Guanosine Molecules Research Articles

Guanosine-driven hyaluronic acid-based supramolecular hydrogels with peroxidase-like activity for chronic diabetic wound treatment

Guanosine is often used to construct supramolecular hydrogels due to its self-assembly properties, however, the high temperature and strong alkaline construction methods greatly limit its application in biomedical fields. In this work, a guanosine-driven hyaluronic acid-based supramolecular hydrogel was developed under mild condition by employing phenylboronic acid-functionalized hyaluronic acid (HA-PBA) backbone and guanosine molecules. Guanosines self-assembled into G-quartet planes under potassium ion conditions, and formed boronic ester bonds with HA-PBA, which induced rapid formation of dynamically cross-linked hydrogels. Hemin was then binding to the G-quartet plane via π-π interactions in the hydrogels, which exhibited peroxidase activity and were highly effective in killing bacteria by generating hydroxyl radicals in the presence of H2O2. Furthermore, glucose oxidase (GOx) was incorporated into the hydrogels and the HP/G@hemin@GOx hydrogels showed good antibacterial properties, modulation of wound glucose and ROS level, and good therapeutic efficacy for diabetic chronic wounds. Overall, the self-assembly of guanosine has been shown for the first time to be a feasible method for constructing natural polymer-based supramolecular hydrogels. This guanosine-driven HA-based supramolecular hydrogel can act as a potential wound dressing for chronic diabetic wound treatment. Statement of significanceChronic wound repair remains an unsolved clinical challenge. Herein, we propose to utilize phenylboronic acid-modified hyaluronic acid and guanosine to construct supramolecular gels with peroxidase activity for chronic wound treatment. The self-assembly behavior of guanosine drives the natural macromolecular backbone to form the hydrogel, and the proposed method simplifies the gelation conditions and improves its biosafety. The G-quartets formed by the self-assembly of guanosine can act as the loading site for hemin. G-quartet/hemin complex imported peroxidase activity to the hydrogels, endowing them with the ability to kill bacteria and regulate ROS levels of cells in the wound site. This guanosine-driven supramolecular hydrogel significantly increased the rate of wound healing in diabetic mice, promising a new strategy for chronic wound treatment.

Improving the accuracy of GIPAW chemical shielding calculations with cluster and fragment corrections

Ab initio methods for predicting NMR parameters in the solid state are an essential tool for assigning experimental spectra and play an increasingly important role in structural characterizations. Recently, a molecular correction (MC) technique has been developed which combines the strengths of plane-wave methods (GIPAW) with single molecule calculations employing Gaussian basis sets. The GIPAW + MC method relies on a periodic calculation performed at a lower level of theory to model the crystalline environment. The GIPAW result is then corrected using a single molecule calculation performed at a higher level of theory. The success of the GIPAW + MC method in predicting a range of NMR parameters is a result of the highly local character of the tensors underlying the NMR observable. However, in applications involving strong intermolecular interactions we find that expanding the region treated at the higher level of theory more accurately captures local many-body contributions to the N15 NMR chemical shielding (CS) tensor. We propose alternative corrections to GIPAW which capture interactions between adjacent molecules at a higher level of theory using either fragment or cluster-based calculations. Benchmark calculations performed on N15 and C13 data sets show that these advanced GIPAW-corrected calculations improve the accuracy of chemical shielding tensor predictions relative to existing methods. Specifically, cluster-based N15 corrections show a 24% and 17% reduction in RMS error relative to GIPAW and GIPAW + MC calculations, respectively. Comparing the benchmark data sets using multiple computational models demonstrates that N15 CS tensor calculations are significantly more sensitive to intermolecular interactions relative to C13. However, fragment and cluster-based corrections that include direct hydrogen bond partners are sufficient for optimizing the accuracy of GIPAW-corrected methods. Finally, GIPAW-corrected methods are applied to the particularly challenging NMR spectral assignment of guanosine dihydrate which contains two guanosine molecules in the asymmetric unit.

