Synthesis of N-heteroaryl retinals and their artificial bacteriorhodopsins.
N-Heteroaryl retinals derived from indole, 1-indolizine and 3-indolizine (10 a-c) have been synthesized after their UV/Vis red-shifted absorption properties had been predicted by time-dependent density functional theory (TD-DFT) computations. The three new analogues form artificial pigments upon recombination with bacterioopsin: indolyl retinal 10 a undergoes fast and efficient reconstitution to form a species with a UV/Vis absorbance maximum similar to that of wild-type bacteriorhodopsin, whilst the indolizinyl retinals 10 b and 10 c also reconstitute in significant proportion to give noticeably red-shifted, although unstable, pigments. Significant changes in the pK(a) values of these artificial bacteriorhodopsins are interpreted as arising from nonoptimal binding-site occupancy by the chromophore due to steric constraints.
López
Susana
S
Departamento de Química Orgánica, Facultade de Química, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain. qosuslop@usc.es
Rodríguez
Virginia
V
Montenegro
Javier
J
Saá
Carlos
C
Alvarez
Rosana
R
Silva López
Carlos
C
de Lera
Angel R
AR
Simón
Rosana
R
Lazarova
Tzvetana
T
Padrós
Esteve
E
D000465:Algorithms; D001436:Bacteriorhodopsins / Q000138:chemical synthesis* / Q000737:chemistry*; D010777:Photochemistry; D012172:Retinaldehyde / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
D001436:Bacteriorhodopsins; D012172:Retinaldehyde