Quantitative cw Overhauser DNP Analysis of Hydration Dynamics

Liquid state Overhauser Effect Dynamic Nuclear Polarization (ODNP) has experienced a recent resurgence of interest. In particular, a new manifestation of the ODNP measurement measures the translational mobility of water within 5-10 \AA\ of an ESR-active spin probe (i.e. the local translational diffusivity D_{local} near an electron spin resonance active molecule). Such spin probes, typically stable nitroxide radicals, have been attached to the surface or interior of macromolecules, including proteins, polymers, and membrane vesicles. Despite the unique specificity of this measurement, it requires only a standard X-band (~10 GHz) continuous wave (cw) electron spin resonance (ESR) spectrometer, coupled with a standard nuclear magnetic resonance (NMR) spectrometer. Here, we present a set of developments and corrections that allow us to improve the accuracy of quantitative ODNP and apply it to samples more than two orders of magnitude lower than were previously feasible.Comment: 25 page manuscript submitted to PNMR

Functional consequences of the oligomeric assembly of proteorhodopsin.

The plasma membrane is the crucial interface between the cell and its exterior, packed with embedded proteins experiencing simultaneous protein-protein and protein-membrane interactions. A prominent example of cell membrane complexity is the assembly of transmembrane proteins into oligomeric structures, with potential functional consequences that are not well understood. From the study of proteorhodopsin (PR), a prototypical seven-transmembrane light-driven bacterial proton pump, we find evidence that the inter-protein interaction modulated by self-association yields functional changes observable from the protein interior. We also demonstrate that the oligomer is likely a physiologically relevant form of PR, as crosslinking of recombinantly expressed PR reveals an oligomeric population within the Escherichia coli membrane (putatively hexameric). Upon chromatographic isolation of oligomeric and monomeric PR in surfactant micelles, the oligomer exhibits distinctly different optical absorption properties from monomeric PR, as reflected in a prominent decrease in the pKa of the primary proton acceptor residue (D97) and slowing of the light-driven conformational change. These functional effects are predominantly determined by specific PR-PR contacts over nonspecific surfactant interactions. Interestingly, varying the surfactant type alters the population of oligomeric states and the proximity of proteins within an oligomer, as determined by sparse electron paramagnetic resonance distance measurements. Nevertheless, the dynamic surfactant environment retains the key function-tuning property exerted by oligomeric contacts. A potentially general design principle for transmembrane protein function emerges from this work, one that hinges on specific oligomeric contacts that can be modulated by protein expression or membrane composition

Study of local diffusion coefficients of the hydration layer of lipid vesicle bilayers

Water molecules near the surface of vesicle bilayers exhibit slow dynamics with respect to that of pure bulk water as they belong to the hydration layer. We present a unique analysis tool for the selective detection of local water of the hydration layer on the surface of unilamellar vesicles and the determination of its diffusion coefficients. We utilized stable nitroxide radicals covalently attached to the hydrophilic head groups of DOPC lipid chains that incorporate along with other lipids into vesicles. Through the use of dynamic nuclear polarization (DNP) the 1H NMR signal of local water interacting with the radical is amplified, and we present here an analysis of the local diffusion coefficients of this hydration layer

Deformabilidad en hormigones con agregados reciclados

Diversos trabajos han demostrado la factibilidad de elaborar hormigones con agregados reciclados, sin embargo sobre algunos aspectos poco explorados aún existen informaciones contrapuestas. Entre ellos se destacan el comportamiento diferido del hormigón (contracción y fluencia) y la capacidad de deformación en tracción (extensibilidad). Estas propiedades afectan directamente el grado de fisuración que puede tener una estructura de hormigón, lo que adquiere una significativa relevancia en la práctica, al considerar su vida en servicio. En este trabajo se presenta un estudio de la deformabilidad de hormigones que contienen 50 o 100 % de agregado grueso obtenido a partir de la trituración de losas de pavimento. Los resultados se comparan con los de otros dos hormigones elaborados con idénticas proporciones de materiales componentes variando el tipo de agregado grueso, piedra partida granítica o piedra partida cuarcítica. Se evaluaron la resistencia a tracción, la extensibilidad en flexión bajo cargas rápidas, y la fluencia en compresión. Bajo cargas de corta duración se encontró una deformabilidad creciente en el hormigón con mayor contenido de agregados reciclados, tanto en flexotracción como en compresión; también se midieron mayores valores de contracción libre y de fluencia. A partir de los resultados surge que es posible estimar la deformabilidad del hormigón con agregados reciclados siguiendo criterios similares a los aplicados en hormigones con agregados naturales; las diferencias de deformabilidad se pueden justificar considerando la menor rigidez del agregado reciclado.Different works have demonstrated the feasibility of elaborating concrete with recycled aggregates, nevertheless there is still opposite information about some aspects that have not been widely studied. The differed behaviour (shrinkage and creep) and the deformation capacity in tension (extensibility) of concrete are among them. These properties have a direct effect over the degree of cracking that can have a concrete structure so, considering its service life, they acquire a significant relevance in practice. This paper presents a study on the deformability of concretes that contain 50 or 100 % of coarse aggregate obtained from crushed pavement slabs. The results are compared with those obtained on other two concretes prepared with the same mixture proportions varying only the type of coarse aggregate, granitic crushed stone or quartzitic crushed stone. The tensile strength, extensibility in flexure under rapid rate of loading and creep in compression were evaluated. It was found that under short term loads the deformability of concrete increases with the content of recycled aggregates, both in flexure and in compression, grater values of free shrinkage and creep were also measured. From the obtained results it appears that the deformability of concrete with recycled aggregates can be estimated following the same criteria applied to concrete with natural aggregate, the differences in deformability can be justified considering the lower stiffness of the recycled aggregate

NMR Analysis on Microfluidic Devices by Remote Detection

We present a novel approach to perform high-sensitivity NMR imaging and spectroscopic analysis on microfluidic devices. The application of NMR, the most information rich spectroscopic technique, to microfluidic devices remains a challenge because the inherently low sensitivity of NMR is aggravated by small fluid volumes leading to low NMR signal, and geometric constraints resulting in poor efficiency for inductive detection. We address the latter by physically separating signal detection from encoding of information with remote detection. Thereby, we use a commercial imaging probe with sufficiently large diameter to encompass the entire device, enabling encoding of NMR information at any location on the chip. Because large-diameter coils are too insensitive for detection, we store the encoded information as longitudinal magnetization and flow it into the outlet capillary. There, we detect the signal with optimal sensitivity using a solenoidal microcoil, and reconstruct the information encoded in the fluid. We present a generally applicable design for a detection-only microcoil probe that can be inserted into the bore of a commercial imaging probe. Using hyperpolarized 129Xe gas, we show that this probe enables sensitive reconstruction of NMR spectroscopic information encoded by the large imaging probe while keeping the flexibility of a large coil