This paper presents a brief account of some striking aspects of Professor Hans Stammreich's life. We present in particular the highlights of his contribution to Raman spectroscopy, the contribution made to the development of molecular spectroscopy in Brazil, and details of his personal life. We also report the international recognition of his pioneering work and the legacy he left through the creation of the Molecular Spectroscopy Laboratory at the University of São Paulo.

A reatividade em fase gasosa das alcoxissilanas do tipo Me4-nSi(OEt)n (n = 1-3) foi investigada por ressonância ciclotrônica de íons por transformada de Fourier (FT-ICR) com o intuito de se caracterizar os mecanismos de ataque nucleofílico nesses importantes precursores de novos materiais. Nucleófilos como F-, MeO- e EtO- reagem rapidamente e de forma preferencial atacando o átomo de Si, formando a espécie pentacoordenada de Si. Esta em seguida sofre processos de eliminação iniciados, ou por um íon metídio nascente Me-, ou um íon etoxido EtO-, que por sua vez, podem abstrair um próton gerando carbânions ou silóxidos. Carbânions do tipo X(Me)3-nSi(OEt)nCH2 (X = F, MeO, EtO e n = 1-3) e silóxidos do tipo X(Me)4-nSi(OEt)n-1(X = F, MeO, EtO e n = 2-3) podem ser facilmente dissociados por excitação multifotônica no infravermelho induzida por um laser de CO2 gerando uma grande variedade de silóxidos simples e silicatos análogos à espécies intermediárias encontradas nas primeiras etapas de processos sol-gel. Para as alcoxissilanas que contêm mais grupos etóxido, uma reação competitiva análoga a uma eliminação E2 é observada, onde o nucleófilo abstrai um hidrogênio β de um grupo etoxila, eliminando etileno. A cinética, distribuição relativa de produtos e termoquímica dessas reações também são apresentadas para alguns casos específicos.

The gas-phase reactivity of the Me4-nSi(OEt)n (n = 1-3) alkoxysilanes was investigated by Fourier transform ion cyclotron resonance (FT-ICR) technique in order to characterize the fundamental mechanisms associated with nucleophilic attack on these important precursors of new materials. Typical nucleophiles such as F-, MeO- and EtO- react readily and preferentially by attack at the silicon center with formation of a pentacoordinated siliconate that undergoes elimination processes initiated by either a nascent methide ion, Me, or an ethoxide ion, EtO, that can abstract a proton -to yield either a carbanion or a siloxide-type anion. Carbanions of the type X(Me)3-nSi(OEt)nCH2 (X = F, MeO, EtO and n = 1-3) and siloxide ion of the type X(Me)4-nSi(OEt)n-1O- (X = F, MeO, EtO and n = 2-3) can be easily dissociated by infrared multiphoton excitation with a CO2 laser to give rise to a large variety of simple siloxide and silicate-type anions that are reminiscent of intermediate species in the early stages of sol-gel processes. For the higher-ethoxy containing substrates, a competing reaction is observed that is analogous to an E2 elimination reaction in which the nucleophile abstracts a β-proton from the ethoxy group leading to elimination of ethylene. The kinetics, relative product distribution and thermochemistry of these reactions are also reported for some specific cases.

Arrabidaea chica (crajiru) é uma importante planta da Amazônia. Seus extratos são usados como pigmento, agentes antimicrobianos e adstringentes. Três variedades diferentes desta espécie são cultivadas na região Amazônica. Neste trabalho, infusões diretas de extratos de A. chica destas três variedade foram analisadas por impressão digital via espectrometria de massas com ionização por eletrospray (ESI(+)-MS). Dados derivados destes espectros foram classificados utilizando um método de análise multivariada (PLS-DA, análise discriminante com calibração multivariada por mínimos quadrados parciais). O método direto aqui apresentado baseia-se na extração de folhas secas e em pó com uma solução de metanol/água acidificada sem manipulação adicional da amostra. A solução sobrenadante foi analisada através de infusão direta por ESI(+)-MS, o que resultou em perfis de composição para cada variedade. 3-Desoxiantocianidinas são importantes substâncias presentes na A. chica, seus íons foram usados como marcadores no tratamento de dados utilizando PLS-DA, o que possibilitou a separação das três variedades. Impressão digital por ESI(+)-MS funciona como um método simples e rápido para diferenciação de variedades de A. chica.

Arrabidaea chica (crajiru) is an important Amazonian plant. Its extracts are used as red pigments, antimicrobial agents and astringents. Three different varieties of this species are cultivated in the Amazon region. In this work, direct infusions of A. chica extracts from these three varieties were analyzed via electrospray ionization mass spectrometry (ESI(+)-MS) fingerprinting. Derived data from the spectra were classified by using a multivariate method (PLS-DA, partial least squares-discriminant analysis). The direct method that is herein presented relies on extraction of dry, powdered leaves with acidified methanol/water solution with no further sample preparation. The resulting supernatants were analyzed by direct infusion ESI(+)-MS, which provides characteristic fingerprints of the sample composition. 3-Deoxyanthocyanidins are important substances in A. chica, their ions were used as markers in the PLS-DA data treatment. PLS-DA was able to differentiate the three varieties. ESI(+)-MS fingerprinting works as a simple and fast method to differentiate varieties of A. chica.

Gas-phase SiCl3+ ions undergo sequential solvolysis type reactions with water, methanol, ammonia, methylamine and propylene. Studies carried out in a Fourier Transform mass spectrometer reveal that these reactions are facile at 10-8 Torr and give rise to substituted chlorosilyl cations. Ab initio and DFT calculations reveal that these reactions proceed by addition of the silyl cation to the oxygen or nitrogen lone pair followed by a 1,3-H migration in the transition state. These transition states are calculated to lie below the energy of the reactants. By comparison, hydrolysis of gaseous CCl3+ is calculated to involve a substantial positive energy barrier.

The gas-phase ion-molecule reactions of the Me3SiN(H)SiMe2+ ion, obtained by electron ionization from Me3SiN(H)SiMe3, have been studied in a Fourier transform ion cyclotron resonance spectrometer in order to understand the mechanistic details of an important chemical system presently used in film formation. This silyl cation has been observed to undergo addition reactions at electron rich centers to form stable adducts that may undergo further methane elimination in the case of alcohols and amines. The most important feature of these reactions is the fact that a metathesis type reaction can be observed in the presence of H2O, and other hydrogen labile substrates like alcohols, leading to the formation of the corresponding oxygen-containing ion, i.e. Me3SiOSiMe2+. For alcohols (ROH), facile formation of a tertiary product ion, presumably corresponding to an Me3Si-O-Si(Me)=O+-R structure with elimination of an amine reveals the strong tendency of these nitrogen-containing ions to undergo metathesis type reactions with oxygen containing substrates.