Abstract  A bacterium designated Pseudonocardia sp. strain ENV478 was isolated by enrichment culturing on tetrahydrofuran (THF) and was screened to determine its ability to degrade a range of ether pollutants. After growth on THF, strain ENV478 degraded THF (63 mg/h/g total suspended solids [TSS]), 1,4-dioxane (21 mg/h/g TSS), 1,3-dioxolane (19 mg/h/g TSS), bis-2-chloroethylether (BCEE) (12 mg/h/g TSS), and methyl tert-butyl ether (MTBE) (9.1 mg/h/g TSS). Although the highest rates of 1,4-dioxane degradation occurred after growth on THF, strain ENV478 also degraded 1,4-dioxane after growth on sucrose, lactate, yeast extract, 2-propanol, and propane, indicating that there was some level of constitutive degradative activity. The BCEE degradation rates were about threefold higher after growth on propane (32 mg/h/g TSS) than after growth on THF, and MTBE degradation resulted in accumulation of tert-butyl alcohol. Degradation of 1,4-dioxane resulted in accumulation of 2-hydroxyethoxyacetic acid (2HEAA). Despite its inability to grow on 1,4-dioxane, strain ENV478 degraded this compound for > 80 days in aquifer microcosms. Our results suggest that the inability of strain ENV478 and possibly other THF-degrading bacteria to grow on 1,4-dioxane is related to their inability to efficiently metabolize the 1,4-dioxane degradation product 2HEAA but that strain ENV478 may nonetheless be useful as a biocatalyst for remediating 1,4-dioxane-contaminated aquifers.

Abstract  The effect of five dissolved salts (sodium chloride, calcium chloride, zinc chloride, cadmium chloride, and ammonium chloride) on the enthalpy of mixing of the binary system 1,4-dioxane + acetic acid has been investigated at 303.15 K in an isothermal displacement calorimeter with vapor space. A decreasing trend in excess enthalpy for the salts NH4Cl and NaCl but an increasing trend for the salts CaCl2, ZnCl2, and CdCl2 with increasing salt concentration was observed. The Redlich-Mster equation has been used to fit the experimental enthalpy of mixing data, and the binary parameters have been estimated.

Abstract  A comparative quantitative analysis of the effects of aqueous organic solvents (water-methanol, water-propan-2-ol, water-acetonitrile, water-dioxane, and water-acetone) on the complexation between sodium, potassium, and ammonium cations and 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6), and dicyclohexyl-18-crown-6 (DCH 18C6) ethers was performed in terms of thermodynamic and empirical approaches. In solution, the crown ethers studied form enthalpy-stabilized complexes and complexes with mixed enthalpy-entropy stabilization. The thermodynamic parameters of reagent solvation can affect the stability of NH4+, Na+, and K+ complexes with crown ethers in five ways. It was demonstrated that a changed stability of potassium coronates in water-methanol mixtures is differently contributed by the structure-sensitive parameters of complexation (the enthalpy and entropy of reagent solvation). Changes in the conformational Gibbs energy of solvation of 18C6 and DB18C6 were calculated. Thermodynamic aspects of hypothetical processes in cation extraction with crown ethers were considered. Stabilization of ammonium, sodium, and potassium coronates in aqueous organic solvents was explained, in terms of the nonthermodynamic concept of linear free-energy relations. by a decreased cohesion energy density of solvents.<

Abstract  Complexes equilibrium of (BHPAP) with proton and Sm+3 ion has been measured in various mixed aqueous solvents, viz.; methanol-water, ethanol-water, acetone-water and dioxane-water. Based on potentiometric equilibrium measurements of hydrogen ion concentration at 30 degreesC, ionic strength 0.1 M KNO3 and in the above various mixed solvents, the values of protonation constant of BHPAP-Sm+3 complex have been evaluated. The variation of protonation and stability constants with the inverse of dielectric constant or mole fraction of solvent was studied. Application of Fuoss expression and consideration of electrostatic and non-electrostatic effects are made to explain the above constants.The solid complexes were isolated for each Pr+3 and Nd+3-BHPAP. Elemental analysis, conductance, infrared spectra, and electronic spectra for these solutions and TG, DTG and DTA measurements characterized these solids. The ligand behaves towards the metal ion as a dibasic tetradentate ligand.<

