Effect of the radiolitic sterilization in polyethylene/starch blends

Samples of LDPE/modified starch blends 80/20 m/m before and after exposure to gamma rays were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The effect of gamma radiation is clearly seen in the samples irradiated at a dose of 25 kGy. The main alteration in the polymeric material after exposure at the radiation range was a decrease in the mechanical properties, alterations in the chemical structure of the blend with an increase in the carbonyl and vinyl indices and the appearance of new crystalline symmetry generating a crystalline domain not existing before in the blend.

Estudos espectroscópicos e estruturais dos polímeros de coordenação 2D, ∞[Tb(DPA)(HDPA)] e ∞[Gd(DPA)(HDPA)]

This paper presents the synthesis of the coordination polymers ∞[Ln(DPA)(HDPA)] (DPA=2,6-pyridinedicarboxylate; Ln= Tb and Gd), their structural and spectroscopic properties. The structural study reveals that the ∞[Ln(DPA)(HDPA)] has a single Ln+3 ion coordinated with two H2DPA ligands in tridentade coordination mode, while two others H2DPA establish a syn-bridge with a symmetry-related Ln3+, forming a two-dimensional structure. The spectroscopic studies show that ∞[Tb(DPA)(HDPA)] compound has high quantum yield (q x≈ 50.0%), due to the large contribution of radiative decay rate. Moreover triplet level is localized sufficiently over the emitter level 5D4 of theTb3+ ion, avoiding a retrotransference process between these states.

A primeira lei da termodinâmica dos processos homogêneos

Thermodynamics of homogeneous processes, which corresponds to the very special situation in thermodynamics of continuous media, is used to discuss the first law. An important part of this work is the exposition of some typical mathematical errors, frequently found in the traditional presentation of thermodynamics. The concepts of state and process functions are discussed, as well as reverse and reversible processes, temporality and its implications on thermodynamics, energy reservoirs and symmetry. Our proposal is to present the first law by using a time dependent viewpoint coherent with mechanics and the foundations of that viewpoint.

Oxocarbonos, pseudo-oxocarbonos e esquaraínas

Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.

Evolução biomolecular homoquiral: a origem e a amplificação da quiralidade nas moléculas da vida

The fact that biologically relevant molecules exist only as one of the two enantiomers is a fascinating example of complete symmetry breaking of chirality and has long intrigued our curiosity. The origin of this selective chirality has remained a fundamental enigma with regard to the origin of life since the time of Pasteur, 160 years ago. The symmetry breaking processes, which include autocatalytic crystallization, asymmetric autocatalysis, spontaneous crystallization, adsorption and polymerization of amino acids on mineral surfaces, provide new insights into the origin of biomolecular homochirality.

Eixo quinário: um elemento de simetria presente em moléculas e quasi-cristais - um experimento didático em cristalografia

Axis of quinary symmetry occur in molecular symmetry, as in the case of fullerenes, and in crystalline symmetry, in the quasicrystals. Minerals with pentagonal faces do not have this element of symmetry, as the pyrite (FeS2) which shows a ridge that is different from the other ones, in any face of the crystal. The purpose of this paper is to demonstrate conceptual differences between pyritohedron and regular pentagonal dodecahedron symmetries, discussing students' difficulties to identify them. Also is proposed a didactic experiment with spatial models of the above-mentioned forms and the demonstration of its symmetries in clinographic projections.

A brief introduction to molecular orbital theory of simple polyatomic molecules for undergraduate chemistry students

A simple, four-step method for better introducing undergraduate students to the fundamentals of molecular orbital (MO) theory of the polyatomic molecules H2O, NH3, BH3 and SiH4 using group theory is reported. These molecules serve to illustrate the concept of ligand group orbitals (LGOs) and subsequent construction of MO energy diagrams on the basis of molecular symmetry requirements.

SAPT: ligação de hidrogênio ou interação de van der Waals?

It is through the application of an electronic partition approach called Symmetry-Adapted Perturbation Theory (SAPT) that the nature of hydrogen bonds and van der Waals interactions can be unveiled according to the contribution of electrostatic, charge transfer, exchange repulsion, polarization, and dispersion terms. Among these, electrostatic partition governs the formation of the hydrogen bonds, whose energies are arguably high. However, the weakness of the interaction strength is caused by dispersion forces, whose contribution decisively lead to the stabilization of complexes formed via van der Waals interactions.

O ESTADO DA ARTE DA LIGAÇÃO DE HIDROGÊNIO

Along the historical background of science, the hydrogen bond became widely known as the universal interaction, thus playing a key role in many molecular processes. Through the available theoretical approaches, many of these processes can be unveiled on the basis of the molecular parameters of the subject intermolecular system, such as the variation of bond length and mainly the frequency shift observed in the proton donor. Supported by the natural bond analysis (NBO) with the quantification of the hybridization contributions, the structural deformations and vibrational effects cited above are also attributed to the outcome of the intermolecular interaction strength, which consequently can be estimated by means of the quantum theory of atoms in molecules (QTAIM) as well as evaluated by the symmetry-adapted perturbation theory (SAPT). Moreover, to identify the preferential interaction sites for proton donors and acceptors, the molecular electrostatic potential (MEP) is useful in this regard.

