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Spin-lattice Relaxation Time (spin-lattice + relaxation_time)
Selected AbstractsCombined Optical and MR Bioimaging Using Rare Earth Ion Doped NaYF4 NanocrystalsADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Rajiv Kumar Abstract Here, novel nanoprobes for combined optical and magnetic resonance (MR) bioimaging are reported. Fluoride (NaYF4) nanocrystals (20,30,nm size) co-doped with the rare earth ions Gd3+ and Er3+/Yb3+/Eu3+ are synthesized and dispersed in water. An efficient up- and downconverted photoluminescence from the rare-earth ions (Er3+ and Yb3+ or Eu3+) doped into fluoride nanomatrix allows optical imaging modality for the nanoprobes. Upconversion nanophosphors (UCNPs) show nearly quadratic dependence of the photoluminescence intensity on the excitation light power, confirming a two-photon induced process and allowing two-photon imaging with UCNPs with low power continuous wave laser diodes due to the sequential nature of the two-photon process. Furthermore, both UCNPs and downconversion nanophosphors (DCNPs) are modified with biorecognition biomolecules such as anti-claudin-4 and anti-mesothelin, and show in vitro targeted delivery to cancer cells using confocal microscopy. The possibility of using nanoprobes for optical imaging in vivo is also demonstrated. It is also shown that Gd3+ co-doped within the nanophosphors imparts strong T1 (Spin-lattice relaxation time) and T2 (spin-spin relaxation time) for high contrast MR imaging. Thus, nanoprobes based on fluoride nanophosphors doped with rare earth ions are shown to provide the dual modality of optical and magnetic resonance imaging. [source] NMR search for polymorphic phase transformations in chlorpropamide form-A at high pressuresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2009sicki Abstract The high-pressure effects on chlorpropamide (C10H13ClN2O3S) form-A have been studied by 1H NMR spectroscopy at high pressures up to 800 MPa in the temperature range 90,300 K. A study of the NMR second moment and spin-lattice relaxation time has been completed by a calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the NMR line by the Monte,Carlo method, which enabled a precise description of molecular dynamics in the compound studied. Reorientations of the methyl group, oscillations and reorientations of the chlorophenyl ring and reorientations of the propyl group have been revealed and respective activation parameters extracted. No phase transformation of the compound form-A has been detected. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1426,1437, 2009 [source] Solid-State NMR Characterization of the Multiphase Structure of Polypropylene In-reactor AlloyMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2010Haijin Zhu Abstract A variety of solid-state NMR techniques were used to characterize the chain dynamics, miscibility and the micro-phase structure of a polypropylene (PP) in-reactor alloy system. The alloy was physically separated into three fractions, and the molecular dynamics and relaxation behavior of the pure fractions was then compared with the components in the alloy to achieve comprehensive understanding of the phase structure of the PP in-reactor alloy. The miscibility among different components of the alloy was studied by the rotational frame spin-lattice relaxation time. Proton spin-diffusion methods were used to quantify the domain thicknesses of different regions in the alloy. The results show that the alloy is composed of three phases, namely, a homo-polyethylene (HPE) matrix, a homo-polypropylene (HPP) dispersed phase, and a linear low-density polyethylene (LLDPE) interphase. The thickness of the LLDPE interphase is estimated to be 7.7,nm at room temperature, and changes dramatically with temperature. Finally, based on all the solid-state NMR results, a model for the micro-phase-structure of the PP in-reactor alloy is proposed, and a correlation between the micro-phase structure and the excellent mechanical property is established. [source] Effect of Branch Length on 13C NMR Relaxation Properties in Molten Poly[ethylene- co -(, -olefin)] Model SystemsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19-20 2007Matthew Parkinson Abstract The potential of branch length discrimination for branches containing six and more carbons via bulk NMR relaxation properties in the melt-state has been explored. A systematic increase in the 13C spin-lattice relaxation time (T) of the terminal branch carbons 1 and 2 was observed when the branch increased from 6 to 16 carbons in length. The measurement of T via inversion recovery at high-field showed the most reliable data. The effects of saturation and NOE were addressed by using recycle delays longer than 5,×,T and the use of the saturation recovery was found to be unsatisfactory. All nuclear relaxation times were determined in a highly time efficient manner using a previously developed melt-state MAS NMR method. [source] Rapid 3D-T1, mapping of the knee joint at 3.0T with parallel imagingMAGNETIC RESONANCE IN MEDICINE, Issue 3 2006S. Kubilay Pakin Abstract Three-dimensional spin-lattice relaxation time in the rotating frame (3D-T1,) with parallel imaging at 3.0T was implemented on a whole-body clinical scanner. A 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster was combined with generalized autocalibrating partially parallel acquisitions (GRAPPA) to acquire T1, -weighted images. 3D-T1, maps of an agarose phantom and three healthy subjects were constructed using an eight-channel phased-array coil without parallel imaging and with parallel imaging acceleration factors of 2 and 3, in order to assess the reproducibility of the method. The coefficient of variation (CV) of the median T1, of the agarose phantom was 0.44%, which shows excellent reproducibility. The reproducibility of in vivo 3D-T1, maps was also investigated in three healthy subjects. The CV of the median T1, of the patellar cartilage varied between ,1.1% and 4.3%. Similarly, the CV varied between ,2.1,5.8%, ,1.4,8.7%, and ,1.5,4.1% for the biceps femoris and lateral and medial gastrocnemius muscles, respectively. The preliminary results demonstrate that 3D-T1, maps can be constructed with good reproducibility using parallel imaging. 3D-T1, with parallel imaging capability is an important clinical tool for reducing both the total acquisition time and RF energy deposition at 3T. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Spin and energy transfer between magnetic ions and freecarriers in diluted-magnetic semiconductor heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004D.R. Yakovlev Abstract In this paper we give a brief overview of our studies on dynamical processes in diluted-magnetic-semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. Presence of free carriers is an important factor which determines the energy- and spin transfer in a coupled systems of magnetic ions, lattice (the phonon system) and carriers. We report also new data on dynamical response of magnetic ions interacting with photogenerated electron-hole plasma. (Zn,Mn)Se/(Zn,Be)Se structures with relatively high Mn content of 11% provide spin-lattice relaxation time of about 20 ns, which is considerably shorter then the characterictic times of nonequilibrium phonons ranging to 1 ,s. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structures and spectroscopic characterization of chiral and racemic 4-phenyl-1,3-oxazolidin-2-oneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2004S. Kitoh Abstract Crystal structures of (R)- and (rac)-4-phenyl-1,3-oxazolidin-2-one (4-POO) have been determined by X-ray diffraction and characterized by the solid state 13C NMR and IR spectra. Molecular geometries and intermolecular interactions in (R)- and (rac)-4-POO crystals are very similar to each other; 4-POO molecules are linked via the N-H,O intermolecular hydrogen bonds to form the chained structure. Chemical shifts of the solid state 13C NMR spectra are very similar to each other, whereas the 1H spin-lattice relaxation times (T1H) value for (R)-4-POO is five times as large as that for (rac)-4-POO, reflecting the more restricted mobility of the (R)-4-POO chain. Although both crystals contain an unique molecule in the asymmetric unit, a doublet feature is observed for the C=O stretching mode in the IR spectra of (R)- and (rac)-4-POO crystals. The frequency gap of the C=O bands are correlated with the strength of the dipole-dipole interactions between the neighboring C=O groups. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] A solid-state NMR study of phase structure, molecular interactions, and mobility in blends of citric acid and paracetamolJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2009S. Schantz Abstract Citric acid anhydrate (CAA) and paracetamol (PARA), prepared as crystalline physical mixtures and as amorphous blends, were studied using 13C solid-state cross polarization magic angle spinning (CPMAS) NMR. Amorphous blends showed significant line broadening from the conformational distribution as compared to the crystalline samples. Also, chemical shift variations were observed between crystalline and amorphous blends, which were attributed to differences in intermolecular interactions. Averaging of proton rotating-frame spin-lattice relaxation times (T1,) probed via different 13C sites in the amorphous blends confirmed molecular level mixing. For some, initially amorphous, sample compositions the onset of crystallization was evident directly from spectra and from the significantly longer T1, relaxations. Thus, crystallization caused phase separation with properties of the two phases resembling those of pure CAA and PARA, respectively. 13C spectra of amorphous 50/50 (w/w, %) CAA/PARA recorded from above the glass transition temperature broadened as the temperature increased to a maximum at T,,,Tg,+,33 K. This was the result of a dynamic interference between the line narrowing techniques being applied and the time scale of molecular reorientation in the miscible melt. The derived average correlation time was found to correspond well with previous results from melt rheology. We conclude that the underlying reasons for physical instability (i.e., crystallization from the miscible melt, including molecular interactions and dynamics) of this class of amorphous binary mixtures can be effectively evaluated using NMR spectroscopy. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1862,1870, 2009 [source] Solid-state 13C and 129Xe NMR study of poly(vinyl alcohol) and poly(vinyl alcohol)/lactosilated chitosan gelsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2003Simona Lai Abstract Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a-PVA) and 61% (s-PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with 129Xe and cross-polarization/magic-angle-spinning 13C NMR techniques. Although the dry gels exhibit two broad 129Xe resonances in the slow-to-intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a-PVA/LC) or two (s-PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin-lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123,3131, 2003 [source] Measurement of spin-lattice relaxation times and chemical exchange rates in multiple-site systems using progressive saturationMAGNETIC RESONANCE IN MEDICINE, Issue 1 2007Craig J. Galbán Abstract A new method for measuring spin-lattice relaxation times and chemical exchange (CE) rate constants in multiple-site exchanging systems is described. The method, chemical exchange and T1 measurement using progressive saturation (CUPS), was applied to determine T1s and analyze phosphorus exchange among phosphocreatine (PCr), ATP, and inorganic phosphate (Pi), mediated by creatine kinase (CK) and ATP synthase, using 31P-MRS. Two-site exchange was analyzed in vitro and in the rat leg, and three-site exchange was analyzed in the rat heart. Data were fitted to a model of progressive saturation incorporating T1 relaxation and CE. For the in vitro system at 8.45T, we found T1(PCr) = 2.86 s and T1(,-ATP) = 1.72 s. For the rat gastrocnemius at 1.9T, we found T1(PCr) = 6.60 s and T1(,-ATP) = 2.06 s. For the rat heart at 9.4T, we found T1(PCr) = 3.35 s, T1(,-ATP) = 0.69 s, and T1(Pi) = 1.83 s. All of these values were within 20% of literature values. Similarly, the determined exchange rates were in the same range as published values. Using simulations, we compared CUPS with transient saturation transfer as a method for measuring T1s and rates. The two methods showed similar sensitivity to noise. We conclude that CUPS is a viable alternative for measuring T1s and CE rates in exchanging systems. Magn Reson Med 58:8,18, 2007. © 2007 Wiley-Liss, Inc. [source] | |||||||||||||