Transport properties of aqueous solutions of calcium lactate in the absence and presence of β-cyclodextrin

Mutual diffusion coefficients and electrical conductivity of a well-known food additive and supplement, or excipient in pharmaceutical formulations, calcium lactate, have been measured in the absence and presence of β-cyclodextrin in aqueous solutions, at 298.15 K. The dependence of conductivity on concentration has been analysed using the Fuoss-Edelson method. The values of the Nernst diffusion coefficients, for binary solutions, derived from conductance and from diffusion experiments are in good agreement. The presence of β-cyclodextrin leads to a non-expected effect on the transport properties of the aqueous solutions of calcium lactate. These data have been justified with help of ¹H NMR spectroscopy. The effect on the water structure, reducing the hydration shell of lactate, is argued. This leads to an increase of the effective concentration of calcium lactate in solution contributing to an increase in the diffusion coefficients and a decrease in the dependence of the electrical conductance on the concentration.     

Spectrofluorimetric Study and Detection of Ketoconazole in the Presence of β-cyclodextrin

The formation of a complex between ketoconazole and β-cyclodextrin was followed by spectrofluorimety. The inclusion of ketoconazole in β-cyclodextrin cavity enhanced the native fluorescence of the drug. The stoichiometry of the complex was 1:1 β-cyclodextrin to ketoconazole and the stability constant of the complex (log K _f) was determined to be 4.3 ± 0.01 at pH = 7.9 and 3.7 ± 0.04 at pH = 2.6. A sensitive spectrofluorimetric method for the detection of ketoconazole is presented. At optimized experimental conditions, a linear relationship between the fluorescence intensity of the solution and concentration of ketoconazole is observed in the range of 0.01–10 μg ml⁻¹ (5 × 10⁻⁸ M–1.88 × 10⁻⁵ M). The method was applied to the detection of ketoconazole in pharmaceutical products and the results were satisfactory in comparison to the official method (relative error = 2.8% and standard deviation = 0.06 for tablets of ketoconazole). The recovery of ketoconazole from a blood serum sample, determined by the proposed method, was 97.1 ± 2.4%.     

Fluorescence of the Schiff bases of pyridoxal and pyridoxal 5′-phosphate withl-isoleucine in aqueous solutions

The present study reports on the absorption and emission properties of the Schiff bases formed by pyridoxal and pyridoxal 5-phosphate withl-isoleucine in aqueous solutions. Species protonated at the imine and ring nitrogen are the most fluorescent in both Schiff bases with a quantum yield of 0.02, i.e., 20-fold the value found for species in alkaline solutions. In agreement with other studies, species protonated at the imine nitrogen shows an emission around 500 nm upon excitation at 415 nm. In contrast to previous observations on other PLP Schiff bases, emissions at 560 nm (PL-Ile) and 540 nm (PLP-Ile) are observed upon excitation at 365 and 415 nm, respectively. The emission at 470 nm found in PLP-Ile Schiff base upon excitation at 355 nm is ascribed to a multipolar monoprotonated species. An estimation for the pK _a of the imine in the excited state ( 8.5) for both Schiff bases is also reached. Our results suggest that fast protonation reactions on the excited state are responsible for the observed fluorescence. These effects, in which the hydrogen bond and the phosphate group seem to play a role, could be extended to understanding coenzyme environments in proteins.     

Concentration dependence of water self-diffusion coefficients in dilute glycerol–water binary and glycerol–water–sodium chloride ternary solutions and the insights from hydrogen bonds

Water self-diffusion coefficients for glycerol–water binary and glycerol–water–sodium chloride ternary solutions at low glucose concentrations have been predicted using the mean square displacements method. It was found that the water self-diffusion coefficient decreases as the glycerol concentration increases. The reasons for the decrease have been analysed from the viewpoint of the hydrogen bonds.     

Effects of partial charge-transfer solute – solvent interactions in absorption spectra of aromatic hydrocarbons in aqueous and alcoholic solutions

A method for study of charge-transfer interactions between solute molecules and solvent based on the comparison of the ratios of spectral shifts of different electronic transitions in solute molecules in chemically inert solvent is proposed. The method is applicable to molecules that do not change their dipole moment on excitation. As an example, a presence of charge transfer interactions in higher electronic states of aromatic hydrocarbons (benzene, phenanthrene, and naphthalene) dissolved in water and alcohols was demonstrated.     

