Donor pseudo

The intermediate diphenylhydroxymethyl radical has been detected after generation by flash photolysis. Photolysis of benzophenone in benzene solution containing potential hydrogen donors results in the formation of two intermediates that are detectable, and their rates of decay have been measured. One intermediate is the PhjCOH radical. It disappears by combination with another radical in a second-order process. A much shorter-lived species disappears with first-order kinetics in the presence of excess amounts of various hydrogen donors. The pseudo-first-order rate constants vary with the structure of the donor with 2,2-diphenylethanol, for example, k = 2 x 10 s . The rate is much less with poorer hydrogen-atom donors. The rapidly reacting intermediate is the triplet excited state of benzophenone. 

The slow protonation rate of the conjugated anion of the sulphone (1st step) leads to the obtainment of a pseudo one-electron process. However, no self-protonatiori process exists in the presence of an excess of a proton donor of lower pKa than that of the electroactive substrate and Figure 6a, curve 2 shows evidence for a two-electron step. Full substitution on the a carbon, as in the case of phenyl 2-phenylbut-2-yl sulphone, does not allow one to observe any deactivation (Figure 6b, curve 1). It is worth mentioning that cathodic deactivations of acidic substrates in aprotic solvents are rather general in electrochemistry, e.g. aromatic ketones behave rather similarly, showing deprotonation of the substrate by the dianion of the carbonyl compound39. 

Alkali metal derivatives of 2-(trimethylsilyl)aminopyridines can be further derivatized by insertion of 1,3-dicyclohexylcarbodiimide. Functionalized guani-dinates are formed in this reaction via a 1,3-silyl shift. Scheme 170 illustrates the reaction sequence as well as the preparation of an aluminum complex of the modified ligand, which exhibits pseudo jS-diketiminate binding of the metal center, thus exemplifying the coordinative versatility of this new multi-N-donor system. ... 

Figure 5B. Correlation of right-angle light scatter measured by fluorometry and flow cytometry. The top panel shows flow-cytometric data of side scatter of fixed, stained cells during the time course of stimulation by 1-nM (solid line, solid circles) or 0.01-nH (dashed line, open circle) FLPEP. The bottom panel shows the corresponding right-angle light-scatter data acquired pseudo-simultaneously on live cells in the fluorometer. The flow-cytometric data have been averaged, but the fluorometry data are plotted for both duplicates from one donor. Reproduced with permission from Ref. 27. Copyright 1985 Rockefeller University Press.

Stimulated by extensive research activities on donor/acceptor substituted stilbenes, Mullen and Klarner have reported a donor/acceptor substituted poly(4,4 -biphenyl-diylvinylene) derivative (85) in which the NR2 donor and CN acceptor substituents are located on the vinylene unit [111]. The synthesis is based on a C-C-coupling reaction of in situ generated carbanion functions with a (pseudo)cation function, followed by a subsequent elimination of MeSH with formation of the olefinic double bond. 

Rule 2 can also be tested when the Lewis base B carries no n-pairs but two or more tt-electron pairs, either conjugated or cumulative. Strictly, cyclopropane might be considered in this category but has been discussed in Sect. 3.2.2 as the prototype of a pseudo-k donor for convenience. 

In PAMPA measurements each well is usually a one-point-in-time (single-timepoint) sample. By contrast, in the conventional multitimepoint Caco-2 assay, the acceptor solution is frequently replaced with fresh buffer solution so that the solution in contact with the membrane contains no more than a few percent of the total sample concentration at any time. This condition can be called a physically maintained sink. Under pseudo-steady state (when a practically linear solute concentration gradient is established in the membrane phase see Chapter 2), lipophilic molecules will distribute into the cell monolayer in accordance with the effective membrane-buffer partition coefficient, even when the acceptor solution contains nearly zero sample concentration (due to the physical sink). If the physical sink is maintained indefinitely, then eventually, all of the sample will be depleted from both the donor and membrane compartments, as the flux approaches zero (Chapter 2). In conventional Caco-2 data analysis, a very simple equation [Eq. (7.10) or (7.11)] is used to calculate the permeability coefficient. But when combinatorial (i.e., lipophilic) compounds are screened, this equation is often invalid, since a considerable portion of the molecules partitions into the membrane phase during the multitimepoint measurements. 

Ni11 complexes of various amine/thiophenolate ligands have been investigated (for Ni complexes of ortho-aminothiophenol see Section 6.3.4.9.2(iv)). Thiophenolate is expected to exhibit decreased bridging tendency compared to aliphatic thiolates, but complexes (466) and (467) still consist of two pseudo-octahedral NiL fragments bridged via thiolate donors. In contrast to the parent complex (466), the thiolate and thioether donors in (467) coordinate cis to the Ni center... 

The treatment of gold(III) complexes with the rigid bidentate ligand phen allows the synthesis of pseudo-pentacoordinate gold(III) derivatives. This is the case of [Au(dmp)(phen)PPh3](BF4)2 (288) (dmp = 2-(dimethylaminomethyl)phenyl)1699 or [AuCl(C4Ph4)(phen)].16 2 The donor atoms of the phenanthroline ligand occupy one equatorial and the axial position of a square pyramid with distances 2.154(8)A and 2.627(10)A in (288). 

The complex has crystallographic ///-symmetry, the mirror plane bisecting the unique benzyl group, the nitrogen atom to which it is attached, and the ethylzinc moiety. The pseudo-tetrahedral zinc atom has a short (1.930(4) A) zinc-ethyl bond, but comparatively long (2.230(2) A) nitrogen-zinc donor bonds. 

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