- Photoprocesses on Colloidal Clay Systems. 2. Quenching Studies and the Effect of Surfactants on the Luminescent Properties of Pyrene and Pyrene Derivatives Adsorbed on Clay Colloids
-
The cationic fluorescent probe trimethylammonium bromide (PN+) is adsorbed by the colloidal particles of the clay minerals montmorillonite and kaolin.The emission spectrum, polarization of fluorescence measurements, and transient fluorescence decay characteristics of PN+ are used to study the nature of its adsorbed state.Quaternary ammonium surfactants of varying hydrocarbon chain length cause a rearrangement of the PN+ molecules on the surface and decrease its interaction with the mineral surface.Quenching studies with nonionic andcationic molecules indicate that diffusion on the surface of montmorillonite is reduced below that observed in aqueous solution while the apparent rates obtained with kaolin particles are increased.Montmorillonite particles with a surfactant bilayer surrounding their surfaces are formed by the addition of an excess amount of surfactant to the colloid.The emission spectrum and the steady-state quenching studies yield information on the location of pyrene on these particles, as well as on the nature of the colloidal particles.
- DellaGuardia, R. A.,Thomas, J. K.
-
-
Read Online
- Effect of Cationic Surfactants on the Conformational Transition of Poly(methacrylic acid)
-
The interaction between poly(methacrylic acid) and alkyltrimethylammonium bromide, CnTAB, cationic surfactants has been investigated in aqueous solutions of pH 8, by use of the photophysics of pyrene and its derivatives.Photophysical studies of these fluorescent probes, both steady-state and pulsed laser studies, show that a conformational transition of PMA is induced by CnTAB.The surfactant induces a coiling up of PMA chains at pH 8, which takes place via a cooperative process.This effect takes places when the concentration of CnTAB is above a critical aggregate concentration, CAC.The CAC is 1 or 2 orders of magnitude less than the cmc of the corresponding micelle.There is a significant effect of surfactant chain length and PMA concentration on the CAC, which provides information on the nature of the CAC and the mechanism of the PMA transition.A model is suggested for the aggregation of PMA-C10TAB based on experimental data.Studies show that the aggregate consists of about 100 C10TAB molecules and 1 coiled polymer chain.
- Chu, Deh-ying,Thomas, J. K.
-
-
Read Online
- Striking improvement in peroxidase activity of cytochrome c by modulating hydrophobicity of surface-functionalized gold nanoparticles within cationic reverse micelles
-
This work demonstrates a remarkable enhancement in the peroxidase activity of mitochondrial membrane protein cytochrome c (cyt c) by perturbing its tertiary structure in the presence of surface-functionalised gold nanoparticles (GNPs) within cetyltrimethylammonium bromide (CTAB) reverse micelles. The loss in the tertiary structure of cyt c exposes its heme moiety (which is buried inside in the native globular form), which provides greater substrate (pyrogallol and H2O2) accessibility to the reactive heme residue. The surfactant shell of the CTAB reverse micelle in the presence of co-surfactant (n-hexanol) exerted higher crowding effects on the interfacially bound cyt c than similar anionic systems. The congested interface led to protein unfolding, which resulted in a 56-fold higher peroxidase activity of cyt c than that in water. Further perturbation in the protein's structure was achieved by doping amphiphile-capped GNPs with varying hydrophobicities in the water pool of the reverse micelles. The hydrophobic moiety on the surface of the GNPs was directed towards the interfacial region, which induced major steric strain at the interface. Consequently, interaction of the protein with the hydrophobic domain of the amphiphile further disrupted its tertiary structure, which led to better opening up of the heme residue and, thereby, superior activity of the cyt c. The cyt c activity in the reverse micelles proportionately enhanced with an increase in the hydrophobicity of the GNP-capping amphiphiles. A rigid cholesterol moiety as the hydrophobic end group of the GNP strikingly improved the cyt c activity by up to 200-fold relative to that found in aqueous buffer. Fluorescence studies with both a tryptophan residue (Trp59) of the native protein and the sodium salt of fluorescein delineated the crucial role of the hydrophobicity of the GNP-capping amphiphiles in improving the peroxidase activity of cyt c by unfolding its tertiary structure within the reverse micelles.