Crystal structures of 5-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Zn(II)

The crystal and molecular structures of [bis(5-chloro-2-methoxybenzoate)tetraaquamanganese(II)], [pentaaqua(5-chloro-2-methoxybenzoato)cobalt(II)] (5-chloro-2-methoxybenzoate), [pentaaqua(5-chloro-2-methoxybenzoato)nickel(II)] (5-chloro-2-methoxybenzoate) and [aquabis(5-chloro-2-methoxybenzoate)zinc(II)] monohydrate were determined by a single-crystal X-ray analysis. Mn(H2O)4L2 (where L = C8H6ClO3) crystallizes in the monoclinic system, space group P21/c. [Co(H2O)5L]L and [Ni(H2O)5L]L both are isostructural, space group P212121. The crystals of [Zn(H2O)L2] H2O are monoclinic, space group Pc. Mn(II) ion is positioned at the crystallographic symmetry center. Mn(II) and Co(II) ions adopt the distorted octahedral coordination but Zn(II) tetrahedral one.The carboxylate groups in the complexes with M(II) cations function as monodentate, bidentate and/or free COO-groups. The ligands exist in the crystals as aquaanions. The complexes of 5-chloro-2-methoxybenzoates with Mn(II), Co(II) and Zn(II) form bilayer structure.

Thermal and spectral properties of di-and trimethoxybenzoates of silver (I)

The complexes of silver(I) with 2,3-, 2,4-, 2,6-, 3,4-, 3,5-dimethoxy-, and 2,3,4- and 3,4,5-trimethoxybenzoic acid anions have been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric and X-ray studies. Their solubility in water has been also determined at 293K. All analysed complexes were found to be crystalline, anhydrous compounds with low symmetry. The carboxylate groups act as bidentate or monodentate ligands. The thermal stability of compounds has been examined in air in temperature range of 293-1173K. The analysed complexes were found to be stable at room temperature and their solubilities in water at 293K to be in the order of 10-4 mol.dm-3.

Lecythidaceae Poit. in the Tupé Sustainable Development Reserve, Manaus, Brazil

Lecythidaceae is the family of the Brazil nut, and comprises about 300 species belonging to 17 genera with pantropical distributions. One hundred and twenty-two species belonging to nine genera are distributed throughout Brazil, demonstrating its greatest diversity in the Amazon rainforest where Lecythidaceae is also one of the most abundant families. It is usually difficult to collect fertile material from these trees because of their canopy heights, and species determinations using sterile material can be complex because of their morphological similarities. There have been relatively few studies of this family even though it is one of the most important groups in the Amazon region, and a detailed taxonomic treatment of the species of Lecythidaceae in the Tupé Sustainable Development Reserve was therefore the goal of the present work. Ten species were found, Allantoma lineata (Mart. ex O.Berg) Miers, Bertholletia excelsa Bonpl., Couratari tenuicarpa A.C.Sm., Lecythis poiteaui O. Berg; and six species of Eschweilera, the richest genus. The descriptions and identification keys of the species used 56 characters. The main reproductive characters useful for distinguishing the species were the pubescence of the inflorescence rachis, pedicel length and trichomes presence, floral symmetry, hood type, filament shape, stigma shape, fruit shape and size, and aril type. The most diagnostic vegetative characters were the type and color of the outer bark, inner bark color, midrib prominence, and petiole shape and pubescence.

Occurrence of Akodon cursor (Rodentia, Cricetidae) with 14, 15 and 16 chromosome cytotypes in the same geographic area in Southern Brazil

The karyotype of Akodon cursor (initially identified as A. arviculoides) had been reported with chromosomal numbers 14 and 15 in the South and Southeast and 16 in Northeastern Brazil. We found the three cytotypes in a region of Southern Brazil. The G-band patterns of these specimens were the same as those from southeastern and northeastern regions. Seventeen different combinations of chromosomes due to a complex rearrangement in pair 1 and pericentric inversions in pairs 2 and 3 were identified. Seven of these combinations are new to in the literature.

Trisomy 13 mosaicism demonstrated only in skin fibroblasts in a patient presenting psychomotor retardation, pigmentary dysplasia and some dysmorphic features

A Brazilian female infant presented delayed psychomotor development, skin pigmentary dysplasia and some dysmorphic features. Chromosome analysis from peripheral blood culture was normal, but the karyotype from skin fibroblasts revealed mosaicism for trisomy 13. This case demonstrates the relevance of performing chromosomal analysis of skin fibroblasts in patients with mental retardation, associated with pigmentary dysplasia of the skin and a normal karyotype in peripheral blood lymphocytes. To our knowledge, it is the first report of trisomy 13 demonstrated only in skin fibroblasts.

First description of microchromosome in the Anostomidae fish Schizodon nasutus from Argentina

Thirty-six specimens of Schizodon nasutus (Anostomidae-Characiformes) from the middle Paraná River (Posadas, Argentina) were analyzed cytogenetically. The karyotype of this species was similar to those described for this species in the literature. C-banding technique showed a rich heterochromatic pattern relative to other Anostomidae species. The NORs were located on one chromosome pair in terminal position and showed a very marked size heteromorphism. A microchromosome was observed with a frequency of about 20% in the sample studied. This additional element was punctiform, negative C-band, and constant in all metaphase plates of the seven carriers. The present study is the first karyotypic approach to Schizodon nasutus from Argentina and the first description of microchromosome in Anostomidae