Axial Positions Research Articles

Effect of pulsed jet generated by boundary condition and fluid oscillator on the cascade performance

By introducing pulsed jet with boundary condition styles and fluidic oscillator on the upper end wall, the paper analyzes, through validated numerical simulation, the impact of the two jet methods on the aerodynamic performance and flow field structure of the compressor cascade under different jet positions. The results show that under the frequency doubling condition of the prototype flow field, the boundary condition jet scheme demonstrates better performance at the positions of 76% and 86% axial chord, whereas the oscillator jet scheme exhibits superior control at the 96% axial chord position. The pulsed jet with jet pipe reduces the total pressure loss by a maximum of 10.51%, while the pulsed jet with fluid oscillator decreases the total pressure loss coefficient by 9.24%. After the two types of jets interact with the cascade flow field, the intricate flow conditions within the flow field exert varying influences on the pulsed jet. Specifically, the boundary condition-style jet increases the jet velocity due to the pressure difference between the inlet and outlet. Conversely, the oscillator jet reduces the outlet velocity due to the decreased pressure ratio between the inlet and outlet, ultimately resulting in the differences in the control performance of the two schemes. At the 76% and 86% of the axial chord positions, the boundary condition jet injects additional momentum into the low-energy fluid within the corner region, effectively inhibiting the development of trailing-edge shedding vortex, narrowing the range of corner separation, and decreasing cascade losses. At the position of 96% axial chord, which is near the trailing edge of the cascade, the high-momentum fluid from the boundary condition jet enhances flow mixing. The pressure difference that had increased on both sides of the trailing edge causes significant deflection of the jet fluid, thereby reducing the control effectiveness. In contrast, the oscillator jet significantly reduces the intensity and scope of passage vortex and trailing-edge shedding vortex, lowering the turbulent kinetic energy in the area and decreasing mixing losses.

An approach to functionalization of cucurbit[n]uril through a tetrahydrothiopheno equatorial substituent

An approach to functionalization of cucurbit[n]uril through a tetrahydrothiopheno equatorial substituent

Arrangement of Azidomethyl Group in Lupinine Azide: Structural and Spectroscopic Properties

Quinolizidine derivatives are an important class of substances that are used in the pharmaceutical industry. In previous studies, the synthesis of these substances is carried out using lupinine azide (IUPAC: 1-(azidomethyl)octahydro-2H-quinolizine), which is often used to obtain new biologically active compounds. In this regard, its structural characterization is critically important. In this work, the conformational diversity of the molecular structure of this compound has been studied. It is shown that the structure with the axial position of the methyl azide group contains a number of low-energy conformer states with energies higher than the ground state by 0.15–0.60 kcal/mol. Such structural ambiguity should manifest itself in the chemical reactions and biological activity of lupinine azide. The spectroscopic properties of the conformers were studied by modeling chemical shifts for carbon and hydrogen atoms, as well as by simulating IR absorption spectra. An analysis of the most specific spectroscopic features of all of the conformers was carried out. Based on the correlation of the theoretical results and the experimental spectroscopic data, a conclusion was made for the first time regarding the most probable conformational states in the solution.

Electrochemical Conversion of 5-Hydroxymethylfurfural to 2,5-Furandicarboxaldehyde Using Mn(III)–Schiff Base Catalysts

2,5-furandicarboxaldehyde (DFF) is one of the most promising biomass-based building blocks for the synthesis of biobased polymers. DFF can be obtained from 5-hydroxymethylfurfural (HMF), a fructose derivate, and it is a key molecule in the sequence of reactions of furan chemistry to develop biobased plastics. In this frame, four manganese(III)–Schiff base complexes 1–4 have been obtained. The general formula for the complexes, MnLn(OCN)(H2O/CH3OH)m (Ln being the Schiff base ligands L1–L4, formed as the result of the condensation of different substituted hydroxybenzaldehydes with diverse diamines, and m = 1–3), has been confirmed by characterization through different analytical and spectroscopic techniques. X-ray crystallographic studies for 1 and 2 showed tetragonally distorted octahedral structures, where the Schiff base was placed in the equatorial coordination positions of the Mn(III) ion. Complexes 1 and 2 behaved as efficient catalysts in the oxidation of HMF to DFF in an electrolytic reaction at pH 8.5, with phosphate buffer at room temperature, with conversion rates of 70–80%. On the other hand, complexes 3 and 4, where the axial position was sterically less accessible, yielded only an 11% conversion of HMF to DFF. The results indicate that a correct selection of metal complexes allows the development of a new efficient way to obtain DFF.

