A comparative electron spin resonance investigation on the effects of barbital and tetracaine on DPPC multilayers

We have performed a comparative spin label ESR investigation of the effects of tetracaine and barbital on DPPC multilamellar vesicles (MLV). The investigation has been carried out both at pH 5.0 and 9.0, by using the spin labels 5-SASL, 5-PCSL and DTBN as magnetic probes. Information on the thermotropic properties of the multilamellae, such as molecular orientational degree of order, packing density and permeability has been obtained. The results show that tetracaine induces fluidization of the phospholipid bilayers, reduction of the molecular packing density and downward shift of the main phase transition temperature of the multilayers of DPPC. Moreover, increasing concentrations of tetracaine are able to induce the lyotropic gel → liquid-crystal phase transition at a fixed temperature, in particular at pH 5.0. Barbital, instead, is much less effective than tetracaine in perturbing the membrane properties. In fact, the most important effect observed is only a progressive fluidization of the DPPC bilayers especially at pH 9.0. The dependence on pH of the effects observed suggests that the anesthetic molecules locate at different position in the lipid bilayers depending on the protonation state of both molecules.     

Contouring of artwork surface by fringe projection and FFT analysis

In the present work, we propose a simple optical method to perform profilometry on works of art. The method is based on the projection of a Ronchi grating onto the surface to be analyzed. When viewed at an angle different from the projection angle, the grid pattern appears deformed by the surface shape. This pattern is digitized, by a high-resolution CCD camera, and then processed using a Fourier transform analysis. The technique is free from the errors caused by higher harmonic components of the grating pattern. Furthermore, the method relies on very simple equipment and it is therefore suitable for in situ measurements. Theoretical details and examples of the technique in operation are given.     

Absolute frequency stabilization of a tunable Tm:Ho:YAG laser to the HBr P(12) line at 2097 nm

We demonstrate absolute frequency stabilization of a widely tunable Tm:Ho:YAG laser by locking the oscillator to the P(12) absorption line of the H(79)Br molecule at 2097.222 nm, using the fringe side-locking technique. We perform time and spectral analysis of open- and closed-loop error signals to evaluate the frequency noise. In closed-loop operation a long-term frequency stability of better than 2 MHz with rms frequency fluctuations of ~112 kHz is obtained over an observation time of 10(3) s.     

Mitogens-DPPC-vesicles interaction: A spin label ESR study

Summary The electron spin resonance spectroscopy with the spin labelling technique has been used to investigate the interaction of sonicated di-palmitoyl-phosphatidylcholine (DPPC) small unilamellar vesicles with concanavalin A (Con A), phytohemagglutinin (PHA) and staphylococcal enterotoxin B (SEB) in the temperature range 0–50°C. Conventional ESR measurements show that the addition of mitogens to the vesicles suspensions up to the number of mitogens/number of vesicles ratio of 60 increases the orientational degree of order of the lipid molecules in the gel phase and the gel→liquid-crystalline phase transition temperature. No effects on the liquid-crystalline phase have been observed, also no matter for the mitogen used. The effectiveness results in the order: ConA>SEB>PHA. Saturation transfer-ESR measurements evidence more restricted rotation of the DPPC molecules in the gel phase in the presence of Con A and SEB than in the presence of PHA if compared to pure DPPC-vesicles. The effective rotational correlation time, σ_c, of the spin label 5-SASL results about one order of magnitude higher in the presence of 60 mitogen molecules/vesicle. The ESR findings suggest a mitogen-induced increase in the packing density of lipid bilayers which is attributed to a morphological change from sonicated vesicles, with a small radius of curvature, to a more planar mesophase. Con A is more effective than SEB and PHA in inducing this process. The authors of this paper have agreed to not receive the proofs for correction.     

Measurement and characterization of the frequency noise of a laser-diode-pumped single-frequency Tm-Ho:YAG laser

The frequency noise characteristics of a single-frequency 2.1-m Tm-Ho:YAG laser have been thoroughly investigated. From the measurement of the frequency noise spectral density, performed by means of an interferometric technique, a short-term laser linewidth of 550 kHz over 1-ms time interval has been obtained. The frequency stability, defined as the two sample standard deviation of the frequency fluctuations with dead time T, has been also evaluated, obtaining values ranging from 250 kHz to 2.5 MHz for T values between 1 and 100 ms over an observation time of 100 ns. It has been shown through a numerical analysis that a significant improvement is achievable, attaining a frequency stability of 25 kHz for T up to 100 ms, by using the Pound–Drever locking technique in connection with a roto-vibrational line of the HBr molecule.     

Procain interaction with DPPC multilayers: an ESR spin label investigation

A spin label electron spin resonance (ESR) study has been carried out on the interaction between the local anesthetic procaine (PRC) and multilamellar dispersions of di-palmitoylphosphatidylcholine (DPPC). The investigation has been performed either in the gel or in the liquid crystal phase of DPPC varying the anesthetic/DPPC molar ratio as well as the pH of the dispersion medium and using spin labeled DPPC molecules (5- and 16-PCSL) and the di-tert-butyl nitroxide (DTBN) spin probe. On increasing the anesthetic concentration in the dispersion medium up to PRC/DPPC molar ratio of 33 mol.%, a lyotropic transition of the bilayer from the lamellar gel phase L_β, to the interdigitated L_βi one is observed either at pH 5.0 or at pH 10.0. At intermediate pH values, about pH 7.0, such a PRC concentration dependent transition is absent. A decrease of the partition of the DTBN molecules between the dispersion medium and the fluid hydrophobic phase of DPPC multilayers is observed at pH 5.0 with anesthetic concentration, while an opposite behaviour is evidenced at pH 10.0. The pre- and main-phase transition temperatures of the DPPC multilayers are also affected although to different extent. These results are interpreted in terms of adsorption of the PRC molecules at the surface of the model membrane at the extreme pH values investigated, while at about neutral pH values they intercalate among the DPPC molecules. The protonation state of procaine plays an important role as it determines the way of surface adsorption of the PRC molecules in the neutral form at the high pH value and in the charged cationic form at pH 5.0.     

Improved thin-layer chromatographic method for sugar separations

A method is described for the utilization of pre-coated, non-impregnated silical gel thin layers in one- and two-dimensional separations of carbodhyrates and related compounds. Boric and phenylboronic acids were added to the organic elution systems in different concentrations and their interactions with the sugar molecules during the chromatographic process were studied. A comparison was made between solvent systems containing boric or phenylboronic acid and systems devoid of both acids as eluents. With boric acid-containing solvents the migration of some sugars was considerably inhibited, whereas phenylboronic acid produced an increase in the RF values of certain sugars. The combination of these two types of solvent in two dimensional development resulted in the clear separation of a group of mono- and disaccharides of bioclinical interest.     

Novel TiO2-based catalysts employed in photocatalysis and photoelectrocatalysis for effective degradation of pharmaceuticals (PhACs) in water: A short review

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