2E State Research Articles

Dephosphorylation and ion binding in prokaryotic calcium transport

Calcium (Ca 2+ ) signaling is fundamental to cellular processes in both eukaryotic and prokaryotic organisms. While the mechanisms underlying eukaryotic Ca 2+ transport are well documented, an understanding of prokaryotic transport remains nascent. LMCA1, a Ca 2+ adenosine triphosphatase (ATPase) from Listeria monocytogenes , has emerged as a prototype for elucidating structure and dynamics in prokaryotic Ca 2+ transport. Here, we used a multidisciplinary approach integrating kinetics, structure, and dynamics to unravel the intricacies of LMCA1 function. A cryo–electron microscopy (cryo-EM) structure of a Ca 2+ -bound E1 state showed ion coordination by Asp 720 , Asn 716 , and Glu 292 . Time-resolved x-ray solution scattering experiments identified phosphorylation as the rate-determining step. A cryo-EM E2P state structure exhibited remarkable similarities to a SERCA1a E2-P* state, which highlights the essential role of the unique P-A domain interface in enhancing dephosphorylation rates and reconciles earlier proposed mechanisms. Our study underscores the distinctiveness between eukaryotic and prokaryotic Ca 2+ ATPase transport systems and positions LMCA1 as a promising drug target for developing antimicrobial strategies.

The nephelauxetic fonction he applied to the luminescence of Mn4+ and Mn5+ ions in oxides and oxyhalides

It was shown recently that the emission energy of octahedrally-coordinated Mn4+ ions in 101 oxides and 51 fluorides can be estimated from the nephelauxetic function he. Here, we extent this concept to Mn4+ ions incorporated in oxyfluorides and in compounds that do not primarily offer octahedral positions for this dopant in their crystal structure. We show that Mn4+ tends to reconstitute a 6-fold coordinated environment in these crystal lattices and tends to reconstitute either pure [MnF6]2- or pure [MnO6]8- octahedra in oxyfluorides, depending on the O/F ratio in the virgin host lattice. We also show that the “he model” can be used to estimate the energy of the NIR emitting 1E state of tetrahedrally-coordinated Mn5+ with an accuracy of ±350 cm−1.

Research on the Markov-Chain State Interval Division Based on Predicted Data Correction

By 2022, the total length of roads in Tibet Autonomous Region reached 121,447 kilometers. Due to the unique geological conditions in Tibet, various natural disasters such as earthquakes, mudslides, landslides, avalanches, and strong winds frequently occur. Along the Sichuan-Tibet Highway alone, over 300 disasters happen each year, significantly impacting the region’s economic development. This study focuses on the complexity and randomness of natural disaster mechanisms and combines Markov chain theory to improve the accuracy of prediction data for mudslides, landslides, and earth subsidence etc. The main method is to modify the state interval of the prediction model parameter-Markov chain based on the distribution of discrete points on the number axis. The following state interval division methods are proposed: (1) If the relative error of the predicted value exceeds 50%, adjust the prediction model. (2) Obtain the lower bound of state E1 by taking the floor value downward. (3) The width of each interval does not need to be uniform. (4) Arrange continuous, dense, and close points on the number line in the same side in batches, and represent a state continuously, dividing it into one suitable interval or batches. Using this method, an improved RMSE of 0.28mm and MAPE of 0.87% were obtained for engineering examples, outperforming other models such as GM(1,1), Verhulst, DGM(2,1) with corresponding RMSE values of 0.86 mm, 0.69 mm, and 1.38 mm, and MAPE values of 2.75%, 2.53%, and 5.99%. The combined prediction results for five sets of data yielded an RMSE of 0.14 mm and MAPE of 0.56%, which are quite close to the results obtained using Markov selection correction with an RMSE of 0.37 mm and MAPE of 1.01%. Furthermore, comparing the four sets of case, the average reduction in RMSE and MAPE is 3.56mm and 1.72%, respectively, demonstrating that this method can further improve the performance of Markov chain prediction.

