Autobiography of Biman Bagchi - The Journal of Physical Chemistry B

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Autobiography of Biman Bagchi I came out of M.Sc. class, I found a small group of students had gathered around a student two years senior, and they all were reading a letter typed on a nice paper with a “cool” looking seal on top and the writing “If we don’t, who will”. It was an offer letter from Brown. The student did not go, but I came to know from discussions that several of our seniors had gone to Brown. This triggered me to apply, but there was a lot of legwork to be done and a lot of unfamiliarity, as nobody in my class was applying and nobody from my family had ever been to the US. Anyway, I did clear the necessary exams and surprisingly received an offer from Brown itself. For me, a dream journey began. At Brown, the choice of Professor H. Julian Gibbs as my Ph.D. Thesis Adviser was a great decision. He encouraged me to take a lot of courses outside the chemistry department and as a result could take several courses in math. Here I was fortunate to have Professor Lawrence (Larry) Sirovich (now at the Rockfeller University, NY) as a teacher. He was magnificent. I learned innumerable mathematical techniques from him. I not only credited several courses in Applied Math with him but also started a collaborative project on dielectric relaxation. Professor Sirovich taught me many nuances of partial differential equations, properties of many Special Functions, how to perform polynomial approximations to functions and asymptotic analysis, among other things. That really helped me understand the intricacies of time dependent statistical mechanics and the need for correct strategies of model building. A significant part of my Ph.D. years was spent on self-training on mathematical analysis that I greatly enjoyed. I also wanted to enroll in English creative writing courses at Brown but neither had money nor time. However, I read a large number of books of Franz Kafka, Albert Camus, Luigi Pirandello, Stefan Zweig, Bertolt Brecht, and many others some of which I did not have easy access to in Calcutta. For my Ph.D., I worked primarily on phase transitions (gas− liquid, sol−gel, Bose−Einstein condensation). It was the idea of Julian Gibbs that, if we could reformulate Mayer’s theory of condensation, then we could describe the liquid state, in addition to the gas−liquid phase transition. Thus, Mayer’s theory needed to be reformulated such that divergences could be avoided. Gibbs’ idea was to take the thermodynamic limit properly, by evaluating the Mayer partition function for a finite system first, and then take the limit to large systems. Despite a considerable amount of efforts by all of us, the project was not quite successful. However, there was an incident that made a lasting impression on me. One of my fellow Ph.D. students, Udayan Mohanty, discovered that Mayer’s partition function is exactly a generalized Bell polynomial. This allowed us to make significant progress in the evaluation of the Mayer partition function and led to numerous applications. I was already fond of Special Functions of mathematics; having read Lebedev’s famous monograph with the same name, I had increased faith

I was born in Kolkata, West Bengal, India, in 1954 to Abha Bagchi and Binay K. Bagchi. My father was a school principal and a social worker, and my mother was a perpetual student, a part-time teacher, and a homemaker. They were both from erstwhile East Bengal (now Bangladesh), although they were living in Calcutta at the time (1947) Bengal was being partitioned into East and West. During the 1930s, my father was a freedom fighter for which he had to spend 5 years in British jail as a “Prisoner of the Queen”. This and his continued social work had a large impact on our family. I grew up in a suburb named Bally about 10 km north of Calcutta. It was a small town. My childhood memories include catching fish, flying kites, climbing trees, and nonstop sporting activities that found strong encouragement and support from my father who had a dislike of so-called “good” students. The majority of my school years were spent in Uttarpara Government School which was one of the best schools in the locality. Even though he himself was a principal of a school, and a strict disciplinarian, he was never too strict about my school attendance and was always ready to give me a “leave letter” justifying my absences which were quite frequent. On the other hand, he provided me continuously with many different kinds of books and also made me a member of all the public libraries in the locality. I think my father, more than anybody else, shaped my academic and intellectual life. Another important influence came from my mother who herself was continuously going to college and university as a student during my own school and college years. I learned to love poetry from her. She kept an eye on my studies. Despite all my extra-curricular activities, I stood first in the school-leaving board exam in the whole district, with highest marks in Physics in the whole state (among about 200,000 students). Except for my father, and several school teachers, everybody was kind of shocked. I have only one brother, Bidyut, two years older who was nick-named “Lecturer” even when he was ten years old and indeed went on to become a teacher. He has remained delightful company and support, never stopped talking and lecturing, even at this age. A bit of a turnaround in my academic life occurred when I was in college. The famous Presidency College (now a university of the same name) remained closed for my entire first year of B.Sc. (where I was studying for Honors in Chemistry) due to political disturbances. During this time, I could get busy with a local Science Club and we also brought out a science magazine in Bengali of which I was the Editor. Our motto was to promote science through our own language. The magazine used to sell a few copies but helped me practice writing and kept me quite busy. Also one year of forced vacation allowed me to start studying books on physics and mathematics, as I found undergraduate texts on chemistry somewhat boring. During the continued political disturbance and closure of college and university (we lost more than a year due to late exams and nondeclaration of results), I became pretty desperate to find some kind of escape. However, my decision to go to Brown University (USA) was kind of accidental. One day while © 2015 American Chemical Society

