Laser-induced emission from Te2, TeSe,TeS, and SeS in argon matrices

Laser-induced fluorescence spectra are reported for Te₂, TeSe, TeS, and SeS in argon matrices with both natural and isotopically enriched samples. From the total of nine band systems, two new electronic states are believed to have been identified for Te₂ and one each for TeSe and TeS.     

Effects of Side Arm Length and Structure of Para-Substituted Phenyl Derivatives on Their Binding to the Host Cyclobis(paraquat-p-phenylene)

The binding constants with the host cyclobis(paraquat-p-phenylene), 1(4+), have been determined in CH(3)CN by UV-vis spectrophotometry for a series of p-phenylene guests, symmetrically substituted with side arms of varying length and functionality. Semiempirical molecular orbital theory was employed to provide a detailed structural and energetic interpretation of the experimental binding data. In particular, the length of the side arms and the type and position of the heteroatoms on the side arms were systematically varied in order to understand the effects of external interactions on the association constants of the guests with host 1(4+). A large chelate effect involving the ethyleneoxy side arm oxygen atoms and a cooperative effect between the guest aromatic core and the side arms are significant factors which determine the binding with this host. Sequential ethyleneoxy linkages along the side arms markedly increase the binding constant with respect to a compound in which the same number of oxygens along the side arms are separated by longer aliphatic linkages. In addition, a multiplicative rather than additive effect on the binding constant is observed which demonstrates that the oxygen atoms exhibit a strong chelate effect. It was also discovered that while the side arms of these guests contribute most of the driving force for complexation, an aromatic core is necessary for the guest to reside in the cavity of the host. The binding of these guests then is dependent upon cooperation between the arms and the aromatic core. Furthermore, elongation of the central aromatic core with aliphatic side arms containing no heteroatoms leaves the association constant relatively unchanged and replacement of the oxygen atoms with sulfur markedly decreases the observed binding. These effects have been used to rationalize several observations regarding this system in the literature and may serve to improve the design of new supramolecular systems and to better understand the host/guest interaction process.     

Tri-, penta-, and hexa-phospha ruthenocenes

Synthesis and structural studies of the ruthenium(II) ‘sandwich’ complexes [Ru(η⁵-P₃C₂^tBu₂)₂], [Ru(η⁵-P₃C₂C₂^tBu₂)(η⁵-P₂C₃^tBu₃)], [Ru(η⁵-C₅R₅)(η⁵-P₃C₂^tBu₂)] (R=H, Me) are described. The results of a single crystal X-ray structural study of [Ru(η⁵-P₃C₂^tBu₂)₂] are discussed.     

Block copolymers of ethylene oxide and phenyl glycidyl ether: micellization, gelation, and drug solubilization

Three triblock copolymers of ethylene oxide and phenyl glycidyl ether, type E(m)G(n)E(m), where G = OCH2CH(CH2OC6H5) and E = OCH2CH2, were synthesized and characterized by gel-permeation chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and NMR spectroscopy. Their association properties in aqueous solution were investigated by surface tensiometry and light scattering, yielding values of the critical micelle concentration (cmc), the hydrodynamic radius, and the association number. Gel boundaries in concentrated micellar solution were investigated by tube inversion, and for one copolymer, the temperature and frequency dependence of the dynamic moduli served to confirm and extend the phase diagram and to highlight gel properties. Small-angle X-ray scattering was used to investigate gel structure. The overall aim of the work was to define a block copolymer micellar system with better solubilization capacity for poorly soluble aromatic drugs than had been achieved so far by use of block copoly(oxyalkylene)s. Judged by the solubilization of griseofulvin in aqueous solutions of the E(m)G(n)E(m) copolymers, this aim was achieved.     

Synthesis and catalytic activity of some π-allylic bis(trifluorophosphine)(triphenylphosphine)cobalt(I) complexes

The syntheses of Co(π-all)(PF₃)₂(PPh₃) complexes (π-all = π-allyl, anti-1-Me-π-allyl, syn-1-Me-π-allyl, 1,1-dimethyl-π-allyl, anti-1,2-diMe-π-allyl, syn,syn-1,3-diMe-π-allyl, 2Et-π-allyl, π-cyclooctenyl, h³-π-cycloheptadienyl) are described. ¹H and ¹⁹F NMR data are presented and discussed in relation to the structures of the complexes. The compound Co(π-C₅H₉)(PF₃)(PPh₃)₂ is also reported. Several of the π-allylic complexes are found to be active catalysts for the isomerisation of 1-octene to 2-octene under a hydrogen atmosphere.     

Reaction of crotonaldehyde with various ethyl aluminum chlorides in methylene chloride. A 1H-NMR study

The reactions of crotonaldehyde (CA) with ethyl aluminum chlorides have been examined using a titration technique at low temperature. The titrations were followed by ¹H-NMR spectroscopy. Evidence for complexes of the type (Et₂AlCl)₂CA and (Et₂AlCl-CA)₂ has been obtained. Ethyl aluminum sesquichloride undergoes sequential addition of CA to the EtAlCl₂ moiety, to the Et₂AlCl moiety, and again to the EtAlCl₂ moiety. Ethyl aluminum dichloride undergoes ligand redistribution, alternately disproportionating and reproportionating, the ultimate product being EtAlCl₂-CA₂.     

Micelles and gels of mixed triblock copoly(oxyalkylene)s in aqueous solution

The micellization in dilute aqueous solution of a 50/50 wt% mixture of two triblock copolymers, E45B14E45 and E62P39E62, and the gelation of concentrated micellar solutions have been investigated over a range of temperatures. Here E, B, and P denote oxyethylene, oxubutylene, and oxypropylene chain units. Comparison is made with aqueous solutions of the individual copolymers. The results of light scattering measurements are consistent with effectively separate micellization of the two copolymers in the mixture. Hard gel formed when the extent of micellization was high for both copolymers. Because of the relatively high critical micellization temperatures of copolymer E62P39E62, the low-temperature boundary of the hard gel was high for this copolymer and for the mixture. The minimum concentration for hard-gel formation was higher for the mixture than for either of the individual copolymers, as would be expected for packing of two distributions of micelles of different average size.