Liquid-liquid equilibria in binary solutions formed by [Pyridinium-Derived][F4B] ionic liquids and alkanols:new experimental data and validation of a multiparametric model for correlating LLE data

[EN]Experimental solubility data are presented for a set of binary systems composed of ionic liquids (IL) derived from pyridium, with the tetrafluoroborate anion, and normal alcohols ranging from ethanol to decanol, in the temperature interval of 275 420 K, at atmospheric pressure. For each case, the miscibility curve and the upper critical solubility temperature (UCST) values are presented. The effects of the ILs on the behavior of solutions with alkanols are analyzed, paying special attention to the pyridine derivatives, and considering a series of structural characteristics of the compounds involved.

New high nuclearity carbonyl clusters

The thesis reports the synthesis, and the chemical, structural and spectroscopic characterization of a series of new Rhodium and Au-Fe carbonyl clusters. Most new high-nuclearity rhodium carbonyl clusters have been obtained by redox condensation of preformed rhodium clusters reacting with a species in a different oxidation state generated in situ by mild oxidation. In particular the starting Rh carbonyl clusters is represented by the readily available [Rh7(CO)16]3- 9 compound. The oxidized species is generated in situ by reaction of the above with a stoichiometric defect of a mild oxidizing agents such as [M(H2O)x]n+ aquo complexes possessing different pKa’s and Mn+/M potentials. The experimental results are roughly in keeping with the conclusion that aquo complexes featuring E°(Mn+/M) < ca. -0.20 V do not lead to the formation of hetero-metallic Rh clusters, probably because of the inadequacy of their redox potentials relative to that of the [Rh7(CO)16]3-/2- redox couple. Only homometallic cluster s such as have been fairly selectively obtained. As a fallout of the above investigations, also a convenient and reproducible synthesis of the ill-characterized species [HnRh22(CO)35]8-n has been discovered. The ready availability of the above compound triggered both its complete spectroscopic and chemical characterization. because it is the only example of Rhodium carbonyl clusters with two interstitial metal atoms. The presence of several hydride atoms, firstly suggested by chemical evidences, has been implemented by ESI-MS and 1H-NMR, as well as new structural characterization of its tetra- and penta-anion. All these species display redox behaviour and behave as molecular capacitors. Their chemical reactivity with CO gives rise to a new series of Rh22 clusters containing a different number of carbonyl groups, which have been likewise fully characterized. Formation of hetero-metallic Rh clusters was only observed when using SnCl2H2O as oxidizing agent because. Quite all the Rh-Sn carbonyl clusters obtained have icosahedral geometry. The only previously reported example of an icosahedral Rh cluster with an interstitial atom is the [Rh12Sb(CO)27]3- trianion. They have very similar metal framework, as well as the same number of CO ligands and, consequently, cluster valence electrons (CVEs). .A first interesting aspect of the chemistry of the Rh-Sn system is that it also provides icosahedral clusters making exception to the cluster-borane analogy by showing electron counts from 166 to 171. As a result, the most electron-short species, namely [Rh12Sn(CO)25]4- displays redox propensity, even if disfavoured by the relatively high free negative charge of the starting anion and, moreover, behaves as a chloride scavenger. The presence of these bulky interstitial atoms results in the metal framework adopting structures different from a close-packed metal lattice and, above all, imparts a notable stability to the resulting cluster. An organometallic approach to a new kind of molecular ligand-stabilized gold nanoparticles, in which Fe(CO)x (x = 3,4) moieties protect and stabilize the gold kernel has also been undertaken. As a result, the new clusters [Au21{Fe(CO)4}10]5-, [Au22{Fe(CO)4}12]6-, Au28{Fe(CO)3}4{Fe(CO)4}10]8- and [Au34{Fe(CO)3}6{Fe(CO)4}8]6- have been isolated and characterized. As suggested by concepts of isolobal analogies, the Fe(CO)4 molecular fragment may display the same ligand capability of thiolates and go beyond. Indeed, the above clusters bring structural resemblance to the structurally characterized gold thiolates by showing Fe-Au-Fe, rather than S-Au-S, staple motives. Staple motives, the oxidation state of surface gold atoms and the energy of Au atomic orbitals are likely to concur in delaying the insulator-to-metal transition as the nuclearity of gold thiolates increases, relative to the more compact transition-metal carbonyl clusters. Finally, a few previously reported Au-Fe carbonyl clusters have been used as precursors in the preparation of supported gold catalysts. The catalysts obtained are active for toluene oxidation and the catalytic activity depends on the Fe/Au cluster loading over TiO2.

