Spectroscopic Changes Research Articles

Direct Probe of Room-Temperature Quantum-Tunneling Processes in Type-II Heterostructures Using Terahertz Emission Spectroscopy

Charge-carrier-transport phenomena on nanoscopic length and ultrashort timescales are of great interest for a multitude of ultrafast dynamic processes occurring in chemical reactions as well as modern devices such as solar cells or transistors. However, the investigation of such ultrashort current pulses is very challenging and mostly based on indirect methods such as spectroscopic changes induced by the charge transport. Here we monitor the short current pulse generated by the dissipative tunneling of charge carriers through a barrier between two adjacent quantum wells via its radiated legacy in the terahertz frequency range. By examining quantum structures with intermediate barriers of different thickness, we demonstrate that the spectrum of the emitted radiation is a direct measurement of the charge-transfer dynamics associated with the tunneling process. Our findings indicate that these incoherent tunnel currents do not start instantaneously but build up on a timescale of approximately 170 fs.

Copper-induced spectroscopic and structural changes in short peptides derived from azurin

The active sites of metalloproteins may be mimicked by designing peptides that bind to their respective metal ions. Studying the binding of protein ligands to metal ions along with the associated structural changes is important in understanding metal uptake, transport and electron transfer functions of proteins. Copper-binding metalloprotein azurin is a 128-residue electron transfer protein with a redox-active copper cofactor. Here, we report the copper-binding associated spectroscopic and structural properties of peptide loops (11 and 13 residues) from the copper-binding site of azurin. These peptides develop a β-turn upon copper-binding with a 1:1 Cu2+:peptide stoichiometry as seen in circular dichroism and exhibit electronic transitions centered at 340 nm and 540 nm. Further addition of copper develops a helical feature along with a shift in the absorption maxima to ~360 nm and ~580 nm at 2:1 Cu2+:peptide stoichiometry, indicating stoichiometric dependence of copper-binding geometry. Mass spectrometry indicates the copper-binding to cysteine, histidine and methionine in the peptide with 1:1 stoichiometry, and interestingly, dimerization through a disulfide linkage at 2:1 stoichiometry, as observed previously for denatured azurin. Fluorescence quenching studies on peptides with tryptophan further confirm the copper-binding induced changes in the two peptides are bi-phasic.

Electrochemical Oxidation of Δ9-Tetrahydrocannabinol: A Simple Strategy for Marijuana Detection.

Recently, it has been estimated that nearly 200 million people use marijuana with growing usage being attributed to the legalization and decriminalization of the drug around the world. A concerning implication of increased marijuana use is the alarming number of individuals who report driving under the influence of the drug, which has prompted the development of detection technologies. An electrochemical-based detection technology, akin to how the alcohol breathalyzer functions, would provide an attractive solution to this growing societal problem. The first step toward this goal is to develop a reaction that converts Δ9-tetrahydrocannabinol (Δ9-THC), the primary psychoactive substance in marijuana, to a derivative with diagnostic spectroscopic changes. We report the development of a mild electrochemical method for the oxidation of Δ9-THC to its corresponding p-quinone isomer. The photophysical and electrochemical properties of the resultant quinone show a dramatic shift in comparison to Δ9-THC. This simple protocol provides the foundation for the development of an electrochemical-based marijuana breathalyzer.

Mercury (II) sensing via cyclization of a dithioamide into a benzimidazole derivative: A structural and spectroscopic study

An o-phenylenediamine-derived dithioamide L was found to sense Hg(II) in the UV–visible via Hg(II)-mediated cyclization leading to a new benzimidazole derivative (L′). Both L and L′ have been characterized by single-crystal X-ray crystallography. The structure of L reveals relatively strong intramolecular H-bonding interactions of NH...S type. The extended structure is consolidated by several classical hydrogen bonding interactions. For L′, analysis of the packing pattern reveals few non-classical H-bonding contacts. Spectroscopic studies by FT-IR, UV–Visible, 1H-and 13C NMR support the single-crystal X-ray crystallography results and confirm the formation of the new benzimidazole derivative. UV–Vis titrations suggest and NMR confirms that the cyclization reaction occurs via an initial formation of a Hg(II) complex, which is too transient to be fully characterized. As this reaction is Hg(II)-mediated, dithioamide L acts as a selective Hg(II) sensor as shown by UV–Visible titrations and a selectivity study against Pb(II), Cd(II), Ca(II), Zn(II), Ag(I), and Cr(III): For Hg(II), but not for other metals, a distinct color change from yellow to pink is observed with corresponding UV–Vis spectroscopic changes and an isosbestic point at 270 nm.

