Cooperative effects in phospholipid monolayers induced by a peptide from HIV-1 capsid protein

The study of interactions between biological molecules and model membranes is essential for the understanding of a number of physiological mechanisms involved in viral infections and dissemination. In this paper, the analysis of the interaction between a peptide from the p24 protein of Human Immunodeficiency Virus type 1 (HIV-1) and a phospholipid monolayer has pointed to a cooperative response in which very small amounts of peptide p24-1 (e.g. 0.05 mol%) can lead to measurable effects. Monolayer surface pressure and surface potential isotherms were affected for peptide concentrations as low as 0.05 mol%, with saturation at 0.5 mol%. The expansion effect from p24-1 is confirmed by changes in morphology of the monolayers using Brewster angle microscopy. Even though p24-1 is disordered in aqueous solutions, the interaction with dipalmitoyl phosphatidylcholine (DPPC) causes it to adopt an alpha-helix structure, as shown by circular dichroism (CD) data for multilamellar vesicles (MLV). The expansion of the phospholipid monolayer in a cooperative way may imply that p24-1 has potential antiviral activity, by participating in the cell rupture, with no need of specific receptors in the membrane.     

Spectroscopic Studies on the Interaction of Tetramethylpyridylporphyrins and Cationic Clays

In the present work, the interaction between5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine (TMPyP) and its metallated form(CoTMPyP) with three cationic clays was investigatedby X-ray diffraction (XRD), UV-VIS and resonance Ramanspectroscopies. Sodium montmorillonites K10 and KSFand a synthetic fluorohectorite (FHT) containingdifferent macrocycle loadings, were prepared by an ionexchange reaction. In nonsaturated KSF and FHT, theCoTMPyP molecule assumes a flat orientation, relativeto the host layers, giving rise to at least twoabsorption bands in the Soret region (ca. 445 and 465 nm)assigned to adsorbed and intercalated CoTMPyP,respectively. For the delaminated K10 sample, a broadband centered around 456 nm, indicates a majorcontribution from the metalloporphyrin on the clayexternal surfaces. The electronic spectra of FHTsamples containing increasing amounts of CoTMPyPshow bands red shifted even when a small amount ofporphyrin is used, suggesting that the electroniclevels of the macrocycle are more affected by theinteraction with the clay than by the metalloporphyrindistortion inside the galleries. The resonance Ramanspectra obtained for all CoTMPyP samples presentedonly minor shifts in peak positions and band width,with the exception of the FHT saturated sample, wherethe bands are clearly broader when compared to otherloadings, suggesting that porphyrin aggregation isoccurring. In the case of TMPyP, the bands at ca. 430and 468 nm were assigned to nonprotonated andprotonated molecules, respectively. This assignment issupported by resonance Raman spectroscopy, which alsoshowed the ₂ mode (ca. 1550 cm^-1) to bethe most sensitive peak to protonation.     

Amberlite XAD-2 functionalized with 2-aminothiophenol as a new sorbent for on-line preconcentration of cadmium and copper

A new functionalized resin has been applied in an on-line preconcentration system for copper and cadmium determination. Amberlite XAD-2 was functionalized by coupling it to 2-aminothiophenol (AT-XAD) by means of an NN spacer. This resin was packed in a minicolumn and used as sorbent in the on-line system. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). Elution of Cd(II) and Cu(II) from minicolumn can be made with 0.50 mol l⁻¹ HCl or HNO₃. The enrichment factors obtained were 28 (Cd) and 14 (Cu), for 60 s preconcentration time, and 74 (Cd) and 35 (Cu), if used 180 s preconcentration time. The proposed procedure allowed the determination of cadmium and copper with detection limits of 0.14 and 0.54 μg l⁻¹, respectively, when used preconcentration periods of 180 s. The effects of foreign ions on the adsorption of these metal ions are reported. The validation of the procedure was carried out by analysis of certified reference material. This procedure was applied to cadmium and copper determination in natural, drink and tap water samples.     

Formation of a stable cyano-bridged dinuclear iron cluster following oxidation of the superoxide reductases from Treponema pallidum and Desulfovibrio vulgaris with K(3)Fe(CN)(6)

Superoxide reductases catalyze the monovalent reduction of superoxide anion to hydrogen peroxide. Spectroscopic evidence for the formation of a dinuclear cyano-bridged adduct after K(3)Fe(CN)(6) oxidation of the superoxide reductases neelaredoxin from Treponema pallidum and desulfoferrodoxin from Desulfovibrio vulgaris was reported. Oxidation with K(3)Fe(CN)(6) reveals a band in the near-IR with lambda(max) at 1020 nm, coupled with an increase of the iron content by almost 2-fold. Fourier transform infrared spectroscopy provided additional evidence with CN-stretching vibrations at 2095, 2025-2030, and 2047 cm(-)(1), assigned to a ferrocyanide adduct of the enzyme. Interestingly, the low-temperature electronic paramagnetic resonance (EPR) spectra of oxidized TpNlr reveal at least three different species indicating structural heterogeneity in the coordination environment of the active site Fe ion. Given the likely 6-coordinate geometry of the active site Fe(3+) ion in the ferrocyanide adduct, we propose that the rhombic EPR species can serve as a model of a hexacoordinate form of the active site.     

