Formation of ternary complexes by coordination of (diethylenetriamine)-platinum(II) to N1 or N7 of the adenine moiety of the antiviral nucleotide analogue 9.

The synthesis of (Dien)Pt(PMEA-N1), where Dien = diethylenetriamine and PMEA2- = dianion of 9-[2-(phosphonomethoxy)ethyl]adenine, is described. The acidity constants of the threefold protonated H3[(Dien)Pt(PMEA-N1)]3+ complex were determined and in part estimated (UV spectrophotometry and potentiometric pH titration): The release of the proton from the (N7)H+ site in H4[(Dien)Pt(PMEA-N1)]3+ occurs with a rather low pKa (= 0.52+/-0.10). The release of the proton from the -P(O)2(OH) group (pKa = 6.69+/-0.03) in H[(Dien)Pt(PMEA-N1)]+ is only slightly affected by the N1-coordinated (Dien)Pt2+ unit. Comparison with the acidic properties of the H[(Dien)Pt(PMEA-N7)]+ species provides evidence that in the (Dien)Pt(PMEA-N7) complex in aqueous solution an intramolecular, outer-sphere macrochelate is formed through hydrogen bonds between the -PO3(2-) residue of PMEA2- and a PtII-coordinated (Dien)NH2 group; its formation degree amounts to about 40%. The stability constants of the M[(Dien)Pt(PMEA-N1)]2+ complexes with M2+ = Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+ were measured by potentiometric pH titrations in aqueous solution at 25 degrees C and I = 0.1 M (NaNO3). Application of previously determined straight-line plots of log K(M(R-PO3))M versus pK(H(R-PO3)H for simple phosph(on)ate ligands. R-PO3(2-), where R represents a non-inhibiting residue without an affinity for metal ions, proves that the primary binding site of (Dien)Pt(PMEA-N1) is the phosphonate group with all metal ions studied; in fact, Mg2+, Ca2+ and Ni2+ coordinate (within the error limits) only to this site. For the Cu[(Dien)Pt(PMEA-N1)]2+ and Zn[(Dien)Pt(PMEA-N1)]2- systems also the formation of five-membered chelates involving the ether oxygen of the -CH2-O-CH2-PO3(2-) residue could be detected; the formation degrees are about 60% and 30%, respectively. The metal-ion-binding properties of the isomeric (Dien)Pt(PMEA-N7) species studied previously differ in so far that the resulting M[(Dien)Pt(PMEA-N7)]2+ complexes are somewhat less stable, but again Cu2+ and Zn2+ also form with this ligand comparable amounts of the mentioned five-membered chelates. In contrast, both M[(Dien)Pt(PMEA-N1/N7)]2+ complexes differ from the parent M(PMEA) complexes considerably; in the latter instance the formation of the five-membered chelates is of significance for all divalent metal ions studied. The observation that divalent metal-ion binding to the phosphonate group of (Dien)Pt(PMEA-N1) and (Dien)Pt(PMEA-N7) is only moderately inhibited (about 0.2-0.4 log units) by the twofold positively charged (Dien)Pt2+ unit at the adenine residue allows the general conclusion, considering that PMEA is a nucleotide analogue, that this is also true for nucleotides and that consequently participation of, for example, two metal ions in an enzymatic process involving nucleotides is not seriously hampered by charge repulsion.

Metal ion-binding properties of 1-methyl-4-aminobenzimidazole (=9-methyl-1,3-dideazaadenine) and 1,4-dimethylbenzimidazole (=6,9-dimethyl-1,3-dideazapurine). quantification of the steric effect of the 6-amino group on metal ion binding at the N7 site of the adenine residue.

