Chitosan-graphene oxide films and CO2-dried porous aerogel microspheres: Interfacial interplay and stability.

The intimate interplay of chitosan (CS) and graphene oxide (GO) in aqueous acidic solution has been explored to design upon casting, nanostructured "brick-and-mortar" films (CS-GO-f) and by acidic-to-basic pH inversion, porous CO2-dried aerogel microspheres (CS-GO-m). Owing to the presence of oxygenated functional groups in GO, good-quality crack-free hybrid films were obtained. Mechanical properties were improved independently of the GO content and it was found that a 20wt% loading affords hybrid film characterized with a Young modulus three times superior to that reached with the same loading of layered clay. The presence of graphene oxide was found to be detrimental for the thermal stability of the polysaccharide at T <350°C, a fact attributed to the well-established decomposition of the oxygenated functional groups of the graphene sheets. Irrespective to the graphene oxide loading, chitosan-graphene oxide mixture preserves the gelation memory of the polysaccharide. Supercritical drying of the resulting soft hydrogels provides macroporous network with surface areas ranging from 226m2g-1 to 554m2g-1. XPS and RAMAN analyses evidenced the selective reduction of GO sheets inside of these microspheres, affording the hitherto unknown macroporous chitosan-entangled-reduced graphene oxide (CS-rGO-m) aerogels. Improvement in both hydrothermal stability (under water reflux) and chemical stability (under acidic conditions) have been noticed for chitosan-graphene oxide microspheres with respect to non-modified chitosan and chitosan-clay bio-hybrids, a result rooted in the substantial hydrophobic character imparted by the addition of graphenic material to the polysaccharide skeleton. In essence, this contribution demonstrates that graphene oxide loading do not disturb neither the filmogenicity of chitosan nor its gelation ability and constitutes a promising route for novel chitosan-based functional hybrid materials.

1,1''-Bis(prop-2-en-1-yl)-1,1'',2,2''-tetra-hydro-dispiro-[indole-3,7'-[6,9]diaza-tricyclo-[7.3.0.0(2,6)]dodecane-8',3''-indole]-2,2''-dione.

The mol-ecule of the title compound, C(30)H(32)N(4)O(2), lies on a twofold rotation axis that passes through the mid-points of the C-C bonds of the piperazine ring, which adopts a chair conformation. The pyrrolidine ring that is fused to the piperazine ring adopts an envelope conformation (in which the N atom represents the flap). The indoline fused-ring system is nearly planar (r.m.s. deviation = 0.044 Å); the two symmetry-related indoline fused-rings systems are aligned at 71.44 (3)°.

5,5''-Dibromo-1,1''-bis-(prop-2-en-1-yl)-1,1'',2,2''-tetra-hydro-dispiro-[indole-3,7'-[6,9]diaza-tricyclo-[7.3.0.0(2,6)]dodecane-8',3''-indole]-2,2''-dione.

In the mol-ecule of the title compound, C(30)H(30)Br(2)N(4)O(2), the piperazine ring adopts a chair conformation. The pyrrolidine rings that are fused to the piperazine ring adopt envelope conformations (in which the N atom represents the flap). The indoline fused-ring systems are nearly planar (r.m.s. deviations = 0.009 and 0.019 Å); the two fused rings are aligned at 60.63 (6)°.

1,1'-Dibenzyl-5,5''-dichloro-1,1'',2,2''-tetra-hydro-dispiro-[indole-3,7'-[6,9]diaza-tricyclo-[7.3.0.0(2,6)]dodecane-8',3''-indole]-2,2''-dione.

In the title compound, C(38)H(34)Cl(2)N(4)O(2), the piperazine ring adopts a chair conformation. The pyrrolidine rings that are fused to the piperazine ring adopt envelope conformations (in which the C atoms connecting the two rings represent the flap). The indoline ring systems are approximately planar (r.m.s. deviations = 0.026 and 0.034 Å) and are aligned at a dihedral angle of 54.98 (3)°.

2-[3-(1H-Benzimidazol-2-yl)prop-yl]-1-decyl-1H-benzimidazole.

The asymmetric unit of the title compound, C(27)H(36)N(4), contains two independent mol-ecules. Except for the atoms of the decyl chain, the non-H atoms of each mol-ecule are approximately coplanar (r.m.s. deviations = 0.075 and 0.164 Å) and the -CH(2)CH(2)CH(2)- link connecting the two benzimidazolyl fused-ring systems is slightly opened up at the middle C atom. The decyl substituent adopts an extended zigzag conformation in both mol-ecules. In the crystal, adjacent mol-ecules inter-act by N-H⋯N hydrogen bonds, generating a chain parallel to the c axis.

2-(3H-1,3-Benzothia-zol-2-yl-idene)-propane-dial.

In the title compound, C(10)H(7)NO(2)S, the dihedral angle between the benzimidazole and malonaldehyde group is 1.41 (2)°. An intra-molecular hydrogen bond is formed between the NH group and one of the adjacent carbonyl O atoms. In addition, the NH group forms an inter-molecular hydrogen bond to a symmetry equivalent of this carbonyl O atom, connecting the mol-ecules into centrosymmetric dimers. The structure also contains C-H⋯O inter-molecular inter-actions.

1,3-Dibenzyl-2-methyl-benzimidazolium chloride.

The cation of the title salt, C(22)H(21)N(2) (+)·Cl(-), contains a planar benzimidazolium unit (r.m.s. deviation = 0.02 Å); the phenyl rings of the benzyl substituents form dihedral angles of 68.2 (1) and 79.7 (1)° with the plane of the benzimidazolium fragment.

1,3-Diallyl-2-methyl-benzimidazolium bromide dihydrate.

The bonds in the five-membered ring of the title hydrated salt, C(14)H(17)N(2) (+)·Br(-)·2H(2)O, are delocalized. The cation lies on a special position of m site symmetry such that the mirror plane passes through the imidazol-yl-methyl bond and is perpendicular to the plane of the cation. The anion lies on another special position of 2 site symmetry. The anion and uncoordinated water mol-ecule are linked into a chain by O-H⋯O hydrogen bonds. One of the water O atoms is disordered over two sites of equal occupancy.