Jeanlex Soares de Sousa

Diverse deformation properties of polymeric nanocapsules and lipid-core nanocapsules

The deformation properties of submicrometric drug carriers can influence their tissue-penetration ability and thus the drug targeting. The aim of this study was to determine whether the oily core composition (raw oils or a dispersion of oils and solid lipid) surrounded by a polymeric wall [poly(e-caprolactone), (PCL)] can affect the deformation properties of nanocapsules (NCs) or lipid-core nanocapsules (LNCs). Formulations were prepared as aqueous suspensions using a polymer and either a mixture of caprylic/capric triglyceride (CCT) and octyl methoxycinnamate (OMC) or a mixture of CCT, OMC and sorbitan monostearate (SM) as core components, respectively. Formulations had mean diameters close to 200 nm presenting monomodal distributions. A polysorbate 80 coating rendered ζ-potential values close to zero, acting as a steric stabilizer. Atomic force microscopy (AFM) showed, through force curves analysis, that the cantilever deflection was more pronounced for the LNCs than for the NCs. The same force applied to NC produced an indentation around twice that observed for the LNCs. The Youngs modulus (E) values were 0.537 MPa (LNC) and 0.364 MPa (NC) considering conical geometry while E = 0.17 MPa (NC) and E = 0.241 (LNC) for spherical geometry. These data confirm that the LNCs are stiffer than the NCs. The rigidity of both the polymer wall and lipid core is higher for LNCs. In conclusion, LNCs presented distinct mechanical properties compared to the conventional polymeric NCs.

Effect of subinihibitory and inhibitory concentrations of Plectranthus amboinicus (Lour.) Spreng essential oil on Klebsiella pneumoniae.

We evaluated the antimicrobial activity and some mechanisms used by subinhibitory and inhibitory concentrations of the essential oil, obtained from leaves of Plectranthus amboinicus, against a standard strain of Klebsiella pneumoniae and 5 multiresistant clinical isolates of the bacteria. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), the rate of kill and the pH sensitivity of the essential oil were determined by microdilution tests performed in 96-well plates. Subinhibitory and inhibitory concentrations of the essential oil were tested in order to check its action on K. pneumoniae membrane permeability, capsule expression, urease activity and cell morphology. The MIC and MBC of the essential oil were 0.09±0.01%. A complete inhibition of the bacterial growth was observed after 2 h of incubation with twice the MIC of the essential oil. A better MIC was found when neutral or alkaline pH broth was used. Alteration in membrane permeability was found by the increase of crystal violet uptake when the bacteria were incubated with twice the MIC levels of the essential oil. The urease activity could be prevented when all the subinhibitory concentrations were tested in comparison to the untreated group (p<0.001). Alteration of the bacterial morphology besides inhibition of the capsule expression was verified by atomic force microscopy, and Anthonys stain method, respectively. Our data allow us to conclude that the essential oil of P. amboinicus can be a good candidate for future research.

Crystal structure of an antifungal osmotin-like protein from Calotropis procera and its effects on Fusarium solani spores, as revealed by atomic force microscopy: Insights into the mechanism of action.

CpOsm is an antifungal osmotin/thaumatin-like protein purified from the latex of Calotropis procera. The protein is relatively thermostable and retains its antifungal activity over a wide pH range; therefore, it may be useful in the development of new antifungal drugs or transgenic crops with enhanced resistance to phytopathogenic fungi. To gain further insight into the mechanism of action of CpOsm, its three-dimensional structure was determined, and the effects of the protein on Fusarium solani spores were investigated by atomic force microscopy (AFM). The atomic structure of CpOsm was solved at a resolution of 1.61Å, and it contained 205 amino acid residues and 192 water molecules, with a final R-factor of 18.12% and an Rfree of 21.59%. The CpOsm structure belongs to the thaumatin superfamily fold and is characterized by three domains stabilized by eight disulfide bonds and a prominent charged cleft, which runs the length of the front side of the molecule. Similarly to other antifungal thaumatin-like proteins, the cleft of CpOsm is predominantly acidic. AFM images of F. solani spores treated with CpOsm resulted in striking morphological changes being induced by the protein. Spores treated with CpOsm were wrinkled, and the volume of these cells was reduced by approximately 80%. Treated cells were covered by a shell of CpOsm molecules, and the leakage of cytoplasmic content from these cells was also observed. Based on the structural features of CpOsm and the effects that the protein produces on F. solani spores, a possible mechanism of action is suggested and discussed.

The impact of high-k dielectrics in nanocrystal flash memories

The consequences of the use of high-k dielectrics in nanocrystal based non-volatile flash memories focusing on the electrical and electronic properties are investigated through computational simulations. In the light of these results, we discuss several aspects which must be addressed for the design of such devices. We focus on nanocrystals flash memories with HfO2 and SiO2 for analysis. Due to significant reductions of the single-electron tunneling time and improvements on the data retention, high-k dielectrics offers important improvements for the non-volatile flash memories technology.

