Specific interactions between molecules, including those produced by a given solute, and the surrounding solvent are essential to drive molecular recognition processes. A simple molecule such as benzene is capable of recognizing and differentiating among very similar entities, such as methyl 2,3,4,6-tetra-O-methyl-alpha-D-galactopyranoside (alpha-Me(5)Gal), methyl 2,3,4,6-tetra-O-methyl-beta-D-galactopyranoside (beta-Me(5)Gal), 1,2,3,4,6-penta-O-acetyl-beta-D-galactopyranose (beta-Ac(5)Gal), and methyl 2,3,4,6-tetra-O-methyl-alpha-D-mannopyranoside (alpha-Me(5)Man). In order to determine if these complexes are formed, the interaction energy between benzene and the different carbohydrates was determined, using Calvet microcalorimetry, as the enthalpy of solvation. These enthalpy values were -89.0 +/- 2.0, -88.7 +/- 5.5, -132.5 +/- 6.2, and -78.8 +/- 3.9 kJ mol(-1) for the four complexes, respectively. Characterization of the different complexes was completed by establishing the molecular region where the interaction takes place using NMR. It was determined that beta-Me(5)Gal is stabilized by the CH/pi interaction produced by the nonpolar region of the carbohydrate on the alpha face. In contrast, alpha-Me(5)Man is not specifically solvated by benzene and does not present any stacking interaction. Although alpha-Me(5)Gal has a geometry similar to that of its epimer, the obtained NMR data seem to indicate that the axial methoxy group at the anomeric position increases the distance of the benzene molecules from the pyranose ring. Substitution of the methoxy groups by acetate moieties, as in beta-Ac(5)Gal, precludes the approach of benzene to produce the CH/pi interaction. In fact, the elevated stabilization energy of beta-Ac(5)Gal is probably due to the interaction between benzene and the methyl groups of the acetyls. Therefore, methoxy and acetyl substituents have different effects on the protons of the pyranose ring.

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Thaumatin, lysozyme, and ferritin single crystals were grown in solutions and gels without and with surrounding strong stationary magnetic fields. The crystal size, number and alignment in dependence on the induction force were analysed. The crystal quality, like mosaicity, as function of the magnetic force is discussed by using synchrotron X-ray diffraction analysis.

Can a benzene molecule differentiate between two isomeric carbohydrates? It is generally accepted that two factors govern molecular recognition: complementarity and preorganization. Preorganization requires the presence of cavities for positioning the host's groups of complementary nature to those of the guest. This study shows that, in fact, groups should be complementary to recognize each other (for the case presented here, it is controlled by the CH/pi interaction) but preorganization is not essential. Since weak interactions have their origin in dispersion forces, they also have impact on the enthalpic term of the free energy, so it was considered that their participation can be demonstrated by measuring the energy involved. For recognition to happen, two conditions must be satisfied: specificity and associated stabilizing energy. In this study we evaluated the heat of dissolution of different carbohydrates such as methyl 2,3,4,6-tetra-O-methyl-alpha-d-mannopyranoside and methyl 2,3,4,6-tetra-O-methyl-beta-d-galactopyranoside using different aromatic solvents. The solvation enthalpies in benzene were -78.8 +/- 3.9 and -88.7 +/- 5.5 kJ mol(-1) for each carbohydrate, respectively; and these values yielded a CH/pi energy of interaction of 9.9 kJ mol(-1). In addition, NMR studies of the effect of the addition of benzene to chloroform solutions of the two carbohydrates showed that benzene specifically interacts with the hydrogen atoms of the pyranose ring at positions 3, 4, and 5 located on the alpha face of the methyl-beta-galactoside, so it is, in fact, able to recognize it. Thus, the interactions between carbohydrates and the aromatic residues of proteins occur in the absence of the confinement generated by the protein structure. By experimentally measuring the energy associated with this interaction and comparing it to theoretical calculations, it was also possible to unequivocally determine the existence of CH/pi interactions between carbohydrates and proteins.

Simple acid–base properties explain the differences in amide and imide dimerisation, and represent an alternative to the secondary interactions hypothesis.

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The lower-rim functionalised distal bis-(4-picolyl)-p-tert-butylcalix[4]arene () selectively and quantitatively self-assembles into a series of discrete [2 + 2] blue-emitting metallacycles of general formula M2L2Xn with diverse metal salts (M = Zn(2+), Pd(2+), Ag(+), and Cd(2+); X = Cl(-), NO3(-), ClO4(-), BF4(-) , CF3SO3(-), PF6(-), SbF6(-); n = 2, 4). Macrocycle assembly has been corroborated by 2D-DOSY NMR and ESI-MS analyses, which further indicate that the M2L2Xn entities are quite stable and persist as robust and discrete macrocyclic species in solution. While free units display modest blue emission (λmax = 307-405 nm), self-assembly of M2L2Xn results in amplified fluorescence (up to 13-fold). This remarkable enhancement may be primarily ascribed to the increase in conformational rigidity imposed on the units by supramolecular assembly formation upon metal coordination to the pyridyl groups; in addition, subtle intensity-emission modulation may be provided by the different metal components. Titrations aimed at exploring the possibilities for ratiometric detection of metal cations or sensing of nitroaromatic species, revealed that the M2L2Xn platform may be a suitable "turn-on/off" system. Our results provide valuable insights into luminescence enhancement within the context of coordination-driven assemblies, which may be engineered to increase their fluorescence by imposing rigidity on the chromophores.