Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

&nbsp;

&nbsp;

VIT University

In this study, we report the synthesis and structural characterization of N-arylated ferrocenyl pyrazole [Fc-Pz-(CF3)-C6H5-R] (R = CH3, 1; OCH3 2), where Pz = pyrazole and Fc = ferrocenyl = Fe(η5-C5H5)(η5-C5H4) chromophores with D–π–A–π–D system. The solvatochromic behaviour of compounds 1 and 2 was investigated in various solvents from non-polar to polar. When solvent polarity increases, the charge transfer process produces the more polarized excited state, and consequently, positive solvatochromism was observed. The emission performance of the compounds is weak luminescence in CH3CN solution but becomes high emissive in a mixture of water/CH3CN fraction at (fw) 90%, demonstrating aggregation-induced emission (AIE) characteristics, and the mechanism of AIE has been attributed to restricted intramolecular rotation (RIR) process. The time-resolved fluorescence lifetime studies have been demonstrated in water/CH3CN mixture at 90%, as it shows three relaxation pathways in their fluorescence decay. In addition, density functional theory calculations have been employed to optimize the geometry of the molecules, followed by computation of dipole moment (μ), first hyperpolarizability (β) using various functionals (B3LYP, long-range corrected CAM-B3LYP and LC-BLYP) and frontier molecular orbital levels for understanding the charge transfer, electrochemical and non-linear optical (NLO) properties. The second-order non-linear optical properties were studied by hyper-Rayleigh scattering (HRS) technique using an incident wavelength at 1064 nm. The chromophores exhibited the first hyperpolarizability (βHRS = 38.6 × 10−30 e.s.u. for 1 and βHRS = 116.8 × 10−30 e.s.u. for 2) and were found to be 6.8 times greater than that of the reference material, p-nitroaniline (pNA) (βHRS = 17.1 × 10−30 e.s.u.). Also, compound 2 shows higher NLO effect because the presence of –OCH3 group makes effective charge transfer process by mesomeric effect (+M). © 2021 John Wiley &amp; Sons, Ltd.

World University root node

Department of Chemistry

School of Advanced Sciences

Vellore Campus

Applied Organometallic Chemistry

Aggregation induced emission (AIE)-active N-arylated ferrocenyl pyrazole-based push–pull chromophores: Structural, photophysical, theoretical and effect of substitution on second-order non-linear optical properties

Insights into structure-mechanical property correlations in molecular and multicomponent crystals have recently attracted significant attention owing to their practical applications in the pharmaceutical and specialty fine chemicals manufacturing. In this contribution, we systematically examine the mechanical properties of dimorphic forms, Forms I and II, of a 1:1 caffeine-glutaric acid cocrystal on multiple faces using nanoindentation to fully understand their mechanical anisotropy and mechanical stability under an applied load. The higher hardness, H, and elastic modulus, E, of stable Form II has been rationalized based on its corrugated layers, higher interlayer energy, lower interlayer separation, and presence of more intermolecular interactions in the crystal structure compared to metastable Form I. Our results show that mechanical anisotropy in both polymorphs arises due to the difference in orientation of the same two-dimensional structural features, namely, the number of possible slip systems, and the strength of the intermolecular interactions with respect to the indentation direction. The mechanical properties results suggest that the 1:1 caffeine-glutaric acid cocrystal, metastable form (Form I) could be a suitable candidate with desired tablet performance to that of stable Form II. Overall, it demonstrates that the multiple faces of nanoindentation are critical to determine mechanical anisotropy and structure-mechanical property correlations. Further, the structural-mechanical property correlations aid in the selection of the best solid phase for macroscopic pharmaceutical formulation. © 2020 American Chemical Society.

