RESUMO
Oxidative stress caused by pollution and lifestyle changes causes an excess of free radicals that react chemically with cell constituents leading to irreversible damage. There are molecules known as antioxidants that reduce the levels of free radicals. Some pigments of fruits and vegetables known as anthocyanins have antioxidant properties. Their interaction with the cell membrane becomes a crucial step in studying these substances. In this research, molecular dynamics simulations, particularly, coarse-grained molecular dynamics (CGMD) were used. This technique aims to replace functional groups with corresponding beads that represent their level of polarity and affinities to other chemical groups. Also, umbrella sampling was carried out to obtain free energy profiles that describe well the orientation and location of antioxidants in a membrane considering Trolox, Cyanidin, Gallic Acid, and Resveratrol molecules to study the structural effects they cause on it. It was concluded in this study that an antioxidant when crossing the membrane does not cause either damage to the structural properties or the loss of packing and stratification of phospholipids. it was also observed that the most reactive part of the molecules could easily approach area A prone to lipid oxidation, which can describe the antioxidant capacity of these molecules.Communicated by Ramaswamy H. Sarma.
RESUMO
Oxidative stress plays an essential role in the regulation of vital processes in living organisms. Reactive oxygen species can react chemically with the constituents of the cells leading to irreversible damage. The first structure of the cell in contact with the environment that surrounds it is the membrane, which protects it and allows the exchange of substances. Some signals manifest when the components of a bilayer are undergoing oxidation, like an increase in the lipid area, decrease in the thickness of the bilayer, and exchange of the oxidized groups toward the bilayer surface. In this investigation, a molecular dynamics simulation was done on a set of Dioleoylphosphatidylcholine membranes with different percentage of oxidized lipids, in order to observe the effect of the oxidation degree on the membrane structure. It was found that, as higher the concentration of oxidized lipids is, the larger the damage of the membrane. This is reflected in the increase in the lipid area and the decrease in the thickness and membrane packing. Also, it was observed that hydrophobicity inside the membrane decreases as the oxidation percentage increases.Communicated by Ramaswamy H. Sarma.
Assuntos
Bicamadas Lipídicas , Simulação de Dinâmica Molecular , Membrana Celular/química , Interações Hidrofóbicas e Hidrofílicas , Bicamadas Lipídicas/química , OxirreduçãoRESUMO
An experimental and theoretical study of the photoinduced homolysis of the carbon-chlorine bond in an ice matrix of chlorobenzene is presented. A condensed chlorobenzene film has been grown in situ and near edge X-ray fine structure (NEXAFS) spectra were collected after exposing the condensed film to a monochromatic photon beam centered at the 2822 eV resonant excitation of chlorine and at 2850 eV. The photoabsorption to the Cl 1s â σ* and Cl 1s â π* states has been measured and the hypothesis of free radical coupling reactions was investigated via time-dependent density functional theory (TD-DFT) and complete active space self-consistent field (CASSCF) calculations. Also, potential energy pathways to the C-Cl cleavage have been obtained at the CASSCF level to the Cl 1s â σ*, 1s â π*, and 1s â ∞ states. A strong dissociative character was only found for the Cl 1s â σ* resonance.
RESUMO
We present fast proton impact induced fragmentations of pyrimidine and pyridazine as an experimental resource to investigate isomeric signatures. Major isomeric imprints are identified for few fragment ions and differences of more than an order of magnitude for the cross sections of fragments of the same mass were measured. The observation of the molecular structure of these isomers gives no apparent indication for the reasons for such substantial differences. It is verified that the simple displacement of the position of one nitrogen atom strongly inhibits or favors the production of some ionic fragment species. The dependency of the fragmentation cross sections on the proton impact energy, investigated by means of time of flight mass spectroscopy and of a model calculation based in first order perturbation theory, allows us to disentangle the complex collision dynamics of the ionic fragments. The proton-induced fragmentation discriminates rather directly the association between a molecular orbital ionization and the fragment-ions creation and abundance, as well as how the redistribution of the energy imparted to the molecules takes place, triggering not only single but also double vacancy and leads to specific fragmentation pathways.
RESUMO
Absolute total non-dissociative and partial dissociative cross sections of pyrimidine were measured for electron impact energies ranging from 70 to 400 eV and for proton impact energies from 125 up to 2500 keV. MOs ionization induced by coulomb interaction were studied by measuring both ionization and partial dissociative cross sections through time of flight mass spectrometry and by obtaining the branching ratios for fragment formation via a model calculation based on the Born approximation. The partial yields and the absolute cross sections measured as a function of the energy combined with the model calculation proved to be a useful tool to determine the vacancy population of the valence MOs from which several sets of fragment ions are produced. It was also a key point to distinguish the dissociation regimes induced by both particles. A comparison with previous experimental results is also presented.
Assuntos
Pirimidinas/química , Elétrons , Íons/química , PrótonsRESUMO
OBJECTIVES: The best treatment of clinical stage I non-seminomatous germ cell testicular cancer (NSGCTC) is controversial. Lymphadenectomy allows an adequate retroperitoneal staging and cures up to 70% of patients in pathological stage II. The objective of this study is to analyse our experience in the treatment of this patients with radical orchiectomy and reduced retroperitoneal lymphadenectomy (RRL) as the initial treatment. METHODS: Retrospective study of patients with clinical stage I NSGCTC submitted to radical orchiectomy and RRL at the Urology Service of the University of Chile Clinical Hospital, from January 1990 to December 2000. INCLUSION CRITERIA: retroperitoneal staging with computed tomography (CT), normal tumor markers after orchiectomy and testicular and retroperitoneal biopsy informed at our hospital. The following metastatic risk factors in the testicular biopsy were checked: vascular invasion (venous and/or lymphatic), infiltration of tunica albuginea, rete testis, epididymis, and spermatic cord. RESULTS: 36 patients with 37 testicular tumors were analysed (1 bilateral case). Average age 28 years old. Twenty nine mixed tumors (78%); most frequent histology embryonal carcinoma (76%). Average surgery time 2 hr 7 min; average dissected lymph nodes 13. Introoperative complications: 2,8%; postoperative complications: a) early 5,6%; b) late: 5,6%. No mortality, no second surgeries nor blood transfusions. Four cases of positive RRL (11%). Only retroperitoneal relapses in 2 cases (8%), one out of the limits of dissection. Chemotherapy in 7 patients (19%) a total of 18 cycles. Four cases of contralateral tumor during follow-up (11%). Hundred percent survival at 76 months (16-160). We described sensibility, specificity, positive and negative predictive value of metastatic risk factors. Only epididymis infiltration was a significant predictor of metastasis (p=0,04). CONCLUSIONS: In our hands RRL is a safe surgery, with 5,6% mayor complications. The low false negative rate of CT in staging (11%) and the high number of retroperitoneal relapses (8%) in our study contrast with those of other publications. Limited by the size of our study group, the epididymis infiltration was the only statistically significant predictor of metastasis. Clinical stage I NSGCTC initially managed with RRL has a 100% survival.