Fluorescent high-performance liquid chromatographic analysis of vigabatrin enantiomers after derivatizing with naproxen acyl chloride

Vigabatrin is widely used as an anticonvulsant in the treatment of seizures. Vigabatrin is usually supplied as racemate in formulation, but only the (S)-(+)-enantiomer of vigabatrin is pharmacologically active. A simple and sensitive liquid chromatographic method is described for the separation and quantification of vigabatrin enantiomers. The method is based on derivatizing racemic vigabatrin with a fluorescent chiral reagent (naproxen acyl chloride). The resulting diastereomeric derivatives are highly responsive to a fluorimetric detector (lambda(ex)=230 nm, lambda(em)=350 nm). The lower quantitation limit of the method is attainable at 25 nM for (S)-(+)-vigabatrin or (R)-(-)-vigabatrin with a detection limit of about 2.5 nM (S/N=3 with 10 microl injected). Application of the method to the analysis of vigabatrin in serum of dosed patients proved feasible.     

Correspondence of Ru(III) Ru(II) and Ru(IV) Ru(III) mixed valent states in a small dinuclear complex

The diruthenium(III) compound [(μ-oxa){Ru(acac)(2)}(2)] [1, oxa(2-) =oxamidato(2-), acac(-) =2,4-pentanedionato] exhibits an S=1 ground state with antiferromagnetic spin-spin coupling (J=-40 cm(-1)). The molecular structure in the crystal of 1?2 C(7)H(8) revealed an intramolecular metal-metal distance of 5.433 ? and a notable asymmetry within the bridging ligand. Cyclic voltammetry and spectroelectrochemistry (EPR, UV/Vis/NIR) of the two-step reduction and of the two-step oxidation (irreversible second step) produced monocation and monoanion intermediates (K(c) =10(5.9)) with broad NIR absorption bands (ε ca. 2000 M(-1)cm(-1)) and maxima at 1800 (1(-)) and 1500 nm (1(+)). TD-DFT calculations support a Ru(III)Ru(II) formulation for 1(-) with a doublet ground state. The 1(+) ion (Ru(IV)Ru(III)) was calculated with an S=3/2 ground state and the doublet state higher in energy (ΔE=694.6 cm(-1)). The Mulliken spin density calculations showed little participation of the ligand bridge in the spin accommodation for all paramagnetic species [(μ-oxa){Ru(acac)(2)}(2)](n), n=+1, 0, -1, and, accordingly, the NIR absorptions were identified as metal-to-metal (intervalence) charge transfers. Whereas only one such NIR band was observed for the Ru(III)Ru(II) (4d(5)/4d(6)) system 1(-), the Ru(IV)Ru(III) (4d(4)/4d(5)) form 1(+) exhibited extended absorbance over the UV/Vis/NIR range.     

Near-infrared and mid-infrared investigations of Na-dodecylbenzenesulfate intercalated into hydrocalumite chloride (CaAl-LDH-Cl)

Hydrocalumite (CaAl-LDH-Cl) belongs to layered double hydroxides (LDHs). The intercalation of Na-dodecylbenzenesulfate (SDBS) into CaAl-LDH-Cl has been investigated by X-ray diffraction (XRD), mid-infrared (MIR) spectroscopy and near-infrared (NIR) spectroscopy. The mid-infrared spectra indicated that SDBS could be intercalated into CaAl-LDH-Cl, with the same lattice structure to that of CaAl-LDH-Cl, and the interlayer distance of resultant product was expanded to 2.78 nm as confirmed by XRD. The near-infrared spectra (9200-4000 cm(-1)) showed that a special spectral range from 6200 to 5600 cm(-1) and prominent bands of CaAl-LDH-Cl intercalated with SDBS around 8300 cm(-1). This band was assigned to the second overtone of the first fundamental of C-H stretching vibrations of SDBS, and can be used to determinate the result of CaAl-LDH-Cl modified by anionic surfactants. The bands of water stretching vibrations and -OH groups shifted to higher wavenumbers when CaAl-LDH-Cl was intercalated by SDBS, and their intensity of MIR and NIR spectra became lower in intensity.     

