Generation of a Chiral Giant Micelle.

Over the past few years, chiral supramolecular assemblies have been successfully used for recognition, sensing and enantioselective transformations. Several approaches are available to control chirality of discrete assemblies (e.g., cages and capsules), but few are efficient in assuring chirality for micellar aggregates. Optically active amino acid-derived surfactants are commonly used to generate chiral spherical micelles. To circumvent this limitation, we benefited from the uniaxial growth of spherical micelles into long cylindrical micelles usually called wormlike or giant micelles, upon the addition of cosolutes. This paper describes the unprecedented formation of chiral giant micelles in aqueous solutions of cetyltrimethylammonium bromide (CTAB) upon increasing addition of enantiopure sodium salt of 1,1'-bi-2-naphthol (Na-binaphtholate) as a cosolute. Depending on the concentrations of CTAB and Na-binaphtholate, chiral gel-like systems are obtained. The transition from spherical to giant micellar structures was probed using rheology, cryo-transmission electron microscopy, polarimetry, and electronic circular dichroism (CD). CD can be effectively used to monitor the incorporation of Na-binaphtholate into the micelle palisade as well as to determine its transition to giant micellar structures. Our approach expands the scope for chirality induction in micellar aggregates bringing the possibility to generate "smart" chiral systems and an alternative asymmetric chiral environment to perform enantioselective transformations.

The chameleon-like nature of zwitterionic micelles: effect of cation binding.

Addition of salts, especially perchlorates, to zwitterionic micelles of SB3-14, C(14)H(29)NMe(2)(+)(CH(2))(3)SO(3)(-), induces anionic character and uptake of H(3)O(+) by SB3-14 micelles. Thus, the addition of alkali metal perchlorates accelerates the acid hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane, HPD, in the presence of SB3-14 micelles, which depends on the local proton concentration at the micelle surface. The addition of metal chlorides to solutions of such perchlorate-modified SB3-14 micelles decreases both the negative zeta potential of the micelles and the observed rate constant for acid hydrolysis of HPD. The effect of the monovalent cations Li(+), Na(+), and K(+) is smaller than that of the divalent cations Be(2+), Mg(2+), and Ca(2+), and much smaller than that of the trivalent cations Al(3+), La(3+), and Er(3+). The major factor responsible for this cation valence dependence of these effects is shown to be electrostatic in nature, reflecting the strong dependence of the micellar surface potential on the cation valence. The fact that the salt effects are not identical after correction for the electrostatic effects indicates that additional secondary nonelectrostatic effects may contribute as well.

Anion-specific binding to n-hexadecyl phosphorylcholine micelles.

Hexadecyl phosphorylcholine (HPC) micelles incorporate anions rather than cations in the interfacial region, giving an anionoid micelle with a negative zeta potential. Hydronium ion incorporation in the micellar pseudophase parallels the increase in the negative zeta potential, and salts increase the rate of A1 hydrolysis of 2-(p-heptyloxyphenyl)-1,3-dioxolane in micellized HPC and inhibit the reaction of OH(-) with naphthoic anhydride. The kinetic effects are larger with NaClO(4) than with NaCl. The increased micellar negative charge with added salts increases the repulsion between headgroups and decreases the aggregation number. These observations are relevant to understanding the behaviors of biological phosphorylcholine amphiphiles.

Efficient intramolecular general-acid catalysis of the reactions of alpha-effect nucleophiles and ammonia oxide with a phosphate triester.

The S(N)2(P) reactions with alpha-effect nucleophiles of the cationic form 1.H(+) of phosphate triester diethyl 8-(N,N-dimethylamino)-1-naphthyl phosphate are catalyzed by the neighboring dimethylammonium group, with accelerations as high as 10(6). Hydroxylamine and its N-methyl and N,N-dimethyl derivatives, which react through oxygen, we presume by way of the zwitterionic ammonia oxide tautomers, are of special interest. The alpha-effect and the efficient general-acid catalysis in this system are mutually reinforcing. The alpha-effect is greater for the reactions of the triester than for the corresponding mono- and diesters and qualitatively different for hydroxylamines RR'NOH, where the likely role of the ammonia oxide tautomer NH(3)(+)-O(-) is evaluated by ab initio calculations. The initial phosphorus-containing product NH(2)OPO(OEt)(2) reacts further with hydroxylamine to generate diethyl phosphate and diimide, identified by its disproportionation to hydrazine and N(2) and its reducing potential.

The chameleon-like nature of zwitterionic micelles: the intrinsic relationship of anion and cation binding in sulfobetaine micelles.