Strong exciton energy blue shift in annealed Si/SiO2 single quantum wells

Abstract A theoretical study is presented on how the annealing-induced interfacial transition region changes the confined ground state exciton in Si/SiO2 single quantum wells (QWs). The interface thickness and the mean well width confinement depend on the time and temperature of annealing, as well as on the diffusion coefficient of oxygen in silicon. It is shown that an annealing-related interface width increase of a few Angstroms can strongly blue shift (hundreds of milli-electron volts) the confined ground state exciton energy in Si/SiO2 single quantum wells. The results allow to suggest that annealing processes can be used to tune (from red to blue) the light emission in Si/SiO2 single quantum wells.

Peptidases and peptidase inhibitors in gut of caterpillars and in the latex of their host plants

Studies investigating the resistance–susceptibility of crop insects to proteins found in latex fluids have been reported. However, latex-bearing plants also host insects. In this study, the gut proteolytic system of Pseudosphinx tetrio, which feeds on Plumeria rubra leaves, was characterized and further challenged against the latex proteolytic system of its own host plant and those of other latex-bearing plants. The gut proteolytic system of Danaus plexippus (monarch) and the latex proteolytic system of its host plant (Calotropis procera) were also studied. The latex proteins underwent extensive hydrolysis when mixed with the corresponding gut homogenates of the hosted insects. The gut homogenates partially digested the latex proteins of foreign plants. The fifth instar of D. plexippus that were fed diets containing foreign latex developed as well as those individuals who were fed diets containing latex proteins from their host plant. In vitro assays detected serine and cysteine peptidase inhibitors in both the gut homogenates and the latex fluids. Curiously, the peptidase inhibitors of caterpillars did not inhibit the latex peptidases of their host plants. However, the peptidase inhibitors of laticifer origin inhibited the proteolysis of gut homogenates. In vivo analyses of the peritrophic membrane proteins of D. plexippus demonstrate resistance against latex peptidases. Only discrete changes were observed when the peritrophic membrane was directly treated with purified latex peptidases in vitro. This study concludes that peptidase inhibitors are involved in the defensive systems of both caterpillars and their host plants. Although latex peptidase inhibitors inhibit gut peptidases (in vitro), the ability of gut peptidases to digest latex proteins (in vivo) regardless of their origin seems to be important in governing the resistance–susceptibility of caterpillars.

Validation and Uncertainty of the method for multiresidue analysis of 35 pesticides in melon using Gas Chromatography Coupled to Quadrupole Mass Spectrometry (GC-QP/MS)

QuEChERS method and detection in GC/SQ-MS were validated for the analysis of 35 pesticides in melon. Validation parameters (selectivity, linearity, LOD, LOQ, accuracy and precision) were determined according ABNT NBR 14029:2005. The recoveries rates for all the pesticides studied were from 63% to 117% with relative standard deviation (RSD) lower than 15% in the concentration range of 0.05 - 0.20 mg/kg. The limit of quantification (LOQ) for most compounds were below the MRLs established in Brazil. The combined relative uncertainty (Uc) and expanded uncertainty (Ue) was determined using repetitivity, recovery and calibration curves data for each pesticide.

Computational modeling of physical and chemical properties of nanomaterials

1School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou, Hubei 434023, China 2School of Physics, Nanjing University, Nanjing 210093, China 3School of Physics and Electronics, Central South University, Changsha, Hunan 410083, China 4Research and Development Division, Actinium Chemical Research, Via Casilina 1626/A, 00133 Rome, Italy 5Laboratory of Computational and Structural Physical Chemistry for Nanosciences and QSAR, West University of Timisoara, 300115 Timisoara, Romania 6Departamento de Fisica, Universidade Federal do Ceara, Caixa Postal 6030, 60455-760 Fortaleza, CE, Brazil

Feasibility of IR-to-UV detection in SiC/SiO2 heterostructures

We will discuss the advantages of the realization of SiC/SiO2 quantum structures and their optical absorption properties. Our calculations suggest that it is possible to extend the range of the optical absorption of such structures to build applications that operates from infrared to UV spectrum using a single material and band-structure engineering.

Smooth interface effects on the confinement properties of GaSb/AlxGa1−xSb quantum wells

Abstract A theoretical investigation on the confinement properties of GaSb/Al x Ga 1− x Sb single quantum wells (QWs) with smooth interfaces is performed. Error function ( erf )-like interfacial aluminum molar fraction variations in the QWs, from which it is possible to obtain the carriers effective masses and confinement potential profiles, are assumed. It is shown that the existence of smooth interfaces blue shifts considerably the confined carriers and exciton energies, an effect which is stronger in thin QWs.