Mixed-ligand cis and trans complexes of platinum(II) with cytosine and adenine nucleobases: crystal structures and solution studies of cis and trans isomers of (9-methyladenine-N7)(1-methylcytosine-N3)diammineplatinum(II) perchlorate. Different selectivities of aquadiammine(1-methylcytosine)platinum(II) isomers for N1 and N7 donor atoms of adenine

Beyerle-Pfnür, R.; Brown, B. E.; Faggiani, R.; Lippert, Bernhard; Lock, C. J. L.

doi:10.1021/ic00218a008

Cited by 49 publications

(28 citation statements)

References 21 publications

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“…The Pt atom lies on an inversion centre and the environment is planar and almost exactly square; both the chelate and nonchelate cis-N--Pt--N angles are close to 90 °. The Pt--N bond lengths [2.023 (3), 2.014 (3)•] do not differ significantly and agree well with those we have measured previously, where Pt was bound to the imidazole ring in purine derived molecules (BeyerlePfnur, Brown, Faggiani, Lippert & Lock, 1985;Faggiani, Lippert, Lock & Speranzini, 1982;Faggiani, Lock & Lippert, 1980;Lippert, Lock & Pilon, 1984;Lock, Speranzini, Turner & Powell, 1976). Bond lengths within the bound phosphinic acid agree well with those observed in the free phosphonic acid (Howard-Lock et al, 1989), particularly when compared to the unprotonated ring.…”

Section: Introductionsupporting

confidence: 88%

Bis[di(imidazol-2-yl)phosphinato-N3,N3']platinum(II) tetrahydrate

Britten¹,

Lock²,

Wang³

1993

Acta Crystallogr C

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Section: Introductionsupporting

confidence: 88%

Bis[di(imidazol-2-yl)phosphinato-N3,N3']platinum(II) tetrahydrate

Britten¹,

Lock²,

Wang³

1993

Acta Crystallogr C

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“…Though there is one previous quantitative example [47] as well as a few qualitative ones, [48,49] this is the first time that the apparent basicity-enhancing effect of (N1)-coordinated Pt 2 on the N7 site is described in a quantitative manner in several examples (entries 3, 4, and 7), making the result unequivocal. From the qualitative examples mentioned it becomes in Table 3.…”

Section: 4mentioning

confidence: 82%

“…[48] What is the reason for the apparent basicity enhancement of the N7 site upon Pt 2 coordination to N1 of a purine-type residue as seen in entries 3, 4, and 7 of Table 3? One is tempted to conclude that Pt 2 replaces a proton at the (N1)H site and that H is always more polarizing than a metal ion, which is in principle correct.…”

Section: 4mentioning

confidence: 99%

Effects of (N7)-Coordinated Nickel(II), Copper(II), or Platinum(II) on the Acid-Base Properties of Guanine Derivatives and Other Related Purines[≠]

Song

Zhao

Griesser

et al. 1999

Chemistry - A European Journal

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121

151

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This study is dedicated to Professor Dr. R. Bruce Martin, University of Virginia, Charlottesville (USA), on the occasion of his 70th birthday, with the very best wishes of the authors for all his future endeavors and with deep appreciation for friendship and unselfish advice provided over many years to H.S. and B.L.Abstract: The effect of Ni 2 , Cu 2 , and cis-a 2 Pt 2 or trans-a 2 Pt 2 (where a NH 3 or CH 3 NH 2 ), if coordinated to the N7 site of guanine residues, on the acid ± base properties of complexes containing guanine derivatives as ligands is considered. The various acidity constants were determined by potentiometric pH titrations. Over 60 acidity constants are listed; about half of these are new. In many instances micro acidity constants have been derived that allow a quantification of the intrinsic acid ± base properties of a certain site, which are otherwise blurred by the pK a values of overlapping buffer regions. This material allows many comparisons; among these is the observation that the acidifying properties of (N7)-coordinated divalent metal ions on the corresponding (N1)H sites in a guanine derivative decrease in the following series:The data also indicate that the effects are similar for guanine and hypoxanthine residues, but that they are more pronounced for adenine derivatives because in the latter case a (N7)-bound M 2 affects a (N1)H site; hence, a further charge effect is operative here. The available material does not yet allow certain prediction of the more subtle differences occurring between the cis and trans isomers of Pt 2 complexes, but replacement of, for example, NH 3 in the coordination sphere of Pt 2 with CH 3 NH 2 has an effect. Of course, as one might expect, the effect of (N7)-bound Pt 2 in guanine nucleotide complexes is smaller on the more remote phosphate groups than it is on the closer (N1)H sites. By evaluation (by means of micro acidity constants) of data available for hypoxanthine derivatives it is also shown that (N1) À -bound Pt 2 has an acidifying effect on the (N7)H site comparable to that of (N7)-coordinated Pt 2 on the (N1)H site.

