arXiv subjects

H. Srinivasan

Publications and source records attributed to H. Srinivasan.

12 recordsLinked to original sources

arXiv2025

Dynamics of Choline Chloride based Deep Eutectic Solvents: Neutron Scattering Study

In this study, we investigate the microscopic diffusion dynamics of choline chloride (ChCl) based deep eutectic solvents (DESs) to elucidate the influence of hydrogen bond donor (HBD) identity on the mobility of cholinium ions. The DES systems examined include ethaline, glyceline, and reline, comprising ChCl mixed with ethylene glycol, glycerol, and urea, respectively, in a 1:2 molar ratio. Quasielastic neutron scattering experiments was used to probe the self-diffusion of cholinium ions at molecular length and time scales. The dynamics were modelled as a combination of jump diffusion of the molecular center of mass and localized translation within transient hydrogen-bond cages. Among the three systems, ethaline consistently exhibited the highest cholinium self-diffusion coefficients across all investigated temperatures, attributed to shorter residence times and more frequent molecular jumps. In contrast, reline displayed longer residence times with significantly larger jump length, leading to a temperature-dependent dynamical crossover: While reline and glyceline exhibited comparable diffusivities at low temperatures, reline surpassed glyceline above 330 K. These findings highlight the crucial role of HBD identity in modulating microscopic diffusion and provide valuable molecular-level insights for the rational design of DESs for targeted applications.

cond-mat.soft↗

arXiv2025

Non-universal Impact of Cholesterol on Ionic Liquid-Membrane Interactions

Understanding the role of cholesterol in ionic liquid (IL)-membrane interactions is essential for advancing biomedical applications of ILs, including the development of innovative antimicrobial agents. In this study, we explore the intricate and multifaceted role of cholesterol in modulating IL-membrane interactions, employing a comprehensive suite of biophysical techniques. We systematically examine how IL alkyl chain length and membrane physical state influence the impact of cholesterol on IL-lipid membrane interaction. The incorporation of ILs is shown to increase the area per lipid in both pristine dipalmitoylphosphatidylcholine (DPPC) and DPPC-cholesterol membranes. Cholesterol modulates the impact of ILs on lipid conformation, membrane viscoelasticity, and phase behavior. Small-angle neutron scattering and dynamic light scattering measurements reveal that cholesterol mitigates IL-induced structural perturbations in vesicles. Our isothermal titration calorimetry measurements reveal that the presence of cholesterol significantly weakens the binding of ILs to membranes. Intriguingly, despite this reduced binding affinity, cholesterol-containing membranes demonstrate enhanced permeabilization. This counterintuitive effect is attributed to cholesterol's ordering of lipid membranes, which increases susceptibility to stress and defects. Our results underscore the complex and non-universal interplay between lipid composition, IL alkyl chain length, and membrane phase state. These insights provide a deeper understanding of cholesterol's role in IL-membrane interactions, paving the way for the design of advanced applications of ILs in antimicrobial therapy and drug delivery.

cond-mat.soft↗

arXiv2025

Fickian Yet non-Gaussian Diffusion in Complex Molecular Fluids via a non-local diffusion framework

Fickian yet non-Gaussian diffusion (FnGD) has gained popularity in the recent times owing to it's ubiquity in a variety of complex fluids. However, whether FnGD can be observed experimentally in molecular fuids is still obscure with very little study in real systems. In this letter, we show existence of FnGD in molecular fluids based on compelling evidence from incoherent quasielastic neutron scattering (IQENS). Using a cage-jump diffsion model, we show that while the approach to Fickianity is exponentially fast, the Gaussianity is restored at a much slower algebraic rate. We propose a non-local diffusion (NLD) model to describe a d-dimensional jump-diffusion in FnGD regime and show their universal applicability in such systems. This study establishes that cage-jump diffusion process inevitably lead to FnGD and provides the framework of NLD models to explore such diffusion phenomena in any arbitrary dimensions.

cond-mat.soft↗

arXiv2025

Quantifying Ionic Liquid Affinity and Its Effect on Phospholipid Membrane Structure and Dynamics

In this study, we examine the impact of imidazolium based ILs on the viscoelasticity, dynamics, and phase behavior of two model membrane systems, (i) lipid monolayers and (ii) unilamellar vesicles composed of dipalmitoylphosphatidylcholine (DPPC). Our findings demonstrate that both ILs induce significant disorder in lipid membranes by altering the area per lipid molecule, thereby modulating their viscoelastic properties. ILs with longer alkyl chains show stronger interactions with membranes, causing more pronounced disorder. Fourier transform infrared spectroscopy indicates that IL incorporation shifts the membrane main phase transition to lower temperatures and introduces gauche defects, signifying increased structural disorder. This effect is amplified with longer alkyl chains and higher IL concentrations. Quasielastic neutron scattering studies highlight that ILs markedly enhance the lateral diffusion of lipids within the membrane leaflet, with the extent of enhancement determined by the membrane physical state, IL concentration, and alkyl chain length. The most pronounced acceleration in lateral diffusion occurs in ordered membrane phase with higher concentrations of the longer chain IL. Molecular dynamics simulations corroborate these experimental findings, showing that longer chain ILs extensively disrupt lipid organization, introduce more gauche defects, increase the area per lipid, and consequently enhance lateral diffusion. This increase in lipid fluidity and permeability provides a mechanistic basis for the observed higher toxicity associated with longer chain ILs.

