Showing papers on "Circular dichroism published in 2020"
TL;DR: The inhibitory mechanisms of ferulic acid against α-amylase and α-glucosidase were investigated by enzyme kinetic analysis, circular dichroism, Fourier-transform infrared spectroscopy, fluorescence quenching and molecular docking to provide a theoretical basis for the designing of novel functional foods with ferulic Acid.
157 citations
TL;DR: Direct CPL detection by a photodiode using a helical one-dimensional structure of lead halide perovskites composed of naphthylethylamine-based chiral organic cations is reported, which largely surpasses the direct detecting CPL devices (<4) using chiral plasmonic metamaterials and organic materials.
Abstract: Detection of circularly polarized light (CPL) has a high potential for development of various optical technologies. Conventional photodetectors require optical polarizers on the device to detect polarized light, and this causes substantial losses of sensitivity and resolution in light detection. Here, we report direct CPL detection by a photodiode using a helical one-dimensional (1D) structure of lead halide perovskites composed of naphthylethylamine-based chiral organic cations. The 1D structure with face-sharing (PbI6)4− octahedral chains whose helicity is largely affected by chiral cations shows intense circular dichroism (CD) signals over 3000 mdeg at 395 nm with the highly anisotropy factor (gCD) of 0.04. This high CD enables photocurrent detection with effective discrimination between left-handed and right-handed CPLs. The CPL detector based on this 1D perovskite achieved the highest polarization discrimination ratio of 25.4, which largely surpasses the direct detecting CPL devices (
120 citations
TL;DR: Tuning the wavelength of CD by modulating the excitonic band structure and switching the CD on and off by inducing a crystalline-structure change can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.
Abstract: The effect of chemical-composition modification on the chiroptical property of chiral organic ammonium cation-containing organic inorganic hybrid perovskite (chiral OIHP) is investigated. Varying the mixing ratio of bromide and iodide anions in S- or R-C6H5CH2(CH3)NH3)2PbI4(1-x)Br4x modifies the band gap of chiral OIHP, leading to a shift of the circular dichroism (CD) signal from 495 to 474 nm. However, it is also found that an abrupt crystalline structure transition occurs, and the CD signal is turned off when iodide-determinant phases are transformed into the bromide-determinant phase. To obtain CD in the wavelength range where the bromide-determinant phase is supposed to exhibit chiroptical activity, that is, <474 nm, S- or R-C12H7CH2(CH3)NH3 with a larger spacer group can be adopted; thus, the CD signal can be further blue-shifted to ∼375 nm. Here, we show that chemical-composition modification of chiral OIHP affects the chiroptical properties of chiral OIHP in two ways: (1) tuning the wavelength of CD by modulating the excitonic band structure and (2) switching the CD on and off by inducing a crystalline-structure change. These properties can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.
119 citations
TL;DR: The induced conformational changes of two proteins throughout the binding of Nano-CUR to HSA and HTF as binary and ternary systems are evaluated by employing the CD technique, while the formation of self-assemblies has been studied through MD simulation.
Abstract: In this study, we have investigated the effects of Nano-curcumin (Nano-CUR) binding on HSA-HTF interactions as binary and ternary systems, which had been done through multiple spectroscopic and MD ...
90 citations
TL;DR: Chiral-optical spectroscopies, such as circular dichroism, are critical in the biomedical, pharmaceutical, and agrochemical industries for revealing structural information about molecules.
Abstract: Chiral-optical spectroscopies, such as circular dichroism, are critical in the biomedical, pharmaceutical, and agrochemical industries for revealing structural information about molecules and deter...
84 citations
TL;DR: The performed study reveals that CHA has the potential to inhibit the activity of α-amylase, thereby representing a novel idea to delay the digestion of starch.
83 citations
TL;DR: The studied stereo metasurface unfolds a new degree of freedom for advanced photonic applications in a quasi-flat optical platform, and the proposed concept of Fano-enhanced circular dichroism opens new venues to explore interesting fundamental phenomena of chiral optics.