Abstract  A new anionic phosphorothioate ligand that incorporates the bioactive cholesteryl group was obtained (2), Na(RR'P(S)O; R, O-phenyl; R', O-cholesteryl) from the phenylphosphoramidate (1) and NaH in dioxane. In order to test the coordination ability of 2, two organoarsenic derivatives were prepared O(C6H4)(2)AsS(O)PRR' (3) and S(C6H4)(2)AsS(O)PRR' (4) by reacting 2 with 10-chlorophenoxarsine or 10-chlorophenothiarsine. Compounds 2, 3, and 4 were characterized by elemental microanalysis, IR, multielement NMR (H-1, C-13, and P-31), and mass spectrometry. The spectroscopic data suggest that the ligand is bonded to the arsenic only through the sulfur donor atom in both organoarsenic derivatives. (C) 2000 John Wiley & Sons, Inc.

Abstract  The electromotive forces (emF) E-A and E-C of the following concentration cells with transference: Ag/AgCl/KCl(m(2))parallel to KCl (m(1))\AgCl\Ag and KxHg1-x\KCl (m(1))parallel to KCl (m(2))\KxHg1-x, respectively, together with the emfs E-MAX of the corresponding double cell without transference: KxHg1-xKCl (m(1))\AgCl\Ag-Ag\AgCl\KCl (m(2))\KxHg1-x have been measured at KCl molalities m (m(1) fixed and m(2) varied, with m(2) > m(1)) approximately up to the KCl solubility limit in 12 solvent mixtures for the three aqueous-oganic solvent systems (ethylene glycol + water),(acetonitrile + water), and (1,4-dioxane + water) up to 0.8 mass fraction of organic component. For all the cases explored, the E-A vs. E-MAX relation is linear over the whole KCI molality range. The ionic transference numbers tof KCI determined therefrom show a curvilinear dependence on the mass fraction of the organic component of the relevant solvent mixture and are found to fall in the range 0.52-0.48, viz, within +/-4% of exact equitransference (t(+) = t(-) = 0.5). In particular, KCI becomes exactly equitransferent (i.e., an ideal salt bridge) in aqueous mixtures with the following mass fractions of organic component: 0.4 ethylene glycol and 0.09 acetonitrile, as well as 0.12 methanol, and 0.08 and 0.34 ethanol from our recent work. Even if use of KCI as a salt bridge would be somewhat restricted by its limited solubility in high mass fractions of dioxane and acetonitrile and pending extension of investigation to other mixed-solvent systems, the above figures characterize KCI as a fairly good "intersolvental" salt bridge in electrochemistry, electroanalysis, and corrosion science.

Abstract  The solvatochromic behavior of 2,6-dichloro-4-(2,4,6-triphenyl-1-pyridinio)phenolate (WB) was studied by UV-visible spectrophotometry in 32 pure solvents, in binary mixtures of l-butanol-cyclohexane (BuOH-Cyhx), and of water with methanol, ethanol, I-propanol, 2-butoxyethanol (2-BE), acetonitrile, 1,4-dioxane and THF. The solvent polarity, E-T(33) in kcal mol(-1), was calculated from the position of the longest-wavelength intramolecular charge-transfer absorption band of WE and the results were compared with those for 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate [RB, E-T(30)] add of 1-methyl-8-oxyquinolinium betaine [QB, E-T(QB)]. For pure solvents, ET(33) is a linear function of ET(30), with a slope of practically unity. Steric crowding from the two ortho phenyl rings of RE hinders the formation of H-bonds with solvents, which results in similar susceptibilities of WE and RE to solvent acidity. For binary solvent mixtures, all plots of ET versus the mole fraction of l-butanol or water are nonlinear owing to preferential solvation of the probe by one component of the mixed solvent and, when applicable, to solvent micro-heterogeneity. Preferential solvation due to non-specific and specific probe-solvent interactions was calculated for BuOH-Cyhx and water-acetonitrile. Both solvation mechanisms contribute to the non-ideal behavior in the former binary mixture, whereas probe-solvent specific interactions dominate the solvatochromic behavior in the latter. The composition of the probe solvation shell was calculated. In aqueous alcohols, preferential solvation is by the alcohol. In water-aprotic solvent mixtures, preferential solvation of RE and WE is by the solvent which is present in lower concentration, whereas QB seems to form its own, water-rich solvation shell over a wide range of water concentration. Copyright (C) 2000 John Wiley & Sons, Ltd.<

Abstract  (no abstract)

Abstract  The solubilities of 16 alpha,17 alpha-epoxyprogesterone in methanol, ethanol, acetone, ethyl acetate, acetic acid, and 1,4-dioxane were measured using an isothermal method from 283 K to 323 K. A laser monitoring observation technique was used to determine the dissolution of the solid phase in a solid + liquid mixture. The solubility of 16 alpha,17 alpha-epoxyprogesterone in the above solvents increased in the order methanol < ethanol < ethyl acetate < acetone < acetic acid < 1,4-dioxane.

