1,8-Naphthyridinecarbaldehydes bearing chlorine, pyrrolidinyl, piperidinyl or morpholinyl groups, were synthesised by oxidation of their methyl-substituted precursors. The prepared carbaldehydes represent valuable starting materials for the construction of systems that are useful for supramolecular and medicinal chemistry. Single-crystal X-ray diffraction studies of four carbaldehydes and six methyl derivatives provided interesting information about the supramolecular motifs in the crystal structures of solvent-free and solvated naphthyridines. The formation of interesting water clusters, for example, T4(2) water tape, was observed in the case of 7-methyl-2-(piperidin-1-yl)-1,8-naphthyridine as well as in the crystal structure of a by-product 7-(morpholin-1-yl)-1,8-naphthyridine-2-carboxylic acid. Knowledge of the detailed structural properties of water clusters is of great research interest to a broad range of scientific disciplines.

Single crystal X-ray diffraction allowed the identification and characterization of new solvates of tripodal trimethylbenzene- and triethylbenzene-based compounds bearing 1H-indole-2,3-dione (isatin) groups. Both unsubstituted and methyl or methoxy substituted isatins were used as building blocks for the construction of the host molecules 1–6. Four different conformations of 1–6 have been observed in the crystal structures, which differ not only in the position of the heterocyclic side arms (above or below the central benzene ring) but also in the orientation of the carbonyl groups of the isatin units. In the case of the trimethylbenzene derivative 2, single crystal X-ray diffraction allowed the identification and characterization of three solvates (2a, 2b and 2c), two of which represent the polymorphic forms 2·CH3CN-I (2a, baa/all-out) and 2·CH3CN-II (2b, aaa/out,out,in). The crystal packings of 1–6 are characterized by the presence of C–H⋯O, C–H⋯N, C–H⋯π, π⋯π and CO⋯π interactions as well as Cl⋯Cl contacts in the case of the chloroform-containing solvates.

X-ray analyses of a series of benzene-based tripodal molecules 1–9, bearing either bromo-substituted pyrazole groups or analogues lacking the bromo substituents, provide interesting insights into the molecular recognition phenomena and also give information about the different conformations which adopt the tripodal molecules in the solvent-free crystals and in solvates. The crystal packings are characterized by the presence of C–H⋯O, C–H⋯N, C–H⋯Br and C–H⋯Cl hydrogen bonds as well as C–Br⋯N, C–Br⋯Br, C–Br⋯Cl and C–Br⋯π halogen bonds. The conformations observed in the case of the triethyl- and trimethoxybenzene-based compounds can be defined as ab'ab'ab', ab'ab'ba', ab'ab'bb', ab'aa'ba', ab'aa'bb', aa'ab'ba' and aa'aa'aa' with the pyrazole-bearing arms arranged either in an aaa or an aab fashion.

Due to the problems with the exact prediction of the binding properties of an artificial carbohydrate receptor, the identification of characteristic structural features, having the ability to influence the binding properties in a predictable way, is of high importance. The purpose of our investigation was to examine whether the previously observed higher affinity of 2-aminopyrimidine-bearing carbohydrate receptors in comparison with aminopyridine substituted analogues represents a general tendency of aminopyrimidine-bearing compounds. Systematic binding studies on new compounds consisting of 2-aminopyrimidine groups confirmed such a tendency and allowed the identification of interesting structure–activity relationships. Receptors having different symmetries showed systematic preferences for specific glycosides, which are remarkable for such simple receptor systems. Particularly suitable receptor architectures for the recognition of selected glycosides were identified and represent a valuable base for further developments in this field.

New crystalline complexes of hexapodal pyrazole-based hosts with NH4+PF6−and/or solvent molecules were obtained and detailed analysed. The binding motifs observed between the binding partners give valuable insights into the phenomena of molecular recognition processes. Analyses of the conformations of the hexasubstituted benzene derivatives have shown that both ababab as well as abbabb and aaabbb conformations of the haxapodal compounds 1–3 are observed in the crystal structures 1a–d, 2, 2a, 3a and 3b. Key topics: Molecular recognition (Complexes of ammonium ions with artificial receptors).

