Lipid-rhodopsin hydrophobic mismatch alters rhodopsin helical content

The ability of photoactivated rhodopsin to achieve the enzymatically active metarhodopsin II conformation is exquisitely sensitive to bilayer hydrophobic thickness. The sensitivity of rhodopsin to the lipid matrix has been explained by the hydrophobic matching theory, which predicts that lipid bilayers adjust elastically to the hydrophobic length of transmembrane helices. Here, we examined if bilayer thickness adjusts to the length of the protein or if the protein alters its conformation to adapt to the bilayer. Purified bovine rhodopsin was reconstituted into a series of mono-unsaturated phosphatidylcholines with 14-20 carbons per hydrocarbon chain. Changes of hydrocarbon chain length were measured by (2)H NMR, and protein helical content was quantified by synchrotron radiation circular dichroism and conventional circular dichroism. Experiments were conducted on dark-adapted rhodopsin, the photo-intermediates metarhodopsin I/II/III, and opsin. Changes of bilayer thickness upon rhodopsin incorporation and photoactivation were mostly absent. In contrast, the helical content of rhodopsin increased with membrane hydrophobic thickness. Helical content did not change measurably upon photoactivation. The increases of bilayer thickness and helicity of rhodopsin are accompanied by higher metarhodopsin II/metarhodopsin I ratios, faster rates of metarhodopsin II formation, an increase of tryptophan fluorescence, and higher temperatures of rhodopsin denaturation. The data suggest a surprising adaptability of this G protein-coupled membrane receptor to properties of the lipid matrix.     

Multinuclear NMR studies of single lipid bilayers supported in cylindrical aluminum oxide nanopores

Lipid bilayers were deposited inside the 0.2 microm pores of anodic aluminum oxide (AAO) filters by extrusion of multilamellar liposomes and their properties studied by 2H, 31P, and 1H solid-state NMR. Only the first bilayer adhered strongly to the inner surface of the pores. Additional layers were washed out easily by a flow of water as demonstrated by 1H magic angle spinning NMR experiments with addition of Pr3+ ions to shift accessible lipid headgroup resonances. A 13 mm diameter Anopore filter of 60 microm thickness oriented approximately 2.5 x 10(-7) mol of lipid as a single bilayer, corresponding to a total membrane area of about 500 cm2. The 2H NMR spectra of chain deuterated POPC are consistent with adsorption of wavy, tubular bilayers to the inner pore surface. By NMR diffusion experiments, we determined the average length of those lipid tubules to be approximately 0.4 microm. There is evidence for a thick water layer between lipid tubules and the pore surface. The ends of tubules are well sealed against the pore such that Pr3+ ions cannot penetrate into the water underneath the bilayers. We successfully trapped poly(ethylene glycol) (PEG) with a molecular weight of 8000 in this water layer. From the quantity of trapped PEG, we calculated an average water layer thickness of 3 nm. Lipid order parameters and motional properties are unperturbed by the solid support, in agreement with existence of a water layer. Such unperturbed, solid supported membranes are ideal for incorporation of membrane-spanning proteins with large intra- and extracellular domains. The experiments suggest the promise of such porous filters as membrane support in biosensors.     

全氟壬烯氧基苯磺酸钠与烷基季铵盐的相互作用

通过六氟丙烯三聚体(全氟壬烯)氧基苯磺酸钠(C₉F₁₇OC₆H₄SO₃Na, OBS)与阳离子碳氢表面活性剂C_nNR[C_nH_2n+1N(CH₃)₃Br, C_nNM, n=8, 10和C_nH_2n+1N(CH₂CH₃)₃Br, C_nNE, n=8, 10, 12]复配, 研究了OBS与C_nNR的摩尔比、 C_nNR疏水链长及C_nNR亲水基团大小对此类阴、 阳离子碳氟-碳氢表面活性剂混合体系的临界胶束浓度(cmc)、 最低表面张力(γ_cmc)、 总饱和吸附量(Γ_tm)及极限分子面积(A_min)的影响. 结果表明, 通过与C_nNR复配, OBS的cmc和γ_cmc均大幅下降, 达到了全面增效的结果. 不同摩尔比的OBS-C₈NE混合体系中, 摩尔比为1:1时表面活性最好, cmc和γ_cmc均最小; 偏离等摩尔比时, OBS过量时混合体系的cmc小于C₈NE过量时混合体系的cmc, 但γ_cmc相差不大. 与单体系相比, OBS-C₈NE混合体系的Γ_tm明显增大、 A_min明显变小. OBS与不同疏水链长的C_nNE复配时, cmc的变化规律为C₈NE>C₁₀NE>C₁₂NE, 表明C_nNE疏水链长的增加能降低混合体系的cmc. 通过比较C_nNM和C_nNE(n=8, 10)的表面活性发现, 改变混合体系中C_nNR的亲水基团大小对混合体系的表面活性无明显影响.     

