Absorption Microspectroscopy Research Articles

Evolution of myoglobin diffusion mechanisms: exploring pore and surface diffusion in a single silica particle.

This study elucidates the mass transfer mechanism of myoglobin (Mb) within a single silica particle with a 50nm pore size at various pH levels (6.0, 6.5, 6.8, and 7.0). Investigation of Mb distribution ratio (R) and distribution kinetics was conducted using absorption microspectroscopy. The highest R was observed at pH 6.8, near the isoelectric point of Mb, as the electrostatic repulsion between Mb molecules on the silica surface decreased. The time-course absorbance of Mb in the silica particle was rigorously analyzed based on a first-order reaction, yielding the intraparticle diffusion coefficient of Mb (Dp). Dp-(1 + R)-1 plots at different pH values were evaluated using the pore and surface diffusion model. Consequently, we found that at pH 6.0, Mb diffused in the silica particle exclusively through surface diffusion, whereas pore diffusion made a more substantial contribution at higher pH. Furthermore, we demonstrated that Mb diffusion was hindered by slow desorption, associated with the electrostatic charge of Mb. This comprehensive analysis provides insights into the diffusion mechanisms of Mb at acidic, neutral, and basic pH conditions.

Investigating hydrophobic environment in alkyl-group-functionalized silica particle with various chain lengths using absorption microspectroscopy.

A well-known solvatochromic dye, Reichardt's dye (R-dye), was used to evaluate the hydrophobicity of alkyl-group-functionalized silica particles (ASPs) with different chain lengths. The absorption spectra of R-dye were measured in a single ASP in a mixed solution of water and an organic solvent (methanol (MeOH), ethanol (EtOH), acetonitrile (ACN), tetrahydrofuran (THF), or N,N-dimethylformamide (DMF)) using absorption microspectroscopy. The polarity parameter in the ASPs (ET), determined by the absorption maximum, was observed to be smaller than those in bulk solutions, indicating that R-dye was present in a more hydrophobic environment. In EtOH, THF, and DMF, R-dye was distributed within the alkyl chain layer including the organic solvent. An increase in the organic solvent content of the bulk solution led to a higher organic solvent concentration in the alkyl chain layer, resulting in a decrease in ET. In MeOH and ACN, the R-dye was distributed within the alkyl chain layer and concentrated phase. Moreover, with the increase in the organic molecule content, the distribution of R-dye in the concentrated phase became dominant in MeOH and ACN system, leading to an increase in the ET value. The findings presented in this paper are expected to attract the attention of a wide range of researchers in chromatography.

Optical bulk-boundary dichotomy in a quantum spin Hall insulator

The bulk-boundary correspondence is a critical concept in topological quantum materials. For instance, a quantum spin Hall insulator features a bulk insulating gap with gapless helical boundary states protected by the underlying Z2 topology. However, the bulk-boundary dichotomy and distinction are rarely explored in optical experiments, which can provide unique information about topological charge carriers beyond transport and electronic spectroscopy techniques. Here, we utilize mid-infrared absorption micro-spectroscopy and pump–probe micro-spectroscopy to elucidate the bulk-boundary optical responses of Bi4Br4, a recently discovered room-temperature quantum spin Hall insulator. Benefiting from the low energy of infrared photons and the high spatial resolution, we unambiguously resolve a strong absorption from the boundary states while the bulk absorption is suppressed by its insulating gap. Moreover, the boundary absorption exhibits strong polarization anisotropy, consistent with the one-dimensional nature of the topological boundary states. Our infrared pump–probe microscopy further measures a substantially increased carrier lifetime for the boundary states, which reaches one nanosecond scale. The nanosecond lifetime is about one to two orders longer than that of most topological materials and can be attributed to the linear dispersion nature of the helical boundary states. Our findings demonstrate the optical bulk-boundary dichotomy in a topological material and provide a proof-of-principal methodology for studying topological optoelectronics.

Light Emission in 2D Silver Phenylchalcogenolates.

