National University of La Plata

About: National University of La Plata is a education organization based out in La Plata, Argentina. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 12993 authors who have published 30013 publications receiving 495118 citations. The organization is also known as: UNLP & Universidad Nacional de La Plata.

Comparison of UV and visible Raman spectroscopy of bulk metal molybdate and metal vanadate catalysts.

Abstract: The visible (532 and 442 nm) and UV (325 nm) Raman spectra of bulk mixed metal oxides (metal molybdates and metal vanadates) were compared on the same spectrometer, for the first time, to allow examination of how varying the excitation energy from visible to UV affects the resulting Raman spectra. The quality of the Raman spectra was found to be a strong function of the absorption properties of the bulk mixed oxide. For bulk mixed metal oxides that absorb weakly in the visible and UV regions, both the visible and UV Raman spectra were of high quality and exhibit identical vibrational bands, but with slightly different relative intensities. For bulk mixed metal oxides that absorb strongly in the UV and visible regions and/or strongly in the UV and weakly in the visible regions, the visible Raman spectra are much richer in structural information and of higher resolution than the corresponding UV Raman spectra. This is a consequence of the strong UV absorption that significantly reduces the sampling volume and number of scatterers giving rise to the Raman signal. The shallower escape depth of UV Raman, however, was not sufficient to detect vibrations from the surface metal oxide species that are present on the outermost surface layer of these crystalline mixed metal oxide phases as previously suggested. It was also demonstrated that there is no sample damage by the more energetic UV excitation when very low laser powers and fast detectors are employed, thus avoiding the need of complicated fluidized bed sample arrangements sometimes used for UV Raman investigations. The current comparative Raman investigation carefully documents, for the first time, the advantages and disadvantages of applying different excitation energies in collecting Raman spectra of bulk mixed metal oxide materials.

Photophysics and photochemistry of pterins in aqueous solution.

Abstract: Pterins belong to a family of heterocyclic compounds present in a wide range of living systems and participate in relevant biological functions. Interest in the photochemistry and photophysics of this group of compounds has increased since the participation of pterin derivatives in different photobiological processes has been suggested or demonstrated in recent decades. This account describes and connects basic studies on the fluorescence emission, the photooxidation, and the photosensitizing properties of oxidized six-substituted pterins in aqueous solution under UV-A irradiation. The biological implications of these studies are also discussed.

Stretch-Induced Alkalinization of Feline Papillary Muscle: An Autocrine-Paracrine System

Abstract: —Myocardial stretch is a well-known stimulus that leads to hypertrophy. Little is known, however, about the intracellular pathways involved in the transmission of myocardial stretch to the cytoplasm and nucleus. Studies in neonatal cardiomyocytes demonstrated stretch-induced release of angiotensin II (Ang II). Because intracellular alkalinization is a signal to cell growth and Ang II stimulates the Na + /H + exchanger (NHE), we studied the relationship between myocardial stretch and intracellular pH (pH i ). Experiments were performed in cat papillary muscles fixed by the ventricular end to a force transducer. Muscles were paced at 0.2 Hz and superfused with HEPES-buffered solution. pH i was measured by epifluorescence with the acetoxymethyl ester form of the pH-sensitive dye 2′,7′-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF-AM). Each muscle was progressively stretched to reach maximal developed force (L max ) and maintained in a length that was ≈92% L max (L i ). During the “stretch protocol,” muscles were quickly stretched to L max for 10 minutes and then released to L i ; pH i significantly increased during stretch and came back to the previous value when the muscle was released to L i . The increase in pH i was eliminated by (1) specific inhibition of the NHE (EIPA, 5 μmol/L), (2) AT 1 -receptor blockade (losartan, 10 μmol/L), (3) inhibition of protein kinase C (PKC) (chelerythrine, 5 μmol/L), (4) blockade of endothelin (ET) receptors with a nonselective (PD 142,893, 50 nmol/L) or a selective ET A antagonist (BQ-123, 300 nmol/L). The increase in pH i by exogenous Ang II (500 nmol/L) was also reduced by both ET-receptor antagonists. Our results indicate that after myocardial stretch, pH i increases because of stimulation of NHE activity. This involves an autocrine-paracrine mechanism in which protein kinase C, Ang II, and ET play crucial roles.

Inhibition of mild steel corrosion in HCl solution using chitosan

Abstract: The efficiency of chitosan (a naturally occurring polymer) as a corrosion inhibitor for mild steel in 0.1 M HCl was investigated by gravimetric, potentiodynamic polarization, electrochemical impedance spectroscopy measurements, scanning electron microscopy, and UV–visible analysis. The polymer was found to inhibit corrosion even at a very low concentration. Inhibition efficiency increases with a rise in temperature up to 96 % at 60 °C and then drops to 93 % at 70 °C, while it slightly increases with an increase in chitosan concentration. Polarization curves indicate that chitosan functions as a mixed inhibitor, affecting both cathodic and anodic partial reactions. Impedance results indicate that chitosan was adsorbed on the metal/solution interface. Adsorption of chitosan at the mild steel surface is found to be in agreement with Langmuir adsorption isotherm model. Chemical adsorption is the proposed mechanism for corrosion inhibition considering the trend of protection efficiency with temperature. Calculated kinetic and thermodynamic parameters corroborate the proposed mechanism.