G-quartet-induced nanoparticle assembly

The design and synthesis of a new class of gold nanoparticle with guanosine monophosphate derivatives or G-rich oligonucleotides as their surface ligands are described. These nanoparticles spontaneously form macroscopic assemblies at low temperature and relatively high salt concentrations, which is attributed to the cooperative formation of guanosine quartets and G-quadruplexes between the individual nanoparticles. Significantly, the solution behavior of these nanoparticles is highly controllable by adjusting solution parameters (including temperature, ionic strength, and ion species) and the sequence of the G-rich oligonucleotide     

SERS studies of the adsorption of guanine derivatives on gold colloidal nanoparticles

Surface enhanced Raman scattering spectra of guanine, guanosine and 2'-deoxyguanosine adsorbed on gold colloidal nanoparticles were obtained. From the striking similarity of the SERS spectra of these compounds, it can be evidenced that guanosine and 2'-deoxyguanosine adsorb on gold nanoparticles through the guanine moiety. The molecular sites involved in the interaction with the gold surface are the same for the 3 compounds: the oxygen of the carbonilic group and the N(7) atom. Guanine, guanosine and 2'-deoxyguanosine adsorb on the gold substrates with a tilted orientation with respect to the metal surface. SERS data were interpreted taking into account density functional theoretical (DFT) calculations of guanine.     

Selective Voltammetric and Flow-Injection Determination of Guanosine and Adenosine at a Glassy Carbon Electrode Modified with a Ruthenium Hexachlororuthenate Film

An inorganic film of ruthenium hexachlororuthenate (RuRuCl₆), deposited on the surface of a glassy carbon electrode, exhibits electrocatalytic activity in the oxidation of purine nucleosides, such as guanosine and adenosine. Appropriate operating conditions are found for fabricating a polymer film on the surface of glassy carbon and for recording the maximum electrocatalytic current for the modified electrode. A method for the selective voltammetric determination of guanosine and adenosine in their simultaneous presence at an electrode modified by a RuRuCl₆ film is developed. A procedure is proposed for the amperometric detection of purine nucleosides with this modified electrode under the conditions of flow-injection analysis. The linear dependence of the analytical signal on the concentration of guanosine and adenosine is observed up to 5 × 10^–6 M in the stationary mode and up to 5 × 10^–7 M in the flow system. The proposed method for the selective determination of guanosine and adenosine was tested in the analysis of human urine.     

Excitation of vibrations in microtubules in living cells

Microtubules, which are thought to be the primary organizers of the cytoskeleton, are electrical polar structures with extraordinary elastic deformability at low stress and with energy supply from hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP). At least a part of the energy supplied from hydrolysis can excite vibrations. Energy is mainly lost by viscous damping of the surrounding cytosol. Viscous damping is diminished by a slip layer which is formed by an attracted ionic charge layer and by a thin surface layer of the microtubule. Relaxation time caused by viscous damping may be several orders of magnitude greater than period of vibrations at 10 MHz. Energy supplied to the microtubule is of the order of magnitude of 10(-14) W cm(-1) (per unit length of the microtubule).     

Quantum dot nanocrystals having guanosine imprinted nanoshell for DNA recognition

Molecular imprinted polymers (MIPs) as a recognition element for sensors are increasingly of interest and MIP nanoparticles have started to appear in the literature. In this study, we have proposed a novel thiol ligand-capping method with polymerizable methacryloylamido-cysteine (MAC) attached to CdS quantum dots (QDs), reminiscent of a self-assembled monolayer and have reconstructed surface shell by synthetic host polymers based on molecular imprinting method for DNA recognition. In this method, methacryloylamidohistidine-platinium (MAH-Pt(II)) is used as a new metal-chelating monomer via metal coordination-chelation interactions and guanosine templates of DNA. Nanoshell sensors with guanosine templates give a cavity that is selective for guanosine and its analogues. The guanosine can simultaneously chelate to Pt(II) metal ion and fit into the shape-selective cavity. Thus, the interaction between Pt(II) ion and free coordination spheres has an effect on the binding ability of the CdS QD nanosensor. The binding affinity of the guanosine imprinted nanocrystals has investigated by using the Langmuir and Scatchard methods, and experiments have shown the shape-selective cavity formation with O6 and N7 of a guanosine nucleotide (K(a) = 4.841x10(6) mol L(-1)) and a free guanine base (K(a) = 0.894x10(6) mol L(-1)). Additionally, the guanosine template of the nanocrystals is more favored for single stranded DNA compared to double stranded DNA.     

