Thermodynamic characterization of the prevailing molecular interactions in mixed floating monolayers of phospholipids and usnic acid

The investigation of the characteristics of mixed floating monolayers of phospholipids and usnic acid (UA), an active metabolite from lichens, can provide valuable information on how to prepare stable liposomes that could serve as carriers of UA for therapeutic proposes. The present paper is concerned with the thermodynamic analysis of the behavior of Langmuir monolayers formed by mixing different phospholipids (dibehenoylphosphatidylcholine, DBPC, dipalmitoylphosphatidylcholine, DPPC, and dioleoylphosphatidylcholine, DOPC) and UA at varied molar fractions. Relevant thermodynamic parameters such as excess areas, excess free energies and free energy of mixing were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. For the largest lateral pressure examined (25 mN/m), negative values of the excess free energy were found only for the DOPC/UA monolayer, which should be the most stable of them. Based on the calculated values of the free energy of mixing, we note that the DBPC/UA and DPPC/UA systems present the best mixed character at low pressures and when the molar fraction of the UA is 0.5; at that relative concentration and at low values of the external pressure, the UA molecules can better mix and interact with the phospholipid molecules. The compression isotherms for mixed monolayers show no visible transitions, exhibiting a more organized phase that corresponds to a negative free energy of mixing. We have established that the most stable monolayers were those corresponding to DOPC/UA mixtures with a UA molar fraction of 0.75.     

Evaluation of polymorphisms in repair and detoxification genes in alcohol drinkers and non-drinkers using capillary electrophoresis

Alcohol use disorder (AUD) causes about 3.3 million deaths around the world each year. It is the primary risk factor for the global burden of diseases in American countries. Long-term abuse of alcohol induces numerous molecular and biochemical changes in tissues exposed to alcohol. The toxic effects of alcohol are mediated by DNA damage through various mechanisms, such as induction of oxidative damage, DNA adducts, crosslinks, and DNA strand breaks. The main aim of the current study was to compare the frequency of SNP polymorphisms in XRCC1 (rs7997782) and GSTP1 (rs1695) genes involved in DNA repair of single strand breaks (SSB) and xenobiotic detoxification between alcohol addicts and a control group comprised of non-drinkers. Genetic polymorphisms were identified following allelic specific PCR designed to generate the amplicons containing the variants. Then amplicons were sequenced, and sequences were aligned against the human genome reference deposited in GenBank using the CLC Sequence Viewer software (version 7.6.1). The GG homozygotes in rs1695 (GSTP1) were significantly (p = 0.023) 3.8x more frequent among those with AUD when compared to the control group. No SNP variation was observed in rs7997782 (XRCC1). rs1695 variant has been associated with susceptibility to various diseases, including those related to alcohol consumption.     

Thermal and structural investigation of SnO<Subscript>2</Subscript>/Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> obtained by the polymeric precursor method

SnO₂-based materials are used as sensors, catalysts and in electro–optical devices. This work aims to synthesize and characterize the SnO₂/Sb₂O₃-based inorganic pigments, obtained by the polymeric precursor method, also known as Pechini method (based on the metallic citrate polymerization by means of ethylene glycol). The precursors were characterized by thermogravimetry (TG) and differential thermal analysis (DTA). After characterization, the precursors were heat-treated at different temperatures and characterized by X-ray diffraction. According to the TG/DTA curves basically two-step mass loss process was observed: the first one is related to the dehydration of the system; and the second one is representative to the combustion of the organic matter. Increase of the heat treatment temperature from 500 to 600°C and 700°C resulted higher crystallinity of the formed product.     

Optical Fiber Communications: Recent Contributions in Photonic Device Technology

The current status of the research and development as well as the recent contributions in optical communications at INESC Porto is reviewed. This review includes all the work carried out in the last few years in optical fiber communications, namely the development of passive and active optical devices. Some of the passive structures that have been studied and developed are: add-drop multiplexers, multiplexer/demultiplexer based on Bragg grating technology, dispersion compensators, and optical cross-connects. Active photonic devices such as wavelength converters, fiber lasers, and fiber amplifiers have also been studied. New ideas are being continuously developed and tested.     

