H-bond Formation Research Articles

V2CTX MXene-based hybrid sensor with high selectivity and ppb-level detection for acetone at room temperature

High-performance, room temperature-based novel sensing materials are one of the frontier research topics in the gas sensing field, and MXenes, a family of emerging 2D layered materials, has gained widespread attention due to their distinctive properties. In this work, we propose a chemiresistive gas sensor made from V2CTx MXene-derived, urchin-like V2O5 hybrid materials (V2C/V2O5 MXene) for gas sensing applications at room temperature. The as-prepared sensor exhibited high performance when used as the sensing material for acetone detection at room temperature. Furthermore, the V2C/V2O5 MXene-based sensor exhibited a higher response (S% = 11.9%) toward 15 ppm acetone than pristine multilayer V2CTx MXenes (S% = 4.6%). Additionally, the composite sensor demonstrated a low detection level at ppb levels (250 ppb) at room temperature, as well as high selectivity among different interfering gases, fast response-recovery time, good repeatability with minimal amplitude fluctuation, and excellent long-term stability. These improved sensing properties can be attributed to the possible formation of H-bonds in multilayer V2C MXenes, the synergistic effect of the newly formed composite of urchin-like V2C/V2O5 MXene sensor, and high charge carrier transport at the interface of V2O5 and V2C MXene.

A study of the valence photoelectron spectrum of uracil and mixed water-uracil clusters.

The valence ionization of uracil and mixed water-uracil clusters has been studied experimentally and by ab initio calculations. In both measurements, the spectrum onset shows a red shift with respect to the uracil molecule, with the mixed cluster characterized by peculiar features unexplained by the sum of independent contributions of the water or uracil aggregation. To interpret and assign all the contributions, we performed a series of multi-level calculations, starting from an exploration of several cluster structures using automated conformer-search algorithms based on a tight-binding approach. Ionization energies have been assessed on smaller clusters via a comparison between accurate wavefunction-based approaches and cost-effective DFT-based simulations, the latter of which were applied to clusters up to 12 uracil and 36 water molecules. The results confirm that (i) the bottom-up approach based on a multilevel method [Mattioli et al. Phys. Chem. Chem. Phys. 23, 1859 (2021)] to the structure of neutral clusters of unknown experimental composition converges to precise structure-property relationships and (ii) the coexistence of pure and mixed clusters in the water-uracil samples. A natural bond orbital (NBO) analysis performed on a subset of clusters highlighted the special role of H-bonds in the formation of the aggregates. The NBO analysis yields second-order perturbative energy between the H-bond donor and acceptor orbitals correlated with the calculated ionization energies. This sheds light on the role of the oxygen lone-pairs of the uracil CO group in the formation of strong H-bonds, with a stronger directionality in mixed clusters, giving a quantitative explanation for the formation of core-shell structures.

Enhancing the Chemical Stability of MXene Through Synergy of Hydrogen Bond and Coordination Bond in Aqueous Solution.

MXenes with unique physicochemical properties have shown substantial potential in electromagnetic interference (EMI) shielding. However, the chemical instability and mechanical fragility of MXenes has become a major hurdle for their application. Abundant strategies have been dedicated to improving the oxidation stability of colloidal solution or mechanical properties of films, which always come at the expense of electrical conductivity and chemical compatibility. Here, hydrogen bond (H-bond) and coordination bond are employed to achieve chemical and colloidal stability of MXenes (0.1mg mL-1 ) by occupying the reaction sites of Ti3 C2 Tx attacking of water and oxygen molecules. Compared to the Ti3 C2 Tx , the Ti3 C2 Tx modified with alanine via H-bond shows significantly improved oxidation stability (at room temperature over 35 days), while the Ti3 C2 Tx modified with cysteine by synergy of H-bond and coordination bond can be maintained even after 120 days. Simulation and experimental results verify the formation of H-bond and Ti-S bond by a Lewis acid-base interaction between Ti3 C2 Tx and cysteine. Furthermore, the synergy strategy significantly improves the mechanical strength of the assembled film (up to 78.1 ± 7.9MPa), corresponding the increment of 203% compared to untreated one, almost without compromising the electrical conductivity and EMI shielding performance.

