Protonation Of Species Research Articles

Ketohydrazone dyes derived from 4-morpholino-2-naphthol and ortho-substituted anilines: Further examination of the hyperchromism induced by the 4-morpholino-2-naphthol moiety

A series of ketohydrazone dyes has been synthesised from 4-morpholino-2-naphthol and ortho-substituted anilines by conventional diazotisation coupling chemistry. Whilst the new, dull orange-red, dyes exhibit only a minor variation of absorption maxima across the range of substituents, they are hyperchromic relative to Sudan 1 and their none ortho-substituted analogue. Protonation of selected dye examples results in a bathochromic and hyperchromic shift in absorption maxima to afford vibrant purple-coloured protonated species.

Low‐Temperature Protonic Ceramic Fuel Cells through Interfacial Engineering of Nanocrystalline BaCe0.7Zr0.1Y0.1Yb0.1O3−δ Electrolytes

Nanocrystalline BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb) is designed by a novel strategy with improved proton transport properties at low temperatures (<300 °C). In situ Raman spectroscopy and electrical conductivity relaxation (ECR) are used to quantitatively evaluate the surface exchange coefficients during the hydrogen isotope exchange process. Similar surface exchange coefficients are measured via in situ Raman spectroscopy and ECR measurements, representing new tools to better understand proton transport behaviors at the materials’ interface. The surface exchange coefficient in nanocrystalline BCZYYb is nearly four times higher than that in conventional dense BCZYYb at 300 °C, indicating higher surface mobility of protonic species in the designed BCZYYb membrane. The improved performance originates from the combined interfacial and bulk effects for proton transport at low temperatures. In addition, low‐temperature protonic ceramic fuel cells (PCFCs) are built based on a nanocrystalline BCZYYb electrolyte with improved single‐cell performance at 300 °C, which indicates enhanced proton transport properties in contemporary energy conversion and storage materials can be achieved through interfacial engineering.

Direct observation of the active sites in methane dehydroaromatization by NMR

Direct observation of the active sites in methane dehydroaromatization by NMR

Rapid Interchangeable Hydrogen, Hydride, and Proton Species at the Interface of Transition Metal Atom on Oxide Surface.

Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material.

Coarse-Grained Parameterization of Nucleotide Cofactors and Metabolites: Protonation Constants, Partition Coefficients, and Model Topologies.

Nucleotides are structural units relevant not only in nucleic acids but also as substrates or cofactors in key biochemical reactions. The size- and timescales of such nucleotide-protein interactions fall well within the scope of coarse-grained molecular dynamics, which holds promise of important mechanistic insight. However, the lack of specific parameters has prevented accurate coarse-grained simulations of protein interactions with most nucleotide compounds. In this work, we comprehensively develop coarse-grained parameters for key metabolites/cofactors (FAD, FMN, riboflavin, NAD, NADP, ATP, ADP, AMP, and thiamine pyrophosphate) in different oxidation and protonation states as well as for smaller molecules derived from them (among others, nicotinamide, adenosine, adenine, ribose, thiamine, and lumiflavin), summing up a total of 79 different molecules. In line with the Martini parameterization methodology, parameters were tuned to reproduce octanol-water partition coefficients. Given the lack of existing data, we set out to experimentally determine these partition coefficients, developing two methodological approaches, based on 31P-NMR and fluorescence spectroscopy, specifically tailored to the strong hydrophilicity of most of the parameterized compounds. To distinguish the partition of each relevant protonation species, we further potentiometrically characterized the protonation constants of key molecules. This work successfully builds a comprehensive and relevant set of computational models that will boost the biochemical application of coarse-grained simulations. It does so based on the measurement of partition and acid-base physicochemical data that, in turn, covers important gaps in nucleotide characterization.

Cover Picture: Characterization of Proton Dynamics for the Understanding of Conduction Mechanism in Proton Conductive Metal‐Organic Frameworks (Chem. Rec. 11/2020)

The cover picture shows spectroscopic methods to characterize mobile protons in a proton-conductive porous metal–organic frameworks with a regular crystalline structure. The long range ordering of host materials facilitates to uncover the molecular mechanism of the charged proton species formation and migration. As we use optical and radio-frequency instruments to probe the night sky secrets, we combine different types of molecular spectroscopies to shed light on the mysteries of the proton transfer in solids. See the Personal Account by Daniil I. Kolokolov, Dae-Woon Lim, and Hiroshi Kitagawa (DOI: 10.1002/tcr.202000072).

