Deprotonation Of Acid Research Articles

Probing the Closed Association of Oligoquinoline Foldamers by Time-Resolved Fluorescence Anisotropy.

The metal-mediated dimerization of oligoquinoline foldamers terminated at one end with an oligo(phenylenevinylene) and at the other with a carboxylic acid (OPV-QnA, where n = 4, 8, 17, and 33), and the complexation of OPV-Q8A and Q16A was promoted in chloroform by the addition of a concentrated 16 M aqueous sodium hydroxide solution. UV-vis absorption and time-resolved fluorescence anisotropy (TRFA) experiments were conducted to determine, respectively, the concentration and the average rotational time ⟨ϕ⟩ of the mixture of unassociated and associated foldamers across a range of foldamer concentrations spanning 5 orders of magnitude. Plots of ⟨ϕ⟩ as a function of acid group concentration revealed that ⟨ϕ⟩ increased with increasing foldamer concentration only when the foldamer solution in chloroform was vigorously mixed with the 16 M sodium hydroxide aqueous solution. Furthermore, all plots showed that ⟨ϕ⟩ reached a plateau at high foldamer concentration. The increase in ⟨ϕ⟩ reflected the association of foldamers into larger objects through metal ion coordination with the carboxylate anions generated by deprotonation of the carboxylic acid of OPV-QnA with NaOH, while the plateau obtained at high foldamer concentration indicated that these interactions led to the dimerization of the foldamers via a closed association mechanism. Analysis of the ⟨ϕ⟩ trends yielded the equilibrium constants (K) describing the foldamer dimerization, whose value equaled 1.0 (±0.2) × 106 M-1 for the three longer OPV-QnA foldamers, but was about 10 times smaller for the shortest one (n = 4). Association of OPV-Q8A and Q16A yielded a complex with a ⟨ϕ⟩ matching that of OPV-Q24A, and K for this complexation was similar to that for dimerization. These experiments illustrate the robust nature of TRFA as an experimental method to probe the size of rigid, self-assembled foldamers in solution.

A General Iron-Catalyzed Decarboxylative Oxygenation of Aliphatic Carboxylic Acids.

We report an iron-catalyzed decarboxylative C(sp3)-O bond-forming reaction under mild, base-free conditions with visible light irradiation. The transformation uses readily available and structurally diverse carboxylic acids, iron photocatalyst, and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) derivatives as oxygenation reagents. The process exhibits a broad scope in acids possessing a wide range of stereoelectronic properties and functional groups. The developed reaction was applied to late-stage oxygenation of a series of bio-active molecules. The reaction leverages the ability of iron complexes to generate carbon-centered radicals directly from carboxylic acids by photoinduced carboxylate-to-iron charge transfer. Kinetic, electrochemical, EPR, UV/Vis, HRMS, and DFT studies revealed that TEMPO has a triple role in the reaction: as an oxygenation reagent, an oxidant to turn over the Fe-catalyst, and an internal base for the carboxylic acid deprotonation. The obtained TEMPO adducts represent versatile synthetic intermediates that were further engaged in C-C and C-heteroatom bond-forming reactions using commercial organo-photocatalysts and nucleophilic reagents.

A General Iron‐Catalyzed Decarboxylative Oxygenation of Aliphatic Carboxylic Acids

AbstractWe report an iron‐catalyzed decarboxylative C(sp3)−O bond‐forming reaction under mild, base‐free conditions with visible light irradiation. The transformation uses readily available and structurally diverse carboxylic acids, iron photocatalyst, and 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO) derivatives as oxygenation reagents. The process exhibits a broad scope in acids possessing a wide range of stereoelectronic properties and functional groups. The developed reaction was applied to late‐stage oxygenation of a series of bio‐active molecules. The reaction leverages the ability of iron complexes to generate carbon‐centered radicals directly from carboxylic acids by photoinduced carboxylate‐to‐iron charge transfer. Kinetic, electrochemical, EPR, UV/Vis, HRMS, and DFT studies revealed that TEMPO has a triple role in the reaction: as an oxygenation reagent, an oxidant to turn over the Fe‐catalyst, and an internal base for the carboxylic acid deprotonation. The obtained TEMPO adducts represent versatile synthetic intermediates that were further engaged in C−C and C‐heteroatom bond‐forming reactions using commercial organo‐photocatalysts and nucleophilic reagents.

