Raman Optical Activity Research Articles

Detection of Guanine Quadruplexes by Raman Optical Activity and Quantum-Chemical Interpretation of the Spectra.

Quadruplexes formed by guanine derivatives or guanine-rich nucleic acids are involved in metabolism and genetic storage of many living organisms, they are used in DNA nanotechnologies or as biosensors. Since many quadruplex geometries are possible the determination of their structures in aqueous solutions is difficult. Raman optical activity (ROA) can make it easier: For guanosine monophosphate (GMP), we observed a distinct change of the spectra upon its condensation and quadruplex formation. The vibrational bands become more numerous, stronger, and narrower. In particular, a huge ROA signal appears below 200 cm-1. The aggregation can be induced by high concentration, low temperature, or by a metal ion. We focused on well-defined quadruplexes stabilized by potassium, where using molecular dynamics and density functional theory the spectra and particular features related to GMP geometric parameters could be understood. The simulations explain the main experimental trends and confirm that the ROA spectroscopy is sensitive to fine structural details, including guanine base twist in the quadruplex helix.

A Novel Incident Circular Polarized Light Raman Optical Activity (ICP‐ROA) Spectrometer With Advanced Polarization Control

ABSTRACTThe design and setup of a novel and simple backscatter Raman optical activity (ROA) spectrometer with incident light circular polarization (ICP) is presented, constructed from commercially available components. Incident light polarization is controlled using a combination of waveplates, compensating for unwanted birefringence and beam offsets. Realignment of the spectra in post‐processing reduced artifacts caused by spatial offsets. Spurious signals from achiral solvents like toluene and water are almost completely removed. The setup was validated by measuring references samples, including α‐pinene, carvone, and glucose in aqueous solution. The spectra show very good agreement with previously published results.

Glutathione and its structural modifications recognized by Raman Optical Activity and Circularly Polarized Luminescence

Raman Optical Activity combined with Circularly Polarized Luminescence (ROA-CPL) was used in the spectral recognition of glutathione peptide (GSH) and its model post-translational modifications (PTMs). We demonstrate the potential of ROA spectroscopy and CPL probes (EuCl3, Na3[Eu(DPA)3], NaEuEDTA) in the study of unmodified peptide, i.e. GSH, and its derivatives, i.e. glutathione oxidized (GSSG), S-acetylglutathione (GSAc) and S-nitrosoglutathione (GSNO). ROA spectral features of GSH, GSSG, and GSAc were determined along with thier changes upon the different pH conditions. Apart from the ROA, induced CPL signals of Eu(III) probes also proved to be sensitive to the structural modifications of GSH-based model PTMs, enabling their spectral recognition, especially by the NaEuEDTA probe.

Ultrasensitive Raman Detection of Biomolecular Conformation at the Attomole Scale using Chiral Nanophotonics.

Understanding the function of a biomolecule hinges on its 3D conformation or secondary structure. Chirally sensitive, optically active techniques based on the differential absorption of UV-vis circularly polarized light excel at rapid characterisation of secondary structures. However, Raman spectroscopy, a powerful method for determining the structure of simple molecules, has limited capacity for structural analysis of biomolecules because of intrinsically weak optical activity, necessitating millimolar (mM) sample quantities. A breakthrough is presented for utilising Raman spectroscopy in ultrasensitive biomolecular conformation detection, surpassing conventional Raman optical activity by 15 orders of magnitude. This strategy combines chiral plasmonic metasurfaces with achiral molecular Raman reporters and enables the detection of different conformations (α-helix and random coil) of a model peptide (poly-L/D-lysine) at the ≤attomole level (monolayer). This exceptional sensitivity stems from the ability to detect local, molecular-scale changes in the electromagnetic (EM) environment of a chiral nanocavity induced by the presence of biomolecules using molecular Raman reporters. Further signal enhancement is achieved by incorporating achiral Au nanoparticles. The introduction of the nanoparticles creates highly localized regions of extreme optical chirality. This approach, which exploits Raman, a generic phenomenon, paves the way for next-generation technologies for the ultrasensitive detection of diverse biomolecular structures.

Observation of Chirality Transfer in Twisted Few-Layer Graphene.