Phosphatidylcholine in the tear film of the eye: Enhanced topical delivery of fluorometholone to the eye

In this study, the ability of the phosphatidylcholine (PC) molecule, which is in the tear films in human eyes, to release the fluorometholone (FLU) drug from the sulfobutylether-β-cyclodextrin (SBE-β-CD) carrier, is investigated. The binding energy obtained from the density functional theory (DFT) calculations shows that the PC molecule affinity to bind with the SBE-β-CD is higher than that of the FLU molecule. In addition, the results of molecular dynamic (MD) simulations revealed that PC couldinteractwith the carrier through both coulombic and L-J interactions (Ecoul = ∼−206 and EL-J = ∼−190 kJ/mol), while FLU interaction with SBE-β-CD is mainly via van der Waals interactions (Ecoul = ∼−49 and EL-J = ∼−125 kJ/mol). The obtained results show that in both studied systems, H-bond formation is the driving force in stabilizing these structures. The results confirmed that the Phosphatidylcholine could replace the fluorometholone in the carrier cavity and release the drug in the target site. Overall, our findings demonstrate that SBE-β-CD&FLU complex can be a suitable alternative for treating inflammatory disorders of the eye over the conventional delivery systems.

Virtual screening, pharmacokinetic, and DFT studies of anticancer compounds as potential V600E-BRAF kinaseinhibitors

ObjectivesV600E-BRAF kinase is an essential therapeutic target in melanoma and other types of tumors. Because of its resistance to known inhibitors and the adverse effects of some identified inhibitors, investigation of new potent inhibitors is necessary. MethodsIn the present work, in silico strategies such as molecular docking simulation, pharmacokinetic evaluation, and density functional theory (DFT) computations were used to identify potential V600E-BRAF inhibitors from a set of 72 anticancer compounds in the PubChem database. ResultsFive top-ranked molecules (12, 15, 30, 31, and 35) with excellent docking scores (MolDock score ≥90 kcal mol−1, Rerank score ≥60 kcal mol−1) were selected. Several potential binding interactions were discovered between the molecules and V600E-BRAF. The formation of H-bonds and hydrophobic interactions with essential residues of V600E-BRAF suggested the high stability of these complexes. The selected compounds had excellent pharmacological properties according to the drug likeness rules (bioavailability) and pharmacokinetic properties. Similarly, the energy for the frontier molecular orbitals, such as the HOMO, LUMO, energy gap, and other reactivity parameters, was computed with DFT. The frontier molecular orbital surfaces and electrostatic potentials were investigated to demonstrate the charge-density distributions potentially associated with anticancer activity. ConclusionThe identified compounds were found to be potent hit compounds for V600E-BRAF inhibition with superior pharmacokinetic properties; therefore, they may be promising cancer drug candidates.

Surface Properties of N,N-Dimethylformamide-Water Mixtures, As Seen from Computer Simulations.

The liquid-vapor interface of N,N-dimethylformamide (DMF)-water mixtures, spanning the entire composition range, is investigated in detail at 298 K by molecular dynamics simulation and intrinsic surface analysis. DMF molecules are found to adsorb strongly at the liquid surface, but this adsorption extends only to the first molecular layer. Water and DMF molecules mix with each other on the molecular scale even in the surface layer; thus, no marked self-association of any of the components is seen at the liquid surface. The major surface component prefers such orientation in which the molecular dipole vector lays parallel with the macroscopic plane of the surface. On the other hand, the preferred orientation of the minor component is determined, at both ends of the composition range, by the possibility of H-bond formation with the major component. The lack of H-donating ability of DMF leads to a rapid breakup of the percolating H-bond network at the surface; due to the strong adsorption of DMF, this breakup occurs below the bulk phase DMF mole fraction of 0.03. The disruption of the surface H-bond network also accelerates the exchange of both species between the liquid surface and bulk liquid phase, although, for water, this effect becomes apparent only above a bulk phase DMF mole fraction of 0.4. H-bonds formed by a DMF and a water molecule live, on average, 25-60% longer than those formed by two water molecules at the liquid surface. A similar, but smaller (i.e., about 10-20%) difference is seen in the bulk liquid phase. The enhanced surface mobility of the molecules results in 2-6 times larger diffusion coefficient and 2-5 times shorter H-bond lifetime values at the liquid surface than in the bulk liquid phase. The diffusion of both molecules is slowed down in the presence of the other species; in the case of DMF, this effect is caused by the formation of water-DMF H-bonds, whereas for water, steric hindrances imposed by the bulky DMF neighbors are responsible for this slowing down.

