Στην εργασία αυτή μελετάμε μια σειρά από αντιπροσωπευτικά νανοφασικά συστήματα πυριτίου, στο πλαίσιο κοινών ιδιοτήτων και αρχών που θα βοηθήσουν σε μελλοντικές εφαρμογές σχεδιασμού μοριακών υλικών βασισμένων σε αυτά τα συστήματα. Οι κατηγορίες των συστημάτων με τα οποία ασχολούμαστε είναι (α) υδρογονωμένα και μη-υδρογονωμένα νανοσυσσωματώματα και νανοκρυσταλλικά συστήματα πυριτίου με ή χωρίς ενσωματωμένα μέταλλα μετάπτωσης, που αποτελούν χαρακτηριστικά μοντέλα ενδοεπιφάνειας μετάλλου−ημιαγωγού, (β) υπέρλεπτα υδρογονωμένα νανοσύρματα πυριτίου και (γ) οργανομεταλλικά πολλαπλών στρώσεων (multidecker-sandwiches) πυριτίου−άνθρακα. Εκτός από τη μελέτη των δομικών, ηλεκτρονικών, οπτικών, δονητικών και μαγνητικών ιδιοτήτων των συστημάτων, εστιάζουμε στην αναζήτηση μηχανισμών σταθεροποίησης και την εύρεση και καθορισμό κανόνων που μπορούν να λειτουργήσουν ως «εργαλεία μοριακού σχεδιασμού» με τη γενικότερη δυνατή ισχύ. Τα συσσωματώματα πυριτίου σταθεροποιούνται μέσου των μετάλλων μετάπτωσης σε δομές κλωβού και χαρακτηρίζονται συχνά από υψηλή συμμετρία και μεγάλα ενεργειακά χάσματα, ιδιότητες επιθυμητές για εφαρμογές στην οπτοηλεκτρονική και νανοηλεκτρονική. Στη μελέτη των νανοσυρμάτων πυριτίου συγκρίνουμε την σταθερότητα μεταξύ νανοσυρμάτων με διαφορετικές επιφανειακές δομές ενώ διατυπώνουμε κανόνα «μαγικότητας» νανοσυρμάτων με τον οποίο ερμηνεύουμε την σταθερότητά τους και την συνδέουμε με την ελαστικότητα και την κατανομή υδρογόνου στην επιφάνεια τους. Τέλος, βασιζόμενοι στην ισολοβική αρχή the boron connection, σχεδιάζουμε και μελετάμε μια νέα κατηγορία νανοδομών τύπου multidecker sandwiches οργανοπυριτίου. Στη διάρκεια εκπόνησης αυτής της διατριβής δημοσιεύτηκαν συνολικά 19 εργασίες σε διεθνή περιοδικά και σε πρακτικά συνεδρίων. / In this work we study a series of representative nanoscale systems based on silicon, in the context of common properties and principles which will assist in future applications in designing molecular materials based on these systems. The categories of the systems which we work on are (a) hydrogenated and non-hydrogenated silicon nanoclusters and nanocrystallic systems with or without embedded transition metals, which constitute models of metal−semiconductor interfaces, (b) ultrathin hydrogenated silicon nanowires and (c) organometallic silicon−carbon multidecker-sandwiches. In addition to the study of structural, electronic, optical, vibrational and magnetic properties of these systems, we focus on a search for stabilizing mechanisms and in finding and defining rules that can function as “molecular designing tools” with the broadest possible validity. The silicon nanoclusters are stabilized to cage-like structures by the insertion of transition metals and are characterized by high symmetry and large energy gaps, desirable properties for applications in optoelectronics and nanoelectronics. In the study of silicon nanowires we compare the stability between nanowires with different surface structures while we formulate “magicity” rules for nanowires with which we interpret their stability and associate it with their elasticity and the distribution of the surface hydrogen. Finally, based on the isolobal principle the boron connection, we design and study a new class of organometallic multidecker-sandwich type nanostructures. During the elaboration of this dissertation we published overall 19 papers in international scientific journals and conferences’ proceedings.

