SIVA UMAPATHY

Indian Institute of Science, Inorganic and Physical Chemistry, Faculty Member

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Marcello Andreeta

Universidade Federal De Sao Carlos

Zeyad Alahmed

King Saud University

Peter Hobson

Queen Mary, University of London

Irina Kolesnik

Moscow State University

Bartolomeo Megna

Università degli Studi di Palermo

Gayatri Kumari

Jawaharlal Nehru Centre for Advanced Scientific Research

nihal simsek ozek

Middle East Technical University

Mustafa Odabasoglu

Pamukkale University

nedjma bendiab

Centre National de la Recherche Scientifique / French National Centre for Scientific Research

Martín A. Rodríguez

Universidad Nacional de San Martin

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Papers by SIVA UMAPATHY

Future challenges: general discussion

Faraday discussions, 2015

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Transient absorption studies on 3,6-dibromo polyvinylcarbazole and its model compounds

Journal of Photochemistry and Photobiology A-chemistry, Jun 1, 1997

3, 6-Dibromo-N-ethylcarbazole (DBNEC) and its polymeric analogue poly-3, 6-dibromovinylcarbazole ... more

Identification of a resonance Raman marker for cytochrome to monitor stress responses in Escherichia coli

Analytical and Bioanalytical Chemistry, Jun 17, 2020

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Ultrafast laser spectroscopy : a tool for chemists and biologists

Current Science, 1993

Application of ultrafast lasers to chemistry and biology has been an active area of research in t... more Application of ultrafast lasers to chemistry and biology has been an active area of research in the international scene for over a decade for physical and biophysical chemists. Perhaps, ultrafast laser spectroscopy is one of the most versatile tools available today to experimentally study structure and dynamics in the time domain of nanoseconds (10(-9) sec) to femtoseconds (10(-15) sec). In this article we attempt to highlight some of the recent developments in ultrafast laser spectroscopy with particular reference to vibrational spectroscopy, viz. infrared and Raman spectroscopy, in the above time domain.

Assessment of Radiation Resistance and Therapeutic Targeting of Cancer Stem Cells: A Raman Spectroscopic Study of Glioblastoma

Analytical chemistry, Jan 28, 2018

Radiation is the standard therapy used for treating Glioblastoma (GBM), a grade IV brain cancer. ... more Radiation is the standard therapy used for treating Glioblastoma (GBM), a grade IV brain cancer. Glioma Stem-like Cells (GSCs), an integral part of GBM, enforces resistance to radiation therapy of GBM. Studying the differential biomolecular composition of GSCs with varying levels of radiation sensitivity can aid in identifying the molecules and their associated pathways which impose resistance to cells thereby unraveling new targets which would serve as potential adjuvant therapy. Raman spectroscopy being a noninvasive, label free technique can determine the biomolecular constituent of cells under live conditions. In this study, we have deduced Raman spectral signatures to predict the radiosensitivity of any GSC accurately using the inherent and radiation induced biomolecular composition. Our study identified the differential regulation of several biomolecules which can be potential targets for adjuvant therapy. We radiosensitized the resistant GSCs using small molecule inhibitors s...

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Raman spectroscopy study of CdS nanorods and strain induced by the adsorption of 4-mercaptobenzoic acid

The Journal of Chemical Physics

In this study, near- and off-resonance Raman spectra of cadmium sulfide (CdS) quantum rods (NRs) ... more In this study, near- and off-resonance Raman spectra of cadmium sulfide (CdS) quantum rods (NRs) and 4-mercaptobenzoic acid (4-MBA) adsorbed CdS NRs are reported. The envelopes of characteristic optical phonon modes in the near-resonance Raman spectrum of CdS NRs are deconvoluted by following the phonon confinement model. As compared with off-resonant Raman spectra, optical phonon modes scattering cross section is amplified significantly in near-resonance Raman spectra through the Fröhlich interaction. The Huang–Rhys factor defining the strength of the Fröhlich interaction is estimated (∼0.468). Moreover, the adsorption of different concentrations of 4-mercaptobenzoic acid (4-MBA) onto CdS NRs produces surface strain in CdS NRs originating due to surface reconstruction and consequently blue and red shifts in off-resonance (514.5 nm) Raman spectra depending on the concentration of 4-MBA. These consequences are attributed to compressive and tensile strains, respectively. Relative to b...

