Enthalpy of dilution of tetra-n-butylammonium bromide in mixtures of water and N-methylacetamide

The enthalpy of dilution of tetra-n-butylammonium bromide in mixtures of water and N-methylacetamide has been measured from approximately 0.1 to 1.0m at 35°C. The mole fraction of water in the solvent varied from 0.250 to 0.969. The results are strikingly nonlinear in the mole fraction of water. As the mole fraction of water varies from 0 to 0.7, there is only a small change in the enthalpy of dilution. At higher mole fractions of water, the excess enthalpy rises sharply to the unusually high values found in water. This indicates that the unusually high values of excess enthalpy associated with hydrophobic bonding in water are destroyed by relatively small amounts of N-methylacetamide.Taken in part from the Ph.D. thesis of J. S. Falcone, Jr., University of Delaware, Newark, Delaware, June 1972.     

Guest dependent inversion of enantiomeric recognition in dehydrocholic acid host–guest enclathration

A guest dependent inversion of enantiomeric recognition operated by the host dehydrocholic acid on a second guest is observed during host–guest dehydrocholic acid–sulfoxide assembly formation.     

Infrared spectroscopic properties of sodium bromide aerosols

The infrared extinction spectra of aqueous NaBr aerosols at ambient temperature have been measured as a function of relative humidity. Submicron-sized aerosol particles atomized from aqueous NaBr solutions at various concentrations are dried and/or mixed with nitrogen at different humidities and spectroscopically monitored as they flow through an infrared absorption cell. Estimated dry particle median diameters range from 0.24 to 0.15 microm, as calculated from Mie extinction theory. Measured deliquescence and efflorescence relative humidities (35-40% and 25-30%, respectively) are in accordance with previously reported ones. Our results show that NaBr particles take up water only moderately over the deliquescence point, with a significant increase at relative humidities above 70%. The effect of particle size onto water uptake properties has been studied, indicating that smaller particles take up lower amounts of water, and only increase their size significantly at relative humidities near saturation. Particle composition and diameter growth factors have been calculated from spectral data and are shown to be consistent with those predicted from thermodynamic data and Kohler theory. Band centers of liquid water in NaBr aerosols relative to pure water are blue-shifted up to 50 cm-1 at low humidities. Particle structure and phase, together with atmospheric implications, are also discussed.     

Enthalpies of solution of tetra-n-butylammonium bromide in binary mixtures of water,formamide, N-methylformamide,and N,N-dimethylformamide

The enthalpies of solution of tetra-n-butylammonium bromide have been measured in mixtures of formamide (F) with water, N-methylformamide (NMF) with water, N,N-dimethylformamide (DMF) with water, F with NMF, DMF with F, and NMF with DMF at 25°C in the whole mole-fraction range. The enthalpies of solution vs composition profiles show a maximum value in the DMF-H₂O and in the DMF-F systems. In the F-NMF and NMF-DMF mixturesn-Bu₄NBr displays a nearly ideal behavior, whereas in the other solvent systems the excess enthalpy of solution deviates substantially from zero.     

Chemical stability and reactivity of deprotonated oligonucleotides (DNA) in the gas phase: protonation and solvation with hydrogen bromide

Selected deprotonated oligodeoxynucleotides generated by electrospray ionization were exposed to a variety of neutral molecules in the gas phase at room temperature in flowing helium gas at 0.35 Torr. Single-stranded [AGTCTG-nH]n- and single- and double-stranded [GCATGC-nH]n- anions were found to be remarkably unreactive with strong oxidants (O3, O2, N2O) and potential intercalators (benzene, pyridine, toluene, and quinoxaline). Hydration also was observed to be inefficient. However, [AGTCTG-nH]n- anions with n=2, 3, 4, and 5 were seen to be sequentially protonated and/or hydrobrominated with HBr (but not damaged) and displayed an interesting "end effect" against protonation. Measurements are provided for the rate coefficients of reaction and the efficiencies of protonation. These experimental results point toward the exciting prospect of measuring the intrinsic chemistry of other bare DNA-like anions, including double-stranded oligonucleotide anions in the gas phase at room temperature.     

Effects of H/D-isotope substitution and temperature on the volume characteristics of tetra-n-butylammonium bromide dissolved in methanol and its D-isotopomers

Densities of Buⁿ ₄NBr solutions in MeOH, MeOD, and CD₃OH were measured at salt concentrations of up to 1.5 solvomolality units (nearly 2.63·10^–2 mole fraction) at 278.15, 288.15, 298.15, 308.15, and 318.15 K. The limiting partial molar volumes of Buⁿ ₄NBr dissolved in these alcohols were calculated. The isotope effects in the volume characteristics of the stoichiometric mixture of ions, [Buⁿ ₄N⁺ + Br^–], are mainly due to the vibrational changes in the solvent structure upon deuteration of different molecular fragments. Structural transformations in infinitely dilute solution of Buⁿ ₄NBr in methanol are governed by non-specific solvation of the symmetrical Buⁿ ₄N⁺ cation.     

