Spacers heterogeneous

Tang, J., Laurent, T., Back, C. and Unnasch, T. (1996) Intra-specific heterogeneity of the rDNA internal transcribed spacer in the Simulium damnosum (Diptera Simulidae) complex. Molecular Biology andEvolution 13, 244—252. 

Alkylation of 2-naphthoxide ion (Eq. (6)) occurs mainly on carbon in aqueous solvents and mainly on oxygen in aprotic solvents. The product distribution is often used as a probe of the solvent environment in heterogeneous reactions. Brown and Jenkins 54) found that 40-100 % RS spacer chain catalysts 15 and 16 gave up to 98 % O-benzylation of 2-naphthoxide ion with benzyl bromide. The shorter spacer chain catalyst 16 gave 85% O-alkylation, and a conventional benzyltrimethylammonium ion resin 2 gave about 70 % O-alkylation. Because of low activity, product distribution data were obtained with varied amounts of catalyst and were extrapolated to equimolar amounts of catalyst and substrate to obtain the catalyzed O/C product ratios. Interpretation of the data also was complicated by independent evidence that catalysts 15 adsorbed 2-naphthoxide ion, in addition to that bound by ion exchange54). Essentially the same results were obtained with catalysts 24 which lack the ester link in the spacer chain 106). 

Influence of molecular spacers on ultrafast heterogeneous electron transfer... 

The distance dependence of electron transfer has been studied extensively for the homogeneous case. An approximately exponential decay of the electronic coupling has been found with the number of saturated bonds in the spacer unit (see for example [6,7]). The results presented here suggest that an exponential dependence fits also our data for heterogeneous electron transfer in ultra-high vacuum. A different result has been reported for electron transfer from Re complexes to anatase where a local triplet state can play a role [8]. 

The very heterogeneous chemical structure of the compounds with MDR reversal activity has prevented structure-activity studies, although most MDR-inhibiting molecules share a basic structural pattern comprising a cationic protonable site linked to an aromatic lipophilic part by a spacer of variable length [61]. Structure-activity relationship (SAR) studies yielded only qualitative indications [62-64] unless very homogeneous series of molecules are studied [65]. 

PET may take place between donor and acceptor molecules located in heterogeneous or solid environments (Fig. 3), or linked together by a flexible chain or rigid spacer group (Fig. 4). Appropriate examples of these systems and their theoretical and practical ramifications will be presented in this paper. 

Whiley, R.A., Duke, B., Hardie, J.M., Hall L.M. (1995). Heterogeneity among 16S-23S rRNA intergenic spacers of species within the Streptococcus milleri group. Microbiology, 141, 1461-1467. 

In the other models, the hydrophobic methyl groups of the polypeptide backbone are envisioned to play more major roles. Generally, methyl groups can assume the role of either spacer molecules, barrier molecules, or hydrophobic matrices for heterogeneous nucleation and propagation. 

Mixed ligand titanocenes may be supported using covalent spacers attached to a resin via a stable C-C bond (Scheme 446). The titanium content of this heterogenized system has been determined using inductively coupled plasma-atomic emission spectroscopy.1061... 

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