Novel perspectives on the mechanism of phosphate conversion coating on magnesium alloys

Chemical conversion coating (CCC) is a cost-effective and industrially scalable technique to tackle the issue of corrosion of Magnesium and its alloys, crucial for reducing global greenhouse gas emissions by the road transportation sector. Amongst all the possible CCCs, the phosphate conversion coating (PCC) has one of the highest industrial application potential. This article demonstrates limitations in the traditional understanding of Mg-PCC mechanism, primarily dictated by increased local pH near the Mg-substrate leading to double deprotonation of phosphoric acid (H3PO4 → H2PO4− + H+; H2PO4− → HPO42− + H+). The HPO42− further reacts to Mg2+ and subsequent supersaturation of precipitate, MgHPO4.3H2O results in the coating formation. The new hypothesis proposed for Mg-PCC is based on the argument that the second deprotonation reaction is energetically unfavorable, instead, the reaction is mostly limited to the first deprotonation of the phosphoric acid resulting in H2PO4−. This H2PO4− reacts to the Mg2+ and forms an intermediate complex ion, (Mg2+-H2PO4−)+. The Mg substrate, when exposed to an aqueous environment, releases Mg2+, resulting in a negatively charged substrate. The complex (Mg2+-H2PO4−)+ ions are electrostatically attracted to the negatively charged substrate resulting in the reaction responsible for MHPT (MgHPO4.3H2O) coating. This new hypothesis is supported by thermodynamic calculations through density functional theory (DFT) and experiments.

Deprotonation of formic, acetic acids and bicarbonate ion in slit silica nanopores at infinite dilution and in the presence of electrolytes

Dielectric effects and the coupled electrostatics between the nanoconfined and the internal/external aqueous media contribute to the observed deviations of chemistry within the nanoconfined environment when compared with unconfined systems. A systematic understanding has remained elusive, especially with respect to background salt concentration and boundary condition effects like the nanopore surface chemistry and the reference state used to calculate free energies. We utilize molecular dynamics simulations along with thermodynamic integration to determine the free energy difference associated with acid-base chemistry in 2 nm and 4 nm slit pores open to a bulk-like reservoir. pKa increases are predicted when confining acetic acid, formic acid, and bicarbonate in the slits at infinite dilution conditions. We find that confinement weakens the acids, and the modulation of outer pore surface dipole magnitudes can tune the pKa shift values, suggesting that purely “intrinsic” electrostatic effect on confinement may not exist. At sufficiently high salt concentrations, the dielectric/electrostatic effects on pKa values diminish due to charge screening effects. These discoveries enable future modifications of nanopore chemistries to achieve desirable properties for industrial applications.

Assembly of Amorphizing Porous Bimetallic Metal‐Organic Frameworks Spheres with Zn─O─Fe Cluster and Coordination Deficiency via Ligand Competition for Efficient Electro‐Fenton Catalysis

AbstractElectro‐Fenton process stands out as a highly promising approach for generating reactive oxygen‐containing radicals to address the escalating issue of environmental pollution. However, the long‐term goal of application necessitates ongoing pursuit of high‐quality catalysts with both sufficient activity and stability. Herein, a general route is reported for large‐scale synthesis of amorphizing porous bimetallic metal‐organic framework (MOF) spheres with Zn─O─Fe structure and coordination deficiency through facile and low‐cost synthesis of ligand competition. Assisted by a coordination modulator, deprotonation of terephthalic acid is accelerated and rapid synthesis of amorphous bimetallic MOF spheres is successfully achieved at room temperature. As inactive metal Zn is introduced into metal clusters of MOFs, the cycling efficiency of Fe3+/Fe2+ is improved and a secondary building unit of Zn─O─Fe is constructed, greatly accelerating electron conduction rate. Compared to crystalline spindle cMIL‐88B(Fe2Zn) by traditional solvothermal route, amorphous aMIL‐88B(Fe2Zn) has a unique spherical porous structure with larger surface area, higher conductivity, and more exposed active sites. Endowed with unique textural and surface chemistry, aMIL‐88B(Fe2Zn) exhibits superior catalytic activity in the degradation of refractory organic pollutants. The progress offers a feasible way to rational design of iron‐based hybrid MOF materials with tunable structures and enhance properties for various applications.

