Imperial College London
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DrGunjanTyagi

Faculty of Engineering, Department of Chemical Engineering

Research Associate
 
 
 
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g.tyagi

 
 
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ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

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25 results found

Tyagi G, Sharratt WN, Erikson S, Seddon D, Robles ESJ, Cabral JTet al., 2022, Solution structures of anionic-amphoteric surfactant mixtures near the two-phase region at fixed pH, Langmuir: the ACS journal of surfaces and colloids, Vol: 38, Pages: 7198-7207, ISSN: 0743-7463

We examine the solution structures in a mixed surfactant system of sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO) in water, on both sides of the two-phase boundary, employing dynamic light scattering, small-angle neutron scattering, and Fourier transform infrared spectroscopy. The precipitate phase boundary was accessed by lowering pH to 8, from its floating pH 9.5 value, and was experimentally approached from the monomeric and micellar regions in three ways: at fixed DDAO or SDS concentrations and at a fixed (70:30) SDS:DDAO molar ratio. We characterize the size, shape, and interactions of micelles, which elongate approaching the boundary, leading to the formation of disk-like aggregates within the biphasic region, coexisting with micelles and monomers. Our data, from both monomeric and micellar solutions, indicate that the two phase structures formed are largely pathway-independent, with dimensions influenced by both pH and mixed surfactant composition. Precipitation occurs at intermediate stoichiometries with a similar SDS:DDAO ratio, whereas asymmetric stoichiometries form a re-entrant transition, returning to the mixed micelle phase. Overall, our findings demonstrate the effect of stoichiometry and solution pH on the synergistic interaction of mixed surfactants and their impact on phase equilibrium and associated micellar and two-phase structures

Journal article

Sharratt WN, Lopez CG, Sarkis M, Tyagi G, O'Connell R, Rogers SE, Cabral JTet al., 2021, Ionotropic gelation fronts in sodium carboxymethyl cellulose for hydrogel particle formation, Gels, Vol: 7, ISSN: 2310-2861

Hydrogel microparticles (HMPs) find numerous practical applications, ranging from drug delivery to tissue engineering. Designing HMPs from the molecular to macroscopic scales is required to exploit their full potential as functional materials. Here, we explore the gelation of sodium carboxymethyl cellulose (NaCMC), a model anionic polyelectrolyte, with Fe3+ cations in water. Gelation front kinetics are first established using 1D microfluidic experiments, and effective diffusive coefficients are found to increase with Fe3+ concentration and decrease with NaCMC concentrations. We use Fourier Transform Infrared Spectroscopy (FTIR) to elucidate the Fe3+-NaCMC gelation mechanism and small angle neutron scattering (SANS) to spatio-temporally resolve the solution-to-network structure during front propagation. We find that the polyelectrolyte chain cross-section remains largely unperturbed by gelation and identify three hierarchical structural features at larger length scales. Equipped with the understanding of gelation mechanism and kinetics, using microfluidics, we illustrate the fabrication of range of HMP particles with prescribed morphologies

Journal article

Hole A, Tyagi G, Deshmukh A, Deshpande R, Gota V, Chaturvedi P, Krishna CMet al., 2021, Salivary Raman Spectroscopy: Standardization of Sampling Protocols and Stratification of Healthy and Oral Cancer Subjects, APPLIED SPECTROSCOPY, Vol: 75, Pages: 581-588, ISSN: 0003-7028

Journal article

Tyagi G, Seddon D, Khodaparast S, Sharratt WN, Robles ESJ, Cabral JTet al., 2021, Tensiometry and FTIR study of the synergy in mixed SDS:DDAO surfactant solutions at varying pH, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 618, ISSN: 0927-7757

The interactions between a model anionic and amphoteric surfactant pair in aqueous solution are examined as a function of composition, at floating and fixed pH, employing a combination of tensiometry, regular solution theory analysis, and FTIR spectroscopy. An extensive series of pure and mixed ratios of sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO), ranging from 0.0016 to 100 mM, yielding 77 data points below and above the critical micelle concentrations (CMC), is investigated. Compared to either pure surfactant solutions, the CMC of mixed SDS:DDAO solutions is found to decrease by up to 20-fold, and the surface tension (γ) at CMC down to ≃ 23 mN/m. At all concentrations, the most prominent effects are observed at equimolar SDS:DDAO ratios. Further, the pH of mixed micellar solutions is found to increase with respect to the pure surfactant solutions (from ≃ 7 up to ≃ 9.5), which is attributed to the enhanced protonation of DDAO in the presence of SDS, and supported by FTIR frequency shifts of isolated O‒H stretching vibrations. Vibrational responses from CH2 stretching of the methylene tails, and the S‒O stretching modes for the sulfate headgroups indicate strong lateral interaction and enhanced packing between SDS and DDAO. From regular solution theory analysis of tensiometry data, the molecular interaction parameters are found to have a larger magnitude (i.e., more negative) at the interface as compared to within micelles. At fixed solution pH, a decrease from pH 9.5 to 7.5 results in minimal changes in both interfacial and micellar parameters, indicating the intrinsic origin of these pairwise interactions. Overall, our findings demonstrate a pronounced synergistic interaction between SDS and DDAO, arising from diminished electrostatic and steric repulsions in, respectively, SDS and DDAO, accompanied by enhanced lateral surfactant packing.

