Robust Hydrogen-bonded Networks Research Articles

Gamma glycine enhances efficiency of organic hybrid piezoelectric-triboelectric nanogenerators

This study presents a comprehensive exploration of enhancing the electrical output of flexible hybrid piezoelectric-triboelectric nanogenerators (P-TENG) through the incorporation of γ-glycine (γ-GC) into fully organic γ-GC/chitosan (CS) composites. A systematic investigation of the effects of γ-GC content (wt%) on the material characteristics and resulting electrical output signal is conducted. The research demonstrates the pivotal role of optimized γ-GC and CS concentrations in achieving superior performance. Through adherence to the percolation threshold principle, a critical γ-GC content is identified, leading to the attainment of the highest output signal. Three theoretical explanations substantiate this observation: firstly, molecular polarization occurring at the interface; secondly, the establishment of a well-connected filler internetwork; and thirdly, mitigation of air breakdown limitations. The interaction of γ-GC and CS fosters a robust hydrogen bond network, aligning interface polarization coherently. Efficient internetwork connections between γ-GC fillers facilitate facile charge generation and transfer. Furthermore, utilizing an appropriate quantity of γ-GC ensures optimal charge entrapment while circumventing issues related to air breakdown. The optimal electrical output is achieved by using 50% γ-GC, resulting in an open-circuit voltage (VOC) of 79 V and a short-circuit current (ISC) of 64 µA. The maximum power output (Pmax) registers at 705.96 µW under an external load resistance of 1 MΩ. Importantly, practical applications are demonstrated, including capacitor charging (0.22 μF and 0.33 μF), illumination of 100 LEDs, and operation of a scientific calculator-equipped watch.

Crystal structure, molecular structural analysis, optical absorption and thermal analysis of 2-amino-6-methyl pyridine-1-ium 2-carboxy-6-nitro benzoate – A third harmonic nonlinear optical organic single crystal

Single crystals of the newly concocted 2-amino-6-methyl pyridine-1-ium 2-carboxy-6-nitro benzoate (MPNP) were grown by slow evaporation approach using an equimolar ethanol-water mixed solvent. The crystal structure of MPNP with the single-crystal X-ray diffraction technique revealed a centrosymmetric triclinic molecular arrangement. A robust hydrogen bond network with a cloud of supramolecular assemblies, S (4), S (8), S (10) and S (11), ring graph set motifs, R22 (8), R44 (18) and R (10) and π – π linkages establish molecular packing. Hirshfeld surface analysis substantiated non-bonded interactions in the structure. Experimental FT-IR and Raman vibration modes were analyzed in order to establish the presence of functional groups and the amine-imine tautomeric form. Molecular structure confirmation was corroborated with experimental NMR spectra. UV–Visible spectral profiling with Tauc, Urbach, and dispersion plots for refractive index variations were performed to understand the origin of optical band in the material. TCSPC lifetime studies envisaged the immense scintillating efficacy of MPNP. The experimental Z-scan data of MPNP in the closed and open aperture modes were deployed to estimate the magnitude of the nonlinear optical properties of MPNP, thereby establishing a good scope for optical applications. Thermogravimetry coupled with Differential Scanning Calorimetry (DSC) declares high thermal stability of the material till 177.6 °C.

Aggregation Number in Water/n-Hexanol Molecular Clusters Formed in Cyclohexane at Different Water/n-Hexanol/Cyclohexane Compositions Calculated by Titration 1H NMR.

Upon titration of n-hexanol/cyclohexane mixtures of different molar compositions with water, water/n-hexanol clusters are formed in cyclohexane. Here, we develop a new method to estimate the water and n-hexanol aggregation numbers in the clusters that combines integration analysis in one-dimensional 1H NMR spectra, diffusion coefficients calculated by diffusion-ordered NMR spectroscopy, and further application of the Stokes-Einstein equation to calculate the hydrodynamic volume of the clusters. Aggregation numbers of 5-15 molecules of n-hexanol per cluster in the absence of water were observed in the whole range of n-hexanol/cyclohexane molar fractions studied. After saturation with water, aggregation numbers of 6-13 n-hexanol and 0.5-5 water molecules per cluster were found. O-H and O-O atom distances related to hydrogen bonds between donor/acceptor molecules were theoretically calculated using density functional theory. The results show that at low n-hexanol molar fractions, where a robust hydrogen-bond network is held between n-hexanol molecules, addition of water makes the intermolecular O-O atom distance shorter, reinforcing molecular association in the clusters, whereas at high n-hexanol molar fractions, where dipole-dipole interactions dominate, addition of water makes the intermolecular O-O atom distance longer, weakening the cluster structure. This correlates with experimental NMR results, which show an increase in the size and aggregation number in the clusters upon addition of water at low n-hexanol molar fractions, and a decrease of these magnitudes at high n-hexanol molar fractions. In addition, water produces an increase in the proton exchange rate between donor/acceptor molecules at all n-hexanol molar fractions.

Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations.