Submitted by Geandra Rodrigues (geandrar@gmail.com) on 2018-09-27T15:51:52Z No. of bitstreams: 1 daniellelobojustopinheiro.pdf: 20180936 bytes, checksum: 98e45bb923da9d2234c5a70398868760 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-10-01T18:08:20Z (GMT) No. of bitstreams: 1 daniellelobojustopinheiro.pdf: 20180936 bytes, checksum: 98e45bb923da9d2234c5a70398868760 (MD5) / Made available in DSpace on 2018-10-01T18:08:20Z (GMT). No. of bitstreams: 1 daniellelobojustopinheiro.pdf: 20180936 bytes, checksum: 98e45bb923da9d2234c5a70398868760 (MD5) Previous issue date: 2018-09-09 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Azalactonas são heterociclos derivados de aminoácidos protegidos e ciclizados. Por conter em sua estrutura um sítio eletrofílico, um sítio pro-nucleofílico, além de um sítio nucleofílico ou eletrofílico (que será determinado pelas condições reacionais), esses compostos são extremamente versáteis. Nesse trabalho é demonstrado a reação das azalactonas com o reagente de Schwartz, que através de uma de redução quimiosseletiva gera derivados de aminoaldeídos com excelentes rendimentos em apenas 2 minutos de reação. Outra reação de redução quimiosseletiva demonstrada no trabalho envolve o uso de azalactonas de Erlenmeyer, hidrogênio e Pd/C como catalisador. Dessa forma, azalactonas saturadas funcionalizadas, foram possíveis de ser obtidas em uma metodologia simples, com excelentes rendimentos. O processo foi ainda adaptado para reações em um sistema one-pot, produzindo assim, adutos de Michael, Mannich e produtos de abertura de maneira simples e eficiente. O sítio nucleofílico das azalactonas também é explorado em reações de dimerização diastereosseletivas, utilizando uma base de Brønsted formada in situ pela reação entre acetonitrila e sal tricloroacetato de potássio ou sódio. O mecanismo da reação e estudos cinéticos são demonstrados a partir de uma análise obtida por experimentos online no RMN de ¹H. Além disso, um análogo de um produto natural é obtido através de uma redução estereosseletiva dos dímeros. O sítio nucleofílico das azalactonas também é explorado em reações de carbonilação α-arilativa catalisadas por Pd, utilizando o sistema de duas câmaras, seguido de sua abertura, obtendo, dessa forma, aminoácidos α,α-dissubstituídos protegidos. O mecanismo da reação é proposto após reações controle terem sido realizadas. Os mesmos aminoácidos também puderam ser sintetizados e marcados com o ¹³C. Esses compostos marcados foram aplicados em reações quimiosseletivas, como a reação de descarboxilação de Krapcho, reduções quimiosseletivas, e síntese de heterociclos como as oxazolonas e pirazolonas. / Azlactones are heterocycles derived from amino acids. There are an electrophilic site, a pro-nucleophilic site, and a nucleophilic or electrophilic site (determined by the reaction conditions). These compounds are extremely versatile. In this work the reaction of the azlactones with Schwartz reagent is demonstrated. A chemosselective reduction of these compounds is possible to generate aminoaldehydes in excellent yields in only 2 minutes reaction. Chemosselective reduction of Erlenmeyer azlactones is also demonstrated by using hydrogen gas and Pd / C as a catalyst. In this way, functionalized saturated azlactones are possible to obtain in excellent yields. The process was further adapted to reactions in a one-pot system, producing Michael, Mannich and opening products in a simple and efficient manner. The nucleophilic site of azlactones is also explored in the diastereoselective dimerization reactions promoted by a Brønsted base, affording by the reaction in situ between acetonitrile and potassium or sodium trichloroacetate salt. The mechanism of the reaction and kinetic studies are demonstrated from an analysis obtained by ¹H NMR online experiments. In addition, a stereoselective reduction of a dimer analogue gave a natural product in high both yield and diastereoselectivity. The nucleophilic site of the azalactones is exploited in Pd catalyzed α- arylation carbonylation reactions, using the two-chamber system, followed by their opening, thereby obtaining protected α,α -disubstituted amino acids. The mechanism of the reaction is proposed based on control reactions. The same amino acids could also be synthesized with ¹³C-labeled CO. These coumpounds were applied in chemosselective reactions, such as krapcho decarboxylation reaction, chemosselective reduction, and synthesis of heterocycles such as oxazolones and pyrazolones.