Frozen solutions

Figure Bl.15.14. Comparison of 95.1 GHz (A) and 9.71 GHz (B) EPR spectra for a frozen solution of a nitroxide spin label attached to insulin measured at 170 K.

Kits. Kits for the preparation of radiopharmaceuticals are a convenient solution to synthesis of products containing short-Hved radionucHdes (eg, In, I, Tc) bound to a nonradio active moiety. The labeling step is performed either at a commercial radiopharmacy, or within the institutional nuclear medicine laboratory. The kits are usually stored as a frozen solution or lyophilized product. The material of interest is then metered out into kit dosages. The kit vials are thawed or reconstituted and mixed with the appropriate radionucHde. 

Frozen solution. Portionwise addition of the liquid solution with a pipette, followed by repeated thawing and freezing furnishes a layer of frozen solution as indicated. 

The compound HI.H2O does not appear as a stable hydrate in the phase diagram, but the vibrational spectra of frozen solutions of this composition indicate the formulation [H30]+I . Higher hydrates appear at HI.2H2O (mp ... 

In partly frozen solutions, M is independent both of the nature of the solutes and of their total concentration prior to freezing. At constant pressure it is dependent only on temperature. For a solution containing a single solute, this is also roughly true of the molality m (It is only roughly true because < > changes somewhat with concentration.)... 

Exposure of frozen solutions of CdS04 in H2SO4 to y rays at 77 K results in the formation of a species with ESR and UV spectra consistent with Cd . When annealed at 120 K the Cd reacts with xs Cd ... 

Similar reactions take place in frozen solutions of Cd(C104)2 in MeOH and EtOH, and in the y irradiation of solid K2Cd(CN)4. 

Figure 1. ESR spectra at some temperatures of X-irradiated polycrystalline frozen solutions (c a 1 mol%) of C5H5 and CgH5D, respectively, a) at 15 K. b) simulated spectrum by using the parameters shown in Table 4. c) 05 150 " " at 30 K in CFCI3. d) simulation using hyperfme coupling data shown in Table 4 for a mixture of component 1 component 2 of C6H5D . The ratio 1 2 = 0.38 0.62 obtained from the component analysis of Figure 2 was employed.

Figure 2. Component analysis of an X-irradiated polycrystalline frozen solution (c a 1 mol%) of C6H5D in CFCI3. a) simulated components 1 (dashed) and 2 (solid) using hyperfine coupling data from ENDOR (Table 4). b) experimental (solid) and fitted (dashed) ESR spectra of CgH5D...

Isotope effects in neutron-activated ruthenocene were studied by Harbottle and Zahn . Crystalline samples showed a small ( 10%) effect, but a much larger isotope difference was found in benzene solutions. Frozen solutions were found to be similar to the crystalline samples. 

Zahn found that Mn2(CO)io irradiated in dilute ( 10%) solution showed very low retention—as low as 0.004 %. This value, she contended, must represent the true failure of bond rupture. When these same solutions were irradiated as frozen solutions, the retention was 11.4%, quite similar to the value found for the solid. 

The irradiation (or ion bombardment) of solid solutions, where a scavenger can be present, should also be explored further. Here it will be important to ensure that the solids are indeed solutions before conclusions can be safely drawn. It is curious to note that the yields observed in frozen solutions are in several cases very similar to the yields in the pure crystalline solutes. This suggests the possibility that the frozen targets had segregated, and that the solute was in fact present as micro crystals. (If this is the case, it may well be that a new method can be developed on this basis for making phase studies at high dilution.)... 

Fig. 6. The electron-paramagnetic resonance spectrum of Kpl in frozen solution at 10 K.

EPR investigations are necessarily carried out in frozen solution at low temperature. Room temperature binding of thiols to FeMoco has been monitored by F NMR spectroscopy using /J-CF3C6H4S as the reporter ligand. These experiments revealed that the binding of thio-late is characterized by a dynamic equilibrium between the FeMoco and thiolate (159) and that cyanide and methyl isocyanide can bind to isolated FeMoco complexed with thiol (160). 

Recent work (51) on FeCpj irradiated in Fe(CO)5 solutions (to give FeCpj) has shown that the Fe atom can come from the Fe(CO)j molecule. The mechanism is unknown and may well involve exchange or other reactions in solution in addition to hot atom reactions. The results do show, however, that it is not necessary to preserve the Fe-Cp bonding in order to reform FeCpj. In frozen solutions the yield of FeCpj is much lower than in liquid solutions. 

The literature dealing with EPR studies of transition metal dithiocarbamato complexes is extensive. Interesting results were obtained about the interaction of copper compounds with various solvents 165,166,167,168) and about dimer formation of Cu(R2other transition metal dithiocarbamato complexes are reported as well 170,5,171, 37). As the measurements of the planar systems are most suitable for comparison with theoretical studies, we shall pay attention to the results of these investigations on Cu(II), Ag(II) and Au(II). 

Vertes, A., Nagy, D.L. Mossbauer Spectroscopy of Frozen Solutions. Akademiai Kiado, Budapest (1990)... 

Very thick absorbers may be required for applied-field measurements to achieve reasonable absorption depths and measuring times because the Mossbauer spectra are usually split into several hyperfine components. Here the iron content may be as large as 100 pg Fe per cm (1.75 pmol Fe per cm ), which would correspond to t 1 for a two-line spectrum. For smdies of frozen solutions, Fe concentrations of 1 mM are desirable for each nonequivalent iron site [35]. 

The recoil-free fraction /a of transition metal complexes or proteins in frozen solution can be as small as 0.1-0.3, when measured just below the melting point, but the /-factor increases strongly when the temperature is lowered to fiquid nitrogen temperatures (77 K), and at fiquid helium temperatures (4.2 K) it may reach values of 0.7-0.9 [35]. This makes a substantial difference to the acquisition time of the spectra because of the square dependency on the signal (3.1). 

Distinct quadrupole shifts do occur as well in magnetically split spectra of single-crystals, poly crystalline powder or frozen solution samples. In all three cases, the line shifts obey the simple first-order expression at high-field condition. 

The dipole interaction depends on the distance between the ions (6.4). Therefore, the transition probability increases with increasing concentration of magnetic ions. Studies of the concentration dependence of the relaxation can be conveniently performed on samples of amorphous frozen solutions with a uniform distribution... 

In amorphous frozen solutions with only one type of species (e.g. [Fe(H20)g] ) the crystal field interaction of the Fe " ions may be similar, but the orientations of the crystal field axes in general differ. When magnetic fields are applied, this... 

The mathematical description of the time-differential NFS intensity is, in many cases (e.g., in cases when frozen solutions are investigated), not as straightforward as it may appear in (9.2). The reason is that couplings between the various components of the delocalized radiation field in the sample have to be taken into account by an integration over all frequencies. This problem has been solved in different ways in a series of program packages, the most prominent of which are called CONUSS [9, 10], MOTIF [11, 12] and SYNFOS [13, 14]. 

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