Vibrational signatures of dynamic excess proton storage between primary amine and carboxylic acid groups.

Ammonium and carboxylic moieties play a central role in proton-mediated processes of molecular recognition, charge transfer or chemical change in (bio)materials. Whereas both chemical groups constitute acid-base pairs in organic salt-bridge structures, they may as well host excess protons in acidic environments. The binding of excess protons often precedes proton transfer reactions and it is therefore of fundamental interest, though challenging from a quantum chemical perspective.

Correlated proton dynamics in hydrogen bonding networks: the benchmark case of 3-hydroxyglutaric acid.

Proton and hydrogen-bonded networks sustain a broad range of structural and charge transfer processes in supramolecular materials. The modelling of proton dynamics is however challenging and demands insights from prototypical benchmark systems. The intramolecular H-bonding networks induced by either protonation or deprotonation of 3-hydroxyglutaric acid provide intriguing case studies of correlated proton dynamics.

Sulfonate-Based Triazine Multiple-Electron Anolyte for Aqueous Organic Flow Batteries.

A new highly soluble triazine derivative showing three reversible redox processes with fast kinetics and high diffusion coefficients has been synthesized using an efficient, low-cost, and straightforward synthetic route. Concentrated single cell tests and DFT studies reveal a tendency of the reduced triazine species to form aggregates which could be avoided by tuning the supporting electrolyte concentration. Under the right conditions, shows no capacity decay and good Coulombic, voltage, and energy efficiencies for the storage of two electrons.

Clean H Production by Lignin-Assisted Electrolysis in a Polymer Electrolyte Membrane Flow Reactor.

Biomass-derived products, such as lignin, are interesting resources for energetic purposes. Lignin is a natural polymer that, when added to the anode of an alkaline exchange membrane water electrolyser, enhances H production rates and efficiencies due to the substitution of the oxygen evolution reaction. Higher efficiencies are reported when different catalytic materials are employed for constructing the lignin anolyte, demonstrating that lower catalytic loadings for the anode improves the H production when compared to higher loadings.

Strategies to Enhance CO Electrochemical Reduction from Reactive Carbon Solutions.

CO electrochemical reduction (CO ER) from (bi)carbonate feed presents an opportunity to efficiently couple this process to alkaline-based carbon capture systems. Likewise, while this method of reducing CO currently lags behind CO gas-fed electrolysers in certain performance metrics, it offers a significant improvement in CO utilization which makes the method worth exploring. This paper presents two simple modifications to a bicarbonate-fed CO ER system that enhance the selectivity towards CO.

A Dynamic Proton Bond: MH·HO ⇌ M·HO Interconversion in Loosely Coordinated Environments.

The interaction of organic molecules with oxonium cations within their solvation shell may lead to the emergence of dynamic supramolecular structures with recurrently changing host-guest chemical identity. We illustrate this phenomenon in benchmark proton-bonded complexes of water with polyether macrocyles. Despite the smaller proton affinity of water versus the ether group, water in fact retains the proton in the form of HO, with increasing stability as the coordination number increases.

Alpha-Germanium Nanolayers for High-Performance Li-ion Batteries.

The exfoliation of tridimensional crystal structures has recently been considered a new source of bidimensional materials. The new approach offers the possibility of dramatically enlarging the library of bidimensional materials, but the number of nanolayers produced so far is still limited. Here, we report for the first time the use of a new type of material, α-germanium nanolayers (2D α-Ge).

Insights into the binding of arginine to adenosine phosphate from mimetic complexes.

The amino acid arginine plays a key role in the interaction of proteins with adenosine phosphates, as its protonated guanidinium side group is capable of building multipodal H-bonding interactions with the oxygen atoms of the phosphate, phosphoester and ribose moieties and with the nitrogen atoms of adenine. Protein interactions often take place in competition with other ionic species, typically metal cations, which are prone to build concerted coordination arrangements with the same centers of negative charge as guanidinium. We report on a vibrational spectroscopy and computational investigation of a positively charged ternary complex formed by adenosine monophosphate (AMP) with methyl guanidinium and Na.

