Homologous complexants

The complementation experiments in which the A domain of a class 111 E-II is used as the phosphoryl group donor to the B domain of a second E-II molecule with either the same or different sugar specificity, while both are fixed in a membrane matrix, raises some intriguing issues about the association state of these proteins and the kinetics of their interactions. Do E-IIs form stable homologous complexes in the membranes If so, is it necessary to postulate the formation of stable heterologous complexes to explain, for example, the phosphorylation of the B domain of E. coli 11° by the A domain of ll , or can the data be explained by assuming a... 

It should be kept in mind that this type of study, treated here in terms of single complexes, acquires greater importance when carried out on a series of homologous complexes. This allows one to evaluate how the electronic and/or structural variations of the ligand influence the reorganization processes of the solvent molecules. In fact, such a comparison has recently led to a reinterpretation of the A °c parameter also in terms of the structural reorganisations of the first coordination sphere.18,19 For example, if one compares the A-Sr°c values for... 

Furthermore, the homologous complex 286 condenses with ethyl orthoformate to give, in the course of a new y-tropolone synthesis, tropolone ether 287 by O-ethylation it is transformed to tropylium salt 288 (Scheme 72 70JA6382) the corresponding tropone complex was synthesized from dibenzotroporic and Cr (CO)6 [83AG(S)734]. 

Like the homologous Complex III in mitochondria, the cytochrome bci complex of purple bacteria carries electrons from a quinol donor (QH2) to an electron acceptor, using the energy of electron transfer to pump protons across the membrane, producing a proton-motive force. The path of electron flow through this complex is believed to be very similar to that through mitochondrial Complex III, involving a Q cycle (Fig. 19-12) in which protons are consumed on one side of the membrane and released on the other. The ultimate... 

All groups of homologous complexants (PROM, AROM, humics, proteins, polysaccharides, cell wall debris, clays, metal oxyhydroxides) exhibit at least three major properties ... 

FetSp and Ftrlp most hkely form a heterodimeric complex in the yeast plasma membrane (Stearman et al., 1996). FetSp and Fthlp form a homologous complex in the vacuolar membrane (Urbanowski and Piper, 1999). The evidence for this model is indirect in that a specific physical interaction between the two proteins has not been directly demonstrated. The lack of evidence for a similar functional interaction between Cp and Tf was noted above. FetSp and Ftrlp do localize to the plasma membrane. However, the most compelling evidence for a physical interaction between the two is that this localization depends on the presence of both proteins if one is not produced, then the other remains intracellular (Stearman et al., 1996). Furthermore, in the absence of Ftrlp production, the FetS protein that is made remains in an enzymatically inactive form, presumably as the a/io-protein. 

The carboxylato ligands also participate in metathetical reactions. These have been exploited to prepare homologous complexes. The carboxylato ligands can be replaced stepwise, and a few mixed carboxylato complexes have been isolated. The carboxylato complexes have been shown to be inefficient alkene hydrogenation catalysts. 

The LiAlH4 reduction of the homologous complex [MoCp (CO)3(L)][PF6] (L = phosphine) proceeded similarly to give a neutral radical resulting from electron transfer this was followed by the formation of ]MoCp (CO)(L)2(H)] or [MoCp (CO)2(L)(H)] [90], LiAlH4 also reduces polyaromatics and diarylketones... 

Nonaka, T., Nakamura, K. T., Uesugi, S., et al. (1993) Crystal structure of ribonuclease Ms (as a ribonuclease T1 homolog) complexed with a guanylyl-3, 5 -cytidine analog. Biochemistry, 32, 11825-11837. 

The bis-Cp titanium bis(/-butanethiolato) and bis(ethanethiolato) complexes have been used as a single-source precursors for the preparation of thin films of titanium sulfides by metal-organic chemical vapour deposition (MOCVD). The crystal and molecular structures of the precursor complexes have been determined for comparison with homologous complexes of the general formula Cp2Ti(SR)2.1618... 

As mentioned above and as demonstrated by model studies using various acetyl complexes, the insertion of styrene usually takes place with secondary regiochemistry [8]. However, styrene was found to insert with both primary and secondary regiochemistry into the metal-acetyl bond of a complex obtained by carbonylation of 66. It is very remarkable that primary regiochemistry only was observed for the insertion in a homologous complex, in which a polyketone chain (CH ),CO CH(CH ),)CH2C()[ i--,) was substituted for the acetyl ligand. Thus, it was proposed that, for this catalytic system, primary insertion of styrene is responsible... 

New complexes of the type [(P-P)Pt(C6F5)(H2O)]+ (P-P = diphosphine) were synthesized according to the route indicated in Fig. 2.1 and were characterized by elemental analysis, multinuclear H, " PI H, and " F H nuclear magnetic resonance (NMR) spectroscopy [27]. The synthetic pathway is very flexible, allowing the preparation of homologous complexes with a wide variety of diphosphine ligands. These are all commercially available except 2g which was prepared following a procedure reported in the literature [34]. 

Because the geometric structures and bonding are very similar for the entire series of actinocenes, we might expect their vibrational frequencies to be very similar as well. Table 7 lists the PW91 calculated frequencies for the An(Cot)2 complexes, with An = Pa-Am. We see a smooth trend in the vibrational frequencies across the series, with similar values to those discussed earlier for Th(Cot)2. The ability to calculate the predicted changes in the vibrational frequencies across a series of homologous complexes is certainly a strength of the application of DFT to vibrational problems. 

After listing the activated zones and homologous complexes involved in a given reaction type, the method is based on a threefold observation, see Fig. 36 ... 

In general agreement with the above theory, the most stable hydrides contain strong field ligands such as cyanide or tertiary phosphines. Also, where suitable series of homologous complexes are known, the thermal stability appears to increase with increasing atomic number of the metal, e.g.,... 

The homologous complex [VO(acac)2] anchored onto two different amine-functionalized oxidized ACs, were tested in the epoxidation of... 

Four chiral homologous complexes were also prepared. None of the palladium complexes showed mesomorphic properties, whereas a monotropic chiral discotic nematic phase was observed for the platinum complex (Table 18). The absence of mesomorphism for the dinuclear palladium complexes may be due to the type of chiral chain used, which differed from that used for the platinum system. All of the complexes form charge-transfer complexes with TNF. A Colh phase was induced for the two halo-bridged palladium complexes and for the platinum complex, as was observed for their non-chiral analogs. Flowever, the chiral nematic phase of the platinum compound was suppressed. At low TNF content, a chiral Nq phase was stabilized for the thiocyanato-bridged compound along with a non-chiral No phase at higher concentration. 

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