Determination of pore sizes in wood cellulose fibers by 2H and ′H NMR

1993 ◽  
Vol 8 (3) ◽  
pp. 326-330 ◽  
Author(s):  
Tie-Qiang Li ◽  
Ulf Henriksson ◽  
Lars Odberg
1993 ◽  
Vol 58 (1) ◽  
pp. 173-190 ◽  
Author(s):  
Eva Klinotová ◽  
Jiří Klinot ◽  
Václav Křeček ◽  
Miloš Buděšínský ◽  
Bohumil Máca

Reaction of 3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) and 20β,28-epoxy-21,22-dioxo-19α,19βH-ursan-3β-yl acetate (IIIb) with diazomethane afforded derivatives XII-XIV with spiroepoxide group in position 21 or 22, which were further converted into hydroxy derivatives XV and XVII. Ethylene ketals VIII-X were also prepared. In connection with the determination of position and configuration of the functional groups at C(21) and C(22), the 1H and 13C NMR spectral data of the prepared compounds are discussed. Complete analysis of two four-spin systems in the 1H NMR spectrum of bisethylenedioxy derivative Xb led to the proton-proton coupling constants from which the structure with two 1,4-dioxane rings condensed with ring E, and their conformation, was derived.


1998 ◽  
Vol 63 (7) ◽  
pp. 955-966
Author(s):  
Eva Přibylová ◽  
Miroslav Holík

Four programs for the 1H NMR line shape analysis: two commercial - Winkubo (Bruker) and DNMR5 (QCPE 165) and two written in our laboratory - Newton (in Microsoft Excel) and Simtex (in Matlab) have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond. For this purpose four testing criteria were used, two of them were also developed by us. As supplementary determinations the rate constants obtained for the coalescence temperature and for the thermal racemization of chromatographically separated enantiomers were used which fitted well the temperature dependence of the rate constants determined by the line shape analysis. As a test compound adamantan-1-yl 3-bromo-2,4,6-trimethylphenyl ketone was prepared and studied. It was shown that supermodified simplex method used in our algorithm (Simtex), though time consuming, gives the most accurate values of the rate constants and consequently the calculated thermodynamic parameters Ea, ∆H≠, and ∆S≠ lay in relatively narrow confidence intervals.


2021 ◽  
Vol 34 (7) ◽  
pp. 483-487
Author(s):  
L.N. Sinitsa ◽  
N.M. Emel’yanov ◽  
A.A. Lugovskoi ◽  
A.P. Shcherbakov ◽  
V.V. Annenkov

1992 ◽  
Vol 6 (4) ◽  
pp. 413-428 ◽  
Author(s):  
C.J. Van Oss ◽  
R.F. Giese ◽  
Z. Li ◽  
K. Murphy ◽  
J. Norris ◽  
...  

1978 ◽  
Vol 33 (4) ◽  
pp. 361-365 ◽  
Author(s):  
Margret Sommer ◽  
Klaus Weidenhammer ◽  
Henning Wienand ◽  
Manfred L. Ziegler

The species R−C7H7Mo(CO)3 (R=−CH2COCH3,−CH(CH3)COCH3,−CH(CH)(CH3)2COCH3) have been synthesized by electrolysing [η7-C7H7Mo(CO)3]+, η7-C7H7Mo(CO)2Br and the dimers [C7H7Mo(CO)3]2 and (C7H7)2Mo(CO)3, respectively, in suitable ketones and HBr. 1H NMR spectra and the X-ray structure determination of (CH3−CO−CH(CH3)−C7H7)Mo(CO)3 revealed the CH3−CO−CH(CH3)-group being bonded to the cycloheptatriene ligand via the α-carbon atom of the ethyl group.


2009 ◽  
Vol 2009 ◽  
pp. 1-11 ◽  
Author(s):  
Ashraf M. Mahmoud

New rapid, sensitive, and accurate kinetic spectrophotometric methods were developed, for the first time, to determine omeprazole (OMZ) in its dosage forms. The methods were based on the formation of charge-transfer complexes with both iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The variables that affected the reactions were carefully studied and optimized. The formed complexes and the site of interaction were examined by UV/VIS, IR, and1H-NMR techniques, and computational molecular modeling. Under optimum conditions, the stoichiometry of the reactions between OMZ and the acceptors was found to be 1 : 1. The order of the reactions and the specific rate constants were determined. The thermodynamics of the complexes were computed and the mechanism of the reactions was postulated. The initial rate and fixed time methods were utilized for the determination of OMZ concentrations. The linear ranges for the proposed methods were 0.10–3.00 and 0.50–25.00   with the lowest LOD of 0.03 and 0.14   for iodine and DDQ, respectively. Analytical performance of the methods was statistically validated; RSD was <1.25% for the precision and <1.95% for the accuracy. The proposed methods were successfully applied to the analysis of OMZ in its dosage forms; the recovery was 98.91–100.32%  0.94–1.84, and was found to be comparable with that of reference method.


2018 ◽  
Vol 10 (36) ◽  
pp. 4454-4462 ◽  
Author(s):  
Liyakat Hamid Mujawar ◽  
Mohammad Soror El-Shahawi

A simple one-step assay for the trace determination of Co2+ was developed on filter paper modified with solubilized polymethyl methacrylate (PMMA) and arrays of 3-[(2-mercapto-vinyl)-hydrazono]-1,3-dihydro-indol-2-one (MHDI) reagent.


2021 ◽  
pp. 174751982110664
Author(s):  
Jue Chen ◽  
Tengmei Gao ◽  
Yinxia Chang ◽  
Yanming Wei ◽  
Yonghui Wang

Folate (FA) plays a key role in the biosynthesis of amino acids, purines, and pyrimidines in the human body, and intracellular folate metabolism has become an attractive target of tumor chemotherapy. In this work, an inclusion interaction was found between FA and cucurbit[7]uril (CB[7]), and the formation of a CB[7]-FA 2:1 supramolecular inclusion complex was confirmed by fluorescence spectra, UV-Vis absorption spectroscopy, 1H NMR, and molecular modeling calculations. In addition, FA is generally determined through the indirect fluorescent method because it shows weak fluorescence in aqueous solution. Therefore, a simple, direct fluorescence probe method for rapidly measuring FA was investigated, and the linear equation of FA was ΔF = 14.691C + 37.366 within the concentration ranges of 0.82 ~ 18.31 µg mL–1. The proposed direct fluorescence method was applied to the determination of spiked plasma. We demonstrated that this method could provide an experimental basis for the targeted administration of the CB[7]-FA complex, and it could be extended as a promising fluorescence detection method for drugs in vivo.


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