Unlocking the Myths of Molecular Bonding State in Modulating Oxidation and Anderson Localization for Inorganic Sn/Pb‐based Perovskite Solar Cells

AbstractThe improvement of photovoltaic and stability performance of tin (Sn)‐based halide perovskite solar cells is impeded by notorious oxidation issues and Anderson localization. Despite previous implements in antioxidation through the incorporation of Lewis base additives, there still exist ongoing uncertainties surrounding its complex interaction mechanisms. A perplexing phenomenon regarding accelerated oxidation in acrylic acid is discovered that deviates from conventional Lewis base–acid reaction. The underlying insights into the deprotonation of acrylic acid followed by the formation of a “tripod” ionic bonding form are provided, which results in amplifying the delocalization effect of electrons of Sn2+. Furthermore, with the assistance of acrylamide and acrolein, synergistic enhancement in terms of the antioxidation and suppression of Anderson localization can be achieved — a concept referred to as “Dual Synergistic Engineering”. This suppresses the oxidation of Sn2+ and reduces Sn4+ content by ≈76%. Meanwhile, the diffusion length is prolonged significantly from 195.9 to 458.9 nm. The optimized all‐inorganic Sn/Pb‐based perovskite solar cells exhibit a power conversion efficiency of above 14% with enhanced stability. These findings provide an alternative viewpoint for comprehending the impact of chemical interaction on oxidation and crystal growth in Sn/Pb‐based perovskites.

Features of analytical control of glyphosate salts in preparative formulations

Goal. Development of a method of analytical control of glyphosate in preparative forms of herbicides.
 Methods. Determination of glyphosate was carried out by the chromatographic method of thin-layer chromatography (TLC) using Sorbfil plates with a thin layer of silica gel KSK adsorbent. The active substance was identified by the value of Rf, quantitative determination was based on the formalized dependence of the size of the area of the chromatographic zones on the amount of glyphosate.
 Results. Physicochemical properties of herbicides — electrolytes, to which glyphosate belongs, create special problems when developing methods for its determination in various matrices. In herbicides and desiccants, glyphosate (as a salt) usually takes the form of a deprotonated acid residue and a corresponding cation. Therefore, the determination of the active substance is carried out by the acid residue, which is important for the quantitative assessment of its content in the matrix both in the acid equivalent and in the form of the corresponding salt. The density of the preparative form serves, in particular, as a criterion for controlling the form of the glyphosate salt. The method is based on dissolution of the preparation form in 44% ethanol and quantitative determination by TLC method. The determination of the active substance is not hindered by other components of the preparations, derivatives of glycine and amines.The optimal conditions of analysis were chosen using the conceptual designs of the laboratory «Algorithm of chemical-analytical monitoring of pesticides» and «System of multi-quantitative determination of pesticides in matrices», according to which the main stages of the process are extraction/dissolution, purification of extracts, elution (chromatographic process), identification and quantitative analysis . Selective conditions for TLC determination — mobile phase with pH 9: distilled water + ethanol + aqueous ammonia (22 + 20 + 0.25 by volume), developing reagent: a specific complex of ninhydrin with cadmium acetate in an acidic medium. Quantitative determination is carried out taking into account the coefficients of conversion of the corresponding salt form to the acid equivalent.
 Conclusions. The use of the chromatographic method of thin-layer chromatography makes it possible to control the content of the active substance glyphosate in various salt formulations in preparative forms of herbicides and desiccants with high accuracy and reproducibility.

