Crystal Structures and Physicochemical Properties of 3-Chloro-4-hydroxyphenylacetic Acid Salts with Amines.

3-chloro-4-hydroxyphenylacetic acid (CHPAA) is a fungal metabolite. It is a small molecule that is useful in crystal engineering studies due to the functional groups present. Six amines were selected to form salts with CHPAA. Linear derivatives included diethylamine (DEA) and di-N-butylamine (DBM). The aromatic compounds chosen were 2-aminopyridine (A2MP), 2-amino-4-methylpyridine (A24MP), 2-amino-6-methylpyridine (A26MP) and 4-dimethylaminopyridine (DMAP). The salts were characterised using single-crystal X-ray diffraction, thermal analysis, FTIR spectroscopy and Hirshfeld surface analysis. For all the crystal structures, N-H···O and C-H···Cl contacts were present. O-H···O contacts were found in all the crystal structures except for (CHPAA2-)2DEA+, which was also the only structure that displayed a Cl···Cl contact. Furthermore, C-H···O contacts were found in all the crystal structures except for (CHPAA-)(DBM+). The thermal stability trend showed that the DBM salt was more stable than the DEA salt. For the aromatic co-formers, the thermal stability trend showed the following: CHPAA-(DMAP+) > (CHPAA-)(A2MP+)>2CHPAA-2A26MP+>(CHPAA-)(A24MP+).

Antimycobacterial, Cytotoxic, and Antioxidant Activities of Abietane Diterpenoids Isolated from Plectranthus madagascariensis.

Medicinal plants of the Plectranthus genus (Lamiaceae) are well known for their ethnomedicinal applications. Plectranthus madagascariensis, which is native to South Africa, is traditionally used in the treatment of respiratory conditions, scabies, and cutaneous wounds. The phytochemical studies of P. madagascariensis led to the isolation of five known royleanone abietanes, namely, 6ß,7α-dihydroxyroyleanone (1), 7α-acetoxy-6ß-hydroxyroyleanone (2), horminone (3), coleon U quinone (4), and carnosolon (5). The relative configuration of compound 2 was established by X-ray analysis. Compounds 1-4 showed antimycobacterial activity (Minimum inhibitory concentration for 90% inhibition, MIC90 = 5.61-179.60 µM) against Mycobacterium tuberculosis H37Rv. Compound 4 and 5 showed comparable toxicity (Concentration for 50% inhibition, IC50 98.49 µM and 79.77 µM) to tamoxifen (IC50 22.00 µg/mL) against HaCaT cells. Compounds 1-5 showed antioxidant activity through single-electron transfer (SET) and/or hydrogen-atom transfer (HAT) with compound 5 being the most active antioxidant agent. Compounds 3 and 5 were isolated for the first time from P. madagascariensis. The observed results suggest P. madagascariensis as an important ethnomedicinal plant and as a promising source of diterpenoids with potential use in the treatment of tuberculosis and psoriasis.

Organic Salts of p-Coumaric Acid and Trans-Ferulic Acid with Aminopicolines.

p-Coumaric acid (pCA) and trans-ferulic acid (TFA) were co-crystallised with 2-amino-4-picoline (2A4MP) and 2-amino-6-picoline (2A6MP) producing organic salts of (pCA-)(2A4MP+) (1), (pCA̶ )(2A6MP+) (2) and (TFA̶ )(2A4MP+)·( 3 2 H2O) (3). For salt 3, water was included in the crystal structure fulfilling a bridging role. pCA formed a 1:1 salt with 2A4MP (Z' = 1) and a 4:4 salt with 2A6MP (Z' = 4). The thermal stability of the salts was determined using differential scanning calorimetry (DSC). Salt 2 had the highest thermal stability followed by salt 1 and salt 3. The salts were also characterised using Fourier transform infrared (FTIR) spectroscopy. Hirshfeld surface analysis was used to study the different intermolecular interactions in the three salts. Solvent-assisted grinding was also investigated in attempts to reproduce the salts.

Functional characteristics of Bambara groundnut starch-catechin complex formed using cyclodextrins as initiators.

Bambara groundnut (BGN) starch extracted from BGN flour was modified through complexation methods using alpha and beta cyclodextrin. Complexation methods used included the microwave, co-evaporation and kneading methods. Cyclodextrin (alpha and beta) were used as initiators for grafting catechin to the BGN starch molecule. The functional properties of native and modified BGN starches were assessed. The swelling capacity of BGN starches increased with an increase in temperature. The swelling capacities of BGN starches ranged from 0.36 g/g (BGN starch modified through the co-evaporation method, beta cyclodextrin + catechin) to 4.84 g/g (BGN starch modified through the microwave method, beta cyclodextrin + catechin). Complexation methods significantly reduced the swelling capacity of native BGN starch. Temperatures had a significant (p ≤ 0.05) effect on the swelling capacity of BGN starches. The solubility of BGN starches ranged from 0.61 g/100 g (native BGN starch) to 46.04 g/100 g (BGN starch modified through the kneading method, alpha cyclodextrin); using water as a solvent. The water absorption of native and modified BGN starches ranged from 0.23 to 1.17 g/g, respectively. Starches complexed with ß-cyclodextrin showed increased water absorption capacity in comparison to the starches complexed with alpha cyclodextrin. The modification methods had a significant (p ≤ 0.05) effect on the water absorption capacities of BGN starches. There was no significant difference in the oil absorption capacities of BGN starches and they ranged from 1.02 to 1.07 g/g. Pasting properties of BGN starches were assessed using a rapid visco analyser (RVA). The modified starches exhibited lower breakdown, setback, and final viscosities as well as significant increase in gelatinisation temperature compared to the native BGN starch.