How acidic amino acid residues facilitate DNA target site selection

Despite the negative charge of the DNA backbone, acidic residues (Asp/Glu) commonly participate in the base readout, with a strong preference for cytosine. In fact, in the solved DNA/protein structures, cytosine is recognized almost exclusively by Asp/Glu through a direct hydrogen bond, while at the same time, adenine, regardless of its amino group, shows no propensity for Asp/Glu. Here, we analyzed the contribution of Asp/Glu to sequence-specific DNA binding using classical and ab initio simulations of selected transcription factors and found that it is governed by a fine balance between the repulsion from backbone phosphates and attractive interactions with cytosine. Specifically, Asp/Glu lower the affinity for noncytosine sites and thus act as negative selectors preventing off-target binding. At cytosine-containing sites, the favorable contribution does not merely rely on the formation of a single H-bond but usually requires the presence of positive potential generated by multiple cytosines, consistently with the observed excess of cytosine in the target sites. Finally, we show that the preference of Asp/Glu for cytosine over adenine is a result of the repulsion from the adenine imidazole ring and a tendency of purine-purine dinucleotides to adopt the BII conformation.

IR cavity ringdown spectroscopy and density functional theory calculation of pyrrole-diethyl ketone clusters: impacts of carbon-chain flexibility on the diversity of N-H⋯OC hydrogen bonds.

The N-H⋯OC hydrogen bond (H-bond) plays a key role in stabilizing the geometry and energy of biomolecules such as protein folding and DNA double strand. To investigate N-H⋯OC H-bonds in a microscopic view, we apply IR cavity ringdown spectroscopy (IR-CRDS) and density functional theory (DFT) calculation to pyrrole-diethyl ketone (Py-Dek) clusters in the gas phase. Dek exhibits a pentane carbon chain, which provides various conformations such as anti, gauche, and their mixtures. An introduction of the carbon-chain flexibility to Py-Dek clusters is expected to cause a diversity of the N-H⋯OC H-bond formation. In the observed IR spectra, there are seven prominent bands of the NH stretches due to Py-Dek clusters. These bands are classified into three groups: one for Py1-Dek1, two for Py1-Dek2, and four for Py2-Dek1. Stable structures and their harmonic frequencies obtained by DFT calculations provide the proper NH band assignments and appropriate cluster structures. Py1-Dek1 exhibits a single isomer, which is formed by an ordinary N-H⋯OC H-bond between Py and anti-conformation of Dek (Dek(a)) with a linear carbon-chain. Py1-Dek2 shows two isomeric structures, in which both isomers are commonly constructed by the N-H⋯OC H-bond for the first Dek and by the stacking interaction between π electrons of Py and the second Dek. Both isomers exhibit the Dek(a) for the stacking interaction, but are distinguished between Dek(a) and gauche-conformation Dek (Dek(g)) for the N-H⋯OC H-bond. Py2-Dek1 shows a triangular cyclic structure, which is formed by the N-H⋯OC H-bond, the N-H⋯π H-bond, and the stacking interaction between Py and Dek. The observed four bands are assigned to two N-H⋯OC and two N-H⋯π H-bonds for two isomeric structures due to Dek(a) and Dek(g). Not only smaller clusters but also higher hetero-tetramers are characterized based on the architecture of smaller clusters. In particular, Py2-Dek(a)2(I) was the first to be found with a highly symmetric (Ci) cyclic structure. Calculated potential energy surfaces of Py-Dek clusters shed light on the impact of Dek flexibility on N-H⋯OC H-bond diversity. Selective formation of isomeric structures for Py-Dek clusters is discussed in terms of a mechanism of a two- and three-body collision process in a supersonic expansion.

Sulfur-mediated chalcogen versus hydrogen bonds in proteins: a see-saw effect in the conformational space.