Design and Characterization of New Luminescent Sensors and Labels

The aim of this Ph.D. project has been the design and characterization of new and more efficient luminescent tools, in particular sensors and labels, for analytical chemistry, medical diagnostics and imaging. Actually both the increasing temporal and spatial resolutions that are demanded by those branches, coupled to a sensitivity that is required to reach the single molecule resolution, can be provided by the wide range of techniques based on luminescence spectroscopy. As far as the development of new chemical sensors is concerned, as chemists we were interested in the preparation of new, efficient, sensing materials. In this context, we kept developing new molecular chemosensors, by exploiting the supramolecular approach, for different classes of analytes. In particular we studied a family of luminescent tetrapodal-hosts based on aminopyridinium units with pyrenyl groups for the detection of anions. These systems exhibited noticeable changes in the photophysical properties, depending on the nature of the anion; in particular, addition of chloride resulted in a conformational change, giving an initial increase in excimeric emission. A good selectivity for dicarboxylic acid was also found. In the search for higher sensitivities, we moved our attention also to systems able to perform amplification effects. In this context we described the metal ion binding properties of three photoactive poly-(arylene ethynylene) co-polymers with different complexing units and we highlighted, for one of them, a ten-fold amplification of the response in case of addition of Zn2+, Cu2+ and Hg2+ ions. In addition, we were able to demonstrate the formation of complexes with Yb3+ an Er3+ and an efficient sensitization of their typical metal centered NIR emission upon excitation of the polymer structure, this feature being of particular interest for their possible applications in optical imaging and in optical amplification for telecommunication purposes. An amplification effect was also observed during this research in silica nanoparticles derivatized with a suitable zinc probe. In this case we were able to prove, for the first time, that nanoparticles can work as “off-on” chemosensors with signal amplification. Fluorescent silica nanoparticles can be thus seen as innovative multicomponent systems in which the organization of photophysically active units gives rise to fruitful collective effects. These precious effects can be exploited for biological imaging, medical diagnostic and therapeutics, as evidenced also by some results reported in this thesis. In particular, the observed amplification effect has been obtained thanks to a suitable organization of molecular probe units onto the surface of the nanoparticles. In the effort of reaching a deeper inside in the mechanisms which lead to the final amplification effects, we also attempted to find a correlation between the synthetic route and the final organization of the active molecules in the silica network, and thus with those mutual interactions between one another which result in the emerging, collective behavior, responsible for the desired signal amplification. In this context, we firstly investigated the process of formation of silica nanoparticles doped with pyrene derivative and we showed that the dyes are not uniformly dispersed inside the silica matrix; thus, core-shell structures can be formed spontaneously in a one step synthesis. Moreover, as far as the design of new labels is concerned, we reported a new synthetic approach to obtain a class of robust, biocompatible silica core-shell nanoparticles able to show a long-term stability. Taking advantage of this new approach we also showed the synthesis and photophysical properties of core-shell NIR absorbing and emitting materials that proved to be very valuable for in-vivo imaging. In general, the dye doped silica nanoparticles prepared in the framework of this project can conjugate unique properties, such as a very high brightness, due to the possibility to include many fluorophores per nanoparticle, high stability, because of the shielding effect of the silica matrix, and, to date, no toxicity, with a simple and low-cost preparation. All these features make these nanostructures suitable to reach the low detection limits that are nowadays required for effective clinical and environmental applications, fulfilling in this way the initial expectations of this research project.

Entwicklung eines Verfahrens zur Ultraspurenbestimmung der Platingruppenelemente in Umwelt- und geologischen Proben mit einem ICP-QMS unter Verwendung der Isotopenverdünnungsanalyse sowie geeigneter Separationstechniken

ZusammenfassungSchwerpunkt dieser Arbeit war die Verfahrensentwicklung zur Ultraspurenbestimmung der Platingruppenelemente (PGE) in Umwelt- und geologischen Proben unter Verwendung der massenspektrometrischen Isotopenverdünnungsanalyse mit anschließender Bestimmung an einem Quadrupol ICP-MS (ICP-QMSIVA). Geeignete Separationstechniken in der Probenaufbereitung, um die PGE von der Matrix der untersuchten Proben zu trennen, stellten eine richtige und präzise Bestimmung der Ultraspuren an einem Quadrupol ICP-MS sicher.Das Verfahren konnte anhand von geologischen Referenzmaterialien aus Kanada sichergestellt werden. Gerade die Wiederholungsbestimmungen der verschiedenen Referenzmaterialien unter Verwendung des ICP-QMSIVA Verfahrens sind beispiellos und in dieser Form noch nicht in der Literatur beschrieben. Durch systematische Messungen konnten Richtigkeit und Präzision des Verfahrens bestätigt werden und die Inhomogenität des Referenzmaterials UMT-1 bezüglich Pt bewiesen werden. Das in dieser Arbeit entwickelte Verfahren zur Ultraspurenbestimmung der PGE mit ICP-QMSIVA wurde im Rahmen des Projektes 'Production and certification of a road dust reference material for platinum, palladium and rhodium (PGEs) in automative catalytic converters (PACEPAC)' der Europäischen Union zur Zertifizierung von zwei Referenzmaterialien für Umweltproben eingesetzt. Hierbei wurde bei der Zertifizierung ('intercomparison round') eine sehr gute Übereinstimmung der Ergebnisse mit dem gewichteten Mittelwert der Ergebnisse für Pd und Pt mit den übrigen teilnehmenden Laboratorien festgestellt. Die mit der hier entwickelten Methode erhaltenen Ergebnisse wurden ohne Ausnahme für alle gemessenen Elemente zur Zertifizierung herangezogen. Damit leistete die vorliegende Arbeit einen erheblichen Beitrag zum erfolgreichen Abschluß dieses Projekts. Den Erwartungen hinsichtlich Richtigkeit und Reproduzierbarkeit des entwickelten Verfahrens wurde somit voll entsprochen. Erneut konnte die große Bedeutung der Isotopenverdünnungstechnik für die Zertifizierung von Referenzmaterialien aufgezeigt werden, da mit dieser Technik bei sachgerechtem Einsatz Ergebnisse hoher Richtigkeit erzielt werden. Durch vergleichende Messungen mit der NiS-Dokimasie und NAA, die in einer Kooperation mit dem Kernchemischen Institut der Universität Mainz durchgeführt wurden, und dem hier verwendeten Verfahren, konnten übereinstimmende Daten, hinsichtlich der Abnahme der Konzentrationen von Pd und Pt in Abhängigkeit von der Entfernung zu einer Autobahn, erzielt werden. Diese Arbeit und die Forschungsergebnisse, die mit der anerkannten NAA erzielt wurden, zeigen, daß die PGE durch Katalysatoren von Automobilen überwiegend metallisch emittiert werden. Der anthropogene Eintrag der PGE in die Umwelt kann mit dem ICP-QMSIVA Verfahren weiterhin sehr gut verfolgt werden.