Special Issue: Biman Bagchi Festschrift Published: August 27, 2015 10813

DOI: 10.1021/acs.jpcb.5b06114 J. Phys. Chem. B 2015, 119, 10813−10816


The Journal of Physical Chemistry B

Special Issue Preface

Almost at the same time in 1983, we worked out a theory of dipolar solvation dynamics and obtained an analytical expression for longitudinal relaxation time for solvation of a dipole. This was a continuum model based study and used an earlier theory of Nee and Zwanzig of rotational dielectric friction to obtain the time dependence of solvation energy. It predicted a solvation time of about 500 fs for a dipole in water. That estimate seemed extremely small and unrealizable in 1983. However, the real solvation time that was measured in 1991 turned out to be even smaller, by a factor of 10! The progress in ultrafast laser spectroscopy between 1980 and 1990 was truly astounding! It is good to narrate a few things at this point, especially for students. Many of the results I obtained were initially not believed to be true by many, including my advisers. The reason was, perhaps, that my approach was simple and straightforward. However, they almost always turned out to be correct. I later realized that I could have made them look far more impressive. I found all through my life that theoreticians, especially theoretical chemists, often do not like a straightforward and simple approach. Theory is often made to look sophisticated and formidable in order to make them look impressive. That is not to say that we do not need complicated theories, and we often do these days in complex systems. For students, however, a straightforward approach is more appealing. Maybe the unnecessary complications have driven students away from analytical theory and I find that most of the students are using computer simulations or carrying out package-based calculations. Toward the end of my stay at Chicago, I started to work with Professor Stuart Rice and Dr. Charles Cerjan on a density functional theory of freezing which was essentially an extension of earlier work from the Rice group. During this work, I learned density functional theory to understand inhomogeneous fluids which later I could use in many future problems, including time dependent density functional theory, leading partially to mode coupling theory. After Chicago, I went for a second postdoc to work with Professor R. Zwanzig at the University of Maryland. I probably never worked with anybody quite as unique as Bob, and he probably influenced my scientific and rational thinking like no other. As the only student or postdoc working with him, I got to interact with him closely. He was a great mentor for me. He spent a considerable amount of time teaching me different aspects of statistical mechanics. Despite all the rumors to the contrary, I found him a patient and kind man, although he had little patience for sloppy thinking and no tolerance for hypocrisy. Scientists often asked me how did I get along so well with Bob. My answer had always been that people who failed to recognize (or underestimated) his smartness or depth of his knowledge had difficulty with him. I remain ever grateful to Bob for all that he had taught me, although I feel I never could live up to his expectations of me. From the small town Bally to the Brown University at Providence, Rhode Island, USA, and later from Chicago to Maryland were all big changes in my life in every possible way. Those days people around were friendly, hospitable, nice, and accommodative. We could make trips to Boston and Cambridge, also to many distant places like Niagara Falls, Chesapeake Bay, Montreal, Quebec, and many others. However, I missed home terribly, and my long-term decision was perhaps formed at that time to return to India after adequate education. I always remembered Pablo Neruda’s