Structural studies of the monolayers and bilayers formed by a novel cholesterol-phospholipid chimera

Langmuir isotherm, neutron reflectivity, and small angle neutron scattering studies have been conducted to characterize the monolayers and vesicular bilayers formed by a novel chimeric phospholipid, ChemPPC, that incorporates a cholesteryl moeity and a C-16 aliphatic chain, each covalently linked via a glycerol backbone to phosphatidylcholine. The structures of the ChemPPC monolayers and bilayers are compared against those formed from pure dipalmitoylphoshatidylcholine (DPPC) and those formed from a 60:40 mol % mixture of DPPC and cholesterol. In accord with previous findings showing that very similar macroscopic properties were exhibited by ChemPPC and 60:40 mol % DPPC/cholesterol vesicles, it is found here that the chimeric lipid and lipid/sterol mixture have very similar monolayer structures (each having a monolayer thickness of ～26 ?), and they also form vesicles with similar lamellar structure, each having a bilayer thickness of ～50 ? and exhibiting a repeat spacing of ～65 ?. The interfacial area of ChemPPC, however, is around 10 ?(2) greater than that of the combined DPPC/cholesterol unit in the mixed lipid monolayer (viz., 57 ± 1 vs 46 ± 1 ?(2), at 35 mN·m(-1)), and this difference in area is attributed to the succinyl linkage which joins the ChemPPC steroid and glyceryl moieties. The larger area of the ChemPPC is reflected in a slightly thicker monolayer solvent distribution width (9.5 vs 9 ? for the DPPC/cholesterol system) and by a marginal increase in the level of lipid headgroup hydration (16 vs 13 H(2)O per lipid, at 35 mN·m(-1)).     

Effects of lipid chain length on molecular interactions between paclitaxel and phospholipid within model biomembranes

Molecular interactions between an anticancer drug, paclitaxel, and phosphatidylcholine (PC) of various chain lengths were investigated in the present work by the Langmuir film balance technique and differential scanning calorimetry (DSC). Both the lipid monolayer at the air-water interface and lipid bilayer vesicles (liposomes) were employed as model biological cell membranes. Measurement and analysis of the surface pressure versus molecular area curves of the mixed monolayers of phospholipids and paclitaxel under various molar ratio showed that phospholipids and paclitaxel formed a nonideal miscible system at the interface. Paclitaxel exerted an area-condensing effect on the lipid monolayer at small molecular surface areas and an area-expanding effect at large molecular areas, which could be explained by the intermolecular forces and geometric accommodation between the two components. Paclitaxel and phospholipids could form thermodynamically stable monolayer systems: the stability increased with the chain length in the order DMPC (C14:0)>DPPC (C16:0)>DSPC (C18:0). Investigation of paclitaxel penetration into the pure lipid monolayer showed that DMPC had a higher ability to incorporate paclitaxel and the critical surface pressure for paclitaxel penetration also increased with the chain length in the order DMPC>DPPC>DSPC. A similar trend was testified by DSC studies on vesicles of the mixed paclitaxel/phospholipids bilayer. Paclitaxel showed the greatest interaction with DMPC while little interaction could be measured in the paclitaxel/DSPC liposomes. Paclitaxel caused broadening of the main phase transition without significant change at the peak melting temperature of the phospholipid bilayers, which demonstrated that paclitaxel was localized in the outer hydrophobic cooperative zone of the bilayer. The interaction between paclitaxel and phospholipid was nonspecific and the dominant factor in this interaction was the van der Waals force or hydrophobic force. As the result of the lower net van der Waals interaction between hydrocarbon chains for the shorter acyl chains, paclitaxel interacted more readily with phospholipids of shorter chain length, which also increased the bilayer intermolecular spacing.     

