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141.
Immobilized penicillin acylase is a moderately priced versatile enzyme, that is able to catalyze the synthesis of derived
penicillins and cephalosporins from the corresponding β-lactam nuclei and proper side-chain precursors. Kinetically controlled
synthesis is a better strategy when product yield is a key issue. Yield should increase at reduced water activity by depressing
the competing hydrolytic reactions in favor of synthesis; therefore, organic cosolvents can be a suitable reaction media for
synthesis. Using response surface methodology and product yield as objective function, temperature and pH were optimized in
the kinetically controlled synthesis of ampicillin using previously screened cosolvents and reaction conditions. Optimum pH
was 6.0 for ethylene glycol (EG) and glycerol (GL) and 6.6 for 1–2 propanediol (PD); optimum temperature was 30°C for GL and
for EG and PD was in the lower extreme of the range studied, optimum lying below 26°C. Maximum molar yields predicted by the
model were 58,51, and 46% for EG, GL, and PD, respectively, which were experimentally validated. Highest yield in aqueous
buffer was always <40%. Molar yields about 60% compare favorably with values reported for the kinetically and thermodynamically
controlled synthesis of ampicillin and other derived penicillins. 相似文献
142.
Optimal control of infinite dimensional bilinear systems: application to the heat and wave equations
Mathematical Programming - In this paper we consider second order optimality conditions for a bilinear optimal control problem governed by a strongly continuous semigroup operator, the control... 相似文献
143.
Solvents used in microextraction require high solubilising capability to efficiently extract the target compounds. In this article, nanostructured solvents made up of alkyl carboxylic acids (ACAs) aggregate are proposed for the efficient microextraction of acidic pesticides from natural waters. The target compounds were chlorophenoxy acid herbicides (CPAHs) widely used in agriculture, forestry and gardening (viz. 2,4-D, MCPA, MCPP, 2,4,5-T and MCPB). The supramolecular solvents (SUPRASs) tested were generated from solutions of reverse micelles of octanoic (OcA), decanoic (DeA) and dodecanoic (DoA) acid in THF by the addition of water, which acted as the coacervating agent. The DeA-based SUPRAS was the most efficient extractant for CPAHs; actual concentration factors (ACFs) of 260 for 2,4-D, 290 for MCPA, and 400 for MCPP, 2,4,5-T and MCPB were obtained. The explanation for so high ACFs can be found in the extremely efficient retention mechanisms that the DeA-based SUPRAS provides for CPAHs (i.e. formation of hydrogen bonds and hydrophobic interactions), and the high number of binding sites that it contains (i.e. the concentration of biosurfactant in the SUPRAS was 0.56 mg μL−1). Both characteristics permitted to effectively extract the target analytes in a low volume of solvent (about 2 μL of solvent per mL of sample). Others assets of the proposed supramolecular solvent-based microextraction (SUSME) approach included recoveries no dependent on matrix composition, rapidity (sample treatment spent about 15 min), use of low volume of sample (63 mL per analysis) and simplicity (no special lab equipments was needed). Combination with liquid chromatography/ion–trap mass spectrometry [LC–(IT)MS] afforded method quantitation limits for CPAHs within the interval 22–30 ng L−1. The precision of the method, expressed as relative standard deviation (n = 11, [CPAH] = 200 ng L−1), was in the range 2.9–5.8%. The applicability of the method to the analysis of natural waters was assessed by determining the target analytes in fortified river and underground water samples. 相似文献
144.
145.
Noe Oña Antonio Romero-Carrasco M. Soledad Pino-González 《Tetrahedron: Asymmetry》2013,24(2-3):156-163
Epoxyamides obtained from d-glucose have been evaluated as tools to obtain polyhydroxyazepanes. The stereoselectivity in formation of the epoxyamides was proven to be dependent of the protecting group. The conversion of epoxyamides into epoxyalcohols was necessary to obtain polyhydroxyazepanes, because the direct cyclization of 2-N-amides to azepanecarboxamides was unsuccessful from derivatives obtained from d-glucose. Epoxyamides and epoxyalcohols were regioselectively (alpha) opened by nitrogen nucleophiles. Reduction of diethyl epoxyamide by catalytic transfer hydrogenation gave the alpha deoxy product. 相似文献
146.
