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51.
Kálmán A Fábián L Argay G Bernáth G Gyarmati Z 《Journal of the American Chemical Society》2003,125(1):34-35
The polymorphs of trans-2-hydroxycycloheptanecarboxylic acid have exactly the same lattice parameters and thus mimic isomorphism. They differ only in their space group: Pna21 versus Pn21a. In form II, the screw axes turn the 18-membered rings of hydrogen-bonded tetramers around the b axis. In this way, the stacking of the layers becomes antiparallel, which cancels out the dipoles within the unit cell. In form I, the same turn around the c axis leaves the stacking of the layers parallel. Thus, the dipoles are canceled out by antiparallel domains in the crystals. Between the antiparallel domains of I, each frontier is a double layer of II. This implies that (a) a pure form of I cannot be isolated and (b) the percentage of II in I may alter from crystal to crystal. 相似文献
52.
Alaize de P. Martins A. A. Craveiro M. I. L. Machado Fernanda N. Raffin T. F. Moura Cs. Novák Zsuzsanna éhen 《Journal of Thermal Analysis and Calorimetry》2007,88(2):363-371
Inclusion complex between the essential oil
of Mentha x villosa Hudson and β-cyclodextrin,
with a 1:9 mass/mass oil–β-cyclodextrin ratio was prepared by co-precipitation
and kneading methods in a hydroethanolic medium. The GC/MS analysis showed
a total volatile content of 99.5% in the Mentha x
villosa oil. The characterization of the complex involved the analysis
of the original essential oil, the surface and the total extracted oils. Among
28 detected compounds in the original essential oil, 13 are monoterpenes and
10 sesquiterpenes, furthermore, piperitenone-oxide is the major component
(35.4%). 12 compounds were totally and 11 partially complexed, 3 have been
adsorbed only on the surface of the β-CD and 2 have not been detected
neither in the surface oil nor in the complexed oil. A 13.6% encapsulation
efficiency was observed, while the total oil and volatiles retention was 15
and 77%, respectively. Non-parametric statistic analysis of the data showed
that the profile of the volatiles were not significantly different comparing
the original oil and the complexed oil (p>0.04).
The results of thermogravimetry-mass spectrometry and XRD analysis have proven
the inclusion complex formation between the essential oil and cyclodextrin. 相似文献
53.
Zsuzsanna Riedl Katrien Monsieurs Petra Dunkel Pál Tapolcsányi Sándor Boros Luc Pieters György Hajós 《Tetrahedron》2006,62(1):121-129
New synthetic pathways have been elaborated to 1-methyl-1H-pyridazino[3,4-b]indoles starting from halopyridazin-3(2H)-ones. Suzuki cross-coupling reaction of chloro, iodo, dichloro, and dibromo substituted pyridazin-3(2H)-ones with 2-pivaloylaminophenylboronic acid followed by hydrolysis of the amide and subsequent ring closure via condensation gave fused indoles. Some of these compounds showed biological activity as antitrypanosomal agents. 相似文献
54.
János Szépvölgyi Zoran Marković Biljana Todorović-Marković Zoran Nikolić Ilona Mohai Zsuzsanna Farkas Mária Tóth Éva Kováts Paul Scheier Stefan Feil 《Plasma Chemistry and Plasma Processing》2006,26(6):597-608
Synthesis of fullerenes from graphite powders of different grade was studied in a radiofrequency (RF) plasma reactor. Dependence of fullerene yield on the properties and feed rate of precursors and on the helium content of plasma gas was studied in details. The fullerene yield was influenced by the mean size and the thermal conductivity of graphite particles on the one hand, and the helium content of the gas phase on the other. Soot containing fullerene mixture of 5.9% was produced in best conditions found in this work. The main component of the fullerene mixture was C60. In addition, it contained about 30% of C70 (corresponding to a C60/C70 mass ratio of 2.64). Higher fullerenes such as C84 were also detected by mass spectroscopy (MS) and high performance liquid chromatography (HPLC). 相似文献
55.
Dehouck P Visky D Vander Heyden Y Adams E Kovács Z Noszál B Massart DL Hoogmartens J 《Journal of chromatography. A》2004,1025(2):189-200
56.
Determination of aflatoxin B1 and total aflatoxin (B1 + B2 + G1 + G2) in red paprika powder is described using column chromatographic sample clean-up, overpressured layer chromatography (OPLC) separation and fluorescence densitometric evaluation. Two OPLC methods were developed for separation of the four aflatoxins. The detection limit and quantification limit of aflatoxins in red paprika were 0.5 and 1 μg/kg in both methods, respectively. Recovery experiment was carried out with sample containing 1.74 μg/kg aflatoxin B1 and 3.56 μg/kg total aflatoxins measured by European standard HPLC method. Mean recovery amounted to 78.5% (SD 16.1%, n = 5) for aflatoxin B1 and 81.8% (SD 17.1%, n = 5) for total aflatoxins in the case of method 1. It was 105.3% (SD 10.7%, n = 5) for aflatoxin B1 and 97.4% (SD 18.6%, n = 5) for total aflatoxins using the method 2. Despite of that the Hungarian climate is not proper for the toxin production of moulds high aflatoxin B1 contaminated red paprika purchased from the market was found, which may originate from mixing of imported paprika containing very high level toxin with Hungarian one. 相似文献
57.