Crystal Growth and Design

Structural Basis for Mechanical Anisotropy in Polymorphs of a Caffeine-Glutaric Acid Cocrystal

Gold nanoparticle (GNP) interaction with hen egg white lysozyme (Lyz) has been investigated by many groups in order to understand protein mediated aggregation of GNPs and the underlying mechanism of aggregation. In this article, we have studied the interaction of citrate-capped GNPs of 16, 28, 41, and 69 nm sizes with Lyz by the non-destructive label-free second harmonic light scattering (SHLS) technique at physiological pH in phosphate buffer. The surface sensitivity of the nonlinear optical SHLS technique is very high and we have looked at the GNP-Lyz interaction at nanomolar concentrations. We have followed the increase in the SHLS intensity of GNPs as a function of the added concentration of Lyz in small aliquots. The SH intensity profile exhibits saturation behaviour and was fitted with a modified Langmuir adsorption model which yielded the binding constant (Kb), the binding stoichiometry (nsat) at saturation and the free energy change (ΔG) in the adsorption process. The free energy change was further decomposed into changes in the enthalpy (ΔH) and entropy (ΔS) of adsorption by carrying out temperature dependent SHLS measurements in a specially designed cell. The thermodynamic quantities extracted from the measurements show that the binding is exothermic (ΔH &lt; 0) as well as spontaneous (ΔS &gt; 0). We find that the first step in the adsorption of Lyz on the GNP surface is nanoparticle protein corona (NP-PC) formation driven predominantly by electrostatic attraction. In the second step of adsorption, the adsorbed lysozymes on the surface form a bridge between two or more GNPs leading to the latter's aggregation, which is the main reason for the enhancement of the SH scattering signal. Although the interaction between the GNPs and Lyz is driven by strong electrostatic attraction, the thermodynamic quantities reported here indicate that the protein is physisorbed on the nanoparticle surface. We have also demonstrated that SHLS provides a new tool for full thermodynamic characterization of protein adsorption on metal nanoparticles at ultralow concentrations. © 2019 the Owner Societies.

Physical Chemistry Chemical Physics

Thermodynamics of adsorption of lysozyme on gold nanoparticles from second harmonic light scattering

In this article, we have studied the binding of different naturally occurring hemoglobin (Hb) variants on erythrocyte skeletal protein, spectrin surface using the label free nondestructive second harmonic light scattering (SHLS) technique in aqueous buffer. Hemoglobin variants like sickle hemoglobin (HbS) and hemoglobin E (HbE) were chosen as they associate with sickle cell disease and HbEβ-thalassemia, respectively, and their interaction with spectrin is compared with normal adult hemoglobin (HbA). The concentration dependent change in the second harmonic light intensity from nanomolar spectrin solution has been measured after addition of small aliquots of hemoglobins. From the second harmonic titration data, the binding constant is calculated using a modified Langmuir adsorption model of hemoglobin binding to the spectrin surface. Interestingly, it is found that the binding constant for HbE (13.8 × 108 M-1) is 1 order of magnitude higher than that of HbS (1.6 × 108 M-1) or HbA (2.1 × 108 M-1) which indicates higher affinity of HbE for spectrin compared to HbA and HbS. The number of the Hb molecules bound to the spectrin surface was estimated to be of the order of hundred's which is determined for the first time. © 2017 American Chemical Society.

Journal of Physical Chemistry B

Protein-Protein Interaction Probed by Label-free Second Harmonic Light Scattering: Hemoglobin Adsorption on Spectrin Surface as a Case Study

The structural dynamics of two elastically bendable, halogenated N-benzylideneaniline organic crystals were studied using an in situ three-point bending test and Raman spectroscopy. This study reveals the inhomogeneous molecular distribution in the elastic crystal lattice during the bent stage and further validates the known qualitative mechanistic model of elastic bendable crystals. © 2017 The Royal Society of Chemistry.

Chemical Communications

Structural analysis of elastically bent organic crystals using in situ indentation and micro-Raman spectroscopy

We report the binding of the membrane skeletal protein, spectrin with several hemoglobin variants like normal hemoglobin (HbA), sickle hemoglobin (HbS), and hemoglobin E (HbE) by using non-destructive second harmonic light scattering (SHLS) in solution. © OSA 2016.