Solving Mysteries à la Sherlock Holmes and Chasing an Elusive Bond: Case Studies from our Laboratory
Mechanistic studies of organometallic reactions make fascinating detective stories. Unlike crime scenes, reaction scenarios can be repeated with ease. Most organometallic reaction pathways are well established, but surprises continue to crop up. In this talk I will primarily discuss the use of isotopic labels to unravel reaction pathways. I will use two reactions studied in our laboratory to illustrate general principles one should use to understand complex reactions and crime scenes.
Just as difficult it is to solve a mysterious crime; it is difficult to understand invisible chemical forces that hold atoms together. All of us are familiar with the covalent bond, the ionic bond, or the hydrogen bond, but several “bonds” in chemistry are just as elusive or even more elusive than Mr. Bond. One such bond is the copper-copper bond in d10 systems. Our efforts to unravel the basis of repeated occurrences of this motif, short Cu-Cu contacts in d10 systems, is another detective story.
December 05, 2016
Prof. Armido Studor, Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, 48149 Münster, Germany
In the lecture the concept of using the electron as a catalyst will be introduced and discussed.1,2 It will be shown that the electron is an efficient catalyst for conducting various types of radical cascade reactions that proceed via radical and radical ion intermediates. The “electron is a catalyst” paradigm unifies mechanistically an assortment of synthetic transformations that otherwise have little or no apparent relationship. Some recent examples on the use of the electron as a catalyst will be discussed.3 (1) A. Studer, D. P. Curran, Angew. Chem. Int. Ed. 2016, 55, 58-102.
(2) A. Studer, D. P. Curran, Nature Chem. 2014, 6, 765-773.
(a) Zhang, B.; Studer, A. Org. Lett. 2014, 16, 3990-3993.
(b) Leifert, D.; Studer, A. Org. Lett. 2015, 17, 386-389.
(c) Hartmann, M.; Daniliuc, C. G.; Studer, A. Chem. Commun. 2015, 51, 3121-3123.
(d) D. Leifert, D. G. Artiukhin, J. Neugebauer, A. Galstyan, C. A. Strassert, A. Studer, Chem. Commun. 2016, 52, 5997-6000.
(e) W. Wang, A. Studer, J. Am. Chem. Soc. 2016, 138, 2977-2980.
(f) A. Dewanji, C. Mück-Lichtenfeld, A. Studer, Angew. Chem. Int. Ed. 2016, 55, 6749-6752.
(g) E. G. Mackay, A. Studer, Chem. Eur. J. 2016, 22, 13455-13458.
(h) D. Leifert, A. Studer, Angew. Chem. Int. Ed. 2016, 55, 11660-11663.
(i) J. Xuan, D. Gonzalez-Abradelo, C. A. Strassert, C.-G. Daniliuc, A. Studer, Eur. J. Org. Chem. 2016, doi:10.1002/ejoc.201601033.]
To a researcher dealing with long chain molecules, the term “random walk” signifies one of the most common starting descriptors to understand the chain conformation of long string-like molecules. However, the title I have chosen is more to describe the path my students and I have taken during the past two decades to solve a variety of interesting problems in polymer science; some of which actually have to do with countering the strong tendency of polymer chains to adopt random-coil conformations. Constructing polymer molecules that are not long string-like objects but are more like highly branched trees possessing a “branch-upon-branch topology”, has been one of our major preoccupations; in this context, we have developed novel methods to prepare such highly branched polymers that are called “hyperbranched polymers (HBPs)”, examined the effect of branching density on their chain conformation, created and explored core-shell type HBPs, examined the curious case of Janus (twofaced) HBPs, etc. A more recent preoccupation of ours has been to develop strategies to resist the strong tendency of polymer chains to adopt random-coil conformations and consequently generate specifically folded conformations by the use of weak non-covalent interactions between periodically spaced segments along the polymer backbone. This journey has led us to explore the use of chargetransfer interactions, solvophobic exclusion, metal-ion coordination, alkylene segment crystallization, etc., in an effort to get to the yet-elusive goal of translating the ordering in solution on to the solid state.
In this talk, I shall describe some of these selected explorations during our random walks that provide us with the most joyous moments of discovery.
With experience and knowledge man learnt to make new materials from what was available in nature. Now we can design materials with precision and with the property we desire for an application. I plan to discuss the variety of techniques and the versatility of advanced materials giving examples from our work on nanostructured materials for energy harvesting[1-3] and sensing, intermetallics and superconductors[6-9].