Abstract: 2D metasurfaces have emerged as a paradigm-shifting platform for light management with considerable miniaturization and alleviated fabrication challenges than their 3D counterparts. However, the appearance of in-plane mirror symmetry and reduced dimensions impose fundamental restraints to advanced chiroptical responses and reconfiguration capabilities. Here, a new concept of Fano-enhanced circular dichroism by introducing a reconfigurable stereo metasurface, which possesses deformable out-of-plane twists that are readily achieved by a simple nano-kirigami fabrication method, is demonstrated. The stereo height and twisting geometries can be reproducibly controlled, providing a facile and automated fashion to tailor the distinct profiles of Fano resonances under circularly polarized incidence. As a result, a recorded high efficiency of circular dichroism generation per unit sample thickness is achieved with Fano resonances in opposite lineshapes. Leveraging this feature, large-range reconfiguration of circular dichroism at optical wavelengths is demonstrated through reversible compression of the stereo metasurfaces with a fiber tip. The studied stereo metasurface unfolds a new degree of freedom for advanced photonic applications in a quasi-flat optical platform, and the proposed concept of Fano-enhanced circular dichroism opens new venues to explore interesting fundamental phenomena of chiral optics.
76 citations
TL;DR: It is concluded that (R)- and (S)-MBAPbBr3 single crystals not only show the notable CD signals, but also exhibit the outstanding CPL characteristics with short PL decay lifetime.
Abstract: Motivated by the chirality research of the hybrid halide perovskite, we reported the controllable growth of single crystals of (R)-, (S)-, and (R,S)-C6H5CH(CH3)NH3 (MBA)-based lead (Pb) halide perovskites. The crystal structures were redetermined and further refined to clarify the previously ambiguous crystal structure problems. We further investigated the chiral optical properties of these single crystals including nonlinear optical (NLO) properties and photoluminescence (PL) properties. The as-fabricated (R)- and (S)-MBAPbBr3 single crystals not only show notable circular dichroism (CD) signals in the absorption spectra but also exhibit obvious circularly polarized luminescence (CPL) characteristics. The available chiral hybrid perovskite single crystals open up the possibility to study these intrinsic chirality properties for optoelectronic applications.
75 citations
TL;DR: An efficient and straightforward approach is presented to achieve early examples of highly luminescent chiral systems ( P5NN and P5BN) and an interesting thermochromic shift of the emission over a wide range of temperature is afforded.
Abstract: Enantiopure molecules based on macrocyclic architecture are unique for applications in enantioselective host-guest recognition, chiral sensing and asymmetric catalysis. Taking advantage of the chiral transfer from the intrinsically planar chirality of pillar[5]arenes, we herein present an efficient and straightforward approach to achieve early examples of highly luminescent chiral systems (P5NN and P5BN). The optical resolution of their enantiomers has been carried out via preparative chiral HPLC, which was ascribed to the molecular functionalization of pillar[5]arenes with π-conjugated, sterically bulky triarylamine (Ar3 N) as an electron donor and triarylborane (Ar3 B) as an acceptor. This crucial design enabled investigations of the chiroptical properties, including circular dichroism (CD) and circularly polarized luminescence (CPL) in the solid state. The intramolecular charge transfer (ICT) nature in P5BN afforded an interesting thermochromic shift of the emission over a wide temperature range.
68 citations
TL;DR: It is suggested that active flavonoids could bind to the active center of XO, prevent the entrance of substrate, and induce the rearrangement and conformation change of its secondary structures, ultimately resulting in the significant inhibition effect.
67 citations
TL;DR: For the first time, a standard procedure is established for the integrated molar chiral sensing with high sensitivity of CD spectrum and molar concentration over an individual metasurface with high sensitivities.
