What do We do?
Light is a tool to dwell into very small space and is the shortest scale in our reach to measure fastest events. Spectroscopic techniques have come a long way to unravel the mysteries of happening at molecular level. We use these novel spectroscopic techniques for a better understanding of processes taking place in nature. You can read about basics on our resources page
Any experiment in the laboratory begins with measuring steady state absorption and fluorescence spectra of the sample. We have JASCO V 770 UV-Vis-NIR (180nm to 3200 nmm) absorption spectrophotometer to measure absorption spectrum. The absorption spectrum can recorded from 4 to 90 degree Celcius. We can also record absorbance and reflectance for solid samples using an integrating sphere.
The sample is then taken to Cary Eclipse Spectrofluorimeter where the samples are checked for steady state lumeniscent properties. The wavelength range for its detection is 190 to 800 nm. We can carry out polarisation dependent measurements as well. Just like absorbance, here also we can do temperature dependent measurements between 4 and 90 degree centrigrade and can measure fluorescence from solid surfaces.
We then proceed for doing Time resolved measurements. At IIT Goa, we are setting up femtosecond transient absorption spectroscopy setup. We have a Coherent Asterlla femtosecond ampliefied laser which produces ~35 fs pulses of energy ~5 mJ/pulse centred at 800 nm and operates at 1 kHz. The output of the amplifier is directed to an OPA from ultrafast systems which can generate femtosecond pulses between 280 and 2200 nm. These are used as pump pulses for a pump-probe spectroscopic measurements. The probe pulse is a white light. The transient abosrption measurements are done on Helios Transient absorption spectrometer from ultrafast systems. The detection is done on a CCD spectrograph (320 nm-850 nm) and semiconductor spectrograph (850nm-1600 nm).
Current projects going on in lab
Spectroscopic investigation of marine photopigments
The role of visual pigments is biology is well realised. It has been established that the role of pigments is not limited to process of vison but has energy harvesters as well. Recent developments in biochemistry and spectroscopy have provided insights for the molecular understanding of the functioning of such pigments. Biochemical and Genetic studies on the limited number of pigments studied so far have revealed striking similarities between the amino acid sequences of vertebrate and invertebrate pigments. The nature of receptors including their molecular components and physiological responses are yet obscure. The first steps of photoinitiation which result in isomerization is ultrafast. Albeit, the rate differs from species to species. The process of isomerisation in visual pigments the occurs in the orders of few femtoseconds while in lower micro-organisms this is observed to be rather slow, the reasons for which are not clearly understood. In this proposal we are attempting to observe pigments from microbes found in Indian sea waters and try to understand the photochemical features of the chromophore associated with them. This will help us to understand the key features of light adaptation that has occurred among various organisms. The microbial pigments will be expressed and extracted from E. Coli, which would be subjected to femtosecond time resolved absorption studies to decipher the photophysics of the molecules involved. The extraction, purification and characterisation will be done by Co-PI, while the PI will perform all the steady state and time resolved characterisation. We shall try to address the unanswered questions pertaining to the function of photosensitive pigments, as well as their origin in organisms by spectroscopic investigations of these molecules. This study may possibly introduce us to some novel pigments, which could find profound use in cosmetic and biological industry. Apart from these, from the point of view of evolution, this study might help in understanding the necessity for evolutionary branching of various photoreceptors. The ultrafast investigations would be a first ever study in pigments found in microbes living in Indian waters.Spectroscopic investigation of novel organometallic compounds
Development of renewable energy technologies as alternatives to fossil fuels is a crucial research area for a sustainable future, in order to meet ever growing global energy demands. In this regard metalloporphryins and transitional metal organometallic compounds have emerged as good candidates. However, the need of the hour is to prepare novel molecules with low bandgaps and easily tunable redox potentials, to improve the electron transfer rates and conductivity. Time resolved spectroscopy will help to confirm the molecular structures and also unearth the energies of the frontier molecular orbitals and efficiencies of various electron transfer processes they can undergo.Understanding ultrafast dynamics in the water-water interface , DST Inspire grant (2016-2021)
Interfaces play important role in physics chemistry and biology. The behaviour of the substances at different interfaces has helped enormously in various applications. Among the earliest known applications include the discovery of soap, some three millennia ago. Ever since then use of emulsions has been profound. It had been widely believed that emulsions may be formed only between two immiscible liquids, viz. oil and water. The science of emulsions has been believed to depend on the existence of amphi-philic molecules in a solution, where the aliphatic part of the molecule is excluded from water to either self-assemble into different aggregate structures or solvate hydrophobic molecules into a dispersion of oily materials in water. Micro-emulsions have been used to in order to mimic the hydrophobic environment found in cell. This provided a wonderful tool to understand dynamics occurring nature, e.g. interaction of proteins with drugs. It is obvious that the properties of the two liquids are drastically different and thus, the molecular probes would be experiencing very different environments. On the contrary, the real natural system, such as a cell, seldom has such drastic differences in interfaces. Often one encounters very contrasting environments induced by the same aqueous water. Water does it so by distributing itself as interfacial water and bulk water. It is intriguing how the dynamics may be affected at this water-water interface?