Didodecyl Phosphate Research Articles

Synthesis of acid–base bifunctional CaO/ITQ-2 zeolite catalyst for phosphorylation of dodecanol

A series of acid–base bifunctional CaO/ITQ-2 zeolite catalysts were prepared by introducing calcium into the ITQ-2 zeolite. The catalysts were characterized by X-ray diffraction, FT-IR, NH3-TPD and CO2-TPD. The characterization results proved that ITQ-2 zeolite was synthesized by delaminating the MCM-22 zeolite. After modification by CaO, the catalysts could simultaneously have alkaline and acidic sites with little structural change. We then studied the catalytic capabilities of the prepared catalysts in the phosphorylation of dodecanol to di-dodecyl phosphate (DAP). The results show that ITQ-2 catalyst has higher selectivity for DAP than MCM-22. Versus ITQ-2 zeolite, the CaO/ITQ-2 catalysts have excellent acid–base cooperativity. The conversion of phosphoric acid and the selectivity of di-dodecyl phosphate could reach 80.2% and 77.5%, respectively over 3wt.%CaO/ITQ-2 at optimal conditions. The catalytic activity of CaO/ITQ-2 catalyst could be regenerated by roasting after four times of reusing.

Effect of Double-Tailed Surfactant Architecture on the Conformation, Self-Assembly, and Processing in Polypeptide−Surfactant Complexes

This work describes the solid-state conformational and structural properties of self-assembled polypeptide-surfactant complexes with double-tailed surfactants. Poly(L-lysine) was complexed with three dialkyl esters of phosphoric acid (i.e., phosphodiester surfactants), where the surfactant tail branching and length was varied to tune the supramolecular architecture in a facile way. After complexation with the branched surfactant bis(2-ethylhexyl) phosphate in an aqueous solution, the polypeptide chains adopted an alpha-helical conformation. These rod-like helices self-assembled into cylindrical phases with the amorphous alkyl tails pointing outward. In complexes with dioctyl phosphate and didodecyl phosphate, which have two linear n-octyl or n-dodecyl tails, respectively, the polypeptide formed antiparallel beta-sheets separated by alkyl layers, resulting in well-ordered lamellar self-assemblies. By heating, it was possible to trigger a partial opening of the beta-sheets and disruption of the lamellar phase. After repeated heating/cooling, all of these complexes also showed a glass transition between 37 and 50 degrees C. Organic solvent treatment and plasticization by overstoichiometric amount of surfactant led to structure modification in poly(L-lysine)-dioctyl phosphate complexes, PLL(diC8)(x) (x = 1.0-3.0). Here, the alpha-helical PLL is surrounded by the surfactants and these bottle-brush-like chains self-assemble in a hexagonal cylindrical morphology. As x is increased, the materials are clearly plasticized and the degree of ordering is improved: The stiff alpha-helical backbones in a softened surfactant matrix give rise to thermotropic liquid-crystalline phases. The complexes were examined by Fourier transform infrared spectroscopy, small- and wide-angle X-ray scattering, transmission electron microscopy, differential scanning calorimetry, polarized optical microscopy, and circular dichroism.

Influence of the Structure and Composition of Mono- and Dialkyl Phosphate Mixtures on Aluminum Complex Organogels

The rheological properties and structure of organogels formed by the in situ complexation and self-assembly of aluminum isopropoxide and didodecyl phosphate surfactant in decane are investigated as mono-n-dodecyl phosphoric acid and bis(2-ethylhexyl) phosphoric acid complexing agents are added. At low loadings, the bulky bis(2-ethylhexyl) additive disrupts the physical gel structure by changing the packing around the aluminum centers, weakening the transition from viscoelastic fluid to physical network of branched cylinders, and completely suppresses gelation at high loadings. Monododecyl phosphate affects coordination at the Al center. At low substitution, it shifts the composition at which the transition to a physical gel occurs while simultaneously improving long-term stability. Structures deduced from the rheological response are confirmed by small-angle neutron scattering, which shows that the aggregates are locally cylindrical and molecularly thin at all compositions studied, although the cross section of the cylinders depends on the alkyl chain structure and composition of the organic phosphate mixtures.