鸟嘌呤、鸟苷及其甲基化衍生物的近红外傅里叶变换表面增强拉曼光谱

本文给出了采用表面增强傅里叶变换拉曼光谱法测定的鸟嘌呤、鸟苷及其甲基化衍生物的拉曼散射。实验结果表明，采用了近红外波长的拉曼散射及傅里叶变换技术成功地获得鸟嘌呤、鸟苷及其甲基化衍生物的水溶液在较低浓度下（0．1～0．01mg／L）不受荧光干扰的拉曼光谱图，其频率与相对强度分布表明，水溶液状态下吸附在Ag膜上的鸟嘌呤（苷）及其衍生物结构中的有关振动谱带r（C＝O）、NH2和杂环上的N获得显著增强。本文对水溶液鸟嘌呤（苷）及其衍生物的FT－Raman谱带的归宿进行了讨论。     

Electrochemical Oxidation of Guanosine and Xanthosine at Physiological pH: Further Evidences of a Convergent Mechanism for the Oxidation of Purine Nucleosides

The electrochemical oxidation of guanosine and xanthosine, which only differ in the presence of an oxygen atom at C2 position instead of an amine group, is studied on pyrolytic graphite electrodes at different electrolysis time scales in solutions of physiological pH. The oxidation products adsorbed on the electrode surface were electrochemical characterized in terms of variation of the formal potential with pH and catalytic activity towards the oxidation of NADH. The results were compared with those previously described for the oxidation of guanosine and adenosine in alkaline solutions. A common oxidation product is described, the oxidized form of 9‐β‐D ‐ribofuranosyluric acid, which is proposed as the point of convergence in the oxidation routes of all three purine nucleosides.     

Guanosine tetra- and pentaphosphate analysis: PEI-cellulose thin-layer purification and luciferin-luciferase liquid scintillation quantitation

A system is presented that can separate and quantitate in picomole amounts various guanosine tetra and penta phosphates namely guanosine 5′ triphosphate, 3′ diphosphate (pppGpp), guanosine 5′ tetraphosphate (ppppG), and diguanosine 5′ tetraphosphate (GppppG). It was found to be inactive with guanosine 5′ diphosphate, 3′ diphosphate (ppGpp), and a synthetic compound pCppG.The analytical detection system uses a crude firefly luciferin-luciferase system in which the various derivatives probably transphosphorylate ADP to produce the ATP necessary to emit light with the luciferin-luciferase system.The system should be useful in quantitating reactions in which guanosine tetraphosphates and pentaphosphates are involved. Their role is apparently one of control at either RNA polymerase or ribosomal levels and should be important in further research in molecular biology.     

Stacked and continuous helical self-assemblies of guanosine monophosphates detected by vibrational circular dichroism

The aim of this study was to characterize self-assembled structures of guanosine derivatives in aqueous solutions by vibrational circular dichroism (VCD) and electronic circular dichroism (ECD). Three guanosine derivatives were studied [5'-guanosine monophosphate (GMP), diphosphate (GDP), and triphosphate (GTP)] using a broad range of concentrations and various metal/guanosine ratios. VCD was used for the first time in this field and showed itself to be a powerful method for obtaining specific structural information in solution. It can also help to determine the impact that the cations have, when added to the solution, on the versatile structures of guanine derivatives in terms of their association and disassociation. Based on the markedly different intensities and signs of the VCD signals observed for different concentrations of guanosine derivatives, we propose various structures based on guanine quartets for high guanosine concentrations and high K(+)/guanosine ratios (i.e., columnar helical organization of the quartets, which are rearranged into a continuous helix). We performed a degenerate coupled oscillator (DCO) calculation to interpret the VCD spectra obtained and how they vary during the assembly of guanosine derivatives. The calculations correctly predicted the VCD spectra and enabled us to identify the structures of the metal cation/guanosine monophosphate aggregates. ECD in the ultraviolet region was used as a diagnostic tool to characterize the studied systems and as a contact point between the previously defined structures of the guanine derivative assemblies and the molecular systems studied here. These studies revealed that the VCD technique is a powerful new method for determining the structures of optically active guanosine motifs.     