Abstract  NOABSTRACT - no abstract found

Abstract  Solvolytic rate constants at 25-degrees-C are reported for p-methoxybenzyl chloride (1) in aqueous binary mixtures with acetone, acetonitrile, dioxane, dimethyl sulfoxide, ethanol, methanol, and 2,2,2-trifluoroethanol and for benzoyl chloride and p-methoxybenzoyl chloride (2) in aqueous acetonitrile and aqueous dioxane. Product selectivities are reported for solvolyses of 1 in aqueous ethanol and methanol. Logarithms of rate constants for solvolyses of 2 correlate linearly with solvolyses of 1 (unit slope and only a small ''dispersion''-the tendency for the various binary mixtures to show separate correlations), showing that the solvation requirements of S(N)1 reactions of aromatic carboxylic acid chlorides are very similar to those of benzylic chlorides. Similar good correlations are reported vs solvolyses of alpha-phenylethyl chloride and vs Z values. For S(N)1 reactions of chlorides in binary mixtures having similar electrophilicities, the phenomenon of dispersion in Grunwald-Winstein plots (vs Y) and the poor correlation vs Y(Cl) (reported previously) appears to be due to the differences in solvation between aromatic rings and alkyl groups; this difference is largest for binary aqueous mixtures with methanol > ethanol > aprotic solvents. The complex rate-rate profile for similar solvolytic reactions of benzoyl chloride is dissected quantitatively into contributions from two competing reaction channels, one of which shows only a small ''dispersion'' in a correlation with solvolyses of 2; these results are consistent with a mainly dissociative reaction channel for solvolyses of benzoyl chloride in highly aqueous media.<

Abstract  HCl-catalyzed reactions of the hemiperacetals 3-methoxy-3-methyl-7-hydroxy-1,2-dioxepane (1a) and 3-methoxy-3-methyl-6-hydroxy-1,2-dioxane (1b) and of the related ozonides 1-methyl-6,7,8-trioxabicyclo[3.2.1]octane (2a) and 1-methyl-5,6,7-tri-oxabicyclo[2.2.1]heptane (2b) gave peroxidic monocyclic (11-13), bicyclic (14), and (or) tricyclic (15) products. By contrast, reactions of the peracetals corresponding to 1a and 1b, viz., 3-methyl-3,7-dimethoxy-1,2-dioxepane (13a) and 3-methyl-3,6-dimethoxy-1,2-dioxane (13b) gave only non-peroxidic products. Reactions of the persubstituted peracetals 3,6-dimethoxy-3,6-dimethyl-1,2-dioxane (25) and 3,6-dimethoxy-3-isopropyl-6-methyl-1,2-dioxane (27) also gave non-peroxidic products, which resulted from fragmentation of the carbon skeletons.

Abstract  A method for the determination of pravastatin sodium (PS), a cholesterol-lowering agent, in plasma was developed by using an immobilized antibody column extraction followed by high-performance liquid chromatography (HPLC). The analyte was monitored by a laser-induced fluorescence detector after fluorogenic derivatization. The PS antibody was coupled to Sepharose 4B and used as an extraction phase for sample cleanup and extraction of the drug. A plasma sample was applied to the column and washed with water, and the drug was eluted with methanol. N-Dansylethylenediamine (DNS-ED) was coupled to the carboxyl moiety of the drug in the presence of diethyl phosphorocyanidate (DEPC) and triethylamine (TEA) in dioxane. Derivatization was completed in 5 min at room temperature. A column-switching technique was utilized to remove excess reagents and byproducts. A He-Cd laser-induced fluorescence detector was applied to achieve an ultrasensitive determination. The detection limit was 2 pg/injection of PS, which was 20 times more sensitive than the conventional fluorescence detection. The limit of quantitation was 100 pg/mL when 1 mL of plasma sample was available. An average coefficient of variations of the overall method were less than 8% at the concentration range of 1-100 ng/mL. A single oral dose of PS in rats (20 mg/kg) and dogs (5 mg/kg) resulted in average maximum concentrations of 142 sand 310 ng/mL, respectively.<

