Papers by Keyword: Nuclear Magnetic Resonance

Abstract: The novel bicycloamino acid, 1−carboxyl−4−amino−2−aza−3−oxo−[2.2.2] bicyclooctane was synthesized and its physical characteristics have been compared to those predicted using quantum chemical calculations. The crystal structure of novel compound was determined by X-ray diffraction measurements at room temperature. Unit cell is monoclinic, with space group P 2₁/n (14) and a = 5.8587(6) Ǻ, b = 11.2454(16) Ǻ, c = 13.9723(16) Ǻ, β=97.840(6)°, Z = 2. Refinement was performed using all 1598 reflections with R = 0.4085 and wR = 0.6024. Theoretical calculation of full optimization and atomic net charge, and frontier orbital energies of the title compound was carried out at the B3LYP/6−31G(d,p) level. The NMR chemical shielding tensors and vibrational frequencies were calculated with B3LYP/6-311+G(2d, p)− level in which were close values and similar spectrum structures with experimental results and used to interpret the experimental measurements.

Abstract: We have carried out ⁷⁵As nuclear magnetic resonance (NMR) measurements to investigate a new antiferromagnetic (AFM) state, the so-called hedgehog spin-vortex crystal (SVC) in CaK(Fe_0.967Ni_0.033)₄As₄. The hedgehog SVC order is clearly demonstrated by the direct observation of internal magnetic induction along the c axis at the As1 site (close to K) and a zero net internal magnetic induction at the As2 site (close to Ca) below an AFM ordering temperature of T_N ~ 45 K. In the superconducting (SC) state, the NMR signal intensity decreases suddenly just below T_c ~ 20 K due to Meissner effect, evidencing the coexistence of the hedgehog SVC AFM and SC states from a microscopic point of view.

Abstract: Nanoporous materials find widespread application in material upgrading by separation (“molecular sieving”) and catalytic conversion. Mass transfer in these materials is a key phenomenon deciding about their technological performance. This chapter deals with the application of measurement techniques which are able to follow the diffusive fluxes of the guest molecules in such materials over “microscopic” distances, including the pulsed field gradient (PFG) technique of Nuclear Magnetic Resonance (NMR) and the techniques of microimaging by interference microscopy (IFM) and by IR microscopy (IRM). Microscopic measurement is a prerequisite for attaining unbiased information about the elementary steps of mass transfer and about their role within the overall process of technological exploitation. We dedicate this treatise to the memory of our dear and highly esteemed colleague Nicolaas Augustinus Stolwijk, notably in recognition of his manifold activities in the field of diffusion, distinguished by their impressively high standard in connecting the message of various techniques of measurement and in combining them to comprehensive views on quite intricate subjects.

Abstract: Polystyrene-block-polyisoprene-block-poly (butyl acrylate) or PS-b-PI-b-PBA triblock copolymer with different ratio (5:5 and 4:6) of styrene and isoprene unit have been synthesized by anionic polymerization. The product had been characterized by using Scanning Electron Microscopy (SEM) and N-Nuclear Magnetic Resonance (H-NMR). The results of SEM images reveal that more rubber matrix can be seen for 4:6 ratios as compared to 5:5 ratios due to high content of isoprene in the copolymer. H-NMR results indicate that the peaks of polystyrene, polyisoprene and butyl acrylate for ratio 5:5 exists at 6.50 – 7.28 ppm, 4.68 – 4.88 ppm, and 0.80 – 1.83 ppm. As for ratio 4:6, the peaks can be observed at 6.30 – 7.33 ppm, 5.19 – 5.70 ppm, and 1.18 – 1.78 ppm respectively. The H-NMR analysis of the copolymer microstructure confirms that both copolymer are primarily consists of polystyrene, polyisoprene and polybutyl acrylate segment.

