Resonance Raman Research Articles

Cooperative effects of zinc interstitials and oxygen vacancies on violet-blue photoluminescence of ZnO nanoparticles: UV radiation induced enhanced latent fingerprint detection

Understanding the mechanisms of the violet-blue (VB) photoluminescence (PL) emissions is very important for possible applications of ZnO nanoparticles (NPs) in optoelectronics and forensic. Origin of the VB PL emissions of ZnO NPs of sizes of 27–54 nm synthesized in water using chemical co-precipitation method at a temperature of ∼100 oC for heating duration of 1–3 h, respectively, has been established here. For both below band gap excitation (BBE) and above band gap excitation (ABE), narrow ultraviolet and broad visible PL emissions including VB emissions have been observed. For BBE, VB emission is due to the direct transition of electrons from Zni/ex-Zni to valence band edge. The weak VB emission in case of ABE, usually ignored in earlier studies, has been studied here very carefully and systematically. The two predominant defect states and their cooperative effects are clearly found to be responsible for VB emissions. The Zni and Vo defect centers have been confirmed from the Raman and electron paramagnetic resonance spectroscopic measurements. As an important forensic applications, detection of latent finger prints (taken on different substances) using as-synthesized ZnO NPs through PL emissions has been demonstrated by illuminating using ultraviolet light even after 40 days.

The impact of ferric iron and pH on photo-degradation of tetracycline in water

There is a significant interest in understanding coordination and photo-chemistry of tetracycline antibiotics, primarily in relation to the development of advanced oxidation processes for degradation of these pollutants in water processing. Herein we analyzed the pH-dependence of interactions of tetracycline with ferric iron and photosensitivity of tetracycline to UV-A and UV-B, using a set of methods – UV–vis, Raman and electron paramagnetic resonance spectroscopy, MS spectrometry, HPLC, and cyclic voltammetry. Tetracycline and Fe3+ mainly bind through amide and OH groups in tricarbonylamide moiety to form a stable complex with 1:1 stoichiometry at pH ≤ 5. The interaction is reversible and tetracycline is released from the complex with pH increase. Tetracycline in the complex is stabilized and less susceptible than free tetracycline to oxidation by hydroxyl radical that is produced by UV-induced photolysis of Fe3+–OH- complexes. Redox properties of tetracycline were altered with increasing pH and it showed increased susceptibility to UV-induced degradation. In close, the system composed of tetracycline and ferric iron shows coordination and photo-redox chemistry that is dependent of pH in relation to the solubility of Fe3+ species and protonation of tetracycline. The development and optimization of advanced oxidation processes should take into account that iron may bind and stabilize pollutants and that the redox landscape of water changes drastically with pH.

Vibrational Spectro-Electrochemistry of Heme Proteins

Heme proteins perform a plethora of distinct cellular functions, including e.g. electron transport (ET), energy conversion, detoxification, catalysis, signaling, and gene regulation, and as such inspire a myriad of biotechnological applications. We use resonance Raman (RR) and Surface enhanced RR (SERR) spectroscopies to probe the architecture of the heme pocket in diverse heme proteins and enzymes, which is essential for the understanding of their physiological properties as well as for the evaluation of their potential for development of the 3rd generation bioelectronic devices (1,2). Moreover, plasmonic metal that gives origin to the surface enhancement of the Raman signal of the molecules found in its close proximity can serve as an electrode, thus driving electrochemical processes. In the case of heme proteins attached to plasmonic Ag electrodes, SERR spectra selectively show vibrational bands originating from the heme moiety only, which are sensitive to spin, coordination and redox state and of the heme iron. These properties that govern the catalytic performance of heme enzymes can be monitored in potential dependent manner by SERR spectro-electrochemistry.We have demonstrated that SERR spectro-electrochemistry possesses unique capacity of to i) disentangle ET processes in multi hemic proteins, such as 28 heme containing nitrite reductase, which represent a challenge for all other experimental approaches and ii) detect subtle immobilization induced structural changes in enzymes of biotechnological interest, which e.g. in the case of cytochrome P450 may prevent their successful applications (1-4). Here we show that SERRS monitoring of electrocatalytic processes by immobilized heme peroxidases, can provide information on catalytically relevant species in situ. Several members of a recently discovered family of heme dye-decolorizing peroxidases (DyPs) that possess remarkable catalytic properties in solution and high biotechnological potential, have been immobilized on biocompatible Ag electrodes. Their structural and electrocatalytic properties studied by RR, SERR spectro-electrochemistry and electrochemistry (2). The immobilized DyP from Pseudomonas putida (PpDyP), in particular, shows native structure and outstanding analytical and catalytic parameters, and hence an exceptional potential for development of 3rd generation biosensors for H2O2 detection. In terms of sensitivity, the bioelectrodes carrying immobilized PpDyP outperform HRP based counterparts reported in the literature (2,4). The biosensor based on a PpDyP variant that harbors mutations at the second shell of the heme cavity reveals further improved storage. Our work highlights the importance of integrated, multidisciplinary approach to simultaneously evaluate the structure and catalytic properties of the enzymes, which ensures faster identification and optimization of the promising candidates for biotechnological applications.

