Fluorescence Spectroscopy Measurements Research Articles

Design of parallel 𝛽-sheet nanofibrils using Monte Carlo search, coarse-grained simulations, and experimental testing.

Peptide self-assembly into amyloid fibrils provides numerous applications in drug delivery and biomedical engineering applications. We augment our previously-established computational screening technique along with experimental biophysical characterization to discover 7-mer peptides that self-assemble into "parallel β-sheets", that is, β-sheets with N-terminus-to-C-terminus 𝛽-strand vectors oriented in parallel. To accomplish the desired β-strand organization, we applied the PepAD amino acid sequence design software to the Class-1 cross-β spine defined by Sawaya et al. This molecular configuration includes two layers of parallel β-sheets stacked such that N-terminus-to-C-terminus vectors are oriented antiparallel for molecules on adjacent β-sheets. The first cohort of PepAD identified peptides were examined for their fibrillation behavior in DMD/PRIME20 simulations, and the top performing sequence was selected as a prototype for a subsequent round of sequence refinement. The two rounds of design resulted in a library of eight 7-mer peptides. In DMD/PRIME20 simulations, five of these peptides spontaneously formed fibril-like structures with a predominantly parallel 𝛽-sheet arrangement, two formed fibril-like structure with <50% in parallel 𝛽-sheet arrangement and one remained a random coil. Among the eight candidate peptides produced by PepAD and DMD/PRIME20, five were synthesized and purified. All five assembled into amyloid fibrils composed of parallel β-sheets based on Fourier transform infrared spectroscopy, circular dichroism, electron microscopy, and thioflavin-T fluorescence spectroscopy measurements.

Synthesis, Crystal Structure, Fluorescence and Theoretical Calculations of Three Zn(II)/Cd(II) Complexes with Bis-dentate N,N-Quinoline Schiff Base.

Three d10 metal complexes, ZnL(OAc)2 (1), CdL(OAc)2 (2) and [CdL2(NO3)2]·CH3CN (3) were synthesized using the ligand (E)-N-(3-methoxy-4-methylphenyl)-1-(quinolin-2-yl)methanimine (L) and characterized by FT-IR spectra, NMR spectra, and CHN elemental analysis. Single-crystal X-ray diffraction analysis revealed that complexes 1 and 2 are isostructural, with the central metal adopting a hexacoordinate octahedral geometry, while complex 3 adopts a triangular dodecahedron geometry. Thermal gravimetric analysis showed that these complexes exhibit good thermal stability. Solid-state fluorescence spectroscopy measurements demonstrated that complexes 1-3 exhibit bright yellow-green fluorescence (λem = 564nm for 1; 524nm for 2; 542nm for 3), suggesting their potential as photoluminescent materials. Furthermore, DFT calculations, including frontier molecular orbitals, energy levels, and surface electrostatic potential, provided insights into the structural and electronic spectral properties of complexes 1-3.

Conjugated diacetylene polymers with intrachain D-A block heterostructure for efficient photocatalytic hydrogen production

Solar-driven photocatalytic hydrogen production has been considered as a promising candidate technology for supplying green and sustainable energy source alternative to fossils. But its low solar-to-hydrogen conversion efficiency level hampers its practical application, and lack of effective structure for promoting charge separation is one of the accounts. Herein, intrachain heterojunction structure comprised of donor-acceptor (D-A) blocks has been proved to be one of effective structures for addressing such an issue. Utilizing the facile oxidative coupling polymerization reactions of diacetylene monomers and oligomers, a block heterojunction polymeric photocatalyst named PDTPDPA-BP bearing D-A blocked heterostructure was synthesized by first separative oligomerizations of diacetylene-functionalized dibenzothiophene sulfone (DTP) and triphenylamine (TPA) monomers and then mixed together and undergoing further polymerization. In photocatalytic hydrogen production, PDTPDPA-BP displayed a hydrogen evolution rate of 2164 μmol g−1 h−1, which is much larger than those of PDTP (1270 μmol g−1 h−1) and PTPA (57 μmol g−1 h−1) synthesized by homopolymerization of DTP and TPA monomers, respectively, and their 1:1 molar ratio physical blend (363 μmol g−1 h−1). By means of Fluorescence spectroscopy and photo-responsive measurements, it was found PDTPDPA-BP has narrower bandgap and more efficient charge separation than the other polymers. Therefore, the work highlights intrachain heterojunction structure promotes exciton dissociation into free charge carries, and thus deserves the consideration in the design of high performance organic photocatalysts.