Silver phenylselenolate (AgSePh, also known as "mithrene") and silver phenyltellurolate (AgTePh, also known as "tethrene") are two-dimensional (2D) van der Waals semiconductors belonging to an emerging class of hybrid organic-inorganic materials called metal-organic chalcogenolates. Despite having the same crystal structure, AgSePh and AgTePh exhibit a strikingly different excitonic behavior. Whereas AgSePh exhibits narrow, fast luminescence with a minimal Stokes shift, AgTePh exhibits comparatively slow luminescence that is significantly broadened and red-shifted from its absorption minimum. Using time-resolved and temperature-dependent absorption and emission microspectroscopy, combined with subgap photoexcitation studies, we show that exciton dynamics in AgTePh films are dominated by an intrinsic self-trapping behavior, whereas dynamics in AgSePh films are dominated by the interaction of band-edge excitons with a finite number of extrinsic defect/trap states. Density functional theory calculations reveal that AgSePh has simple parabolic band edges with a direct gap at Γ, whereas AgTePh has a saddle point at Γ with a horizontal splitting along the Γ-N1 direction. The correlation between the unique band structure of AgTePh and exciton self-trapping behavior is unclear, prompting further exploration of excitonic phenomena in this emerging class of hybrid 2D semiconductors.

The role of chromium in the corrosion performance of cobalt- and cobalt-nickel based hardmetal binders: A study centred on X-ray absorption microspectroscopy

The corrosion control of WC-Co type hardmetals is steadily gaining momentum for novel crucial applications in the Oil & Gas and food industries. The corrosion rate of the Co-based binder, and the extent to which coupling to WC speeds it up, are strongly influenced by alloying. In this paper, we investigate the impact of Cr on the corrosion-product film formation of Co- and CoNi based hardmetal binders in acidic, neutral and alkaline aqueous solutions. We centred our study on the role of Cr in driving the distribution of oxidized Co and Ni at the micrometre scale, thanks to synchrotron-based soft-X ray microspectroscopy. We have investigated morphochemical distributions for the following grades: Co96Cr4, Co48Ni48Cr4, Co50Cr50. Chemical-state mapping has been complemented by electrochemical measurements and metallographic observations. Amounts of Cr and Ni of ca. 50% notably increase the corrosion resistance in all ambients, with a stronger beneficial effect of the former element. 4% addition of Cr results in slight positive effects, with the exception of the CoNi system in alkaline ambient, that, together with Co50Cr50, outperforms the other grades. In all investigated alloy-ambient combinations, a continuous oxidized metal film grows, onto which micrometric island form of shape and dimensions that depend on the specific grade and aggressive conditions. Quantitative descriptors of chemical-state maps and their theoretical interpretation in terms of electrochemical phase-formation by oxy-hydroxide precipitation, allow to correlate the island patterns with the degree of pseudopassivation.

In Situ Absorption and Fluorescence Microspectroscopy Investigation of the Molecular Incorporation Process into Single Nanoporous Protein Crystals.

Protein crystals exhibit distinct three-dimensional structures, which contain well-ordered nanoporous solvent channels, providing a chemically heterogeneous environment. In this paper, the incorporation of various molecules into the solvent channels of native hen egg-white lysozyme crystals was demonstrated using fluorescent dyes, including acridine yellow G, rhodamine 6G, and eosin Y. The process was evaluated on the basis of absorption and fluorescence microspectroscopy at a single-crystal level. The molecular loading process was clearly visualized as a function of time, and it was determined that the protein crystals could act as nanoporous materials. It was found that the incorporation process is strongly dependent on the molecular charge, leading to heterogeneous molecular aggregation, which suggests host–guest interaction of protein crystals from the viewpoint of nanoporous materials.

In vitro localisation and degradation of few-layer MoS2 submicrometric plates in human macrophage-like cells: a label free Raman micro-spectroscopic study