Journal article

Khodaparast S, Sharratt WN, Tyagi G, Dalgliesh RM, Robles ESJ, Cabral JTet al., 2021, Pure and mixed aqueous micellar solutions of Sodium Dodecyl sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO): Role of temperature and composition, Journal of Colloid and Interface Science, Vol: 582, Pages: 1116-1127, ISSN: 0021-9797

Aqueous mixtures of anionic and nonionic/cationic surfactants can form non-trivial self-assemblies in solution and exhibit macroscopic responses. Here, we investigate the micellar phase of pure and mixed aqueous solutions of Sodium Dodecyl Sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO) using a combination of Small Angle Neutron Scattering (SANS), Fourier-Transform Infrared Spectroscopy (FTIR) and rheological measurements. We examine the effect of temperature (0–60 °C), on the 20 wt% SDS micellar solutions with varying DDAO (5 wt%), and seek to correlate micellar structure with zero-shear solution viscosity. SANS establishes the formation of prolate ellipsoidal micelles in aqueous solutions of pure SDS, DDAO and SDS/DDAO mixtures, whose axial ratio is found to increase upon cooling. Elongation of the ellipsoidal micelles of pure SDS is also induced by the introduction of the non-anionic DDAO, which effectively reduces the repulsive interactions between the anionic SDS head-groups. In FTIR measurements, the formation of elongated mixed ellipsoidal micelles is confirmed by the increase of ordering in the hydrocarbon chain tails and interaction between surfactant head-groups. We find that the zero-shear viscosity of the mixed surfactant solutions increases exponentially with decreasing temperature and increasing DDAO content. Significantly, a master curve for solution viscosity can be obtained in terms of micellar aspect ratio, subsuming the effects of both temperature and DDAO composition in the experimental range investigated. The intrinsic viscosity of mixed micellar solutions is significantly larger than the analytical and numerical predictions for Brownian suspensions of ellipsoidal colloids, highlighting the need to consider interactions of soft micelles under shear, especially at high concentrations.

Journal article

Khodaparast S, Marcos J, Sharratt WN, Tyagi G, Cabral JTet al., 2021, Surface-induced crystallization of sodium dodecyl sulfate (SDS) micellar solutions in confinement, Langmuir: the ACS journal of surfaces and colloids, Vol: 37, Pages: 230-239, ISSN: 0743-7463

We investigate the role of confinement on the onset of crystallization in subcooled micellar solutions of sodium dodecyl sulfate (SDS), examining the impact of sample volume, substrate surface energy, and surface roughness. Using small angle neutron scattering (SANS) and dynamic light scattering (DLS), we measure the crystallization temperature upon cooling and the metastable zone width (MSZW) for bulk 10–30 wt% SDS solutions. We then introduce a microdroplet approach to quantify the impact of surface free energy (18–65 mN/m) and substrate roughness (Rα ≃ 0–60 μm) on the kinetics of surface-induced crystallization through measurements of induction time (ti) under isothermal conditions. While ti is found to decrease exponentially with decreasing temperature (increasing subcooling) for all tested surfaces, increasing the surface energy could cause a significant further reduction of up to ∼40 fold. For substrates with the lowest surface energy and longest ti, microscale surface roughness is found to enhance crystal nucleation, in particular for Rα ≥ 10 μm. Finally, we demonstrate that tuning the surface energy and microscopic roughness can be effective routes to promote or delay nucleation in bulk-like volumes, thus greatly impacting the stability of surfactant solutions at lower temperatures.

