Journal of Supramolecular Chemistry最新文献

The van der Waals and Platteeuw hydrate equation of state, coupled with the classical thermodynamic equation for hydrates, has been used in the prediction of hydrate formation for over 40 years. The standard state used in these equations is a hypothetical empty hydrate lattice. In part I of this series, we proposed an alternative derivation of these equations using a different standard state. The new hydrate equations were shown to be simpler to use. In part II of this series, we proposed an aqueous phase model tailored specifically for the presence of hydrate inhibitors such as salts and methanol in the aqueous phase. Part III provides a prescription for the incorporation of the new hydrate and aqueous phase models into a multi-phase Gibbs energy minimization program (CSMGem). Part IV compares predictions from the CSMGem program with four other commercially available programs. In this paper, we give a brief overview of each of the papers in the series, discussing the non-ideal solid solution hydrate model, incorporation of all fugacity models using the Gibbs energy minimization technique, and overall results of the CSMGem program.

The crystal structures of 1:2 binary complexes of 18-crown-6 with two thiosemicarbazide derivatives, phenylthiosemicarbazide (PH), (1) and quinoline thiosemicarbazide (QH), (2) are reported. Compound 1 displays a layered structure formed by the association of PH zigzag chains and crown molecules. In compound 2 centrosymmetric QH dimers alternate with the crown spacers in the chains. Both structures are sustained by N–H^…O and N–H^…S hydrogen bonds.

Large-scale nanosecond classical molecular dynamics calculations have been employed to simulate initial clathrate hydrate formation. Preferential formation of small (5¹²) cages in the initial stages of clathrate formation is not found. This observation is compared to the recent NMR observations on the formation of small cages preceding the crystallization process. The result seems to support experimental observations that the formation of structure II SF₆ hydrate does not require occupation of small cages. The decomposition mechanism of gas hydrates has been investigated using classical molecular dynamics. The ‘preservation effect’ that inhibits decomposition of gas hydrates at temperatures above its thermodynamic melting or decomposition points may be explained with a phenomenological model assuming the formation of a thin ice crust layer.

Under acidic conditions and in the presence of appropriate inorganic ions, bipyridyl-type molecules will self-assemble with C-methylcalix[4]resorcinarene to yield a host–guest supramolecular structure in which the resorcinarene adopts the open boat conformation, with the resorcinarene chains linked by the inorganic ions, and bipyridinium-type molecules included as guests that do not interact specifically with the host.

The miscibility of three amphiphilic calix[4]arenes, para-dodecanoylcalix[4]arene, 25,27-bis-diethoxyphosphorytetradodecanoyl-calix-[4]-arene and 25,27-bis-dihydroxyphosphoryloxytetradodecanoyl-calix[4]arene in mixed monolayers, with cholesterol has been studied by Langmuir film method and Brewster angle microscopy (BAM).

Recent advances in single crystal X-ray diffraction have allowed this technique to be used as a valuable tool for the analysis of hydrate structure and composition. With detailed analysis of guest disorder, not only are the guest positions clearly defined, but by using the cage occupancy as a free parameter it becomes possible to obtain estimates of hydrate composition from the absolute cage occupancies. In this way, it is found that the small cage in ethane hydrate is weakly occupied (∼5%), something not seen in previous NMR work. The tilt angle between the ethane C–C bond and the equatorial plane of the large cage was found to be 23°, in good agreement with the value of 25.2° found previously from NMR studies. For the structure H hydrate of methylcyclohexane and methane, methane fills both small cavities to about 80% occupancy. For the structure II hydrate of benzene and xenon, the orientation of benzene in the structure II large cage was located, and xenon was confined strictly to the small cage. Tetrahydropyran in structure II hydrate was shown to float in a boat conformation on the wall of the large cage. We also report lattice parameters for a number of structure II hydrates determined by single crystal diffraction. A rough trend of unit cell parameter with guest size or volume is illustrated, although it is not as yet clear if there are other correlating factors.