Carbohydrate receptors combining a macrocyclic building block and two flexible side arms were designed on the base of the analysis of the binding motifs found in the crystal structures of the complexes formed between artificial receptors and monosaccharides, reported previously by our group. Binding studies in two-phase systems, such as extractions of sugars from water into organic phase, as well as in homogeneous organic media, using 1H NMR and fluorescence spectroscopic titrations, confirmed the suitability of the designed compounds to act as highly effective and selective carbohydrate receptors. Depending on the nature of the bridges and side arms used as the building blocks, various receptors with different binding properties could be developed. The obtained results confirmed the validity of the receptor design and revealed that crystalline receptor–sugar complexes are particularly a valuable basis for the design of new effective receptor systems.

The aim of the study was to evaluate the potential of trimethoxybenzene- and trimethylbenzene-based compounds bearing imidazole or indole groups as recognition sites in the complexation of carbohydrates. Representatives of these compounds were prepared and their binding properties toward selected carbohydrates evaluated. The results of the binding studies were compared with those obtained for the prepared pyrrole bearing analogues and for the previously described triethylbenzene-based receptors.

The binding motifs found in the crystal structures of complexes formed between artificial receptors and monosaccharides, reported previously by our group, have inspired us to design new macrocyclic and acyclic receptors, which were expected to form strong 1:1 complexes with monosaccharides, in particular with β-glucosides, through participation in the formation of CH-π interactions and hydrogen bonds with the sugar substrate. As first representatives of these compounds we have prepared the macrocycles 8–12 and the acyclic molecules 13–16, incorporating two central triethylbenzene units. The new compounds had been designed to bind monosaccharides via interactions of both central benzene rings with the sugar CH groups. Initial binding studies have confirmed the expected favorable binding capabilities of the macrocyclic compounds and indicated interesting binding properties of the acyclic analogues.

Compounds 5b–8b and 10b, and 11b, containing a triethylbenzene scaffold substituted with both neutral and cationic recognition sites, were shown to be effective receptors for N-acetylneuraminic acid (NeuAc), the most common occurring sialic acid, in highly competitive solvents. These compounds were established to be more powerful receptors for NeuAc than the symmetrical pyridinium- and quinolinium-based compounds 9b and 12b in aqueous media. As in natural protein–sialic acid complexes, the combination of neutral/charge-reinforced hydrogen bonds, ion pairs, CH−π, and van der Waals interactions seems to be responsible for the effective binding of this naturally widespread anionic carbohydrate in aqueous media.

Due to the problems with the exact prediction of the binding properties of an artificial carbohydrate receptor, the identification of characteristic structural features, having the ability to influence the binding properties in a predictable way, is of high importance. The purpose of our investigation was to examine whether the previously observed higher affinity of 2-aminopyrimidine-bearing carbohydrate receptors in comparison with aminopyridine substituted analogues represents a general tendency of aminopyrimidine-bearing compounds. Systematic binding studies on new compounds consisting of 2-aminopyrimidine groups confirmed such a tendency and allowed the identification of interesting structure–activity relationships. Receptors having different symmetries showed systematic preferences for specific glycosides, which are remarkable for such simple receptor systems. Particularly suitable receptor architectures for the recognition of selected glycosides were identified and represent a valuable base for further developments in this field.

The aim of the study was to evaluate the potential of trimethoxybenzene- and trimethylbenzene-based compounds bearing imidazole or indole groups as recognition sites in the complexation of carbohydrates. Representatives of these compounds were prepared and their binding properties toward selected carbohydrates evaluated. The results of the binding studies were compared with those obtained for the prepared pyrrole bearing analogues and for the previously described triethylbenzene-based receptors.

New representatives of compounds combining both a macrocyclic building block and two flexible side arms as recognition units were prepared and their binding properties toward selected carbohydrates were evaluated. The aim of this study was to examine the effects of the replacement of the heterocycle-bearing side arms by smaller units, such as hydroxy groups, on the binding capability. The design of this type of receptor was inspired by the participation of the side chain hydroxy group of serine and threonine in the biorecognition of carbohydrates. Such structural modifications enable the recognition of structure–activity relationships, which are of high importance in the development of carbohydrate receptors with predictable binding strength and selectivity.