Study Of Temperature Dependence Research Articles

Enzyme mimicking activity of the Ru(pic)3 complex in the oxidation NADH coenzymes: kinetic and mechanistic studies

Mimicking the enzymatic oxidation of NADH and obtaining mechanistic insight into the electron transfer reaction pertinent to the redox inter-conversion of NADH/NAD+ couple is a long-term challenge in biological and energy-related chemistry. The kinetics and mechanism of the oxidation of NADH by [RuIII(pic)3] (pic– = picolinate anion) has been studied spectrophotometrically and kinetically in aqueous solution at pH 7.0 (MES buffer). The reaction was followed over time at 466 nm (metal to ligand charge transfer band of [RuII(pic)3]–). The rate of NADH oxidation was found to be first-order with respect to Ru(III)-complex concentration. The values of the observed rate constant (k obs) increased linearly with increase in the concentration of NADH. The rate of the reaction was independent of the ionic strength of the reacting solution. Activation parameters (ΔH≠ = 56 ± 1 kJ mol−1 and ΔS≠ = −65 ± 3 J.deg−1 mol−1) were determined from the temperature dependence studies (15-35 °C) of the reaction. Kinetic data and activation parameters are interpreted in terms of a mechanism involving outer-sphere electron transfer.

Magnetic properties and coupled spin‒phonon behavior of M‒type Sr1-xSmxFe12O19 (0 ≤ x ≤ 0.15) nanoparticles

We thoroughly investigated the effects of Sm³⁺ doping on the magnetic, structural, hyperfine, and vibrational properties of Sr1-xSmxFe12O19 (0 ≤ x ≤ 0.15) nanoparticles, which were synthesized using the proteic sol-gel process. The Rietveld refined XRD patterns confirmed the presence of M-type SrFe12O19, alongside a minor fraction of α-Fe2O3. As Sm³⁺ doping increased, the unit cell volume fluctuated, decreasing from 691.73 ų at x = 0 to 690.67 ų at x = 0.10 and slightly rising thereafter. The incorporation of Sm³⁺ induced a conversion of Fe3+ to Fe2+, affecting lattice parameters and crystallinity. At x = 0.10, maximum crystallite size (56.48 nm) and X-ray density (4.83 g/cm³) were attained, alongside decreased microstrain, indicating improved crystallinity and reduced defects. However, at x = 0.15, an increase in microstrain suggested lattice instability. FTIR confirmed that bands in the range 400–600 cm⁻1 might be due to the stretching vibration of oxygen and metal (Fe–O) ions, confirming the formation of hexaferrite. Temperature-dependent Raman spectroscopy studies confirmed the presence of spin-phonon coupling in all samples in the ferrimagnetic transition at ∼725-735 K. Mössbauer spectroscopy elucidated that the substitution of Sr2+ by Sm3+ induced the most pronounced effect on the 12k, 4f2, and 2a sites, corroborating the evolution of the lattice constants and the fact that these three sites have Sr sites in their close vicinity. The room-temperature hysteresis loops exhibited narrow features, indicative of soft magnetic behavior. Saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) varied with Sm3+ doping content (x). Ms initially decreased from 62.62 emu/g and 22.03 emu/g at x = 0.00 to 54.96 emu/g and 19.63 emu/g at x = 0.10, respectively, and then increase to 59.77 emu/g and 21.86 emu/g at x = 0.15. Conversely, Mr and Hc showed a non-monotonic trend with x, suggesting complex interactions between dopant concentration and magnetic properties.

Effects of Ionic Liquids on the Nucleofugality of Bromide.

The nucleofugality of bromide was measured in solvent mixtures containing ionic liquids. The solvolysis rate constants of the bromides of well-defined electrofuges were determined in mixtures containing different proportions of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide in ethanol. Temperature-dependent kinetic studies allowed an explanation of the observed solvent effects in different mixtures in terms of interactions in solution. Using the solvolysis data, the nucleofugality of bromide in these systems was determined. Likewise, nucleofugality data for bromide were determined in mixtures containing high proportions of seven further ionic liquids. These data allowed quantification of the effects of both varying the amount of ionic liquid and the nature of ionic liquid components on the nucleofugality of bromide. Importantly, ionic liquid mixtures were shown to affect the nucleofugality in a manner similar to chloride, providing a method for predicting the effects of ionic liquids on other electrofuges. Further, the ionic liquids were shown to move the transition state earlier along the reaction coordinate, meaning that there is less charge development in the transition state.

