Gelating Abilities of Two-Component System of Catecholic Derivatives and a Boronic Acid.

In the last two decades, various kinds of the low-molecular-weight organogelators (LMOGs) have been investigated in terms of technological applications in various fields as well as their fundamental scientific properties. The process of gelation is generally considered to arise from immobilization of the solvents in the three-dimensional networks formed by the assembly of gelator molecules through weak intermolecular noncovalent interactions. From these points of view a huge number of organogelators have been developed so far. In the course of our research on LMOGs we have noticed a mixture of two gelators could show a different trend in gelation compared to the single gelator. It is well known that the catecholic moiety easily forms cyclic boronate esters with the boronic acid. Thus, we have investigated the two-component system based on cyclic boronate esters formed by the catechols and a boronic acid in terms of the control of gelation capability. Basic gelation properties of the constituent catecholic gelators have also been clarified. The catecholic gelators with the amide unit form no gel by addition of the boronic acid. In contrast, the catecholic gelators with the glutamic acid moiety improve their gelation abilities by mixing with the boronic acid. Furthermore, the gelation ability of the catecholic gelators having the urea unit is maintained after addition of the boronic acid. It has been found that gelation abilities of the catecholic gelators are highly affected by addition of the boronic acid. In terms of practical applications some gels can be obtained by on-site mixture of two kinds of solutions.

Crystal structure of benzyl 3-oxo-2-oxa-5-aza-bicyclo-[2.2.1]heptane-5-carboxyl-ate.

The title compound, C13H13NO4 (also known as N-benzyl-oxycarbonyl-4-hy-droxy-l-proline lactone), crystallizes with two mol-ecules in the asymmetric unit. They have slightly different conformations: the fused ring systems almost overlap, but different C-O-C-C torsion angles for the central chains of -155.5 (2) and -178.6 (2)° lead to different twists for the terminal benzene ring. In the crystal, the mol-ecules are linked by C-H⋯O inter-actions, generating a three-dimensional network. The absolute structure was established based on an unchanging chiral centre in the synthesis.

Crystal structure of (1R,4R)-tert-butyl 3-oxo-2-oxa-5-aza-bicyclo-[2.2.2]octane-5-carboxyl-ate.

In the title compound, C11H17NO4, commonly known as N-tert-but-oxy-carbonyl-5-hy-droxy-d-pipecolic acid lactone, the absolute configuration is (1R,4R) due to the enantiomeric purity of the starting material which remains unchanged during the course of the reaction. In the crystal there no inter-molecular hydrogen bonds.

Crystal structure of (tert-butyl-carbamo-yl)(4-chloro-2-oxo-2H-chromen-3-yl)methyl acetate.

In the title compound, C17H18ClNO5, which was synthesized by reacting 4-chloro-3-formyl-coumarin, acetic acid and tert-butyl isocyanide, the acetamido side chain is convoluted with ring-to-side chain C-C-C-C, C-C-C-N and C-C-N-C torsion angles of -123.30 (14), -135.73 (12) and 176.10 (12)°, respectively. In the crystal, N-H⋯O and weak C-H⋯O hydrogen bonds are present, which together with π-π coumarin-ring inter-actions [ring centroid separations = 3.4582 (8) and 3.6421 (9) Å], give rise to a layered structure lying parallel to (001).

Crystal structure of 3,4-dimethyl 2-(tert-butyl-amino)-5-[2-oxo-4-(thio-morpholin-4-yl)-2H-chromen-3-yl]furan-3,4-di-carboxyl-ate ethyl acetate hemisolvate.

In the title hemisolvate, C25H28N2O7S·0.5C4H8O2, the thio-morpholine ring adopts a chair conformation, with the exocyclic N-C bond in an equatorial orientation. The dihedral angle between the coumarin ring system (r.m.s. deviation = 0.044 Å) and the furan ring is 64.84 (6)°. An intra-molecular N-H⋯O hydrogen bond closes an S(6) ring. The ethyl acetate solvent mol-ecule is disordered about a crystallographic inversion centre. In the crystal, the components are linked by C-H⋯O and C-H⋯S hydrogen bonds, generating a three-dimensional network.

Crystal structure of ethyl 2-(2-{1-[N-(4-bromo-phen-yl)-2-oxo-2-phenyl-acetamido]-2-tert-butyl-amino-2-oxo-ethyl}-1H-pyrrol-1-yl)acetate.

In the title compound, C28H30BrN3O5, there is an intra-molecular N-H⋯O hydrogen bond and an intra-molecular C-H⋯O hydrogen bond, both forming S(9) ring motifs. The planes of the 4-bromo-phenyl ring and the phenyl ring are inclined to that of the pyrrole ring by 48.05 (12) and 77.45 (14)°, respectively, and to one another by 56.25 (12)°. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds and C-H⋯π inter-actions, forming slabs parallel to (10-1).

Syntheses, structural properties, and charge-transfer complexes of pyrenophanes.

Dithia[3.3](4,9)benzenopyrenophanes carrying various functional groups at the inner position or the outer position of the benzene ring have been prepared. The pyrenophanes with the substituent at the inner position of the opposite benzene ring exhibit the conformation in which the pyrene and the benzene components exist in the parallel manner (parallel conformation). On the contrary the conformation characterized by the perpendicular orientation of the pyrene and the benzene components has been confirmed for the pyrenophanes having the substituent at the outer position of the opposite benzene ring (perpendicular conformation). The NH-pi interaction between the inner amino group on the opposite benzene ring and the pyrene ring was observed. Formation of charge-transfer complexes of the pyrenophanes and tetracyanoethylene (TCNE) was performed. It has been found out that the orientation of two aromatic components and the NH-pi interaction as well as the electronic nature of the substituent on the opposite benzene ring significantly affect characteristics of the charge-transfer complexes in this pyrenophane system.