The stability constants of the 1:1 complexes formed between Mg(2+), Ca(2+), Sr(2+), Ba(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) (=M(2+)) and 1-methyl-4-aminobenzimidazole (MABI) or 1,4-dimethylbenzimidazole (DMBI) were determined by potentiometric pH titrations in aqueous solution (25 degrees C; I = 0.5 M, NaNO(3)). Some of the stability constants were also measured by UV spectrophotometry. The acidity constants of the species H(2)(MABI)(2+) and H(DMBI)(+) were determined by the same methods, some twice. Comparison of the stability constants of the M(MABI)(2+) and M(DMBI)(2+) complexes with those calculated from log versus p straight-line plots, which were established previously for sterically unhindered benzimidazole-type ligands (=L), reveals that the stabilities of the M(MABI)(2+) and M(DMBI)(2+) complexes are significantly reduced due to steric effects of the C4 substituents on metal ion binding at N3. This effect is more pronounced in the M(DMBI)(2+) complexes. Considering the steric equivalence of methyl and (noncoordinating) amino groups (as they occur in adenines), it is concluded that the same extent of steric inhibition by the (C6)NH(2) group is to be expected on metal ion binding at N7 with adenine derivatives. The basicity of the amino group in MABI is significantly higher than in its corresponding adenine derivative. Indeed, it is concluded that in the M(MABI)(2+) complexes chelate formation involving the amino group occurs to some extent. The formation degrees of these "closed" species are calculated; they vary for the complexes of Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) between about 50 and 90%. The stability of the M(MABI)(2+) and M(DMBI)(2+) complexes with the alkaline earth ions is very low but unaffected by the C4 substituent; this probably indicates that in these instances outersphere complexes (with a water molecule between N3 and the metal ion) are formed.

Intramolecular stacking interactions in ternary copper(II) complexes formed with 2,2'-bipyridine or 1,10-phenanthroline and 9-(4-phosphonobutyl)adenine (dPMEA), the carba relative of the antiviral nucleotide analogue 9.

The stability constants of the mixed ligand complexes formed between Cu(Arm)2+, where Arm=2,2'-bipyridine (Bpy) or 1,10-phenanthroline (Phen), and the monoanion or the dianion of 9-(4-phosphonobutyl)adenine (dPMEA=3'-deoxa-PMEA), which is the carba analogue of the antivirally active 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), were determined by potentiometric pH titrations in aqueous solution at 25 degrees C and I=0.1 M (NaNO3). Detailed stability constant comparisons reveal that in the monoprotonated ternary Cu(Arm)(H;dPMEA)+ complexes the proton is at the phosphonate group and that stacking between Cu(Arm)2+ and H(dPMEA)- plays a significant role. For the Cu(Arm)(dPMEA) complexes a large increase in complex stability (compared to the stability expected on the basis of the basicity of the phosphonate group) is observed, which is due to intramolecular stack formation between the aromatic ring systems of Phen or Bpy and the purine moiety of dPMEA2-. The formation degree of the stacked isomer in the Cu(Arm)(dPMEA) systems is on the order of 90%, though it is somewhat more pronounced with Phen than with Bpy. Comparisons of the Cu(Arm)(N) systems, where N=dPMEA2- and PMEA2- or adenosine 5'-monophosphate (AMP2-), reveal that the stacking properties of dPMEA2- and PMEA2-resemble closely those of their parent nucleotide AMP2-.

Evaluation of intramolecular equilibria in complexes formed between substituted imidazole ligands and nickel (II), copper (II) or zinc (II).

The metal ion-binding properties of imidazole-4-acetate (ImA-), 4(5)-aminoimidazole-5(4)-carboxamide (AImC), 2,2'biimidazole(BiIm) (I. Török et al., J. Inorg. Biochem. 71 (1998) 7-14), and bis (imidazol-2-yl)methane(BiImM) (K. Várnagy et al., J. Chem. Soc., Dalton Trans. (1994) 2939-2945) have been evaluated by using the recently published stability constants and by applying the recently established log K(ML)M versus pK(HL)H straight-line plots (L. E. Kapinos et al., Inorg. Chim. Acta 280 (1998) 50-56) which hold for simple imidazole-type ligands. The indicated analysis regarding the intramolecular equilibrium between a monodentatally imidazole-nitrogen-coordinated (open) species and a chelated isomer provides helpful insights, e.g., the formation degree of chelates is more favored if six-membered rings can be formed, as in the case with M(BiImM)2+ compared to M(BiIm)2+, though in both instances the formation degree of the chelates is large. The formation degree of chelates in the M(ImA)+ complexes increases in the series Zn(ImA)+ (87%)

Ternary Copper(II) Complexes in Solution Formed With 8-Aza Derivatives of the Antiviral Nucleotide Analogue 9-[2-(Phosphonomethoxy)Ethyl]Adenine (PMEA).