Synchrotron FTIR spectroscopy of weak torsional bands: A case study of cis-methyl formate

The far infrared spectrum of cis-methyl formate has been recorded on the AILES beamline of the synchrotron SOLEIL using a Fourier transform infrared spectrometer coupled to a long path cell. The very weak fundamental band associated with the methyl-top torsion mode (ν(18)) was observed. The frequency analysis was performed using the "rho axis method", and the microwave and millimeter-wave data from the literature. A precise determination of the band origins (ν(18) (A) = 132.4303 cm(-1) and ν(18) (E) = 131.8445 cm(-1)) and of the barrier height [V(3) = 370.7398 (58) cm(-1)] have been obtained. The intensity of the ν(18) fundamental band was determined to be 3.4 × 10(-21) cm(-1)∕(molecule cm(-2)) at 297 K, equally shared among A-A and E-E transitions, thus leading to a dipole moment component μ(c) ((3)) equal to 0.0483 D. The results were compared with the ab initio calcula-tions of Senent et al. [Astrophys. J. 627, 567 (2005)].     

FT-Raman spectroscopy - analytical tool for routine analysis of diazinon pesticide formulations

FT-Raman spectroscopy based on band intensity and band area measurements, was used for the quantitative determination of diazinon in pesticide formulations. Bands at 554, 604, 631, 1562 and 2971 cm(-1) were used for calibration. Spectra were acquired by averaging 100 scans at a resolution of 4 cm(-1). Calibration curves were linear (correlation coefficients, 0.992-0.9992 and 0.99-0.999 for band intensity and band area measurements, respectively) in the range of 0.2-3.5 M for 554 and 2971 cm(-1), 0.3-3.5 M for 604 cm(-1), 0.6-3.5 M for 1562 cm(-1) and 1.0-3.5 M for 631 cm(-1) bands. Normalization of calibration curves against the 802 cm(-1) cyclohexane band improved their long term stability and minimized the effect of laser beam power fluctuations. No interference was found by commonly used surfactants and the proposed method was applied to the analysis of diazinon formulations. Results obtained compare well as indicated by the t-test, with those obtained by the HPLC reference method. Precision ranged between 0.2-7.8 and 0.1-7.2% RSD, (n=4) for band intensity and band area measurements, respectively. The proposed method is rapid, simple and safe, as toxic samples are analyzed 'as received' without sample pre-treatment, permiting the routine analysis of pesticides formulations.     

A new coordination mode of the photometric reagent glyoxalbis(2-hydroxyanil) (H2gbha): bis-bidentate bridging by gbha2- in the redox series [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2), including a radical-bridged diruthenium(III) and a Ru(III)/Ru(IV) intermediate

The bis-bidentate bridging function of gbha2- with N,O-/N,O- coordination was observed for the first time in the complex (mu-gbha)[Ru(III)(acac)2]2 (1). Density functional theory calculations of 1 yield a triplet ground state with a large (deltaE > 6000 cm(-1)) singlet-triplet gap. Intermolecular antiferromagnetic coupling was observed (J approximately -5.3 cm(-1)) for the solid. Complex 1 undergoes two one-electron reduction and two one-electron oxidation steps; the five redox forms [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2) were characterized by UV-vis-NIR spectroelectrochemistry (NIR = near infrared). The paramagnetic intermediates were also investigated by electron paramagnetic resonance (EPR) spectroscopy. The monoanion with a comproportionation constant K(c) of 2.7 x 10(8) does not exhibit an NIR band for a Ru(III)/Ru(II) mixed-valent situation; it is best described as a 1,4-diazabutadiene radical anion containing ligand gbha*3-, which binds two ruthenium(III) centers. A Ru(III)-type EPR spectrum with g1 = 2.27, g2 = 2.21, and g3 = 1.73 is observed as a result of antiferromagnetic coupling between one Ru(III) and the ligand radical. The EPR-active monocation (K(c) = 1.7 x 10(6)) exhibits a broad (deltanu(1/2) = 2600 cm(-1)) intervalence charge-transfer band at 1800 nm, indicating a valence-averaged (Ru3.5)2 formulation (class III) with a tendency toward class II (borderline situation).     

