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Comprehensive Array of Ample Analytical Strategies for Characterization of Nanomaterials
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials I, 2020
Nitesh Dhiman, Amrita Singh, Aditya K. Kar, Mahaveer P. Purohit, Satyakam Patnaik
Many biomolecules such as nucleic acids and proteins are chiral in nature, i.e., they can polarize the incident light beam. The chirality of a biomolecule can be studied optically by using light pulses of opposite circular polarizations and is absorptive in nature. The difference in the absorbance of right and left circularly polarized light is called circular dichroism (CD). Naturally, abundant biomolecules exist in a wide range of stereo-conformers and have their own characteristic intense CD signals in the UV region (200–300 nm). On the other hand, metallic (silver, gold) NPs exhibit strong absorption in the visible range but are achiral with no inherent chiroptical properties. When chiral biomolecules are conjugated to these NPs, biomolecules can impart chirality to the particles and exhibit a plasmon-induced CD signal in the visible spectral region.
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Published in Luis Liz-Marzán, Colloidal Synthesis of Plasmonic Nanometals, 2020
Andrés Guerrero-Martinez, José Lorenzo Alonso-Gómez, Baptiste Auguie, M. Magdalena Cid, Luis M. Liz-Marzán
Going back to the uses of chirality at the nanoscale, many are related with the preparation of materials with optical activity. Circular dichroism (CD), defined as the difference in extinction of left and right circularly polarized light, is one of the most commonly used spectroscopic techniques when studying chirality. The optical activity of chiral systems is thus often measured through the anisotropy factor, also known as g-factor [32, 33]: g=Δεε where ∆ε and ε are the molar circular dichroism and molar extinction, respectively. In this review, we will not only focus on a particular shape and/or spatial ordering of objects, but also on the efficiency of the sample to differentiate between left and right circularly polarized light, comparing the chirality of different example cases by means of their anisotropy factor.
Proteins and proteomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
Circular dichroism is one of the most general and basic tools to study protein folding. Circular dichroism spectroscopy measures the absorption of circularly polarized light. In proteins, structures such as alpha helices and 13-sheets are chiral and thus absorb such light. The absorption of this light acts as a marker of the degree of foldedness of the protein ensemble. This technique can be used to measure equilibrium unfolding of the protein by measuring the change in this absorption as a function of denaturant concentration or temperature. A denaturant melt measures the free energy of unfolding as well as the protein’s m value or denaturant dependence. A temperature melt measures the melting temperature (Tm) of the protein. This type of spectroscopy can also be combined with fast-mixing devices, such as stopped flow, to measure protein-folding kinetics and to generate chevron plots.
A comparative DFT study of structural, electronic, thermodynamic, optical, and magnetic properties of TM (Ir, Pt, and Au) doped in small Tin (Sn5 & Sn6) clusters
Published in Phase Transitions, 2022
Aoly Ur Rahman, Dewan Mohammad Saaduzzaman, Syed Mahedi Hasan, Md. Kabir Uddin Sikder
When the materials absorb left and right circularly polarized light with the existence of the chiral group in any structure, circular dichroism (CD) spectrum is detected. It is a technique used to analyse chirality in molecules through their optical activity about the material whether it is optically active or not. Both the pristine pure Sn5 and Sn6, Sn4-Au-M, Sn5-Au-M, Sn5-Au-S, Sn5-Pt-M, Sn5-Pt-S clusters are optically active and absorb circularly polarized light on both sides (L and R) which is shown in Figure 5(a–c). Among all those cluster, the order of optically activeness is Sn5 > Sn6 > Sn5-Pt-M > Sn5-Pt-S > Sn5-Au-M > Sn4-Au-M > Sn5-Au-S.
Cholesterol-based nonsymmetric dimers comprising phenyl 4-(benzoyloxy)benzoate core: the occurrence of frustrated phases
Published in Liquid Crystals, 2021
Channabasaveshwara V. Yelamaggad, Sachin A. Bhat
Circular dichroism (CD) is realised when the absorption of left- and right-hand circularly polarised light by an optically active (chiral absorbing) media differs. Thus, CD, being an absorption spectroscopic technique, uses circularly polarised light to probe the macroscopic structural aspects of the chiral media, i.e. the analysis of the CD spectrum provides invaluable information of the chiral (helical) structure under investigation. The chiral nematic (N*) phase is a defect-free helical superstructure and hence exhibits the CD phenomenon intrinsically wherein the incident light gets resolved into its two circularly polarised (CP) components, left and right at a given wavelength. In general, the helical twist sense (handedness or helicity), which is either left or right of the N* phase, depends on the chirality (absolute configuration), R and S of the constituent conventional chiral mesogens. However, interestingly, the handedness of the N* phase formed by the cholesterol-based dimers has been reported to be dictated by the parity of the central spacer connecting the two mesogenic segments. To verify this observation, the dimers CPD-3,10, CPD-4,10, CPD-5,10 and CPD-7,10 were chosen where the length and parity of the spacer vary markedly.
DNA-interaction studies of a copper(II) complex containing ceftobiprole drug using molecular modeling and multispectroscopic methods
Published in Journal of Coordination Chemistry, 2018
Nahid Shahabadi, Soraya Moradi Fili
Circular dichroism spectroscopy can be used to study conformational changes of biomolecules [29]. A typical CD spectrum of B-form of DNA exhibits a negative band at 245 nm and a positive peak at 275 nm. The negative peak represents the right-handed helicity of DNA and positive peak is due to the base-pair stacking. Intercalation of molecules into the double helical structure of DNA significantly changes the native CD spectrum of DNA while the molecules having electrostatic and groove binding mode of interaction do not have any remarkable effect on the native CD spectrum of DNA [30]. The effect of [Cu(cef)(phen)Cl2] on the conformation of the secondary structure of ct-DNA was investigated by keeping the concentration of ct-DNA constant (8 × 10−5 M) while varying the drug concentration (ri = [Cu(cef)(phen)Cl2]/[ct-DNA] = 0–0.38). The CD spectrum of ct-DNA in the presence of [Cu(cef)(Phen)Cl2] (Figure 4) showed that both the positive and negative band intensities of the CD spectra of DNA increased. The changes in the CD spectra in the presence of [Cu(cef)(phen)Cl2] show stabilization of the right-handed B form of ct-DNA [31, 32]. This phenomenon may be due to the intercalation of [Cu(cef)(phen)Cl2] through π-π stacking which stabilizes the right-handed B form DNA [33, 34].