Chiral materials are the focus of research in a variety of fields such as chiroptical sensing, biosensing, catalysis, and spintronics. Twisted two-dimensional (2D) materials are rapidly developing into a class of atomically thin chiral materials that can be effectively modulated through interlayer twist. However, chirality transfer in chiral 2D materials has not been reported. Here, we show that the chirality from the twist interface of graphene can directly transfer to achiral few-layer graphene and lead to a strong chiroptical response probed with circularly polarized Raman spectroscopy. Distinct Raman optical activity (ROA) for the interlayer shear modes in achiral few-layer graphene is observed, with the degree of polarization reaching as high as 0.5. These findings demonstrate the programmability of chiroptical response through stacking and twist engineering in 2D materials and offer insights into the transfer of chirality in atomically thin chiral materials for optical and electronic applications.

Impact of Machine Learning on Raman and Raman Optical Activity (ROA) Spectroscopic Analyses of ribonucleic acid structure

Impact of Machine Learning on Raman and Raman Optical Activity (ROA) Spectroscopic Analyses of ribonucleic acid structure

Efficacy of blood plasma spectroscopy for early liver cancer diagnostics in obese patients

Introduction and ObjectivesHepatocellular carcinoma (HCC) represents one of the most common cancers worldwide. A considerable proportion of HCC is caused by cirrhosis related to metabolic dysfunction-associated steatohepatitis (MASH). Due to the increasing prevalence of metabolic syndrome, it is estimated that MASH-related HCC will become the most prevalent etiology of HCC. Currently, HCC screening is based on liver ultrasonography; however, the sensitivity of ultrasonography for early HCC stages in obese patients only reaches 23 %. To date, no studied biomarker shows sufficient efficacy for screening purposes. Nevertheless, the usage of spectroscopic methods offers a new perspective, as its potential use would provide cheap, fast analysis of samples such as blood plasma. Material and MethodsWe employed a combination of conventional and chiroptical spectroscopic methods to study differences between the blood plasma of obese cirrhotic patients with and without HCC. We included 20 subjects with HCC and 17 without evidence of liver cancer, all of them with body mass index ≥ 30. ResultsSensitivities and specificities reached values as follows: 0.780 and 0.905 for infrared spectroscopy, 0.700 and 0.767 for Raman spectroscopy, 0.840 and 0.743 for electronic circular dichroism, and 0.805 and 0.923 for Raman optical activity. The final combined classification model based on all spectroscopic methods reached a sensitivity of 0.810 and a specificity of 0.857, with the highest area under the receiver operating characteristic curve among all models (0.961). ConclusionsWe suggest that this approach can be used effectively as a diagnostic tool in patients who are not examinable by liver ultrasonography. Clinical trial registrationNCT04221347

Chiral-Induced Surface-Enhanced Raman Optical Activity on a Single-Particle Substrate.

Surface-enhanced Raman optical activity (SEROA) is a promising method for analyzing chiral molecules' molecular chirality and structural changes. However, conventional SEROA measurements face challenges related to substrate stability, signal uniformity, and interference from electronic circular dichroism (ECD). Therefore, in this study, we present a uniform and stable substrate for SEROA measurements by utilizing Au nanoparticles on the Au nanofilm structure to confine hotspots to the film-particle junctions and minimize ECD interference. This method also uses the induction of chirality from chiral molecules to achiral molecules to overcome the limitation of chiral molecules in SEROA measurements, specifically their lower signal efficiency. Successful chirality transfer is demonstrated through distinguishable SEROA signals when the l/d-alanine mixture is present. Enantiomeric discrimination of different l/d-alanine ratios was achieved with linear responses in the circular intensity difference (CID). Altogether, the proposed chiral-induced SEROA on the AuNP_on_AuNF substrate shows promising potential for detecting and characterizing structural changes in biomolecules, thus making it a valuable tool for various research applications.

Phosphorylation site of L-alanyl-L-glutamine identified by Raman optical activity spectroscopy

Phosphorylated peptides are instrumental in studying protein phosphorylation events. In the present study, Raman optical activity (ROA) is employed to elucidate the structure of a dipeptide, L-alanyl-L-glutamine (L-Ala-L-Gln) and its two differently alkylated N-phosphorylated derivatives. Theoretical simulations were conducted to aid the interpretation of peptide conformation variations upon phosphorylation, and of the measured Raman and ROA spectra. Induced circularly polarized luminescence (CPL) was also recorded in solution, in the presence of a simple europium aqua ion. As the spectra are peptide specific, this type of stereochemical analysis is expected to aid identification of the phosphorylation sites also in other peptides and possibly proteins.