Tau-borides (Mnx{Ru,Os,Ir}1-x)23B6: X-ray single crystal and TEM data, physical properties

Investigation (electron microprobe and X-ray powder and single crystal diffraction analyses) of the phase relations in the Mn-rich corner (> 45 at% Mn) of the systems Mn-{Ru,Os,Ir}-B, prompted in all three systems a ternary compound with formula (Mnx{Ru,Os,Ir}1-x)23B6. For the systems Mn-Ru-B, Mn-Ir-B phase equilibria have been determined at 950°C (Ru), 900°C (Ir) revealing in both cases a small homogeneity region at constant B-content (Mn1-xRux)23B6 (0.29 < x < 0.37); (Mn1-xOsx)23B6 (0.33 < x < 0.37), as well as (Mn1-xIrx)23B6 (0.29 < x < 0.34). The crystal structure of the three compounds was determined from single crystal and X-ray powder intensity data analyses to be isotypic with the Cr23B6-type (so-called tau-phase, space group Fm3¯m, No. 225). In all cases Mn atoms fully occupy the 4a site (0,0,0) at the origin of the unit cell. For the 8c site (¼,¼,¼) we observed a random distribution of Mn1-x(PM)x with decreasing PM content (PM stands for a platinum group metal atom) going from Ru to Os and Ir, where Mn atoms fully occupy 8c. Whereas the remaining sites (48h, 32f) show various ratios of the two metal species, boron atoms fully occupy the centers (24e site) of the Archimedean metal atom antiprisms. A transmission electron microscopic study confirms the absence of superstructures related to these metal atom disorder, thus Mn and PM atoms randomly share their sites. The latter is well reflected in the behavior of the electrical resistivity of these compounds, which is dominated by disorder scattering. For (Mn0.6{Ru,Os}0.4)23B6, temperature dependent dc magnetization studies reveal distinct antiferromagnetic-like anomalies at TN ≅ 72 K and 114 K, respectively. Low field dc and ac magnetic susceptibility data of (Mn0.7Ir0.3)23B6 display a distinct ferromagnetic-like transition at TC = 280 K, consistent with a pronounced specific heat anomaly and a rather continuous temperature dependent evolution of magnetic anisotropy effects. Mechanical properties (hardness) characterize the tau phases among rather hard and brittle intermetallics (about 5–6 GPa).

Synthesis and characterization of the electrical and energy storage properties of new Barium titanate - Europium titanate solid solution

In the present work, the investigation of the structural, dielectric, ferroelectric and energy storage properties of polycrystalline samples of (1-x)BaTiO3 – xEuTiO3 (BT-ET) solid solution materials prepared by conventional solid-state reaction method has been carried out. X-ray diffraction analyses have revealed the formation of a single-phase tetragonal structure with the P4mm space group. Furthermore, the temperature dependence of the dielectric constants marked the presence of the following sequence of structural phase transitions, namely from rhombohedral to orthorhombic, from orthorhombic to tetragonal and from tetragonal to cubic phase transitions with the increase of temperature. A diffuse phase transition has been observed from the dielectric permittivity peak and has been analyzed using the modified Curie-Weiss law and the degree of diffuseness is found to be in the range of 1.16–1.76 due to the existence of different states of polarization. A phase diagram has been established based on the temperature-dependent dielectric permittivity studies. The room temperature ferroelectric properties point to a coercive field larger than that of BaTiO3 ceramics. Broad dielectric peaks associated with diffuse phase transition appear in a wide temperature range (40–100 °C) with the highest dielectric permittivity ε' = 6498 found in the x = 0.05 ceramics. Moreover, an improved energy storage performance is obtained in the 0.95BaTiO3-0.05EuTiO3 ceramic with a recoverable energy density of Wrec = 0.797 J/cm3, coupled with an efficiency η = 73 % at 170 kV/cm and the highest storage energy density of Wst = 1.571 J/cm3 is obtained for 0.90BaTiO3-0.10EuTiO3, which is superior to other lead-free BT-based ceramics. All these features demonstrate that the BT-ET ceramics can be widely used in energy storage applications and also in high-temperature multilayer capacitors for automotive, aerospace and related industries.

