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991.
Boris Mahltig Jean-François Gohy Sayed Antoun Robert Jérôme Manfred Stamm 《Colloid and polymer science》2002,280(6):495-502
This paper reports on the pH-dependent adsorption of weak the polyelectrolytic diblock copolymer poly(2-vinylpyridine)-block-poly(dimethylaminoethyl methacrylate), (PVP-b-PDMAEMA). Aqueous PVP-b-PDMAEMA solutions have been adsorbed on alkaline pretreated silicon substrates. Altogether two copolymers differing in block ratio and molecular weight were used for the investigations. While the electrical charge of both samples in solution was investigated by electrophoretic measurements, the adsorbed polymer layers were studied with ellipsometry and atomic force microscopy (AFM). Depending on pH the electrical charge of both blocks of the diblock copolymer varied. Three different regimes have been identified. Under acidic conditions at pH<5, both blocks are mainly positively charged. At medium pH between 5 and 8, only the PDMAEMA block is positively charged. At pH>8, both blocks are nearly uncharged and a polymer precipitation occurred in solution. Each of these pH regimes was characterized by a specific adsorption behaviour leading to two adsorption maxima at acidic and alkaline pH values, while at medium pH a plateau in the adsorbed amount was observed. Moreover, the structures of the polyelectrolytes formed on the substrate after adsorption were specific to each of the three pH regimes. 相似文献
992.
Ren Yan-Wei Dang Li-Long Li Jun Gao Wei-wei Zhang Feng-Xing 《Journal of Structural Chemistry》2005,46(2):352-357
A novel one-dimensional (1D) chain coordination polymer [Mn2(2,2′-dipha)2(phen)]n has been synthesized by hydrothermal reaction, and characterized by elemental analysis, IR spectroscopy, TGA, and X-ray diffraction. Orange crystals crystallized in the monoclinic system, space group C2/c with a = 19.393(7) Å, b = 19.183(7) Å, c = 19.729(7) Å, β = 90.826(6)°, V = 7338(5) Å3, Z = 8. In the crystal structure, one manganese atom is six-coordinated with four carboxylate oxygen atoms from one pentadentate 2,2′-dipha ligand and two tetradentate 2,2′-dipha ligands, and with two nitrogen atoms of one phen ligand, giving a slightly distorted octahedral geometry. The other manganese atom is five-coordinated with five oxygen atoms from two tetradentate 2,2′-dipha ligands and two pentadentate 2,2′-dipha ligands and has a trigonal bipyramidal environment. The TGA curve shows that the compound is stable below 310°. 相似文献
993.
Yanbing Zhao Wanyu Chen Yajiang Yang Xiangliang Yang Huibi Xu 《Colloid and polymer science》2007,285(12):1395-1400
Ionically cross-linked polyampholytic hydrogels were synthesized by redox copolymerization of acrylamide and an ionic complex
of (N,N-diethylamino)ethyl methacrylate and acrylic acid (designated as PADA hydrogel). The swelling behavior of the hydrogels in
water indicated that a minimal equilibrium swelling ratio is found when the molar ratio of anionic/cationic monomers was 1.55.
In NaCl solution, the hydrogels exhibited the typical swelling behavior of conventional polyampholytic gels. Their equilibrium
swelling ratios increased with an increase in the NaCl concentration. In solutions of multivalent ions (CaCl2 and trisodium citrate solutions), the equilibrium swelling ratios of the hydrogels increased first and were then followed
by a decrease with an increase in salt concentration. Interestingly, an unexpected abrupt swelling phenomenon was observed
when the fully swollen hydrogels in salt solution were transmitted to pure water. The unique swelling behavior of PADA hydrogels
depends not only on the molar ratio of the anionic/cationic monomers but also on the valency of the ions. 相似文献
994.
G.K. Surya Prakash Jinbo Hu Ying Wang George A. Olah 《Journal of fluorine chemistry》2005,126(4):527-532
A fluoride-induced nucleophilic (phenylthio)difluoromethylation method using TMS-CF2SPh has been achieved. This new methodology efficiently transfers “PhSCF2” group into both enolizable and non-enolizable aldehydes and ketones to give corresponding (phenylthio)difluoromethylated alcohols in good to excellent yields. Diphenyldisulfide can also be (phenylthio)difluoromethylated into PhSCF2SPh in high yield. The reaction with methyl benzoate, however, gives only low yield of (phenylthio)difluoromethyl phenyl ketone. The above-obtained PhSCF2-containing alcohols can be further transformed into difluoromethyl alcohols using an oxidation-desulfonylation procedure. This new type of nucleophilic (phenylthio)difluoromethylation methodology may have other potential applications in the medicinal and agrochemical fields. 相似文献
995.