Use of solvents and environmental friendly materials for applications in Green Chemistry

The present Thesis studies three alternative solvent groups as sustainable replacement of traditional organic solvents. Some aspects of fluorinated solvents, supercritical fluids and ionic liquids, have been analysed with a critical approach and their effective “greenness” has been evaluated from the points of view of the synthesis, the properties and the applications. In particular, the attention has been put on the environmental and human health issues, evaluating the eco-toxicity, the toxicity and the persistence, to underline that applicability and sustainability are subjects with equal importance. The “green” features of fluorous solvents and supercritical fluids are almost well-established; in particular supercritical carbon dioxide (scCO2) is probably the “greenest” solvent among the alternative solvent systems developed in the last years, enabling to combine numerous advantages both from the point of view of industrial/technological applications and eco-compatibility. In the Thesis the analysis of these two classes of alternative solvents has been mainly focused on their applicability, rather than the evaluation of their environmental impact. Specifically they have been evaluated as alternative media for non-aqueous biocatalysis. For this purpose, the hydrophobic ion pairing (HIP), which allows solubilising enzymes in apolar solvents by an ion pairing between the protein and a surfactant, has been investigated as effective enzymatic derivatisation technique to improve the catalytic activity under homogeneous conditions in non conventional media. The results showed that the complex enzyme-surfactant was much more active both in fluorous solvents and in supercritical carbon dioxide than the native form of the enzyme. Ionic liquids, especially imidazolium salts, have been proposed some years ago as “fully green” alternative solvents; however this epithet does not take into account several “brown” aspects such as their synthesis from petro-chemical starting materials, their considerable eco-toxicity, toxicity and resistance to biodegradation, and the difficulty of clearly outline applications in which ionic liquids are really more advantageous than traditional solvents. For all of these reasons in this Thesis a critical analysis of ionic liquids has been focused on three main topics: i) alternative synthesis by introducing structural moieties which could reduce the toxicity of the most known liquid salts, and by using starting materials from renewable resources; ii) on the evaluation of their environmental impact through eco-toxicological tests (Daphnia magna and Vibrio fischeri acute toxicity tests, and algal growth inhibition), toxicity tests (MTT test, AChE inhibition and LDH release tests) and fate and rate of aerobic biodegradation in soil and water; iii) and on the demonstration of their effectiveness as reaction media in organo-catalysis and as extractive solvents in the recovery of vegetable oil from terrestrial and aquatic biomass. The results about eco-toxicity tests with Daphnia magna, Vibrio fischeri and algae, and toxicity assay using cultured cell lines, clearly indicate that the difference in toxicity between alkyl and oxygenated cations relies in differences of polarity, according to the general trend of decreasing toxicity by decreasing the lipophilicity. Independently by the biological approach in fact, all the results are in agreement, showing a lower toxicity for compounds with oxygenated lateral chains than for those having purely alkyl lateral chains. These findings indicate that an appropriate choice of cation and anion structures is important not only to design the IL with improved and suitable chemico-physical properties but also to obtain safer and eco-friendly ILs. Moreover there is a clear indication that the composition of the abiotic environment has to be taken into account when the toxicity of ILs in various biological test systems is analysed, because, for example, the data reported in the Thesis indicate a significant influence of salinity variations on algal toxicity. Aerobic biodegradation of four imidazolium ionic liquids, two alkylated and two oxygenated, in soil was evaluated for the first time. Alkyl ionic liquids were shown to be biodegradable over the 6 months test period, and in contrast no significant mineralisation was observed with oxygenated derivatives. A different result was observed in the aerobic biodegradation of alkylated and oxygenated pyridinium ionic liquids in water because all the ionic liquids were almost completely degraded after 10 days, independently by the number of oxygen in the lateral chain of the cation. The synthesis of new ionic liquids by using renewable feedstock as starting materials, has been developed through the synthesis of furan-based ion pairs from furfural. The new ammonium salts were synthesised in very good yields, good purity of the products and wide versatility, combining low melting points with high decomposition temperatures and reduced viscosities. Regarding the possible applications as surfactants and biocides, furan-based salts could be a valuable alternative to benzyltributylammonium salts and benzalkonium chloride that are produced from non-renewable resources. A new procedure for the allylation of ketones and aldehydes with tetraallyltin in ionic liquids was developed. The reaction afforded high yields both in sulfonate-containing ILs and in ILs without sulfonate upon addition of a small amount of sulfonic acid. The checked reaction resulted in peculiar chemoselectivity favouring aliphatic substrates towards aromatic ketones and good stereoselectivity in the allylation of levoglucosenone. Finally ILs-based systems could be easily and successfully recycled, making the described procedure environmentally benign. The potential role of switchable polarity solvents as a green technology for the extraction of vegetable oil from terrestrial and aquatic biomass has been investigated. The extraction efficiency of terrestrial biomass rich in triacylglycerols, as soy bean flakes and sunflower seeds, was comparable to those of traditional organic solvents, being the yield of vegetable oils recovery very similar. Switchable polarity solvents as been also exploited for the first time in the extraction of hydrocarbons from the microalga Botryococcus braunii, demonstrating the efficiency of the process for the extraction of both dried microalgal biomass and directly of the aqueous growth medium. The switchable polarity solvents exhibited better extraction efficiency than conventional solvents, both with dried and liquid samples. This is an important issue considering that the harvest and the dewatering of algal biomass have a large impact on overall costs and energy balance.

Tris(trimethylsilyl)silyl substituted alkali- and transition metal guaiazulenides

