Study of the retention behavior of small polar molecules on different types of stationary phases used in hydrophilic interaction liquid chromatography

The retention behavior of a large group of analytes (35) with varied properties (pK_a and logP) was studied on eight hydrophilic interaction LC columns with different surfaces, stationary phase chemistries, and types of particles. The acetonitrile content (5–95%), buffer concentration (0.5–200 mM), and pH of the mobile phase (3.8 and 6.8) were evaluated for their effects on the retention behavior. The type of stationary phase had a significant impact on the selectivity and retention time of the tested analytes. Completely different selectivity was observed on the aminopropyl stationary phase. In this study, the influence of the buffer concentration was similar for all tested columns, except for the aminopropyl stationary phase. Increasing the buffer concentration led to decreased retention times for the basic compounds and increased retention times for the acidic compounds, while the inverse behavior was observed on the aminopropyl stationary phase. The selectivity of the individual stationary phases was evaluated at pH 3.8 and 6.8. Much lower selectivity differences between the stationary phases were observed at pH 6.8 than pH 3.8. Bare silica stationary phases were used in the comparison of the particles (fused‐core and fully porous particles of 3 and 1.7 μm) and the columns provided by different manufacturers.     

Experimental study of the dynamics of penetration of a solid body into a soil medium

An experimental system is developed to determine the main parameters of the impact and penetration of a solid deformable body into a soft soil medium. This system is based on the technique of an inverse experiment with a measuring rod and the technique of a direct experiment with photo recording and the application of a shadow picture of the interaction of a striker with a soil target. To verify these techniques, the collision of a solid body with soil is studied by a numerical calculation and the time intervals in which the change of the resistance force is proportional to the penetration velocity squared are determined. The penetration resistance coefficients determined in direct and inverse experiments are shown to agree with each other in the collision velocity range 80–400 m/s, which supports the validity of the techniques and the reliability of measuring the total load.     

Enzymatic synthesis of a chiral chalcogran intermediate

Two lipases, Novozyme 435 (lipase B from Candida Antarctica) and Lipozyme TL IM (Thermomyces lanuginosus) were used successfully for the kinetic resolution of racemic 1-(2-furyl)-3-pentanol, the key intermediate in synthesis of the bark beetle pheromone, chalcogran. The desired S-(+)-enantiomer was prepared in enantiomeric excesses higher than 98 % and with yields of 26.3 % and 32.5 %, respectively. Methyl tert-butyl ether and vinyl acetate were found to be the best reaction media and the acetyl donor to achieve fast and effective resolution.     

Local field and radiative relaxation rate in a dielectric medium

The effect of macroscopic parameters of a substance on the optical characteristics of impurity particles is investigated. A generalized control equation is derived for two-level emitters forming an ensemble of optical centers in a transparent dielectric medium. In this equation, the effective values of the acting pump field and the radiative relaxation rate of an optical center are taken into account. The formalism developed here is a completely microscopic approach based on the chain of the Bogoliubov-Born-Green-Kirkwood-Yvon equations for reduced density matrices and correlation operators for material particles and modes of a quantized radiation field. The method used here makes it possible to take into account the effects of individual and collective behavior of emitters, which are associated with the presence of an intermediate medium, consistently without using phenomenological procedures. It is shown that the resultant analytic expression for the effective lifetime of the excited state of an optical center conforms with experimental data.     

Analysis of the CH3D Nonad from 2000 to 3300 cm

As part of the simultaneous analysis of line positions and intensities of the first two polyads of monodeuterated methane, the results achieved for the region 3-5 μm are reported. It involves the three highest fundamentals, (ν₁, ν₂, ν₄), overlapped by overtone (2ν₃, 2ν₅, 2ν₆) and combination (ν₃+ν₆, ν₃+ν₅, ν₅+ν₆) bands. The theoretical model was based on the global tensorial model implemented in the MIRS package. Some 10 000 line positions and 2400 line intensities have been modeled to ±0.000 88 cm⁻¹ and ±3.6% respectively, using measurements obtained at 0.0056 and 0.011 cm⁻¹ resolution with the Fourier transform spectrometer at National Solar Observatory located at Kitt Peak. The strongest band in this polyad is ν₄(E) at 3016.7 cm⁻¹ with a strength of 6.3×10⁻¹⁸ cm⁻¹/(molecule cm⁻²) at 296 K; the weakest band is 2ν₃(E) at 2597.7 cm⁻¹ with a strength of 1.9×10⁻²⁰ cm⁻¹/(molecule cm⁻²) at 296 K. The total calculated absorption arising from the CH₃D nonad is 8.95×10⁻¹⁸ cm⁻¹/(molecule cm⁻²) at 296 K.     

Extended Analysis of Line Positions and Intensities of Ozone Bands in the 2900-3400 cm Region

The 2900-3400 cm⁻¹ spectral range is revisited for an accurate determination of line positions and line intensities of the 3ν₃, ν₁+2ν₃, 2ν₁+ν₃, and 3ν₁ bands of ozone. The fit on 4520 rotational energy levels of (012), (111), (210), (130), (003), (102), (201), and (300) vibrational states determined from observed transitions of cold and hot bands in the 2400-3400 cm⁻¹ region with J_max=65 and K_{a max}=20 gives a r.m.s.=7×10⁻⁴ cm⁻¹ and provides a satisfactory agreement between calculated and observed line positions (dimensionless standard deviation is χ=1.44). The set of 2580 line intensities of 7 rovibrational bands has been measured and fitted with a r.m.s.=6.9% (χ=1.2), leading to the determination of transition moment parameters for these bands. Using these parameters we have obtained more precise estimation for the integrated band intensities S(3ν₃)=1.41×10⁻¹⁹, S(ν₁+2ν₃)=1.28×10⁻²⁰, S(2ν₁+ν₃)=7.91×10⁻²¹, S(3ν₁)=4.72×10⁻²² cm⁻¹/mol cm⁻² at 296 K, with a cutoff 2×10⁻²⁶ cm⁻¹/mol cm⁻². The interactions of the tetrad (003)/(102)/(201)/(300) with the (130) state and the tetrad (040)/(012)/(111)/(210) are studied.     

Block copolymer adsorption from a homopolymer melt to an amine-terminated surface

Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiO_x, and SiO_x functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiO_x.     

Analysis of High-Resolution Spectra of (18)O(3)

Using a Fourier transform spectrometer, we have recorded the spectra of the (18)O(3) species of ozone in the region 1300-3100 cm(-1), with a resolution of 0.003 cm(-1). The large product pathlength x pressure enable us to record 18 bands, 14 for the first time. The analysis has been performed using effective Hamiltonians for polyads of strongly interacting states for ozone, accounting for Coriolis and anharmonic resonances. The spectral parameters are derived for 16 vibrational states, including the two "dark" states (040) and (130). Various resonances are studied through the mixing coefficients of rovibrational wavefunctions. Systematic intensity measurements allow determination of transition moment parameters for 16 bands. Finally, a complete list of all transitions from 1300 to 3100 cm(-1), with cutoffs 10(-26) cm(-1)/mol cm(-2) (296 K), is calculated. Copyright 2001 Academic Press.