Catalyst concentration distribution in fluidized bed by gamma-ray absorption

Summary The axial and radial distribution of the catalyst concentration, in the riser of an EMC - experimental cold model of a fluid catalytic cracking type unit, was measured by gamma-absorption. The solid concentration in the circulating fluidized bed was determined by measurements with a ²⁴¹Am gamma-source and a NaI(Tl) detector. The operation, instrumental measurements and data acquisition system of the cold unit were automated. The catalyst concentration measurements were carried out in static experiments and in the circulating fluidized bed. A calibration of the distribution concentration was made with experimental data from gas velocity and pressure drop along the riser that gave the best multi-regression model. A spatial resolution of 5.0 ^. 10^-3 m by scanning the riser and a catalyst density resolution of 5.0±0.8 kg/m³ were obtained. The axial catalyst concentration distribution, in the 5-13 kg/m ³ interval, showed a predicted pattern according to the literature. The radial distribution was in an annular configuration for this diluted catalyst concentration.     

Temperature dependence of ultra-exothermic charge recombinations.

We measured the temperature dependence (from +32 to -50 degrees C) of charge-recombination rates between contact radical ion pairs in isopropyl ether. In the systems selected for this study, aromatic hydrocarbon cations are the electron acceptors and the fumaronitrile anion is the electron donor. Nearly quantitative electron transfers occur at all temperatures. The charge recombinations have excess exothermicities of -60 kcal mol(-1) and exhibit a very weak temperature dependence. Our observations emphasize the absence of solvent effects and the relevance of nuclear tunneling in charge recombinations.     

Monitoring the thermal efficiency of fouled heat exchangers: A simplified method

Fouling is a problem whether we are aware of it or not. In an industrial plant, it is important not only to be able to measure the buildup of unwanted deposits, but also to do it in the simplest and most economically possible way. This paper addresses the question of monitoring fouling in an oil refinery plant, where the high number of heat exchanger units and the variability of the feedstock charge pose additional problems in terms of the practicability of following the energetic performance of such equipment. In this case, the flow rates and quality of the fluids flowing through the heat exchangers do not usually correspond to the design conditions, because they change with time. Therefore, to assess the fouling level of the exchangers, the day-to-day measured thermal efficiency should not be compared with the efficiency predicted in the design calculations. The latter should be recalculated by introducing whenever necessary new values of flow rates, physical properties, and so forth, and by evaluating new heat transfer coefficients. However, the procedures are too time consuming to be applied frequently. The present work describes a simplified method for following heat exchanger performances, based on the assessment of the number of transfer units and thermal efficiencies, where the effects of changing the feedstock charge, particularly the flow rates of the fluids, are taken into account. The only data that need to be collected are the four inlet/outlet temperatures of the heat exchanger unit and one of the flow rates. Several heat exchanger units in an oil refinery were successfully monitored by means of this method, and it was found that the variations in the physical properties did not significantly affect the results obtained for the particular plant under study.     

Absolute configurations of griseorhodins A and C

The known antibiotic and cytotoxic compounds griseorhodin A (1) and griseorhodin C (2) were produced in solid culture by Streptomyces puniceus AB10, which was isolated from the leaf-cutter ant Acromyrmex rugosus rugosus. Their absolute configurations were unambiguously established as 6S,6aR,7S,8S and 6R,6aR,7S,8R, respectively, using vibrational circular dichroism (VCD) and density functional theory (DFT) calculations.     

Biofouling in water systems

The paper describes the mechanisms in the development of biofouling layers (initial surface conditioning, microbial transport and attachment, mass transfer of nutrients to the biofilm surface and through the microbial layer, cell metabolism, and detachment of cells and of larger parts of the biofilm) and summarizes the effects of several factors on the buildup and stability of biofilms (nutrient availability, fluid velocity and turbulence, temperature, surface condition, and nonliving particles). Mass transfer within biofilms is treated in more detail. A biofouling model applied to the development of biofilms in heat exchangers is presented. Finally, references are made to biofouling control methods (biocide and the proper design and operation of heat exchangers) and to future research needs in this area.