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91.
Alexander E. Khudozhitkov Masaki Donoshita Prof. Dr. Alexander G. Stepanov Dr. Frederik Philippi Dr. Daniel Rauber Prof. Dr. Rolf Hempelmann Prof. Dr. Hiroshi Kitagawa Dr. Daniil I. Kolokolov Prof. Dr. Ralf Ludwig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(23):e202200257
We report the complex phase behavior of the glass forming protic ionic liquid (PIL) d3-octylphosphonium bis(trifluoromethylsulfonyl)imide [C8H17PD3][NTf2] by means of solid-state NMR spectroscopy. Combined line shape and spin relaxation studies of the deuterons in the PD3 group of the octylphosphonium cation allow to map and correlate the phase behavior for a broad temperature range from 71 K to 343 K. In the solid PIL at 71 K, we observed a static state, characterized by the first deuteron quadrupole coupling constant reported for PD3 deuterons. A transition enthalpy of about 12 kJ mol−1 from the static to the mobile state with increasing temperature suggests the breaking of a weak, charge-enhanced hydrogen bond between cation and anion. The highly mobile phase above 100 K exhibits an almost disappearing activation barrier, strongly indicating quantum tunneling. Thus, we provide first evidence of tunneling driven mobility of the hydrogen bonded P−D moieties in the glassy state of PILs, already at surprisingly high temperatures up to 200 K. Above 250 K, the mobile phase turns from anisotropic to isotropic motion, and indicates strong internal rotation of the PD3 group. The analyzed line shapes and spin relaxation times allow us to link the structural and dynamical behavior at molecular level with the phase behavior beyond the DSC traces. 相似文献
92.
Theoretical Studies on the Intermolecular Interactions of Potentially Primordial Base‐Pair Analogues
Judit E. Šponer Dr. Álvaro Vázquez‐Mayagoitia Dr. Bobby G. Sumpter Dr. Jerzy Leszczynski Prof. Jiří Šponer Prof. Michal Otyepka Dr. Pavel Banáš Dr. Miguel Fuentes‐Cabrera Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(10):3057-3065
Recent experimental studies on the Watson–Crick type base pairing of triazine and aminopyrimidine derivatives suggest that acid/base properties of the constituent bases might be related to the duplex stabilities measured in solution. Herein we use high‐level quantum chemical calculations and molecular dynamics simulations to evaluate the base pairing and stacking interactions of seven selected base pairs, which are common in that they are stabilized by two N? H???O hydrogen bonds separated by one N? H???N hydrogen bond. We show that neither the base pairing nor the base stacking interaction energies correlate with the reported pKa data of the bases and the melting points of the duplexes. This suggests that the experimentally observed correlation between the melting point data of the duplexes and the pKa values of the constituent bases is not rooted in the intrinsic base pairing and stacking properties. The physical chemistry origin of the observed experimental correlation thus remains unexplained and requires further investigations. In addition, since our calculations are carried out with extrapolation to the complete basis set of atomic orbitals and with inclusion of higher electron correlation effects, they provide reference data for stacking and base pairing energies of non‐natural bases. 相似文献
93.
I. Losito R. Angelico A. Ceglie S. Diomede F. Palmisano 《Journal of mass spectrometry : JMS》2009,44(7):1053-1065
Alkylation of a pair of complementary ribonucleotides, adenosine monophosphate (AMP) and uridine monophosphate (UMP), was accomplished by 1,2‐dodecyl‐epoxide (DE) in a oil‐in‐water microemulsion based on the cationic surfactant Cetyl‐trimethyl‐ammonium‐bromide, providing a suitable catalytic interface for the reagents. Several, often isomeric, alkylation products, bearing one or two hydroxy–dodecyl moieties on their structures, were identified in the reaction mixtures by high‐performance liquid chromatography coupled to electrospray ionization ion trap mass spectrometry. In particular, mass spectrometry (MS)/MS spectra, implemented by extracted ion chromatograms obtained for peculiar MS/MS product ions, indicated alkylation to occur on uracil and on uracil/phosphate OH groups in singly and doubly alkylated UMP, respectively. Adenine NH2 group and phosphate or ribose OH groups were found to be involved as such (single alkylation) or in combination, in the case of alkylated derivatives of AMP. The reaction of both endocyclic N and C?O groups (tautomerized to C? OH groups) of uracil and the predominance of nucleophilic attack to the more accessible carbon of the DE epoxydic bridge (the only exception being the reaction by the NH2 group of adenine) were inferred from MS3 spectra with the help of extracted ion chromatograms for specific fragment ions, after their structural characterization. Interestingly, alkylation on one of the uracil C?O groups and, partially, on the adenine NH2 group, both potentially involved in AMP/UMP base pairing in the micellar environment, were found to be hindered when both ribonucleotides were present in the reaction mixtures. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
94.
Jack Thorne 《Journal of Number Theory》2010,130(9):2092-2098
The Tate-Shafarevich groups of certain elliptic curves over Fq(t) are related, via étale cohomology, to the group of points of an elliptic curve with complex multiplication. The Cassels-Tate pairing is computed under this identification. 相似文献
95.
