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CIRCLE 3 1 ON READER SERVICE CARD MAY 3,1993 C&EN
fiber instead of a membrane. The membranes are two-dimensional arrays of such filaments. "It's a very unusual molecule, and I think it is probably the beginning of a large family of such molécules/' says Rich. "If s easy to see how you could vary them/' EAK16 membranes are similar to the insoluble plaques found in Alzheimer's disease, which have a β-pleated sheet
structure and consist of similar filaments. Drugs that inhibit self-assembly of EAK16 therefore might be useful for treatment of this disease. Membraneforming peptides may also find applicability as novel biomaterials and in origin-of-life studies. The membranes could potentially compartmentalize and "establish an enclosed environment for a primitive metabolism," the researchers say. Stu Borman
'Chemical computer' can recognize patterns Researchers have designed a simulated network of nonlinear reaction vessels that can be used to make a "chemical computer" capable of pattern recogni tion. The work could lead to a better un derstanding of complex chemical and biochemical reactions, which sometimes act as computer logic gates. The simulation was a collaborative effort by Allen Hjelmfelt and Friedeman W. Schneider of the Institute of Physical Chemistry at the University of Wurzburg, Germany, and chemistry professor John Ross of Stanford Uni versity [Science, 260, 335 (1993)]. Last year Hjelmfelt (then at Max Planck Institute for Biophysical Chemis try, Gôttingen, Germany), Edward D. Weinberger (also at Gottingen), and Ross published papers explaining how macroscopic chemical kinetics systems might be used to construct logic gates (AND, OR, and NOR gates), a universal Turing machine (which implements the basic logic of digital computers), and a parallel computer (neural network). Hjelmfelt, Schneider, and Ross have now extended this to conceptualize a network of coupled vessels that would be capable of performing a type of pattern recognition. Each vessel is a chemical system with two possible stationary states—low and high levels of a reaction product. The example they give is the iodate-arsenate reaction, which acts like a binary computing element because iodide product concentration maintains only two stable values (low or high). In the simulation, a set of tubes, each containing a valve, is used to connect 36 vessels in a network. Each vessel takes the value zero or one (low or high product concentration). Because these concentrations are adjustable, different 36digit binary numbers can be stored in the network. When a network containing a specific stored number, or pattern,
Ross: logic gates from chemical kinetics is presented with a number containing several "errors," the network evolves to correct the errors, up to a point. "If you put in as many as 18 errors, most of the time you get the right recognition," says Ross. "If you put in more errors, the system doesn't work. This shows how macroscopic kinetics can be used to do pattern recognition." The researchers hope to use the concept of chemical computation to elucidate complex reaction mechanisms. "Let's say you take a complicated biological mechanism, like glycolysis," says Ross. "Having learned that we can make logic gates out of chemical kinetics, can we recognize computational functions in a complex biochemical mechanism? And if so, can we then use artificial intelligence, logic gates, and electronic circuits to probe its properties and function? We're trying to develop a strategic approach to probing such mechanisms." Stu Borman