V. L Gein E. N. Bezmaternykh L. F. Gein I. V. Krylova 《Chemistry of Heterocyclic Compounds》2004,40(10):1332-1334
It has been shown that 5-aryl-3-arylamino-4-benzoyl-1H-3-pyrrolin-2-ones cyclize in the presence of conc. H2SO4 to give pyrrolo[3,4-b]quinolines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1543–1545, October, 2004. 相似文献
996.
Comparison
of the fragility index of different eudragit polymers determined by activation
enthalpies
Gabriella Csóka A. Gelencsér Dorottya Kiss Eszter Pásztor I. Klebovich Romána Zelkó 《Journal of Thermal Analysis and Calorimetry》2007,87(2):469-473
The present study aimed to apply fragility
index (m) of polymers in the determination
of the optimal amount of plasticizer in polymer films. The fragility index
of different Eudragit polymers (RS, RL, EPO) was assessed by differential
scanning calorimerty (DSC), applying the Arrhenius connection (logq–1/T
g).
The fragility of Eudragit EPO films proved to be the highest, while in the
case of RS and RL, the increase of the alkyl-chain length caused the increase
of fragility. Studying the effect of plasticizer (triethyl citrate, TEC) on
the m value of Eudragit RL and RS films,
a near linear reduction of the fragility index could be observed between 5–30%
TEC concentration, but above 30%, this value leveled out to constant. 相似文献
997.
998.
999.
Mixed micelles formed by zwitterionic surfactant dimethyldodecylammniopropane sulfonate and short-chain phospholipid 1,2-diheptanoyl-sn-glycero-3-phosphocholine in different proportions in an aqueous medium have been studied physicochemically at an air/water interface and in the bulk by using interfacial tension and pyrene fluorescence intensity measurements, respectively. The critical micellar concentration and free energies of micellization and of interfacial adsorption have been determined. The interfacial study reveals that a mixed monolayer is formed at the air/water interface by the adsorption of surfactant and phospholipid monomers. This has been confirmed by evaluating the interfacial parameters; the maximum surface excess, the minimum area per molecule of a surface-active compound, and the Gibbs surface excess related to surface pressure. The nonideality of mixing, expressed in the terms of the regular solution interaction parameter, #, has negative values over the whole mole fraction range. The negative # values indicate the mutual synergism between the surfactant and phospholipid monomers. The equilibrium distribution of components between micelle and monomer phases was evaluated using a theoretical treatment based on excess thermodynamics quantities evaluated by Motomura's formulation. 相似文献
1000.
Yeh‐Long Chen Po‐Hsu Chen Chao‐Ho Chung Kuang‐Chieh Li Haw‐Yaun Jeng Cherng‐Chyi Tzeng 《Helvetica chimica acta》2003,86(3):778-786
2‐(Aryloxymethyl)‐5‐benzyloxy‐1‐methyl‐1H‐pyridin‐4‐ones 8a – 8g , 2‐(aryloxymethyl)‐5‐hydroxy‐4H‐pyran‐4‐ones 9a – 9g , and 2‐(aryloxymethyl)‐5‐hydroxy‐1‐methyl‐1H‐pyridin‐4‐ones 10a – 10g were prepared from the known 5‐benzyloxy‐2‐(hydroxymethyl)pyran‐4‐one ( 3 ) in a good overall yield. These compounds were evaluated in vitro against a three‐cell lines panel consisting of MCF7 (breast), NCI‐H460 (lung), and SF‐268 (CNS), and the active compounds passed on for evaluation in the full panel of 60 human tumor cell lines derived from nine cancer cell types. The results indicated that 5‐hydroxy derivatives are more favorable than their corresponding 5‐benzyloxy precursors ( 10a – 10g vs. 8a – 8g ), and 1‐methyl‐1H‐pyridin‐4‐ones are more favorable than their corresponding pyran‐4(1H)‐ones ( 10a – 10g vs. 9a – 9g ). Among these three types of compounds, 2‐(aryloxymethyl)‐5‐hydroxy‐1‐methyl‐1H‐pyridin‐4‐ones 10a – 10g were the most cytotoxic; they inhibited the growth of almost all the cancer cells tested. On the contrary, compound 8a (a mean GI50=27.8 μM ), 8b (38.5), 8d (11.0), and 8e (30.5) are especially active against the growth of SK‐MEL‐5 (a melanoma cancer cell) with a GI50 of <0.01, 5.65, 0.55, and 0.03 μM , respectively (cf. Table 2). 相似文献