Many of water's remarkable properties arise from its tendency to form an intricate and robust hydrogen bond network. Understanding the dynamics that govern this network is fundamental to elucidating the behavior of pure water and water in biological and physical systems. In ultrafast nonlinear infrared experiments, the accessible time scales are limited by water's rapid vibrational relaxation (1.8 ps for dilute HOD in H2O), precluding interrogation of slow hydrogen bond evolution in non-bulk systems. Here, hydrogen bonding dynamics in bulk D2O were studied from the perspective of the much longer lived (36.2 ps) CN stretch mode of selenocyanate (SeCN-) using polarization selective pump-probe (PSPP) experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, and molecular dynamics simulations. The simulations make use of the empirical frequency mapping approach, applied to SeCN- for the first time. The PSPP experiments and simulations show that the orientational correlation function decays via fast (2.0 ps) restricted angular diffusion (wobbling-in-a-cone) and complete orientational diffusive randomization (4.5 ps). Spectral diffusion, quantified in terms of the frequency-frequency correlation function, occurs on two time scales. The initial 0.6 ps time scale is attributed to small length and angle fluctuations of the hydrogen bonds between water and SeCN-. The second 1.4 ps measured time scale, identical to that for HOD in bulk D2O, reports on the collective reorganization of the water hydrogen bond network around the anion. The experiments and simulations provide details of the anion-water hydrogen bonding and demonstrate that SeCN- is a reliable vibrational probe of the ultrafast spectroscopy of water.

Spontaneous resolution of heterometallic complex: cis-[Co(NH3)4(H2O)2][Fe(ox)3]·2H2O – A rare example for labile iron(III) complex

The new conglomerate forming compound of the formula cis-[Co(NH3)4(H2O)2][Fe(ox)3]·2H2O (1) (ox=C2O42−) was synthesized and structurally, spectroscopically and magnetically characterized revealing weak antiferromagnetic couplings. Two forms of (1) crystallizing in hexagonal enantiomorphic space groups, P6522 and P6122, were identified proving that spontaneous resolution of the racemic mixture occurred at the crystallization stage, because chiral (1a) and (1b), respectively, were obtained from the same synthesis using racemic K3[Fe(ox)3]·3H2O substrate. It is rare example of conglomerate formation with labile Fe(III) ion as a coordination center. In packing along z axis for (1a) and (1b) structures we observe pattern with iron and cobalt complexes as well as water molecules arranged in separated helices, left-handed for (1a) and right-handed for (1b). Analysis of the intermolecular contacts formed by the “false block” with inverted chirality placed in the homochiral network revealed steric hindrance as well as disruption of approximately 50% of hydrogen bonds inside a helix and between adjacent helices. This analysis was supported by calculations performed using gaussian-03 run with DFT B3LYP potential using 6–31+G(d,p) basis. They revealed significantly more stable structure for the true block due to disruption of several hydrogen bonds and steric hindrance introduced by the false block. Hence, the helices imposed by chiral [Fe(ox)3]3− blocks are a template for supramolecular structure, which reveals achiral water molecules and Co(III) moieties forming helices of the same handedness as iron blocks. These Fe(III) moieties are trapped inside tightly packed crystal network, which is maintained by the robust hydrogen bond network. In this structure Co(III) blocks transmit interactions between adjacent helices. Analysis of intermolecular interactions network allows also for deeper insight into a nature of light- and/or time-catalyzed degradation as well as spontaneous resolution processes.

An update view on the substrate recognition mechanism of phosphodiesterases: A computational study of PDE10 and PDE4 bound with cyclic nucleotides

Early studies strongly implied that the specificity of cyclic nucleotide phosphodiesterases (PDEs) toward its endogenous substrates can be uniquely determined by the amido orientation of the invariant glutamine locating in the binding pocket of the enzyme. However, recently solved crystal structures of PDE4 (cAMP specific) and PDE10 (dual specific) in the presence of endogenous substrates have revealed that their invariant glutamine orientations are very similar despite exhibiting different substrate specificities proven physiologically. To understand this subtle specificity issue in the PDE family, here several experimentally inaccessible PDE-substrate complex models have been studied computationally, and the results are juxtaposed and compared in detail. Modeling results show that PDE10 in fact favors cAMP energetically but still can bind to cGMP owing to the robust hydrogen-bond network in the vicinity of the invariant glutamine side chain. PDE4 fails to accommodate cGMP is correlated to the weakening of this same hydrogen-bond network but not owing to any steric strain in the binding pocket. An Asn residue in the binding pocket of PDE4 has enhanced the specificity of the binding to cAMP sideway as observed in our computer simulation. Further to the previously studied syn- versus anti-conformational specificity of cAMP in PDE10, the unexpected substrate-binding mode in PDE10 versus PDE4 as reported here strongly suggested that there are remaining uncertainties in the substrate orientation and recognition mechanism in the PDE families. The molecular details of the binding pocket observed in this study provide hints for more optimal PDE4 and PDE10 inhibitor design.

Exploration of charge-transfer complexes of a nucleobase: Crystal structure and properties of cytosine–Et 2TCNQ salt

A charge-transfer solid composed of a hemiprotonated cytosine pair and fully ionized Et 2TCNQ radical anion was investigated in terms of crystal structure analysis, optical spectra, and electrical and magnetic measurements. Complementary hydrogen bonds and π-stack of the hemiprotonated cytosine pair established a two-dimensional cation layer, and the hydrogen bond with Et 2TCNQ moiety aligned them to construct a segregated bilayer structure of this salt. The robust hydrogen bond network strengthened the crystal packing against structural distortion and preserved the uniform arrangement down to low temperature.