Abstract: Circular dichroism (CD) spectroscopy is conventionally utilized for the enantiomer-specific analysis of chiral samples, which is of great significance in academia and industry. Recently, metasurfaces have been introduced for enhancing the sensitivity of CD spectroscopy. However, the obtained CD spectrum alone cannot provide the enantiomer composition of a chiral sample. It should be normalized by the molar concentration of chiral molecules, which is usually measured on a different platform. Here, for the first time we demonstrate the integrated acquisition of CD spectrum and molar concentration over an individual metasurface with high sensitivities. High-Q resonances are supported on the metasurface, governed by bound states in the continuum. The generated superchiral field enables a 59-times enhancement of CD signal. Meanwhile, the refractive index-based detection of molar concentration achieves a large figure-of-merit of 80.6. Accordingly, a standard procedure is established for the integrated molar chiral sensing with high sensitivity.
TL;DR: The synthesis of a new perylene-diimide-based helical nanoribbon, which exhibits the largest molar electronic circular dichroism in the visible range of any molecule, and implicates the configuration of the double-[6]helicene within the larger nanorIBbon as the source of the observed chiroptical amplification.
Abstract: We report the synthesis of a new perylene-diimide-based helical nanoribbon, which exhibits the largest molar electronic circular dichroism in the visible range of any molecule. This nanoribbon also displays a substantial increase in molar circular dichroism relative to a smaller helical analogue, even though they share a similar structure: both nanoribbons incorporate two conformationally dynamic double-[4]helicene termini and a rigid [6]helicene-based core within their helical superstructures. Using DFT and TDDFT calculations, we find that the double-[4]helicenes within both nanoribbons orient similarly in solution; as such, conformational differences do not account for the disparities in circular dichroism. Instead, our results implicate the configuration of the double-[6]helicene within the larger nanoribbon as the source of the observed chiroptical amplification.
TL;DR: The crystallization induced helical arrangement of (R/S-MBA)4Cu4I4 clusters and their largely distorted polynuclear configuration demonstrate new platform for the study of chiral-related properties.
Abstract: Circularly polarized luminescent (CPL) materials are promising in applications such as 3D displays and quantum communication. Hybrid organic-inorganic copper(I) iodides have been rapidly developed due to their intense photoluminescence and structural diversity; nevertheless, the reported Cu-I clusters rarely show CPL activities. In this study, we introduced chiral organic molecules R/S-methylbenzylammonium (R/S-MBA) into Cu-I inorganic skeletons to achieve chiral tetranuclear (R/S-MBA)4Cu4I4 clusters with intense orange luminescence and CPL activity at room temperature. These enantiomeric (R/S-MBA)4Cu4I4 clusters show oppositely signed circular dichroism (CD) signals, which agree well with their simulated electronic CD spectra. The crystallization-induced helical arrangement of (R/S-MBA)4Cu4I4 clusters and their largely distorted polynuclear configuration demonstrate a new platform for the study of chiral-related properties.
TL;DR: New chiroptical phenomena have been observed, such as enhanced circular dichroism of biopolymers (protein fibrils, nucleic acids), plasmonic and resonance chirality-transfer ROA experiments, and some of them are not yet understood or attributed to instrumental artifacts so far.
Abstract: Chiroptical spectroscopy exploring the interaction of matter with polarized light provides many tools for molecular structure and interaction studies. Here, some recent discoveries are reviewed, primarily in the field of vibrational optical activity. Technological advances results in the development of more sensitive vibrational circular dichroism (VCD), Raman optical activity (ROA) or circular polarized luminescence (CPL) spectrometers. Significant contributions to the field also come from the light scattering and electronic structure theories, and their implementation in computer systems. Finally, new chiroptical phenomena have been observed, such as enhanced circular dichroism of biopolymers (protein fibrils, nucleic acids), plasmonic and resonance chirality-transfer ROA experiments. Some of them are not yet understood or attributed to instrumental artifacts so far. Nevertheless, these unknown territories also indicate the vast potential of the chiroptical spectroscopy, and their investigation is even more challenging.
TL;DR: Interactions between β-lactoglobulin and ferulic acid were investigated at ambient temperature in relation to the dimer and monomer forms of the protein at pH 7.3 and 2.4, suggesting molecular interactions do occur in both the monomer and dimer forms.
TL;DR: Light is shed on a new interaction model beyond the protein corona, indicating a possible biological identity of USNPs, which was quite different from the conventional model of protein coronas.