(Invited) Raman Scattering By Exciton-Polaritons in Carbon Nanotubes

Resonant Raman scattering has been used for decades to study single walled carbon nanotubes (CNTs), but lacks a consistent theory that simultaneously explains all characteristic signatures. We argue that a proper description requires introducing exciton polaritons as couples excitonic and photonic states. We describe the polaritons by waveguided theory for a nanometre thick cylinder with modified dielectric function. During their propagation along the tube, the polaritons scatter with phonons and are re-emitted as photons with smaller energy (Stokes scattering event). This approach consistently explains the energetic positions of the Raman resonances for the radial-breathing mode (RBM), the G and the 2D line as well as the asymmetry in the scattering intensity of the incoming and outgoing resonances without resorting to higher-order scattering events. We measured the Raman effect on chirality-sorted nanotubes over the first and second exciton resonance and excellently predict its behaviour, which has not been achieved before. The formation of polaritonic states will affect other optical processes in CNTs. Furthermore, exciton-polariton effects appear inevitable in all one-dimensional excitonic systems, similar to our observations in single walled carbon nanotubes.

Roles of High-valent Hemes and pH Dependence in Halite Decomposition Catalyzed by Chlorite Dismutase from Dechloromonas aromatica.

The heme-based chlorite dismutases catalyze the unimolecular decomposition of chlorite (ClO2 -) to yield Cl- and O2. The work presented here shows that chlorite dismutase from Dechloromonas aromatica (DaCld) also catalyzes the decomposition of bromite (BrO2 -) with the evolution of O2 (k cat = (2.0±0.2)×102 s-1; k cat/K M = (1.2±0.2)×105 M-1 s-1 at pH 5.2). Stopped-flow studies of this BrO2 - decomposition as a function of pH show that 1) the two-electron oxidized heme, compound I (Cpd I), is the primary accumulating heme intermediate during O2 evolution in acidic solution, 2) Cpd I and its one-electron reduction product, compound II (Cpd II) are present in varying ratios at intermediate pHs, and 3) only Cpd II is observed at pH 9.0. The pH dependences of Cpd I and Cpd II populations both yield a pK a of 6.7±0.1 in good agreement with the pK a of DaCld activity with ClO2 -. The observation of a protein-based amino acid radical (AA•) whose appearance coincides with that of Cpd II supports the hypothesis that conversion of Cpd I to Cpd II occurs via proton-coupled electron transfer (PCET) from a heme-pocket amino acid to the oxidized porphyrinate of Cpd I to yield a dead-end decoupled state in which the holes decay at different rates. The site of the amino acid radical is tentatively assigned to Y118, which serves as a H-bond donor to propionate 6 (P6). The favoring of Cpd II:AA• accumulation in alkaline solution is consistent with the amino acid oxidation being rate limited by transfer of its proton to P6 having pK a 6.7. Examination of reaction mixtures comprising DaCld and ClO2 - by resonance Raman and electron paramagnetic resonance spectroscopy reveal formation of Cpd II and •ClO2, which forms in preference to the analogous to AA• in the BrO2 - reaction. Addition of ClO- to Cpd II did not yield O2. Together these results are consistent with heterolytic cleavage of the O-BrO- and O-ClO- bonds yielding Cpd I, which is the catalytically active intermediate. The long-lived Cpd II that forms subsequently, is inactive toward O2 production, and diminishes the amount of enzyme available to cycle through the active Cpd I intermediate.