In der vorliegenden Arbeit wird ein prochirales, aus natürlichen Resourcen gewonnenes Azulen, das Guajazulen genutzt, um neuartige chirale Cyclopentadienyl-Systeme aufzubauen. Mit Alkalimetallhypersilaniden als starke und sperrige Nukleophile gelingt es hypersilylsubstituierte Gujazulenide zu synthetisieren. Diese wurden mittels Elementaranalyse, NMR-Spektroskopie und Röntgendiffraktometrie charakterisiert. Durch nachfolgende Metathesen mit Übergangsmetallhalogeniden konnten in vielen Fällen die entsprechenden Metallocene erhalten werden. Die Experimente enthüllen eine ausgeprägte Regioselektivität der Addition des sperrigen Hypersilyanions an das Guajazulen, die durch das eingesetzte Lösungsmittel graduell verändert werden kann. In nicht-koordinierenden Lösungsmitteln findet man ausschließlich eine Addition an der 6-Position, die 6-Hypersilyl-2,6-dihydroguajazulenide (6-Hyp-Hgual) (M=Li 1, K 2, Cs 4) in ausgezeichneten Ausbeuten liefert. In polaren Solventien erhält man hingegen Mischungen der 6- und 8-Regioisomeren: 2 bzw. (8-Hyp-Hgual) (3). 2 bleibt aber hierbei das Hauptprodukt. Röntgenbeugungsexperimente zeigen, dass 1 im Kristall als dimerer Sandwich-Komplex, meso-[Li2(6-Hyp-Hgual)2], und die THF-Solvate (thf)4K(6-Hyp-Hgual) (2a) sowie (thf)4K(8-Hyp-Hgual) (3a) jeweils als Halb-Sandwich-Komplexe in einer racemischen Mischung vorliegen. Die Verbindungen 1, 2, 3 and 4 eignen sich sehr gut dazu, in Metathesereaktionen als Precursor für neuartige chirale Metallozen-Komplexe eingesetzt zu werden. Insbesondere das Kaliumderivat 2 besticht durch die einfache und relativ preiswerte Synthese, die erzielten hohen Ausbeuten (>80%) und seine leichte Handhabbarkeit. In THF als Solvent wurden die Metallocene 5:5-M’(6-Hyp-Hgual)2 (M’ = Mn 5, Fe 6, Ni 8) und 5:5-Fe(8-Hyp-Hgual)2 (7) erhalten. Bei Verwendung einiger redox-aktiver Metallhalogenide beobachtet man jedoch die Zersetzung der Metallocene unter Bildung des oxidativen Kopplungsproduktes (3-Hyp-6-Hgual)2 (9) sowie der Ausscheidung von Metall. Die Umsetzung von Halogeniden der Gruppe 4 (TiCl3 and M’’Cl4 (M’’ = Ti, Zr, Hf)) mit 2 liefert in THF ausschließlich die Metallozendichloride M’’(6-Hyp-Hgual)2Cl2 (M’’ = Ti (10), Zr (11), Hf (12)). Die erhaltenen Metallozenderivate fallen als Diastereomeren-Gemische an, die sich durch fraktionierende Kristallisation teilweise oder vollständig in ihre Bestandteile, das jeweilige R,R-Racemat und das R,S-meso-Diastereomer auftrennen lassen. Die Strukturen der rac-Diastereomere konnten durch Beugungsexperimente aufgeklärt werden. Durch eine Metathese von 2 mit Hyp-Cl kann eine zweite Hypersilylgruppe in die 2-Position des Guajazulen-Gerüstes eingeführt werden. Das entstehende 2,6-bis(Hyp)-H2gua (14) kann anschließend mit nBuLi in das extrem luft- und feuchtigkeitsempfindliche Li[2,6-bis(Hyp)-Hgual] (15) überführt werden, dass wie 1 eine dimere Sandwich-Struktur aufweist. Durch Einführung des zweiten Hypersilylrestes werden die chemischen Eigenschaften des Azulenids dramatisch verändert. Während Verbindung 1 sich als guter Precursor für Metallocene erwies, gelang es uns bislang nicht, entsprechende Derivate der Verbindung 15 zu isolieren.

Tris(trimethylsilyl)silyl stabilized phosphorus and lead clusters

Die Hypersilylgruppe (Me3Si)3Si stellt einen sehr sperrigen, Elektronen liefernden Substituenten dar und kann zur Stabilisierung niedriger Oxidationsstufen sowie ungewöhnlicher Strukturelemente dienen. Durch Reaktionen der base-freien Hypersilanide der Alkalimetalle sowie des Dihypersilylplumbandiyls mit unterschiedlichsten phosphorhaltigen Reagenzien konnten eine Reihe hypersilyl-stabilisierter Phosphor- und Bleicluster-Verbindungen erhalten werden. Kaliumhypersilanid reagiert in Toluol glatt mit weißem Phosphor bei Raumtemperatur in Toluol unter quantitativer Bildung von rotem Kalium-bis(hypersilyl)tetraphosphenid [(Me3Si)3Si]2P4K2 (1), einem Kaliumsalz des Tetraphosphens (Me3Si)3Si-PH-P=P-PH-Si(SiMe3)3. In Benzol oder Toluol steht 1 im Gleichgewicht mit dem dimeren Octaphosphanid [(Me3Si)3Si]4P8K4 (2). Bei längerem Stehen der toluolischen Lösungen zerfällt 1 langsam vermutlich in Folge einer Protolyse zum gelben Pentaphosphanid [(Me3Si)3Si]3P5K2 (4). Aus benzolischer Lösung konnte hingegen ein weiteres Oktaphosphanid, [(Me3Si)3Si]3P8K3 (5), isoliert werden. Führt man die Reaktion Kaliumhypersilanid mit P4 in stärker koordinierenden Lösungsmitteln wie Diethylether durch, so entstehen neben 1 größere Mengen des Triphosphenids [(Me3Si)3Si]2P3K (3); dieses enthält ein Triphosphaallyl-Anion mit partieller P-P-Doppelbindung. Setzt man Lithiumhypersilanid mit weißem Phosphor um, so beobachtet man eine vollständig andere Produktpallette. Als Hauptprodukte lassen Polyphosphane wie beispielsweise [(Me3Si)3Si]2P4 (6) nachweisen, das zu 1 analoge [(Me3Si)3Si]2P4Li2 (7) entsteht nur in vergleichsweise kleinen Mengen. In der Gegenwart von Hexahydro-1,3,5-trimethyl-S-triazin, entsteht aus Lithiumhypersilanid und P4 hingegen im wesentlichen [(Me3Si)3Si]2P3Li (8) neben beträchtlichen Mengen von (Me3Si)4Si. Dessen Bildung erfordert eine Si-Si-Bindungsspaltung im Verlauf der Reaktion. Die Reaktion von Natriumhypersilanid mit P4 verläuft sehr unübersichtlich, das Pentaphosphanid [(Me3Si)3Si]3P5Na2 (9) ist das einzige isolierbare Produkt. Setzt man 1 mit [(Me3Si)2Si]2Sn um, so bilden sich überraschenderweise, je nach verwendetem Solvens [(Me3Si)3Si]3P4SnK (10) oder [(Me3Si)3Si]2[(Me3Si)2N]P4SnK (11). Alle neuen Verbindungen wurden NMR-spektroskopisch charakterisiert, die Phosphenide 1, 7, 8 sowie die Phosphanide 2, 4, 5, 9, 10 darüber hinaus durch Kristallstrukturanalysen. Dihypersilylplumbandiyl und -stannandiyl reagieren bei tiefer Temperatur mit P4, MPH2 (M=Li, K), PMe3, and PH3 zu formalen Lewis-Säure-Base-Addukten. Die Addukte {[(Me3Si)3Si]2PbPH2}M [M = Li (15), K (18)], {{[(Me3Si)3Si]2Pb}2PH2}M [M = Li (19), K (20)], und [(Me3Si)3Si]2EPMe3 [E = Pb (21), Sn (22)] wurden als kristalline Feststoffe erhalten und konnten vollständig charakterisiert werden. Die metastabilen Addukte {[(Me3Si)3Si]2E}4P4 (E = Pb, Sn) und [(Me3Si)3Si]2PbPH3 konnten lediglich NMR-spektroskopisch nachgewiesen werden. Bei Raumtemperatur entstehen in Folge von Ligandenaustausch-Prozessen die kristallographisch charakterisierten Heterokubane [(Me3Si)3Si]4P4E4 [E = Pb (12), Sn (14)], das Diphosphen (Me3Si)3SiP=PSi(SiMe3)3 (13) sowie der Pb2P2-Heterocyclus [(Me3Si)3SiPbP(H)Si(SiMe3)3]2 (17). Bei tiefer Temperatur wird aus einer sehr langsamen Reaktion von Dihypersilylplumbandiyl und PH3 in sehr kleinen Ausbeuten ein weiteres, völlig unerwartetes Produkt gebildet: der Bleicluster [(Me3Si)3Si]6Pb12 (23). Er weist ein verzerrt ikosaedrisches, zentrosymmetrisches Pb12-Gerüst auf. Nach jetzigen Erkenntnissen läuft seine Bildung über das nicht fassbare Hydridoplumbandiyl HPbSi(SiMe3)3, das intermediär durch Substituentenaustausch zwischen Pb[Si(SiMe3)3]2 and PH3 entsteht. Der Ersatz des Phosphans durch andere Hydridquellen wie (Ph3PCuH)6, (iBu)2AlH, and Me3NAlH3 führt ebenfalls zur Bildung von Bleiclustern, allerdings ist jetzt der Cluster [(Me3Si)3Si]6Pb10 (24) das Hauptprodukt. Beide Cluster, 23 und 24, gehorchen den Wade-Regeln.

