Hydrolysis of the tumor-inhibiting ruthenium(III) complexes HIm trans-[RuCl4(im)2] and HInd trans-[RuCl4(ind)2] investigated by means of HPCE and HPLC-MS

High performance capillary electrophoresis (HPCE) as well as high performance liquid chromatography-mass spectrometry (HPLC-MS) have been applied to the separation, identification and quantification of the tumor-inhibiting ruthenium compounds HIm trans-[RuCl4(im)2] (im = imidazole) and HInd trans-[RuCl4(ind)2] (ind = indazole) and their hydrolysis products. The half-lives for the hydrolytic decomposition of the Ru(III) compounds were determined by monitoring the relative decrease of the original complex anion under different conditions by means of capillary electrophoresis. The decomposition follows pseudo-first-order kinetics. The rate constants in water at 25 degrees C are 1.102 +/- 0.091 x 10(-5) s-1 for HIm trans-[RuCl4(im)2] and 0.395 +/- 0.014 x 10(-5) s-1 for HInd trans-[RuCl4(ind)2]. About 8% of HIm trans-[RuCl4(im)2] but only about 2% of HInd trans-[RuCl4(ind)2] were hydrolyzed after 1 h at room temperature. Whereas the hydrolysis rate of the imidazole complex is independent of the pH value, the indazole complex hydrolyzes much faster at higher pH. The half-life of HInd trans-[RuCl4(ind)2] in phosphate buffer at pH 6.0 and 37 degrees C is 5.4 h, whereas it is less than 0.5 h at pH 7.4. In contrast to the imidazole complex, where no dependence on the buffer system was observed, hydrolysis of the indazole complex is even faster if a buffer containing hydrogen carbonate is used. The formation of [RuCl2(H2O)2(im)2]+ could be demonstrated by HPLC-MS measurements. In the case of the indazole complex, a release of the indazole ligands results in the formation of [RuCl4(H2O)2]-.     

Complexes trans-[RuCl(2)(nic)(4)] and trans-[RuCl(2)(i-nic)(4)] as free radical scavengers

This study evaluates the action of the new ruthenium complexes trans-RuCl(2)(nic)(4)] (I) and trans-[RuCl(2)(i-nic)(4)] (II) as free radical scavengers. In our experiments, both compounds acted as scavengers of superoxide anion (O(2)*(-)), hydroxyl radicals (HO*) and nitrogen monoxide (formally known as 'nitric oxide'; NO*). In addition, complexes I and II potentiated the release of NO* from S-nitroso-N-acetyl-DL-penicilamine (SNAP), a NO* donor. Complex II, but not I, also decreased the nitrite levels in culture media of activated macrophages. A hypsochromic shift of lambda(max) and a significant change in half-wave potential (E(1/2)) was observed when NO* was added to the Complex II. Thiobarbituric reactive substance (TBARS) levels were significantly reduced in rats treated for 1 week with Complex II plus tert-butylhydroperoxide, when compared to rats treated only with tert-butylhydroperoxide. None of the complexes showed cytotoxicity. These findings support the suggestion that the new ruthenium complexes, especially trans-[RuCl(2)(i-nic)(4)] or its derivatives, might provide potential therapeutic benefits in disorders where reactive nitrogen (RNS) or oxygen (ROS) species are involved.     

Syntheses,characterization and X-ray structures of the fac-[RuCl3(NO)(dppe)] and the trans-[RuCl(NO)(dppe)2]2+ species

Trans-[RuCl(NO)(dppe)2]2+ species were prepared. The complexes have been characterized by microanalysis, IR and 31P[1H] NMR spectroscopy and cyclic voltammetry. The trans-[RuCl(NO)(dppe)2](ClO4)2 complex shows a reversible one-electron-reduction process at E(1/2) = 0.200 V and another one-electron-reduction irreversible process at -0.620 V, both centered at the NO+ group. The dissociation of the NO group from the trans-[RuCl(NO)(dppe)2]2+ after two one-electron reductions results in the formation of the trans- and cis-[RuCl2(dppe)2] isomers. The product of an electrolyzed solution of the same complex at -0.300 V shows an EPR signal consistent with the presence of the [RuCl(NO(0))(dppe)2]+ complex. Crystal data for trans-[RuCl(NO)(dppe)2]2+*[RuCl4(NO)(H2O)]*1/2[RuCl6]4-*2[H2O] (I) and trans-[RuCl(NO)(dppe)(2)]2+*2[RuCl4(NO)(CH3O)]-*3[CH3OH] (II) are as follow: (I) Space group P-1, a=10.4040(3) A, b=12.3470(4) A, c=23.5620(8) A, alpha=95.885(2) degrees, beta=99.608(2) degrees, gamma=104.378(2) degrees, R=0.0521; (II) space group P-1, a=10.9769(2) A, b=13.2753(3) A, c=24.0287(4) A, alpha=99.743(1) degrees, beta=95.847(1) degrees, gamma=97.549(1) degrees; R=0.0496. The fac-[RuCl3(NO)(dppe)] (III) complex has been also prepared; its crystal data are: space group P2(1)/n (No. 14), a=11.841(2) A, b=13.775(2) A, c=16.295(4) A, beta=92.81(2) degrees; R1=0.0395.     

