Leping Dang

Crystallization control of thermal stability and morphology of hen egg white lysozyme crystals by ionic liquids.

Ionic liquids (ILs) exhibit a variety of properties that make them attractive additives for biomaterials. 1-Butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim]BF(4)), 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl), 1-butyl-3-methylimidazolium bromide ([C(4)mim]Br), and 1,3-dimethylimidazolium iodine([bmim]I), as additives during lysozyme crystallization, were tested for their effects on the thermal stability and morphology of lysozyme crystals obtained. [C(4)mim]Cl was chosen to evaluate the effect of IL addition concentration on the thermal stability of lysozyme. It is shown that the characteristic peak temperature and endothermic enthalpy values (DeltaH) for denaturation increase with increasing addition concentration. As for the degradation, peak temperatures decrease, whereas endothermic enthalpy values markedly increase with the rise of [C(4)mim]Cl addition concentration. In the case of adding [C(4)mim]BF(4), [C(4)mim]Br, and [bmim]I, similar thermal behaviors of lysozyme crystals were observed. The effect of ILs on thermal behaviors of lysozyme can be attributed to enhancing crystal contacts, changing conformational stability, or interaction among molecules, as evidenced by difference in crystal growth morphology. This study is especially helpful in controlling the thermal stability of lysozyme crystals and in gaining initial insight into potential crystallization conditions for prescreening ILs that stabilize the protein and other macromolecule crystals.

The in situ monitoring of the transformation of moxidectin ethanol solvate to form I in an ethanol–water mixture

Moxidectin is a single-component and semisynthetic macrocyclic lactone antibiotic, which has been widely used in the prevention and treatment of parasites in farm animals. In this paper, the transformation of ethanol solvate to form I of moxidectin in an ethanol–water mixture was studied. Offline methods and online instruments were used to monitor and identify the transformation process, and the influences of water content and temperature were discussed. It is noted that the transformation kinetics are highly sensitive to both the solvent composition and temperature and the transformation rate is a function of the ethanol content in aqueous ethanol mixtures. The solvent-mediated polymorphic transformation mechanism from ethanol solvate to form I was suggested, and the process is controlled by the nucleation and growth rate of the stable form. Understanding these effects can aid optimization and improve process control in the crystallization of moxidectin.

Thermodynamic analysis of lipoic acid crystallized with additives

Differential scanning calorimetry (DSC) was used as a screening technique to study the interaction between lipoic acid and amino acids. The samples containing lipoic acid and amino acids were prepared by two different methods (milling method and cooling crystallization method). Firstly, cooling method was used to prepare the sample with amino acids as additives. DSC results indicated that only phenylalanine has some interaction with lipoic acid. Further, in order to study the interaction between lipoic acid and phenylalanine, another method (milling method) was used to prepare the sample containing phenylalanine, and the effect of sample preparation methods was studied through IR analysis and the X-ray powder diffraction. On the basis of above researches, the possible interaction mechanisms between lipoic acid and phenylalanine were proposed.

Preparation, crystal structure and solution-mediated phase transformation of a novel solid-state form of CL-20

Herein, the 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) acetonitrile solvate, a novel solid-state form of CL-20, was first discovered and characterized by various analytical techniques. The results of single-crystal X-ray diffraction (SCXRD) indicate that it is a channel-type solvate. Intermolecular interactions inside the crystal were investigated to elucidate the assembly behaviors with the assistance of the Hirshfeld surface analysis. The solvation profile and solubility data were determined to identify the thermodynamic stability of the acetonitrile solvate and form e. The solution-mediated phase transformation (SMPT) from the acetonitrile solvate to form e in acetonitrile–chloroform mixed solvents was online monitored by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and in situ Raman spectroscopy. The results reveal that the nucleation and growth of the form e is the rate-determining step. Moreover, the Johnson–Mehl–Avrami (JMA) model was employed to obtain deeper insights into the transformation kinetics. Furthermore, the effects of solvent composition, solid loading, and agitation rate were examined. This study provides an alternative approach for obtaining the desired form e crystals and lays a foundation for the optimization of the crystallization process in the future.

Stability and dehydration kinetics of the monohydrate racemic tartaric acid

Racemic tartaric acid (race-TA) exists in the solid state as a monohydrate and an anhydrous. There is a large difference in their bioavailability and product performance. In this paper, the stability of monohydrate race-TA was investigated. The results show that water activity is the major factor determining the stability of race-TA, monohydrate or anhydrous, which crystallizes from the mixed solvent at certain temperature. Meanwhile, the effect of temperature on the stability of monohydrate race-TA was studied using DSC, which is important to control the stability of monohydrate race-TA during drying and storage. Finally, the dehydration kinetics of monohydrate race-TA was investigated in nitrogen purge using TG–DSC. Based on the result, the kinetic parameters (activation energy and pre-exponential factor) and the most probable kinetic model that gives the best description of the dehydration process for monohydrate race-TA are obtained.

Effects of inorganic additives on polymorphs of glycine in microdroplets

Salt-dependent polymorphic control of glycine was investigated by using the microdroplet technique in this work. Sodium chloride (NaCl) was chosen as the additive to probe the influence of inorganic ions on the polymorphic nucleation of glycine. The thermodynamics and nucleation kinetics of glycine polymorphs in microdroplets were systematically analyzed based on the microdroplet technique. The crystal structures of the polymorphs were confirmed by powder X-ray diffraction (PXRD). The results illustrate that the critical concentration of NaCl required to induce the pure γ-form in the microdroplets is lower than that in the conventional method, which means that the microdroplet technique is more sensitive for the control of polymorph nucleation. The polymorphic nucleation selectivity of glycine was then discussed in view of classical nucleation theory. The results demonstrate that NaCl reduces the nucleation energy barrier of the γ-form of glycine, and for the same form of glycine, crystallization by the conventional method has a higher interfacial tension than in microdroplets.

Manipulating crystallization in lysozyme and supramolecular self-arrangement in solution using ionic liquids

Manipulating crystallization for macromolecule using ionic liquids (ILs) as an additive has received great attention, but how ILs accurately control their formation and crystallization pathway remains unclear. Here, we aim to illuminate the role of ILs on the solution chemistry of macromolecules by investigating their effects on the crystallization of lysozyme. The solubility findings show ILs changed intermolecular contacts, leading to lysozyme supramolecular repulsive interactions being induced or attractive interactions enhanced. Lysozyme was crystallized in the form of tetragonal crystals in the presence of [C4mim]BF4 (1-butyl-3-methylimidazolium tetrafluoroborate), [C4mim]Cl (1-butyl-3-methylimidazolium chloride) and [C4mim]Br (1-butyl-3-methylimidazolium bromide), while it was crystallized in the form of monoclinic crystals in the presence of [dmim]I (1,3-dimethylimidazolium iodine). Compared with that in the absence of ILs, lysozyme in the presence of [C4mim]Cl and [dmim]I contained a decreased α-helix content, but increased β-sheet content. The presence of [dmim]I also caused the β-turn content to increase and random coil content to decrease. This demonstration shows the formation of crystal nucleus is involved in transition at the protein secondary structure level, which may contribute to a better understanding of the role of ILs in the crystallization of bio-macromolecular materials and to developing a strategy to produce new bio-macromolecular materials using ILs.