Conserved N-terminal Regulation of the ACA8 Calcium Pump with Two Calmodulin Binding Sites

The autoinhibited plasma membrane calcium ATPase ACA8 from A. thaliana has an N-terminal autoinhibitory domain. Binding of calcium-loaded calmodulin at two sites located at residues 42–62 and 74–96 relieves autoinhibition of ACA8 activity.Through activity studies and a yeast complementation assay we investigated wild-type (WT) and N-terminally truncated ACA8 constructs (Δ20, Δ30, Δ35, Δ37, Δ40, Δ74 and Δ100) to explore the role of conserved motifs in the N-terminal segment preceding the calmodulin binding sites. Furthermore, we purified WT, Δ20- and Δ100-ACA8, tested activity in vitro and performed structural studies of purified Δ20-ACA8 stabilized in a lipid nanodisc to explore the mechanism of autoinhibition.We show that an N-terminal segment between residues 20 and 35 including conserved Phe32, upstream of the calmodulin binding sites, is important for autoinhibition and the activation by calmodulin. Cryo-EM structure determination at 3.3 Å resolution of a beryllium fluoride inhibited E2 form, and at low resolution for an E1 state combined with AlphaFold prediction provide a model for autoinhibition, consistent with the mutational studies.

Evaluation of the collapse susceptibility of loess using machine learning

Evaluating collapse susceptibility of loess is essential for the construction of transportation lines in loess regions as it provides guidance for ground treatment. For the existing methods, a large number of boreholes need to be drilled along transportation lines to collect intact samples for laboratory tests, which make them very time and cost-consuming. In this study, loess’s collapse susceptibility is evaluated using Multi Expression Programming (MEP) and Back-Propagation Neural Network (BPNN). According to analysis of wetting-induced loess collapse, the gravimetric water content at the initial state (w0), net vertical stress (σ-ua), void ratio at the initial state (e0), void ratio at the liquid limit state (eL), and plastic index (Ip) are chosen as input variables. A comprehensive database incorporating 200 oedometrically soaking tests is established to train and test the two algorithms. The collapse potentials of loess are well predicted using MEP and BPNN, as demonstrated by high values of coefficient of determination (R2>0.88) and small values of mean absolute error (MAE<0.008) and root mean squared error (RMSE<0.012). Following ASTM D5333-03 [5], the degree of loess collapse is classified with accuracies of 98 % and 90 % for MEP and BNPP respectively. Furthermore, sensitivity analysis shows the contribution of each variable to the prediction of collapse potential follows the order of e0>eL>Ip>σ-ua>w0. The machine learning is expected to assist the code of practice ASTM D5333-03 [5] in achieving an efficient site-investigation of collapsible loess for the construction of transportation lines.

Nitrogen-vacancy centers in diamond: discovery of additional electronic states

Nitrogen-vacancy (NV) defect centers in diamond are key to applications in quantum sensing and quantum computing. They create localized electronic states in the diamond lattice with distinct population relaxation pathways following photoexcitation that ultimately enable its unique properties. The defect is known to exist in two charge states: neutral and negative, with respectively one and two known optically-active electronic transitions. Here, we report on the observation of a large number of hitherto undiscovered excited electronic states in both charge states as evidenced by distinct optical transitions in the infrared to ultraviolet part of the spectrum. These transitions are observed by monitoring the electronic relaxation of NV centers after photoexcitation using transient absorption spectroscopy, directly probing transient phenomena occurring on timescales from femtoseconds to microseconds. We also for the first time probed the electron transfer dynamics from the 3E state of NV− to nearby single-substitutional nitrogen defects (N s ) that leads to the well-known effect of NV photoluminescence quenching.

Analysis of early intermediate states of the nitrogenase reaction by regularization of EPR spectra

Due to the complexity of the catalytic FeMo cofactor site in nitrogenases that mediates the reduction of molecular nitrogen to ammonium, mechanistic details of this reaction remain under debate. In this study, selenium- and sulfur-incorporated FeMo cofactors of the catalytic MoFe protein component from Azotobacter vinelandii are prepared under turnover conditions and investigated by using different EPR methods. Complex signal patterns are observed in the continuous wave EPR spectra of selenium-incorporated samples, which are analyzed by Tikhonov regularization, a method that has not yet been applied to high spin systems of transition metal cofactors, and by an already established grid-of-error approach. Both methods yield similar probability distributions that reveal the presence of at least four other species with different electronic structures in addition to the ground state E0. Two of these species were preliminary assigned to hydrogenated E2 states. In addition, advanced pulsed-EPR experiments are utilized to verify the incorporation of sulfur and selenium into the FeMo cofactor, and to assign hyperfine couplings of 33S and 77Se that directly couple to the FeMo cluster. With this analysis, we report selenium incorporation under turnover conditions as a straightforward approach to stabilize and analyze early intermediate states of the FeMo cofactor.

