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931.
932.
We have used UV and visible spectrophotometry to study self-association of aromatic riboflavin molecules (RFN, vitamin B2, 7,8-dimethyl-10-N-(1′-D-ribityl)isoalloxazine) in aqueous solution (pH 6.86) at T = 298 K, using a dimer model. We have
determined the equilibrium dimerization constant for riboflavin, KdB = 125 ± 40 M−1. We have studied heteroassociation in the system of molecules of 7,8-dimethyl-10-ribitylisoalloxazine with 1,3,7-trimethylxanthine
(caffeine) and sodium salicylate (NAS) in aqueous solution (pH 6.86; T = 298 K). We have determined the heteroassociation
constants for RFN-NAS and RFN-caffeine molecules in the absence and in the presence of urea in solutions using a modified
Benesi-Hildebrand equation: 25 ± 4, 17 ± 3, and 74 ± 11, 53 ± 7 M−1 respectively. We have determined the dimerization constants for NAS (2.7 ± 0.5 M−1) and caffeine (17.0 ± 1.5 M−1). We conclude that heteroassociation of the aromatic molecules leads to a lower effective riboflavin concentration in solution,
and the presence of urea in mixed solutions leads to an decrease in the complexation constants for the RFN-NAS and RFN-caffeine
systems.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 188–194, March–April, 2007. 相似文献
933.
Virgil Percec Anatoliy V. Popov 《Journal of polymer science. Part A, Polymer chemistry》2005,43(6):1255-1260
The chloroiodomethyl chain ends of poly(vinyl chloride) (PVC) obtained by the single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization of vinyl chloride initiated with iodoform were quantitatively functionalized by the reaction with 2‐allyloxyethanol (CH2?CHCH2OCH2CH2OH). This reaction was performed in dimethyl sulfoxide at 70 °C and was catalyzed by sodium dithionite/sodium bicarbonate. The resulting product is the first example of telechelic PVC [α,ω‐di(hydroxy)PVC]. A possible mechanism for this reaction was suggested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1255–1260, 2005 相似文献
934.
Synthesis and structural characterization of a polyoxometalate compound Na3(H2O)6 [Al(OH)6Mo6O18]-2H2O (1) have been described. Compound1 exhibits three-dimensional network structure in the solid state, which is assembled by Anderson-type heteropolyanions, [Al(OH)6Mo6O18]n
3n-
, as building blocks sharing sodium cations.1 possesses “sinuous” channels occupied by supramolecular water dimers as guests. Anderson anions, sodium-coordinated water
and crystal water are additionally involved in an intricate hydrogen-bonding network in the crystal of1. 相似文献
935.
Virgil Percec Ernesto Ramirez‐Castillo Anatoliy V. Popov Luis A. Hinojosa‐Falcon Tamaz Guliashvili 《Journal of polymer science. Part A, Polymer chemistry》2005,43(10):2178-2184
Sodium dithionite in the presence of NaHCO3 in water acts as a single‐electron‐transfer agent and facilitates the single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization (SET–DTLRP) of acrylates initiated with iodoform at room temperature. The resulting α,ω‐di(iodo)polyacrylates can be used as macroinitiators for the SET–DTLRP of other acrylates. Ultrahigh‐molar‐mass poly(tert‐butyl acrylate) can be synthesized via the SET–DTLRP of tert‐butyl acrylate and has a very low weight‐average molecular weight/number‐average molecular weight ratio of 1.15. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2178–2184, 2005 相似文献
936.
在硝酸铈铵催化下,酰肼可被溴酸钠氧化成羧酸。本方法具有试剂价廉、反应迅速、操作简便、产率较高的特点。 相似文献
937.
Giuseppe Petrella Mario Petrella Maurizio Castagnolo Angelo Dell'Atti Angelo De Giglio 《Journal of solution chemistry》1981,10(2):129-138
Conductances of sodium bromide, iodide, and perchlorate, potassium chloride, and tetraphenylboride (BPh
4
–
) as well as triisoamyl-n-butylammonium iodide (i-Am3BuNI) have been measured in aqueous mixtures containing up to 20 mole percent dimethylsulfoxide (DMSO) at 25°C. Experimental data were analyzed by the 1965 Fuoss-Onsager-Skinner (FOS) equation. Single-ion limiting equivalent conductances were calculated by assuming that 0 (i–Am
3
BuN
+=0 (BPh
4
–
). The variations of the limiting ionic Walden products are discussed on the basis of acid-base type interactions for cations, and on the basis of structural effects for anions. 相似文献
938.
A differential scanning calorimeter has been used to study the nonfreezing of water in a series of solutions of sodium carboxymethylcellulose. In particular, the effects of molecular weight, degree of substitution, and particle size have been investigated. The results show that large amounts of water are associated with all the samples of sodium carboxymethylcellulose, suggesting a multilayer arrangement of water molecules about the solute. A change in degree of substitution has some effect on the hydration, but it appears less significant than a change in molecular weight. 相似文献
939.
We have developed a simple and effective means of using alkylammonium ion-pairing agents, such as cetyltetramethylammonium bromide, to recover matrix assisted laser desorption/ionization mass spectrometric (MALDI-MS) signals from sodium dodecyl sulfate (SDS)-containing protein and peptide samples. A two-layer method of matrix preparation, with a bottom matrix layer of ion-pairing agents and a top matrix layer of SDS protein samples, is essential for reproducible MALDI mass spectra with good recovery. Both buffer ions and ion-pairing agents have profound effects on signal recovery and can be rapidly and systematically optimized. This practical technique, termed ion-pair assisted recovery (IPAR), is compatible with major SDS-based biotechniques and can be easily incorporated into high-throughput proteomic analysis. 相似文献
940.
Zoran Samardzžija Slavko Bernik Ryna B. Marinenko Barbara Malič Miran Čeh 《Mikrochimica acta》2004,145(1-4):203-208
Single crystals of KNbO3 and NaNbO3 were selected from the limited number of suitable alkali compounds that are available and evaluated as possible reference materials for the electron-probe microanalysis (EPMA) of alkaline niobates with a composition described by the general formula K1–XNaXNbO3. The EPMA study verified that KNbO3 and NaNbO3 single crystals are stable under the electron beam and compositionally homogeneous. A quantitative microanalysis confirmed the composition of pure KNbO3, while the NaNbO3 crystal contained 0.3 mass fraction % of Ca. A significant improvement in the accuracy of the quantitative EPMA of polycrystalline potassium–sodium niobates was achieved using these single crystals as standards. The crystals can also be useful as reference materials for the analysis of sodium and potassium in other materials. 相似文献