in the use of such mathematics in the study of statistical mechanical problems. During my graduate years at Brown, I also spent a lot of time studying fundamental papers of Kubo, Mori, and Zwanzig. This self-study helped me enormously and somewhat unexpectedly soon after graduation. After finishing my Ph.D. in the late 1980s, I went to the University of Chicago, taking a postdoctoral fellowship with Professor David W. Oxtoby. David was a wonderful guide and a teacher. He always suggested great problems. The first problem I dealt with was on the effects of non-Markovian solvent forces in vibrational energy relaxation in two- and three-level systems. I really liked this project, as I had already developed a feel for such problems from self-study. That was fortuitous. I could solve the problems by using an approach based on Kubo’s stochastic Liouville equation that allowed me to combine the quantum nature of the system with the classical nature of the solvent. I did not quite realize the full strength of the method (that I mastered with some difficulty). I did apply the method to explore non-Markovian excitation energy transfer and found a nice crossover from coherent transport to incoherent diffusion that depended on the correlation time of bath fluctuations. Subsequently, I worked on many problems, including isomerization dynamics and breakdown of Kramers’ theory of viscosity dependence of barrier crossing rate, solvation dynamics, and liquid−solid transitions. I worked pretty hard and published a large number of papers. Actually, my memory of this period is of spending most of the days and even the nights at the James Franck Institute third floor. There were many excellent colleagues, and I made long-term friends. It was extremely lucky that I was able to work with Professor Graham Fleming (at David Oxtoby’s suggestion) and Professor Stuart Rice. However, my learning came mostly from student and postdoctoral colleagues. I must mention Sherwin Singer and Charles Cerjan; they were both wonderful colleagues, and I got to spend a lot of time with them, especially in the Microvax II computer room between 10 pm and 3 am. Charlie taught me many numerical techniques that proved useful later. In the early 1980s was the beginning of study of ultrafast chemical dynamics in liquids by ultrashort lasers. The group of Professor Graham Fleming was reporting path breaking results in many areas. This provided a particularly exciting opportunity, as I could use the methods of time dependent statistical mechanics I taught myself at Brown. David and Graham recommended several problems that I could solve by building suitable models, like localized sink on a harmonic surface to model barrierless reactions, use generalized hydrodynamics (à la Zwanzig) to explain weak viscosity dependence of isomerization rates in systems like diphenyl butadiene and dye DODCI. It demonstrated a breakdown of Kramers theory. I still remember solving the pinhole sink model of barrierless reaction on the blackboard in Graham’s office when Graham told me that “there is no theory of barrierless electronic relaxation in solution”. By introducing a few new models to describe position dependence of sink, I could essentially solve this problem analytically or with minimal amount of numerical work. The theory explained many of the observed results and found extensive use in several areas. Interestingly, Hiroshi Sumi and Rudy Marcus developed a similar theory of barrierless electron transfer which also employed a position dependent sink. 10814





Chandra. In our molecular theory of solvation dynamics, we could demonstrate the important role of solvent translational modes which were neglected in earlier studies. A fun problem was to analyze Onsager’s “inverse snow-ball” picture. Our studies on solvation dynamics were followed by several groups across the world, and made quite an impact. Pursuing a related venture, we developed a mode coupling theory of electrolyte dynamics with Amalendu Chandra and a few others. This theory provided microscopic derivations of many of the limiting laws of electrochemistry: (i) Debye− Huckel theory of ionic conductivity, (ii) Onsager−Fuoss law of the concentration dependence of viscosity, and (iii) Debye− Falkenhagen expression for the anomalous frequency dependence of conductivity. The new thing we introduced was a set of slow hydrodynamic variables (charge density and charge current) for electrolyte solutions, in addition to the conventional ones. All the limiting laws came out nicely to our great satisfaction. Of real fun was the derivation of the Onsager− Fuoss expression of viscosity with exactly the same numerical prefactor (that is 1/480). We could also extend our mode coupling theory to intermediate ion concentrations with some success. It was a self-consistent theory. We later teamed up with Professor Pierre Turq and Dr. J.-F. Dufrêche for further work in this area. Another topic that inspired a lot of future research was a paper (with Nilashis Nandi) on biological water which was based on a simple idea of a dynamical equilibrium between free and quasi-bound water at the surface of biomolecules. This also created a significant impact (and some controversy). As often happened in my case (maybe because I was working more or less alone from India and hardly went to international conferences), our “bound water” was taken by many as the “bound water” trapped inside the core of proteins, a terminology already popular in NMR studies of protein hydration dynamics. However, we were monitoring only the water molecules on the surface and distinguishing them by the residence times. We clarified this later and called it “quasibound” to emphasize the transient but longer-lived nature of a few water molecules on a protein surface. Happily for us, this work motivated much work in India and even now several groups of young faculty members are working on this and related subjects. We briefly revisited solvation dynamics to explain the observation of ultrafast sub-100 fs dipolar solvation in water and acetonitrile, and also its role in several chemical processes like ionic conductivity, electron transfer reaction, etc. It was fun to work out analytical theories which agreed well with experiments and simulations. In recent times, we have moved into computer simulation studies of complex systems due to increased availability of high speed computers, although personally I still enjoy obtaining analytical solution of models designed to mimic complex systems. However, students have become increasingly disinterested in theory based research involving analytical methods. I particularly benefitted from many trips I made abroad, on sabbaticals and summer visits, especially the longer visits where I got the isolation to learn new things, like protein folding during a visit to NIH (Bethesda, Maryland) with Bob Zwanzig and single molecule spectroscopy during a visit to Austin, Texas, with Paul Barbara and Peter Rossky. During my first sabbatical at NIH, I was able to come up with a connection of new Darwanian theory to protein folding (and also to Shakespeare’s Hamlet) and offer (with Bob and Attila Szabo)