Abstract: Nanoparticles (NPs) will inevitably interact with proteins and form protein coronas once they are exposed to biological fluids. This conventional model for nano-bio interactions has been used for over twenty years. Growing numbers of new nanomaterials are emerging every year. Among them, noble metal nanoclusters (NMNCs) are new types of fluorescent nanomaterials with considerable advantages in biomedical applications. Compared with NPs (typically >10 nm) like Au NPs, carbon nanotubes, etc., NMNCs have ultrasmall sizes (∼2 nm), so when NMNCs are exposed to biological milieu, will they form protein coronas like NPs? Due to a lack of characterization techniques for ultrasmall nanoparticles (USNPs), to date, studies on the binding stoichiometries of USNPs to proteins have been heavily hampered. To address this challenge, we combined the characteristics of various methods and selected human serum albumin (HSA) and transferrin (Trf) as model proteins to study their interactions with dihydrolipoic acid (DHLA) protected gold nanoclusters (DHLA-AuNCs). Steady-state fluorescence, transient fluorescence spectroscopy and isothermal titration calorimetry (ITC) were used to study the thermodynamic parameters (K, ΔH, ΔS, ΔG) and interaction mechanisms. The results showed that the intrinsic fluorescence of both proteins was quenched by DHLA-AuNCs, and the quenching process of HSA was an endothermic dynamic process. In contrast, the quenching process of Trf was an exothermic static process. The combination of ITC, agarose gel electrophoresis (AGE) and zeta potential showed that one HSA could bind 8 ± 1 DHLA-AuNCs and one Trf could bind 7 ± 2 DHLA-AuNCs, which was quite different from the conventional model of protein coronas. Based on these findings, the "protein complex" was termed for proteins upon binding with USNPs. Dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) showed that DHLA-AuNCs could induce the agglomeration of proteins. Circular dichroism (CD) and synchronous fluorescence spectroscopy showed that DHLA-AuNCs had a very minor effect on the secondary structures of HSA and Trf, which demonstrated the good biocompatibility of DHLA-AuNCs at the molecular scale. This work has shed light on a new interaction model beyond the protein corona, indicating a possible biological identity of USNPs.
TL;DR: Results indicate that closely packed and helically arranged PNCs on silica nanohelices result in an increase of the optically active properties in the film state.
Abstract: Perovskite nanocrystals (PNCs) exhibit excellent absorption and luminescent properties. Inorganic silica right (or left) handed nanohelices are used as chiral templates to induce optically active p...
TL;DR: In this paper, a cavity composed of two parallel arrays of helicity-preserving silicon disks is proposed to enhance the dominant handedness of chiral molecules by circular dichroism (CD), the normalized difference between their optical response to incident left and right-handed circularly polarized light.
Abstract: Researchers routinely sense molecules by their infrared vibrational "fingerprint" absorption resonances. In addition, the dominant handedness of chiral molecules can be detected by circular dichroism (CD), the normalized difference between their optical response to incident left- and right- handed circularly polarized light. Here, we introduce a cavity composed of two parallel arrays of helicity-preserving silicon disks that allows one to enhance the CD signal by more than 2 orders of magnitude for a given molecule concentration and given thickness of the cell containing the molecules. The underlying principle is first-order diffraction into helicity-preserving modes with large transverse momentum and long lifetimes. In sharp contrast, in a conventional Fabry-Perot cavity, each reflection flips the handedness of light, leading to large intensity enhancements inside the cavity, yet to smaller CD signals than without the cavity.
TL;DR: Complexation of achiral pillar[5]arenes with chiral amines induced strong circular dichroism (CD) signals that allowed for the unprecedented simultaneous enantiomeric and structural differentiation of α-amino esters with homologous molecular hosts.
TL;DR: It is shown that chiral plasmonic nanocrystals can enable chiral surface growth based on the generation of energetic (hot) electrons, and the proposed chiral-growth mechanism for the transformation of plAsmonic colloids is fundamentally different to the traditional schemes of chiral photochemistry at the molecular level.
