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71.
Marcos Mandaji Tiago Buckup Rafael Rech Ricardo Rego Bordalo Correia Tarso Ledur Kist 《Talanta》2007,71(5):1998-2002
The performance of fluorescence detectors in capillary electrophoresis is maximized when the excitation light intensity is modulated in time with optimal frequencies. This is especially true when photomultiplier tubes are used to detect the fluorescent light. The photomultiplier tube amplified raw output signal can in principle be captured directly by a personal computer sound card (PCSC) and processed by a lock-in emulated by software. This possibility is demonstrated in the present work and the performance of this new setup is compared with a traditional data acquisition system. The results obtained with this “PCSC and lock-in emulated by software” were of the same quality or even better compared to that obtained by conventional time integrators (Boxcars) and data acquisition boards. With PCSC the limits of detection (LOD) found for both naphthalene-2,3-dicarboxaldehyde-derivatized tyrosine and alanine were 3.3 and 3.5 fmol (injection of 5 nL of samples at 0.66 and 0.70 μmol/L), respectively. This is at least three times better compared to conventional systems when light emitting diodes (LEDs) are used as the excitation source in fluorescence detectors. The PCSC linear response range was also larger compared to conventional data acquisition boards. This scheme showed to be a practical and convenient alternative of data acquisition and signal processing for detection systems used in capillary electrophoresis. 相似文献
72.
The present paper states and proves an asymptotic spin-statistics theorem for composites consisting of electrically and magnetically charged particles. We work in the framework of a nonrelativistic theory, taking as the classical configuration space aU(1) bundle over the space of physical configurations, and as the quantum hilbert space the homogeneous square integrable functions on that bundle. The theorems are proved using a formalism we develop here for treating gauge spaces —U(1) bundles with connections; in particular, two products related to tensor products of vector bundles prove to be extremely useful in displaying the structure of the gauge spaces that naturally arise in this theory.Supported in part by the National Science Foundation under grant number PHY 77-07111Supported in part by the National Science Foundation under grant number PHY 78-24275 相似文献
73.
[reaction: see text] Tetrasubstituted pyrazines containing two phosphonate groups 2 in positions 2 and 5 and trisubstituted pyrazines containing a phosphonate 5 or a phosphine oxide group 7 in position 2 are obtained by thermal treatment of 2H-azirine-2-phosphonates 1 and -phosphine oxides 6. These pyrazines can also be prepared from beta-ketoxime tosylates 9 and 10 or from oxime derived from phosphine oxide 11. 相似文献
74.
Belén Abarca Rafael Ballesteros Gurnos Jones 《Journal of heterocyclic chemistry》1984,21(6):1585-1588
A synthesis of the methylthieno[3,2-c]cyclohepteno[b]indole 7 from 2-methylthieno[3,2-b]cycloheptanone 3 is described. Unsuccessful attempts to prepare the isomeric thienocycloheptenoindole system present in formula 2 , from the dihydrobenzothiophenone 8 , and from derivatives of 5-(2-thienyl)-4-oxopentanoic acid, 17 and 18 , and from N-benzylcycloheptindol-1-one 22 were unsuccessful. The preparation of 4,5-dihydro-2-phenyl-1-thienylmethyl-3H-pyridazin-3-one 20 and of the 5-aminopyrazole 21 are reported. 相似文献
75.
de Meijere A Khlebnikov AF Kozhushkov SI Kostikov RR Schreiner PR Wittkopp A Rinderspacher C Menzel H Yufit DS Howard JA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(4):828-842
(M)-(-)- and (P)-(+)-Trispiro[2.0.0.2.1.1]nonanes [(M)- and (P)-3] as well as (M)-(-)- and (P)-(+)-tetraspiro[2.0.0.0.2.1.1.1]undecanes [(M)- and (P)-4]-enantiomerically pure unbranched [4]- and [5]triangulanes-have been prepared starting from racemic bicyclopropylidenecarboxylic [(1RS)-12] and exo-dispiro[2.0.2.1]heptane-1-carboxylic [(1RS,3SR)-13] acids. The optical resolutions of rac-12 and rac-13 furnished enantiomerically pure acids (S)-(+)-12, (R)-(-)-12, (1R,3S)-(-)-13, and (1S,3R)-(+)-13. The ethyl ester (R)-25 of the acid (R)-(-)-12 was cyclopropanated to give carboxylates (1R,3R)-26 and (1R,3S)-26. The ester (1R,3S)-26 and acids (1R,3S)-13 and (1S,3R)-13 were converted into enantiomerically pure methylene[3]triangulanes (S)-(-)- and (R)-(+)-28. An alternative approach consisted of an enzymatic deracemization of endo-[(1SR,3SR)-dispiro[2.0.2.1]heptyl]methanol (rac-20) or anti-[(1SR,3RS)-4-methylenespiropentyl]methanol (rac-18). This afforded (S)-(-)- and (R)-(+)-28 (starting from rac-20), as well as enantiomerically pure (M)-(-)- and (P)-(+)-1,4-dimethylenespiropentanes [(M)- and (P)-23] starting from rac-18. The methylenetriangulanes (S)-(-)- and (R)-(+)-28 were cyclopropanated furnishing (M)- and (P)-3. The rhodium-catalyzed cycloaddition of ethyl diazoacetate onto (S)-(-)- and (R)-(+)-28 yielded four diastereomeric ethyl trispiro[2.0.0.2.1.1]nonane-1-carboxylates in approximately equal proportions. The enantiomerically pure esters (1R,3S,4S)- and (1S,3R,4R)-30 were isolated by careful distillation and then transformed into [5]triangulanes (M)- and (P)-4 using the same sequence of reactions as applied for (M)- and (P)-3. The structures of the key intermediates (R)-12 and rac-31 were confirmed by X-ray analyses. Although [4]- and [5]triangulanes have no chromophore which would lead to any significant absorption above 200 nm, they have remarkably high specific rotations even at 589 nm with [alpha](20)D=-192.7 [(M)-3, c=1.18, CHCl(3))] or +373.0 [(P)-4, c=1.18, CHCl(3))]. This remarkable optical rotatation is in line with their helical arrangement of sigma bonds, as confirmed by a full valence space single excitation configuration interaction treatment (SCI) in conjunction with DFT computations at the B3LYP/TZVP//B3LYP/6-31+G(d,p) level of theory which reproduce the ORD very well. Thus, it is appropriate to call the helically shaped unbranched [n]triangulanes the "sigma-[n]helicenes", representing the sigma-bond analogues of the aromatic [n]helicenes. 相似文献
76.
