Studies of La 0.7 Ca 0.3 MnO 3 epitaxial films on substrates with a range of lattice constants reveal two dominant contributions to the occurrence of colossal negative magnetoresistance (CMR) in these manganites: at high temperatures (T → T C , T C being the Curie temperature), the magnetotransport properties are predominantly determined by the conduction of lattice polarons, while at low temperatures (T T C ), the residual negative magnetoresistance is correlated with the substrate-induced lattice distortion which incurs excess magnetic domain wall scattering. The importance of lattice polaron conduction associated with the presence of Jahn-Teller coupling in the manganites is further verified by comparing the manganites with epitaxial films of another ferromagnetic perovskite, La 0.5 Ca 0.5 CoO 3 . Regardless of the differences in the substrate-induced lattice distortion, the cobaltite films exhibit much smaller negative magnetoresistance, which may be attributed to the absence of Jahn-Teller coupling and the high electron mobility that prevents the formation of lattice polarons. We therefore suggest that lattice polaron conduction associated with the Jahn-Teller coupling is essential for the occurrence of CMR, and that lattice distortion further enhances the CMR effects in the manganites.

Deuterium spin relaxation was used to examine the motion of enzyme-bound water on subtilisin Carlsberg colyophilized with inorganic salts for activation in different organic solvents. Spectral editing was used to ensure that the relaxation times were associated with relatively mobile deuterons, which were contributed almost entirely by D2O rather than hydrogen-deuteron exchange on the protein. The results indicate that the timescale of motion for residual water molecules on the biocatalyst, ( c)D 2 O, in hexane decreased from 65 ns (salt-free) to 0.58 ns (98% CsF) as (kcat͞KM)app of the biocatalyst preparation increased from 0.092 s ؊1 ⅐M ؊1 (saltfree) to 1,140 s ؊1 ⅐M ؊1 (98% CsF). A similar effect was apparent in acetone; the timescale decreased from 24 ns (salt-free) to 2.87 ns (98% KF), with a corresponding increase in (kcat͞KM)app of 0.140 s ؊1 ⅐M ؊1 (salt-free) to 12.8 s ؊1 ⅐M ؊1 (98% KF). Although a global correlation between water mobility and enzyme activity was not evident, linear correlations between ln[(kcat͞KM)app] and ( c)D 2 O were obtained for salt-activated enzyme preparations in both hexane and acetone. Furthermore, a direct correlation was evident between (kcat͞KM)app and the total amount of mobile water per mass of enzyme. These results suggest that increases in enzymebound water mobility mediated by the presence of salt act as a molecular lubricant and enhance enzyme flexibility in a manner functionally similar to temperature. Greater flexibility may permit a larger degree of local transition-state mobility, reflected by a more positive entropy of activation, for the salt-activated enzyme compared with the salt-free enzyme. This increased mobility may contribute to the dramatic increases in biocatalyst activity.enzyme activation ͉ organic solvents ͉ salts ͉ subtilisin Carlsberg I n recent years, the application of selective, nonhazardous biocatalysts for chemical synthesis has become an increasingly attractive alternative to traditional chemical methods. This trend is driven in part by the exquisite chemo-, regio-, and enantioselectivities commonly demonstrated by enzymes. The high demand for enantiomerically pure and selectively functionalized molecules, especially within the pharmaceutical industry, continues to spur the expanding interest in biocatalysis. Unfortunately, many compounds of interest to the pharmaceutical and related industries exhibit poor solubility and undergo deleterious side reactions (e.g., hydrolysis) in water; hence, they are not amenable to enzymatic reactions in conventional media.Nonaqueous biocatalysis, including enzymatic reactions in nearly anhydrous organic solvents, has emerged as an alternative approach to circumvent the limitations of aqueous-based reaction systems. There are drawbacks, however, to performing enzymatic reactions in organic solvents, most notably low biocatalytic activity (1-5). Much effort has been directed toward elucidating the mechanism(s) underlying the low activity exhibited by insoluble enzyme formulations in organic solvents. Poor com...

The intact globe expansion method (GEM) imposes a loading geometry comparable to in vivo conditions and can quantify changes in mechanical stability as a function of testing conditions (e.g., IOP, tissue maturation, and therapeutic cross-linking) with small sample sizes and small variability. Rabbit kit eyes provide a model of weak tissue suitable for screening treatments that strengthen the cornea and sclera.

The effects of lattice distortion on the physical properties of La 0.7 Ca 0.3 MnO 3 epitaxial films are investigated. Our results suggest that larger substrate-induced lattice distortion gives rise to larger zero-field resistivity and larger negative magnetoresistance. Similar effects are also observed in samples of different thicknesses and on the same substrate material, with larger resistivity and magnetoresistance associated with thinner samples. In addition to x-ray diffraction spectroscopy, the degrees of lattice distortion in different samples are further verified by the surface topography taken with a low-temperature scanning tunneling microscope. Quantitative analyses of the transport properties suggest that the high-temperature (T→T C) colossal magnetoresistance ͑CMR͒ in the manganites is consistent with the conduction of lattice polarons induced by the Jahn-Teller coupling, and that the low-temperature (TӶT C) magnetoresistance may be attributed to the magnetic domain wall scattering. In contrast, the absence of the Jahn-Teller coupling and the large conductivity in La 0.5 Ca 0.5 CoO 3 epitaxial films yield much smaller negative magnetoresistance, which may be attributed to disorder-spin scattering.