Structure and Dynamics of Self-Assembling Aluminum Didodecyl Phosphate Organogels

A self-assembled organogel of aluminum isopropoxide and didodecyl phosphate surfactant in decane is studied as a function of the ratio of aluminum:surfactant. The rheology and structure is shown to depend sensitively on this ratio. Small angle neutron scattering shows the aggregates to be locally cylindrical and molecularly thin at all compositions studied. In the presence of excess surfactant, the system displays Maxwellian rheology and behavior reminiscent of transient, entangled networks of wormlike micelles. A large transition in the relaxation time of the system occurs over a narrow composition range near stoichiometric equivalence (aluminum:surfactant = 1:3), indicating the formation of a connected network with physical gel behavior. At a large excess of aluminum this results in a phase separation into gel and nonviscoelastic liquid. The formation of the gel network and subsequent phase separation are rationalized in terms of localized branch points formed in the aggregates by the excess of aluminum isopropoxide.

Effect of the membrane surface charge on the host-guest complex of valinomycin in a synthetic lipid monolayer at the air-water interface

The effect of the membrane surface charge on the host-quest complexation of valinomycin molecules with K[sup +] ions in synthetic lipid monolayers was studied by measuring surface pressure-molecular area isotherms. It was found that the formation of K[sup +]/valinomycin complexes took place when valinomycin was embedded in the monolayer of lipid with negatively charged head groups, such as didodecyl phosphate. On the contrary, no evidence for the complex formation was observed with valinomycin embedded into cationic lipid monolayers such as dioctadecyldimethylammonium bromide monolayer, or with a pure valinomycin monolayer without lipid. It was concluded that the use of negatively charged lipids was a prerequisite for the formation of the K[sup +]/valinomycin complex cation in the mixed monolayer assembly, thereby providing anionic sites for electroneutrality in the membrane environment. Furthermore, the result that two components, valinomycin and didodecyl phosphate, were found immiscible in the mixed monolayer assembly indicated that a possible location for the K[sup +]/valinomycin complex to be formed was at the boundary of the two immiscible micro-monolayer domains. 19 refs., 4 figs., 1 tab.

Phase separation of polymerized mixed liposomes: analysis of release behavior of entrapped molecules with skeletonization

The mixed liposomes, composed of a polymerizable lipid, 1,2-bis(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine (DODPC), and nonpolymerizable membrane constituents, 1,2-dipalmitoyl-3-phosphatidylcholine and sodium didodecyl phosphate, were prepared by an extrusion method. After polymerization, nonpolymerizable constituents were removed to obtain the skeletonized liposome. The release of 5(6)-carboxyfluorescein (CF) and saccharides with various molecular weights through resulting holes was studied

Thermal Decomposition of Long-chain Alkyl Phosphates

Assessment was made of the thermal stability of long-chain alkyl phosphate by thermal analysis (TG/DTA/DSC). Several monoalkyl phosphates (Cn-MAP) differing in chain length (C12, C14, C16) showed essentially the same thermal stability. The decomposition temperature of didodecyl phosphate (C12-DAP) was 257.8°C [40-50°C higher than that of monododecyl phosphate (C12-MAP)]. C12-MAP·2 Na salt was thermally more stable than C12-MAP, but C12-MAP·Na salt was less stable than this.Gas chromatographic analysis of the decomposition gas indicated dodecene to be mainly formed from C12-MAP, whereas 1-dodecanol from C12-MAP·Na salt and C12-MAP·2 Na salt.31P-NMR analysis of C12-MAP decomposition mixtures revealed that the disproportionation of C12-MAP to phosphoric acid (PA) and C12-DAP and condensed phosphate formation fromC12-MAP were competetive with the elimination of olefin from C12-MAP.The elimination of olefins from monoalkyl pyrophosphate [Py- (1.0)] and dialkyl pyrophosphate [Py- (1, 1)] besides from C12-MAP thus must be taken into consideration for assessement of the thermostability of long-chain alkyl phoshates. The formation of [PA+ Py- (0, 0)] from [MAP+DAP +Py- (1, 0) +Py- (1, 1)] appears to be a zero order reaction with an activation energy of 26.2kcal/mol.

Effect of poly(ethylene glycol) on the Ca2+-induced fusion of didodecyl phosphate vesicles.