Effect of GTP and GDP nucleotides on vinblastine binding affinity to tubulin: a DFT study

Vinblastine (VLB) is an anticancer agent that inhibits microtubule assembly by binding with tubulin. Density functional theory (DFT) calculations are used to examine low-energy minima of the energy surface of vinblastine-tubulin complex. Thermodynamic data of the binding site of vinblastine to tubulin are extracted with the hybrid DFT (B3LYP (Becke, three-parameter, Lee–Yang–Parr)) method, and then the influence of several solvents, such as water, methanol and ethanol, and different temperatures are discussed on infrared parameters by self-consistent reaction field (SCRF = dipole) method. The effect of guanosine triphosphate (GTP) and guanosine diphosphate (GDP) nucleotides on vinblastine binding affinity to tubulin was realised in water solvent by comparing the changes of ?G (Gibbs free energy) of VLB-tubulin and VLB-tubulin bonded to GTP or GDP. The result showed that GDP and GTP increase significantly the binding affinity and the role of GDP is more important than that of GTP.     

Method of determining the position of guanosine residues in oligodeoxyribonucleotides

A method is proposed for determining the position of guanosine residues in oligo-deoxyribonucleotides. After limited modification of the oligonucleotide with glyoxal, a mixture of molecules of the initial oligonucleotide with different degrees of modification is formed. In the presence of borate ions, the glyoxal-modified guanosine residues form negatively charged borate complexes which inhibit the action of snake venom phosphodiesterase. The treatment of such a complex with the enzyme forms a mixture of fragments of the initial oligonucleotide the 5-terminal sequences of which are identical while at the 3-end there are modified guanosine residues. The determination of the length of these fragments provides the necessary information on the positions of the guanosine residues in the chain of the initial oligonucleotides. The positions of the guanosine residues in eight synthetic oligodeoxyribonucleotides have been confirmed with the aid of the method developed.A. N. Belozerskii Interfaculty Problem Scientific-Research Laboratory of Molecular Biology and Bioorganic Chemistry of the M. V. Lomonosov Moscow State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 570–573, July–August, 1979.     

The stepwise supramolecular organisation of guanosine derivatives

Several supramolecular architectures generated by guanosine derivatives are described. The research started from the fortuitous observation of a lyotropic behavior exhibited by a guanylic nucleotide in water. This observation stimulated extensive research on several natural and lipophilic guanosine derivatives which self-assemble in different architectures (discs, ribbons, helices...), according to their structure and environment. These ordered structures can be used as scaffolds for photo- or electro-active moieties and for the fabrication of molecular electronic devices.     

Insight into the deamination mechanism of 6-cyclopropylamino guanosine analogs for anti-HIV drug design

Deamination is a crucial step in the transformation of 6-cyclopropylamino guanosine prodrug to its active form. A convenient method using capillary electrophoresis (CE) without sample labeling was developed to analyze the deamination of a series of D-/L-6-cyclopropylamino guanosine analogs by mouse liver homogenate, mouse liver microsome, and adenosine deaminase (ADA). A two-step process involving a 6-amino guanosine intermediate formed by oxidative N-dealkylation was demonstrated in the metabolism of 6-cyclopropylamino guanosine to 6-hydroxy guanosine. The results indicated that the transformation rates of different prodrugs to the active form varied greatly, which were closely correlated with the configuration of nucleosides and the structure of glycosyl groups. Most importantly, D-form analogs were metabolized much faster than their L-counterparts, thus clearly pointed out that compared to guanine, modification of glycosyl part might be a better choice for the development of L-guanosine analogs for the treatment of HIV.     

