Ab-initio calculations on the retinal Schiff base – formic acid and allylimine – formic acid hydrogen bonds

Abstract

M~LAN HODOSCEK and DUSAN HADZI. Can. J. Chem. 63, 1528 (1985). The proton potential functions of Schiff base -formic acid complexes were calculated in the ab-initio scheme with STO-3G and 4-31G basis sets without and with the inclusion of a perturbing charge. The comparison of the curves with the retinal Schiff base and allylimine obtained by using the short base encouraged further calculations with the longer base on the truncated system only. The curve obtained with the 4-31G set on the allylimine -formic acid complex is of a double minimum type with the deeper well still at the formyl oxygen. Inclusion of a perturbing negative charge near the hydrogen bond reverses the depth of the wells making the N-protonated form more stable.MILAN HODOS~EK et DUSAN HADZI. Can. J. Chem. 63, 1528 (1985). Faisant appel i des schemas ab-itzitio et utilisant des bases STO-3G et 4-31G avec ou sans I'inclusion d'une charge perturbante, on a calcul6 les fonctions de potentiel des protons de complexes entre I'acide formique et des bases de Schiff.Une comparaison des courbes relatives a la base de Schiff du retinal et de I'allylamine, obtenues a I'aide de la base la plus courte, nous a encourage i proceder des calculs plus approfondis que nous avons effectues uniquement sur le systeme tronque en utilisant un base de calcul elargie. La courbe que nous avons obtenue pour le complexe de l'acide formique et de l'allylimine, en utilisant une base de calcul 4-31G, comporte un double minimum et le puit le plus profond est encore fix6 a l'oxygene. L'inclusion, pres de la liaison hydrogene, d'une charge perturbantc negative renverse la profondeur des puits et rend ainsi la forme N-protonke plus stable.[Traduit par le journal] Introduction In the series of hydrogen bonds involved in the light transduction mechanisms of both rhodopsin and bacteriorhodopsin (1, 2), the bond between the retinal Schiff base nitrogen (N,,) and a proton offering group in the opsin deserves particular attention. In explaining the bathochochromic shift that occurs upon bonding of retinal to the apoprotein it was necessary to invoke both a positive charge on N16 of the retinal Schiff base and a negative charge in the vicinity of C14 of retinal (refs. 3, 4 and references therein). Although the electronic absorption of the retinylic chromophore in the ground state could be explained equally well by assuming covalent N' -H bonding or by a strong hydrogen bond between Ni6 and a proton donor belonging to the apoprotein (5), it was the interpretation of the resonance Raman spectra of rhodopsin that led to the prevalent opinion in favour of protonated N16 (6, 7). However, the I3C nmr spectra of rhodopsin appeared to oppose this view (8) and also the results of differential kinetic infrared spectroscopy were interpreted in terms of the initially unprotonated N16 (9). Sandorfy and co-workers have elaborated a scheme (10-15) reconciling both extreme views, i.e. the protonated and unprotonated Schiff base. The essence of this scheme is a strong hydrogen bond with a double minim...

FT-infrared study of the interaction between all-trans retinylidene isopropylamine and model proton donors

“…Both extreme views can be reconciled by admitting a strong hydrogen bond with a double minimum potential function (9)(10)(11)(12)(13)(14)(15). This is in agreement with ab initio calculations (16,17) on retinal chromophore modelling systems such as the alkylimine -formic acid system. It is thus essential to know the shape of the potential function governing the proton motion.…”

Proton Transfer in Bacteriorhodopsin: Structure, Excitation, IR Spectra, and Potential Energy Surface Analyses by an ab Initio QM/MM Method

“…The importance of this protein environmental effect was demonstrated by Hadži et al . , by using a theoretical model using an external point charge and dielectric continuum picture, which is, however, not a strict microscopic model. In the present study, we attempt to construct a microscopic molecular model of the proton transfer in bR by using the QM/MM method.…”

An infrared study of the interaction between ethyl N-(diphenylmethylene)glycinate with proton donors: comparison with N-benzylidenemethylamine

“…These studies have been done using conventional infrared or Raman spectroscopies (1-5), resonance Raman spectroscopy (6-lo), flash induced differential, kinetic infrared spectroscopy (I 1, 12), 13C (1 3, 14) and nmr spectroscopy (15), or both nmr and uv spectroscopy (16)(17)(18). Recently, the possibility of a double well potential in the proton bridge of visual pigments interacting with proton donors has been discussed (19,20). In most of these studies, proton donors such as halogenated alcohols, carboxylic acids, or hydrochloric acid have been studied and it was found that the strength of the interaction and the shape of the proton potential depended on their intrinsic acidity.…”