Hydrogen bonds detection

Especially, the subdivision in different hydrogen bond acceptor atom sets improves the performance of the SEN approach while a subdivision depending on the hydrogen bond donor atom showed only a minor improvement compared to the general fit of Reiher et al. Thus, the SEN approach has proven as a tool to investigate hydrogen bonds of, e.g., transition metal compounds (171,174-177), peptides (178), enzymes (179), DNA and RNA (173), molecular switches (180), ionic liquids (181,182), and rotaxanes (183). However, the SEN approach is not solely restricted to hydrogen bond detection. This approach can also be apphed to determine the covalent interaction between metal atoms (184) or phosphorus atoms (162,185). Therefore, it is suitable for different kind of interactions. 

Although the secrets of maximal rates of proton conduction are well illustrated in gA, multifunctional proteins that couple H+ conduction to other events do not exhibit well-formed, proton-conducting hydrogen bond networks. Indeed, in the bacterial reaction center the putative active path is poorly connected by hydrogen bonds detectable in the best current X-ray structures (2.2 A resolution Stowell et al., 1997). Paddock et al. (1999) have shown that chemical blockage or a simple mutational lesion of this active path diminishes proton transfer rates by at least 1000-fold. Thus, the several well-connected (but not quite continuous) files of water that are seen in the X-ray structures, reaching toward the Qg site from the cytoplasmic side, do not conduct protons at significant rates. 

Assadi-Porter FM, Abildgaard F, Blad H, Markley JL (2003) Correlation of the sweetness of variants of the protein brazzein with patterns of hydrogen bonds detected by NMR spectroscopy. J Biol Chem 278 31331-31339... 

A new development is the discovery of hydrogen-bonds in phenylsilanols, based upon Si-OH- aryl (described as ti HO) interactions. Thus, in (Me3Si)CSiPh(X)-OH, where X = I or OMe, the OH function of the silanol interacts with the aryl group of a neighboring molecule, leading to dimer formation [45]. In the compound with X = OH this n - HO interaction is additional to the normal hydrogen-bond detected earlier. 

A microwave pulse from a tunable oscillator is injected into the cavity by an anteima, and creates a coherent superposition of rotational states. In the absence of collisions, this superposition emits a free-mduction decay signal, which is detected with an anteima-coupled microwave mixer similar to those used in molecular astrophysics. The data are collected in the time domain and Fourier transfomied to yield the spectrum whose bandwidth is detemimed by the quality factor of the cavity. Hence, such instruments are called Fourier transfomi microwave (FTMW) spectrometers (or Flygare-Balle spectrometers, after the inventors). FTMW instruments are extraordinarily sensitive, and can be used to examine a wide range of stable molecules as well as highly transient or reactive species such as hydrogen-bonded or refractory clusters [29, 30]. 

Unexpectedly strong intermolecular hydrogen bonding has been reported by IR spectroscopic studies for tetrahydro-4,7-phenanthroline-l,10-dione-3,8-dicarboxylic acids, which exist in the oxo-hydroxy form 165 in both solid state and in solution [78JCS(CC)369].Tlie conclusion was based on comparison of B-, C-, and D-type bands for 165 and their dimethyl esters (detection of hydrogen bonding) and on analysis of IR spectra in the 6 /xm region (pyridine- and pyridone-like bands). 

After 19 hours, no reaction between the zinc chelate 2 and benzaldehyde can be detected at 20 °C. However, 10 mol % of the zinc chelate effectively catalyzes theenantioselective addition of diethylzinc to aromatic aldehydes. The predominant formation of the S-configurated products, effected by this conformationally unambiguous catalyst, can be explained by a six-mem-bered cyclic transition state assembly17. The fact that the zinc chelate formed from ligand M is an equally effective catalyst clearly demonstrates that activation of the aldehyde moiety does not occur as a consequence of hydrogen bond formation between the ammonium proton of the pyrrolidine unit and the aldehydic oxygen. 

Water was also investigated as a proton donor for the hydrogen bond with DMSO and other Lewis bases at infinite dilution detected by means of 1H NMR54-69. A comparison of the hydrogen bonding ability of DMSO in various other aprotic solvents was presented by Delpuech70 who measured the H-NMR chemical shift of CHC13. 

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