Impact of gamma-irradiation on some mass transfer driven operations in food processing

The effect of gamma-irradiation pretreatment on some mass transfer driven operations such as dehydration, osmotic dehydration and rehydration, commonly used in food processing, was studied. Applied irradiation up to 12.0 kGy resulted in decrease in hardness of the samples, as indicated by texture analysis. The effective diffusion coefficients of water and solute determined for dehydration, osmotic dehydration as well as for rehydration using a Fickian diffusion model. The effective diffusion coefficients for water (in case of osmotic dehydration and dehydration) and solid diffusion (in case of osmotic dehydration) were found to increase exponentially with doses of gamma-irradiation (G) according to an equation of the form D=A exp(−B/G), where A and B are constants. Microstructures of irradiated-carrot samples revealed that the exposure of carrot to gamma irradiation resulted in the breakage of cell wall structure, thereby causing softening of irradiated samples and facilitating mass transfer during dehydration and osmotic dehydration. The rehydration characteristics showed that gamma-irradiated sample did not absorb as much water as control, probably due to loss of cell integrity.     

Conductivity, calorimetry and phase diagram of the NaHSO4–KHSO4 system

Physico-chemical properties of the binary system NaHSO₄–KHSO₄ were studied by calorimetry and conductivity. The enthalpy of mixing has been measured at 505 K in the full composition range and the phase diagram calculated. The phase diagram has also been constructed from phase transition temperatures obtained by conductivity for 10 different compositions and by differential thermal analysis. The phase diagram is of the simple eutectic type, where the eutectic is found to have the composition X(KHSO₄) = 0.44 (melting point ≈ 406 K). The conductivities in the liquid region have been fitted to polynomials of the form κ(X) = A(X) + B(X)(T − T_m) + C(X)(T − T_m)², where T_m is the intermediate temperature of the measured temperature range and X, the mole fraction of KHSO₄. The possible role of this binary system as a catalyst solvent is also discussed.     

Interaction of sodium cholate with dioctadecyldimethylammonium chloride vesicles in aqueous dispersion

Mixtures of dioctadecyldimethylammonium chloride (DODAC) cationic vesicle dispersions with aqueous micelle solutions of the anionic sodium cholate (NaC) were investigated by differential scanning calorimetry, DSC, turbidity and light scattering. Within the concentration range investigated (constant 1.0 mM DODAC and varying NaC concentration up to 4 mM), vesicle → micelle → aggregate transitions were observed. The turbidity of DODAC/NaC/water depends on time and NaC/DODAB molar concentration ratio R. At equilibrium, turbidity initially decreases smoothly with R to a low value (owing to the vesicle–micelle transition) when R = 0.5–0.8 and then increases steeply to a high value (owing to the micelle–aggregate transition) when R = 0.9–1.0. DSC thermograms exhibit a single and sharp endothermic peak at T_m ≈ 49 °C, characteristic of the melting temperature of neat DODAC vesicles in water. Upon addition of NaC, T_m initially decreases to vanish around R = 0.5, and the main transition peak broadens as R increases. For R > 1.0 two new (endo- and exothermic) peaks appear at lower temperatures indicating the formation of large aggregates since the dispersion is turbid. All samples are non-birefringent. Dynamic light scattering (DLS) data indicate that both DODAC and DODAC/NaC dispersions are highly polydisperse, and that the mean size of the aggregates tends to decrease as R increases.     

Conformational identification of cyclohexylphosphine by microwave spectroscopy

The microwave spectra of cyclohexylphosphine have been recorded in the 18.0–26.5 GHz region. A-type rotational transitions have been assigned. The ground state rotational constants were determined to be A = 4153.75 ± 0.23, B = 1362.31 ± 0.01 and C = 1104.14 ± 0.01 MHz for C₆H₁₁PH₂, and A = 4030.03 ± 0.25, B = 1312.72 ± 0.01 and C = 1072.33 ± 0.01 MHz for C₆H₁₁PD₂. From the experimental rotational constants, it is suggested that the assigned spectra have resulted from the chair conformation with the gauche phosphine group in an equatorial position (CESG). This form is believed to be the most populated conformational isomer in the gas phase.     