α-Helical protein absorption at post-traumatic epileptic foci monitored by Fourier transform infrared mapping

Tissue analysis by Fourier transform infrared (FTIR) imaging can determine the biodistribution of molecules, without pre-analytical modification. We aimed to study the infrared spectroscopic changes of α-helical proteins at post-traumatic epileptic (PTE) foci by FTIR. FITR mapping was applied to detect α-helical proteins in rat brain tissue samples with post-traumatic epilepsy. Histological examination of brain sections showed that the rat model of PTE was successfully established. At the PTE foci, high α-helical absorption regions were evident, where the color difference and absorption were significantly different from those in the low-absorption regions. This provided a distinctive and characteristic pattern at the site of lesions. The use of FTIR imaging means that it is possible to measure the molecular structural changes resulting from PTE pathologies in tissues, providing a novel adjunct to conventional pathological diagnostic techniques.

Multianalytical approach of stay-in-place polyvinyl chloride formwork concrete exposed to high temperatures

This work presents results of the first study of the variation by exposure to high temperatures from two stay-in-place polyvinyl chloride (SIP-PVC) formwork concrete exposed to the ISO 834 fire curve. A systematic sampling based on the proximity of the fire and the spalling of the concrete was carried out and microstructural, thermal, crystallographic and spectroscopic changes were studied according to the degree of affectation by fire using SEM, TGA-DTA, XRD and FTIR. The response to high temperature exposure of the microstructure of SIP-PVC formwork concrete after fire was established using the experimental results. Results show a relationship between the microstructure of concrete paste and exposure temperature, as well as, the relationship between exposure temperature and dehydration of calcium hydrates, CSH gel and Portlandite and decarbonation of Calcite. These reactions can be considered as tracers of the degree of exposure to high temperatures from stay-in-place PVC formwork concrete.

Reversible Interlayer Sliding and Conductivity Changes in Adaptive Tetrathiafulvalene-Based Covalent Organic Frameworks.

Ordered interlayer stacking is intrinsic in two-dimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors.

Platinum(II) Probes for Sensing Polyelectrolyte Lengths and Architectures.

Platinum(II) polypyridine complexes of a square-planar geometry have been used as spectroscopic reporters for quantification of various charged species through non-covalent metal-metal interactions. The characterization of molecular weights and architectures of polyelectrolytes represents a challenging task in polymer science. Here, we report the utilization of platinum(II) complex probes and non-covalent metal-metal interactions for sensing polyelectrolyte lengths and architectures. It is found that the platinum(II) probes can bind to linear polyelectrolytes via electrostatic attractions and give rise to significant spectroscopic changes associated with the formation of metal-metal interactions, and the extent of the spectroscopic changes is found to increase with the lengths of the linear polyelectrolytes. Besides, the platinum(II) probes have been found to co-assemble with the linear polyelectrolytes to form well-defined nanofibers, and the lengths of the linear polyelectrolytes can be directly estimated from the diameter of the nanofibers under transmission electron microscopy observation. Interestingly, upon mixing with the platinum(II) probes, polyelectrolytes with bottlebrush architectures have been found to exhibit larger spectroscopic changes than linear polyelectrolytes with the same chemical composition. Combined with the reported theoretical studies on counterion condensation of polyelectrolytes, the platinum(II) complexes are found to function as spectroscopic probes for sensing the charge densities of the polyelectrolytes with different lengths and diverse architectures. Moreover, platinum(II) probes pre-organized in nanostructured aggregates have been found to intercalate into double-stranded DNA, which are naturally occurring biological polyelectrolytes with helical architectures and intercalation sites, to give significant enhancement of spectroscopic changes when compared to the intercalation of monomeric platinum(II) probes into double-stranded DNA.

