DNA-mediated electron transfer reactions

ELECTRON TRANSFER

A()24 DNA-MEDIATED .

therme

ELECTRON

-1. Murphy

and

TRANSFER

Jacqueline

111

REACTIONS Division

K. Barton,

of

Chemistry and Chemical Engineering, California Institute of Technology, Mail Code I64-3OCH, Pasadena, CA 91125, U.S.A. The luminescence

of Ru(phen)3 2+ (phen = l,lO- phenanthroline)

quenched

via intermolecular

complexes

also intercalate

pairs

[l].

Recent

electron

transfer

into double-stranded

work suggests

to Rh(phen)33+.

is The

DNA, spanning four base

that the rate of electron

transfer

is

accelerated

in the presence of calf thymus DNA [2]. We are exploring this

possibility

by covalent

double-stranded

attachment

oligonucleotides.

Ru(phen)2(phen’)2+

and

l,lO-phenanthroline

of the complexes

to the 5’ ends of

We have prepared

Rh(phen)2(phen’)3+,

with a carboxylate-terminating

The new Ru(I1) complex luminesces

the complexes where

S-CGATTAGC-3’

in aqueous solution, &ax

and its complement,

enough

complex

is expected

for the pendant

- 610 nm. fashion,

W e h ave also prepared the oligonucleotides

arm at the 5’ end of the strand. DNA-metal

is

arm in the 5 position.

The new Rh(III) complex quenches this emission in a Stern-Volmer yielding kq - 8 x 108 M-ls-1.

phen’

each bearing an amino-terminating

The coupling to produce

M(phen)2(phen’)n+

of the two arms to form a a species with a linker long to intercalate

in between the

second and third base pairs from either end. With one bound Ru(I1) and one bound Rh(II1) per duplex, the expected electron transfer distance is -16 A. The photophysical

behavior of the metal complexes bound to small and large

DNAs will be compared. 1.

J. K. Barton, J. M. Goldberg,

C. V. Kumar, and N. J. Turro,

J.

Am. Chem. SOL 108, 2081 (1986). 2.

M. D. Purugganan,

C. V. Kumar, N. J. Turro,

Science, 241, 1645 (1988).

and J. K. Barton,