Correlation of solute retention in gas chromatography with properties of the anion for tetra-n-butylammonium salts

Variations in the molar retention volume of organic solutes on thirteen tetra-n-butyl-ammonium salts with a common liquid temperature range are correlated with the properties of the anion. The anions studied include the chloride, bromide, nitrate, nitrite, methanesulfonate, trifluoromethanesulfonate, ethanesulfonate, 4-toluenesulfonate, sulfamate, thiocyanate, picrate, pentacyanopropenide, and tetra-n-butylborate. The high melting points and poor thermal stabilities of camphorsulfonate, dihydrogenphosphate, hydrogensulfate, and perrhenate precluded their use. The properties of the anions have only smallinfluences on the magnitudes of dispersive, orientative, and proton-donor interactions with the test solutes. Orientative interactions are strong for polar solutes but vary little with anion structure. There was no correlation between the dipole moment of the tetra-n-butylammonium salts and the retention of polar solutes. The structures of the anion do, however, have large influences on the retention of proton-donor solutes. for these solutes, a good correlation was found between molar retention volume and the basicity of the anions, represented by their pK_a values in aqueous solution.     

Phenylborylene: direct spectroscopic characterization in inert gas matrices

The photolysis of bisazidophenylborane isolated in cryogenic matrices results in phenylborylene, a subvalent boron(I) species with a singlet ground state. Broad band irradiation of phenylborylene causes formation of benzoborirene by insertion into an ortho-CH bond.     

Molecular potential functions from joint analysis of gas electron diffraction and spectroscopic data

A joint analysis of electron diffraction and spectroscopic data is carried out for BF₃, PBr₃, AsBr₃, SbCl₃, SeO₂ and ClO₂ in terms of the harmonic force fields. The scheme of analysis was extended to include the following spectroscopic observables: vibrational frequencies, rotational, Coriolis coupling and centrifugal distortion constants and, whenever available, those for the isotopic species. For ClO₂ a simplified anharmonic analysis was also performed, the anharmonic spectroscopic observables being involved in this case.

Compelling evidence has been presented that the conventional harmonic approximation for the force field in terms of rectilinear internal coordinates yields the simplest satisfactory representation of diffraction and spectroscopic observations. However, a consistently better fit to experimental data was found when natural curvilinear internal coordinates were used. It is shown here that for the systems considered the joint analysis of data from various sources ensures that reliable and accurate values for equilibrium distances and force field parameters are obtained. The optimized values of spectroscopic constants, structural and force field parameters obtained are presented and compared with those available from the literature.     

Long-term stability of a gas chromatography/mass spectrometry system in quantitative gas analysis

A gas chromatograph/quadrupole mass spectrometer (GC/MS) system was used to supervise a test programme for evaluating the potential of a natural gas storage plant. The dispersion characteristics of a large nitrogen reservoir located in a tight sandstone formation 1600 m below sea level between claystones, was investigated by injection and withdrawal of 350 000 m³ nitrogen with argon as tracer gas. The GC/MS system was installed in a shed in an open field and operated under computer control continuously 24 h a day for three weeks; about 3000 analyses were done. The on-line results were in good agreement with those obtained from additional gas samples withdrawn every 4 h for independent quantitative gas analyses with a purpose-built mass spectrometer.     

Kinetic and spectroscopic characterization of the isomers of the allyl bromide molecular ion

The kinetics of the ion/molecule reactions of the molecular ion of allyl bromide (3-bromopropene), C₃H₅Br⁺., with its neutral show that only (82 ± 2)% of these ions are reactive. This percentage is mildly sensitive to ionization energy below 13 eV, but is pressure insensitive. The collisionless infrared multiphoton-induced photofragmentation of these ions at 10.25 μm and at variable power densities is consistent with the presence of two ionic species in the ratio obtained from the kinetic experiments. The most abundant species undergoes much faster photofragmentation at this wavelength, but at 10.59 μm the photofragmentation rates become comparable. Experiments performed by isolating the remaining molecular ions after completion of the ion/molecule reaction confirm that the unreactive species corresponds to the slow photodissociating ion at 10.25 μm. A combination of kinetic experiments and photodissociation is used to establish that the less abundant species behaves unlike the molecular ion obtained from 1-bromopropene, 2-bromopropene, or bromocyclopropane. The two structures for the molecular ion are shown to originate from ionization and not by isomerization through collisions.     

Thermal stability of octadecyltrimethylammonium bromide modified montmorillonite organoclay

Organoclays are significant for providing a mechanism for the adsorption of organic molecules from potable water. As such their thermal stability is important. A combination of thermogravimetric analysis and infrared emission spectroscopy was used to determine this stability. Infrared emission spectroscopy (IES) was used to investigate the changes in the structure and surface characteristics of water and surfactant molecules in montmorillonite, octadecyltrimethylammonium bromide and organoclays prepared with the surfactant octadecyltrimethylammonium bromide with different surfactant loadings. These spectra collected at different temperatures give support to the results obtained from the thermal analysis and also provide additional evidence for the dehydration which is difficult to obtain by normal thermoanalytical techniques. The spectra provide information on the conformation of the surfactant molecules in the clay layers and the thermal decomposition of the organoclays. Infrared emission spectroscopy proved to be a useful tool for the study of the thermal stability of the organoclays.     

