Activity trends

Significant (and even spectacular) results were contributed by the group of Norskov to the field of electrocatalysis [102-105]. Theoretical calculations led to the design of novel nanoparticulate anode catalysts for proton exchange membrane fuel cells (PEMFC) which are composed of trimetallic systems where which PtRu is alloyed with a third, non-noble metal such as Co, Ni, or W. Remarkably, the activity trends observed experimentally when using Pt-, PtRu-, PtRuNi-, and PtRuCo electrocatalysts corresponded exactly with the theoretical predictions (cf. Figure 5(a) and (b)) [102]. 

Figure 1.141. Temperature-aK+/°H+ activity) trend due to the mixing of hydrothermal solution and groundwater accompanied by hydrothermal alteration (Hemley and Jones, 1964). HS hydrothermal solution, GW groundwater, A hydrothermal solution-groundwater mixing line, B hydrothermal solution-acidic groundwater mixing line (Shikazono et al., 2002).

In addition to the establishment and understanding of activity trends on nanosegregated surfaces, it has been anticipated that finding relationships between chemical and electronic properties of thin metal films of Pt group metals deposited over 3d and 5d elements has the potential to open up new opportunities in the quest to... 

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Further extended the study by using azides with varying functional groups (-OCH3 and -NO2) and studied the effect of shape of the nanostructures on the rate of the reaction and yield of the triazole products. The activity trend observed was CuO-NW> CuO-NR> CuO-NS, irrespective of the presence of electron withdrawing or donating groups on the azide. 

Based on equation 2.99, the corresponding activity trend of component 2 may be deduced, whenever the activity trend of component 1 in the mixture with the increase in the molar fraction of component 2 is known. 

Figure 3.14 Stability relations in a binary mixture (A,B)N as a function of temperature. Heavy, solid line activity trend for component (B)N in the case of binodal decomposition. Dashed line activity trend in the case of spinodal decomposition.

The activity trend obtained with Cui xCoxFe204 catalysts is well supported by the surface metal ions composition determined from XPS analysis. Figure 8 displays the Cu/(Co+Fe) (Co/Fe for X = 1) ratio calculated from XPS results in the left panel and phenol conversion with products selectivity for all catalyst compositions in the right panel. This exercise is mainly to imderstand the distribution of metal ions and their heterogeneity on the smface, as it directly influences catalytic activity. On fresh catalysts, relative Cu-content decreases linearly with decreasing Cu-content and it is in good correlation with bulk Cu-content measmed by x-ray fluorescence. A high Cu/Fe ratio is found on spent catalysts at 0.25 < x < 0.75. It is to be... 

Optimization of biological properties in a series of miticidal and mite ovicidal 2-aryl-l,3-cycloalkanediones, Ia,b, and enol esters, II, was achieved through analog synthesis and testing supported by the development of quantitative structure/ activity trends during the course of the project. QSAR equations developed during an initial phase provided the basis for both... 

Recently, tris-p-diketiminate lanthanide complexes [LnL3 ] (X = Cl, L Ln = Pr 111, Nd 112, Sm 113 X = H, L Ln = Nd 114 X = Me, L Ln = Nd 115) (Scheme 12) displaying a high activity in producing PLAs under mild conditions via ROP of L-lactide have been reported. This reactivity may be attributed to the crowded coordination sphere around the central metal, which incidentally affords an activated Ln-N(p-diketiminate) bond. The activity depends on the central metals, and the active trend of Sm < Nd < Pr is consistent with the sequence of the ionic radii [113]. 

Huang KP The mechanism of protein kinase C activation. Trends Neurosci 12 ... 

McEntee WJ, Mair RG Memory enhancement in Korsoff s psychosis with clonidine further evidence for a noradrenergic deficit. Ann Neurol 7 466-470, 1980 McEwen BS Non-genomic and genomic effects of steroids on neural activity. Trends Pharmacol Sci 12 141-147, 1991... 