New insight into the ultrafast excited state deactivation mechanism of guanosine in the gas phase

The deactivation process of guanosine molecule on the first singlet excited state in the gas phase has been explored through the density functional theory (DFT/TDDFT) and the complete active space self-consistent field (CASSCF) methods. To unravel the decay mechanism of this system, the topography of excited potential energy surfaces relevant to the deactivation process were mapped. Two deactivation decay channels characterized by the excited state intramolecular proton transfer process and the puckering motion of ring were explored, and the latter one was proposed to play significant roles in the deactivation process of guanosine for the barrierless energy profile. However, the probability for the excited state intramolecular proton transfer process pathway is lower because of the existence of an energy barrier. This conclusion was further confirmed by the two minimum energy conical intersections (MECIs) located between S1 and S0 states, characterized by the ESIPT process and pyramidalization of the C2 atom, respectively. In addition, by comparing the decay mechanism with the previously reported adenosine and pyrimidine nucleosides, it was found that two competitive decay pathways coexist in the purine nucleosides, which is different from the pyrimidine nucleosides. As the next step in the bottom-up investigation of the DNA photostability properties, the new mechanism of the guanosine in gas phase will be conducive for more comprehensive understanding of the photostability of DNA and RNA molecules and provide theoretical guidance for the investigation of the different decay mechanism of the purine nucleosides and pyrimidine nucleosides.

Controlled supramolecular structure of guanosine monophosphate in the interlayer space of layered double hydroxide.

Guanosine monophosphates (GMPs) were intercalated into the interlayer space of layered double hydroxides (LDHs) and the molecular arrangement of GMP was controlled in LDHs. The intercalation conditions such as GMP/LDH molar ratio and reaction temperature were systematically adjusted. When the GMP/LDH molar ratio was 1:2, which corresponds to the charge balance between positive LDH sheets and GMP anions, GMP molecules were well-intercalated to LDH. At high temperature (100 and 80 °C), a single GMP molecule existed separately in the LDH interlayer. On the other hand, at lower temperature (20, 40 and 60 °C), GMPs tended to form ribbon-type supramolecular assemblies. Differential scanning calorimetry showed that the ribbon-type GMP assembly had an intermolecular interaction energy of ≈101 kJ/mol, which corresponds to a double hydrogen bond between guanosine molecules. Once stabilized, the interlayer GMP orientations, single molecular and ribbon phase, were successfully converted to the other phase by adjusting the external environment by stoichiometry or temperature control.

Analysis of the [CuL n ]2+ and [CuG n ]2+ (n = 2–4) complex structures: Comparison with CID experiment and DFT calculation

The collision-induced dissociation (CID) of the copper-cytidine complex [CuL n ]2+ (L is cytidine, n = 2–4) shows that the inter-ligand proton transfer (PT) is the dominating process. This is quite different from the CID of copper-guanosine complex [CuG n ]2+ (G is guanosine, n = 2–4), in which the inter-electron transfer (ET) dominates. The possible structures and zero-point energies for the majority of these structures were calculated using density functional theory (DFT) methods, and the ΔG Gibbs energy analysis of the CID processes also demonstrated the difference between the two complex structures. The results show that the steric hindrance effects and the intermolecular hydrogen bonds are the main reasons that cause the coordination between Cu(II) and the ligands of the cytidine and guanosine molecule. Cu(II) coordinates 4 ligands for [CuL n ]2+, forming the primary order sphere and presenting non-covalent bonding of the ligands. A greater steric effect was observed in the purine ring, which could be unstable if the guanosine molecules distributed around the copper ions to form coordination compounds. The [CuG n ]2+ complex tends to form intermolecular hydrogen bonds to enhance its structural stability by amino N and carbonyl O of purine ring.