This paper reports a study of the effect of the dehydrating agent poly(ethylene glycol) (PEG) on didodecyl phosphate (DDP) bilayers and on the fusion activity of DDP vesicles as a function of the molecular weight of PEG. PEG 8K in a concentration of 10 wt % does not induce fusion. However, Ca2+-induced fusion is promoted as reflected by a lowering of the Ca2+ threshold concentration. This effect can most likely be attributed to the dehydrating capacity of the polymer. Interestingly, low concentrations (0.1 wt %) of PEG 20 K induce a moderate fusion capacity. At higher concentrations (0.5 wt %) fusion is inhibited, irrespective of the presence of Ca2+. These molecular weight dependent effects can be rationalized by taking into account that the clouding temperature differs for PEGs of different molecular weights. In the case of PEG 20K a microscopic phase separation will occur at the bilayer-water interface because PEG-PEG interactions and presumably PEG-DDP interactions are favored over PEG-water interactions. As a consequence, the DDP vesicle surface becomes covered with PEG 20K, resulting in a steric stabilization of the vesicles. This will impede or prevent, depending on the polymer concentration, the vesicles from approaching each other sufficiently close for fusion to occur.

PH-dependent fusion of didodecyl phosphate vesicles: role of hydrogen-bond formation and membrane fluidity

Etude par spectrometrie RMN et microscopie electronique des vesicules de didodecylphosphate de sodium

Ca 2+-mediated fusion of didodecyl phosphate vesicles

Ca 2+ induces fusion of didodecyl phosphate (DDP) vesicles and the mechanism of this process has been investigated. The kinetics of aggregation and fusion were monitored by turbidity measurements and by a resonance energy transfer fusion assay, respectively. It appears that fusion represents the rate-limiting step of the overall reaction, since aggregation reveals a Ca 2+ threshold concentration of 1.4 m M while fusion occurs only above 1.75 m M. Interestingly, Mg 2+ does not induce fusion although massive aggregation was observed. Furthermore, it is shown that Mg 2+ inhibits the Ca 2+-induced fusion of DDP vesicles. The occurrence of fusion is further confirmed by electron microscopy and takes place only above the phase transition temperature (28°C) of the DDP bilayer, i.e., an overall fluid membrane is required for the initiation of fusion. To probe Ca 2+-triggered changes in the bilayer-water interface 31P NMR measurements were performed. As a function of the Ca 2+ concentration a splitting of the NMR signal was observed. An assignment was made for phosphate head groups on the inner and outer leaflets of the DDP vesicle bilayer. At a Ca 2+ threshold concentration of 0.13 m M, there is a shift of the signal arising from the inner phosphate head groups, which indicates that Ca 2+ leaks across the bilayer. This process presumably occurs via an unstable inverted structure that may closely resemble the fusion intermediate. The upfield shifts and the substantial line broadening of the 31P NMR signal suggest that the binding of Ca 2+ causes a dehydration of the head groups and a concomitant reduction of the head group mobility. Since these alterations occur on separate vesicles, i.e., prior to aggregation, the involvement of a specific trans (interbilayer) Ca 2+-phosphate complex, triggering the actual fusion process, is discussed. In a process secondary to these Ca 2+-induced physical alterations of the bilayer-water interface, an isothermal phase transition occurs, resulting in an upward shift of the phase transition temperature from 28°C to a temperature higher than 65°C. The results are discussed in the light of comparable results previously obtained on the fusion of didodecyldimethylammonium bromide vesicles. The significant differences between both systems are related to differences in head group hydration thus emphasizing the crucial role of membrane (de)hydration in the mechanism of membrane fusion.

SIGNAL RECEPTIVE CAPSULE MEMBRANE. Ca2+-INDUCED PERMEABILITY CONTROL OF LARGE NYLON CAPSULE COATED WITH SYNTHETIC BILAYER MEMBRANE

Abstract Nylon ultrathin capsules coated with sodium didodecyl phosphate bilayer membrane were prepared. Permeation of NaCl from the inner aqueous phase of the coated capsule was reversibly increased by treating with Ca2+, and decreased to the original rate by washing with EDTA from outside.

Interfacial Adsorption of a Psychotomimetic Drug Using Liquid Scintillation

A study was conducted on the oil–water partitioning and interfacial adsorption of 3H-2-pyrrolidylmethyl N-methyl cyclopentylphenylglycolate (I), an anticholinergic psychotomimetic agent. A new technique for radiotracer adsorption was developed involving the use of liquid scintillation counting. Among the physical parameters examined were partition coefficient, permeation constant, stability constant, and rate constant of I in a two-phase system of water and a lipid, didodecyl phosphate (II). II greatly accelerated the rate of oil–water partitioning of I and exhibited interfacial adsorption with I. The presence of polyanions, such as hyaluronic acid in the aqueous phase, promotes the transfer of drug from the oil to water phase. Equations found applicable to permeation of ions across membranes have been used to describe drug transfer through an oil–water interface.