Stability of singly hydrated silanone on silicon quantum dot surfaces: density functional simulations.

A key to understanding the optical characteristics of silicon quantum dots is the role of surface bonded species that introduce states to the band-gap. In particular, oxygen bonded in a silanone configuration is thought to be a source of shifts in emission during oxidation. We report the results of density-functional calculations examining the properties of such surface structures. We find single hydration of a simple, neutral silanone molecule leads to a barrierless conversion into a di-hydroxyl structure, and that similar processes are weakly activated on larger systems. However, we show that charging has a significant impact upon stability, with the attachment of an electron greatly increasing the barrier for converting silanone to di-hydroxyl termination. The relatively stable, negatively-charged silanone structures are predicted to lead to large red-shifts in the onset of optical absorption.

Theory of Jahn-Teller distortions of the P donor in diamond.

Phosphorus, the current standard n-type dopant in diamond, has been correlated with isotropic, trigonal and tetragonal paramagnetic centres, suggesting that it may undergo a symmetry lowering distortion, perhaps of a Jahn-Teller type. We present first-principles calculations for examining the energetics of various sub-group symmetries of the on-site, tetrahedral donor, and show that C2v, C3v and D2d conformations reduce the total energy and conform to the Jahn-Teller theorem. We also present a qualitative explanation of the resulting quantum-mechanical states. The small amount of energy saved by the distortion may indicate a dynamic Jahn-Teller effect.

Adduction of hemoglobin and albumin in vivo by metabolites of trichloroethylene, trichloroacetate, and dichloroacetate in rats and mice.

Adducts to macromolecules from trichloroethylene formed by in vivo and in vitro metabolism have been reported by many investigators. We examined the in vivo adduction of the blood proteins hemoglobin (Hb) and albumin in rats and mice dosed orally with [14C]trichloroethylene ([14C]TRI) to explore the development of a protein adduct biomarker of TRI exposure. We also examined the adduction of these two proteins from doses of [14C]trichloroacetate (TCA) and [14C]dichloroacetate (DCA), two metabolites of TRI. Association of label with albumin peaked at 4-8 hr in the rat (2480 nmol eq TRI/mg protein) and 2-4 hr in the mouse (1580 nmol eq TRI/mg protein). The decay was exponential with a half-life consistent with that of rat or mouse albumin (approx 24 hr). The time course of label with Hb was characterized by an early plateau at 8 hr in rat (28 nmol eq TRI/mg protein), 4 hr in mouse (7 nmol eq TRI/mg protein), and followed by a slow steady increase, peaking at 120 hr (54 nmol eq TRI/mg protein, rat; 38 nmol eq TRI/mg protein, mouse). This apparent binding was linear with dose in the rat, but was convex in the mouse albumin (mouse Hb label was below detection at low dose). We also found that a portion of the irreversibly associated label, referred to by previous investigators as "binding," could be accounted for as metabolic incorporation of label into glycine and serine.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-labile adducts to protein can be used as indicators of the cysteine S-conjugate pathway of trichloroethene metabolism.

Covalent binding of radiolabel to tissue proteins following [14C]trichloroethene (TRI) exposure has been used as a measure of TRI activation. Gross binding of 14C label does not differentiate between alternate routes of metabolism and can be confounded when there is significant metabolic incorporation of radiolabel. We examined the covalent association of 14C label to hepatic and renal proteins in male F344 rats and B6C3F1 mice following oral treatment with [14C]TRI and three metabolites of TRI: [14C]trichloroacetate (TCA), [14C]dichloroacetate (DCA), and [14C]dichlorovinylcysteine (DCVC) in vivo. Association of radiolabel from [14C]TRI with hepatic proteins reached a maximum at 2 and 4 h in mouse and rat hepatic proteins, respectively. Association of radiolabel with renal proteins reached a maximum at 8 h in both species. An approach was developed based upon formation of protein adducts that release acetate and monochloroacetate (MCA) on acid hydrolysis. These adducts were found to be specifically associated with the activation of DCVC to reactive intermediates. Acetate and MCA were identified by using two different conditions of high-performance liquid chromatography (HPLC) separation with differing selectivity. Diethylmaleate and aminooxyacetic acid pretreatment inhibited the formation of these adducts from TRI, consistent with requirements for glutathione and beta-lyase. No evidence of these adducts was detected following [14C]TCA and [14C]DCA treatment. Renal acid-labile adduct formation from 25 mg/kg DCVC was approximately 12-fold greater in male B6C3F1 mice than in male F344 rats. They accounted for 7.8 and 4.6% of the total adducts to renal protein in rats and mice, respectively. Acid-labile adducts formed from 1000 mg/kg TRI were approximately two times greater in mice than rats. In this case, they accounted for 1.4 and 3.3% of the total adduct formed in renal proteins from TRI (corrected for metabolic incorporation), respectively. This greater dilution of adducts associated with DCVC in renal proteins of the rat suggests that covalent binding of TRI has less specificity for the DCVC pathway in rats than in mice.

Renal activation of trichloroethene and S-(1,2-dichlorovinyl)-L-cysteine and cell proliferative responses in the kidneys of F344 rats and B6C3F1 mice.

Covalent binding of reactive intermediates formed by renal beta-lyase activation of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) has been suggested to be responsible for the greater renal sensitivity of rats than mice to the carcinogenic effects of chronic treatment with trichloroethene (TRI). Previous work demonstrated that the activation of DCVC results in acid-labile adducts to protein that can be distinguished from adducts formed by other pathways of TRI metabolism. By analyzing acid-labile adduct formation, the relationship between DCVC formation and activation from TRI and increases in rates of cell division in the kidneys of male F344 rats and B6C3F1 mice could be investigated. The delivered dose of DCVC from an oral dose of 1000 mg/kg TRI was approximately six times greater in rats than mice. However, renal activation of DCVC in mice was approximately 12 times greater than in rats. Therefore, the overall activation of TRI was about two times greater in mice than rats. Induction of cell replication in liver and kidney following doses of 1, 5, or 25 mg/kg DCVC or 1000 mg/kg TRI was also measured through the use of miniosmotic pumps that delivered BrdU subcutaneously for 3 d. Acid-labile adduct formation from DCVC and TRI displayed a consistent relationship with increased cell replication in mice and between mice and rats. Both cell replication and acid-labile adduct formation in rats given 25 mg/kg DCVC were approximately equal to that observed in mice given 1 mg/kg. Increased cell replication was not observed in rats receiving 1 or 5 mg/kg DCVC or 1000 mg/kg TRI, nor were there histological signs of nephrotoxicity. Thus, net activation of TRI by the cysteine S-conjugate pathway was found to be greater in mice than rats and these findings appeared related to differences in cell proliferative responses of the kidneys of the two species. Based on these data, it would appear that other factors must contribute to the greater sensitivity of the rat to the induction of renal carcinogenesis by TRI.