Binding of Sulfonamide Antibiotics to CTABr Micelles Characterized Using (1)H NMR Spectroscopy.

Interactions of nine sulfonamide antibiotics (sulfadoxine, sulfathiazole, sulfamethoxazole, sulfamerazine, sulfadiazine, sulfamethazine, sulfacetamide, sulfaguanidine, and sulfanilamide) with cetyltrimethylamonium bromide (CTABr) micelles were examined using (1)H NMR spectroscopy. Seven of the nine provided a significant change in the (1)H NMR chemical shift such that the magnitude and direction (upfield vs downfield) of the chemical shift could be used to propose a locus and orientation of the sulfonamide within the micelle structure. The magnitude of the chemical shift was used to estimate the binding constant for seven sulfonamides with CTABr micelles, providing values and an overall pattern consistent with previous studies of these sulfonamides.

Evidence for a catalytic six-membered cyclic transition state in aminolysis of 4-nitrophenyl 3,5-dinitrobenzoate in acetonitrile: comparative brønsted-type plot, entropy of activation, and deuterium kinetic isotope effects.

A kinetic study for reactions of 4-nitrophenyl 3,5-dinitrobenzoate (1a) with a series of cyclic secondary amines in acetonitrile is reported. Plots of the pseudo-first-order rate constant (kobsd) vs [amine] curve upward, while those of kobsd /[amine] vs [amine] exhibit excellent linear correlations with positive intercepts, indicating that the reaction proceeds through both uncatalyzed and catalyzed routes. Brønsted-type plots for uncatalyzed and catalyzed reactions are linear with βnuc = 1.

Dissection of activation parameters in the bell-shaped α-effect following solvent modulation (DMSO-H2O media).

This paper comprises results of our investigation of the α-effect phenomenon for the reaction of O-p-nitrophenyl thionobenzoate (PNPTB) with butane-2,3-dione monoximate (Ox(-), α-nucleophile) and p-chlorophenoxide (p-ClPhO(-), normal-nucleophile) in DMSO-H2O mixtures of varying compositions at 15.0 °C, 25.0 °C, and 35.

Switchable polarity solvent (SPS) systems: probing solvatoswitching with a spiropyran (SP)-merocyanine (MC) photoswitch.

The switchable polarity solvent (SPS) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and an alcohol (e.

Rapidly formed quinalphos complexes with transition metal ions characterized by electrospray ionization mass spectrometry.

Rationale: Electrospray ionization tandem mass spectrometry (ESI-MS/MS) offers the unique opportunity to characterize complexes of the organophosphorus pesticide (OP) quinalphos (PA-Q) with transition metal ions immediately formed after contact. This study complements research looking at longer term kinetics of quinalphos hydrolysis in the presence of transition metal ions and gives insights into the structural features of the initial complex formation in solution. (Hydrolysis reaction: PA-Q + H2 O → PA-OH + HQ, where PA-OH is the diethyl phosphate product and HQ is hydroxyquinoxaline.

A kinetic study on nucleophilic displacement reactions of aryl benzenesulfonates with potassium ethoxide: role of K+ ion and reaction mechanism deduced from analyses of LFERs and activation parameters.

Pseudofirst-order rate constants (k(obsd)) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a-f and Y-substituted phenyl benzenesulfonates 5a-k with EtOK in anhydrous ethanol. Dissection of k(obsd) into k(EtO(-)) and k(EtOK) (i.e.

Photochemical and thermal spiropyran (SP)-merocyanine (MC) interconversion: a dichotomy in dependence on viscosity.

The current study extends our work with spiropyran-merocyanines (SP-MC) as molecular photoswitches by delving into the effects of viscosity. This has led to the interesting finding of a dichotomy in viscosity dependence. Solutions of SP [6'-nitro-1,3,3-trimethylspiro(indolino-2,2'-benzopyran)] in a wide range of ethylene glycol-methanol (EG-MeOH) media (3.

Alkali-metal-ion catalysis and inhibition in the nucleophilic displacement reaction of y-substituted phenyl diphenylphosphinates and diphenylphosphinothioates with alkali-metal ethoxides: effect of changing the electrophilic center from P=O to P=S.

A kinetic study of the nucleophilic substitution reaction of Y-substituted phenyl diphenylphosphinothioates 2 a-g with alkali-metal ethoxides (MOEt; M = Li, Na, K) in anhydrous ethanol at (25.0±0.1) °C is reported.

Pitfalls in assessing the α-effect: reactions of substituted phenyl methanesulfonates with HOO(-), OH(-), and substituted phenoxides in H(2)O.