Beiträge zur Chemie der schwersten Elemente in den Bereichen Elektrochemie und Chromatographie

Im Rahmen dieser Arbeit wurden Experimente auf verschiedenen Gebieten der chemischen Charakterisierung der schwersten Elemente durchgeführt. So wurden Vorarbeiten zur Elektrochemie der superschweren Elemente geleistet. Hier konnte gezeigt werden, dass sich Po aus verdünnten Säuren auf Metallelektroden spontan abscheiden lässt. Als wichtigste Reaktionsparameter wurden Temperatur, Konvektion und Viskosität des Elektrolyten identifiziert. Für die Elektrodeposition ist es von Bedeutung, reproduzierbar saubere Elektroden einzusetzen. Auch hierzu konnten Erkenntnisse gewonnen werden. Auf dem Gebiet der Charakterisierung von Nukliden wurde der Elektroneneinfang in Db-263 untersucht. Aus diesem Zerfall geht Rf-263 hervor, welches mit einer Halbwertszeit von 15min überwiegend durch Spontanspaltung zerfällt. Im Experiment wurde Rf-263 mittels Ionenaustauschchromatographie und nachfolgender Flüssig-Flüssig-Extraktion von Db und Aktiniden getrennt. Das erhaltene Präparat wurde auf Alpha-Zerfall und Spontanspaltung untersucht. Die Zahl der Rf-263 Zerfälle lässt auf einen Zerfallszweig durch Elektroneneinfang in Db-263 von 3% schließen. Ein Großteil der Arbeit beschäftigt sich mit der Bestimmung des Kd-Wertes von Sg am Anionenaustauscher Aminex A27 in 0.1M HNO3/5E-3M HF. Beim mit dem ALOHA-System durchgeführten Experiment wurde die Mehrsäulentechnik (MCT) erstmals für die wässrige Chemie von Sg genutzt. Aufgrund zahlreicher Probleme konnte letztlich kein Kd-Wert bestimmt werden. Stattdessen wurde das Experiment einer Fehleranalyse unterzogen. Hier zeigte sich eine Anfälligkeit der MCT auf natürliche Radionuklide. Weiterhin konnten Probleme bei ALOHA aufgedeckt werden, die eine Wiederholung des Experiments ausschlossen. In der Folge wurde ein alternativer Anionenaustauscher charakterisiert, sowie die Elektrolysebedingungen, als wichtiger Schritt der chemischen Aufarbeitung bei der MCT, genauer spezifiziert.

Funktionelle und morphologische Untersuchungen der Silikataufnahme und Nadelbildung im marinen Schwamm Suberites domuncula

Die für Metazoen einzigartige Fähigkeit, hochdifferenzierte Silikatstrukturen herzustellen und als Gerüstsubstanz zu verwenden, steht bei den Porifera in einem scheinbaren Gegensatz zu der niedrigen Konzentration an Silizium in dem die Schwämme umgebenden Medium. In der zweiten bedeutenden silikatpolymerisierenden Species, den einzelligen Kieselalgen (Diatomeen), konnte bereits ein Silikattransporter identifiziert werden, dessen Sequenzdaten jedoch aufgrund der phylogenetisch geringen Verwandtschaft der Demospongien mit den Diatomeen keine Verwendung finden konnte Im Zuge der Suche nach einem Silikat-Transportsystem im Schwamm Suberites domuncula wurde ein potentielles Kandidatengen mittels molekularbiologischer Techniken aus einer cDNA Bank des Instituts isoliert, vervollständigt und analysiert. Es zeigte sich, dass dieser Transporter durch seine Sequenzdaten der Familie der Bikarbonattransporter angehörte, und somit membranständig war. Seine Transportfunktion zeigte sich mittels spezifischer Inhibitoren hemmbar. Damit der Schwamm in der Lage ist, eine regulierbare und schnelle Anreicherung von Silikat durchführen zu können, lag eine Annahme einer Induzierbarkeit der Transportergene durch das Substrat Silikat nahe. Mittels Northern-Blot Analyse konnte in einem Primmorphensystem des Schwammes eine Hochregulation der Transkription der Transportergene festgestellt werden. Die Lokalisation der Exprimierung des Transporters innerhalb des Schwammgewebes konnte mittels In situ Hybridisierung untersucht werden und zeigte eine direkte Nähe zu den Polysilikatstrukturen des Schwammes. Um Hinweise auf eine Bifunktionalität des Transporters aufgrund der Ähnlichkeit von Carbonat und Silikat zu erhärten, wurden fluoreszenzmikroskopische Studien an isolierten Zellkulturen des Schwammes durchgeführt. Es kam zu einer intensive Reaktion der Zellen auf Silikat als Substrat. Dieser Effekt konnte nicht nur durch einen spezifischen Transportinhibitor (DIDS) gehemmt werden, sondern zeigt auch eine deutliche Temperaturabhängigkeit. Um den potentiellen Silikattransporter in Zusammenhang mit dem Gesamtmechanismus der Silikatnadelherstellung in Schwämmen zu bringen, wurden zusätzliche elektronenmikroskopische Studien angestellt. Hier konnte zunächst gezeigt werden, wie sich das die Polykondensation auslösende und dirigierende Proteinfilament des Schwammes bei der Nadelbildung entwickelt. Mittels einer darauf folgenden Immunogold-Markierung des Hauptaxialfilamentproteins des Schwammes in elektronenmikroskopischen Gewebepräparaten, konnte dessen Vorkommen nicht nur im Zentrum der Silikatnadel, sondern auch in den die Nadel umgebenden Strukturen nachgewiesen werden