The tilting motion of the central core reveals the transport mechanism of the sarco/endoplasmic reticulum Ca2+-ATPase

The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) transports two Ca2+ ions per ATP hydrolyzed from the cytoplasm to the lumen. However, how the ATP hydrolysis remotely drives the Ca2+ transport is unclear. In the SERCA1a crystal structures, the ATP hydrolysis is accompanied by the notably increasing tilting angle of the central core (CC) and the Ca2+ transport, and the CC tilting angle dramatically decreases in the E2 to E1 transition. We demonstrated that the significantly increasing tilting motion of the CC drove the Ca2+ release in the molecular dynamics simulation of the R836A variant, and the dramatic spontaneous decrease in the CC tilting angle of the E2 state triggers the restart of the SERCA1a's transport cycle. The repulsion between the phosphorylated D351 and the phosphate groups in ADP triggers the release of ADP from the SERCA1a headpiece. We proposed a novel SERCA transport mechanism in which ATP hydrolysis drives a significant tilting motion of the CC, which drives Ca2+ transport and the A domain rotational motion in the E1P-ADP-2Ca2+ to E2P transition. The dramatic spontaneous decrease in the CC tilting angle of the E2 state drives the restart of the transport cycle.

Unraveling Broadband Near-Infrared Luminescence in Cr3+-Doped Ca3Y2Ge3O12 Garnets: Insights from First-Principles Analysis.

In this study, we conducted an extensive investigation into broadband near-infrared luminescence of Cr3+-doped Ca3Y2Ge3O12 garnet, employing first-principles calculations within the density functional theory framework. Our initial focus involved determining the site occupancy of Cr3+ activator ions, which revealed a pronounced preference for the Y3+ sites over the Ca2+ and Ge4+ sites, as evidenced by the formation energy calculations. Subsequently, the geometric structures of the excited states 2E and 4T2, along with their optical transition energies relative to the ground state 4A2 in Ca3Y2Ge3O12:Cr3+, were successfully modeled using the ΔSCF method. Calculation convergence challenges were effectively addressed through the proposed fractional particle occupancy schemes. The constructed host-referred binding energy diagram provided a clear description of the luminescence kinetics process in the garnet, which explained the high quantum efficiency of emission. Furthermore, the accurate prediction of thermal excitation energy yielded insights into the thermal stability of the compound, as illustrated in the calculated configuration coordinate diagram. More importantly, all calculated data were consistently aligned with the experimental results. This research not only advances our understanding of the intricate interplay between geometric and electronic structures, optical properties, and thermal behavior in Cr3+-doped garnets but also lays the groundwork for future breakthroughs in the high-throughput design and optimization of luminescent performance and thermal stability in Cr3+-doped phosphors.

Switching Go̅-Martini for Investigating Protein Conformational Transitions and Associated Protein-Lipid Interactions.

Proteins are dynamic biomolecules that can transform between different conformational states when exerting physiological functions, which is difficult to simulate using all-atom methods. Coarse-grained (CG) Go̅-like models are widely used to investigate large-scale conformational transitions, which usually adopt implicit solvent models and therefore cannot explicitly capture the interaction between proteins and surrounding molecules, such as water and lipid molecules. Here, we present a new method, named Switching Go̅-Martini, to simulate large-scale protein conformational transitions between different states, based on the switching Go̅ method and the CG Martini 3 force field. The method is straightforward and efficient, as demonstrated by the benchmarking applications for multiple protein systems, including glutamine binding protein (GlnBP), adenylate kinase (AdK), and β2-adrenergic receptor (β2AR). Moreover, by employing the Switching Go̅-Martini method, we can not only unveil the conformational transition from the E2Pi-PL state to E1 state of the type 4 P-type ATPase (P4-ATPase) flippase ATP8A1-CDC50 but also provide insights into the intricate details of lipid transport.

Design of Cr3+-activated broadband NIR phosphors with tunable and abnormal thermal quenching behavior for NIR pc-LEDs

The decreased energy difference between 4T2 and 2E states leads to tunable and abnormal thermal quenching performance of Lu3−xCaxGa5−xSixO12:Cr3+ phosphors.

H2 formation from the E2-E4 states of nitrogenase.