CARS spectra of polystyrene sheet at excitation of fs pulses and chirped pulses

Two-beam coherent anti-Stokes Raman scattering (CARS) spectroscopy setup is built. Measurements of CARS spectra generated from polystyrene (PS) sheet under excitation of femtosecond (fs) pulses and chirped pulses are demonstrated. The pump-Stokes time delay is adjusted at fixed step of 6 fs and transient CARS spectra is measured at every pump-Stokes time delay. Two-dimensional plots depicting intensity of fs CARS, chirped Stokes CARS, chirped pump/probe CARS and spectral focusing CARS as a function of the wavenumber and the pump-Stokes time delay are realized. Excitation situation of Raman resonances in fingerprint region of polystyrene molecule is discussed in conditions of un-chirped and chirped CARS spectra. Capacity of chirped Stokes CARS, chirped pump/probe CARS and spectral focusing CARS in improving spectral resolution over fs CARS is systematically analyzed.

Amide Spectral Fingerprints are Hydrogen Bonding-Mediated.

The origin of the peculiar amide spectral features of proteins in aqueous solution is investigated, by exploiting a combined theoretical and experimental approach to study UV Resonance Raman (RR) spectra of peptide molecular models, namely N-acetylglycine-N-methylamide (NAGMA) and N-acetylalanine-N-methylamide (NALMA). UVRR spectra are recorded by tuning Synchrotron Radiation at several excitation wavelengths and modeled by using a recently developed multiscale protocol based on a polarizable QM/MM approach. Thanks to the unparalleled agreement between theory and experiment, we demonstrate that specific hydrogen bond interactions, which dominate hydration dynamics around these solutes, play a crucial role in the selective enhancement of amide signals. These results further argue the capability of vibrational spectroscopy methods as valuable tools for refined structural analysis of peptides and proteins in aqueous solution.

Femtosecond coherent Raman system with >75 dB dynamic range for probing vibration modes across 250-2400 cm-1.

We report on the design and performance of a time-resolved Coherent Raman spectroscopy system with time resolution of better than 120 fs. The coherent transients can be traced with more than 75 dB dynamic range while accessing and probing Raman active modes across a 250-2400 cm-1 frequency. The system delivers an equivalent spectral resolution of better than 0.1 cm-1 regarding line bandwidth parameters for probed Raman resonances.

Optically active cross-band transition in double-walled carbon nanotube and its impact on Raman resonances

Double-walled carbon nanotubes (DWNTs), often regarded as the simplest one-dimensional (1D) van der Waals moiré superlattices, are the ideal structures to explore the interlayer coupling, including mechanical and electronical coupling, at the nanoscale in 1D systems. By combining spatial modulation spectroscopy (SMS) and resonant Raman scattering (RRS) experiments on well-identified individual free-standing DWNTs with the calculations of their optical absorption by using the recursion method with non-orthogonal tight-binding (NTB) basis functions, we are able to unambiguously assign the nature, namely mirror transition or cross transition, of each optical transitions in DWNTs. Our study identifies and allows to determine the conditions of the mixing of the electronic states leading to the appearance of cross transitions in the optical absorption of DWNTs, beyond of the so-called Koshino's criteria previously derived. On the other hand, the striking behavior of the resonant excitation profile (REP) of the Raman active modes around the cross transition reveals the strong sensitivity of the modes intensity on the electronic interlayer coupling in DWNTs, emphasizing the relevance of Raman spectroscopy for studying the electronic and mechanical coupling at the nanoscale.

