How far do electrons move? A semiempirical investigation of thermal electron-transfer distances in cationic bis(hydrazine) and bis(hydrazyl) mixed-valence compounds.

A computational approach for estimating thermal electron-transfer reaction distances in symmetrical mixed-valence compounds is described and applied to a series of bis(hydrazine) and bis(hydrazyl) radical cations and derivatives, some of which have been investigated experimentally by Nelsen and co-workers. Ground-state semiempirical charge distributions are obtained by using optimized reactant geometries. Advantage is then taken of the approximate C(2) symmetry, or the approximate mirror symmetry, of each of the targeted compounds, and the inherent degeneracy of the corresponding electron-transfer reactions, such that the change in dipole moment (Delta-mu) upon charge transfer can be estimated from an appropriately distance-weighted sum of charge differences between approximately symmetry-equivalent atoms found on the donor and acceptor sides of the molecule.

Resonance Raman and semiempirical electronic structure studies of an odd-electron dinickel tetraiminoethylenedimacrocycle complex.

Resonance Raman studies of Ni2TIED3+ (TIED = tetraiminoethylenedimacrocycle) reveal that many modes couple to the intense electronic transition centered at 725 nm, a feature that is nominally similar to the intense delocalized intervalence absorption bands observed in the same region for Fe2(TIED)L4(5+) and Ru2(TIED)L4(5+) (L is any of several axial ligands). Time-dependent spectral modeling of the Raman and absorption spectra for the nickel compound was undertaken to understand the electronic transition. We were unable to model the Raman and absorption spectra successfully with a single electronic transition, suggesting that the absorption band is made up of two overlapping transitions.

Imaging size-selective permeation through micropatterned thin films using scanning electrochemical microscopy.

This paper describes a new approach for quantification of rates of molecular transport through patterned, or otherwise heterogeneous, porous films supported on conductive substrates. Scanning Electrochemical Microscopy (SECM) has been used to image molecular sieving of redox active probes by thin, electropolymerized films of Fe(5-amino-1,10-phenanthroline)3(2+) on micropatterned and microdisk array electrodes. Films as thin as 12 nm completely block redox mediators with average molecular diameters greater than 12 A, whereas smaller diameter probes (radii 5-8 A) were observed to permeate selectively.

Histological periapical repair after obturation of infected root canals in dogs.

Histological periapical healing of infected roots obturated in one-step or with prior calcium hydroxide (Ca(OH)2) disinfection was compared. Seventy-two roots of vital dog teeth were instrumented to ISO size 45. Sixty roots were infected with dental plaque and closed.

Porphyrin-Based Thin-Film Molecular Materials with Highly Adjustable Nanoscale Porosity and Permeability Characteristics.

Mesoporous thin films based on neutral, porphyrin-bridged, tetrarhenium "square" compounds (metallacycles) display permeability to molecules smaller than the dimensions of an individual square cavity, but blocking behavior toward larger species (see schematic representation). The characteristic permeant size cutoff can be systematically and predictably manipulated by decorating the walls of the porphyrin square with axially bound, mono-, bi-, and tetradentate ligands.

Periodontal ligament vitality and histologic healing of teeth stored for extended periods before transplantation.

A previous study evaluated the viability of dog periodontal ligament cells as indicated by tritiated thymidine uptake after extended storage in Hank's balanced salt solution and Conditioned Medium. The purpose of this study was to evaluate histologic healing following the identical storage parameters established in the earlier study. Additionally, for Conditioned Medium, matched pairs (teeth evaluated for tritiated thymidine uptake and transplanted teeth) were examined in an attempt to correlate periodontal ligament vitality and healing.

Tritiated thymidine uptake in periodontal ligament cells of dogs' teeth stored in various media for extended time periods.

The purpose of this study was to evaluate a new storage solution, Conditioned Medium, vs Hank's balanced salt solution and ViaSpan with respect to the viability of periodontal ligament cells of exarticulated teeth. Teeth were stored for periods of 6, 48, and 96 hours in Hank's balanced salt solution, ViaSpan (Dupont Pharmaceuticals), or Conditioned Medium. Teeth were cultured for 24 hours in Dulbecco's medium supplemented with tritiated thymidine.