Not all radical aromatic substitutions are as immune to polar effects as is attack by phenyl. Some radicals reveal marked electrophilic or nucleophilic character. Oxygen-centered radicals, for example, are electrophilic, as would be expected if there is substantial polar contribution to the transition state. Table 9.13 lists partial rate factors for substitution by benzoyl radicals note that the orientation and activation trends found in typical electrophilic substitutions have begun to appear, but are still modest compared with the dramatic effects shown in Table 9.12 for a true heterolytic substitution.179... 

Rossman, K. L., and Sondek, J. (2005). Larger than Dbl New structural insights into RhoA activation. Trends Biochem. Sci. 30, 163-165. 

The development of new and improved electrocatalysts begins with the discovery of materials displaying improved intrinsic electrochemical activity. Intrinsic activity is best observed and compared in a well-controlled catalyst environment where variables that may disguise the intrinsic activity trends are minimized or absent. Particle size, particle size distribution, surface area, catalyst utilization and the distribution of crystallographic phases are parameters that are typically difficult to control. Vapor deposition of unsupported thin film electrocatalysts eliminates many of these variables. This method provides a controlled synthetic route to smooth, single-phase or multi-phase, ordered or disordered metal alloy phases depending on deposition and processing conditions. 

Fig. 11.13 Summary of activity trends from Fig. 11.12. The area-specific activities are plotted after normalization with repect to Pt. The logarithmic value represents an activation energy difference (relative kinetic improvement) and follows the DFT-calculations discussed in the text. The gains in activity on going from pure Pt to Pt-Ru, Pt-Ru-Ni and Pt-Ru-Co compositions are obvious. Quaternary compositions offer additional potential for improvement.

Pure Pt = 10096 Pt "Pt = Pt binary alloy Pt-Ru with a Pt top layer on two Ru layers. The observed activity trend from Pt to Pt-Ru to Pt-Ru-Ni to Pt-Ru-Co is similar to the trends observed in the experimental screening results. (Reproduced from [18]). 

Since the formation of strongly bonded surface CO constitutes the major kinetic hurdle for the oxidation of methanol at low overpotentials, model calculations of the CO tolerance should also give guidance in the development of ternary methanol oxidation catalysts. In fact, model calculations of the CO tolerance of ternary Pt-Ru-X alloys have been performed (Fig. 11.14) [18] revealing activity trends similar to those observed in the experimental combinatorial methanol oxidation study (Fig. 11.13) Figs 11.13 and 11.14 identify Pt-Ru-Co ternary composi-... 

Fig. 11.17 Chronoamperometric screening results from the ternary catalyst library described in Figs. 11.15 and 11.16. Surface-area-normalized activity values of each individual composition are plotted as a function of composition. Color-coding indicates activity red = high, blue = low. The pt-Ru binary compositions are connected by a solid line to underscore the activity trends observed in this binary system. Conditions 1 M methanol, 0.5 M H2S04, 550 mV/RHE, 5 min.

Figure 9.12). In addition, our arbitrary cut-off for the energy score may have missed some interesting inhibitors, e.g. the ethyl- and isobutylamines which are labeled as Below cutoff in Figure 9.12. However, the score versus activity trend is clear, including a true negative control, the tert-butylamine reagent, which was predicted (and subsequently observed) to yield an inhibitor with very low BACE-1 activity. In addition to demonstrating the utility of an in situ virtual reagent selection, this study served to validate the hypothesis that the BACE-1 SF pocket is large, open and promiscuous, as a variety of reagents led to potent BACE-1 inhibitors.

One more obvious factor must not be overlooked is the availability of relevant biological target information where it exists. If good target-related information has been collated (perhaps in the form of a pharmacophore or structure-activity trend),... 

Lead explosion where a lead or leads are followed up by an analoguing experiment designed to probe the neighboring (bioisosteric) property space with the intention of finding active analogues and detecting structure-activity trends. 

Leff, P. The Two-State Model of Receptor Activation. Trends Pharmacol. Sci. 1995, 16, 89-97. 

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