1. Chem. Soc. Rev. (2010) 39 (2), 474-485, 474; JACS (2012) 134 (48), 19677-19684; J. Phys Chem B (2014) 118 (15), 4122-4131.
2. J Phys Chem C (2012) 116 (44), 23653-23662; J Phys Chem C (2014) 118 (31), 17332-17341,
3. ACS Appl. Mater Inter. (2016) 8 (35), 22860-22868; ACS Sust. Chem. & Engg.(2016) 4 (3), 1487-1499.
4. Biosens & Bioelectronics(2015) 72, 56-60; RSC Advances(2016) 6 (90), 86955-86958
5. JACS(1998) 120 (6), 1223-1229; Inorg Chem (2005) 44 (21), 7443-7448; J. Mag. Mag. Mater (2016) 397, 315-318.
6. Chem.Soc.Rev(1995); Chem Soc.Rev(2013) 42 (2), 569-598.
7. Inorg. Chem.54 (2015) 54 (3), 1076-1081, 1076. Inorg. Chem., 2016 (under Revision).
8. Scientific Reports(Under Review); ArXiv:1511.07692.
9. Nature Mater. (2016) 15 (1), 32-37,
There has been a renaissance in the chemistry of lanthanide ion complexes in view of their applications involving photophysical properties, magnetism and catalysis. Both homometallic and heterometallic (3d/4f) lanthanide complexes are being increasingly studied for their magnetic properties in general and as single-molecule magnets (SMMs) in particular. In this talk we will present some of our work on trinuclear 3d/4f complexes which exhibit SMM properties.
Protein Folding-Unfolding Dynamics and Hydrophobic Force Law
Folding of an unfolded protein into its complex, but unique and biologically active , three dimensional native state is a non-trivial process. Great progress has been made in recent years in solving the mystery of protein folding and unfolding. One major driving force in protein folding is an effective attraction between the hydrophobic amino acid residues. We shall discuss aspects of this hydrophobic force and its role in protein folding and unfolding dynamics. We shall also discuss how one can tune the hydrophobic force by adding a co-solvent.
August 16, 2016
Prof. R. N. Mukherjee, Department of Chemical Sciences, IISER Kolkata
Synthesis and Reactivity of Metal-Coordinated Ligand Radicals
Generation of ligand radicals can lead to interesting ligand-centered reactivity, with the mechanism of galactose oxidase serving as an inspiration for synthetic inorganic chemists. The design of metal complexes to catalyze multielectron reactions usually relies on one or more transition-metal ions capable of two-electron changes in a formal oxidation state. An alternative strategy to multielectron chemistry employs redox-active ligands, as reservoirs of electrons to supply oxidizing or reducing equivalents for bond-breaking and bond-making reactions at coordinatively unsaturated metal complexes. In this presentation, an account of detailed molecular (X-ray), spectroscopic and magnetic, and reactivity (redox) aspects of a number of ligand radical-coordinated metal complexes involving a group of redox-active ligands to correctly assign the spin-state and/or oxidation level of the metal ion and oxidation level of the coordinated ligands will be discussed. Our designed chelating ligands provide bis-phenolate(2−) and phenoxyl(1−) radical, o-amidophenolate(2−), o-iminobenzosemiquinonate(1−) p radical and o-benzoquinone forms of the coordinating ligands. The electronic structure of the complexes, assigned based on structural, redox and spectroscopic properties is then rationalized by the Density Functional Theory (DFT) and Time-Dependent (TD)-DFT calculations, which successfully rationalize the observed properties of the complexes. Radical-driven reactivity aspects (N–N, C–N, –C–O–C– and –O–C–O– bond formation) will also be discussed.
 A. Mukherjee, F. Lloret and R. N. Mukherjee, Inorg. Chem. 2008, 47, 4471-4480.
 A. Mukherjee and R. N. Mukherjee, Indian J. Chem. 2011, 50A, 484-490
(Special Issue on Bioinorganic Chemistry).
 A. Rajput, A. K. Sharma, S. K. Barman, D. Koley, M. Steinert and R. N. Mukherjee,
Inorg. Chem. 2014, 53, 36-48.
 A. Ali, S. K. Barman and R. N. Mukherjee, Inorg. Chem. 2015, 54, 5182-5194.
 A. Ali, A. Sengupta and R. N. Mukherjee, J. Ind. Chem. Soc. 2015, 92, 1981-1991 (Special Issue on Professor Animesh Chakravorty’s 80th Birth Anniversary).