Excimer Fluorescence of Acriflavine Dye in Glycerol and Ethylene Glycol.

This research investigates the excimerisation of acriflavine dye in ethylene glycol and glycerol solvents. Acriflavine, a member of the acridine dye family, exhibits unique fluorescence properties with applications in various fields, including cellular nucleus observation, nucleic acid analysis, and dye laser active media etc. The study explores the impact of solvent and concentration on acriflavine's emission properties, with a focus on excimer formation, which can influence its suitability as a dye laser active medium. UV-Visible absorption spectroscopy reveals concentration-dependent absorption profiles, with distinctive monomer bands. Steady-state fluorescence studies demonstrate the emergence of red-shifted excimer fluorescence bands as concentrations increase in both solvents. Temperature-dependent fluorescence studies reveal the dynamics of excimer formation, suggesting dynamic diffusion as the excimerisation mechanism. Time-resolved fluorescence spectroscopy confirms the singlet character of both monomer and excimer states, providing insights into the excimerisation process. Critical concentration values are determined, representing the equilibrium between monomeric and excimeric forms. The study also explores pH-induced spectral shifts, highlighting the influence of acidity on fluorescence properties. Overall, this research deepens our understanding of acriflavine's excimerisation in ethylene glycol and glycerol, offering insights that can enhance its diverse applications, especially in laser technologies.

Enhanced electrical performance of LiMnPO4 by carbon coating for solid-state battery applications

High-energy ball milling was employed to fabricate LiMnPO4 coated with varying carbon ratios (3%wt, 7%wt, and 10%wt), using glucose as a carbon source. The process involved pre-milling of LiMnPO4 precursors, followed by granulation through high-energy ball milling at 270 rpm for 2 h, and subsequent calcination at 700 °C without an inert gas flow. XRD analysis discerned the phases and structure of LiMnPO4, confirming the successful attainment of a single-phase LiMnPO4 without impurities. Rietveld refinement of the XRD data elucidated the crystallographic details, affirming the material's orthorhombic olivine structure with precise lattice parameters, thereby underpinning the structural integrity essential for electrochemical applications. FE-SEM analysis revealed uniformly distributed semi-sphere particles, with sizes ranging from 130 nm for LM to 183 nm for LM-10%C. FTIR analysis delineated the internal modes of vibration in the olivine structure and verified the presence of carbon on the powder surface. Electrical measurements conducted within the frequency range of 20 Hz–100 kHz demonstrated an increase in electrical conductivity with an escalation in carbon concentration, ranging from 31 μΩ−1m−1 to 75 μΩ−1m−1 for 0%C and 10%C, respectively. A temperature-dependent study spanning 30–160 °C revealed stable electrical conductivity behavior for the samples, with a marginal increase observed at elevated temperatures.

Molecular Dynamics Study of Temperature Dependence of Grain Boundaries (100) in Pure Aluminum with Application of Machine Learning

As is known, grain boundary (GB) energy determines the mobility of GBs and their population in metals. In this work, we study the energy of GBs in the (100) crystallographic plane and in the temperature range from 100 to 700 K. The study is carried out using both the molecular dynamic (MD) method and machine learning approach to approximate the MD data in order to obtain functional dependence in the form of a feed-forward neural network (FCNN). We consider the tilt and twist grain boundaries in the range of misorientation angles from 0 to 90°. Also, we calculate the average and minimum energy over the ensemble of GB states, since there are many stable and metastable structures with different energies even at a fixed grain misorientation. The minimum energies decrease with increasing temperature, which is consistent with the results of other studies. The scatter of GB energies in the temperature range from 100 to 700 K is obtained on the basis of MD simulation data. The obtained energy spread is in reasonable agreement with the data from other works on the values of GB energy in pure aluminum. The predictive ability of the trained FCNN as well as its ability to interpolate between the energy and temperature points from MD data are both demonstrated.

