Hydrogen bond n

Figure 10. Hydrogen bonding scheme between 7,9-dimethylguanine (7,9-dmgua) and 1-methycytosine (mcyt) in fra/is-[Pt(MeNH2)2(7,9-dmgua-N1)2(CI04)2-2mcyt with two hydrogen bonds, N(2)-N(3a ) 2.881 (8) A and N(3)—N(4a ) 3.194(8) A. (Reproduced with permission from ref. 48).

EL pyridine-phenylene copolymers 564 [666] and 565 [667] have been synthesized and studied by Bryce and coworkers. Although a rather low el(<0.1%) was reported for the devices, an interesting phenomenon was found for polymers 565. When the PLED (ITO/PEDOT/565/Ca/Al) was fabricated using acidic solutions, a strong red shift in the EL band compared to that obtained with the neutral solution (from 510 to 575 nm) was observed. The authors explained this concept by planarization of the protonated polymer chain as a result of intramolecular hydrogen bonding N H- O. Variation of pyridine linkage in copolymers 565, 566, and 567 affects the PL and EL emissions (AEL = 444, 432,... 

The biological interest of hydrogen bonding in aqueous solutions is well known pro-tonated amines and phenolate ions in water are associated by hydrogen bonds. The association constant (K = 0.81 mol 1 dm3, measured in buffered aqueous solution) for the complex of the dication of ethylenediamine with the phenolate ion agrees with a weak hydrogen bonding N—H- O68. 

The internal hydrogen bond (N—H—N) is responsible for suppression of cis-trans isomerization in the singlet excited state of cA-l-(2-indolyl)-2-(2-pyridyl)ethene (32) of reaction 13. Clearly, the reverse isomerization is possible125. On the contrary, irradiation of c -l-(2-pyrrolyl)-2-(2-quinolyl)ethene126 (35) induces the isomerization to 34. The isomerization (cis-trans) is possible because the excitation allows the tautomerization of 35 to 36 (equation 14). 

Noncovalent interactions such as van der Waals, hydrogen bonding, n-n stacking and electrostatic interactions have been widely used to hybridize pristine nanocarbons via ex situ approaches. The major advantage of this route is that the nanocarbons do not require modification prior to hybridization and their structure remains undisturbed, an important factor in many electronic applications. The strength of hybridization is weaker compared to covalent interactions but the synthetic process is generally simpler. Noncovalent attachment of small molecules to nanocarbons is often used to change the surface chemistry for subsequent ex situ or in situ hybridization. 

The change from CDCI3 to C5D5N and further to ( 03)280 as solvent stabilizes the hydrazone 75A, and especially the enhydrazine 75A, because these tautomers have a greater tendency to form intermolecular hydrogen-bonds (N—H solvent) than does the pyrazoline tautomer 75B, where the OH group (O —H solvent) is shielded by the sterically demanding substituent R = f-Bu. 

Privileged Hydrogen-Bonding N,N -bis-[3,5-(Trifluoromethyl)phenyl]thiourea... 

Finally, bidentate bis(guanidinium) hosts like 26 reported by Anslyn et al. have recently been shown to bind phenyl phosphate anions in a bis(bidentate) fashion. Hydrogen-bonding N(H) -0 distances are in the range 2.658(7)-2.868(6) A, while solution studies in 15% HjO/DMSO give binding constants of ca. 500 M" with dibenzyl phosphate. ... 

The detection of l4N nuclei from the surrounding amino acids using ESEEM techniques has been discussed by Weber45. These results show that the quinones are coupled to amino acids via hydrogen bond (N-H donors). 

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