The stability constants of the mixed-ligand complexes formed between Cu(Arm)(2+), where Arm= 2,2'-bipyridine (Bpy) or 1,10-phenanthroline (Phen), and the dianions of 9-[2-(phosphonomethoxy)ethyl]-8-azaadenine (9,8aPMEA) and 8-[2-(phosphonomethoxy)ethyl]-8-azaadenine (8,8aPMEA) (both also abbreviated as PA(2-)) were determined by potentiometric pH titrations in aqueous solution (25 ( degrees )C; I = 0.1 M, NaNO(3)). All four ternary Cu(Arm)(PA) complexes are considerably more stable than corresponding Cu(Arm)(R-PO(3)) species, where R-PO(3) (2-) represents a phosph(on)ate ligand with a group R that is unable to participate in any kind of interaction within the complexes. The increased stability is attributed to intramolecular stack formation in the Cu(Arm)(PA) complexes and also to the formation of 5-membered chelates involving the ether oxygen present in the -CH(2)-O-CH(2)-PO(3) (2-) residue of the azaPMEAs. A quantitative analysis of the intramolecular equilibria involving three structurally different Cu(Arm)(PA) species is carried out. For example, about 5% of the Cu(Bpy)(8,8aPMEA) system exist with the metal ion solely coordinated to the phosphonate group, 14% as a 5-membered chelate involving the -CH(2)-O-CH(2)-PO(3) (2-)residue, and 81% with an intramolecular stack between the 8-azapurine moiety and the aromatic rings of Bpy. The results for the other systems are similar though with Phen a formation degree of about 90% for the intramolecular stack is reached. The existence of the stacked species is also proven by spectrophotometric measurements. In addition, the Cu(Arm)(PA) complexes may be protonated, leading to Cu(Arm)(H;PA)(+) species for which it is concluded that the proton is located at the phosphonate group and that the complexes are mainly formed by a stacking adduct between Cu(Arm)(2+) and H(PA)(-). Conclusions regarding the biological properties of these azaPMEAs are shortly indicated.

[Calorimetric study of the helix-coil transition in DNA during interaction with Cu2+ ions]. / Kalorimetricheskoe izuchenie perekhoda spiral'-klubok v DNK pri vzaimodeistvii s ionami Cu2+.

Using the method of differential scanning calorimetry, the DNA helix-coil transition was studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent copper ions at relative metal ion concentrations (Mt2+/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on relative ion concentration were determined. An aggregation of Cu(2+) + DNA complexes in the range of average ion concentration was established. It is shown that the melting enthalpy of "units" increases with copper ion concentration. The data obtained were compared with values determined by UV-spectroscopy. Association constants for Cu2+ binding to DNA were defined by the ligand theory.

[Calorimetric study of Ca2+ and Mn2+ ions' effect on DNA helix-coil transition]. / Kalorimetricheskoe issledovanie vliianiia ionov Ca2+ i Mn2+ na perekhodspiral'-klubok v DNK.

Using the method of differential scanning calorimetry, the DNA helix-coil transition studied in solutions (10(-3) M Na+, 10(-3) M tris HCl, pH 7.0) containing divalent metal ions (Mn2+ and Ca2+) at relative metal ion concentrations (Me/PDNA) ranging from 0.2 to 20. Dependences of the melting temperature and enthalpy on the ion relative concentration were stated. The fine structure of melting curves in DNA+Me complexes was observed. The resolution degree of this structure was shown to increase in the range of moderate ion concentrations. The data obtained were compared with values determined by UV-spectroscopy. Association constants were defined for Mn2+ and Ca2+ binding to DNA by the ligand theory.

