The 31 P NMR spectra of (TMA) 2 (5′-GMP), where TMA is [(CH 3 ) 4 N] + and 5′-GMP is guanosine 5′-monophosphate, and K 2 (5′-GMP), containing various amounts of KCl or TMACl, have been obtained at 2 °C. Variable-temperature spectra have also been obtained for K 2 (5′-GMP). The TMA + ion serves to neutralize the charge on the dianionic 5′-GMP and permits the added K + to bond preferentially in structureforming sites. 1 H NMR spectra (one-and two-dimensional) have been obtained for K 2 (5′-GMP) and used to assign the proton resonances in the self-associated structures and determine that all residues have the anti glycosidic conformation. The 31 P and 1 H NMR spectra are very complex and indicate the presence of a large number of molecular environments and a structural variation dependent upon the mole ratio of 5′-GMP to K + . A new model for the solution structure is proposed in which the 5′-GMP forms a pseudofour-stranded helix with guanine-guanine hydrogen bonding forming a continuous helical strand, rather than the usual planar G-tetrad structure. The guanine-guanine hydrogen bonding sites are the same as that found in a G-tetrad. The K + ions would be located in the center of the helix and bonding to the carbonyl oxygens. They are interacting with the phosphates as well. Integration data from the largest sized species give an estimate of 14.3 ( 1.1 residues in a helical structure.

Abstract[Au(en)Cl 2 ]Cl·2H 2 O has been synthesized and its structure has been solved for the first time by the single crystal X-ray diffraction method. The complex has square planar geometry about the Au(III) and the anionic Cl − is located in the apical position and at a distance of 3.3033(10) Å compared to 2.2811 (9) 3+ . 1 H, 13 C, and 31 P NMR reveal that in aqueous solution [Au(en)Cl 2 ] + bonds to guanosine 5'-monophosphate, 5'-GMP, (1:1 mole ratio) via N7, although the stability is not very high. NMR data also indicate that N7-O6 or N7-phosphate 5'-GMP chelation, as found in some Au(III)-nucleotide complexes, is not present. The Au(III) complex undergoes hydrolysis at pH > 2.5−3.0 and, therefore N1 coordination to 5'-GMP is not observed. No direct coordination between 5'-GMP and [Au(en) 2 ]Cl 3 is observed. KeywordsGold(III); guanosine 5'-monophosphate; NMR; cyclic voltammetry; X-ray structure Gold(III) complexes are isoelectronic and generally isostructural to platinum(II) complexes, and therefore it is anticipated that they will have similar activity to the Pt(II) antitumor drugs.1-5 However, compared to the corresponding Pt(II) complexes, Au(III) complexes have not been well explored chemically or electrochemically, possibly because few gold(III) complexes have been shown to be sufficiently stable in aqueous solution.6,7Ethylenediamine (en) is a common chelating ligand that is widely used in transition metal complexes. Its gold complexes have been known since 1931,8-10 Methods and Materials MaterialsNaAuCl 4 ·2H 2 O, ethylenediamine, D 2 O, and dmso-d 6 were purchased from Aldrich Chemical Co. and used as received. H 2 (5'-GMP) and Na 2 (5'-GMP) were purchased from Sigma and used as received. All solutions other than those for NMR measurements were prepared using deionized water that was purified with a Barnstead NANOpure cartridge system (18 MΩ). Nucleotide Stock Solutions-Na 2 (5'-GMP) or H 2 (5'-GMP) was dissolved in H 2 O or D 2 O and the concentration of the nucleotide was determined by UV spectroscopy (λ max 252 nm; ε = 1.37 × 10 4 M −1 cm −1 ; pH 7). The required amount of Au(III) compound was added to the 5'-GMP solution. Syntheses MethodsThermogravimetric Analysis-Measurements were made on a Shimadzu TGA-50 analyzer under N 2 atmosphere with a flow rate of 20 mL min −1 in a Pt cell. Samples weighed 3−7 mg. The temperature increased at 20 °C min −1 from room temperature to 900°C .NMR-Spectra were obtained in D 2 O on a Varian Inova 500 MHz in D 2 O. The temperature dependent 1 H studies were referenced to internal tetramethylammonium ion at 3.185 ppm and the spectra at 26 °C were referenced to the HOD line at 4.800 ppm (The TMA + resonance is very near that of ethylenediamine and can overlap at times). 31 P spectra were referenced to external 85 % H 3 PO 4 and 13 C spectra to DSS. pD = pH (meter reading) + 0.40.Electrochemical Measurements-A CHI 832 workstation (CH Instruments, Inc.) was used to collect electrochemical data. Experiments were performed at room temperature (20 ± 1 °C) in ...

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The self-association of 2-pyrrolidinone in cyclohexane and in carbon tetrachloride has been investigated using infrared and Raman spectroscopy and dielectric polarization measurements. In CC14 solutions up to 0.3 M the results have been interpreted as being indicative of the presence of monomers, dimers, and trimers. A computer fit of the data gives a dimerization constant, K1, of 118 ± 30 M_1 and a trimerization constant, K2, of 15 ± 10 M-1. The dipole moments of the species in CC14 are 3.74, 1.64, and 3.8 D for the monomer, dimer, and trimer, respectively. The Raman and infrared spectra show that the dimer probably has a cyclic, essentially planar structure and, along with the magnitude of the dipole moment, suggest that the trimer is also a cyclic species. The presence of some acyclic dimer and trimer as well as small amounts of higher oligomers cannot be excluded. In cyclohexane the predominant species appear to be the monomer and dimer although no model system was found which would best fit the experimental electric moment data. The dipole moment of the monomeric species in cyclohexane has been found to be 3.3 D by a graphical procedure. Selfassociation of 2-pyrrolidinone does not occur in 1,4-dioxane and the dipole moment in this solvent is 3.80 trans conformation, when < 9 it adopts the cis conformation and when = 9 both cis and trans isomers coexist.1-3 Dielectric polarization measurements indicate that the trans lactams undergo self-association in non-polar solvents forming chain oligomers while cis lactams form predominantly cyclic dimers.3 Numerous infrared spectroscopic investigations of dilute solutions of 2-pyrrolidinone and other cis lactams in carbon tetrachloride have been reported. In all cases the data and the thermodynamic parameters derived from it were interpreted on the basis of a two species system: monomer and cyclic dimer.4-9 However, in their study of e-caprolactam in CC14, Lord and Porro noted that they did not obtain a constant value for the dimerization constant for solutions with a concentration greater than about 0,2 M.9 Vapor phase osmometry was used to investigate the function of ring size on the selfassociation of a series of lactams in benzene10 and equilibrium constants and thermodynamic parameters were determined assuming a monomer-dimer system. Ebullioscopic mea-D.