Structures of the dimers

Figure 10.25 Structure of the dimerization region of MyoD. The a helices HI (red and brown) and H2 (light and dark green) of the two monomers form a four-helix bundle that keeps the dimer together. The loops (yellow and orange) are on the outside of the four-helix bundle. (Adapted from P.C.M. Ma et al.. Cell 77 4S1-4S9, 1994.)...

The structure of the dimer can be derived simply by evaluation of the cross signals in the HH COSY plot. The cycloalkene protons form two AB systems with such small shift differences that the cross signals lie within the contours of the diagonal signals. 

Figure 7.22 (a) Structure of the dimeric unit in the solvated complex [Ga(/) -C6H6)2][GaCl4].3QH6 indicating the... 

Figure 1.75 The structure of the dimeric nitrido complex [Ru2NC18(H20)2]3. ...

Figure 2.39 The lantern structure of the dimeric rhodium antipyrine complex Rh2(ap)4Cl. (Reprinted with permission from Inorg. Chem., 1988, 27, 3783. Copyright (1988) American...

Figure 3.21 Structure of the dimeric palladium(I) complex [(dppp)Pd]2(CF3 S03)2. (Reprinted with permission from Organometallics, 1992, 11, 23. Copyright (1992) American Chemical Society.)...

Figure 6 Molecular structure of the dimeric [K(FPhF)]2 units.

Fig. 3.10 Recognition of the DNA minor groove with benzimidazole derivatives, (a) Structure of the dimeric core for Py-benzimi-dazole (Bi), Py-hydroxybenzimidazole (Hz) and Py-imidazopyridine (Ip) (left) in comparison with the five-membered ring system (right). H-bonding surfaces along the recogni-...

Polyphosphonic acids are conveniently esterified by treatment with orthoformate esters with distillation of the lower-boiling alcohol. This procedure worked well for the acid (74), which readily dimerizes, and was also used to establish the structure of the dimer (75). ... 

Another illustration of the structural changes that may result as a consequence of alkyl substitution at the 3-position of the pyrazolyl group is provided by the structures of the dimeric copper(I) complexes [Tp]Cu 2 (36), [TpMe2]Cu 2 (36), [TpPh2]Cu 2 (37), and [TpBut]Cu 2 (37), which differ in the manner in which the tris(pyrazo-lyDhydroborato ligand bridges the two copper centers (Fig. 16). 

The aniline-zinc porphyrin interaction has also been exploited to form dimers. Hunter (60) reported the dimerization of porphyrins functionalized at one meso position with ortho or meta aniline groups (47, 48, Fig. 15). Both compounds showed concentration-dependent H NMR spectra with large upfield shifts for the aniline protons. The dimerization constants are 160 and 1080 M-1 respectively for 47 and 48, and these values are an order of magnitude higher than the association constants of simple reference complexes (K — 10 and 130 M 1 respectively), which is indicative of cooperative self-assembly. The complexa-tion-induced changes in chemical shift were used to obtain three-dimensional structures of the dimers. 

Reductive activation of the quinone shown in Scheme 7.9 and incubation in methanol afforded a complex mixture of products consisting mainly of head-to-tail coupling at C-5 or C-7 (Scheme 7.10). Minor reactions involve transfer of H2 from the hydroquinone to the ene-imine (internal redox reaction) and methanol trapping. The structures of the dimers and trimers in Scheme 7.10 were derived from H-NMR,... 

FIGURE 4.7 Structure of the dimeric complex between FGF2 and FGF receptor 1. The Ig-like domains 2 and 3 of the two FGF receptor 1 molecules are composed of parallel p sheets and they are shown in medium and light gray, respectively. The two FGF2 molecules are composed of a bundle of p sheets that are shown in dark gray. PDB id 1CVS. (Plotnikov, A. N. et al., Cell, 98, 641, 1999.)... 

The characterization and crystal structure of the dimer [Pt2( -dppm)3] (dppm = bis(diphenyl-phosphino)methane), first reported as a deep red complex in 1978, was described by Manojlovic-Muir et al. in 1986.11 The structure, the first of its type, is made up of two parallel and almost eclipsed trigonal-planar platinum moieties bridged by three diphosphine ligands. The Pf Pt separation is 3.0225(3) A, too long to be considered a bond.11 [Pt2(//-dppm)3] catalyzes the hydrogenation/reduction of carbon dioxide with dimethylamine to give dimethylformamide12 (Equation (1)) and the reverse reaction.13... 

The structure of the dimers from mero-substituted derivatives was initially determined by comparison of the observed and calculated dipole moments. For a head-to-tail dimer the dipole moments resulting from the 9 and 9 substituents should cancel each other and the resultant dipole moment should be essentially zero. For a head-to-head arrangement the dipoles would be in the same direction and the resultant should be considerably greater than zero. The dimers produced upon irradiation of 9-chloro and 9-bromoanthracene solutions were observed to be 0.36 and 0.60 D, respectively. Since these values are much less than expected for a head-to-head arrangement for these derivatives (3.8 D), it was concluded that both of these dimers were formed in a head-to-tail configuration/30 ... 