Iron-hydroxide controlled by cobalt and aluminium as an advanced electrocatalysts for overall water splitting and its temperature dependence

Multimetal hydroxide catalysts have the potential to combine their advantages to facilitate the synergistic effects for enhanced catalytic activity in alkaline medium. In this work we assessed the performance of the electrodeposited Cox-Fey-Alz hydroxide electrode as an electrocatalyst in an alkaline electrolyzer, showcasing its superior functionality compared to other control systems. The catalysts demonstrate exceptional electrochemical properties, achieving low overpotentials of η = 264 mV for OER and η = 197 mV for HER at a current density of 100 mA cm−2. Moreover, they maintain excellent durability even after 50 hours of continuous operation and exhibit a low Tafel slope of 41.4 mV dec−1. Temperature-dependent studies in electrocatalysis become particularly relevant when we consider the practical applications of these remarkable catalysts. A water electrolyzer constructed using the Cox-Fey-Alz hydroxide at the anode and cathode displays an extremely low cell voltage of 1.56 V at 25°C and 1.47 V at 55 °C, respectively, at a current density of 10 mA cm−2 for 50 h. The variation in temperature from 25 °C to 55 °C has a substantial impact on the overall performance, emphasizing the need for temperature-dependent studies. Understanding the catalyst's behaviour under different temperature regimes is crucial for optimizing its efficiency and durability in real-world applications. This insight can lead to the development of more energy-efficient and robust electrochemical systems for a sustainable future.

Spectroscopic investigation and molecular docking analysis of an FRET probe: Trypsin from bovine pancreas@Coumarin 440 dye conjugate

Herein, a systematic investigation of energy transfer from bovine pancreas trypsin to coumarin 440 (C440) dye is presented with an aim to design a FRET probe, as trypsin is an important enzyme for absorption and digestion of nutrients in the small intestine. Conformational changes in trypsin upon interaction with C440 dye are studied by employing both spectroscopic and molecular docking techniques. Steady state and time resolved measurements validate the formation of trypsin-C440 complex via dynamic quenching, that confirms the role of C440 as an inhibitor to suppress the activity of trypsin. Spectral overlap integral, Förster's distance, rate and energy transfer efficiency are calculated from steady state measurements. The observed blue shift in fluorescence suggests conformational changes due to hydrophobicity that arises in trypsin structure on binding with C440 possibly due to their interaction through H-bond (SER195 and GLN192), hydrophobic (GLN192 and HIS57) and π-π stacking bonding (HIS57). The stability of trypsin@C440 bio-conjugate at higher temperature was established from temperature dependent PL studies and the thermodynamic parameters determined agree with second law of thermodynamics. The thermodynamic parameters such as change in enthalpy (ΔH=172.2Jmol−1), change in entropy (ΔS=15.3Jmol−1K−1) and the respective approximately same and unity values of Gibb's free energy (ΔG) and Hill coefficient (n), as well as binding affinities determined from temperature dependent fluorescence studies validate the hydrophobic, spontaneous, exothermic process engaged in trypsin@C440 bio-conjugate.

In-situ polymerization of polythiophene/silicon carbide nanocomposites for gas sensing and optoelectronic devices

Silicon carbide (SiC)-reinforced polythiophene (PTh) nanocomposites were synthesized by oxidative in-situ polymerization. The successful inclusion of SiC nanoparticles into the PTh was confirmed by the characteristic peak of Si–C bond around 865 cm−1 in the Fourier transform infrared (FT-IR) spectra. The X-ray diffraction (XRD) patterns demonstrate that the amorphous nature of PTh reduces with the addition of SiC. The intensity of UV–Vis absorbance increased proportionally with filler loading, indicating improved optical properties for PThSiC7 (polythiophene/silicon carbide 7 wt%) nanocomposite compared to pristine PTh. Field emission scanning electron microscopy (FE-SEM) images illustrate the changes in surface morphology of PTh with the addition of SiC and uniform dispersion was observed in PThSiC7. The formation of spherical-shaped moieties was confirmed using transmission electron microscopy (TEM). The shifts in degradation and glass transition temperatures towards higher values were attributed to the enhanced thermal properties of the nanocomposites. Temperature-dependent studies on the electrical and dielectric properties of the samples underscored the excellent conductivity exhibited by PThSiC7 (7 × 10−3 S/cm) with a low activation energy of 0.058 eV. In response to the growing demand for gas sensors, samples were tested to sense ammonia gas, demonstrating that PThSiC nanocomposites were more sensitive than PTh. The controllable optical properties, thermal stability, electrical characteristics, and gas sensing performance of the PThSiC nanocomposites suggest their potential as a promising material for the development of advanced energy storage systems, sensors, and optoelectronic devices.

