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91.
Andrzej Wisniewski Eugenia Skorupowa Janusz Sokolowski Lech Rozanski Daniel Glod Gerard Descotes 《Journal of carbohydrate chemistry》2013,32(1):73-83
Abstract Conditions have been established for the microsyntheses of dianhydro-hexitols by reaction of 1, 4-monoanhydro-D, L-galactitols and 1, 5-monoanhydro-D-galactitol as well as of 1, 4- and 1, 5-monoanhydro-D-glucitols and -D-mannitols with tosyl chloride in pyridine followed by cyclization of the resulting 6-O-tosyl derivatives in methanolic solution of sodium methoxide. The dianhydrohexitols were formed by intramolecular nucleophilic substitution of the C-6 O-tosyl group with a properly stereochemically oriented hydroxyl group. Components of the mixtures were separated by capillary gas chromato-graphy using columns coated with SP-2340 and identified by GC-MS. The identities of the synthesized dianhydrohexitols were confirmed by comparison with the GC retention times and mass spectra of authentic samples. 相似文献
92.
Jan Michalski Andrzej Łopusinski Lech Łuczak 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):115-118
Abstract Phosphoranesulphenyl halides of the general formula RR'P(Y)SX and their selenium analogues RR'P(Y)SeX (X=Cl,Br; Y=O,S) have been shown to be useful intermediates for access to many new classes of compounds con-taining phosphorus, sulphur, or selenium centers.' 相似文献
93.
Klaudia Masztalerz Adam Figiel Anna Michalska-Ciechanowska Aneta Wojdyo Paulina Nowicka Krzysztof Lech 《Molecules (Basel, Switzerland)》2020,25(22)
Osmotic dehydration (OD) performed in concentrated fruit juices used as osmotic solution (OS) comes with some limitations resulting from the material cell structure and is not entirely recognized at the moment. Filtration of the juice could provide some insight into the phenomena occurring throughout the OD. Therefore, the main aim of the study was to recognize the mechanism of selective penetration during OD and evaluate the effect of filtration on physical and chemical properties of osmo-dehydrated material. For this purpose, OD of pumpkin in non-filtrated and filtrated (filters 0.2, 0.45, 0.8, 1.2, 3, 5 and 8 μm) concentrated chokeberry juice was carried out in the study. Moreover, scanning electron microscope (SEM) images were provided. Total phenolic content (TPC) and antioxidant capacity measured by Ferric Reducing Antioxidant Potential (FRAP) and Trolox Equivalent Antioxidant Capacity (TEAC ABTS) of OS and the material were determined. It was found that even though filtration of osmotic solution had a moderate influence on the mass transfer, it greatly affected the chemical composition of dehydrated material. The best option, considering both chemical and physical properties of the dehydrated material, is the use of non-filtrated solution. However, when shorter time of OD is considered, much better results are obtained for filtrated solutions. 相似文献
94.
Bohdan Mroziewicz Emil Kowalczyk Lech Dobrzanski Jacek Ratajczak Stainslaw J. Lewandowski 《Optical and Quantum Electronics》2007,39(7):585-595
Performance of external cavity diode lasers with silicon gratings produced by E-beam writing and subsequent reactive ion etching
is described. Optical amplifiers used in the experiments were based on single quantum well heterostructures grown by molecular
beam epitaxy. The lasers were set up in the Littrow configuration and have been designed to allow for wavelength tuning in
the range centred at 960 nm. 相似文献
95.
Archiv der Mathematik - 相似文献
96.
Lech Stefaniak 《Magnetic resonance in chemistry : MRC》1979,12(6):379-382
Nitrogen chemical shifts are shown to provide a means of estimating equilibrium compositions of tautomeric systems of mercapto- and amino-derivatives of pyridine. Carbon chemical shifts can afford only qualitative information about such equilibria. 相似文献
97.
A 13C magnetic resonance investigation of 22 compounds of the general formula O?C1(R1)C2(R2)?C3(R3) NR4R4′ has been carried out in order to confirm the conformational assignments estimated previously by PMR and IR spectroscopy. The effects of nonplanarity and hindered rotation have been discussed based on chemical shifts and shapes of the C1, C2 and C3 signals. 相似文献
98.
Delocalisation of the nitrogen lone electron pair by an acyl and acylvinylogue group simultaneously, results in a lowering of both C? N rotational barriers. MeC(O)CBr?CHNMe2 and MeC(O)C(OCOMe)?CHNMe2 exhibit restricted rotation around what is formally a double bond C?C. 相似文献
99.
Leszek Pazderski Andrzej Surdykowski Magorzata Pazderska-Szabowicz Jerzy Sitkowski Lech Kozerski Bohdan Kamieski Edward Szyk 《Central European Journal of Chemistry》2008,6(1):55-64
trans-[Co(py)4Cl2]Cl·6H2O, mer-[Co(py)3Cl3] and mer-[Co(py)3(CO3)Cl] were studied by UV-Vis, far-IR and 1H, 13C, 15N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of 1H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands.
13C nuclei were deshielded upon Co(III) coordination, while 15N NMR studies exhibited ca. 85–110 ppm shielding effects (ca. 15–25 ppm more expressed for nitrogens trans to N than trans to Cl or O). 13C and 15N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)4Cl2]Cl·6H2O and mer-[Co(py)3Cl3], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)4Cl2]Cl → mer-[Co(py)3Cl3] + py reaction was monitored by 1H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)3Cl3] preparation.
相似文献
100.
A submeasure μ defined on the subsets of is nonatomic if for every ℓ ≥ 1 there exists a partition of into a finite number of parts on which μ is bounded from above by 1/ℓ. In this paper we answer several natural questions concerning nonatomic submeasures d
F
that are determined (like the standard density) by a family F of finite subsets of . We first show that if the number of n-element sets in F grows at most exponentially with n, then d
F
is nonatomic; but if this growth condition fails, then d
F
need not be nonatomic in general. We next prove that, for a nonatomic submeasure d
F
, the minimal number of sets in a 1/ℓ-small partition of can grow arbitrarily fast with ℓ. We also give a simple example of a nonatomic submeasure that is not equivalent to a submeasure of type d
F
.
The second author acknowledges a generous support of the Foundation for Polish Science. 相似文献