Abstract  Two approaches have been used to prepare N-alpha-tert-butoxycarbonyl-alpha-methy-beta-3,4-dimethoxy-, or dibenzyloxyphenyl-L-alanine, N-alpha-Boc-alpha-MeDopa (R)2, where R is the methyl or benzyl ether. In the first approach, alpha-methyl-beta-3,4-dihydroxyphenyl-L-alanine (alpha-MeDopa) is reacted with di-tert-butyl dicarbonate (Boc2O) in the presence of sodium bicarbonate under anhydrous conditions. The resultant N-protected derivative (Boc-alpha-MeDopa) is methylated with methyl iodide/sodium carbonate, followed by reaction with methyl iodide/tetramethylammonium hydroxide, and saponification with potassium hydroxide in aqueous dioxane to give N-alpha-tert-butoxycarbonyl-alpha-methyl-beta-3,4-dimethoxyphenyl-L-alanine, Boc-alpha-MeDopa(Me)2, in 30 % overall yield. In the second approach, methyl ester of alpha-methyl-beta-3,4-dihydroxyphenyl-L-alanine is prepared by the thionyl chloride/methanol procedure, followed by N-protection with di-tert-butyl dicarbonate/sodium bicarbonate, sidechain protection with benzyl chloride/tetramethylammonium hydroxide, and saponification with sodium hydroxide in aqueous dioxane to give N-alpha-tert-butoxycarbonly-alpha-methyl-beta-3,4-dibenzyloxyphenyl-L-alanine, Boc-alpha-MeDopa(CH2Ph)2, in 46 % overall yield. The latter derivative has been incorporated into angiotensin II under stepwise solid-phase peptide synthesis and solution coupling conditions.<

Abstract  The kinetics of base hydrolysis of (alphabetaS)-(o-methoxy benzoato)(tetren)cobalt(III) have been investigated in aquo-organic solvent media [0-70% (v/v) cosolvents] at 10 less-than-or-equal-to t/degree-C less-than-or-equal-to 40 (l = 0.01 mol dm-3) using methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, tert-butyl alcohol, ethylene glycol, 2-methoxyethanol, acetone, acetonitrile, 1,4-dioxane and dimethyl sulfoxide as cosolvents. The second-order base hydrolysis rate constant increased non-linearly with increasing mole fraction (X(org)) of all cosolvents, except for the ethylene glycol-water system; ethylene glycol had a rate-retarding effect. The transfer Gibbs energy of the transition state (TS) relative to that of the initial state (IS), for transfer of species from water to mixed solvent varied non-linearly with D(s)-1 and X(org), reflecting the individuality of the cosolvents and thereby suggesting that the relative stabilities of the transition state and the initial state were governed by the preferential solvation effect. The solvent stabilisation of the initial state and the transition state has been assessed for the methanol-water and ethanol-water systems by combining the solubility data of the dithionate salt of the complex with the transfer Gibbs energy data for S2O6(2-). The thermodynamic parameters (DELTAH(dagger) and DELTAS(dagger)) were sensitive to the structural changes in the bulk solvent phase.

Abstract  The sensitized-photoreactions of diphenyliodonium salt and four of its technically relevant derivatives bearing lipophilic substituents were investigated by pseudo-steady-state and time-resolved CIDNP experiments. Singlet (naphthalene, diphenylanthracene, dimethylanthracene) and triplet (xanthone, thioxanthone, Michler's ketone) sensitizers were used in a variety of solvents (acetonitrile, dimethyl sulfoxide, dimethylformamide, methanol, chloroform, tetrahydrofurane, diethylene glycol dimethyl ether, dioxane, toluene). Under all conditions, the primary step leading to CIDNP was found to be electron transfer from the excited sensitizer *Sens to the onium cation On(+). All spin-polarization effects could be explained consistently within the framework of radical pair theory (S-T-0-type CIDNP). Pair substitution, i.e., the transformation of the primary radical pairs RP I (On(.)Sens(.+)) into secondary pairs RP 2 (Ph(.)Sens(.+), where Ph. is the phenyl or an aryl radical) plays a key role for the CIDNP effects and even leads to a field dependence of the polarization phases for the system diphenyliodonium cation/naphthalene in dioxane. Decreasing solvent polarity causes an increase of the rate RP 1 --> RP 2. The introduction of a long lipophilic side chain into the onium salt has the same effect, presumably owing to self-solvation.<

