Pressure-induced formation of a solvate of paracetamol

Recrystallisation of paracetamol from a solution in methanol at a pressure of 0.62 GPa gives a new 1:1 solvate that has been characterised by single crystal X-ray diffraction.     

Solubility and solvate formation of lithium hexafluoroarsenate in acetonitrile

The solubility of LiAsF₆ in CH₃CN has been determined by the use of cooling curves. A partial phase diagram is presented which reveals a distinct dystectic corresponding to the formation of tetraacetonitrilolithium hexafluoroarsenate.     

Reactions of oximate alpha-nucleophiles with esters: evidence from solvation effects for substantial decoupling of desolvation and bond formation

This communication is concerned with deviations from linearity in Br?nsted-type nucleophilicity plots as indicators of changes in transition-state structures, in particular as related to solvational effects. Increasing dimethyl sulfoxide (DMSO) content of DMSO-water mixtures removes the leveling off observed in Br?nsted type plots of the reaction of p-nitrophenylacetate (PNPA) with oximate alpha-nucleophiles. This is interpreted as due to virtually complete decoupling between desolvation of the oxyanion nucleophile and bond formation in the rate-determining transition state (solvational imbalance).     

Preparation of sterically stabilized nanoparticles by desolvation from graft copolymers

A new method is described for the preparation of sterically stabilized nanoparticles of defined size and polydispersity which are stabilized in aqueous solution by the presence of covalently linked monomethoxy–poly (oxyethylene) (MeOPOE) chains. The nanoparticles (100–270 nm mean diameter) were prepared by a process of desolvation of a graft copolymer prepared from poly(2-aminoethylmethacrylate) (PAEMA) and MeOPOE. Reproducible desolvation was achieved by the addition of sodium phosphate buffer to the copolymer in aqueous solution to give particles which were crosslinked in situ with the addition of glutaraldehyde. The size (mean diameter) and polydispersity (Q) of the particles were determined by Photon Correlation Spectroscopy (PCS). The temperature at which the desolvation reaction was performed was found to influence the particle size; at low temperatures (5–12°C), small particles were produced (99–121 nm, Q = 0.090–0.121), whereas at much higher temperatures (40–55°C), particles as large as 224–275 nm (Q = 0.138–0.127) were generated. Other parameters such as the graft copolymer concentration, the amount of glutaraldehyde added, the pH of the sodium phosphate buffer added, and the reaction time were found to be of relative insignificance in influencing the particle size. In addition to those involved in drug delivery, our method of nanoparticle preparation may be of interest to those engaged in the preparation of particulate materials and colloidal dispersions for other specific applications (e.g. stabilized photographic emulsions).     

1,2,4-Thiadiazol derivatives of cytisine alkaloid: solvate formation and phase transitions

1,2,4-Thiadiazol derivatives of cytisine alkaloid—N-(3-methylthio-1,2,4-thiadiazol-5-yl-aminocarbonylmethyl) (1), N-(3-ethylthio-1,2,4-thiadiazol-5-yl-aminocarbonylmethyl) (2), N-(3-hexylthio-1,2,4-thiadiazol-5-yl-aminocarbonylmethyl) (3) cytisine have been crystallized from different solvents and by X-ray and TG–DSC method were studied. By X-ray analysis the structures of the crystal solvate of 2 with dioxane have been determined. By topology represented solvate belongs to tabulate type. In the crystal structure two conformers of the host molecules were determined. By TG–DSC method has been shown, that methyl-, ethyl-, and hexyl cytisine derivatives can exist in two phase forms. But, unlike methyl- and ethyl-derivatives, hexyl-derivative of cytisine not form inclusion compounds.     

Nucleation-controlled crystallization of a new,spontaneously resolved solvate of [Ru(bpy)3](PF6)2 and its desolvation reaction

Simply by increasing the supersaturation level, racemic [Ru(bpy)(3)](PF(6))(2) no longer crystallises as the well-known true racemate (beta-modification; P$\bar 3$c1, a=10.6453(5), c=16.2987(9) A, Z=2). Rather, it spontaneously resolves and forms a conglomerate of pure Lambda- and pure Delta-crystals with a so far unknown structure type. This new modification actually is a solvate ([Ru(bpy)(3)](PF(6))(2).1.5 CH(3)COCH(3); delta-type; P32, a=13.8133(7) A, c=11.6523(7) A, Z=2). By a solution-mediated equilibration the new modification is shown to be the metastable (Ostwald) product, which is formed based on nucleation kinetics. Upon desolvation the solvate transforms into a second enantiomorphic crystal structure (gamma-type; P3(1), a=10.3809(4), c=26.2576(13) A, Z=3). The latter could previously only be obtained by chemical resolution prior to crystallisation, but could not be accessed directly from racemic solutions. However, the new delta-modification can now be utilised for optical resolution by the so-called method of "resolution by entrainment". This example emphasises the potential that both kinetically controlled crystallisation and desolvation of solvates bear with respect to crystal engineering.     

Polymorph Separation by Ordered Patterning

We herein address the problem of polymorph selection by introducing a general and straightforward concept based on their ordering. We demonstrated the concept by the ordered patterning of four compounds capable of forming different polymorphs when deposited on technologically relevant surfaces. Our approach exploits the fact that, when the growth of a crystalline material is confined within sufficiently small cavities, only one of the possible polymorphs is generated. We verify our method by utilizing several model compounds to fabricate micrometric “logic patterns” in which each of the printed pixels is easily identifiable as comprising only one polymorph and can be individually accessed for further operations.     