Interaction of cis- and trans-RuCl2(DMSO)4 with the nucleotides GpA, d(GpA), ApG, d(ApG) and d(CCTGGTCC): high-field NMR characterization of the reaction products

 Both cis- and trans-RuCl₂(DMSO)₄ (cis-Ru and trans-Ru) react with ApG, GpA, d(ApG) and d(GpA) to yield products with bifunctional metal coordination of the bases. For each dinucleotide one major product and several minor species are formed. This is in contrast to previous results on analogous reactions between trans-Ru and d(GpG) where a substantial amount of an intermediate species was found. The rates of reaction between dinucleotides and cis-Ru are approximately 20-fold slower than for trans-Ru. The compounds formed with the two isomers exhibit identical proton NMR spectra, suggesting the same coordination mode for ruthenium in the final product. The two purine bases are coordinated to ruthenium through N7 in a head-to-head conformation with the glycosidic angles being in the anti range. Coupling constants indicate a relatively pure 3′-endo conformation for the 5′-sugar and mainly 2′-endo for the 3′-sugar. The similar bifunctional binding mode of cis- and trans-Ru(II) with dinucleotides as evident from the NMR spectra are in contrast to the different mode of interaction suggested earlier for cis- and trans-Ru complexes with DNA. trans-Ru interacts with the deoxyoctanucleotide d(CCTGGTCC), giving two main products during the first 2 h of incubation time. Four H8 guanine resonances are shifted downfield, characteristic of N7 metal coordination. The products are not analyzed in detail, but it is suggested that the structures may be described as two chiral G(N7/N7) chelates. Received: 20 August 1998 / Accepted: 20 January 1999     

A comparative study of adduct formation between the anticancer ruthenium(III) compound HInd trans-[RuCl4(Ind)2] and serum proteins

Formation of adducts between the antitumor ruthenium(III) complex [HInd]trans-[RuCl(4)(Ind)(2)] (KP1019) and the plasma proteins serum albumin and serum transferrin was investigated by UV-vis spectroscopy, for metal-to-protein ratios ranging from 1:1 to 5:1. In both cases, formation of tight metal-protein conjugates was observed. Similar spectroscopic features were observed for both albumin and transferrin derivatives implying a similar binding mode of the ruthenium species to these proteins. Surface histidines are the probable anchoring sites for the bound ruthenium(III) ions in line with previous crystallographic results. In order to assess the stability of the KP1019-protein adducts the influence of pH, reducing agents and chelators was analysed by UV-vis spectroscopy. Notably, there was no effect of addition of EDTA on the UV-vis spectra of the conjugates. The pH-stability was high in the pH range 5-8. Experiments with sodium ascorbate showed that there was just some alteration of selected bands. The implications of the present results are discussed in relation to the pharmacological behavior of this novel class of antitumor compounds.     

NMR study of ammonium ion binding to d[G3T4G4]2 and d[G4(T4G4)3] G-quadruplexes

Quantitative NMR study has shown a significant difference in affinity of (15)NH(4)(+) ions for cation binding sites within G-quadruplexes adopted by d[G3T4G4]2 and d[G4(T4G4)3].     

