Shape Preserving Single Crystal to Amorphous to Single Crystal Polymorphic Transformation Is Possible.

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)2 which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.

Magnetic, Photo- and Electroluminescent: Multifunctional Ionic Tb Complexes.

In the search for new multifunctional materials, particularly for application in solid-state lighting, a set of terbium salicylato (Sal) complexes of general composition [Cat][Tb(Sal)4] with the commonly ionic liquid-forming (IL) cations [Cat] = (2-hydroxyethyl)trimethylammonium (choline) (Chol+), diallyldimethylammonium (DADMA+), 1-ethyl-3-methylimidazolium (C2C1Im+), 1-butyl-3-methylimidazolium (C4C1Im+), 1-ethyl-3-vinylimidazolium (C2Vim+), and tetrabutylphosphonium (P4444+) were synthesized. All Tb compounds exhibit strong green photoluminescence of high color purity by energy transfer from the ligand in comparison with what the analogous La compounds show, and quantum yields can reach up to 63% upon ligand excitation. When excited with an HF generator, the compounds show strong green electroluminescence with the same features of mission. The findings promise a high potential of application as emitter materials in solid-state lighting. As an additional feature, the Tb compounds show a strong response to applied external fields, rendering them multifunctional materials.

Terbium chelation, a specific fluorescent tagging of human transferrin. Optimization of conditions in view of its application to the HPLC analysis of carbohydrate-deficient transferrin (CDT).

Transferrin (Tf) is the major iron-transporting protein in the human body and, for this reason, has been extensively studied in biomedicine. This protein undergoes a complex glycosylation process leading to several glycoforms, some of which are important in the diagnosis of alcohol abuse and of congenital glycosylation defects under the collective name of carbohydrate-deficient transferrin (CDT). Exploiting the Tf ability to bind not only iron but also other ions, specific attention has been devoted to binding activity towards Tb3+, which was reported to greatly enhance its intrinsic fluorescence upon the interaction with Tf. However, the structural properties of the Tb3+-Tf complex have not been described so far. In the present work, the formation of the Tf-Tb3+ complex has been investigated by the employment of several biophysical techniques, such as fluorescence resonance energy transfer (FRET), "native" mass spectrometry (MS), and near-UV circular dichroism (CD). Each method allowed the detection of the Tf-Tb3+ complex, yielding a specific signature. The interaction of Tb3+ with Fe3+-free Tf (apoTf) has been described in terms of stoichiometry, affinity, and structural effects in comparison with Fe3+. These experiments led to the first direct detection of the Tf-Tb3+ complex by MS, indicating a 1:2 stoichiometry and allowing the investigation of structural effects of metal binding. Either Tb3+ or Fe3+ binding affected protein conformation, inducing structural compaction to a similar extent. Nevertheless, near-UV CD and pH-dependence profiles suggested subtle differences in the coordination of the two metals by Tf side chains. Experimental conditions that promote complex formation have been identified, highlighting the importance of alkaline pH and synergistic ions, such as carbonate. On the basis of these studies, sample pretreatment, separation, and detection conditions of a high-performance liquid chromatographic method for CDT analysis are optimized, achieving relevant increase (by a factor of ∼3) of analytical sensitivity. Graphical abstract Schematic representation of HPLC-separated transferrin glycoforms detected by fluorescence emission of the terbium ions bound to the protein.

Optical Study of Diamine Coupling on Carboxyl-Functionalized Mesoporous Silicon.

A functionalization strategy, consisting of a silylation reaction by acrylic acid followed by diamine coupling, preserves and stabilizes the photoluminescence (PL) of porous silicon (pSi) microparticles suspended in ethanol. We found that under the condition of efficient amine coupling, besides the orange emission typical of the native pSi, an emission band in the blue region appears. The investigation of the interaction between pSi and diamine shows that diamine quenches and shifts the orange band meanwhile it induces an increase of the intensity of the blue one. PL lifetimes of the orange and blue bands are in the micro and nano second range, respectively. These values and their wavelength dependence clearly prove that the two bands have different origin: quantum confinement and nitrogen impurities introduced at silicon/silicon oxide interface, respectively. Thus, they can be used to discriminate between the pSi microparticles obtained by silylation, which expose carboxylic groups and the pSi microparticles after the diamine coupling, which bear amine functionalities at the surface. The increase in the stability of the PL emission of pSi in aqueous solution after functionalization, with quantum yields of the order of 1­2%, supports the use in biological systems of these brightly emitting, largely porous microparticles, bearing positive or negative surface charge.

Enhanced stability and complex phase behaviour of organic-inorganic green-emitting ionic manganese halides.

Light-emitting materials based on earth-abundant metals, such as manganese hold great promise as emitters for organic lighting devices. In order to apply such emitter materials and, in particular, to overcome the problem of self-quenching due to cross-relaxation, we investigated a series of tetrabromidomanganate ([MnBr4]2-) salts with bulky tetraalkylphosphonium counter cations [Pnnn]+, namely [Pnnnn]2[MnBr4] (n = 4 (1), 6 (2) and 8 (3)), which can be obtained by a straightforward reaction of the respective phosphonium bromide and MnBr2. Variation of the cation size allows control of the properties of the resulting ionic materials. 1 and 3 qualify as ionic liquids (ILs), where 1 features a melting point of 68 °C, and 3 is liquid at room temperature and even at very low temperatures. Furthermore, 1 and 2 show the formation of higher-ordered thermotropic mesophases. For 1 a transition to a thermodynamically metastable smectic liquid crystalline phase can be observed at room temperature upon reheating from the metastable glassy state; 2 appears to form a plastic crystalline phase at ∼63 °C, which persists up to the melting point of 235 °C. The photoemission is greatly affected by phase behaviour and ion dynamics. A photoluminescence quantum yield of 61% could be achieved, by balancing the increase in Mn2+-Mn2+ separation and reducing self-quenching through increasingly large organic cations which leads to adverse increased vibrational quenching. Compared to analogous ammonium compounds, which have been promoted as ̈inorganic hybrid perovskites̈, the phosphonium salts show superior performance, with respect to photoluminescent quantum yield and thermal and air/humidity stability. As the presented compounds are not sensitive to the atmosphere, in particular moisture, and show strong visible electroluminescence in the green region of light, they are important emitter materials for use in organic light-emitting devices.

Asialo-transferrin: Biochemical aspects and association with alcohol abuse investigation.

Asialo-human transferrin (asialo-hTf) is a glycoform of the human serum protein transferrin characterized by the lack of the sialic acid (SA) terminal unit. It is known that glycosylation micro-heterogeneity and the presence of SA are strongly involved in protein functioning and pathophysiological activities. Some hTf glycoforms are valuable biomarkers for the detection of both genetic defects of glycosylation and/or sialoform distribution changes. The detection of the carbohydrate deficient transferrin (CDT) glycoforms is currently a widely employed method for the diagnosis of chronic alcohol abuse. The physiological significance of asialo-hTf is still unclear, despite its important biological implications. The current knowledge suggests that asialo-hTf may be involved in regulation of iron transport and release at the hepatic level, which, consequently, could strongly be affected by alcohol consumption. For these reasons, a deeper understanding of asialo-hTf structure and its physiological role is required, and an improved method of its analysis would favor the detection of both chronic abuse and other habits of alcohol intake and/or misuse. Thus, suitable analytical methods possessing higher sensitivity and specificity in comparison with the currently available techniques are certainly recommended. The present review summarizes the studies on asialo-hTf structure, roles, and detection techniques mainly in relation to its possible use as a potentially additional useful biomarker of alcohol abuse, and underlines its prospective value as a forensic and diagnostic tool.