鸟嘌呤和次黄嘌呤的铜络合物的吸附作用和伏安特性研究

本文研究了鸟瞟呤(Gua)和次黄嘌呤(Hxa)铜络合物在悬汞电极(HMDE)上的吸附作用和电极反应机理,溶液中形成的1:1络合物有强烈吸附性,通过分子结构的比较,推断出Cu~(2+)与Gua和Hxa的咪唑环N(7)和外环氧O(6)原子结合形成封闭的五元环。嘌呤环的π-电子有使分子呈平面吸附的趋势,但是Gua络合物分子优先取“倾斜”定向;随着表面吸附浓度增加,Hxa络合物分子存在从“平面”向“垂直”的再定向作用。本文测定了单层吸附浓度、包含的电量和每个分子占据的面积。络合物吸附得到S形等温线,它与Frumkin吸附等温线接近。本文还列出有关吸附参数B、a、△G_A~O和θ~*的计算结果。     

Controlling the self-assembly of a deoxiguaninosine on mica

We report a tapping mode scanning force microscopy investigation on the growth from solutions of a lipophilic deoxiguanosine derivative on the basal plane of a muscovite mica surface. By varying the chemical composition of the substrate surface it is possible to drive the self-assembly towards either layered thin films, which are very likely to consist of guanosine quartets, or nanoribbons, comprising hydrogen bonded networks. Both these two architectures, which are peculiar to the guanine base itself, are of notable importance for the fabrication of molecular nanowires. Moreover, the first arrangement provides evidence that the guanosine is able to behave as ionophore, thus, suggesting its utilization in the development of solid-state ion selective sensors.     

Structure and torsional flexibility of the linkage between guanine and fluorene residues in the deoxyguanosine–aminofluorene and deoxyguanosine–acetylaminofluorene carcinogenic adducts

Potential energy surfaces for rotations around two central CN bonds in N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (AAF–dG) and its deacetylated derivative (AF–dG) were studied using Amber 95 molecular mechanics. Both of these adducts are known to be strong mutagens and carcinogens. New Amber 95 force field parameters were derived for the linkage connecting guanine and fluorene moieties in AAF–dG and AF–dG. For this purpose, we determined ab initio MP2/cc-pVDZ//B3-LYP/6-31G* and polarized continuum model Hartree–Fock/6-31G* potential energy surfaces of smaller model systems that included the N-methylimidazole–acetylaniline and N-methylimidazole–aniline adducts. The molecular mechanics parameters were adjusted to minimize differences between the gas-phase ab initio and molecular mechanics surfaces of these model systems. The resulting parameters were transferred to AF–dG and AAF–dG. The barrier for the rotation of the fluorene residue in AF–dG was found to be less than 2 kcal/mol. Such a small barrier renders the fluorene moiety freely rotatable at room temperature. In contrast, the fluorene rotation in AAF–dG is hindered by a significantly larger barrier of 10 kcal/mol. This barrier corresponds to conformations in which the fluorene and acetyl groups lie in the same plane, and is largely due to steric repulsion. Similarly, the coplanar arrangement of guanine and the bridging amino or acetyl groups is disfavored by 5–10 kcal/mol, with AAF–dG again being the more rigid of the two molecules. Energy minima for a rotation around a bond between guanine and the bridging nitrogen are found at ±80° in AAF–dG, and at 120° and –90° for AF–dG. Overall, the fluorene–dG linkages in AF–dG and AAF–dG adducts have significantly different equilibrium structures and torsional flexibilities. These differences may be contributing factors for the observed disparity in mutagenic effects of these adducts.Electronic Supplementary Material: Supplementary material is available in the online version of this article at Acknowledgements. This work was supported by the NSF REU grant no. CHE-0243825 to Loyola University Chicago. We thank to Tom Ellenberger and Shuchismita Dutta for providing us with their results prior to publication.     

Forever Young: Structural Stability of Telomeric Guanine Quadruplexes in the Presence of Oxidative DNA Lesions**

Human telomeric DNA, in G-quadruplex (G4) conformation, is characterized by a remarkable structural stability that confers it the capacity to resist to oxidative stress producing one or even clustered 8-oxoguanine (8oxoG) lesions. We present a combined experimental/computational investigation, by using circular dichroism in aqueous solutions, cellular immunofluorescence assays and molecular dynamics simulations, that identifies the crucial role of the stability of G4s to oxidative lesions, related also to their biological role as inhibitors of telomerase, an enzyme overexpressed in most cancers associated to oxidative stress.     