statement in his autobiography that one is the happiest in one’s own land. I eventually returned to India in 1984 to take up a position of lectureship at the Indian Institute of Science (IISc), Bangalore, where I have remained ever since. Professor C. N. R. Rao was then the director of IISc. He not only offered me the job but also guided and encouraged me through the crucial initial years. I was eventually promoted to the position of a full professor in 1995. I was a chairman of the department for almost four years between 2000 and 2004. Frankly, doing theoretical chemistry in India was difficult, as there was hardly any person in chemistry departments working on statistical mechanical problems in liquids. It was hard to have any discussion, and there was hardly any scope for collaborative work. In contrast, there were quite a few quantum chemists who did not take statistical mechanics seriously. There were quite a few sarcastic comments about liquid state problems. I felt quite isolated. Fortunately, I could talk with senior Ph.D. students in our department (not my studentsI did not have any in the first year or two) who were more receptive to my ideas and work. There was no postdoc in India those days (or, for that matter, even now). Actually, this total absence of postdoc culture (especially in theoretical chemistry in India) greatly hampered our work. Most of the Ph.D. students go abroad immediately after finishing their Ph.D.’s. However, there was a beneficial aspect of this too! We had to be closely involved in every project, as students were often new to the area of theoretical physical chemistry/physics, and had no prior exposure to statistical mechanics or computer simulations. Therefore, we had to start them afresh. Fortunately, many of my professors and ex-colleagues kept close contact with me in those difficult early years and that helped me get over the phase before I could build a group of my own. I also visited the groups of Bob Zwanzig, Graham Fleming, and Stuart Rice several times during the summer months. In hindsight, those trips and contacts helped me survive in India, as I knew almost nobody here in India and was slow to get accepted. The computational facility at IISc those days was very limited. We just had one DEC-10 for the whole Institute, and that was occupied largely by the MTech and engineering students. We often had to work after 9 pm and continue until 2 am. As I used to live about 3 miles from the campus, I often walked back through empty muddy roads (as I used a shortcut). My lovely first wife Suhrita (then quite young herself), however, never complained, as she understood the difficult struggle I was going through. Even with all these, we could not diagonalize even a 100 × 100 matrix! Life was hard. I tried to find problems that could be solved analytically. Things improved after 1988/89 or so when our department got a Microvax II. Our new faculty and students cannot imagine what difficulty some of us had to go through to accomplish even small things. After an initial lull, several excellent students joined my group. We achieved quite a bit from 1987. It was real fun to work and obtain results on ultrafast solvation dynamics, electron transfer reactions in solution, ionic conductivity, protein hydration dynamics, mode coupling theory of diffusion and electrolyte conduction, liquid crystal dynamics, vibrational relaxation, and many other topics of physical and biophysical chemistry. I am particularly fond of the work on solvation dynamics, dielectric relaxation, and mode coupling theory of electrolyte conductance that was done with Amalendu 10815