Monitoring the uptake, micro-environment and fate of micro or nano scaled particulate materials in cells is of paramount importance for the emerging fields of toxicology and medicine. Such particulate materials are known to interfere with colorimetric assays and many such assays record only a single end-point. Therefore, there is a need for a label-free, cost effective technique with little or no inference from the particulate materials.Raman micro-spectroscopy was used to simultaneously interrogate the integrity of few-layer MoS2 submicrometric plates in human macrophage-like cells, in vitro, as well as the biochemical characteristics of the local micro-environment in which they are encompassed. Firstly, the degradation profile of MoS2 plates induced by hydrogen peroxidase was established using UV–vis absorption and Raman micro-spectroscopy. Raman micro-spectroscopic maps interrogated all aspects of the cell, including the nucleus, cytoplasm and perinuclear region, and the location/distribution of MoS2 was monitored as a function of time (4, 24 and 72 h). Whereas only pristine MoS2 was detectable after 4 and 72 periods, degradation in vitro was confirmed following a 24 h incubation. Analysis of the MoS2 micro-environments revealed the presence of both phosphatidyl lipidic vesicles and enzymatic regions containing lysozyme, the former being most associated with the MoS2 degradation. There was an increase and saturation of cytosolic neutral lipids detected following a 24 h incubation with MoS2, which reduces following a prolonged incubation of 72 h. This study reveals that macrophage-like cells perform degradation of the material in vitro within lipidic vesicles subsequent to phagocytosis, which manifest as an increase in the production of lipid bodies as a mechanism of defense following exposure to industrial grade MoS2.

Be, Fe2+-substitution in natural beryl: an optical absorption spectroscopy study

Collection of variously colored gem quality iron-bearing beryl from two Brazilian deposits, Lavra do Abilio (Minas Gerais) and Garimpo do Cercadinho (Bahia) was studied by polarized optical absorption microspectroscopy and microprobe analysis. The main attention was paid to spatial distribution of Fe2+ in tetrahedral structural site of Be2+, estimated by intensity of E⊥c-polarized electronic spin-allowed band of BeFe2+ at ~ 12,000 cm−1, mainly along c-axis of the crystals. It is found that in the samples from the two deposits these characteristics are different: in beryl from Lavra do Abilio the distribution is nearly homogeneous, while in those from Garimpo do Cercadinho BeFe2+-content strongly varies along the crystal’s elongation that may indicate the different physico-chemical conditions of crystallization. It is found that there is no correlation between distribution of BeFe2+, Fetotal, detected by microprobe, and Fe2+ in octahedral Al-site, which causes blue color of aquamarine and green—of “green” beryl, wherein heliodor centers are also involved in process of coloration. Judging from intensity of weak narrow spin-forbidden bands of octahedral Fe3+ in Al-sites and narrow near-infrared lines of vibration transition of H2O-molecules in the structural channels, these two admixtures are distributed homogenously in beryl from both deposits. A light-blue synthetic hydrothermal beryl was also studied for comparison. It is found that BeFe2+-distribution along and across elongation of the sample is essentially homogeneous.

Temperature Dependent Spectroscopic Properties of Cu+ and Dy3+ Co-Doped Phosphate Glass: Band Gap Analysis and Cu Nanocluster-Enhanced Dy3+ Luminescence.

This paper reports on the effects of temperature on light absorption and emission in Cu+ and Dy3+ co-doped phosphate glass, which is of interest for photonic applications. First, the temperature dependence of the absorption edge of the glass in connection with Cu+ ions absorption was assessed. A thermally-induced red shift attributed to Cu+ ion-lattice interactions was observed and analyzed through optical band gap determinations in the context of indirect-allowed transitions. Application of the Varshni model for the dependence of the energy gaps with temperature allowed to estimate the 0 K energy gap at 2.87 (±0.01) eV. Furthermore, Dy3+ photoluminescence (PL) along with Cu nanoparticles (NPs) absorption was monitored in real-time during an isothermal treatment by the in situ concurrent PL and absorption microspectroscopy technique. Periods of enhancement and quenching of Dy3+ emission linked to bidirectional energy transfer processes involving non-plasmonic Cu clusters and plasmonic Cu NPs were revealed. The formation of Cu NPs was promoted by tin(II) used as reductant. It is the first time to the author's knowledge that the 0 K energy gap is estimated for a highly Cu+ -doped glass and that the enhancement of Dy3+ PL by Cu clusters is exposed.