Infrared and 2-Dimensional Correlation Spectroscopy Study of the Effect of CH3NH3PbI3 and CH3NH3SnI3 Photovoltaic Perovskites on Eukaryotic Cells.

We studied the effect of the exposure of human A549 and SH-SY5Y cell lines to aqueous solutions of organic/inorganic halide perovskites CH3NH3PbI3 (MAPbI3) and CH3NH3SnI3 (MASnI3) at the molecular level by using Fourier transform infrared microspectroscopy. We monitored the infrared spectra of some cells over a few days following exposure to the metals and observed the spectroscopic changes dominated by the appearance of a strong band at 1627 cm−1. We used Infrared (IR) mapping to show that this change was associated with the cell itself or the cellular membrane. It is unclear whether the appearance of the 1627 cm−1 band and heavy metal exposure are related by a direct causal relationship. The spectroscopic response of exposure to MAPbI3 and MASnI3 was similar, indicating that it may arise from a general cellular response to stressful environmental conditions. We used 2D correlation spectroscopy (2DCOS) analysis to interpret spectroscopic changes. In a novel application of the method, we demonstrated the viability of 2DCOS for band assignment in spatially resolved spectra. We assigned the 1627 cm−1 band to the accumulation of an abundant amide or amine containing compound, while ruling out other hypotheses. We propose a few tentative assignments to specific biomolecules or classes of biomolecules, although additional biochemical characterization will be necessary to confirm such assignments.

Benzimidazole-isoquinolinone functioned thiourea for selective and reversible recognition of fluoride ion

Two novel fluoride ion probes 11-(2-iminothiourea-2-phenyl)benzimidazole-isoquinolinone (3) and 10-(2-iminothiourea-2-phenyl)benzimidazole-isoquinolinone (3′) have been designed, synthesized and confirmed structurally by 1H NMR、13C NMR and HRMS-ESI. Obvious color changes could be seen by naked-eye after the addition of F− to the DMSO solution of above probes. Both probes showed dual-channel properties: UV–vis absorption red-shift and fluorescence turn-off upon reacting with F−. More importantly, the F− induced visual and spectroscopic changes were fully reversible upon addingHSO4-.And the new probes could realize the distinguish recognition of F− and OH− by adding over 40 equivalents OH−. The detection limits of new probes were 0.6 nM. The recognition mechanism deduced from the 1H NMR titration experiment and theoretical calculation was a combined process including hydrogen bonding and deprotonation between the probes and fluoride ion.

Preferential solvation and perichromic behavior of the dyes indigo carmine, amaranth and tartrazine: Spectroscopic approach using binary mixtures

The spectroscopic characteristics of three food dyes, two azo dyes (amaranth and tartrazine) and one indigo dye (indigo carmine), were studied using five amphiprotic alcohols in solvent mixtures: water-methanol, water-ethanol, water-iso-propanol, water-n-propanol and water-t-butanol. The preferential solvation of each dye in different binary mixtures was investigated. The dyes studied are widely used as food dyes and although they do not have solvatochromic properties slight spectroscopic changes were observed in the binary mixtures in the presence of tartrazine and indigo carmine. Tartrazine (TTY) presented spectral changes at the maximum wavelength (λmax) in the ultraviolet region while indigo carmine (INC) presented spectral changes at λmax in the visible region of the electronic spectrum. The parameters obtained from the nonlinear fit of the preferential solvation (PS) indicate that with the use of TTY as a spectroscopic probe the parameters f12/1 and f2/1 being >1 for the mixtures water-iso-propanol and water-t-butanol for which the values are less than 1 (<1), indicating that the solute is preferentially solvated by water rather than alcohol. The use of INC as a colorimetric probe provides a similar profile and it is preferentially solvated by water.