Determination of cilnidipine, a new calcium antagonist, in human plasma using high performance liquid chromatography with tandem mass spectrometric detection

A rapid, sensitive and reliable high performance liquid chromatographic method coupled with tandem mass spectrometry (HPLC–MS/MS) has been developed and validated for the determination of cilnidipine, a relatively new calcium antagonist, in human plasma. The reversed-phase chromatographic system was interfaced with a TurboIonSpray (TIS) source. Nimodipine was employed as the internal standard (IS). Sample extracts following protein precipitation were injected into the HPLC–MS/MS system. The analyte and IS were eluted isocratically on a C18 column, with a mobile phase consisting of CH₃OH and NH₄Ac (96:4, v/v). The ions were detected by a triple quadrupole mass spectrometric detector in the negative mode. Quantification was performed using multiple reaction monitoring (MRM) of the transitions m/z 491.2 → 122.1 and m/z 417.1 → 122.1 for cilnidipine and for the IS, respectively. The analysis time for each run was 3.0 min. The calibration curve fitted well over the concentration range of 0.1–10 ng mL⁻¹, with the regression equation Y = (0.103 ± 0.002)X + (0.014 ± 0.003) (n = 5), r = 0.9994. The intra-day and inter-day R.S.D.% were less than 12.51% at all concentration levels within the calibration range. The recoveries were between 92.71% and 97.64%. The long-term stability and freeze-thaw stability were satisfying at each level. The present method provides a modern, rapid and robust tool for pharmacokinetic studies of cilnidipine.     

'Genome order index' should not be used for defining compositional constraints in nucleotide sequences

A “genome order index,” defined as S = a² + c² + t² + g², where a, c, t, and g are the nucleotide frequencies of A, C, T, and G, respectively, was used to suggest that there exist genome-specific constraints on nucleotide composition. We show that the “evidence” for constraint, S < 1/3, is in fact a mathematical property that is always true regardless of data. Moreover, we show that S is strictly equivalent to and derivable from the Shannon H-function and has no advantage over it.     

Heavy atom structure and conformer stabilities of cyclopropyl carbinol from rotational spectroscopy and ab initio calculations

A remeasurement of the rotational spectra of the normal and hydroxyl deuterated isotopomers of cyclopropyl carbinol (cyclopropane methanol, (CH₂)₂CH(CH₂OH)) using Fourier-transform microwave spectroscopy has provided refined rotational constants and centrifugal distortion constants for this molecule. Rotational constants for an additional four singly substituted ¹³C isotopomers, the OD isotopomer, and the ¹⁸O isotopomer are consistent with a conformer in which the OH group forms an intramolecular hydrogen bond with the edge of the cyclopropyl ring. The observed a-type transition frequencies for the normal and deuterated species are in reasonable agreement with a previous microwave study (although some frequencies differ by several hundred kilohertz), but the few b- and c-type lines that were measured in the range of our spectrometer were found to differ by several megahertz from the previous literature measurements, leading to A rotational constants that differ significantly from those reported previously. The refined rotational constants for the normal isotopic species are A=12470.7795(23) MHz, B=3236.4678(7) MHz, C=2894.4831(7) MHz, while those of the deuterated species are A=12069.2653(24) MHz, B=3177.1540(8) MHz and C=2826.2658(7) MHz. Results of ab initio optimizations on seven conformers for this molecule carried out at the MP2/6-311+G(d,p) level will be compared with the experimentally determined structural parameters.     

On the thermodynamic equilibrium between ice and electrolyte solutions in the conditions of confined geometry

For a small volume (of about 10⁻⁶ cm³) of NaCl and other electrolyte solutions (C = 0.1 and 1 M) in thin (r = 5/10 μm) single quartz capillaries, dependencies of the column length l of frozen solutions on the temperature t were measured using comparator IZA-2 in a thermostated chamber. At temperatures range t > −4 °C (for C = 0.1 M) and t > −8 °C (for C = 1 M) the l(t) dependencies are reversible and therefore correspond to establishment of an equilibrium between ice-1 and the solution.

From the constants mass condition of the dissolved salt in a frozen column, the l(t) expression was derived, which includes thermodynamic relation between solution concentration in an equilibrium with ice, C_s, and the temperature t for bulk systems. Deviations from the data known for bulk solutions were observed in thin capillaries when temperature t decreased to −3 °C (for 0.1 M NaCl) and to −6 °C for 1 M NaCl solution.