 A. Ali, S. K. Barman, F. Lloret and R. N. Mukherjee, Inorg. Chem. 2016, 55, 5759-5771.
Over the years, we have been exploring covalent and noncovalent chemistry to create molecular functional materials using synthetic organic molecules as building blocks. In the case of aromatic p-systems, electronic properties such as fluorescence, charge carrier mobility and conductivity can be modulated as a consequence of self-assembly. For the past several years we have been learning to use fluorescent molecular building blocks to the creation of a variety of supramolecular polymers and architectures with diverse, size, shape and properties. Many of these molecular assemblies form organogels with intriguing reversible properties. Some of them are excellent donor scaffolds for energy transfer which allows tuning of the emission colors. The fluorescence of these materials is extremely sensitive to the surroundings and hence useful for sensing and imaging. We have developed several fluorescent molecules and dyes for sensing of analytes and imaging of biological samples. The fascinating chemistry of the two different aspects of our research with fluorescent molecules will be discussed.
1. S. S. Babu, V. K. Praveen, A. Ajayaghosh, Chem. Rev. 2014, 114, 1973.
2. K. P. Divya, S. Sreejith, A. Pichandi, Y. Kang, Q. Peng, S. K. Maji, Y.Tong, H.Yu, Y. Zhao, P. Ramamurthy, A. Ajayaghosh Chem. Sci. 2014, 5, 3469.
3. R. Thirumalai, R. D. Mukhopadyay, V. K. Praveen, A. Ajayaghosh, Sci. Rep. 2015 DOI: 10.1038/srep09842.
4. P. Anees, S. Sreejith, A. Ajayaghosh, J. Am. Chem. Soc. 2014, 136, 13233.
5. R. D. Mukhopadhyay, A. Ajayaghosh, Science 2015, 349, 241.
6. S. Prasanthkumar, S. Ghosh, V. C. Nair, A. Saeki, S. Seki, A. Ajayaghosh, Angew. Chem. Int. Ed. 2015, 54, 946.
7. S. Anjamkudy, V. K. Praveen, K. K. Kartha, V. Karunakaran, A. Ajayaghosh, Chem. Sci. 2016, 7, 4460.
8. P. Anees et al., Chem. Sci. 2016, 7, 0000 (in print).
9. B. Vedhanarayanan, V. S. Nair, V. C. Nair, A. Ajayaghosh, Angew. Chem. Int. Ed. 2016, 55, 0000 (in print).
August 05, 2016
Prof. Anunay Samanta, School of Chemistry, University of Hyderabad
Our interest lies in photo-excited systems. We employ a variety of light-based techniques to study the behaviour of molecular systems and materials in their electronically excited state, determine the identity of the short-lived transient species through their spectral and temporal characteristics and investigate the dynamics of the ultrafast events. Quite often, we also exploit the photo-response of molecular systems as a tool for probing unknown and complex environments. In this Colloquium, I wish to present a brief outline of our recent research activities and then discuss in somewhat greater detail what we have learnt about the room temperature ionic liquids from the fluorescence response of specifically chosen molecular systems in these media.
Bile acids are naturally occurring degradation products of cholesterol,
which are present in the bile as their taurine and glycine conjugates.
They perform a number of important biological functions such as the
prevention of cholesterol gallstone formation, emulsification of fats for
subsequent digestion, etc.1
During the past two decades our group has developed new molecular and
supramolecular chemistry with bile acids and their derivatives. We have
used modified bile acids as chiral templates and chiral auxiliaries, as
molecular tweezers, and as organo- and hydrogelators. More recently, we
have used a variety of bile acid derived metallogels for designing
nanostructured and photoluminescent materials with interesting properties.
Some of these results will be highlighted in this lecture.2
1 S. Mukhopadhyay, U. Maitra, Curr. Sci., 2004, 87, 1666-1683.
2 For a recent review of our work see: V.S. Sajisha, U. Maitra,
Chimia, 2013, 67, 44-50.
February 16, 2016
Prof. Amy C. Rosenzweig,Depts. of Molecular Biosciences and of Chemistry
Northwestern University, IL.