Surface adsorption of zwitterionic surfactants: n-alkyl phosphocholines characterised by surface tensiometry and neutron reflection

The surface adsorption of n-dodecyl phosphocholine (C12PC) has been characterised by a combined measurement of surface tension and neutron reflectivity. The critical micellar concentration (CMC) was found to be 0.91 mM at 25 degrees C in pure water. At the CMC, the limiting area per molecule (A(cmc)) was found to be 52+/-3 A2 and the surface tension (gamma(cmc)) to be ca. 40.0+/-0.5 mN/m. The parallel study of chain isomer n-hexadecyl phosphocholine (C16PC) showed a decrease of the CMC to 0.012 mM and a drop of gamma(cmc) to 38.1+/-0.5 mN/m. However, A(cmc) for C16PC was found to be 54+/-3 A2, showing that increase in alkyl chain length by four methylene groups has little effect on A(cmc). The almost constant A(cmc) suggested that the limiting area per molecule was determined by the bulky PC head group. It was further found that the surface tension and related key physical parameters did not vary much with temperature, salt addition, solution pH or any combination of these, thus showing that surface adsorption and solution aggregation from PC surfactants is largely similar to the zwitterionic betaine surfactants and is distinctly different from ionic and non-ionic surfactants. The thickness of the adsorbed monolayers measured from both dC12hPC and dC16hPC was found to be 20-22 A at the CMC from neutron reflectivity. Neither A(cmc) nor layer thickness varied with alkyl chain length, indicating that as the alkyl chain length became longer it was further tilted away from the surface normal direction and the layer packing density increased. It was also observed that the thickness of the layer varied little with surfactant concentration, indicating that the average conformational orientation of the alkyl chain remained unchanged against varying surface coverage.     

The role of molecular shape in bilayer elasticity and phase behavior

A previously developed molecular level model for lipid bilayers [G. Brannigan and F. L. H. Brown, J. Chem. Phys. 120, 1059 (2004)] is extended to allow for variations in lipid length and simulations under constant surface tension conditions. The dependence of membrane elasticity on bilayer thickness is obtained by adjusting lipid length at constant temperature and surface tension. Additionally, bilayer fluidity at various lipid lengths is quantified by analysis of a length versus temperature phase diagram at vanishing tension. Regions of solid, gel-like (hexatic) and fluid bilayer behavior are established by identification of phase boundaries. The main melting transition is found to be density driven; the melting temperature scales inversely with lipid length since thermal expansion increases with lipid aspect ratio.     

A novel strategy to prepare conducting LB films based on TTF derivatives

A new method is described for the preparation of conducting Langmuir-Blodgett films based on tetrathialfulvalene (TTF) derivatives without long alkyl chain substitution. The mixed molecular system of behenic acid (BA) and oxygen-substituted TTF-type donor molecules such as 4,5-ethylenedioxy-4′,5′-ethylenedithio-tetrathiafulvalene (EOET) or bis-ethylenedioxy-tetrathiafulvalene (BO) provides a stable bilayer film at the air/water interface. In the LB films prepared by Y-type deposition, the donor molecules form mixed-valence dimers such as D⁺ D⁰, without secondary treatments. The maximum conductivities of the LB films reached 1.0S cm⁻¹ (EOET + BA) and 25 S cm⁻¹ (BO + BA) at room temperature. The surface pressure/area isotherms and Fourier transform infra-red spectra are also reported with regard to, respectively, film formation on the water surface and the mixed-valence dimer state under different molar ratios of the donors to B A.     

Bilayer thickness in unilamellar extruded 1,2-dimyristoleoyl and 1,2-dierucoyl phosphatidylcholine vesicles: SANS contrast variation study of cholesterol effect

Small-angle neutron scattering on extruded unilamellar vesicles in water was used to study bilayer thickness when cholesterol (CHOL) was added at 44.4 mol% to 1,2-dimyristoleoylphosphatidylcholine (diC14:1PC) and 1,2-dierucoylphosphatidylcholine (diC22:1PC) bilayers. Using the (1)H(2)O/(2)H(2)O contrast variation and the small-angle form of Kratky-Porod approximation, the bilayer gyration radii at infinite contrast R(g,infinity) and the bilayer thickness parameters d(g,infinity) = 12(0.5)R(g,infinity) were obtained at 30 degrees C. Addition of cholesterol to diC14:1PC increased the d(g,infinity) from 3.72 +/- 0.02 to 4.26 +/- 0.01 nm, while in the diC22:1PC bilayers the d(g,infinity) change observed was within the experimental error: +0.23 +/- 0.23 nm.     