Abstract: The realization of chiral photochemical reactions at the molecular level has proven to be a challenging task, with invariably low efficiencies originating from very small optical circular dichroism...
TL;DR: Molecular docking and simulation studies confirm that catechin binds at the central cavity of β-Lg with high affinity (~105 M−1) and hydrophobic interactions play significant role in the formation of a stable β- Lg-catechin complex.
Abstract: Polyphenols has attained pronounced attention due to their beneficial values of health and found to prevent several chronic diseases. Here, we elucidated binding mechanism between frequently consumed polyphenol "tea catechin" and milk protein bovine beta-lactoglobulin (β-Lg). We investigated the conformational changes of β-Lg due to interaction with catechin using spectroscopic and in silico studies. Fluorescence quenching data (Stern-Volmer quenching constant) revealed that β-Lg interacted with catechin via dynamic quenching. Thermodynamic data revealed that the interaction between β-Lg and catechin is endothermic and spontaneously interacted mainly through hydrophobic interactions. The UV-Vis absorption and far-UV circular dichroism (CD) spectroscopy exhibited that the tertiary as well as secondary structure of β-Lg distorted after interaction with catechin. Molecular docking and simulation studies also confirm that catechin binds at the central cavity of β-Lg with high affinity (~105 M-1) and hydrophobic interactions play significant role in the formation of a stable β-Lg-catechin complex.
TL;DR: The experimental results from fluorescence spectroscopy showed that the changes in pepsin's tertiary structure were caused by NYS binding, and NYS could be considered as an inhibitor with adverse effects on pepingin structure and function.
TL;DR: It is concluded that it is not only the chemistry of the amino acid ligand that affects both CD and PL but also the exact geometry of binding that modifies these properties, potentially enabling the design of chiral semiconductor QDs for chiroptic applications.
Abstract: Ligand-induced chirality in semiconducting nanocrystals has been the subject of extensive study in the past few years and shows potential applications in optics and biology. Yet, the origin of the chiroptical effect in semiconductor nanoparticles is still not fully understood. Here, we examine the effect of the interaction with amino acids on both the fluorescence and the optical activity of chiral semiconductor quantum dots (QDs). A significant fluorescence enhancement is observed for l/d-Cys-CdTe QDs upon interaction with all the tested amino acids, indicating suppression of nonradiative pathways as well as the passivation of surface trap sites brought via the interaction of the amino group with the CdTe QDs' surface. Heterochiral amino acids are shown to weaken the circular dichroism (CD) signal, which may be attributed to a different binding configuration of cysteine molecules on the QDs' surface. Furthermore, a red shift of both CD and fluorescence signals in l/d-Cys-CdTe QDs is only observed upon adding cysteine, while other tested amino acids do not exhibit such an effect. We speculate that the thiol group induces orbital hybridization of the highest occupied molecular orbital (HOMOs) of cysteine and the valence band of CdTe QDs, leading to the decrease of the energy band gap and a concomitant red shift of CD and fluorescence spectra. This is further verified by density functional theory calculations. Both the experimental and theoretical findings indicate that the addition of ligands that do not "directly" interact with the valence band (VB) of the QD (noncysteine moieties) changes the QD photophysical properties, as it probably modifies the way cysteine is bound to the surface. Hence, we conclude that it is not only the chemistry of the amino acid ligand that affects both CD and PL but also the exact geometry of binding that modifies these properties. Understanding the relationship between the QD's surface and chiral amino acid thus provides an additional perspective on the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, potentially enabling us to optimize the design of chiral semiconductor QDs for chiroptic applications.
TL;DR: It is experimentally demonstrated that suitably self-assembled achiral plasmonic nanostructures produce a high degree of enhancement in the optical dichroism observed from chiral molecules placed in their vicinity, supporting potential applications in ultrasensitive analysis.