Polymorph transition kinetics by DTA

The polymorph transition kinetics of the changes vaterite to calcite and aragonite to calcite have been followed using a DTA technique. The method eliminates the grinding process present in other analytical techniques and so has certain advantages. For both transitions the kinetic equation describing the process is found to be: $$\frac{{\partial \alpha }}{{\partial t}} = \frac{4}{3}k[ - \ln (1 - \alpha )]^{3/4} (1 - \alpha ).$$ Values of activation energy were found to be 452±19 KJ mole^?1 and 208±8 KJ mole^?1 for aragonite and vaterite transitions respectively using a procedure which enabled the calculation of kinetic parameters from a rising temperature experiment.     

Polymorph selectivity under nanoscopic confinement

Polymorph selectivity has been achieved during crystallization of anthranilic acid (AA) and 5-methyl-2-[(2-nitrophyenyl)amino]-3-thiophenecarbonitrile (ROY), both considered benchmarks of polymorphic behavior, within nanoporous glass beads and polymer monoliths. Whereas polymorph III of AA crystallizes from the melt on nonporous glass beads or within larger pores, the metastable polymorph II crystallizes in pores with diameters <23 nm, with the selectivity toward this form increasing with decreasing pore size. Of the six ROY polymorphs characterized by single-crystal X-ray diffraction, the yellow form (Y) crystallizes during evaporation of pyridine solutions imbibed by the 30-nm cylindrical pores of porous polycyclohexylethylene (p-PCHE) monoliths. Although both R and ON grow from the melt on the external surfaces of PCHE, only the red form (R) crystallizes in the pores. Amorphous ROY also forms in p-PCHE pores during evaporation from pyridine solutions, subsequently crystallizing to the R nanocrystals upon heating. Although heterogeneous nucleation on the pore walls may play a role, these observations suggest that nucleation and polymorph selectivity is governed by critical size constraints imposed by the ultrasmall pores. The ability to achieve polymorph selectivity in both glass and polymer matrices suggests wide-ranging compatibility with various organic crystalline solids, promising a new approach to controlling polymorphism and searching for unknown polymorphs.     

Solvent dependency though not solvate formation in the derivative–derivative resolution of N-formylphenylalanine

The efficiency of the resolution of N-formylphenylalanine was remarkably improved using (S)-(+)-2-benzylaminobutanol resolving agent in acetone. The efficiency of the resolution strongly depended on the quality of the solvent. Nevertheless, solvate formation did not occur during the process. The nature of the solvent-dependence was studied. The solid-melt binary phase diagram of the diastereomeric salts formed during the resolution by (S)-(+)-2-benzylaminobutanol was measured and discussed. It was recognized that the (S)-(+)-benzylaminobutanol (S)-(+)-N-formylphenylalanine salt exists in two polymorphic modifications.The effect of structurally related chiral and achiral auxiliary reagents in the above resolution was also studied. Thus, (S)-(+)-2-benzylaminobutanol was applied together with an (R)-(+)-1-phenylethylamine auxiliary resolving agent and benzylamine was used as a half-equivalent achiral basic reagent in a Pope–Peachey type resolution of N-formylphenylalanine by (S)-(+)-2-benzylaminobutanol. The results are compared to those obtained by the structurally related (R)-(+)-1-phenylethylamine chiral auxiliary.     

Hexaphenylhexaphosphinane benzene solvate

In the molecular crystal of hexaphenylhexaphosphinane benzene solvate, C₃₆H₃₀P₆·C₆H₆, representing the trigonal form of phosphobenzene as a solvate, the six‐membered ring of P atoms adopts a chair conformation wherein the six phenyl groups are located in equatorial positions. The molecules [molecular symmetry (C_3i)] are stacked infinitely along the c‐axial direction.     

Monoclinic Low-Temperature Polymorph of Cesium Nitrate

A new CsNO₃ polymorph with space group P2₁/c, Z = 4, a = 4.5699(9) Å, b = 11.1871(10) Å, c = 9.1484(18) Å, β = 131.24(3)° has been prepared by crystallization from a mixture of water and DMSO. Flat triangles NO₃ are located in the (010) and (020) planes between the layers formed by coordination polyhedra of Cs atoms in the (040) plane. In contrast to the previously known low-temperature polymorph, the new modification is characterized by the crystal equivalence of all Cs and NO₃ groups.     

Crystal-to-crystal transformation from a chain polymer to a two-dimensional network by thermal desolvation

Single-crystal to single-crystal transformation of a new lead(II) coordination polymer with ligands 8-hydroxyquinoline (8-Quin) and nitrate, [Pb2(8-Quin)2(NO3)2(MeOH)] () to [Pb(8-Quin)(NO3)] (1beta), is reported and the structures of and determined by X-ray crystallography.     

Tylophorine B benzene solvate

The crystal structure of tylophorine B (or 2,3,6‐tri­methoxy­phen­an­thro­[9,10‐f]­indol­izidine) as the benzene solvate, C₂₃H₂₅NO₃·­C₆H₆, has been determined. The compound was isolated from albizzia julibrissin and this is the first definitive report of the steochemistry of tylo­phorine.     

Investigation of desolvation process in lanthanide dinicotinates

The desolvation process in lanthanide pyridine-3,5-dicarboxylates of the formulae [Tb₂pdc₃(dmf)₂]·dmf (1), [Ho₂pdc₃(dmf)₂]·dmf (2), [Erdc₃(dmf)₂]·dmf (3), and [Yb₂pdc₃(dmf)₂]·dmf (4) where pdc-C₅H₃N(COO)₂²⁻, dmf-N,N′-dimethylformamide) has been investigated by means of the TG–DSC, TG–FTIR, IR and XRD methods. Heating of the complexes in the range 30–260 °C lead to evolution of weakly bonded dmf molecules included in the channels as well those directly bonded with lanthanide atoms. The kinetic analysis revealed a multistep desolvation pattern.