Intramolecular complexes, formation

Protein tyrosine kinases (PTKs) are enzymes (EC 2.7.1.112) that catalyze the transfer of the y-phosphate group of ATP to tyrosine residues of protein substrates. The activity of PTKs is controlled in a complex manner by posttranslational modifications and by inter- and intramolecular complex formations. 

Intramolecular complex formation between tertiary amines and aromatic hydrocarbons is strongly affected by the hybridisation of the nitrogen. Van... 

To observe complex formation in monofunctional systems, rather high concentrations may be needed, while in the blchromophorlc systems under investigation, two chromophores are near each other even in very dilute solutions. This makes it possible to investigate the excited state behavior of such complexes at high dilution, although the chain, linking the chromophores, may Impose new restrictions on Intramolecular processes. An extensive review on intramolecular exclmers, including excimer formation in polymers, has been made recently by Klopffer (9). Recent developments in this area have broadened substantially the scope of intramolecular complex formation. 

On the basis of these results De Schryver and co-workers reformulated Hirayama s rule as follows the possibility of intramolecular complex formation is limited by the probability to reach, within the lifetime of the excited state involved, a favorable conformation and by the extent of stabilization in the complex, covalent bond formations being the extreme. 

Mataga and others (28) have made a very Interesting study of Intramolecular complex formation in compounds [6]. These results indicate that within the excited state lifetime an... 

Morrison has made a detailed mechanistic study (70) of [77c] and [77d]. On irradiation, compound [77d] leads only to [77c] with a quantum yield of 0.029. Compound [77c], however, forms oxetane [78] ( =0.015) in competition with isomerization to [77d] ( =0.02) no crossed adduct [79] was observed. Triplet quenching did have very little effect on Isomerization or oxetane formation, while on sensitization cis-trans Isomerization but no oxetane formation occurred. The authors concluded that the reaction occurred via that intramolecular complex formation in... 

FarreraJ-A, Hidalgo-Femandez P, HanninkJM, et al. Divalent ligand for intramolecular complex formation to streptavidin. Org Biomol Chem. 2005 3 2393-2395. 

The analysis of excimer and monomer emission in fluid systems is complex. A general kinetic scheme for excimer formation, including the inter- and intramolecular complex formation in terms of a singlet ground and excited states, and the various photophysical processes occurring in polymers, is given in Table 4.1. The three routes of energy... 

Metal ions are usually linked to a macrochain through the formation of several bonds with one (intramolecular complexes) or more (intermolecular complexes) chains. Dilute solutions prefer intramolecular complexes and concentrated solutions and matrixes provide intermolecular complexes. In intramolecular complex formation... 

The analysis is performed for the calculations with rrot=0 K for the CH3C1 reactant, so that the angular momentum distribution for the complex P(j) is the distribution of orbital angular momentum for complex formation P(i). This latter distribution is given in ref. 37. Jm , the quantum number for j, varies from 282 for Enl = 0.5 kcal/mol to 357 for rel = 3.0 kcal/mol. The term k iEJ) in equation 24 is written as k (.EJ)=k Ejyf E), where k EJ) is the classical RRKM rate constant with the CH3C1 intramolecular modes inactive and / ( ) is treated as a fitting factor. 

In order to rationalize the catalyst-dependent selectivity of cyclopropanation reaction with respect to the alkene, the ability of a transition metal for olefin coordination has been considered to be a key factor (see Sect. 2.2.1 and 2.2.2). It was proposed that palladium and certain copper catalysts promote cyclopropanation through intramolecular carbene transfer from a metal carbene to an alkene molecule coordinated to the same metal atom25,64. The preferential cyclopropanation of terminal olefins and the less hindered double bond in dienes spoke in favor of metal-olefin coordination. Furthermore, stable and metastable metal-carbene-olefin complexes are known, some of which undergo intramolecular cyclopropane formation, e.g. 426 - 427 415). 

Referring to the ADMET mechanism discussed previously in this chapter, it is evident that both intramolecular complexation as well as intermolecular re-bond formation can occur with respect to the metal carbene present on the monomer unit. If intramolecular complexation is favored, then a chelated complex, 12, can be formed that serves as a thermodynamic well in this reaction process. If this complex is sufficiently stable, then no further reaction occurs, and ADMET polymer condensation chemistry is obviated. If in fact the chelate complex is present in equilibrium with re complexation leading to a polycondensation route, then the net result is a reduction in the rate of polymerization as will be discussed later in this chapter. Finally, if 12 is not kinetically favored because of the distant nature of the metathesizing olefin bond, then its effect is minimal, and condensation polymerization proceeds efficiently. Keeping this in perspective, it becomes evident that a wide variety of functionalized polyolefins can be synthesized by using controlled monomer design, some of which are illustrated in Fig. 2. 

The experimental observations were interpreted by assuming that the redox cycle starts with the formation of a complex between the catalyst and the substrate. This species undergoes intramolecular two-electron transfer and produces vanadium(II) and the quinone form of adrenaline. The organic intermediate rearranges into leucoadrenochrome which is oxidized to the final product also in a two-electron redox step. The +2 oxidation state of vanadium is stabilized by complex formation with the substrate. Subsequent reactions include the autoxidation of the V(II) complex to the product as well as the formation of aVOV4+ intermediate which is reoxidized to V02+ by dioxygen. These reactions also produce H2O2. The model also takes into account the rapidly established equilibria between different vanadium-substrate complexes which react with 02 at different rates. The concentration and pH dependencies of the reaction rate provided evidence for the formation of a V(C-RH)3 complex in which the formal oxidation state of vanadium is +4. 

A cyclic homoallylic alcohol is efficiently provided by a sequence of Jt-allylpalla-dium complex formation, transmetallation with hexa-n-butyldistannane and intramolecular allylation (Scheme 16.17) [22]. The same transformation can be conducted by means of indium (Scheme 16.18) [23]. 

The viscosity dependence of intramolecular excimer formation is complex. As in the case of molecular rotors (Section 8.2), most of the experimental observations can be interpreted in terms of free volume. However, compared to molecular rotors, the free volume fraction measured by intramolecular excimers is smaller. The volume swept out during the conformational change required for excimer formation is in fact larger, and consequently these probes do not respond in frozen media or polymers below the glass transition temperature. 

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