新型偶氮苯硫醇衍生物自组装膜的制备与结构表征

自组装单分子膜(ＳＡＭｓ)是近年来引起广泛注意的一种稳定的、二维有序的、致密的有机超薄膜体系,由于其优越的性能,在润滑、吸附、防腐、电化学及微电子等领域中显示出广阔的应用前景[1～4].自组装单分子膜是使用含有各种活性官能团(如-ＣＯＯＨ,-ＳＨ,-Ｓ-Ｓ-,-ＯＨ,-ＣＮ等)的分子,以化学键的形式与相应的基底(如Ａｕ,Ａｇ,Ｃｕ,Ｐｔ,Ｓｉ,Ｍｉｃａ等)相互作用从而自发地形成自组装膜.根据不同的研究或应用目的合理设计组装分子的结构及基底表面,从而得到具有所需功能的自组装单分子膜是近年来界面科学和材料科学等领域研究的热点之一.…     

Structural properties of docosahexaenoyl phospholipid bilayers investigated by solid-state 2H NMR spectroscopy.

Polyunsaturated lipids in cellular membranes are known to play key roles in such diverse biological processes as vision, neuronal signaling, and apoptosis. One hypothesis is that polyunsaturated lipids are involved in second messenger functions in biological signaling. Another current hypothesis affirms that the functional role of polyunsaturated lipids relies on their ability to modulate physical properties of the lipid bilayer. The present research has employed solid-state 2H NMR spectroscopy to acquire knowledge of the molecular organization and material properties of polyunsaturated lipid bilayers. We report measurements for a homologous series of mixed-chain phosphatidylcholines containing a perdeuterated, saturated acyl chain (n:0) at the sn-1 position, adjacent to docosahexaenoic acid (DHA, 22:6omega3) at the sn-2 position. Measurements have been performed on fluid (L(alpha))-state multilamellar dispersions as a function of temperature for saturated acyl chain lengths of n = 12, 14, 16, and 18 carbons. The saturated sn-1 chains are therefore used as an intrinsic probe with site-specific resolution of the polyunsaturated bilayer structure. The 2H NMR order parameters as a function of acyl position (order profiles) have been analyzed using a mean-torque potential model for the chain segments, and the results are discussed in comparison with the homologous series of disaturated lipid bilayers. At a given absolute temperature, as the sn-1 acyl length adjacent to the sn-2 DHA chain is greater, the order of the initial chain segments increases, whereas that of the end segments decreases, in marked contrast with the corresponding disaturated series. For the latter, the order of the end segments is practically constant with acyl length, thus revealing a universal chain packing profile. We find that the DHA-containing series, while more complex, is still characterized by a universal chain packing profile, which is shifted relative to the homologous saturated series. Moreover, we show how introduction of DHA chains translates the order profile along the saturated chains, making more disordered states accessible within the bilayer central region. As a result, the area per lipid headgroup is increased as compared to disaturated bilayers. The systematic analysis of the 2H NMR data provides a basis for studies of lipid interactions with integral membrane proteins, for instance in relation to characteristic biological functions of highly unsaturated lipid membranes.     

Dodecyl maltoside as a solubilizing agent of stratum corneum lipid liposomes

The lytic interactions of the nonionic surfactant dodecyl maltoside (DM) with liposomes formed by a mixture of lipids modeling the stratum corneum (SC) lipid composition were investigated. To this end, the surfactant to lipid molar ratios (Re) and the normalized bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light-scattering (SLS) of the system during solubilization. The fact that the free surfactant concentration was always similar to its critical micelle concentration indicates that the liposome solubilization was mainly ruled by formation of mixed micelles. In addition, the linear dependence established between the level of SLS and Re indicates a progressive incorporation of DM in the liposomes as well as the progressive formation of mixed micelles. DM showed in all cases lower bilayer activity (higher Re values) and greater affinity with vesicles (higher K values) than those reported for its interaction with phosphatidylcholine (PC) liposomes. Thus, whereas the SC lipid liposomes were more resistant to the action of this surfactant, its degree of partitioning into SC bilayers was higher throughout the solubilization process than that exhibited in PC vesicles. Comparison of the present Re values with those reported for the lytic interaction of dodecyl glucoside (DG) with SC liposomes reveals that in the case of DM the bilayer activity was more than three times higher than that for DG in spite of the identical alkyl chain length. Received: 19 July 2001 Accepted: 10 October 2001     

新型偶氮苯硫醇衍生物自组装膜的制备与结构表征

Self Assembled Monolayers(SAMs) of a series of mercapto contained azobenzene derivatives with the structure of CnH2n+1AzoO(CH 2)mSH (where n =4,6,8,10,12; with m =3,5 respectively) were prepared and characterized. Wettability measurement of water on the SAMs demonstrates that molecular packing density in the monolayers increases while the alkyl chain in the molecules is lengthened. Both the n and m values have similar contribution to the wetting property of SAMs. The RA IR spectra reveal that the alkyl chains in the SAMs tilt away dramatically from the surface normal direction with the increase in their length. However, the orientation of azobenzene moiety is found to be influenced slightly by the alkyl chain length, which is due to the tenderness of the molecule.     

