Robert Nowakowski

Atomic force microscopy of Au/Hg alloy formation on thin Au films

Abstract Atomic force microscopy was applied to the study of thin Au films deposited under ultra-high vacuum conditions on a glass support maintained at 78 K. A variety of thin gold film structures were thus determined and characterized ranging from (i) nanometric isolated gold islands, (ii) nanometric gold structures, to (iii) continuous gold films, all depending on the amount of Au deposited. The influence of the amalgamation process on the thin Au films topography was studied. The fundamental importance of surface defects on the rate of amalgamation was clearly seen. The movement of small Au islands on glass obtained as the result of thermal decomposition of Au Hg alloys was observed.

Joint use of cyclodextrin additives in chiral discrimination by reversed-phase high-performance liquid chromatography: temperature effects

The temperature dependence of chiral separations was investigated in combined system of reversed-phase (RP) liquid chromatography using two chiral additives: single α or β native cyclodextrins and their permethylated derivatives. The model tested compounds of pharmaceutical interest were: methylphenobarbital, mephenytoin, morsuximide and camphor. Taking the localization of a complexation process as a criterion – the combined system with two selectors has been rationalized as occurring in three stages. The influence of temperature (in narrow range of 20°C) on retention and enantioselectivity was studied in; System I (complexation occurs in the mobile phase), in System II (complexation on the stationary phase) and in System III (complexation in both phases together). In System III (as for System I) it has been found that the model compounds could be classified into three groups based on their retention dependence on temperature: retention decrease with temperature decrease, retention increase with temperature decrease or no influence of temperature on retention. For all the compounds investigated, decrease in temperature increases the selectivity. Standard enthalpy (ΔH0) and entropy (ΔS0) changes of solute transfer between the mobile and the stationary phase and standard enthalpy (ΔH0CD) and entropy (ΔS0CD) changes of complex formation were also calculated. In Systems I and III, if the complexation in the mobile phase is favored process compared with interaction with the stationary phases (RP or covered by permethylated cyclodextrin), the shortest retention time and the best selectivity is observed at low temperature.

Improved chiral recognition of some compounds via the simultaneous use of β-cyclodextrin and its permethylated derivative in a reversed-phase high-performance liquid chromatographic system

Two chiral additives, β-cyclodextrin and (2,3,6-tri-O-methyl)-β-cyclodextrin, were applied to improve the enantioselectivity of reversed-phase high-performance liquid chromatography for methylphenobarbital, glutethimide, mephenytoin and morsuximide. It was found that the joint use of these two additives leads to an improved enantioselectivity, except for mephenytoin.

Chiral recognition ability of α-cyclodextrin with regard to some monoterpenoids under gas–liquid chromatographic conditions

Gas-liquid chromatography was applied to investigate the mechanism of alpha-cyclodextrin (alpha-CD) complexation processes with some chiral monoterpenoids differing from each other in chemical properties and structure. They were chosen from hydrocarbons, alcohols, aldehydes and ketones of acyclic, monocyclic and bicyclic structure. The relationships between the retention factor, k, of a guest solute (G) and alpha-CD concentration were studied. The obtained data enabled the stoichiometry, the stability of individual complexes and the separation factor of enantiomers to be determined. It was found that almost all the investigated monoterpenoids, apart from the acyclic ones, form inclusion complexes with alpha-CD. Straight-line relations (r vs. [alpha-CD]) were observed for monocyclic alcohols and pulegone, without any trace of enantioselectivity. This behaviour indicates that the 1:1 stoichiometry of the G-CD complexes does not lead to chiral recognition. Parabolic relations arising from 1:2 stoichiometry were found for limonene, alpha-phellandrene, some monocycylic ketones and all the investigated bicyclic terpenoids. It appeared that only the second step of complexation displayed marked enantioselectivity. However, a loss of efficiency resulting from slower equilibration is then noticeable. Attempts are made to rationalize the chromatographic results with respect to the structure of the investigated compounds.

Studies on the behaviour of α-, β- and γ-cyclodextrins and some derivatives under reversed-phase liquid Chromatographic conditions

Abstract The separation processes of α-, β- and γ -cyclodextrins and their various methyl derivatives have been investigated with Knauer polarimetric (Chiralyser) and refractive index (RI) detectors. RP18 and RP8 hydrocarbon packings and an NH 2 bonded phase were applied as stationary phases. Aqueous methanolic or ethanolic solutions were used as mobile phases. It has been found that the Chiralyser detector response is approximately linear at low concentrations of solutes and that its detection capabilities are about 40 times better than those of the RI detector. Differences in the order of elution of α-, β- and γ -cyclodextrins have been observed for various stationary phases as well as for various mobile phase compositions. The optimal conditions for analytical determinations of cyclodextrins and their derivatives have been discussed.

