Curie shift

The molar diamagnetic susceptibility of thiazole and some derivatives was initially determined by the classical Curie-Cheneveau method (5,315,316) and later confirmed by a method (317) based on the difference of NMR proton chemical shift of a sample of tetramethylsilane immersed in the liquid to be investigated, according to the shape (cylindrical or spherical) of the sample tube (Table 1-47) (318),... 

Historically, materials based on doped barium titanate were used to achieve dielectric constants as high as 2,000 to 10,000. The high dielectric constants result from ionic polarization and the stress enhancement of k associated with the fine-grain size of the material. The specific dielectric properties are obtained through compositional modifications, ie, the inclusion of various additives at different doping levels. For example, additions of strontium titanate to barium titanate shift the Curie point, the temperature at which the ferroelectric to paraelectric phase transition occurs and the maximum dielectric constant is typically observed, to lower temperature as shown in Figure 1 (2). 

Four strongly downshifted signals in each spectrum, between 50 and 110 ppm, were assigned to the four CB protons of the cysteines coordinating the Fe ". The contact shifts of the protons reflect the coordination of cysteine to the Fe " of the antiferromagnetically coupled Fe "-Fe" pair as the cysteine protons sense the spin down orientation of the Fe " (S = ) site. This is supported by the observation that the temperature dependence of the cysteine H" protons (measured between 276 and 308 K) follows Curie behavior (decreasing contact shift with increasing temperature). 

The 113Cd Ti values estimated for the various peaks varied from 10 to 50 ms and obeyed the qualitative dependence upon 1/R6 (R = Mn-Cd distance) of the dipolar relaxation mechanism expected to be operative. The broad line widths were also shown to have significant contributions from the T2 relaxation induced by Mn++, with both dipolar and contact terms contributing. The 113Cd shifts of the peaks assigned to different shells were measured as a function of temperature, and observed to follow a linear 1/T dependence characteristic of the Curie-Weiss law, with slopes proportional to the transferred hyperfine interaction constant A. 

The NMR spectra [27] of [Fe(HB(pz)3)2] exhibit shifted resonances as would be expected for a paramagnetic complex, but the shifts are intermediate between those observed for fully diamagnetic complexes and the comparable resonances in the fully high-spin [Fe(HB(3,5-(CH3)2pz)3)2] complex. In contrast to the increasing chemical shifts, either in the positive or negative direction, that follow the Curie law, observed at lower temperatures for [Fe(HB(3,5-(CH3)2pz)3)2] and [Fe(HB(3,4,5-(CH3)3pz)3)2], the chemical shifts of [Fe(HB(pz)3)2] decrease as the temperature is decreased, as would be expected for an increase in the percentage of the low-spin complex. 

L.A. Cury, L.O. Ladeira, and A. Righi, Large blue shift in the absorption spectra of BEH-PPV films containing gold nanoparticles, Synth. Met., 139 283-286, 2003. 

As another example, the three-dimensional structure of Cytochrome c has been determined on the basis of structural information from pseudocontact paramagnetic chemical shifts, Curie-Dipolar cross-correlation, secondary structure constraints, dipolar couplings and 15N relaxation data [103]. This protein has a paramagnetic center, and therefore the above-mentioned conformational restraints can be derived from this feature. Dipolar couplings do not average to zero because of the susceptibility tensor anisotropy of the protein. The structure determination of this protein without NOE data gives an RMSD (root... 

On cooling, the opposite behavior of the microhardness, increase with decreasing temperature, is observed. However, the Curie transition temperatures are shifted towards lower temperatures. 

Barium titanate, BaTi03, is probably the most widely studied ferroelectric oxide. Extensive studies were conducted on this compound during World War II in the United States, England, Russia, and Japan, but the results were not revealed until after the war. Barium titanium(IV) oxide was found to be a ferroelectric up to a temperature of 120°C., which is its Curie point. Above 120°C., barium titanium(IV) oxide has the cubic perovskite structure, and below this temperature the oxygen and titanium ions are shifted and result in a tetragonal structure with the c axis approximately 1% longer than the a axis. Below 0°C., the symmetry of barium titanate becomes orthorhombic, and below —90°C., it becomes trigonal. 

The basic features of the Mb111 (Ns) spectrum are similar to those of cyanoferrimyoglobin (Fig. 14). Only one set of hyperfine-shifted resonances is observed, but the hyperfine shifts are larger and the lines broader than in MbmCN. Furthermore the temperature dependences of the resonances positions show drastic deviations from Curie s law (Eq. 4). Similar data were also obtained for azidoporphyrin-iron(III) complexes in pyridine solution 116). 

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