Abstract
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.
Highlights
Speciation studies can be related by setting up fundamental models based on properties of biomimetic coordination compounds that provide the stability of the complexes in order to understand the bioavailability of the involved metal.Speciation models are mainly based on the classic approach by studies in different solution conditions
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)
It is well known that the thermal stability of a complex in the solid state is inversely proportional to the stability of the same complex in aqueous solution
Summary
Speciation studies can be related by setting up fundamental models based on properties of biomimetic coordination compounds that provide the stability of the complexes in order to understand the bioavailability of the involved metal. Speciation models are mainly based on the classic approach by studies in different solution conditions. It is well known that the thermal stability of a complex in the solid state is inversely proportional to the stability of the same complex in aqueous solution. Metal complexes containing imidazoledicarboxylate ligands have been extensively studied because of their interesting properties. They are recognized to be realistic models as biomimetic simulators because of their characteristics, such as versatile structures useful for flexible tailoring. Additional interest has been demonstrated because of promising applications in gas storage, catalysis, Molecules 2019, 24, 3013; doi:10.3390/molecules24163013 www.mdpi.com/journal/molecules
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