RESUMO

We present a combined experimental and theoretical study dedicated to analyze the variations in the surface chemistry of hydroxylated multiwalled carbon nanotubes (MWCNTs), so called nanotubols, when exposed to H2O2 at high temperatures. The formation, surface density, and distribution of oxygen-containing functional groups are studied by infrared (IR) and X-ray photoelectron spectroscopy (XPS), as well as density functional theory (DFT) calculations performed on model functionalized carbon nanotubes (CNTs). After H2O2 exposure, the initial composition of -OH, -C[double bond, length as m-dash]O, and -COOH substituents notably changes, with carbonyl -C[double bond, length as m-dash]O groups being the ones that show the most notable increase on the carbon surface. Our highly oxidized MWCNTs are partially soluble and form complex two-dimensional patterns at the air-water interface, as evidenced by Brewster angle microscopy. In a second step, these films can be transferred to solid substrates to form porous multilayered carbon nanostructures with complex morphologies. In particular, and for the first time, we report the synthesis of "stadium-like" configurations made of MWCNT units whose formation and stability are a direct consequence of the self-assembly process occurring at the air/water interface. DFT calculations suggest the formation of molecular islands of oxygen-containing functional groups on the CNT surface. In addition, nudged elastic band studies reveal that, for these adsorbed phases, the reaction between two neighboring OH groups to produce atomic oxygen and a physisorbed water molecule is characterized by energy barriers of ∼0.2 eV. These small values could be at the origin of the sizable increase in chemisorbed single-oxygen species determined by XPS data after H2O2 treatment at 60 °C. The simulation of the C 1s binding energies (BE) allows us to more clearly identify the different oxygen-containing functionalities as well as to reveal how the local atomic environment affects their characteristic BEs. Even if we were unable to polyhydroxylate our carbon nanotubes, we believe that H2O2-treated MWCNTs are interesting materials for more complex post-functionalization procedures that might lead to the fabrication of novel carbon nanostructures.

RESUMO

We present a combined experimental and theoretical study to analyze the structure, electronic properties, and aggregation behavior of hydroxylated multiwalled carbon nanotubes (OH-MWCNT). Our MWCNTs have average diameters of ~2 nm, lengths of approximately 100-300 nm, and a hydroxyl surface coverage θ~0.1. When deposited on the air/water interface the OH-MWCNTs are partially soluble and the floating units interact and link with each other forming extended foam-like carbon networks. Surface pressure-area isotherms of the nanotube films are performed using the Langmuir balance method at different equilibration times. The films are transferred into a mica substrate and atomic force microscopy images show that the foam like structure is preserved and reveals fine details of their microstructure. Density functional theory calculations performed on model hydroxylated carbon nanotubes show that low energy atomic configurations are found when the OH groups form molecular islands on the nanotube's surface. This patchy behavior for the OH species is expected to produce nanotubes having reduced wettabilities, in line with experimental observations. OH doping yields nanotubes having small HOMO-LUMO energy gaps and generates a nanotube → OH direction for the charge transfer leading to the existence of more hole carriers in the structures. Our synthesized OH-MWCNTs might have promising applications.

Assuntos

RESUMO

Amaranth seeds are one of the more promising food ingredients, due to their high protein content, among which the most important are storage proteins known as globulins. However, little is known about the physicochemical of the globulin proteins. In this work, we study the physicochemical behavior of films made of amaranth 7S globulin and its interaction with a model membrane made of L-α-dipalmitoylphosphatidylcholine (L-α-DPPC) at the air-liquid interface. The study was done by means of Langmuir balance, Brewster angle microscopy (BAM), fluorescence microscopy, and atomic force microscopy (AFM). We found that isotherms of pure 7S globulin directly deposited on either water or buffer subphases behave similarly and globulin forms a condensed film made of globular and denature structures, which was confirmed by BAM observations. Good mixtures of the protein with L-α-DPPC are formed at low surface pressure. However, they phase separate from moderate to high surface pressure as observed by BAM. Isotherms detect the presence of the protein in the mixture with L-α-DPPC, but we were unable to detect it through BAM or AFM. We show that fluorescence microscopy is a very good technique to detect the presence of the protein when it is well-mixed within the LE phase of the lipid. AFM images clearly show the formation of protein mono- and multilayers, and in phase mode, we detected domains that are formed by protein and LE lipid phase, which were corroborated by fluorescence microscopy. We have shown that globulin 7S mix well with lipid phases, which could be important in food applications as stabilizers or emulsifiers, but we also show that they can phase separate with a moderate to high surface pressure.

