Molecular memories

Studies devoted to create high-density molecular memory devices (ideally, it is hoped to find materials in which each bit of digital information might be stored on a single molecule) are very active89 and larger manganese-carboxylate assemblies have been obtained (up to... 

Multiple cyclic proton transfers occur in hydrogen bonded arrays of heterocyclic units [8.220, 8.221] or inside rings such as porphyrins [8.222]. Macrocyclic polyamines present various protonation patterns [3.13a] that could be of interest as information units. Data storage in a molecular memory by hole burning makes... 

The first reported attempt of using MIPs to control the stereochemical course of a reaction dates back to 1980, when the two research groups of Neckers and Shea published, simultaneously, examples of bulk polymers able to control the formation of the product by using a chiral template. Shea et al. reported that bulk polymers imprinted with stereochemically pure ( )-/ra/w-l,2,cyclobutane-dicarboxyilic acid (6) were able to keep a molecular memory of the asymmetry of the template [8]. In fact, this was transferred to an achiral substrate, such as fumaric acid (7), inducing a diastereoselective methylation, which led to trans-1,2,cyclopropane-dicarboxyilic... 

Not only do enzymes work in anhydrous organic media, but in this unnatural milieu they acquire remarkable properties such as enhanced stability, altered substrate and enantiomeric specificities, molecular memory, and the ability to catalyze unusual reactions (Klibanov, 1989). Regarding the latter point, hydrolases, such as lipases, catalyze not only transesterifications in organic media but also other types of reactions, including esterification, aminolysis, thiotransesterification, and oximolysis. As all of these reactions compete with hydrolyses, which tend to dominate in aqueous media, some of them proceed to an appreciable extent only in non-aqueous solvents. 

In principle any molecule able to exist in two reversible, switchable states can represents a molecular switch (bistable device) with potential to form part of molecular circuitry or act as molecular memory. An excellent component for switchable molecular devices is the 1,2-dithienylethene system, which has been exploited ingeniously by Lehn in a number of bistable systems.54 The core switching element is the transformation of the dithienylethene unit between two stable states as a function of the wavelength of incident radiation (Scheme 11.8). 

This remarkable molecular memory was preceded by two other related examples of addressable molecular electronics from the Stoddart and Heath groups in collaboration with Hewlett-Packard scientists. First in 1999 a [2] rotaxane based system was configured into molecular AND and OR logic gates,63 then in 2000 a [2] catenane based molecular switch was reported.64 The molecular basis for the operation of this switch is the same as in 11.67, namely reorientation in response to reduction of... 

Berchtold, N.C. et al., Exercise primes a molecular memory for brain-derived neurotrophic factor protein induction in the rat hippocampus, Neuroscience, 133, 853, 2005. 

As discussed in the introduction, a major motivation for the development of methods to controllably functionalize silicon surfaces is the opportunity to create novel hybrid organic/silicon devices. By integrating organic molecules with silicon substrates it should be possible to expand the functionality of conventional microelectronic devices. Possibilities include high-density molecular memory and logic as well as chemical and biochemical sensors. Realization of these opportunities requires not only the development of the attachment chemistries, as discussed in the previous sections, but also detailed studies of the electronic properties of the resulting surfaces. 

While enzymes, as a rule, essentially lose their normal activity and specificity, they possess new useful features 1) utilization of substrates non-soluble in water 2) their ability to change substrate and inhibitor selectivity and specificity 3) they alternate of reactions thermodynamics and kinetics reactions so that desirable products are favoured 4) improvements of enzyme stability and 5) the possibility to fix enzymes and reaction intermediates at states of certain pH and ionic strength in both solution and crystal form ( molecular memory effects ). 

Fig. 4.32. Chiral recognition and induction of molecular memory in Ce(IV) complexes with a substituted porphyrin. Redrawn from S. Shinkai et al., J. Chem. Soc., Perkin Trans. I 3259, 1999.

DNA is said to be the molecular memory of living things. DNA is expected as electro-conductive [2] and ion conductive [3] materials, base materials for electroluminescence [4], and so on. There is wide number of trials of DNA reported in electrochemistry. We have been trying to solubihze DNAs in several organic solvents including ELs [5]. J. Davis and coworkers have also pursued this subject, and both groups have determined some ELs to be good solvents for DNA [6]. 

The notion of using molecules as storage centers for electronic memory is seductive. Use of molecules in memory clearly allows for extraordinary miniaturization, thereby permitting a high density of information storage. Because of their capacity to store multiple electrons (bits) and to exhibit diverse stereochemistries, metal complexes are of particular interest. One feature needed for a practical molecular memory is the ability of the redox functionahty to sustain multiple read-write cycles, that is, to withstand multiple oxidations and reductions without decomposition. Such a consideration is a concern for metal complexes that are typically more stable in one redox form compared to the others. 

Liu, Z., Yasseri, A.A., Lindsey, J.S., and Bocian, D.F. (2003) Molecular memories that survive sihcon device processing and real-world operation. Science, 302, 1543. 

Alexis Perry conducted his undergraduate studies at the University of Glasgow, where he obtained his MSci in 2001. He joined the research group of Prof. Adam Nelson at the University of Leeds, where he developed methodology for the synthesis of C-linked azasaccharides and obtained his PhD in 2005. After a year of postdoctoral research into porphyrin-based molecular memory with Prof Maxwell Crossley (University of Sydney), he accepted a further postdoctoral position in the research group of Prof Richard Taylor at the University of York, where he is involved in the development of tandem reactions and their application in natural product synthesis. 

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