Divalent sulfur (S) forms a chalcogen bond (Ch-bond) via its σ-holes and a hydrogen bond (H-bond) via its lone pairs. The relevance of these interactions and their interplay for protein structure and function is unclear. Based on the analyses of the crystal structures of small organic/organometallic molecules and proteins and their molecular electrostatic surface potential, we show that the reciprocity of the substituent-dependent strength of the σ-holes and lone pairs correlates with the formation of either Ch-bond or H-bond. In proteins, cystines preferentially form Ch-bonds, metal-chelated cysteines form H-bonds, while methionines form either of them with comparable frequencies. This has implications for the positioning of these residues and their role in protein structure and function. Computational analyses reveal that the S-mediated interactions stabilise protein secondary structures by mechanisms such as helix capping and protecting free β-sheet edges by negative design. The study highlights the importance of S-mediated Ch-bond and H-bond for understanding protein folding and function, the development of improved strategies for protein/peptide structure prediction and design and structure-based drug discovery.

Interaction of phytate with cyclic polyamines

Potentiometric and computational studies demonstrated the strong interaction based on electrostatic attraction and modulated by H-bond contact formation and dimensional fit. Cyclization leads to a marked selectivity of phytate towards hexamine.

Fluorination of naphthalimide-cyanostilbene derivatives to achieve dual-state emission luminogens with strong fluorescence in highly polar environments for bioimaging.

Organic luminogens (OLs) that emit strong fluorescence in both solution and the aggregated state, referred to as dual-state emission luminogens (DSEgens), are highly desirable because of their capability to achieve multiple functions within onefold materials. The fluorescence of OLs, including DSEgens, with intramolecular charge transfer characteristics, often decreases in solution as the solvent polarity increases, namely the positive solvatokinetic effect, resulting in inferior environmental stability. In this work, fluorination to naphthalimide (NI)-cyanostilbene (CS) derivatives was adopted to construct novel DSEgens (NICSF-X, X = B, P, M, and T, respectively). Steady-state and transient spectroscopies were utilized to study their photophysical properties, evidencing their DSE properties with fluorescence quantum yields (φ) ∼0.2-0.4 in solution and ∼0.5-0.9 as solids. In particular, strong fluorescence emission in highly polar solvents i.e., φ up to ∼0.4-0.5 in ethanol, was sustained for NICSF-Xs, possibly assisted by hydrogen bonding (H-bonding) formation. Theoretical calculations and single-crystal structure analysis rationalized the intense photoluminescence (PL) emission of NICSF-Xs in the solid state. In addition, NICSF-Xs showed two-photon absorption (2PA) behaviors in dual states and were successfully applied for HepG2 cell imaging with one-photon and 2PA excitation, with lipid droplet targeting. Our study suggests that functionalization of molecules by fluorination to introduce H-bonding is a promising strategy to enhance the environmental stability of fluorescence in solution and realize strong PL emission in highly polar solvents, which could be favorable for bioimaging.

New Hydrogels Based on Agarose/Phytagel and Peptides.

Short aromatic peptide derivatives, i.e., peptides or amino acids modified with aromatic groups, such as 9-fluorenylmethoxycarbonyl (Fmoc), can self-assemble into extracellular matrix-like hydrogels due to their nanofibrillar architecture. Among different types of amino acids, lysine (Lys) and glycine (Gly) are involved in multiple physiological processes, being key factors in the proper growth of cells, carnitine production, and collagen formation. The authors have previously successfully presented the possibility of obtaining supramolecular gels based on Fmoc-Lys-Fmoc and short peptides such as Fmoc-Gly-Gly-Gly in order to use them as a substrate for cell cultures. This paper investigates how the introduction of a gelling polymer can influence the properties of the network as well as the compatibility of the resulting materials with different cell types. A series of hydrogel compositions consisting of combinations of Fmoc-Lys-Fmoc and Fmoc-Gly-Gly-Gly with Agarose and Phytagel are thus obtained. All compositions form structured gels as shown by rheological studies and scanning electron microscopy. Fourier transform infrared spectroscopy analysis evidences the formation of H-bonds between the polysaccharides and amino acids or short peptides. Moreover, all gels exhibit good cell viability on fibroblasts as demonstrated by a live-dead staining test and good in vivo biocompatibility, which highlights the great potential of these biomaterials for biomedical applications.