Uptake of Cm (III) and Eu (III) by C–S–H phases under saline conditions in presence of EDTA: A batch sorption and TRLFS study

Eu (III) and Cm (III) uptake by calcium silicate hydrate phases (C–S–H) was investigated in presence of EDTA in NaCl and CaCl2 solutions. Different experimental parameters, i.e., ionic strength (0.1 m ≤ I'm ≤ 5.05 m), ligand concentration (10−5 m ≤ [EDTA] ≤ 10−2 m), calcium-to-silicon ratio (0.6 ≤ C/S ≤ 1.3) and sorption time (7 d ≤ t ≤ 365 d) were varied in the frame of batch sorption experiments and Time Resolved Laser Fluorescence spectroscopy (TRLFS) measurements. No effect of EDTA on the retention of Eu(III)/Cm(III) by C–S–H phases in NaCl or CaCl2 systems was observed at ligand concentrations ≤ 10−3 M. In NaCl solutions with [EDTA] = 10−2 M and C/S < 1.3, low retention (log Rd = 2–3, with Rd in L∙kg−1) of Eu(III) was detected after 7 d of sorption time, while strong retention (log Rd = 5–6) was observed after 50 d. This behaviour was explained by the initial stabilization of Eu(III)/Cm(III) in the aqueous phase due to the formation of two aqueous Eu(III)/Cm(III)-(OH)n-EDTA complexes, followed by the slow incorporation of Eu(III)/Cm(III) into the C–S–H structure. In CaCl2 solutions for all C/S ratios, as well as in NaCl solutions for C/S ∼ 1.3, the presence of [EDTA] = 10−2 M led to a significant decrease of the uptake (log Rd = 2–3) after 7 and 50 d of contact time. This effect was explained by the formation of stable aqueous Ca–Eu(III)/Cm(III)-EDTA complexes triggered by the presence of moderate to high Ca concentrations. No evident effect caused by increased ionic strength conditions could be confirmed in our sorption experiments.Results obtained in batch sorption experiments are underpinned by TRLFS data, with the observation of three main aqueous species, tentatively defined as Cm(OH)(EDTA)2-, Cm(OH)x (EDTA)-(x+1) and Ca–Cm(III)-EDTA, as well as a fourth species corresponding to Cm(III) incorporated in the CaO-layer of the C–S–H phases. In spite of the thermodynamic stability of the CaEDTA2− complex, which reduces the concentration of free EDTA, the formation of ternary Ca–Eu(III)/Cm(III)-EDTA complexes is expected to result in a significant impact of EDTA on the uptake of An (III)/Ln (III) by cement at high ligand concentrations. The assumption that Ca outcompetes actinides for the complexation with EDTA in cementitious systems may need to be revisited under these conditions.

Investigation of collagen reconstruction mechanism in skin wound through dual-beam laser welding: Insights from multi-spectroscopy, molecular dynamics simulation, and finite element multiphysics simulation

Since the mechanism underlying real-time acquisition of mechanical strength during laser-induced skin wound fusion remains unclear, and collagen is the primary constituent of skin tissue, this study investigates the structural and mechanical alterations in collagen at temperatures ranging from 40 °C to 60 °C using various spectroscopic techniques and molecular dynamics calculations. The COMSOL Multiphysics coupling is employed to simulate the three-dimensional temperature field, stress-strain relationship, and light intensity distribution in the laser thermal affected zone of skin wounds during dual-beam laser welding process. Raman spectroscopy, synchronous fluorescence spectroscopy and circular dichroism measurement results confirm that laser energy activates biological activity in residues, leading to a transformation in the originally fractured structure of collagen protein for enhanced mechanical strength. Molecular dynamics simulations reveal that stable hydrogen bonds form at amino acid residues within the central region of collagen protein when the overall temperature peak around the wound reaches 60 °C, thereby providing stability to previously fractured skin incisions and imparting instantaneous strength. However, under a 55 °C system, Type I collagen ensures macrostructural stability while activating biological properties at amino acid bases to promote wound healing function; this finding aligns with experimental analysis results. The COMSOL simulation outcomes also correspond well with macroscopic morphology after laser welding samples, confirming that by maintaining temperatures between 55 °C–60 °C during laser welding of skin incisions not only can certain instantaneous mechanical strength be achieved but irreversible thermal damage can also be effectively controlled. It is anticipated that these findings will provide valuable insights into understanding the healing mechanism for laser-welded skin wounds.