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Time-Resolved Resonance Raman Spectral Analysis of Ruthenium Tris(bipyridine) Excited State: Revisited

Springer Proceedings in Physics, 1992

Time-resolved resonance Raman spectroscopy (TR3S) has widely been used to establish the vibration... more Time-resolved resonance Raman spectroscopy (TR3S) has widely been used to establish the vibrational structure and the nature of the metal-ligand charge transfer (MLCT) triplet excited state of d6 transition metal complexes [1–6]. In particular, bipyridyl complexes of ruthenium(II) have been studied extensively by TR3S [1, 3–6]. Recently however, certain aspects of the procedures used to interpret the TR3S data have been questioned [3–5]. In this paper, we reconsider those aspects with particular reference to ruthenium(II) tris (bipyridine) (RBY).

Rapid detection of bacterial infection and viability assessment with high specificity and sensitivity using Raman microspectroscopy

Analytical and Bioanalytical Chemistry, 2020

Infectious diseases caused by bacteria still pose major diagnostic challenges in spite of the ava... more Infectious diseases caused by bacteria still pose major diagnostic challenges in spite of the availability of various molecular approaches. Irrespective of the type of infection, rapid identification of the causative pathogen with a high degree of sensitivity and specificity is essential for initiating appropriate treatment. While existing methods like PCR possess high sensitivity, they are incapable of identifying the viability status of the pathogen and those which can, like culturing, are inherently slow. To overcome these limitations, we developed a diagnostic platform based on Raman microspectroscopy, capable of detecting biochemical signatures from a single bacterium for identification as well as viability assessment. The study also establishes a decontamination protocol for handling live pathogenic bacteria which does not affect identification and viability testing, showing applicability in the analysis of sputum samples containing pathogenic mycobacterial strains. The minimal sample processing along with multivariate analysis of spectroscopic signatures provides an interface for automatic classification, allowing the prediction of unknown samples by mapping signatures onto available datasets. Also, the novelty of the current work is the demonstration of simultaneous identification and viability assessment at a single bacterial level for pathogenic bacteria.

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Raman spectroscopy reveals distinct differences between two closely related bacterial strains, Mycobacterium indicus pranii and Mycobacterium intracellulare

Analytical and Bioanalytical Chemistry, 2019

A common technique used to differentiate bacterial species and to determine evolutionary relation... more A common technique used to differentiate bacterial species and to determine evolutionary relationships is sequencing their 16S ribosomal RNA genes. However, this method fails when organisms exhibit high similarity in these sequences. Two such strains that have identical 16S rRNA sequences are Mycobacterium indicus pranii (MIP) and Mycobacterium intracellulare. MIP is of significance as it is used as an adjuvant for protection against tuberculosis and leprosy; in addition, it shows potent anti-cancer activity. On the other hand, M. intracellulare is an opportunistic pathogen and causes severe respiratory infections in AIDS patients. It is important to differentiate these two bacterial species as they co-exist in immuno-compromised individuals. To unambiguously distinguish these two closely related bacterial strains, we employed Raman and resonance Raman spectroscopy in conjunction with multivariate statistical tools. Phenotypic profiling for these bacterial species was performed in a kinetic manner. Differences were observed in the mycolic acid profile and carotenoid pigments to show that MIP is biochemically distinct from M. intracellulare. Resonance Raman studies confirmed that carotenoids were produced by both MIP as well as M. intracellulare, though the latter produced higher amounts. Overall, this study demonstrates the potential of Raman spectroscopy in differentiating two closely related mycobacterial strains.

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Probing the effect of solvation on photoexcited 2-(2′-hydroxyphenyl)benzothiazole via ultrafast Raman loss spectroscopic studies