Parallel electromembrane extraction of peptides with monoterpene and medium-length fatty acid deep eutectic solvents

BackgroundElectromembrane extraction (EME) involves the process of mass transfer of charged analytes from an aqueous sample through an organic liquid membrane into an aqueous acceptor medium under the influence of an electrical field. Successful solvation of the analyte within the liquid membrane is of paramount importance and involves molecular interactions with the liquid membrane. In this comprehensive investigation, parallel EME was examined using a training set of 13 model peptides employing deep eutectic solvents as the liquid membrane. These deep eutectic solvents were formulated by mixing specific monoterpenes (thymol, menthol, camphor) with medium-chain fatty acids (1-octanoic acid and 1-decanoic acid). ResultsFrom an array of different liquid membrane compositions explored, it was revealed that the combination of camphor and 1-decanoic acid (in a 1:1 w/w ratio) with 2% di (2-ethylhexyl) phosphate (DEHP) delivered the most efficient extraction system. The solvation of the model peptides within this liquid membrane predominantly relied on ionic interactions between protonated basic functionalities and DEHP, along with hydrogen bond interactions between the deprotonated acid functionalities (hydrogen bond acceptor) and 1-decanoic acid (hydrogen bond donor). Selectivity was modulated by the pH of the sample and acceptor solutions, with a direct correlation to the polarity and net charge of the model peptides. The ionization of 1-decanoic acid in the interfacial region between the sample and liquid membrane emerged as an important factor influencing the selectivity. Significance and noveltyAlthough parallel EME of peptides has been reported previously, the current liquid membrane provides an extraction system with sufficient stability for the first time. Selective extraction of peptides through EME holds substantial promise within the realm of next-generation environmentally-friendly sample preparation methodologies. The findings presented in this paper contribute significantly to our fundamental understanding of these processes, and may serve as an important reference for the development of future methods in this field.

Theoretical study of the formation of pyrazole and indazole carbamic acids

A theoretical study of the formation of carbamic acids of pyrazole and indazole has been carried out using DFT computational methods. The effects of the substituents and the solvent (using explicit and implicit solvent models) have been considered. In addition, the deprotonation of the carbamic acid and its influence on the stability of the system has been calculated. In the neutral systems, only the formation of indazole-1-carbamic acid derivatives is favored vs. the non-covalent complexes between pyrazole or indazole with CO2. The deprotonation of the carbamic acid highly stabilizes the system preventing its dissociation.

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. The vibrational signatures associated with the fluxional proton bonding and its coupling with the hydroxyglutaric backbone are investigated here with infrared action ion spectroscopy experiments and Born-Oppenheimer molecular dynamics (BOMD) computations. Despite the formally similar symmetry of protonated and deprotonated hydroxyglutaric acid, the relative proton affinities of the oxygen centers of the carboxylic and carboxylate groups with respect to that of the central hydroxyl group lead to distinct proton dynamics. In the protonated acid, a tautomeric arrangement of the type HOCO·[HOH]+·OCOH is preferred with the proton binding tighter to the central hydroxyl moiety and the electronic density being shared between the two nearly symmetric H-bonds with the carboxylic end groups. In the deprotonated acid, the asymmetric [OCO]-·HO·HOCO configuration is more stable, with a stronger H-bonding on the bare carboxylate end. Both systems display active backbone dynamics and concerted Grothuss-like proton motions, leading to diffuse band structures in their vibrational spectra. These features are accurately reproduced by the BOMD computations.

Visualizing the Promoting Role of Interfacial Water in the Deprotonation of Formic Acid on Cu(111).

Water plays a crucial role in various heterogeneous catalytic reactions, but the atomic-scale characterization of how water participates in these chemical processes remains a significant challenge. Here we directly visualize the promoting role of interfacial water in the deprotonation of formic acid (FA) on a metal surface, using combined scanning tunneling microscopy and qPlus-based noncontact atomic force microscopy. We find the dissociation of FA when coadsorbed with water on the Cu(111) surface, resulting in the formation of hydronium and formate ions. Interestingly, most of the hydrated proton and formate ions exhibit a phase-separated behavior on Cu(111), in which Eigen and Zundel cations assemble into a monolayer hexagonal hydrogen-bonding (H-bonding) network, and bidentate formate ions are solvated with water and aggregate into one-dimensional chains or two-dimensional H-bonding networks. This phase-separated behavior is essential for preventing the proton transfer back from hydronium to formate and the reformation of FA. Density functional theory calculations reveal that the participation of water significantly reduces the deprotonation barrier of FA on Cu(111), in which water catalyzes the decomposition of FA through the Grotthuss proton transfer mechanism. In addition, the separate solvation of hydronium and bidentate formate ions is energetically preferred due to the enhanced interaction with the copper substrate. The promoting role of water in the deprotonation of FA is further confirmed by the temperature-programmed desorption experiment, which shows that the intensity of the H2 desorption peak significantly increases and the desorption of FA declines when water and FA coadsorbed on the Cu(111) surface.