Temperature and frequency dependent conductive behavior study on polymer-derived SiBCN ceramics

Conductive behavior research is vital for in-depth understanding the conductive capabilities of materials as well as promoting the development of their applications in fields such as electronics, energy and sensing. In the article, the AC conductive behavior was systematically evaluated for polymer-derived SiBCN ceramics by complex impedance spectroscopy and electrical modulus methods. The results suggest that SiBCN ceramics have a frequency-independent conductivity at low frequencies, whereas it exhibits a relaxation process with increasing frequency at high frequencies. In addition, the SiBCN ceramics follow the electron hopping conductive mechanism in both low and high-frequency bands over the testing temperature range. By considering the relationship between the prefactor σ0 and T0, the conductive mechanism is revealed to be the band-tailed state hopping instead of the variable range hopping. It is worth noting that although the material has the same conductive mechanism at various testing temperatures, hopping is mainly controlled by the matrix phase at low frequencies; while at high frequencies, hopping is dominated by free carbon phase. Our results provide the underlying insights needed to guide the design of amorphous SiBCN ceramics for applications in electrically relevant fields.

Temperature dependent dielectric studies of pure and Sr doped Pr2NiMnO6

The physical properties of Sr doped Pr2NiMnO6 have been discussed. The Samples of Pr2-xSrxNiMnO6 (x = 0.0, 0.2, 0.4) have been synthesized via Solid State Reaction. The X-Ray diffraction and Scanning Electron Microscopy characterizations were applied to examine the structure and surface morphology. Observed XRD patterns reveal the structure to be monoclinic with P21/n space group. Increase in the Sr doping resulted in the reduction in the particle size and crystallite size. Raman peak corresponding to the wave number 515 cm−1 represents the asymmetric mode and the other one at 655 cm−1 represents symmetric mode of the NiO6/MnO6 octahedra. The frequency and temperature dependent dielectric studies on samples of Pr2-xSrxNiMnO6 (x = 0.0, 0.2, 0.4) suggest the decrease in dielectric constant with the increase in Sr doping. The appearance of relaxation peak has been also observed in the temperature dependent dielectric loss plots. Furthermore, the ac conductivity reduction has been seen with the increase in Sr doping.

Tin oxide thin films on Ag(111): Thickness and temperature dependent study of surface structure and electronic properties

Growth and structure of tin oxide films on Ag(111) from submonolayer to 10 monolayer equivalent thickness have been studied using low energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS) and angle-resolved photoemission spectroscopy techniques for room temperature (RT) and high temperature (HT) (573 K). For RT growth, most of the tin is oxidised to form tin oxide (SnOx) as confirmed by XPS where no metallic component is noticed. However, the grown films are not epitaxial or ordered which can be confirmed by no spots in LEED for higher coverage. Metallic Sn along with two oxidation states of Sn are noticed for HT growth, with the surface mainly composed of SnO2. LEED pattern shows the presence of c(2 × 2) and (3 × 1) along with two different hexagonal multidomain type patterns. The electronic structure for lower coverage resembled the Sn/Ag(111) alloy structures for lower coverage. For higher coverages appearance of three bands below 2 eV binding energy was noticed.

Temporal Resolution of Activity-Related Solvation Dynamics in the TIM Barrel Enzyme Murine Adenosine Deaminase.

Murine adenosine deaminase (mADA) is a prototypic system for studying the thermal activation of active site chemistry within the TIM barrel family of enzyme reactions. Previous temperature-dependent hydrogen deuterium exchange studies under various conditions have identified interconnected thermal networks for heat transfer from opposing protein-solvent interfaces to active site residues in mADA. One of these interfaces contains a solvent exposed helix-loop-helix moiety that presents the hydrophobic face of its long α-helix to the backside of bound substrate. Herein we pursue the time and temperature dependence of solvation dynamics at the surface of mADA, for comparison to established kinetic parameters that represent active site chemistry. We first created a modified protein devoid of native tryptophans with close to native kinetic behavior. Single site-specific tryptophan mutants were back inserted into each of the four positions where native tryptophans reside. Measurements of nanosecond fluorescence relaxation lifetimes and Stokes shift decays, that reflect time dependent environmental reoroganization around the photo-excited state of Trp*, display minimal temperature dependences. These regions serve as controls for the behavior of a new single tryptophan inserted into a solvent exposed region near the helix-loop-helix moiety located behind the bound substrate, Lys54Trp. This installed Trp displays a significantly elevated value for ; further, when Phe61 within the long helix positioned behind bound substrate is replaced by a series of aliphatic hydrophobic side chains, the trends in mirror the earlier reported impact of the same series of function-altering hydrophobic side chains on the activation energy of catalysis, .The reported experimental findings implicate a solvent initiated and rapid (>ns) protein restructuring that contributes to the enthalpic activation barrier to catalysis in mADA.