Co (II), Ni (II), and Cu (II) ternary complexes with 2,6‐pyridinedicarboxylic acid: Thermal decomposition, DNA interaction, and biological activity studies

Three novel ternary complexes [MII (PDA)(o‐phen)(H2O)] (MII = CoII, NiII, and CuII) were synthesized using 2,6‐pyridinedicarboxylicacid as a primary ligand and 1,10‐phenanthroline(o‐phen) as the auxiliary ligand and analyzed by FT‐IR, mass, UV–Vis, thermogravimetry analysis, and conductivity measurement data. Based on electronic spectral measurements, all three of the metal complexes were found to have octahedral stereochemistry. The way metal complexes interact with ct‐DNA was studied using various methods including absorption spectroscopy, fluorescence spectroscopy, and viscosity measurements. UV–Vis absorption technique has been used to explore the binding characteristics of M (II) complexes with ct‐DNA. The complexes bind to DNA via groove mode of binding, according to the spectral data. The salt‐dependent binding of ternary metal complexes to ct‐DNA has been studied by UV–Vis spectrophotometric titration experiment. Furthermore, gel electrophoresis is used to examine how the metal complexes interacted with the pBR322 DNA. The outcomes showed that these compounds can function as efficient DNA cleaving agents. Studies on the complexes' in vitro antibacterial activity demonstrated their importance and good antimicrobial activity at three distinct concentrations (50, 75, and 100 g/mL).

Nanogel-type nano-objects from a random polyelectrolyte through intermolecular cross-linking

Polyelectrolyte nanogel-like nano-objects were synthesized from poly((2-dimethylamino) ethyl methacrylate-co-oligoethylene glycol methacrylate), P(DMAEMA-co-OEGMA), random copolymers through covalent cross-linking with the hydrophobic 1,12-dibromododecane difunctional quaternizing agent, with varying degrees of cross-linking, corresponding to different dimethylamino group molar conversions to quaternized, permanently cationic amino groups. Physicochemical characterization, employing dynamic and electrophoretic light scattering (DLS, ELS), along with fluorescence spectroscopy (FS) measurements under various solution conditions elucidated distinct self-assembled structures of the formed polymer networks, most probably due to the utilization of the hydrophilic random copolymers as precursor macromolecules. The nanogels demonstrated pH responsiveness and temperature sensitivity, advantageous for applications requiring controlled release or environmental adaptability, while the stability under high ionic strength conditions indicated their resilience in complex physiological environments and varying salinities. Furthermore, Nanogel 2, displaying a balanced response to environmental factors, was successfully complexed with protein ovalbumin (OVA). The produced OVA/Nanogel 2 complexes maintained their size under high salt concentrations and sustained colloidal stability over time, even under ultrasound exposure. Further characterization through Cryo-TEM and ATR-FTIR spectroscopy highlighted the efficient complexation of OVA, revealing varying co-assembled structures, including irregular nano-objects consisting of thread-like structures and sphere-like morphologies comprised of branched-like internal structures, dependent on the protein concentration. We expect that such hybrid nanostructures may be promising for enzyme immobilization and as vaccine-delivering vehicles with special morphologies.