Ultraviolet absorption and vibrational spectra of 2-fluoro-5-bromopyridine

The ultraviolet absorption spectrum in the range 340-185 nm in the vapour and solution phase has been measured for 2-fluoro-5-bromopyridine. Three fairly intense band systems identified as the pi* <-- pi transitions II, III and IV have been observed. A detailed vibronic analysis of the vapor and solution spectra is presented. The first system of bands is resolved into about sixty-two distinct vibronic bands in the vapour-phase spectrum. The 0,0 band is located at 35944 cm(-1). Two well-developed progressions, in which the excited state frequencies nu'25 (283 cm(-1)) and nu'19 (550 cm(-1)) are excited by several quanta, have been observed. The corresponding excited state vibrational and anharmonicity constants are found to be omega'i = 292 cm(-1), x'ii = 4.5 cm(-1) (i = 25) and omega'i = 563.8 cm(-1), x'ii = 6.9 cm(-1) (i = 19). The other two band systems show no vibronic structure, the band maxima being located at 48346 and 52701 cm(-1), respectively. The oscillator strength of the band systems in different solutions and the excited state dipole moments associated with the first two transitions have been determined by the solvent-shift method. The infrared spectrum in the region 4000-130 cm(-1) and the laser Raman spectrum of the molecule in the liquid state have been measured and a complete vibrational assignment of the observed frequencies is given. A correlation of the ground and excited state fundamental frequencies observed in the UV absorption spectrum with the Raman or infrared frequencies is presented.     

Electronic spectroscopy of CoNe+ via mass-selected photodissociation

The CoNe(+) diatomic cation is produced by laser vaporization in a pulsed-nozzle source and studied with photodissociation spectroscopy at visible wavelengths. Vibronic structure is assigned to the (3)Π(2) ← (3)Δ(3) band system correlating to the Co(+)((3)P(2) ← (3)F(4)) + Ne asymptote. The origin band (13,529 cm(-1)) and a progression of 14 other vibrational bands are detected ending in the dissociation limit at 14,191 cm(-1). The excited state dissociation energy is therefore D(0)(') = 662 cm(-1), and an energetic cycle using this, the origin band energy, and the atomic transition produces a ground state dissociation energy of D(0)(") = 930 cm(-1). The excited state vibrational frequency is 116.1 cm(-1). A rotationally resolved study of the origin band confirms the electronic transition assignment and provides the bond distance of r(0)(") = 2.36 ?. The properties of CoNe(+) are compared to those of other CoRG(+) and MNe(+) complexes studied previously.     

Emitting-state displacements in ligand-centered vibrational modes in the trans-[OsO2(NCS)4]2- complex determined from near-infrared luminescence spectroscopy

Low-temperature luminescence spectra from three salts of the trans-[OsO(2)(NCS)(4)](2-) complex exhibit highly resolved vibronic structure in both metal-ligand high-frequency O=Os=O (885 cm(-1)) and lower-frequency Os-N(CS) (255 cm(-1)) symmetric stretching modes as well as in a ligand-centered CS stretching mode (858 cm(-1)). Band maxima range from 10000 to 12000 cm(-1), and spectra contain irregular frequency intervals that correspond to transitions from more than one origin and phonon sidebands. Experimental band shapes are distinctly different for all three compounds and are calculated assuming harmonic potential energy surfaces for both the ground and emitting states. Normal-coordinate offsets along all displaced vibrational modes are determined and compared for the three compounds. The analyses reveal emitting-state displacement of high-frequency ligand-centered (CS) and metal-ligand (O=Os=O) symmetric stretching modes, leading to observed high-frequency intervals (855-880 cm(-1)) that do not match any frequencies determined from ground-state Raman spectra. The values for the high-frequency normal-coordinate offsets, DeltaQ(O=Os=O) and DeltaQ(CS), were found to be on the order of 0.06 A. Offsets along the 255 cm(-1) Os-N mode varied noticeably between the three compounds and were largest for the compound with the largest value of DeltaQ(CS).     

Persistence rewarded: successful observation of the B 2Sigmau+-X 2Pig electronic transition of jet-cooled BS2

The B-X electronic transition of jet-cooled BS2 has been observed using laser-induced fluorescence techniques. The boron disulfide radical was produced in a pulsed electric discharge jet using a mixture of BCl3 and CS2 in high-pressure argon as the precursor. The spectrum consists of a strong 0(0)(0) band with the 2Sigma-2Pi(3/2) component at 24,393.2 cm(-1) and short progressions in the symmetric stretching (nu1' = 506.7 cm(-1)) and bending (nu2' = 303.2 cm(-1)) modes. A rotational analysis of both spin-orbit components of the 0(0)(0) band gave an upper state B value of 0.0932779(19) cm(-1) and a ground-state spin-orbit coupling constant of A = -405.163(4) cm(-1). The ground-state bond length of 1.66492 angstroms increases to 1.6812(1) angstroms on sigmau --> pig electronic excitation. The B-X data have been used to further refine the Renner-Teller analysis, which is in good agreement with our previous work [J. Chem. Phys. 119, 2047 (2003)].     