New tetrads formed by deprotonated guanosine molecules and stabilized by alkali earth metal cations, as studied by electrospray ionization mass spectrometry

New tetrads formed by deprotonated guanosine molecules and stabilized by alkali earth metal cations, as studied by electrospray ionization mass spectrometry

Role of RelA and SpoT in Burkholderia pseudomallei virulence and immunity.

Burkholderia pseudomallei is a Gram-negative soil bacterium and the causative agent of melioidosis, a disease of humans and animals. It is also listed as a category B bioterrorism threat agent by the U.S. Centers for Disease Control and Prevention, and there is currently no melioidosis vaccine available. Small modified nucleotides such as the hyperphosphorylated guanosine molecules ppGpp and pppGpp play an important role as signaling molecules in prokaryotes. They mediate a global stress response under starvation conditions and have been implicated in the regulation of virulence and survival factors in many bacterial species. In this study, we created a relA spoT double mutant in B. pseudomallei strain K96243, which lacks (p)ppGpp-synthesizing enzymes, and investigated its phenotype in vitro and in vivo. The B. pseudomallei ΔrelA ΔspoT mutant displayed a defect in stationary-phase survival and intracellular replication in murine macrophages. Moreover, the mutant was attenuated in the Galleria mellonella insect model and in both acute and chronic mouse models of melioidosis. Vaccination of mice with the ΔrelA ΔspoT mutant resulted in partial protection against infection with wild-type B. pseudomallei. In summary, (p)ppGpp signaling appears to represent an essential component of the regulatory network governing virulence gene expression and stress adaptation in B. pseudomallei, and the ΔrelA ΔspoT mutant may be a promising live-attenuated vaccine candidate.

DBU induced formation of 8-bromoguanosine dimer with three hydrogen bonds between the GG − base pairs

Upon hemideprotonation of 8-bromoguanosine (8-BrG) at the N1 position, induced by DBU, the adduct [8-BrG][8-BrG] −[DBU–H] + was formed. Slow evaporation of the 8-BrG methanol solution, in the presence of 0.5 equiv of DBU, yielded two polymorphic structures ( 1 and 2), where a neutral [8-BrG] ( A) and N1 deprotonated, anionic 8-bromoguanosine [8-BrG] − ( B) were joined together through three intermolecular hydrogen bonds involving O6, N1 and C2–NH 2 sites. Such pairing gave planar GG − dimers as the basic motif of crystal packing in both polymorphs. Both neutral and deprotonated guanosine molecules in the structure of 1 had the ribose units in a syn conformation. In the structure of polymorph 2, the N1 deprotonated guanosine molecule ( B) retained the syn glycosidic conformation, while the non-deprotonated guanosine molecule ( A) adopted the natural anti conformation of the ribose unit with respect to the nucleobase. Ribose rings revealed different puckering; only those of deprotonated molecules 1B and 2B possessed the usual C2′- endo envelope conformation. Crystal packing in both structures was guided by the highly complex H-bonded pattern. The CSD was searched for related structures, which are discussed with reference to polymorphs 1 and 2. 1H and 13C NMR spectroscopic evidence is provided showing that the three H-bonded adduct [8-BrG][8-BrG] −[DBU–H] + was also formed in the highly H-bond competitive DMSO solution.

A continuum mechanics framework and a constitutive model for predicting the orthotropic elastic properties of microtubules

Abstract This paper presents a theoretical framework for modeling the orthotropic elastic properties of microtubules. We propose a constitutive model to describe the detailed microscale information and continuum properties of the microtubules. The microtubule is viewed as being transformed from an equivalent planar structure, a fictitious-bond is introduced to evaluate the system energy and related with deformation gradients, and a representative unit cell is considered to bridge the microscale energy and the continuum strain energy. In a representative unit cell, the tubulin monomers and guanosine molecules are treated as spheroids, and the fictitious-bond vectors are evaluated through the higher-order Cauchy–Born rule. To deal with this polyatomic bio-composite structure that has large quantities of different types of chemical elements, a homogenization technique is performed to calculate the fictitious-bond energy. The structure of the microtubule is thus determined by minimizing the potential of the representative unit cell. With the established model, the fictitious-bond lengths between adjacent molecules are evaluated and the longitudinal and circumferential moduli are calculated.

