Homo-dimer

Irradiation of 5-acetyldibenz[i>,/]azepine (19) in the presence of. V-methylmaleimide results in a mixture of the homo dimer 20 and the mixed dimer 21. No [2 + 2] cycloadducts are obtained, however, with other alkenes such as styrene, acetylenedicarboxylic acid, dimethyl fumarate or acrylonitrile.32 Later studies have demonstrated that the dimerization occurs via the excited triplet state.196... 

The cAMP responsive element binding factor (CREB) is also activated by phosphorylation. Depending on the stimuli, CREB is the target of a cAMP dependent protein kinase or of kinases called MAPKs, RSK, and CamKIV. As in AP-1, CREB carries a basic leucine zipper motif (bZDP), which mediates homo dimerization of CREB when bound to the CRE. 

Scheme 18 Palladium-catalyzed homo-dimerization of 2(llf)-pyrazinones...

Fig. 1 A ribbon diagram of the crystal structure of a substrate complex of the homo-dimer HIV-1 protease (lkj7) (Prabu-Jeyabalan et al. 2002), Each monomer is shown in cyan and pink the substrate is shown in green, and the catalytic aspartic acids are highlighted in yellow...

CBCA 6.517 A 0.04 None None 71 Probably homo- dimeric CBGA and CBNRA [40]... 

Fig. 4. Possible homo-dimers of psPtDNA (A) antiparallel duplex, (B) parallel duplex, (C) quadruplex. Adapted from Ref. (28).

Mixed phosphole oxide dimers (98 and 99) were prepared by the possible combinations of two different phosphole oxides (96 and 84d), generated simultaneously in the same flask. In the reaction shown, homo dimers 97 and 85d were also formed (Scheme 25) [68],... 

Effect of Ag+ complexation on relative aromaticity in various rings was examined by NICS in two representative cases. Structures and energies of the acetyl pyrene-Ag -pyrene hetero-dimer and acetyl pyrene-Ag -acetyl pyrene homo-dimer complexes were determined with the same model. Interestingly, only sandwich complexes were formed and no stable structures in which the silver ion was not sandwiched between two PAH units could be found. 

Chapter 17, Fig. 7. Helical wheel and sequence representation of the parental homo-dimeric coiled coil. The substitution positions within the hydrophobic domain are highlighted with open squares and those in the charged domain with open circles. Their interaction partners are highlighted with shaded squares and circles, respectively. The arrows mark the ligation site of nucleophilic and electrophilic fragments. 

Crystals of stoichiometric 1 1 mixtures of compounds that can complex with each other have been shown to form preferentially to pure crystals of the individual components. In some cases these crystals may have potential non-linear optical properties. An interesting example is the 1 1 mixture of p-aminobenzoic acid and 3,5-dinitrobenzoic acid. (15) A view of the crystal structure is shown in figure 3. Examination of this figure leads one to the hypothesis that the preference for the mixed crystal may be due to a) a more stable H-bonding interaction between the different benzoic acids in the hetero-dimer than in the homo-dimer b) the ability of the mixed crystal (hetero- dimers) to H-bond between their amino and nitro groups. It is likely that both of these factors play a role in the stability of the crystal structure. Calculational modelling can aid in determining the importance of these factors. 

Fig. 2 Relative placement of HOMO and LUMO energy levels in a molecular dimer. The dashed lines indicate the energies for the homo-dimer. For the heterodimer, these levels are shifted up or down by e so that the band off-set is 2e. In the discussion, we assume that AEa = AEb. Shown also is the electron/hole configuration corresponding to state 3 = — .

When 2e < (U+J), the exciton state is lower in energy than the corresponding exciplex state. Also, we can see from this analysis how an exciplex state can acquire oscillator strength to the ground state through mixing with ipo- Taking e —> 0 as in the case of the homo-dimer,... 

Lecourt, T. Mallet, J.-M. Sinay, P. Efficient synthesis of doubly connected primary face-to-face cyclodextrin homo-dimers. Eur. J. Org. Chem. 2003, 4553-4560. 