Enhanced electrical properties of few layers MoS2-PVA nanocomposite film via homogeneous dispersion and annealing effect induced by 80 MeV Carbon6+ swift heavy ion irradiation

Swift heavy ion beam irradiation is an advanced method to tune or modify the properties of a wide class of materials up to an electronic level. High-performance polymer nanocomposites are a class of materials that have drawn immense scientific attention due to their remarkable properties in the field of organic electronics. In this work, MoS2 nanosheets are first synthesized via solvent assisted exfoliation and then incorporated as filler in Polyvinyl alcohol matrix. The free-standing polymer nanocomposite film was irradiated using 80 MeV Carbon swift ion beam at 1 × 1010 ions/cm2, 1 × 1011 ions/cm2 and 3 × 1011 ions/cm2 to induce structural, spectroscopic and electrical changes due to high deposition of energy. XRD and Raman reveal the annealing effect at low fluence of at 1 × 1010 ions/cm2. Upon Swift heavy ion irradiation, a remarkable rise in the conductivity for application in organic electronics, from 2.58E-5 S/cm to 2.43E-3 S/cm at 1 × 1010 ions/cm2 has been observed. The conductivity continues to rise with increase in ion fluence and attains a value of 4.92E-3 S/cm at 3 × 1011 ions/cm2. This is attributed to the formation of conductive tracks and homogeneous dispersion upon SHI irradiation in accordance with Thermal spike model.

A water-soluble fluorescent probe for the detection of thiophenols in water samples and in cells imaging

Water pollution is the main cause of death of aquatic organisms such as fish et al. Content of thiophenols in water samples is an important indicator for assessing the degree of water pollution. The development of fluorescent probes with high selectivity and high sensitivity to detect thiophenols in water samples is extremely important in both environmental and life sciences. Although several fluorescent probes for thiophenols detection have been reported in recent years, most of them required the assistance of organic solvents to remedy the restriction caused by the poor water solubility of the probe, which did not fully reflect the actual situation of thiophenols in actual water samples. To fully overcome this shortage, we modified the 1,8-naphthylimide moiety with carboxyl to obtain a water-soluble fluorescent probe which could react with thiophenols specifically through nucleophilic aromatic substitution reaction (SNAr) reaction with turn-on fluorescent responses. The corresponding detection limit was 71nM. Supported by the spectroscopic changes, test strips based on the probe could detect thiophenols quantificationally and conveniently. At the same time, the probe could detect thiophenols in water sample with quantitative recovery. Besides, cell imaging experiments demonstrated the possibility of the probe to detect thiophenols in living cells.

Real-time monitoring of newly acidified organelles during autophagy enabled by reaction-based BODIPY dyes

Real-time monitoring of newly acidified organelles during autophagy in living cells is highly desirable for a better understanding of intracellular degradative processes. Herein, we describe a reaction-based boron dipyrromethene (BODIPY) dye containing strongly electron-withdrawing diethyl 2-cyanoacrylate groups at the α-positions. The probe exhibits intense red fluorescence in acidic organelles or the acidified cytosol while exhibiting negligible fluorescence in other regions of the cell. The underlying mechanism is a nucleophilic reaction at the central meso-carbon of the indacene core, resulting in the loss of π-conjugation entailed by dramatic spectroscopic changes of more than 200 nm between its colorless, non-fluorescent leuco-BODIPY form and its red and brightly emitting form. The reversible transformation between red fluorescent BODIPY and leuco-BODIPY along with negligible cytotoxicity qualifies such dyes for rapid and direct intracellular lysosome imaging and cytosolic acidosis detection simultaneously without any washing step, enabling the real-time monitoring of newly acidified organelles during autophagy.

The Multiple Roles of the Protein in the Photoactivation of Orange Carotenoid Protein

Summary Orange carotenoid protein (OCP) is a carotenoid-binding protein involved in photo-protection mechanisms of cyanobacteria. Upon exposure to high light, OCP interconverts from an orange resting form (OCPO) to a red active one (OCPR); the mechanism of this interconversion, even if extensively studied, has still not been fully elucidated. In this work, we use multiscale atomistic models ranging from classical to hybrid quantum-classical (QM/MM) molecular dynamics to give a comprehensive molecular explanation of the drastic spectroscopic changes observed upon interconversion. The findings are finally used to formulate a new hypothesis on the role of the protein in the photoactivation mechanism.

