| Περίληψη: | The general aim of the present Thesis was the development, characterization or/and study of novel sensors and scavengers that could be potentially used in “smart” food packaging materials.
The Thesis is divided in two main sectors. In the first one, which constituted research activities of the Research Project “Nanobarrier”, we focused on the development/study of temperature sensors and O2/moisture scavengers and in the meticulous investigation of ascorbic acid, a basic component of the temperature sensors and O2/moisture scavengers. In order to ensure the consumers’ health safety in the case of a potential migration of the sensors/scavengers into food, migration release study was also performed. The easy oxidation of ascorbic acid, however, could lead to bottlenecks concerning its migration release study. To that end, several parameters were examined. In terms of the development of novel O2/moisture scavengers, iron(II) based oxygen/moisture scavengers were proposed and their oxygen/moisture scavenging ability was evaluated.
Spin Crossover (SCO) phenomenon in 3d coordination complexes constitutes a long-lasting research topic of the Inorganic Chemistry. The exhibition of SCO phenomenon - the transition from the high spin (HS) state to the low spin (LS) state and vice versa - is accompanied by change on the Metal-Ligand distances, with subsequent colour change. The spin state of the complex can be conveniently monitored by variable-temperature χMT measurements. Since many other properties, except spin, change upon SCO, the spin state can be followed by other spectroscopic techniques, including variable-temperature Raman spectroscopy. The exploitation of Raman vibrational data on systems displaying the SCO phenomenon, for both structural characterization and more importantly for indirect monitoring of the SCO behaviour (HS species population as a function of external stimuli, i.e. pressure, temperature), is still lacking in the literature. The incorporation of spin-crossover (SCO) properties into Metal-Organic Frameworks (MOFs) leads to an appealing subclass of multifunctional MOFs with potential applications in molecular sensing. The Hofmann type coordination polymers with chemical structure [Fe(pyrazine)M(CN)4] (M = Ni, Pt) are considered the most well-studied among the Hofmann coordination polymers. In the second part of this Thesis, the SCO behaviour of Fe(II) mononuclear and Fe(II)/3d Hofmann type coordination complexes/polymers was monitored in depth via Temperature Dependent Raman Spectroscopy. A relevant study of the coordination complex [Fe(abpt)2{N(CN)2}2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) is described in terms of its temperature induced SCO ability. The sample was synthesized in a controllable manner that enables the formation of nanostructures with different average particle sizes. These samples are thoroughly characterized at molecular level by spectroscopic techniques (Raman, ATR, UV/VIS) and powder-XRD while their morphological characteristics are explored by scanning electron microscopy (SEM). In addition, spectroscopic evidence of the particle size effect on the SCO phenomenon is revealed by low temperature Raman measurements. The impact of the terminal ligand was also examined; an analogous study for the complex [Fe(abpt)2(SCN)2] was performed. The SCO Hofmann-type coordination polymers with the general chemical formula [FeII(L)2M(CN)4], where L= pyrazine (pz), methylpyrazine (mpz) and 1,2-Di(4-pyridyl)ethylene (1,2 dipyeth) and M= Ni, Pt, in form of both bulk material and nanoparticles, were examined referring to their SCO behaviour, through temperature-dependent Raman measurements.
SCO phenomenon is well documented but its potential use for temperature sensing applications has never been recorded. To that end, an optimum goal of this research was the exploitation of the SCO phenomenon for the development of temperature sensors, which could be potentially used in the packaging of refrigerated food products, for the certification of the food consuming suitability. The development of a “smart packaging” could be achieved in two ways; the incorporation of the sensors in the entire food packaging or by the deposition of the sensor as an external patch in the packaging material. The study of the potential migration-release of the temperature sensor incorporated (embedded) in polymeric films immersed into food simulants was also performed.
|
|---|