Ethyne Functionalized Meso-Phenothiazinyl-Phenyl-Porphyrins: Synthesis and Optical Properties of Free Base Versus Protonated Species.

Synthesis, structural characterization and photophysical properties for a series of new trans-A2B2- and A3B-type ethynyl functionalized meso-phenothiazinyl-phenyl porphyrin derivatives are described. The new compounds displayed the characteristic porphyrin absorption spectra slightly modified by weak auxochromic effects of the substituents and fluorescence emission in the range of 651–659 nm with 11–25% quantum yields. The changes recorded in the UV-vis absorption spectra in the presence of trifluoroacetic acid (TFA) are consistent with the protonation of the two internal nitrogen atoms of the free-base porphyrin (19 nm bathochromic shift of the strong Soret band and one long wave absorption maxima situated in the range of 665–695 nm). Protonation of the phenothiazine substituents required increased amounts of TFA and produced a distinct hypsochromic shift of the long wave absorption maxima. The density functional theory (DFT) calculations of a porphyrin dication pointed out a saddle-distorted porphyrin ring as the ground-state geometry.

Effect of acceptor and donor doping on the state of protons in block-layered structures based on BaLaInO4

The present work describes the effect of acceptor and donor doping on the state of protons in block-layered proton conductors based on BaLaInO4. It was proved that the increase of the dopant concentration (both Ba2+ and Ti4+) leads to the increase of the amount of water uptake and at the same time to the decrease in the contribution of protons, involved in the strong H-bonds. The main factor determined the increase of concentration of protonic species is not the nature of appeared oxygen defects (oxygen vacancy or oxygen interstitial), but the increase in the unit cell volume during doping.

NMR study of the influence and interplay of water, HCl and LiCl with the extraction agent Aliquat 336 dissolved in toluene

The quaternary amine Aliquat 336 (A336·Cl) was dissolved in toluene and thoroughly mixed with aqueous solutions containing LiCl or HCl. After mixing, the organic phase was separated from the aqueous phase and analysed using NMR and acid–base titration. The different proton species HCl, H2O and H3O+ present in the aqueous phase are normally not distinguishable using NMR due to fast exchange conditions (on the NMR time scale) and therefore they give rise to mainly one single peak in the proton spectrum. The chemical shift of this single ‘composite’ peak is affected by the relative distribution of the various proton species present in the aqueous solution and is made use of in this work. For instance, ratio of molecular hydrochloric acid (HCl) and dissociated acid (H3O+-Cl−) was found to be between 0.966 and 1.005 in a concentrated (37 wt%) HCl solution, assuming a HCl chemical shift of 0.5 ppm. Moreover, by applying 7Li NMR, the number ratio between Li+ and A336 in the organic phase was found to increase from 0.12 to 5.4 as the LiCl concentration increased from 0.2 to 5 mol/kg in the aqueous phase, before extraction. In addition, the average chemical shift of the –N-CH3 protons in A336 was found to increase linearly with the concentration of Li+ and introduces a simple and fast technique to determine the concentration of Li+ in the organic phase. Not surprisingly, the NMR data suggest that most cations in the organic phase are located in spatial proximity to the –N-CH3 group. Finally, the relative number of Cl− ions in the organic phase, after extraction, was estimated from the NMR data by imposing electrical neutrality, on the solution.