Understanding extreme quasar optical variability with CRTS – II. Changing-state quasars

ABSTRACT We present the results of a systematic search for quasars in the Catalina Real-time Transient Survey exhibiting both strong photometric variability and spectroscopic variability over a decadal baseline. We identify 111 sources with specific patterns of optical and mid-infrared photometric behaviour and a defined spectroscopic change. These ‘changing-state’ quasars (CSQs) form a higher luminosity sample to complement existing sets of ‘changing-look’ AGNs and quasars in the literature. The CSQs (by selection) exhibit larger photometric variability than the changing-look quasars (CLQs). The spectroscopic variability is marginally stronger in the CSQs than CLQs as defined by the change in H β/[$\rm {O \,\rm {\small {III}}}$] ratio. We find 48 sources with declining H β flux and 63 sources with increasing H β flux, and discover 8 sources with $z$ &amp;gt; 0.8, further extending the redshift arm. Our CSQ sample compares to the literature CLQ objects in similar distributions of H β flux ratios and differential Eddington ratios between high (bright) and low (dim) states. Taken as a whole, we find that this population of extreme varying quasars is associated with changes in the Eddington ratio and the time-scales imply cooling/heating fronts propagating through the disc.

Dual macro-cyclic component based logic diversity

In continuation of our recent studies on the photophysics of a photodynamic therapeutic agent, harmine (HM) in model membrane, the present contribution highlights a new model to design multiple logic circuits, a memory device and a molecular lock regulated by dual macrocyclic components as chemical inputs. The unique reversible photoswitching regulated by macrocyclic components plays decisive role in the manifestation of the final outputs for the logic functions. Inspired by this phenomenon, herein, we are reporting the use of a photosensitizer molecule for designing of various logic circuits at molecular level with the intention to escalate the next generation molecular logic arena. For these desired outsets, fluorescence spectroscopic changes of HM upon addition of macrocyclic components (CTAB and β-CD) were utilised. Beyond the simple single input single output logic gates (NOT, YES, PASS 0 and PASS 1), we were also able to design IMPLICATION and INHIBIT gates. In addition to different logic functions, the modulations of the optical responses of HM driven by the macrocyclic components were employed to design “Erase-Read-Write-Read” and “Write-Read-Erase-Read” type memory units. Moreover, considering the optical responses of HM we proposed a supramolecular keypad lock operated through unique sequential entry of opto-chemical passwords.

Studying crystal-field splitting difference of Eu3+ ions from orthorhombic to cubic Ca4Al6SO16

Eu3+ lanthanide ion possesses abundant 4f-4f transition lines in the visible spectral region, and its spectroscopic changes can sensitively reflect the variation of local ligand environments. Here, Eu3+ ions are successfully introduced into Ca4Al6SO16 lattice, and the structural difference from orthorhombic (o-Ca4Al6SO16) to cubic (c-Ca4Al6SO16) phases is systematically analyzed. On that basis, the related influence on crystal-field splitting of Eu3+ ions is discussed in detail. The obtained results indicate that Eu:o-Ca4Al6SO16 and Eu:c-Ca4Al6SO16 have three and two non-degenerate 5D0→7F0 transition peaks, respectively. Through the theoretical analysis and low-temperature (78 K) luminescent investigation with changing the excitation wavelength, those non-equivalent Ca2+ sites are assigned as o-Ca(1) (~577.6 nm), o-Ca(3) (~579.6 nm), o-Ca(4) (~580.6 nm), c-Ca(1) (~578.7 nm), and c-Ca(2) (~580.2 nm), respectively. In addition, with the increase of c-Ca4Al6SO16 content in the sintered product, the fluorescence intensity ratios of I580.6/I613.7, I616.2/I613.7 and I621/I613.7 present a gradual decreasing tendency. And, the introduction of c-Ca4Al6SO16 into the as-prepared product is beneficial for increasing the decay lifetime of the 5D0 excited state and enhancing the resistance capability to thermally induced fluorescence quenching. What discussed in this work might provide some useful thoughts for multi-phase studies and broaden the application range of lanthanide fluorescent probes.

