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31.
Ona T Ohshima J Adachi K Yokota S Yoshizawa N 《Analytical and bioanalytical chemistry》2004,380(7-8):958-963
Length analysis of vessel elements in tree trunks used for water and nutrient transport is a lengthy, multistep procedure although it reflects environmental stresses on a tree. The feasibility of using FT-Raman spectroscopy for rapid determination of vessel element length in a tree was examined using wood powders of two Eucalyptus species, including samples of various ages and colors. The first-derivative transformation followed by the multiplicative scatter correction of Raman spectroscopic data and the partial least-squares regression revealed highly significant correlation between conventionally measured and Raman-predicted vessel element length with correlation coefficients (r) of 0.843 and 0.826, respectively, in the calibration (for known samples, n=186) and in the prediction (for unknown samples, n=40). FT-Raman spectroscopy coupled with multivariate data analysis will contribute to solving the interactions between emerging environmental issues and the anatomical structure of wood, which allow efficient management practices in growing forests to fix atmospheric CO2 effectively. 相似文献
32.
Gytis-Kazimieras Kupetis Gintautas Šaduikis Ona Nivinskienė Olegas Eicher-Lorka 《Monatshefte für Chemie / Chemical Monthly》2002,133(3):313-321
Summary. A series of 1-alkyl-4-dialkylaminopyridinium halides derived from 4-dimethylamino- and 4-morpholinopyridines were synthesized
and tested as phase-transfer catalysts in three typical reactions of dichlorocarbene: dehydration of benzamide, N-formylation
of diphenylamine, and dichlorocyclopropanation of styrene. The catalytic performance of the above compounds was found comparable
or higher than that of conventional quaternary ammonium catalysts. The influence of catalyst structure on the reactivity was
evaluated.
Received June 27, 2001. Accepted (revised) September 25, 2001 相似文献
33.
Muray E Illa O Castillo JA Alvarez-Larena A Bourdelande JL Branchadell V Ortuño RM 《The Journal of organic chemistry》2003,68(12):4906-4911
The photodenitrogenation of chiral trisubstituted 1-pyrazolines has been studied by laser flash photolysis. These experiments have permitted the detection of two transients that have been assigned, for each pyrazoline, to the trimethylene-type diradical resultant from the extrusion of nitrogen (lifetime tau = 0.1-0.8 micros) and to the pyrazoline triplet (tau < 9 ns), respectively. The efficiency of the photosensitization process has been evaluated by determination of the corresponding quenching rate constant in each instance. Theoretical calculations support a mechanistic pathway involving a trimethylene radical as intermediate that rapidly evolves to the corresponding cyclopropane derivative. The cyclopropane ring-closure is predicted to be faster than rotation around the C-C bond, thus accounting for the observed stereospecificity. 相似文献
34.
35.
ydrnas Stanius Mantas Ddnas Vilma Kakonien Mantas Stankevi
ius Elbieta Skrzydlewska Tomas Drevinskas Ona Ragainskien Kstutis Obelevi
ius Audrius Maruka 《Molecules (Basel, Switzerland)》2022,27(9)
This work involves a comprehensive chemical composition analysis of leaf and cone samples of Lithuanian hop varieties. This study aimed to determine the chemometric properties of the leaves and cones of five Lithuanian hop varieties. Determined properties were the following: (a) xanthohumol content, (b) phenolic compounds, (c) flavonoids, (d) radical scavenging activity, and (e) the qualitative composition of volatile compounds. The total content of phenolic compounds in aqueous 75% methanolic extracts varied between 31.4–78.2 mg of rutin equivalents (RE)/g, and the concentration of flavonoids was between 11.0–23.3 mg RE/g. Radical scavenging activity varied between 34.4–87.2 mg RE/g. A QUENCHER analysis procedure showed 91.7–168.5 mg RE/g of the total phenolic compound content, 12.7–21.4 mg RE/g of flavonoids, and 48.4–121.0 mg RE/g of radical scavenging activity. ‘Fredos taurieji’ and ‘Fredos derlingieji’ varieties have shown maximum values of phenolic compounds and radical scavenging activity both in leaf and cone suspensions. These varieties accumulated a higher amount of xanthohumol in leaves. The concentration of xanthohumol in the samples varied between 0.0014–0.2136% of dry mass, with the highest concentration in the cones of ‘Kauno gražieji’. We identified 19 volatile compounds in leaves, and in cones, we identified 32. In both of them, α-humulene and β caryophyllene dominated. ‘Raudoniai’ leaves were exceptional in their aroma due to dominating compound nagina ketone (Kovats index 1306). The QUENCHER procedure has shown a great potential for the unextractable residue of hop raw material. Further investigation and valorization of different hop biomass components, not only cones, are essential. 相似文献
36.