Inclusion complexes of the macrocycle nonactin with benchmark protonated amines: aniline and serine.

The biological activity of the macrocycle nonactin is intimately related to its ionophore properties and ability to act as a selective cation carrier. While the focus of most investigations on nonactin has been on the binding of metal cations and small molecular ions, this study pursues the characterization of its inclusion complexes with primary amines with bulky structured side groups of different polarity. To this end, the complexes of nonactin with aniline and with the amino acid L-serine, both in protonated form, are considered as case studies and their relevant coordination arrangements are assessed by means of infrared action spectroscopy, quantum chemical density functional theory and Born-Oppenheimer molecular dynamics.

Gas-phase hydration of nopinone: the interplay between theoretical methods and experiments unveils the conformational landscape.

The structure of microsolvated nopinone formed in the supersonic jet expansion is investigated in the gas phase. The rotational spectra of nopinone(HO) (n = 1, 2, 3) were analysed by means of Fourier transform microwave spectroscopy. In the present study, three monohydrates, two dihydrates and two trihydrates were observed and characterized.

Proton in the ring: spectroscopy and dynamics of proton bonding in macrocycle cavities.

The proton bond is a paradigmatic quantum molecular interaction and a major driving force of supramolecular chemistry. The ring cavities of crown ethers provide an intriguing environment, promoting competitive proton sharing with multiple coordination anchors. This study shows that protons confined in crown ether cavities form dynamic bonds that migrate to varying pairs of coordinating atoms when allowed by the flexibility of the macrocycle backbone.

Molecular Characterization of Nonvolatile Fractions of Algerian Petroleum with High-Resolution Mass Spectrometry.

Algerian crude oil displays a marked propensity for asphaltene precipitation, leading to solid deposits during extraction, transportation, and storage. The relationship between precipitation and chemical composition is unclear; in fact, Algerian crude oil actually features a low asphaltene concentration, despite its relatively large rate of deposit formation. The rationalization of the precipitation process and its remediation should benefit from a molecular characterization of the crude oil.

Multipodal coordination and mobility of molecular cations inside the macrocycle valinomycin.

The macrocycle valinomycin displays an outstanding ability in cation binding and carriage across hydrophobic environments (e.g., cell membranes) and constitutes a central landmark for the design of novel ionophores for the regulation of biochemical processes.

The synergy of different solid-state techniques to elucidate the supramolecular assembly of two 1H-benzotriazole polymorphs.

1H-Benzotriazole crystallizes as two different polymorphs, namely 4aα and 4aβ. One polymorph is chiral and it resolves spontaneously as conglomerates. The other polymorph crystallizes in a centrosymmetric space group and it is therefore achiral.

Insights into the Recognition of Phosphate Groups by Peptidic Arginine from Action Spectroscopy and Quantum Chemical Computations.

The side group of the amino acid arginine is typically in its guanidinium protonated form under physiological conditions and participates in a broad range of ligand binding and charge transfer processes of proteins. The recognition of phosphate moieties by guanidinium plays a particularly key role in the interactions of proteins with ATP and nucleic acids. Moreover, it has been recently identified as the driving force for the inhibition of kinase phosphorilation activity by guanidinium derivatives devised as potential anticancer agents.

A Cl Hinge for Cyclen Macrocycles: Ionic Interactions and Tweezer-Like Complexes.

The supramolecular networks derived from the complexation of polyazamacrocycles with halide anions constitute fundamental building blocks of a broad range of modern materials. This study provides insights into the conformational framework that supports the binding of protonated cyclen macrocyles (1,4,7,10-Tetraazacyclododecane) by chloride anions through NH···Cl interactions. The isolated complex comprised of two cyclen hosts linked by one Cl anion is characterized by means of infrared action spectroscopy and ion mobility mass spectrometry, in combination with quantum chemical computations.