This effect may be a result of strong adhesion of the ice column to capillary walls. In this case, some internal stresses arise in frozen solution resulting in a deviation from thermodynamic equilibrium conditions for bulk systems. When approaching the temperature of ice melting, adhesion forces decrease due to formation of a thin non-freezing water interlayer on the capillary wall. In this temperature range the experimental data are in agreement with the predictions for bulk systems. It was supposed that the observed deviation in thin capillaries may be caused by formation of an amorphous ice phase with higher density as compared with the ice-1 during rapid freezing, or by an effect of ice microlenses formation. Both effects will result in a deviation from the phase diagram corresponding to a bulk solution.     

Conformational identification and dipole moment of 4-fluoro-1-butene by microwave spectroscopy

The microwave spectrum of 4-fluoro-1-butene has been recorded in the frequency region 26.5–40.0 GHz. A-type rotational transitions in the ground vibrational state have been assigned. The effective rotational constants and centrifugal distortion constants were determined to be A = 19 196 ± 323, B = 2132.48 ± 0.01, C = 2112.52 ± 0.01 MHz, D_J = 0.70 ± 0.03 and D_JK = −26.16 ± 0.05 kHz. Analysis of the measured Stark effects gave a dipole moment of 1.80 D with components of |u_a| = 1.62 ± 0.01, |u_b| = 0.68 ± 0.05 and |u_c| = 0.39 ± 0.14 D. From the experimental rotational constants and dipole moments, it is suggested that the assigned spectra have resulted from the skew—trans conformer.     

Refined heat capacity of LaPO4 in the temperature range 0–1600 K

In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p° (T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO₆ is refined by the Rietveld method: space group F d3m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å³. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion.     

Photodynamics of azobenzene in a hindering environment

We have run trajectory surface hopping simulations of the trans → cis photoisomerization of azobenzene, subject to a pulling force. The model mimics two situations: a trans-azobenzene derivative with bulky substituents that may not be easily displaced, and a recent experiment by Gaub’s group [T. Hugel, N.B. Holland, A. Cattani, L. Moroder, M. Seitz, H.E. Gaub, Science 296 (2002) 1103; N.B. Holland, T. Hugel, G. Neuert, A. Cattani-Scholz, C. Renner, D. Oesterhelt, L. Moroder, M. Seitz, H.E. Gaub, Macromolecules 36 (2003) 2015; G. Neuert, T. Hugel, R.R. Netz, H.E. Gaub, Macromolecules 39 (2005) 789], in which a polymer with azobenzene units was stretched in an atomic force microscope. In both cases, the shortening of the azobenzene moiety in going from the trans to the cis form is opposed by a pulling force. Our simulations show that the trans → cis photoconversion is only partially suppressed by considerably large forces (≈500 pN or more). However, the cis isomer reverts to trans in the ground state, with the help of the pulling force and using the vibrational energy that is available in the first 1–2 ps. The lowering of the quantum yields is therefore the combined result of hindering of the excited state process and of the hot ground state back reaction.     

Langmuir monolayer properties of the fluorinated-hydrogenated hybrid amphiphiles with dipalmitoylphosphatidylcholine (DPPC)

Surface pressure–area (π–A), surface potential–area (ΔV–A), and dipole moment–area (μ–A) isotherms were obtained for the Langmuir monolayer of two fluorinated-hydrogenated hybrid amphiphiles (sodium phenyl 1-[(4-perfluorohexyl)-phenyl]-1-hexylphosphate (F6PH5PPhNa) and (sodium phenyl 1-[(4-perfluorooctyl)-phenyl]-1-hexylphosphate (F8PH5PPhNa)), DPPC and their two-component systems at the air/water interface. Monolayers spread on 0.02 M Tris buffer solution (pH 7.4) with 0.13 M NaCl at 298.2 K were investigated by the Wilhelmy method, ionizing electrode method and fluorescence microscopy. Moreover, the miscibility of two components was examined by plotting the variation of the molecular area and the surface potential as a function of the molar fraction for the fluorinated-hydrogenated hybrid amphiphiles on the basis of the additivity rule. The miscibility of the monlayers was also examined by construction of two-dimensional phase diagrams. Furthermore, assuming the regular surface mixture, the Joos equation for analysis of the collapse pressure of two-component monolayers allowed calculation of the interaction parameter (ξ) and the interaction energy (−Δ) between the fluorinated-hydrogenated hybrid amphiphiles and DPPC. The observations by a fluorescence microscopy also supported our interpretation as for the miscibility in the monolayer state. Comparing the monolayer behavior between the two binary systems, no remarkable difference was found among various aspects. Among the two combinations, the mole fraction dependence in monlayer properties was commonly classified into two ranges: 0 ≤ X ≤ 0.3 and 0.3 < X ≤ 1. Dependence of the chain length of fluorinated part was reflected for the molecular packing and surface potential.     

