Rotating frame spin—lattice relaxation in solid hydrated methaemoglobin

Proton T_1? relaxation times in two samples of methaemoglobin with different water contents showed that a process occurs with a correlation time of the order 10^?s s at 240 K. This is probably an exchange of molecules between bound and free water.     

Adsorption of octadecyltrimethylammonium chloride and adsolubilization on to cellulosic fibers

The coadsorption of different organic solutes on cellulosic fibers treated with octadecyltrimethylammonium chloride (ODTMA) has been studied. In the absence of ODTMA cellulosic fibers had little tendency to retain organic compounds. The enhanced solute incorporation was ascribed to the adsolubilization of these compounds on the aggregated domains of the adsorbed surfactant molecules at the solid/liquid interface. The specific shape of solute coadsorption isotherms indicated that the adsolubilization process may be regarded as a partition phenomenon between the aqueous bulk phase and the adsorbed surfactant aggregates. The decrease in solute uptake at the cellulose/water interface above the CMC of ODTMA was ascribed to micelle formation in the bulk solution and to the ensuing micellar solubilization of organic solutes. Preliminary experiments performed using vertical fixed bed columns showed that modified cellulosic fibers can be conveniently used as substrate for treating organic pollutants.     

Metastable crystalline lamella of cetylpyridinium chloride in the Krafft transition

The metastable crystalline lamella was found in the Krafft transition of aqueous cetylpyridinium chloride (CPC) solutions. Temperature-dependent profiles of small-angle X-ray scattering (SAXS) for the CPC solution incubated for 10 min at 5 degrees C exhibited the metastable lamella structure with a lattice spacing of dL = 3.19 nm at temperatures below 12 degrees C and the stable lamella structure with a lattice spacing of dL = 2.85 nm at temperatures between 12 and 19 degrees C. The former lamella structure, however, was not observed in the temperature scanning SAXS profiles of the CPC solution incubated for 24 h at 5 degrees C. The latter lamella structure observed in the SAXS profile mentioned above started melting at 18 degrees C. The electric conductance change of the CPC solution with a time elapsed after dropping the temperature showed the existence of the temperature-dependent induction period in the Krafft transition, indicating high activation energies for the transition. In the differential scanning calorimetry measurements over temperatures ranging from 5 to 30 degrees C, a single endothermic enthalpy peak at 19 degrees C observed for the CPC solution incubated at 5 degrees C for a longer period than 6 h was split into double peaks at 14 and 19 degrees C when the same solution was incubated at 5 degrees C for a shorter period than 6 h. The observed calorimetric behavior is explained by the existence of the metastable crystalline state that grows faster and melts at a lower melting temperature than the stable crystalline state.     

Thermally induced oxidative trimerization of benzimidazole by copper(II) chloride in the solid state

Benzimidazolium trichlorocuprate(II) undergoes a redox reaction in the solid state at elevated temperature (∼240°C) to produce the cyclic trimer of benzimidazole and cuprous chloride. The trimer has been characterized by IR, NMR, and Mass spectroscopy. It has also been synthesized in lower yield by heating the mixtures of CuCl₂ and benzimidazole in different ratios or heating other compounds of CuCl₂ and benzimidazole. The absorption, emission, and excitation spectra of the trimer in two different solvents (TFA and DMSO) and a comparison of these results with those of benzimidazole are presented here.     

Conformations of fold part in isotactic polypropylene lamella with diamond lattice model

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Complexes of octadecyltrimethylammonium polyacrylate: properties in solution,gel and solid forms

A polymer-surfactant complex (OTAPA) was prepared by titration of aqueous poly(sodium acrylate) with stoichiometric amounts of octadecyltrimethylammonium chloride. The resulting product is not water-soluble and does not dissolve in most polar and nonpolar, liquids. OTAPA has peculiar thermal behaviour and interesting structural properties. It has a high melting temperature and decomposes around 350 °C. According to preliminary X-ray findings, the complex is formed by an arrangement of alkyl chains around the polymer skeleton, packed into a layered structure. The complex forms an elastic gel in ethylene glycol, and, to a much lesser extent, in glycerol or tetrahydrofuran, but is hardly water-soluble. Indeed, the occurrence of micelle-assisted dissolution and the precipitation of OTAPA from such mixtures, upon dilution with water, have been observed. Applications of OTAPA as a hydrophobic modifier of surfaces can be considered.     

