Paramagnetic resonance of ions of the iron group in single crystals of periclase

Summary Our data mainly agree with the data given in the literature [1–6]. The slight deviations can apparently be attributed to different heat treatment conditions. A correlation between the magnitude of hyperfine interaction and proportion of covalent bonds was shown in work [7]. We compared the hyperfine structure constants obtained for MgO · V with the data in [8] for the same ion in the strongly ionic crystal Al₂O₃ · V. For MgO · V A_V = 80.3, and for Al₂O₃ · V A_V = 89. In conformity with this we can conclude that in MgO · V there is about 14% covalent bonds.The g factors of V²⁺, Cr³⁺ are less than the g factor of the free electron. These deviations, apparently, should be attributed to bonds with excited states⁴P,⁴F,⁴q.With a rather rough comparison of the concentrations of V²⁺ and Mn²⁺, on the assumption that the forms of their lines are identical, a good agreement was obtained of the concentration ratios with the data of the spectral analysis.Since the ion Fe³⁺ is in the S-state, the anisotropy of the spectrum observed in the experiment is apparently due to splitting in the zero field. The terms due to the crystalline field are of importance in the spin Hamiltonian.Translated from Poroshkovaya Metallurgiya, No. 2 (50), pp. 86–89, February, 1967.     

Paramagnetic liposomes as magnetic resonance imaging contrast agents. Assessment of contrast efficacy in various liver models

RATIONALE AND OBJECTIVES: Liposomal gadolinium (Gd)-HP-DO3A has been evaluated as a contrast agent for liver magnetic resonance imaging. The influence of various liposomal physicochemical properties on the liver uptake and contrast efficacy was investigated in various ex vivo and in vivo liver models. METHODS: Liposomes of different size and membrane properties were prepared. The liposome size ranged from 74 to 304 nm. Two types of phospholipid compositions were studied; a mixture of hydrogenated phosphatidylcholine (HPC) and hydrogenated phosphatidylserine (HPS) with a phase transition temperature (Tm) of 51 degrees C and, a blend composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) displaying a Tm of 41 degrees C. Ex vivo tissue relaxometry and in vivo liver imaging were used to study the influence of liposome composition on the liver uptake and contrast efficacy of intravenously injected liposomes. The influence of liposome size and composition on the kinetics of liver uptake and imaging effect was assessed ex vivo in the perfused rat liver. RESULTS: The HPC/HPS preparations showed generally a higher and faster liver uptake than the DPPC/DPPG preparations due to a higher stability in blood/perfusate (high Tm) and to the HPS component. The liposome size modulated the extent and kinetics of liver uptake; the larger the size, the faster and more extensive was the liver uptake. Both types of liposome preparations were shown to be efficient liver susceptibility agents both ex vivo and in vivo due to their uptake by the Kupffer cells of liver. The lack of full correlation between the extent of liver uptake and degree of contrast enhancement might be attributed to different regimes of susceptibility-based relaxation. CONCLUSIONS: The present study has demonstrated the influence of key liposomal physicochemical properties on the liver uptake and contrast efficacy of liposome-encapsulated Gd chelates, exemplified by Gd-HP-DO3A.