Kruk D, Korpała A, Taheri S Mehdizadeh, Kozłowski A, Förster S, Rössler E A
Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, Słoneczna 54, 10-710 Olsztyn, Poland.
Department of Biophysics, Jagiellonian University Medical College, Łazarza 16, 31-530 Kraków, Poland.
J Chem Phys. 2014 May 7;140(17):174504. doi: 10.1063/1.4871461.
Magnetic nanoparticles that induce nuclear relaxation are the most promising materials to enhance the sensitivity in Magnetic Resonance Imaging. In order to provide a comprehensive understanding of the magnetic field dependence of the relaxation enhancement in solutions, Nuclear Magnetic Resonance (1)H spin-lattice relaxation for decalin and toluene solutions of various Fe2O3 nanoparticles was investigated. The relaxation experiments were performed in a frequency range of 10 kHz-20 MHz by applying Field Cycling method, and in the temperature range of 257-298 K, using nanoparticles differing in size and shape: spherical--5 nm diameter, cubic--6.5 nm diameter, and cubic--9 nm diameter. The relaxation dispersion data were interpreted in terms of a theory of nuclear relaxation induced by magnetic crystals in solution. The approach was tested with respect to its applicability depending on the magnetic characteristics of the nanocrystals and the time-scale of translational diffusion of the solvent. The role of Curie relaxation and the contributions to the overall (1)H spin-lattice relaxation associated with the electronic spin-lattice and spin-spin relaxation was thoroughly discussed. It was demonstrated that the approach leads to consistent results providing information on the magnetic (electronic) properties of the nanocrystals, i.e., effective electron spin and relaxation times. In addition, features of the (1)H spin-lattice relaxation resulting from the electronic properties of the crystals and the solvent diffusion were explained.
能引起核弛豫的磁性纳米颗粒是增强磁共振成像灵敏度最具前景的材料。为全面了解溶液中弛豫增强的磁场依赖性，研究了各种Fe2O3纳米颗粒的萘烷和甲苯溶液的核磁共振（1）H自旋 - 晶格弛豫。通过应用场循环法在10 kHz - 20 MHz频率范围内进行弛豫实验，并在257 - 298 K温度范围内，使用尺寸和形状不同的纳米颗粒：球形 - 直径5 nm，立方体 - 直径6.5 nm，立方体 - 直径9 nm。根据溶液中磁性晶体引起的核弛豫理论对弛豫色散数据进行了解释。根据纳米晶体的磁性特征和溶剂平移扩散的时间尺度，测试了该方法的适用性。深入讨论了居里弛豫的作用以及与电子自旋 - 晶格和自旋 - 自旋弛豫相关的对整体（1）H自旋 - 晶格弛豫的贡献。结果表明，该方法能得出一致的结果，提供有关纳米晶体磁性（电子）性质的信息，即有效电子自旋和弛豫时间。此外，还解释了由晶体电子性质和溶剂扩散导致的（1）H自旋 - 晶格弛豫的特征。