Abstract: Plasmonically enhanced optical dichroism has attracted substantial interest for its application in optical sensing, where the interplay between chirality emanating from both molecules and plasmon-supporting structures has been regarded as a critical ingredient. Here, we experimentally demonstrate that suitably self-assembled achiral plasmonic nanostructures produce a high degree of enhancement in the optical dichroism observed from chiral molecules placed in their vicinity. Specifically, we identify a near-field enhancement associated with plasmonic hotpots as the mechanism enabling our observation of visible-NIR circular dichroism emanating from small amounts of chiral molecules. Our structures consist of linear arrays of gold nanorods obtained by introducing chiral anionic surfactants, such as modified bile salts, which lead to selective destabilization of a cetyltrimethylammonium bromide coating layer on Au nanorods, thereby promoting a tip-to-tip oriented assembly. The proposed mechanism of plasmonically-enhanced circular dichroism is supported by deriving a simple, yet general theoretical formalism that confirms the observed results, revealing the role of optical hotspots at the gaps of linear tip-to-tip nanorod assemblies as the origin of enhancement in the dichroism from chiral molecules. Importantly, it is the refractive rather than the absorption-mediated chiral response of the molecules that produces dichroism in the visible-NIR plasmonic regime, far from their UV absorption resonances. The observed self-assembly mechanism suggests that chiral analytes not directly interacting with the nanorod surfaces, but just able to induce tip-to-tip aggregation, can be revealed by a CD signature in the plasmonic region, thereby supporting potential applications in ultrasensitive analysis.
TL;DR: The blood de-staining, gelatin hydrolysis, silver recovery and deproteinization of crab shells established the biotechnological potential of the enzyme, suggesting stability and spontaneity of the reaction.
TL;DR: The results suggest that the chiroptical signatures and photoluminescence in these cluster systems cannot be solely attributed to any one of the structural components, i.e., the metal core or the protecting metal-ligand oligomeric units, but rather to their interaction, and that the ligand shell plays a crucial role.
Abstract: We probe the origin of photoluminescence of an atomically precise noble metal cluster, Ag24Au1(DMBT)18 (DMBT = 2,4-dimethylbenzenethiolate), and the origin of chirality in its chirally functionalized derivatives, Ag24Au1(R/S-BINAS)x(DMBT)18-2x, with x = 1-7 (R/S-BINAS = R/S-1,1'-[binaphthalene]-2,2'-dithiol), using chiroptical spectroscopic measurements and density functional theory (DFT) calculations. Combination of chiroptical and luminescence spectroscopies to understand the nature of electronic transitions has not been applied to such molecule-like metal clusters. In order to impart chirality to the achiral Ag24Au1(DMBT)18 cluster, the chiral ligand, R/S-BINAS, was incorporated into it. A series of clusters, Ag24Au1(R/S-BINAS)x(DMBT)18-2x, with x = 1-7, were synthesized. We demonstrate that the low-energy electronic transitions undergo an unexpected achiral to chiral and back to achiral transition from pure Ag24Au1(DMBT)18 to Ag24Au1(R/S-BINAS)x(DMBT)18-2x, by increasing the number of BINAS ligands. The UV/vis, luminescence, circular dichroism, and circularly polarized luminescence spectroscopic measurements, in conjunction with DFT calculations, suggest that the photoluminescence in Ag24Au1(DMBT)18 and its chirally functionalized derivatives originates from the transitions involving the whole Ag24Au1S18 framework and not merely from the icosahedral Ag12Au1 core. These results suggest that the chiroptical signatures and photoluminescence in these cluster systems cannot be solely attributed to any one of the structural components, that is, the metal core or the protecting metal-ligand oligomeric units, but rather to their interaction and that the ligand shell plays a crucial role. Our work demonstrates that chiroptical spectroscopic techniques such as circular dichroism and circularly polarized luminescence represent useful tools to understand the nature of electronic transitions in ligand-protected metal clusters and that this approach can be utilized for gaining deeper insights into the structure-property relationships of the electronic transitions of such molecule-like clusters.
TL;DR: Gas-phase circular dichroism spectra of DNA oligonucleotides are reported based on detection of photodetached electrons rather than transmitted light, allowing the DNA helical topology to be assigned.