Synthesis, potentiometric titration, electrochemical investigation and biological properties of trans-[RuCl2(dinic)4] (dinic = 3,5-pyridinecarboxylic acid)

This work discusses both the synthesis of trans-[RuCl2(dinic)4], dinic = 3,5-pyridinecarboxylic acid, and its main characteristics including potentiometric titration, spectroscopic and electrochemical properties, and some biological properties. The complex was synthesized using ruthenium blue solution as the precursor in a synthetic route. The complex was characterized using electronic spectroscopy, vibrational FT-IR spectroscopy, and Raman spectroscopy, as well as 1H and 13C NMR. The results indicated that the complex exhibits a trans-geometry. Cyclic voltammetry carried out in water:acetone 1:1 solution revealed a quasi-reversible process centered on the Ru(II) atom, as well as a dependence of the redox potential, E1/2, on pH. An analysis of the electronic spectra revealed that the MLCT (metal ligand charge transfer) band underwent a hypsochromic shift as the pH increased. Spectroelectrochemical analysis indicated that the visible region band progressively faded out upon oxidation. The equilibrium constants for the eight protons of the complex were determined by potentiometric titration. The complex neither inhibits the activity of nitrogen monoxide synthase nor acts as a scavenger for nitrogen monoxide. Nevertheless, the complex shows antinociceptive properties and acts as a scavenger for hydroxyl radicals.     

On the lability of dimethylsulfoxide (DMSO) coordinated to the [Ru(II)-NO(+)] species: X-ray structures of mer-[RuCl(3)(DMSO)(2)(NO)] and mer-[RuCl(3)(CD(3)CN)(DMSO)(NO)

The syntheses of nitrosyl–dimethylsulfoxide–ruthenium(II) complexes with general formula mer-[RuCl₃(L)(DMSO)(NO)] (L=DMSO or CD₃CN) is reported. The mer-[RuCl₃(DMSO)₂(NO)] (1) complex was obtained from the reaction of [RuCl₃(NO)] with the sulfoxide ligand in acetone. The mer-[RuCl₃(CD₃CN)(DMSO)(NO)] (2) compound was obtained from mer-[RuCl₃(DMSO)₂(NO)] maintained in deuterated acetonitrile. These data suggest a slow kinetic reaction due the low lability of the DMSO ligand coordinated to the {Ru^II–NO⁺} species. The crystal and molecular structures of (1) and (2) have been determined from X-ray studies. Crystal data: for (1), monoclinic, P2₁/c, a=8.8340(2) Å, b=12.0230(3) Å, c=13.7064(4) Å, β=114.546(2)°, Z=4, R1=0.0429; for (2), monoclinic, P21/n, a=10.0180(7) Å, b=9.5070(7) Å, c=13.3340(9) Å, β=102.264(4)°, Z=4, R1=0.0472. The spectroscopic characterization of (1), in solid state (infrared spectrum) and in solution (nuclear magnetic resonance and cyclic voltammetry) is also described.     

Synthesis and characterization of trans-[Pt(NH3)2Cl2] adducts of d(CCTCGAGTCTCC).d(GGAGACTCGAGG)

The reaction of trans-diamminedichloroplatinum(II) (trans-DDP), the inactive isomer of the anticancer drug cisplatin, with the single-stranded deoxydodecanucleotide d(CCTCGAGTCTCC) in aqueous solution at 37 degrees C was monitored by reversed-phase HPLC. Consumption of the dodecamer follows pseudo-first-order reaction kinetics with a rate constant of 1.25 (4) x 10(-4) s-1. Two intermediates, shown to be monofunctional adducts in which Pt is coordinated to the guanine N7 positions, were trapped with NH4(HCO3) and identified by enzymatic degradation analysis. These monofunctional adducts and a third, less abundant, one are rapidly removed from the DNA by thiourea under mild conditions. When allowed to react further, the monofunctional intermediates formed a single main product that was characterized by 1H NMR spectroscopy and enzymatic digestion as the bifunctional 1,3-intrastrand cross-link trans-[Pt(NH3)2[d(CCTCGAGTCTCC)-N7-G(5),N7-G(7]]). Binding of the trans-[Pt(NH3)2]2+ moiety to the guanosine N7 positions decreases the pKa at N1 and leads to destacking of the intervening A(6) base. The double-stranded trans-DDP-modified and unmodified DNAs were obtained by annealing the complementary strand to the corresponding single strands and then studied by 31P and 1H NMR and UV spectroscopy. trans-DDP binding does not induce large changes in the O-P-O bond or torsional angles of the phosphodiester linkages in the duplex, nor does it significantly alter the UV melting temperature. trans-DDP binding does, however, cause the imino protons of the platinated duplex to exchange rapidly with solvent by 50 degrees C, a phenomenon that occurs at 65 degrees C for the unmodified duplex. A structural model for the platinated double-stranded oligonucleotide was generated through molecular dynamics calculations. This model reveals that the trans-DDP bifunctional adduct can be accommodated within the double helix with minimal distortion of the O-P-O angles and only local disruption of base pairing and destacking of the platinated bases. The model also predicts hydrogen bond formation involving coordinated ammine ligands that bridge the two strands.     