The Journal of Chemical Physics, 2018

2-(2-Hydroxyphenyl)benzothiazole (HBT) molecule is known to exhibit efficient excited state intra... more 2-(2-Hydroxyphenyl)benzothiazole (HBT) molecule is known to exhibit efficient excited state intramolecular proton transfer. As a consequence, it shows fluorescence with a large Stokes shift (∼10 000 cm −1) in non-polar solvents. However, fluorescence in polar solvents has a dual-band which corresponds to the emission from both the enol * and the keto * forms. Also, the excited state lifetime significantly varies with the solvent polarity. Recently, Mohammed et al. [J. Phys. Chem. A 115, 7550 (2011)] have shown that the excited state of HBT in acetonitrile (ACN) relaxes back to its ground electronic state through two competitive decay pathways, i.e., intramolecular proton transfer and intramolecular twisting between hydroxyphenyl and benzothiazole units in contrast to its behavior when it is in tetrachloroethene, a non-polar solvent. Here, by following the time-evolution of vibrational features of excited state HBT in ACN through ultrafast Raman loss spectroscopy, we demonstrate a direct evidence for the involvement of torsional motion leading to an ultrashort lifetime of HBT. The time evolution of the C 7-N vibrational frequency exhibited a red-shift in its peak position, clearly indicating the evolution of the initially planar cis-keto * form to the more twisted keto * form. Density functional theory calculations also well corroborate the experimental findings. Furthermore, wavepacket analysis of this mode reveals a strong correlation with the torsional motion in ACN.

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Synthesis and luminescence of ceria decorated graphene quantum dots (GQDs): Evolution of band gap

Integrated Ferroelectrics, 2017

ABSTRACT Graphene quantum dots (GQDs) and CeO2-GQDs were synthesized by using a facile hydrotherm... more ABSTRACT Graphene quantum dots (GQDs) and CeO2-GQDs were synthesized by using a facile hydrothermal method at 140°C. All the synthesized materials were characterized by TEM, UV-Vis Spectroscopy, FT-IR, Raman Spectroscopy and PL. Ceria decorated GQDs show different emission peaks with different excitation of wavelengths. The discrete change in dominant luminescence features of the GQDs and their composites indicate that the variation in PL occurs because of alteration in its shape, size and bandgap. Based on the experimental results of PL peak wavelength, the emission is attributed to quasi-molecular PL from the fragments composed of a few aromatic rings with oxygen containing functional groups.

Basic principles of ultrafast Raman loss spectroscopy#

Journal of Chemical Sciences, 2012

When a light beam passes through any medium, the effects of interaction of light with the materia... more When a light beam passes through any medium, the effects of interaction of light with the material depend on the field intensity. At low light intensities the response of materials remain linear to the amplitude of the applied electromagnetic field. But for sufficiently high intensities, the optical properties of materials are no longer linear to the amplitude of applied electromagnetic field. In such cases, the interaction of light waves with matter can result in the generation of new frequencies due to nonlinear processes such as higher harmonic generation and mixing of incident fields. One such nonlinear process, namely, the third order nonlinear spectroscopy has become a popular tool to study molecular structure. Thus, the spectroscopy based on the third order optical nonlinearity called stimulated Raman spectroscopy (SRS) is a tool to extract the structural and dynamical information about a molecular system. Ultrafast Raman loss spectroscopy (URLS) is analogous to SRS but is more sensitive than SRS. In this paper, we present the theoretical basis of SRS (URLS) techniques which have been developed in our laboratory.

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Femtosecond time-resolved UV-visible absorption spectroscopy of trans-azobenzene: dependence on excitation wavelength

Chemical Physics Letters, 1998

Femtosecond time-resolved UV-visible absorption spectroscopy has been used to study the photochem... more Femtosecond time-resolved UV-visible absorption spectroscopy has been used to study the photochemistry of trans-Ž). Ž. azobenzene in n-hexane. Excitation to the S np state results in transient absorption bands at ca. 400 nm strong and 550 1 Ž. nm weaker which decay with a lifetime 2.5 " 0.2 ps on excitation at 503 nm, close to the S origin, and with an additional 1 Ž). fast component of ca. 0.6 ps on excitation at 390 or 420 nm, both well above the S origin. Excitation to the S p p state 1 2 results in transient absorption at 400 nm which decays with a dominant component of ca. 0.9 ps and a weaker component of ca. 15 ps; this 400 nm band itself is observed to rise synchronously as a transient band at 475 nm decays with a lifetime of-200 fs. These results are discussed in terms of the dual mechanism proposed for azobenzene photoisomerization.