Higher Order Structure Characterization of Two Interdomain Disulfide Bond Variants of a Bispecific Monoclonal Antibody

Characterization and understanding of protein higher order structure (HOS) is essential at all stages of biologics development. Here, two folding variants of a bispecific monoclonal antibody, the correctly folded form and an alternative configuration with reduced potency, were characterized by several HOS characterization techniques. Specifically, differential scanning calorimetry (DSC), circular dichroism (CD), Fourier-transform infrared spectroscopy (FTIR), Raman and Raman optical activity (ROA) spectroscopy were used together to elucidate the impacts of disulfide bond scrambling in the fused scFv domains on the structure and thermal stability of the antibody. This study illustrates the importance of selecting appropriate biophysical characterization techniques based on the nature and magnitude of the HOS change.

Circular Polarization-Resolved Raman Optical Activity: A Perspective on Chiral Spectroscopies of Vibrational States.

Circular polarization-resolved Raman scattering methods include Raman optical activity (ROA) and its derivative─surface-enhanced Raman optical activity (SEROA). These spectroscopic modalities are rapidly developing due to their high information content, stand-off capabilities, and rapid development of Raman-active chiral nanostructures. These methods enable a direct readout of the vibrational energy levels of chiral molecules, crystals, and nanostructured materials, making it possible to study complex interactions and the dynamic interfaces between them. They were shown to be particularly valuable for nano- and biotechnological fields encompassing complex particles with nanoscale chirality that combine strong scattering and intense polarization rotation. This perspective dives into recent advancements in ROA and SEROA, their distinction from surface-enhanced Raman scattering, and the potential of these information-rich label-free spectroscopies for the detection of chiral biomolecules.

Why Does One Measure Resonance Raman Optical Activity? A Unique Case of Measurements under Strong Resonance versus Far-from-Resonance Conditions.

Raman optical activity (ROA) spectroscopy exhibits significant potential in the study of (bio)molecules as it encodes information on their molecular structure, chirality, and conformations. Furthermore, the method reveals details on excited electronic states when applied under resonance conditions. Here, we present a combined study of the far from resonance (FFR)-ROA and resonance ROA (RROA) of a single relatively small molecular system. Notably, this study is the first to employ the density functional theory (DFT) analysis of both FFR-ROA and RROA spectra. This is illustrated for cobalamin derivatives using near-infrared and visible light excitation. Although the commonly observed monosignate RROA spectra lose additional information visible in bisignate nonresonance ROA spectra, the RROA technique acts as a complement to nonresonance ROA spectroscopy. In particular, the combination of these methods integrated with DFT calculations can reveal a complete spectral picture of the structural and conformational differences between tested compounds.

Chiral Spectroscopy of Bulk Systems with Propagated Localized Orbitals.

We present approaches for the simulation of electronic circular dichroism, Raman, and Raman optical activity (ROA) spectra for isolated and periodic systems as well as subsystem analysis thereof. The method is based on the use of time-dependent maximally localized Wannier functions in the CP2K package and accounts for origin dependencies inherent to the Gaussian and plane wave with pseudopotentials approach as well as the origin dependence of the magnetic dipole and electric quadrupole operators. Tests on the H-bonded enantiomers of alanine by harmonic normal-mode analysis and on an aqueous solution of l-alanine by ab initio molecular dynamics obeying periodic boundary conditions (PBCs) are presented as total and subsystem-resolved spectra. To our knowledge, this is the first instance of an ROA spectrum derived from real-time propagation obeying PBCs and the first ROA simulation considering off-, pre-, and on-resonance effects within PBCs.

Induced Chirality in Canthaxanthin Aggregates Reveals Multiple Levels of Supramolecular Organization

AbstractCarotenoids tend to form supramolecular aggregates via non‐covalent interactions where the chirality of individual molecules is amplified to the macroscopic level. We show that this can also be achieved for non‐chiral carotenoid monomers interacting with polysaccharides. The chirality induction in canthaxanthin (CAX), caused by heparin (HP) and hyaluronic acid (HA), was monitored by chiroptical spectroscopy. Electronic circular dichroism (ECD) and Raman optical activity (ROA) spectra indicated the presence of multiple carotenoid formations, such as H‐ and J‐type aggregates. This is consistent with molecular dynamics (MD) and density functional theory (DFT) simulations of the supramolecular structures and their spectroscopic response.

Induced Chirality in Canthaxanthin Aggregates Reveals Multiple Levels of Supramolecular Organization.