Figure 2.8 The structure of the dimeric cytochrome bcomplex of the respiratory chain, (a) The cave for chemistry constituted by the hollow between the two monomers (the essential dimer ) in a cartoon representation. Reprinted with permission from Smith, 1998. Copyright (1998), American Association for the Advancement of Science, (b) The structure viewed perpendicular to the twofold axis and parallel to the membrane. All of the eleven subunits are completely traced and their sequences assigned. The top of the molecule extends 3.8 nm into the intermembrane space, the middle spans the membrane (4.2 nm), and the bottom extends some 7.5 nm into the matrix. Reprinted with permission from Iwata et al., 1998. Copyright (1998) American Association for the Advancement of Science.

Scheme 3 shows the details of the synthetic strategy adopted for the preparation of heteroleptic cis- and trans-complexes. Reaction of dichloro(p-cymene)ruthenium(II) dimer in ethanol solution at reflux temperature with 4,4,-dicarboxy-2.2 -bipyridine (L) resulted the pure mononuclear complex [Ru(cymene)ClL]Cl. In this step, the coordination of substituted bipyridine ligand to the ruthenium center takes place with cleavage of the doubly chloride-bridged structure of the dimeric starting material. The presence of three pyridine proton environments in the NMR spectrum is consistent with the symmetry seen in the solid-state crystal structure (Figure 24). 

Figure 12 The structure of the dimeric complex [MgBr(C6H3-Mes-2,6)(THF)]2 26.

Figure 33 The structure of the dimeric monocyclopentadienyl [CpMg(MeNCH2CH2NMe2)]2 62.

Figure 38 The structure of the dimeric solvated complex [( 5-Cp)Mg(/i2-SBut)(THF)]2 72.

Figure 59 The structure of the dimeric arsolide complex (rj5-AsC4(2,5-SiMe3)2(3,4-Me)2)Ca(/i-CI)(THF)2 2 114.

Figure 100 The structure of the dimeric complex Ba[(3,5-dimethylpyrazol-1-yl)3Ge]2(dioxane)o.5 186.

In the paper published in 1900, he reported that hexaphenylethane (2) existed in an equilibrium mixture with 1. In 1968, the structure of the dimer of 1 was corrected to be l-diphenylmethylene-4-triphenylmethyl-2,5-cyclohexadiene 3, not 2 [38]. Since Gomberg s discovery, a number of stable radicals have been synthesized and characterized, e.g., triarylmethyls, phenoxyls, diphenylpicryl-hydrazyl and its analogs, and nitroxides [39-43]. The radical 1 is stable, if oxygen, iodine, and other materials which react easily with it are absent. Such stable radicals scarcely initiate vinyl polymerization, but they easily combine with reactive (short-lived) propagating radicals to form non-paramagnetic compounds. Thus, these stable radicals have been used as radical scavengers or polymerization inhibitors in radical polymerization. 

Yoshino reports a novel and general method for the C-3 acylation of indoles with acyl chlorides in the presence of dialkylaluminium chloride which obviates the need for prior N-protection . Interestingly, as described in this preliminary communication, the unprotected indoles 147 are first treated with the Lewis acids prior to addition of the acid chlorides, yielding the desired 3-acyl derivatives 148. In reactions more typical of indoles under acidic conditions, Nakatsuka determined the structures of the dimers and trimers of 1-trimethylacetylindole produced in the presence of aluminium chloride . 

A new class of secondary metabolites tyrolobibenzyls A 36 and B 37 were isolated from Scorzonera humilis (Asteraceae) of Tyrolean origin. Compounds 36 and 37 were shown to possess a unique phenylethylbenzofuran skeleton <00HCA292O>. The structure of the dimeric coumarin 38 was confirmed by an X-ray diffraction study, as well as by a photochemical synthesis from its co-occurring monomer bergapten <00H(53)441>. 

Fig. 20. (a) Structure of the dimeric subunits in [K C(SiMe3)2(C6H4-2-CH2NMe2)2 L (53) (b) sheet arrangement of the subunits in 53. Reproduced with permission from W. Clegg et al., Organometallics 1999,18, 2939. Copyright 1999, the American Chemical Society. 

The geometries of the open (HF) clusters in Figs. 5.23(a)-(c) were chosen to mimic (and extend) the bent structure of the dimer in the manner that might be expected from a simple dipole-dipole picture. In these species the angle was constrained to be the same for each monomer, thus creating a zig-zag onedimensional chain of an extended herringbone pattern (but with 0hf - f and all other... 

Fig. 3 Magnetic properties and molecular structure of the dimeric species [Fe(H2 0)4]2(bpym) (S04)2 (adapted from [3])... 

Figure 15. X-ray crystal structure of the dimer of 201. [Adapted from (133).]...

Chang, C., Mooser, A., Pliickthun, A. and Wlodawer, A. (2001). Crystal structure of the dimeric C-terminal domain of TonB reveals a novel fold, J. Biol. Chem., 276, 27 535-27 540. 

Fig. 4. Suggested structure of the dimer of SeF4 S03. From Gillespie and Whitla (81).

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