Applicability of Microaerobic Technology to Enhance BTEX Removal from Contaminated Waters

As the addition of low concentrations of oxygen can favor the initial degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds, this work verified the applicability of the microaerobic technology to enhance BTEX removal in an anaerobic bioreactor supplemented with high and low co-substrate (ethanol) concentrations. Additionally, structural alterations on the bioreactor microbiota were assessed throughout the experiment. The bioreactor was fed with a synthetic BTEX-contaminated water (~ 3 mg L^?1 of each compound) and operated at a hydraulic retention time of 48 h. The addition of low concentrations of oxygen (1.0 mL min^?1 of atmospheric air at 27 °C and 1 atm) assured high removal efficiencies (> 80%) for all compounds under microaerobic conditions. In fact, the applicability of this technology showed to be viable to enhance BTEX removal from contaminated waters, especially concerning benzene (with a 30% removal increase), which is a very recalcitrant compound under anaerobic conditions. However, high concentrations of ethanol adversely affected BTEX removal, especially benzene, under anaerobic and microaerobic conditions. Finally, although bacterial community richness decreased at low concentrations of ethanol, in general, the bioreactor microbiota could deal with the different operational conditions and preserved its functionality during the whole experiment.     

Affinity Matrices of Cratylia mollis Seed Lectins for Isolation of Glycoproteins from Complex Protein Mixtures

This work reports the use of matrices containing Cratylia mollis lectins (Cramoll 1,2,3-Sepharose and Cramoll 3-Sepharose) for isolation of glycoproteins from fetal bovine serum, human colostrum, hen egg white, and human blood plasma. Cramoll 1,2,3-Sepharose was able to bind a glycoprotein from fetal bovine serum which showed the same fetuin electrophoretic profile. The data indicate that this protein adsorbed to the matrix by interaction with Cramoll 3. Cramoll 1,2,3-Sepharose was not efficient to retain glycoproteins from human colostrum or commercial ovalbumin. Cramoll 3-Sepharose bound ovalbumin, and the support retained protein from hen egg white. Protein peaks eluted from the column with 1.0 M NaCl or 0.3 M galactose showed apparent molecular mass of ovalbumin. Two main proteins from blood plasma with apparent molecular mass 67 (similar to albumin) and 50 kDa (similar to fetuin) adsorbed on Cramoll 3-Sepharose and were eluted with 1.0 M NaCl as a single peak. Elution of adsorbed plasma proteins with 0.3 M galactose was less selective than with 1.0 M NaCl as revealed by SDS-PAGE. In conclusion, the Cramoll 1,2,3-Sepharose and Cramoll 3-Sepharose matrices were useful to separate glycoproteins from complex protein mixtures, and the adsorption phenomena was a carbohydrate-dependent event.     

A green-emitting α-substituted β-diketonate Tb3+ phosphor for ultraviolet LED-based solid-state lighting

The α-substituted β-diketonate [Ln(3Cl-acac)₃(H₂O)₂] [Ln = Tb, Gd] complexes (with 3Cl-acac^– being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)₃(H₂O)₂] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)₃(H₂O)₂], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)₃(H₂O)₂. Additionally, the possibility of Tb(3Cl-acac)₃(H₂O)₂ to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370 nm) with the Tb(3Cl-acac)₃(H₂O)₂ complex.     

Inclusion complexes of rosmarinic acid and cyclodextrins: stoichiometry,association constants,and antioxidant potential

The interaction between β-cyclodextrin (β-CD) and the polyphenol rosmarinic acid (RA) is here reported by ¹H NMR titration experiments. The formation of an aqueous soluble inclusion complex is confirmed and valuable information regarding mode of penetration of guest into β-CD, stoichiometry, and stability of the complex is obtained. The analysis by the continuous variation method shows the undoubted formation of 1:1 β-CD/RA complex. Additionally, the estimated apparent association constants reveal the importance of the asymmetry of the RA in the complexation; the incorporation of the catechol moiety closer to the carboxylic group is more favorable (K?=?2,028 M^?1) than from the other end of the RA molecule (K?=?1,184 M^?1). Finally, we have also investigated the antioxidant activity and storage stability of the β-CD/RA complexed system; the presence of β-CD was found to produce a remarkable enhancement on the antioxidant activity.     

Convex separation by regular pairs

It is known that the existence of a convex (resp., concave) separator between two given functions can be characterized via a simple inequality. The notion of convexity can be generalized applying regular pairs (in other words, two dimensional Chebyshev systems). The aim of the present note is to extend the above mentioned result to this setting. In the proof, a modified version of the classical Carathéodory’s theorem and the characterization of convex functions play the key role.