Ultrasonic and DFT study of intermolecular association through hydrogen bonding in aqueous solutions of d(−)-arabinose

The experimental measurements of density, viscosity and ultrasonic velocity of aqueous d-arabinose solutions were carried out as functions of concentration (0.1 ≤ m [mol kg^? 1] ≤ 1.0) and temperature (303.15 ≤ T [K] ≤ 323.15). The isentropic compressibility (β_s), acoustic impedance (Z), hydration number (H_n), intermolecular free length (L_f), classical sound absorption (α/f²)_class and shear relaxation time (τ) were calculated by using the measured data. These parameters have been interpreted in terms of solute–solvent interactions. The quantum chemical calculations were performed to study the hydrogen bonding in interacting complex formed between α-D-arabinopyranose in ¹C₄ conformation and water molecules. Computations have been done by using Density Functional Theory (DFT) method at B3LYP/6-31+g(d) level of theory to study the equilibrium structure of α-d-arabinose, α-D-arabinopyranose–water interacting complex and vibrational frequencies. The solution phase study was carried out using Onsager's reaction field model in water solvent. The computed and scaled vibrational frequencies are in good agreement with the main features of the experimental spectrum when seven water molecules are considered explicitly with α-D-arabinopyranose in ¹C₄ conformation. The interaction energy (E_total), hydrogen bond lengths and dipole moment (μ_m) of the interacting complex are also presented and discussed with in the light of solute–solvent interactions.     

Diffusion of chromium and manganese in γ-TiAl

The γ-TiAl intermetallic compound with suitable alloying additions has shown considerable promise as a material for high-temperature applications. Diffusion studies in this alloy system are useful in assessment of their creep behaviour and structural stability in service conditions. Tracer diffusion coefficients of ⁵¹Cr and ⁵⁴Mn in a γ-TiAl intermetallic compound containing 54.1 at. % aluminium were determined in the temperature range from 1095 to 1470?K. The temperature dependence of both the diffusing species follows a linear Arrhenius behaviour and can be expressed as D _Cr?=?4.4?×?10^?3exp(?350?kJ?mol^?1/RT)?m^2?s^?1 and D _Mn?=?1.2?×?10^?3?×exp(?326?kJ?mol^?1/RT)?m^2?s^?1. The data are analysed on the basis of empirical correlations between the diffusion and melting parameters applicable for conventional mono-vacancy diffusion mechanism in metals. It is concluded that impurity diffusion in γ-TiAl occurs through the migration of thermal vacancies via nearest-neighbour or next-nearest neighbour jumps.     

Molecular encapsulation of amodiaquine in 2-hydroxypropyl β-cyclodextrin cavity. Characterization and its in vitro cytotoxicity

Amodiaquine has been used widely as an antimalarial drug. Amodiaquine is a mannich base 4-amino quinolone with a mode of action similar to that of chloroquine. The inclusion complex of amodiaquine with 2-(hydroxypropyl)-beta-cyclodextrin in solution phase is studied from the ground and excited state with absorption and fluorescence spectroscopic techniques, respectively. A binding constant and stoichiometric ratio between amodiaquine and 2-(hydroxypropyl)-beta-cyclodextrin are calculated by the use of Benesi–Hildebrand equation. The solid complexes are prepared by physical, kneading and coprecipitation methods. The solid complexes are characterized by Fourier-transform infrared spectral analysis, Differential scanning calorimetric curves and powder X-ray diffraction patterns. The anticancer activity was tested for pure amodiaquine and their complex with 2-(hydroxypropyl)-beta-cyclodextrin against MDA MB 231 cell line. It clearly showed that a significant improvement of anticancer activity of amodiaquine when forming a complex with 2-(hydroxypropyl)-beta-cyclodextrin.     

