Quantifying the effects of long-range 13C-13C dipolar coupling on measured relaxation rates in RNA

Selective stable isotope labeling has transformed structural and dynamics analysis of RNA by NMR spectroscopy. These methods can remove 13C-13C dipolar couplings that complicate 13C relaxation analyses. While these phenomena are well documented for sites with adjacent 13C nuclei (e.g. ribose C1′), less is known about so-called isolated sites (e.g. adenosine C2). To investigate and quantify the effects of long-range (> 2 Å) 13C-13C dipolar interactions on RNA dynamics, we simulated adenosine C2 relaxation rates in uniformly [U-13C/15N]-ATP or selectively [2-13C]-ATP labeled RNAs. Our simulations predict non-negligible 13C-13C dipolar contributions from adenosine C4, C5, and C6 to C2 longitudinal (R1) relaxation rates in [U-13C/15N]-ATP labeled RNAs. Moreover, these contributions increase at higher magnetic fields and molecular weights to introduce discrepancies that exceed 50%. This will become increasingly important at GHz fields. Experimental R1 measurements in the 61 nucleotide human hepatitis B virus encapsidation signal ε RNA labeled with [U-13C/15N]-ATP or [2-13C]-ATP corroborate these simulations. Thus, in the absence of selectively labeled samples, long-range 13C-13C dipolar contributions must be explicitly taken into account when interpreting adenosine C2 R1 rates in terms of motional models for large RNAs.

IMPROVEMENT OF ENGINE OIL RELAXATIONAL ELECTRIC PARAMETERS MEASUREMENT SYSTEM

Mathematical model of the measured relaxation electric parameters of engine oil is designed. There are two subsystems of measuring conversion in the model: function of capacitance conversion and function of resistance of transition processes durations. In the result of physical realization of the model, own spurious capacitance and conductivity of mockup are experimentally determined depending on temperature in conditions with no external measurable parameters. The use of elements with optimal parameters in the circuitry of the measuring transducer minimized the influence of spurious conductivity. This made it possible to reduce the measurement error of the relaxation electric parameters of engine oils, increase the sensitivity along the resistance channel, and practically eliminate the mutual influence of both measurement channels. In addition to the measurement channels, a Brown filter is used to separate useful information from noise.

Deciphering the intrinsic dynamics from the beam-induced atomic motions in oxide glasses

Probing the microscopic slow structural relaxation in oxide glasses by X-ray photon correlation spectroscopy (XPCS) revealed faster than expected dynamics induced by the X-ray illumination. The fast beam-induced dynamics mask true slow structural relaxation in glasses and challenges application of XPCS to probe the atomic dynamics in oxide glasses. Here an approach that allows estimation of the true relaxation time of the sample in the presence of beam-induced dynamics is presented. The method requires two measurements either with different X-ray beam intensities or at different temperatures. Using numerical simulations it is shown that the slowest estimated true relaxation time is limited by the accuracy of the measured relaxation times of the sample. By analyzing the reported microscopic dynamics in SiO2, GeO2 and B2O3 glasses, it is concluded that the beam-induced dynamics show rich behavior depending on the sample.

The impact of pore-scale magnetic field inhomogeneity on the shape of the nuclear magnetic resonance relaxation time distribution

Measurements of the nuclear magnetic resonance (NMR) signal’s behavior with time provide powerful noninvasive insight into the pore-scale environment. The time dependence of the NMR signal, which is a function of parameters called relaxation times, is intimately linked to the geometry of the pore space and has been used successfully to estimate pore size and permeability. The basis for the pore size and permeability estimates is that interactions occurring at the grain surface often function as the primary mechanism controlling the time dependence of the NMR signal. In this limit, called the fast diffusion limit, and when each pore can be considered to be isolated, the measured relaxation times are often interpreted as representative of pore sizes. In heterogeneous media, where the NMR signal is described by a distribution of relaxation times, the measured relaxation time distribution is often interpreted as representative of the underlying pore-size distribution. We have explored a scenario in which an additional relaxation mechanism, which arises due to magnetic field inhomogeneity across the pore space, violates the assumption that interactions occurring at the grain surface are the dominant relaxation mechanism. Using both synthetic and laboratory studies, we demonstrate that magnetic field inhomogeneity can lead to a complex relationship between the measured relaxation time distribution and the underlying pore-size distribution. Magnetic field inhomogeneity is observed to lead to a spatially heterogeneous magnetization density across the pore space requiring multiple eigenmodes to describe the evolution of the magnetization within a single pore during the NMR experiment. This results in a breakdown of the validity of the interpretation of the relaxation time distribution as representative of the underlying pore-size distribution for sediments with high magnetic susceptibility.