Adsorption and thermal reactions of alkanethiols on pt(111): Dependence on the length of the alkyl chain

The adsorption and thermal decomposition of alkanethiols (R-SH, where R = CH3, C2H5, and C4H9) on Pt(111) were studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation. Dissociation of sulfhydryl hydrogen (RS-H) of alkanethiol results in the formation of alkanethiolate; the extent of dissociation at an adsorption temperature of 110 K depends on the length of the alkyl chain. At small exposure, all chemisorbed CH3SH, C2H5SH, and C4H9SH decompose to desorb hydrogen below 370 K and yield carbon and sulfur on the surface. Desorption of products containing carbon is observed only at large exposure. In thermal decomposition, alkanethiolate is proposed to undergo a stepwise dehydrogenation: R'-CH2S --> R'-CHS --> R'-CS, R' = H, CH3, and C3H7. Further decomposition of the R'-CS intermediate results in desorption of H2 at 400-500 K and leaves carbon and sulfur on the surface. On the basis of TPD and XPS data, we conclude that the density of adsorption of alkanethiol decreases with increasing length of the alkyl chain. C4H9SH is proposed to adsorb mainly with a configuration in which its alkyl group interacts with the surface; this interaction diminishes the density of adsorption of alkanethiols but facilitates dehydrogenation of the alkyl group.     

Bolalipid membrane structure revealed by solid-state 2H NMR spectroscopy

Membranes made from three specifically deuterium-labeled ether-linked bolalipids, [1',1',20',20'-2H4]C20BAS-PC, [2',2',19',19'-2H4]C20BAS-PC, or [10',11'-2H2]C20BAS-PC, were analyzed by 2H NMR spectroscopy. Unlike more common monopolar, ester-linked phospholipids, C20BAS-PC exhibits a high degree of orientational order throughout the membrane and the sn-1 chain of the lipid initially penetrates the bilayer at an orientation different from that of the bilayer normal, resulting in inequivalent deuterium atoms at the C1 position. The approximate hydrophobic layer thickness and area per lipid are 18.4 A and 60.4 A2, respectively, at 25 degrees C, and their respective thermal expansion coefficients are within 20% of the monopolar phospholipid, DLPC.     

Igepal CO 520/CnH2n+1OH/H2O体系的相行为与结构特性

随直键醇CnH2n 1OH的链长增加,IgepalCO520/CnH2n 1OH/H2O体系三组分相图中层状液晶区域增加,使得W/O区域上移,W/O区域中最大水增溶量处所需摩尔比CnH2n 1OH/IgepalCO520降低,W/O区域中水的最大增溶量（摩尔分数）却不变．层状液晶中CnH2n 1OH的最佳链长为n＞8,W/O区域中CnH2n 1OH的最佳键长为n＞10,即能获得比较好的与IgepalCO520的配伍性．     

Spectroscopic and semiempirical studies of a proton channel formed by the methyl ester of monensin A

Monensin A is an ionophore able to carry protons and cations through the cell membrane. Its methyl ester (MON1) and its hydrates have been studied in acetonitrile, and its deuterated analogue by Fourier transform infrared (FTIR) and (1)H and (13)C NMR spectroscopies as well as by vapor pressure osmotic and PM5 semiempirical methods. Interestingly, these hydrates show new and unexpected biophysical and biochemical properties. The formation of the hydrates starts with a transfer of a proton from the O(IV)-H hydroxyl group of MON1 to an oxygen atom of a water molecule, which is subsequently hydrated by other water molecules forming the (MON1 + 3H(2)O) species. This hydrate exhibits a ringlike structure in which the water molecules form an almost linear hydrogen-bonded chain. Within this chain, the excess proton fluctuates very fast inside the water cluster as indicated by a continuous absorption in the FTIR spectra. The formation of the (MON1 + 3H(2)O) species is accompanied by a self-assembly process, leading to the formation of a proton channel made up of eight (MON1 + 3H(2)O) units with a length of 60 A, in which the proton can fluctuate over the whole distance. Semiempirical calculations suggest that due to the hydrophobic surface the channel can be incorporated readily in a lipid bilayer. This hypothetical new channel is thought to be able to transport protons through the cell membrane. Thus it is a suitable model for studying proton-transfer processes, and in addition, it may open interesting new fields of application.     

