TIP Revista Especializada en Ciencias QuimicoBiologicas最新文献

The different isomer yields observed in many aromatic electrophilic substitution reactions can be explained by steric hindrance. However, this is not the case when there are drastic differences in the reaction yields of the isomeric products obtained. This is generally due to the presence of other factors, for instance, electric rejection between two positive charges in the reaction stage. Thus, a very important point to bear in mind is electric hindrance, a new theoretical concept. We have taken as an example 2-aminopyridine nitration. We provide an extended theory on this subject, which is in accordance with the observed regiochemistry and with the reaction yields of the isomeric products obtained. Dipole moments were also taken into account.

We discuss too the 2-nitraminopyridine rearrangement in acidic medium. The theoretical discussion is also in agreement with reported trans-nitration experimental results. Our proposals were also contrasted with the findings from thermolysis and photolysis carried out with 2- nitraminopyridine.

The interaction of ethanol on the cellular membrane inhibits the interaction with membrane proteins or cellular receptors. Ethanol and other small alcohols are natural surfactants of aqueous/organic interfaces, and also affect the cellular membrane stressing it mechanically, and inhibit the natural adsorption of terminal groups at the aqueous/organic interface. In this work we show how methanol inhibits the adsorption of terminal groups even at very small concentrations. As methanol concentration increases in the aqueous phase, the interfacial tension decreases, showing additional stress over the cellular membrane.

The theory of population genetics originated over 80 years ago and allowed to explain, in terms of the evolutionary forces, the patterns of genetic variation within and between the populations that conform species. This research program generated the questions that have been empirically analyzed with the use of molecular markers for the last 50 years. A fundamental question within population genetics is if a reduced number of genes are representative of the evolutionary forces that affect the total genome of a species. This question has led to the development of molecular methods that allow the study of large sections of the genome in natural populations, giving rise to the field of population genomics. In recent years, techniques that are able to sequence DNA massively, usually called “Next generation sequencing” or “next-gen”, are helping us to obtain genome wide data in many species, without needing previous molecular information. Comparing the genomes of many individuals from different populations, now we have access to an archive of their evolutionary history that narrates the complex and dynamic balance in time between natural selection and other evolutionary forces, such as genetic drift and gene flow, which act mainly in neutral regions of the genomes. The amount of information that is being produced has required the development of new statistical and bioinformatics tools for their analyses. Diverse disciplines have profited from these new developments. In particular in evolutionary biology it is now possible to study in a more precise way the adaptive patterns of variation. The annotation of genomes and the mapping of traits are important and complicated, but recent technical developments are making these goals easier, and thus the future challenge will be in asking the right questions to make relevant inferences from the sea of information these new methods generate. The evolutionary and population genetics perspective will enrich genomics, in the same way that the genomic data will help us advance in the development of the program initiated by Theodosius Dobzhansky several decades ago.

In this paper we present: a) a design process for manufacturing alloys to be used as sacrificial anodes in marine environments; b) the proposal to replace In with Ag, in search of alloys that could contribute to environmental sustain; and c) the proposal to include the parameters related to anode structure and their manufacturing process in the regulation of sacrificial anodes.

Eight Al-Zn 2% alloys were manufactured, tested, and compared in our laboratory. These had a lower content than the one indicated by the alloy standards - 3.5-5% and 4-5% content for In and Sn respectively- looking for a more sustainable environment. Four of them were alloyed with In (from 0.59 to 0.766%), and four with Ag (from 0.23 to 0.428%). In order to modify the structure, two cooling rates were used during solidification, seeking to modify their properties, and hence their behavior against corrosion, i.e. corrosion potential, corrosion rate, anode activation, type of corrosion and current efficiency. It was found that the variation of the cooling rate changes the structure of the alloys, their properties and corrosion behaviors. The overall behavior of some of the Ag alloys is superior to those containing In. The higher efficiencies were obtained for alloys with the lower amount of In (69%) and Ag (71%).

Myb family proteins are ubiquitous in eukaryotes, and contain a characteristic DNA binding domain called Myb domain. The Myb domain consists in a conserved amino acid sequence (50-53 amino acids) that can be repeated from two (essential domain for DNA binding) to four times in the same protein. In plants, the Myb family is very numerous while in animals there are only three members; at least, one member of this family has been identified in other eukaryotes. Myb proteins participate as transcriptional activators or repressors in the regulation of fundamental cellular processes in metabolism or cell differentiation. Activity from Myb proteins is regulated through several post-translational modifications: redox state, phosphorylation and ubiquitylation stand out among them.