Salts of Mefenamic Acid With Amines: Structure, Thermal Stability, Desolvation, and Solubility.

Salt formation has been known to improve some physicochemical properties of active pharmaceutical ingredients particularly solubility. In this study, mefenamic acid (MA) formed salts with ethylenediamine (EDM), triethylamine (TA), 1-methylpiperazine (MP), and morpholine (MOP). In the salt structures studied, the proton of the carboxylic acid group of the MA molecule was transferred to a nitrogen atom of the amine. Both crystal structures of the ethylenediammonium and morpholinium salts were solved successfully by single-crystal X-ray diffraction in the space group PI. The triethylammonium and the 1-methylpiperazinium salts solved in Pbca and P21/c, respectively. The thermal behavior of the salts was investigated, and the desolvated powders were analyzed using powder X-ray diffraction. Grinding and slurry experiments were also investigated as alternate methods for preparation of the salts. The desolvation experiments yielded interesting results with the desolvation of (MA-)(MP+) resulting in MA form I, desolvation of (MA-)(TA+) gave mixtures of MA form I and MA form II, whereas desolvation of (MA-)(MOP+) gave MA form II. The solubility trend in water was determined as (MA-)(MP+) > (MA-)(TA+) > (MA-)(MOP+) > (MA-)(EDM+), with (MA-)(MP+) the most-soluble and (MA-)(EDM+) the least-soluble salt.

Solvates of selected fenamic acids with substituted pyridines: structure, thermal stability and desolvation.

Mefenamic acid (MA) formed solvates with 2-picoline (2PIC), 3-picoline (3PIC), 4-picoline (4PIC) and 3-chloropyridine (3CLPYR). The solvates crystallized in the space group P\bar 1 with the carboxylic acid of MA hydrogen-bonded to the nitrogen of the substituted pyridine. Tolfenamic acid (TFA) formed solvates with 2PIC and 3PIC, the crystal structures successfully solved in the space groups P21/n and Pbca, respectively. The fenamate conformation varied depending on the acid and the included solvent. Similarities were observed in the structures involving MA. The two solvate structures of TFA had different packing arrangements. Grinding and slurry experiments were also successful for the preparation of all of the compounds except MA·2PIC. Recrystallization, grinding and slurry investigations of MA and 2PIC yielded a polymorph; the structure was successfully solved in P21/n. Additionally, the thermal stability of the solvates was determined. Desolvation experiments were also performed and the resultant powders were analysed using powder X-ray diffraction.

9-Meth-oxy-9-(2-meth-oxy-phen-yl)-9H-xanthene.

In the title compound, C(21)H(18)O(3), the xanthene system and the meth-oxy-phenyl ring are practically orthogonal with a dihedral angle between their mean planes of 89.27 (3)°. The meth-oxy group attached to the phenyl ring makes a C-O-C-C torsion angle of 11.56 (18)°. In the crystal, mol-ecules are linked by C-H⋯O inter-actions into chains along [010]. Weak C-H⋯π inter-actions also occur.

Inclusion of volatile guests by a tetrapedal host: structure and kinetics.

The host compound tetra(3-hydroxy-3,3-diphenyl-2-propynyl)ethene, TET, forms inclusion compounds with acetone, dimethyl sulfoxide, dioxane and pyridine. All the structures were successfully solved in the triclinic space group P1[combining macron]. We found variable host : guest ratios for the acetone (TET.ACE, H : G = 1 : 4), dimethyl sulfoxide (TET.DMSO, H : G = 1 : 4) and pyridine compounds (TET.PYR, H : G = 1 : 5). Solutions of the host compound and dioxane formed TET.2DIOX, H : G = 1 : 2 when left to crystallise at room temperature, whereas TET.4DIOX, H : G = 1 : 4 was formed during crystal growth at low temperature. We have correlated the structures with their thermal stabilities and kinetics of desolvation.

Xanthenol clathrates: structure, thermal stability, guest exchange and kinetics of desolvation.

A series of clathrates comprising the xanthenol host, 9-(4-methoxyphenyl)-9H-xanthen-9-ol, with a variety of aromatic guests displays similar structures in the space group P(-1). We have elucidated the structures of the inclusion compounds H x 1/2G, where H is 9-(4-methoxyphenyl)-9H-xanthen-9-ol and G is benzene, o-, m- and p-xylene. The structures are isostructural with respect to the host and display consistent (Host)-OH...O-(Host) hydrogen bonding. The guests lie on a centre of inversion and with the exception of the symmetrical guests, benzene and p-xylene, are disordered. An interesting case arises with m-xylene, which is ordered at low temperature (113 K) with both the host and guest molecules in general positions. At a higher temperature (283 K) the inclusion compound with m-xylene fits the series. We have correlated the structures with their thermal stabilities, guest exchange and kinetics of desolvation.

Desorption kinetics of a xanthenol-dioxane clathrate.

The host xanthenol compound forms a 1:1 clathrate with dioxane, namely 9-(1-naphthyl)-9H-xanthen-9-ol-1,4-dioxane, C23H16O2.C4H8O2. The structure of this clathrate is reported, along with a study of the kinetics of desolvation and the determination of an activation energy. The guest molecules are stabilized by O(host)-H...O(guest) hydrogen bonds [O-H = 0.968 (2) A, O...O = 2.7532 (13) A and O-H...O = 151.9 (4) degrees].