Band Intensity Research Articles

Spectator Exciton Effects in Nanocrystals III: Unveiling the Stimulated Emission Cross Section in Quantum Confined CsPbBr3 Nanocrystals.

Quantifying stimulated emission in semiconductor nanocrystals (NCs) remains challenging due to masking of its effects on pump-probe spectra by excited state absorption and ground state bleaching signals. The absence of this defining photophysical parameter in turn impedes assignment of band edge electronic structure in many of these important fluorophores. Here we employ a generally applicable 3-pulse ultrafast spectroscopic method coined the "Spectator Exciton" (SX) approach to measure stimulated-emission efficiency in quantum confined inorganic perovskite CsPbBr3 NCs, the band edge electronic structure of which is the subject of lively ongoing debate. Our results show that in 5-6 nm CsPbBr3 NCs, a single exciton bleaches more than half of the intense band edge absorption band, while the cross section for stimulated emission from the same state is nearly 6 times weaker. Discussion of these findings in light of several recent electronic structure models for this material proves them unable to simultaneously explain both measures, proving the importance of this new input to resolving this debate. Along with femtosecond time-resolved photoluminescence measurements on the same sample, SX results also verify that biexciton interaction energy is intensely attractive with a magnitude of ∼80 meV. In light of this observation, our previous suggestion that biexciton interaction is repulsive is reassigned to hot phonon induced slowdown of carrier relaxation leading to direct Auger recombination from an excited state. The mechanism behind the extreme slowing of carrier cooling after several stages of exciton recombination remains to be determined.

Co-chaperonin GroES subunit exchange as dependent on time, pH, protein concentration, and urea

The discovery of a subunit exchange in some oligomeric proteins, implying short-term dissociation of their oligomeric structure, requires new insights into the role of the quaternary structure in oligomeric protein stability and function. Here we demonstrate the effect of pH, protein concentration, and urea on the efficiency of GroES heptamer (GroES7) subunit exchange. A mixture of equimolar amounts of wild-type (WT) GroES7 and its Ala97Cys mutant modified with iodoacetic acid (97-carboxymethyl cysteine or CMC-GroES7) was incubated in various conditions and subjected to isoelectric focusing (IEF) in polyacrylamide gel. For each sample, there are eight Coomassie-stained electrophoretic bands showing different charges that result from a different number of included mutant subunits, each carrying an additional negative charge. The intensities of these bands serve to analyze the protein subunit exchange. The protein stability is evaluated using the transverse urea gradient gel electrophoresis (TUGGE). At pH 8.0, the intensities of the initial bands corresponding to WT-GroES7 and CMC-GroES7 are decreased with a half-time of (23 ± 2) min. The exchange decreases with decreasing pH and seems to be strongly hindered at pH 5.2 due to the protonation of groups with pK ~ 6.3, which stabilizes the protein quaternary structure. The destabilization of the protein quaternary structure caused by increased pH, decreased protein concentration, or urea accelerates the GroES subunit exchange. This study allows visualizing the subunit exchange in oligomeric proteins and confirms its direct connection with the stability of the protein quaternary structure.

Similarities and Differences of Hydridic and Protonic Hydrogen Bonding.

Ab initio calculations were employed to investigate the interactions between selected electron-donating groups, characterized by M-H bonds (where M represents a transition metal and H denotes a hydridic hydrogen), and electron-accepting groups featuring both σ- and π-holes. The study utilized the ωB97X-D3BJ/def2-TZVPPD level of theory. Hydridic hydrogen complexes were found in all complexes with σ- and π-holes. A comparative analysis was conducted on the properties hydridic H-bond complexes, presented here and those studied previously, alongside an extended set of protonic H-bonds complexes. While the stabilization energies changes in M-H bond lengths, vibrational frequencies, intensities of the spectral bands, and charge transfer for these complexes are comparable, the nature of hydridic and protonic H-bonds fundamentally differ. In protonic H-bond complexes, the main stabilization forces arise from electrostatic contributions, while in hydridic H-bond complexes, dispersion energy, is the primary stabilization factor due to the excess of electrons and thus larger polarizability at hydridic H. The finding represents an important characteristic that distinguishes hydridic H-bonding from protonic H-bonds.