pleasant place to work and study. I thank all of them for friendship and generosity. I would like to comment on the two books I have written recently: the first, “Molecular Relaxation in Liquids” (by Oxford University Press, 2012), and the second, “Water in Biological and Chemical Processes: From Structure and Dynamics to Function” (by Cambridge University Press, 2013). I wrote these books from an innate desire to explain my thinking to the academic world, as I found that I was sometimes not properly understood. I do not know whether I succeeded. They were demanding tasks, and I want to acknowledge the substantial help received from my students. My advice to young faculty members is that they should certainly try their hands at writing books and monographs early in their career, as such activities not only enrich one’s own understanding but are very useful for the group. I have found that new students of my group turn to these books for easy reference and to understand my comments and suggestions. I am now finishing my third book which is a text on statistical mechanics. It is also turning out to be an arduous task. Over the last ten years, my interests have moved steadily toward the study of biophysical chemistry, as I found that biology can offer unusual problems for a theoretical physical chemist like me. We worked on protein folding, protein−DNA interactions, kinetic proof reading, protein conformational and also hydration dynamics in aqueous binary mixtures, to mention a few. More recently, we worked out a theory of the role of vitamin D in human immunity. We are pursuing that line of research. I wish to continue working on newer problems in the future. I hope “Tis not too late to seek a newer world”.

a simple solution to the Levinthal paradox. During my visit to Austin, I was able to team up with Paul Barbara and Peter Rossky to explain the conformation of conjugated polymers and establish that these polymers display statistical features different from Gaussian. That is, these strongly interacting polymers are actually not Flory polymers but they exist in solution in certain ordered forms. We also demonstrated the breakdown of Forster’s theory of energy transfer at short distances. During my stay at Harvard in 2007, I was able to work with Sunney Xie, Paul Blainey, and Wei Min to develop a theory of protein diffusion along a DNA chain and also a theory of enzyme kinetics. Both of the works were almost entirely analytical and were quite satisfactory. We also received many visitors from abroad at IISc, Bangalore. We learned many new subjects from them. Visitors include Arun Yethiraj (Wisconsin), Peter Wolynes (then at San Diego), Casey Hynes (ENS, Paris), Michael Fayer, G. R. Fleming, and many others. Arun taught us how to simulate polymers that turned out to have a far reaching impact on our future studies. I had a tremendously happy and active life with my wife and two children until 2009 when Suhrita was detected as having a terminal illness. During the ensuing difficult period, my two sons, Kaushik and Kushal, were a tremendous source of strength, although they themselves suffered greatly. I am so very fortunate to have them. Many of my students were highly supportive. Lastly (but not the least), my second wife Sukla brought music and vitality back to my life. Science has opened up a world for me that I never dreamed of when I was growing up at Bally. I came in contact with great individuals and made great friends across continents. I would particularly like to mention and thank Professor Iwao Ohmine, Professor Paul Barbara, Professor Ahmed Zewail, Professor Peter Wolynes, Professor James (Casey) Hynes, Professor R. N. Zare, and Professor Rudy Marcus, in addition to my mentors mentioned above. Paul Barbara who died early at 57 was a dear friend and valuable colleague full of helpful advice. It was a terrible loss for me. I knew Paul from my Brown days. I shall always miss him, his insightful comments, his youthful energy, and excitement of science. Close to home I found continued support and encouragement from Professor Kankan Bhattacharyya, Professor Srikanth Sastry, Professor Swapan Ghosh, Professor B. L. Tembe, Professor J. Gopalakrishnan, Professor Amalendu Chandra, Professor Ashok Ganguly, Professor Kamanio Chattopadhyay, Professor S. Yashonath, and many other colleagues, friends, and students. I feel that younger physical chemists in India, both theoreticians and experimentalists, like to interact with me and often follow my studies closely. I do not fully understand the reason, but it seems that I brought to them close at home certain areas and concepts that appealed to them greatly. It is interesting because the areas that attracted me seem to elicit a positive response (like hitting a resonant chord) in them also. This may be partly sociological. It is hard to say. When I started, there were hardly any theoreticians working on statistical mechanics in chemistry departments, but now there are at least 30 or so actively pursuing this area. Many of them are my students or my students’ students. This gives me immense pleasure. My department, the Solid State and Structural Chemistry Unit at the Indian Institute of Science, has been and remains a

Biman Bagchi

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Autobiography of Biman Bagchi - The Journal of Physical Chemistry B

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