Pulse sequences for measuring exchange rates between proton species: From unlocalised NMR spectroscopy to chemical exchange saturation transfer imaging

Within the field of NMR spectroscopy, the study of chemical exchange processes through saturation transfer techniques has a long history. In the context of MRI, chemical exchange techniques have been adapted to increase the sensitivity of imaging to small fractions of exchangeable protons, including the labile protons of amines, amides and hydroxyls. The MR contrast is generated by frequency-selective irradiation of the labile protons, which results in a reduction of the water signal associated with transfer of the labile protons’ saturated magnetization to the protons of the surrounding free water. The signal intensity depends on the rate of chemical exchange and the concentration of labile protons as well as on the properties of the irradiation field. This methodology is referred to as CEST (chemical exchange saturation transfer) imaging. Applications of CEST include imaging of molecules with short transverse relaxation times and mapping of physiological parameters such as pH, temperature, buffer concentration and chemical composition due to the dependency of this chemical exchange effect on all these parameters. This article aims to describe these effects both theoretically and experimentally. In depth analysis and mathematical modelling are provided for all pulse sequences designed to date to measure the chemical exchange rate. Importantly, it has become clear that the background signal from semi-solid protons and the presence of the Nuclear Overhauser Effect (NOE), either through direct dipole-dipole mechanisms or through exchange-relayed signals, complicates the analysis of CEST effects. Therefore, advanced methods to suppress these confounding factors have been developed, and these are also reviewed. Finally, the experimental work conducted both in vitro and in vivo is discussed and the progress of CEST imaging towards clinical practice is presented.

What Coordinate Best Describes the Affinity of the Hydrated Excess Proton for the Air-Water Interface?

Molecular dynamics simulations and free energy sampling are employed in this work to investigate the surface affinity of the hydrated excess proton with two definitions of the interface: The Gibbs dividing interface (GDI) and the Willard-Chandler interface (WCI). Both the multistate empirical valence bond (MS-EVB) reactive molecular dynamics method and the density functional theory-based ab initio molecular dynamics (AIMD) were used to describe the hydrated excess proton species, including "vehicular" (standard diffusion) transport and (Grotthuss) proton hopping transport and associated structures of the hydrated excess proton net positive charge defect. The excess proton is found to exhibit a similar trend and quantitative free energy behavior in terms of its surface affinity as a function of the GDI or WCI. Importantly, the definitions of the two interfaces in terms of the excess proton charge defect are highly correlated and far from independent of one another, thus undermining the argument that one interface is superior to the other when describing the proton interface affinity. Moreover, the hydrated excess proton and its solvation shell significantly influence the location and local curvature of the WCI, making it difficult to disentangle the interfacial thermodynamics of the excess proton from the influence of that species on the instantaneous surface curvature.

Facilitated proton transfer via water autoprotolysis-electron transfer coupled reactions at thick-film modified electrodes

We present the derivation of a general mathematical model for facilitated proton transfer (FPT) reactions across a liquid|liquid (L|L) interface assisted by a protonatable neutral weak base at a thick organic film modified electrode setup. The effect of the explicit consideration of water autoprotolysis is analysed. The model reported in this paper allows us to simulate the system under different experimental conditions, such as initial pH, organic phase to aqueous phase volume ratio and concentration of redox probe and transferring protonated species. This model for the FPT reactions via water autoprotolysis in a system with two polarized interfaces is compared to our previous results calculated for a single polarizable interface [J. Electroanal. Chem. 578 (2005) 159–170]. We simulate a system with a single redox probe with two reversible non-simultaneous reduction processes with the goal of obtaining detailed mechanistic information of the facilitated proton transfer via water autoprotolysis process at thick-film modified electrodes. Our conclusions can be straightforwardly applied in experiments. We focus on a system consisting of 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a redox probe and 2,9-dimethyl-1,10-phenanthroline (2,9-DMP) as a neutral weak base.

Polymer electrolyte membrane with magnetic nanoparticles containing benzimidazole terminals: An approach to induce proton transfer species on membrane surface

Proton conductive species incorporated in polymer electrolyte membrane (PEM), in general, are randomly existed in the membrane, and this limits the proton transfer efficiency. The present work proposes an approach to align the proton conductive species on the PEM surface so that the first contact of proton species from anode effectively initiates proton transfer efficiently. By simply conjugating benzimidazole (Bz) with magnetic nanoparticles (MagNPs) followed by applying magnetic field, Bz can be induced and aligned on the surface of sulfonated poly (ether ether ketone) (SPEEK) membrane and this results in 10% increment of the proton conductivity. The present work demonstrates a simple way to create a pathway on the membrane surface for proton hopping to improve the proton conductivity.

