Intermolecular Interactions in Crystalline Hydroxychloroquine Sulfate in Comparison with Those in Selected Antimalarial Drugs

Abstract The crystal structure of hydroxychloroquine sulfate (OHClQ) was determined in order to compare its conformation and intermolecular interactions to those in the crystalline chloroquine phosphate (ClQP) and quinine salicylate (QSal) monohydrate. The crystals of OHClQ are monoclinic with the space group P2₁/c and unit-cell dimensions: a = 10.4966(1) ?, b = 8.8056(1) ?, c = 21.8603(3) ?, β = 101.074(1)°. The quinoline antimalarial drugs may interact with their putative receptors by formation of characteristic hydrogen-bonded rings. The protonated nitrogen atoms and/or hydroxyl groups of the drug cation are proton donors, while the oxygen atoms of anions are proton acceptors. Water molecules may intermediate in these interactions. Graphical Abstract Hydroxychloroquine sulfate is a drug used in the treatment of malaria and rheumatic diseases. The X-ray structure analysis shows an important role of intermolecular hydrogen bonds in the crystal architecture. Comparison with chloroquine phosphate and quinine salicylate indicates that the organization of the drug cations is determined by the anions.      

Structure of 4,6-dimethylisothiazolo[5,4-b]pyridin-3(2H)-one and its 2-[4-(2-methylphenyl) piperazin-1-ylmethyl] derivative

The crystal and molecular structures of 4,6-dimethylisothiazolo[5,4-b]pyridin-3(2H)-one, C₈H₈N₂OS, 1, and its 2-[4-(2-methylphenyl)piperazin-1-ylmethyl] derivative, C₂₀H₂₄N₄OS, 2c, are described. These compounds crystallize in the monoclinic system in the space group P2 ₁/c. The cell constants for compound 1 are a = 5.049(1), b = 14.897(1), c = 11.330(1) Å, = 98.07(1)°, Z = 4, T = 293 K, and D _cal = 1.419 g cm^–3, and for compound 2c are a = 15.525(1), b = 12.021(1), c = 10.911(1) Å, = 106.42(1)°, Z = 4, T = 293 K, and D _cal = 1.253 g cm^–3 The structures were solved by direct methods and refined to R values of 0.0411 and 0.0380 for 1640 and 3504 reflections for 1 and 2c, respectively. The analysis of the geometry and difference electron density map reveal that the dimethylisothiazolopyridine 1 exists in the amino tautomeric form in the crystalline state. The conformation of the o-methylphenylpiperazine part of the molecule 2c strongly depends on the substituents effect in the phenyl ring and is very similar to those observed in crystals for other investigated arylopiperazine derivatives of the isothiazolopyridine.     

Colorimetric and fluorimetric pH sensing using polydiacetylene embedded within PVC-PCL nanofibers

The applicability of model polydiacetylenes (PDAs) in hydrogen ions sensitive optodes was tested. Nanofibers mats were electrospun using a mixture of polyvinyl chloride (PVC) and polycaprolactone (PCL) together with 10, 12-tricosadiynoic acid (TCDA) or 10,12-pentacosadiynoic acid (PCDA). After the polymerization the mats were applied in colorimetric and fluorimetric pH sensors. The PDAs were formed by photopolymerization with a UV lamp (254 nm), resulting in a change of mats color from white to dark blue. The morphology of both fiber mats is similar (SEM images), and the average diameters of fibers were estimated as equal to 228±73 and 248±61 nm for TCDA and PCDA, respectively. As the pH increases, the color of the fiber mat changes from blue to red and the process can be followed visually. The result obtained by computer image analysis showed a sigmoidal increase in the intensity of red and a decrease in the intensity of blue color with increasing pH. A similar sigmoidal response is observed for the dependence of the emission intensity on the pH. Changes in the recorded signal occur in the pH range from 7 to 8.5 or from 8 to 9.5 for mats with TCDA and PCDA, respectively. Both readout modes can be successfully used for pH sensing with proposed nanofibrous mats in the range of pH close to the physiological pH range.     

Periodic solutions of asymptotically linear autonomous Newtonian systems with resonance

In this paper, we study the existence, continuation and bifurcation from infinity of2π$2\pi$-periodic solutions of autonomous Newtonian systems. We underline that the resonant case is considered. To prove the results, we apply the degree for S¹$S^1$-equivariant gradient maps defined by Rybicki (1994) in [15] and the angle condition introduced by Bartsch and Li (1997) in [16].     

Diastereoselective methylation of bis(N-confused porphyrinatonickel(II)): access to configurationally stable chiral bis(porphyrinoid) and non-symmetric dimers

Bis- and tris(methylated) derivatives of 3,3'-bis(N-confused porphyrin) were obtained. Methylation of C21 stabilizes the geometry of the axially chiral system allowing separation of enantiomers and assignment of an absolute configuration by X-ray methods.     

Microwave-assisted Cannizzaro reaction—Optimisation of reaction conditions

The microwave-assisted Cannizzaro reaction was studied in order to develop fully reproducible synthetic protocols for transformation of aldehydes to carboxylic acid and alcohols. Optimised were the following process parameters: power, temperature, and time. Aromatic, heteroaromatic and aliphatic aldehydes were used in the studies. It was found that furfural, thiophene-2-carbaldehyde, pyridinecarboxaldehyde and aromatic aldehydes react under mild conditions, while 1-methyl-pyrrole-2-carboxaldehyde derivatives and aliphatic aldehydes require more drastic reaction conditions and a longer exposure time to microwave radiation.     

Liquid crystalline properties of salicylaldimine-based dimers: influence of terminal alkyl chain length and central part

The synthesis and thermotropic properties of four homologous series of salicylaldimine-based dimer liquid crystals are reported. Two 4-(4-alkoxy-2-hydroxybenzylideneamino)benzoyloxy groups are connected to a central part consisting of a 1,3-phenylene, 1,5-pentylene, 2,2-dimethyl-1,5-pentylene or 3,3-dimethyl-1,5-pentylene unit. The terminal alkoxy chains have been varied from 4 to 16 carbon atoms in length. All the compounds exhibit liquid crystalline phases whose behaviour depends on the nature of the central part and the length of the alkoxy terminal chains. All compounds of the series with the central phenyl part exhibit enantiotropic B-phases, and the sequence B₆-B₁-B₂ on increasing terminal chain length was observed. Replacement of the phenyl group with a pentyl central group partly suppresses the formation of B-phases. The longer homologues of this series show the B₁ phase, while the shorter exhibit an intercalated SmC_c mesophase. The introduction of methyl substituents to the pentyl spacer causes the melting points to fall dramatically and the formation of B-phases is totally suppressed. The compounds with the long tails show intercalated SmA_c phases and those with short tails show intercalated SmC_c phases.