principles, forming a promising total analysis platform for a variety of applications.  相似文献   
12.
The crystal structure of a protected l ‐tyrosine, namely N‐acetyl‐l ‐tyrosine methyl ester monohydrate, C12H15NO4·H2O, was determined at both 293 (2) and 123 (2) K. The structure exhibits a network of O—H...O and N—H...O hydrogen bonds, in which the water molecule plays a crucial role as an acceptor of one and a donor of two hydrogen bonds. Molecules of water and of the protected l ‐tyrosine form hydrogen‐bonded layers perpendicular to [001]. C—H...π interactions are observed in the hydrophobic regions of the structure. The structure is similar to that of N‐acetyl‐l ‐tyrosine ethyl ester monohydrate [Soriano‐García (1993). Acta Cryst. C 49 , 96–97].  相似文献   
13.
SARS-CoV-2 Mpro is one of the enzymes essential for the replication process of the virus responsible for the COVID-19 pandemic. This work is focused on exploring its proteolysis reaction by means of QM/MM methods. The resulting free energy landscape of the process provides valuable information on the species appearing along the reaction path and suggests that the mechanism of action of this enzyme, taking place in four steps, slightly differs from that of other cysteine proteases. Our predictions, which are in agreement with some recently published experimental data, can be used to guide the design of COVID-19 antiviral compounds with clinical potential.

The molecular mechanism of the proteolysis reaction catalyzed by SARS-CoV-2 Mpro, one of the enzymes essential for the replication process of the virus responsible for the COVID-19 pandemic, is described using computational QM/MM methods.  相似文献   
14.
    
A selective and sensitive method for the determination of europium was developed. Other lanthanides and oxidants do not require separation. The method is based on the redox reaction of Eu(III) with 2,2-biquinoxalyl. It was checked for the range of 0.5 to 10 g/Eu/mL. Sm(III) does not interfere in 1000-fold excess.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday  相似文献   
15.
We study the electronic properties of a mesoscopic system composed of an array of straight, infinite rods made of an isotropic medium and embedded in a regular way in an isotropic background. Such a composite system has two-dimensional periodicity in the plane perpendicular to the rods. Using a Fourier series expansion, the corresponding Schrödinger equation is solved within the effective-mass approximation. The electronic band structure is computed for the wave vector in the transverse plane, and is illustrated by dispersion curves along the principal directions of the two-dimensional Brillouin zone as well as by the histograms of the density of states. The main result is the appearance of absolute energy gaps in the two-dimensional band structure.  相似文献   
16.
This study focused on the detection/identification of possible selenium metabolites in human urine. Organoselenium compounds not commercially unavailable were synthesized and characterized by electrospray mass spectrometry. Separation of selenomethionine, methylselenomethionine, trimethylselonium, selenoethionine, and selenoadenosylmethionine was achieved by ion-pairing HPLC with a mobile phase of 2 mmol L–1 hexanesulfonic acid, 0.4% acetic acid, 0.2% triethanolamine (pH 2.5), and 5% methanol. The column effluent was introduced on-line to inductively coupled plasma–mass spectrometry for selenium-specific detection (77Se and 78Se). For selenium speciation in urine, solid-phase extraction was carried out using C18 cartridges modified with hexanesulfonic acid. Selective retention of cationic species was observed from acidified urine (perchloric acid, pH 2.0). After elution with methanol, evaporation, and dissolution in the mobile phase, the sample was introduced to the HPLC–ICP–MS system and the chromatographic peaks were assigned by adding standards. The species identified in urine were selenomethionine, trimethylselonium ion, and selenoadenosylmethionine. The last species was detected for the first time and our results suggest that selenomethionine might enter the metabolic pathway of its sulfur analog in the activated methylation cycle.Kazimierz Wrobel and Katarzyna Wrobel are on the leave from the Institute of Scientific Research, University of Guanajuato, L. de Retana No. 5, 36000 Guanajuato, Gto., Mexico  相似文献   
17.
Microcalorimetry and measurement of culture turbidity using a Bioscreen C Analyzer System were applied to study the toxic effect of phenanthrene on Cunninghamella elegans IM 1785/21Gp spore germination. The results of C. elegans spore incubation in Bioscreen C microbiology reader showed the inhibition of spore germination by 70% (with 25 mg l−1 of phenanthrene) and total inhibition of the fungus growth with a higher content of the xenobiotic (50-100 mg l−1). The microcalorimetric technique showed to be useful for the estimation of metabolic activity of C. elegans spores in growth medium up to xenobiotic concentrations of 90 mg l−1. These data corresponded with the microscopic observations. The obtained results showed that the microcalorimetry method could be a valuable supplement in the study on the mechanism of PAHs detoxification by fungi.  相似文献   
18.