Anchoring self-assembled monolayer at perovskite/hole collector interface for wide bandgap Sn-based solar cells with a record efficiency over 12%

In perovskite solar cells (PSCs), surface and interfacial conditions play a crucial role in determining overall device performance. In typical p-i-n architecture of wide bandgap (WBG, 1.6–1.8 eV) Sn-based PSCs, the interface between hole transport layer (HTL) and perovskite (PVK) has a significant impact on hole transport, interfacial chemical interactions, and perovskite film quality. This study aims to address these issues by incorporating self-assembled monolayers (SAMs) MeO-2PACz and 2PACz at the PEDOT:PSS HTL/Sn-PVK interface. X-ray photoelectron spectroscopy confirmed the interaction between the anchoring group (P-O−) of the SAM and S+ in PEDOT:PSS through phosphonic acid deprotonation at the interface, and improved work function was observed through the UPS study. Furthermore, the SAMs contributed to the formation of a compact PVK film with enhanced preferential orientation. Interestingly, a chemical interaction between the oxygen-donor of the methoxy (CH3O−) terminal group in MeO-2PACz and the Sn-halide octahedra was observed, which partly contributed to suppress the oxidation of Sn2+ state and defect density of perovskite. Additionally, femtosecond transient absorption spectroscopy (fs-TAS) showed faster trap filling (τ1) characteristics (τ1∼19 ps). Fs-TAS and photoluminescence further indicated fast hole extraction (τ2∼125 ps) as well as high quenching efficiency of 47%. Based on these findings, an unprecedented efficiency of η∼12.16% (certified 11.60%) was achieved in WBG Sn-PSCs using the HTL/MeO-2PACz/PVK structure, outperforming the HTL/2PACz/PVK (8.78%) and HTL/PVK (7.44%) structures. This study provides crucial guidelines on interfacial engineering for WBG Sn-PSCs.

Advantages of Multidimensional Biasing in Accelerated Dynamics: Application to the Calculation of the Acid pKa for Acetic Acid.

The use of accelerated sampling methods such as metadynamics has shown a significant advantage in calculations that involve infrequent events, which would otherwise require sampling a prohibitive number of configurations to determine the difference in free energies between two or more chemically distinct states such as in the calculation of acid dissociation constants Ka. In this case, the most common method is to bias the system via a single collective variable (CV) representing the coordination number of the proton donor group, which yields results in reasonable agreement with experiments. Here we study the deprotonation of acetic acid using the reactive force field ReaxFF and observe a significant dependence of Ka on the simulation box size when biasing only the coordination number CV, which is due to incomplete sampling of the deprotonated state for small simulation systems and inefficient sampling for larger ones. Incorporating a second CV representing the distance between the H3O+ cation and the acetate anion results in substantially more efficient sampling, both accelerating the dynamics and virtually eliminating the computational box size dependence.

Investigation of thiol compounds (L-cysteine, thioacetic acid and ethanethiol) with V(V) and V(IV) using combined spectroscopy and chromatography