Effects of degassing and ionic strength on AFM force measurements in octadecyltrimethylammonium chloride solutions

Sakamoto et al. (Langmuir 2002, 18, 5713) conducted AFM force measurements between silica sphere and fused-silica plate in aqueous octadecyltrimethylammonium chloride (C18TACl) solutions and concluded that long-range attractive force is not observed in carefully degassed solutions. In the present work, AFM force measurements were conducted by following the procedures described by Sakamoto et al. The results showed the presence of an attractive force that was much stronger than the van der Waals force both in air-saturated and degassed solutions. The force was most attractive at 5 x 10(-6) M C18TACl, where contact angle was maximum. At this concentration, which is close to the charge compensation point (ccp) of the glass sphere, the long-range decay lengths (D) were 34 and 38 nm in air-saturated and degassed solutions, respectively. At 10(-5) M, the decay length decreased from 30 to 4 nm upon degassing. This decrease in decay length can be explained by a pH increase (from 5.7 to 6.6), which in turn causes additional surfactant molecules to adsorb on the surface with inverse orientation. The attractive force was screened by an added electrolyte (NaCl), indicating that the attractive force may be of electrostatic origin. Therefore, the very long decay lengths observed in the absence of electrolyte may be ascribed to the fact that the ccp occurs at a very low surfactant concentration.     

On the lattice dynamics of solid nitrogen

Lattice statics and dynamics calculations for α-nitrogen have been done using the 6-exp atom-atom interaction to derive intermolecular forces. The three parameters of this interaction are reduced to one by constraining them so that the unit cell and sublimation energy are calculated to agree with experiment. Choice of the one parameter is then made using spectroscopic data. This 'best' potential is then used to calculate the statics and dynamics of β-nitrogen. This is stable only under pressure, and the calculation of the lattice dynamics under pressure gives a satisfactory agreement with experiment.     

Thermally induced conformational changes in poly(vinyl chloride)

Fourier transform infrared spectroscopy has been used for the detection of thermally induced conformational changes in atactic poly(vinyl chloride) (PVC). Difference spectra emphasize changes in the distribution of gauche defects in the chains as functions of temperature and annealing. Specific bands in the ν(CCl) and δ(CH₂) regions varied with inverse temperature, allowing a calculation of the activation energies of the rotamer species. Conformational changes were also detected in quenched PVC films as a result of annealing below the glass transition temperature, T_g.     

Consequences of lattice relaxability in solid state photodimerizations

With the view to understand the photobehaviour of olefinic crystalline compounds lattice energy calculations have been performed for a number of photodimerizable olefins. It is shown that to rationalize the photoreactivity of the compounds, dynamic topochemical concepts have to be invoked. Although the calculations have been carried out using the ground state geometry with the dispersion constants applicable to the ground state, the results are in agreement with the experimental observations. The limitations of the approach employed are pointed out.     

Microdynamics of solid anilinium chloride

Intraionic C₃ reorientation of the anilinium NH⁺₃ group was evidenced by measurements of the temperature dependence of the proton spin—lattice relaxation time, by rotating frame experiments and cw NMR data. Analysis of the results yielded a rotor hindering potential E = 33.6 kJ/mole and τ_o = 4 × 10⁻¹³ s.     

Theoretical calculation of structures and proton transfer in hydrated ammonia-hydrogen chloride clusters

Ab initio molecular orbital calculations have been performed to investigate the structures and quantum effects of the proton motion in NH(3):HCl:(H(2)O)(n) (n = 0-3) clusters using a MP2/aug-cc-pVDZ level of theory. Three new stable structures and one transition-state structure are investigated for these clusters. The detailed analyses of the intermolecular interactions suggest that three-body interactions play an important role to determine the relative stability in each size of cluster. The quantum effects of the proton motion result in frequency shifts for proton-stretching modes. Our one-dimensional and two-dimensional models fairly closely reproduce the experimental proton-stretching vibrational frequency of the NH(3):HCl cluster. The most stable isomer for n = 1 has a proton-transfer structure, which is weakened by the quantum effects of the proton motion.     