Unexpected enhancement of pH-stability in Au3+/Ag+ loaded H-bonded layer-by-layer thin films.

In this work, a polymeric film was synthesized through a layer-by-layer (LBL) self-assembly technique using polyacrylic acid (PAA) and polyethylene oxide (PEO), resulting in the formation of a hydrogen-bonded LBL film. The formation of these films was evaluated by PMIRRAS and QCM-D. The synergy of these techniques allowed the understanding of the mechanism of formation of the film by showing the H-bonding formation and film growth. Au and Ag metal ions were successfully incorporated into the films, as corroborated by the combination of the information obtained by XRR and PMIRRAS. The films were exposed to increasing pH, showing a pronounced improvement in stability in films loaded with Au ions, extending the stability from pH 4 to 10. This behavior allows the use of this system in a wider range of applications, including the possibility of working in biological conditions. On the other hand, films loaded with Ag disintegrated at pH above 4. At acidic pH (below 3), these films released the Ag ions, which may be useful for the preparation of antibacterial stimuli-responsive nanomaterials. In both cases, the films were adequate to produce metal nanoparticles by metal loading and in situ reduction.

Molecular interactions of tannic acid and matrix metalloproteinases 2 and 9

Tannic acid (TA) has antibacterial, antioxidant, and anti-inflammatory properties and acts as an adhesive, hemostatic, and crosslinking agent in hydrogels. Matrix metalloproteinases (MMPs), a family of endopeptidase enzymes, play important roles in tissue remodeling and wound healing. TA has been reported to inhibit MMP-2/− 9 activities, thereby improving both tissue remodeling and wound healing. However, the mechanism of interaction of TA with MMP-2 and MMP-9 has not been fully elucidated. In this study, the full atomistic modeling approach was applied to explore the mechanisms and structures of TA binding with MMP-2 and MMP-9. Macromolecular models of the TA–MMP-2/− 9 complex were built by docking based on experimentally resolved MMP structures, and further equilibrium processes were examined by molecular dynamics (MD) simulations to investigate the binding mechanism and structural dynamics of the TA–MMP-2/− 9 complexes. The molecular interactions between TA and MMPs, including H-bond formation and hydrophobic and electrostatic interactions, were analyzed and decoupled to elucidate the dominant factors in TA–MMP binding. TA binds to MMPs mainly at two binding regions, residues 163–164 and 220–223 in MMP-2 and residues 179–190 and 228–248 in MMP-9. Two arms of TA participate in binding MMP-2 with 3.61 hydrogen bonds. On the other hand, TA binds MMP-9 with a distinct configuration involving four arms with 4.75 hydrogen bonds, resulting in a tighter binding conformation. Understanding the binding mechanism and structural dynamics of TA with these two MMPs provides crucial and fundamental knowledge regarding the inhibitory and stabilizing effects of TA on MMPs.

Estimation of electrostatic and covalent contributions to the enthalpy of H-bond formation in H-complexes of 1,2,3-benzotriazole with proton-acceptor molecules by IR spectroscopy and DFT calculations

Using the methods of IR-spectroscopy and quantum chemical calculations, we determined the formation of an H-bond between the 1,2,3-benzotriazole molecule and the molecules of acetone, dioxane, DMF, and DMSO. Quantum chemistry methods have been used to calculate the sums of charge changes in the atoms of the 1,2,3-benzotriazole molecule and of proton acceptor molecules (acetone, dioxane, DMF, and DMSO) due to the formation of their complexes with an H-bond (H-complexes NH…O). The sum of charge changes was taken as a contribution of a covalent component to H-bond formation. It has been established that as the sum of charge changes in N, H, and O or H and O, forming the H-complex, increases, the enthalpy of H-complex formation (EF) decreases. On the contrary, the EO of H-complexes increases when the product of the initial charges on the H and O atoms increases. In the absence of H-complexes, the product of charges was considered the electrostatic component of H-bond formation. The criterion of the value of H-bond EF was the value of a low-frequency shift of the initial position of the maximum IR absorption band of the NH vibration of the 1,2,3-benzotriazole molecule relative to its position in a neutral CCl4 solvent. The results of QTAIM, NCI, and RDG analyses showed that the values of energy densities in BCPs have a positive value in the complexes formed by 1,2,3-benzotriazole with acetone, dioxane, and DMFA, and such hydrogen bonds are electrostatic in nature. In the complex formed by 1,2,3-benzotriazole and DMSO, it has a negative value and a covalent character. The data obtained have allowed for two main conclusions: (i) In the formation of the H-complexes of the 1,2,3-benzotriazole molecule with proton-acceptor molecules containing oxygen atoms, the main contribution to H-bond formation is made by the electrostatic component. (ii) The contribution of the covalent component increases with increasing enthalpy of H-bond formation.