Thermal stability of poly(vinyl bromide) and copolymers of vinyl bromide with methyl vinyl ketone

Thermal stability and degradation behaviour have been studied for PVB and VB-MVK copolymers spanning the whole composition range, using thermogravimetric analysis. The reactivity ratios in the radial copolymerization were determined by using an NMR technique, leading to r_i(VB) = 3.6 ± 0.2 and r₂(MVK) = 0.2 ± 0.1. The introduction of MVK units into the VB chain leads to an interaction with release of methyl bromide. The stability of the copolymers increases with increasing MVK concentration.     

Studies of interaction of emodin and DNA in the presence of ethidium bromide by spectroscopic method

Emodin interacting with deoxyribonucleic acid (DNA) has been studied by different spectroscopic techniques, such as fluorescence, ultraviolet and visible (UV-vis), and fourier transform infared (FT-IR) spectroscopies, using ethidium bromide (EB) as a fluorescence probe of DNA. The decrease in the fluorescence of DNA-EB system on addition of emodin shows that the fluorescence quenching of DNA-EB complex by emodin occurs. The binding constants of emodin with DNA in the presence of EB are 6.02x10(4), 9.20x10(4) and 1.17x10(5)Lmol(-1) at 20, 35 and 50 degrees C, respectively. FT-IR spectrum further suggests that both the phosphate groups and the bases of DNA react with emodin. The reaction of DNA with emodin in the presence of EB is affected by ionic strength and temperature. The values of melting temperature (T(m)) of DNA-EB complex and emodin-DNA-EB complexes were determined, respectively. From the experiment evidences, the major binding mode of emodin with DNA should be the groove binding.     

Extraction separation of cadmium and zinc with tetra-n-butylammonium iodide

Tetra-n-butylammonium iodide (TBAI) forms associations in chloroform and aqueous solutions. A TBAI solution in chloroform extracts hydroiodic acid by addition. From 0.5M hydroiodic acid medium cadmium is quantitatively extracted into a TBAI solution in chloroform. Under these conditions zinc is not extracted. This makes possible the extractive separation of cadmium from zinc in micro-or macroamounts.     

Selective determination of bromide and iodide in serum and urine by gas chromatography

A gas chromatographie method with electron capture detection is described for the simultaneous determination of bromide and iodide in biological matrices such as serum and urine. Samples are purified by passing them through a disposable C-18 reversed phase silica cartridge; bromide and iodide are derivatized in acid medium to 2-bromoethanol and 2-iodoethanol by ethylene oxide and the derivatives are extraced into ethyl acetate. Detection limits are in the low ng/ml-range.     

Valence anions of N-acetylproline in the gas phase: computational and anion photoelectron spectroscopic studies

We report the photoelectron spectrum of anionic N-acetylproline, (N-AcPro)(-), measured with 3.49 eV photons. This spectrum, which consists of a band centered at an electron binding energy of 1.4 eV and a higher energy spectral tail, confirms that N-acetylproline forms a valence anion in the gas phase. The neutrals and anions of N-AcPro were also studied computationally at the B3LYP∕6-31++G(d,p) level. Based on the calculations, we conclude that the photoelectron spectrum is due to anions which originated from proton transfer induced by electron attachment to the π* orbital localized at the acetyl group of N-AcPro. We also characterized the energetics of reaction paths leading to pyrrolidine ring opening in the anionic N-AcPro. These data suggest that electron induced decomposition of peptides/proteins comprising proline strongly depends on the presence of proton donors in the close vicinity to the proline residue.     

Conformational stability,barriers to internal rotation,normal coordinate analysis,and vibrational assignment of chloroacetyl bromide

The infrared spectra (3200 to 30 cm^–1) of gaseous and solid chloroacetyl bromide, CH₂ClC(O)Br, and the Raman spectra (3200 to 10 cm^–1) of the gas, liquid (with depolarization data), and solid have been recorded. From the observed asymmetric torsional transitions, the potential function governing internal rotation of the CH₂Cl moiety has been determined with the following coefficients:V ₁=336±11,V ₂=73±10,V ₃=757+7,V ₄=103±3, andV ₆=5±2 cm^–1. This potential function is consistent with s-trans to gauche and gauche to gauche barriers of 963±11 and 709±12cm^–1, respectively, and enthalpy difference of 373 ± 24 cm^–1 with the dihedral angle of the gauche rotamer being 115°. The enthalpy difference has been determined experimentally from the studies of the Raman spectra at different temperatures to be 359±68 cm^–1 (1.03±0.19 kcal mol^–1) and 507±24 cm^–1 (1.45±0.07 kcal mol^–1) for the gas and liquid, respectively, with the s-trans conformer being the more stable conformer in the gas and liquid and the only one present in the annealed solid. A complete assignment of the vibrational fundamentals is proposed from spectral data obtained for the gas, liquid, and solid. The assignment is supported by a normal coordinate calculation utilizing a modified valence force field to obtain the frequencies for the normal vibrations and the potential energy distribution. The results are discussed and compared to the corresponding quantities for some similar molecules.Taken in part from the thesis of H. V. Phan, which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.