Thermodynamics of calcium chloride in highly concentrated aqueous solution and in hydrated crystals

Measured values of the pressure of H₂O over saturated solutions in equilibrium with the dihydrate, tetrahydrate or hexahydrate of CaCl₂ are converted to osmotic coefficients and compared with literature values for solutions of smaller molality. It is found that the osmotic coefficient is constant, within the uncertainty, from about 7 mol-kg^–1 to soturation at all temperatures from 25 to 100°C. From this simple approximation, the activity coefficient is calculated for high molalities and at saturation. By combination of these results with other established data, entropies and Gibbs energies of formation are calculated for the crystalline hydrates of CaCl₂.     

Loading of praziquantel in the crystal lattice of solid lipid nanoparticles

Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans. Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this article, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential (ZP) were 500 nm and −34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography, were 99.06 ± 0.3 and 17.48 ± 0.05, respectively. Effective incorporation of PZQ into the particles was confirmed by small angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room temperature (25 °C) and at 4 °C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days. Results showed a relatively long-term physical stability after storage at 4 °C, without drug expulsion.     

An unusual structure of the hydrated sodium chloride complex of cryptand [2.2.2]

The solid state structure of the Na[2.2.2]C1 · 3H₂O complex has the sodium ion displaced towards one of the cryptand nitrogens and the chloride and water molecules associated by hydrogen bonds to form a pseudo cube with two chloride ions at opposite corners of the cube and water oxygens at the other six corners.     

Lattice dynamics of solid hydrogen chloride

Lattice dynamics of solid hydrogen chloride is studied, assuming a rigid molecule, in the harmonic and pair potential (Lennard-Jones interaction) approximation between atoms with the inclusion of electrostatic interactions between point dipoles placed on atomic centres. The potential parameters for each of the different non-bonded atom pairs were obtained by means of an optimization routine to give a least-squares fit to observed zone centre (k = 0) frequencies, equilibrium conditions and lattice energy of the lattice.     

Complex formation of vinylidene chloride with hydrogen chloride in the solid phase at low temperatures

Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 170–174, March–April, 1992.     

Solvated positron chemistry. The reaction of hydrated positrons with chloride ions

The reaction of hydrated positrons (c_aq⁺ with cloride ions in aqueous solutions has been studied by means of positron annihilation angular correlation measurements. A rate constant of k = (2.5 ± 0.5) × 10¹⁰ M^?1 s^?1 was found. Probably the reacting positrons annihilated from an e⁺ Cl^? bound state resulting in an angular correlation curve 8% narrower than for the hydrated positron. Carbontetrachloride in benzene seems to give similar, but smaller effect.     

Thermogravimetric analysis of organoclays intercalated with the surfactant octadecyltrimethylammonium bromide

Summary High resolution thermogravimetric analysis has been used to study the thermal decomposition of montmorillonite modified with octadecyltrimethylammonium bromide. Thermal decomposition occurs in 4 steps.The first step of mass loss is observed from ambient to 100°C temperature range and is attributed to dehydration of adsorbed water. The second step of mass loss occurs between 87.9 to 135.5°C temperature range and is also attributed to dehydration of water hydrating metal cations such as Na⁺. The third mass loss occurs between 179.0 and 384.5°C; it is assigned to the loss of surfactant. The fourth step is ascribed to the loss of OH units due to dehydroxylation of the montmorillonite and takes place between 556.0 and 636.3°C temperature range. These TG steps are related to the arrangement of the surfactant molecules intercalating the montmorillonite. Changes in the basal spacing of the clay with surfactant are followed by X-ray diffraction. Thermal analysis provides an indication of the stability of the organo-clay.