The solid and liquid-crystalline phases of two long chain lead(II) carboxylates have been studied by 13C and 1H NMR spectroscopy. High resolution 13C NMR spectra of the solid phase of lead(II) decanoate and octadecanoate, reveal splittings of the peaks attributed to the carboxylate and adjacent methylene groups. This may result from two different environments for the carboxylate chains coordinated to the same Pb(II) ion. On going from the solid to liquid-crystalline or liquid phases, this splitting is lost, and small changes in chemical shift of the bands due to the methyl and methylene groups are observed. These are attributed to the onset of conformational disordering, and analysis of the data gives a gauche population in good agreement with that from Raman spectra and theoretical calculations. Longitudinal 13C relaxation times are reported. From these, and from spectral data, the -CH3 group is seen to have different dynamics from the rest of the chain, and to retain high mobility even in the solid phase. Further information on the structural changes comes from proton NMR spectroscopy. The transverse 1H relaxation of lead(II) decanoate shows two components, which are suggested to arise from a crystalline, and a relatively amorphous region of the compound. Study of the evolution of these as a function of temperature shows that the amorphous fraction is relatively low up to 335 K. but then increase rapidly, until at 365 K, close to the transition to the L, phase, it is 99 per cent- In parallel to these observations, changes in band shape were also observed and suggest a progressive fusion of the chains up to the temperature of this transition. The global 1H spin-lattice relaxation was also studied as a function of temperature. and two components were observed between room temperature and approximately the tint phase transition. These are associated with populations of hydrogen nuclei with different mobilities. 相似文献
Aqueous solutions of 7,7'-disodiumcromoglycate (7,7'-DSCG) form a variety of mesophases, whose natures depend on concentration and temperature. We have used optical microscopy, N.M.R. (of 2H, 17O and 23Na) and X-ray techniques to construct a phase diagram for this system and to characterize the various mesophases. In the concentration range 3 to 25 wt % 7,7'-DSCG four different mesophases are found. On cooling the isotropic solution an opaque gel phase is first obtained, followed on further cooling by a birefringent glassy liquid. At concentrations below 14wt% it is nematic, while at higher concentrations it appears to be a different, more ordered, phase. At lower temperatures a hexagonal phase is formed which finally solidifies on cooling to - 15°C. The N.M.R. and X-ray characteristics of these mesophases are discussed. 相似文献
The complexes formed from copper(II) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP or HL) in aqueous methanol solution was studied by electrospray ionization mass spectrometry. The solution of a 1:1 complex of Cu(II) with 5-Br-PADAP showed five peaks assignable to a binuclear complex [Cu2L2(AcO)]+ and mononuclear complexes [CuL]+, [CuL(H2O)]+, [CuL(AcOH)]+ and [CuL(HL)]+ (AcO=acetate). Collision activated dissociation revealed the relative order of bonding strengths; Cu–L>Cu–HL>CuL–AcOH>CuL–H2O. The peak intensities of the binuclear complex showed second-order dependency on those of the mono complex. As for the solution of Ni(II)–5-Br-PADAP, no binuclear complex was observed in the mass spectra. Thus, it was suggested that [Cu2L2(AcO)]+ was formed by the fast gas phase reaction: 2[CuL]++AcO−[Cu2L2(AcO)]+. 相似文献
Abstract207Pb N.M.R. data are reported for a number of even chain length lead(II) carboxylates (soaps) at various temperatures. At room temperature, the solid lead(II) decanoate and tetradecanoate show similar spectra, with a single metal ion site, and modest shielding anisotropy. As the temperature is increased, the soaps (hexanoate to octadecanoate) all form a highly ordered smectic phase, which gives a very broad 207Pb signal of linewidth comparable to that of the solid phase. At higher temperatures, the hexanoate to dodecanoate soaps form a lamellar Lα (smectic A) phase, whilst the longer chain length carboxylates melt directly to the liquid phase. Both the lamellar Lα and liquid phase give fairly sharp, isotropic signals, whose chemical shifts and linewidths are strongly temperature dependent. Possible explanations for this effect include paramagnetic contributions to the shielding tensor from low-lying electronic states of Pb(II), and contributions to the observed signal from different coordination species produced in the lead(II) carboxylate system. Although there are discrete changes in chemical shift at the phase transition, the magnitudes observed in all the phases are similar, suggesting that there are no dramatic changes in the metal coordination environment. 相似文献
