On the Information Theory for Magnetic Resonance Imaging.

This work presents the mathematical formulation of the Magnetic Resonance Imaging (MRI) system modeled as a wireless communication system to establish its information theory foundations. The MRI system conceived as a source-sink communication system has channel impairments that affect the transmitted data. The information source is a stochastic process that produces a sequence of information symbols governed by a set of probabilities. The adverse effects on the transmitted MRI signal shall limit the amount of information capable of being received at the sink. Therefore, reliable detection at the receiver shall be accomplished by estimating the channel capacity and an approximation of the source entropy. Modeling the MRI system using a wireless model shall simplify the receiver architecture, yielding new methods to improve MRI signal acquisition, i.e., different values of bandwidth and signal strength yield the same channel capacity. Achieving capacity bridges information and computation efficiency.Clinical relevance This work establishes the basics to reduce MRI scan times by acquiring sufficient information with less redundant information.

Functionalized lipid nanoparticles-cellophane hybrid films for molecular delivery: preparation, physicochemical characterization, and stability.

Lipid nanoparticles functionalized with the sunscreen 2,4-dihydroxybenzophenone (FLNPs) have been prepared by the ultrasound method and embedded in highly hydrophilic cellophane supports (regenerated cellulose, RC), creating biocompatible hybrid films (RC-FLNPs samples). The morphology of the FLNPs was studied with transmission microscopy, whereas the surface and interior chemical composition was analyzed by micro-Raman spectroscopy. RC-FLNPs hybrid films were prepared from the immersion of two cellophane supports with different thicknesses and water uptake properties (RC-3 and RC-6) in an aqueous dispersion of FLNPs. The structure of this hybrid material was visualized with bright-field microscopy, which clearly showed the inclusion of the FLNPs in the cellophane matrix. The stability of the RC-FLNPs films with respect to both aqueous environments and time was demonstrated by NaCl diffusion measurements. The reduction in the diffusion coefficient through the nanoparticle-modified films compared with the original supports confirms the presence of nanoparticles for concentration gradients of up to 0.4 M (osmotic pressure around 10 bar), indicating the stability of the hybrid hydrophilic material, even in aqueous environments and under matter flow conditions for a period of 21 days.

Highly stable, protein resistant thin films on SiC-modified silicon substrates.

Thin films terminated with oligo(ethylene glycol) (OEG) could be photochemically grafted onto ultrathin silicon carbide layers that were generated on silicon substrates via carbonization with acetylene at 820 degrees C. The OEG coating reduced the non-specific adsorption of fibrinogen on the substrates by 99.5% and remained resistant after storage in PBS for 4 weeks at 37 degrees C.

Synthesis of theophylline derivatives and study of their activity as antagonists at adenosine receptors.

The synthesis of oligo(ethylene glycol)-alkene substituted theophyllines in positions 7 and/or 8 is described. The binding activity at adenosine receptors of selected derivatives was studied. Compound 2 showed high affinity for human A(2B) receptor (K(i) = 4.16 nM) with a selectivity K(iA2A)/K(iA2B) of 24.1, and a solubility in water of 1 mM. The alkenyl substituent in some of the theophylline derivatives allows for covalent attachment of them onto hydrogen-terminated silicon substrate surfaces via hydrosilylation. Alternatively, an azido group was incorporated to an oligo(ethylene glycol)theophylline derivative as an anchor for tethering the molecules on ethynyl presenting surfaces via click reaction.

Raman study of the rigidity of penta-p-phenylene derivatives used as legs in molecular tripods.

Molecular planarity of penta-p-phenylene (P5P) and several substituted derivatives with four side chains of various lengths, including deca(ethylene glycol) groups, is discussed by considering the changes in the intensity ratio between the Raman bands recorded at 1280 and 1220 cm(-1). The intensity ratio between both bands I(1280)/I(1220) shows a small increase with the size of the substituent, indicating a high rigidity for all these compounds, even those with long oligo(ethylene glycol) side chains. This result is important given that these phenylene derivatives are versatile building blocks for the construction of nanometric tripod-shaped adsorbates for biological applications since the side chains should prevent the nonspecific interaction with proteins.

X-Ray Photoelectron Spectroscopy Analysis of Di-(2-ethylhexyl) Phosphoric Acid Activated Membranes.

Surface chemical characterization of activated composite membranes, which consist of a polyamide/polysulfone support containing different amounts of di-(2-ethylhexyl) phosphoric acid as carrier, was performed by X-ray photoelectron spectroscopy (XPS) in order to obtain information about the nature of the chemical bonding between the carrier and the membrane top layer. XPS spectra of the top layer of the polymeric support (polyamide) show bands in the C 1s, N 1s, O 1s, and P 2p regions. The N 1s and O 1s signals of the polyamide layer were asymmetric and could be deconvoluted in two peaks that correspond to the coexistence of free and hydrogen bonded polyamide. To support this assignment, primary amides such as benzamide and n-butyramide, which can associate themselves forming hydrogen bonding, and a tertiary amide, N-benzoyl morpholine, unable to form hydrogen bonding, were also studied by XPS. The N 1s asymmetric signals of benzamide and n-butyramide were deconvoluted in two peaks due to the coexistence of free and hydrogen bonded species, while the N 1s signal of N-benzoyl morpholine is symmetric and corresponds to the existence of free amide alone. As a result of the addition of di-(2-ethylhexyl) phosphoric acid to the polymeric matrix, the N 1s signal intensities decrease, while the P 2p signal intensities increase with carrier concentration to a maximum corresponding to surface site saturation. Upon acid addition, the polyamide was protonated and an expected chemical shift of the N 1s signal to higher binding energies was observed due to the increase of the positive charge of the nitrogen atom. This type of chemical interaction allows to fix the carrier in the membrane without its complete immobilization. On the other hand, the surface concentration of N and P, determined by XPS, indicates that a concentration of 400 mM of the carrier in the casting solution is sufficient to saturate the surface of the membrane. Copyright 2000 Academic Press.