Imaging of cerebrovascular reserve and oxygenation in Moyamoya disease

This study aimed to determine whether measurements of cerebrovascular reserve and oxygenation, assessed with spin relaxation rate R2′, yield similar information about pathology in pre-operative Moyamoya disease patients, and to assess whether R2′ is a better measure of oxygenation than other proposed markers, such as R2* and R2. Twenty-five pre-operative Moyamoya disease patients were scanned at 3.0T with acetazolamide challenge. Cerebral blood flow mapping with multi-delay arterial spin labeling, and R2*, R2, and R2′ mapping with Gradient-Echo Sampling of Free Induction Decay and Echo were performed. No baseline cerebral blood flow difference was found between angiographically abnormal and normal regions (49 ± 12 vs. 48 ± 11 mL/100 g/min, p = 0.44). However, baseline R2′ differed between these regions (3.2 ± 0.7 vs. 2.9 ± 0.6 s−1, p < 0.001), indicating reduced oxygenation in abnormal regions. Cerebrovascular reserve was lower in angiographically abnormal regions (21 ± 38 vs. 41 ± 26%, p = 0.001). All regions showed trend toward significantly improved oxygenation post-acetazolamide. Regions with poorer cerebrovascular reserve had lower baseline oxygenation (Kendall's τ = −0.24, p = 0.003). A number of angiographically abnormal regions demonstrated preserved cerebrovascular reserve, likely due to the presence of collaterals. Finally, of the concurrently measured relaxation rates, R2′ was superior for oxygenation assessment.

Electrically Tethered DNA Stretching in Nanochannels

In present study, stretching dynamics of electrically tethered λ-DNA (48.5kbp) in SiO2 nanochannels has been investigated. At high electrical fields (above 20kV/m), elongations of electrically tethered DNA molecules were observed. At high E-fields, DNAs were tethered in nanochannels and were spontaneously elongated along the nanochannels up to about 90 percent of its contour length. With E-field turned off, the measured relaxation time was about 10 sec from stretching with 20kV/m. In current study, observed behaviors of DNA molecules in nanochannels were explained by field-induced dielectrophoretic DNA trap due to the particular cross-sectional geometry of nanochannels. Also the elongation ratio between 20kV/m and 60kV/m cases and the effect of E-field distribution in the transverse plane on field-induced dielectrophoretic tethering force are discussed based on “worm-like chain” model. The FEM simulation was done to verify induced dielectrophoretic tethering force into the nanohorn.

Effect of UV radiation and temperature on rheological features of multi-layer agricultural packaging foils

The objective of the work reported here was to determine the influence of UV radiation and environmental temperature on the strength and rheological characteristics of multilayer agricultural packaging foils. The transmission properties of the experimental foils were tested in 286–363.5 nm range. The analysis of transmission properties of the foils showed that the maximum transmission was 10 % and 45 % with the experimental violet foils having 20 % and 5 % UV inhibitor in them, respectively. However, the transmission was higher than 80 % with the white foils of 5 % and 20 % inhibitor.The effect of the temperature on the tensile stress of commercial foils was investigated gated in the −20 ≤ T ≤ 50 °C temperature range. The measured relaxation curve was found to have a close correlation both for −10°C and 45°C with the calculated results. The highest reduced strength decreased as the function of the temperature according to the σ= −0,1861 T +19,107 [MPa] equation. Therefore, the probability of the break of the foils in cold weather is definitely higher than under warm weather conditions.

Phosphorylation of phospholamban and troponin I in β-adrenergic-induced acceleration of cardiac relaxation

Activation of cAMP-dependent protein kinase A (PKA) in ventricular myocytes by isoproterenol (Iso) causes phosphorylation of both phospholamban (PLB) and troponin I (TnI) and accelerates relaxation by up to twofold. Because PLB phosphorylation increases sarcoplasmic reticulum (SR) Ca pumping and TnI phosphorylation increases the rate of Ca dissociation from the myofilaments, both factors could contribute to the acceleration of relaxation seen with PKA activation. To compare quantitatively the role of TnI versus PLB phosphorylation, we measured relaxation rates before and after maximal Iso treatment for twitches of matched amplitudes in ventricular myocytes and muscle from wild-type (WT) mice and from mice in which the PLB gene was knocked out (PLB-KO). Because Iso increases contractions, even in the PLB-KO mouse, extracellular [Ca] or sarcomere length was adjusted to obtain matching twitch amplitudes (in the presence and absence of Iso). In PLB-KO myocytes and muscles (which were allowed to shorten), Iso did not alter the time constant (τ) of relaxation (∼29 ms). However, with increasing isometric force development in the PLB-KO muscles, Iso progressively but modestly accelerated relaxation (by 17%). These results contrast with WT myocytes and muscles where Iso greatly reduced τ of cell relaxation and intracellular Ca concentration decline (by 30–50%), independent of mechanical load. The Iso treatment used produced comparable increases in phosphorylation of TnI and PLB in WT. We conclude that the effect of β-adrenergic activation on relaxation is mediated entirely by PLB phosphorylation in the absence of external load. However, TnI phosphorylation could contribute up to 14–18% of this lusitropic effect in the WT mouse during maximal isometric contractions.

A Weak Field EPR Study of TANOL in Water and Water-Oil Using Dynamic Nuclear Polarization

Solutions of 4-hydroxy-TEMPO(TANOL) in water and water-soyabean oil were investigated in the concentration range 0.1 mM-10mM. Dynamic nuclear polarization (DNP) and electronic relaxation time T1e measurements were performed at each well resolved hyperfine line. In the TANOL/water-soyabean oil solutions, the effect of the presence of soyabean oil was an increase in the measured relaxation rates and a decrease in the observed enhancements. In addition, the observed enhancements diminished in time. For all of the samples, the relaxation rates decreased as the frequency of the transition increased.