Minimalist De Novo Design of an Artificial Enzyme.

We employed a reductionist approach in designing the first heterochiral tripeptide that forms a robust heterogeneous short peptide catalyst similar to the “histidine brace” active site of lytic polysaccharide monooxygenases. The histidine brace is a conserved divalent copper ion-binding motif that comprises two histidine side chains and an amino group to create the T-shaped 3N geometry at the reaction center. The geometry parameters, including a large twist angle (73°) between the two imidazole rings of the model complex, are identical to those of native lytic polysaccharide monooxygenases (72.61°). The complex was synthesized and characterized as a structural and functional mimic of the histidine brace. UV–vis, vis-circular dichroism, Raman, and electron paramagnetic resonance spectroscopic analyses suggest a distorted square-pyramidal geometry with a 3N coordination at pH 7. Solution- and solid-state NMR results further confirm the 3N coordination in the copper center of the complex. The complex is pH-dependent and could catalyze the oxidation of benzyl alcohol in water to benzaldehyde with yields up to 82% in 3 h at pH 7 and above at 40 °C. The catalyst achieved 100% selectivity for benzaldehyde compared to conventional copper catalysis. The design of such a minimalist building block for functional soft materials with a pH switch can be a stepping stone in addressing needs for a cleaner and sustainable future catalyst.

Stability of Studtite in Saline Solution: Identification of Uranyl–Peroxo–Halo Complex

Hydrogen peroxide is produced upon radiolysis of water and has been shown to be the main oxidant driving oxidative dissolution of UO2-based nuclear fuel under geological repository conditions. While the overall mechanism and speciation are well known for granitic groundwaters, considerably less is known for saline waters of relevance in rock salt or during emergency cooling of reactors using seawater. In this work, the ternary uranyl–peroxo–chloro and uranyl–peroxo–bromo complexes were identified using IR, Raman, and nuclear magnetic resonance (NMR) spectroscopy. Based on Raman spectra, the estimated stability constants for the identified uranyl–peroxo–chloro ((UO2)(O2)(Cl)(H2O)2–) and uranyl–peroxo–bromo ((UO2)(O2)(Br)(H2O)2–) complexes are 0.17 and 0.04, respectively, at ionic strength ≈5 mol/L. It was found that the uranyl–peroxo–chloro complex is more stable than the uranyl–peroxo–bromo complex, which transforms into studtite at high uranyl and H2O2 concentrations. Studtite is also found to be dissolved at a high ionic strength, implying that this may not be a stable solid phase under very saline conditions. The uranyl–peroxo–bromo complex was shown to facilitate H2O2 decomposition via a mechanism involving reactive intermediates.

Electron transfer between cytochrome c and microsomal monooxygenase generates reactive oxygen species that accelerates apoptosis

Generation of reactive oxygen species (ROS) are possibly induced by the crosstalk between mitochondria and endoplasmic reticula, which is physiologically important in apoptosis. Cytochrome c (Cyt c) is believed to play a crucial role in such signaling pathway by interrupting the coupling within microsomal monooxygenase (MMO). In this study, the correlation of ROS production with the electron transfer between Cyt c and the MMO system is investigated by resonance Raman (RR) spectroscopy. Binding of Cyt c to MMO is found to induce the production of ROS, which is quantitatively determined by the in-situ RR spectroscopy reflecting the interactions of Cyt c with generated ROS. The amount of ROS that is produced from isolated endoplasmic reticulum depends on the redox state of the Cyt c, indicating the important role of oxidized Cyt c in accelerating apoptosis. The role of electron transfer from MMO to Cyt c in the apoptotic mitochondria-endoplasmic reticulum pathway is accordingly proposed. This study is of significance for a deeper understanding of how Cyt c regulates apoptotic pathways through the endoplasmic reticulum, and thus may provide a rational basis for the design of antitumor drugs for cancer therapy.