Gas-phase isolation of diethyl guanosine 5′-monophosphate and its conformational assignment

We show that intact neutral molecules of guanosine 5'-monophosphate can be vaporized by laser desorption when its phosphate group is esterified. The UV and IR spectroscopic measurements of this nucleotide reveal the existence of a novel internal hydrogen-bonding conformation of the phosphate group and guanine moiety.

Intrinsic Polarization of Self-Assembled Guanosine Supramolecules in GaN-Based Metal–Semiconductor–Metal Nano-Structures

The transport properties of self-assembled guanosine supramolecules (SAGS) confined within nanoscale metal electrodes on transparent GaN semiconductor substrates have been studied. The modified guanosine molecules have been used as self-assembled nanowires to realize nanoscale UV-Visible photodetectors with self-assembly length ranging from 30 to 450 nm. The ribbon-like guanosine supramolecules exhibit semiconductor properties and have polarization along its axis due to the strong intrinsic dipole moment of guanosine molecules. The charge transport through the SAGS wire with nanoscale metal-semiconductor-metal structure on passivated Ga-terminated GaN surface can be explained by Schottky type conductivity and near-surface-states. The intrinsic polarization in SAGS nano-wires changes the band-offset at the metal-semiconductor interface similar to semiconductor photodiodes.

Influence of Tunable External Stimuli on the Self-Assembly of Guanosine Supramolecular Nanostructures Studied By Atomic Force Microscope

The self-assembly of guanosine (G) molecules on solid surfaces is investigated by tapping-mode atomic force microscopy (AFM) upon controlling and introducing external factors (stimuli) to the G stock solution such as incubation time, presence/absence of metal cations, and mechanical shaking. Surprisingly, at different stages of incubation time at room temperature and in the absence of any metal cations in the G stock solution, which are known to be one of the governing factors in forming G-nanostructures, two assembly pathways resulting into two distinct supramolecular nanostructures were revealed. Astonishingly, by introducing a mechanical shaking of the tube containing the G stock solution, one-dimensional (1D) wires of G molecules are observed by AFM, and very interestingly, novel "branched" supramolecular nanostructures are formed. We have also observed that the later branched G nanostructures can grow further into a two-dimensional (2D) thin film by increasing the incubation time of the G stock solution at room temperature after it is exposed to the external mechanical stimuli. The self-assembled nanostructures of G molecules are changed significantly by tuning the assembly conditions, which show that it is indeed possible to grow complex 2D nanostructures from simple nucleoside molecules.

G-quadruplex self-assembly regulated by Coulombic interactions

Self-assembly offers the possibility to organize molecules in a given architecture through a subtle interplay between different noncovalent interactions. Although the kind of molecular association can often be predicted from information present in the individual molecules, the synthesis of supramolecular assemblies having a perfectly defined size and shape remains challenging. Here, we introduce the use of Coulombic interactions to control the supramolecular synthesis of finite, well-defined nanostructures. In particular, we demonstrate that the energy associated with the separation of ion pairs can regulate very precisely guanosine self-assembly into discrete G-quadruplexes. Assemblies comprising 8, 12, 16 or 24 guanosine molecules can be selectively and quantitatively obtained simply by tuning the stabilization of the dissociated anions in the solvent environment. Thus, factors such as solvent polarity, the nature of the anion and the cation-anion distance are shown to have a decisive role in the growth of G-quadruplexes.

Crystal Structure of Ganciclovir

The crystal of the title compound, C9H13N5O4, belongs to space group P21 with cell dimensions a = 4.380(2), b = 10.909(4), c = 11.601(4)Å, and β = 99.11(3)°. The final R value is 0.0583. The chain moiety corresponding to the ribose ring in guanosine does not adopt a fully extended conformation. The relative orientation of the purine ring and the ether oxygen atom is similar to that observed in one of the crystallographically independent guanosine molecules in the crystal structure of guanosine dehydrate.