Journal article

Pandey N, Tyagi G, Kaur P, Pradhan S, Rajam MV, Srivastava Tet al., 2020, Allicin Overcomes Hypoxia Mediated Cisplatin Resistance in Lung Cancer Cells through ROS Mediated Cell Death Pathway and by Suppressing Hypoxia Inducible Factors., Cell Physiol Biochem, Vol: 54, Pages: 748-766

BACKGROUND/AIMS: The hypoxic microenvironment in NSCLC has been widely accepted as a contributor to both therapeutic resistance and tumor progression. In this study, we have explored Allicin, a key organosulfur compound present in garlic for its previously unreported effectiveness in the heterogeneous hypoxic tumor microenvironment of NSCLC. METHODS: The effect of Allicin on the viability of NSCLC cells was determined by MTT assay. To determine the migration rate of treated cells compared to the control, scratch and transwell migration assays were performed. Flowcytometry was done to explore cell cycle distribution, apoptosis and ROS production in cells. Fluorescence microscopy was used to examine autophagy and DNA damage in cells. Dot blot was done to check genome wide methylation. RNA expression was detected by RT-PCR and protein expression by western blotting. RESULTS: Allicin significantly decreases cell viability, proliferation and migration of NSCLC cells in both normoxia and hypoxia. It elicits both apoptosis and autophagy pathway in A549 cells by ROS accumulation and facilitating S/G2-M phase arrest in both normoxia as well as hypoxia. We suggest that ROS/MAPK and ROS/JNK signaling pathway together govern the cytotoxic effect of allicin in NSCLC cells. Notably, allicin suppresses the expression of HIF-1α and HIF-2α in hypoxic cells, pointing towards a mechanism of its effectiveness in hypoxia. A long term passive demethylation was observed, with decreased mC and no change in TET expression, thereby ruling out active demethylation by allicin. Furthermore, allicin synergistically enhances growth inhibitory activity of low dose cisplatin to effectively overcome hypoxia induced cisplatin resistance in A549 cells. CONCLUSION: Altogether, our results elucidate a potential use of allicin in sensitizing hypoxic and chemoresistant NSCLC to cisplatin-based chemotherapy and provide new, affordable therapeutic strategy with reduced side effects.

Journal article

Hole A, Tyagi G, Sahu A, Shaikh R, Krishna CMet al., 2018, Exploration of Raman exfoliated cytology for oral and cervical cancers, VIBRATIONAL SPECTROSCOPY, Vol: 98, Pages: 35-40, ISSN: 0924-2031

Journal article

Mehrotra R, Tyagi G, Charak S, Ray B, Kadayaprath G, Chaturvedi H, Mukherjee U, Abrari Aet al., 2018, Biospectroscopic analysis of human breast cancer tissue: probing infrared signatures to comprehend biochemical alterations, JOURNAL OF BIOMOLECULAR STRUCTURE & DYNAMICS, Vol: 36, Pages: 761-766, ISSN: 0739-1102

Journal article

Sahu A, Gera P, Pai V, Dubey A, Tyagi G, Waghmare M, Pagare S, Mahimkar M, Krishna CMet al., 2017, Raman exfoliative cytology for oral precancer diagnosis, JOURNAL OF BIOMEDICAL OPTICS, Vol: 22, ISSN: 1083-3668

Journal article

Tyagi G, Mehrotra R, 2017, DNA ‐Interacting Molecules and Cancer Treatments, Encyclopedia of Physical Organic Chemistry, Publisher: Copyright © 2017 John Wiley & Sons, Inc.

This article discusses the DNA‐interacting molecules and cancer treatments. A crucial step in reproduction is the passage of genetic information from the parent cell to the daughter cell. DNA replication starts with a double‐stranded DNA molecule and produces its two identical copies. The process of transcription commences by binding of an enzyme RNA polymerase (RNA Pol) to the template DNA strand. Noncovalent drug binding can be classified into two categories: DNA groove binders and intercalators. Numerous enzymes are involved in this important cellular event, namely, DNA polymerases, helicases, topoisomerases, primase, telomerase, recombination/repair enzymes, DNA ligase, endonucleases, exonucleases, and DNA‐modifying enzymes (acetylases and methylases). The growth of cancer may be initiated by environmental agents (physical, chemical, radiation, and viruses) and inherited genetic mutations. Cancer immunotherapy exploits this property of immune system to treat cancer. Cancer immunotherapy is categorized into three main categories, that is, cell‐base therapy, cytokine therapy, and antibody‐based therapy.

Book chapter

Hole A, Sahu A, Shaikh R, Tyagi G, Murali Krishna Cet al., 2017, Raman spectroscopic studies on exfoliated cells of oral and cervix, ISSN: 0277-786X

