Factors affecting the C=N stretching in protonated retinal Schiff base: a model study for bacteriorhodopsin and visual pigments

Journal Article · Tue Jun 02 00:00:00 EDT 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00385a041· OSTI ID:6212873

Baasov, T; Friedman, N; Sheves, M

Factors affecting the C=N stretching frequency of protonated retinal Schiff base (RSBH/sup +/) were studied with a series of synthetic chromophores and measured under different conditions. Interaction of RSBH/sup +/ with nonconjugated positive charges in the vicinity of the ring moiety or a planar polyene conformation (in contrast to the twisted retinal conformation in solution) shifted the absorption maxima but did not affect the C=N stretching frequency. The latter, however, was affected by environmental perturbations in the vicinity of the Schiff base linkage. Diminished ion pairing achieved either by substituting a more bulky counteranion or by designing models with a homoconjugation effect lowered the C=N stretch energy. Decreasing solvation of the positively charged nitrogen leads to a similar trend. These effects in the vicinity of the Schiff base linkage also perturb the deuterium isotope effect observed upon deuteriation of the Schiff base. The results are interpreted by considering the mixing of the C=N stretching and C=N-H bending vibration. The C=N mode is shifted due to electrostatic interaction with nonconjugated positive charges in the vicinity of the Schiff base linkage, an interaction that does not influence the isotope effect. Weak hydrogen bonding between the Schiff base linkage in bacteriorhodopsin (bR) and its counteranion or, alternatively, poor solvation of the positively charged Schiff base nitrogen can account for the C=N stretching frequency of 1640 cm/sup -1/ and the deuterium isotope effect of 17 cm/sup -1/ observed in this pigment. Conversion of bR to the photochemically induced intermediate K/sub 610/ involves environmental perturbation in the vicinity of the C=N linkage, lowering the C=N stretch energy.

• Research Organization: Weizmann Inst. of Science, Rehovot (Israel)
• OSTI ID: 6212873
• Journal Information: Biochemistry; (United States), Vol. 26:11
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
PIGMENTS
STRUCTURAL MODELS
RHODOPSIN
SCHIFF BASES
ISOTOPE EFFECTS
CHEMICAL BONDS
DEUTERIUM
DOUBLE BONDS
IONS
PHOTOSYNTHETIC BACTERIA
PROTONS
BARYONS
CHARGED PARTICLES
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HYDROGEN ISOTOPES
IMINES
ISOTOPES
LIGHT NUCLEI
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PROTEINS
STABLE ISOTOPES
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)