Through-Plane Cerium Ion Migration and Diffusion Analysis on Plymer Electrolyte Membrane by Operando X-Ray Fluorescence Spectroscopy

High durability is a critical requirement for expanding the use of polymer electrolyte fuel cells (PEFCs). One degradation factor of PEFCs under typical operating conditions is electrolyte membrane degradation. Radical species formed from the reaction between hydrogen peroxide and impurities during fuel cell operation cause significant degradation of the PEM. To scavenge the radicals, cerium species are added to the PEM, which react with the radicals by redoxing the cerium ion [1]. To maintain the effectiveness of the cerium radical quencher in the PEM, the concentration of cerium in the PEM must be maintained during the long-term operation of the PEFC. However, cerium species easily diffuse and migrate out of the PEM [2]. If the cerium ion is depleted, the PEM will be severely attacked by radicals. To prevent such cerium depletion, it is important to understand the cerium migration phenomena. Experimental detection of cerium distribution phenomena through PEM by operando X-ray fluorescence spectroscopy with resolution of several micrometers has been reported [3]. We have also developed operando XRF using focused micron X-ray with submicrometer resolution [4]. In this study, we further develop the analysis method for cerium diffusion through planar PEM with sub-second time resolution. This method is used to estimate the apparent diffusion coefficient of cerium in PEM.MEAs were prepared by a conventional method using a Pt/C catalyst and a cerium-containing polymer electrolyte with a thickness of 12 μm(GORE-SELECT® MEMBRANEM788.12). The active electrode area was 1.0 cm2. Single cells were assembled using custom end plates with an X-ray permeation window. Operando X-ray fluorescence spectroscopy measurements were performed on BL37XU at SPring-8 (Japan). The monochromated X-ray at an energy of 45 keV was focused to less than 500 nm by a Kirkpatrick-Baez mirror. To detect the cerium distribution in MEA, the fluorescence intensity of Ce-Kα was counted with a Ge semiconductor detector by scanning the position of the cell.In the open circuit condition, most of the cerium is present in the PEM, but during cell loading, the cerium moves to the cathode layer. Immediately after the start of 2.0 A cm-2 loading, the intensity of cerium in the cathode layer increases in a few seconds. Simultaneously, a cerium concentration gradient is observed through the MEA. The cerium concentration gradient shows the current density dependence. When the current load is stopped, the concentrated cerium in the catalyst layer diffuses into the PEM. The diffusion coefficient of cerium ion is estimated from the time dependence of cerium concentration in PEM.Acknowledgments: This work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. E. Endoh et al, ECS Electrochem. Lett., 2, F73 (2013).S. M. Stewart et al, ECS Electrochem. Lett., 3, F19 (2014).A. M. Baker et al, ECS Trans., 92, 107 (2019).Y. Orikasa et al, ECS Trans., 109 109 (2022).

A pure tetragonal europium-doped yttrium-stabilized zirconia thermal barrier coating: Phase structure and luminescence

YSZ:Eu powder was prepared by sol spray pyrolysis method. Thermal barrier coatings (TBCs) composed of Eu3+-doped pure tetragonal yttrium-stabilized zirconia (namely, YSZ:Eu) were fabricated by air-plasma spraying technique. Crystal structure and fluorescence intensity of YSZ:Eu coating were investigated after aging at 1200 °C for 5 − 100 h. X-ray diffraction (XRD) indicates that tetragonal phase in YSZ:Eu coating had high resistance to degradation over a wide range of time periods and temperatures. Luminescence results indicate that asymmetry ratios of the fluorescence emission spectra were stable in a range of 1.2 ± 0.2. Relationships between phase structure and lattice distortion were further studied by fluorescence spectroscopy measurement using I606/I590 intensity ratio. The fluorescence results were consistent with those drawn by XRD, where the high stability of YSZ:Eu coating was confirmed. Excellent thermal stability, in terms of both the phase structure and luminescence intensity, of YSZ:Eu coating indicates that the present preparation method is suitable for phosphor powder applications.

