Proton-Coupled Redox Switching in an Annulated π-Extended Core-Modified Octaphyrin.

Proton-coupled electron transfer (PCET) is an important chemical and biological phenomenon. It is attractive as an on-off switching mechanism for redox-active synthetic systems but has not been extensively exploited for this purpose. Here we report a core-modified planar weakly antiaromatic/nonaromatic octaphyrin, namely, a [32]octaphyrin(1.0.1.0.1.0.1.0) (1) derived from rigid naphthobipyrrole and dithienothiophene (DTT) precursors, that undergoes proton-coupled two-electron reduction to produce its aromatic congener in the presence of HCl and other hydrogen halides. Evidence for the production of a [4 n + 1] π-electron intermediate radical state is seen in the presence of trifluoroacetic acid. Electrochemical analyses provide support for the notion that protonation causes a dramatic anodic shift in the reduction potentials of octaphyrin 1, thereby facilitating electron transfer from halide anions (viz. I-, Br-, and, Cl-). Electron-rich molecules, such as tetrathiafulvene (TTF), phenothiazine (PTZ), and catechol, were also found to induce PCET in the case of 1. Both the oxidized and two-electron reduced forms of 1 were characterized by X-ray diffraction analyses in the solid state and in solution via spectroscopic means.

Modeling (15)N NMR chemical shift changes in protein backbone with pressure.

Nitrogen chemical shift is a useful parameter for determining the backbone three-dimensional structure of proteins. Empirical models for fast calculation of N chemical shift are improving their reliability, but there are subtle effects that cannot be easily interpreted. Among these, the effects of slight changes in hydrogen bonds, both intramolecular and with water molecules in the solvent, are particularly difficult to predict. On the other hand, these hydrogen bonds are sensitive to changes in protein environment. In this work, the change of N chemical shift with pressure for backbone segments in the protein ubiquitin is correlated with the change in the population of hydrogen bonds involving the backbone amide group. The different extent of interaction of protein backbone with the water molecules in the solvent is put in evidence.

A THz/FTIR fingerprint of the solvated proton: evidence for Eigen structure and Zundel dynamics.

In continuation of earlier work on La(III), Ni(II) and Mn(II) halides, we present low frequency (30-400 cm(-1)) spectra of solvated HCl and HBr as a function of solute concentration. This frequency range provides direct access to water network modes and changes induced by solvated solutes. We were able to dissect the spectra into components associated to solvated ions and ion pairs using a chemical equilibrium model in combination with principal component analysis. While the Cl(-) rattling mode at 190 cm(-1) is found to be unchanged, the Br(-) resonance around 90 cm(-1) is decreased in intensity below the detection threshold when replacing the divalent or trivalent metal ions by a proton. The solvated proton shows two resonances: a solvation water mode around 140 cm(-1) and a high frequency resonance at 325 cm(-1) that we assign to the rattling motion of an Eigen structure H3O(+) in its solvation cage. This assignment is corroborated by isotopic substitution measurements which show a redshift of the high frequency peak when HCl/H2O is replaced by DCl/D2O. The linewidth of the H3O(+) rattling mode corresponds to a relaxation time of the oscillatory process of τ ≈ 60 fs, considerably faster than the relaxation time of τ ≈ 160 fs for Cl(-). In addition, we find a broad background that we attribute to fast non-oscillatory motions of a proton in a Zundel-like complex. Our results are in agreement with an Eigen-Zundel-Eigen (EZE) model of proton transport. Upon ion pairing the broad background is strongly reduced indicating a reduction of fast proton transfer processes. The Cl(-) resonance blueshifts by 20 cm(-1) which indicates a transition from free ions to a solvent shared ion pair. Surprisingly, the center frequency of the Eigen complex does not change upon ion pairing. This can be rationalized in terms of an unchanged local solvation structure.

Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range.

The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene → products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k1b = (3.70 ± 0.42) × 10(-11) exp[-(772 ± 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k1 = (1.82 ± 0.48) × 10(-12) exp[(607 ± 70)/T] or, in a biexponential form, k1 = k1a + k1b = 3.7 × 10(-11) exp(-772/T) + 6.3 × 10(-13) exp(856/T), independent of the pressure between 1 and 5 Torr of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant.

