Interaction of 2-hydroxy-substituted Nile red fluorescent probe with organic nitrogen compounds

The fluorescent properties of 2-hydroxy Nile red dye (HONR) proved to be highly sensitive to the basicity of hydrogen bond acceptors. Fluorescence quantum yields and fluorescence decay profiles were measured as the function of the concentration of organic nitrogen compounds in solvents of various polarities. The detailed mechanism and the kinetics of the fluorescence quenching were revealed with the combined analysis of the steady-state and time-resolved spectroscopic data. The relative contribution of the competing reaction steps was found to be very sensitive to the basicity of the additive and to solvent polarity. The most profound change appeared in the unimolecular deactivation pathways of the excited hydrogen-bonded HONR, whereas the formation rate of this species varied to a lesser extent. The dissociation into excited HONR and ground-state base was able to compete with the energy dissipation only when 2,4,6-trimethylpyridine was used as hydrogen bond acceptor in toluene. The bimolecular quenching of the excited hydrogen-bonded complex played significant role in apolar solvents. Proton displacement along the hydrogen bond in the excited complex led to excited ion pairs in polar media.     

Surface Characterization of Sepiolite by Inverse Gas Chromatography

Inverse gas chromatography (IGC) was applied to characterize the surface of sepiolite. The adsorption thermodynamic parameters (the standard enthalpy (ΔH ⁰), entropy (ΔS ⁰) and free energy of adsorption (ΔG ⁰)), the dispersive component of the surface energy (γ _S ^d ), and the acid/base character of sepiolite surface were estimated by using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (ΔG ^sp ), the specific enthalpy of adsorption (ΔH ^sp ), and the specific entropy of adsorption (ΔS ^sp ) of polar probes on sepiolite were determined. ΔH ^sp were correlated with the donor and modified acceptor numbers of the probes to quantify the acidic K _A and the basic K _D parameters of the sepiolite surface. The values obtained for the parameters K _A and K _D indicated an acidic character for sepiolite surface.     

Solvent extraction of lead using a nitrobenzene solution of strontium dicarbollylcobaltate in the presence of polyethylene glycol PEG 400

Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb²⁺(aq)+SrL²⁺ (nb)↔PbL²⁺ (nb)+Sr²⁺ (aq) taking place in the two-phase water-nitrobenzene system (L=PEG 400; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logK_ex(Pb²⁺, SrL²⁺)=2.0±0.1. Further, the stability constant of the PEG 400 - lead complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β_nb(PbL²⁺)=12.9±0.1.     

Study of fragmentation pattern and adsorption of 9-O-(triphenylsilyl)-10,11-dihydrocinchonidine on platinum by hydrogen/deuterium exchange using electrospray ionization ion-trap tandem mass spectrometry

We have studied the adsorption on a platinum (Pt) catalyst of two compounds utilizable as a chiral basic catalyst and a chiral modifier, dihydrocinchonidine (DHCD), and a new cinchona alkaloid derivative containing a bulky group, the Ph3SiO-DHCD molecule. The method of choice was the detection by electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS) of hydrogen/deuterium (H/D) exchange at room temperature, in tetrahydrofuran, at a D2 pressure of 1 bar. Based on the ESI-MS/MS spectrum of the new compound, we propose a mechanism for the formation of the silatropylium cation containing a Si-O bond. From the fragmentation pattern of Ph3SiO-DHCD it was confirmed that ESI-ion-trap MS/MS can be used to study the adsorption processes of complicated carbon compounds by investigating their H/D exchange reactions. In the case of Ph3SiO-DHCD, the results demonstrate that H/D exchange takes place mainly on the quinoline skeleton. However, the strong pi-bonded adsorption of the quinoline skeleton parallel with the imaginary plane of Pt is not preferred because the bulky Ph3Si group inhibits the multiple pi-bonded adsorption of the Ph3SiO-DHCD. Because of this hindrance the molecule was adsorbed tilted via the nonbonding electron pair of the N atom and C2' atom of the quinoline skeleton; consequently, mainly alkaloid-d1 and alkaloid-d2 are formed.     