Development of analytical methodologies for iodine species in gaseous and particulate phases of the coastal atmosphere

It has been demonstrated that iodine does have an important influence on atmospheric chemistry, especially the formation of new particles and the enrichment of iodine in marine aerosols. It was pointed out that the most probable chemical species involved in the production or growth of these particles are iodine oxides, produced photochemically from biogenic halocarbon emissions and/or iodine emission from the sea surface. However, the iodine chemistry from gaseous to particulate phase in the coastal atmosphere and the chemical nature of the condensing iodine species are still not understood. A Tenax / Carbotrap adsorption sampling technique and a thermo-desorption / cryo-trap / GC-MS system has been further developed and improved for the volatile organic iodine species in the gas phase. Several iodo-hydrocarbons such as CH3I, C2H5I, CH2ICl, CH2IBr and CH2I2 etc., have been measured in samples from a calibration test gas source (standards), real air samples and samples from seaweeds / macro-algae emission experiments. A denuder sampling technique has been developed to characterise potential precursor compounds of coastal particle formation processes, such as molecular iodine in the gas phase. Starch, TMAH (TetraMethylAmmonium Hydroxide) and TBAH (TetraButylAmmonium Hydroxide) coated denuders were tested for their efficiencies to collect I2 at the inner surface, followed by a TMAH extraction and ICP/MS determination, adding tellurium as an internal standard. The developed method has been proved to be an effective, accurate and suitable process for I2 measurement in the field, with the estimated detection limit of ~0.10 ng∙L-1 for a sampling volume of 15 L. An H2O/TMAH-Extraction-ICP/MS method has been developed for the accurate and sensitive determination of iodine species in tropospheric aerosol particles. The particle samples were collected on cellulose-nitrate filters using conventional filter holders or on cellulose nitrate/tedlar-foils using a 5-stage Berner impactor for size-segregated particle analysis. The water soluble species as IO3- and I- were separated by anion exchanging process after water extraction. Non-water soluble species including iodine oxide and organic iodine were digested and extracted by TMAH. Afterwards the triple samples were analysed by ICP/MS. The detection limit for particulate iodine was determined to be 0.10~0.20 ng•m-3 for sampling volumes of 40~100 m3. The developed methods have been used in two field measurements in May 2002 and September 2003, at and around the Mace Head Atmospheric Research Station (MHARS) located at the west coast of Ireland. Elemental iodine as a precursor of the iodine chemistry in the coastal atmosphere, was determined in the gas phase at a seaweed hot-spot around the MHARS, showing I2 concentrations were in the range of 0~1.6 ng∙L-1 and indicating a positive correlation with the ozone concentration. A seaweed-chamber experiment performed at the field measurement station showed that the I2 emission rate from macro-algae was in the range of 0.019~0.022 ng•min-1•kg-1. During these experiments, nanometer-particle concentrations were obtained from the Scanning Mobility Particle Sizer (SMPS) measurements. Particle number concentrations were found to have a linear correlation with elemental iodine in the gas phase of the seaweeds chamber, showing that gaseous I2 is one of the important precursors of the new particle formation in the coastal atmosphere. Iodine contents in the particle phase were measured in both field campaigns at and around the field measurement station. Total iodine concentrations were found to be in the range of 1.0 ~ 21.0 ng∙m-3 in the PM2.5 samples. A significant correlation between the total iodine concentrations and the nanometer-particle number concentrations was observed. The particulate iodine species analysis indicated that iodide contents are usually higher than those of iodate in all samples, with ratios in the range of 2~5:1. It is possible that those water soluble iodine species are transferred through the sea-air interface into the particle phase. The ratio of water soluble (iodate + iodide) and non-water soluble species (probably iodine oxide and organic iodine compounds) was observed to be in the range of 1:1 to 1:2. It appears that higher concentrated non-water soluble species, as the products of the photolysis from the gas phase into the particle phase, can be obtained in those samples while the nucleation events occur. That supports the idea that iodine chemistry in the coastal boundary layer is linked with new particle formation events. Furthermore, artificial aerosol particles were formed from gaseous iodine sources (e.g. CH2I2) using a laboratory reaction-chamber experiment, in which the reaction constant of the CH2I2 photolysis was calculated to be based upon the first order reaction kinetic. The end products of iodine chemistry in the particle phase were identified and quantified.

