Activity probe structures

An interesting study of oxidic spinel ferrites of the type CO cNi5/3 xFeSbi/304 was reported [21], where three different Mbssbauer-active probes Fe, Ni and Sb were employed on the same material. The results have been interpreted in terms of the cation distributions over spinel A- and B-lattice sites, magnetic moments and spin structure, and the magnitude of the supertransferred hyperfine... 

Gales C, Van Durm JJ, Schaak S, Pontier S, Percherancier Y, Audet M, Paris H, Bouvier M (2006) Probing the activation-promoted structural rearrangements in preassembled receptor-G protein complexes. Nat Struct Mol Biol 13(9) 778—786... 

Unlike, e.g. in pharmaceutical metabolism studies, where the parent compound is known and thus some preliminary knowledge of the expected structures is available, the composition of a natural products extract is often completely unknown beforehand ( non-target analysis ). In such cases, NMR spectroscopy is especially well suited as a detection system since it does not discriminate any classes of compounds. (Sufficient relaxation delays provided, the NMR signal depends only on the number of nuclei in the active probe volume.)... 

Micromechanical experiments made so far can be roughly divided into two parts (i) design of special techniques to measure and evaluate separately different contributions in the net force, such as adhesion, friction, deformation, and (ii) imaging of various heterogeneous surfaces such as blends, composites and microphase separated structures by conventional SFM s to collect statistical information and understand the origin of the mechanical contrast. Many of the micromechanical experiments were discussed elsewhere [58, 67, 68, 381, 412-414]. Here we will focus on recent advances in analytical applications of the active probe SFM. 

Fykse EM, Li C, and Stidhof TC (1995) Phosphorylation of rabphilin-3A by Ca2+/calmodulin-and cAMP-dependent protein kinases in vitro. J Neurosci 15 2385-95 Gales C, Van Durm JJ, Schaak S et al (2006) Probing the activation-promoted structural rearrangements in preassembled receptor-G protein complexes. Nat Stmct Mol Biol 13 778-86 Gamper N, Reznikov V, Yamada Y et al (2004) Phosphatidylinositol [correction] 4,5-bisphosphate signals underlie receptor-specific Gq/11-mediated modulation of N-type Ca2+ channels. J Neurosci 24 10980-92... 

In order to characterize the active site structure of Ca ATPase from sarcoplasmic reticulum, we have employed Gd + as a paramagnetic probe of this system in a series of NMR and EPR investigations. Gadolinium and several other lanthanide ions have been used in recent years to characterize Ca + (and in some cases Mg2+) binding sites on proteins and enzymes using a variety of techniques, including water proton nuclear relaxation rate measurements (35,36,37), fluorescence (38) and electron spin resonance (39). In particular Dwek and Richards (35) as well as Cottam and his coworkers (36,37) have employed a series of nuclear relaxation measurements of both metal-bound water protons and substrate nuclei to characterize the interaction of Gd + with several enzyme systems. 

These examples and many others have provided evidence of significant changes in catalyst structures resulting from changes in operating conditions. Techniques are thus necessary that can be applied to catalysts in the presence of probe molecules, in reactive environments (e.g., when catalysts undergo reduction, oxidation, etc.), and under catalytic reaction conditions. Moreover, the simultaneous determination of catalyst structure and activity or selectivity is needed to establish structure-activity or structure-selectivity relationships, which provide a basis for improvement and development of catalysts (Banares, 2005 Thomas, 1980 Thomas, 1999 Topsoe, 2000 Wachs, 2005). The need for characterization of catalysts during... 

Peisach, J.. (1995) ESEEM spectroscopy - probing active site structures of metalloproteins, Bioradicals Detected by ESR Spectroscopy 203-215. 

N-substituted iron porphyrins form upon treatment of heme enzymes with many xenobiotics. The formation of these modified hemes is directly related to the mechanism of their enzymatic reactivity. N-alkyl porphyrins may be formed from organometallic iron porphyrin complexes, PFe-R (a-alkyl, o-aryl) or PFe = CR2 (carbene). They are also formed via a branching in the reaction path used in the epoxidation of alkenes. Biomimetic N-alkyl porphyrins are competent catalysts for the epoxidation of olefins, and it has been shown that iron N-alkylporphyrins can form highly oxidized species such as an iron(IV) ferryl, (N-R P)Fe v=0, and porphyrin ir-radicals at the iron(III) or iron(IV) level of metal oxidation. The N-alkylation reaction has been used as a low resolution probe of heme protein active site structure. Modified porphyrins may be used as synthetic catalysts and as models for nonheme and noniron metalloenzymes. 

D of protoporphyrin-IX depends on the steric constraints of the substrate binding pocket. Ortiz de Montellano (59) has used this selectivity to probe the active site structure of several heme enzymes. The structure of phenyl-cyt P-450cam has been determined by X-ray crystallography and indicates that N-phenyl heme formation is an accurate, low-resolution probe of active site structure. 

Originally, photoluminescence spectroscopy was applied to characterize the local coordination of metal ions as well as to probe structural perturbations that occur due to alkaline earth and rare earth metal ions in oxides such as silica and alumina. Emphasis has turned to elucidating the mechanisms of catalytic and photocataljTic reactivity, i.e., the characterization, at the molecular level, of the active surface sites as well as the significant role of these sites in catalysis and photocatalysis. 

P. J. Maddox, J. Stachurski and J. M. Thomas, Probing structural changes during the onset of catalytic activity by in situ diffractometry, Catal. Lett., 1988, 1, 191. 

Stezowski, J. J., Kollat, P., Bogucka-Ledochowska, M., and Glusker, J. P. Tau-tomerism and steric effects in l-nitro-9-(alkylamino)acridines (ledakrin or ni-tracrine analogues) probing structure-activity relationships at the molecular level. J. Amer. Chem. Soc. 107, 2067-2077 (1985). 

Tyr 254 is an active site residue (Section III,D, Fig. 6) that interacts with the hydroxyl group of L-lactate (and keto group of pyruvate). Based on the active site structure, Lederer and Mathews (39) proposed that the Tyr 254 hydroxyl group forms a hydrogen bond to the substrate 02 throughout the catalytic cycle and facilitates electron transfer from substrate carbanion to FMN by deprotonating the substrate hydroxyl group. To probe the function of the Tyr 254 hydroxyl, Reid et... 

Development of Electrocatalysts for Carbon Dioxide Reduction Using Polydentate Ligands to Probe Structure-Activity Relationships... 

Electroactive dendrimers are defined as those that contain functional groups capable of undergoing fast electron transfer reactions [85], The combination of specific electron transfer properties of redox active probes with the unique structural properties of dendrimers offers attractive prospects of their exploitation in electrocatalytic processes of biological and industrial importance [86], Further, the interest in dendrimers containing electroactive units also relies on the fact that electrochemistry is a powerful technique to elucidate the structure and purity of dendrimers, to evaluate the degree of electronic interaction of their chemically and/or topologically equivalent or non- equivalent moieties, and also to study their endo- and exo-receptor capabilities [87],... 

Keywords Cannabinoid receptors Cannabinoid receptor probes Structure-activity relationships Selecrivity... 

Makriyannis and co-workers designed and synthesized a series of pyrazole derivatives to aid in the characterization of the CB receptor binding sites and also to serve as potentially useful pharmacological probes. Structural requirements for potent and selective brain cannabinoid CBi receptor antagonistic activity included (1) a para-substituted phenyl ring at the 5-position, (2) a carboxamido group at the 3-position, and (3) a 2,4-dichlorophenyl substituent at the 1-position of the pyrazole ring (Lan et al. 1999). 

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