Nitrogenase is the only enzyme that can cleave the strong triple bond in N2, making nitrogen available for biological lifeforms. The active site is a MoFe7S9C cluster (the FeMo cluster) that binds eight electrons and protons during one catalytic cycle, giving rise to eight intermediate states E0-E7. It is experimentally known that N2 binds to the E4 state and that H2 is a compulsory byproduct of the reaction. However, formation of H2 is also an unproductive side reaction that should be avoided, especially in the early steps of the reaction mechanism (E2 and E3). Here, we study the formation of H2 for various structural interpretations of the E2-E4 states using combined quantum mechanical and molecular mechanical (QM/MM) calculations and four different density-functional theory methods. We find large differences in the predictions of the different methods. B3LYP strongly favours protonation of the central carbide ion and H2 cannot form from such structures. On the other hand, with TPSS, r2SCAN and TPSSh, H2 formation is strongly exothermic for all structures and En and therefore need strict kinetic control to be avoided. For the E2 state, the kinetic barriers for the low-energy structures are high enough to avoid H2 formation. However, for both the E3 and E4 states, all three methods predict that the best structure has two hydride ions bridging the same pair of Fe ions (Fe2 and Fe6) and these two ions can combine to form H2 with an activation barrier of only 29-57 kJ mol-1, corresponding to rates of 7 ×102 to 5 × 107 s-1, i.e. much faster than the turnover rate of the enzyme (1-5 s-1). We have also studied H-atom movements within the FeMo cluster, showing that the various protonation states can quite freely be interconverted (activation barriers of 12-69 kJ mol-1).

Protonation of Homocitrate and the E1 State of Fe-Nitrogenase Studied by QM/MM Calculations.

Nitrogenase is the only enzyme that can cleave the strong triple bond in N2, making nitrogen available for biological life. There are three isozymes of nitrogenase, differing in the composition of the active site, viz., Mo, V, and Fe-nitrogenase. Recently, the first crystal structure of Fe-nitrogenase was presented. We have performed the first combined quantum mechanical and molecular mechanical (QM/MM) study of Fe-nitrogenase. We show with QM/MM and quantum-refinement calculations that the homocitrate ligand is most likely protonated on the alcohol oxygen in the resting E0 state. The most stable broken-symmetry (BS) states are the same as for Mo-nitrogenase, i.e., the three Noodleman BS7-type states (with a surplus of β spin on the eighth Fe ion), which maximize the number of nearby antiferromagnetically coupled Fe-Fe pairs. For the E1 state, we find that protonation of the S2B μ2 belt sulfide ion is most favorable, 14-117 kJ/mol more stable than structures with a Fe-bound hydride ion (the best has a hydride ion on the Fe2 ion) calculated with four different density-functional theory methods. This is similar to what was found for Mo-nitrogenase, but it does not explain the recent EPR observation that the E1 state of Fe-nitrogenase should contain a photolyzable hydride ion. For the E1 state, many BS states are close in energy, and the preferred BS state differs depending on the position of the extra proton and which density functional is used.

FRI411 Pharmacologically Induced Hypoestrogenism And Experimentally Induced Menopause-Pattern Sleep Fragmentation Independently Influence Circulating Lipids, Heart Rate, And Blood Pressure In Women