Measurement of the knees of proton and H&He spectra below 1 PeV

Galactic Cosmic ray (CR) origin is still a mystery. Measuring the knees of the CR spectra for individual species is a very important approach to solve the problem. ARGO-YBJ and LHAASO-WFCTA[1] combined experiment made the first step by measuring the spectrum of hydrogen plus helium nuclei and finding the knee around 0.7 PeV[2]. A significant boost is expected by using LHAASO experiment[3] to measure the spectra and their knees for pure proton and other species in few years. The key is to separate the specific species from all CR samples. In this paper, a multi variate analysis (MVA) approach for the CR composition analysis in LHAASO experiment is discussed. Preliminary results of the analysis and expectations are presented.

Mechanistic role of protonated polar additives in ethanol for selective transformation of biomass-related compounds

We report on a combined experimental, spectroscopic and theoretical study of acid catalysed dehydration-etherification of fructose in ethanol for understanding the mechanistic role of polar solvent additives and product selectivity. Herein, we show that polar solvent additives (e.g. tetrahydrofuran, acetone, acetonitrile, gamma-valerolactone, dimethyl sulfoxide) protonated with a common solid acid catalyst in ethanol allow transformation of biomass-related compounds into desired dehydration or etherification products. Fructose in ethanol with DMSO additive is selectively transformed into 5-hydroxymethylfurfural with negligible formation of 5-ethoxymethylfurfural due to preferential DMSO protonation according to its polarity. Spectroscopic methods and density functional theory show that additives having higher polarity than ethanol are readily protonated and act as the key catalytic protonation species and as the key stabilization species for reaction intermediates. Understanding the mechanism of protonated polar additives in reaction systems allows one to tailor selectivity in acid-catalyzed dehydration-etherification schemes and to develop sustainable chemistry for biomass resources.

In vivo quantification of proton exchange rate in healthy human brains with omega plot.

To implement omega plot method for in vivo mapping of proton exchange rates in human brain by taking into account the water direct saturation (DS) effect and multiple saturation transfer exchanging species in vivo. Four Z-spectra were collected with chemical exchange saturation transfer (CEST) saturation power =1, 2, 3 & 4 µT. Water DS was estimated by fitting the Z-spectrum to a linear combination of multiple Lorentzian components and its contribution to the signal was subsequently removed. Exchange rate maps were derived by the omega plot, consisting of fitting the inverse of the signal intensity, Mz /(M 0-Mz ), as a function of 1/(γB1)2. The exchange rate values quantified with the DS removed omega plot were significantly higher in the GM region than in the WM region (616±29 vs. 575±20 s-1, P<0.001). Phantom studies confirmed that the exchange rates from DS-removed plots varied linearly with pH (R2=0.998) for the pH range of 6.2 to 7.4, whereas exchange rates from conventional omega plots failed to show such linearity in the entire physiological pH range. The calculated exchange rate with DS-corrected omega plot is a weighted average for all saturation transfer exchanging proton species which contribute to Z-spectral signal. The healthy brain exchange rate map provided by DS-removed omega plots may serve as a baseline for detecting any pathological changes.

Mechanisms of Blockade of the Muscle-Type Nicotinic Receptor by Benzocaine, a Permanently Uncharged Local Anesthetic

Most local anesthetics (LAs) are amine compounds bearing one or several phenolic rings. Many of them are protonated at physiological pH, but benzocaine (Bzc) is permanently uncharged, which is relevant because the effects of LAs on nicotinic acetylcholine (ACh) receptors (nAChRs) depend on their presence as uncharged or protonated species. The aims of this study were to assess the effects of Bzc on nAChRs and to correlate them with its binding to putative interacting sites on this receptor. nAChRs from Torpedo electroplaques were microtransplanted to Xenopus oocytes and currents elicited by ACh (IAChs), either alone or together with Bzc, were recorded at different potentials. Co-application of ACh with increasing concentrations of Bzc showed that Bzc reversibly blocked nAChRs. IACh inhibition by Bzc was voltage-independent, but the IACh rebound elicited when rinsing Bzc suggests an open-channel blockade. Besides, ACh and Bzc co-application enhanced nAChR desensitization. When Bzc was just pre-applied it also inhibited IACh, by blocking closed (resting) nAChRs. This blockade slowed down the kinetics of both the IACh activation and the recovery from blockade. The electrophysiological results indicate that Bzc effects on nAChRs are similar to those of 2,6-dimethylaniline, an analogue of the hydrophobic moiety of lidocaine. Furthermore, docking assays on models of the nAChR revealed that Bzc and DMA binding sites on nAChRs overlap fairly well. These results demonstrate that Bzc inhibits nAChRs by multiple mechanisms and contribute to better understanding both the modulation of nAChRs and how LAs elicit some of their clinical side effects.This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Vibrational signatures of curcumin's chelation in copper(II) complexes: An appraisal by IRMPD spectroscopy.