Toward resolving the current controversy regarding the validity of the α-effect, we have examined the reactions of Y-substituted phenyl methanesulfonates 1a-1l with HOO(-), OH(-), and Z-substituted phenoxides in the gas phase versus solution (H(2)O). Criteria examined in this work are the following: (1) Brønsted-type and Hammett plots for reactions with HOO(-)and OH(-), (2) comparison of β(lg) values reported previously for the reactions of Y-substituted phenyl benzenesulfonates 2a-2k with HOO(-) (β(lg) = -0.73) and OH(-) (β(lg) = -0.

Spirooxazine to merooxazine interconversion in the presence and absence of zinc: approach to a bistable photochemical switch.

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at -30.

Assessing the superelectrophilic dimension through sigma-complexation, SNAr and Diels-Alder reactivity.

In the domain of organic chemistry, S(N)Ar substitutions represent a class of reactions of overwhelming importance, both in synthesis and in the understanding of structure-reactivity relationships, especially the role of sigma-complex intermediates. The primary factor necessary for achievement of S(N)Ar reactions is the presence of a good leaving group, which allows facile rearomatization of the ring undergoing nucleophilic attack. Consistent is the finding that the superelectrophilic chloronitrobenzofuroxans--or furazans--exhibit a very high S(N)Ar reactivity, allowing a number of C-C, C-N, C-O couplings to be achieved that are not accessible with the classical series of nitro-substituted aromatics.

Energy transfer in the azobenzene-naphthalene light harvesting system.

We have investigated the model light harvesting systems (LHSs) A and B typifying energy transfer (ET) between a naphthalene, Np (donor, D), and an azobenzene, Az (acceptor, A), shown schematically in Scheme 2 . These models were actualized as the naphthyl azo molecules 1 and 4 containing a methylene tether (Scheme 1). The methoxy azo molecules 2 and 5, respectively, served as benchmarks for the assessment of ET.

Effects on the reactivity by changing the electrophilic center from C==O to C==S: contrasting reactivity of hydroxide, p-chlorophenoxide, and butan-2,3-dione monoximate in DMSO/H2O mixtures.

Second-order rate constants have been measured spectrophotometrically for the reactions of O-p-nitrophenyl thionobenzoate (1, PNPTB) with HO(-), butan-2,3-dione monoximate (Ox(-), alpha-nucleophile), and p-chlorophenoxide (p-ClPhO(-), normal nucleophile) in DMSO/H(2)O of varying mixtures at (25.0+/-0.1) degrees C.

High sensitivity to transmission of attenuation in the metal activating effect of platinum on sequential H-D exchange at the four C8 sites of inosines in tetrakis(inosine)platinum(II) chloride.

Hydrogen-deuterium exchange of the carbon-bound C(8)-H protons of the inosine residues in tetrakis(inosine)platinum(ii) chloride, S, with Pt binding at N(7), was studied in aqueous buffer solutions at 60 degrees C by (1)H NMR spectroscopy. The kinetics at all four C(8) sites as a function of pD of the D(2)O/OD(-) medium was measured through the disappearance of the C(8)-H signal, which yielded the pseudo first-order rate constant for exchange, k(obs). Plots of k(obs)versus [OD(-)] showed curvature reminiscent of saturation type kinetics and indicative of competitive deprotonation of N(1)-H sites.

1H and 13C NMR assignments for new heterocyclic TAM leuco dyes, (2Z,2'E)-2,2'-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives. Part II.

The (1)H and (13)C NMR spectra of the novel heterocyclic Leuco-TAM dyes, (2Z, 2'E)-2,2'-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives 1-4 as precursors of triarylmethane (TAM)(+) (Malachite Green FB-analog) dyes were completely assigned by 1D and 2D NMR experiments, including DEPT, COSY, HSQC, HMBC, and NOESY. Especially, the diastereotopic gem-dimethyl protons at the C3 and C3' positions of the FB rings were definitively assigned. The (Z,E) isomers adopt the energetically favored three-bladed propeller conformation in solution.

Alkali metal ion catalysis and inhibition in nucleophilic displacement reactions at phosphorus centers: ethyl and methyl paraoxon and ethyl and methyl parathion.

We report on the ethanolysis of the P=O and P=S compounds ethyl and methyl paraoxon (1a and 1b) and ethyl and methyl parathion (2a and 2b). Plots of spectrophotometrically measured rate constants, kobsd versus [MOEt], the alkali ethoxide concentration, show distinct upward and downward curvatures, pointing to the importance of ion-pairing phenomena and a differential reactivity of free ions and ion pairs. Three types of reactivity and selectivity patterns have been discerned: (1) For the P=O compounds 1a and 1b, LiOEt > NaOEt > KOEt > EtO-; (2) for the P=S compound 2a, KOEt > EtO- > NaOEt > LiOEt; (3) for P=S, 2b, 18C6-crown-complexed KOEt > KOEt = EtO(-) > NaOEt > LiOEt.

