Compound imaging

A chiral center in a molecule is carbon atom with four different atoms or groups of atoms attached to it. If a molecule has a chiral center, it is very likely to be non-superimposable on its mirror image. Compounds (a) and (d) have no chiral center. Compounds (b) and (c) each have one asymmetric carbon atom, also called a chiral center. 

Note that the enantiomer of a particular compound can be drawn by reversing two of the substituents this is actually much easier than drawing the mirror image compound, especially in more complicated structures. As an alternative, the wedge-dot relationship could be reversed. 

The enantiomer will have the configuration changed at all chiral centres, whereas the 6-epimer retains all configurations except for that at position 6. Note that it is not necessary to draw the mirror image compound for the enantiomer, just reverse the wedge-dot relationship for the bonds at each chiral centre. This is much easier and less prone to errors whilst transcribing the structure. 

However, it is also possible to visualize spiro compounds with groupings that are not aU different, where enantiomeric forms exist because mirror image compounds are not superimposable. The diamine shown is chiral, in that the mirror image forms are not superimposable, even though only two types of ring. 

Optical isomers—also called enantiomers—arc mirror image compounds that cannot be superimposed. For example, the natural amino acid building blocks of proteins are L-amino acids. 

It seems a pity that there are a total of 153 compounds in the combined U, S, and T categories. The large number of untasted compounds is due in part to the fact that some of these compounds were developed as potential brain imaging compounds, and were never intended to be psychedelics, and so have not been tasted. However, these account for less than half of the U category. 

However, both soft ionization of analytes and tandem MS are difficult to achieve with typical SIMS technique (8). In contrast, spatial resolution of MALDI-IMS is lower than that of SIMS. The spatial resolution depends on the experimental conditions and the instrument used but is typically 20-100 jim. Limitations of the spatial resolution of MALDI-IMS include the size of the organic matrix crystal and the analyte migration during the matrix application process. To overcome these problems, Taira and colleagues reported a nanoparticle (NP)-assisted laser desorption/ionization (nano-PALDI)-based IMS, in which the matrix crystallization process is eliminated (9). The use of nano-PALDI has enabled researchers to image compounds with spatial resolution at the cellular level (15 (xm almost equal to the size of the diameter of a laser spot). 

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