Complex, covalently-bound

Tris(2,2 -bipyridine)ruthenium(II) complex (Ru(bpy)3+) has been most commonly employed as a chromophore in the studies of photoinduced ET. Electrostatic effects on the quenching of the emission from the Ru(II) complex covalently bound to polyeletrolytes have been studied by several groups [79-82]. 

A similar study was performed on ruthenium-modified myoglobins, in which AG variations were obtained by changing the nature of the ruthenium complex covalently bound to the protein, and by substituting a porphyrin to the heme [137]. It is gratifying to observe that, in spite of the rather heterogeneous character of this series, the study leads to an estimation of 1.9 to 2.4 eV for A which is consistent with the value 2.3 eV derived in section 3.2.1 from temperature dependent experiments. Satisfactory agreement between the results given by the two methods is also observed in the case of ruthenium-modified cytochrome c [138]. 

Baleizao, C. Gigante, B. Sabater, M. J. Garcia, H. Corma, A. (2002) On the activity of chiral chromium salen complexes covalently bound to solid silicates for the enantioselective epoxide ring o emag Applied Catalysis A General 228 279-288. 

The occurrence of vectorial energy transfer (126, 195, 210-212) was reported for a zinc porphyrin species modihed with four trw-(4,4 -dimethyl-2,2 -bpy) ruthenium(ll) complexes covalently bound at the meso-positions (211), [ZnTBpyP Ru(dmbpy)2 4] (Fig. 23). 

Ru-porphyrin complexes covalently bound to MCM-41 were used as catalysts for the oxidation of alkenes, giving turnover numbers 20-40 times higher than the free complex [190]. Porphyrin complexes have also been attached to Nb dopants in the MCM-41 matrix, and behaved as cyclohexene epoxidation catalysts and were stable towards ligand degradation [44b]. Grafting of ethylenediamine ligands on... 

Pd is an expensive metal. In Pd(0) or Pd(II)-catalyzed reactions, particularly in commercial processes, repeated uses of Pd catalysts are required. When products are low-boiling, they can be separated from the catalyst by distillation. The Wacker process for the production of acetaldehyde is an example, hi order to separate from less volatile products, there are several approaches for the economical use of Pd catalysts. Active Pd complexes covalently bound to a polymer chain are frequently used. After the reaction, the supported catalyst can be recovered by filtration and reused several times. Polymers such as the Merrifield resin [25], amphiphilic poly(ethylene glycol)-polystyrene copolymer [26] and polyethylene [27] are typical examples. Also polymer-supported microencapsulated Pd is used as a reusable... 

The most efficient enantioface discriminating agents seem to be transition metal complexes covalently bound to the growing chain end, which are also able to achieve a very high regio-selectivity in the attack to the double bond. Unfortunately, the type of monomers which are polymerized stereospecifically with this type of catalysts are mainly unsaturated hydrocarbons. Propylene (14) and butadiene (46) can be polymerized by the above catalysts both to isotactic and syndiotactic polymers. 

Four possible mechanisms for solid-state extraction (a) adsorption onto a solid substrate (b) absorption into a thin polymer or chemical film coated on a solid substrate (c) metal-ligand complexation in which the ligand is covalently bound to the solid substrate and (d) antibody-antigen binding in which the receptor is covalently bound to the solid substrate. 

In the chymotrypsiii mechanism, the nitrophenylacetate combines with the enzyme to form an ES complex. This is followed by a rapid second step in which an acyl-enzyme intermediate is formed, with the acetyl group covalently bound to the very reactive Ser . The nitrophenyl moiety is released as nitrophenolate (Figure 16.22), accounting for the burst of nitrophenolate product. Attack of a water molecule on the acyl-enzyme intermediate yields acetate as the second product in a subsequent, slower step. The enzyme is now free to bind another molecule of nitrophenylacetate, and the nitrophenolate product produced at this point corresponds to the slower, steady-state formation of product in the upper right portion of Figure 16.21. In this mechanism, the release of acetate is the rate-llmitmg step, and accounts for the observation of burst kinetics—the pattern shown in Figure 16.21. 