Integration of low-thermal-budget In2O3 NMOS inverter and GaN HEMT for power electronics

Herein, we demonstrated an “interposer”-style integration of In2O3 FET-based gate-driver circuitry wire bonded to an AlGaN/GaN high electron mobility transistor (HEMT) device grown on a GaN-on-Si substrate, and its feasibility for power electronics was discussed. The normally-on AlGaN/GaN HEMT exhibited a threshold voltage of −2.8 V, with a maximum drain current density of 265 mA/mm. The device also showed good off-state performance, such as a high ON/OFF ratio (Ion/Ioff) of ∼1010 with a breakdown voltage of ∼445 V and an off-state leakage current of ∼10−12 A. The low-temperature processed In2O3 driver circuitry exhibited a high gain of ∼64 and a maximum operating frequency of 2 kHz. The temperature-dependent study of the voltage transfer characteristics (VTC) of In2O3 driver circuitry exhibited stable operation up to 125 °C. An integrated In2O3 driver circuitry with GaN HEMT was demonstrated, marked by a 50 mA/mm drain current for circuit response of one cycle during the ON state. These results pave the way for future monolithic integration of oxide semiconductor-based gate-driver circuitry with power switches for energy-efficient integrated circuits.

Experimental studies on noncentrosymmetric Nd3Se4: Strongly correlated noncollinear ferromagnet

We have synthesized polycrystalline Nd3Se4 by the solid state sealed tube reaction route followed by structural characterization and magnetic property measurements. The temperature-dependent magnetization studies reveal the existence of competing magnetic interactions below the ferromagnetic ordering (TC ≈ 48.4 K). The observation of hysteresis in the isothermal magnetization M(H) data with the coercive field of ≈ 0.25 T at 2 K indicates dominant ferromagnetic interactions in the applied field. The nonsaturating behavior of M(H) data at higher applied field and kinks in corresponding dM/dHvs. H plots suggest the coexistence of multiple magnetic interactions at low temperatures. Using the M(T,H=2 T) data, the Rhodes-Wohlfarth ratio (qc/qs) has been estimated to be ≈ 3.6, which supports the itinerant magnetism in Nd3Se4. These competing interactions have been further investigated by AC-susceptibility measurements at various excitation frequencies. The χ′ reduces drastically with an increase in the applied DC field, as observed from isothermal field-dependent AC-χ studies. Additionally, the strong correlation between delocalized charge and localized magnetic moments is evident from ρ(T) measurements at H = 0 and 5 T. The ρ(T,H=0 T) data shows a clear drop having quadratic temperature dependence, below TC. Furthermore, the inter-dependence between electrical transport and magnetism has been established firmly through negative magnetoresistance, in which the maxima correspond to the coercive field obtained from M(H) data.

Dynamics and Coordination of a P2N2 Ligand - from Twisted Conformation to Chelation.

Based on their general spacial flexibility, their Lewis and Brønsted basicity, and ability to mimic second sphere effects the 1,5-diaza-3,7-diphosphacyclooctane ligand family and their complexes have regained substantial scientific interest. It was now possible to structurally analyze a recently reported member of this family with p-tolyl and t-butyl substituents on P and N, respectively, (P2 p-tolN2 tBu). Notably, the ligand crystallizes with a 'twisted' backbone. This compound is the very first of its kind to have been unambiguously characterized with regard to its chemical and molecular structure as being in this conformation. A temperature-dependent NMR study provides insight into the molecular dynamics of two isomers in solution, which are most likely also both twisted, as judged by the observed limited reactivity. Despite the in principle unfavorable conformation of the free ligand, it was successfully chelated to tungsten and molybdenum centers in mononuclear carbonyl complexes. The ligand, a derivative thereof and four new complexes were comprehensively characterized and analyzed in comparison. This includes single crystal XRD molecular structures of P2 p-tolN2 tBu and all four complexes. P2 p-tolN2 tBu, regardless of its twisted conformation, is able to coordinate to metal centers given that enough energy (heat) for a conformational change is provided.

