Variable trends in R-X bond dissociation energies (R = Me, Et, i-Pr, t-Bu)

[structure: see text] High level ab initio molecular orbital calculations confirm experimental indications that the effect of alkyl substituents (R = Me, Et, i-Pr, t-Bu) on R-X bond dissociation energies varies considerably according to the nature of X. A simple qualitative explanation in terms of valence-bond theory is presented, highlighting the increasing importance of the stabilization of R-X by the ionic R(+)X(-) configuration for electronegative X substituents (such as F, OH, and OCH(3)).     

Photodynamic therapy with endogenous protoporphyrin IX: basic principles and present clinical experience

5-Aminolaevulinic acid (ALA) is a precursor of protoporphyrin IX (Pp IX) in the biosynthetic pathway for haem. Certain types of cells have a large capacity to synthesize Pp IX when exposed to an adequate concentration of exogenous ALA. Since the conversion of Pp IX into haem is relatively slow, such cells tend to accumulate photosensitizing concentrations of Pp IX. Pp IX photosensitization can be induced in cells of the epidermis and its appendages, but not in the dermis. Moreover, since ALA in aqueous solution passes readily through abnormal keratin, but not through normal keratin, the topical application of ALA in aqueous solution to actinic keratoses or superficial basal cell or squamous cell carcinomas induces Pp IX photosensitization that is restricted primarily to the abnormal epithelium. Subsequent exposure to photoactivating light selectively destroys such lesions. In our ongoing clinical trial of ALA-induced Pp IX photodynamic therapy, the response rate for basal cell carcinomas following a single treatment has been 90% complete response and 7.5% partial response for the first 80 lesions treated. The cosmetic results have been excellent, and patient acceptance has been very good.     

Characterization of Cd implanted and annealed GaAs and InP by perturbed angular correlation (PAC) spectroscopy

Investigations of ^111mCd implanted GaAs and InP crystals using the microscopically sensitive perturbed angular correlation technique show that the implanted Cd is incorporated on unperturbed substitutional lattice sites during rapid thermal annealing at significant lower temperatures than for electrical activation is required. In GaAs the higher implantation temperature at 473 K did not show any influence on this annealing stage, whereas as higher implantation dose hinders the annealing. We conclude that not only the local environment of the implant but also the long-range lattice perfection has to be restored for the electrical activation of implants in III-V compound semiconductors.     

Systems of oblate molecules. Monte Carlo study

Monte Carlo (MC) simulations were performed for systems of hard oblate spherocylinders with breadth-to-height ratios φ = 0.5–3.5 and packing fractions y = 0.25–0.45 and for Kihara oblate molecule systems of φ = 1 at reduced temperatures T* = 0.75 and 1.0 and y = 0.05–0.45. The compression factors and the dependence of the average correlation functions on the shortest surface-to-surface distance were determined for the case of hard oblate spherocylinders and the compression factors, residual internal energies and average correlation functions for the case of the generalized Kihara molecule systems. In addition, values of the third virial coefficient of the hard oblate spherocylinders were evaluated in the range of φ = 1–3. Results of the MC simulations for the hard oblate spherocylinders compare well with the available data in the literature and theoretical values; thermodynamic functions of the Kihara molecule systems were determined from the second-order perturbation theory. They agree well with our MC values at lower densities and higher reduced temperatures.     

RELATIONSHIP BETWEEN SURVIVAL AND THYMINE-DIMER EXCISION IN ULTRAVIOLET-IRRADIATED ESCHERICHIA COLI

Abstract— The influence of amino acid prestarvation on both the resistance to u.v. light and excision of thymine dimers of bacterial strains E. coli B/r hcr ⁺ thy- trp ^-, E. coli B/r hcr ^-thy^- trp ^-, and E, coli 15 T^- 555–7 thy ^- meth ^- trp ^- arg ^- has been studied.
The prestarvation increased the resistance of all the strains but reasonably inhibited excision of thymine dimers. Thus the enhancement of u.v. resistance after amino acid prestarvation was not due to more complete excision of thymine dimers.     