Ruthenium-modified proteins. Reactions of cis-[ Ru(NH3)4(OH2)2]2+ and cis-[ Ru(en)2(OH2)2]2+ with azurin,myoglobin and cytochrome c

Reactions of cis-[Ru(en)₂(OH₂)₂]²⁺ (or cis-[Ru (NH₃)₄(OH₂)₂]²⁺) with Pseudomonas aeruginosa azurin (Az), horse heart myoglobin (Mb^h), and horse heart cytochrome c (cyt c) give Ru-labelled proteins. The ruthenium binding sites in the singly modified derivatives are His-83 (Az), His-81 (Mb^h), and His-33 (cyt c). Spectroscopic and electrochemical measurements indicate that the structures of the proteins are not perturbed by the surface-bound ruthenium complexes. The E°_f values of the Ru(III)/(II) couple in these Ru-modified proteins fall between −0.07 and −0.13 V vs. NHE.     

Ligand effects on the binding of cis- and trans-[PtCl2Am1Am2] to proteins

As part of a systematic study of the basic principles that govern the formation and reactivity of Pt-protein adducts, we report the effect of substituting the amine ligand of cis- and trans-[PtCl(2)(NH(3))(2)] complexes with bulkier planar aromatic or nonplanar cyclic amine ligands on the binding properties of the complexes to ubiquitin and to horse heart myoglobin. The ligand replacement had a different effect on the cis or trans isomers investigated. In the cis-Pt complexes, replacing one or both amine ligands by piperidine or 4-picoline dramatically decreased the binding of the complexes to the proteins studied, whereas in the substituted trans-Pt complexes replacement of the amine by a piperidine or 4-picoline increased the binding rate. This behavior may have to do with the different preferred binding sites of the cis- and trans-Pt complexes. The bulkier cis- or trans-Pt complexes investigated also did not display a preference for Met1 of ubiquitin, possibly owing to steric constraints imposed by the substituted ligands. The introduction of a charged piperazine ligand significantly decreased the rate of binding to the protein, possibly owing to electrostatic interactions or hydrogen-bond formations with the surface of the protein. The binding of the complexes to ubiquitin and myoglobin does not disrupt the folding of the proteins as judged by electrospray ionization mass spectrometry.     

The macrocyclic effect and vasodilation response based on the photoinduced nitric oxide release from trans-[RuCl(tetraazamacrocycle)NO](2+)

Irradiation of trans-[RuCl(cyclam)(NO)](2+), cyclam is 1,4,8,11-tetraazacyclotetradecane, at pHs 1-7.4, with near UV light results in the release of NO and formation of trans-[Ru(III)Cl(OH)(cyclam)](+) with pH dependent quantum yields (from approximately 0.01 to 0.16 mol Einstein(-1)) lower than that for trans-[RuCl([15]aneN(4))(NO)](2+), [15]aneN(4) is 1,4,8,12-tetaazacyclopentadecane, (0.61 mol Einstein(-1)). After irradiation with 355 nm light, the trans-[RuCl([15]aneN(4))(NO)](2+) induces relaxation of the aortic ring, whereas the trans-[RuCl(cyclam)(NO)](2+) complex does not. The relaxation observed with trans-[RuCl([15]aneN(4))(NO)](2+) is consistent with a larger quantum yield of release of NO from this complex.     

NMR structural characterization of the reaction product between d(GpG) and the octahedral antitumor complex trans-RuCl2(DMSO)4.

The reaction between the antitumor octahedral complex trans-RuCl2(DMSO)4 and d(GpG) leads to the formation of a stable compound characterized by a covalent bifunctional coordination of the bases to the metal center. The structure of the compound has been fully characterized by NMR and molecular modeling studies, showing the presence of two N7-coordinated guanine moieties in a head to head conformation, two dimethyl sulfoxide molecules, and one halogen atom in the coordination sphere of the ruthenium. The glycosidic chi angles are essentially in the anti range, the sugar puckering of the 5'G is 3'-endo (100% N), whereas that of the 3'G is more flexible but mainly in 2'-endo conformation (85% S), the two bases are strongly destacked. The compound shows structural features which are surprisingly similar to those exhibited by the corresponding cisplatin complex, indicating that such a way of interaction with DNA is not exclusive to Pt or to metals with square planar coordination geometries.     