Encapsulation of Labetalol, Pseudoephedrine in β-cyclodextrin Cavity: Spectral and Molecular Modeling Studies

The absorption and fluorescence spectra of labetalol and pseudoephedrine have been studied in different polarities of solvents and β-cyclodextrin (β-CD). The inclusion complexation with β-CD is investigated by UV-visible, steady state and time resolved fluorescence spectra and PM3 method. In protic solvents, the normal emission originates from a locally excited state and the longer wavelength emission is due to intramolecular charge transfer (TICT). Labetalol forms a 1:2 complex and pseudoephedrine forms 1:1 complex with β-CD. Nanosecond time-resolved studies indicated that both molecules show triexponential decay. Thermodynamic parameters (ΔG, ΔH, ΔS) and HOMO, LUMO orbital investigations confirm the stability of the inclusion complex. The geometry of the most stable complex shows that the aromatic ring is deeply self included inside the β-CD cavity and intermolecular hydrogen bonds were established between host and guest molecules. This suggests that hydrophobic effect and hydrogen bond play an important role in the inclusion process.     

Ultrasound promoted efficient and green synthesis of β-amino carbonyl compounds in aqueous hydrotropic medium

Ultrasound promoted synthesis of β-amino carbonyl compounds in aqueous hydrotropic medium at ambient temperature is reported. The remarkable features of the new procedure are shorter reaction time, excellent yields in aqueous medium, cleaner reaction profile and simple experimental and work-up procedure.     

Dielectric behaviour of α-cyclodextrin,heptakis (2,3,6-tri-Omethyl)-β-cyclodextrin,randomly methylated β-cyclodextrin and low frequency Raman spectra of α- and β-cyclodextrins

The frequency and temperature dependence of the real (?′) and imaginary (?″)parts of the dielectric constant of α-cyclodrextrin (form 1; α-CD. 5.9H₂O) and α-cyclodextrin (form III; α-CD.7.6H₂O) and of the corresponding dried forms (α-CD.1.1H₂O, α-CD.2.9H₂O, respectively) has been investigated over the frequency range 0–100 k Hz and temperature range 130–350 K. In addition the dielectric behaviour has been investigated of heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin (β-CD.TRIME. 0.3H₂O) and randomly methylated β-cyclodextrin (β-CD.RAME.0.8H₂O). The dielectric behaviour is described well by Debyetype relaxation (α-disperson). All α-CD systems exhibit an additional ω-dispersion at low frequencies, which is attributed to proton transport. The fact that the ?′ values of α-CD form III are larger than those of α-CD form I is attributed to the different numbers and different strengths of the intramolecular hydrogen bonds. Form III has a stable conformation which is shown by the constant values of ?′ in the temperature range 125–250 K. By contrast, in form I the ?′ values increased linearly with temperature, indicating that the system passed through succesive conformations. The temperature dependence of ?″ and phase shift ∞ in all the specimens of α-CD (forms I, III) and fully methylated β-CD do not reveal any orderdisorder transition, because the developed hydrogen bonds ae not of the flip-flop type according to their crystal structures. The partially methylated β-CD reveals the characteristics of the order-disorder transition, which was observed before in the systems dried β-CD.2H₂O and non-dried β-CD.9.8H₂O. There is a direct relation between the hydroxyl groups of β-CD and the order-disorder transition. The order-disorder transition could also be shown in dried β-CD.2.4H₂O and non-dried β-CD.9.8H₂O samples but not in dried α-CD.1.1H₂O and non-dried a-CD.5.9H₂O samples, by low frequency Raman spectroscopy (< 180 cm^?1). The step-like temperature dependence of the band at 33.7cm^?1 reveals a transition at about 223K for both β-CD samples. In the case of α-CD samples the almost linear temperature dependence of the band at 49.1 cm^?1 does not reveal any transition.     

Optical polarization of neutron-rich sodium isotopes and β-NMR measurements of quadrupole moments

The nuclear quadrupole moments of neutron-rich sodium isotopes are being investigated with the help of in-beam polarization by optical pumping in combination with-NMR techniques. First measurements have yielded the quadrupole splittings of NMR signals in the lattice of LiNbO₃ for the isotopes²⁶Na,²⁷Na and²⁸Na. Interaction constants and ratios of the electric quadrupole moments are derived. In view of future experiments,-decay asymmetries for the sequence of isotopes up to theN=20 neutron shell closure,^26–31Na, have been measured.     

