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71.
Summary Amino acids have been esterified with n-butanol and isobutanol in the presence of perchloric acid. It has been established that in the concentration range of [H2O]/[n-BuOH]=0.10–0.40 esterification can be utilized for the determination of alanine, glycine, valine, leucine, proline, methionine, aspartic acid, phenylalanine, tyrosine, glutamic acid, lysine, arginine, histidine and cystine. In the case of [H2O]/[i-BuOH] =0.05–0.20 the esterification yield decreases from 100% to 70%, in proportion to the water content. 相似文献
72.
Szegvári D Horváth P Gergely A Németh S Görög S 《Analytical and bioanalytical chemistry》2003,375(5):713-717
Quick and accurate direct and indirect circular dichroism (CD) spectrometric methods were developed for the simultaneous determination of ethisterone (17alpha-ethinyl-17-hydroxy-4-androstene-3-one) and its delta(5)-isomer (delta(5)-ethisterone). The direct method is based on the selective negative Cotton effect of the delta(4)-3-oxo group in ethisterone (negative maximum at 348 nm in dioxan) and measurement of the ellipticity at 296 nm (positive maximum of delta(5)-ethisterone), where the measured ellipticity is the sum of those of the two isomers. In the indirect procedure delta(5)-ethisterone is transformed to ethisterone by base-catalysed isomerization and the ellipticities are measured at 339 nm in ethanol before and after isomerization. Preliminary experiments show the usefulness of CD detector in the HPLC determination of the mixture of the isomers. A major advantage of the direct CD spectrometric and the HPLC/CD methods is that the delta(5)-isomer with extremely low UV activity can also be directly measured with high sensitivity. 相似文献
73.
74.
Gergely Gyetvai Sören Sundblom Lívia Nagy Ari Ivaska Géza Nagy 《Electroanalysis》2007,19(10):1116-1122
New solid contact ammonium micropipette electrodes (ISE), well applicable in scanning electrochemical microscopy are reported. The solid contact was made of a PEDOT nanowire coated carbon fiber, lowered down close to the orifice, and dipped inside the cocktail being in the pipette tip. This configuration provided low electrical resistance and good potential stability. Submicron tip size, usual in case of micropipette ISE‐s easily can be fabricated in this way. The applicability of the electrode in SECM has been proved in SG/TC mode imaging urease enzyme active spots in urea solutions. 相似文献
75.
We studied, strongly correlated states in triangular artificial atoms. Symmetry-driven orbital degeneracy of the single particle states can give rise to an SU(4) Kondo state with entangled orbital and spin degrees of freedom, and a characteristic phase shift δ=π/4. Upon application of a Zeeman field, a purely orbital Kondo state is formed with somewhat smaller Kondo temperature and a fully polarized current through the device. The Kondo temperatures are in the measurable range. The triangular atom also provides a tool to systematically study the singlet-triplet transitions observed in recent experiments [Phys. Rev. Lett., 88 (2002) 126803, cond-mat/0208268 (2002)]. 相似文献
76.
Ohne Zusammenfassung 相似文献
77.
Quantitative analysis of natural gas depends on the calibration of a gas chromatograph with certified gas mixtures and the determination of a response relationship for each species by regression analysis. The uncertainty in this calibration is dominated by variations in the amount of the sample used for each analysis that are strongly correlated for all species measured in the same run. The "harmonisation" method described here minimises the influence of these correlations on the calculated calibration curves and leads to a reduction in the root-mean-square residual deviations from the fitted curve of a factor between 2 and 5. Consequently, it removes the requirement for each run in the calibration procedure to be carried out under the same external conditions, and opens the possibility that new data, measured under different environmental or instrumental conditions, can be appended to an existing calibration database. 相似文献
78.
Anion‐, Solvent‐, Temperature‐, and Mechano‐Responsive Photoluminescence in Gold(I) Diphosphine‐Based Dimers 下载免费PDF全文
Dr. Andrea Deák Csaba Jobbágy Gábor Marsi Miklós Molnár Zoltán Szakács Dr. Péter Baranyai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11495-11508
A series of [Au2(nixantphos)2](X)2 (nixantphos=4,6‐bis(diphenylphosphino)‐phenoxazine; X=NO3, 1 ; CF3COO, 2 ; CF3SO3, 3 ; [Au(CN)2], 4 ; and BF4, 5 ) complexes that exhibit intriguing anion‐switchable and stimuli‐responsive luminescent photophysical properties have been synthesized and characterized. Depending on their anions, these complexes display yellow ( 3 ), orange ( 4 and 5 ), and red ( 1 and 2 ) emission colors. They exhibit reversible thermo‐, mechano‐, and vapochromic luminescence changes readily perceivable by the naked eye. Single‐crystal X‐ray studies show that the [Au2(nixantphos)2]2+ cations with short intramolecular Au ??? Au interactions are involved as donors in an infinite N?H ??? X (X=O and N) hydrogen‐bonded chain formation with CF3COO? ( 2 C ) and aurophilically linked [Au(CN)2]? counterions ( 4 C ). Both crystals show thermochromic luminescence; their room temperature red ( 2 C ) and orange ( 4 C ) emission turns into yellow upon cooling to 77 K. They also exhibit reversible mechanochromic luminescence by changing their emission color from red to dark ( 2 C ), and orange to red ( 4 C ). Compounds 1 – 5 also display reversible mechanochromic luminescence, altering their emission colors between orange ( 1 ) or red ( 2 ) to dark, as well as between yellow ( 3 ) or orange ( 4 and 5 ) to red. Detailed photophysical investigations and correlation with solid‐state structural data established the significant role of N?H ??? X interactions in the stimuli‐responsive luminescent behavior. 相似文献
79.
The cold unspreadable consistency of butter after taking it out of the refrigerator is a rightful objection on behalf of consumers.
The possibilities to improve the cold spreadability of butter are: the enrichment with low melting point triglycerides and
the application of a good cream-ripening method. In our investigations milk fat fractions of different low melting points
and plant oils of low melting points obtained by cold pressing and extraction have been used to change the original fatty
acid composition of milk fat. The cream-ripening, the traditional method and the heat-step ripening method, which seemed to
be the most effective to our earlier research, have been applied. The consistency of butter was examined by penetration measurements
and its thermal characteristics by differential scanning calorimetric (DSC) method. The cold unspreadable consistency of butter
can only be improved by the combination of the heat-step cream ripening and enrichment with low melting point triglycerides
to get stable consistency at room temperature. The milk fat fraction of melting point below 5°C made the spreadability better
but the spreadable consistency of margarine still cannot be attained. Plant oils with melting point below 0°C improved the
cold spreadability of butter to a significantly higher degree than the former did. In the case of the same melting point the
plant oil obtained by a cold method (pressing) was more effective. There is a close relationship between the consistency of
butter and its product characteristics. From DSC curves the cold spreadability and room temperature stability of butter can
be directly concluded.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.