Impact of structural defects on the photocatalytic properties of ZnO

ZnO photocatalytic materials have been prepared using three precursors (Zinc Acetate, Zinc Hydroxide, and Zinc Peroxide), and the effect of calcination temperature on structural and photocatalytic properties of ZnO has been investigated. XRD, UV–Vis, BET, XPS, Time-Resolved Microwave Conductivity (TRMC), Raman, and Electron Paramagnetic Resonance (EPR) have been used to correlate the impact of the surface area, the introduction of oxygen and/or zinc vacancies, and the charge carrier dynamics, with their photocatalytic properties. The main objective is to provide a new approach to the impact of structural defects on ZnO semiconductors determined by using Raman and EPR techniques, and by coupling with the important role of the surface area considered as one of the most relevant characteristics in photocatalysis in terms of performance. The fewer surface defects, the more photoactive the catalyst is. The results are discussed for the model degradation of formic acid and phenol under UV-irradiation.

Influence of Na2O on the thermodynamics properties, viscosity, and structure of CaO–SiO2–MgO–Al2O3–BaO–Na2O slag

This article investigated the effect of Na2O on the viscosity and structure of CaO–SiO2–MgO–Al2O3–BaO–Na2O slag. To understand the stability of slag at high temperatures, the “excessive heat of slag” was calculated. The structure of slag was analyzed using Raman and 27Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The results showed that the viscosity decreased with an increase in Na2O content in the range of 0 to 4 wt%, while the excessive heat of slag increased because the effect of slag composition on its heat capacity was more significant than that of temperature. From the perspective of heat supply, it should increase the fuel ratio of the blast furnace to ensure a stable furnace temperature when raising Na2O content. The mole fraction of Q Si0 (QSin, n is the number of bridging oxygen in a [SiO4]-tetrahedron) and Q Si2 increased gradually, whereas that of Q Si3 decreased obviously. The [SiO4]-tetrahedral structures were depolymerized, which reduced the number of bridging oxygen. Simultaneously, the increment in non-bridging oxygen caused the transformation from AlO4 to AlO5 and AlO6, thus decreasing the fraction of the network former (AlO4). The connection between [SiO4] and AlO5 or AlO6 weakened the strength of the network structure and increased the proportion of the Al–O bond.

Raman imaging of atoms inside a high-bandwidth cavity

High-bandwidth, fiber-based optical cavities are a promising building block for future quantum networks. They are used to resonantly couple stationary qubits such as single or multiple atoms with photons routing quantum information into a fiber network at high rates. In high-bandwidth cavities, standard fluorescence imaging on the atom-cavity resonance line for controlling atom positions is impaired since the Purcell effect strongly suppresses all-directional fluorescence. Here, we restore imaging of $^{87}\mathrm{Rb}$ atoms strongly coupled to such a fiber Fabry-P\'erot cavity by detecting the repumper fluorescence which is generated by continuous and three-dimensional Raman sideband cooling. We have carried out a detailed spectroscopic investigation of the repumper-induced differential light shifts affecting the Raman resonance, dependent on intensity and detuning. Our analysis identifies a compromise regime between imaging signal-to-noise ratio and survival rate, where physical insight into the role of dipole-force fluctuations in the heating dynamics of trapped atoms is gained.

Structural and dynamic properties of MgO–Al2O3–SiO2 glasses from molecular dynamics simulations and NMR

Magnesium aluminosilicate glasses have a wide range of applications in composite fiber reinforcements, aircraft windshields, due to their excellent chemical stability and mechanical properties. In this work, molecular dynamics simulations were used to obtain the short- and medium-range structural evolution of MgO/Al2O3 in MgO–Al2O3–SiO2 glass. The structural information was verified using a combination of combining Raman and Nuclear Magnetic Resonance (NMR) spectroscopy. The composition-structure-property relationship of the MgO–Al2O3–SiO2 glasses was constructed, using high-temperature viscosity results calculated by the Einstein-Stoke equation. The results showed that with the increase of MgO/Al2O3 ratio, Mg2+ changed from charge compensator to network modifier, which led to the gradual depolymerization of the glass network. Moreover, with the gradual replacement of Si by Al in the glass network, the disorder of the glass system increases, evidenced by the high-frequency Raman bands and the average chemical shifts of [AlOn] (n = 4, 5) shift linearly. In addition, we found that the de-polymerization led to a decrease in viscosity and an increase in fragility. The viscosity is negatively correlated with both the fragility and the atomic diffusion coefficient. It provides a theoretical basis for improving the preparation process of MgO–Al2O3–SiO2 glass and optimizing the glass properties.