4,5‐Di­hydro‐3‐methyl‐5‐(4‐methyl­phenyl)‐1H‐pyrazole‐1‐carboxamidinium acetate acetone hemisolvate

The X‐ray structure analysis of the unexpected product of the reaction between 4‐(4‐methyl­phenyl)­but‐3‐en‐2‐one and amino­guanidine revealed the title compound, C₁₂H₁₇N₄⁺·C₂H₃O₂^?·0.5C₃H₆O, consisting of a protonated amidine moiety joined to a substituted pyrazoline ring at the N1 atom. The amidine group is protonated and the positive charge is delocalized over the three C—N bonds in a similar manner to that found in guanidinium salts. The amidinium moiety of the cation is linked to the acetate anions through four N—H?O hydrogen bonds, with N?O distances of 2.749 (4), 2.848 (4), 2.904 (4) and 2.911 (4) Å. The pyrazoline ring adopts a flattened envelope conformation and the substituted phenyl ring is oriented perpendicular to the attached heterocycle. The acetone solvate molecule lies across a twofold rotation axis.     

Analysis of DTA curves and calculation of kinetic data using computer technique

Principles of two computer programs useful for the evaluation of heterogeneous kinetics are described.The first program ALANTA allows to obtain the non-isothermal kinetic curve from the shape of general DTA peak using the DTA-equation derived elsewhere¹.The second program SQUEST determines the kinetic mechanism which is the most appropriate to a given non-isothermal kinetic curve and evaluates the corresponding kinetic parameters. The program decides between 19 kinetic models and uses both integral and differential methods of evaluation.     

Retention of85Sr and147Pm on insoluble hydroxides and phosphates prepared by the sol-gel procedure

Retention of strontium and promethium on hydroxides (hydrated oxides) and phosphates of iron and chromium prepared by the sol-gel method was studied. The sorption was determined under static conditions depending on the pH of the solution. The sorption isotherms and retention were investigated under dynamic conditions.     

Gel permeation chromatographic characterization of sodium hyaluronate and its fractions prepared by ultrasonic degradation

Summary High-molecular-weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. The molecular weight of hyaluronate and its polydispersity was determined by gel-permeation chromatography. During 75-min treatment the molecular weight value decreased from 1.39×10⁶ Da to 2.25×10⁵ Da while the polydispersity of the molecular weight increased from 1.29 to 2.36. The reciprocal value of the square of the hyaluronate's molecular weight was linearly proportional to the time of ultrasonication.     

Size exclusion chromatographic characterization of sodium hyaluronate fractions prepared by high energetic sonication

Summary A high molecular weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. High-performance size exclusion chromatography allowed rapid and accurate determination of molecular weight parameters (M_z, M_w, M_n) and distributions. The time dependence of hyaluronan ultrasonication to the molecular characteristics of the polymer was investigated. A non-random nature of the degradation process was demonstrated and the reciprocal M_n value was found to be linearly proportional to the time of ultrasonication.     

In situ enzymatic digestion of oligopeptides on a direct insertion probe tip combined with fast atom bombardment and tandem mass spectrometry

The applicability of an approach to establish the sequence of oligopeptides involving on-probe-tip enzymatic fragmentation and subsequent direct fast atom bombardment (FAB) mass spectrometry (MS) and FAB-MS/MS of the subpeptide mixture was tested using two model peptides consisting of 19 and 25 amino acid residues. The method was found to be both time and sample sparing and flexible enough to use even subsequent digests, if necessary, with enzymes of different specificity. It provided in both cases complete information, not only for the sequence of enzymic fragments but also for their order in the original oligopeptide. Consequently, this approach to the sequence analysis of oligopeptides can be a method of choice when the FAB-MS/MS technique itself is unsuitable for obtaining detailed structural information. The method seems to be applicable to enzymically digestible peptides with an upper mass limit of about 3500.