Determination of concentration-dependent transport coefficients in nanofiltration: Defining an optimal set of coefficients

The currently used equation for solute transport in nanofiltration contains two parameters (ω and 1 – σ) that may be concentration-dependent. A force balance equation allows interpretation of these parameters (as well as L_p) in terms of distribution and friction coefficients, as was demonstrated for a neutral solute and a single 1:1 salt. It is generally assumed in model calculations that it is the distribution coefficient that determines the concentration dependence of ω and 1 – σ. This suggests that a more practically convenient form of the equation may be proposed, in which only one concentration-dependent parameter, ω, appears, while the other is replaced with the ratio of the two, A, which has the meaning of the membrane Peclét number divided by the volume flux and may be assumed to be constant. This may facilitate the analysis of flux–rejection curves and parameter evaluation including concentration dependence, which is a crucial and unavoidable step towards predictive NF modeling. The direct connection between transport parameters and distribution coefficients also suggests that experimentally measured concentration dependence may help to discriminate between different exclusion mechanisms. An approximate analysis based on the connection between A and solute–water friction shows that for presently used NF membranes and realistic fluxes the expected contribution of convection to solute flow cannot become dominant so that the limiting value for salt rejection, R = σ, cannot be reached.     

High-field EPR investigation of a series of mononuclear Mn(II) complexes doped into Zn(II) hosts

The five-coordinate mono-halide mononuclear Zn(II) complexes [Zn(tpa)X]⁺ (tpa = tris(2-pyridylmethyl)amine; X = I ([Zn(tpa)I]I; 1a), Br ([Zn(tpa)Br](ZnBr₄)_0.5; 2a) and Cl ([Zn(tpa)Cl](ZnCl₄)_0.5; 3a)) and the six-coordinate mononuclear complex [Zn(tpa)(NCS)₂] (4a) have been synthesized and characterized by X-ray crystallography. The [Zn(tpa)X]⁺ complexes doped with the corresponding [Mn(tpa)X₂] complexes (X = I (1b), Br (2b) and Cl (3b)) have been synthesized and their electronic properties investigated by multifrequency high field EPR (HF-EPR) (95–285 GHz). The magnetically diluted conditions allow the determination of the hyperfine coupling constant A (A = 68.10⁻⁴ cm⁻¹ for 1b–3b). The zero-field splitting parameters (D and E) found for 1b–3b are comparable to those found for neat samples of the [Mn(tpa)X₂] complexes (1b: D = 0.635 cm⁻¹, E/D = 0.189; 2b: D = 0.360 cm⁻¹, E/D = 0.192; 3b: D = 0.115 cm⁻¹, E/D = 0.200). The efficacy of using multifrequency EPR under dilute conditions to precisely determine spin Hamiltonian parameters is discussed.     

Microwave spectrum and conformation of isopropyl fluoroformate

The microwave spectrum of isopropyl fluoroformate is characterized by intense a-type R-branch transitions from one conformational species. The rotational constants of the ground state, A₀ = 4967.0(8) MHz, B₀ = 1704.69(2) MHz, C₀ = 1468.86(1) MHz and κ = −0.8651(2) are consistent with a τ₁ (O=COC) = 0°, τ₂(COCH) ˜35° structure. This structure can be viewed as a combination of the two conformational species found in ethyl fluoroformate. Two vibrational satellites having rotational constants A₀ = 4963(5) MHz, B₀ = 1694.11(7) MHz. C₀ = 1471.43(4) MHz and A₀=4998(6) MHz, B₀ = 1705.21(7) MHz, C₀ = 1471.10(4) MHz have been assigned.     

