Table 2. Identification of the platinum chelates formed by reaction of trans-[Pt(NH₃)₂(H₂O)₂]²⁺ 2 with AG₃(T₂AG₃)₃ I^a.

Analysis of the platinated fragments from gel bands 2.1, 2.2, 2.3 and 2.4 (Fig. 3)		Platinated sites
		A1	G4	A7	G10	A13	A19	G22
% Platinated G	2.1		<15		<15			<15
(DMS)	2.2 and 2.3		<15		60			80
	2.4		<15		<15			<15
% Platinated A–N7	2.1	<15		60		<15	60
(DEPC)b	2.2 and 2.3	<15		<15		35	<15
	2.4	<15		30		45	35
3′-Exonuclease	2.1	A1 and G2c		A7	G10	A13	A19	G22
stopc	2.2 and 2.3	A1			G10	A13		G22
	2.4	A1	G4	A7		A13	A19	G22
‘n-mer like’ migration of the platinated fragment after digestion	2.1 2.2 and 2.32.4	9 99	10	1313	16 9–10d	16–17d 1216 and 12e	18 18	18–19d 19 (2.2) 20 (2.3) 21
Base position	2.1	5′		5′	3′e	5′ and 3′f	3′	3′
in the chelate	2.2 and 2.3	5′			3′	5′f		3′
	2.4	5′	5′	5′		5′ and 3′e	3′	3′
Conclusion	2.1	Three bis-chelates A1–G10/A7–A19; A1–A13/A7–A19 and A13–G22/A7–A19
	2.2 and 2.3	One bis-chelate A1–G10/A13–G22g
	2.4h	Four chelates A1–A13; A13–G22; A7–A19; G4–A19

^aSee text for step-by-step analysis.

^bDEPC/piperidine treatment does not detect A–N1 binding. The lower limit of reliable quantification by gel analysis is 15%.

^cFor some adducts, the 3′-exonuclease exhibits a 1 nt premature arrest. This is easily detected thanks to the assignment of the platination sites by chemical digestion.

^dThe two values result from the non-identity of the migration scales of the free and platinated fragments.

^eThe two fragments result from the same A13 digestion stop. See text.

^fBecause of the presence of another platinum chelate at the 5′ side of this base, its position in the chelate cannot be deduced from the migration length of the digested platinated fragment. This was done thanks to the measured distances between the purine nitrogens in structure A, indicating the geometrically feasible chelates (Table 4).

^gThe same bis-chelate is present in the products from 2.2 and 2.3. The latter carries a supplementary platinum complex whose binding site has not been identified.

^hMass spectrometry data indicate one platinum per oligonucleotide.