Dr. Sinu C. Rajappan Dillon R. McCarthy Dr. Joseph P. Campbell Jonathon B. Ferrell Dr. Mona Sharafi Ona Ambrozaite Prof. Jianing Li Prof. Severin T. Schneebeli 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16811-16817
Selective monofunctionalization of substrates with distant, yet equally reactive functional groups is difficult to achieve, as it requires the second functional group to selectively modulate its reactivity once the first functional group has reacted. We now show that mechanically interlocked catalytic rings can effectively regulate the reactivity of stoppering groups in rotaxanes over a distance of about 2 nm. Our mechanism of communication is enabled by a unique interlocked design, which effectively removes the catalytic rings from the substrates by fast dethreading as soon as the first reaction has taken place. Our method not only led to a rare example of selective monofunctionalization, but also to a “molecular if function”. Overall, the study presents a way to get distant functional groups to communicate with each other in a reaction-history-dependent manner by creating linkers that can ultimately perform logical operations at the molecular level. 相似文献
37.
Illa O Gornitzka H Baceiredo A Bertrand G Branchadell V Ortuño RM 《The Journal of organic chemistry》2003,68(20):7707-7710
The [2+1] addition of the stable (phosphanyl)(silyl)carbene 1 to aromatic aldehydes affords phosphoranyl aryloxiranes, a new class of polyfunctional epoxides, in high yields and excellent diastereoselectivity. No reaction is observed for aldehydes bearing strongly electron-donating groups. Theoretical calculations show a good correlation between Gibbs activation energy and the electronic nature of the substituent on the phenyl ring. 相似文献
38.
Several oligomers constructed with (1R,2S)-2-aminocyclobutane-1-carboxylic acid and glycine, β-alanine, and γ-amino butyric acid (GABA), respectively, joined in alternation have been synthesized and studied by means of NMR and CD experiments as well as with computational calculations. Results account for the spacer length effect on folding and show that conformational preference for these hybrid peptides can be tuned from β-sheet-like folding for those containing a C(2) or C(4) linear segment to a helical folding for those with a C(3) spacer between cyclobutane residues. The introduction of cyclic spacers between these residues does not modify the extended ribbon-type structure previously manifested in poly(cis-cyclobutane) β-oligomers. 相似文献
39.
Tomas Drevinskas Rūta Mickienė Audrius Maruška Mantas Stankevičius Nicola Tiso Jurgita Mikašauskaitė Ona Ragažinskienė Donatas Levišauskas Violeta Bartkuvienė Vilija Snieškienė Antanina Stankevičienė Chiara Polcaro Emanuela Galli Enrica Donati Tomas Tekorius Olga Kornyšova Vilma Kaškonienė 《Analytical and bioanalytical chemistry》2016,408(4):1043-1053
40.
Total synthesis of dl-asparenomycins was accomplished with direct conversion of carbonates 13a, 13b and 14a, 14b to asparenomycin esters 15 and 16 and carboxy deprotection by the AlCl3-anisole method. 相似文献