Hydrogen bond pyridyl

Molecular arrangements in the as-prepared dimer and 2 OPr-a-dimer-PrOH crystals are shown schematically in Figs 16(a) and (b), respectively. In the complex, propanol molecules are hydrogen-bonded to the pyridyl groups and, as expected from its high photoreactivity, the... 

In an effort to apply the cooperative principles of metalloenzyme reactivity, involving a combination of metal-ligand and hydrogen bonding, we have reported a ruthenium catalyst incorporating imidazolyl phosphine ligands that efficiently and selectively hydrates terminal alkynes (5). We subsequently found that application of pyridyl phosphines to the reaction resulted in a >10-fold rate enhancement and complete anti-Markovnikov selectivity, even in the... 

Yu WS, Cheng CC, Cheng YM et al (2003) Excited-state intramolecular proton transfer in five-membered hydrogen-bonding systems 2-pyridyl pyrazoles. J Am Chem Soc 125 10800-10801... 

The same effect is observed for the substituted pyridyl-pyrazole and -imidazole systems. While 2-(pyrazol-l-yl)pyridine 24 gives a low spin iron(II) complex a continuous spin transition is observed centred just above room temperature in solid salts of [Fe (31)3]2+ and just below in solution [39]. Spin crossover occurs in the [Fe N6]2+ derivative of 2-(pyridin-2-yl)benzimidazole 32 (Dq(Ni2+)=1050 cm"1) but not in that of the 6-methyl-pyridyl system 33 (Dq(Ni2+)=1000 cm"1). Although the transition in salts of [Fe 323]2+ is strongly influenced by the nature of the anion and the extent of hydration, suggesting an influence of hydrogen-bonding, in all instances it is continuous [40]. 

The structural characterization of this assembly has revealed that chloride coordination (via hydrogen bonding to the protonated pyridyl groups of the strands) induce the strands to adopt a double-helical structure in the solid state. 

When the co-crystallised samples were irradiated with UV light for several hours, the stereospecific (100%) formation of rcff-tetrakis(4-pyridyl)cyclobutane (99) was observed. This was confirmed by spectroscopic, analytical and structural methods. The latter showed that, once irradiated, the new co-crystallized materials (99) 2(97) and (99)-2(98) are formed respectively. In both these structures the molecular components are held together by hydrogen bonding interactions. 

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). 

The first example of a counterthermodynamic one-way E - Z photoisomerization based upon intramolecular hydrogen bonding was reported for the 7V-methyl-3-(2-pyridyl)-propenamide systems. 

As seen, the shift of the pyridyl nitrogen atom from para (PATS-4) to ortho (PATS-3), to meta position (PATS-2), making more and more difficult the hydrogen bond formation with the -NH residues of the protein, progressively worsens the voltammetric response. 

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