Photoinduced flavin-tryptophan electron transfer across vesicle membranes generates magnetic field sensitive radical pairs

ABSTRACTDue to the photobiology of the flavoproteins DNA photolyase and cryptochrome, electron transfer reactions between flavins and tryptophan are of significant biological relevance. In addition, electron transfer across vesicle membranes has also seen much attention. In this work, we study the electron transfer reaction between flavins and tryptophan across lipid bilayer membranes in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine small unilamellar vesicles using time-resolved optical absorption microspectroscopy and magnetically affected reaction yield spectroscopy. We demonstrate that riboflavin tetrabutyrate is embedded in the vesicle bilayer and can undergo electron transfer with tryptophan molecules in either the inner water pool or the bulk solution. Remarkably, flavin mononucleotide encapsulated in the inner water pool can undergo electron transfer across the vesicle bilayer to generate a magnetically sensitive radical pair with tryptophan molecules located in the bulk solution. The observed kinetics suggest that back electron transfer occurs between radical pairs generated by diffusive reencounter, either in the vesicle surface water or via electron hopping through degenerate electron exchange.

Time-resolved optical absorption microspectroscopy of magnetic field sensitive flavin photochemistry.

The photochemical reactions of blue-light receptor proteins have received much attention due to their very important biological functions. In addition, there is also growing evidence that the one particular class of such proteins, the cryptochromes, may be associated with not only a biological photo-response but also a magneto-response, which may be responsible for the mechanism by which many animals can respond to the weak geomagnetic field. Therefore, there is an important scientific question over whether it is possible to directly observe such photochemical processes, and indeed the effects of weak magnetic fields thereon, taking place both in purified protein samples in vitro and in actual biochemical cells and tissues. For the former samples, the key lies in being able to make sensitive spectroscopic measurements on very small volumes of samples at potentially low protein concentrations, while the latter requires, in addition, spatially resolved measurements on length scales smaller than typical cellular components, i.e., sub-micron resolution. In this work, we discuss a two- and three-color confocal pump-probe microscopic approach to this question which satisfies these requirements and is thus useful for experimental measurements in both cases.

Chemical-state evolution of Ni in Mn[sbnd]Ni/polypyrrole nanocomposites under bifunctional air electrode conditions, investigated by quasi-in situ multi-scale soft X-ray absorption spectroscopy

Rechargeable metal-air batteries are highly prospective energy conversion and storage devices with enormous potential impact on broad deployment of renewable energies as well as on transportation. Nevertheless, efficient and durable systems are not yet available, mainly owing to limited chemical stability and durability of bifunctional air electrodes, that undergo poorly understood changes in chemical state and space distribution of the electrocatalytic materials. Manganese oxides (MnOx) are popular non-precious oxygen-reduction reaction (ORR) catalysts due to their low cost and relatively high activity. Unfortunately, the stability of MnOx under ORR conditions and its performance in the oxygen-evolution reaction (OER) are not completely satisfactory. Previous work in our group has shown that mixed MnNi oxides exhibit a notably improved ORR activity and durability, strongly enhanced by dispersing the oxides in a polypyrrole (PPy) matrix. Moreover, PPy exhibits high stability as well as catalytic activity in the OER. This study thus focuses on the ORR/OER behaviour of MnNi/PPy nanocomposite and is aimed at following the changes in chemical state distribution of dopant Ni at the sub-microscale. These changes result from the cathodic and anodic operation of this material under conditions relevant to the oxygen electrode of Zn-air batteries. Our study is based on quasi-in situ identical-location soft-X ray absorption microspectroscopy at the Ni L-edge, complemented by spectroscopy performed through ptychography for the case of ORR. Electrochemical operation results in a space- and potential-dependent rearrangement of the distribution of elemental and oxidized Nickel and in a change of their ratios. Operation under ORR conditions is accompanied by an increase of the oxidized Nickel fraction owing to the presence of an oxidizer in the electrolyte. As expected, oxidizing OER conditions cause an increase of the oxidized Nickel fraction.

In-operando studies of Ag-TCNQ nanocrystals using Raman and soft x-ray microspectroscopy

We characterize individual Ag-TCNQ nanocrystals during switching their resistivity state in operando. Raman and soft X-ray absorption microspectroscopy are employed to disclose the electronic state of the organic component in dependency of applied voltage. Whereas Raman microspectroscopy offers qualitative insight into the conversion of negatively charged TCNQ molecules to their neutral counterpart, quantification of the neutral fraction can be achieved using X-ray absorption spectroscopy. These results allow a detailed investigation of resistivity switching in electrically bistable Ag-TCNQ nanocrystals.

Copper Uptake, Intracellular Localization, and Speciation in Marine Microalgae Measured by Synchrotron Radiation X-ray Fluorescence and Absorption Microspectroscopy.