Inspection of Maruzen models and force‐field calculations suggest that oligonucleotide analogues integrating backbone and bases (ONIBs) with an aminomethylene linker form similar cyclic duplexes as the analogous oxymethylene linked dinucleosides. The self‐complementary adenosine‐ and uridine‐derived aminomethylene‐linked A*[n ]U dinucleosides 15 – 17 were prepared by an aza‐Wittig reaction of the aldehyde 10 with an iminophosphorane derived from azide 6 . The sequence‐isomeric U*[n ]A dinucleosides 18 – 20 were similarly prepared from aldehyde 3 and azide 12 . The N‐ethylamine 5 , the acetamides 7 and 14 , and the amine 13 were prepared as references for the conformational analysis of the dinucleosides. In contradistinction to the results of calculations, the N‐ethylamine 5 exists as intramolecularly H‐bonded hydroxyimino tautomer. The association in CDCl3 of these dinucleosides was studied by 1H‐NMR and CD spectroscopy. The A*[n ]U dinucleosides 16 and 17 associate more strongly than the sequence isomers 19 and 20 ; the cyclic duplexes of 16 form preferentially Watson–Crick‐type base pairs, while 17, 19 , and 20 show both Watson–Crick‐ and Hoogsteen‐type base pairing. The cyclic duplexes of the aminomethylene‐linked dinucleosides prefer a gg‐orientation of the linker. No evidence was found for an intramolecular H‐bond of the aminomethylene group. The CD spectra of 16 and 17 show a strong, those of 19 a weak, and those of 20 almost no temperature dependence. 相似文献
96.
97.
Summary Theβ-exotoxin fromBacillus thuringensis is a well known insecticide. The bioassay usually employed for its analysis is time-consuming and subject to many disturbances.
The previously reported HPLC analysis has been shown to give erroneous results in some cases.
A new analysis system has how been designed. The system is based on separation ofβ-exotoxin from the culture broth, and from various preparations containingβ-exotoxin by ion-pairing. For sample preparation in more complex matrices an method employing solid phase extraction was developed.
In order to obtain a standard for quantitative analysis a preparative method for the isolation ofβ-exotoxin from concentrated culture broth after successive precipitations was also developed. 相似文献
98.
Sofia A. Zakharenkova Marina I. Lebedeva Alexandra N. Lebedeva Irina A. Doroshenko Ksenya Yu Vlasova Anastasiya A. Bartoshevich Vladimir M. Senyavin Sergey S. Abramchuk George G. Krivtsov Alexander A. Ezhov Tatyana A. Podrugina Natalia L. Klyachko Mikhail K. Beklemishev 《Molecules (Basel, Switzerland)》2021,26(24)
Imaging-guided delivery is developed for hydrophobic drugs, and to a much lesser extent, hydrophilic ones. In this work we have designed a novel strategy for real-time monitoring of hydrophilic drug delivery. Traditionally, the drug and the dye are covalently attached to a nanocarrier or are electrostatically adsorbed. Recently, we found an efficient way to bind the drug by ion-paring with an appropriate counter-ion to form the aggregate that embeds a hydrophobic dye with a considerable fluorescence enhancement. We synthesized a series of carbocyanine dyes of hydrophobicity sufficient for solubilization in hydrophobic ion pairs, which restores their emission in the near-infrared (NIR) region upon the formation of the ternary aggregates. To avoid using toxic surfactants, we applied an amphiphilic polymer-oligomer poly(hexamethylene guanidine) (PHMG) as a counter-ion. Сeftriaxone was used as a model hydrophilic drug ensuring the highest fluorescent signal. The so-formed drug–counter-ion–dye aggregates were encapsulated into a cross-linked maleated chitosan carrier. Confocal laser scanning microscopy (CLSM) studies have demonstrated internalization of the encapsulated model drug by breast adenocarcinoma cells at 40 min after treatment. These results suggest the potential application of hydrophobic ion pairs containing an NIR dye in imaging-guided delivery of hydrophilic compounds. 相似文献
99.
Ulf Diederichsen 《Angewandte Chemie (International ed. in English)》1998,37(16):2273-2276
Alanyl peptide nucleic acids organize in a similar manner to the DNA structure motif by stabilizing two cytosine–cytosine+ pairing double strands by intercalation (i-motif). These analogues demonstrate that a tetrameric arrangement of nucleobases is necessary for C–C+ pairing (see diagram), whereas formation of the i-motif does not depend on the ribosyl–phosphodiester backbone. 相似文献
100.
Zhang Rongye 《应用数学和力学(英文版)》2000,(7)
IntroductionTimeandspaceisabasicforminwhichthemattersexist.Allmattersandthingsintheworldoccur,exist,move ,developandvariateinthespacetime.Allprocessesinthematerialworldaretheprocessesofthemotion ,developmentandvariationofmatters.Tostudytheobjectsthatoccu… 相似文献