Abstract Disclosure: L.K. Grant: Grant Recipient; Self; Brigham and Women’s Hospital, Women’s Health Access Matters. A. Cohn: None. S. Crawford: None. J. Harder: Consulting Fee; Self; Altman Health, O’Rouke &amp; Hawk, LLP. Grant Recipient; Self; Brigham and Women’s Hospital, President and Fellows of Harvard College. Owner/Co-Owner; Self; Jessica Harder, MD. Stock Owner; Self; Altman Health. Other; Self; Centerfield Media Holding Company. M.D. Nathan: None. I. Gonsalvez: None. T. Luo: None. E. Menezes: None. A. Roy: None. A. Wiley: None. F.A. Scheer: Consulting Fee; Self; University of Alabama. Other; Self; Board of Directors for the Sleep Research Society. E. Klerman: Consulting Fee; Self; American Academy of Sleep Medicine Foundation, Sleep Research Society Foundation, Circadian Therapeutics, National Sleep Foundation, Yale University Press. U.B. Kaiser: None. S. Mora: Consulting Fee; Self; Pfizer, Inc. J. Taylor: None. H. Joffe: Consulting Fee; Self; Bayer, Inc., Hello Therapeutics. Grant Recipient; Self; Merck, Pfizer, Inc., NIH. S.A. Rahman: Consulting Fee; Self; Sultan &amp; Knight Limited, Bambu Vault LLC, Lucidity Lighting Inc. Grant Recipient; Self; Seoul Semiconductor Co. Ltd, Biological Innovation and Optimization Systems, LLC, Pfizer, Inc., Merck &amp; Co., Lighting Science Group. Speaker; Self; Starry Skies Lake Superior, University of Minnesota Medical School, PennWell Corp, Seoul Semiconductor Co. Ltd. Stock Owner; Self; Melcort Inc. Introduction: The risk of cardiovascular disease (CVD) in women increases at menopause. Although declining levels of estradiol (E2) have been implicated in the increase in CVD risk for midlife women, it remains difficult to isolate these effects from the parallel changes in chronological age, and other potential contributing, mediating and modifying factors such as menopause-pattern sleep fragmentation (increased awakenings but no change in overall sleep duration). Here, we investigated whether hypo-estrogenism (hypo-E2) and sleep fragmentation increase CVD risk factors [lipids, blood pressure (BP)] in an experimental menopause model implemented in premenopausal women. Method: Two 5-night inpatient studies performed in the mid-to-late follicular phase (E2 = 48.7±29.5 pg/mL) and repeated following leuprolide-induced hypo-E2 (E2 = 7.5±5.9 pg/mL) were completed in 27 premenopausal women (mean age = 28.4±5.6 years). Each admission involved 2 nights of unfragmented sleep [8-h time-in-bed (TIB)] followed by 3 nights of sleep fragmentation, induced by auditory stimuli distributed across the night, producing 1-hr of cumulative wakefulness while enabling equal sleep opportunity (9-h TIB). BP and heart rate (HR) measurements were collected within 1 hour of wake in a semi-supine position each morning; fasting serum lipids were collected during unfragmented sleep and again after 3 nights of sleep fragmentation, during both inpatient stays. The effect of sleep fragmentation, E2 state and their interaction were assessed using generalized linear models to account for repeated measures. Results: Relative to the estrogenized state, the hypo-E2 state had a significant increase in total cholesterol (156±5 vs. 167±6 mg/dL, p&amp;lt;.001), triglycerides (72±5 vs 79±7 mg/dL, p&amp;lt;.001), HDL-C (58±3 vs. 62±3 mg/dL, p&amp;lt;.01), LDL-C (81±4 vs. 86±5 mg/dL, p&amp;lt;.05) and mean arterial pressure (MAP; 79±1 vs. 81±1 mmHg, p&amp;lt;.05) and a trend toward increased diastolic BP (63±1 vs. 65±1 mmHg, p=.07), with a significant compensatory decrease in HR (67±2 vs. 65±2 bpm, p&amp;lt;.001). Compared to the unfragmented sleep condition, sleep fragmentation resulted in a significant increase in HR (64±2 vs. 68±2 bpm, p&amp;lt;.001) and a trend toward increased systolic BP (109±1 vs. 110±1 mmHg, p=.08). There was no effect of sleep fragmentation on lipid levels, diastolic BP, or MAP, and no interaction between sleep fragmentation and E2 for any of the variables. Conclusion: These experimental findings show that pharmacologically induced hypo-E2, but not sleep fragmentation, increase circulating lipids levels in pre-menopausal women. Additionally, pharmacological E2-suppression increased BP and decreased HR, whereas sleep fragmentation increased both BP and HR. Together, these findings suggest that both E2 decline, and sleep fragmentation may uniquely contribute to the increase in CVD risk during the menopause transition. Presentation: Friday, June 16, 2023

Mechanism of Oxygen Quenching of the Excited States of Heteroleptic Chromium(III) Phenanthroline Derivatives.

