The Behaviour of Some Benzene Derivatives on Thin Layers of Aluminum Oxide—Comparation with Plain and Fe(III)Impregnated Silica Gel

Abstract

The behaviour of some carboxy and hydroxy benzene derivatives related to humic material was examined by thin layer chromatography on aluminium oxide as the support and water as developer. Their Rf-values were compared with those on plain and Fe(III)-impregnated silica gel plates.     

Studies of correlation between chemical structure and Rf-value in high performance TLC

Correlation between chemical structure and Rf-values was studied in the case of aniline and its derivatives using high performance TLC and a U-chamber. The characteristic group constants referring to each substituent were determined by chromatographing derivatives with one substituent and aniline in toluene and dibutyl ether respectively. On the basis of these constants the R_M and Rf values of derivatives with more substituents were calculated. Comparing the calculated and measured values good agreement was found.     

Utilization of O-phthalaldehyde-sulphuric acid as a spray reagent in thin-layer chromatographic detection of some indolealkylamines and application to cutaneous secretion extracts of toad species

An expansion of the utilisation of o-phthalaldehyde in sulphuric acid medium as spray reagent was carried out when tryptophan and some tryptophan-derived indole alkylamines such as tryptamine, serotonin, bufotenine, dehydrobufotenine and bufotenidine were examined by thin-layer chromatography. Rf-values and limits of detection ranging from 20 (serotonin) to 100 (dehydrobufotenine) ng per spot were found. Application of this reagent for the detection of some of these compounds was carried out, using either methanolic extracts or column chromatographic fractions of the skin secretion of the toads Bufo ictericus and Odontophrynus cultripes.     

Anticircular high performance thin-layer chromatography

The principal analytical details for the third of three possible modes in high performance thin-layer chromatography are given, namely the anticircular mode. Separation is achieved by allowing the mobile phase to enter the plate layer on a precise outer circle line, from where it flows towards the centre with nearly constant speed. This technique is theoretically and practically the fastest of all three possible in HPTLC. It permits maximum sample capacity with a minimum of time, layer and mobile phase consumption. It is therefore the most economical HPTLC technique. A new carrier-free mobile phase transfer principle is used. The conditions for qualitative and quantitative analysis are good: repeatability, reproducibility and accuracy of routine TLC analyses are superior to those achieved by the classical trough technique. The specially narrow spot-path in anticircular HPTLC facilitates automated quantitation. Compared with the linear and circular modes, the anticircular mode shows better separation and significantly increased sensitivity at higher Rf-values. The drawback, however, is that the separation power (expressed by the separation number) is lower compared with the other two modes.     

Thin-layer chromatography as a pilot technique for HPLC demonstrated with pesticide samples

The transferability of chromatographic conditions from TLC precoated plates to HPLC columns have been investigated using 62 different pesticides. For the investigation different stationary phases (silica gel, RP-18, RP-8, Diol, NH₂, CN) have been used with standard substances on the one hand and a real sample on the other hand. Rf-values of the pesticides have been converted to k'p, a retention value comparable to HPLC, and have been then compared with k'c values of the HPLC columns with the corresponding chromatographic system. For the evaluation of the results the respective data pairs have been correlated by linear regression. Good results of transfer have been obtained on every stationary phase. In the case of silica gel- and Diol-phases some restrictions have to be made, because of different activity between TLC and HPLC sorbent. In order to show that the transfer of chromatographic conditions is not limited to standards, the experiments have been extended to a spiked real sample (lettuce). The influence of the matrix is shown to be negligible and excellent transfer results are able to be realised.     

Solvent effects on two-dimensional molecular self-assemblies investigated by using scanning tunneling microscopy

Self-assembly structures investigated by using scanning tunneling microscopy (STM) at liquid/solid interface have been a topic of broad interest in surface science, molecular materials, molecular electronics. The delicate balance among the adsorbate–solvent, adsorbate–adsorbate, solvent–solvent interactions would give rise to the coadsorption or competitive deposition of solvent with adsorbate. The solvents at the interface enable dynamic absorption and desorption of the adsorbates leading to the controlled assembly of the molecular architectures. The solvent-induced polymorphism, coadsorption effect, as well as solvent effects on chirality and electronic structures are discussed in this report in view of the polarity, solubility and viscosity of the solvent, the hydrogen bonding formation between solute and solvent, and the solvophobic and solvophilic effects. The systematic studies on the solvent effects would shed light on better control of assembly structures for design of new molecular materials and molecular electronics.     

