Ultrasonic studies of alcohol-induced transconformation in beta-lactoglobulin: the intermediate state

ABSTRACT In mixed alcohol-water solvents, bovine b-lactoglobulin undergoes a cooperative transition from b-sheet to a high a-helix content conformer. We report here the characterization of b-lactoglobulin by compressibility and spectroscopy measurements during this transconformation. Both the volume and compressibility increase as a function of alcohol concentration, up to maximal values which depend on the chemical nature of the three alcohols used: hexafluoroisopropanol, trifluoroethanol, and isopropanol. The order of effectiveness of alcohols in inducing the compressibility transition is identical to that previously reported for circular dichroism and thus independent of the observation technique. The highly cooperative sigmoidal curves found by compressibility determination match closely those obtained by circular dichroism at 222 nm, indicating a correlation between the two phenomena measured by the two different techniques. The presence of an equilibrium intermediate form was shown by the interaction of b-lactoglobulin with 8-anilino-1-naphthalene sulfonic acid, a probe widely used to detect molten-globule states of proteins. It was correlated with the plateau region of the volume curves and with the inflexion points of the sigmoidal compressibility curves. Ultrasound characterization of proteins can be carried out in optically transparent or nontransparent media

Finite difference time domain numerical simulation of ultrasonic propagation in coated contrast agents

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Interactions between transmembrane proteins embedded in a lamellar phase, stabilized by steric interactions

We have investigated the distribution of the transmembrane myelin proteolipid protein when inserted into an oil-swollen lamellar phase, stabilized by steric interactions. When the hydrophobic membrane thickness, D, is larger than the hydrophobic length of the protein, $d_{\pi}$, only repulsive interactions are found between proteins. The repulsive forces are of electrostatic nature, arising from charges carried by the protein. The interaction potential between proteins, deduced from digitized freeze-fracture micrographs, is well fitted when the classical screened electrostatic model is used. When D is smaller than $d_{\pi}$, an attractive force is observed in addition to the repulsive electrostatic interactions. The attractive force originates from the membranes fluctuations. The model of membrane-mediated interactions due to the membrane thermal undulations permits us to describe our results when used in combination with the electrostatic potential

Finite difference time domain numerical simulation of ultrasonic propagation in coated contrast agents

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Numerical study of the ultrasonic propagation in a solution of ultrasound contrast agent at high frequency

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High frequency wave propagation in a suspension of rigid particles: experimental validation of a time domain numerical simulation

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Nano ultrasound contrast agents for drug delivery

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In vitro evaluation of polymeric nanoparticles with a fluorine core for drug delivery triggered by focused ultrasound

Polymeric nanoparticles are being intensively investigated as drug carriers. Their efficiency could be enhanced if the drug release can be triggered using an external stimulus such as ultrasound. This approach is possible using current commercial apparatus that combine focused ultrasound with MRI to perform ultrasonic surgery. In this approach, nanoparticles made of a perfluoro-octyl bromide core and a thick polymeric (PLGA-PEG) shell may represent suitable drug carriers. Indeed, their perfluorocarbon core are detectable by 19F MRI, while their polymeric shell can encapsulate drugs. However, their applicability in ultrasound-triggered drug delivery remains to be proven. To do so, we used Nile red as a model drug and we measured its release from the polymeric shell by spectrofluorometry. In the absence of ultrasound, only a small amount of Nile red release was measured (<5%). Insonations were performed in a controlled environment using a 1.1 MHz transducer emitting tone bursts for a few minutes, whereas a focused broadband hydrophone was used to detect the occurrence of cavitation. In the absence of detectable inertial cavitation, less than 5% of Nile red was released. In the presence of detectable inertial cavitation, Nile red release was ranging from 10 to 100%, depending of the duty cycle, acoustic pressure, and tank temperature (25 or 37°C). Highest releases were obtained only for duty cycles of 25% at 37°C and 50% at 25°C and for a peak-to-peak acoustic pressure above 12.7 MPa. Electron microscopy and light scattering measurements showed a slight modification in the nanoparticle morphology only at high release contents. The occurrence of strong inertial cavitation is thus a prerequisite to induce drug release for these nanoparticles. Since strong inertial cavitation can lead to many unwanted biological effects, these nanoparticles may not be suitable for a therapeutic application using ultrasound-triggered drug delivery

Novel ultrasound contrast agents with a liquid core for imaging and therapy .

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High frequency wave propagation in a suspension of rigid particles: experimental validation of a time domain numerical simulation

International audienc