Curcumin (Cur) is a natural polyphenol with a wide spectrum of biological activities and appealing therapeutic potential. Herein, it has been delivered by electrospray ionization as gaseous protonated species, [Cur + H]+, and as a Cu(ii) complex, [Cu(Cur - H)]+, a promising antioxidant and radical scavenger. The gas phase structures were assayed by infrared multiple photon dissociation (IRMPD) spectroscopy in both the fingerprint (800-2000 cm-1) and hydrogen stretching (3100-3750 cm-1) ranges. Comparison between the experimental features and linear IR spectra of the lowest energy structures computed at the B3LYP/6-311+G(d,p) level reveals that bare [Cu(Cur - H)]+ exists in a fully planar and symmetric arrangement, where the metal interacts with the two oxygens of the syn-enolate functionality of deprotonated Cur and both OCH3 groups are engaged in H-bonding with the ortho OH. The effect of protonation on the energetic and geometric determinants of Cur has been explored as well, revealing that bare [Cur + H]+ may exist as a mixture of two close-lying isomers associated with the most stable binding motifs. The additional proton is bound to either the diketo or the keto-enol configuration of Cur, in a bent or nearly planar arrangement, respectively.

The Raman signature of protonic species as a potential tool for dating or authentication of glazed pottery

AbstractIn this study, the potential of Raman spectroscopy is discussed for the comparative dating or authentication of glazed pottery based on the Raman signature of protonic species incorporated in the glazes due to the corrosion processes as a function of time, chemical composition, and environmental conditions. According to the literature and analyses on a reference set of glass samples that had previously been subjected to heavy corrosion in laboratory conditions and extensively studied by Infrared spectroscopy, the accumulation of protonic species such as water and hydroxyl groups on the surface of glassy silicates gives rise to a specific Raman signature in the 2,000–3,800 cm−1 range. The relative intensity of this Raman signature is mainly considered to act as a means of discriminating between old and modern artefacts. In order to check this hypothesis, glazed pottery with different origins (Chinese and Vietnamese stoneware or celadons, blue‐and‐white and painted enamelled porcelains, Islamic terra cottas) and different chemical compositions or processing conditions from a wide time span (~1000 to the present) were analysed by Raman microspectroscopy. Further comparative data was obtained by modifying the experimental parameters such as laser wavelength, objective magnification, and confocal hole. The results showed that Raman intensity of the protonic species shows a correlation with age for lead free glazed pottery in the case of celadons and porcelains. The intensity strongly depends on the chemical composition of the glaze as well as the preservation conditions to a certain degree.

Different Protonic Species Affecting Proton Conductivity in Hollow Spherelike Polyoxometalates.

Polyoxometalates (POMs), which possess strong acidity and chemical stability, are promising solid proton conductors and potential candidates for proton exchange membrane fuel cell applications. To investigate how factors such as proton concentration and carrier affect the overall proton conduction, we have synthesized new compounds HImMo132 (Im, imidazole), HMeImMo132, ILMo132, and TBAMo132 with hollow structures and HImPMo12 with a solid spherelike structure. These crystal models were prepared by encapsulating POM with organic molecules with different proton contents. Among them, the single-crystal sample of the hollow structure HImMo132 containing more proton sources shows a high proton conductivity of 4.98 × 10-2 S cm-1, which was approximately 1 order of magnitude greater than that of the solid cluster HImPMo12 with the same proton sources and 3 orders of magnitude greater than that of the proton-free organic cation-encapsulated giant ball TBAMo132. This study provides a theoretical guidance toward designing and developing new-generation proton conductors and studying their performances at the molecular level.