Development of a planar multibody model of the human knee joint

The aim of this work is to develop a dynamic model for the biological human knee joint. The model is formulated in the framework of multibody systems methodologies, as a system of two bodies, the femur and the tibia. For the purpose of describing the formulation, the relative motion of the tibia with respect to the femur is considered. Due to their higher stiffness compared to that of the articular cartilages, the femur and tibia are considered as rigid bodies. The femur and tibia cartilages are considered to be deformable structures with specific material characteristics. The rotation and gliding motions of the tibia relative to the femur cannot be modeled with any conventional kinematic joint, but rather in terms of the action of the knee ligaments and potential contact between the bones. Based on medical imaging techniques, the femur and tibia profiles in the sagittal plane are extracted and used to define the interface geometric conditions for contact. When a contact is detected, a continuous nonlinear contact force law is applied which calculates the contact forces developed at the interface as a function of the relative indentation between the two bodies. The four basic cruciate and collateral ligaments present in the knee are also taken into account in the proposed knee joint model, which are modeled as nonlinear elastic springs. The forces produced in the ligaments, together with the contact forces, are introduced into the system’s equations of motion as external forces. In addition, an external force is applied on the center of mass of the tibia, in order to actuate the system mimicking a normal gait motion. Finally, numerical results obtained from computational simulations are used to address the assumptions and procedures adopted in this study.     

Combined application of DP4+ and ANN-PRA to determine the relative configuration of natural products: The alpha-bisabol case study

The combination of computational methods and experimental data from Nuclear Magnetic Resonance (NMR) is a considerably valuable tool in the elucidation of new natural product structures and, also, in the structural revision of previously reported compounds. Until recently, only classical statistical parameters were used, for example, linear correlation coefficient (R²), mean absolute error (MAE), or root mean square deviation (RMSD), as a way to statistically “validate” the structure pointed out by experimental NMR spectra. Regarding the resolution of the relative configuration of organic molecules, novel tools were available in the last few years to assist in the NMR elucidation process. The most relevant are DP4+, which is based on a Bayesian probability, and ANN-PRA, which is based on artificial neural networks. The combined application of these tools has become the most accurate and important alternative to solve structural and stereochemical problems in natural product chemistry. Therefore, herein, in this case study, we intended to promote these novel tools, exploring the strengths and limitations of each approach in resolving the relative configuration of the sesquiterpene alpha-bisabol. We also highlighted the advantages of the complementary use of H- and C-DP4+ to obtain optimal results in the differentiation of the stereoisomers, validating the proposal with ANN-PRA method.     

DNA Damage Induced by Late Spring Sunlight in Antarctica

Sunlight ultraviolet (UV) radiation constitutes an important environmental genotoxic agent that organisms are exposed to, as it can damage DNA directly, generating pyrimidine dimers, and indirectly, generating oxidized bases and single-strand breaks (SSBs). These lesions can lead to mutations, triggering skin and eye disorders, including carcinogenesis and photoaging. Stratospheric ozone layer depletion, particularly in the Antarctic continent, predicts an uncertain scenario of UV incidence on the Earth in the next decades. This research evaluates the DNA damage caused by environmental exposure to late spring sunlight in the Antarctic Peninsula, where the ozone layer hole is more pronounced. These experiments were performed at the Brazilian Comandante Ferraz Antarctic Station, at King’s George Island, South Shetlands Islands. For comparison, tropical regions were also analyzed. Samples of plasmid DNA were exposed to sunlight. Cyclobutane pyrimidine dimers (CPDs), oxidized base damage and SSBs were detected using specific enzymes. In addition, an immunological approach was used to detect CPDs. The results reveal high levels of DNA damage induced by exposure under the Antarctic sunlight, inversely correlated with ozone layer thickness, confirming the high impact of ozone layer depletion on the DNA damaging action of sunlight in Antarctica.     

Detailed 1H and 13C NMR structural assignment of ent-polyalthic acid,a biologically active labdane diterpene

In this paper, a complete ¹H and ¹³C NMR data assignment of ent-polyalthic acid, a biologically active labdane-type diterpene, is presented. The assignments were carried on the basis of spectroscopic data from ¹H NMR, ¹³C{¹H} NMR, gCOSY, gHMQC, and gHMBC experiments. Furthermore, a software-assisted methodology, using FOMSC3_rm_NB and NMR_MultSim programs, supported the detailed and unequivocal assignment of ¹H and ¹³C signals, allowing all hydrogen coupling constants to be determined and thus clarifying all hydrogen signal multiplicities.     

Thermal,spectroscopic and antimicrobial activity characterization of some norfloxacin complexes

Journal of Thermal Analysis and Calorimetry - Coordination compounds of transition metals with norfloxacin (Nor) have potential to improve its effectiveness, as already discussed for some compounds...     

Entropy analysis of human death uncertainty

Nonlinear Dynamics - Uncertainty about the time of death is part of one’s life, and plays an important role in demographic and actuarial sciences. Entropy is a measure useful for...     

Structural and physical–chemical evaluation of Bradykinin Potentiating Peptide and its high soluble supramolecular complex

The supramolecular interactions between a Bradykinin Potentiating Peptide (BPP10c) and β-cyclodextrin (βCD) have been investigated by using several techniques. These new properties acquired by the inclusion phenomena are important in developing a strategy for pharmaceutical formulation. The BPP10c structural elucidation and its inclusion complex formed have been investigated using Nuclear Magnetic Resonance techniques. The peptide secondary structure was investigated using infrared spectroscopy in solution, Circular Dichroism and NMR. In addition, the thermodynamic parameters of the inclusion process were also evaluated using Isothermal Titration Calorimetry. The results obtained by these physical–chemical techniques suggested a 1:1 complex formed by interaction between the Tryptophan amino acid residue and the βCD cavity. The peptide secondary structure was not substantially modified for the inclusion process. In addition, the inclusion process proved to be spontaneous (ΔGº = ?2.53 kcal mol^?1), with an enthalpy reduction (ΔHº = ?3.72 kcal mol^?1) and a favored entropic variation (TΔSº = ?1.19 kcal mol^?1).     

A new methodology for processing mouthparts of hemipterans (Hemiptera) for microscopic studies

A new methodology has been developed to produce sections as thin as 5 μm of stink bug (Heteroptera: Pentatomidae) mouthparts for morphological studies. Heads of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae) were fixed on Bouin solution, and treated with EDTA (ethylenediamine tetraacetic acid 7%) in an ice bath within a microwave oven for 0.5, 1, 2, 3, 4, and 5 h. The chitin structures and labium soft parts were well preserved after 0.5 h EDTA treatment. Longer times of exposure to EDTA and microwave irradiation caused damage to mouthpart structures.