Summary The design of enzyme mimics with therapeutic and industrial applications has interested both experimental and computational chemists for several decades. Recent advances in the computational methodology of restrained molecular dynamics, used in conjunction with data obtained from two-dimensional 1H NMR spectroscopy, make it a promising method to study peptide and protein structure and function. Several issues, however, need to be addressed in order to assess the validity of this method for its explanatory and predictive value. Among the issues addressed in this study are: the accuracy and generizability of the GROMOS peptide molecular mechanics force field; the effect of inclusion of solvent on the simulations; and the effect of different types of restraining algorithms on the computational results. The decapeptide Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly, which corresponds to the sequence of ACTH1–10, has been synthesized, cyclized, and studied by two-dimensional 1H NMR spectroscopy. Restrained molecular dynamics (RMD) and time-averaged restrained molecular dynamics (TARMD) simulations were carried out on four different distance-geometry starting structures in order to determine and contrast the behavior of cyclic ACTH1–10 in vacuum and in solution. For the RMD simulations, the structures did not fit the NOE data well, even at high values of the restraining potential. The TARMD simulation method, however, was able to give structures that fit the NOE data at high values of the restraining potential. In both cases, inclusion of explicit solvent molecules in the simulation had little effect on the quality of the fit, although it was found to dampen the motion of the cyclic peptide. For both simulation techniques, the number and size of the NOE violations increased as the restraining potential approached zero. This is due, presumably, to inadequacies in the force field. Additional TARMD vacuum-phase simulations, run with a larger memory length or with a larger sampling size (16 additional distance-geometry structures), yielded no significantly different results. The computed data were then analyzed to help explain the sparse NOE data and poor chymotryptic activity of the cyclic peptide. Cyclic ACTH1–10, which contains the functional moieties of the catalytic triad of chymotrypsin, was evaluated as a potential mimic of chymotrypsin by measurement of the rate of hydrolysis of esters of L-and d-phenylalanine. The poor rate of hydrolysis is attributed to the flexibility of the decapeptide, the motion of the side chains, which result in the absence of long-range NOEs, the small size of the macrocycle relative to that of the substrate, and the inappropriate orientation of the Gly, His, and Ser residues. The results demonstrate the utility of this method in computer-aided molecular design of cyclic peptides and suggest structural modifications for future work based on a larger and more rigid peptide framework.  相似文献   
19.
We have previously reported that motile photophobic response in ciliate Blepharisma japonicum correlates with dephosphorylation of a cytosolic 28 kDa phosphoprotein (PP28) exhibiting properties similar to those of phosducin. Here we demonstrate in in vivo phosphorylation assay that the light-elicited dephosphorylation of the PP28 is significantly modified by cell incubation with substances known to modulate protein phosphatase and kinase activities. Immunoblot analyses showed that incubation of ciliates with okadaic acid and calyculin A, potent inhibitors of type 1 or 2A protein phosphatases, distinctly increased phosphorylation of PP28 in dark-adapted cells and markedly weakened dephosphorylation of the ciliate phosducin following cell illumination. An enhancement of PP28 phosphorylation was also observed in dark-adapted ciliates exposed to 8-Br-cAMP and 8-Br-cGMP, slowly hydrolysable cyclic nucleotide analogs and 3-isobutyryl-1-methylxanthine (IBMX), a non-specific cyclic nucleotide phosphodiesterase (PDEs) inhibitor. Only slight changes in light-evoked dephosphorylation levels of PP28 were observed in cells treated with the cyclic nucleotide analogs and IBMX. Incubation of ciliates with H 89 or KT 5823, highly selective inhibitor of cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG), respectively, decreased PP28 phosphorylation levels in dark-adapted cells, whereas the extent of light-evoked dephosphorylation of the phosphoprotein was only slightly influenced. Cell treatment with higher Ca2+ concentration together with ionophore A23187 in culture medium resulted in marked increase in PP28 phosphorylation levels, while quite an opposite effect was observed in cells exposed to Ca2+ chelators, EGTA or BAPTA/AM as well as calmodulin antagonists, such as trifluoperazine (TFP), W-7 or calmidazolium. Light-dependent dephosphorylation was not considerably affected by these treatments. The experimental findings presented here suggest that an endogenous light-dependent protein kinase-phosphatase system may be engaged in the alteration of phosducin phosphorylation in ciliate B. japonicum thereby to modulate the cell motile photophobic behavior.  相似文献   
20.
The dimeric rhodium(II) complexes [Rh2(leu)4(H2O)2]- (ClO4)4 and [Rh2(pro)4(H2O)2](ClO4)4 have been prepared and characterized by elemental analyses, i.r., u.v.–vis. and 1H-n.m.r. spectroscopy. The amino acid molecules are coordinated as bridging ligands via their carboxylato groups. Cyclic voltammetry in DMF has shown that the complexes undergo a quasi-reversible reduction to yield dimers containing a Rh 2 3+ core. Oxidation processes within the 0–1.5V range were not observed.  相似文献   
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