The role of the socket in the periodontal healing of replanted dogs' teeth stored in ViaSpan for extended periods.

In a previous study on the extended storage of extracted dogs' teeth, it was hypothesized that changes in the socket environment might play a role in the periodontal healing of these teeth. The purpose of this study was to evaluate the role of the socket in the periodontal healing of replanted dogs' teeth. Extracted endodontically treated dogs' teeth were stored in ViaSpan for 6 hours and replanted into sockets after 6, 48 or 96 hours.

Electroabsorption Studies of Metal-to-Ligand Charge Transfer in Ru(phenanthroline)(3)(2+): Evidence for Intrinsic Charge Localization in the Initially Formed Excited State.

Electroabsorption studies of ruthenium(II) tris(phenanthroline) show that a substantial change in dipole moment (|Delta&mgr;| = 6.7 +/- 1 D) accompanies ground state to "singlet" metal-to-ligand charge transfer (MLCT) excited-state formation. The change is nearly identical to that reported for the 2,2'-bipyridine analogue (Oh; et al.

Periodontal healing of extracted dogs' teeth air-dried for extended periods and soaked in various media.

The aim of this study was to determine the periodontal healing of replanted dogs' teeth which, after extended extra-oral dry times, had been soaked in various media before replantation. Incisors and premolars of beagle dogs were root canal treated, extracted and bench dried. The teeth were grouped according to dry times of 30, 45 and 60 minutes.

Forage digestibility and intake by lesser snow geese: effects of dominance and resource heterogeneity.

We measured forage intake, digestibility, and retention time for 11 free-ranging, human-imprinted lesser snow geese (Chen caerulescens caerulescens) as they consumed underground stembases of tall cotton-grass (Eriophorum angustifolium) on an arctic staging area in northeastern Alaska. Geese fed in small patches ([Formula: see text]=21.5 m) of forage that made up ≤3% of the study area and consisted of high-quality "aquatic graminoid" and intermediate-quality "wet sedge" vegetation types.

Primitive Molecular Recognition Effects in Electron Transfer Processes: Modulation of ((Trimethylammonio)methyl)ferrocenium/ferrocene Self-Exchange Kinetics via Hydrophobic Encapsulation.

1H NMR line broadening measurements show that the electron self-exchange rate constant for ((trimethylamino)methyl)ferrocenium/ferrocene (TMAFc(2+/+)) in D(2)O as solvent is decreased by ca. 20-50 fold in the presence of excess beta-cyclodextrin. The rate effect is associated with the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.

Changing methods of preventing infective endocarditis following dental procedures: 1943 to 1993.

The report by Northrop and Crowley in the inaugural issue of the Journal of Oral Surgery heralded the appearance of studies designed to confirm both the relationship between dental procedure-induced bacteremia and infective endocarditis and the best methods to interrupt this chain of causation. Their discovery that antibiotics can modulate bacteremias produced by dental procedures eventually led to the universal adoption of the prophylactic regimens to prevent cases of infective endocarditis following dental procedures. Advances since their work have involved a greater understanding of the role of adherence in the mechanism of action of prophylactic antibiotics, an appreciation of the ability to limit antibiotic administration to only the immediate preoperative period, the need to keep prophylactic regimens as uncomplicated as is safe, and greater knowledge about the interaction between dental procedures and bacteremias.

Aesthetic maxillo-facial surgery: face lifting and S.M.A.S.

The article illustrates the importance of face lifting and S.M.A.

Advances in cardiovascular pharmacological therapy.

Progress in the pharmacological management of cardiovascular disease has been accompanied by the appearance of drugs with never before seen capabilities to alter human physiological processes. The widespread use of these potent agents poses a challenge to the oral and maxillofacial surgeon attempting to safely manage patients in the ambulatory setting. This article reviews the field of contemporary cardiovascular pharmacotherapy from the aspect of how it affects the practice of oral and maxillofacial surgery.

Myocardial infarction: current management strategies.

Coronary artery disease is a common malady in industrialized societies. The end stage of this progressive disorder frequently results in myocardial infarction (MI), now known to be due to acute thrombosis of a narrowed coronary artery. In the past, supportive care was all that could be offered to patients suffering MI.