- Maiti, Subhabrata,Das, Krishnendu,Dutta, Sounak,Das, Prasanta Kumar
-
p. 15021 - 15030
(2013/01/15)
-
- Synthesis, characterization and conductivity of quaternary nitrogen surfactants modified by the addition of a hydroxymethyl substructure on the head group
-
Two novel series of hydroxymethyl group-appended quaternary nitrogen surfactants (QNSs) based on the aliphatic N-alkyl-trimethylammonium and aromatic N-alkylpyridinium head groups were synthesized from the appropriate nitrogen head group precursor and 1-bromoalkane. The QNSs were characterized using 1H and 13C nuclear magnetic resonance and infrared spectroscopy, and their purity confirmed using elemental analysis. The solution behavior of the QNSs was investigated by conductivity, assessing both the aggregation concentration as well as the amount of counter-ion dissociation. The results showed a general decrease in the aggregation concentration for the compounds with the hydroxymethyl addition, where the pyridinium compounds were more affected than the ammonium QNSs. In contrast, the extent of counter-ion dissociation (α) from the aggregate was slightly increased for the ammonium compounds but that of the pyridinium compounds was not generally affected by the structural modification.
- Jordan, Deborah,Tan, Eng,Hegh, Dylan
-
p. 587 - 592
(2012/10/29)
-
- Odd-even effect and unusual behavior of dodecyl-substituted analogue observed in the crystal structure of alkyltrimethylammonium-[Ni(dmit) 2]- salts
-
A series of [Ni(dmit)2]- (dmit: 1,3-dithiole-2- thione-4,5-dithiolato) salts of alkyltrimethylammonium (Cn: n represents the alkyl chain length; n = 3 and 518) have been prepared and analyzed by X-ray structural analysis. All complex salts have been found to be composed of alternate sheets of [Ni(dmit)2]- anions and sheets of cations with a pronounced interdigitation of the alkyl chains. However, molecular arrangement differed between (C3)[Ni(dmit)2] and other (Cn)[Ni(dmit)2] (n = 518). Adjacent cations were aligned along the long axis of [Ni(dmit)2]- anion in C3 complex salt, while in others (C5-C18 complex salts), they were aligned toward the short axis. Such a difference in arrangement arose from correlativity between the lengths of the long axis of cation and anion, namely CLCA. Furthermore, relative orientation between the alkyl chain of cation and [Ni(dmit)2]- anion differed between the odd- and even-numbered cations for C10-C18. Whereas the plane of alkyl chain for odd-numbered cation was normal to the plane of [Ni(dmit)2]- anion, that of even-numbered cation was parallel. It was also found that C12 analog behaved like odd-numbered cations. However, in C12 salt, the end methyl group of the dodecyl group adopted unusual end-gauche conformation.
- Dai, Kotaro,Nomoto, Kuniharu,Ueno, Shinji,Tomono, Kazuaki,Miyamura, Kazuo
-
experimental part
p. 312 - 319
(2011/05/13)
-
- Effects of Single-Stranded n-Alkyl Amphiphiles on the Conformational and Dynamic Behavior of Lecithin Sonicated Bilayers and Micelles Studied by 13C NMR. A Measure of Lipid Resistance against Disruption of the Bilayer Orientation
-
The triplet fine structures in the 13C NMR spectra of carbons in the ?-position to nitrogen in several n-alkyltrimethylammonium bromides (TAB's), DMPC, and DPPC have been studied in different aggregational states under conditions of enhanced proton noise decoupling.Under the same conditions, the signals of the hydrophobic tails of the lecithins could also be studied better than hitherto, mainly by virtue of relatively narrow signals.It is shown that relatively small changes in packing and lateral motions can be detected.Intercalation of several n-alkyltrimethylammonium bromides in lecithin vesicles causes no decrease of the lipid -N+(CH3)3 mobility around the CH2-CH2 head-group linkage nor a decrease in acyl chain mobility.Moreover, no changes in acyl chain kinking are detected.On the other hand, the incorporated TAB molecules are forced by the lecithin molecules toward severely restricted head-group and tail mobilities.For those combinations of PC and TAB's where the TAB 13C NMR signals are detectable, a change in the conformational equilibrium toward more extension is found.A packing model for the incorporation of TAB's in PC vesicles is presented which probably has a rather general validity.The behavior of mixed micelles of PC's and TAB's, originating from enhancing the latter's concentration, is also described.In these systems, mobilities and chain kinking are increased with respect to the vesicular state.
- Haan, Jan W. de,Weerd, Roel J. E. M. de,Ven, Leo J. M. van de,Buck, Henk M.
-
p. 5093 - 5099
(2007/10/02)
-