Tilapia Protein Hydrolysate Enhances Transepithelial Calcium Transport in Caco2 cells

Background: Potent calcium uptake is essential for calcium balance and normal health. Prolonged low intake of calcium is associated with osteoporosis, dental changes, cataracts, and alterations in the brain. However, calcium is difficult to be directly absorbed from the food due to the insoluble calcium salt precipitation that occurs in the intestinal environment. Methods: Tilapia protein hydrolysate (TPH) was prepared by alcalase digestion. The Calcium-binding activity was measured using calcium colorimetric assay, the absorption at 612 nm. The interaction between TPH and calcium was examined by spectroscopic analysis, ultraviolet absorption and fluorescence measurement. TPH-calcium-binding stability in the human digestion system was evaluated by in vitro pepsin-pancreatin hydrolysis simulating human gastric and intestinal digestion. The effects of food components on TPH-calcium-binding activity was also analyzed. The enhancement of transepithelial calcium transport by TPH was determined by in vitro Caco2 epithelial cell-like monolayer. Results: TPH produced from Nile tilapia (Oreochromis niloticus) exhibited calcium-binding activity. It was the peptides in the hydrolysate that contributed to calcium-binding since the spectroscopic changes induced by calcium were characteristic of peptide bonds and tryptophan residues. The calcium binding of TPH was compatible with food matrices. Most food components including saccharides, amino acids and vitamins showed positive or no effects on calcium-binding. The calcium-binding of TPH was also stable in the simulated gastrointestinal digestion system. Pepsin and pancreatin did not considerably change the calcium-binding activity of TPH. Of note, TPH reduced precipitation of calcium by oxalate and phytate, the two most anti-nutritional factors present in green leafy vegetables. Finally, we showed that TPH significantly promoted transepithelial calcium transport in the Caco-2 cell permeability model. Conclusions: Tilapia protein hydrolysate produced by alcalase digestion possessed calcium-binding activity and prevent precipitation of calcium by a mineral chelating agent as well as enhanced transepithelial calcium transport in Caco2 cell. The result implicated the potential of TPH as a functional food ingredient for promoting calcium absorption. Keywords: Tilapia protein hydrolysate; Calcium binding peptides; Calcium absorption

Theoretical Studies of IR and NMR Spectral Changes Induced by Sigma-Hole Hydrogen, Halogen, Chalcogen, Pnicogen, and Tetrel Bonds in a Model Protein Environment.

Various types of σ-hole bond complexes were formed with FX, HFY, H2FZ, and H3FT (X = Cl, Br, I; Y = S, Se, Te; Z = P, As, Sb; T = Si, Ge, Sn) as Lewis acid. In order to examine their interactions with a protein, N-methylacetamide (NMA), a model of the peptide linkage was used as the base. These noncovalent bonds were compared by computational means with H-bonds formed by NMA with XH molecules (X = F, Cl, Br, I). In all cases, the A–F bond, which lies opposite the base and is responsible for the σ-hole on the A atom (A refers to the bridging atom), elongates and its stretching frequency undergoes a shift to the red with a band intensification, much as what occurs for the X–H bond in a H-bond (HB). Unlike the NMR shielding decrease seen in the bridging proton of a H-bond, the shielding of the bridging A atom is increased. The spectroscopic changes within NMA are similar for H-bonds and the other noncovalent bonds. The C=O bond of the amide is lengthened and its stretching frequency red-shifted and intensified. The amide II band shifts to higher frequency and undergoes a small band weakening. The NMR shielding of the O atom directly involved in the bond rises, whereas the C and N atoms both undergo a shielding decrease. The frequency shifts of the amide I and II bands of the base as well as the shielding changes of the three pertinent NMA atoms correlate well with the strength of the noncovalent bond.