Browning hydrogen bonds

Cruzan J D, Braly L B, Liu K, Brown M G, Loeser J G and Saykally R J 1996 Quantifying hydrogen bond oooperatively in water VRT speotrosoopy of the water tetramer Science 271 59-62... 

Figure 4.18 Side chains of the tyrosyl-tRNA synthetase that form hydrogen bonds to tyrosyl adenylate. Green residues are from p strand 2 and the following loop regions, yellow residues are from the loop after P strand S, and brown residues are from the a helix before P strand S. (Adapted from T. Wells and A. Fersht, Nature 316 656-657, 1985.)...

Figure 13.14 (a) Schematic diagram of the main chain and four almost invariant residues of the fourth WD repeat of Gp from transducin. The view is roughly perpendicular to the central tunnel and the plane of the sheet. The red stripes denote hydrogen bonds, (b) Schematic view of two WD repeats illustrating the structural relationships between two consecutive repeats. The first repeat is brown and the second repeat is orange. The positions of the four almost invariant residues in the first repeat are circled. (Adapted from J. Sondek et al., Nature 379 369-374, 1996.)... 

Scatena, L. F., Brown, M. G. and Richmond, G. L. (2001) Water at hydrophobic surfaces weak hydrogen bonding and strong orientation effects. Science, 292, 908-912. 

C. I. Pigment Red 183 (214), which range in shades from yellow to bluish-red and brown and exhibit excellent fastness properties. Their good stability to light and heat and their insolubility is attributed to extensive intermolecular association as a result of hydrogen bonding and dipolar forces in the crystal structure, as illustrated in Figure 9.3. 

The timescale of a microwave observation is ca 10 12s so that an average of the properties of the species in equilibrium (35) is obtained if the equilibrium occurs in a time shorter than this. The X-ray photoelectron spectra of intramolecularly hydrogen-bonded species in the gas phase have been studied in an attempt to obtain an instantaneous picture of the structure of these molecules. In this technique the ionisation of core electrons which occurs within 10 16s is observed. For malondialdehyde, 6-hydroxy-2-formyl-fulvene, 2-hydroxy-1,1,1,5,5,5-hexafluoropent-2-ene-4-one, 9-hydroxyphen-alenone [19], and tropolone [20], two peaks are observed in the Ou region of the photoelectron spectrum (Brown et al., 1979). If these molecules existed in the C2v form with a symmetrical hydrogen bond and equivalent oxygen... 

Hydroboration, the addition of a boron-hydrogen bond across an unsaturated moiety, was first discovered by H. C. Brown in 1956. Usually, the reaction does not require a catalyst, and the borane reagent, most commonly diborane (B2H6) or a borane adduct (BH3-THF), reacts rapidly at room temperature to afford, after oxidation, the /AMarkovnikov alkene hydration product. However, when the boron of the hydroborating agent is bonded to heteroatoms which lower the electron deficiency, as is the case in catecholborane (1,3,2-benzodioxaborole) 1 (Scheme 1), elevated temperatures are needed for hydroboration to occur.4 5... 

Nitro dyes exhibit benzenoid-quinonoid tautomerism (1.25) and their colour is attributed mainly to the o-quinonoid form, since this can be stabilised by hydrogen bonding. The tautomeric o-nitrosonaphthols (1.26) readily form chelate complexes with metals. A few yellow nitro disperse dyes, including Cl Disperse Yellow 1 (1.25), and brown acid dyes remain of significance. The remaining nitro and nitroso colorants, such as (1.26) and its 1 3 iron (II) complex (1.27), are no longer of commercial interest. 

In 1959, Eberson (1959, 1992) found that a family of derivatives of succinic acid shows a remarkably large negative cooperativity, i.e., gjj < < 1, which is difficult to explain on the basis of electrostatic theories only. We shall discuss these compounds in Subsection 4.8.6. At present, there is no satisfactory molecular interpretation of these findings. One of the more popular ideas, originally suggested by Jones and Soper (1936) and further elaborated upon by McDaniel and Brown (1953), is that an intramolecular hydrogen bond would facilitate the first dissociation of the proton, i.e., Kj becomes smaller (or Kj becomes larger). Also, the second proton will dissociate with more difficulty. The net effect would be a... 

Breakdown of hydrogen bondings at 75°C and above has been proposed to explain the absence of nucleation observed by Misra and White, and Brown. This study has found that the conditions were unfavourable for nucleation at these high... 

Zeng HQ, Yang XW, Brown AL, Martinovic S, Smith RD, Gong B. An extremely stable, self-complementary hydrogen-bonded duplex. Chem Commun 2003 1556-1557. 

Fig. 1. —The Crystal Structure of a-D-Glucopyranose, Viewed Along the [001] Axis. (There are two hydrogen bonds at each 0-4, but one has been omitted for clarity. Diagram kindly provided by Dr. George M. Brown, Oak Ridge National Laboratory, Oak Ridge, Tennessee.)...

Brown, I. D. (1976 ). Hydrogen bonding in perchloric acid hydrates. Acta Cryst. A32, 786-92. 

Brown, I. D. (1995). Anion-anion repulsion, coordination numbers and the asymmetry of the hydrogen bond. Can. J. Phys. 73, 616-il. 

Brown, McDaniel, and Hafliger (9) pointed out that if there are two acidic groups close to each other in a molecule, the mutual electrostatic influence can substantially increase the pK difference between the two groups. This pK difference would be especially large if a hydrogen bond could form between the two acidic groups, as shown in Figure 3. 

The possibility of formation of an O—O bond at a single Mn site of the OEC, on the other hand, seems remote, but nevertheless, two mononuclear model Mn-peroxo complexes, a peroxo-Mnm porphinato 64 [157] and a peroxo-Mn111 pyrazolylborato complex 65 [158], have been structurally characterized. Both complexes contain side-on peroxo groups. Complex 65 has been crystallized in two forms, one brown and one blue. A peroxo-H—N (pyrazole) hydrogen bond is found only in the blue form (Figure 29). 

Compound 18 showed a remarkable color change from orange to brown (Amax=670 nm) in DMSO upon adding F". Color changes are most probably due to a charge-transfer process and electron-rich formation of hydrogen bonds between thiourea-bound F and the electron-deficient anthraquinone moiety. The anion was believed to form a 2 1 anion-to-ligand ratio as shown in Fig. 4. 

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