Highly Specific Recognition of Guanosine Using Engineered Base-Excised Aptamers

Purines and their derivatives are highly important molecules in biology for nucleic acid synthesis, energy storage, and signaling. Although many DNA aptamers have been obtained for binding adenine derivatives such as adenosine, adenosine monophosphate, and adenosine triphosphate, success for the specific binding of guanosine has been limited. Instead of performing new aptamer selections, we report herein a base-excision strategy to engineer existing aptamers to bind guanosine. Both a Na⁺-binding aptamer and the classical adenosine aptamer have been manipulated as base-excising scaffolds. A total of seven guanosine aptamers were designed, of which the G16-deleted Na⁺ aptamer showed the highest bindng specificity and affinity for guanosine with an apparent dissociation constant of 0.78 mm . Single monophosphate difference in the target molecule was also recognizable. The generality of both the aptamer scaffold and excised site were systematically studied. Overall, this work provides a few guanosine binding aptamers by using a non-SELEX method. It also provides deeper insights into the engineering of aptamers for molecular recognition.     

Gas-phase formation of radical cations of monomers and dimers of guanosine by collision-induced dissociation of Cu(II)-guanosine complexes

An electrosprayed water/methanol solution of guanosine and Cu(NO3)2 was observed to give rise to gas-phase copper complexed ions of [CuLn]*2+, [CuL(MeOH)n]*2+, and [CuG n(NO3)]*+, as well as the ions [L]*+, [L+H]+, [G]*+, and [G+H]+ (L=guanosine, G=guanine). The Collision-Induced Dissociation (CID) of [CuL3]*2+ and [CuL(MeOH)n]*2+ (n=2, 3) generates guanosine radical cations [L]*+, while dimeric guanosine radical cations [L2]*+ are generated in the dissociation of [CuL4]*2+. Protonated guanosine [L+H]+ is one of the main products in the primary dissociation of [CuL2]*2+, while the dissociation of the higher-order [CuG2]*2+ produces the [G]*+ radical cation. The guanosine dimer radical cation, [L2]*+ presumably arises from the interaction of two guanosine molecules via proton and hydrogen bonding and is observed to dissociate into [L+H]+ and [L-H]* at low energies. We propose that the first two ligands bind strongly with Cu(II) through N7 and O6 to form a [CuL2]*2+ complex with a four-coordinated planar structure and that a third ligand binds loosely with copper to form [CuL3]*2+. Additional ligation observed in the formation of [CuLn]*2+ (n相似文献   

Electrochemical behaviors of guanosine on carbon ionic liquid electrode and its determination

The electrochemical behaviors of guanosine on the ionic liquid of N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CPE) was studied in this paper and further used for guanosine detection. Guanosine showed an adsorption irreversible oxidation process on the carbon ionic liquid electrode (CILE) with the oxidation peak potential located at 1.12 V (vs. SCE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with that on the traditional carbon paste electrode, small shift of the oxidation peak potentials appeared but with a great increment of the oxidation peak current on the CILE, which was due to the presence of ionic liquid in the modified electrode adsorbed the guanosine on the surface and promoted the electrochemical response. The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n), and the electrode reaction standard rate constant (k_s) were calculated as 0.74, 1.9 and 1.26 × 10⁻⁴ s⁻¹, respectively. Under the optimal conditions the oxidation peak current showed a good linear relationship with the guanosine concentration in the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol/L by cyclic voltammetry with the detection limit of 2.61 × 10⁻⁷ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine oxidation. The CILE showed good ability to distinguish the electrochemical response of guanosine and guanine in the mixture solution. The urine samples were further detected by the proposed method with satisfactory results.     