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“…Pt II binding to N7 of an N9-substituted adenine, for example, 9-methyladenine (9MeA), makes protonation of the preferred N1 position more difficult by approximately 2 log units, that is, the pK a value of N1H drops from 4.10 in free 9-methyladeninium (9MeAH + ) to approximately 2 in its Pt II complexes. [13] If Pt II is bonded to N1, protonation occurs at N7 with a pK a value of approximately 1.2, [20] and if the N3 site is carrying a Pt II entity, the overall basicity of the adenine ring drops by 4 log units, with N7 then being more basic than N1.…”

Section: Resultsmentioning

confidence: 99%

“…, [20] trans-[(NH 3 ) 2 Pt(9-MeAH-N7) 2 ](ClO 4 ) 4 ¥2 H 2 O (4), [56] cis-[(NH 3 ) 2 Pt(9MeA-N7) 2 ](NO 3 ) 2 ¥ 1.5 H 2 O (5), [57] cis-[{(NH 3 ) 2 Pt(1MeC-N3) 2 }(9MeA-N1,N7)](ClO 4 ) 4 (8), [20] trans-[{(NH 3 ) 2 Pt(1MeC-N3)} 2 (9MeA-N1,N7)](ClO 4 ) 4 (9), [20] trans,trans- [22] trans,trans-…”

Section: Determination Of Acidity Constantsmentioning

confidence: 99%

Perturbation of the NH₂ pK_a Value of Adenine in Platinum(II) Complexes: Distinct Stereochemical Internucleobase Effects

Añorbe

Lüth

Roitzsch

et al. 2004

Chemistry A European J

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The degree of acidification of the exocyclic N6 amino group of the model nucleobase 9-methyladenine (9MeA) in relation to the number and site(s) of Pt(II) binding has been studied in detail. It is found that twofold Pt(II) binding to N1 and N7 lowers the pK(a) value from 16.7 in the free base to 12-8. The lowest pK(a) values are observed when the resulting N6H(-) amide group is intramolecularly stabilized by an H-bond donor such as the N6H(2) group of a suitably positioned second 9MeA ligand. Deprotonation of the N6 amino group facilitates Pt migration from N1 to N6, and subsequent reprotonation of the N1 position yields a twofold N7,N6-metalated form of the rare imino tautomer of 9MeA, which has a pK(a) value of 5.03. These findings demonstrate a principle that is of potential relevance to the topic of "shifted pK(a)" values of adenine nucleobases, which is believed to be important with regard to acid-base catalysis of RNAs at physiological pH values. The principle states that a nucleobase pK(a) value can be sufficiently lowered to reach near-neutral values and that the pK(a) value of the protonated base does not necessarily have to be increased to accomplish this effect.

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Cited by 49 publications

References 21 publications

Bis[di(imidazol-2-yl)phosphinato-N3,N3']platinum(II) tetrahydrate

Bis[di(imidazol-2-yl)phosphinato-N3,N3']platinum(II) tetrahydrate

Effects of (N7)-Coordinated Nickel(II), Copper(II), or Platinum(II) on the Acid-Base Properties of Guanine Derivatives and Other Related Purines[≠]

Perturbation of the NH₂ pK_a Value of Adenine in Platinum(II) Complexes: Distinct Stereochemical Internucleobase Effects

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Cited by 49 publications

References 21 publications

Bis[di(imidazol-2-yl)phosphinato-N3,N3']platinum(II) tetrahydrate

Bis[di(imidazol-2-yl)phosphinato-N3,N3']platinum(II) tetrahydrate

Effects of (N7)-Coordinated Nickel(II), Copper(II), or Platinum(II) on the Acid-Base Properties of Guanine Derivatives and Other Related Purines[≠]

Perturbation of the NH2 pKa Value of Adenine in Platinum(II) Complexes: Distinct Stereochemical Internucleobase Effects

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Perturbation of the NH₂ pK_a Value of Adenine in Platinum(II) Complexes: Distinct Stereochemical Internucleobase Effects