Rafael Fogel Rafaela Rodrigues Garcia Rebeca da Silva Oliveira Denise Neves Menchero Palacio Luciana da Silva Madeira Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates
containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t
C) to 75 h (without nitrogen source addition t
C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions,
resulted in enhanced conversion rates, reducing t
C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation. 相似文献
77.
Manuel Cano Beatriz Palenzuela J. Luis Ávila Rafael Rodríguez‐Amaro 《Electroanalysis》2007,19(9):973-977
A PVC/TTF‐TCNQ composite electrode has been employed as detector in a flow injection system. The proposed method allows the simultaneous detection of ascorbic acid (AA) and uric acid (UA) in mixtures by using a FIA system in a simple manner, without pre‐treatment or modified electrode. This method is based on the amperometric determination of (a) ascorbic acid at 0.15 V and (b) both analytes at 0.35 V, being the response linear in the range 1×10?2–4×10?4 M for both analytes with detection limits (S/N=3) of 1.2×10?4 M and 8.1×10?5 M for AA and UA, respectively. 相似文献
78.
Bustamante JJ Garcia M Gonzalez L Garcia J Flores R Aguilar RM Trevino A Benavides L Martinez AO Haro LS 《Electrophoresis》2005,26(23):4389-4395
A method for separating proteins with a molecular mass difference of 2 kDa using SDS-PAGE under nonreducing conditions is presented. A sample mixture containing several human growth hormone (hGH) isoforms was initially separated on a weak anion-exchange column. Fractions rich in 24 kDa hGH as determined by analytical SDS-PAGE were pooled and further separated by cation-exchange chromatography. The fractions pooled from the cation-exchange chromatography contained two hGH isoforms with a 2 kDa molecular mass difference according to SDS-PAGE analysis, 22 and 24 kDa hGH. The 22 and 24 kDa hGH were separated using continuous-elution preparative double-inverted gradient PAGE (PDG-PAGE) under nonreducing conditions. The preparative electrophoresis gel was composed of three stacked tubular polyacrylamide matrices, a 4% stacking gel, a 13-18% linear gradient gel, and a 15-10% linear inverted gradient gel. Fractions containing purified 24 kDa hGH were pooled and Western blot analysis displayed immunoreactivity to antihGH antibodies. PDG-PAGE provides researchers with an electrophoretic technique to preparatively purify proteins under nonreducing conditions with molecular mass differences of 2 kDa. 相似文献
79.
Emmanuel Blas Patricio-Rangel Margarita Tlahuextl Hugo Tlahuext Antonio Rafael Tapia-Benavides 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):322-327
The synthesis and characterization of two new 1,3,5‐triazines containing 2‐(aminomethyl)‐1H‐benzimidazole hydrochloride as a substituent are reported, namely, 2‐{[(4,6‐dichloro‐1,3,5‐triazin‐2‐yl)amino]methyl}‐1H‐benzimidazol‐3‐ium chloride, C11H9Cl2N6+·Cl? ( 1 ), and bis(2,2′‐{[(6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(azanediyl)]bis(methylene)}bis(1H‐benzimidazol‐3‐ium)) tetrachloride heptahydrate, 2C19H18ClN92+·4Cl?·7H2O ( 2 ). Both salts were characterized using single‐crystal X‐ray diffraction analysis and IR spectroscopy. Moreover, the NMR (1H and 13C) spectra of 1 were obtained. Salts 1 and 2 have triclinic symmetry (space group P) and their supramolecular structures are stabilized by hydrogen bonding and offset π–π interactions. In hydrated salt 2 , the noncovalent interactions yield pseudo‐nanotubes filled with chloride anions and water molecules, which were modelled in the refinement with substitutional and positional disorder. 相似文献
80.
Barro R Ares S Garcia-Jares C Llompart M Cela R 《Analytical and bioanalytical chemistry》2005,381(1):255-260
A combination of sorbent enrichment and ultrasound-assisted solvent extraction has been used to determine polychlorinated biphenyls in air. Analytes were sampled by pumping a known volume of air through a porous polymer (Tenax TA). The enriched adsorbent was transferred into a glass vial, and ultrasound-assisted extraction of the analytes was then performed in n-hexane. Quantification was carried out by using gas chromatography coupled to tandem mass spectrometry. Breakthrough volume of the sampling step was studied, indicating that 10 m3 of air could be processed without losses of the most volatile compounds. Good recoveries (75–96%) were obtained, and limits of detection at the sub ng m–3 were achieved for all the analytes. The proposed method is very simple and fast, avoiding the use of large solvent volumes and time-consuming preconcentration steps. 相似文献