Encarnación Borrego Dolores Sicilia Soledad Rubio Dolores Pérez-Bendito 《International journal of environmental analytical chemistry》2013,93(1-2):181-200
Abstract The determination of dialkyldimethylammonium surfactants (DDAS) based on the measurement of the critical micelle concentration (CMC) of mixed sodium dodecylsulphate (SDS)-DDAS aggregates in a basic medium ([NaOH]=4.8 × 10?3 M) is proposed. The dye Coomassie Brilliant Blue G (CBBG) was used as a photometric probe for the rapid determination of CMCs. Formation of CBBG-DDAS and DDAS-SDS premicellar aggregates of well-defined stoichiometrics at cationic and anionic surfactant concentrations far below their CMCs is demonstrated. Increased SDS concentration in the titration medium results in the formation of DDAS-SDS mixed micelles. The strong interaction between the opposite charged head group of DDAS and SDS permits these cationic surfactants to be determined at the ng ml?1 level with a nearly uniform response for all the DDAS tested (12–18 alkyl carbons). The relative standard deviation for 1.10 μg ml?1 ditetradecyldimethylammonium bromide (DTDAB) was 1.5%. The mixed-micelle based methodology was applied to the determination of DDAS in softeners and aqueous environmental samples (river water and laundry effluents) with average recoveries ranged from 87.1 to 100.6 and from 96.3 to 104.0, respectively. 相似文献
147.
148.
Rodil R Quintana JB López-Mahía P Muniategui-Lorenzo S Prada-Rodríguez D 《Journal of chromatography. A》2009,1216(14):2958-2969
This paper describes the development and validation of a method for the simultaneous determination of 53 multi-class emerging organic pollutants in water samples using solid-phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using electrospray ionisation (ESI) in both positive and negative modes. Target compounds include acidic herbicides, UV filters, insect repellents, organophosphorous flame retardants, a bactericide, pharmaceuticals and metabolites. A single SPE consisting on the loading of 200-500 mL of sample adjusted to pH 7 on Oasis HLB 200mg cartridges and elution with methanol, permitted obtaining good recoveries: higher than 60% for tap, surface and wastewater in most cases. The 7 isotopically labelled internal standards effectively compensated losses during sample preparation and matrix effects at LC-MS/MS determination. The precision of the method, calculated as relative standard deviation (RSD) was below 15% for all compounds and all tested matrices. Detection limits (LODs) based on the confirmation, less intense, MRM (multiple reaction monitoring) transition and considering blanks varied between 0.3 and 30 ngL(-1). Finally, the developed method was applied to the determination of target analytes in various samples, including tap, surface and waste water. Among the tested emerging pollutants, 31 were found in wastewater in concentrations reaching up to 10 microgL(-1) in the case of ibuprofen. Also, 13 species were detected in tap water with concentrations up to 0.13 microgL(-1) for tri(chloropropyl) phosphate (TCPP). 相似文献
149.
Soledad Chazarra Salvador Aznar-Cervantes Luis Sánchez-del-Campo Juan Cabezas-Herrera Wu Xiaofeng José Luis Cenis José Neptuno Rodríguez-López 《Applied biochemistry and biotechnology》2010,162(7):1834-1846
Recent reports describe the inhibition of human dihydrofolate reductase (hDHFR) by natural tea polyphenols. This finding could
explain the epidemiologic data on their prophylactic effects for certain forms of cancer, and it raises the possibility that
natural and synthetic polyphenols could be used in cancer chemotherapy. In order to obtain larger quantities of hDHFR to support
structural studies, we established and validated a baculovirus system for the expression of this protein in Bombyx mori chrysalides (pupae of the silkworm enclosed in a cocoon). To isolate the expressed protein, whole infected pupae were homogenized,
and the expressed protein was purified by affinity chromatography. Here, we demonstrate the efficient expression of recombinant
hDHFR in this model and report that this newly expressed protein has high enzymatic activity and kinetic properties similar
to those previously reported for recombinant hDHFR expressed in Escherichia coli. The purified protein showed dissociation constants for the binding of natural polyphenols similar to that expressed in E. coli, which ensures its usage as a new tool for further structural studies. Although the hDHFR yield per individual was found
to be lower in the chrysalides than in the larvae of B. mori, the former system was optimized as a model for the scaled-up production of recombinant proteins. Expression of proteins
in chrysalides (instead of larvae) could offer important advantages from both economic and biosecurity aspects. 相似文献
150.
Since the introduction of the euro as the common currency in most of the countries of the European Union, the production of counterfeit banknotes has increased steadily. The European Central Bank has distributed information on a systematic procedure to distinguish genuine notes from counterfeits based on the look, feel and tilt of the notes. Counterfeits, however, have remained difficult to detect. In order to improve such detection, a procedure based on the analysis of several areas of euro notes using microscope ATR-infrared spectroscopy is proposed. This procedure is fast, robust and non-destructive and it can be applied in situ. The present study is focused on the denomination most frequently falsified, the 50€ note, but 100€ notes were also analysed. The inter- and intra-bank reproducibility of the original notes was also evaluated. Results indicate that characteristics of the spectra depend mainly on the area of the note studied and, furthermore, these characteristics do not change with the nominal value of the notes. Counterfeit banknotes were also analysed and were clearly distinguished from authentic notes in all cases. Unlike genuine notes, the spectra of fakes are the same in all areas of the note analysed. 相似文献