Mercury adsorption characteristics of HBr-modified fly ash in an entrained-flow reactor.

In this study, the mercury adsorption characteristics of HBr-modified fly ash in an entrained-flow reactor were investigated through thermal decomposition methods. The results show that the mercury adsorption performance of the HBr-modified fly ash was enhanced significantly. The mercury species adsorbed by unmodified fly ash were HgCl2, HgS and HgO. The mercury adsorbed by HBr-modified fly ash, in the entrained-flow reactor, existed in two forms, HgBr2 and HgO, and the HBr was the dominant factor promoting oxidation of elemental mercury in the entrained-flow reactor. In the current study, the concentration of HgBr2 and HgO in ash from the fine ash vessel was 4.6 times greater than for ash from the coarse ash vessel. The fine ash had better mercury adsorption performance than coarse ash, which is most likely due to the higher specific surface area and longer residence time.

Highly stable photoelectrochemical water splitting and hydrogen generation using a double-band InGaN/GaN core/shell nanowire photoanode.

We report on the first demonstration of stable photoelectrochemical water splitting and hydrogen generation on a double-band photoanode in acidic solution (hydrogen bromide), which is achieved by InGaN/GaN core/shell nanowire arrays grown on Si substrate using catalyst-free molecular beam epitaxy. The nanowires are doped n-type using Si to reduce the surface depletion region and increase current conduction. Relatively high incident-photon-to-current-conversion efficiency (up to ~27%) is measured under ultraviolet and visible light irradiation. Under simulated sunlight illumination, steady evolution of molecular hydrogen is further demonstrated.

Orbital compartment syndrome in a burn patient without aggressive fluid resuscitation.

INTRODUCTION: Orbital compartment syndrome may rarely occur in the setting of burns where therapy includes aggressive fluid resuscitation. CASE: We report a case of bilateral orbital compartment syndrome in a 13-year-old male, with superficial facial burns secondary to hydrobromic acid, who did not receive aggressive fluid resuscitation. The patient was treated successfully with bilateral lateral canthotomy and cantholysis. COMMENT: Facial burns may lead to orbital compartment syndrome without aggressive fluid resuscitation, likely due to excessive leakage of fluid and protein into the orbit combined with an inflammatory reaction.

Crystal structures of a type-1 ribosome inactivating protein from Momordica balsamina in the bound and unbound states.

The ribosome inactivating proteins (RIPs) of type 1 are plant toxins that eliminate adenine base selectively from the single stranded loop of rRNA. We report six crystal structures, type 1 RIP from Momordica balsamina (A), three in complexed states with ribose (B), guanine (C) and adenine (D) and two structures of MbRIP-1 when crystallized with adenosine triphosphate (ATP) (E) and 2'-deoxyadenosine triphosphate (2'-dATP) (F). These were determined at 1.67Å, 1.60Å, 2.20Å, 1.70Å, 2.07Å and 1.90Å resolutions respectively. The structures contained, (A) unbound protein molecule, (B) one protein molecule and one ribose sugar, (C) one protein molecule and one guanine base, (D) one protein molecule and one adenine base, (E) one protein molecule and one ATP-product adenine molecule and (F) one protein molecule and one 2'-dATP-product adenine molecule. Three distinct conformations of the side chain of Tyr70 were observed with (i) χ(1)=-66°and χ(2)=165° in structures (A) and (B); (ii) χ(1)=-95° and χ(2)=70° in structures (C), (D) and (E); and (iii) χ(1)=-163° and χ(2)=87° in structure (F). The conformation of Tyr70 in (F) corresponds to the structure of a conformational intermediate. This is the first structure which demonstrates that the slow conversion of DNA substrates by RIPs can be trapped during crystallization.

An electronic structure theory investigation of the physical chemistry of the intermolecular complexes of cyclopropenylidene with hydrogen halides.

