Chemists thinking logically

A molecular unit that carries out the computer logical function known as inhibit (INH) has been developed by UK and Irish chemists. The work builds on previous successful developments by others, such as AP de Silva at Queen's University Belfast to build ID, AND, NOT and NOR molecular gates and work by Vincenzo Balzani at Bologna University, Italy. The ultimate aim will be to link these various units to produce a true molecular-based computer, which would be many times more powerful and faster than silicon-based devices.

Thorfinnur Gunnlaugsson of Trinity College Dublin and a former member of the QUB team, and 'molecular programmer' Dónall Mac Dónail have worked with Durham University's David Parker, an expert in lanthanide-based macrocyclic systems for use in biological applications, such as MRI and in luminescence, to build a simple-seeming molecule containing a terbium ion. The molecule produces a sharp Tb emission line when two chemical conditions, the inputs, are met - the presence of protons and the absence of molecular oxygen. The molecule then simulates the electronic logical function known as 'two-input INH' which is a special combination of the AND and NOT functions and a critical component of more complex computational logic functions.

The molecule conjugates a quinoline group, which very effectively detects protons, to a macrocycle, 1,4,7,10-tetraazacyclododecane (cyclen), holding a terbium(III) ion, which responds to the 'absence' of O₂.

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According to Gunnlaugsson this arrangement allows them to reproduce the two-input INH 'truth table' represented by the production of the Tb glow or not depending on the combinations of the two chemical inputs. The designed combination of various logic gates of this kind should allow circuits to carry out calculations.

De Silva has pointed out that devices of this type based on molecules would not have to be 'hard-wired' like conventional logic circuits so may have unique applications. For instance, they could be used in labelling and inventory of the polymer support beads used in combinatorial chemistry, an aspect, which is being developed by his QUB team.

Chem. Commun, 2000, 93.

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