Code: PA	Time Slot/Poster Number: 006	Session: Diffusion & Flow, Poster
Proteins specifically impact protein diffusion
Yaqiang Wang; Conggang Li; Gary J. Pielak
University of North Carolina, Chapel Hill, NC
Abstract
Despite increased attention, little is known about how the crowded intracellular environment affects protein diffusion. Here, we quantify the rotational and translational diffusion of a 7.4-kDa test protein, chymotrypsin inhibitor 2 (CI2), in solutions of glycerol, synthetic polymers, proteins, and cell lysates. As expected, diffusion decreases with increasing viscosity. Synthetic polymers cause negative deviation from the Stokes Laws and affect translation more than rotation. Surprisingly, protein crowders have the opposite effect, reducing rotation more than translation. Similarly, CI2 diffusion in cell lysates is comparable to its diffusion in crowded protein solutions, supporting the biological relevance of the results. Our results reveal the complex nature of the intracellular environments, and suggest that synthetic polymers are unsuitable mimics of that environment.

Code: PA	Time Slot/Poster Number: 007	Session: Diffusion & Flow, Poster
A PFG-NMR study of the Na+/Ca2+ exchanger large intracellular loop
Roberto Salinas; Lei Bruschweiler-Li; Rafael Brüschweiler
Florida State University, Tallahassee, FL
Abstract
The Na+/Ca2+ exchanger (NCX) is the major exporter of cytosolic Ca2+ across the plasma membrane, consisting of a transmembrane segment and a large intracellular loop. The intracellular loop is involved in Ca2+ regulation; it contains two Ca2+ binding domains CBD1 and CBD2. The molecular mechanism by which CBD1 and CBD2 respond to intracellular Ca2+ levels, inhibiting or activating the NCX transport functions, is unknown. Nevertheless, interactions between the individual CBD domains might introduce structural and dynamic effects that could be involved in the allosteric regulation of NCX. Here, we report a study of the hydrodynamic behavior of CBD12, a sequential construct that contains both CBD1 and CBD2, by NMR diffusion spectroscopy for both the apo and the Ca2+-bound states.

Code: PA	Time Slot/Poster Number: 008	Session: Diffusion & Flow, Poster
Field Equations for Nuclear Magnetization
Stanislav Sykora
Extra Byte, Castano Primo, Italy
Abstract
This presentation proposes phenomenological equations of a Spin Magnetization (SM) Field Theory encompassing all the known aspects of spin magnetization and polarization in heterogeneous samples such as porous media, suspensions, emulsions, solutions of macromolecules, cellular tissues, etc. In all such systems, relaxation occurs predominantly in a very limited fraction of the sample volume. Consequently, the NMR signal is affected principally by magnetization transport from other parts of the sample to localized magnetization sinks. Some aspects of this process are reminiscent of the classical heat-field theory (despite substantial qualitative differences) which has stimulated the presented approach. The purpose is to open a critical discussion and stimulate experimental verification of the description by novel MR techniques (some will be proposed).

Code: PA	Time Slot/Poster Number: 009	Session: Diffusion & Flow, Poster
Unifying Transverse Relaxation and Diffusion: An Effective Medium Approach
Dmitry S. Novikov1; Valerij G. Kiselev2
1CBI, NYU Langone Medical Center, New York, NY; 2Diagnostic Radiology, University Hospital Freiburg, Freiburg, Germany
Abstract
MR signal from a microscopically heterogeneous sample is massively volume-averaged. Which parameters of sample microstructure can survive this averaging, and be quantified by MRI? The answer is given by the effective medium description yielding the voxel-averaged equation for the magnetization. Heterogeneous diffusivity, relaxation rate and Larmor frequency offset give rise to corrections to the magnetization dynamics. We show that the quantifiable sample parameters are the distinct length scales on which the local diffusivity, relaxation rate and Larmor frequency vary. The effective medium approach unifies diffusion and relaxation, focusing on the single quantity whose frequency and wavevector dependence contains all measurable information about sample microstructure. The approach is illustrated with explicit analytical calculations, which agree well with Monte Carlo simulations.

Code: PA	Time Slot/Poster Number: 010	Session: Diffusion & Flow, Poster
NMR Studies of Proton Transport in Fuel Cell Membranes at Sub-freezing Conditions
Zhiru Ma1; Ruichun Jiang1; Mark Myers2; Eric Thompson1; Craig Gittleman1
1General Motors, Warren, MI; 2Bartech Group, Livonia, MI
Abstract
Water uptake activities and transport properties are critical for the water management in the fuel cell membrane. In this work, three sets of fuel cell membranes at several different hydration states have been studied using variable temperature 1H spin-lattice relaxation times (T1) and pulsed field gradient (PFG) NMR techniques in the temperature range of 25 to – 34 oC. Water self-diffusion coefficients and proton transport activation energies in fuel cell membranes were obtained from PFG-NMR experiments. The results show that the water self-diffusion coefficients in fuel cell membranes increase with increasing hydration level, and decrease with decreasing temperature. The water uptake activity and diffusivity in these membranes were compared as a function of temperature and hydration level.