Mayr electrophilicity predicts the dual Diels-Alder and sigma-adduct formation behaviour of heteroaromatic super-electrophiles.

We report on the dual reactivity, i.e. anionic Meisenheimer sigma adduct formation and Diels-Alder adduct formation, of a series of heteroaromatic super-electrophiles, including 4,6-dinitro-benzofuroxan, -N-arylbenzotriazoles (4), -benzothiadiazole and -benzoselenadiazole.

Alkaline degradation of the organophosphorus pesticide fenitrothion as mediated by cationic C12, C14, C16, and C18 surfactants.

The effect of varying surfactant chain length (C12, C14, C16, C18) on the alkaline hydrolysis of the organophosphorus pesticide fenitrothion was determined for the following series of inert counterion cationic surfactants: dodecyltrimethylammonium bromide (DTABr), tetradecyltrimethylammonium bromide (TTABr), hexadecyltrimethylammonium bromide (CTABr), and octadecyltrimethylammonium bromide (OTABr). Plots of kobs versus [surfactant] at constant [KOH] showed saturation behavior at low total [Br-], and (constrained) S-shaped curvature was observed at high total [Br-]. kobs values increased with increasing surfactant chain length but decreased with added KBr.

Elucidating the mechanisms of acidochromic spiropyran-merocyanine interconversion.

The thermal and photochemical processes associated with the acid-induced conversions of 6-nitroBIPS, SP-1, to form the protonated merocyanine (MC-OH+) were investigated via UV/vis spectrophotometric studies in acetone. It was found that the mechanism of trifluoroacetic acid (TFA)-induced ring-opening of the SP and the rate of MC-OH+ formation follows a general acid catalysis mechanism. In accord with this mechanism, the thermal growth of the acid-induced ring-opened form (MC-OH+) was retarded as the concentration of TFA in the medium was increased.

Degradation of the pesticide fenitrothion as mediated by cationic surfactants and alpha-nucleophilic reagents.

The reaction of fenitrothion with a series of alpha-nucleophile oximates having pK(a) values in the range of 7.7-11.8 was studied both in the absence and presence of cetyltrimethylammonium (CTA(+)) surfactants.

Solvent effect on the alpha-effect: ground-state versus transition-state effects; a combined calorimetric and kinetic investigation.

In a study of the solvent effect on the alpha-effect, second-order rate constants (kNu-) have been determined spectrophotometrically for reactions of a series of substituted phenyl acetates with butan-2,3-dione monoximate (Ox-, alpha-nucleophile) and p-chlorophenoxide (p-ClPhO-, reference nucleophile) in DMSO-H2O (DMSO = dimethyl sulfoxide) mixtures of varying compositions at 25.0 +/- 0.1 degrees C.

Micellar catalyzed degradation of fenitrothion, an organophosphorus pesticide, in solution and soils.

We report on a study of the decomposition of fenitrothion (an organophosphorus pesticide that is a persistent contaminant in soils and groundwater) as catalyzed by cetyltrimethylammonium (CTA+) micelles. The CTA micelles were associated with two types of counterions: (1) inert counterions (e.g.

Catalysis of the ethanolysis of aryl methyl phenyl phosphinate esters by alkali metal ions: transition state structures for uncatalyzed and metal ion-catalyzed reactions.

This paper reports on a spectrophotometric kinetic study of the effects of the alkali metal ions Li+ and K+ on the ethanolysis of the aryl methyl phenyl phosphinate esters 3a-f in anhydrous ethanol at 25 degrees C. Rate data obtained in the absence and presence of complexing agents afford the second-order rate constants for the reaction of free ethoxide (k(EtO-)) and metal ion-ethoxide ion pairs (k(MOEt)). The sequence k(EtO-) < k(MOEt) is established for all the substrates, contrary to the generally observed reactivity order in nucleophilic substitution processes.

Superacidifiers: assessing the activation and the mode of charge transmission of the extraordinary electron-withdrawing SO2CF3 and S(O)(=NSO2CF3)CF3 substituents in carbanion stabilization.

We report on a structural (multinuclear NMR), thermodynamic (pK(a)), and kinetic (Marcus intrinsic reactivity) study of the ionization of benzylic carbon acids activated by an exocyclic (alpha) SO(2)CF(3) group and SO(2)CF(3) or S(O)(=NSO(2)CF(3))CF(3) in the para position of the phenyl ring. The latter exerts an enormous acidifying effect of ca. 8 pK units as compared with 4-H benzyltriflone in Me(2)SO solution, (corresponding to remarkably high Hammett sigma values sigma(p) approximately 1.