Computational investigations of ion conduction mechanisms using enhanced sampling methods

Proper ion channels’ functioning is a prerequisite for a normal cell and disorders involving ion channels, or channelopathies, underlie many human diseases. Long QT syndromes (LQTS) for example may arise from the malfunctioning of hERG channel, caused either by the binding of drugs or mutations in HERG gene. In the first part of this thesis I present a framework to investigate the mechanism of ion conduction through hERG channel. The free energy profile governing the elementary steps of ion translocation in the pore was computed by means of umbrella sampling simulations. Compared to previous studies, we detected a different dynamic behavior: according to our data hERG is more likely to mediate a conduction mechanism which has been referred to as “single-vacancy-like” by Roux and coworkers (2001), rather then a “knock-on” mechanism. The same protocol was applied to a model of hERG presenting the Gly628Ser mutation, found to be cause of congenital LQTS. The results provided interesting insights about the reason of the malfunctioning of the mutant channel. Since they have critical functions in viruses’ life cycle, viral ion channels, such as M2 proton channel, are considered attractive targets for antiviral therapy. A deep knowledge of the mechanisms that the virus employs to survive in the host cell is of primary importance in the identification of new antiviral strategies. In the second part of this thesis I shed light on the role that M2 plays in the control of electrical potential inside the virus, being the charge equilibration a condition required to allow proton influx. The ion conduction through M2 was simulated using metadynamics technique. Based on our results we suggest that a potential anion-mediated cation-proton exchange, as well as a direct anion-proton exchange could both contribute to explain the activity of the M2 channel.

Tetrafenilciclopentadienon-derivati ed analoghi: sintesi, "self-assembly" e caratterizzazione reologica

Gels are materials that are easier to recognize than to define. For all practical purpose, a material is termed a gel if the whole volume of liquid is completely immobilized as usually tested by the ‘tube inversion’ method. Recently, supramolecular gels obtained from low molecular weight gelators (LMWGs) have attracted considerable attention in materials science since they represent a new class of smart materials sensitive to external stimuli, such as temperature, ultrasounds, light, chemical species and so on. Accordingly, during the past years a large variety of potentialities and applications of these soft materials in optoelectronics, as electronic devices, light harvesting systems and sensors, in bio-materials and in drug delivery have been reported. Spontaneous self-assembly of low molecular weight molecules is a powerful tool that allows complex supramolecular nanoscale structures to be built. The weak and non-covalent interactions such as hydrogen bonding, π–π stacking, coordination, electrostatic and van der Waals interactions are usually considered as the most important features for promoting sol-gel equilibria. However, the occurrence of gelation processes is ruled by further “external” factors, among which the temperature and the nature of the solvents that are employed are of crucial importance. For example, some gelators prefer aromatic or halogenated solvents and in some cases both the gelation temperature and the type of the solvent affect the morphologies of the final aggregation. Functionalized cyclopentadienones are fascinating systems largely employed as building blocks for the synthesis of polyphenylene derivatives. In addition, it is worth noting that structures containing π-extended conjugated chromophores with enhanced absorption properties are of current interest in the field of materials science since they can be used as “organic metals”, as semiconductors, and as emissive or absorbing layers for OLEDs or photovoltaics. The possibility to decorate the framework of such structures prompted us to study the synthesis of new hydroxy propargyl arylcyclopentadienone derivatives. Considering the ability of such systems to give π–π stacking interactions, the introduction on a polyaromatic structure of polar substituents able to generate hydrogen bonding could open the possibility to form gels, although any gelation properties has been never observed for these extensively studied systems. we have synthesized a new class of 3,4-bis (4-(3-hydroxy- propynyl) phenyl) -2, 5-diphenylcyclopentadienone derivatives, one of which (1a) proved to be, for the first time, a powerful organogelator. The experimental results indicated that the hydroxydimethylalkynyl substituents are fundamental to guarantee the gelation properties of the tetraarylcyclopentadienone unit. Combining the results of FT-IR, 1H NMR, UV-vis and fluorescence emission spectra, we believe that H-bonding and π–π interactions are the driving forces played for the gel formation. The importance of soft materials lies on their ability to respond to external stimuli, that can be also of chemical nature. In particular, high attention has been recently devoted to anion responsive properties of gels. Therefore the behaviour of organogels of 1a in toluene, ACN and MeNO2 towards the addition of 1 equivalent of various tetrabutylammonium salts were investigated. The rheological properties of gels in toluene, ACN and MeNO2 with and without the addition of Bu4N+X- salts were measured. In addition a qualitative analysis on cation recognition was performed. Finally the nature of the cyclic core of the gelator was changed in order to verify how the carbonyl group was essential to gel solvents. Until now, 4,5-diarylimidazoles have been synthesized.

Oligosilyl- und Stannylderivate des Kupfers

Benzyltris(trimethylsilyl)silan konnte durch Reaktion mit Lithiummethanid oder Alkalimetall-tert-butanolaten (M-OtBu, M = Na, K, Rb, Cs) in die entsprechenden Alkalimetall-benzylbis(trimethylsilyl)silanide (M-Bnz, Bnz = Si(SiMe3)2CH2Ph) überführt werden. Die Strukturen dieser Verbindungen weisen viele Gemeinsamkeiten mit den entsprechenden Hypersilylverbindungen (Hypersilyl bzw. Hyp = Si(SiMe3)3) auf. Mit Ausnahme der Lithiumverbindung weisen die Natrium-, Kalium- und Rubidiumverbindungen jedoch noch intramolekulare Wechselwirkungen des Benzylrestes mit den Alkalimetallkationen auf. Die Benzylbis(trimethylsilyl)silanide der Alkalimetalle eignen sich zur Darstellung von Kupfersilylverbindungen. So konnten heteroleptische Cuprate (Bnz-Cu-OtBu-, Bnz-Cu-Hyp-) und monoleptische Cuprate (CuBnz2-), aber auch das ungeladene Kupfer-benzyl-bis(trimethylsilyl)silanid hergestellt werden. Auf analoge Weise wurde versucht, Alkalimetall- und Kupferverbindungen des Phenylbis(trimethylsilyl)silanides herzustellen. Da aber bereits bei der Synthese der Alkalimetallverbindungen die entsprechenden Hypersilanide als schwer abtrennbare Nebenprodukte entstanden, konnten keine ausführlichen Untersuchungen angestellt werden. Es konnten die Natrium- und Kaliumsalze des Dihypersilylcuprates hergestellt und strukturell charakterisiert werden. Die Natriumverbindung wurde nur als Nebenprodukt einer Reaktion von Kupfer(I)-cyanid mit Natriumhypersilanid erhalten, die entsprechende Kaliumverbindung ließ sich jedoch mit guten Ausbeuten gezielt aus Kupfer(I)-tert-butanolat herstellen. Beide Verbindungen weisen ein hantelförmiges Hyp-Cu-Hyp-Anion auf, die THF- bzw. THP-koordinierten Kationen liegen isoliert vom Anion vor. Eine neue Klasse von Kupfersilylverbindungen konnten durch Reaktion von Kupfer(I)-cyanid mit Alkalimetallhypersilaniden erzeugt werden. Dabei entstehen heteroleptische Cyano-hypersilyl-cuprate. Großen Einfluss auf die Strukturen üben die Alkalimetallkationen und Lösungsmittelmoleküle aus. So findet man bei den Lithiumverbindungen zweikernige Kupferkomplexe, die je nach Lösungsmittelgehalt unterschiedliche Anordnungen der Cyanid- und Hypersilanidanionen aufweisen. Lediglich die Kaliumverbindung weist lineare Cyanid-Kupfer-Hypersilanid-Einheiten auf, wie man sie analog von Organyl-cyano-cupraten kennt. Trotz vieler Gemeinsamkeiten vieler Silyl- und entsprechender Stannylverbindungen bezüglich Struktur und Reaktivität, erwies sich die Darstellung von Kupferstannyl-verbindungen schwieriger als erwartet. Zwar konnte in einer mehrstufigen Reaktion Kupfer-tris(trimethylsilyl)stannanid erhalten werden, auftretende Zwischen- und Nebenprodukte weisen jedoch auf das Auftreten von Umlagerungen und Redoxprozesse hin, die bei entsprechenden Kupfersilylverbindungen nicht beobachtet wurden.