The interactions of V(V) and L-cysteine, thioacetic acid and ethanethiol were studied in aqueous solution using chromatographic and spectral analysis. The chromatographic determination of V(V) and V(IV) species in the presence of thiols was enabled by inducing the ligand exchange reaction with EDTA as the competing ligand. Analytical setup allowed investigation of the possible redox and structural transformations of V(V) in the presence of thiols used over a wide pH range. Obtained data strongly suggest that the reduction of V(V) is proton catalyzed in case of L-cysteine and thioacetic acid. In the case of ethanethiol, the reduction did not seem to be proton dependent, as no reduction was observed above pH = 2. Thus, reduction was inhibited by the deprotonation of L-cysteine and thioacetic acid, with L-cysteine being the strongest reducing agent of V(V), followed by thioacetic acid and finally ethanethiol. Apart from structural thiol properties, the reduction reaction seems to be influenced by the aqueous V(V) speciation due to the observed nonlinear kinetics. In the case of all investigated thiols, the formation of V(V)-thioester intermediate species was an essential step for V(V) reduction. The structural properties of the V(IV)-thiol complexes were also found to be pH-dependent.

Ultrafast protein response in the Pfr state of Cph1 phytochrome

Photoisomerization is a fundamental process in several classes of photoreceptors. Phytochromes sense red and far-red light in their Pr and Pfr states, respectively. Upon light absorption, these states react via individual photoreactions to the other state. Cph1 phytochrome shows a photoisomerization of its phycocyanobilin (PCB) chromophore in the Pfr state with a time constant of 0.7 ps. The dynamics of the PCB chromophore has been described, but whether or not the apoprotein exhibits an ultrafast response too, is not known. Here, we compare the photoreaction of 13C/15N labeled apoprotein with unlabeled apoprotein to unravel ultrafast apoprotein dynamics in Cph1. In the spectral range from 1750 to 1620 cm−1 we assigned several signals due to ultrafast apoprotein dynamics. A bleaching signal at 1724 cm−1 is tentatively assigned to deprotonation of a carboxylic acid, probably Asp207, and signals around 1670 cm−1 are assigned to amide I vibrations of the capping helix close to the chromophore. These signals remain after photoisomerization. The apoprotein dynamics appear upon photoexcitation or concomitant with chromophore isomerization. Thus, apoprotein dynamics occur prior to and after photoisomerization on an ultrafast time-scale. We discuss the origin of the ultrafast apoprotein response with the ‘Coulomb hammer’ mechanism, i.e. an impulsive change of electric field and Coulombic force around the chromophore upon excitation.Graphical abstract

About Gas Barrier Performance and Recyclability of Waterborne Coatings on Paperboard

For preserving food packed in environmentally friendly and recyclable paperboard packages, it is important to have sufficient gas barrier performance of the paperboard container. Paperboard has poor intrinsic barrier properties and to overcome this deficiency, so a barrier coating is needed that does not hinder the recycling of the paperboard substrate. However, the gas barrier properties and the recyclability of such coatings have been rarely studied. Here, both the gas barrier performance and the removal of an alkali-soluble resin (ASR)-stabilized waterborne barrier coatings from paperboard are investigated. For barriers for gases, such as nitrogen, carbon dioxide, and oxygen, defect-free coatings are needed which is achieved by applying three coating layers. The oxygen transmission rate (OTR) of the three-layered coating on paperboard was 920 cm3/(m2∙day). For water vapor barriers, two coating layers already show a strong improvement, as water follows a different penetration mechanism than the other tested gases. The water vapor transmission rate WVTR of double coated paperboard was 240 g/(m2∙day). Preliminary results show that the coating is removed by immersion of the coated paperboard in an aqueous alkaline solution at room temperature. This causes de-protonation of the carboxylic acids of the ASR and subsequent re-dispersion of the coating in water. Removing double-layer coatings from the paperboard is more challenging, possibly due to the coating/coating interface between the two coating layers and enhanced adhesion between coating and paperboard.

A potential novel and general route for bromide replacement in diimine ReI tricarbonyl complexes leading to carboxylates: The effect in luminescence