Poly(N-vinyl triazole-b-N-vinyl imidazole) Grafted on MWCNTs as Nanofillers to Improve Proton Conducting Membranes

Carbon nanotubes (CNTs) are of particular interest because of their ability to enhance the mechanical strength in the material; however, processing difficulties of CNTs often restrict utilization up to its full potential. To resolve this, in the current study, we have developed a simple and efficient method to functionalize the surface of a multiwalled carbon nanotube (MWCNT) with precise functional polymer chains, which were covalently grafted on the surface of the MWCNT, and delved into an application to demonstrate this material as an efficient nanofiller in developing a proton conducting membrane (PEM) from polybenzimidazole (PBI). At first, the MWCNT surface was converted to a polymerizable surface by attaching a trithiocarbonate based chain transfer agent (CTA). Then, a N-heterocyclic block copolymer, namely poly-N-vinyl-1,2,4-triazole-b-poly-N-vinyl imidazole (pNVT-b-pNVI), was grown from the CTA anchored surface with a one-pot surface initiated reversible addition–fragmentation chain transfer (SI-RAFT) technique. Grafting of block copolymer chain was confirmed by GPC, NMR, TGA, TEM, FESEM, and EDX studies. To the best of our knowledge, this will be the first report of a growing block copolymer structure grafted covalently on the surface of the MWCNT. The novelty of the work was further enhanced by incorporating pNVT-b-pNVI-g-MWCNT as a nanofiller into the oxypolybenzimidazole (OPBI) membrane to obtain homogeneous nanocomposite membranes with excellent thermomechanical and tensile properties, thermal stability, superior proton conduction when doped with phosphoric acid (PA), and PA holding capacity. The nanocomposite membrane with 2.5 wt % nanofiller loading displayed a tensile stress of 1.8 MPa and a strain of 176% at break. The basic N-heterocyclic rings dangling from the block copolymer chains grafted on the MWCNT surface allowed formation of strong H-bonding, acid–base interaction with PA, which is responsible for high acid uptake and superior PA retention, and also exhibited proton conductivity as high as 0.164 S cm–1 at 180 °C, which is a 2.6-fold increment when compared with a pristine OPBI membrane. This significant increase in conductivity is attributed to the proton conducting nanochannel pathway generated along the polymer-g-MWCNT surface.

17 O Hyperfine Spectroscopy Reveals Hydration Structure of Nitroxide Radicals in Aqueous Solutions.

The hydration structure of nitroxide radicals in aqueous solutions is elucidated by advanced 17 O hyperfine (hf) spectroscopy with support of quantum chemical calculations and MD simulations. A piperidine and a pyrrolidine-based nitroxide radical are compared and show clear differences in the preferred directionality of H-bond formation. We demonstrate that these scenarios are best represented in 17 O hf spectra, where in-plane coordination over -type H-bonding leads to little spin density transfer on the water oxygen and small hf couplings, whereas -type perpendicular coordination generates much larger hf couplings. Quantitative analysis of the spectra based on MD simulations and DFT predicted hf parameters is consistent with a distribution of close solvating water molecules, in which directionality is influenced by subtle steric effects of the ring and the methyl group substituents.

Anticancer Activity, Reduction Mechanism and G-Quadruplex DNA Binding of a Redox-Activated Platinum(IV)-Salphen Complex.