Broadening of peaks eluted before the solvent in capillary GC Part II: The role of phase soaking

Summary Phase soaking is a solvent effect which tends to reconcentrate peaks eluted after and to broaden peaks eluted before the solvent. The principles of the phase soaking effect on peaks eluted before the solvent are discussed. The broadening effect is distinguished from the broadening effect occurring in the flooded column inlet by partial solvent trapping. It was found that in most cases broadening by partial solvent trapping strongly predominated over broadening by phase soaking. Phase soaking was noticeable only in the neighbourhood of the solvent peak.Phase soaking does not broaden peaks eluted before the solvent as much as it re-concentrates those eluted after it. The two phase soaking effects on the front and the rear of the solvent band (that is, of the soaked zone) differ strongly from each other.Peak broadening by phase soaking is negligible for non-trapped components, because such solutes start their chromatography before a significant quantity of solvent enters the column. Phase soaking only broadens solute bands which were retained by the solvent in the column inlet, that is, bands already broadened by partial solvent trapping.     

The Solution Precursor Plasma Spray Coatings: Influence of Solvent Type

The influence of solvent type on splat formation and coating microstructure using the Solution Precursor Plasma Spray process was studied. Droplet with a high surface tension and high boiling point solvent experiences incomplete solvent evaporation process in the plasma jet leading to a porous coating. Droplet created from a low surface tension and low boiling point solvent undergoes rapid solvent evaporation, solute precipitation, pyrolysis, melting process in the plasma jet and forms splat upon impacting on the substrate; the build-up of splats results in a dense coating.     

Solvent release upon ion association from entropy data. II

When a cation and an anion associate, the charge on the product is lower than that on the individual ions and solvent is released from their solvation shells to the bulk solvent. This release occurs when the associate is a solvent-shared or contact ion pair or an inner-type complex. The measurable molar entropy change involved is considered to be made up of four contributions: translational, rotational, electrostatic, and desolvation entropies. The former three can be calculated from the properties of the ions and solvents involved; hence, the fourth is obtained by difference. The release of solvent molecules from the crystalline frozen solvent to the liquid on melting is analogous to the solvent release from translational immobilization in the solvation shells of the ions. The molar entropy of melting of the solvent is used to estimate the amount of solvent released in the association process.     

A Study on the ordering of intercalated solvents in poly-benzyl-l-glutamate; In-situ raman and X-ray scattering investigations

A polymer/solvent system can form a gel due to specific interactions between the polymer and the solvent. For poly-benzyl-L-glutamate/solvent systems, gelation can be based on carbonyl or phenyl ring interactions, depending on the solvent. The present paper describes X-ray scattering and Raman investigations on cast films of poly-benzyl-L-glutamate (PBLG) and benzylmethacrylate (BzMA). The studies indicate that in the cast samples separate zones of PBLG and BzMA are present. Upon heating, the system homogenises and the PBLG molecules pack in a pseudo hexagonal lattice. At approximately 150°C a new reflection at 11.4 Å in the WAXS pattern arises. This reflection is attributed to structural ordering of the solvent, due to intercalation of the solvent molecules within the helices of PBLG. The observed changes in the WAXS pattern upon heating are supported by Raman experiments.     

Solvent dependent analysis of isotropic Raman band shape of C=O stretching vibration

The isotropic Raman band shape corresponding to C=O stretching vibration of some molecules has been studied in neat liquids and as a function of solvent concentration using both polar and non-polar solvents. The Raman band shape was analyzed on the basis of correlation with the Lorentzian line shape by employinga simple method of linear curve fitting. In neat liquids and in low solvent concentration region, the band shape was found to be non-Lorentzian. With the gradual increase in solvent concentration the band shape approaches a Lorentzian function. The plot of the correlation coefficient for a Lorentzian shape shows a discontinuity in the intermediate range of solvent concentration. The influence of the structural characteristics of the solute and the solvent systems on the reference mode and various multipolar interactions together with the time varying spatial distribution of solvent molecules with respect to the reference molecule are expected to govern the microenvironmental fluctuations. This may be responsible for the discontinuity in the intermediate solvent concentration region.     

Solvent effect on the absorption spectra of coumarin 120 in water: A combined quantum mechanical and molecular mechanical study

The solvent effect on the absorption spectra of coumarin 120 (C120) in water was studied utilizing the combined quantum mechanical∕molecular mechanical (QM∕MM) method. In molecular dynamics (MD) simulation, a new sampling scheme was introduced to provide enough samples for both solute and solvent molecules to obtain the average physical properties of the molecules in solution. We sampled the structure of the solute and solvent molecules separately. First, we executed a QM∕MM MD simulation, where we sampled the solute molecule in solution. Next, we chose random solute structures from this simulation and performed classical MD simulation for each chosen solute structure with its geometry fixed. This new scheme allowed us to sample the solute molecule quantum mechanically and sample many solvent structures classically. Excitation energy calculations using the selected samples were carried out by the generalized multiconfigurational perturbation theory. We succeeded in constructing the absorption spectra and realizing the red shift of the absorption spectra found in polar solvents. To understand the motion of C120 in water, we carried out principal component analysis and found that the motion of the methyl group made the largest contribution and the motion of the amino group the second largest. The solvent effect on the absorption spectrum was studied by decomposing it in two components: the effect from the distortion of the solute molecule and the field effect from the solvent molecules. The solvent effect from the solvent molecules shows large contribution to the solvent shift of the peak of the absorption spectrum, while the solvent effect from the solute molecule shows no contribution. The solvent effect from the solute molecule mainly contributes to the broadening of the absorption spectrum. In the solvent effect, the variation in C-C bond length has the largest contribution on the absorption spectrum from the solute molecule. For the solvent effect on the absorption spectrum from the solvent molecules, the solvent structure around the amino group of C120 plays the key role.     