Sensitive and selective fluorescence detection of guanosine nucleotides by nanoparticles conjugated with a naphthyridine receptor

Novel fluorescent nanosensors, based on a naphthyridine receptor, have been developed for the detection of guanosine nucleotides, and both their sensitivity and selectivity to various nucleotides were evaluated. The nanosensors were constructed from polystyrene nanoparticles functionalized by (N-(7-((3-aminophenyl)ethynyl)-1,8-naphthyridin-2-yl)acetamide) via carbodiimide ester activation. We show that this naphthyridine nanosensor binds guanosine nucleotides preferentially over adenine, cytosine, and thymidine nucleotides. Upon interaction with nucleotides, the fluorescence of the nanosensor is gradually quenched yielding Stern–Volmer constants in the range of 2.1 to 35.9 mM⁻¹. For all the studied quenchers, limits of detection (LOD) and tolerance levels for the nanosensors were also determined. The lowest (3σ) LOD was found for guanosine 3’,5’-cyclic monophosphate (cGMP) and it was as low as 150 ng/ml. In addition, we demonstrated that the spatial arrangement of bound analytes on the nanosensors’ surfaces is what is responsible for their selectivity to different guanosine nucleotides. We found a correlation between the changes of the fluorescence signal and the number of phosphate groups of a nucleotide. Results of molecular modeling and ζ-potential measurements confirm that the arrangement of analytes on the surface provides for the selectivity of the nanosensors. These fluorescent nanosensors have the potential to be applied in multi-analyte, array-based detection platforms, as well as in multiplexed microfluidic systems.     

Synthesis and PMR spectra of 7-hydroxyalkylguanosinium acetates

Guanosine and 9-methylguanine treated with epoxides in glacial acetic acid are hydroxyalkylated stereoselectively at the N₇ position of the guanine moiety. Previously unreported 7-(hydroxyalkyl)guanosinium acetates from the reactions of six epoxides with guanosine and 7-(hydroxyalkyl)-9-methylguaninium acetates from the reactions of two epoxides with 9-methyl guanine in glacial acetic acid have been prepared and characterized by their pmr spectra. By using an excess of epoxide, quantitative conversion of guanosine or 9-methylguanine to the corresponding 7-hydroxyalkylguanosinium or 7-hydroxyalkyl-9-methylguaninium acetate was achieved. Comparisons of the pmr spectra of the 7-(hydroxyalkyl)guanosinium acetates in DMSO-d₆ to the spectrum of guanosine reveal that the H₈ and amino group proton absorptions common to guanosine are shifted to a lower field, the absorptions of the H₁ proton is absent, and the coupling constant of the H′₁-H′₂ protons of the ribosyl group is decreased from about 5.7 ± 0.1 Hz in guanosine to about 3.5 ± 0.1 Hz in the products. The use of the pmr spectral features of 7-(hydroxyalkyl)-9-methylguaninium compounds in characterizing 7-hydroxyalkylguanosinium compounds is discussed. Evidence is presented which suggests that extensive delocalization of positive charge exists in both the pyrimidine and imidazole rings of N₇-hydroxyalkylated guanosine and N₇-hydroxyalkylated-9-methylguanine. The possible effects of charge delocalization upon the hydrogen bonding potential of 7-hydroxyalkylated guanine moieties in DNA is discussed.     

Analysis of Guanylate Cyclase Activity by High-Pressure Liquid Chromatography

Abstract

A method for the assay of guanylate cyclase which permits the correction of concurrent phosphatase and phosphodiesterase reactions has been developed using HPLC. The method, based on the conversion of tritium labelled guanosine triphosphate to tritium labelled cyclic guanosine monophosphate, uses [¹⁴C]-cGMP as the internal standard to account for the degradative and procedural-losses. Radiolabelled reaction products are isolated by high pressure liquid chromatography on a Partisil SAX column with a single step isocratic elution using 12.5 mM potassium phosphate buffer (pH 3.25). Since column recovery of the nucleotides is virtually quantitative and complete purification is achieved, the method possesses a high degree of accuracy and precision.