Correlated angular and quantum state-resolved CO2 scattering dynamics at the gas-liquid interface

Molecular beam scattering dynamics at the gas-liquid interface are investigated for CO2 (E(inc) = 10.6(8) kcal/mol) impinging on liquid perfluoropolyether (PFPE), with quantum state (v, J) populations measured as a function of incident (theta(inc)) and final (theta(scat)) scattering angles. The internal state distributions are well-characterized for both normal and grazing incident angles by a two-component Boltzmann model for trapping desorption (TD) and impulsive scattering (IS) at rotational temperatures T(rot)(TD/IS), where the fractional TD probability for CO2 on the perfluorinated surface is denoted by TD and IS densities (rho) as alpha = rhoTD/(rhoTD + rhoIS). On the basis of an assumed cos(theta(scat)) scattering behavior for the TD flux component, the angular dependence of the IS flux at normal incidence (theta(inc) = 0 degrees) is surprisingly well-modeled by a simple cos(n)(theta(scat)) distribution with n = 1.0 +/- 0.2, while glancing incident angles (theta(inc) = 30 degrees, 45 degrees, and 60 degrees) result in lobular angular IS distributions scattered preferentially in the forward direction. This trend is also corroborated in the TD fraction alpha, which decreases rapidly under non-normal incident conditions as a function of backward versus forward scattering direction. Furthermore, the extent of rotational excitation in the IS channel increases dramatically with increasing angle of incidence, consistent with an increasing rotational torque due to surface roughness at the gas-liquid interface.     

The assessment of absorption of periplocin in situ via intestinal perfusion of rats by HPLC

Periplocin is an important compound of Cortex Periplocae, which shows poor absorption when administered orally. The effective intestinal permeability of periplocin was investigated using single-pass intestinal perfusion technique in male Wistar rats. SPIP was performed in rat jejunum. The samples of perfusate were collected at the designated time points after rat intestinal perfusion and analyzed by HPLC. The specificity of this method was demonstrated by the absence of interference of the drug peak with the intestinal sac artifacts and the components of the KRB solution. Recovery studies, as well as the intra-day and inter-day variations, were within statistical limits. This technique was applied to the study of the intestinal absorption of periplocin. The determined fraction absorbed (F(a)) of periplocin was 0.151 +/- 0.072 (n = 6) at a concentration of 6 microg/mL; the absorption rate constant (K(a)) was 0.0102 +/- 0.0039/min and the effective permeability coefficient (P(eff)) was 0.0021 +/- 0.0012 cm/min. These data suggest that periplocin has high permeability and might be absorbed in rat intestine.     

Cluster-based networks: 1D and 2D coordination polymers based on {MnFe2(μ3-O)}-type clusters