EPR studies of ferredoxin in spinach and cyanobacterial thylakoids related to photosystem I-driven NADP+ reduction.

Photosynthetic light-dependent reactions occur in thylakoid membranes where embedded proteins capture light energy and convert it to chemical energy in the form of ATP and NADPH for use in carbon fixation. One of these integral membrane proteins is Photosystem I (PSI). PSI catalyzes light-driven transmembrane electron transfer from plastocyanin (Pc) to oxidized ferredoxin (Fd). Electrons from reduced Fd are used by the enzyme ferredoxin-NADP+ reductase (FNR) for the reduction of NADP+ to NADPH. Fd and Pc are both small soluble proteins whereas the larger FNR enzyme is associated with the membrane. To investigate electron shuttling between these diffusible and embedded proteins, thylakoid photoreduction of NADP+ was studied. As isolated, both spinach and cyanobacterial thylakoids generate NADPH upon illumination without extraneous addition of Fd. These findings indicate that isolated thylakoids either (i) retain a "pool" of Fd which diffuses between PSI and membrane bound FNR or (ii) that a fraction of PSI is associated with Fd, with the membrane environment facilitating PSI-Fd-FNR interactions which enable multiple turnovers of the complex with a single Fd. To explore the functional association of Fd with PSI in thylakoids, electron paramagnetic resonance (EPR) spectroscopic methodologies were developed to distinguish the signals for the reduced Fe-S clusters of PSI and Fd. Temperature-dependent EPR studies show that the EPR signals of the terminal [4Fe-4S] cluster of PSI can be distinguished from the [2Fe-2S] cluster of Fd at > 30K. At 50K, the cw X-band EPR spectra of cyanobacterial and spinach thylakoids reduced with dithionite exhibit EPR signals of a [2Fe-2S] cluster with g-values gx = 2.05, gy = 1.96, and gz = 1.89, confirming that Fd is present in thylakoid preparations capable of NADP+ photoreduction. Quantitation of the EPR signals of P700+ and dithionite reduced Fd reveal that Fd is present at a ratio of ~ 1 Fd per PSI monomer in both spinach and cyanobacterial thylakoids. Light-driven electron transfer from PSI to Fd in thylakoids confirms Fd is functionally associated (< 0.4 Fd/PSI) with the acceptor end of PSI in isolated cyanobacterial thylakoids. These EPR experiments provide a benchmark for future spectroscopic characterization of Fd interactions involved in multistep relay of electrons following PSI charge separation in the context of photosynthetic thylakoid microenvironments.

Synthesis, Optical, Dielectric, SHG, Magnetic and Visible Light Driven Catalytic Studies on Compounds Belonging to the Swedenborgite Structure.

A new compound, InBaZn3GaO7, with swedenborgite structure along with transition metal (TM) substituted variants have also been prepared. The structure contains layers of tetrahedral ions (Zn2+/Ga3+) connected by octahedrally coordinated In3+ ion forming the three-dimensional structure with voids where the Ba2+ ions occupy. The TM substituted compounds form with new colors. The origin of the color was understood based on the ligand-field transitions. The near IR reflectivity studies indicate that the Ni - substituted compounds exhibit good near - IR reflectivity behavior, making them possible candidates for 'cool pigments'. The temperature dependent dielectric studies indicate that the InBaZn3GaO7 compound undergoes a phase transition at ~360 °C. The compounds are active towards second harmonic generation (SHG). Magnetic studies show the compounds, InBaZn2CoFeO7 and InBaZn2CuFeO7 to be anti-ferromagnetic in nature. The copper containing compounds were found to be good catalysts, under visible light, for the oxidation of aromatic alkenes. The many properties observed in the swedenborgite structure-based compounds suggests that the mineral structure offers a fertile ground to investigate newer compounds and properties.