15N NMR relaxation data reveal significant chemical exchange broadening in the alpha-domain of human α-lactalbumin

Human alpha-lactalbumin (alpha-LA), a 123-residue calcium-binding protein, has been studied using (15)N NMR relaxation methods in order to characterize backbone dynamics of the native state at the level of individual residues. Relaxation data were collected at three magnetic field strengths and analyzed using the model-free formalism of Lipari and Szabo. The order parameters derived from this analysis are generally high, indicating a rigid backbone. A total of 46 residues required an exchange contribution to T(2); 43 of these residues are located in the alpha-domain of the protein. The largest exchange contributions are observed in the A-, B-, D-, and C-terminal 3(10)-helices of the alpha-domain; these residues have been shown previously to form a highly stable core in the alpha-LA molten globule. The observed exchange broadening, along with previous hydrogen/deuterium amide exchange data, suggests that this part of the alpha-domain may undergo a local structural transition between the well-ordered native structure and a less-ordered molten-globule-like structure.

Ag+- and Zn2+-exchange kinetics and antimicrobial properties of 11 angstrom tobermorites

Ag+- and Zn2+-exchanged zeolites zeolites and clays have been used as coatings and in composites to confer broad-spectrum antimicrobial properties on a range of technical and biomedical materials. 11 angstrom tobermorite is a bioactive layer lattice ion exchanger whose potential as a carrier for Ag+ and Zn2+ ions in antimicrobial formulations has not yet been explored. In view of this, batch Ag+- and Zn2+-exchange kinetics of two structurally distinct synthetic 11 angstrom tobermorites and their subsequent bactericidal action against Staphylococcus aureus and Pseudomonas aeruginosa are reported. During the exchange reactions, Ag+ ions were found to replace labile interlayer cations; whereas, Zn2+ ions also displaced structural Ca2+ ions from the tobermorite lattice. In spite of these different mechanisms, a simple pseudo-second-order model provided a suitable description of both exchange processes (R-2 >= 0.996). The Ag+- and Zn2+-exchanged tobermorite phases exhibited marked bacteriostatic effects against both bacteria, and accordingly, their potential for use as antimicrobial materials for in situ bone tissue regeneration is discussed. (C) 2008 Elsevier Ltd. All rights reserved.

The performance and persistence of exchange-traded funds: evidence for iShares MSCI country-specific ETFs

The aim of this paper is to investigate the performance and persistence of 20 iShares MSCI country-specific exchange-traded funds (ETFs) in comparison with S&P 500 index over the period July 2001 to June 2006. There are several studies analysing mutual funds performance in past years, but very little is known about ETFs. In our analysis the Sharpe, Treynor and Sortino ratios are used as risk-adjusted performance measures. To evaluate performance persistence and therefore if there is any relationship among past performance and future performance, we apply to the Spearman Rank Correlation Coefficient and the Winner-loser Contingency Table. The main findings are at two levels. First, ETFs can beat the U.S. market index based on risk-adjusted performance measures. Second, there is evidence of ETFs performance persistence based on annual return.