Side-on binding of p-sulphonatocalix[4]arene to the dinuclear platinum complex trans-[{PtCl(NH3)2}2μ-dpzm]2+ and its implications for anticancer drug delivery

The utility of p-sulphonatocalix[4]arene (s-CX[4]) as a drug delivery vehicle for multinuclear platinum anticancer agents, using trans-[{PtCl(NH(3))(2)}(2)mu-dpzm](2+) (di-Pt; where dpzm=4,4'-dipyrazolylmethane) as a model complex, has been examined using (1)H nuclear magnetic resonance, electrospray ionisation mass spectrometry, molecular modelling and in vitro growth inhibition assays. s-CX[4] binds di-Pt in a side-on fashion in a ratio of 1:1, with the dpzm ligand of the metal complex located within the s-CX[4] cavity with binding further stabilised by ion-ion interactions and hydrogen bonding between the metal complex am(m)ine groups and the s-CX[4] sulphate groups. Partial encapsulation of di-Pt within the cavity does not prevent binding of 5'-guanosine monophosphate to the metal complex. When bound to two individual guanosine molecules, di-Pt also remains partially bound by s-CX[4]. The cytotoxicity of free di-Pt and s-CX[4] and their host guest complex was examined using in vitro growth inhibition assays in the A2780 and A2780cis human ovarian cancer cell lines. Free di-Pt has an IC(50) of 100 and 60 microM, respectively, in the cell lines, which is significantly less active than cisplatin (1.9 and 8.1 microM, respectively). s-CX[4] displays no cytotoxicity at concentrations up to 1.5mM and does not affect the cytotoxicity of di-Pt, probably because its low binding constant to the metal complex (6.8 x 10(4)M(-1)) means the host-guest complex is mostly disassociated at biologically relevant concentrations.

Self‐Assembly of N2‐Modified Guanosine Derivatives: Formation of Discrete G‐Octamers

In the presence of Na(+) ions, two N(2)-modified guanosine derivatives, N(2)-(4-n-butylphenyl)-2',3',5'-O-triacetylguanosine (G1) and N(2)-(4-pyrenylphenyl)-2',3',5'-O-triacetylguanosine (G2), are found to self-associate into discrete octamers that contain two G-quartets and a central ion. In each octamer, all eight guanosine molecules are in a syn conformation and the two G-quartets are stacked in a tail-to-tail fashion. On the basis of NMR spectroscopic evidence, we hypothesize that the pi-pi-stacking interaction between the N(2)-side arms (phenyl in G1 and pyrenyl in G2) can considerably stabilize the octamer structure. For G1, we have used NMR spectroscopic saturation-transfer experiments to monitor the kinetic ligand exchange process between monomers and octamers in CD(3)CN. The results show that the activation energy (E(a)) of the ligand exchange process is 31 +/-5 kJ mol(-1). An Eyring analysis of the saturation transfer data yields the enthalpy and entropy of activation for the transition state: DeltaH(not =)=29 +/-5 kJ mol(-1) and DeltaS(not =)=-151 +/-10 J mol(-1) K(-1). These results are consistent with an associative mechanism for ligand exchange.

Self-assembled deoxyguanosine based molecular electronic device on GaN substrates

Nanoscale hybrid molecular organic photodetectors based on self-assembled guanosine molecules conjugated to wide-bandgap GaN semiconductors has been realized in the ultraviolet wavelength regime. Metal-semiconductor-metal based photodetector is fabricated using ordering of modified guanosine based semiconductor nanowires which exhibit I-V characteristics with high current response and higher rectification ratio compared to Si based hybrid photodetectors. Photocurrent response of a two-terminal device shows the typical characteristics of a semiconductor photodiode with a cutoff wavelength at ∼325nm. The I-V characteristics have been elucidated using the induced polarization properties of self-assembled guanosine semiconductor.

