Substrate quality

In all the above processes, the optimised quantities of the chemicals indicated will be specific to the substrate quality evaluated. They would require further re-optimisation for each substrate to take account of the type and concentration of size, the presence of other impurities and the degree of natural yellowness. In particular, the amount of oxidant will need to be adjusted to give the optimum balance between oxidative desizing and the degree of bleaching required. 

The presence of a transporter can be assessed by comparing basolateral-to-apical with apical-to-basolateral transport of substrates in polarized cell monolayers. If P-gp is present, then basolateral-to-apical transport is enhanced and apical-to baso-lateral transport is reduced. Transport experiments are in general performed with radioactively labeled compounds. Several studies have been performed with Caco-2 cell lines (e.g. Ref. [85]). Since Caco-2 cells express a number of different transporters, the effects measured are most probably specific for the ensemble of transporters rather than for P-gp alone. P-gp-specific transport has been assayed across confluent cell layers formed by polarized kidney epithelial cells transfected with the MDR1 gene [86], Figure 20.11 shows experimental data obtained with these cell lines. A rank order for transport called substrate quality was determined for a number of compounds [86]. The substrate quality is a qualitative estimate, but nevertheless allows an investigation of the role of the air/water (or lipid/water) partition coefficient, log Kaw, for transport as seen in Fig. 20.11(A). For most of the compounds, a linear correlation is observed between substrate quality and log Kaw- However, four compounds are not transported at all despite their distinct lipophilicity. A plot of the substrate quality as a function of the potential of a... 

Fig. 20.11. Substrate quality obtained by comparing basolateral-to-apical with apical-to-basolateral transport of substrates in polarized cell monolayers of MDR1-transfected cell lines [86] plotted versus (A) the log of the air/water partition coefficient, or (B) H-bond energy (arbitrary units, EUh cf. text). Units of the air/ water partition coefficient were [M ]. Compound (concentrations in Ref. [86] in brackets) were clozapine (50 nM) (1) cyclosporin A (2 tM) (2) daunorubicin (3) dexamethasone (2 tM) (4) digoxin (2 pM) (5) domperidone (2 pM) (6) etoposide (7) flunitrazepam (500 nM) (8) haloperidol (50 nM) (9) ivermectin (50 nM) (10) loperamide (2 pM) (11) morphine (2 pM) (12) ondansetron...

A comparison of the transport quality (Fig. 20.11(B)) with the rate of P-gp-ATPase activation (see Fig. 20.9) as a function of the H-bond energy (EUh) shows that compounds inducing a high rate of ATP hydrolysis (e.g., progesterone) can have a low substrate quality , and vice versa (e.g., cyclosporin). 

Drug properties Relevance far increase in Klu, and decrease in Km Relevance far increase in Kt, change in Vy2, increase in substrate quality"... 

A collaboration with A.H.Marks Ltd. helped to solve substrate quality issues. 

Even though substrate quality (i.e., chemical composition) is widely believed to be an important factor influencing microbial utilization of DOM, there are relatively few studies relating the composition and bioavailability of DOM. Sensitive assays for the measurement of the relative activities of various extracellular enzymes can provide an indication of the chemical composition of the bioreactive components of DOM (Sinsabaugh and Findlay, 1995 Findlay et al., 1998). The enzymatic potential of bacterial populations appears to respond fairly rapidly to seasonal changes in DOM composition in the Hudson River system. These observations clearly indicate that the chemical composition of DOM influences the microbial processing of DOM. 

Temperature Water Oxygen e Substrate quality Fitey... 

In their now classic text on decomposition in terrestrial ecosystem, Swift et al. (1979) outlined three broad groups of factors that govern decomposition of organic residues in soils. The three groups of factors are the resource (or substrate) quality of the organic residue, the environmental factors, and the presence and activity of decomposer organisms. 

As well as the lattice mismatch between the layer and the substrate, other factors influence the FWHM of the RC, including thickness of the buffer layer, miscut of the substrate, substrate quality, growth conditions etc. For example, Warren Weeks et al [16] reported 00.2 FWHMs of 58 and 151 arc sec for 1.4 pm GaN layers grown on on-axis and off-axis (3 - 4° toward the <11.0>) SiC substrates, respectively. The corresponding FWHMs for the 0.1 pm AIN buffer layers were approximately 200 and 400 arc sec. For a thicker GaN layer of 2.7 pm, the off-axis sample also exhibited an FWHM of 66 arc sec. 

The main issue involving GaN substrates for nitride epitaxy concerns obtaining optoelectronic devices without mismatch dislocations. The critical conditions for misfit-dislocation creation include lattice mismatch between the layer and the substrate, layer thickness, growth conditions and substrate quality. 

Therefore, HREELS is capable, like SIMS, of disclosing molecular, long-range information on the polymer surface. However, at this stage, it is fair enough to address our ignorance of the influence of the substrate on the vibrational response of a polymer thin film What are the effects of substrate quality - pure metal or with native oxide -, roughness on the atomic scale, and polarizability Authors (8.11) do feel these external parameters must be controlled and taken into account. 

Blagodatskaya, E. Anderson, T. H. (1998). Interactive effects of pH and substrate quality on the fungal-to-bacterial ratio and Q CO2 of microbial communities in forest soils. Soil Biology and Biochemistry, 30, 1269-74. 

Bloomfield, J., K. A. Vogt, and D. J.Vogt. 1993. Decay rate and substrate quality of fine roots and foliage of two... 

Touratier, F., Field, J. G., and Moloney, C. L. (2001). A stoichiometric model relating growth substrate quality (C N P ratios) to N P ratios in the products ofheterotrophic release and excretion. Ecol. Model. 139, 265-291. 

In a review of global patterns of root decomposition, Silver and Miya (2001) found that the substrate quality parameters, root Ca concentration and C/N ratio, could explain the greatest proportion of the variance in decay rates across a range of sites and species (r = 0.89, ft = 17) ... 

Substrate quality The enantioselective hydrogenation of a-keto esters proved to be exceptionally sensitive to the origin of the substrate [44b]. 

Fogel, R. and K. Cromack, Jr. (1977). Effects of habitat and substrate quality on Douglas-fir litter decomposition in western Oregon. Can. ]. Bot. 55, 1632-1640. 

In order to produce SiC material of the level of quality required for device applications, chemical vapor deposition (CVD) is currently used as the primary growth technique for SiC epitaxy [2], Due to the continuous improvements in commercial substrate quality, the presence of micropipes in SiC epilayers is not the device yield limiting issue as it was a decade ago. However, the epitaxially grown SiC films still suffer from other extended defects such as basal plane and threading edge dislocations as well as point defects. The vision of growing SiC on porous SiC was to reduce the concentration of these defects and thus improve the epitaxial layer quality for device applications. 

Indices based on microbial activity, microbial biomass, SIR, and organic carbon have been proposed to provide an operationally defined means for describing the response of soil microbial populations to substrate quality and environmental conditions (see Chapter 15 for details). The ratio of MBC to soil organic carbon has been related to the soil organic carbon availability and... 

Unfortunately, the best ee (96%) obtained with the use of latter homogeneous complex was obtained only at a low substrate/eatalyst ratio of 50. The heterogeneous catalyst, on the other hand, revealed an ee of 95%, high activity, and high productivity. The main problem aeeompanying the high rate and ee value was the substrate quality. 

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