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Band assignments for the IR spectra [26], [27]

<p>Band assignments for the IR spectra <a href="http://www.plosone.org/article/info... more

Space-Resolved Raman Spectroscopy Applications: From Single Cells to Tissues

Encyclopedia of Analytical Chemistry

Potential of Raman spectroscopic techniques to study proteins

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2021

Proteins are large, complex molecules responsible for various biological processes. However, prot... more Proteins are large, complex molecules responsible for various biological processes. However, protein misfolding may lead to various life-threatening diseases. Therefore, it is vital to understand the shape and structure of proteins. Despite numerous techniques, a mechanistic understanding of the protein folding process is still unclear. Therefore, new techniques are continually being explored. In the present article, we have discussed the importance of Raman spectroscopy, Raman Optical Activity (ROA) and various other advancements in Raman spectroscopy to understand protein structure and conformational changes based on the review of our earlier work and recent literature. A Raman spectrum of a protein provides unique signatures for various secondary structures like helices, beta-sheets, turns, random structures, etc., and various amino acid residues such as tyrosine, tryptophan, and phenylalanine. We have shown how Raman spectra can differentiate between bovine serum albumin (BSA) and lysozyme protein based on their difference in sequence and structure (primary, secondary and tertiary). Although it is challenging to elucidate the structure of a protein using a Raman spectrum alone, Raman spectra can be used to differentiate small changes in conformations of proteins such as BSA during melting. Various new advancements in technique and data analyses in Raman spectroscopic studies of proteins have been discussed. The last part of the review focuses on the importance of the ROA spectrum to understand additional features about proteins. The ROA spectrum is rich in information about the protein backbone due to its rigidity compared to its side chains. Furthermore, the ROA spectra of lysozyme and BSA have been presented to show how ROA provides extra information about the solvent properties of proteins.

Pathogenic Escherichia coli (E. coli) detection through tuned nanoparticles enhancement study

Biotechnology Letters, 2020

Objective This study aims to detect pathogenic Escherichia coli (E. coli) bacteria using non-dest... more Objective This study aims to detect pathogenic Escherichia coli (E. coli) bacteria using non-destructive fluorescence microscopy and micro-Raman spectroscopy. Results Raman vibrational spectroscopy provides additional information regarding biochemical changes at the cellular level. We have used two nanomaterials zinc oxide nanoparticles (ZnO-NPs) and gold nanoparticles (Au-NPs) to detect pathogenic E. coli. The scanning electron microscope (SEM) with energy dispersive X-ray (EDAX) spectroscopy exhibit surface morphology and the elemental composition of the synthesized NPs. The metal NPs are useful contrast agents due to the surface plasmon resonance (SPR) to

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Potential of Raman spectroscopy towards understanding structures of carbon-based materials and perovskites

Emergent Materials, 2019

Sp 3 and sp 2 hybridised carbon materials have been exploited for myriad applications owing to th... more Sp 3 and sp 2 hybridised carbon materials have been exploited for myriad applications owing to their unique electronic features. Novel carbon materials and its composites are synthesised by researchers with improved physico-chemical properties for various applications. These novel materials need to be characterised to decipher the structures. Vibrational spectroscopic studies have been used to understand the lattice dynamics of such carbon materials for the last six decades. Raman spectroscopy in particular has been a unique technique in such investigations as it provides bond-specific information at a molecular level which is desirable in understanding the microstructure of carbon. In this review, we highlight the potential of Raman spectroscopy to study the microstructure of different carbon allotropes such as graphene, carbon nanotubes, fullerene, and carbon nitride and its composites. In addition, perovskites has been receiving a lot of attention recently as the scientific community has realised their potential in the areas of material science and energy storage and conversion. This review also covers a few aspects of Raman spectroscopic studies of oxide and halide perovskites.

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Signal Enhancement from Tunable SERS Substrates: Design and Demonstration of Multiple Regimes of Enhancement

The Journal of Physical Chemistry C, 2018

The interaction between plasmonic nanoparticle and substrate is of utmost importance for optimal ... more The interaction between plasmonic nanoparticle and substrate is of utmost importance for optimal design of surfaceenhanced Raman spectroscopy (SERS) substrates. Substrates can either quench or enhance the strength of the localized plasmon resonance of nanoparticles depending on the optical properties. The substrate optical properties were modified by introducing different dielectric films between silver nanoparticle and silicon base substrates. The thickness of the films was varied over a large range (5−200 nm) to observe SERS enhancement because of nonradiative and radiative interactions of the plasmons and the substrate. Energy transfer between the plasmons and the polarization charges in Si was observed for a film thickness of less than 10 nm where SERS intensity followed the permittivity trend of the spacer film. As the spacer thickness increases beyond 40 nm, the effect of Si base substrate subsides and the enhancement/quenching of the SERS signals exhibit an oscillatory behavior with the thickness of the film. The extent of enhancement and quenching can be tuned by optical property of substrate and the excitation wavelength of choice.

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