On the positronium spin conversion reactions caused by some macrocyclic Co complexes

The rate constants, k_CR, of ortho- into para-positronium (o-Ps→p-Ps) spin conversion reactions, CR, caused by the high-spin [Co^IIsep]²⁺, [Co^IIdinosar]²⁺ and [Co^IIdiamsar]²⁺ macrocyclic complexes and also by high-spin [Co^II sen]²⁺ tripod complex were measured at several temperatures. The delocalizations, β, of Co^II unpaired electrons, promoted by the mentioned ligands, were determined by using the previously established correlations between k_CR and the electron delocalization β of unpaired metal electrons. β is given by the ratio between the Racah inter-electronic repulsion parameters of complexes, B, and that of the free ions, B₀. The β values are compared with those of the Co^II complexes with en (1,2-ethanediamine), pn (1,2 propanediamine) and dien (2,2′ diamino diethylamine) ligands. The k_CR rate constants are also compared with those of the Ps oxidation reactions, OR, promoted by the corresponding Co^III complexes. It is concluded that, unlike OR's, the CR's do not occur by formation of hepta-coordinate adducts with Ps atoms.     

Inelastic scattering matrix elements, cross sections and rate constants for transition B(P1/2) + H2(j = 0) ↔ B(P3/2) + H2(j = 0)

The non-adiabatic wave packet collisions of B(²P_1/2) + H₂(j = 0) ↔ B(²P_3/2) + H₂(j = 0) were calculated using the time dependent Channel Packet Method to compute transition probabilities, cross sections and rate constants. While the H₂ angular momentum j was fixed to 0, the total angular momentum of the system J, was varied from 1/2 to 153/2. The feature of the Stückelberg oscillation was shown in transition probabilities. The transition from B(²P_3/2) to B(²P_1/2) state was shown to be favored over the reverse process. The ratio of the computed rate constants was well compared with that of the analytic result obtained from the Boltzmann factor and the detailed balance.     

Theoretical study on the intramolecular proton transfer reactions of 3-methyl-5-hydroxyisoxazole and its water complexes

The optimized structures and proton transfer reactions of 3-methyl-5-hydroxyisoxazole and its water complexes (3-M-5-HIO · (H₂O)_n · (n = 0–3)) were computed at B3LYP and MP2 theoretical level. The results indicates that 3-M-5-HIO has four isomers (Ecis, Etrans, K1 and K2), and the keto tautomer, and K2 is the most stable isomer in the gas phase. Hydrogen bonding between 3-M-5-HIO and the water molecules can dramatically lower the barrier by the concerted transfer mechanism. Ecis · (H₂O)₃ → K1 · (H₂O)₃ and Ecis · (H₂O)₂ → K2 · (H₂O)₂ is found to be very efficient. Comparing with the proton transfer mechanism of 5-HIO shows that the methyl substitution prevents the intramolecular proton transfer.     

Synthesis and structure of the iron-substituted silylacetylene [(η-C5H5)Fe(CO)2SiMe2C]2 and its cobalt hexacarbonyl derivative [(η-C5H5)Fe(CO)2SiMe2C]2 · Co2(CO)6

A transition metal-substituted silylacetylene [(η⁵-C₅H₅)Fe(CO)₂SiMe₂C]₂, [FpMe₂SiC]₂ (I) was synthesized and characterized spectroscopically and structurally. I crystallized in the monoclinic space group P2₁/n, A = 13.011(3) Å B = 12.912(3) Å, C = 13.175(5) Å, β = 94.95(2). The acetylene linkage is reactive toward Co₂(CO)₈ to form I. Co₂(CO)₆ (II) which was also characterized spectroscopically and by single crystal X-ray diffraction. II crystallized in the orthorhombic space group Pbca, A = 17.64(2) Å, B = 14.225(10) Å, C = 24.49(2) Å.     

Experimental determination of the Stark widths of Pb I spectral lines in a laser-induced plasma

Stark widths of 34 spectral lines of Pb I have been measured in a Laser-Induced-Plasma (LIP). The optical emission spectroscopy from a LIP generated by a 10 640 Å radiation, with an irradiance of 1.4 × 10¹⁰ W cm^− 2 on a Sn–Pb target in an atmosphere of argon was analyzed between 1900 and 7000 Å. The Local Thermodynamic Equilibrium (LTE) conditions and plasma homogeneity have been checked. The 34 spectral lines measured in this paper correspond to the transitions n(n = 7, 8)s→6p², n(n = 6, 7)d→6p². The population levels distribution and the corresponding temperatures were obtained using Boltzmann plots. The plasma electron densities were determined using well-known Stark broadening parameters of spectral lines. Special attention was dedicated to the possible self-absorption of the different transitions. Stark broadening parameters of the spectral lines were measured at 2.5 µs after each laser light pulse, where the electron temperature was close to 11 200 K and the electron density to 10¹⁶ cm^− 3. The experimental results obtained have been compared with the experimental values given by other authors.