Low-potential amperometric determination of purine derivatives through surface oxide regeneration method

This article described a novel amperometry which can be used for determination of purine derivatives including uric acid, xanthine, hypoxanthine, guanine, and adenine without surface contamination. By applying a constant potential of −0.125 V (vs. Ag/AgCl) in a flow injection system, the chelating capability of these purine derivatives converts the cuprous oxide layer into a soluble complex. This behavior would dissolve the passive oxide layer and expose the bottom copper layer to the solution, subsequently; an oxidation current which attributed to the regeneration of the original cuprous oxide layer is used to reflect the concentration of these purine derivatives. In a 50 mM phosphate buffer, pH 7.0, this approach provides a high sensitivity with LOQ of sub-micro molar level of five purines and high stability with a RSD of 2.5% for 10 μM xanthine (N = 12). This method does not suffer from most biological species including ascorbic acid, acetaminophen, creatine, dopamine, sarcosine, ammonium ion, chloride ion, and urea at equal or higher than its physiological concentration.     

Recognition of Guanine by a Designed Triazine-based Fluorescent Probe through Intermolecular Multiple Hydrogen Bonding

A new fluorescent probe with a long-wavelength emission and multiple hydrogen bond sites for guanine, 3-(4-chloro-6-p-nitrophenoxy-1,3,5-triazinylamino)-7-dimethylamino-2-methylphenazine (CNTDP), was designed and synthesized by using cyanuric chloride as a molecular scaffold, neutral red as a fluorophore and p-nitrophenol as an assistant unit. The recognition behavior of CNTDP for guanine and its spectroscopic properties in different solvents were investigated. It was found that the probe's fluorescence can be selectively quenched by guanine instead of thymine, indicating that fully complementary hydrogen bonding plays a key role in such a recognition process. In addition, the fluorescence quenching mechanism of the probe by guanine and the electronic effects of neutral red, triazine ring and p-nitrophenol moieties on the fluorescence of the whole molecule were also discussed.     

盐酸鸟嘌呤与牛血清白蛋白的相互作用

应用荧光光谱、紫外-可见分光光度法研究了盐酸鸟嘌呤(GH)与牛血清白蛋白(BSA)的相互作用。结果表明:GH能猝灭BSA的荧光强度,其猝灭机理为静态猝灭。采用位点结合模型公式和热力学公式计算了结合常数、结合位点数及结合类型。用同步荧光技术研究GH对BSA构象的影响。     

Infrared and Raman Spectra of Solid Guanine Derivatives. 7-METHYLGUANINE, 9-METHYLGUANINE, 9-ETHYLGUANINE, 1,7-DIMETHYLGUANINE,and 1,9-DIMETHYLGUANINE.

The infrared and Raman spectra of 7-methylguanine, 9-methylguanine, 9-ethylguanine, 1,7-dimethylguanine, and 1,9-dimethylguanine in the solid state have been reported and discussed. Hydrogen bonds in these solid guanine derivatives bring about strong perturbations which are discussed in terms of structural data given by X-ray diffraction methods. The spectra of guanine and 9-methylguanine are compared with the spectra of the monomers isolated in low-temperature matrices.     

Modification of guanine residues in PNA-synthesis by PyBOP

The phosphonium-type coupling reagent PyBOP, when applied to the synthesis of peptide nucleic acid (PNA) oligomers, was found to form O⁴-phosphonium compounds of the nucleobase guanine which can be converted into C⁴-modified guanine-derived PNAs by nucleophiles.     

PolyGuanine methacrylate cryogels for ribonucleic acid purification

The isolation and purification of ribonucleic acid have attracted attention recently for the understanding of the functions in detail because of the necessity for the treatment of genetic diseases. In this study, guanine‐incorporated polymeric cryogels were developed to obtain highly purified ribonucleic acid. The satisfactory purification performance was achieved with the guanine‐incorporated poly (2‐hydroxyethyl methacrylate‐guanine methacrylate) cryogels. The most crucial advantages to use guanine as a functional monomer are to obtain a real natural interaction between guanine on the polymeric material and cytosine on the ribonucleic acid. Moreover, using cryogel with a highly porous structure and high swelling ratio provide advantages of getting more water within the structure to get more analyte to interact. The characterization of cryogels has proved the success of the synthesis and the perfect natural interaction to be taken place between the ligand (guanine methacrylate) and the cytosine in the ribonucleic acid molecules. Although the pores within the structure of cryogels are small, they provide efficient and fast adsorption. The chromatographic separation performance was investigated for different conditions (pH, temperature etc.). The desorption ratio and reusability were also analyzed at the end of the five adsorption–desorption cycles with no significant changes.