Characterization and thermogravimetric analysis of lanthanide hexafluoroacetylacetone chelates

Evaluation of the Sublimation Process of Some Purine Derivatives: Sublimation Rate, Activation Energy, Mass Transfer Coefficients and Phenomenological Models

Caffeine and theophylline are compounds with important applications in the pharmaceutical industry and other fields of the chemical industry. These purine derivatives have simple chemical structures, therefore, the evaluation of their sublimation process contributes to the development of mass transfer analysis methods that can later be applied to other compounds with more complex structures. With the help of thermogravimetric analysis in isothermal conditions, the kinetic study of the sublimation of caffeine and theophylline, along with the evaluation of kinetic parameters (activation energy and the pre-exponential factor), was carried out. Global mass transfer coefficients were determined, which vary for caffeine between 53 × 10^-8 and 631 × 10^-8 mol/s·m²·Pa, and for theophylline between 68 × 10^-8 and 441 × 10^-8 mol/s·m²·Pa. The dimensionless equations of the form: Sh=a+b·Rec·Scd have been proposed, which allow the determination of individual mass transfer coefficients at temperatures between 130 and 160 °C for caffeine and between 170 and 200 °C for theophylline.

Characterization of an exopolysaccharide produced by Enterobacter sp. YU16-RN5 and its potential to alleviate cadmium induced cytotoxicity in vitro

Natural biopolymers have gained remarkable attention for bioremediation particularly in heavy metal removal and oil degradation due to their non-toxic nature and lack of secondary pollution. The exopolysaccharides (EPS) produced by the bacteria have become an important class of biopolymers that are employed in bioremediation. The bacteria isolated from the rhizospheric soil have higher metal tolerance and their EPS are effective in biosorption of heavy metals. Here, we report the characterization of an EPS (EPS-RN5) isolated from the root nodule-associated bacteria, Enterobacter cancerogenus strain YU16-RN5 and its heavy metal biosorption abilities. The bacteria isolated from the West coast of India was cultured in yeast extract mannitol (YEM) medium for EPS extraction and to study the production kinetics on a temporal scale. The biochemical composition, rheological properties and thermostability of EPS-RN5 was characterized by standard methods. The biosorption potential of EPS-RN5 against the selected heavy metals was analyzed by employing the inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique. Further, cell culture experiments were used to test the role of EPS-RN5 in reducing the cytotoxicity exerted by the heavy metals in vitro using a human embryonic kidney cell line (HEK 293T). The bacteria showed good growth in YEM media and the maximum EPS yield was 1800 mg/L at 96 h. The molecular weight of EPS-RN5 was 0.7 × 106 Da and it contained 61.5% total sugars and 14.5% proteins. The monosaccharide composition of the EPS included glucose, sorbose and galactose in the ratio 0.25:0.07:1.0. The EPS-RN5 showed high thermal stability with a degradation temperature of 273 °C. Rheological analysis revealed the non-Newtonian behavior, with pseudoplastic characteristics. The EPS-RN5 efficiently absorbed cadmium and other heavy metals such as mercury, strontium, copper, arsenic, and uranium. In vitro studies revealed significant protective effect against the cadmium-induced cytotoxicity in HEK 293T cells. These results indicate the potential applications of EPS-RN5.

Modeling Solid State Stability for Speciation: A Ten-Year Long Study

Speciation studies are based on fundamental models that relate the properties of biomimetic coordination compounds to the stability of the complexes. In addition to the classic approach based on solution studies, solid state properties have been recently proposed as supporting tools to understand the bioavailability of the involved metal. A ten-year long systematic study of several different complexes of imidazole substituted ligands with transition metal ions led our group to the definition of a model based on experimental evidences. This model revealed to be a useful tool to predict the stability of such coordination complexes and is based on the induced behavior under thermal stress. Several different solid state complexes were characterized by Thermally Induced Evolved Gas Analysis by Mass Spectrometry (TI-EGA-MS). This hyphenated technique provides fundamental information to determine the solid state properties and to create a model that relates stability to coordination. In this research, the model resulting from our ten-year long systematic study of complexes of transition metal ions with imidazole substituted ligands is described. In view of a systematic addition of information, new complexes of Cu(II), Zn(II), or Cd(II) with 2-propyl-4,5-imidazoledicarboxylic acid were precipitated, characterized, and studied by means of Thermally Induced Evolved Gas Analysis performed by mass spectrometry (TI-EGA-MS). The hyphenated approach was applied to enrich the information related to thermally induced steps, to confirm the supposed decomposition mechanism, and to determine the thermal stability of the studied complexes. Results, again, allowed supporting the theory that only two main characteristic and common thermally induced decomposition behaviors join the imidazole substituted complexes studied by our group. These two behaviors could be considered as typical trends and the model allowed to predict coordination behavior and to provide speciation information.

Synthesis, thermogravimetric analysis and enthalpy determination of lanthanide β-diketonates

This work reports thermodynamic characterizations of lanthanide β-diketonates for use in nuclear fission product separation. Adsorption and sublimation enthalpies have been shown to be linearly correlated, therefore there is motivation to determine sublimation thermodynamics. An isothermal thermogravimetric analysis method is employed on fourteen lanthanide chelates for the ligands 2,2,6,6-tetramethyl-3,5-heptanedione and 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione to determine sublimation enthalpies. No linear trend is seen across the series; values show a cyclical nature, possibly indicating a greater influence of chemisorption for some complexes and less of a role of physisorption in dictating adsorption differences between lanthanides in the same series. This is in line with previous reports in terms of the chromatographic separation order of the lanthanides. The results reported here can be used to manipulate separations parameters and column characteristics to better separate these lanthanide chelates. Fourteen chelates of the ligand 1,1,1-trifluoro-2,4-pentanedione are also thermally characterized but found to not sublime and be undesirable for this method. Additionally, all chelates are characterized by constant heating thermogravimetric analysis coupled with mass spectrometry, melting point analysis, elemental analysis and FTIR.

Structural Analysis of the Complexation of Uranyl, Neptunyl, Plutonyl, and Americyl with Cyclic Imide Dioximes

Knowledge-based design of extracting agents for selective binding of actinides is essential in stock-pile stewardship, environmental remediation, separations, and nuclear fuel disposal. Robust computational protocols are critical for in depth understanding of structural properties and to further advance the design of selective ligands. In particular, rapid radiochemical separations require predictive capabilities for binding in the gas phase. This study focuses on gas-phase binding preferences of cyclic imide dioximes to uranyl, neptunyl, plutonyl, and americyl. Structural properties, electron withdrawing effects, and their effects on binding preferences are studied with natural bond-order population analysis. The aromatic amidoximes are found to have a larger electron-donation effect than the aliphatic amidoximes. It is also found that plutonyl is more electron withdrawing than uranyl, neptunyl, and americyl when bound to the cyclic imide dioximes studied.