Effect of alkanethiol chain length on gold nanoparticle monolayers at the air-water interface

In this study, we report the effects of the alkyl chain length on alkanethiol-capped gold nanoparticle Langmuir films. Gold nanoparticles (2-3 nm) capped with C(n)H(2n+1)SH (n = 5-12, 14-16, 18) were prepared via a two-phase synthesis. The films were sampled by Langmuir-Schaefer horizontal transfer at various points in the pressure-area isotherm and monitored with transmission electron microscopy. Changes in surface pressure, temperature, and alkyl chain length did not lead to observable differences in the mesoscale film morphology. Pressure-area isotherms at 22 °C, however, revealed that the work of compression and the collapse pressure are directly dependent on alkyl chain lengths of 14 carbons or greater. Variable temperature isotherms suggest that the work of compression is strongly affected by the phase state (i.e., crystalline vs liquid-like) of the gold-thiolate self-assembled monolayer (SAM) capping the nanoparticles.     

The structure of zwitterionic phosphocholine surfactant monolayers

The structure of a zwitterionic phosphocholine (PC) surfactant monolayer adsorbed on the surface of water has been determined using neutron reflectivity in combination with H/D isotopic substitution. The most significant results of this study are the level of hydration of the PC headgroup and the lack of dehydration with increasing temperature and salt addition. The fraction of the alkyl chain (f(c)) immersed in water for all three chain isomers studied was found to be around 0.15, suggesting that the PC headgroup geometries influenced not only the headgroup hydration but also the degree of immersion of the alkyl chain in water. At the critical micelle concentration (CMC), the number of water molecules associated with the PC headgroup in C(m)PC (m = 12, 14, 16) was on order of 15. This value was significantly greater than that obtained for nonionic and ionic surfactants with similar limiting area per molecule at the CMC (A(cmc)). However, the fraction of the chain immersed in water for the ionic and nonionic surfactants was much greater. This suggests that the unique surface biocompatibility of PC surfactants arises from their strong affinity for water, and the relatively low fraction of mixing with the alkyl chain arises from the higher structural order within the PC monolayer. As surface coverage decreased, the number of water molecules associated with each PC headgroup increased, but f(c) remained constant for all the surfactants. This observation was consistent with the small variation in the thickness of the headgroup region, and the entire layer changed little with surfactant concentration. This is attributed to the role of PC headgroup geometries to maintain the conformational order within the layer as packing density varies. Further structural analysis based on a kinematic approach showed that, as the chain length was increased from C12 to C14 to C16 at the CMC, the angle of tilt for the alkyl chain increased from 40 degrees to 48 degrees to 53 degrees , respectively, whereas the thickness of the whole layer and that of the PC head region was largely constant. The almost vertical projection of the PC headgroup from these single alkyl chain surfactants is in sharp contrast to its strongly tilted conformation, as reported for dichain phospholipids such as dipalmitoyl glycerol phosphocholine (DPPC).     

Intercalation of n-alkyltrimethylammonium ions into layered calcium octyl phosphates thermally treated in vacuo

Layered calcium octyl phosphate (CH3(CH2)7OPO3Ca.1.6H2O: CaOP), which is composed of a multilayer alternating bilayer of octyl phosphates and a dicalcium phosphate dihydrate (DCPD)-like phase, was thermally treated in vacuo and the intercalation of n-alkyltrimethylammonium ions into the materials was examined. The octyl groups in the layer were eliminated by outgassing above 250 degrees C to give the amorphous calcium phosphates. Further, the specific surface area was steeply increased and mesopores with a diameter of ca. 2.0 nm were formed. IR results indicated that the surface P-OH groups were generated by outgassing at 250 degrees C. When the CaOP outgassed at 250 degrees C was treated with n-alkyltrimethylammonium ion solutions (carbon number of alkyl group, n=14-18), three XRD peaks reappeared below 2theta=15 degrees and the d-spacing ratio of these peaks was 1:1/2:1/3. These facts indicate that the n-alkyltrimethylammonium ions were intercalated into the amorphous calcium phosphate phases.