In this study, we report the synthesis and characterization of some heteroleptic Cr(III) complexes of the form [Cr(Phen)2L](OTf)3, where Phen = 1,10-phenanthroline and L is either 2,2'-bipyridine (bpy) or its derivatives, such as 4,4'-dimethyl-2,2'-bipyridine (4,4'-DMB), 4,4'-dimethoxy-2,2'-bipyridine (4,4'-DMOB), 4,4'-ditert-butyl-2,2'-bipyridine (4,4'-dtbpy), 5,5'-dimethyl-2,2'-bipyridine (5,5'-DMB), 4,4'-dimethoxycarbonyl-2,2'-bipyridine (4,4'-dmcbpy) or 1,10-phenanthroline derivatives, such as 5-methyl-1,10-phenanthroline (5-Me-Phen) and 4,7-dimethyl-1,10-phenanthroline (4,7-DMP). Heteroleptic complexes were prepared in two stages via the intermediate [Cr(Phen)2(CF3SO3)2](CF3SO3) and five examples have been crystallographically characterized. Steady-state absorption and luminescence emission characteristics of these complexes were measured in 1 M HCl solutions. The luminescence quantum yield of these complexes was found to be the lowest for [Cr(Phen)2(4,4'-dmcbpy)](OTf)3 and the highest for [Cr(Phen)2(4,4'-DMB)](OTf)3 with values of 0.31 × 10-2 and 1.48 × 10-2, respectively. The calculated excited state energy, E0-0, was found to vary within the narrow range of 163.1-165.0 kJ mol-1 across the series. Transient absorption spectra in degassed, air-equilibrated, and oxygen-saturated 1 M HCl aqueous solutions were also measured at different time decays and demonstrated no significant differences, indicating the absence of any ion-separated species in the excited state. Excited-state decay traces at the wavelength of maximum absorption were used to calculate oxygen quenching rate constants, kq, which were found to be in the range 3.26-5.27 × 107 M-1 s-1. Singlet oxygen luminescence photosensitized by these complexes was observed in D2O, and its luminescence intensity at 1270 nm was used for the determination of singlet oxygen quantum yields for these complexes, which were in the range of 0.20-0.44, while the fraction of the excited 2E state quenched by oxygen was in the range of 0.22-0.68, and the efficiency of singlet oxygen production was in the range of 0.44-0.90. The mechanism by which the excited 2E state is quenched by oxygen is explained by a spin statistical model that predicts the balance between charge transfer and noncharge transfer deactivation pathways, which was represented by the parameter pCT that was found to vary from 0.35 to 0.68 for this series of Cr(III) complexes.

Highly Sensitive Lifetime‐Based Luminescent Manometer on Mn4+ Luminescence in Sr4Al14O25 Mn4+

AbstractEnabling remote and temperature‐independent pressure sensing based on luminescence kinetics holds significant potential for the development of a luminescence pressure sensor with a wide array of applications. To meet these requirements, in this work, a unique lifetime‐based luminescence manometer is demonstrated for which an increase in pressure results in an elongation of lifetime of 2E state of Mn4+ due to a change in the probability of radiative depopulation of the 2E level of Mn4+ ions with an unprecedentedly high sensitivity of 35% GPa−1. Furthermore, the pressure‐induced modification in the covalency of the Mn4+─O2− bond facilitates a manometer operating in spectral band shift and ratiometric modes with sensitivities of 26 cm−1 GPa−1 (1.2 nm GPa−1) and 24.8% GPa−1, respectively. This study firmly supports the belief that the distinct pressure‐dependent kinetics governing the depopulation of Mn4+ ions at the 2E level, along with the resulting advantageous manometric performance, will pave the way for a new research trajectory in luminescence manometry.

Raman scattering, absorption and luminescence spectroscopy of CoSiF6·6H2O crystal and CoSiF6·6H2O:Mn4+ red-emitting phosphor

CoSiF6·6H2O and CoSiF6·6H2O:Mn4+ crystals were investigated by means of Raman, optical absorption, and luminescence spectroscopy. Absorption spectra of CoSiF6·6H2O are analyzed by Tanabe-Sugano technique and are proved to be well-describable at crystal field strength Dq = 1000 cm−1, and Racah parameters B = 896 cm−1, C = 4408 cm−1, Dq/B = 1.116. Raman spectroscopy reveals a phase transition associated with the ordering of both the CoO6 and SiF6 octahedra, which occurs through the ordering of the H2O subsystem. Luminescence spectrum of Mn4+ ions in CoSiF6·6H2O lattice consists of six components corresponding to Stokes and anti-Stokes emission from 2E state of Mn4+ ion at vibrational frequencies of MnF6 octahedron ν6 = 230 cm−1, ν4 = 335 cm−1, and ν3 = 645 cm−1. Quantum efficiency of red emission maximizes at excitation wavelength 357 nm and equals to 5%. Decrease of quantum efficiency in comparison to other related materials is explained by absorption of Co2+ ions and non-radiative relaxation in the Co2+ subsystem.

