M. Ramos Silva

One-step synthesis of dipyrromethanes in water

In this communication we describe the first results of an efficient synthesis of β-free-dipyrromethanes in water. This new method affords very pure products in moderate to high yields, using a cheap, non-toxic, environment friendly solvent, in a one-step procedure from pyrrole and carbonyl compounds, needing little or no work up procedures.

Erythritol: Crystal growth from the melt

The structural changes occurring on erythritol as it is cooled from the melt to low temperature, and then heated up to the melting point have been investigated by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM), X-ray powder diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). By DSC, it was possible to set up the conditions to obtain an amorphous solid, a crystalline solid, or a mixture of both materials in different proportions. Two crystalline forms have been identified: a stable and a metastable one with melting points of 117 and 104 degrees C, respectively. The fusion curve decomposition of the stable form revealed the existence of three conformational structures. The main paths of the crystallization from the melt were followed by PLTM. The texture and colour changes allowed the characterization of the different phases and transitions in which they are involved on cooling as well as on heating processes. The type of crystallization front and its velocity were also followed by microscopic observation. These observations, together with the data provided by PXRD, allowed elucidating the transition of the metastable form into the stable one. The structural changes occurring upon the cooling and subsequent heating processes, namely those arising from intermolecular hydrogen bonds, were also accompanied by infrared spectroscopy. Particular attention was given to the spectral changes occurring in the OH stretching region.

Pyrrolidine-based amino alcohols: novel ligands for the enantioselective alkylation of benzaldehyde

A series of easily obtained pyrrolidine-based -amino alcohols derived from tartaric acid and primary amines was synthesized and used as chiral ligands in the enantioselective alkylation of benzaldehyde. Using diethylzinc, 1-phenyl-1-propanol was obtained with enantiomeric excesses of up to 80% when (3S,4S)-N-(1-naphthylmethyl)-3,4-dihydroxypyrrolidine was used. The nature of the N-substituent on the ligand, as well as the reaction temperature proved to significantly influence reaction product distribution as well as the enantiomeric excess of the chiral alcohol.

Novel erbium(III) complexes with 2,6-dimethyl-3,5-heptanedione and different N,N-donor ligands for ormosil and PMMA matrices doping

Three novel complexes, [Er(dmh)3(bipy)], [Er(dmh)3bath] and [Er(dmh)3(5NO2phen)], with 2,6-dimethyl-3,5-heptanedione (Hdmh) as the main sensitizer and either 2,2′-bipyridine (bipy), bathophenanthroline (bath) or 5-nitro-1,10-phenanthroline (5NO2phen) as synergistic ligands were synthesized. Upon excitation at the maximum absorption of the ligands, the complexes show the characteristic near-infrared (NIR) luminescence of the Er3+ ions, due to efficient energy transfer from the ligands to the central Er3+ ion via the antenna effect. Single crystals were grown and their structures were determined showing different Er–N distances. The compound with shorter Er–N distances, [Er(dmh)3(5NO2phen)], was found to be the best light harvester and the best for transferring the energy to the lanthanide among the three studied compounds. Finally, the novel complexes have been assessed for their application in sol–gel and polymer-based waveguides and optical amplifiers through their inclusion into ormosil and polymethylmethacrylate matrices. The dispersion was successful in the bipy and 5NO2phen cases, with the properties of the hybrid materials mimicking those of the pure complexes.

A thermodynamic based approach on the investigation of a diflunisal pharmaceutical co-crystal with improved intrinsic dissolution rate

A thermodynamic based approach is used to investigate diflunisal+nicotinamide binary and solution mixtures. A 2:1 co-crystal could be prepared by liquid assisted ball mill grinding and by solution crystallization from ethanol. The diflunisal+nicotinamide+ethanol ternary phase diagram points out conditions for co-crystal scaling-up. From the diflunisal+nicotinamide binary phase diagram, besides identification of the co-crystal stoichiometry, two additional useful binary compositions, eutectic mixtures, were characterized. From a solution enthalpy based approach, the enthalpic stabilization of the co-crystal relative to the pure solid components is quantified. Intrinsic dissolution rate, IDR, in test conditions consistent with USP requirements, including those referred in the diflunisal tablet monograph, were carried out, indicating that the co-crystal improves diflunisal IDR by about 20%. The systematic study of diflunisal+nicotinamide mixtures presented in this work is of particular interest due to the relevance of diflunisal, both as a non-steroidal anti-inflammatory drug and also due to the potentiality of orally administrated diflunisal in familial amyloid polyneuropathy.