A straightforward approach to heterometallic Mn-Fe cluster-based coordination polymers is presented. By employing a mixed-valent μ(3)-oxo trinuclear manganese(II/III) pivalate cluster, isolated as [Mn(II)Mn(III)(2)O(O(2)CCMe(3))(6)(hmta)(3)]·(solvent) (hmta = hexamethylenetetramine; solvent = n-propanol (1), toluene (2)) in the reaction with a μ(3)-oxo trinuclear iron(III) pivalate cluster compound, [Fe(3)O(O(2)CCMe(3))(6)(H(2)O)(3)]O(2)CCMe(3)·2Me(3)CCO(2)H, three new heterometallic {Mn(II)Fe(III)(2)} cluster-based coordination polymers were obtained: the one-dimensional polymer chain compounds {[MnFe(2)O(O(2)CCMe(3))(6)(hmta)(2)]·0.5MeCN}(n) (3) and {[MnFe(2)O(O(2)CCMe(3))(6)(hmta)(2)]·Me(3)CCO(2)H·(n-hexane)}(n) (4) and the two-dimensional layer compound {[MnFe(2)O(O(2)CCMe(3))(6)(hmta)(1.5)]·(toluene)}(n) (5). Single-crystal X-ray diffraction analysis reveals a μ(3)-oxo trinuclear pivalate cluster building block as the main constituent in all polymer compounds. Different M:hmta ratios in 1-5 are related to the different structural functions of the N-containing ligand. In clusters 1 and 2, three hmta ligands are monodentate, whereas in chains 3 and 4 two hmta ligands act as bridging ligands and one is a monodentate ligand; in 5, all hmta molecules act as bidentate bridges. Magnetic studies indicate dominant antiferromagnetic interactions between the metal centers in both homometallic {Mn(3)}-type clusters 1 and 2 and heterometallic {MnFe(2)}-type coordination polymers 3-5. Modeling of the magnetic susceptibility data to a isotropic model Hamiltonian yields least-squares fits for the following parameters: J(1)(Mn(II)-Mn(III)) = -6.6 cm(-1) and J(2)(Mn(III)-Mn(III)) = -5.4 cm(-1) for 1; J(1) = -5.5 cm(-1) and J(2)(Mn(III)-Mn(III)) = -3.9 cm(-1) for 2; J(1)(Mn(II)-Fe(III)) = -17.1 cm(-1) and J(2)(Fe(III)-Fe(III)) = -43.7 cm(-1) for 3; J(1) = -23.8 cm(-1) and J(2) = -53.4 cm(-1) for 4; J(1) = -13.3 cm(-1) and J(2) = -35.4 cm(-1) for 5. Intercluster coupling plays a significant role in all compounds 1-5.     

三价砷阴离子AsS43-的化合物[InAsS4(2，2’-bipy)]2的合成及性质

用水热法合成了含三价砷阴离子AsS3-4的化合物[InAsS4(2,2′-bipy)]2。 该化合物晶体为单斜晶系,空间群为P21/c,晶胞参数a=0.89799(9) nm,b=2.1794(2) nm,c=1.43736(14) nm,β=91.274(2)°,V=2.8123(5) nm3。 在此化合物中用金属螯合物[In(2,2′-bipy)]3+稳定了不常见的三价砷阴离子AsS3-4,讨论了金属价态对最终产物结构的影响,并且研究了该化合物的半导体性质(禁带带宽1.35 eV)。     

New charge transfer salts based on bis(ethylenedithio)tetrathiafulvalene (ET) and ferro- or antiferromagnetic oxalato-bridged dinuclear anions: syntheses, structures and magnetism of ET5[MM'(C2O4)(NCS)8] with MM' = Cr(III)Fe(III), Cr(III)Cr(III)

Electrochemical combination of the magnetic dinuclear anion [MM'(C2O4)(NCS)8](4-) (MM' = Cr(III)Cr(III), Cr(III)Fe(III)) with the ET organic pi-donor (ET = BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) gives rise to two new isostructural molecular hybrid salts ET5[MM'(C2O4)(NCS)8], with MM' = CrCr (1), CrFe (2). The molecular structure of compound 1 has been determined by single crystal X-ray diffraction. The particular arrangement of the organic units consists of an unprecedented two-dimensional organic sublattice nearly similar to that observed in kappa-phase structures. For both compounds, the magnetic susceptibility measurements indicate (i) the ET radicals do not contribute to the magnetic moment probably due to the presence of strong antiferromagnetic interaction between them, and (ii) in the anion, the magnetic coupling is antiferromagnetic for 1 (J = -3.65 cm(-1)) and ferromagnetic for 2 (J = 1.14 cm(-1), J being the parameter of the exchange Hamiltonian H = -2JS1S2). The field dependence of the magnetization of compound 2 at 2.0 K gives further evidence of the S = 4 ground-state arising from the interaction between S = 3/2 Cr(III) and S = 5/2 Fe(III). EPR measurements confirm the nature of the magnetic interactions and the absence of any contribution from the organic part, as observed from the static magnetic measurement. Conductivity measurements and electronic band structure calculations show that both salts are semiconductors with low activation energies.     

