Free Acid Molecules Research Articles

A DFT study of chemical sensors based on organic semiconductors (OSC) derived from 1−H−Borole

Initially, two parent molecules were designed to possess semiconductor features based on 1−H−borole. Each molecule has two active sites available to abduct ammonia molecules since both ammonia and boron behave as a Lewis acid and base, respectively. Taking the parent molecules, five derivatives were obtained using hydrogen (H), fluorine (F), methyl (Met), tert-butyl (Tert), and phenyl (Phen) groups, aiming to modulate the acidity of boron. The molecular geometries from the parent molecules and their derivatives, as well as their complexes, were optimised using the Gaussian 09 package with the B3LYP hybrid functional. The HOMO–LUMO gap was analysed, as well as the gap shift that occurs when free acid molecules abduct ammonia and create a Lewis complex, which was taken as a criterion of sensitivity. Finally, the binding energy was calculated by the counterpoise method, correcting the error due to the basis set superposition to give an insight of how feasible it is to remove the ammonia molecules from the hypothetical sensing material.

The Existence of Hexafluoroarsenic(V) Acid

The homogeneous mixture of anhydrous hydrogen fluoride aHF and antimony pentafluoride AsF5 is known as a superacidic system. The high acidity is derived from the formation of [H2F](+) [AsF6](-). No experimental evidence exists for the existence of the free acid molecule HAsF6. The reaction of trimethylsilyl N,N-dimethylcarbamate in the binary system aHF/AsF5 led to decomposition of trimethylsilyl N,N-dimethylcarbamate at -50 °C to dimethylammonium hexafluoridoarsenate and cocrystallization of HAsF6. The single-crystal X-ray structure displays an HAsF6 molecule involved in an asymmetric hydrogen bridge to the hexafluoridoarsenate anion. As a result of the incalculable situation in the crystal lattice, the molecular structure of HAsF6 is calculated by quantum chemical structure optimization of the extreme cases of [FHF-AsF5](-) (strong hydrogen bond) and HAsF6 (no hydrogen bond) at the PBE1PBE/6-311G(3df,3pd) level of theory.

Effect of Surfactant Excess in Non-Polar Ferrofluids Probed by Small-Angle Neutron Scattering

The microstructure of ferrofluids (magnetite/oleic acid/benzene) with an excess of free oleic acid is investigated by small-angle neutron scattering (SANS). For such excess higher than 25 vol. % a sharp break in the stability of ferrofluids occurs followed by coagulation and precipitation. Below this value the influence of the surfactant excess on the stability of ferrofluids is insignificant; neither particle aggregation nor surfactant agglomeration is observed. The interaction of free acid molecules in the ferrofluids is compared with that in pure benzene solutions. A significant increase in the attraction is observed for acid molecules in the ferrofluids, which is related to the loss of magnetic fluids stability at high excess of acid.

Specific features of physical chemistry and electronic structure of lower dicarboxylic acids

The static and complex dielectric permittivities and dc electrical conductivities of solid oxalic, malonic, and succinic acids were measured. The relaxation times of single crystal blocks (3–5 days) and mean relaxation frequencies of molecules and low-molecular-weight associates of oxalic acid dihydrate (5 MHz) and malonic acid (160 kHz) at 19°C were estimated. Aqueous oxalic acid can absorb electromagnetic energy owing to the presence of solvated electrons and holes. The electrical conductivity of this acid is protonic, and that of the anhydrous acids, electronic; the electron-hole pairs are mainly generated in these acids by lattice vibrations. The applied alternating electric field caused desorption of active gases from the acids. In some experiments with malonic acid, fast isothermal rearrangements of hydrogen bond networks and avalanche ionization of molecules were observed at a slight increase in temperature. The diagrams of charge distribution in the free acid molecules were constructed on the basis of the previous dipole moment measurements and IR data.

