Calculation of normal vibrations and intra- and intermolecular force constants in crystalline imidazole

Abstract

Couplings between molecular and crystal vibrational modes in imidazole have been investigated and the influence of the hydrogen bond on these modes has been studied. In normal-mode calculations a program has been used which allows all possible couplings between vibrations of the molecules and those of the crystal lattice. In this way molecular modes coupled to lattice vibrations and lattice modes describing predominantly hydrogen-bond vibrations have been isolated.The pOSitions of protons are then given by D, R, and <J>. D is the distance of the H atom in the Xo direction,

Chemical complementation identifies a proton acceptor for redox-active tyrosine D in photosystem II

“…In the N-H stretching region, the lines assignable to reconstituted imidazole and to native histidine are similar in frequency. The observed infrared spectral changes are consistent with protonation of imidazole and histidine in imidazole-rescued HL189D2 and in wild-type PSII, respectively (44)(45)(46). Modeling leads to the expectation that a conserved surface-accessible pocket is located near tyrosine D. This result predicts that imidazole will have access to tyrosine D in HL189D2.…”

“…The conclusion that imidazole is reversibly protonated in PSII is based on comparison with previous investigations, which have reported vibrational modes of the protonated and unprotonated species (44)(45)(46)(51)(52)(53)(54). This work and our own data on the protonation of imidazole in vitro (data not shown) predict that the protonation spectrum will exhibit vibrational modes in the 3,400-3,100 cm regions.…”

“…The variation observed in the ring stretching and N-H bending modes in the 1,800-1,350 cm Ϫ1 region (44)(45)(46)(51)(52)(53)(54) may be caused by environmental heterogeneity affecting the spectrum of imidazole, which is not rigidly bound. The N-H stretching modes in the 3,350-3,250 cm Ϫ1 spectral region of both imidazole and histidine are substantially broader than the lines in the 1,800-1,350 cm Ϫ1 region, and, thus, these vibrational modes may be less sensitive to these effects.…”

“…For imidazole in vitro, vibrational lines between 3,300 and 3,100 cm Ϫ1 are assigned to the N-H stretching mode of molecules that are hydrogen-bonded (44,45,51). For example, hydrogen bonding of imidazole to dioxane gives a N-H stretching mode at 3,305 cm Ϫ1 (45).…”

Oxidation effect on double H-bonded imidazole–adenine–imidazole trimer

“…The unique ring structure of ImH permits one proton to be picked up by the bare N atom and the other one to be released from the other N atom. This action has been employed to explain the proton conductivity properties [10,11] of ImH in the solid state and also in the actual biological surrounding where a long H-bonded chain is present, many investigations have been carried out in both experimental [12][13][14][15] and theoretical [16][17][18][19][20][21][22] fields in recent years. The ImH-(HImH) ?…”