Terminal dimerizations

Recently, Freudenberg and co-workers (//) briefly reported the isolation of small amounts of dehydrodiconiferyl alcohol (XXVII) from the methanolysis of wood at room temperature. By this procedure, again, only benzyl aryl ether-linked terminal dimers can be obtained whereas acidolysis liberates (a- and) /3-ether-linked phenylcoumaran systems from the core of the lignin molecule as well. 

Mutations of the human APC gene are associated with both sporadic and familial forms of colon cancer. The APC protein is a large, multi-domain protein that has a 55-residue, N-terminal dimeric coiled coil (APC-55). Alber and colleagues used rules of thumb and those derived from an analysis of the covariation of a d and d d pairs in the cytokeratins (which form obligate heterodimers) to create a mutant of APC-55, anti-APCpl, as a potential probe for the APC protein (Sharma et al, 1998). 

Mad was recently shown to form a dimer stabilized by a C-terminal dimerization motif (residues 388-406) (Serpe et al., 1999). A deletion mutation in the dimerization element abolished Mac 1 function (Serpe et al., 1999). Cu inhibition of Mad may alter the dimeric state of Mad. However, this cannot entirely account for the Cu inhibition of Mad since Cu regulation of Mad occurs with a minimal Mad molecule lacking the C-terminal dimerization motif (Jensen and Winge, 1998). 

In many microorganism, multidomain FKBPs of the Mip-type have been detected, characterized by a homodimeric assembly of Mip monomers consisting of a N-terminal dimerization module, a long (65 A) connecting a-helix, and a C-terminal FKBP domain [108-110]. Mip proteins have been identified as virulence factors of many human pathogens including Legionella pneumophila, Neis-... 

Fig. 6. ATPase-coupled N-terminal dimerization in Hsp90. BindingofATPtoan Hsp90 dimer promotes association of the N-terminal nucleotide-binding domains into a tense state, which in turn promotes ATP hydrolysis. The ADP thus generated does not favor N-terminal association and allows relaxation into the relaxed state, completing the cycle (From Prodromou et al, 2000, with permission).

Fig. 3. The crystal structure of DsbC. DsbC forms a V-shaped homodimer. The monomer consists of a C-terminal thioredoxin domain and an N-terminal dimerization domain. The two domains are joined via a linker helix. The monomers interact via two consecutive /3-strands, which form two extended /3-sheets in the dimer.

Local vibration mode dichroism makes anisotropic (110) por-Si a unique object for the assignment of vibration bands to the corresponding surface modes of porous silicon. The simultaneous examination of deformation and stretching bands makes it possible to validate the existence of H-terminated dimers in por-Si and, moreover, to state the growth of dimers amount after thermal annealing. 

Quantitative comparison of the scissors and the stretching modes before and after TA (Fig. 4) allows us to conclude that thermovacuum annealing at 700 K leads to an increase in H-terminated dimer concentration indicating a restructurization of the (OOl)-oriented inner surfaces. 

The birefringence as well as the ffee-carrier dichroism exhibited by por-Si in IR spectral region originates from the anisotropy of nanocrystals and voids comprising the material. The local surface mode dichroism is highly sensitive to the microrelief of the nanocrystal surface. The surface reconstruction of por-Si upon selective thermodesorption of hydrogen is demonstrated. This process results in a considerable increase in the concentration of surface H-terminated dimers. 

In other studies of polyester-polyurethanes, it has been shown that the dry spun fibers of these compositions show hydrolysis resistance and good strength [53]. Urethane rubbers have been formulated from hydroxyl-terminated dimer acid polyester. These saturated urethane elastomers show good resistance to hydrolysis [54]. 

RhB-COOH, TPP(C0CI)4 and ZnTPP(COOH)4 Benzene derivatives benzoic, phthalic or salicylic acid Carboxylate-terminated dimeric viologen Mc2 merocyanine acid... 

E.L. Knuth Dimer-formation rate coefficients from measurements of terminal dimer concentrations in free-jet expansions. J. Chem. Phys. 66, 3515 (1977)... 

Kurokawa, R, Yu, V C., Naar, A., Kyakumoto, S., Han, Z, Silverman, S, Rosenfeld, M G, and Glass, C. K (1993) Differential orientations of the DNA-binding domain and carboxy-terminal dimerization interface regulate binding site selection by nuclear receptor heterodimers Genes Dev 7,1423-1435... 

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