Homomeric molecules

The use of pairs of matched spectral variants of GFP, like cyan and yellow or GFP and mRed, to differentially tag proteins and look for interactions, is now in routine use. The approach can be readily applied to homodimerization of molecules that differ only by their living color or epitope tag. For example, homomultimer-ization of a viral coat protein can be observed by imaging a mixture of cyan and yellow tagged homomeric molecules [46], whereas oc-synuclein stacking can be detected by utilizing a-synuclein transcripts that encoded different epitope tags for detection by immunostaining [47],... 

Students are familiar with the terms applied to relationships between stereoisomeric molecules homomeric molecules (superposable molecules), enantiomeric... 

Students are familiar with the terms applied to relationships between stereoisomeric molecules homomeric molecules (superposable molecules), enantiomeric molecules (nonsuperposable mirror images), and diastereomeric molecules (stereoisomers that are not mirror images of one another). These familiar terms are parallel to the terms that we have introduced above homotopic, enantiotopic, and diastereotopic, which are applied to nuclei or groups within the molecule. 

Mislow [18] has proposed a classification of isomers based not on the bonding connectivity of atoms as above, but on the pairwise interactions of all atoms (bonded and nonbonded) in a molecule. The operation of comparison of all pairwise interactions is called isometry (for detailed explanations, see [19]). Isomers in which all corresponding pairwise interactions are identical are said to be isometric, and they are anisometric if this condition is not fulfilled. Isometric molecules may be superimposable, in which case they are identical (homomeric), or they may be nonsuperimposable, in which case they share an enantiomeric relationship. As regards anisometric molecules, they are categorized as diastereoisomers or constitutional isomers, depending on whether their constitution is identical or not. This discussion is schematically summarized in the lower half of Fig. 2. 

There are, in fact, very few occurrences of binary hydrogen-bond-based cocrystals that do not contain a primary intermolecular interaction between the two different molecules. Two such examples include 4-nitrobenzamide pyrazine-carboxamide (1 1) [70] and 3,5-dintrobenzoic acid 4-(N,N-dimethylamino)benzoic acid (1 1) [132]. The latter is a rare example of a carboxylic acid- carboxylic acid cocrystal that contains two homomeric dimers instead of one heteromeric dimer [133]. 

An analogous example is provided by the diaryl ureas, of which the parent molecule is 3. These are found to preferentially crystallize in homomeric fashion, i.e., with their own kind, as in 4, rather than forming cocrystals with guest molecules [99], This is true even for solutions containing strong hydrogen bond acceptors such as dimethylsulfoxide, which would be expected to interact with the amino hydrogens of... 

In eukaryotes and prokaryotes, ACCase is a key enzyme in fatty acid biosynthesis [1]. The reaction product, malonyl-CoA, is both an intermediate in the de novo synthesis of primary fatty acids and also a substrate in the formation of long-chain fatty acids and flavonoids in plants [2, 3]. Aryloxyphenoxypropionates (APPs) and cyclohexandiones (CHDs) are two chemical classes of molecules that selectively inhibit homomeric, chloroplastic ACCase from grasses [4, 5], which makes them post emergent herbicides used worldwide to control grassy weeds. 

The existence of a irans biradical, presumably homomeric (see preceding footnote) with the reactants [10], has been confirmed computationally, whereas a distinct cis-stable one has not [11]. A second biradical in a gauche conformation was reported in the same computational study it was identified as a loosely coupled complex of two ethylene molecules, but is separated from them by a higher barrier than the irans biradical. 

An examination of reported cocrystals found in the CSD shows that most of them have been prepared using strategies that rely on the deliberate combination of chemical entities (or functional groups) located on different molecules capable of forming complementary heteromeric motifs (Scheme 6) rather than homomeric interactions (which leads to recrystallizations instead of cocrystalliza-... 

Conversely, there are very few reported examples of cocrystals where a primary noncovalent interaction is not present between the two different molecules in the lattice. Rare examples include 4-nitrobenzamide pyrazinecarbox-amide (1 1) ° and 3,5-dinitrobenzoic acid 4-(A, A -dime-thylamino)benzoic acid (1 1). In the latter structure, each forms a homomeric dimer instead of the much more commonly occurring heteromeric dimer (when two different carboxylic acids are present). ... 

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