Abstract  New 17-picolyl and 17-picolinylidene androstane derivatives, 3-10, 15, 18, 19, 22 and 23, were synthesized starting from 17α-picolyl-androst-5-en-3β,17β-diol (1) and 17(Z)-picolinylidene-androst-5-en-3β-ol (2). Reaction of 1 with m-chloroperoxybenzoic acid gives 5α,6α-epoxy N-oxide derivative 3, or, with Jones reagent, 3,6-dione derivative 4; while 17α-picolyl-androst-5-en-3β,4α,17β-triol (5) or 3β,4β,17β-triol (6) derivatives are obtainable from 1 using SeO(2) in dioxane. Base-catalyzed tosyl group elimination from 7 or 9 affords AB conjugated derivatives 8 and 10. Oppenauer oxidation of 1 and 2 yields 4-en-3-one derivatives 11 and 12, which, with H(2)O(2) in 4 M NaOH, affords 4α,5α and 4β,5β-epoxides 13, 14, 16 and 17. New 4-methoxy-3-keto derivatives 15 and 18 were obtained from 13 and 14, or, with methanol in 4 M NaOH, from 16 and 17. Reduction of 11 with NaBH(4) gives 22, which was then acetylated to obtain 23. All new derivatives were screened for antitumor activity against human breast adenocarcinoma ER+, MCF-7; human breast adenocarcinoma ER-, MDA-MB-231; prostate cancer AR-, PC-3; human cervix carcinoma, HeLa; and colon cancer, HT-29 cells; as well as one human non-tumor cell line, MRC-5. Compounds 3, 5, 6, 8, 10, 18, 19 and 22 exhibited significant antitumor activity against MDA-MB-231 breast cancer cells; while 5, 6 and 10 also showed strong cytotoxicity against HT-29. Only compound 19 exhibited significant activity against MCF-7 breast cancer cells. No compounds displayed cytotoxicity against non-tumor MRC-5 cells.

Abstract  Terminal aryl alkynes RC6H4C?CH with substituents of different electronic properties and ring position (R = H, 4-CF3, 4-OMe, 2-CF3, 2-OMe, 2-Me) were exposed to ?-radiation (50-400 kGy) in organic solvents (hexane, 1,4-dioxane, ethylacetate, methanol, tetrahydrofuran), at room temperature. The effects arising from substituent, solvent, dilution, and radiation dose allowed to define the conditions suitable for polymerization, which was favored in methanol at increasing dilution of the alkyne. Ortho-substitution represented the key structural element in the substrate, and the derived polyarylacetylenes were characterized in detail, including gel permeation chromatography, thermal analysis, infrared, NMR, UVvis, fluorescence, and scanning electron microscope spectroscopy. The results are consistent with the formation of irregular polymers mainly composed of trans-transoid chains. Controlled aggregation of the polymers by means of an osmosis-based procedure in solvent/non-solvent mixtures allowed the formation of nanostructured materials, in particular of hollow nanospheres from THF/water. The methodology sets the basis for the development of ?-rays-induced polymerization of alkynes, in a transition metal catalyst-free environment. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Abstract  A semi-theoretical approach for predicting k(L)a values (referred to liquid volume) in 18 organic liquids [acetone, aniline, 1-butanol, benzene, cyclohexane, decalin, 1,2-dichloroethane, 1,4-dioxane, ethanol (96%), ethylacetate, ethylbenzene, ligroin, methanol, nitrobenzene, 2-propanol, tetralin, toluene, and xylene] at various operating conditions (including elevated temperatures and pressures) was developed. It was found that the approach is applicable regardless of the hydrodynamic regime (at u(G) <= 0.1 m/s). Temperatures up to 353 K and pressures up to 0.5 MPa were tested. Two different distributors (multiple-hole and single-hole type) were employed. The liquid-phase mass transfer coefficient k(L) was calculated theoretically from the penetration theory on the basis of original definition of gas-liquid contact time. The interfacial area a was defined with respect to the liquid volume. It was found that their product k(L)a must be multiplied by some correction factor in order to take account of the non-spherical (ellipsoidal) shape of the bubbles. When the correction term is correlated to both the Eotvos number (Eo) and the dimensionless temperature ratio, 198 experimental k(L)a values can be fitted reasonably well (average relative error 9.3%).

