Picket-fence method

Some students and instructors find it easier to write out the solution to a problem so that units in the denominator of each succeeding term eliminate the units in the numerator of the preceding one until the units of the answer are obtained. This method has been referred to as the factor-label method, dimensional analysis, or the picket fence method. For instance, in Example 4-2, the units of the answer are g Na" and the units given are g Na2S04. Thus, we can write... 

In order to prepare and isolate solid-state, crystalline, oxygenated iron-heme model complexes, chemists learned to synthesize (by self-assembly methods) and oxygenate many types of hindered porphyrins. For instance, capped porphyrins were synthesized by direct condensation of a suitable tetraaldehyde with four pyrrole molecules.37 Picket-fence porphyrins such as I e(TPP)((V-MeIm) (where TPP = meso-tetraphenylporphyrin and /V-Melm = (V-methylimidazole)... 

In order to accelerate the slow metalation, several methods have been proposed (1) use of substitution reaction of cadmium(II) or mercuty(II) porphyrin, (2) use of N-substituted porphyrins at the pyrrole nitrogen, (3) addition of aromatic heterocyclic bases such as pyridine and imidazole, (4) introduction of functional groups to bind metal ions in the vicini of the porphyrin nucleus (e. g. tetracarboxylic add "picket-fence" porphyrins) and (5) use of reducing agents such as hydroxylamine and ascorbic add in copperfll) incorporation. 

Two methods are used to prevent tray liquid blowing. The simplest is probably the picket-fence exit weir (see Fig. 13). In this arrangement, a high exit weir interrupts the trajectory of flying liquid droplets. The slots control liquid depth on the tray. 

Illustrative examples of calculations with these methods are given. The ONIOM method yields reasonable results for energies. Model and real metallobiochemical systems treated by the QM/MM/CT method illustrate its feasibility with quite reasonable results in modeling iron picket-fence porphyrin, vitamin Bn, aquocobalamin, and coenzyme Bn. 

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