I’m a long-time fan of Oktay Sinanoğlu. I use the word “fan” quite deliberately: I don’t think there’s any other way to describe my relationship to the man. We’ve never met, or even exchanged emails. But I read some of his papers in graduate school and was immediately drawn in. I was therefore sad when I learned recently that he had died. One more scientific hero I’ll never meet…

Sinanoğlu had a long and productive career at Yale. Nevertheless, he was almost certainly better known in Turkey, where he became something of a national hero, than in the Western world. His papers covered a very wide cross-section of theoretical chemistry, including electronic structure, atomic clusters, solvent effects on chemical reactions, spectroscopy, automated generation of synthetic pathways, irreversible thermodynamics, dissipative structures, graph theoretical methods for studying the stability of reaction networks, and model reduction methods. It was the latter two topics that attracted my attention to Sinanoğlu when I was a graduate student. They intersected nicely with my interests at the time, which revolved around the dynamical systems approach to chemical kinetics.

My main research interest at the time was model reduction. Sinanoğlu, with his student Ariel Fernández, was among the first people to consider the construction of attracting manifolds for reaction-diffusion systems.^{1,2} This is a very difficult problem that is still a very active area of research. When I look back on the Fernández-Sinanoğlu papers on this topic, it seems to me that they anticipate later work on inertial manifolds.^{3} Because there weren’t many people following the field at the time, I don’t think that these papers are as well known as they deserve to be. Fernández and Sinanoğlu were just a bit ahead of their time. Had this work been published in the 1990s rather than the mid-1980s, I’m sure these papers would have received a great deal more attention.

Although I wasn’t working on these problems myself at the time, I became very interested in applications of graph theory in chemical kinetics while still a graduate student. It would be many years before I made any contributions to this topic myself, in association with my then-postdoc Maya Mincheva.^{4–6} Among the papers I read way back then were a pair written by Sinanoğlu in which chemical reaction networks were conceptualized as graphs.^{7,8} This allowed Sinanoğlu to enumerate all graphs corresponding to reactions with given numbers of reactions and species.^{7} A subsequent paper contained a conjecture about a topological feature of the graphs of chemical mechanisms capable of oscillations,^{8} thus attempting to tie together the structural features of his graphs and the dynamics generated by the rate equations. This is the theme we picked up many years later, although we followed a line of research initiated by Clarke^{9} and Ivanova^{10} rather than Sinanoğlu’s theory.

So, Oktay, thanks for inspiring a young graduate student. Rest in peace.

^{1}A. Fernández and O. Sinanoğlu (1984) Global attractors and global stability for closed chemical systems. *J. Math. Phys.* **25**, 406–409.

^{2}A. Fernández and O. Sinanoğlu (1984) Locally attractive normal modes for chemical process. *J. Math. Phys.* **25**, 2576–2581.

^{3}A. N. Yannacopoulos, A. S. Tomlin, J. Brindley, J. H. Merkin and M. J. Pilling (1995) The use of algebraic sets in the approximation of inertial manifolds and lumping in chemical kinetic systems. *Physica D* **83**, 421–449.

^{4}M. Mincheva and M. R. Roussel (2006) A graph-theoretic method for detecting potential Turing bifurcations. *J. Chem. Phys.* **125**, 204102.

^{5}M. Mincheva and M. R. Roussel (2007) Graph-theoretical methods for the analysis of chemical and biochemical networks. I. Multistability and oscillations in ordinary differential equation models. *J. Math. Biol.* **55**, 61–86.

^{6}M. Mincheva and M. R. Roussel (2007) Graph-theoretical methods for the analysis of chemical and biochemical networks. II. Oscillations in Networks with Delays. *J. Math. Biol.* **55**, 87–104.

^{7}O. Sinanoğlu (1981) 1- and 2-topology of reaction networks. *J. Math. Phys.* **22**, 1504–1512.

^{8}O. Sinanoğlu (1993) Autocatalytic and other general networks for chemical mechanisms, pathways, and cycles: their systematic and topological generation. *J. Math. Chem.* **12**, 319–363.

^{9}B. L. Clarke (1974) Graph theoretic approach to the stability analysis of steady state chemical reaction networks. *J. Chem. Phys.* **60**, 1481–1492.

^{10}A. N. Ivanova (1979) Conditions for the uniqueness of the stationary states of kinetic systems, connected with the structures of their reaction mechanisms. 1. *Kinet. Katal.* **20**, 1019–1023.