Magnetic moments and magnetic site susceptibilities in Mn5Si3

Polarized neutron diffraction has been used to determine the manganese magnetic moments aligned by magnetic fields applied parallel to the [001] axis in the antiferromagnetic phases of Mn5Si3. It has been found that in the two antiferromagnetic phases which exist below TN the magnetic moments on the manganese sites which can be aligned by a magnetic field all have the same order of magnitude, although in the antiferromagnetic structures the ordered moments are very different. The transition, on cooling, from the AF2 to the AF1 phase is accompanied by a sharp decrease in the susceptibilities of all the sites. This uniform decrease is not consistent with disordered local moments on the sites which do not have ordered moments, but can be understood using the same criteria for stability of Mn moments as have been invoked for manganese rare-earth compounds (Ballou R, Lacroix C and Nunez Regueiro M D 1991 Phys. Rev. Lett. 66 1910).

Crystal structure of tetrakis (μ-betaine-O,O′) dichloro-dicopper(II) dichloride tetrahydrated

Abstract[Cu2(bet)4Cl2]Cl2·4H2O (bet = betaine: IUPAC name: trimethylammonioacetate) is monoclinic, space group P21/c, a = 11.0510(10) Å, b = 14.7140(4) Å, c = 11.1620(15) Å, β = 107.40(2)°. The dinuclear copper(II) cation [Cu2(bet)4Cl2]2+ is counterbalanced by two naked Cl− ions. The copper(II) ions have a square bipyramidal environment with oxygen atoms from the acetato groups in the basal planes and a chlorine and a copper atom occupying the apical positions. The metal atoms are μ2-bridged by four acetato groups and the molecular symmetry is close to C2h. The two symmetry-independent chelating betaine molecules are present in their zwitterionic, neutral form.

Structure, luminescence and magnetic properties of an erbium(III) β-diketonate homodinuclear complex

The photoluminescence properties and field-induced single-molecule-magnetic behavior of a novel erbium(III) β-diketonate homodinuclear complex, [Er2(nd)6(μ-bpm)] (nd = 2,4-nonanedione and bpm = 2,2′-bipyrimidine), are presented. On the basis of structural data, ab initio calculations using the SO-CASSCF method have been performed so as to gain insight into the spin-relaxation mechanism, giving evidence of the nature of the mJ ground state and the orientation of the related magnetic anisotropy axis. The overlap integrals between the natural spin orbitals (NSOs) of the mononuclear fragments, related to the magnitude of the antiferromagnetic exchange, show that the two fragments have no magnetic interaction.

Crystal and Molecular Structure of dl-Serine Hydrochloride Studied by X-Ray Diffraction, Low-Temperature Fourier Transform Infrared Spectroscopy and DFT(B3LYP) Calculations

The structure of dl-serine.HCl was studied by three complementary techniques. Experimental Fourier transform infrared (FT-IR) spectra of pure NH/OH polycrystalline dl-serine.HCl [HO-CH2-CH(NH3+)-COOH.Cl(-)] and the respective deuterated derivatives [ND/ODAlcohol/Acid (<10% and ca. 60% D)] were recorded in the region 4000-400 cm(-1) in the temperature range 300-10 K and interpreted. The assignments were confirmed by comparison with the vibrational spectra of crystalline dl- and l-serine zwitterions [HO-CH 2-CH(NH3+)-COO(-)]. Further insight into the structure of the title compound was provided by theoretical DFT(B3LYP)/6-311++G(d,p) calculations of the infrared spectra and energies of 13 different conformers. Potential energy distributions resulting from normal co-ordinate analysis were calculated for the most stable conformer ( I) in its hydrogenated and deuterated modification. Frequencies of several vibrational modes were used in the estimation of enthalpies of individual H-bonds present in the crystal, using empirical correlations between enthalpy and the frequency shift that occurs as a result of the establishment of the H-bonds. X-ray crystallography data for dl-serine.HCl were recorded for the first time and, together with the experimental vibrational spectra and the theoretical calculations, allowed a detailed characterization of its molecular structure.

Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxyl-ate.

In the title compound, C9H13NO2, there are two independent molecules per asymmetric unit. The molecules are very similar and almost planar, with the ethoxycarbonyl group anti to the pyrrole N atom. The two independent molecules are joined into dimeric units by strong hydrogen bonds between NH groups and carbonyl O atoms.