Roman Luboradzki

Solvent Effect on 1,2-O-(1-Ethylpropylidene)-α-D-glucofuranose Organogel Properties

The solvent effect on organogel formation in nitrobenzene and chlorobenzene using 1,2-O-(1-ethylpropylidene)-alpha-d-glucofuranose (1) as the gelator is presented. Fourier transform infrared (FTIR) spectroscopy revealed that hydrogen bonding between the molecules of gelator 1 is the main driving force for gelator self-aggregation. The gels are characterized by different hydrogen-bonding patterns, which are reflected in a different microstructure of the networks. The morphology of fibers of nitrobenzene organogel consists of straight, rod-like, and thinner fibers, in comparison to the elongated but generally not straight and thicker fibers in chlorobenzene organogel. The thermal stability of gels also differs, and the DeltaH is equal to 50.1 and 65.0 kJ/mol for nitrobenzene and chlorobenzene gels, respectively. The properties of the gels reported here were compared to benzene and toluene gels of 1 presented in previous work and correlated with different solvent parameters: epsilon, delta, and E(T)(30). We have shown that the polarity of the solvent influences the thermal stability of the gel, the hydrogen-bonding network, and finally the structure of gel network. Therefore, in the studied sugar-based gelator, the hydrogen bonding alone is insufficient to fully describe the gelation process.

Novel supramolecular organogels based on a hydrazide derivative: non-polar solvent-assisted self-assembly, selective gelation properties, nanostructure, solvent dynamics

In this work, we report the complementary studies of supramolecular organogels composed of a newly synthesized low molecular mass gelator 4-(4-morpholinyl)-3-nitro-benzoylhydrazide (1) with benzene, toluene, and p-xylene. Intermolecular hydrogen bonding and π–π stacking interactions are the main driving forces promoting gelation of the system and the self-assembly of the new gelator molecules. The former interactions were revealed by the FT-IR and Raman studies, whereas the latter ones were postulated on the basis of the molecular structure of the gelator, UV-Vis spectra and comparison with the previously published data for other hydrazide derivatives. The strengths of the hydrogen bonding interactions are comparable as indicated by the FT-IR spectra analysis. Therefore, we correlated the differences in the calculated enthalpies of the gelator aggregates of 1 in the gels studied with the differences in the strengths of the π–π stacking interactions. The gel of 1 with benzene is characterized by the highest value of enthalpy. The images taken by the SEM and POM methods reveal differences in the architecture of gelator 1 aggregates, which are lamellar-like in toluene and fibrillar in benzene and p-xylene. The dispersion of spin–lattice relaxation times of solvents in the gel phase, observed by the NMR relaxometry method at low frequencies, is an indicator of the solvent–gelator interactions. As a result of this interaction, a significant slowing down of the motion (5 orders of magnitude as compared to bulk solvents) of the fraction of solvent molecules at the pore surface in the gel phase takes place. The diffusion of solvents in gels is restricted as shown by PGSE NMR. The apparent diffusion coefficient measured as a function of diffusion time can be used to estimate the pore size of the gel matrix, which for the gel of 1 with toluene is about 22 μm.

Ring-expanded bicyclic β-lactams: a structure-chiroptical properties relationship investigation by experiment and calculations.

In the present work, the validity of the helicity rule relating the absolute configuration of the bridgehead carbon atom in bicyclic β-lactams to the sign of the 220 nm band observed in their electronic circular dichroism (ECD) spectra is examined for ring-expanded cephalosporin analogues. To this end, a series of model compounds with a seven-membered ring condensed with the β-lactam unit was synthesized. A key step of their synthesis was either the ring-closing metathesis (RCM) or the free radical cyclization leading to the seven-membered ring with an S, O, or C atom at the 6 position in the bicyclic skeleton. To investigate the scope and limitations of the simple, empirically established helicity rule, a combination of ECD spectroscopy, variable-temperature ECD measurements, X-ray analysis, and time-dependent density functional theory (TD-DFT) calculations was used. A comparison of the experimental ECD spectra with the spectra simulated by TD-DFT calculations gives a reasonable interpretation of the Cotton effects observed in the 240-215 nm spectral range. The results suggest that the helicity rule does not apply to the investigated compounds because of the planarity of their amide chromophore. Thus, these compounds do not constitute an exception to the rule that was established for bi- and polycyclic β-lactams with the nonplanar amide chromophore only.

Interactions with β-cyclodextrin as a way for encapsulation and separation of camphene and fenchene.

The separation of isomeric monoterpenes, camphene and fenchene by complexation with β-cyclodextrin is presented. Both of the monoterpenes form complexes with β-cyclodextrin (as shown by both gas chromatography and (1)H NMR) with similar stability constants nevertheless it is possible to separate them by re-crystallization. The crystal structure of β-cyclodextrin with fenchene was also studied by X-ray diffraction.