Metal toxicity to aquatic organisms depends on the speciation of the metal and its binding to the critical receptor site(s) (biotic ligand) of the organism. The intracellular nature of the biotic ligand for Cu in microalgal cells was investigated using the high elemental sensitivity of microprobe synchrotron radiation X-ray fluorescence (SR-XRF) and X-ray absorption near-edge spectroscopy (XANES). The marine microalgae, Ceratoneis closterium, Phaeodactylum tricornutum, and Tetraselmis sp. were selected based on their varying sensitivities to Cu (72-h 50% population growth inhibitions of 8-47 μg Cu/L). Intracellular Cu in control cells was similar for all three species (2.5-3.2 × 10(-15) g Cu/cell) and increased 4-fold in C. closterium and Tetraselmis sp. when exposed to copper, but was unchanged in P. tricornutum (72-h exposure to 19, 40, and 40 μg Cu/L, respectively). Whole cell microprobe SR-XRF identified endogenous Cu in the central compartment (cytoplasm) of control (unexposed) cells. After Cu exposure, Cu was colocated with organelles/granules dense in P, S, Ca, and Si and this was clearly evident in thin sections of Tetraselmis sp. XANES indicated coexistence of Cu(I) and Cu(II) in control and Cu-exposed cells, with the Cu ligand (e.g., phytochelatin) in P. tricornutum different from that in C. closterium and Tetraselmis sp. This study supports the hypothesis that Cu(II) is reduced to Cu(I) and that polyphosphate bodies and phytochelatins play a significant role in the internalization and detoxification of Cu in marine microalgae.

Far-Field Subdiffraction Imaging of Semiconductors Using Nonlinear Transient Absorption Differential Microscopy

Label-free absorption spectroscopies are frontline techniques to reveal the spectral fingerprint, composition and environment of materials and are applicable to a wide range of samples. In an effort to improve the spatial resolution of far-field absorption microscopy, which is limited by the diffraction of light, an imaging technique based on transient absorption saturation has recently been developed. Here we report a far-field transient absorption microscopy that does not require the sample to exhibit saturable absorption to break the diffraction barrier. By alternating the wavefront of the pump beams and exploiting a nonlinearity in the transient absorption intrinsic to semiconductors, we demonstrate imaging, beyond the diffraction limit, in CdSe nanobelts. This differential technique is applied for label-free super-resolution absorption microspectroscopy.

Tracking ink composition on Herculaneum papyrus scrolls: quantification and speciation of lead by X-ray based techniques and Monte Carlo simulations.

The writing in carbonized Herculaneum scrolls, covered and preserved by the pyroclastic events of the Vesuvius in 79 AD, was recently revealed using X-ray phase-contrast tomography, without the need of unrolling the sensitive scrolls. Unfortunately, some of the text is difficult to read due to the interference of the papyrus fibers crossing the written text vertically and horizontally. Recently, lead was found as an elemental constituent in the writing, rendering the text more clearly readable when monitoring the lead X-ray fluorescence signal. Here, several hypotheses are postulated for the origin and state of lead in the papyrus writing. Multi-scale X-ray fluorescence micro-imaging, Monte Carlo quantification and X-ray absorption microspectroscopy experiments are used to provide additional information on the ink composition, in an attempt to determine the origin of the lead in the Herculaneum scrolls and validate the postulated hypotheses.

Carbon-Promoted in Situ Evolution of Cu Nanoclusters Influencing Eu3+ Photoluminescence in Glass: Bidirectional Energy Transfer

The present work explores the use of carbon powder, recently proposed for producing plasmonic metal nanocomposites, as a means to obtain Eu3+ photoluminescence (PL) enhancements via Cu nanoclusters in glass. Phosphate glasses containing Eu2O3 and CuO were prepared by melting in ambient atmosphere with graphite powder added to the batch materials for the chemical reduction of copper(II). Optical absorption and PL spectroscopy characterizations, including emission decay dynamics, were performed. The data show consistently the effective reduction of Cu2+ ions via carbon during melting which ultimately leads to thermally induced copper particle precipitation. Further, the novel in situ concurrent PL and absorption microspectroscopy technique was employed for the real-time monitoring of the optical properties of the codoped glasses during thermal processing from 470 to 490 °C. Bidirectional energy transfer between europium ions and copper nanoclusters has been manifested through enhancement and quenching regim...