Surface States in a Simple Crystal Model

A very simple crystal model of a semi-infinite heteroatomic planar lattice like boronitride is investigated for the energy, wave functions and existence conditions of surface states, using the one-electron Green function method. σ and π electrons are treated separately. For π electrons, we find two surface state bands, both for the electropositive and the electronegative surface. The consequence is the existence of Shockley “subsurface” states. For σ electrons, similar results were found as for the sphalerite-type lattice. The investigated model can also be used to draw qualitative conclusions about the effect of electronic correlation on surface states of planar graphite. The possibility of finding a certain type of “antiferromagnetism” with π electrons localized on the planar graphite boundary is suggested. On étudie un modèle très simple d'un cristal avec un réseau sémi-infini, héteroatomique, comme le boronitride. L'énergie, les fonctions d'onde et des conditions d'existence d'états de surface ont été obtenus par la méthode de la fonction de Green à un électron. Les électrons σ et π ont été traités séparément. Pour les électrons π on trouve deux bandes d'états de surface pour la surface électropositive ainsi que pour la surface électronégative, ce qui implique l'existence d'états de “sous-surface” de Shockley. Pour les électrons σ on trouve des résultats semblables aux ceux qu'on a obtenu pour le réseau de type sphalérite. Le modèle étudié ici peut aussi être employé pour tirer des conclusions qualitatives sur l'effet de la corrélation électronique sur les états de surface du graphite plan. On propose qu'il serait possible de trouver un certain type de “antiferromagnétisme” avec les électrons π localisés sur le bord du graphite plan. Es wurde ein einfaches Modell für ein halb-unendliches, heteroatomares Kristallgitter, wie Boronitrid untersucht. Die Energie, die Wellenfunktionen und Existenzbedingungen für Oberflächenzustände wurden mit der Einelektron-Green-Funktionsmethode erhalten. Die σ- und π-Electronen wurden getrennt behandelt. Für die π-Elektronen finden wir zwei Bände für Oberflächenzustände, sowohl für die elektropositive als für die elektronegative Oberfläche. Als Folgerung erhalten wir die Shockleysche unteroberflächenzustände. Für die σ-Elektronen wurden ähnliche Resultate als für das Sphaleritgitter gefunden. Das untersuchte Modell kann auch dafür angewendet werden, urn den Effekt der elektronischen Korrelation auf die Oberflächenzustände planares Graphits in qualitativer Weise zu diskutieren. Es wurde vorgeschlagen, dass es möglich wäre, eine gewisse Art von “Antiferromagnetismus” der π-Elektronen die auf der Grenze planares Graphits lokalisiert sind, zu finden.     

Antibacterial Activity and Synergistic Effect of Biosynthesized AgNPs with Antibiotics Against Multidrug-Resistant Biofilm-Forming Coagulase-Negative Staphylococci Isolated from Clinical Samples

Silver nanoparticles form promising template for designing antimicrobial agents against drug resistant pathogenic microorganisms. Thus, the development of a reliable green approach for the synthesis of nanoparticles is an important aspect of current nanotechnology research. In the present investigation, silver nanoparticles synthesized by a soil Bacillus sp. were characterized using UV–vis spectroscopy, FTIR, SEM, and EDS. The antibacterial potential of biosynthesized silver nanoparticles, standard antibiotics, and their conjugates were evaluated against multidrug-resistant biofilm-forming coagulase-negative S. epidermidis strains, S. aureus, Salmonella Typhi, Salmonella Paratyphi, and V. cholerae. Interestingly, silver nanoparticles (AgNPs) showed remarkable antibacterial activity against all the test strains with the highest activity against S. epidermidis strains 145 and 152. In addition, the highest synergistic effect of AgNPs was observed with chloramphenicol against Salmonella typhi. The results of the study clearly indicate the promising biomedical applications of biosynthesized AgNPs.