FIGURE 18.5 Schematic representation of types of multienzyme systems carrying out a metabolic pathway (a) Physically separate, soluble enzymes with diffusing intermediates, (b) A multienzyme complex. Substrate enters the complex, becomes covalently bound and then sequentially modified by enzymes Ei to E5 before product is released. No intermediates are free to diffuse away, (c) A membrane-bound multienzyme system. 

Complex II is perhaps better known by its other name—succinate dehydrogenase, the only TCA cycle enzyme that is an integral membrane protein in the inner mitochondrial membrane. This enzyme has a mass of approximately 100 to 140 kD and is composed of four subunits two Fe-S proteins of masses 70 kD and 27 kD, and two other peptides of masses 15 kD and 13 kD. Also known as flavoprotein 2 (FP2), it contains an FAD covalently bound to a histidine residue (see Figure 20.15), and three Fe-S centers a 4Fe-4S cluster, a 3Fe-4S cluster, and a 2Fe-2S cluster. When succinate is converted to fumarate in the TCA cycle, concomitant reduction of bound FAD to FADHg occurs in succinate dehydrogenase. This FADHg transfers its electrons immediately to Fe-S centers, which pass them on to UQ. Electron flow from succinate to UQ,... 

Complex 1 850 kDa (probably a dimer in membrane) About 40 1 FMN covalently bound, bound 16-24 Fe-S atoms in 5 to 7 centers Spans membrane, NADH site on matrix face, UQ site in membrane 0.06 UQ Pumps protons out of matrix during electron transporl/2e"... 

Complex II 120 kDa 4 1 FAD covalently bound, 8 Fe-S atoms in 3 centers In inner membrane, succinate site on matrix face, UQ site in membrane. 0.19 UQ None... 

Allcock, H. R., Neenan, T. X., and Boso, B., Synthesis, oxygen-binding behavior, and Mossbauer spectroscopy of covalently-bound polyphosphaene heme complexes, Inorg. Chem.. 

The role of coordinated ethylene is evidenced by the recent ab initio calculation performed by Espelid and Borve [121-123], who have shown that ethylene may coordinate in two different ways to the reduced Cr(II) species, either as a molecular complex or covalently bound to chromium. At longer Cr-C distances (2.36-2.38 A) an ethylene-chromium zr-complex forms, in which the four d electrons of chromium remain high-spin coupled and the coordination interaction is characterized by donation from ethylene to chromium. Cr(II) species in a pseudo-tetrahedral geometry may adsorb up to two equivalents of ethylene. In the case of a pseudo-octahedral Cr(II) site a third ethylene molecule can also be present. The monoethylene complex on the pseudo-tetrahedral Cr(II) site was also found to undergo a transformation to covalently bound complex, characterized by shorter Cr-C distances (about... 

Irinotecan (Camptosar ) is a topoisomerase I inhibitor that forms a complex with the covalently bound DNA topoisomerase... 

Reactions at the exocyclic position of cyclophosphazene derivatives represent a means for widely expanding the range of available phosphazenes. The synthesis of covalently bound cyclophosphazene heme complexes starts with N3P3 (OPh), -Cl which is converted to N3P3(OPh)5NMeCH2CH2CN. Following reduction of the... 

Proteins either strengthen the membrane structure (building proteins) or fulfil various transport or catalytic functions (functional proteins). They are often only electrostatically bound to the membrane surface (extrinsic proteins) or are covalently bound to the lipoprotein complexes (intrinsic or integral proteins). They are usually present in the form of an or-helix or random coil. Some integral proteins penetrate through the membrane (see Section 6.4.2). 

Electrocatalysis employing Co complexes as catalysts may have the complex in solution, adsorbed onto the electrode surface, or covalently bound to the electrode surface. This is exemplified with some selected examples. Cobalt(I) coordinatively unsaturated complexes of 2,2 -dipyridine promote the electrochemical oxidation of organic halides, the apparent rate constant showing a first order dependence on substrate concentration.1398,1399 Catalytic reduction of dioxygen has been observed on a glassy carbon electrode to which a cobalt(III) macrocycle tetraamine complex has been adsorbed.1400,1401... 

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