Alcohols, ethers and certain amines also react and a broad series of compounds can be conveniently synthesized by the dimerization procedure. Typical examples are shown in Scheme 1, in which the new bond formed is marked in bold. For alcohols, ethers, and amines, highly selective attack at a C-H bond a to a heteroatom is observed. In cases where two different substances react, the two homo dimers and the hetero dimer are all formed. This can still be synthetically useful because the three compounds are often sufficiently different, either in polarity or volatility, to be readily separable by chromatography or fractional distillation. 

Homo dimers thus formed are assumed to catalyze their own enantiomeric type ... 

Diels-Alder homo-dimerizations of hydroxybutenyl and pentadienyl coumarins have been explored in the context of the plant-derived natural products phebalin, thamnosin, and toddasin <2000TL9909>. The Diels-Alder union of two identical coumarin units occurs under thermal, Lewis acid, or mineral acid conditions (e.g., 294 —> 295 Scheme 38). 

Fig. 26 A Chiral memory effect applied to the construction of a chiral softball homo-dimeric capsule made of achiral units. B Racemic softball binds a chiral guest leading preferentially to one diastereoisomer. Fast exchange, compared to capsule s racemization rate, with a better achiral guest allows preparation of enantioenriched capsule...

Fig. 10.45. The structures of Gilman cuprates in halide- or cyanide-containing solution apart from the (homo-)dimer and/or the monomer in Figure 10.44, the (hetero-)dimers A or C and/or the corresponding "monomers with complex cation" B or D presented here can occur (but no "cyanocuprates" in which the bonding partner of the copper is a CN group).

The reactivity of Me3Al can also be altered by coordination of solvent, and this treatment affects the addition mode of Me3Al to carbonyl, imino, or olefinic substrates. This can be most typically seen in the case of solvated Me3Al monomer giving axial alcohol predominantly, while the stereochemical reversal was observed in hydrocarbon solvents, in which the closed (homo)dimer (Me6Al2) predominates (Figures 35 and 36). 

Closed (homo)dimer Open (homo)dimer... 

The formation of 6a is particularly diagnostic, since this unique carbon-carbon bonded reductive dimer was demonstrated by Wrighton and coworkers to arise via the transient 19-electron radical ( -cyclohexa-dienyl)Fe(CO)3 by regiospecific coupling at a ligand center (105). Furthermore the 17-electron radical CpMo(CO)3- is the precursor to the accompanying oxidative dimer [CpMo(CO)3]2 (7), as described in the earlier anodic studies of CpMo(CO)3 (106). Accordingly these products (6 and 7) of ion-pair annihilation are referred to hereafter as radical (homo) dimers. 

RiSy consists of three identical subunits denoted They form a complex of pseudo-D3 symmetry with a total molecular mass of about 75 kDa. The a-subunit (23 kDa) shows an internal sequence similarity resulting in a 26% identity of the C-and N-terminus. The N-terminal domain can be expressed separately and forms a homo-dimer that binds the substrate with a similar affinity to the complete trimeric protein. " ... 

The homo-dimeric structure of the enzyme from A. nodosum consists of 1111 amino acids with a calculated... 

The X-ray structures of vanadium bromoperoxidases from the red seaweeds Corallina pilulifera and C. officinalis have also been determined and their structures are almost identical. The native structure of these enzymes is dodecameric and the structure is made up of 6 homo-dimers. The secondary stmcture of the chloroperoxidase from the ftmgus Curvularia inaequalis that will be discussed later can be superimposed with the Corallina hromoperoxidase dimer. Many of the a helices of each chloroperoxidase domain are structurally equivalent to the a helices in the Corallina hromoperoxidase dimer. This is in line with the evolutionary relationship between the haloperoxidases that will be discussed later. The disulfide bridges in the enzyme from A. nodosum are not found in the enzyme from Corallina and the two remaining cysteine residues are not involved in disulfide bonds. Additionally, in this enzyme binding sites are present for divalent cations that seem to be necessary to maintain the stmcture of the active site cleft. All the residues directly involved in the binding of vanadate are conserved in the algal bromoperoxidases. ... 

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