Concerted interaction

Scheme 1.8. Polar stepwise vs. concerted interactions of Cp2Zr complexes with n-bonds.

As one might expect the rate of p-nitrophenyl heptanoate hydrolysis increased at low ethanol concentrations as a result of apolar binding. The rate of p-nitrophenyl acetate hydrolysis also increased markedly at low ethanol concentration. This finding was explained by a conformational effect on the polymer, that is, lower ethanol concentration brings about a shrinkage of the polymer, which increases concerted interactions of the imidazole residues. The hydrolysis of 3-nitro-4-dodecanoyloxybenzoate was found to be 1700 times faster in the presence of poly[4(5)-vinylimidazole] compared to free imidazole (77). A double-displacement mechanism was demonstrated for this system (75). 

In the example shown, the two curly arrows suggest a concerted interaction of three entities. This is improbable, and does not tell us why the reaction should actually take place. Using the longer sequence, we see that the acid catalyst activates the carbonyl group towards nucleophilic attack, and is later regenerated. 

One striking characteristic of the coupling ATPase of energy-transducing membranes, apart from the extraordinarily large number of different polypeptide subunits, is the existence of two different polypeptides involved in the response of the enzyme to the inhibitor oligomycin. One binds the inhibitor, the other, separated in space from the former by possibly as much as 10 to 15 A, confers oligomycin sensitivity to the entire enzyme complex. How could the transfer of information between these two polypeptide subunits and their concerted interaction with the ATPase proper be visualized ... 

In biological systems, a macromolecular chain effectively selects a complementary one to form an intermacromolecular complex. In this way, very specific functionalities become effective. Synthetic polymers can also form intermacromolecular complexes, but the ability of a synthetic polymer to select only one objective polymer as in biological systems has not yet been realized, except for several specific systems of pairs of polymers which include one of the complementary base pairs of nucleic add individually, e.g. po y(A)-poly(U) and poly(I)-poly(C) (see Sect. 3.3). The intermacromolecular complex formation of synthetic polymers is controlled by many factors such as interaction forces, solvent, ionic strength, temperature, pH, etc. Moreover, the cooperative and concerted interactions of each active site play an important role in complex formation. These phenomena suggest that the selective intermacromolecular complexation can be realized under suitable conditions. 

A reaction of two alkenes or polyenes to form a cyclic product. Cycloadditions often take place through concerted interaction of the pi electrons in two unsaturated molecules, (p. 684)... 

Dqbkowska I, Rak J, Gutowski M (2005). DNA strand breaks induced by concerted interaction of H radicals and low-energy electrons A computational study on die nucleotide of cytosine. Eur Phys J D 35 429 135. 

A related series of mixed-metal face to face porphyrin dimers (192) has been studied by Collman et al.506 A motivation for obtaining these species has been their potential use as redox catalysts for such reactions as the four-electron reduction of 02 to H20 via H202. It was hoped that the orientation of two cofacial metalloporphyrins in a manner which permits the concerted interaction of both metals with dioxygen may promote the above redox reaction. Such a result was obtained for the Co11 /Co" dimer which is an effective catalyst for the reduction of dioxygen electrochemic-ally.507 However for most of the mixed-metal dimers, including a Con/Mnn species, the second metal was found to be catalytically inert with the redox behaviour of the dimer being similar to that of the monomeric cobalt porphyrin. However the nature of the second metal ion has some influence on the potential at which the cobalt centre is reduced. 

Any mechanism written for this preferential cleavage must take into account the double cleavage on both sides of the aspartyl residue that leads eventually to liberation of free aspartic acid (XXI). The nucleophilic concerted interactions (XVI-XVIII) pictured in the proposed mechanism may lead to a bicyclic orthoesteramide (XVII) which would collapse with the release of aspartic acid (XXI). Although the details of this tentative mechanism remain to be established, there is ample precedent for the formation of anhydride intermediates (XX) in intramolecular electro-... 

It is, however, well established [7] that XeF2 is a strong fluorobase when, in concerted interaction, two molecules donate one F ... 

One of specific features of SOD is an ability to form SAR in an excess of H2O2, which, in turn, can destabilize Cu in active center of the enzyme and to be transformed into hydroxyl radical [7]. Under such conditions, free radical attack of the protein molecule may result in its fragmentation and loss of the activity. Thus one of the conditions of successful operation of SOD in tissues is simultaneous presence of low molecular weight antioxidants. This example demonstrates the importance of concerted interaction of several components of cellular antioxidant defense. 

Scheme 4 [ls,3a]hydrogen, [la,3s]methyl and [la,3s]fluorine sigmatropic rearrangements in the allyl system. ELF analysis reveals a concerted interaction in the first case, a biradical interaction in the second one and a ion-pair interaction in the last one... 

Electrochemical phenomena play a central role in the fabrication and the functional capabilities of a great many materials, processes and devices. A common feature of these systems is that their behavior is largely determined as a result of concerted interactions that extend over many length scales. During the past several decades, the electrochemical field has advanced rapidly based primarily on a suite of remarkable new tools that provide the ability to create precisely characterized... 

Several review articles deal extensively with the absorption and Raman spectroscopic manifestations of localised or resonance modes in impure crystals89 140 149). The experimental status is well documented in these and particularly in a recent compendium9). It is recalled that the emphasis of these reviews is different from that in this Report. They treat effects due to mass or force constant defects in the crystal. These are essentially averages over a vibrational period of the mode. In opposition, our concern is with effects coming from the phase-concerted interaction (linear in the vibrational coordinate). We turn to this in the next section, though for brevity s sake we shall not continue to carry the adjective phase-concerted in specifying the linear interaction. 

A second delayed subacute phase is characterised by infiltration of leukocytes and phagocytic cells. The recruitment of inflammatory cells involves the concerted interaction of several types of chemotactic mediators such as complement factor C5a, platelet activating factor (PAF) and LTB4. Several cytokines, especially interleukin-1 (IL-1) and tumour... 

Illustrative saturation curves for the square, tetrahedral, and concerted interaction geometries are shown in Fig. 18. 

The intermediates that are usually observed after the oxidative addition are trans-[PdRXL2] complexes (2, Scheme 1.2), an observation which has led to the general proposal that these complexes are the primary products of the reaction. However, the oxidative addition for the most common C(sp )-X electrophiles proceeds by a concerted interaction of a reactive [PdLj] or [Pd(L-L)] (L-L=diphosphine) species with the substrate R-X via a three-center transition state that should necessarily lead to cis-[PdRXL2] complexes (Scheme 1.4). In the cis-isomers, a destabihzing... 

Figure 7. Concerted interaction of an adsorbat with a Bronsted site and a basic oxygen, 0(2).

Figure 1 Suggested concerted interaction of Ci2B-BCi2 with olefins.

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