Systems chemistry is a branch of chemical research that examines large, complicated chemical networks and focuses on understanding how complexity and function can emerge from the many diverse chemical interactions within the network. This grant provides support to a team led by Rein Ulijn, Professor of Physics and Director of the Nanoscience Initiative at the City University of New York Graduate Center, to induce a chemical system to demonstrate a life-like behavior; specifically, a primitive form of learning and memory. Dr. Ulijn’s basic chemical system will be composed of peptides (short proteins; a sequence of amino acids) that -with the help of an enzyme- can be reversibly combined into more complex peptides (oligopeptides). The team plans to expose a chemical network to a molecule that acts as an environmental stimulus that will cause a reaction, the formation of new peptide molecules and various phase-separated peptide ‘structures.’ After removing the stimulus molecules from the network, they will be re-introducing at some later time.  If the network responds more rapidly to the stimulus than when the molecules were first introduced, it has, in a basic sense, “remembered” the initial stimulus and ‘learned’ to respond faster.  The project begins by choosing an initial set of (2-6) interacting dipeptides. Molecular dynamics simulations will inform selection of the initial dipeptide system to ensure that the dipeptides have a propensity for self-assembly. This makes it likely that more complex peptides and (peptide) structures will form. Once an initial system has been selected, the researchers will synthesize the system in their lab, allow the peptide chemistry to run to a steady state, and then characterize the steady state distribution of peptides and phase-separated structures in the unperturbed system (i.e. before a stimulus molecule is introduced). The formation of oligopeptides and phase-separated structures will be monitored using a combination of microscopy, optical spectroscopy, liquid chromatography, mass spectrometry, and dynamic light scattering. Once the steady state properties of the unperturbed peptide system have been characterized, a stimulus molecule will be introduced and the researchers will characterize how the distribution of peptides and the formation of structures is modified. The characterization will be done for each of several stimulus molecules (flavor molecules grape, raspberry, banana and apple) selected based on their simplicity and because they offer a systematic variation in chemical-interaction potential.  Finally, the researchers will determine whether repeated exposure to a given stimulus molecule can condition the system to respond more rapidly; the stimulus molecules will be removed between exposures. The researchers will study how learning and memory are influenced by variation of experimental parameters such as pH, temperature, and molecular target concentration. They’ll also test the hypothesis that the physical basis of memory lies in remnant structures retained by the solution. This idea will be tested by using heat to melt any remnant structural nuclei; something that should eliminate any observed memory effects. Beyond demonstration of learning and memory induced by a single type of stimulus molecule, the researchers will also explore exposure to competing stimuli, by examining whether mixing of separately conditioned solutions yields a different response when compared to that obtained from a solution conditioned by simultaneous exposure to several types of stimulus molecules.