Bulk and surface switching in Mn-Fe-based Prussian Blue Analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.Comment: 12 pages, 8 figure

Species-specific differences of the spectroscopic properties of P700 - Analysis of the influence of non-conserved amino acid residues by site-directed mutagenesis of photosystem I from Chlamydomonas reinhardtii

We applied optical spectroscopy, magnetic resonance techniques, and redox titrations to investigate the properties of the primary electron donor P700 in photosystem I (PS I) core complexes from cyanobacteria (Thermosynechococcus elongatus, Spirulina platensis, and Synechocystis sp. PCC 6803), algae (Chlamydomonas reinhardtii CC2696), and higher plants (Spinacia oleracea). Remarkable species-specific differences of the optical properties of P700 were revealed monitoring the ((3)P700-P700) and (P700(+.)-P700) absorbance and CD difference spectra. The main bleaching band in the Q(y) region differs in peak position and line width for the various species. In cyanobacteria the absorbance of P700 extends more to the red compared with algae and higher plants which is favorable for energy transfer from red core antenna chlorophylls to P700 in cyanobacteria. The amino acids in the environment of P700 are highly conserved with two distinct deviations. In C. reinhardtii a Tyr is found at position PsaB659 instead of a Trp present in all other organisms, whereas in Synechocystis a Phe is found instead of a Trp at the homologous position PsaA679. We constructed several mutants in C. reinhardtii CC2696. Strikingly, no PS I could be detected in the mutant YW B659 indicating steric constraints unique to this organism. In the mutants WA A679 and YA B659 significant changes of the spectral features in the ((3)P700 - P700), the (P700(+.)-P700) absorbance difference and in the (P700(+.)-P700) CD difference spectra are induced. The results indicate structural differences among PS I from higher plants, algae, and cyanobacteria and give further insight into specific protein-cofactor interactions contributing to the optical spectra

Inibição do metabolismo de diferentes linhagens de Saccharomyces cerevisiae induzida por Brettanomyces custersianus.

Leveduras do gênero Dekkera/Brettanomyces causam problemas ao vinho, afetando as propriedades sensoriais do produto final, como aparência, aroma e sabor.Resumo

Qualidade de sementes de forrageiras utilizadas por agricultores familiares para a formação de pastagens de inverno.

O objetivo foi realizar um levantamento da qualidade de sementes forrageiras utilizadas por agricultores familiares para formação de pastagens de inverno, no noroeste do Rio Grande do Sul, e discutir os dados diante dos padrões legais e em função da origem da semente.Edição do XXV Seminário de Iniciação Científica; XXII Jornada de Pesquisa; XVII Jornada de Extensão; VII Mostra de Iniciação Científica Júnior; VII Seminário de Inovação e Tecnologia, Ijuí. Publicado SIVA, G. M. da

Blade debitage in Southern Brazil: We have cores! [Debitagem laminar no Sul do Brasil: Habemus nucleos!]

Durante a pré-história, a debitagem laminar é um modo de produção característico de determinados períodos e regiões. No Brasil, no momento, foi reconhecida em três sítios arqueológicos situados no alto vale do rio Uruguai (SC/RS), em contextos sedimentares que datam do Holoceno inicial. Até hoje, somente os produtos dessa debitagem, as lâminas, tinham sido encontrados. A falta dos núcleos impedia um entendimento completo do processo de lascamento desses suportes. Graças à retomada das pesquisas na região desde 2013, foi possível coletar núcleos associados a essa produção laminar. Nesse artigo, descrevemos cinco desses núcleos. Suas análises demonstram que essa debitagem laminar corresponde a um único conceito. A estrutura volumétrica do núcleo que resulta desse conceito respeita as seguintes normas: 1) Os núcleos apresentam duas superfícies: um dorso plano e uma superfície de debitagem convexa mas relativamente achatada. Em uma extremidade, uma pequena superfície plana serviu de plano de percussão; 2) A debitagem começa por uma fase de inicialização durante a qual o plano de percussão é produzido por uma grande retirada. Em função das propriedades naturais do volume inicial, o dorso do núcleo é obtido, seja durante a seleção do bloco, seja por uma preparação por grandes retiradas transversais. Quando existem ainda, os negativos de retiradas da inicialização da superfície de debitagem indicam um método centrípeto; 3) As lâminas são sempre produzidas por um método unidirecional paralelo. A variabilidade desta debitagem é principalmente relacionada à técnica de lascamento: a percussão com pedra e a percussão com percutor orgânico foram utilizadas para a obtenção das lâminas. As informações tecnológicas fornecidas pelos núcleos aqui analisados são coerentes com essas observações oriundas da análise das lâminas. Com esses dois estudos consegue-se atingir um conhecimento completo desse sistema de produção do alto vale do rio Uruguai durante o Holoceno inicial, a única debitagem laminar documentada até hoje no Brasil.Blade debitage is a characteristic production pattern of specific periods and regions during Prehistory. In South America, it is well documented in Argentina, in contexts dating back to early Holocene. In Brazil, it was unknown until 2006, when it was found in three archaeological sites (ACH-LP-01, ACH-LP-03, ALP-AA-03) in the Foz do Chapecó area, upper Uruguay River, South Brazil, in layers from early Holocene. It was associated there with a great variety of other production systems: bifacial shaping of projectile points and large tools, unipolar debitage of large flakes, bipolar debitage of tiny flakes. Silicified sandstone, chalcedony and hyaline quartz are the main used raw materials. To this day, only the products of this debitage, the blades, had been discovered. Cores were lacking, which prevented a complete understanding of the flaking process. Due to the resumption of research in the region from 2013, it was possible to find those cores during surveys in the two following archaeological sites: ACH-LP-07 and RS-URG-01, located on both sides of the Uruguay river, near the mouth of the Chapecó river. We describe in this article five of these cores (4 from ACH-LP-07 and 1 from RS-URG-01). Their analyses demonstrate that this blade debitage complies with only one concept. The core volumetric structure that is the result of this concept displays the following features: 1) Cores have two surfaces: a flat back and a convex but relatively flattened flaking surface, so that they have a general “D” shaped transversal section. At one end, a small surface acts as striking platform during the production of the blades; 2) Debitage begins with a initialization phase of the core during which the striking platform is produced by a large removal. According to the natural properties of the initial volume, the back of the core is obtained either during the selection of the blank, and then it is left in his natural state, or by a preparation by one or more large transversal removals. When present, the scars of the initialization phase of the flaking surface indicate the use of a centripetal method. This preparation is made possible by the acute angle of the peripheral ridge formed by the intersection of the back and the flaking surface ; 3) Blades are always produced by a unidirectional parallel method. Production variability is mainly related to the flaking technique: both internal percussion by stone and marginal percussion by organic percussor were used to get the blades. Technical information provided by the cores are complementary and in accordance with those from the previous analyses of the blades from the same area. With these two studies it was possible to reach a relatively exhaustive understanding of this production system in the upper Uruguay River during early Holocene, the only well documented blade debitage in Brazil known until now. Future research will explore the interactions between this production and the other debitage and shaping methods inside this early Holocene technological system. To do this, we will develop a comprehensive study of all lithic artefacts from the archaeological layers in which blade production was identified. In a wider scale, a comparative approach with Argentinian and Uruguayan prehistoric blade productions will allow to better understand the development of the blade phenomenon in the southern cone of South America