Preferential host-guest coordination of nonactin with ammonium and hydroxylammonium.

The biological activity of the macrocycle nonactin is intimately related to its ionophore properties and ability to act as a selective cation carrier. The competitive binding of small protonated amines constitutes a particularly key issue in the biochemistry of nonactin, which finds application in sensing and extraction technologies. In this study, isolated complexes of nonactin with ammonium and hydroxylammonium are investigated with infrared action spectroscopy and quantum chemical computations.

Conformational aspects of polymorphs and phases of 2-propyl-1-benzimidazole.

This paper reports on the polymorphism of 2-propyl-1-benzimidazole (2PrBzIm) induced by temperature change. Upon heating, an irreversible reconstructive-type phase transition at = 384 K from the ordered form (222) to a new polymorph, form (), was observed. The structural transformation between forms and involves significant changes in the crystal packing, as well as a key conformational variation around the propyl chain of the molecule.

Complexes of Crown Ether Macrocycles with Methyl Guanidinium: Insights into the Capture of Charge in Peptides.

Crown ethers are well known as modulating agents of protein function and interactions. The action of crown ethers is driven by an alteration of the charged moieties of proteins through the capping of cationic amino acid side chains. This study evaluates the conformational features involved in the binding of crown ethers to the side chain of arginine.

Intra-cavity proton bonding and anharmonicity in the anionophore cyclen.

Proton bonding drives the supramolecular chemistry of a broad range of materials with polar moieties. Proton delocalization and electronic charge redistribution have a profound impact on the structure of proton-bound molecular frameworks, and pose fundamental challenges to quantum chemical modelling. This study provides insights into the structural and spectral signatures of the intramolecular proton bond formed in a benchmark polyazamacrocycle anionophore (cyclen, 1,4,7,10-tetraazacyclododecane).

A vibrational circular dichroism (VCD) methodology for the measurement of enantiomeric excess in chiral compounds in the solid phase and for the complementary use of NMR and VCD techniques in solution: the camphor case.

For the first time, the success of a methodology for the determination of enantiomeric excess (% ee) in chiral solid samples by vibrational circular dichroism (VCD) spectroscopy is reported. We have used camphor to determine the % ee in a blind sample constituted by a mixture of its two enantiomers as a test for the validity of our approach. IR and VCD spectra of different enantiomeric mixtures of R/S-camphor in Nujol mulls were recorded and linear regressions of VCD intensities (ΔAbs.

Guanidinium/ammonium competition and proton transfer in the interaction of the amino acid arginine with the tetracarboxylic 18-crown-6 ionophore.

The recognition of arginine plays a central role in modern proteomics and genomics. Arginine is unique among natural amino acids due to the high basicity of its guanidinium side chain, which sustains specific interactions and proton exchange biochemical processes. The search for suitable macrocyclic ionophores constitutes a promising route towards the development of arginine receptors.

The gas phase structure of α-pinene, a main biogenic volatile organic compound.

The gas phase structure of the bicyclic atmospheric aerosol precursor α-pinene was investigated employing a combination of quantum chemical calculation and Fourier transform microwave spectroscopy coupled to a supersonic jet expansion. The very weak rotational spectra of the parent species and all singly substituted C in natural abundance have been identified, from 2 to 20 GHz, and fitted to Watson's Hamiltonian model. The rotational constants were used together with geometrical parameters from density functional theory and ab initio calculations to determine the r, r, and r structures of the skeleton, without any structural assumption in the fit concerning the heavy atoms.

Isolated complexes of the amino acid arginine with polyether and polyamine macrocycles, the role of proton transfer.

The distinct basicity of the guanidinium side-group of arginine (Arg) sustains specific interactions involved in essential biochemical processes. The sensing of arginine is therefore key in modern biotechnology and bioanalysis. In this context, the development of molecular receptors based on crown ether building blocks has demonstrated great potential.