Color tunability and NIR luminescence in Cr3+/Li+ co-doped ZnGa2O4 phosphor for solid state lighting and NIR LEDs

In this work, we report the color tunable photoluminescence in the Cr3+/Li+ doped and co-doped ZnGa2O4 (ZGO) phosphors synthesized by solid state reaction method. The phase and surface morphology of ZGO phosphor were examined by XRD and SEM measurements, respectively. The EDS spectra revealed the presence of Zn, Ga, Cr and O elements in the phosphor. The vibrational structure of the phosphor materials has been analyzed by FTIR measurements. The Cr3+ doped phosphor shows electronic absorption bands at 302, 408 and 544 nm alongwith the host CTB at 260 nm. The optical band gap of the phosphor decreases via doping of Cr3+ and Cr3+/Li+ ions. The ZGO is a self-activated host and emits broad blue emission with maximum at 434 nm upon excitation at 260 nm. The Cr3+ doped phosphors show emission bands due to spin-allowed as well as spin-forbidden transitions due to Cr3+ ion in the blue, green and NIR regions on excitation with 260, 302, 408 and 544 nm wavelengths. The emission intensity is optimum for 0.5 mol% concentration of Cr3+ ion. The emission intensity of Cr3+ doped ZGO phosphor increases via doping of Li+ ion. The color tunability has been observed in the phosphor upon 260 and 302 nm excitations. The lifetimes of 4T2 (4F) and 2E states of Cr3+ ion have been measured and it is found that it decreases with increasing concentrations of Cr3+ and Cr3+/Li+ ions. The Cr3+/Li+ doped and co-doped ZGO phosphors may be suitable candidates for display devices, solid state lighting and NIR LEDs.

Combined Experimental and Mechanoelastic Modeling Studies on the Low-Spin Stabilized Mixed Crystals of 3D Oxalate-Based Coordination Materials.

Structural studies involving single-crystal and powder X-ray diffraction analysis have been performed on dehydrated coordination networks of the [NixCo1-x(bpy)3][LiCr(ox)3] series, 0 ≤ x ≤ 1, (bpy = 2,2'-bipyridine). The high-symmetry cubic 3D structure of these materials is formed by oxalate anions bridging alternating Cr3+ and Li+ ions into an anionic framework, which contains large cavities that incorporate the [NixCo1-x(bpy)3]2+ cations. Irrespective of the Co/Ni ratio, all of the mixed samples are phase-pure and retain the high-symmetry cubic structure, with the lattice parameters gradually decreasing upon increasing Ni(II) concentration. The influence of the Ni(II) dilution on the magnetic behavior of these materials is substantial. For pure [Co(bpy)3][LiCr(ox)3], a gradual but incomplete thermal spin-crossover is evident due to the effect of the chemical pressure applied by the [LiCr(ox)3]2- framework, which stabilizes the low-spin (LS) 2E state relative to the high-spin (HS) 4T1 state of the Co(II) ion. Upon increasing the Ni(II) content, the spin-crossover becomes even more gradual and incomplete and eventually is not observed for pure [Ni(bpy)3][LiCr(ox)3]. The average spin-crossover temperature increases with the increasing Ni(II) content, suggesting a higher degree of chemical pressure applied by the oxalate framework manifested by changing the ΔE0HL toward positive values. The magnetic behavior of all these framework materials has been explained by the mechanoelastic model, considering different radii for Co and Ni molecules and different interactions between Co-Co sites and Co-Ni sites. The model reproduced the incomplete transition, with the HS residual fraction at 300 K decreasing with increasing Ni concentration, and provided microscopic snapshots of the systems, showing how the existence of impurities prevented the spreading of Co atoms in the HS state.

Inactivation kinetics of horseradish peroxidase (HRP) by hydrogen peroxide

In recent years, the peroxidase enzymes have generated wide interest in several industrial processes, such as wastewater treatments, food processing, pharmaceuticals, and the production of fine chemicals. However, the low stability of the peroxidases in the presence of hydrogen peroxide (H2O2) has limited its commercial use. In the present work, the effect of H2O2 on the inactivation of horseradish peroxidase (HRP) was evaluated. Three states of HRP (E0, E2, and E3) were identified. While in the absence of H2O2, the resting state E0 was observed, in the presence of low and high concentrations of H2O2, E2, and E3 were found, respectively. The results showed that HRP catalyzed the H2O2 decomposition, forming the species Ex, which was catalytically inactive. Results suggest that this loss of enzymatic activity is an intrinsic characteristic of the studied HRP. A model from a modified version of the Dunford mechanism of peroxidases was developed, which was validated against experimental data and findings reported by the literature.