Indo-French workshop on weak intermolecular interactions

Thirty scientists participated in an Indo-French workshop on 'Static and dynamic aspects of weak intermolecular interactions' in Hyderabad, Feb. 17-21, 2001. The workshop, sponsored by the Indo-French Centre for the Promotion of Advanced Research (CEFIPRA) and organised by G.R. Desiraju (Hyderabad) and P. Batail (Nantes) brought together chemists, crystallographers, physicists, biologists and theoreticians for a discussion of weak hydrogen bonds and other intermolecular interactions in the static and dynamic context and included sessions on crystal engineering, intermolecular interactions, theoretical and computational approaches, and inorganic and biological systems. C.N.R. Rao (Bangalore) described the self-assembly of complex and exotic open-framework inorganic materials and argued that the mesoscopic assembly of 1D and 2D arrays and 3D superlattices in metal nanocrystals is governed by the Aufbau principle. G.R. Desiraju described the significance of multi-point recognition supramolecular synthons. M.W. Hosseini (Strasbourg) showed molecular networks assembled using programmed tectons and specific interaction patterns. A debate on the meaning of the terms, tecton and synthon followed: a tecton is a molecule with potential hydrogen bonding sites on its periphery, and a synthon is an intermolecular interaction pattern of functional groups and contains only parts of molecules. The organization of amphiphilic lipid molecules at the air–water interface (P. Ganguly, Pune), dynamics of C–H···O interactions in trimethyl isocyanurate (K. Boubekeur, Nantes), nonlinear optics and multipolar engineering with 2D and 3D octupolar molecules (J. Zyss, Paris), weak van der Waals interaction effects on the atomic and mesoscopic scale (P. Levitz, Palaiseau), molecular dynamics simulations on atomic argon at the solid–liquid transition temperature (R. Ramaswamy, New Delhi) and the static and dynamics of cooperative phenomenon in neutral–ionic phase transitions (H. Cailleau, Rennes) were described and discussed. Exploring weak interactions based on topographical characteristics of molecular electrostatic potential by S.R. Gadre (Pune) was followed by a lecture by E. Candell (Bellaterra, Spain) on the relationship between the crystal and electronic structures in BEDO-TTF salts. D. Mukherjee (Calcutta) proposed a method to treat inter-fragment interactions in the presence of valence fluctuations and B. Bagchi (Bangalore) spoke about dynamics of tagged water molecules and cesium ions at the aqueous micellar surface.

A visit to 400-year-old monuments was followed by the lecture of G. Tsoucaris (Paris) on the chemistry of cosmetic materials in ancient civilizations. From Greco-Roman texts and powder X-ray diffraction patterns, it appears that laurionite (PbOHCl) and phosgenite (Pb₂Cl₂CO₃) were synthesized by the Egyptians in 2000 BC for use as eye make-up and may have had religious connotations (see Figure).

P. Batail discussed the interplay of hydrogen bonding and redox states in EDT-TTF-amides. A. Nangia (Hyderabad) showed that the halogen...π synthon induces crystallization in a polar, non-centrosymmetric space group while M. Fourmigué (Nantes) discussed the interplay of halogen and hydrogen bonding in TTF molecules. This led to a discussion of what controls crystal packing — shape or interaction? R. Ziessel (Strasbourg) correlated ferromagnetic interactions in nitroxide radicals with C–H...O hydrogen bonds in their crystal structures. K.N. Ganesh (Pune) showed intricate hydrogen bond patterns in crystalline adducts of cyanuric acid and adenine derivatives.

The session on inorganic systems featured discussions of d⁰ transition metal oxides with unique properties (J. Gopalakrishnan, Bangalore), weak interactions in copper and silver coordination complexes (M.V. Rajasekaran, Hyderabad), hydrolytic polycondensation materials (G. Cerveau, Montpellier), and a Monte Carlo simulation of the dynamics of aromatic guests in a zeolite channels (J.A.R.P. Sarma, Hyderabad).

In a session on weak macromolecular interactions, the role of C–H...O and C–H...π interactions in stabilizing enzyme crystal structures (M.A. Viswamitra, Bangalore), the stereochemistry of aromatic residues in protein complexes (P. Chakrabarti, Calcutta), crystallization of proteins on carbon nanotubes (C. Mioskowski, Illkirch), free energy contributions to DNA–protein and drug–protein binding (B. Jayaram, New Delhi), and an overview on enthalpy–entropy balance in ligand–receptor interactions (B. Gopalakrishnan, Chandigarh) were discussed.

The atmosphere was lively and informal and the discussion prompted serious thought about the static and dynamic consequences of weak intermolecular interactions.

Ashwini Nangia, Hyderabad, India and Marc Fourmigué, Nantes, France