cond-mat.soft↗

arXiv2025

Role of Molecular Structure in Defining the Dynamical Landscape of Deep Eutectic Solvents at Nanoscale

The molecular dynamics of deep eutectic solvents (DESs) are complex, characterized by nanoscale spatial and temporal heterogeneity. Understanding these dynamics is crucial for tailoring transport properties like diffusion, viscosity and ionic conductivity. Molecular diffusion in DESs stems from transient caging and translation jumps, necessitating an understanding of how molecular structure regulates these processes. This study explores the influence of alkyl chain length on the nanoscopic dynamics of alkylamide-lithium perchlorate based DESs using quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations. QENS results show that, despite its shorter chain length and lighter mass, acetamide (ACM) exhibited the lowest mobility among the alkylamides, including propanamide (PRM) and butyramide (BUT). Detailed analysis of QENS data reveals that long-range jump diffusion is fastest in ACM and slowest in BUT, essentially due to their differences in molecular size, mass and also enhanced complexation in longer alkyl chain molecules. However, the localized dynamics follows an unusual trend, where PRM is the fastest and ACM is the slowest. Despite greater flexibility in BUT, the slower caged dynamics impedes its localized motion. These findings highlight the interplay between alkyl chain length and DES dynamics, emphasizing role of molecular structure in governing transport properties.

cond-mat.soft↗

arXiv2024

Structural Reorganizations and Nanodomain Emergence in Lipid Membrane Driven by Ionic Liquids

The exceptional physicochemical properties and versatile biological activities of ionic liquids (ILs) have propelled their potential applications in various industries, including pharmaceuticals and green chemistry. However, their widespread use is limited by concerns over toxicity, particularly due to interactions with cell membranes. This study examines the effects of imidazolium-based ILs on the microscopic structure and phase behavior of a model cell membrane composed of zwitterionic dipalmitoylphosphatidylcholine (DPPC) lipid. Small-angle neutron scattering and dynamic light scattering reveal that the shorter chain IL, 1-hexyl-3-methylimidazolium bromide (HMIM[Br]), induces aggregation of DPPC unilamellar vesicles. In contrast, this aggregation is absent with the longer alkyl chain IL, 1-decyl-3-methylimidazolium bromide (DMIM[Br]). Instead, DMIM[Br] incorporation leads to the formation of distinct IL-poor and IL-rich nanodomains within the DPPC membrane, as evidenced by X-ray reflectivity, differential scanning calorimetry, and molecular dynamics simulation. The less evident nanodomain formation with HMIM[Br] underscores the role of hydrophobic interactions between lipid alkyl tails and ILs. Our findings demonstrate that longer alkyl chains in ILs significantly enhance their propensity to form membrane nanodomains and increase membrane permeability, directly correlating with higher cytotoxicity. This crucial link between nanodomains and toxicity provides valuable insights for designing safer, more environmentally friendly ILs, and promoting their use in biomedical applications and sustainable industrial processes.

cond-mat.soft↗

arXiv2024

Lipid Lateral Diffusion: Mechanisms and Modulators

The lateral diffusion of lipids within membrane is of paramount importance, serving as a central mechanism in numerous physiological processes including cell signaling, membrane trafficking, protein activity regulation, and energy transduction pathways. This review offers a comprehensive overview of lateral lipid diffusion in model biomembrane systems explored through the lens of neutron scattering techniques. We examine diverse models of lateral diffusion and explore the various factors influencing this fundamental process in membrane dynamics. Additionally, we offer a thorough summary of how different membrane-active compounds, including drugs, antioxidants, stimulants, and membrane proteins, affect lipid lateral diffusion. Our analysis unveils the intricate interplay between these additives and membranes, shedding light on their dynamic interactions. We elucidate that this interaction is governed by a complex combination of multiple factors including the physical state and charge of the membrane, the concentration of additives, the molecular architecture of the compounds, and their spatial distribution within the membrane. In conclusion, we briefly discuss the future directions and areas requiring further investigation in the realm of lateral lipid diffusion, highlighting the need to study more realistic membrane systems.

cond-mat.soft↗

arXiv2024

The Physics of Antimicrobial Activity of Ionic Liquids

The bactericidal potency of ionic liquids (ILs) is well-established, yet their precise mechanism of action remains elusive. Here, we show evidence that the bactericidal action of ILs primarily involves permeabilizing the bacterial cell membrane. Our findings reveal that ILs exert their effects by directly interacting with the lipid bilayer and enhancing the membrane dynamics. Lateral lipid diffusion is accelerated which in turn augments membrane permeability, ultimately leading to bacterial death. Furthermore, our results establish a significant connection: an increase in the alkyl chain length of ILs correlates with a notable enhancement in both lipid lateral diffusion and antimicrobial potency. This underscores a compelling correlation between membrane dynamics and antimicrobial effectiveness, providing valuable insights for the rational design and optimization of IL-based antimicrobial agents in healthcare applications.