Device-measured sedentary time and intensity-specific physical activity in relation to all-cause and cardiovascular disease mortality: the UK Biobank cohort study

Background and aimsUnderstanding the amounts of intensity-specific movement needed to attenuate the association between sedentary time and mortality may help to inform personalized prescription and behavioral counselling. Herein, we examined the joint associations of sedentary time and intensity-specific physical activity with all-cause and cardiovascular disease (CVD) mortality.MethodsProspective cohort study including 73,729 adults from the UK Biobank who wore an Axivity AX3 accelerometer on their dominant wrist for at least 3 days, being one a weekend day, between June 2013 and December 2015. We considered the median tertile values of sedentary time and physical activity in each intensity band to determine the amount of physical activity needed to attenuate the association between sedentary time and mortality.ResultsDuring a median of 6.9 years of follow-up (628,807 person-years), we documented 1521 deaths, including 388 from CVD. Physical activity of any intensity attenuated the detrimental association of sedentary time with mortality. Overall, at least a median of 6 min/day of vigorous physical activity, 30 min/day of MVPA, 64 min/day of moderate physical activity, or 163 min/day of light physical activity (mutually-adjusted for other intensities) attenuated the association between sedentary time and mortality. High sedentary time was associated with higher risk of CVD mortality only among participants with low MVPA (HR 1.96; 95% CI 1.23 to 3.14).ConclusionsDifferent amounts of each physical activity intensity may attenuate the association between high sedentary time and mortality.

Integrated Intensities of the Main Absorption Band of С2HD in the 6530–6627 cm–1 Region

Integrated Intensities of the Main Absorption Band of С2HD in the 6530–6627 cm–1 Region

Image-assisted quantification of high and low molecular weight glutenin fractions in wheat by SDS-PAGE

Gluten quality in bread wheat is mainly determined by gluten strength and protein content. Traditionally gluten quality has been predicted based only on allelic variation for HMW-GS characterized by SDS-PAGE- The ratio of high to low molecular weight glutenin subunits has received less attention despite its influence on gluten properties is acknowledge. That is mainly because accurate quantification of glutenin fractions is made by RP-HPLC, a more complex, expensive and time-consuming technology. In the present study, a methodology to estimate HMW/LMW glutenin subunit ratio by SDS-PAGE results was assessed. We used a segregating population derived from a cross between two Spanish bread wheat landraces (Richela Blanca and Jeja Pardilla) showing striking differences according to SDSS tests. Quantification of prolamins by RP-HPLC confirmed a wide range of variation in the HMW/LMW glutenin subunit ratio within the population. Then, we selected 22 lines that represented the available variation. Subsequently, we obtained high-quality SDS-PAGE images following a standard protocol to characterize glutenin allelic variants. Estimation of HMW/LMW-GS ratio was obtained by analyzing the intensity of HMW-GS and LMW-GS gel bands. Correlation between RP-HPLC and SDS-PAGE values was greater than 0.85 proving the suitability of the much simpler and cheaper electrophoretic-based alternative.

Structural, optical and luminescent properties of Tm3+-doped phosphate oxyfluoride glasses for blue emission solid state devices