H2S-Induced Reorganization of Mixed Monolayer of Carboxylic Derivatives on Silver Surface

The structure of self-assembled monolayers ofp-terphenyl-4-carboxylic acid and the mixed monolayers of this acid with n-hexadecanoic acid on silver surface were studied by reflection-IR spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) measurement, X-ray photoemission electron microscopy (X-PEEM), and atomic force microscopy. Exposure of the p-terphenyl-4-carboxylate monolayer to H2S vapor resulted in reorganization of the film structure into clusters of the corresponding free acids, in tens of nanometer dimension. Exposure of the mixed monolayer to H2S resulted in reorganization of the mixed monolayer film into phase-separated clusters of respective component molecules. The saturated aliphatic acid formed clusters of submicrometer size, whereas the p-terphenyl-4-carboxylic acid formed clusters of tens of nanometer size, presumably due to different surface mobility and/or intermolecular interaction of the two types of molecule. Restoration of the monolayer film from the clusters, driven by the reaction between the free acid molecules and the basic surface sites, proceeded at different speeds for the two types of molecules. The saturated acid monolayer was restored much faster than the p-terphenyl-4-carboxylic acid monolayer. A domain-separated monolayer in several micrometers scale was obtained. The process was imaged by tapping mode atomic force microscopy.

Surface Treatment of Calcite with Fatty Acids: Structure and Properties of the Organic Monolayer

Thermogravimetric analysis was used to investigate the surface cleanliness of calcite fillers and to determine the optimal amount of fatty acid needed to coat the particles with an organic monolayer. The use of excess surfactant led to the formation of a bilayer as well as to the presence of free acid molecules. Both species could be detected by TGA. Optimal coating of calcite with stearic acid gave a monolayer of calcium stearate bicarbonate in which one acid molecule is attached to every Ca2+ present on the surface. The alkyl chains in the monolayer are vertically oriented to the surface and are restricted in their motion. 13C NMR and IR spectroscopy revealed that the chain conformation shows a high trans population, which leads to an ordered solidlike phase. Monolayers of saturated fatty acids with long alkyl chains (≥C10) showed similar behavior, while the lower homologues (≥C10) gave monolayers with dynamically disordered phases. The immobilization of oleic acid molecules by tethering them to the cal...

Surface characterization of di-(2-ethylhexyl)dithiophosphoric acid-activated composite membranes by x-ray photoelectron spectroscopy

Surface chemical characterization of a set of activated composite membranes containing different concentrations of di-(2-ethylhexyl)dithiophosphoric acid (DTPA) as carrier was performed by x-ray photoelectron spectroscopy (XPS). As a result of the addition of DTPA to the membrane samples, the N 1s signal intensities decrease, whereas the P 2p signal intensities increase with increasing carrier concentration. Upon acid addition, the polyamide component of the membrane was protonated and a new peak at higher binding energies was observed in the N 1s XPS signal, due to the increase of the positive charge of these protonated nitrogen atoms. The S 2p signals indicate the coexistence of two contributions assigned to the presence of the acid carrier ionically bonded to the protonated amide and to free acid molecules.

Molecular vibrations in phosphoenolpyruvate crystals from X-ray diffraction data

The anisotropic mean-square atomic displacement parameters from 18 previously determined crystal structures representing 26 crystallographically independent phosphoenolpyruvate species, ranging from the tribasic free-acid molecule [(HO) 2OPOC(CH 2)CO 2H] to the fully ionized molecular trianion, have been analyzed in terms of external, rigid-body lattice vibration modes coupled with low-frequency modes of internal molecular torsion and bending vibrations. The results indicate that there tends to be more torsional flexibility about the (H 2C)C–CO 2 enolcarboxylate bonds than about the C–O(P) and (C)O–P phosphate ester bonds, apparently because hydrogen bonding or counterion binding interactions in the crystals restrict the phosphate groups more than the carboxylate groups. The analysis provides an example that shows that thermal vibration parameters from crystal structure analyses of good, but not necessarily extraordinary, accuracy are a rich source of molecular dynamical information.

Secondary ion mass spectrometry of sugar nucleotides

AbstractSecondary ion mass spectra of fifteen sugar nucleotide sodium salts were investigated. In the negative‐ion mode. deprotonated free acid molecules, desodiated sodium salts and some structurally significant fragment ion swere obtained. The linked scan at constant B/E gave information on the characteristics of the sugar, nucleosides and base moieties in the sugar nucleotides.