Infrared vacuum-ultraviolet laser pulsed field ionization-photoelectron study of CH3Br+ (X(2)E(3/2))

By preparing methyl bromide (CH3Br) in selected rotational levels of the CH3Br(X(1)A1; v1 = 1) state with infrared (IR) laser excitation prior to vacuum-ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have observed rotationally resolved photoionization transitions to the CH3Br(+)(X(2)E(3/2); v1(+) = 1) state, where v1 and v1(+) are the symmetric C-H stretching vibrational mode for the neutral and cation, respectively. The VUV-PFI-PE origin band for CH3Br(+)(X(2)E(3/2)) has also been measured. The simulation of these IR-VUV-PFI-PE and VUV-PFI-PE spectra have allowed the determination of the v1(+) vibrational frequency (2901.8 +/- 0.5 cm(-1)) and the ionization energies of the origin band (85 028.3 +/- 0.5 cm(-1)) and the v1(+) = 1 <-- v1 = 1 band (84 957.9 +/- 0.5 cm(-1)).     

Magneto-structural studies of two new cobalt(II)-N,N-diisobutylisonicotinamide compounds: [CoLCl2]n and [Co(L)2(H2O)4][CoLBr3]2·2H2O

Two similar synthetic pathways using the ligand N,N-diisobutylisonicotinamide (L) with anhydrous CoX(2) salts (being X = Cl(-), Br(-)) led to different species: a one-dimensional system, [CoLCl(2)](n), 1, and an ionic product [Co(L)(2)(H(2)O)(4)][CoLBr(3)](2)·2H(2)O, 2, respectively. Compound 1 is a polymer in which ligand L coordinates to tetrahedral Co(II) ions in a bidentate bridging fashion using the pyridine nitrogen and carbonyl oxygen atoms. Compound 2 consists of one octahedral cationic [Co(L)(2)(H(2)O)(4)](2+) entity and two tetrahedral anionic [CoLBr(3)](-) units. In this system, the ligand molecules coordinate only through the pyridine nitrogen atoms. The magnetic properties of 1 and 2 were investigated in the temperature range of 2.0 to 300.0 K and correlations between both (due to the existence of similar features) examined. The study of the magnetic properties of 1 was carried out by considering each Co(II) ion as a perfectly isolated system, hence, J = 0, but taking into account a significant zero-field splitting contribution due to distortions on the tetrahedral environment of the cobalt atoms. The fit of the magnetic susceptibility data together with reduced magnetization vs H/T measurements provided similar parameters (|D| = 10.8 cm(-1), g(⊥) = 1.92, g(‖) = 2.92 for the former and |D| = 11.04 cm(-1)and g = 2.05 for the latter, respectively). On the other hand, the magnetic response of compound 2 has been analyzed using a model which considers the presence of two tetrahedral and one octahedral Co(ii) ions (Co(Td) and Co(Oh)). The study was carried out in two separated blocks, above and below 80 K, where only the most significant effects at each interval of temperature were considered. As a result, the analysis of the magnetic data shows weak antiferromagnetic interactions between the Co(Oh)and the two Co(Td) ions (J = -0.41 cm(-1)) in 2. The best fit parameters were g(Co(Td)) = 2.89, g(Co(Oh)) = 3.50, |D(Co(Td))| = 10.62 cm(-1), |E(Co(Td))| = 2.95 cm(-1), Δ = 240.9 cm(-1) and J(L-S) = -107.1 cm(-1), from where λ was calculated with a final value of -144.8 cm(-1) (J(L-S) = Aκλ). The approximations performed to obtain these values provide reasonable results in agreement with compound 1 and also to other systems in the literature.     

Quantification in capillary electrophoresis-mass spectrometry: long- and short-term variance components and their compensation using internal standards

