Putative structure

Determination of the catalytically active species derived from 1 in solution. Spectrophotoraetric titration of the backbone ligand 5 with copper(II) acetate in methanol revealed formation of a dinuclear copper(ll) complex species Cu2L.3h(OAc) above a 1 2 molar ratio. A mononuclear copper(ll) species CuL 2h (6) dominates at a 1 1 molar ratio of 5 and copper(ll) acetate. Control experiments for the assignment of putative structures based on the obtained spectroscopic data included a UVA is spectroscopic titration of 5 with anhydrous sodium acetate in the presence of copper(ll) chloride and revealed that acetate is necessary for the formation of a copper (11) complex in methanol. The composition of 1 in methanol is the same as determined by elemental analysis for the sohd state. 

Villadsen, J., Putting structure into chemical engineering. Chem. Eng. Sci. 52,2857-2864 (1997). Wang, H., Zinchenko, A., and Davis, R. H., The collision rate of small drops in linear flow fields. I. Fluid Mech. 265, 161-188 (1994). 

HMQC/HSQC spectra can be extremely useful in resolving problems where there is a significant carbon chemical shift precedent that could be used to support one putative structure over another - for example, in dealing with cases of O- versus N- alkylation. Take for example the two methylated indoles in Structure 9.1. 

If you have two or more possible structures that fit the data, you will need to look for differences that can be identified by NMR. Often this is HMBC and/or NOE (to identify key connectivities). Every problem is different so you need to use all your skills to look for tools that can help distinguish the putative structures. As in the case of total unknowns, don t use NMR to the exclusion of other techniques as they may be able to make the choice much easier. 

Fig. 21.12. Schematic diagram of the putative structure of a levamisole nicotinic receptor. (A)...

X-ray fiber diffraction can be used to visualize highly hydrated polymer specimens at atomic resolution. An essential part of such an analysis is the inclusion of reliable stereochemical information to supplement the diffraction data. Structure determination involves modelling and refinement of putative structures, and adjudication amongst the optimized models. This technique has been successfully applied to a number of polysaccharides. The precision of resulting structures is often sufficient to identify the critical interactions within and between molecules, that are responsible for the unique properties of these materials. 

Figure 1. Putative structure of Fe3S4 cluster (left) and illustration of conversion into MFe3S4 with M = Fe, Co, Zn and Cd.

It is often the case that the putative structure assigned to an RI is so unusual that vibrational and electronic spectra of analogous molecules are unavailable. How then can an experimentalist know whether an observed IR and/or UV-vis spectmm actually does belong to the putative structure assigned to the RI As exemphfied in the sections on matrix-isolated benzynes in Chapter 16 in this volume and also discussed in Chapter 17 in this volume, suitable electronic structure calculations can provide accurate predictions of the IR spectra and UV-vis excitation energies for RIs. The IR and UV-vis spectra, predicted for a particular structure, can then be compared with those obtained experimentally. 

Table 3 Possible Redox-Catalytic Iron-Sulfur Enzymes, Their Substrates, and the Putative Structures of Their Catalytic Center...

Comins, D.L., Zheng, X., and Goehring, R.R. (2002) Total synthesis of the putative structure ofthe lupin alkaloid plumerinine. Organic Letters, 4, 1611-1613. 

The sampling problem Given two independent protein structures, generate putative structures of the complex. 

R. N. Reusch and H. L. Sadoff (1988). Putative structure and functions of poly-beta-hydroxybutirate/calcium polyphosphate channel in bacterial plasma membranes, Proc. Natl. 

Villadsen, J., Putting structure into chemical engineering. Chem. Eng. ScL 52,2857-2864 (1997). 

The mar region has been cloned and sequenced this reveals an operon composed of three putative structural genes, marR, mar A and marB [211]. The mar regulon of E.coli is a unique antibiotic resistance mechanism in... 

Molecule encoding. Several molecular attributes, such as predicted and measured properties and structural descriptors, span a high-dimensional feature space. The selection of descriptors is mainly driven by the experience of the scientists, project-specific considerations, and existing knowledge about putative structure-activity relationships. 

Our second example again represents the photodeprotection of a 2-nitrobenzyl ether to liberate a phenol in a complex advanced intermediate en route to the putative structure of Diazonamide [Scheme 4.158].298... 

Julius, D., Brake, A., Blair, L., Kunisawa, R., and Thorner, J. (1984). Isolation of the putative structural gene for the lysine-arginine-cleaving endopeptidase required for processing of yeast prepro-alpha-factor. Cell 37 1075-1089. 

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