Silver carboxylates can be made by the reaction of silver nitrate and the corresponding sodium carboxylates. The length of the alkyl chain has a significant impact on the product behavior. In this study, 18, 20, and 22 carbon chains (stearate, arachidate, and behenate, respectively) have been selected. All three sodium carboxylates are very insoluble in water at room temperature. Solutions are obtained above the Krafft temperature, which precipitates lamellar crystals if cooled at the proper cooling rate. Depending on the chain length, metastable morphologies, such as vesicles and tiny fibers, can be seen consecutively before hexagonal plates form. The carboxylate with the shorter chain length reaches equilibrium more quickly. All three silver carboxylates also take on a lamellar structure. Small-angle X-ray scattering (SAXS) shows that the d spacing of the crystals increases as the chain length increases. Cryo-TEM illustrates that the crystallites are the result of micelle nucleation and micelle aggregation. In addition, the crystallization process in the presence of silver bromide nanocrystals has been investigated. In the initial stage, an epitaxial interface is formed between the silver carboxylate crystallites and the cubic silver bromide grains. Budlike and strandlike structures grow because of it. The consequent strand enclosure restrains the crystal growth, which reduces the size and changes the morphology of the crystals. 相似文献
Data are presented for the heats of phase changes and specific heats for the even chain length lead(II) carboxylates from hexanoate to octadecanoate. Structures are proposed by analogy to the properties of “fused” aqueous ampiphilic mesophases. Optical examination under a polarising microscope suggests the phase sequence for the dodecanoate and lower chain length soaps. For tetradecanoate, and above, the V2 phase is absent and the G phase melts directly to the liquid. The chain length dependence of the entropies of the crystal→G and G→V2 or G→liquid transitions demonstrates that disordering of the hydrocarbon chain is a stepwise process. The entropy of the V2→liquid transition is consistent with the melting of a globular solid and may indicate an average micelle size of 4 carboxylate molecules. This leads to a model of the isotropic liquid consistent with the viscosity data previously presented2. 相似文献
The interaction of sodium octanoate, decanoate or dodecanoate with calcium(ii) in aqueous solutions has been studied using turbidity, conductivity and potentiometric measurements. These show a marked alkyl chain length dependence on the behaviour. At the calcium concentration used (1.0 mM), there is little interaction with the octanoate, the decanoate shows initially formation of a 1:1 complex, followed by precipitation, while the dodecanoate precipitates at low surfactant concentrations. The solid calcium carboxylates were prepared, and show lamellar, bilayer structures with planes of calcium(II) ions coordinated to carboxylate groups through bidentate chelate linkages. Thermogravimetry and elemental analyses indicate the presence of coordinated water with the calcium decanoate but not with longer chain carboxylates. The results of both the solution and solid state studies suggest that precipitation of long-chain carboxylates depends on a balance between hydration effects and hydrophobic (largely van der Waals') interactions. Electrostatic effects make little energetic contribution but play the important structural role of ordering the carboxylate anions before precipitation. Differences are observed in the interactions between calcium(II) and long chain alkylcarboxylates and alkylsulfates, and are interpreted in terms of stronger binding to the metal of the carboxylate group. A general mechanism is proposed for calcium carboxylate precipitation from aqueous solution based on this and previous studies. 相似文献
Two series of polymeric mixed-valent diruthenium (II,III) aliphatic carboxylates of formula Ru2[O2C(CH2)n-2CH3]4X (where X=dodecylsulfate (DOS) anion and n=8, 9, 16 and 18, or X=octylsulfonate (OS) anion and n=8, 10, 12, 14 and 18) were synthesized and characterized. Their liquid crystalline properties and crystalline (Cr) structures were analysed; the Cr phases are lamellar in all cases. For long chain DOS derivatives (n=16 and 18) hexagonal and rectangular columnar mesophases (Colh and Colr) with melting temperatures close to 140°C were observed. For long chain OS derivatives (n≥10) a Colh mesophase was observed, with melting temperatures between 140 and 190°C. 相似文献
Discotic β-diketonate liquid crystals containing palladium(II), and oxovanadium(IV), (V≡0), analogous to known copper complexes (which display discotic lamellar and columnar mesophases), have been prepared and characterized. These are the first enantiotropic discotics containing Pd(II) and among the earliest examples containing VO(IV). The best-behaved Pd(II) complex is [Pd(DK 10, 10)2], and it also is probable that the complexes [Pd(DKn,n)2] (n = 7-9) are mesomorphic, however their characterization is difficult due to decomposition in the isotropic phase. The mesophase of [Pd(DK 102,102)2], which appears below 100°C, is suggested to be an example of the rare Nd phase on the basis of optical microscopy. The complex [VO(DK8,8)2] is an enantiotropic discotic vanadyl complex; the monotropic behaviour of [VO(DK 10,10)2] was also confirmed. It is suggested that the discotic phase which occurs for [VO(DK 8,8)2] is more organized than that of [Cu(DK 8,8)2]. 相似文献
The lyotropic mesophases in binary systems of surfactants in water: n-alkylbenzenesulphonates (C8-C12), two chain C12-surfactants, and dodecyl-benzenesulphonic acid, were investigated. The micellar properties were examined by conductometry and viscosimetry. The phase diagrams were determined using crossed polarizers, 2H NMR spectroscopy and polarization microscopy. Besides lamellar and inverse cubic phases, new nematic lyotropic phases have been found, presenting precursors for the lamellar phases, and exhibiting very fast alignment in a magnetic field. 相似文献
