MNDO barrier heights for catalyzed bicycle-pedal, hula-twist, and ordinary cis-trans isomerizations of protonated retinal Schiff base

Journal Article · Wed Mar 18 04:00:00 EST 1987 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00240a004· OSTI ID:6808957

Seltzer, S

Energy barriers to dark cis-trans isomerization in a protonated retinal Schiff base model in the presence and absence of electrostatic and nucleophilic catalysts have been calculated by the MNDO method. Three general processes - ordinary double bond isomerization, concerted isomerization about two double bonds by bicycle-pedal motion, and one-step double bond and adjacent single bond isomerization by hula-twist motion - are considered. Point negative charges or negatively charged nucleophiles near the protonated nitrogen substantially increase the barrier to cis-trans isomerization over what they would be in the absence of these agents. Negative charge or a nucleophile near C13 lowers the barrier to bicycle-pedal isomerization. Dark isomerization by a hula-twist motion required greater energy and is not substantially aided by the placement of a negative charge or nucleophile near any of the skeletal atoms in the isomerizing system. The importance of this to the mechanism of dark-light adaptation of bacteriorhodopsin is discussed.

• Research Organization: Brookhaven National Lab., Upton, NY
• OSTI ID: 6808957
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:6; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400500 -- Photochemistry
ACTIVATION ENERGY
CATALYSIS
CATALYSTS
CHEMICAL BONDS
CHEMICAL REACTIONS
DATA
DOUBLE BONDS
ENERGY
IMINES
INFORMATION
ISOMERIZATION
MATHEMATICAL MODELS
MOLECULAR MODELS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
SCHIFF BASES
STEREOCHEMISTRY
THEORETICAL DATA
THERMODYNAMICS