Sulfonamides stimulate ROS formation upon glycation of human carbonic anhydrase II

Advanced glycation end products are the most important species of glycation pathway, and cause disorders such as oxidative stress and diabetes. Sulfonamide compounds, which are generally known as widespread inhibitors, are potential agents used in different drug products, which can readily enter biological matrices. In the present work, the structure and activity of human carbonic anhydrase II studied in the presence of glucose as well as four sulfonamide agents from different views. These included enzyme kinetics, free lysine content, fluorescence spectroscopy, circular dichroism, and ROS measurement. Our results indicated that upon glycation, the structure of HCA II collapses and 8 to 13 lysine residues will be more available based on ligand incubation. Secondary and tertiary structural changes were also observed in the presence and absence of sulfonamide agents using fluorescence and circular dichroism methods, respectively. These spectroscopic data also showed a remarkable increase in hydrophobicity and decrease in α-helix contents during glycation, especially after 35 days of incubation. ROS assay was studied in the presence of glucose and sulfonamide compounds, that demonstrated the role of sulfonamide compounds in ROS formation in the presence of glucose in a synergistic manner. Overall, our data indicated that sulfonamides act as a stimulant factor upon prolonged interaction with HCA II and may intensify the complications of some disorders, such as diabetes and other conformational diseases.

Exploring the molecular and toxicological mechanism associated with interactions between heavy metals and the reproductive system of Mytilus galloprovincialis

A large number of heavy metals resulted toxic to the reproductive system, but invertebrate infertility has been poorly explored, and above all, there are limited molecular, cellular and toxicological studies. In the present work, we exposed Mytilus galloprovincialis to three individual metal chlorides (CuCl2 15 μM, CdCl2 1.5 μM, NiCl2 15 μM) and their mixture for 24 h, to evaluate the effects on the protamine-like proteins (PLs), sperm DNA and on their interaction in the formation of sperm chromatin. Under all exposure conditions, but particularly after exposure to the metals mix, relevant changes in the electrophoretic pattern, by AU-PAGE and SDS-PAGE, and in fluorescence spectroscopy measurements of PLs were shown. In addition, alterations in DNA binding of these proteins were observed by Electrophoretic Mobility Shift Assay (EMSA) and through their release from sperm nuclei. Moreover, there was evidence of increased accessibility of micrococcal nuclease to sperm chromatin, which was also confirmed by toluidine blue staining. Furthermore, morphological analyses indicated severe gonadal impairments which was also corroborated by increased PARP expression, by Western blotting, and sperm DNA fragmentation, by comet assay. Finally, we investigated the expression of stress genes, gst, hsp70 and mt10, in gonadal tissue. The latter investigations also showed that exposure to this metals mix was more harmful than exposure to the individual metals tested. The present results suggest that these metals and in particular their mixture could have a negative impact on the reproductive fitness of M. galloprovincialis. Based on these evidences, we propose a molecular mechanism.

Chromogenic sensing, biological, and optical properties of Schiff bases of 2-amino-6-methoxybenzothiazole

In this study, a new series of Schiff base benzothiazole derivatives were synthesized and their structures were characterized by elemental analysis, FTIR, UV–VIS and NMR spectroscopy. The biological, sensory and photophysical properties of the benzothiazole derivatives were investigated. The sensing properties of the compounds were investigated UV–VIS spectroscopically, calorimetrically and theoretically. All compounds showed colorimetric, fluorometric and spectroscopic sensor properties for F−, CN−, AcO−, H2PO4− and OH− anions. Furthermore, DNA binding, DNA cleavage and antioxidant activities of compounds 1-4 were investigated. All compounds affected pBR322 DNA both hydrolytically and oxidatively, interacted with DNA in electrostatic mode, and also compounds 1 and 2 exhibited antioxidant activity close to standard BHT. In addition, the effects of electron donating and accepting substituents on the emission properties and charge transfer dynamics were investigated by fluorescence and femtosecond transient absorption spectroscopy measurements, respectively. According to fluorescence measurements, compounds 3 and 4 showed emission signal, while compounds 1 and 2 showed fluorescence quenching and weaker emission signal.