Stabilizzazione del Blu di Prussia con film politiofenici depositati per via elettrochimica

Hydrogen peroxide (H2O2) is a powerful oxidant which is commonly used in a wide range of applications in the industrial field. Several methods for the quantification of H2O2 have been developed. Among them, electrochemical methods exploit the ability of some hexacyanoferrates (such as Prussian Blue) to detect H2O2 at potentials close to 0.0 V (vs. SCE) avoiding the occurrence of secondary reactions, which are likely to run at large overpotentials. This electrocatalytic behaviour makes hexacyanoferrates excellent redox mediators. When deposited in the form of thin films on the electrode surfaces, they can be employed in the fabrication of sensors and biosensors, normally operated in solutions at pH values close to physiological ones. As hexacyanoferrates show limited stability in not strongly acidic solutions, it is necessary to improve the configuration of the modified electrodes to increase the stability of the films. In this thesis work, organic conducting polymers were used to fabricate composite films with Prussian Blue (PB) to be electro-deposited on Pt surfaces, in order to increase their pH stability. Different electrode configurations and different methods of synthesis of both components were tested, and for each one the achievement of a possible increase in the operational stability of Prussian Blue was verified. Good results were obtained for the polymer 3,3''-didodecyl-2,2':5',2''-terthiophene (poly(3,3''-DDTT)), whose presence created a favourable microenvironment for the electrodeposition of Prussian Blue. The electrochemical behaviour of the modified electrodes was studied in both aqueous and organic solutions. Poly(3,3''-DDTT) showed no response in aqueous solution in the potential range where PB is electroactive, thus in buffered aqueous solution is was possible to characterize the composite material, focusing only on the redox behaviour of PB. A combined effect of anion and cation of the supporting electrolyte was noticed. The response of Pt electrodes modified with films of the PB /poly(3,3''-DDTT) composite was evaluated for the determination of H2O2. The performance of such films was found better than that of the PB alone. It can be concluded that poly(3,3''-DDTT) plays a key role in the stabilization of Prussian Blue causing also a wider linearity range for the electrocatalytic response to H2O2.

Spin-crossover in metallomesogens of iron(II)

Covalent grafting mesogenic groups to the coordination cores of the parent mononuclear low-spin and spin-crossover compounds afforded metallomesogenic complexes of iron(II). In comparison with the parent complexes the spin-crossover properties of the alkylated derivatives are substantially modified. The type of the modification was found to be dependent on the properties of the parent system and the nature of the used anion, however, the general tendency is the destabilization of the low-spin state at the favor of spin-crossover or high-spin behavior below 400 K. The structural insight revealed the micro-segregated layered organization. The effect of the alkylation of the parent compounds consists first of all in the change of the lattice to a two-dimensional lamellar one retaining significant intermolecular contacts only within the ionic bilayers. The comprehensive analysis of the structural and thermodynamic data in the homologous series pointed at the mechanism of the interplay between the structural modification on melting and the induced anomalous change of the magnetic properties. A family of one-dimensional spin-crossover polymers was synthesized and characterized using a series of spectroscopic methods, X-ray powder diffraction, magnetic susceptibility measurements and differential scanning calorimetry. The copper analogue of was also synthesized and its crystal structure solved. In comparison with the mononuclear systems, the polymeric mesogens of iron(II) are less sensitive to the glass transition, which was attributed to the moderate concomitant variation of the structure. Nevertheless, the observed increase of the magnetic hysteresis with lengthening of the alkyl substituents was ascribed to the interplay of the structural reorganization of the coordination core due to spin-crossover with the structural delay in the spatial reorganization of the mesogenic substituents. The classification of mononuclear and polymeric metallomesogens according to the interactions between the structural- and the spin-transition and analysis of the data on the reported spin-crossover metallomesogens led to the separation of three types, namely: Type i: systems with coupling between the electronic structure of the iron(II) ions and the mesomorphic behavior of the substance; Type ii: systems where both transitions coexist in the same temperature region but are not coupled due to competition with the dehydration or due to negligible structural transformation; Type iii: systems where both transitions occur in different temperature regions and therefore are uncoupled. Fine-tuning, in particular regarding the temperature at which the spin-transition occurs with hysteresis properties responsible for the memory effect, are still a major challenge towards practical implementation of spin-crossover materials. A possible answer to the problem could be materials in which the spin-crossover transition is coupled with another transition easily controllable by external stimuli. In the present thesis we have shown the viability of the approach realized in the mesogenic systems with coupled phase- and spin-transitions.