Methane gas is underutilized as a feedstock for production of liquid fuels due to low conversion efficiencies and high capital costs. Increasing natural gas reserves combined with an ongoing price spread between natural gas and gasoline have led to renewed interest in bioconversion of methane. In nature, methanotrophic bacteria activate methane with high selectivity under mild conditions using methane monooxygenases (MMOs). However, the use of MMOs in bioconversion processes is hindered by low efficiency, low carbon yields, and suboptimal kinetics. Improving these properties requires detailed understanding of the MMO enzyme systems, which has not been achieved for the primary MMO in nature, particulate MMO (pMMO). pMMO comprises three subunits, PmoA, PmoB, and PmoC, arranged in a trimeric complex. Despite extensive research and the availability of multiple crystal structures, the nature of the pMMO active site remains controversial and the chemical mechanism has not been elucidated. Mounting evidence indicates that methane is oxidized at a dinuclear copper center in the PmoB subunit, but several key questions remain unresolved. In addition, neither the roles of additional metal centers observed by crystallography nor the function of the transmembrane domains has been established. Progress toward answering these fundamental questions will be reported.
February 10, 2016
Prof. Toshiaki Enoki, Tokyo Institute of Technology, Japan
Unconventional Electronic and Magnetic Properties of Nanographene
Graphene, which is formed by fusing an infinite number of benzene rings in 2D manner, is described in terms of massless Dirac fermion in relativistic quantum mechanics. When a graphene sheet is cut into nanofragments, a variety of open-edged graphene nanostructures having different geometries and sizes are created. Here their electronic structures can be understood on the basis of the effect of the edges (zigzag and armchair edges), which work as the boundary condition to the Dirac fermion. Meanwhile the nanofragments are considered as nano-sized polycyclic aromatic hydrocarbon molecules and are extrapolated to anthrathene, naphthalene, and finally benzene as the size decreases. Accordingly the properties of the graphene nanostructures can be understood also in terms of phenomenological Clar’s aromatic sextet rule in chemistry. In particular the chemistry approach becomes intuitive more in understanding their properties and predictable for investigating functionalities for the nanostructures as various functional groups terminating the edge carbon atoms play an important role in their functionalities. Molecular science approach to graphene nanostructures are presented on the basis of investigations with STM/STS, AFM, X-ray absorption spectra, electron transport and magnetic measurements, and DFT calculations. According to our findings, zigzag-edged nanostructures have active nonbonding states in the vicinity of the edge region, which are the origin of electronic, magnetic and chemical activities. In contrast, electron wave interference gives rise to a standing wave, resulting in thermodynamic stability of armchair-edged nanostructures. In addition, chemical species, which terminate edge carbon atoms, give another modification of the electronic structures. The interplay of edge geometry and chemistry is found to be the source of divergent varieties in the electronic, magnetic and chemical properties of graphene nanostructures.
1. T. Enoki, Phys. Scr. T146, 014008 (2012) (Nobel Symposium on Graphene and Quantum Matter).
2. S. Fujii and T. Enoki, Angew. Chem. Int. Ed. 51, 7236 (2012).
3. T. Enoki and T. Ando, Physics and Chemistry of Graphene, Pan Stanford Publishing, 2013.
4. S. Fujii and T. Enoki, Acc. Chem. Res. 46, 220 (2013).
5. S. Fujii, M. Ziatdinov, M. Ohtsuka, K. Kusakabe, M. Kiguchi and T. Enoki, Faraday Discussions, 173, 173 (2014).
Solid Solution, Vegard’s Law, Chemical Pressure and all that
It is well known that lattice parameters of most solid solutions can be interpolated almost linearly with the composition between those of the two end-members. This, confirmed within a reasonable degree of accuracy by a huge body of structural investigations over many decades using the x-ray diffraction technique, is the celebrated Vegard's Law. In fact, many properties, such as the bandgap of a semiconductor solid solution, are also known to show a similar linear behaviour with composition between the end-members. These observations form the basis of the vast literature aimed at tuning of properties by making solid solutions. There is a closely associated concept of chemical pressure achieved by the substitution of typically a cation in a solid with another homovalent ion of dissimilar size defining a solid solution. This technique not only allows to exert a positive pressure by doping a smaller cation akin to the physical pressure, but also makes it feasible to explore of the negative pressure regime inaccessible otherwise with the help of a larger sized dopant. While these concepts are universally accepted and much used in designing new compounds with tailor made properties, a closer, microscopic inspection reveals many surprises not fully appreciated in the past. Based on some of our recent studies1,2, I shall illustrate the limits of these concepts and provide a rationale for their apparent success in spite of several conceptual difficulties.
1. Soham Mukherjee et al., Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution, Phys. Rev. B 89, 224105 (2014).
2. Soham Mukherjee et al., Unpublished results.