Non-bonding molecular factors influencing the stretching wavenumbers of the conjugated carbonyl groups of bacteriochlorophyll a
✍ Scribed by Karine Lapouge; Arne Näveke; James N. Sturgis; Gerhard Hartwich; David Renaud; Ingrid Simonin; Marc Lutz; Hugo Scheer; Bruno Robert
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 221 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0377-0486
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✦ Synopsis
The inÑuence of the macrocycle core size on the keto and acetyl carbonyl stretching wavenumbers of bacteriochlorophyll a and of its Co, Ni, Cu and Zn derivatives was examined. Their sensitivity to the polarity and polarizability of the molecular environment was also studied. It is concluded that the macrocycle core size has a clear, but limited, inÑuence on these wavenumbers. As a consequence, interchange between the Ðve-and six-coordinated states of the central Mg atom of bacteriochlorophyll a should shift the keto and acetyl carbonyl stretching wavenumbers, but by not more than 3 and 1 cm-1, respectively. In line with previous observations on chlorophylls, a marked dependence of the keto and acetyl carbonyl stretching wavenumbers of bacteriophaeophytin a and of bacteriochlorophyll a and its Ni and Zn derivatives on solvent permittivity and refractive index was observed. The sensitivity of the keto carbonyl wavenumber appears to be largely independent of the presence and nature of the central metal and is very close to that reported earlier for chlorophyll a. The wavenumber of the acetyl carbonyl stretching mode of bacteriochlorophyll a derivatives is overall less sensitive to any of these parameters than that of the keto carbonyl group.