The proton accepting and donating abilities of cyclopropenylidene (c-C(3)H(2)) on its complexation with hydrogen halides H-X (X = F, Cl, Br) are analyzed using density-functional theory with three functionals (PBE0, B3LYP, and B3LYP-D) and benchmarked against second-order Møller-Plesset (MP2) theory. Standard signatures including, inter alia, dipole moment enhancement, charge transfer from the carbenic lone pair to the antibonding σ*(H-X) orbital, and H-X bond elongation are examined to ascertain the presence of hydrogen bonding in these complexes. The latter property is found to be accompanied with a pronounced red shift in the bond stretching frequency and with a substantial increase in the infrared intensity of the band on complex formation. The MP2/aug-cc-pVTZ c-C(3)H(2)···H-F complex potential energy surface turns out to be an asymmetric deep single well, while asymmetric double wells are found for the c-C(3)H(2)···H-Cl and c-C(3)H(2)···H-Br complexes, with an energy barrier of 4.1 kcal mol(-1) for proton transfer along the hydrogen bond in the latter complex. Hydrogen-bond energy decomposition, with the reduced variational space self-consistent field approach, indicates that there are large polarization and charge-transfer interactions between the interacting partners in c-C(3)H(2)···H-Br compared to the other two complexes. The C···H bonds are found to be predominantly ionic with partial covalent character, unveiled by the quantum theory of atoms in molecules. The present results reveal that the c-C(3)H(2) carbene divalent carbon can act as a proton acceptor and is responsible for the formation of hydrogen bonds in the complexes investigated.

Monoesterase activity of a purple acid phosphatase mimic with a cyclam platform.

The synthesis and characterization of a novel dinucleating ligand L (L=4,11-dimethyl-1,8-bis{2-[N-(di-2-pyridylmethyl)amino]ethyl}cyclam) and its µ-oxo-bridged diferric complex [(H(2)L){Fe(III)(2)(O)}(Cl)(4)](2+) are reported. This diiron(III) complex is the first example of a truly functional purple acid phosphatase (PAP) mimic as it accelerates the hydrolysis of the activated phosphomonoester 2,4-dinitrophenyl phosphate (DNPP). The spectroscopic and kinetic data indicate that only substrates that are monodentately bound to one of the two ferric ions can be attacked by a suitable nucleophile. This is, most probably, a terminal iron(III)-bound hydroxide. DFT calculations support this assumption and also highlight the importance of secondary interactions, exerted by the protonated cyclam platform, for the positioning and activation of the iron(III)-bound substrate. Similar effects are postulated in the native enzyme but addressed in PAP mimics for the first time.

Structural hierarchy controls deformation behavior of collagen.

The structure of collagen, the most abundant protein in mammals, consists of a triple helix composed of three helical polypeptide chains. The deformation behavior of collagen is governed by molecular mechanisms that involve the interaction between different helical hierarchies found in collagen. Here, we report results of Steered Molecular Dynamics study of the full-length collagen molecule (~290 nm). The collagen molecule is extended at various pulling rates ranging from 0.00003/ps to 0.012/ps. These simulations reveal a new level of hierarchy exhibited by collagen: helicity of the triple chain. This level of hierarchy is apparent at the 290 nm length and cannot be observed in the 7-9 nm models often described to evaluate collagen mechanics. The deformation mechanisms in collagen are governed by all three levels of hierarchy, helicity of single chain (level-1), helical triple helix (level-2), and hereby described helicity of the triple chain (level-3). The mechanics resulting from the three levels is described by an interlocking gear analogy. In addition, remarkably, the full-length collagen does not show much unwinding of triple helix unlike that exhibited by short collagen models. Further, the full-length collagen does not show significant unwinding of the triple helix, unlike that exhibited by short collagen. Also reported is that the interchain hydrogen bond energy in the full-length collagen is significantly smaller than the overall interchain nonbonded interaction energies, suggesting that the nonbonded interactions have far more important role than hydrogen bonds in the mechanics of collagen. However, hydrogen bonding is essential for the triple helical conformation of the collagen. Hence, although mechanics of collagen is controlled by nonbonded interchain interaction energies, the confirmation of collagen is attributed to the interchain hydrogen bonding.