The rate of specific hydrogen ion-catalyzed hydrolysis of 2-( p-heptoxyphenyl)-1,3-dioxolane and acid-base equilibrium of 4-carboxy-1-n-dodecylpyridinium in zwitterionic micelles of SB3-14, C14H29NMe2+(CH2)3SO3(-) are controlled by NaClO4, which induces anionic character and uptake of H3O+ in the micelles. Other salts, e.g., NaF, NaCl, NaBr, NaNO3, NaI, NaBF4, have similar, but smaller, effects on the uptake of H3O+. Salt effects upon zeta potentials of SB3-14 micelles, estimated by capillary electrophoresis, are anion specific, and the anion order is similar to that of the rates of acid hydrolysis and of acid-base equilibria. Fluorescence quenching shows that the micellar aggregation number is not very sensitive to added salts, consistent with electrophoretic evidence. These specific anion effects follow the Hofmeister series and are related to anion hydration free energies.

Hydroxylamine as an oxygen nucleophile. Chemical evidence from its reaction with a phosphate triester.

The reaction of hydroxylamine with 2,4-dinitrophenyl diethyl phosphate gives the O-phosphorylated product, which is rapidly converted to hydrazine and nitrogen gas in the presence of the excess of hydroxylamine.

The chameleon-like nature of zwitterionic micelles. Control of anion and cation binding in sulfobetaine micelles. Effects on acid equilibria and rates.

The rate of specific hydrogen ion catalyzed hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane and equilibrium protonation of 1-hydroxy-2-naphthoate ion in zwitterionic micelles of SB3-14, C14H29NMe2+(CH2)3SO3-, are increased markedly by NaClO4 which induces anionic character and uptake of H3O+ in the micelles. Other salts, for example, NaNO3, NaBr, and NaCl, have similar but much smaller effects on this uptake of H3O+.

Nicotinohydrazide.

The title mol-ecule (alternative name: pyridine-3-carbohydrazide; C(6)H(7)N(3)O) was obtained from the reaction of ethyl nicotinate with hydrazine hydrate in methanol. In the amide group, the C-N bond is relatively short, suggesting some degree of electronic delocalization in the mol-ecule. The stabilized conformation may be compared with those of isomeric compounds picolinohydrazide (pyridine-2-carbohydrazide) and isonicotinohydrazide (pyridine-4-carbohydrazide). In the title isomer, the pyridine ring forms an angle of 33.79 (9)° with the plane of the non-H atoms of the hydrazide group. This lack of coplanarity between the hydrazide functionality and the pyridine ring is considerably greater than that observed in isonicotinohydrazide (dihedral angle = 17.14°), while picolinohydrazide is almost fully planar. The title isomer forms inter-molecular N-H⋯O and N-H⋯N hydrogen bonds, which stabilize the crystal structure.

Pharmacological and phytochemical evaluation of Adiantum ceneatum growing in Brazil.

This work describes the phytochemical analysis and analgesic activity of a non polar fraction obtained from Adiantum cuneatum grown in Brazil. The results showed that the hexane fraction as well as two pure compounds, identified as filicene (1) and filicenal (2), given intraperitoneally, exhibited potent analgesic activity when evaluated in two models of pain in mice, writhing test and formalin-induced pain. Compound 1 presented a calculated ID50 value of 19.5 micromol/kg body weight, when evaluated in writhing test, being about 7-fold more active than some reference drugs, like as acetyl salicylic acid and acetaminophen. It also inhibited both phases (neurogenic and inflammatory) of the formalin test at 10 mg/kg (24 micromol/kg). The chemical composition of the plant grown in Brazil is similar to that grown in other countries. The results confirm and justify the popular use of this plant for the treatment of dolorous processes.

Ammonia oxide makes up some 20% of an aqueous solution of hydroxylamine.

Three independent indirect estimates based on structure-reactivity correlations indicate that ca. 20% of hydroxylamine exists in aqueous solution as ammonia oxide, NH(3)(+)-O(-).

Reactivity and models for anion distribution: specific iodide binding to sulfobetaine micelles.

The reaction of I (-) with methyl naphthalene-2-sulfonate (MeONs) is accelerated by the micellized sulfobetaine surfactants N-decyl, N-dodecyl, N-tetradecyl, and N-hexadecyl- N, N-dimethylammonio-1-propanesulfonate. Concentrations of micellar-bound I (-) were determined by using ion-selective electrodes (ISE), and capillary electrophoresis. At low concentrations, I (-) incorporation fits Langmuir isotherms and is related to changes in micellar surface potentials. Rate effects of dilute KI are fitted quantitatively by a pseudophase model that describes I (-) binding in terms of a sorption isotherm, but at higher [KI], where the simple model predicts saturation, rates increase due to electrolyte invasion. This model considers transfer equilibria of both reactants between water and micelles and second-order rate constants in each pseudophase. Estimated second-order rate constants for reaction of MeONs with I (-) in the micellar pseudophase are 3.2- to 3.5-fold higher than the second-order rate constant, k 2w, in water, depending on surfactant structure and assumptions in the treatment.