In this work, the visible luminescence of P2O5-KF-Al2O3 glasses with Tm2O3 was studied. The Tm3+ ion can have a strong blue emission, which allows the development of LEDs in this color region. This study refers to the synthesis of oxyfluorophosphate glasses, 38P2O5+(50-x)KF+12Al2O3+xTm2O3 (PKAl:Tm), with x = 0.25, 0.50, 0.75, and 1.00 mol%, by the melt-quenching method. The prepared materials showed amorphous characteristics verified by XRD data. The absorption spectra shown six main bands characteristic of Tm3+ ions, from ground state 3H6 to excited levels 3F4, 3H4, 3H5, 3F3,2, 1G4 and 1D2, in which the intensities increased with the concentration of Tm2O3. In the FTIR spectra, it was verified that the profiles of the PKAl samples are similar to glasses based on phosphate systems. The Judd-Ofelt parameters were calculated, where for PKAl glasses the trend was Ω2>Ω4>Ω6. The excitation spectra of PKAl:Tm glasses shown an intense band centered at 358 nm (3H6→1D2). The luminescence spectra with excitation at 358 nm shown two bands at 453 nm (1D2→3F4), and 480 nm (1G4→3H6); the highest emission intensity was observed to the sample doped with 0.75 mol% of Tm2O3. The calculated CIE diagram shown that the doped samples have coordinates close to the primary blue color, which favors the application for the development of blue LEDs and wLEDs. The decay curves for the 1D2 level were fitted by single exponential with lifetime values decreasing with increasing concentration of Tm2O3. These results show that the PKAl:Tm glasses are potential candidates for applications in LEDs.

Synthesis, characterization, and structural analysis of hetero Ni(II)–Na(I) and Homo Ni(II)–Ni(II) dinuclear complexes with a flexible tridendate schiff base ligand

Two different novel [Ni(II)–Na(I)]n and Ni(II)–Ni(II)] complexes have been synthesized successfully using a flexible tridentate Schiff base ligand. These complexes are characterized by IR and single crystal X–ray analysis and the optical properties of these complexes have been studied by UV spectroscopy (solution and solid). The [Ni(II)–Na(I)]n complexes are repeatedly connected with another Ni(II)–Na(I) unit to yield a linear polymeric chain. The Ni(II)–Ni(II) complex shows the nature of supramolecular dimeric cluster. These results are evidenced by x-ray structural analysis. Both as-obtained complexes are shown in different structures, such as hetro metal [Ni(II)–Na(I)]n] and homo metal [Ni(II)–Ni(II)]coordination environments with the same ligand. The first one forms a linear polymeric structure whereas the second one forms a cluster. The more intense band at 2104 cm1 is assigned to the NCS ligand of compound 1. A sharp band at 1068 cm1 together with a band at 625 cm1 in compound 2 is assigned to the ClO4 stretching vibrations and these bands are evidence for the presence of ionic perchlorate (non–coordinated). The electronic spectra of compounds 1 and 2 are recorded in ACN solvent to exhibit a broad peak around 380 nm due to d-d transition.

Chirality Sensing of Cryptochiral Guests with Prism[n]arenes.

Optical chirality sensing has gained significant attention in recent years. Within this field, the quest for stereodynamic chiroptical probes capable of detecting cryptochiral guests presents a formidable challenge. Macrocycles exhibiting planar chirality have emerged as promising candidates for amplifying the chirality of cryptochiral guests. In this study, we demonstrate that the formation of host-guest complexes between cryptochiral molecules and planar chiral prismarenes triggers electronic circular dichroism (ECD) signals via host-guest complexation-induced chirality amplification. The absolute configuration of the most stable chiral macrocyclic host-guest complex has been established by resorting to both exciton model and DFT computations. Furthermore, we demonstrated that this supramolecular chirality sensing system can be employed to determine the enantiomeric composition of scalemic mixtures by measuring the ECD bands intensity. The information described here opens the way for the use of prismarenes as stereodynamic probes for sensing of cryptochiral guests.