Identification and structural elucidation of two process impurities and stress degradants in darifenacin hydrobromide active pharmaceutical ingredient by LC-ESI/MS(n).

The present study describes the identification and characterization of two process impurities and major stress degradants in darifenacin hydrobromide using high performance liquid chromatography (HPLC) analysis. Forced degradation studies confirmed that the drug substance was stable under acidic, alkaline, aqueous hydrolysis, thermal and photolytic conditions and susceptible only to oxidative degradation. Impurities were identified using liquid chromatography coupled with ion trap mass spectrometry (LC-MS/MS(n)). Proposed structures were unambiguously confirmed by synthesis followed by characterization using nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR) and elemental analysis (EA). Based on the spectroscopic, spectrometric and elemental analysis data, the unknown impurities were characterized as 2-{1-[2-(2,3-dihydrobenzofuran-5-yl)-2-oxo-ethyl]-pyrrolidin-3-yl}-2,2-diphenylacetamide (Imp-A), 2-[1-(2-benzofuran-5-yl-ethyl)-pyrrolidin-3-yl]-2,2-diphenylacetamide (Imp-B), 2-{1-[2-(2,3-dihydrobenzofuran-5-yl)-ethyl]-1-oxy-pyrrolidin-3-yl}-2,2-diphenylacetamide (Imp-C) and 2-{1-[2-(7-bromo-2,3-dihydrobenzofuran-5-yl)-ethyl]-pyrrolidin-3-yl}-2,2-diphenylacetamide (Imp-D). Plausible mechanisms for the formation and control of these impurities have also been proposed. The method was validated as per regulatory guidelines to demonstrate specificity, sensitivity, linearity, precision, accuracy and the stability-indicating nature. Regression analysis showed a correlation coefficient value greater than 0.99 for darifenacin hydrobromide and its impurities. The accuracy of the method was established based on the recovery obtained between 86.6 and 106.7% for all impurities.

Fluorescence photoactivation by intermolecular proton transfer.

We designed a strategy to activate fluorescence under the influence of optical stimulations based on the intermolecular transfer of protons. Specifically, the illumination of a 2-nitrobenzyl derivative at an activating wavelength is accompanied by the release of hydrogen bromide. In turn, the photogenerated acid encourages the opening of an oxazine ring embedded within a halochromic compound. This structural transformation extends the conjugation of an adjacent coumarin fluorophore and enables its absorption at an appropriate excitation wavelength. Indeed, this bimolecular system offers the opportunity to activate fluorescence in liquid solutions, within rigid matrixes and inside micellar assemblies, relying on the interplay of activating and exciting beams. Furthermore, this strategy permits the permanent imprinting of fluorescent patterns on polymer films, the monitoring of proton diffusion within such materials in real time on a millisecond time scale, and the acquisition of images with spatial resolution at the nanometer level. Thus, our operating principles for fluorescence activation can eventually lead to the development of valuable photoswitchable probes for imaging applications and versatile mechanisms for the investigation of proton transport.

A simple scheme for magnetic balance in four-component relativistic Kohn-Sham calculations of nuclear magnetic resonance shielding constants in a Gaussian basis.

We report the implementation of nuclear magnetic resonance (NMR) shielding tensors within the four-component relativistic Kohn-Sham density functional theory including non-collinear spin magnetization and employing London atomic orbitals to ensure gauge origin independent results, together with a new and efficient scheme for assuring correct balance between the large and small components of a molecular four-component spinor in the presence of an external magnetic field (simple magnetic balance). To test our formalism we have carried out calculations of NMR shielding tensors for the HX series (X = F, Cl, Br, I, At), the Xe atom, and the Xe dimer. The advantage of simple magnetic balance scheme combined with the use of London atomic orbitals is the fast convergence of results (when compared with restricted kinetic balance) and elimination of linear dependencies in the basis set (when compared to unrestricted kinetic balance). The effect of including spin magnetization in the description of NMR shielding tensor has been found important for hydrogen atoms in heavy HX molecules, causing an increase of isotropic values of 10%, but negligible for heavy atoms.

