No abstract

Three symmetric Mo 2 dimers [Mo 2 (DAniF) 3 ](µ-E 2 CCE 2)[Mo 2 (DAniF) 3 ] (DAniF = N, Nʹ-di(p-anisyl)formamidinate) with oxalate (E = O) or the thiolated derivatives (E = O or S) as bridging ligands have been synthesized, and the optical properties of the mixed-valence (MV) derivatives obtained by one-electron oxidation studied within the framework of the vibronic two-state model. These Mo 2 −Mo 2 systems are effective models for testing electron transfer theories, with the δ electrons of the Mo 2 fragments that are responsible for the redox and optical properties of the MV complex being well isolated from other metal d and ligand π-type orbitals. This in turn gives rise to unique, well-resolved metal to ligand (MLCT) and intervalence charge transfer (IVCT) absorption bands that permit accurate analyses based on band-shape. In the series [Mo 2 (DAniF) 3 ](µ-E 2 CCE 2)[Mo 2 (DAniF) 3 ], the extent of electron delocalization between the Mo 2 cores increases with increasing number of sulfur atoms, E, in the bridge. Higher energy IVCT absorption bands are observed for the more strongly coupled complex, but in contrast to the predictions from the two-state model, the IVCT band becomes more symmetric in shape as the electronic coupling constant increases beyond the Class III border and 2H ab /λ >> 1. Thus, the oxalate-bridged complex (E 2 = O 2) is situated on the Class II-III borderline, while the two thiolated 2 species are well placed deep into Class III, where novel optical behavior can be observed. The electronic coupling matrix elements (H DA) estimated from the transition energy E IT (H DA = E IT /2, 2000-2500 cm − 1) are in excellent agreement with data (H ab , 2400-3000 cm − 1) calculated from the modified Mulliken-Hush expression for Class III systems. DFT calculations show that linear combinations of the δ orbitals of the Mo 2 centers generate the HOMO (out-of-phase, δ−δ) and HOMO-1 (in-phase, δ+δ), with the energy difference corresponding to the E IT. This study illustrates a systematic transition from strongly coupled MV complex near the Class II-III border, to Class III and to systems in which the underlying ground state is better described in terms of simple delocalized electronic states rather evolving from strongly coupled diabatic states which define Class III.

Background/purpose: Given that many patients find the cost of mandibular rehabilitation through complete overdenture implants to be beyond their financial scope, many seek a more affordable treatment. The aims of this study were to compare the clinical outcomes of single mandibular implant-retained overdentures versus that of complete dentures. Materials and methods: Thirteen edentulous patients with a mean age of 71 years were enrolled in this investigation. They were treated with a single implant inserted into the mandibular midline, followed by rehabilitation with complete dentures. The mandibular dentures were adhered with a locator or magnetic attachment after 10 weeks of adaptation.-Patient satisfaction was assessed by means of a visual analogue scale(VAS) questionnaire both on the day of attachment connection and 3 months later. Chewing efficiency was assessed by a sieve test before and after connecting the attachment. Within-subject comparisons were performed either by using paired-sample t-tests or Wilcoxon signed-rank tests to test patient satisfaction and chewing efficiency (P Z 0.05). Results: No implants were lost nor were denture fracture found during the observation period. Significant improvements were observed in all parameters of patient satisfaction (with P values ranging from <0.001 to w0.043) after attachment of the mandibular dentures with a single midline implant. Furthermore, the objective chewing efficiency of patients significantly improved after implant connection (P<0.001).

No abstract

Thermal electron transfer through hydrogen bonds remains largely unexplored. Here we report the study of electron transfer through amide-amide hydrogen bonded interfaces in mixed-valence complexes with covalently bonded Mo 2 units as the electron donor and acceptor. The rate constants for electron transfer through the dual hydrogen bonds across a distance of 12.5 Å are on the order of ∼ 10 10 s −1 , as determined by optical analysis based on Marcus–Hush theory and simulation of ν(NH) vibrational band broadening, with the electron transfer efficiencies comparable to that of π conjugated bridges. This work demonstrates that electron transfer across a hydrogen bond may proceed via the known proton-coupled pathway, as well as an overlooked proton-uncoupled pathway that does not involve proton transfer. A mechanistic switch between the two pathways can be achieved by manipulation of the strengths of electronic coupling and hydrogen bonding. The knowledge of the non-proton coupled pathway has shed light on charge and energy transport in biological systems.

No abstract

No abstract

No abstract