No abstract

Hydrogen/deuterium isotope effects on hydrophobic binding were examined by means of reversed-phase chromatographic separation of protiated and deuterated isotopologue pairs for a set of 10 nonpolar and low-polarity compounds with 10 stationary phases having alkyl and aryl groups bonded to the silica surface. It was found that protiated compounds bind to nonpolar moieties attached to silica more strongly than deuterated ones, demonstrating that the CH/CD bonds of the solutes are weakened or have less restricted motions when bound in the stationary phase compared with the aqueous solvent (mobile phase). The interactions responsible for binding have been further characterized by studies of the effects of changes in mobile phase composition, temperature dependence of binding, and QSRR (quantitative structure-chromatographic retention relationship) analysis, demonstrating the importance of enthalpic effects in binding and differentiation between the isotopologues. To explain our results showing the active role of the hydrophobic (stationary) phase we propose a plausible model that includes specific contributions from aromatic edge-to-face attractive interactions and attractive interactions of aliphatic groups with the pi clouds of aromatic groups present as the solute or in the stationary phase.

No abstract

A high-capacity stationary phase for the separation of fullerenes was prepared by immobilizing 3-[(pentabromobenzyl)oxy]propylsilyl (PBB) groups onto silica surfaces. The stationary phase was developed by a reciprocal approach. This was possible by finding the structure of solvents that provided high solubilities as well as high eluent strength for chromatographic elution of fullerenes. The increased solubility and increased eluent strength for Ceo seen with solvents containing heavy heteroatoms suggested the preferential interaction of Ceo with such solvent molecules. The stationary phases containing sulfur, chlorine, or bromine in fact resulted in longer retention of fullerenes. The PBB silica showed high retentivity with excellent efficiency for fullerenes, permitting the use of solvents providing high solubilities, such as carbon disulfide and 1,2,4-trichlorobenzene for gramscale separations with ordinary HPLC equipment HPLC is an indispensable technique for the purification of fullerenes, although a very convenient method was reported recently for the isolation of Cm using calixarene.2 This is because HPLC can provide a means to separate fullerenes of various sizes through C9o or larger.3 The packing materials for HPLC currently employed, however, possess relatively low capacities, allowing only small-scale separations. An exception is the low-efficiency charcoal column that was used to achieve rough separations of C6o and C70•4Considerable effort has been made to prepare high-capacity HPLC packing materials for fullerene separation. Stationary phases with electron acceptors,5 electron donors,56•6 and aromatic groups shaped to fit fullerene surfaces63•7 showed a greater capacity than conventional ones including inorganic adsorbents,8 octadecylsilyl (Ci«) silica,3b d e•9 or poly (styrene-co-divinylbenzene) beads.10 In the chromatographic separation utilizing fullerene-* Nacaiai Tesque, Inc.