The reaction of the 3,5-dimethylpyrazolyl-pyridazine-6-carboxylic acid (Me2LCOOH) or pyrazolyl-pyridazine-6-carboxylic acid (LCOOH) with [(THF)(CO)3Re(µ-Br)2Re(CO)3(THF)] in DMF followed by the addition of traces of water leads to a series of dehalided rhenium(I) tricarbonyl carboxylates: [(Me2LCOO)(H2O)Re(CO)3] and [(LCOO)(H2O)Re(CO)3] instead of the normal rhenium(I) tricarbonyl bromide obtained by reaction in chloroform, [(Me2LCOOH)Re(CO)3Br]. The reaction is believed to occur through adventitious amine in the reaction media which leads to the carboxylic acid deprotonation and reaction. To test this idea the diimine-rhenium(I) tricarbonyl bromide [(phen)Re(CO)3Br] and [(bppdz)Re(CO)3Br] (phen: 1,10-phenanthroline; bppdz: 3,6-bis(1H-pyrazol-1-yl)pyridazine) were reacted with glacial acetic acid and triethylamine in dry DMF at room temperature. These reaction lead to the corresponding rhenium(I) acetates [(phen)Re(CO)3(OOCCH3)] and [(bppdz)Re(CO)3(OOCCH3)] in good to high yields using soft reaction conditions and without the use of a silver salt. Thiethylammonium bromide is also obtained from the reaction. Moreover, the fact that this unexpected rhenium(I) tricarbonyl carboxylates were obtained in as N,N and N,O coordination isomers for [(Me2LCOO)(H2O)Re(CO)3] and the comparison of the newly synthetized [(phen)Re(CO)3(OOCCH3)] and [(bppdz)Re(CO)3(OOCCH3)] compounds with their corresponding bromides allow to stablish that the replacement of the halide by a carboxylate hypsochromically shift the energy of the MLCT band while the emission experiences the opposite, it is bathochromically shifted. The emission quantum yields are slightly diminished. Interestingly the [(phen)Re(CO)3(OOCCH3)] and [(bppdz)Re(CO)3(OOCCH3)] acetates are dual emitters.

Amino acid deprotonation rates from classical force fields.

Acid ionization constants (pKa's) of titratable amino acid side chains have received a large amount of experimental and theoretical attention. In many situations, however, the rates of protonation and deprotonation, kon and koff, may also be important, for example, in understanding the mechanism of action of proton channels or membrane proteins that couple proton transport to other processes. Protonation and deprotonation involve the making and breaking of covalent bonds, which cannot be studied by classical force fields. However, environment effects on the rates should be captured by such methods. Here, we present an approach for estimating deprotonation rates based on Warshel's extension of Marcus's theory of electron transfer, with input from molecular simulations. The missing bond dissociation energy is represented by a constant term determined by fitting the pKa value in solution. The statistics of the energy gap between protonated and deprotonated states is used to compute free energy curves of the two states and, thus, free energy barriers, from which the rate can be deduced. The method is applied to Glu, Asp, and His in bulk solution and select membrane proteins: the M2 proton channel, bacteriorhodopsin, and cytochrome c oxidase.

Amino Acids Compete with Ammonia in Sulfuric Acid-Based Atmospheric Aerosol Prenucleation: The Case of Glycine and Serine.

We present a computational investigation of the sulfuric acid, glycine, serine, ammonia, and water system to understand if this system can form prenucleation clusters, which are precursors to larger aerosols in the atmosphere. We have performed a comprehensive configurational search of all possible clusters in this system, starting with the four different monomers and zero to five waters. Accurate Gibbs free energies of formation have been calculated with the DLPNO-CCSD(T)/complete basis set (CBS) method on ωb97xd/6-31++G** geometries. For the dry dimers of sulfuric acid, the weakest base, serine, is found to form the most stable complex, which is a consequence of the strong di-ionic complex formed between the bisulfate ion and the protonated serine cation. For the dry dimers without sulfuric acid, the glycine-serine complex is more stable than the glycine-ammonia or serine-ammonia complexes, stemming from the detailed structure and not related to base strength. For the larger complexes, sulfuric acid deprotonates and the proton is shifted to glycine, serine, or ammonia. The two amino acids and ammonia are almost interchangeable and there is no easy way to predict which molecule will be protonated without the calculated results. Assuming reasonable starting concentrations and a closed system of sulfuric acid, glycine, serine, ammonia, and five waters, we predict the concentrations of all possible complexes at two temperatures spanning the troposphere. The most negative ΔG° values are a function of the detailed molecular interactions of these clusters. These details are more important than the base strength of ammonia, glycine, and serine.