Abstract: DNA and proteins are chiral: Their three-dimensional structures cannot be superimposed with their mirror images. Circular dichroism spectroscopy is widely used to characterize chiral compounds, but data interpretation is difficult in the case of mixtures. We recorded the electronic circular dichroism spectra of DNA helices separated in a mass spectrometer. We studied guanine-rich strands having various secondary structures, electrosprayed them as negative ions, irradiated them with an ultraviolet nanosecond optical parametric oscillator laser, and measured the difference in electron photodetachment efficiency between left and right circularly polarized light. The reconstructed circular dichroism ion spectra resembled those of their solution-phase counterparts, thereby allowing us to assign the DNA helical topology. The ability to measure circular dichroism directly on biomolecular ions expands the capabilities of mass spectrometry for structural analysis.
TL;DR: The main goal of the research was aggregation/fibrillation of HSA, the study of the physicochemical properties of formed amyloid fibrils using thioflavin T (ThT) and the analysis of ligand binding to aggregated/ fibrillated albumin in the presence of dansyl-l-glutamine, phenylbutazone and ketoprofen.
Abstract: Human serum albumin (HSA) is a protein that transports neutral and acid ligands in the organism. Depending on the environment's pH conditions, HSA can take one of the five isomeric forms that change its conformation. HSA can form aggregates resembling those in vitro formed from amyloid at physiological pH (neutral and acidic). Not surprisingly, the main goal of the research was aggregation/fibrillation of HSA, the study of the physicochemical properties of formed amyloid fibrils using thioflavin T (ThT) and the analysis of ligand binding to aggregated/fibrillated albumin in the presence of dansyl-l-glutamine (dGlu), dansyl-l-proline (dPro), phenylbutazone (Phb) and ketoprofen (Ket). Solutions of human serum albumin, both non-modified and modified, were examined with the use of fluorescence, absorption and circular dichroism (CD) spectroscopy. The experiments conducted allowed observation of changes in the structure of incubated HSA (HSAINC) in relation to nonmodified HSA (HSAFR). The formed aggregates/fibrillation differed in structure from HSA monomers and dimers. Based on CD spectroscopy, previously absent βstructural constructs have been registered. Whereas, using fluorescence spectroscopy, the association constants differing for fresh and incubated HSA solutions in the presence of dansyl-amino acids and markers for binding sites were calculated and allowed observation of the conformational changes in HSA molecule.
TL;DR: In this paper, an ultrathin graphene metascreen that possesses dispersive optical activity in the early terahertz spectrum is presented. And the authors show via full-wave simulations that the dichroic metasreen supports perfect linear-to-circular polarization conversion (circular dichroism) in two adjacent tera-hertz frequency bands.
Abstract: We present an ultrathin graphene metascreen that possesses dispersive optical activity in the early terahertz spectrum. The metascreen design consists of periodically etched L-shaped voids on a graphene substrate backed by a conductive plane. The specific unit-cell design is based on chirality and leads to highly asymmetric radiations from the plasmon-polariton surface currents, leading to linear and circular dichroism. Hence the incident linearly or circularly polarized electric fields are effectively absorbed by the metasurface in different proportions. Consequently, the metasurface assumes half- and quarter-wave-plate behaviors in different parts of the reflected optical spectrum. In particular, we show via full-wave simulations that the dichroic metascreen supports perfect linear-to-circular polarization conversion (circular dichroism) in two adjacent terahertz frequency bands. In two other terahertz bands, it rotates the incoming linearly polarized wave vector by ${90}^{\ensuremath{\circ}}$ (linear dichroism). Moreover, since graphene has a variable refractive-index dependence on its chemical potential, the dispersion characteristics can be shifted to neighboring frequencies within the early terahertz spectrum. We further demonstrate an angularly stable response for incident angles varying between ${0}^{\ensuremath{\circ}}$ and ${45}^{\ensuremath{\circ}}$. The tunable linear and circular dichroism characteristics are well suited for applications in sensing, imaging, and spectroscopy at terahertz frequencies.
TL;DR: Results of fluorescence spectroscopy, UV-vis, FT-IR and CD demonstrated that the microenvironment and secondary structure of HSA were changed a lot induced by PVC, leading to a decrease in α-helix.