Importance of gas-phase proton affinities in determining the electrospray ionization response for analytes and solvents

The effect of gas-phase proton transfer reactions on the mass spectral response of solvents and analytes with known gas-phase proton affinities was evaluated. Methanol, ethanol, propanol and water mixtures were employed to probe the effect of gas-phase proton transfer reactions on the abundance of protonated solvent ions. Ion-molecule reactions were carried out either in an atmospheric pressure electrospray ionization source or in the central quadrupole of a triple-quadrupole mass spectrometer. The introduction of solvent vapor with higher gas-phase proton affinity than the solvent being electrosprayed caused protons to transfer to the gas-phase solvent molecules. In mixed solvents, protonated solvent clusters of the solvent with higher gas-phase proton affinity dominated the resulting mass spectra. The effect of solvent gas-phase proton affinity on analyte response was also investigated, and the analyte response was suppressed or eliminated in solvents with gas-phase proton affinities higher than that of the analyte.     

Solvent reaction field potential inside an uncharged globular protein: a bridge between implicit and explicit solvent models?

The solvent reaction field potential of an uncharged protein immersed in simple point charge/extended explicit solvent was computed over a series of molecular dynamics trajectories, in total 1560 ns of simulation time. A finite, positive potential of 13-24 kbTec(-1) (where T=300 K), dependent on the geometry of the solvent-accessible surface, was observed inside the biomolecule. The primary contribution to this potential arose from a layer of positive charge density 1.0 A from the solute surface, on average 0.008 ec/A3, which we found to be the product of a highly ordered first solvation shell. Significant second solvation shell effects, including additional layers of charge density and a slight decrease in the short-range solvent-solvent interaction strength, were also observed. The impact of these findings on implicit solvent models was assessed by running similar explicit solvent simulations on the fully charged protein system. When the energy due to the solvent reaction field in the uncharged system is accounted for, correlation between per-atom electrostatic energies for the explicit solvent model and a simple implicit (Poisson) calculation is 0.97, and correlation between per-atom energies for the explicit solvent model and a previously published, optimized Poisson model is 0.99.     

Intrinsic viscosity of polystyrene in mixed solvents

The intrinsic viscosity of a single sample of polystyrene was measured as a function of the composition of solvent in three mixed solvent pairs. The parameter Y introduced by Shultz and Flory was useful for prediction of trends, but severely overestimated the effect of solvent (1)–solvent (2) interaction on the expansion of polymer coils. The system polystyrene–cyclohexane–ethyl acetate was studied in detail for five samples of polystyrene. The analysis of the data provided strong experimental proof of a strict validity of the Mark–Houwink–Sakurada relation. The dependence of the Mark–Houwink–Sakurada exponent α on the composition of the solvent mixture was unexpectedly unsymmetrical. The unperturbed dimentions of the polystyrene chain are reduced by specific interaction of polystyrene with carbonyl groups in the solvent mixture.     

A molecular simulation study of the structure and tribology of polymer brushes: Comparison of behavior in theta and good solvents

Implicit solvent Brownian dynamics simulations of the structure and tribology of opposing polymer-brush covered surfaces have been carried out as a function of surface separation and solvent quality. Consistent with experiment, shear forces were found to be greater under theta solvent conditions than in a good solvent at equal relative separations (normalized by the respective height of the brushes in theta and good solvents). Much higher relative compression is required before the onset of significant shear forces in good solvent compared to theta solvent. The dependence of shear force for a given relative separation on solvent quality can be accounted for by differences in interpenetration of the brushes. When compared as a function of absolute surface separation, greater interpenetration and greater shear force are observed at large separations for the brushes in good solvent than in theta solvent, consistent with the greater brush height in good solvent. At shorter separations, corresponding to moderate to high compression, brush-brush interactions result in significant deformation of the brushes. In this regime, greater interpenetration and greater shear forces are observed in theta solvent at a given separation, in qualitative agreement with experiment.     

A novel solvent dipole-induced rotational isomerism of 1-hxdroxy-2-pyridone in the excited singlet state

The title compound shows dual fluorescence depending on polarity of the solvent used. The fluorescence in the nonpolar solvent, cyclohexane, has a maximuni at 370 nm, while the fluorescence in the polar solvent, methanol, has a maximum at 400nm. The short and long wavelength fluorescences were assigned to the syn and anti conformers, respectively. From these observations one is allowed to conclude that a novel solvent dipole-induced rotational isomerism takes place in the excited singlet state.