Solubilization of N-Alkylpyridinium Ions in Anionic Nematic Lyomesophases

Abstract

Deuterium quadrupole splittings from the aromatic ring of a series of linear N-alkylpyridinium-d 5 ions, with alkyl chains from 1 to 16 carbon atoms, were measured using 2H-NMR spectroscopy. The pyridinium ions, 10% deuteriated in the aromatic ring, were dissolved in nematic anionic lyomesophases prepared from sodium decyl sulfate (SDS) and cesium decyl sulfate (CsDS). With these splittings, the two order parameters that completely describe the average orientation of the aromatic ring with respect to the magnetic field were calculated. The added pyridinium ions have a dramatic effect on the mobility of the CsDS mesophase components. The smaller N-methyl and N-ethylpyridinium ions, C1 and C2, have a disruptive effect on the integrity of the mesophase, C3 and C4 do not have an appreciable effect, and the larger ones, C5 to C12, show the opposite effect, increasing the order of the system with the length of the alkyl chain. This phenomenon, not observed in the SDS mesophase, may be attributed to differences in charge distribution between both surfaces. This interpretation is supported by estimation of the degrees of dissociation and first cmc of SDS and CsDS using conductometric measurements. The results could also be explained if the CsDS mesophase was near to a phase transition and stabilized by the added ions.

Interaction of adrenocorticotropin peptides with microheterogeneous systems — A fluorescence study

“…The alkylpyridinium ions have high affinity for negatively charged aggregates [23,24] and the probability of contact between fluorophore and quencher in the presence of SDS and SDS-PEO micelles is increased, enhancing the quenching compared to PBS medium (Table 3). In those micelles the highest K SV values for ACTH(1-24) fluorescence quenching was observed for N-ethylpyridinium (NEP + ), indicating that its Trp residue is located near to the surface of the aggregates, the preferential location of NEP + .…”

“…Several N-terminal segments of ACTH were found to have hormonal activities and specific receptor binding properties: ACTH binds to steroidogenic receptors, while ACTH(1-10) was found to bind preferentially to central nervous receptors. The fragment ACTH (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) is an antagonist for steroidogenesis without any agonist properties [10]. ACTH may enhance memory cytotoxic responses through a combination of mechanisms such as direct cell alterations or synergy with regulatory cytokines [11].…”

“…As a tool to obtain information about the location of the Trp residue in the presence of the biomimetic systems, we explored the quenching promoted by alkylpyridinium halides, a family of cationic surfactants containing the pyridinium moiety which is an efficient quencher for tryptophan fluorescence, as verified by the decrease in the fluorescence emission of that residue in BSA and small peptides [22]. The convenience of using alkylpyridinium halides as quencher comes also from their high affinity to amphiphilic aggregates with negatively charged surface like SDS [23] and the dependence of its hydrophobicity on the size of the alkyl chain, whose increase causes reduction of the intramicellar mobility and the exchange rate with the aqueous phase [24]. Results from quenching experiments with alkylpyridinium quenchers are thus informative about the location of the peptides in the microheterogeneous systems.…”

Counterion and composition effects on discotic nematic lyotropic liquid crystals

“…They were recrystallized three times from ethyl acetate/ethanol solutions before use. SDS was prepared and purified using a previously reported methodology [13]. Anhydrous NaCl, NaBr and Na 2 SO 4 were purchased from Aldrich and used without further purification.…”

Average Orientation of Benzyl-d5 Alkyl Ethers in Cationic Nematic Lyomesophases

“… − The use of 2 H-NMR quadrupole splittings is possibly one of the simplest methods to estimate molecular order parameters and, from these, to infer the average orientation, and sometimes the location, of guest molecules dissolved in anisotropic solutions. Recently, using 2 H-NMR spectroscopy, we have measured the two order parameters that completely describe the average orientation and have been able to infer the location of the aromatic ring in a series of linear N -alkylpyridinium- d 5 ions, dissolved in cationic and anionic nematic lyotropic liquid crystals. , All the mesophases studied by us were type II systems . We found that addition of small amounts of pyridinium ions to liquid crystal solutions made from hexadecylpyridinium chloride (HDPyCl), tetradecyltrimethylammonium bromide (TDTMABr), and cesium decyl sulfate (CsDS) had an appreciable effect on the mobility of these interfaces.…”