Synthesis, crystal structure determination and Hirshfeld surface analysis of three new salt forms of creatinine with hydrobromic acid, 3-aminobenzoic acid and 3,5-dinitrobenzoic acid.

Creatinine, a biologically important compound, is used to analyze kidney function and kidney diseases in the human body. The salt form of creatinine is used in the formation of drug materials like anti-HIV, antifungal, antiprotozoal, antiviral and antitumour compounds. Here we report the solid-state structures of three new crystalline salts, namely, creatininium (2-amino-1-methyl-4-oxo-4,5-dihydro-1H-imidazol-3-ium) bromide, C4H8N3O+·Br-, (I), creatininium 3-aminobenzoate, C4H8N3O+·C7H6NO2-, (II), and creatininium 3,5-dinitrobenzoate, C4H8N3O+·C7H3N2O6-, (III). These salts have been synthesized and characterized by single-crystal X-ray diffraction and Hirshfeld surface analysis. The structural chemistry of salts (I)-(III) and their crystal packing are discussed in detail. The primary interaction between the creatinine cation and the acid anion in the three salts is N-H...Br/O hydrogen bonds. In salt (I), the creatinine cation and bromide anion are connected through a pair of N-H...Br hydrogen bonds forming R42(8) and R42(12) ring motifs. In salts (II) and (III), the creatinine cation interacts with the corresponding anion via a pair of N-H...O hydrogen bonds. The crystal structure is further stabilized by C-H...O and O-H...O hydrogen bonds with the ring motifs R22(8), R21(7) and R21(6). Furthermore, the crystal structures are stabilized by π-π, C-H...π, C-O...π and N-O...π stacking interactions. The contributions made by each hydrogen bond in maintaining the crystal structure stability has been quantified by Hirshfeld surface analysis.

[The use of ion chromatography for the determination of volatile inorganic acids in workplace air]. / Zastosowanie chromatografii jonowej do oznaczania lotnych kwasów nieorganicznych w powietrzu na stanowiskach pracy.

BACKGROUND: The presence of inorganic acids in the air poses a threat to the health of workers. Volatile inorganic acids, e.g., hydrochloric acid, hydrobromic acid and nitric acid, may cause respiratory, eye and skin irritation. The presented method uses ion chromatography to determine the concentrations of hydrochloric, hydrobromic and nitric acids in air samples. MATERIAL AND METHODS: The method is based on the collection of airborne volatile acids on impregnated quartz fiber filter, extraction of acids with deionized water, and analysis by ion chromatography with conductivity suppression. The separation was performed on the Dionex IonPac™ AS22 (4 × 250 mm) column for trace anion analysis. The carbonate/bicarbonate eluent was maintained at an isocratic flow rate of 1.2 ml/min. The calibration standard solutions have been covering the range of 0.2-5 mg/l of chloride, bromide and nitrate. RESULTS: The specified chromatographic conditions enable selective measurement of chloride, bromide and nitrate anions. The obtained mass concentration of each anion, having factored in the sample dilution, the conversion factor (to convert anion concentration to acid) and the volume of the air sample, allows the calculation of acid concentrations in the analyzed air. CONCLUSIONS: This method makes it possible to determine the concentration of hydrochloric acid, hydrobromic acid and nitric acid in the workplace air within the concentration range corresponding to 0.1-2 times the exposure limit value in Poland. The method meets the criteria for the performance of procedures for the measurement of chemical agents, listed in PN-EN 482. This article discusses the problems of occupational safety and health, which are covered by health sciences and environmental engineering. Med Pr. 2022;73(4):337-47.

High-precision measurement of variations in calcium isotope ratios in urine by multiple collector inductively coupled plasma mass spectrometry.