Spectroscopic detection of chromatin uncoiling and chromosome alignment in neuronal-like cells under exposure to low intensity magnetic fields

In this manuscript we reported the results of our studies concerning the response of vibration bands in deoxyribonucleic acid region in neuronal-like cells under exposure to static and 50 Hz electromagnetic fields using Fourier Transform Infrared spectroscopy. This technique was chosen because it is able to detect alteration of vibration bands of chemical compounds even induced by small stress agents. The aim of this study was to investigate the response of chromatin and chromosome to low intensity electromagnetic fields at values similar to manmade electromagnetic fields. The phosphate bands of asymmetric and symmetric stretching mode (representative of deoxyribonucleic acid spectral region) were observed to decrease after 3 h exposure at 1 mT (both static and 50 Hz magnetic field). Prolonging time exposure or increasing the intensity of applied magnetic field induced a low increasing in intensity of these vibration bands. This finding can be explaining assuming that chromatin uncoiling occurred at low intensity of the field and that increasing time exposure or magnetic field intensity caused an increasing of the torque on chromosome inducing an alignment along the direction of the field.

Deep postnatal phenotyping of a new mouse model of nonketotic hyperglycinemia.

Nonketotic hyperglycinemia due to deficient glycine cleavage enzyme activity causes a severe neonatal epileptic encephalopathy. Current therapies based on mitigating glycine excess have only limited impact. An animal model with postnatal phenotyping is needed to explore new therapeutic approaches. We developed a Gldc p.Ala394Val mutant model and bred it to congenic status in two colonies on C57Bl/6J (B6) and J129X1/SvJ (J129) backgrounds. Mutant mice had reduced P-protein and enzyme activity indicating a hypomorphic mutant. Glycine levels were increased in blood and brain regions, exacerbated by dietary glycine, with higher levels in female than male J129 mice. Birth defects were more prevalent in mutant B6 than J129 mice, and hydrocephalus was more frequent in B6 (40%) compared to J129 (none). The hydrocephalus rate was increased by postnatal glycine challenge in B6 mice, more so when delivered from the first neonatal week than from the fourth. Mutant mice had reduced weight gain following weaning until the eighth postnatal week, which was exacerbated by glycine loading. The electrographic spike rate was increased in mutant mice following glycine loading, but no seizures were observed. The alpha/delta band intensity ratio was decreased in the left cortex in female J129 mice, which were less active in an open field test and explored less in a Y-maze, suggesting an encephalopathic effect. Mutant mice showed no evidence of memory dysfunction. This partial recapitulation of human symptoms and biochemistry will facilitate the evaluation of new therapeutic approaches with an early postnatal time window likely most effective.

Dibenzothiophene Bridged Bis‐Bodipy and Bis‐Metal Dipyrrin Complexes

AbstractDibenzothiophene (DBT) bridged bis‐dipyrromethane was synthesized by treating readily available 4,6‐di(p‐formylphenyl) dibenzothophene with pyrrole under acid catalyzed conditions. The DBT bridged bis‐dipyrromethane was further oxidized with DDQ to afford the DBT bridged bis‐dipyrrin which was used as a ligand to prepare DBT bridged bis‐BODIPY, bis‐Ni(II) dipyrrin and bis‐Pd(II) dipyrrin complexes by treating the ligand with BF3 ⋅ Et2O, Ni(acac)2 and Pd(acac)2 respectively under mild reaction conditions. The DBT‐bridged bis‐BODIPY and bis‐metal dipyrrin complexes were thoroughly characterized and studied by HR‐MS, 1D & 2D NMR, absorption, fluorescence, cyclic voltammetry and DFT techniques. The bis‐BODIPY and bis‐Pd(II) dipyrrin showed highly intense absorption band at ~500 nm along with one low intense absorption band at 340 nm whereas the bis‐Ni(II) dipyrrin complex showed slightly broadened blue shifted high intense band at 490 nm along with one additional band at 426 nm. The bis‐BODIPY was fluorescent with fluorescence band at 524 nm and quantum yield of 0.031 whereas bis‐M(II) dipyrrin complexes were nonfluorescent. DFT optimized structures revealed that the BODIPY units are more planar with the dibenzophene moiety in bis‐BODIPY with an angle of ∼5.68°. However, in 3‐Pd and 3‐Ni, the M(II)‐dipyrrin units are much more deviated from the dibenzothiophene plane with an angle of 12.81°–14.23°.

Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method

Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC.

The effect of ZnSO4 and Fe2(SO4)3 on the pyrolysis of cocoa shells: A tg-FTIR study

Pyrolysis stands out as one potential route for valorizing abundant agro-industrial cocoa residues. However, the products of this reaction, particularly bio-oil, do not possess the required quality for direct use in many applications. Thus, this study explores the use of iron sulfate and zinc sulfate as potential catalysts in the pyrolysis of these residues. In this investigation, the biomass, previously ground and dried, was impregnated with varying percentages of ferric sulfate and zinc sulfate. The TG-FTIR technique was employed to ascertain the effect of these salts on the pyrolysis of cocoa shell. The results were fitted with the DAEM model with three pseudo-components. It was determined that both salts induced alterations in the DTG profiles of the thermal decomposition of cocoa shell. In the evolved gases, compounds such as CO2, H2O, CH4, CO, HCN, and oxygenated compounds like HCOOH and CH3COOH were detected. Ferric sulfate significantly influenced the activation energies governing the reactions of the three pseudo-components. Conversely, the presence of zinc sulfate did not alter the activation energies associated with the decomposition of cocoa shell pseudo-components. Both catalysts induced alterations in the infrared spectra of the evolved gases, which is primarily evident in the relative intensities of bands corresponding to the stretching vibrations of constituent groups within CO2, CO, water, and oxygenated compounds.

High-pressure high-temperature synthesis and characterization of B10C

The boron-rich boron carbide materials have been traditionally synthesized by adding boron powder to B4C material and subjecting it to hot pressing sintering for materials composition containing 8.8–20 at. % carbon in boron (composition range of B10.4C to B4C). Our study explores a synthesis route for B10C starting from high-purity boron and carbon and direct conversion under high pressure and high temperature (HPHT) conditions of 2000 °C and 6–8 GPa. Synthesis was verified via x-ray diffraction analysis, showing the conversion of the high-purity boron and carbon powder mixture into a hexagonal B10C structure (R-3m space group) with lattice parameters of a = b = 5.6115 Å and c = 12.197 Å. The concentration of boron was measured through x-ray photoelectron spectroscopy, confirming the B10C ratio. The measured nanoindentation mean hardness of B10C was 40 GPa. Raman spectroscopy of the HPHT synthesized sample shows characteristic vibrational breathing modes of boron icosahedron and an additional intense band at a vibrational frequency of 380 cm−1. This Raman band, which appears notably weaker in earlier studies and B4C samples, is assigned to the linear chain of B–B–B and attributed to the maximal incorporation of boron within the hexagonal structure.

Spectroscopic studies on natural fluorapatites irradiated with 10 MeV electrons

Fluorapatites are one of the candidate matrices for hosting the nuclear waste from molten salt reactors. To assess their radiation stability and long-term performance, natural analogue study approach was undertaken. Naturally occurring fluorapatites containing with carbonate substitutions were irradiated with 10 MeV electron beam radiation for doses 20 MGy. X-ray diffraction, Raman and Fourier Transform infrared spectroscopy show no evidence of structural degradation or phosphate condensation. However, a change in the intensity of ν3 Phosphate Raman bands was observed indicating that the phosphate tetrahedra is affected by the electron beam consistent with the displacement cross-section calculations for each constituent element. Overall, the study confirmed that fluorapatite possess good structural stability against electron radiation upto 20 MGy.

Wavelength-tunable photoluminescence of CsPbBr3 microcrystal via in situ halogen doping

Lead halide perovskite semiconductors have received significant attention in recent years as promising candidates for optoelectronic applications. Their controllable bandgap in nanostructures (nanocrystals, nanowires) has been widely and successfully investigated. Intentionally manipulating the atomic behavior with dopants in their macroscopic structure with high quality and stability is still challenging. We studied the crystal structure and photoluminescence (PL) behavior of the anion (Cl) doped CsPbBr3 microcrystals. The doped microcrystal with a low doping concentration has shown a large wavelength-tunable PL emission from 535 nm to 457 nm. Two separate emission peaks (blue and green) are carefully studied in the excitation power dependent PL spectra. The doping and excitation endow the perovskite microcrystal adjustable PL emission band and peak intensities, which may serve as a new degree of manipulation freedom in the color-tunable display and functional optoelectronics.