[Interaction of DNA with calcium ions by a vibrational spectroscopy]. / Izuchenie vzaimodeistviia DNK s ionami kal'tsiia metodom kolebatel'noi spektroskopii.

DNA complexes with Ca2+ ions formed in films at various relative humidities were studied by IR-spectroscopy for molar concentration ratio of calcium ions and DNA phosphate groups [Ca2+]/[P] = 0.4-20. It is shown that the transition of DNA complexed with Ca2+ ions into B-form occurs at higher average numbers (n) of water molecules absorbed per nucleotide: n > 18 at the ratio [Ca2+]/[P] = 10, n > 24 at [Ca2+]/[P] = 20 and n > 12 in the absence of Ca2+ ions. This shows stronger binding of water molecules in the hydrate shell of DNA-Ca2+ if compared with free DNA. The results confirm a model proposed earlier. Ca2+ ions interact with phosphate oxygens of DNA and with N(7) nitrogens of guanine forming chelated complexes.

[Structural and physicochemical characteristics of DNA from animal tissue subjected to chronic irradiation in the Chernobyl area]. / Strukturnye i fiziko-khimicheskie kharakteristiki DNK iz tkanei zhivotnykh, podvergavshikhsia dlitel'nomu khronicheskomu oblucheniiu v zone chernobylia.

The properties of animal DNAs exposed to prolonged irradiation in the Chernobyl zone, have been studied by the methods of viscometry, thermal denaturation, IR-spectroscopy, and electrophoresis. High content of low-molecular fractions have been observed in the preparations of DNA from liver and spleen, their quantities increasing with age and generation of animals. This effect is especially strong in DNA from liver. Low-molecular fraction of DNA is shown to be enriched with G-C pairs and to consist of the following four fractions: 1) approximately 500 base pairs (B.p.), 2) approximately 1.5 divided by 2 thousand B.p., 3) approximately 4 divided by 5 thousand B.p. and 4) a mixture of approximately 20 thousand B.p. fragments. Further, it has been observed that the DNA preparations from the tissues of experimental animals contain about ten times higher contents of Fe, Zn, Se and other elements as compared to the control preparations.

[Study of the interaction of DNA with copper ions using IR- and Raman spectroscopy]. / Izuchenie metodami IK- i Ramanovskoi spektroskopii vzaimodeistviia DNK s ionami medi.

DNA with Cu2+ ions in solution and films is studied by IR and Raman spectroscopy at different relative humidities (R.H. = 51 divided by 98%). DNA complexed with Cu2+ ions is shown to transit to the double-helix conformation, passing A-form, the water content per nucleotide (n) being essentially larger: 12 for Cu2+/P = 0.4 (n = 8 for DNA without ions). Cu2+ decrease the biopolymer hydration at R.H. 50-76% interactions with Cu2+ are stated to depend on the hydration degree of macromolecules. The analysis of the absorption band shifts of Raman spectra evidences the changes in the base torsion angle around the glycoside bond to the values characteristic of the syn-conformation and the interaction both with phosphates and nitrogen bases.

[Study of the interaction of DNA with manganese ions by IR-spectroscopy]. / Izuchenie vzaimodeistviia DNK s ionami margantsa metodom IK-spektroskopii.

DNA complexed with Mn2+ ions in films is studied at different relative humidities and ion contents ([Mn2+]/[P] = 0.4-1) by IR spectroscopy. It is shown that substantially more sorbed water molecules are necessary for the transition of DNA complexed with Mn2+ ions into the double helical conformation (preferentially B-form) that for macromolecules in the absence of ions. DNA-Mn2+ complexes ([Mn2+]/[P] = 1) are able to absorb more water molecules than DNA. The results of the work evidence Mn2+ ion interaction with phosphates and nitrogen bases of the macromolecule: N7G, O6G.