Synthesis, vibrational spectroscopic investigation, molecular docking, antibacterial and antimicrobial studies of a new anthraquinone derivative compound

A new anthraquinone derivative, 1-(2,5-dimethylpiperazin-1-yl)anthracene-9,10-dione, was synthesized and characterized by Fourier Transform-Infrared, Raman and nuclear magnetic resonance analysis. The optimized molecular geometry was obtained using Density Functional Theory, B3LYP method with a 6-311++G(d,p) basis set. The fundamental vibrational wavenumbers, IR and Raman intensities were calculated for the optimized structure and simulated spectra were compared with the experimental vibrational spectra. The calculated highest occupied molecular orbital and lowest occupied molecular orbital energies indicated the presence of charge transfer within the molecule. The antibacterial activities of the new amino anthraquinone derivate against gram-positive and gram-negative bacteria were determined. Molecular docking simulations were performed with the new anthraquinone derivative and DNA to reveal its anticancer property. It was found that the anthraquinone derivate was bound to DNA with a high binding affinity (ΔG = −31.8 kJ/mol) and interacted with the DG10, DC11 and DG16 residues via the intermolecular hydrogen bonds. Moreover, to investigate the antiviral activity of the compound and to expose its action mechanism as an antiCOVID-19 agent, in silico molecular docking studies were performed on the Angiotensin-Converting Enzyme-2, and SARS-CoV-2 targets (holo and apo forms of main proteases Mpro and spike glycoprotein).

Strongly Tunable Raman Resonance in InSe under Pressure

Strongly Tunable Raman Resonance in InSe under Pressure

In situ electrochemical spectroscopy for boron-doped diamond electrode reactions: recent progress and perspectives

Over the past years, great attention has been given to the developments of boron-doped diamond (BDD) materials in various fields because of the advantages of electrochemical features, such as large potential range and low background current. This minireview aims to present the recent progress of in situ electrochemical spectroscopy for BDD electrode reactions. After a concise state of the widely used in situ electrochemical spectroscopy techniques, including in situ electrochemical Raman, infrared, and electron paramagnetic resonance spectroscopy, the current progress of BDD electrode reactions using in situ electrochemical spectroscopy has been summarized. Finally, challenges and perspectives for the tendency of the BDD study via in situ electrochemistry are provided, of which several potential electrochemical combined technologies relating to the mechanism exploration of BDD are proposed.

Computational hints for the simultaneous spectroscopic detection of common contaminants in water

In this work, we present a reliable computational methodology with the capability to aid in the identification of ionic water contaminants, such as nitrite, nitrate, and thiocyanate ions, based on the use of Resonance Raman (RR) spectroscopy. The method combines an exhaustive configurational sampling that fully captures the structural complexity inherent to aqueous solutions with state–of–the–art computational techniques that accurately simulate the response properties originating Resonance Raman signals of molecules in solution. Our computational findings show that it is possible to limit the quantum mechanical treatment to only a few explicit water molecules in order to capture the relevant interactions, and thus reproduce the available experimental spectra for NO2- and NO3-. Once validated, the methodology is applied to the prediction of the RR spectrum of aqueous SCN−. Our results indicate that by using an incident wavelength of 210 nm, the three emerging contaminants can be simultaneously detected in an aqueous matrix, thus avoiding the laborious indirect measurements used in current protocols. The designed protocol offers generalized explicit benefits: simultaneous detection of pollutants whose absorption spectra overlap, and because of the very nature of RR, pushes detection limits to lower concentrations.