Metal free fraction

Cu(OAc), H20 (0.75 g, 3.7 mmol) was added to a refluxing solution of metal-free 1,4,8,11.15,18,22,25-octa(propyloxy)phthalocyanine (0.1 g, 0.1 mmol) in BuOH (5 mL). The solution was maintained at reflux for 0.5 h, cooled, and chromatographed (silica gel, CH2C12 and Et20). The green-blue fraction eluted first was crystallized from a slowly evaporating solution in CH2Cl2/py yield 0.086 g (81 %). 

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). 

The high atomic mass yields small recoil energies and thus a large recoU-free fraction even at room temperature (/300 0.95 for Ta metal [175]) this allows measurements of the resonance effect to be made over a wide temperature range up to about 2,300 K. 

Wender and Hershkowitz [237] used the sensitivity of the recoil-free fraction in tungsten Mossbauer spectroscopy to deduce the effect of irradiation of tungsten compounds by Coulomb excitation of the resonance levels (2 states of I82,i84,i8 y with 6 MeV a-particles. While no effect of irradiation on the/-factors could be observed for tungsten metal in agreement with [233], a decrease of/was measured for WC, W2B, W2B5, and WO3 after irradiation. 

PCs comes from a study of the behaviour of PC and Cu when mixed in vitro metal-free PC and Cu only produce CuBS3. This indicates that the other fractions (CuBSl, 2 and 4) detected in vivo, at the very least, must contain other components. 

The conversion of TCB to metal free polymers needs some urea as initiator . The obtained polymers were divided into acetone soluble, DMF soluble, DMF insoluble and cone. H2SO4 insoluble fractions. The highest yield of products soluble in organic solvente (50% acetone or 75-80% DMF soluble) were obtain with 1,5-3 mole % urea at 573 K in 10 h. DMF insoluble fractions resulted at 573 K in 40 h with an urea concentration > 20 mole %. In every case elementary analysis is in good agreement with expected values. But the IR-spectra show some C=0 absorption (saponification) and broad background absorption (possible polynitrile 91) formation). An expected absorption typical for metal free Pc is present at 1000 cm. ... 

The procedures for the prevention of contamination during protein fractionation have therefore been modified. In particular, purifications of chemicals—employed during purification—with chelating agents are held to a minimum to preclude their potentially deleterious effects on enzyme activity. High-speed centrifugations are carried out in metal-free plastic... 

M free metal ion fraction of total metal ions (f>p practical osmotic coefficient G activity coefficient quotient [i] free concentration of species i... 

The effective Debye temperature of the source matrix should be high so that the recoil-free fraction is substantial. High-melting metals and refractory materials such as oxides are the obvious choices. 

Similar situations arise, for example, in Coulomb excitation reactions. In the Ge case, the low Debye temperature of the Ge metal produces a very low recoil-free fraction. As mentioned in more detail later (p. 109), it is possible to displace the excited atoms completely out of the target material and implant them into a new matrix with a high Debye temperature, thereby obtaining a considerable improvement in the quality of the spectra. 

Other metal systems studied include IrSu2 and PtSn2 which have the CaFa lattice [23. Recoil-free fraction and lattice dynamical studies have been made on SnAs, SnSb, SnTe, and SnPt [237] and on NbaSn [238,239]. 

Detailed measurement of the recoil-free fraction in germanium metal [8] has since been reinterpreted [11] using a different lattice-dynamical model. 

The 37T5-keV transition is from the / = f + excited state to the / = f-1-ground state, the multipolarity being pure Ml. The first measurements used a source of chemically separated "Sn electroplated as 8-tin onto copper, and absorbers of Sb metal and SbjOs [24]. Isotopic enrichment of absorbers was not required to obtain a significant absorption with both source and absorber at 80 K. The tin source matrix was used in most of the early work, although "Sn/SnOa has also been used with success [26]. A third source is Ca SnOs, which by analogy with the same sources used in Sn work (see Chapter 14.1) is likely to have the narrowest line and highest recoil-free fraction of the three [27, 28]. Detailed comparative data are not available, but experiments are usually made with the source and absorber at 80 K in all cases. Linewidths close to the natural width (2-1 mm s ) can be obtained with an InSb absorber and a "Sn/jS-Sn source [29]. The recoil-free fraction of a "Sn/SnOj source is 0-32 at 80 K and 0-16 at room temperature [26]. The internal conversion coefficient derived from the same measurements is Or 10. 

Tellurium metal shows a substantial quadrupole splitting [48]. The structure contains spiral chains of Te atoms, and a crude estimation of the electric field gradient at the tellurium nucleus leads to a value for the nuclear quadrupole moment of g = 0-20 bam [48]. This agrees well with an earlier value derived by similar means of 1 g = 0 17 bam [58]. Single-crystal measurements have also been made, showing that e qQ is negative [46]. An anisotropy of the recoil-free fraction was also claimed. 

A number of recoil-free fraction and lattice-dynamical studies have been made on gold metal [90, 91]. The resonance in gold microcrystals of mean diameter 20 and 6 nm shows a greater recoil-free fraction in the smaller crystals corresponding to an increase in the effective Debye temperature from... 

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