Room-temperature fluorescence of a charge-transfer complex of reserpine in aqueous and aqueous–ethanol media

The room-temperature fluorescence of a charge-transfer (CT) complex different from those of the component donor/acceptor in polar organic solvent is not very common. The phenomenon is even rarer in aqueous medium. The present work demonstrates that a CT complex formed between reserpine (Res) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in aqueous and aqueous–ethanol media exhibits fluorescence at room temperature that is entirely different from those of the components, Res and DDQ. With decreasing polarity of the medium on the addition of ethanol, the fluorescence intensity and also the fluorimetrically determined formation constant of the complex increase, but the fluorescence emission wavelength does not change significantly. The quantum yield of fluorescence of the CT complex systematically decreases with increasing ethanol content of the medium. That the observed fluorescence is due to the CT complex is established by the constancy of the assumed proportionality constant (β) between the fluorescence intensity and the complex concentration measured using different equilibrium concentrations of the complex and also by demonstrating the mirror image relationship between its excitation and emission spectra in aqueous medium. To our knowledge, this is the first report on the room-temperature fluorescence of a CT complex in aqueous solution.     

Solid-state2H NMR studies of methyl group dynamics in aspirin and aspirin · β-cyclodextrin

The dynamics of the methyl group in aspirin, and in the inclusion complex aspirin · β-cyclodextrin, have been studied by deuterium nuclear magnetic resonance spectroscopy and relaxation time measurements. The methyl group in aspirin undergoes fast thermally activated rotation about its axis of symmetry within the temperature range studied, 120 ≤T ≤ 295 K, with an activation energy of 4.9±0.05 kJ/mol and a correlation time at 230 K of (2.47±0.3) · 10^?12 s. The motionally averaged electric field gradient tensor, however, remains axially asymmetric because of electronic effects of a neighbouring oxygen atom. In aspirin · β-cyclodextrin the methyl group rotation about its axis of symmetry is less hindered with an activation energy of 2.1 ± 0.7 kJ/mol and a correlation time at 230 K of (2.5 + 0.4) · 10^?12 s. The axis of symmetry undergoes a slow reorientation with a higher activation energy of 21 ±9 kJ/mol and a correlation time at 230 K of (1.7±1.5) · 10^?6 s.     

Ultrafast laser based “green” synthesis of non-toxic nanoparticles in aqueous solutions

Inorganic nanoparticles offer novel promising properties for biological sensing and imaging, as well as in therapeutics. However, these applications are often complicated by the possible toxicity of conventional nanomaterials, arising as a result of inadequate purification procedures of nanoparticles obtained via synthetic pathways using toxic or non-biocompatible substances. We review novel femtosecond laser-assisted methods, which enable the preparation of metal nanomaterials in clean, biologically friendly aqueous environment (“green” synthesis) and thus completely solve the toxicity problem. The proposed methods, including laser ablation and fragmentation, make possible the production of stable metal colloids of extremely small size (∼2 nm) with a low coefficient of variation (15–25%). Those nanoparticles exhibit unique surface chemistry and can be used for bio-imaging, cancer treatment and nanoparticle-enhanced Raman spectroscopy.     

Picosecond spectral-kinetic investigation of Sn ← Sl absorption of β-carotene in solutions

The authors express their gratitude to G. B. Tolstorozhev, S. F. Dobrinevskii, and S. V. Mel'nichuk for their helpful discussions of the results of this work, and G. I. Samokhvalov and L. A. Vakulova for kindly making quantities of -carotene available.     

Reactions of COO− radical-ion with M+ and M3+ states produced in the radiolysis of aqueous solutions

Pure nickel and lithium-implanted nickel were irradiated with 1 MeV electrons at the Argonne HVEM-Tandem facility. The lithium-implanted nickel was not damaged as readily as the pure nickel under 1 MeV electron irradiation in the temperature range 20–600°C. The decreased damage accumulation in the lithiated nickel could arise from both the precipitated lithium and that in solution. The latter could slow down the nickel interstitials produced during irradiation by association, thus enhancing their recombination with vacancies. The interfaces of the precipitated lithium could also act as unbiased sinks for the vacancies and interstitials. Above 600°C, under electron irradiation, a melting process which created small irregular shaped regions occurred in the lithium-implanted nickel. Electron diffraction analysis showed that the compound Li₂NiO₂ was formed inside these regions.