The objective of the present work is to analyze the different mesophases observed in a gel synthesized from hydroxypropyl cellulose (HPC) and polyacrylamide (PAAm) and its phase behavior in water. Hydroxypropyl cellulose is a material derived from cellulose it is non toxic and degradable. HPC is widely used in pharmaceutics, food additives, stabilizer, thickener, etc., HPC is approved by the FDA for use in the food industry. HPC has the characteristic that it forms liquid crystals, depending on the solvent and on the concentration of the polymer. In this work a lower critical solution temperature (LCST) and an upper critical solution temperature (UCST) were observed, the resulting gel showed anisotropic, nematic and cholesteric phases in water, the phase formed depended on the concentration of the polymer. 相似文献
Data were obtained for the solution behaviour of cadmium(II) and mercury(II) carboxylates in alcohols. A brief survey of the arguments about the existence of micelles and the current models of surfactant aggregation in non-aqueous media is presented. The plots of solubility against the carboxylate or alcohol chain length are linear for both cadmium and mercury soaps with the solubility having values higher in secondary than primary alcohols. The solution behaviour of metal 9, 10-dihydroxyoctadecanoates shows the effect on solubility, of substitution of dihydroxyl groups at the middle of the carbon chain. Recrystallisation temperatures of the dihydroxyoctadecanoates suggest the loss of stereochemical configuration in solution and indicate similarity in the mode of aggregation. The solution temperatures of cadmium soaps are very close to the temperatures of their phase transitions while those of mercury and lead soaps are lower than their fusion or phase transition temperatures. This behaviour is interpreted to be due to differences in the energy required for the disruption of the crystal structure which dominates the solubility mechanism. 相似文献
Variable temperature solution 13C NMR of [Mo(CO)3(diglyme)] shows that the chelating diglyme ligand is displaced by the monodentate solvents acetone, methanol and ethanol at low temperature. Free and coordinated solvent are observed at low temperature while at ambient temperature rapid exchange prevents the observation of coordinated solvent. 相似文献
The surface activity and lyotropic phase behaviour of concentrated diglycerol-esters of fatty acids with chain length of C14, C16, C18 and C18:1 (cis-oleic acid) are investigated. Diglycerol-esters show a much stronger reduction in the interfacial tension at a low concentration (0.01–0.1%) than corresponding monoglycerides. The diglycerol-esters form lamellar mesophases above their Krafft point, and no other types of mesophases are found in the temperature region examined (0–80°C). The lamellar phases show a limited swelling capacity, corresponding to a water layer thickness of ≈24 Å, which is found when the ratio of diglycerol-ester to water is 60:40, or lower. At high water concentrations (>90%) multi-lamellar liposomes are formed. The diglycerol-monooleate form lamellar phases in water in the temperature region from zero to 80°C. This is in strong contrast to the corresponding glycerol-monooleate, which forms cubic and reversed hexagonal mesophases in water. Oil in water emulsions are stabilised by diglycerol-esters by formation of liquid crystalline interfacial films around the oil droplets, which can be seen in polarised light microscopy. In presence of milk proteins in the aqueous phase the emulsion stability is depending on the protein to emulsifier ratio. At 40°C a mixed interfacial film of diglycerol-monooleate (DIGMO) and protein is present at the oil–water interface, but when cooled to 5°C, the proteins are displaced by DIGMO. This behaviour affects the stability and rheological properties of emulsions stored at low temperatures. 相似文献
The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×105 and 3×106) was investigated in dilute aqueous solution (NaNO3 0.1 mol l−1; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA2 complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) . It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)β102 was found to be close to 7.0) and allowed the formation of the predominant PbA2 species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed. 相似文献
Two series of unsymmetrical diphenyl-1,3-diketones, each species bearing one terminal alkene, have been synthesized. These diketones have been converted into their respective unsymmetrical diphenylisoxazoles [3(5)-(4-ω-alkenyloxyphenyl)-5(3)-(4-alkoxyphenyl)isoxazoles] which have been isolated as equal mixtures of two regioisomers, due to 3,5- and 5,3-substitution of the isoxazole ring. The mesogenic properties of the isoxazole liquid crystals have been studied by polarizing optical microscopy and DSC. The effect of increasing alkoxy chain length (C6-C10) on the properties of the two series of isoxazoles has been examined. The isoxazoles show enantiotropic smectic C, smectic A and nematic mesophases. A detailed 1H and 13C NMR spectroscopic study has examined both the 1,3-diketones and isoxazoles. Proximity of the terminal alkene to the diphenyl core can greatly affect the complexity of the 13C NMR spectra. 相似文献