Pseudopotential SCF–MO studies of hypervalent compounds. I. XeF2 and XeF4

The (ab initio) effective potential theory developed by Ewig et al. has been applied to a series of hypervalent compounds with a view to elucidating the anomalous properties of several of the higher fluorides of xenon and iodine. In this initial paper the development of a minimal basis set substantially better than an STO‐4G atom‐optimized set is described. Calculations carried out on XeF2 and XeF4 give valence orbital energies in fair agreement with those obtained with the more flexible, all‐electron SCF–MO calculations by Basch et al. Equilibrium structures of XeF2 and XeF4 provided by the effective potential calculations possess the correct symmetries. Bond lengths, although too long by 0.09 Å, correctly reproduce the contraction observed experimentally upon fluorination of XeF2. Calculated bending and stretch–stretch interaction force constants are in pleasing agreement with experiment, as is the stretching anharmonicity. Stretching frequencies evaluated at the experimental bond length, however, are 25% high. Overall, the ability of the present treatment to give a reasonable account of the structures and force fields of XeF2 and XeF4 justifies its application to the higher fluorides where interpretations of observations are more speculative.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70823/2/JCPSA6-73-1-367-1.pd

Pseudopotential SCF–MO studies of hypervalent compounds. II. XeF+5 and XeF6

New evidence bearing upon the anomalous properties of xenon hexafluoride has been obtained via the ab initio molecular orbital approach applied successfully to the di‐ and tetrafluorides in paper I. Structures of both XeF+5 and XeF6 are governed by a stereochemically active lone pair. In the case of the square–pyramidal cation the Fax–Xe–Feq angle calculated for the bare ion is within 2° of the value observed in the crystalline complex. For the hexafluoride, however, the calculated deformation from Oh symmetry is appreciably greater than that deduced from electron diffraction intensities. Nevertheless, the results of calculations are in sufficient conformity with the Bartell–Gavin, Pitzer–Bernstein interpretation and at variance with the ’’electronic‐isomers’’ interpretation to leave little doubt about the answer. With increasing fluorination in the XeFn series the HOMO–LUMO energy difference decreases and the second‐order Jahn–Teller effect is enhanced. Increasing fluorination (and increased positive charge on Xe) also shortens bond lengths; calculated shortenings parallel observed shortenings. The deformation of XeF6 from Oh is along t1u bend and stretch coordinates to a C3v structure with long bonds adjacent to the lone pair, as expected according to the valence‐shell–electron‐pair‐repulsion model. Pure t2g deformations are destabilizing but anharmonic t1u–t2g coupling significantly stabilizes the deformation. Steric aspects of the structure and force field are diagnosed and found to be minor. Values for the force constants f44, f55, f̄4444, f̄444′4′, and f̄445 are derived and found to be of the magnitude forecast in the Bartell–Gavin and Pitzer–Bernstein treatments except that the calculations do not reproduce the delicate balances believed to lead to almost free pseudorotation in XeF6.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69894/2/JCPSA6-73-1-375-1.pd

Structure–properties relationships in fibre drawing of bioactive phosphate glasses

New bioactive phosphate glasses suitable for continuous fibre production are investigated in this work. The structure of both bulk and fibres from Na2O–CaO–MgO–P2O5 glasses has been studied by means of Raman and 31P and 23Na nuclear magnetic resonance spectroscopies, and the structural results have been correlated with the mechanical properties of the fibres and the dissolution rate of the bulk glasses. It has been observed that the mechanical properties of the phosphate glass fibres are influenced by the glass network connectivity, while the dissolution rates are governed by the Qi speciation of the PO4 units. As seen in previous studies, molar volume seems to play an important role in the fragility behaviour of phosphate glasses. Here, a lower molar volume resulting from the increase in the oxygen packing density hinders the cooperative flow of the PO4 units throughout the glass network and, therefore, causes a reduction in the kinetic fragility

Guideline adherence for early breast cancer before and after introduction of the sentinel node biopsy

This population-based study aimed to analyse variations in surgical treatment and guideline compliance with respect to the application of radiotherapy and axillary lymph node dissection (ALND), for early breast cancer, before and after the sentinel node biopsy (SNB) introduction. The study included 13 532 consecutive surgically treated stage I–IIIA breast cancer patients diagnosed in 1989–2002. Hospitals showed large variation in breast-conserving surgery (BCS) rates, ranging between 27 and 72% for T1 and 14 and 42% for T2 tumours. In multivariate analysis marked inter-hospital and time-dependent variation in the BCS rate remained after correction for case-mix. The guideline adherence was markedly lower for elderly patients. In 25.2% of the patients aged ⩾75 years either ALND or radiotherapy were omitted. The proportion of patients with no ALND after an SNB increased from 1.8% in 1999 to 37.8% in 2002. However, in 2002 also 12.2% of the patients with a positive SNB did not have an ALND. Guideline compliance for BCS, with respect to radiotherapy and ALND, fell since the SNB introduction, from 96.1% before 2000 to 91.4% in 2002 (P<0.001). Noncompliance may however reflect patient-tailored medicine, as for elderly patients with small, radically resected primary tumours. The considerable variation in BCS-rates is more consistent with variations in surgeon preferences than patient's choice

Cellular binding partners of the human papillomavirus E6 protein

The high-risk strains of human papillomavirus (HR-HPV) are known to be causative agents of cervical cancer and have recently also been implicated in cancers of the oropharynx. E6 is a potent oncogene of HR-HPVs, and its role in the progression to malignancy has been and continues to be explored. E6 is known to interact with and subsequently inactivate numerous cellular proteins pivotal in the mediation of apoptosis, transcription of tumor suppressor genes, maintenance of epithelial organization, and control of cell proliferation. Binding of E6 to these proteins cumulatively contributes to the oncogenic potential of HPV. This paper provides an overview of these cellular protein partners of HR-E6, the motifs known to mediate oncoprotein binding, and the agents that have the potential to interfere with E6 expression and activity and thus prevent the subsequent progression to oncogenesis