AFM studies of the catalytic reaction of hydrogen with oxygen on thin Pd and Pt films under pressure ∼101 kPa

Abstract Surface phenomena arising on thin Pt and Pd films in the course of the catalytic reaction of hydrogen with oxygen in the flow reactor at 298 K, under pressure ∼101 kPa were studied by atomic force microscopy (AFM). It is known that H 2 interaction with Pd leads to palladium hydride formation (equilibrium pressure ∼1 kPa at 298 K) while Pt does not form hydrides. H 2 interaction with Pd films of average thickness 50–100 nm resulted in the drastic change of the surface corrugation. Local characteristic structures arose, several hundred nanometer high. Replacing H 2 with Ar restored the original Pd surface. We suggest that this phenomenon is evidence for PdH x formation around specific defects. This is associated with the creation of stresses and followed by the uphill diffusion of hydrogen into the reverse side of the film. Hydrogen interaction with oxygen on Pd and Pt films led to multilayer deposit of water detected by AFM as the apparent rectangular shape of the film grains.

Separation ability and stoichiometry of cyclodextrin complexes

Gas-liquid chromatography has been applied to search relations between selectivity towards isomers and stoichiometry of cyclodextrin complexes. The model tested compounds were: dimethylnaphthalenes and alpha- and beta-pinenes as constitutional isomers; cis/trans decalins, anetholes and isosafroles as diastereomers and as enantiomers (+/-)-alpha-pinenes and (+/-)-camphenes. Experimental retention data are used to confirm a simple theoretical model that allows distinguishing formation of G x CD complexes (1:1) and G x CD2 complexes (1:2). Based on the experimental data, stability constants K were evaluated. It has been found that remarkable selectivity factor alpha may appear both within the range of 1:1 stoichiometry (beta-CD complexes of decalins and of alpha- and beta-pinenes) and 1:2 stoichiometry (alpha-CD complexes with (+/-)-alpha-pinenes and (+/-)-camphenes). Occasionally selectivity arises from a different composition, when one isomer forms a 1:1 stoichiometry complex while another forms a 1:2 complex (dimethylnaphthalenes, cis/trans-anetholes and cis/trans-isosafroles).

Atomic hydrogen adsorption on thin discontinuous and continuous gold films—similarities and differences

Atomic hydrogen adsorption on thin discontinuous Au films (nanostructures) and on continuous thin Au films was studied by means of TDMS (thermal desorption mass spectrometry). The surface topography of thin Au films was determined by means of AFM (atomic force microscopy). Thermal desorption (TD) spectra for hydrogen deposit similar for both cases were registered. However, at low coverage (θ < 0.01), atomic hydrogen is somewhat more strongly bound on discontinuous nanostructured thin Au films.

Chiral discrimination by high-performance liquid chromatography with joint use of two cyclodextrin additives

Abstract The diversity of adsorption properties of native and permethylated cyclodextrins enabled us to propose a new advantageous chromatographic system with two chiral selectors working jointly (system III). Fundamental information regarding the retention mechanism in such a system with two chiral additives is presented. Depending on the localisation of the chiral complexation process three chromatographic systems have been designed and experimentally compared under the same chromatographic conditions (solvent composition, temperature). Phenomenological and theoretical models of the above mentioned systems, where complexation occurs in the mobile phase (system I), in the stationary phase (system II) or in both phases together (system III), have been studied and experimentally confirmed. Species of biological interest were used as model compounds. It has been found that almost always system III offers the best results, although all the investigated substances display different chromatographic behaviour, i.e., adsorption on RP18 phase and complexation by native and permethylated cyclodextrin. The final enantioselectivity coefficient ( α 3 ) may be predicted as a product of partial coefficients ( α 1 , α 2 ) according to the equation α 3 = α 1 · ga 2 .

Self-Assembly Properties of Semiconducting Donor–Acceptor–Donor Bithienyl Derivatives of Tetrazine and Thiadiazole—Effect of the Electron Accepting Central Ring

Scanning tunneling microscopy was used to study the effect of the electron-accepting unit and the alkyl substituents position on the type and extent of 2D supramolecular organization of penta-ring donor-acceptor-donor (DAD) semiconductors, consisting of either tetrazine or thiadiazole central acceptor ring symmetrically attached to two bithienyl groups. Microscopic observations of monomolecular layers on HOPG of four alkyl derivatives of the studied adsorbates indicate significant differences in their 2D organizations. Ordered monolayers of thiadiazole derivatives are relatively loose and, independent of the position of alkyl substituents, characterized by large intermolecular separation of acceptor units in the adjacent molecules located in the face-to-face configuration. The 2D supramolecular architecture in both derivatives of thiadiazole is very sensitive to the alkyl substituents position. Significantly different behavior is observed for derivatives of tetrazine (which is a stronger electron acceptor). Stronger intermolecular DA interactions in these adsorbates generate an intermolecular shift in the monolayer, which is a dominant factor determining the 2D structural organization. As a consequence of this molecular arrangement, tetrazine groups (A segments) face thiophene rings (D segments) of the neighboring molecules. Monolayers of tetrazine derivatives are therefore much more densely packed and characterized by similar π-stacking of molecules independently of the position of alkyl substituents. Moreover, a comparative study of 3D supramolecular organization, deduced from the X-ray diffraction patterns, is also presented clearly confirming the polymorphism of the studied adsorbates.