TEM and SEM observations of super-structures constructed in organogel systems from a combination of boronic-acid-appended bola-amphiphiles with chiral diols

Two bola-amphiphilic α,ω-diboronic acids separated by a (CH2)11 or (CH2)12 group were synthesized. Complexation with chiral diols readily gave new amphiphiles end-capped with the chiral substituents. Some of these acted as good gelators of organic solvents. Transmission electron microscope and scanning electron microscope observations established that a variety of super-structures are created in the organogels, depending on the solvents and the structure of the chiral end-cap groups. In most cases, the fibrous aggregates, the network structure which is the driving-force for gelation, showed a helical higher-order structure reflecting the chirality of the end-cap groups. The results indicate that the combinatorial approach utilizing boronic acid functions and diol compounds is useful in creating a variety of new super-structures in the gel phase.

X-ray diffraction study of some indolinones

X-ray diffraction studies are reported for six indolinones. The results show that two different types of associates are present in the crystal state of the compounds having an NH group. The indolinone molecules without any substituents form cyclic dimers while those with one or two methyl groups attached to the C3 atom of the lactam ring form infinite hydrogen bonded chains. It is confirmed that the lactam moiety forms a typical planar amide structure with no sign of the enol form present.

Evidence for the trans-influence of axial substituents as a significant factor determining the structure and stability of five-coordinate complexes: molecular structure of the first simple five-coordinate dialkylaluminum O,O′-chelate complex

The addition of 4-methylpyridine to Me2Al(OC(Me)C6H4-2-O) produced the relatively stable five-coordinate Lewis acid-base adduct Me2Al(OC(Me)C6H4-2-O)P(g-picoline). The resulting compound has been characterized by 1 H and 27 Al NMR spectroscopy and cryoscopic molecular weight measurements and the molecular structure has been confirmed by X-ray crystallography. X-ray structure analysis of this simple five-coordinate complex reveals that thetrans-influence of axial substituents is a significant factor controlling the structure and stability of five-coordinate aluminum compounds. q 1999 Elsevier Science S.A. All rights reserved.

Comprehensive Chiroptical Study of Proline‐Containing Diamide Compounds

The continuously growing interest in the understanding of peptide folding led to the conformational investigation of methylamides of N-acetyl-amino acids as diamide models. Here we report the results of detailed conformational analysis on Ac-Pro-NHMe and Ac-β-HPro-NHMe diamides. These compounds were analyzed by experimental and computational methods, the conformational distributions obtained by Density Functional Theory (DFT) calculations for isolated and solvated diamide compounds are discussed. The conformational preference of proline-containing diamide compounds as a function of the ambience was observed by a number of chiroptical spectroscopic techniques, such as vibrational circular dichroism (VCD), electronic circular dichroism (ECD), Raman optical activity (ROA) spectroscopy, and additionally by single crystal X-ray diffraction analyses. Based on a comparison between Ac-Pro-NHMe and Ac-β-HPro-NHMe, one can conclude that due to the greater conformational freedom of the β-HPro derivative, Ac-β-HPro-NHMe shows different behavior in solid- and solution-phase, as well. Ac-β-HPro-NHMe tends to form cis Ac-β-HPro amide conformation in water, dichloromethane, and acetonitrile in contrast to its α-Pro analog. On the other hand, the crystal structure of the β-HPro compound cannot be related to any of the conformers obtained in vacuum and solution while the X-ray structure of Ac-Pro-NHMe was identified as tα(L)-, which is a trans Ac-Pro amide containing conformer also predominant in polar solvents.

In search for phototautomerization in solid dipyrido[2,3-a:3', 2'-i]carbazole

Abstract Dipyrido[2,3-a:3′,2′-i]carbazole (DPC) is known to undergo excited state double proton transfer in cyclic complexes with alcohols. This process is detected by the appearance of low-energy fluorescence, red-shifted with respect to the “normal” emission. X-ray studies show that DPC forms cyclic, but strongly nonplanar doubly hydrogen-bonded dimers in the crystalline phase. No tautomeric fluorescence could be detected for DPC crystals. However, this emission becomes readily observed for solid DPC samples that have been exposed to water vapor, or prepared on hydroxylic supports, such as wool, filtration paper, or mica. These results suggest possible use of DPC as a probe for detection of humidity and hydroxyl groups. Tautomeric emission was also observed for DPC embedded into a hydroxyl-group-containing polymer, poly(vinyl butyral-co-vinyl-alcohol-co-vinyl acetate). The ability to form cyclic, doubly hydrogen-bonded dimers and complexes with hydroxyl-group-containing partners is compared in a series of structurally related molecules: DPC, 1H-pyrrolo[3,2-h]quinoline, 7-azaindole, 1-azacarbazole. Molecular geometry dictates that the systems with the strongest propensity to form flat dimers should have the weakest tendency for the formation of cyclic solvates, and vice versa.

An X-ray diffraction study of some mesoionic 2,3-diphenyltetrazoles

An X-ray diffraction study is reported for four molecules of mesoionic 2,3-diphenyltetrazoles. The results confirm a dipolar “mesoionic” structure, aromatic character of the tetrazole ring and no conjugation between the phenyl and tetrazole rings. The geometry of the exocyclic group is discussed in detail. The molecular parameters of the compounds investigated are correlated with13C and15N nmr data. The results obtained are compared with similar structures which have already been studied.