To avoid endogamy many flowering plants evolved a mechanism to recognize and reject their self-pollen, which is known as self-incompatibility (SI) system. In many cases the SI is genetically controlled by a single and highly polymorphic locus known as the S-locus. This DNA region carries two tightly linked transcriptional units. One of them encodes the female determinant (pistil expressed) and the second one the male determinant (pollen expressed). In this review, we discuss the most relevant advances in the SI mechanism in S-RNase based systems, which are present in Solanaceae, Rosaceae and Plantaginaceae. In these families, the female determinant encodes a ribonuclease named S-RNase and the male determinant encodes a protein called SLF/SFB (S-locus F-Box). We finally describe the role of the role of modifier genes, not coded by S-locus, in the pollen rejection response and propose a model including the main events so far described.

We evaluated the relevance of threshold selection in species distribution models on the delimitation of areas of endemism, using as case study the North American mammals. We modeled 40 species of endemic mammals of the Nearctic region with Maxent, and transformed these models to binary maps using four different thresholds: minimum training presence, tenth percentile training presence, equal training sensitivity and specificity, and 0.5 logistic probability. We analyzed the binary maps with the optimality method in order to identify areas of endemism and compare our results regarding previous analyses. The majority of the species tend to have very low values for the minimum training presence, whereas most of the species have a value of the tenth percentile training presence around 0.5, and the equal training sensitivity and specificity was around 0.3. Only with the tenth percentile threshold we recovered three out of the four patterns of endemism identified in North America, and detected more endemic species.The best identification of areas of endemism was obtained using the tenth percentile training presence threshold, which seems to recover better the distributional area of the mammals analyzed.

Endophytic fungi are microorganisms that live inside plant tissues without causing disease symptoms. In most cases, their relationship with the host plant is considered beneficial because the endophyte is able to produce bioactive metabolites that the host can use as defense mechanisms, and this allows survival of both organisms. Recent studies have demonstrated that the endophytic fungus confers protection to the host plant against attack by pathogens and herbivores. Since they have the ability to benefit the host plant, it is reasonable to think that the diverse bioactive compounds produced by the endophyte might exhibit potential applications in agriculture and medicine, and also serve as a source of inspiration for the discovery of new and more active molecules. In this paper, some aspects regarding endophytic fungi are described: definition, discovery, classification, interactions with their host plants, ecological role, selected examples of bioactive metabolites, host selection strategy, and methodological strategies for their isolation. Finally, we show some recent results of our research, which demonstrate that endophytic fungi are promising sources of new bioactive secondary metabolites.

Numerical Weather Prediction has become a fundamental tool in Civil Protection Institutions. Short term numerical weather prediction for the Valley of Mexico has rarely been evaluated in a systematic way. By using daily observed precipitation data and those predicted with the mesoscale model known as MM5, an evaluation of rainfall forecast is made. It is found that making predictions of high spatial resolution in the Valley of Mexico is of limited quality mainly because of the effects of urbanization and orography over the rainfall. The lack of consistency between predicted and observed rainfall spatial patterns requires an analysis of stationary physical factors that can influence the quality of forecasts. Errors in short term forecasts require risk management strategies to implement disaster prevention actions.

Ubiquitin (Ub) is a small protein used to label proteins by eukaryotic organisms; in most cases labeled proteins will be degraded afterwards. Ubiquitination occurs in three sequential steps through reactions requiring the action of the ubiquitin-activating enzyme, the ubiquitin-conjugating enzyme and the ubiquitin ligase. After this, the target protein will follow a different fate according to ubiquitination topology. Most ubiquitinated proteins will be degraded in the 2.5 M protein complex termed the 26S proteasome. Plants employ this mechanism of regulated protein degradation to modulate developmental and growing processes as well as to respond to detrimental situations, like water deficit or pathogen attack. During the evolution plants have developed different strategies to cope against pathogen infection, however these organisms have acquired tools that allow them to counteract plant defense mechanisms. Among different ways to undermine plant resistance pathways, pathogens have now the ability to manipulate the Ub/proteasome system to efficiently infect them.