Modeling of ion-exclusion and vacancy ion-exclusion chromatography in analytical and concentration overload conditions

Ion-exclusion chromatography (IEC) finds applications in various different analytical separations of weak acids. Pure, deionized water or a diluted, aqueous solution of a strong mineral acid (such as, e.g., sulphuric acid) is used as the mobile phase, whereas a typical stationary phase is a strongly acidic resin in the H(+) form (e.g., the sulfonated polystyrene-divinylbenzene resin with a high ion-exchange capacity, provided by the sulfonic acid groups). When pure water is used as the mobile phase, then the characteristic leading (i.e., frontally tailing) peaks are obtained, and the retention depends mainly on the concentration of the analyte. An alternative technique is vacancy ion-exclusion chromatography (v-IEC), in which the column is equilibrated with the sample solution, flowing as the mobile phase through the system, and pure water is injected as the sample. In this case, the symmetrical vacant peaks are obtained. The aim of this paper is to describe the retention mechanism in IEC and v-IEC for the adsorptive and nonadsorptive acids in analytical and concentration overload conditions, with pure water and the diluted sulphuric acid solution as the two different mobile phases. The retention times and the peak shapes predicted by the derived equations remain in a good qualitative and quantitative agreement with the experimental data. The model proposed in this paper predicts the new features characteristic of IEC for the adsorptive acids. These are, namely, an increase in the retention time of the peak apexes (up to a certain level and concurring with an increase in the acid concentration), followed by a subsequent decrease of the retention time (with the further growth of the acid concentration in the eluent). Similar changes in the retention time observed for v-IEC in the specific adsorption conditions were also correctly predicted by the model.     

Synthesis and biological properties of 1,8‐naphthalimidebutylamines. Serotonin 5‐HT1A and 5‐HT7 binding data and pass‐assisted search

Syntheses of the N‐substituted butyl derivatives of 1,8‐naphthalimide ( 1‐8 ), containing various arylpiperazines, tetrahydroisoquinoline and methylhomopiperazine moieties attached at 4‐position of the butyl chain have been described. Biological activities were evaluated in vitro for their ability to bind to serotonin 5‐HT_1A and 5‐HT₇ receptors. Due to the structural similarity of derivatives 1‐8 to psychotropic agents, the pharmacological properties of target compounds were predicted using PASS program.     

Mass measurements of short-lived nuclides using the Isoltrap preparation Penning trap

For exotic nuclear species, short decay half-lives make precision mass measurements particularly challenging. Combining isobaric purification and the mass measurement in the same trap may offer an interesting compromise between losses due to half-life and measurement precision. Here we discuss a mass measurement performed in a preparation Penning trap, and perform a study of the resonance lineshape.     

Oligomerization oscillations of L-lactic acid in solution

We employ high-performance liquid chromatography with diode array, evaporative light scattering, and mass spectrometric detection to monitor the oligomerization of L-lactic acid in pure acetonitrile and in 70% aqueous ethanol. The production of higher oligomers appears to proceed in an oscillatory fashion. A model is presented that involves the formation of aggregates (micelles), which catalyze the oligomerization.     

Tuning the hydrogen-bonding strength in 2,6-bis(cycloalkylcarbonylamino)pyridine assemblies by variable flexibility. Association constants measured by hydrogen-bonded vs. non-hydrogen-bonded protons

The association of 2,6-bis(cycloalkylcarbonylamino)pyridines with rigid and non-rigid counterparts in chloroform solution was studied using ¹H NMR and computational methods. The angles within the cycloalkyl ring and the rotation of these substituents determine the strength of the association via triple hydrogen bonding. The dimerisation and methyl–methyl repulsion have been addressed as mechanisms restricting heterocomplexation of diacetamide. The association constants obtained by the shift changes of hydrogen-bonded protons are in agreement with those of methine protons. This ‘dual shift’ method was proposed as an additional verification of association constants obtained generally by amino protons.     

Secondary electron microscopy and transmission electron microscopy studies of carbon nanotubes in C-Ni films

Carbon nanotubes films have been studied with SEM and TEM. The studied films were obtained using a two step method: PVD process and CVD process. Strongly defected and curled carbon nanotubes containing Ni nanoparticles formed the film with thickness of about 300–400 nm. Observed carbon nanotubes were of lengths from 100 nm to 300 nm and did not stick to each other.     

Sulfonated multiblock copoly(ether sulfone)s as membrane materials for fuel cell applications

Arylene ether multiblock copolymers of the (AB)_n-type with various degrees of sulfonation have been prepared by a two-step polycondensation procedure. Multiblock copolymers in high yields and of high molecular weights were obtained. For comparison random copolymers with the same overall composition were synthesized. The theoretical ion-exchange capacities (IEC) of the materials were ranging from 0.50 mmol/g to 1.25 mmol/g. The water-uptake of the multiblock copolymers showed a linear dependency from the IEC and was increasing with increasing IEC. No differences were observed between random and block copolymers. Furthermore, the hydrolytic stability of aromatic sulfonic acid groups was investigated in this study. Aromatic sulfonic acids, having additional electron donating groups, especially in ortho- or para-position to the sulfonic acid group are sensitive to hydrolytic desulfonation. On the other hand electron-withdrawing groups in meta-position showed a stabilizing effect.