Circular dichroism spectra of DNA quadruplexes [d(G(5)T(5))](4) as formed with G(4) and T(4) tetrads and [d(G(5)T(5)). d(A(5)C(5))]2 as formed with Watson-Crick-like (G-C)(2) and (T-A)(2) tetrads

We utilize electrophoresis and find that a thermally treated equimolar mixture of the oligonucleotide d(G(5)T(5)) and its complementary oligonucleotide d(A(5)C(5)) exhibits either two bands or a single band in one lane, depending on the conditions of the incubation solutions. The thermally treated d(G(5)T(5)) solution loaded in a different lane exhibits a single band of the parallel quadruplex [d(G(5)T(5))](4), which is composed of homocyclic hydrogen-bonded G(4) and T(4) tetrads previously proposed. For the thermally treated equimolar mixture of d(G(5)T(5)) and d(A(5)C(5)), the fast band is assigned to a Watson-Crick d(G(5)T(5)). d(A(5)C(5)) duplex, so that the slow band with the same low mobility as that of [d(G(5)T(5))](4) may be assigned to either [d(G(5)T(5))](4) itself or a [d(G(5)T(5)). d(A(5)C(5))](2) quadruplex. If the latter compound is true, this may be the antiparallel quadruplex composed of the heterocyclic hydrogen-bonded G-C-G-C and T-A-T-A tetrads proposed previously. After removing these three bands for the duplex and two kinds of hypothetical quadruplexes, we electrophoretically elute the corresponding compounds in the same electrophoresis buffer using an electroeluter. The eluted compounds are ascertained to be stable by electrophoresis. The circular dichroism (CD) and UV absorption spectra measured for the three isolated compounds are found to be clearly different. For the electrophoretic elution of the hypothetical [d(G(5)T(5))](4) quadruplex, the result of the molecularity of n = 4 obtained from the CD melting curve analysis provides further support for the formation of the parallel [d(G(5)T(5))](4) quadruplex already proposed. For the thermally treated equimolar mixture of d(G(5)T(5)) and d(C(5)A(5)), the fast band with a molecularity of n = 2 corresponds to the Watson-Crick duplex, d(G(5)T(5)). d(A(5)C(5)). The slow band with a molecularity of n = 4 indicates the antiparallel quadruplex [d(G(5)T(5)). d(A(5)C(5))](2), whose observed CD and UV spectra are different from those of [d(G(5)T(5))](4). By electrophoresis, after reannealing the eluted compound [d(G(5)T(5)). d(A(5)C(5))](2), a distinct photograph showing the band splitting of this quadruplex band into the lower duplex and upper quadruplex bands is not possible; but by a transilluminator, we occasionally observe this band splitting with the naked eye. The linear response polarizability tensor calculations for the thus determined structures of the [d(G(5)T(5))](4) quadruplex, the McGavin-like [d(G(5)T(5)). d(A(5)C(5))](2) quadruplex, and the Watson-Crick d(G(5)T(5)). d(A(5)C(5)) duplex are found to qualitatively predict the observed CD and UV spectra.     

Specific platinum chelation by the guanines of the deoxyhexanucleotide d(T-G-G-C-C-A) upon reaction with cis-[Pt(NH3)2(H2O)2](NO3)2

The stoichiometric reaction between d-TpGpGpCpCpA (d(T-G-G-C-C-A)) and $\text{cis}$-[Pt(NH₃)₂(H₂O)₂](NO₃)₂ (8.4 × 10^?6 to 1.3 × 10^?4M in water at pH 5.5–6) gives a single complex. High pressure gel permeation chromatography and pH-dependent ¹H NMR analyses of the nonexchangeable base protons, show that it is a platinum chelate with the $\text{cis}$-Pt^II(NH₃)₂ moiety bound to the two N7 atoms of the adjacent guanines. A 3 × 10^?3M reaction gives the same platinum chelate, via the formation of intermediate complexes, together with unsoluble adducts.     

