Dynamic covalent chemistry

Cacciapaglia, R. Di Stefano, S. Mandolini, L. Metathesis reaction of formaldehyde acetals An easy entry into the dynamic covalent chemistry of cyclophane formation. J. Am. Chem. Soc. 2005,127, 13666-13671. 

Whitney, A. M. Ladame, S. Balasubramanian, S. Templated ligand assembly by using G-quadruplex DNA and dynamic covalent chemistry. Angew. Chem. Int. Ed. 2004,43, 1143-1146. 

Krishnan-Ghosh, Y. Whimey, A. M. Balasubramanian, S. Dynamic covalent chemistry of self-templating PNA oligomers Formation of a bimolecular PNA quadruplex. Chem. Commun. 2005, 3068-3070. 

Philp, D. Dynamic Covalent Chemistry of Boron-Containing Heteroaromatic Systems. Proceedings of the 233rd American Chemical Society National Meeting, Chicago, IL, March 25-29. 2007. 

Rowan SJ, CantriU SJ, Cousins GRL, Sanders JKM, Stoddart JF. Dynamic covalent chemistry. Angew Chem Int Ed 2002 41 899-952. 

Krishnan-Ghosh Y, Balasubramanian S (2003) Dynamic covalent chemistry on self-templating peptides formation of a disulfide-linked -hairpin mimic. Angew Chem Int Ed 42 2171-2173... 

Dirksen, A., Dirksen, S., Hackeng, T.M., Dawson, P. E. Nucleophilic catalysis of hydrazone formation and transimination implications for dynamic covalent chemistry. J. Am. Chem. Soc. 2006, 128, 15602-15603. 

Dynamic covalent chemistry has been used in an atom-efficient self-assembly process to achieve a nearly quantitative one-pot synthesis of a nanoscale molecular container with an inner cavity of approximately 1.7 nm3. 

DCC Dynamic covalent chemistry or dynamic combinatorial chemistry DNCC Dynamic non-covalent chemistry... 

Tauk L, Schroder AP, Decher G, Giuseppone N (2009) Hierarchical functional gradients of pH-responsive self-assembled monolayers using dynamic covalent chemistry on surfaces. Nat Chem 1 649-656... 

Rodriguez-Docampo Z, Otto S (2008) Orthogonal or simultaneous use of disulfide and hydrazone exchange in dynamic covalent chemistry in aqueous solution. Chem Commun 2008 5301-5303... 

Abstract The present chapter is focused on how synthetic molecular machines (e.g. shuttles, switches and molecular motors) and size switches (conversions between polymers and their units, i.e., conversions between relatively large and small molecules) can function through covalent changes. Amongst the interesting examples of devices herein presented are molecular motors and size switches based on dynamic covalent chemistry which is an area of constitutional dynamic chemistry. 

Keywords Constitutional changes Covalent changes Dynamic covalent chemistry Molecular machines Molecular motors Molecular switches Polymer/monomer switches Reversible polymers Size switches... 

One may note that covalent changes that are dealt with in the functioning of this motor are, under the conditions of the reaction, irreversible (kinetically controlled reactions). Thus, the steps of this chemically driven motor do not belong to the field of dynamic covalent chemistry (that is based on covalent changes under equilibrium conditions). 

The small-molecule-based machine conceived by von Delius, Geertsema, and Leigh [45] is a linear (for reviews, see [46], [100]) motor based on dynamic covalent chemistry [19-24] (forming, breaking, and reforming of dynamic covalent bonds with relatively fast equilibration in response to stimuli), namely on acyl-hydrazone and disulfide exchanges. The motor consists of a track that has four functional groups disposed alternately aldehyde-thiol-aldehyde-thiol which are the positions 1,2, 3, and 4 of the track, a walker NH2-NH-CO-(CH2)5-SH which has the feet A (hydrazide or acyl-hydrazine) and B (thiol), and a placeholder with a foot C of type thiol (Fig. 10). 

Once such reversible systems have been identified, it is worth the effort to find conditions for their modulation through external stimuli, ideally in a repetitive way. Examples of reversible systems come from the field of dynamic covalent chemistry [19-24] which involves covalent changes with relatively fast equilibration. 

Fig. 13 The reversible conversion (here, mediated by metal ions M) of a copolymer (A-B) into a much smaller molecule (here, a macrocycle ABM) can be seen as a size-switch which consists of a dramatic change of molecular size (molecular diameter) modulated through external stimuli, and operates through dynamic covalent chemistry. See also Fig. 15...

Some of these machines and devices are based on dynamic covalent chemistry, and consequently belong to the area of constitutional dynamic chemistry. 

This dynamic process is commonly known as constitutional dynamic chemistry (CDC). While the concept of dynamic covalent chemistry defines systems in which the molecular (or supramolecular) reorganization proceeds via reversible covalent bond formation/breakage, dynamic systems based on noncovalent linkage exchanges define the concept of dynamic noncovalent chemistry. Dynamic combinatorial chemistry (DCC) can be defined as a direct application of CDC where libraries of complementary functional groups and/or complementary interactional groups interexchange via chemical (i.e., covalent) reactions or physical (i.e., noncovalent) interactions. 

The synthesis of rotaxanes (and catenanes) carried out under kinetically controlled conditions has as a drawback the employment of an irreversible bond-forming final step, which may yield competitive or unwanted non-interlocked by-products. Methods allowing interlocking to occur in a thermodynamically controlled manner have therefore been developed, so that by-products can be recycled to afford the energetically, most favored, interlocked species, via reversible breakage/formation of covalent bonds ( dynamic covalent chemistry ) <2002AGE898>. 

The excellent yields of the cyclic tetramer over potentially accessible larger structures have been demonstrated to result from thermodynamic product control under equilibrating conditions <2006OL2755, 2006TL4041>. The facile and selective formation of a specific molecule in a thermodynamically controlled reaction, where the covalent bond has the ability to be formed and reversibly broken, is the subject matter of dynamic covalent chemistry <2002AGE898>. 

Aldol addition has a low activation energy, a potentially important consideration in dynamic covalent chemistry (reactions carried out reversibly, under conditions of equilibrium control). ... 

It was recently suggested that carbamate bonds could be employed for a wider variety of dynamic covalent chemistry (DCC) experiments (88) and DCC is quickly emerging as a promising alternative to noncovalent self-assembly (91). This experiment offers an elegant opportunity of performing supramolecular chemistry with covalent bonds. One of the most important advantages here is the robustness of covalently organized structures, which on the other hand can be reversibly broken, at will. Of particular interest are supramolecular polymers and supramolecular materials. 

---