Different approaches were chosen to examine ionization reproducibility of analytes after separation by capillary electrophoresis-mass spectrometry (CE-MS) in a commercially available sheath-flow electrospray interface. For this task three different standard samples were examined. Sample 1 contained neostigmine bromide (cationic), paracetamol (PCM) (neutral) and nicotinic acid (anionic component). Results were evaluated using internal standard (IS) calculations. Sample 2 represented an isotopically labelled IS of the quantified substance (PCM/D4-PCM), while sample 3 (neostigmine bromide/scopolamine hydrobromide) provided an IS closely migrating to the tested substance. Furthermore, short-time variations inside the interface were examined by multiple injections of the same substance. For sample 1, the relative standard deviations (RSD%s) were between 8 and 25% (n at least 58) for the peak area ratios. Multiple injected samples gave 5.5-19.4% (n = 25) for peak area RSD%. Using a closely migrating IS, sample 3, RSD%s between 6.5 and 10% (n at least 63) were achieved. With isotopically labelled IS, sample 2, an RSD% of 3-4% was achieved for peak area ratios over long periods (n = 25), for shorter periods (n = 9) even 1-2% RSD% was obtained. Keeping the instrument settings constant, the influence on the ionization efficiency and reproducibility was tested, varying the buffer pH, the organic buffer modifier and the sample concentration. Repeatabilities of migration time and peak area were measured and compared. Two 10 mM ammonium acetate buffers with pH 4.0 and 8.5 were investigated. No influence of buffer pH on peak area reproducibility was found. Isopropanol as organic buffer modifier significantly improved the ionisation leading to larger peak areas, but reduced reproducibility. The basic buffer produced slightly better RSD%s for migration times (2.5-4.0%) (n = 180) and faster analysis for the different test analytes of sample 1, while with the acetic buffer, RSD%s from 3.9 to 6.0% were obtained (n at least 163). The positioning of the capillary turned out to be the crucial parameter to ensure reproducible results. Thus, a procedure was established to ensure a defined ion-intensity level after capillary changes. The investigation of the different sample concentrations gave negligible differences in RSD%, showing that the signal-to-noise ratio was not the crucial parameter for reproducibility here, in contrast to CE-UV detection.     

Micro-Raman study on the conformation behavior of succinate in supersaturated sodium succinate aerosols

Micro-Raman spectra of supersaturated aerosols of sodium succinate were obtained. The conformation behavior of the succinate dianion as a function of relative humidity (RH) was investigated by combining micro-Raman spectroscopy with theoretical calculations. A shoulder at 968 cm(-1) of the v(C-CO(2)(-)) band on the rise in more concentrated droplets was believed indicative of conformation transformations. The intensity ratio (I(963)/I(997)) of the v(C-CO(2)(-)) band at 963 cm(-1) to the v(C-C) band at 997 cm(-1), versus the molar water-to-solute ratio (WSR), was used to fathom the equilibrium between gauche and trans conformations. Before saturation (WSR = 25.8) for the droplets, the ratio of I(963)/I(997) retains a value of approximately 2.6 independent of WSR, indicating that the equilibrium was not disturbed in the dilute droplets. In supersaturated droplets (WSR < 25.8), however, the ratio sharply decreases from approximately 2.6 to approximately 1.1 at WSR = 9.6, which was attributed to the formation of contact ion pairs (CIPs).     

Anharmonic vibrational frequencies and vibrationally averaged structures and nuclear magnetic resonance parameters of FHF-

The anharmonic vibrational frequencies of FHF(-) were computed by the vibrational self-consistent-field, configuration-interaction, and second-order perturbation methods with a multiresolution composite potential energy surface generated by the electronic coupled-cluster method with various basis sets. Anharmonic vibrational averaging was performed for the bond length and nuclear magnetic resonance indirect spin-spin coupling constants, where the latter computed by the equation-of-motion coupled-cluster method. The calculations placed the vibrational frequencies at 580 (nu(1)), 1292 (nu(2)), 1313 (nu(3)), 1837 (nu(1) + nu(3)), and 1864 cm(-1) (nu(1) + nu(2)), the zero-point H-F bond length (r(0)) at 1.1539 A, the zero-point one-bond spin-spin coupling constant [(1)J(0)(HF)] at 124 Hz, and the bond dissociation energy (D(0)) at 43.3 kcal/mol. They agreed excellently with the corresponding experimental values: nu(1) = 583 cm(-1), nu(2) = 1286 cm(-1), nu(3) = 1331 cm(-1), nu(1) + nu(3) = 1849 cm(-1), nu(1) + nu(2) = 1858 cm(-1), r(0) = 1.1522 A, (1)J(0)(HF) = 124+/-3 Hz, and D(0) = 44.4+/-1.6 kcal/mol. The vibrationally averaged bond lengths matched closely the experimental values of five excited vibrational states, furnishing a highly dependable basis for correct band assignments. An adiabatic separation of high- (nu(3)) and low-frequency (nu(1)) stretching modes was examined and found to explain semiquantitatively the appearance of a nu(1) progression on nu(3). Our calculations predicted a value of 186 Hz for experimentally inaccessible (2)J(0)(FF).