Electrostatics of the point dipole and higher multipoles

It is shown that a distribution theory form for the electrostatics of point multipoles can be constructed, which reduces to the usual theory away from the position of the multipole, but in which the total electromagnetic self-energy is zero and the self-force density is zero.     

Giant core-exciton effects on Si(111) 7 × 7 surfaces

We present the first direct experimental evidence for a large surface influenced core-exciton effect on silicon. The Si(111) 7 × 7 L_2,3 absorption edge has been studied with core-level electron energy loss (ELS) and X-ray photoemission spectroscopy (XPS). An excitonic shift of ～1–2 eV have been found for transitions from Si(2p) to empty surface states.     

Aspects of the synthesis, Characterization and metal–ligand stoichiometry of aminopropyl, nitrobenzamide, and 8-quinolinol silica gels

Surface modification of several silica gels with a number of silanes was studied, as well as further reactions of the modified surfaces. Complete reaction of aminopropylsilane was easily achieved if surface silanols were in excess. Triethoxysilylpropyl-p-nitrobenzamide (TESPN) reacts with difficulty, and complete reaction occured only with long reaction time (at least 12h). The maximum coverage of 100-Å pore silica gel by TESPN was found to be about 1.7 μmol/m², considerably less than the 3–4 /gmmol/m² of available silanol sites, probably due to steric effects of the large silane. Even at this maximum coverage, further reaction of the modified silica with trimethylsilyl capping groups occured, with additional coverage of about 1.0 μmol/m². The maximum amount of silylpropylamido-p-phenylazo-8-quinolinol that could be bound to silica gel was found to be about 1.0 μmol/m², again probably limited by steric effects of the large 8-quinolinol (oxine) moiety. Virtually complete conversion of parent nitrobenzamide silica gel (NBSG) to 8-quinolinol silica gel (QSG) could be achieved if NBSG coverage was less than about 0.7 μmol/m². QSG materials were found to have a 2 oxine to 1 copper(II) stoichiometry, even with surface coverages as low as 0.16 μmol/m².     

Modified polysulfones. IV. Synthesis and characterization of polymers with silicon substituents for a comparative study of gas‐transport properties

We previously conducted a detailed study of gas‐transport and other properties of a series of silicon derivatives of Udel polysulfone (PSf) and Radel polyphenylsulfone; we now report the details of their preparation by the reaction of lithiated polymer intermediates with chlorosilylalkylaryl electrophiles. Ortho‐sulfone‐substituted polymers with pendant trimethylsilyl, dimethylphenylsilyl, and diphenylmethylsilyl and other groups were obtained by direct metalation followed by the reaction of the dilithiated intermediate with the appropriate silyl electrophile. In addition, the structural regularity and geometry of the dilithiated site was also exploited to introduce silicon into the main chain by the reaction of dichlorosilyl electrophiles, leading to the formation of a new tricyclic heteroatom ring. Ortho‐ether PSf derivatives were obtained from a dibrominated polymer via the lithiation of brominated polymer and reaction with a silyl electrophile. The degree of substitution of the silyl groups was 2.0 or less from dilithiated polymers and was dependent on the electrophile reactivity and reaction conditions. A detailed structural characterization of the polymers by NMR and IR spectroscopy is reported in addition to glass‐transition temperatures and thermal stabilities. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2103–2124, 2001     

Structure-based modelling in reproductive toxicology: (Q)SARs for the placental barrier†

The replacement of animal testing for endpoints such as reproductive toxicity is a long-term goal. This study describes the possibilities of using simple (quantitative) structure-activity relationships ((Q)SARs) to predict whether a molecule may cross the placental membrane. The concept is straightforward, if a molecule is not able to cross the placental barrier, then it will not be a reproductive toxicant. Such a model could be placed at the start of any integrated testing strategy. To develop these models the literature was reviewed to obtain data relating to the transfer of molecules across the placenta. A reasonable number of data were obtained and are suitable for the modelling of the ability of a molecule to cross the placenta. Clearance or transfer indices data were sought due to their ability to eliminate inter-placental variation by standardising drug clearance to the reference compound antipyrine. Modelling of the permeability data indicates that (Q)SARs with reasonable statistical fit can be developed for the ability of molecules to cross the placental barrier membrane. Analysis of the models indicates that molecular size, hydrophobicity and hydrogen-bonding ability are molecular properties that may govern the ability of a molecule to cross the placental barrier.