Investigations were made to determine the TLC properties of monosubstituted pyridines. The primary aim was to identify and quantitatively determine the monohydroxypyridines formed during in vitro chemical and enzymatic hydroxylation experiments.TLC studies were carried out not only on the monosubstituted pyridines, but also on 2,3-di-OH-pyridine and 3-OH-pyridine-N-oxide.The UV absorption spectra of pyridine and its substituted derivatives were recorded at a concentration of 10−3 M in ethanol, and were compared.The best TLC detection of these derivatives was elaborated too. 相似文献
2. Rf Values of Monohydroxypyridines and other Monosubstituted Pyridines (Monoamines and Monocarboxylic Acids) in Systems I and II
58.
Kuklenyik Z Ye X Reich JA Needham LL Calafat AM 《Journal of chromatographic science》2004,42(9):495-500
Automated online and off-line solid-phase extraction (SPE) methods coupled to isotope dilution-high-performance liquid chromatography-tandem mass spectrometry for measuring four isoflavones (daidzein, genistein, equol, and O-desmethylangolensin) and two lignans (enterolactone and enterodiol) in urine are developed. The SPE recoveries for the online SPE method are excellent for most analytes (83-94%) and somewhat lower for enterolactone (61%). The recoveries for all analytes with the off-line SPE method are also very good (65-80%). The limit of detection is lower for the online method (0.1-0.7 ng/mL) than for the off-line method (0.4-3.3 ng/mL). Similarly, the reproducibility is generally better for the online method [coefficient of variation (CV) of 4-12%) than for the off-line method, except for enterolactone, which has a higher CV (18-19%) that is consistent with its lower online SPE recovery. Both methods are adequate for analyzing a large number of samples for epidemiological studies to assess the prevalence of human exposure to isoflavones and lignans. 相似文献
59.
Éva Bertalan András Bartha Mária Ballók Zsuzsanna Varga-Barna 《International journal of environmental analytical chemistry》2013,93(11-12):771-784
The Hungarian Geological Survey - Geological Institute of Hungary participated in an INCO-Copernicus project which was aimed at the harmonisation of analytical methods and finished recently. In the first phase, participating geological laboratories entered the International Soil Exchange (ISE) scheme. Laboratories determined total and leachable element contents of soil (and stream sediment) samples, using their own methods. This article in intended to summarise the problems and conclusions regarding the determination of leachable (mobile) elements. Using their own methodologies, laboratories obtained fairly divergent results, especially for some elements. In order to eliminate the variance originating from applying different methodology, a standardised common method was designed for aqua regia leaching. The spread of the results did not improve significantly because of the insufficient control of the applied open vessel method. The final conclusion was: in order to produce internationally comparable results, the use of well-defined and well-controllable digestion methods is strongly recommended. A typical example might be the use of the microwave assisted digestion methods for all geological institutes participating in international geochemical programmes. 相似文献
60.
Zsuzsanna Szalai Tamás F. Molnár Dénes Lőrinczy 《Journal of Thermal Analysis and Calorimetry》2013,113(1):259-264
Chronic obstructive pulmonary disease (COPD) is a major global health challenge with a gloom perspective of being one of the big three cause of death by 2020. No reliable/reproducible biomarker has been identified so far to match the clinically-based staging system (GOLD). Blood samples of 30 subjects divided into 6 groups (no-COPD/-smoker, no-COPD/non-smoker, COPD I, COPD II, COPD III, COPD IV) with 5 patients in each were tested by differential scanning calorimetry. There is a clear 15.4 % difference between the heat flow maxima measured when no-COPD subjects were compared in accordance to their smoking/non-smoking status. Odds ratio of different heat flow in actively smoking COPD patients in stage IV and stage I was 1.61. A reverse tendency is detected in the relevant non-smoking COPD groups. The differences are inconsistent in intermediate stages (COPD II and III). DSC seems to be an applicable and objective method for monitoring nicotine abuse. There is a chance to detect specific typology of thermokinetic patterns in the two extremes of COPD (I vs. IV). Further studies with increased sample size are needed to allow calculations on specificity/sensitivity/positive and negative predictive value of enthalpies and heat flow maximums. The first clinically relevant blood-based COPD marker on the intravascular side of the alveo-capillary screen is demonstrated by our pilot study. 相似文献