Cation‐π interactions are theoretically investigated for alkali metal cation (M+)‐circumcoronene (CC) complexes (M = Li, Na, K), in gas phase and in aqueous solution with consideration of micro‐ and global solvation models using the DFT/PBEh‐3c‐RI/TZVP method. The solvent effect on the M+–CC energy interaction regarding the cation size and the stability of inner‐ and outer‐sphere [M(H2O)
We investigated the effect of the cation‐π interaction on the susceptibility of a tryptophan model system toward interaction with singlet oxygen, that is, type II photooxidation. The model system consists of two indole units linked to a lariat crown ether to measure the total rate of removal of singlet oxygen by the indole units in the presence of sodium cations (i.e. indole units subject to a cation‐π interaction) and in the absence of this interaction. We found that the cation‐π interaction significantly decreases the total rate of removal of singlet oxygen (
- PAR ID:
- 10455096
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Photochemistry and Photobiology
- Volume:
- 96
- Issue:
- 6
- ISSN:
- 0031-8655
- Page Range / eLocation ID:
- p. 1200-1207
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract n ]+–CC complexes are calculated by means of geometry optimizations and potential energy (PE) curves. The PE curves, calculated as a function of perpendicular distance of M+to the CC plane, predicted one energy minimum for each of the isolated M+–CC complexes. However, for microhydrated complexes, two minima assigned to two different surface complexations were obtained. Microhydrated Li+and Na+favored outer‐sphere complexation while inner‐sphere complexation was found more stable for microhydrated K+. These results illustrate nicely the key role, which the cation radius plays for the polarization of the water molecules and the aromatic system. -
more » « less
Abstract Ru(II) complexes were synthesized with π‐expanding (phenyl, fluorenyl, phenanthrenyl, naphthalen‐1‐yl, naphthalene‐2‐yl, anthryl and pyrenyl groups) attached at a 1
H ‐imidazo[4,5‐f ][1,10]phenanthroline ligand and 4,4′‐dimethyl‐2,2′‐bipyridine (4,4′‐dmb) coligands. These Ru(II) complexes were characterized by 1D and 2D NMR, and mass spectroscopy, and studied for visible light and dark toxicity to human malignant melanoma SK‐MEL‐28 cells. In the SK‐MEL‐28 cells, the Ru(II) complexes are highly phototoxic (EC50 = 0.2–0.5 µm ) and have low dark toxicity (EC50 = 58–230 µm ). The highest phototherapeutic index (PI) of the series was found with the Ru(II) complex bearing the 2‐(pyren‐1‐yl)‐1H ‐imidazo[4,5‐f ][1,10]phenanthroline ligand. This high PI is in part attributed to the π‐rich character added by the pyrenyl group, and a possible low‐lying and longer‐lived3IL state due to equilibration with the3MLCT state. While this pyrenyl Ru(II) complex possessed a relatively high quantum yield for singlet oxygen formation (Φ∆ = 0.84), contributions from type‐I processes (oxygen radicals and radical ions) are competitive with the type‐II (1O2) process based on effects of added sodium azide and solvent deuteration. -
more » « less
Abstract The sensitized photooxidation of
ortho ‐prenyl phenol is described with evidence that solvent aproticity favors the formation of a dihydrobenzofuran [2‐(prop‐1‐en‐2‐yl)‐2,3‐dihydrobenzofuran], a moiety commonly found in natural products. Benzene solvent increased the total quenching rate constant (k T) of singlet oxygen with prenyl phenol by ~10‐fold compared to methanol. A mechanism is proposed with preferential addition of singlet oxygen to prenyl site due to hydrogen bonding with the phenol OH group, which causes a divergence away from the singlet oxygen ‘ene’ reaction toward the dihydrobenzofuran as the major product. The reaction is a mixed photooxidized system since an epoxide arises by a type I sensitized photooxidation. -
more » « less
Abstract Mono‐ and dianions of 2‐
tert ‐butyl‐3a2‐azapentabenzo[bc ,ef ,hi ,kl ,no ]corannulene (1 a ) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, [{Na+(18‐crown‐6)(THF)2}3{Na+(18‐crown‐6)(THF)}(1 a 2−)2], revealed the presence of a naked dianion. In contrast, controlled reaction of1 a with Cs allowed the isolation of singly and doubly reduced forms of1 a , both forming π‐complexes with cesium ions in the solid state. In [{Cs+(18‐crown‐6)}(1 a −)]⋅THF, asymmetric binding of the Cs+ion to the concave surface of1 a −is observed, whereas in [{Cs+(18‐crown‐6)}2(1 a 2−)], two Cs+ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules. -
more » « less
Abstract Mono‐ and dianions of 2‐
tert ‐butyl‐3a2‐azapentabenzo[bc ,ef ,hi ,kl ,no ]corannulene (1 a ) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, [{Na+(18‐crown‐6)(THF)2}3{Na+(18‐crown‐6)(THF)}(1 a 2−)2], revealed the presence of a naked dianion. In contrast, controlled reaction of1 a with Cs allowed the isolation of singly and doubly reduced forms of1 a , both forming π‐complexes with cesium ions in the solid state. In [{Cs+(18‐crown‐6)}(1 a −)]⋅THF, asymmetric binding of the Cs+ion to the concave surface of1 a −is observed, whereas in [{Cs+(18‐crown‐6)}2(1 a 2−)], two Cs+ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules.