2,7-Dichlorofluorescein Hydrazide loaded Zeolite HY: Colorimetric, Paper Strip and Fluorescent Sensor for Cu2+

In this work, 2,7-dichlorofluorescein dye is successfully loaded into zeolite HY and investigated as chemosensors. The synthesized sensor was characterized by various instrumental techniques. The dye loaded sensor FH@ZHY acts as a colorimetric as well as paper strip sensor for Cu2+. Fluorescence spectroscopic measurement shows that FH@ZHY exhibits high sensitivity and selectivity towards Cu2+ among various other metal ions in a EtOH/HEPES (1:1, v/v, pH = 7.2) solution. The behaviour of the sensor towards analyte detection was reversible with very low limit of detection. The sensing of Cu2+ ion

Higher sensitive selective spectrofluorometric determination of ritonavir in the presence of nirmatrelvir: application to new FDA approved co-packaged COVID-19 pharmaceutical dosage and spiked human plasma

BackgroundRitonavir was recently combined with nirmatrelvir in a new approved co-packaged medication form for the treatment of COVID-19. Quantitative analysis based on fluorescence spectroscopy measurement was extensively used for sensitive determination of compounds exhibited unique fluorescence features.ObjectiveThe main objective of this work was to develop higher sensitive cost effective spectrofluorometric method for selective determination of ritonavir in the presence of nirmatrelvir in pure form, pharmaceutical tablet as well as in spiked human plasma.MethodsRitonavir was found to exhibit unique native emission fluorescence at 404 nm when excited at 326 nm. On the other hand, nirmatrelvir had no emission bands when excited at 326 nm. This feature allowed selective determination of ritonavir without any interference from nirmatrelvir. The variables affecting fluorescence intensity of ritonavir were optimized in terms of sensitivity parameters and principles of green analytical chemistry. Ethanol was used a green solvent which provided efficient fluorescence intensity of the cited drug.ResultsThe method was validated in accordance with the ICH Q2 (R1) standards in terms of linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, precision and specificity. The described method was successfully applied for ritonavir assay over the concentration range of 2.0–20.0 ng/mL.ConclusionRitonavir determination in the spiked human plasma was successfully done with satisfactory accepted results.

Self‐Assembly of Water‐Soluble Glycoluril Molecular Clips Driven by Naphthalene‐Naphthalene Interaction

AbstractA water‐soluble C‐shaped receptors based on glycoluril and naphthalene building blocks is reported. The complexation formed in water was confirmed by 1H NMR spectroscopy and NOESY technique and DOSY technique. 1H NMR spectroscopy, fluorescence spectroscopy and DLS measurements provide strong evidence that compound 2 undergoes self‐recognition that naphthalene moiety can bind into the bisnaphthalene cleft and head‐to‐tail host–guest complexation to form new supramolecular assemblies in water. SEM and AFM visualized that the complexation formed the cyclic structure. This kind of highly designable monomer structure has great possibility to construct novel supramolecular polymer materials.

Integrating Fluorescent Nanodiamonds into Polymeric Microstructures Fabricated by Two-Photon Polymerization.

Nitrogen-vacancy (NV) and other color centers in diamond have attracted much attention as non-photobleaching quantum emitters and quantum sensors. Since microfabrication in bulk diamonds is technically difficult, embedding nanodiamonds with color centers into designed structures is a way to integrate these quantum emitters into photonic devices. In this study, we demonstrate a method to incorporate fluorescent nanodiamonds into engineered microstructures using two-photon polymerization (2PP). We studied the optimal concentration of nanodiamonds in the photoresist to achieve structures with at least one fluorescent NV center and good structural and optical quality. Fluorescence and Raman spectroscopy measurements were used to confirm the presence and location of the nanodiamonds, while absorbance measurements assessed scattering losses at higher concentrations. Our results show the feasibility of fabricating microstructures embedded within fluorescent nanodiamonds via 2PP for photonics and quantum technology applications.

Steel slags for enhanced removal of landfill leachate in a three-dimensional electrochemical oxidation system

In this study, a three-dimensional electrochemical oxidation system, with steel slags as particle electrodes, was applied to deal with landfill leachate. The characteristics of particle electrodes were investigated by scanning electron microscope (SEM), X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD) measurements. It was found that the steel slag exhibited rough and irregular surface and mainly consisted of SiO2 (Quartz), which indicated the enhanced absorbed and electroconducted abilities. Subsequently, comparative degradation tests between two-dimensional (2D) and three-dimensional (3D) electrochemical oxidation systems were carried out and results indicated removal efficiencies of COD. Moreover, NH4+-N from landfill leachate in 3D system was greatly improved compared with that of 2D system. Besides, operating conditions were also optimized to interelectrode distance of 1 cm, current density of 20 mA·cm−2, initial pH value of 4.4 and steel slag concentration of 0.30 g·mL−1, all of which were determined to guarantee excellent landfill leachate removal efficiency. In addition, a possible removal mechanism for this system was proposed. The introduction of steel slag particle electrodes in three-dimensional electrochemical oxidation system implied the concept for “using waste to treat waste”, providing a workable way in pollutant elimination.