Manifestation of molecular vibrations of polymers in thermoluminescence of nanocomposites

An experimental and theoretical study of the thermoluminescence (TL) of a PDHS/MCM-41 nanocomposite with the introduction of a polymer (poly-di-n-hexylsilane) (PDHS) into MCM nanopores has been carried out in the temperature range 5–150K. TL curve consists of a very narrow intense band and wider less intense band. In the nananocomposite there is a strong shift of the curve toward low temperatures compared to the curve of the film and a significant narrowing of the bands. The calculations used the model of non-adiabatic transitions. Results show a significant role of molecular vibrations in the formation of the TL curve of a nanocomposite.

Structural Changes in 2-Acetoxybenzoic Acid (2ABA) in the Presence of Various Solvents: A Quantum Chemical and Spectroscopic Study

2-Acetoxy benzoic acid (2ABA) can produce structural changes in the molecule when dissolved in different solvents depending on factors such as solvent polarity, Hydrogen bonding and solvent interactions. Therefore, quantum chemical calculations were performed using Gaussian 09: AS64L-G09RevD.01 software. The structural changes of the 2ABA molecule in the presence of solvents were recorded by Fourier Transform Infrared (FT-IR) Spectroscopy in the 4000-0 cm-1 range. Additionally, Nuclear Magnetic Resonance (NMR) Spectroscopy was employed to examine changes in chemical shift values associated with the dissolution of the molecule. In another phase of the study, the geometric parameters of the optimized molecules, atomic charges, intensities of the vibrational bands, and vibrational frequencies were calculated using Density Functional Theory (DFT). These calculations were performed at the DFT/B3LYP level with the LanL2DZ basis set, providing a detailed analysis of solvent effects at the molecular level. This study offers significant insights into the interactions of solvent environments with molecular structures and contributes to potential drug development processes.

The pressure dependence of the experimentally-determined line intensity and continuum absorption of pure CO2 in the 1.6µm region

Fourier-transform measurements of pure CO2 spectra in the 1.6 µm region covering bands from the ground state to the 30011, 30012, 30013, and 30014 states at ambient temperature and 212 K with pressures up to 1 atm have been recorded. The measured spectra have been multispectrum-fitted with the Hartmann-Tran model with first order line-mixing taken into account. In the fits, a linear decrease of the line intensities with increasing pressure was introduced. From the fitted baselines, the self-continuum, which complements the contribution of the local lines within +/− 25 cm−1, was determined for the two strongest bands, 30012–00001 and 30013–00001. The depleted intensity was found to be transferred to the continuum for both temperatures. The intensity in the continuum at 1 atm was about 1 % of the total band intensity for ambient temperature and about 3 % at 212 K. For both temperatures, the average depleted intensity/continuum area was found in excellent agreement with values estimated from the second virial coefficient. From these results, a new spectroscopic database with pure CO2 line profile parameters was produced, with systematic line intensity uncertainties well below 0.1 %.Retrieval simulations for the CO2 1.6 µm and 2 µm bands measurements, planned with the future CO2M mission, similar to the OCO mission, were carried out to assess the impact of intensity depletion and continuum. The impact of the continuum was larger than that of the depletion and larger for the 2 µm band than for the 1.6 µm band, with a substantial column error of 2 % for the 2 µm band when omitting both, depletion and continuum.The findings regarding pressure-dependent intensity and continuum may be applicable to other in-band continua showing similarity to the monomer band in shape and position. The new results may increase the knowledge on the physical nature of continua.