Assuntos

RESUMO

In this work we have investigated the influence of NaCl on the adsorption of the antimicrobial cationic peptide bactenecin in the monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at the air-water interface, as a function of NaCl concentrations in the subphase. We show that the effect of the salt concentration on DPPC monolayers is a monotonic decrease of the liquid-condensed-liquid-expanded (LC-LE) coexistence region. By contrast, the effect of the bactenecin adsorption at the DPPC monolayer not only removed the LC-LE coexistence region plateau, but also shifted the DPPC isotherms to higher pressures and increased the compressibility of the DPPC/bactenecin monolayers with respect to the pure DPPC monolayer around the LC phase. Analysis of the domain structure, obtained by Brewster angle and atomic force microscopes, indicates that the salt concentration in the subphase builds an electrostatic barrier, increasing the rigidity of DPPC monolayers and limiting the bactenecin adsorption at the LC-LE phase coexistence.

Assuntos

RESUMO

3Beta,11beta-dihydroxy-9alpha-fluor-5alpha-androstane-17-one (2), 3beta-acetoxy-9alpha-fluor-11beta-hydroxy-5alpha-androstane-17-one (3), 3beta-acetoxy-9alpha-fluor-11beta,17beta-dihydroxy-5alpha-androstane (4), 3beta,17beta-diacetoxy-9alpha-fluor-11beta-hydroxy-5alpha-androstane (5), 3beta-acetoxy-9alpha-fluor-11beta-hydroxy-5alpha-androstane 17beta-propionate (6), 3beta-acetoxy-9alpha-fluor-11beta-hydroxy-5alpha-androstane 17beta-enanthate (7), 3beta-acetoxy-9alpha-fluor-11beta-hydroxy-5alpha-androstane 17beta-isobutyrate (8) were synthesized in the present study. Compounds 2 and 8 exhibited higher anabolic activity than the rest of the synthesized compounds. The structure of all these newly synthesized compounds was confirmed by analytic spectral data (mass, (1)H NMR and (13)C NMR).

Assuntos

Assuntos

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In the past few years, measurements of the pair interaction potential have shown evidence of micrometer-range attractive interactions between colloidal particles trapped between glass plates. In these experiments it is believed that the glass walls play an important role in the observed attractions. Colloidal particles trapped at the air/water interface show the formation of different 2-D colloidal patterns such as foams, clusters, and chains, whose formation has been taken as evidence of micrometer-range attractive interaction. Here, we present measurements of the pair interaction potential between 0.5-microm colloidal particles at the air/water interface. Indeed, the pair potential shows an attractive secondary minimum at about 1.9sigma, where sigma is the particle's diameter. Surprisingly, the position and depth of the secondary well are similar to those found in colloidal systems trapped between glass plates. However, we do not have a clear explanation on the origin of the attractive component of the interaction potential.

Assuntos

RESUMO

Study of group of 61 patients, nephrectomized as a result of various diseases and who before and three months after surgery underwent blood pressure, effective renal plasma flow (EPFF) and unilateral renal function determinations in order to verify the compensating ability of the remaining kidney. Effective renal plasma flow was determined by a single injection and removal of six serial blood samples with 125-I-Hippuran. Unilateral renal function was determined from the relative uptake of 99mTc-DMSA 24 hours after injection. The patients were divided into four groups according to their overall and unilateral renal function as well as the presence or absence of hypertension. Patients with normal EPFF and symmetrical renal function showed a significantly increase in the function of the remaining kidney after surgery (p < 0.001). Patients with normal or slightly reduced EPFF (< 10%) and highly asymmetrical unilateral function as well as those with decreased EPFF (> 10%) and symmetrical or asymmetrical unilateral renal function did not increased the function of the remaining kidney after nephrectomy, and hypertensive patients whose blood pressure returned to normal values after nephrectomy had a decreased function of the remaining kidney after surgery (< 0.001). It is concluded that it is possible to predict the functional behaviour of the remaining kidney after nephrectomy, and that the compensating ability will basically depend on the previously existing (overall and unilateral) renal function as well as the presence or absence of hypertension.

Assuntos