Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os solos da região tropical úmida do Brasil são diversificados devido ao seu material de origem, clima e relevo. São, na sua maioria, de baixa fertilidade, sendo o fósforo (P) disponível nesses solos, geralmente, baixo. A dinâmica do P no solo torna sua determinação complexa, sobretudo pelas características distintas dos extratores. Objetivou-se com este trabalho avaliar a capacidade máxima de adsorção de fósforo (CMAP) e a eficiência dos extratores Mehlich-1, Mehlich-3, Bray-1 e Resina na determinação do P disponível em solos representativos do estado de Roraima. Sete solos foram coletados em três regiões do Estado e determinadas suas propriedades morfológicas, mineralógicas, físicas e químicas. Para avaliar a CMAP dos solos, foi determinado o P remanescente (P-rem) dos solos em triplicata no laboratório para cada solo e quatro repetições. O P-rem de cada solo foi empregado para definir os padrões de P em solução a serem utilizados na determinação da CMAP por intermédio de isotermas de Langmuir. Para testar a eficiência dos extratores, foi conduzido experimento em condições de casa de vegetação. O delineamento empregado foi em blocos casualizados, em esquema fatorial 7 x 5, com quatro repetições. O primeiro fator consistiu dos sete solos (LA (ITÃ), LV (ITÃ), LA (SERRA DA PRATA), LA (CCA), PA (CCA), FT (BONFIM), SN (SURUMU)) e o segundo fator de cinco doses de P estimadas com base na CMAP de cada solo (0, 25, 50, 75 e 100% da CMAP). A parcela consistiu de um vaso de polietileno preto com 5 dm3 de solo e cinco plantas. A espécie utilizada foi o milho, híbrido 30F35YH Pioneer, cultivada em duas fases de 30 dias com intervalos de dois dias. As doses de P foram aplicadas cinco dias antes do plantio utilizando o fosfato monopotássico (KH2PO4) como fonte. Amostra de solo de cada parcela (200 g) foi retirada antes do plantio para determinação do P disponível empregando os extratores. Ao final de cada período, fez-se o corte das plantas, acondicionando-as em saco tipo Kraft e levando-as à estufa de circulação forçada a 60 C para obtenção da massa seca. Foram realizados teste de correlação para CMAP versus energia de ligação, pH, matéria orgânica, argila e CTC, além da matéria seca x extrator e extrator x extrator. A CMAP é superior no FT (BONFIM) e LV (ITÃ) devido ao tipo de argila e teor da fração respectivamente. Considerando os solos representativos do estado, a CMAP não se correlaciona com nenhuma das propriedades do solo analisadas, obtendo relação forte com a argila quando elencados apenas os Latossolos e Argissolos. Os extratores Mehlich-3 e Bray-1 são mais sensíveis às variações das propriedades dos solos, não sendo indicados para grupos heterogêneos de classes de solos. O método da Resina apresenta as maiores correlações com os diferentes solos individualmente e agrupados. Este extrator demonstra-se adequado na determinação do P disponível para as plantas para os solos da região tropical úmida do país. / The soils of the humid tropical region of Brazil are diversified because of its source material, climate and topography. They are mostly low fertility, with available phosphorus (P) in these soils generally low. The dynamic of soil P becomes a complex determination, especially by the distinct characteristics of the extractors. The objective of this study was to evaluate the maximum phosphorus adsorption capacity (MPAC) and the efficiency of Mehlich-1, Mehlich-3, Bray-1 and Resin extractors in the determination of available P in soils of the state of Roraima. Seven soils were collected in three regions of the state and determined its properties morphological, mineralogical, chemical and physical. To evaluate the MPAC of the soils, was determined the remaining P (P-rem) of the soil in triplicate for each soil in the laboratory and four replications. The P-rem of each soil was used to define the patterns of P in solution to be used in determining the MPAC by Langmuir isotherm. To test the efficiency of extracting, the experiment was conducted in greenhouse conditions. The design applied was in a randomized blocks design, in factorial scheme 5 x 7 with four replications. The first factor consisted of the seven soils (LA (ITA), LV (ITA), LA (SERRA DA PRATA), LA (CCA), PA (CCA), FT (BONFIM), SN (SURUMU)) and the second factor of five P rates estimated based on the MPAC of each soil (0, 25, 50, 75 and 100% of MPAC). The plot consisted of a black pot polyethylene with 5 dm3 of soil and five plants. The species used was corn, hybrid 30F35YH - Pioneer, grown in two phases of 30 day within interval of two days. The P was applied five days before planting using potassium dihydrogen phosphate (KH2PO4) as a source. Soil samples from each plot (200 g) were collected before planting to determine the available P using the extractors. At the end of each period, the plants were cut, packed in kraft bag and taking them to the forced circulation oven at 60 C to obtain the dry mass. Correlation test for MPAC versus binding energy, pH, organic matter, clay and T were performed, in addition to dry matter x extractor and extractor x extractor. The MPAC is higher in FT (BONFIM) and LV (ITA) due to the type and content of clay fraction respectively. Considering the representative soils of the state, the MPAC is not correlated with any of the soil properties analyzed, obtaining strong relationship with the clay when listed only the Oxisols and Ultisols. The Mehlich-3 and Bray-1 extractors are more sensitive to changes in soil properties and are not suitable for heterogeneous groups of soils. The resin method exhibit the highest correlation with the different soils individually and grouped. This extractor is demonstrated appropriate in determining of the available P for plants to soils of the humid tropical region of the country.

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Molecular dynamics simulation was used to study ion permeation through different membrane proteins embedded in a lipid bilayer (DMPC) with different saline solutions. The potential of mean force (PMF) for ion transport was obtained by umbrella sampling simulations. A revised MacKerell force field for tryptophan residues was studied using gramicidin A (gA) channel as a test model. The revised force field contribution to the Na+ PMF was consonant with the prediction from the experimental results, but in stark contrast to the prediction of the CHARMM force field, version 22, for the tryptophan side-chain. A new grid-based correction map algorithm by MacKerell group, called CMAP, was introduced into the CHARMM force field, version 31. The CMAP algorithm focused on optimizing phi, psi dihedral parameters for the peptide backbone. The CMAP corrections reduced the excessive translocation barrier. Decomposition demonstrated the reduction in the translocation barrier was due to effects on the K+ PMFH2O rather than on K+ PMFgA. The presence of negatively charged sulfonate group at the entrance and exit of the gA channel affected the depth and the location of the highly occupied sites. The negatively charged sulfonate group produced a strong attraction for the cations in the bulk towards the channel mouth. In the M2 transmembrane domain channel (M2-TMD), three M2-TMD structures were studied, differing only in whether the selectivity-filter (four His37 side-chains) was uncharged, +2 charged, or +3 charged. M2-TMD structural properties were compared with the structural properties of other models extracted from NMR and X-ray studies. The spontaneous cation and anion entry into the charged selectivity-filter was different from that into a neutral selectivity-filter. Cl- ions had a lower free-energy barrier in the selectivity-filter than either Na+ or NH4+ ions through the M2-TMD channel. NH4+ ions had a lower free-energy barrier in the selectivity-filter than Na+ ions. Based on accessible rotamer conformations, a revised conductance mechanism was proposed. In this conductance mechanism, the His37 side-chain functioned as an acceptor and donor group, whereas the Trp41 side-chain functioned as a carrying group.

No description available.