Carotenoids tend to form supramolecular aggregates via non-covalent interactions where the chirality of individual molecules is amplified to the macroscopic level. We show that this can also be achieved for non-chiral carotenoid monomers interacting with polysaccharides. The chirality induction in canthaxanthin (CAX), caused by heparin (HP) and hyaluronic acid (HA), was monitored by chiroptical spectroscopy. Electronic circular dichroism (ECD) and Raman optical activity (ROA) spectra indicated the presence of multiple carotenoid formations, such as H- and J-type aggregates. This is consistent with molecular dynamics (MD) and density functional theory (DFT) simulations of the supramolecular structures and their spectroscopic response.

Chiral excitations and the intermediate-field regime in the Kitaev magnet α−RuCl3

In the Kitaev magnet α-RuCl3, the existence of a magnetic-field-induced quantum spin-liquid phase and of anyonic excitations is controversially discussed. We address this elusive, exotic phase via helicity-dependent Raman scattering and analyze the Raman optical activity of excitations as a function of magnetic field and temperature. The hotly debated field regime between 7.5 and 10.5T is characterized by clear spectroscopic signatures such as a plateau of the Raman optical activity of the dominant, chiral spin-flip excitation. This provides direct evidence for the existence of a distinct intermediate-field regime with an intriguing ground state featuring chiral excitations. Published by the American Physical Society 2024

Navigating the future of ROA: Can it surprise us?

Raman optical activity (ROA) has truly reached middle age at 50 years. The technique has matured significantly in this period, both with respect to instrument development and number of applications and users. Yet, ROA is still viewed as an auxiliary technique, compared to conventional Raman and infrared absorption spectroscopies. In this perspective, we outline the newest trends in the field of ROA, including exciting opportunities for future developments and of course ask the important question: what is the future of ROA?

Vibrational Optical Activity of Amyloid Fibrils.

Amyloid fibrils are supramolecular systems showing distinct chirality at different levels of their complex multilayered architectures. Due to the regular long-range chiral organization, amyloid fibrils exhibit the most intense Vibrational Optical Activity (VOA) signal observed up to now, making VOA techniques: Vibrational Circular Dichroism (VCD) and Raman Optical Activity (ROA) very promising tools to explore their structures, handedness and intricate polymorphism. This concept article reviews up-to-date experimental studies on VOA applications to investigate amyloid fibrils highlighting its future potential in analyzing of these unique supramolecular systems, in particular in the context of biomedicine and nanotechnology.

Near-Infrared Excited Raman Optical Activity as a Tool to Uncover Active Sites of Photoreceptor Proteins.

Raman optical activity (ROA) is a chiral sensitive technique to measure the difference in Raman scattering intensity between right and left circularly polarized light. The method has been applied to the study of biological molecules such as proteins, and it is now recognized as a powerful tool for investigating biomolecular structures. We have expanded the capability of this chiroptical technique to colored molecules, such as photoreceptor proteins, by using a near-infrared excitation. A photoreceptor protein contains a light-absorbing chromophore as an active site, and the precise determination of its structure is vital for comprehending the protein's function at the atomic level. In a photoreceptor protein, the protein environment can distort an achiral chromophore into a chiral conformation. ROA spectroscopy offers detailed structural information about the chromophore under physiological conditions. Here we explore recent progress in near-infrared ROA spectroscopy and its application to biological systems.

Origination of the chiroptical effect in plasmonic nano-structures in the view of quasi-normal mode theory.

General chiroptical effects describe all of the interaction differences between light carrying opposite spins and chiral matters, such as circular dichroism, optical activity, and chiral Raman optical activity, and have been proven to hold great promise for extensive applications in physics, chemistry, and biology. However, the underlying physical mechanism is usually explained intangibly by the twisted currents in chiral geometry, where the cross coupling between the electric and magnetic dipoles breaks the degeneracy of the helicity eigenmodes. In this Letter, we construct a clear sight on the origination of the chiroptical effect in the view of the eigenstates of a non-Hermitian system, i.e., quasi-normal modes (QNMs). The intrinsic chiroptical effect comes from the chiral QNMs, which have distinct excitation and emission differences in both phase and intensity for lights carrying opposite spins, while the extrinsic chiroptical effect coming from the achiral QNMs requires specific illumination and observation conditions, where the low symmetrical QNM can generate chiroptical effects in both absorption and scattering, but the highly symmetrical QNMs can only generate chiroptical effects in scattering through the coherent superposition of several QNMs. Our findings offer an in-depth understanding of the chiroptical effect and have the potential to bring broad inspiration to the design and applications of chiroptical effects.