Spectroscopic Data Interpretation

The study of biomimetics can be of great benefit for the understanding of enzymatic reactions. The term biomimetic refers, in the context of this work, to a compound that mimics structural, functional and spectroscopic properties of an enzyme [67]. Often only one or two of these aspects are achieved for a model system and they usually display substantially lower activity. There are, however, advantages over the enzyme model complexes are generally more stable and robust than their enzymatic counterpart, they can be readily crystalUzed and provide easy accessible structural information on metal ion coordination. Also as these model systems are considerably less complex, kinetic and spectroscopic data interpretation is simplified and— by comparison to data derived for the enzyme— the mechanism of action and structural features can be elucidated and thus related back to the parent metalloenzyme. Also models can be obtained on a larger scale and are often less costly to synthesize, a distinct benefit for potential applications. A few structures of model complexes for dinuclear hydrolytic enzymes are shown in Fig. 1.4. The approaches for ligand and complex design are diverse. 

Amino-pyrazines and -pyridazines have been shown to exist predominantly in the amino form by infrared spectroscopic studies (cf. Table VI). Ultraviolet spectral data have been interpreted to indicate that 4-aminocinnoline exists predominantly in the imino form 256, but this conclusion, which was based on comparison of its spectrum with those of cinnolin-4-one and 4-ethoxycinnoline, is probably incorrect. Ultraviolet spectroscopic data strongly support the predominance of amino structures for 2-aminopyrazine (257) and 2-aminoquin-oxaline how ever, the former compound was at first erroneously concluded to exist in the imino form from ultraviolet spectral evidence. Isolation of two isomers of 2-amino-8-dimethylamino-3-methylphenazine, assigned the amino and imino structures 258 and 259, respectively, has been claimed, but it is very unlikely that these assignments are correct. 

Hartfield, R.J., Interpretation of spectroscopic data from the iodine molecule using a genetic algorithm, Appl. Math. Comp., 177,597,2006. 

Factors affecting the integrity of spectroscopic data include the variations in sample chemistry, the variations in the physical condition of samples, and the variation in measurement conditions. Calibration data sets must represent several sample spaces to include compositional space, instrument space, and measurement or experimental condition space (e.g., sample handling and presentation spaces). Interpretive spectroscopy where spectra-structure correlations are understood is a key intellectual process in approaching spectroscopic measurements if one is to achieve an understanding in the X and Y relationships of these measurements. 

Some future directions in inorganic photochemistry have been outlined by Adamson (56). A pessimistic picture of the practical uses of solar energy conversion systems is painted, but a rosy view of the academic future of the subject is held. It is anticipated that there will be further examination of thermally equilibrated excited (thexi) states—their lifetimes, and spectroscopic and structural properties—and an extension of present efforts to organometallics and metalloproteins is also envisaged (56). The interpretation of spectroscopic data from excited states will continue to be controversial and require future experimentation (57). 

Figure 10. Comparison of isotopic fractionations determined between Fe(II)aq and Fe carbonates relative to mole fraction of Fe from predictions based on spectroscopic data (Polyakov and Mineev 2000 Schauble et al. 2001), natural samples (Johnson et al. 2003), DIR (Johnson et al. 2004a), and abiotic formation of siderite under equilibrium conditions (Wiesli et al. 2004). Fe(II)aq exists as the hexaquo complex in the study of Wiesli et al. (2004) hexaquo Fe(II) is assumed for the other studies. Total cations normalized to unity, so that end-member siderite is plotted at Xpe = 1.0. Error bars shown reflect reported uncertainties analytical errors for data reported by Johnson et al. (2004a) and Wiesli et al. (2004) are smaller than the size of the symbol. Fractionations measured on bulk carbonate produced by DIR are interpreted to reflect kinetic isotope fractionations, whereas those estimated from partial dissolutions are interpreted to lie closer to those of equilibrium values because they reflect the outer layers of the crystals. Also shown are data for a Ca-bearing DIR experiment, where the bulk solid has a composition of q)proximately Cao.i5Feo.85C03, high-Ca and low-Ca refer to the range measured during partial dissolution studies (Johnson et al. 2004a). Adapted from Johnson et al. (2004a).

Theoretical calculations and simulations using ah initio and density function theory (DFT) methodologies are also seeing increasing use. Combining these theoretical calculations with spectroscopic data can assist in the interpretation of the observed spectral features and an improved understanding of how a probe molecule interacts with the various types of sites in zeolitic systems. 

The results of EPR studies of photoezcited triplets of model systems show that it is not possible to give generally applicable rules for the interpretation of the spectroscopic data. In a number of cases there appears to be a well-understood relationship between dimerization effects and dimer geometry. In most of the systems considered here that is not the case. It is not clear to what difference in make-up of the dimers this discrepancy must be attributed and this is an interesting point of further investigation. Evidently, as long as the data on fairly well characterized model systems are not fully understood it will be impossible to derive definitive conclusions concerning the structure of the special pair from data on its photoexcited triplet state. 

Interpretation of the spectroscopic data from the individual spectroscopic techniques is generally done as the data are amassed. When all of the data are available, it is useful for the participating scientists to integrate their respective data, which is discussed in more detail below. The overall elapsed time for the isolation and identification of a new impurity or degradation product is quite variable. The difficulty of the actual isolation and the structural complexity of the molecule both impinge on the process. On the basis of the author s experience. 

Semiempirical molecular orbital calculations performed for a set of pyrrolo-benzodiazepines using MNDO and AMI were used for the interpretation of their mass-spectroscopic data (1996MI653). 

Since the publication of CHEC(1984) <1984CHEC(2)1>, the use of NMR seriously expanded. The majority of the full papers now published contain NMR spectroscopic data. Unfortunately, this is usually only for characterization of the synthesized compounds and no interpretation of the data is provided. In CHEC-II(1996) <1996CHEC-II(6)1>, a representative and very useful table with assigned shifts of simple pyridazines and pyridazin-3(2/7)-ones was published. Phthalazin-l(27/)-ones were also briefly mentioned. As an extension we here summarize some assigned NMR data of bicyclic derivatives [l,2,4]triazolo[4,3- ]pyridazines and tetrazolo[l,5- ]-pyridazines (Table 2 and Figure 3), and isoxazolo[3,4-, pyridazin-7(6//)-ones (Table 3 and Figure 4). 

The calculation of magnetic parameters such as the hyperfine coupling constants and g-factors for oligonuclear clusters is of fundamental importance as a tool for the evaluation of spectroscopic data from EPR and ENDOR experiments. The hyperfine interaction is experimentally interpreted with the spin Hamiltonian (SH) H = S - A-1, where S is the fictitious, electron spin operator related to the ground state of the cluster, A is the hyperfine tensor, and I is the nuclear spin operator. Consequently, it is... 

---