Internal sodium ions and water molecules in guanine quadruplexes: magnetic relaxation dispersion studies of [d(G3T4G3)]2 and [d(G4T4G4)]2

The structural stability of guanine quadruplexes depends critically on an unusual configuration of dehydrated Na (+) or K (+) ions, closely spaced along the central axis of the quadruplex. Crystallography and NMR spectroscopy indicate that these internal ions can be located between the G-quartet planes as well as in the thymine loops, but the precise ion coordination has been firmly established in only a few cases. Here, we examine the bimolecular diagonal-looped foldback quadruplexes [d(G 3T 4G 3)] 2 (Q3) and [d(G 4T 4G 4)] 2 (Q4) by (2)H, (17)O, and (23)Na magnetic relaxation dispersion (MRD). The MRD data indicate that both quadruplexes contain Na (+) ions between the T 4 loops and the terminal G-quartets and that these ions have one water ligand. These ions exchange with external ions on a time scale of 10-60 mus at 27 degrees C, while their highly ordered water ligands have residence times in the range 10 (-8)-10 (-6) s. The MRD data indicate that Q4 contains three Na (+) ions in the stem sites, in agreement with previous solid-state (23)Na NMR findings but contrary to the only crystal structure of this quadruplex. For Q3, the MRD data suggest a less symmetric coordination of the two stem ions. In both quadruplexes, the stem ions have residence times of 0.6-1.0 ms at 27 degrees C. The equilibrium constant for Na (+) --> K (+) exchange is approximately 4 for both loop and stem sites in Q3, in agreement with previous (1)H NMR findings.     

Mechanistic studies on monodentate-ligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine

Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp₃)](BF₄) (pt = 1-propanethiolate, pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine), with I⁻ in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp₃)]⁺ + I⁻ ? [PtI(pt) (pp₃)], and the kinetic parameters for the chemical exchange were obtained as follows: , ΔH⁰ = − 10 ± 2.4 kJ mol⁻¹, ΔS⁰ = − 36 ± 10 J K⁻¹ mol⁻¹, , ΔH^‡ = 34 ± 4.7 kJ mol⁻¹, ΔS^‡ = − 50 ± 21 J K⁻¹ mol⁻¹. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp₃)]Cl with trans-[PtCl₂(NCC₆H₅)₂] in chloroform. From these facts, ligand substitution reactions of [PtX(pp₃)]⁺ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp₃)]⁺ with Br⁻ and I⁻ in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.     

The reaction of Pt-antitumor drugs with selected nucleophiles. I. The reaction of cis-[Pt(NH3)2Cl2] with glycine

Various Pt(II)-glycine coordination compounds were characterized by 1H and 13C NMR spectroscopy, some of them also by electrophoretic and chromatographic behavior. The results were applied to the analysis of the reaction mixtures of cis-[Pt(NH3)2Cl2] and glycine obtained under various conditions. Cis-[Pt(NH3)2Cl2] reacts with glycine to give cis-diammine-(glycine-N,O)-Pt(II) and cis-diammine-bis(glycine-N-)Pt(II). Their ratio depends primarily on the pH of the reaction medium. Conformation of these compounds is discussed based on the observed Pt-C and Pt-H NMR coupling constants.     

Circular dichroism studies of the interaction of a limited hydrolysate of T4 gene 32 protein with T4 DNA and poly[d(A-T)].poly[d(A-T)].

gp32 I is a protein with a molecular weight of 27 000. It is obtained by limited hydrolysis of T4 gene 32 coded protein, which is one of the DNA melting proteins. gp32 I itself appears to be also a melting protein. It denatures poly[d(A-T)].poly[d(A-T)] and T4 DNA at temperatures far (50-60 degrees C) below their regular melting temperatures. Under similar conditions gp32 I will denature poly[d(A-T).poly[d(A-T)] at temperatures approximately 12 degrees C lower than those measured for the intact gp32 denaturation. For T4 DNA gp32 shows no melting behavior while gp32 I shows considerable denaturation (i.e., hyperchromicity) even at 1 degree C. In this paper the denaturation of poly[d(A-T)].poly[d(A-T)] and T4 DNA by gp32 I is studied by means of circular dichroism. It appears that gp32 I forms a complex with poly[d(A-T)]. The conformation of the polynucleotide in the complex is equal to that of one strand of the double-stranded polymer in 6 M LiCl. In the gp32 I DNA complex formed upon denaturation of T4 DNA, the single-stranded DNA molecule has the same conformation as one strand of the double-strand T4 DNA molecule in the C-DNA conformation.