indicating a common photoactive chromophore and benzyl
alcohol was confirmed in the the photolysate of 2 by gas
chromatography. Moreover, unlike those of the other methyl
amides, the photolysate of 3 remains colourless while others
become deep yellow or orange which, on the basis of other
evidence, we have ascribed to the formation of a highly
conjugated metastable photoisomer arising from charge separa-
tion in the main chain.12
The analogy we see in these results with the redox behaviour
in the water oxidising complex of PSII assumes a similarity in
the oxidising capabilities of P680·+, a product of complete
photoinduced charge separation, and those of the photoexcited
state of the tosyl chromophore, which are typical of the
electronically excited states of ground-state acceptors.13 Pep-
tide bond oxidation dominates in the present series, the notable
exception being a tyrosyl derivative, so may similarly play an
important role in photodamage of protein within the PSII
complex.14
Scheme 2
We thank Pfizer Global R & D for funding and LC-MS
facilities and Stephen Robinson and Graham Jeffs for advice
and technical assistance.
Notes and references
1 J. Barber, Q. Rev. Biophys., 2003, 36, 71; J. Nugent (ed.), Biochim.
Biophys. Acta, 2001, 1503, 1.
2 J. Barber and J. M. Andersson (eds.), Philos. Trans. R. Soc. London, Ser.
B, 2002, 357, 1321.
3 Ref. 2, p. 1326.
4 W. S. Chow, H.-Y. Lee, Y.-M. Park, Y.-N. Hong and J. M. Anderson,
Philos. Trans. R. Soc. London, Ser. B, 2002, 357, 1141; E. Baena-
Gonzales and E.-M. Aro, Philos. Trans. R. Soc. London, Ser. B, 2002,
357, 1451; P. Silva, Y.-J. Choi, A. G. Hassan and P. J. Nixon, Philos.
Trans. R. Soc. London, Ser. B, 2002, 357, 1461; I. Vass, E. Turesányi,
E. Touloupakis, D. Ghanotakis and V. Petrouleas, Biochemistry, 2002,
41, 10200; B. Andersson and J. Barber, in Advances in Photosynthesis
5: Photosynthesis and the Environment, N. R. Baker (ed.), Kluwer,
Dordrecht, 1996, p. 101.
5 L. Sun, L. Hammerström, B. Åkermark and S. Styring, Chem. Soc. Rev.,
2001, 30, 36.
6 Synthesised from commercially available amino acids by standard
methods, all products giving satisfactory elemental analyses and
spectral data.
7 R. R. Hill, J. D. Coyle, D. Birch, E. Dawe, G. E. Jeffs, D. Randall, I. Stec
and T. M. Stevenson, J. Am. Chem. Soc., 1991, 113, 1805.
8 Waters Millennium system with diode array detection; Phenomenex
Luna 5 mm C18 column; gradient elution using water, 0.1 mol dm23
phosphoric acid and MeCN.
Scheme 3
9 R. R. Hill, G. E. Jeffs, D. R. Roberts and S. A. Moore, Chem. Commun.,
1999, 1735.
10 R. R. Hill, D. R. Roberts and S. A. Moore, in preparation.
11 Accurate mass and LC-MS data were obtained by Pfizer Global R & D,
Sandwich, Kent, using a Waters Alliance system with a Waters 474
scanning fluorescence detector, 712 WISP autosampler and Waters
Millennium software version 3.05 using a Phenomenex Luna phenyl-
hexyl 150 mm 3 4.60 mm column at 25 °C with an eluent gradient from
90 : 10 to 25 : 75 10 mM ammonium trifluoroacetate (pH 3.0):
acetonitrile and MS in positive ion-mode detection.
12 R. R. Hill, S. A. Moore and D. R. Roberts, J. Chem. Res. (S), 2003,
511.
13 G. Porter, in Light, Chemical Change and Life, J. D. Coyle, R. R. Hill
and D. R. Roberts (eds.), The Open University Press, Milton Keynes,
1982, p. 362; G. J. Kavarnos, Fundamentals of Photo-induced Electron
Transfer, VCH Pub. Inc., New York, 1993; G. Jones, L. N. Lu, H. Fu,
C. W. Farahat, C. Oh, S. R. Greenfield, D. J. Gosztola and M. R.
Wasielewski, J. Phys. Chem. B, 1999, 103, 572.
14 We note the pertinent recently reported evidence of electronic
interaction between the aryl group and peptide bonds in tyrosyl
peptides: I. Pujols-Ayala, C. A. Sacksteder and B. A. Barry, J. Am.
Chem. Soc., 2003, 125, 7539.
Scheme 4
Further observations in these experiments lend support to our
proposals. The rates of photolysis were closely similar,
CHEM. COMMUN., 2003, 2838–2839
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