表面修飾シリカゲルにおける重金属イオンの分配・放出過程の解析

Distribution and release processes of heavy-metal ions between spherical surface-modified silica gel microparticles and water were analyzed by microcapillary manipulation and absorption microspectroscopy. Silica gel modified with triamine (QuadraSil-TA, Q-TA) or thiol groups (QuadraSil-MP, Q-MP) was used as a surface-modified silica gel. A single microparticle was injected into an aqueous HAuCl4 or CuSO4 solution containing 0.01 M KCl (pH = 6), and the distribution rate of the metal ion from water into the microparticle was measured. The rate of release of Au(III) or Cu(II) from Q-TA into water (pH = 6) was much smaller than that of the distribution of the metal. The microparticle radius dependence of the absorbance of the metal in the microparticle and distribution of the metal by cross-sectional SEM-EDS analysis at the distribution equilibrium indicate that Au(III) and Cu(II) distribute into the microparticle interior for Q-TA, while Au(III) distributes at the outer layer in the spherical microparticle for Q-MP. The distribution processes were analyzed as the intraparticle diffusion, and the diffusion coefficient (Dp) observed in the present systems was compared with that calculated from the theoretical pore and surface diffusion model. We consider that the rate-determining step of the distribution of Au(III) in the Q-TA (pore diameter = 5.9 nm) system is the intraparticle diffusion of AuCl4−. On the other hand, the distribution of Cu(II) into Q-TA was much slower than the intraparticle diffusion.

Uncovering the deactivation mechanism of Au catalyst with operando high spatial resolution IR and X-ray microspectroscopy measurements

Detecting the reaction mechanism of multistep catalytic transformations is essential for optimization of these complex processes. In this study, the mechanism of catalyst deactivation within a flow reactor was studied under reaction conditions. Spectral mapping of the catalyst and the organic phase along a flow reactor were performed with micrometer-sized synchrotron-based X-ray and IR beams, respectively, with a spatial resolution of 15μm. Heterogeneous Au catalyst was packed in a flow reactor and activated toward the cascade reaction of pyran formation. X-ray absorption microspectroscopy measurements revealed that the highly oxidized Au(III), which is the catalytically active species, was continuously reduced along the flow reactor. IR microspectroscopy measurements detected a direct correlation between the reduction of the Au catalyst and deactivation of the catalytic process. It was observed that within 1.5mm from the reactor's inlet all the catalytic reactivity was quenched. Microspectroscopy measurements determined that the reduction of Au(III) was induced by nucleophilic attack of butanol, which is one of the reactants in this reaction. Slower deactivation rates were measured once the reactants concentration was decreased by an order of magnitude. Under these conditions the reaction path within the flow reactor was increased from 1.5 to 6mm. These results demonstrate the molecular level understanding of reaction mechanism which can be achieved by high spatial resolution microspectroscopy measurements.

Electrodeposition and Ageing of Mn‐Based Binary Composite Oxygen Reduction Reaction Electrocatalysts

AbstractElectrodeposition and ageing under oxygen reduction reaction (ORR) of Mn‐X/PPy (X=Co, Mg, Ni; PPy=polypyrrole) and Mn‐Ag/G (G=graphene) composite electrocatalysts have been studied by quasi‐in‐situ soft X‐ray absorption and fluorescence microspectroscopy. The fabricated materials exhibit micro‐grained morphologies in which Mn is present mainly as Mn2+, accompanied by combinations of Co0/Co2+ and Ni0/Ni2+. Ageing leads to the formation of progressively larger mesoscopic aggregates. Initial ageing yields more active Mn3+ and Mn4+, in agreement with an improved ORR behaviour. Prolonged ageing causes the loss of Mn3+ and Mn4+ from the surface, in correlation with a degradation of the ORR response. In the investigated ageing period, Mn‐Mg/PPy exhibits the best durability, with about half of the catalyst grains still showing the presence of Mn3+/Mn4+, while the others consist mainly of Mn2+. In Mn‐Ni/PPy, the Ni2+ content tends to increase with ageing whereas Co3+ forms in the Mn‐Co/PPy composites.