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<or=6) ions is presumed to occur by hydrogen bonding. The ribose group of guanosine appears to play an important role in the stabilization of the doubly charged Cu-guanosine complex and in intraligand proton transfer upon CID. The molecular radical cations [L]*+ observed in the ESI-MS spectrum at low declustering potentials originate primarily from [CuL(MeOH)2,3]*2+ complexes which can dissociate more easily than [CuL3]*2+.

Probing Hydrogen Bonding and Ion−Carbonyl Interactions by Solid-State 17O NMR Spectroscopy: G-Ribbon and G-Quartet

We report solid-state 17O NMR determination of the 17O NMR tensors for the keto carbonyl oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2',3',5'-O-triacetyl-[6-17O]guanosine (G2). In G1.2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6...H-N2 and N7...H-N7 hydrogen bonds in a zigzag fashion. In addition, the keto carbonyl oxygen O6 is also weakly hydrogen-bonded to two water molecules of hydration. The experimental 17O NMR tensors determined for the two independent molecules in the asymmetric unit of G1.2H2O are: Molecule A, CQ=7.8+/-0.1 MHz, etaQ=0.45+/-0.05, deltaiso=263+/-2, delta11=460+/-5, delta22=360+/-5, delta33=-30+/-5 ppm; Molecule B, CQ=7.7+/-0.1 MHz, etaQ=0.55+/-0.05, deltaiso=250+/-2, delta11=440+/-5, delta22=340+/-5, delta33=-30+/-5 ppm. In G1/K+ gel, guanosine molecules form extensively stacking G-quartets. In each G-quartet, four guanine bases are linked together by four pairs of O6...H-N1 and N7...H-N2 hydrogen bonds in a cyclic fashion. In addition, each O6 atom is simultaneously coordinated to two K+ ions. For G1/K+ gel, the experimental 17O NMR tensors are: CQ=7.2+/-0.1 MHz, etaQ=0.68+/-0.05, deltaiso=232+/-2, delta11=400+/-5, delta22=300+/-5, delta33=-20+/-5 ppm. In the presence of divalent cations such as Sr2+, Ba2+, and Pb2+, G2 molecules form discrete octamers containing two stacking G-quartets and a central metal ion, that is, (G2)4-M2+-(G2)4. In this case, each O6 atom of the G-quartet is coordinated to only one metal ion. For G2/M2+ octamers, the experimental 17O NMR parameters are: Sr2+, CQ=6.8+/-0.1 MHz, etaQ=1.00+/-0.05, deltaiso=232+/-2 ppm; Ba2+, CQ=7.0+/-0.1 MHz, etaQ=0.68+/-0.05, deltaiso=232+/-2 ppm; Pb2+, CQ=7.2+/-0.1 MHz, etaQ=1.00+/-0.05, deltaiso=232+/-2 ppm. We also perform extensive quantum chemical calculations for the 17O NMR tensors in both G-ribbons and G-quartets. Our results demonstrate that the 17O chemical shift tensor and quadrupole coupling tensor are very sensitive to the presence of hydrogen bonding and ion-carbonyl interactions. Furthermore, the effect from ion-carbonyl interactions is several times stronger than that from hydrogen-bonding interactions. Our results establish a basis for using solid-state 17O NMR as a probe in the study of ion binding in G-quadruplex DNA and ion channel proteins.

Self-assembled modified deoxyguanosines conjugated to GaN quantum dots for biophotonic applications

The conjugation of self-assembled modified DNA nucleosides (deoxyguanosine lipophilic derivative) to GaN/AlN semiconductor quantum dots for biophotonic application is presented. A resonant energy transfer from GaN nanostructures is observed to enhance the photoluminescence emission from the self-assembled guanosine molecules, which was tailored to achieve a bandgap resonant to the quantum dot emission energy.