Aiming at reducing the unselective cytotoxicity of Pt(II) chemotherapeutics, a great deal of effort has been concentrated into the design of metal-containing drugs with different anticancer mechanisms of action. Inert Pt(IV) prodrugs have been proposed to be a valid alternative as they are activated by reduction directly into the cell releasing active Pt(II) species. On the other hand, a promising strategy for designing metallodrugs is to explore new potential biological targets rather than canonical B-DNA. G-quadruplex nucleic acid, obtained by self-assembly of guanine-rich nucleic acid sequences, has recently been considered an attractive target for anticancer drug design. Therefore, compounds capable of binding and stabilizing this type of DNA structure would be greatly beneficial in anticancer therapy. Here, computational analysis reports the mechanism of action of a recently synthesized Pt(IV)-salphen complex conjugating the inertness of Pt(IV) prodrugs with the ability to bind G-quadruplexes of the corresponding Pt(II) complex. The reduction mechanism of the Pt(IV) complex with a biological reducing agent was investigated in depth by means of DFT, whereas classical MD simulations were carried out to shed light into the binding mechanism of the released Pt(II) complex. The results show that the Pt(IV) prodrug may be reduced by both inner- and outer-sphere mechanisms, and the active Pt(II) complex, as a function of its protonation state, stabilizes the G-quadruplex DNA prevalently, either establishing π-stacking interactions with the terminal G-tetrad or through electrostatic interactions along with H-bonds formation.

Activation of Ibuprofen via Ultrasonic Complexation with Silver in N-Doped Oxidized Graphene Nanoparticles for Microwave Chemotherapy of Cervix Tumor Tissues.

An ultrasonic method (20 kHz) is introduced to activate pristine ibuprofen organic molecular crystals via complexation with silver in nitrogen-doped oxidized graphene nanoplatforms (∼50 nm). Ultrasonic complexation occurs in a single-step procedure through the binding of the carboxylic groups with Ag and H-bond formation, involving noncovalent πC=C → πC=C* transitions in the altered phenyl ring and πPY → πCO* in ibuprofen occurring between the phenyl ring and C-O bonds as a result of interaction with hydroxyl radicals. The ibuprofen-silver complex in ≪NrGO≫ exhibits a ∼42 times higher acceleration rate than free ibuprofen of the charge transfer between hexacyanoferrate and thiosulfate ions. The increased acceleration rate can be caused by electron injection/ejection at the interface of the ≪Ag-NrGO≫ nanoplatform and formation of intermediate species (Fe(CN)5(CNSO3)x- with x = 4 or 5 and AgHS2O3) at the excess of produced H+ ions. Important for microwave chemotherapy, ibuprofen-silver complexes in the ≪NrGO≫ nanoplatform can produce H+ ions at ∼12.5 times higher rate at the applied voltage range from 0.53 to 0.60 V. ≪Ibu-Ag-NrGO≫ NPs develop ∼105 order higher changes of the electric field strength intensity than free ibuprofen in the microwave absorption range of 100-1000 MHz as revealed from the theoretical modeling of a cervix tumor tissue.

Structural elucidation of N-amidothiourea derived from nicotinic acid hydrazide: A detailed study of its application as selective anion sensor

A novelN-amidothiourea receptor (1), synthesized by the reaction of nicotinic acid hydrazide with phenyl isothiocyanate, was evaluated for the detection of fluoride, acetate, and hydroxide ions selectively over other anions. Receptor1was characterized by various spectroscopic methods, and further structural elucidation of it was done by Single Crystal X-ray diffraction analysis. The efficacy of receptor1as a colorimetric sensor for fluoride ions was observed by an instant colour change from colourless to light yellow, which can be attributed to the H-bonding complex formation between receptor1and anion. The binding characteristics of the thiourea receptor with fluoride ion (F−) showed 1:1 binding stoichiometry at a lower concentration, whereas at a higher concentration, the binding stoichiometry increased to 1:2. The receptor, when treated with acetate and hydroxide ion, showed 1:2 and 1:1 binding stoichiometry, respectively. The binding affinity of receptor1was found to be following the Brønsted acidity order, i.e., OH− > AcO− > F−. Detailed quantum chemical calculations also supported the experimental findings.