Mechanically Induced Phase Change in Barbituric Acid

By grinding a commercial sample of barbituric acid in its trioxo form (polymorph II, 99%) for 24 h, a new compound has been isolated. The new phase has been identified as the trihydroxyl isomer. The characterization of the new isomer has been carried out by means of X-ray powder diffraction, solid-state NMR (1H MAS, 13C and 15N CPMAS, 2D PASS, and FSLG-HETCOR), IR and Raman spectroscopies. The conversion results from the complete tautomeric shift of a methylene and of two N−H hydrogen atoms. 1H MAS spectra allow the characterization of the hydrogen bond interactions on the basis of their strength in the starting compound and in the new isomer. In solution, the trihydroxyl isomer immediately converts to the trioxo form as demonstrated by 1H NMR experiments in protic, aprotic, and amphiprotic solvents (D2O, MeOH-d4, DMSO-d6, acetone-d6)

Coupling Solid-State NMR with GIPAW ab Initio Calculations in Metal Hydrides and Borohydrides

An integrated experimental–theoretical approach for the solid-state NMR investigation of a series of hydrogen-storage materials is illustrated. Seven experimental room-temperature structures of groups I and II metal hydrides and borohydrides, namely, NaH, LiH, NaBH₄, MgH₂, CaH₂, Ca­(BH₄)₂, and LiBH₄, were computationally optimized. Periodic lattice calculations were performed by means of the plane-wave method adopting the density functional theory (DFT) generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) functional as implemented in the Quantum ESPRESSO package. Projector augmented wave (PAW), including the gauge-including projected augmented-wave (GIPAW), methods for solid-state NMR calculations were used adopting both Rappe–Rabe–Kaxiras–Joannopoulos (RRKJ) ultrasoft pseudopotentials and new developed pseudopotentials. Computed GIPAW chemical shifts were critically compared with the experimental ones. A good agreement between experimental and computed multinuclear chemical shifts was obtained

A Solid−Gas Route to Polymorph Conversion in Crystalline [Fe^II(η⁵-C₅H₄COOH)₂]. A Diffraction and Solid-State NMR Study

Crystalline form I (monoclinic) and form II (triclinic) of ferrocene dicarboxylic acid [Fe(η5-C5H4COOH)2] have been employed in solid−gas reactions at room temperature with the gaseous bases NH3, NH2(CH3), and NH(CH3)2. The two crystal forms behave in exactly the same way in the solid−gas reaction, generating the same products, identified as the anhydrous crystalline salts [NH4]2[Fe(η5-C5H4COO)2] (1), [NH3CH3]2[Fe(η5-C5H4COO)2] (2), and [NH2(CH3)2]2[Fe(η5-C5H4COO)2] (3). Interestingly though, all these crystals revert via vapor release exclusively to the metastable crystalline form I. Starting materials and products have been investigated by single-crystal and powder diffraction and by 13C, 15N CPMAS and 1H MAS methods

Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

Four lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray powder and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (1H MAS and CRAMPS, and 13C and 15N CPMAS): all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base

A Solid−Gas Route to Polymorph Conversion in Crystalline [Fe^II(η⁵-C₅H₄COOH)₂]. A Diffraction and Solid-State NMR Study

Crystalline form I (monoclinic) and form II (triclinic) of ferrocene dicarboxylic acid [Fe(η5-C5H4COOH)2] have been employed in solid−gas reactions at room temperature with the gaseous bases NH3, NH2(CH3), and NH(CH3)2. The two crystal forms behave in exactly the same way in the solid−gas reaction, generating the same products, identified as the anhydrous crystalline salts [NH4]2[Fe(η5-C5H4COO)2] (1), [NH3CH3]2[Fe(η5-C5H4COO)2] (2), and [NH2(CH3)2]2[Fe(η5-C5H4COO)2] (3). Interestingly though, all these crystals revert via vapor release exclusively to the metastable crystalline form I. Starting materials and products have been investigated by single-crystal and powder diffraction and by 13C, 15N CPMAS and 1H MAS methods

Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

Four lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray powder and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (1H MAS and CRAMPS, and 13C and 15N CPMAS): all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base

Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

Four lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray powder and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (¹H MAS and CRAMPS, and ¹³C and ¹⁵N CPMAS): all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base

Molecular Salts of Anesthetic Lidocaine with Dicarboxylic Acids: Solid-State Properties and a Combined Structural and Spectroscopic Study

Four lidocaine molecular salts of dicarboxylic acids (oxalic, fumaric, malonic, and succinic) were synthesized and characterized by a combined use of X-ray powder and single-crystal diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy (FT-IR), and solid-state NMR (¹H MAS and CRAMPS, and ¹³C and ¹⁵N CPMAS): all molecular salts show a dramatic increase in their melting point with respect to both lidocaine and lidocaine hydrochloride, and a higher dissolution rate and thermodynamic solubility in physiological solution with respect to the free base

Sorption properties toward environmentally important VOCs of half-sandwich Ru(II) complexes containing perylene bisimide ligands

<p>Two py-functionalized perylene bisimide ligands were synthesized and used to make bimetallic half-sandwich Ru(II) complexes. These were characterized by IR, ¹H NMR, ¹³C CPMAS SSNMR spectroscopy, and elemental analysis. The complexes are wheel-and-axle (waa) compounds, where the axle is the divergent ligand and the wheels are the [(p-cymene)RuCl₂] units. The complexes, but not the free ligands, showed absorption of volatile organic compounds such as toluene and xylenes through heterogeneous solid/gas uptakes. The reactivity is ascribable to the waa geometry, likely by an upset of the high stacking characterizing the crystalline frameworks of the free ligands. The kinetic profiles of the uptake reactions were determined.</p

Pseudopolymorphism Driven by Stoichiometry and Hydrated/Anhydrous Reagents: The Riveting Case of Methyl Gallate·l‑Proline

Among GRAS molecules, α-amino acids have been extensively used to produce molecular salts and cocrystals of APIs thanks to their nontoxicity, ready availability, cheapness, and their zwitterionic nature. Here we report on the use of both anhydrous and hydrated l-proline (Pro and Pro·H2O, respectively) with methyl gallate (MG) to selectively obtain by mechanochemical methods anhydrous and hydrated cocrystals: MG·Pro2 and MG2·Pro2·H2O, respectively. The two new forms were characterized by means of single-crystal and powder X-ray diffraction (SCXRD and PXRD), solid-state nuclear magnetic resonance (SSNMR), DSC, and TGA. Interestingly, the choice of the starting material together with the stoichiometry drives the formation of the cocrystal toward either the anhydrous or the hydrate form: the anhydrous form could be obtained only on starting from anhydrous Pro, whereas the hydrate could be obtained with Pro·H2O or with Pro by matching the correct stoichiometry. An energy framework analysis allowed us to rationalize this peculiar water uptake behavior in terms of both the relative interaction strengths of proline–proline, proline–water, and proline–methyl gallate pairs and packing features