Syntheses and Crystal Structures of Diaquatris(m-hydroxybenzoato)lanthanoid(III) m-Hydroxybenzoic Acid Dihydrate (M=La, Ce, Pr, and Nd), and Di-μ-(m-hydroxybenzoato)bis{triaquabis(m-hydroxybenzoato)lanthanoid(III)} Dihydrate (M=Sm, Gd, Dy, Er, and Yb)

Abstract Two types of lanthanoid(III) m-hydroxybenzoates, indicated in the title, have been synthesized, and the crystal and molecular structures of four representative complexes, where M=La (1), Nd (2), Sm (3), and Er (4), were determined by the single-crystal X-ray diffraction method. They are all triclinic, space group P\bar1, and the cell constants are as follows: (1) a=12.351(11), b=15.533(10), c=9.250(4) Å, α=109.86(4), β=101.40(6), γ=62.95(6)°; (2) a=12.287(4), b=15.542(7), c=9.194(3) Å, α=109.64(3), β=101.46(3), γ=62.83(3)°; (3) a=10.580(1), b=12.006(5), c=10.105(2) Å, α=111.14(2), β=90.27(1), γ=97.16(2)°; (4) a=10.586(4), b=11.943(6), c=10.027(5) Å, α=111.11(3), β=90.53(4), γ=97.26(4)°. The final R values obtained were (1) 0.039, (2) 0.038, (3) 0.030, and (4) 0.039. The central metal atoms of both types of complexes are octa-coordinated, and each is in a square-antiprism geometry. In 1 and 2, one free acid molecule is present, and the molecule is hydrogen-bonded to the oxygen atoms of the coordinated water molecules through its carboxyl oxygen atoms. 1 and 2 have linear polymeric structure, and each pair of the metal atoms is bridged by a pair of the carboxylate ligands, while 3 and 4 have a dimeric structure, where metal atoms are bridged by two carboxylate ligands.

Kinetic parameters of the crosslinking of oligoisobutylene dicarboxylic acid by epoxides

A study has been made of kinetic regularities of the initial stage of the reaction of epoxides with oligoisobutylene dicarboxylic acid in bulk and in solution, and the molecular character of this reaction has been established. It was found that the rate constant of the reaction in bulk was higher than in solution. Tertiary amines are effective catalysts of this reaction, although the share of crosslinking reactions decreases in the presence of tertiary amines. The catalytic effect is due to the formation of a complex between catalyst and oligoisobutylene dicarboxylic acid, the latter complex being more reactive than the free acid molecule. It was found that the reactivity of functional end groups is a function of the molecular weight of the oligomer.

The Kinetic Current Phenomenon in the Polarographic Reduction of Bromate

Although bromate and iodate have been known to be electroreducible at the dropping mercury electrode, their reaction processes involve some uncertainties. Two kinds of the reduction waves, acidic and alkaline waves, were first discovered by Rylichl' in the polarography of potassium iodate and bromate in unbufered solutions which contain various rations as supporting electrolyte. Orlemann and Kolthoff performed a systematic study in which influences of various rations onthe irreversible reductions of iodate and bromate anions were both experimentally and theoretically investigated. More recently Cermak pointed out in his short publication that each of these polarographic waves consists of two separate parts in a certain pH range, and assumed the kinetic current phenomena rising between the free acid molecules and their dissociated anions. There have been known few examples for the kinetic current of inorganic acids, but those kinetic mechanisms are expected to be more comprehensible and more convenient to the theoretical treatment, compared with the complexities assumed in the cases of organic depolarizers.The purpose of the present work is to study the reduction of bromate in detail with respect to its kinetic current phenomenon. On the reduction of iodate, it was hardly possible to make the reliable measurements on the first and the second waves separately, because the potential difference of the two waves was always small. The more detailed observation with iodate, therefore, was not made in spite of the expectation of its similar behaviour to bromate.

THE RELATIONSHIP BETWEEN CHEMICAL STRUCTURE AND THE RESPONSE OF BLOWFLIES TO TARSAL STIMULATION BY ALIPHATIC ACIDS

Using the technique of proboscis extension in antennectomized-labellectomized flies, the rejection thresholds of Phormia regina for 18 fatty acids and one mineral acid have been determined. The conclusions reached on the basis of these data may be summarized in the following terms: Tarsal stimulation by acids involves the summation of components from at least two sources. Of these the hydrogen ion is the most important. The other major factor is probably the anion rather than the undissociated acid. The stimulating power of the anions (or free acid molecules) increases with increasing chain length in both the mono- and dicarboxylic series, but the rate of increase decreases as the series is ascended. Acids containing 6 or more carbon atoms are not sufficiently soluble in 0.1 M sucrose to reach the threshold of rejection. Substitution of -H in the acyl grouping by -Cl, -OH, =O or -COOH, the presence of a C=C bond, or a shift from the trans- to the cis- configuration all diminish the effectiveness of the anion (or free acid). But since such alterations also augment the degree of dissociation and consequently the concentration of hydrogen ions, the net result is ordinarily a lowering of threshold in terms of the molar concentration required for rejection.