cond-mat.soft↗

arXiv2024

Nature of Sub-diffusion Crossover in Molecular and Polymeric Glass-Formers

A crossover from a non-Gaussian to Gaussian sub-diffusion has been observed ubiquitously in various polymeric/molecular glass-formers. We have developed a framework which generalizes the fractional Brownian motion (fBm) model to incorporate non-Gaussian features by introducing a jump kernel. We illustrate that the non-Gaussian fBm (nGfBm) model accurately characterizes the sub-diffusion crossover. From the solutions of the nGfBm model, we gain insights into the nature of van-Hove self-correlation in non-Gaussian subdiffusive regime, which are found to exhibit exponential tails, providing first such experimental evidence in molecular and polymeric glass-formers. The results of the model are substantiated using incoherent quasielastic neutron scattering on glass-forming deep eutectic solvents.

cond-mat.soft↗

arXiv2020

Caffeine Modulates the Dynamics of DODAB Membranes: Role of the Physical State of the Bilayer

Caffeine (1,3,7-trimethylxanthine), an ingredient of coffee, is used worldwide as a psychostimulant, antioxidant, and adjuvant analgesic. To gain insights into the action mechanism of caffeine, we report on its effects on the phase behaviour and microscopic dynamics of a dioctadecyldimethylammonium bromide (DODAB) lipid membrane, as studied quasielastic neutron scattering (QENS). Tracking the elastic scattering intensity as a function of temperature showed that caffeine does not alter the phase behaviour of the DODAB membrane and that transition temperatures remain almost unaltered. However, QENS measurements revealed caffeine significantly modulates the microscopic dynamics of the lipids in the system, and that the effects depend on the structural arrangement of the lipids in the membrane. In the coagel phase, caffeine acts as a plasticizing agent which enhances the membrane dynamics. However, in the fluid phase the opposite effect is observed; caffeine behaves like a stiffening agent, restricting the lipid dynamics. Further analysis of the QENS data indicates that in the fluid phase, caffeine restricts both lateral and internal motions of the lipids in the membrane. The present study illustrates how caffeine regulates the fluidity of the membrane by modulating the dynamics of constituent lipids depending on the physical state of the bilayer.

cond-mat.soft↗

arXiv2020

Solvation and Transport of Lithium Ions in Deep Eutectic Solvents

Lithium based deep eutectic solvents (DESs) are excellent candidates for eco-friendly electrolytes in lithium ion batteries. While some of these DES have shown promising results, a clear mechanism of lithium ion transport in DESs is not yet established. This work reports the study on the solvation and transport of lithium in a DES made from lithium perchlorate and acetamide using Molecular Dynamics (MD) simulation and neutron scattering techniques. Based on hydrogen bonding (H-bonding) of acetamide with neighbouring molecules/ions, two states are largely prevalent: 1) acetamide molecules which are H-bonded to lithium ions (~ 36 %) and 2) acetamide molecules that are entirely free (~ 58%). Analysing their stochastic dynamics independently, it is observed that the long-range diffusion of the former is significantly slower than the latter one. This is also validated from the neutron scattering experiment on the same DES system. Further, the analysis the lithium dynamics shows that the diffusion of acetamide molecules in the first category is strongly coupled to that of lithium ions. On an average the lithium ions are H-bonded to ~ 3.2 acetamide molecules in their first solvation. These observations are further bolstered through the analysis of the H-bond correlation function between acetamide and lithium ions, which show that ~ 90% of lithium ionic transport is achieved by vehicular motion where the ions diffuse along with its first solvation shell. The findings of this work are an important advancement in understanding solvation and transport of lithium ion in DES.

physics.chem-ph↗

arXiv2019

Transport Mechanism of Acetamide in Deep Eutectic Solvents

Over the last couple of decades, deep eutectic solvents (DESs) have emerged as novel alternatives to ionic liquids that are extensively used in synthesis of innovative materials, metal processing, catalysis, etc. However, their usage is limited, primarily because of the large viscosity and poor conductivity. Therefore, an understanding of the molecular origin of these properties is essential to improve their industrial applicability. Here, we present the report of the nanoscopic diffusion mechanism of acetamide in a DES synthesized with lithium perchlorate as studied using neutron scattering and molecular dynamics (MD) simulation techniques. Although, the acetamide based DES (ADES) has remarkably lower freezing point compared to pure acetamide, the molecular mobility is found to be enormously restricted in the former. MD simulation indicates a diffusion model with two distinct processes, corresponding to, long range jump diffusion and localised diffusion within a restricted volume. This model is validated by analysis of neutron scattering data in both molten acetamide and ADES. The long range diffusion process of acetamide is slower by a factor of three in ADES in comparison with molten acetamide. MD simulation reveals that the long range diffusion in ADES is restricted mainly due to the formation of hydrogen bond mediated complexes between the ionic species of the salt and acetamide molecules. Hence, the origin of higher viscosity observed in ADES can be attributed to the complexation. The complex formation also explains the inhibition of the crystallisation process while cooling and thereby results in depression of the freezing point of ADES.

cond-mat.mtrl-sci↗