We describe a new chemical separation method to isolate Ca from other matrix elements in biological samples, developed with the long-term goal of making high-precision measurement of natural stable Ca isotope variations a clinically applicable tool to assess bone mineral balance. A new two-column procedure utilizing HBr achieves the purity required to accurately and precisely measure two Ca isotope ratios ((44)Ca/(42)Ca and (44)Ca/(43)Ca) on a Neptune multiple collector inductively coupled plasma mass spectrometer (MC-ICPMS) in urine. Purification requirements for Sr, Ti, and K (Ca/Sr > 10 000; Ca/Ti > 10 000 000; and Ca/K > 10) were determined by addition of these elements to Ca standards of known isotopic composition. Accuracy was determined by (1) comparing Ca isotope results for samples and standards to published data obtained using thermal ionization mass spectrometry (TIMS), (2) adding a Ca standard of known isotopic composition to a urine sample purified of Ca, and (3) analyzing mixtures of urine samples and standards in varying proportions. The accuracy and precision of δ(44/42)Ca measurements of purified samples containing 25 µg of Ca can be determined with typical errors less than ±0.2‰ (2σ).

A novel online approach to the determination of isotopic ratios for organically bound chlorine, bromine and sulphur.

A novel approach for the measurement of (37)Cl, (81)Br and (34)S in organic compounds containing chlorine, bromine, and sulphur is presented to overcome some of the major drawbacks of existing methods. Contemporary methods either require reference materials with the exact molecular compositions of the substances to be tested, or necessitate several laborious offline procedures prior to isotope analysis. In our online setup, organic compounds are separated by gas chromatography (GC) coupled to a high-temperature reactor. Using hydrogen as a makeup gas, the reactor achieves quantitative conversion of chlorinated, brominated and sulphurated organic compounds into gaseous hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen sulphide (H(2)S), respectively. In this study, the GC interface was coupled to a quadrupole mass spectrometer operated in single-ion mode. The ion traces of either H(35)Cl (m/z 36) and H(37)Cl (m/z 38), H(79)Br (m/z 80) and H(81)Br (m/z 82), or H(2)(32)S (m/z 34) and H(2)(34)S (m/z 36), were recorded to determine the isotopic ratios of chlorine, bromine, and sulphur isotopes. The conversion interface presented here provides a basis for a novel method for compound-specific isotope analysis of halogenated and sulphur-containing compounds. Rapid online measurements of organic chlorine-, bromine- and sulphur-containing mixtures will facilitate the isotopic analysis of compounds containing these elements, and broaden their usage in fields of environmental forensics employing isotopic concepts.

Orientation dependence for Br formation in the reaction of oriented OH radical with HBr molecule.

The orientation dependence of Br-atom formation in the reaction of the oriented OH radical with the HBr molecule using the hexapole electrostatic field was studied. Experimental results for the orientation dependence in the reaction were analyzed using a Legendre polynomial fit. The results show two reactive sites. It was found that O-end attack is most favored for this reaction, and that H-end attack also shows a pronounced reactivity. The reactivity of the side-ways attack was found to be small. By comparing the results of the orientation dependence in the reaction with studies of inelastic collisions and theoretical calculations, two reaction pathways are proposed. Reaction by O-end attack is followed by a direct abstraction of the H-atom from the HBr molecule. The mechanism for H-end attack may have H-atom migration from HBr to form the water molecule.

QTAIM analysis of the HF, HCl, HBr, and HOH elimination reactions of halohydrocarbons and halohydroalcohols.

The 1,2-HX elimination reaction (where X = F, Cl, Br, OH) has been established as an important reaction in the degradation of compounds introduced into the upper atmosphere, including common CFC replacement compounds. By analyzing the electron densities of the transition state geometries of these reactions using QTAIM, we see that we can divide these reactions into two types. For HF and HOH elimination, the transition state is a complete ring of bonds, and neither the C-H nor the C-X bonds have been broken at the maximum of energy. There is very little accumulation of electron density on the X atom, with the majority of charge being lost by the hydrogen atom undergoing elimination, being transferred on to the two carbon atoms. In HCl and HBr elimination, a similar loss of electron density of the hydrogen atom is accompanied by significant accumulation of electron density on the X atom and a smaller change in electron density on the carbon atoms. The C-X bond is broken in the transition state geometry, with no ring critical point being present. This may explain the relative stabilities of halohydrocarbons and haloalcohols with respect to loss of H-X.