A New Generation of "Cholaphanes": Steroid-Derived Macrocyclic Hosts with Enhanced Solubility and Controlled Flexibility

The macrocyclic "cholaphanes" 3a-c were synthesized from the inexpensive steroid cholic acid. Like earlier relatives they feature substantial cavities with inward-directed hydroxyl groups, suitable for binding polar molecules such as carbohydrates in nonpolar media. New features are the externally directed alkyl chains, promoting solubility in organic solvents, and (in the case of 3b/c) reduced conformational freedom resulting from truncation of the steroidal side-chain. In particular, modeling shows that the smallest macrocycle 3c possesses very little flexibility, preferring an open conformation which is also revealed in the X-ray crystal structure of its pentahydrate. NMR studies indicated that all three cholaphanes form 1:1 complexes with octyl beta-D-glucoside in CDCl(3), with K(a) = 600-1560 M(-)(1). Cholaphanes 3b/c proved able to extract methyl beta-D-glucoside from aqueous solutions into CHCl(3). The transport of methyl beta-D-glucoside across a chloroform barrier was also demonstrated for 3c.     

Water assisted thermal segregation

Solid state purification generally requires efficient diffusion mechanisms in order to allow impurity migration towards the sample surface, from which it can be removed by a suitable mean. Since solid state diffusion just becomes efficient near the melting point, generally high working temperatures are required, resulting in expensive, energy consuming processes. The addition of small amounts of a common liquid solvent of both matrix and impurity results, even at low temperatures, in effective diffusion mechanisms the thermodynamical aspects of which are discussed in this work. Thermal cycling enhances the efficiency of the described process. Its concerns industrial and analytical applications.     

The Lewis basicity of the [Pt3(μ-CO)3(PR3)3] clusters and the X-ray crystal structure of [{ZnI2}{Pt3(μ-CO)3(PPh(i-Pr)2)3}]

The cluster compounds [Pt₃(μ-CO)₃(PR₃)₃] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX₂, and Group XIII, MX₃, to form cluster compounds of the composition [{MX_n}{Pt₃(μ-CO)₃(PR₃)₃}]. The X-ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt₃(μ-CO)₃(PPh(i-Pr)₂)₃}].     

Structure and reactivity of xanthocorrinoids. Part V. Formation of trans-diol derivatives of 5,6-dihydrocobyrinic acid from xanthocorrinoids under acidic conditions

On treatment with H₂SO₄/MeOH, epimerization of hexamethyl cis-5,6-dihydroxycobyrinate c,8-lactam ( 3 ) takes place quantitatively at C(6), yielding the corresponding trans-diol 4 . The corresponding lactone 7 , whose structure has been established by X-ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions.     

Elution order in gas chromatography

The retention behavior of a heterogeneous group of solutes has been examined on seven different stationary phases under isothermal and temperature-programmed conditions. Both ΔH_v (enthalpy of solute vaporization from the stationary phase) and ΔS_v (entropy of solute vaporization from the stationary phase) values were determined for each solute – stationary phase combination under isothermal conditions. Both program rate and carrier gas velocity were shown to affect solute elution order. Unless these and other experimental factors discussed are controlled, column equivalency studies based on solute elution order have dubious value.