Hydrogen Bond Formation between the Carotenoid Canthaxanthin and the Silanol Group on MCM-41 Surface

Abstract

The formation of one or two hydrogen bonds (H-bonds) between canthaxanthin (CAN), a dye, and the silanol group(s) on the MCM-41 surface has been studied by density functional theory (DFT) calculations and calorimetric experiments. It was found that the formation of the H-bond(s) stabilized the CAN molecule more than its radical cation (CAN(•+)). The charge distribution, bond lengths, and the HOMO and LUMO energies of CAN are also affected. The formation of the H-bond(s) explains the lower photoinduced electron transfer efficiency of CAN imbedded in Cu-MCM-41 versus that for β-carotene (CAR) imbedded in Cu-MCM-41 where complex formation with Cu(2+) dominates. These calculations show that to achieve high electron transfer efficiency for a dye-sensitized solar cell, H-bonding between the dye and the host should be avoided.

Antioxidant Activity in Supramolecular Carotenoid Complexes Favored by Nonpolar Environment and Disfavored by Hydrogen Bonding

“…However, when canthaxanthin is imbedded in Cu-MCM-41, it prefers to form one or two H-bonds with the silanol (-SiOH) groups on the MCM-41 surfaces rather than to form a complex with Cu 2+ . The formation of H-bonds is confirmed by DFT calculations, EPR measurements and calorimetric experiments [72]. DFT calculations show that the interaction energy (IE) due to the H-bonds is much lower than the IE between canthaxanthin and Cu 2+ , explaining why it prefers to form H-bonds [72].…”

“…The formation of H-bonds is confirmed by DFT calculations, EPR measurements and calorimetric experiments [72]. DFT calculations show that the interaction energy (IE) due to the H-bonds is much lower than the IE between canthaxanthin and Cu 2+ , explaining why it prefers to form H-bonds [72]. The formation of the H-bond is due to the interaction between the oxygen atom on the cyclohexene ring of canthaxanthin and the proton of the -SiOH group.…”

“…Carotenoids can be imbedded in MCM-41 and metal ion-substituted MCM-41 [70][71][72][73]. Previous studies [70,71,[74][75][76][77] have shown that such material provides a microenvironment appropriate for retarding back electron transfer (ET) and thus increases the lifetime of photo-produced radical ions.…”

“…It is necessary to investigate the photostability of carotenoids H-bonded or physisorbed on the surface of MCM-41 (see Figure 7) because it is related to the shelf life of the complex. Previous studies [72,73] showed that the formation of H-bonds affects the photo-induced ET efficiency (the net number of electrons transferred to the semiconductor by a certain amount of photons) of carotenoids adsorbed on mesoporous sieves on MCM-41. Carotenoids containing hydroxyl groups, such as retinol and 8'-apo-β-caroten-8'-al, and those containing ketone groups such as canthaxanthin, retinal and 8'-apo-β-caroten-8'-al, were adsorbed onto MCM-41 and surface-modified MCM-41.…”

“…Carotenoids containing hydroxyl groups, such as retinol and 8'-apo-β-caroten-8'-al, and those containing ketone groups such as canthaxanthin, retinal and 8'-apo-β-caroten-8'-al, were adsorbed onto MCM-41 and surface-modified MCM-41. The H-bonding properties and charge separation efficiencies of those carotenoids were investigated by DFT calculations and EPR experiments [72,73], because the radical cations produced in the photo-irradiation are stable enough at low temperature to be detected by EPR techniques. Two types of H-bonds can be formed when a carotenoid containing an -OH group interacts with a -SiOH group on the MCM-41 surface, depending on whether the carotenoid is a H-bond donor or acceptor.…”