Visual inspection followed by biopsy is the standard procedure for cancer diagnosis. Due to invasive nature of the current diagnostic methods, patients are often non-compliant. Hence, it is necessary to explore less invasive and rapid methods for early detection. Exfoliative cytology is a simple, rapid, and less invasive technique. It is thus well accepted by patients and is suitable for routine applications in population screening programs. Raman spectroscopy (RS) has been increasingly explored for disease diagnosis in the recent past. In vivo RS has previously shown promise in management of both oral and cervix cancers. In vivo applications require on-site instrumentation and stringent experimental conditions. Hence, RS of less invasive samples like exfoliated cells has been explored, as this facilitates collection at multiple screening centers followed by analysis at a centralized facility. In the present study, efficacy of Raman spectroscopy in classification of 15 normal and 29 abnormal oral exfoliated cells specimens and 28 normal and 38 abnormal cervix specimens were explored. Spectra were acquired by Raman microprobe (HE 785, Horiba-Jobin-Yvon, France) from several areas to span the pellet. Spectral acquisition parameters were: microscopic objective: 40X, power: 40 mW, acquisition time: 15 s and average: 3. PCA and PC-LDA of pre-processed spectra was carried out on a 4-model system of normal and tumor of both cervix and oral specimens. Leave-one-out-cross-validation findings indicate ∼73 % correct classification. Findings suggest RS of exfoliated cells may serve as a patient-friendly, non-invasive, rapid and objective method for management of cervix and oral cancers.

Conference paper

Agarwal S, Tyagi G, Chadha D, Mehrotra Ret al., 2017, Structural-conformational aspects of tRNA complexation with chloroethyl nitrosourea derivatives: A molecular modeling and spectroscopic investigation, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY, Vol: 166, Pages: 1-11, ISSN: 1011-1344

Journal article

, 2016, Encyclopedia of Physical Organic Chemistry, 5 Volume Set

Journal article

Tyagi G, Agarwal S, Mehrotra R, 2015, tRNA binding with anti-cancer alkaloids-nature of interaction and comparison with DNA-alkaloids adducts, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY, Vol: 142, Pages: 250-256, ISSN: 1011-1344

Journal article

Tyagi G, Jangir DK, Singh P, Mehrotra R, Ganesan R, Gopal ESRet al., 2014, Rapid determination of main constituents of packed juices by reverse phase-high performance liquid chromatography: an insight in to commercial fruit drinks, JOURNAL OF FOOD SCIENCE AND TECHNOLOGY-MYSORE, Vol: 51, Pages: 476-484, ISSN: 0022-1155

Journal article

Tyagi G, Pradhan S, Srivastava T, Mehrotra Ret al., 2014, Nucleic acid binding properties of allicin: Spectroscopic analysis and estimation of anti-tumor potential, BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS, Vol: 1840, Pages: 350-356, ISSN: 0304-4165

Journal article

Charak S, Shandilya M, Tyagi G, Mehrotra Ret al., 2012, Spectroscopic and molecular docking studies on chlorambucil interaction with DNA, INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES, Vol: 51, Pages: 406-411, ISSN: 0141-8130

Journal article

Tyagi G, Charak S, Mehrotra R, 2012, Binding of an indole alkaloid, vinblastine to double stranded DNA: A spectroscopic insight in to nature and strength of interaction, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY, Vol: 108, Pages: 48-52, ISSN: 1011-1344

Journal article

Raghav R, Yadav N, Tyagi G, Jangir DK, Mehrotra R, Ganesan R, Rajagopal ESet al., 2012, Degradation studies of organic acids in commercially packed fruit juices: A reverse phase high performance liquid chromatographic approach, INTERNATIONAL JOURNAL OF FOOD ENGINEERING, Vol: 8, ISSN: 2194-5764

Journal article

Charak S, Jangir DK, Tyagi G, Mehrotra Ret al., 2011, Interaction studies of Epirubicin with DNA using spectroscopic techniques, JOURNAL OF MOLECULAR STRUCTURE, Vol: 1000, Pages: 150-154, ISSN: 0022-2860

Journal article

Mehrotra R, Tyagi G, Jangir DK, Dawar R, Gupta Net al., 2010, Analysis of ovarian tumor pathology by Fourier Transform Infrared Spectroscopy, JOURNAL OF OVARIAN RESEARCH, Vol: 3

Journal article

Tyagi G, Jangir DK, Singh P, Mehrotra Ret al., 2010, DNA Interaction Studies of an Anticancer Plant Alkaloid, Vincristine, Using Fourier Transform Infrared Spectroscopy, DNA AND CELL BIOLOGY, Vol: 29, Pages: 693-699, ISSN: 1044-5498

Journal article

Jangir DK, Tyagi G, Mehrotra R, Kundu Set al., 2010, Carboplatin interaction with calf-thymus DNA: A FTIR spectroscopic approach, JOURNAL OF MOLECULAR STRUCTURE, Vol: 969, Pages: 126-129, ISSN: 0022-2860

Journal article

Singh P, Tyagi G, Mehrotra R, Bakhshi AKet al., 2009, Thermal stability studies of 5-fluorouracil using diffuse reflectance infrared spectroscopy, DRUG TESTING AND ANALYSIS, Vol: 1, Pages: 240-244, ISSN: 1942-7603

Journal article

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