Photophysical characterization of isothiazologuanosine, a unique isomorphic and isofunctional fluorescent analogue of guanosine

Application of fluorescence techniques to investigate molecular interactions with nucleic acids is complicated by their poor emission, making the substitution of natural nucleobases by fluorescent nucleoside analogues (FNAs) a useful strategy. A breakthrough in fluorescent nucleoside analogues has been the development of thienoguanosine (thG) and isothiazologuanosine (tzG), two isosteric mimics of guanosine (G). Due to its N7 atom needed in Hoogsteen base pairs and enzyme recognition, tzG is also an isofunctional G surrogate. Herein, we integrated fluorescence spectroscopy measurements with quantum mechanical (QM) calculations to characterize the mechanisms underlying tzG photophysics in different solvents. In dioxane and ethyl acetate, tzG existed primarily as a H1 keto-amino tautomer with short fluorescence lifetime (τ ∼ 2 ns) and low quantum yield (ϕ ∼ 0.10). In buffer, the H1 tautomer (ϕ = 0.36, τ = 8.84 ns) coexisted with a weakly emissive H3 keto-amino tautomer. The two tautomers were also observed in methanol, but with a 30% decrease in ϕ and τ values for the major H1 tautomer. QM calculations suggested that the main non-radiative pathway of tzG-H1 involves NS bond loosening and is responsible for the more solvent-sensitive ϕ and τ values compared to thG. This pathway is much more efficient for tzG-H3, for which an additional pathway to a dark nπ* state and a large coupling with triplet states further explain its very low emission. This study lays the ground for rationally using tzG as a sensitive FNA.

Fit-free analysis of fluorescence lifetime imaging data using chemometrics approach for rapid and nondestructive wood species classification

Abstract Conventional fluorescence spectroscopy has been suggested as a valuable tool for classifying wood species rapidly and non-destructively. However, because it is challenging to conduct absolute emission intensity measurements, fluorescence analysis statistics are difficult to obtain. In this study, another dimension of fluorescence, that is, fluorescence lifetime, was further evaluated to address this issue. A time-resolved fluorescence spectroscopic measurement system was first designed, mainly using a streak camera, picosecond pulsed laser at 403 nm, and a spectroscope, to collect the fluorescence time-delay (FTD) profiles and steady-state fluorescence intensity (FI) spectra simultaneously from 15 wood species. For data analysis, principal component analysis was used to “compress” the mean-centered FTD and FI spectra. Then, support vector machine classification analysis was utilized to train the wood species classification model based on their principal component scores. To avoid overfitting, ten-fold cross-validation was used to train the calibration model using 70 % of the total samples, and the remaining 30 % hold-out validation was used to test its reproducibility. The cross-validation accuracies were 100 % (5 softwoods) and 96 % (10 hardwoods), with test-validation accuracies of 96 % and 89 %.

Numerical analysis of pulsed extraction of ions from a 16-Pole / 16-Wire ion trap for time-of-flight mass spectrometry

Multipole radiofrequency ion traps are versatile tools for trapping and manipulating ions. The extraction of ions from such a trap leads to broad time-of-flight (ToF) distributions, which make it incompatible with ToF mass spectrometry. In this work, we conducted numerical simulations of biomolecular ions stored in 16-pole and 16-wire ion traps to analyze their extraction characteristics. We show that the ions extracted from a wire trap with a simple upgrade exhibit ToF distributions two orders of magnitude narrower than that typically results from conventional ion traps. Further, in the upgraded design, the ions can be confined within a much narrower region, which, together with higher optical access of the wire trap configuration, makes it compatible with fluorescence spectroscopy measurements.