Advances in elucidating mechanochemical complexities via implementation of a simple organic system

Mechanochemistry is becoming increasingly popular amongst both the academic and industrial communities as an alternative method for inducing physical and chemical reactions. Despite its rapidly expanding application, little is understood of its mechanisms, greatly limiting its capacity. In the present work the application of specialty devices allowed submission of the simple organic system, α-glycine + β-malonic acid, to isolated shearing and impact treatment. In doing so, unique products were observed to result from each of these major mechanical actions; shear inducing formation of the known salt, glycinium semi-malonate (GSM), and impact yielding formation of a novel phase. Correlation of these isolated treatments with a more common ball mill indicated two unique regions within the milling jar, each characterised by varying ratios of shear and impact, leading to different products being observed. It is widely accepted that, particularly when considering organic systems, mechanical treatment often acts by inducing increases in local temperature, leading to volatilisation or melting. A combination of DSC and TGA were used to investigate the role of temperature on the system in question. Invariably, heating induced formation of GSM, with evidence supporting a eutectic melt, rather than a gas-phase reaction. Shear heating alone is unable to describe formation of the novel phase obtained through impact treatment. By considering the formation and character of mechanically produced tablets, a model is described that may account for formation of this novel phase. This system and methodology for mechanochemical study offers intriguing opportunities for continued study of this widely used and exciting field.</p

Observation of subtle dynamic transitions by a combination of neutron scattering, X ray diffraction and DSC A case study of the monoclinic L cysteine

The paper illustrates the benefit of combining several experimental techniques incoherent elastic and inelastic neutron scattering, DSC, and X ray diffraction to study subtle dynamic transitions in a biologically important system, probing a broad time frequency range of the molecular motions in a wide tem perature interval of 2 300 K. As a case study the crystalline form a monoclinic polymorph of L cysteine NH3 CH CH2SH COO amp; 8722; an essential amino acid has been selected. Crystals of amino acids are widely used to mimic important structural and dynamic features of peptides. The conformational lability of cysteine and the dynamics of the thiol side chains are known to account for various phase transitions in the crystalline state and for the conformational transitions important for the biological function in the peptides. The effect of temperature on the monoclinic polymorph of L cysteine, metastable at ambient conditions, has been studied for the first time. A dynamical transition at about 150 K, marking a crossover of the molecular fluctuations between harmonic and non harmonic dynamical regimes, was evidenced by evaluating the evolution of the mean square displacement obtained from the elastic fixed window approach using the backscattering spectrometer IN10 located at the ILL. Although this transition does not manifest itself in the DSC, it was clearly observed by incoherent inelastic neutron scattering. By analyzing the dynamical susceptibility contribution amp; 967; amp; 8242; amp; 8242; amp; 969; obtained using IN6 also at ILL we were able to evidence another relaxation process at a different time scale. The disordered soft L cysteine structure has an excess of inelastic scattering at about 3 meV, analogous to the boson peak observed in glass like materials and proteins. High precision X ray diffraction has revealed an anomaly in the changes of selected unit cell parameters and volume at about 240