Code: PA	Time Slot/Poster Number: 011	Session: Diffusion & Flow, Poster
In Vivo Observation of Membranes in Calf Muscle Using Time-Dependent DWI
Els Fieremans1; Dmitry S. Novikov1; Eric E. Sigmund1; Jens H. Jensen1; Joseph A. Helpern1, 2
1Radiology, New York University School of Medicine, New York, NY; 2Nathan S. Kline Institute, Orangeburg, NY
Abstract
The time-dependent diffusion tensor eigenvalues are measured in vivo in the human calf muscle using stimulated echo. We show that the eigenvalues in the direction across the fibers exhibit the inverse-square-root dependence on the diffusion time between 0.1 and 1.3 s. This time dependence is a characteristic signature of permeable membranes. Estimates are derived for the bare diffusivity, the membrane permeability, the surface-to-volume ratio and the mean intra-membrane spacing, indicating that the predominant restrictions to molecular motion are likely to originate from the intracellular membranes that surround cell organelles.

Code: PA	Time Slot/Poster Number: 012	Session: Diffusion & Flow, Poster
DTI and DEXA Analysis of Resistance Training and HMB Impact on Muscle Fiber CSA and Body Mass in Sarcopenic Rats
Ihssan S. Masad1, 2; Youngmin Park1; Sang-rok Lee 1; Jacob M. Wilson1; Paul C. Henning Henning 1; Bahram H. Arjmandi1; Samuel C. Grant 1, 2; Jeong-su Kim1
1The Florida State University, Tallahassee, FL; 2National High Magnetic Field Laboratory, Tallahassee, FL
Abstract
Sarcopenia, age-related muscle wasting, has drastic medical and financial impacts on the elderly population. In this study, diffusion tensor imaging (DTI), which has shown high sensitivity to muscle architecture, is employed to study the potential benefits of β-hydroxy-β-methylbutyrate (HMB) and resistance training (RT) in a pre-clinical model of aged rats. DTI was used to evaluate muscle cross sectional area (CSA) and water diffusivity while dual energy X-ray absorptiometry was utilized to assess lean body mass (LBM). As well as increasing LBM, results demonstrate that RT caused hypertrophy in aged soleus muscle, as indicated by increased ADC as well as increased second and third eigenvalues. However, results showed that HMB did not have a large impact on muscle CSA.

Code: PA	Time Slot/Poster Number: 013	Session: Diffusion & Flow, Poster
Remotely Detected Flow Imaging and Velocimetry of Porous Beadpacks
Nicholas W Halpern-Manners; Jeffrey Paulsen; Vikram Bajaj; Alexander Pines
LBNL & UC Berkeley, Berkeley, CA
Abstract
We present a novel approach to flow imaging in porous media, allowing us to circumvent the majority of obstacles associated with magnetic resonance experiments in porous systems. Our experiments utilize the technique of remote detection, which physically separates the encoding and detection steps of an experiment, providing an added time-of-flight dimension and a unique means to visualize flow pathways. With the aid of compressed sensing techniques, we acquire high-resolution images of flow through coarse (450-600 μm bead diameter) and fine (150-212 μm) beadpacks. We obtain resolutions down to 45 μm, permitting flow imaging of previously inaccessible sizes of porous materials. We measure three-dimensional velocity vectors and T2 relaxation within the beadpacks and examine the results with respect to beadpack composition.

Code: PA	Time Slot/Poster Number: 014	Session: Diffusion & Flow, Poster
Progress in Bayesian DOSY and ROSY Transforms
Carlos Cobas1; Stanislav Sykora2
1Metrelab Research, Santiago de Compostela, Spain; 2Extra Byte, Castano Primo, Italy
Abstract
An efficient Bayesian approach to the evaluation and graphic representation of multi-array NMR data sets characteristic of the diffusion (DOSY) and relaxation (ROSY) spectroscopies was first presented at ENC 2008. Since than, it was beta tested and a considerable progress has been made which includes (a) a refinement of the LineSNAP section of the algorithm, (b) spectral alignment of the arrayed spectra using the novel Global Spectrum Deconvolution (GSD) algorithm and (c) combination of the Bayesian algorithm with a Bayesian handling of bi-exponentiality of overlapping spectral peaks. This presentation discusses the details of these developments and illustrates them on practical examples.

Code: PA	Time Slot/Poster Number: 015	Session: Diffusion & Flow, Poster
How to Quantify Ordering of Permeable Membranes Using Time-Dependent Diffusion MR
Dmitry S. Novikov; Els Fieremans; Jens H. Jensen; Joseph A. Helpern
CBI, NYU Langone Medical Center, New York, NY
Abstract
What can one infer about the packing geometry (ordering) of permeable membranes from the measured time-dependent diffusion? We focus on a one-dimensional case, and show that the form of the probability distribution of the intervals between membranes crucially affects how the time-dependent diffusivity approaches the tortuosity asymptote. In particular, the prefactor in the inverse-square-root time-dependence of the diffusivity is directly related to the degree of structural irregularity of a sample. If the variance of the distribution of inter-membrane intervals diverges, the diffusion becomes anomalous with a slow fractional power-law dependence on time. Our results agree with Monte Carlo simulations of diffusion in one dimension.