Abstract: The migration of lithium (Li) ions in electrode materials affects the rate performance of rechargeable Li ion batteries. Therefore, the application of LiMn₂O_4, which is an appealing cathode material in high power systems, requires fast electron transfer kinetics which is possible through the use of nanostructured morphologies and conductive material. Nanowires offer the advantage of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. In this study, LiMn₂O₄ nanowires with cubic spinel structure were synthesized by using a α-MnO₂ nanowire-template-based method. LiMn₂O₄ nanowires have diameters less than 10 nm and lengths of several micrometers. Fe-Au nanoparticles were synthesized and used as coating material to improve both the catalytic activities and stability of the LiMn₂O₄ nanowires. The Li[Fe_0.02Au_0.01]Mn_1.97O₄ nanowires with modified architecture effectively accommodates the structural transformation during Li⁺ ion charge and discharge. Hence, the Li[Fe_0.02Au_0.01]Mn_1.97O₄ nanowire cathode system shows outstanding stability and enhanced electrocatalytical properties. Microstructural analysis of Li[Fe_0.02Au_0.01]Mn_1.97O₄ linked its composition and processing to its properties and performance. High resolution transmission electron microscope (HR-TEM) of the nanomaterial showed good crystallinity which contributed towards good reversibility. XRD analysis revealed a pure cubic spinel structure without any impurities. Structural information provided by Raman and solid state spectroscopy further corroborated these findings. The improved rate and cycling performance is related to the conductive particles infused within the nanowires which make up the electrode.

Abstract: In this paper we present a new method for the monitoring of super-paramagnetic nanoparticles (SPANs) in the body. Nowadays, reliable and inexpensive device and method for monitoring the spatial distribution of SPANs in the body are not present in the market of clinical imaging equipments. Importantly, since SPANs can be conjugated to a huge variety of organic (antibodies, proteins, synthetic polymers) and inorganic molecules they can be used to selectively detect targets (e.g. cancer cells) with striking specificity. The existing imaging methods used for clinical diagnostic purposes are the nuclear magnetic resonance (NMR) and computerized axial tomography scan (CAT or CT scan). Detection of SPANs with these methods is still controversial and most import they used strong magnetic field and harmful X-ray radiation, respectively, and the cost for a single analysis is high as well. Herein we describe an innovative magnetic method promises the measurement of the distribution of SPANs with sensitivity quite better than 1 μm³. The method (patented device by our group) is based on magnetic excitation and consequent detection of nanoparticles using super-conducting or magnetic sensors (magnetometers). The device is innovative and novel, and could be considered as a universal breakthrough in tumor diagnosis. Possible other applications could be simultaneous killing of the cancer cells applying inductive heating techniques.

Abstract: Water under the fibre saturation point affects many aspects of the performance of the cellulose. Therefore an understanding of the interaction of water with cellulose is essential for the interpretation and prediction of cellulose response. Because of the complicated structure and the different possibilities of the hydrogen-bonds formation, the mechanism of water sorption in water-cellulose system has been studied by different techniques. This paper gave an outline of the structure of cellulose, also an overview of the researches of the mechanism of cellulose-water interaction using nuclear magnetic resonance. Further observations were made aiming at having a deeper understanding of the water-cellulose system.

Abstract: This paper introduces the design of permanent magnet that can been used to small nuclear magnetic resonance (NMR) system, and its static magnetic field simulation analysis uses Ansoft's Maxwell software. According to the theory of magnetic circuit design and the performance requirements of magnetic field, An H-style permanent magnetic actuator has been designed, and it can generate uniform magnetic field larger than 0.4 T in the interested region of this actuator. The static magnetic field simulation analysis of this permanent magnetic actuator has done by Ansoft's Maxwell 3D software, and the experimental results show that the design of permanent magnet can meet the requirements.

Abstract: In view of oil-water two phase displacement experiment can't from the micro level such as throat problem for reservoir use condition is described,Using nuclear magnetic resonance (NMR) technology can reflect the oil-water distribution from the microscopic view, Combined the macro oil displacement effect and micro pore structure. By using nuclear magnetic resonance T2 spectrum changing into throat radius and saturation calculation method in different throat range. Quantitative description the distribution of bound water, residual oil I and oil produced in different in pores of drainage and Suction process, to a certain extent in the comprehensive understanding of microscopic reservoir pore space, has the vital significance for reservoir evaluation.

Abstract: Structural features of interfaces in [Co/Cu]_n superlattices obtained by magnetron sputtering have been studied by nuclear magnetic resonance (NMR). Modification of interface structural characteristics and magnetoresistive properties of the superlattices with the increase of the number of [Co/C] bilayers is analyzed. Correlation between magnetoresistance and interface structural characteristics has been revealed.