Abstract  Abstract: Azo compounds, both symmetric and unsymmetric, are cleaved to amine(s) by using commercial zinc dust and ammonium formate of formic acid in methanol, tetrahydrofuran or dioxane at room temperature. The reductive cleavage occurs without hydrogenolysis or hydrogenation of reducible moieties, such as -OH, -CH(3), -OCH(3), -COOH, - COCH(3), halogen, etc. The cleavage is very fast, clean, cost effective and high-yielding if compared with earlier methods, such as those using cyclohexene/5% Pd on asbestos, cyclohexane/10% Pd-C or hydrazine/10% Pd C or Raney nickel. (C) 2002 Elsevier Science Ltd. All rights reserved. ds: Chemistry cument Delivery No.: 526ED e field[29]: 1,4-Dioxane

Abstract  AIM: To prepare liposomes of nosiheptide and study its ability to inhibit hepatitis B virus HBsAg and HBeAg secreted.

METHODS: Liposomes of nosiheptide was prepared by sodium deoxycholate dialysis and sonication. Nosheptide was determined by HPLC and partical size was determined by using laser light scattering instrument. Transmission electron microscopy (TEM) was used to examine the morphology of liposomes. Its actions to inhibit hepatitis B virus HBsAg and HBeAg secreted was studied by a HBV-transfectted cell line (HepG2 2. 2. 15 ).

RESULTS: Encapsulation efficiency of liposomes by chloroform:methanol (2:1, v/v) was higher than that by dioxane. With the increase of the ratio of nosiheptide: PC (W/W), the encapsulation efficiency of liposomes decreased with the increase of ratio of sodium deoxycholate: PC, the liposomes partical size decreased. The liposomes kept stable at -20 degrees C after 2 years. The drug concentrations of liposomes that inhibit HBsAg secreted by (46.9 +/- 2. 6) %, (55.4 +/- 1.2) %, (65 +/- 3) % and HBeAg secreted by (15.1 +/- 2.3) %, (36.2 +/- 1.7) %, (36.8 +/- 2.5) % were 1.25, 2.5, 5.0 microg x mL(-1), respectively.

CONCLUSION: Liposomes of nosheptide can be prepared by sodium deoxycholate dialysis and sonication, which ability to inhibit hepatitis B virus HBsAg and HBeAg secreted is better than nosheptide.

Abstract  The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-resolved data decay profiles of the high-labeled polymer in the mixtures were always triple exponential whereas in pure methanol and dioxane they follow biexponential laws. The data in the mixtures are consistent with two types of monomers and one excimer. Both monomers are able to give rise to excimer in the excited state, one type involving the movement of long distant Np chromophores and the other involving a local reorientation of adjacent Np chromophores. These correspond to different decay times: (1) a long which corresponds to the long distant approach of non-neighboring Np chromophores forming an excimer and (2) a short corresponding to the fast adjustment of two neighboring Np chromophores in order to have the adequate parallel geometry. An additional decay time corresponding to the excimer decay was found to be present at all wavelengths. All the decay times were dependent on the water content of the mixture. An estimation of the two excimer forming rate constants values is made for the mixed media considered in this work. On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobes and by the distance between hydrophobes.

Abstract  The rate constant for the reaction of methyl 2,4-dichloro-3,5-dinitrobenzoate (1) with different piperidine concentrations have been measured spectrophotometrically in nine pure solvents, viz. methanol, ethanol, n-propanol, isopropanol, t-butyl alcohol, acetonitrile, dimethysulphoxide, dioxane and benzene at different temperatures to study the effect of the solvents. The kinetic results postulate three solvation models: (a) alkanol extensively solvating the amine and weakening the intramolecular hydrogen bonding in the intermediate; (b) the non-polar solvents enhance the intramolecular hydrogen bonding in the intermediate increasing the nucleophilicity of amine;(c) the dipolar aprotic solvents solvate the amine and timely solvating the intermediate by intermolecular hydrogen bond. The solvent parameters have been correlated with the rate constant for the reaction through linear free energy relationships. The adequacy of the multi-parametric scales as appropriate approaches to describe the solvent features in microscopic environments has also been analyzed.<