Aproximación dendroecológica y caracterización anatómica y física de la madera juvenil de Araucaria angustifolia de Oxapampa, Perú

The study of tree growth in forest plantations for timber use must be complemented by the description of wood characteristics to serve both foresters and wood technologists. Studies based on growth rings allow for the acquisition of growth records in diameter, height, shape, and volume with annual resolution, facilitating the assessment of their relationship with environmental factors. This is crucial for thinning and harvesting decisions in forest plantations. Evaluating differences in wood characteristics in axial and radial directions provides valuable information for analyzing their optimal potential use. This study evaluated the growth of Araucaria angustifolia (Bertol.) Kuntze using dendroecological techniques. Additionally, wood anatomy and basic density were examined at four axial positions and three radial levels as quality indicators. Stem analysis revealed that CAIDBH ranged from 1.72 to 2.33 cm; MAIDBH ranged from 1.70 to 1.99 cm. The climatic variable that best explains the radial growth variability was precipitation, with a R2 of 83.82 %. A higher basic density, tracheid length, and tracheid wall thickness were found near the base and the bark. Based on these findings, A. angustifolia demonstrated promising growth and wood quality under local conditions, such as those in Oxapampa, for timber use.

Unusual variability of isomers in copper(II) complexes with 1,8-bis(2-hydroxybenzyl)-cyclam.

Copper isotopes and their complexes are intensively studied due to their high potential for applications in radiodiagnosis and radiotherapy. Here, we study the CuII complex of 1,8-bis(2-hydroxybenzyl)-cyclam (H2L), which forms an unexpected variety of isomers differing in the mutual orientation of the substituents on the cyclam nitrogen atoms, the protonation of the phenolate pendant, and the ligand denticity. The interconversion of the isomers is rather slow, which made the isolation, identification and investigation of some of the individual species possible. The most stable and the most common form is the hexacoordinated trans-III isomer. However, several other forms were also observed in solution in the course of HPLC, UV-VIS and electrochemical measurements. The isomers present in solution were identified by comparison with the solid-state structures solved by X-ray diffraction analysis on single crystals and with the help of theoretical calculations. The phenolate pendant is coordinated both in the protonated and deprotonated state; however, the coordination in the axial position of the hexacoordinated trans-III complex is weak, especially in its protonated state. Conversely, the CuII ion is pentacoordinated in the cis-V isomer with only one phenolate strongly coordinated in the basal plane of the distorted tetragonal pyramid. The computational data showed that the phenolate groups might form strong intraligand hydrogen bonds competitive with the metal-phenolate bonds, stabilizing the structure of the complex. In addition, theoretical calculations revealed that several geometries are energetically close to the optimal one, which indicates possible dynamic behaviour of the complex in solution.

Synthesis, spectroscopic, crystal structure and DFT investigation of the Cu(II) complex with mixed 2,2’-dimethylmalonate/2,2'-bipyridine ligands

In this study; a mixed ligand Cu(II) complex, [Cu(Me2mal)(bpy)(H2O)]∙H2O (Me2mal-2= Dimethylmalonate dianion, bpy=2,2'-bipyridine) was synthesized and characterized experimentally and theoretically by IR, UV and single crystal X-ray diffraction. The complex crystallizes in the orthorhombic system with space group Pnnm. In the complex, the Cu center is coordinated by a Me2mal-2 dianion and a bpy molecule, and the N2O2 exhibits square-planar geometry. The axial position was occupied by the water molecule. The crystal packing of the complex is stabilized by O-H…O hydrogen bonds and  interactions. The contribution of hydrogen bonding and  stacking interactions to crystal packing was also investigated. Theoretical calculations using the DFT method were also carried out in this study. DFT (B3LYP/6-31G) and TD-DFT (B3LYP/LanL2DZ) calculation methods were used to obtain the geometric, vibrational and electronic properties of the synthesized complex and the obtained theoretical calculation results and experimental results are presented comparatively in this study.

Complex-valued three-dimensional atomic spectroscopy with Gaussian-assisted inline holography

When a laser-cooled atomic sample is optically excited, the envelope of coherent forward scattering can often be decomposed into a few complex Gaussian profiles. The convenience of Gaussian propagation helps address key challenges in digital holography. In this paper, we develop a Gaussian-decomposition-assisted approach to inline holography for single-shot, simultaneous measurements of absorption and phase-shift profiles of small atomic samples sparsely distributed in three dimensions. The samples' axial positions are resolved with micrometer resolution and their spectroscopy are extracted from complex-valued images recorded at various probe frequencies. The phase-angle readout is not only robust against transition saturation but also insensitive to atom-number and optical-pumping-induced interaction-strength fluctuations. Benefiting from such features, we achieve hundred-kHz-level single-shot resolution to the transition frequency of a Rb87 D2 line, with merely hundreds of atoms. We further demonstrate single-shot three-dimensional field sensing by measuring local light shifts to the atomic array with micrometer spatial resolution. Published by the American Physical Society 2025

Green Light Activated Dual-Action Pt(IV) Prodrug With Enhanced PDT activity.

Light induced release of cisplatin from Pt(IV) prodrugs is a promising tool for precise spatiotemporal control over the antiproliferative activity of Pt-based chemotherapeutic drugs. A combination of light-controlled chemotherapy (PACT) and photodynamic therapy (PDT) in one molecule has the potential to overcome crucial drawbacks of both Pt-based chemotherapy and PDT via a synergetic effect. Herein we report green-light-activated Pt(IV) prodrug GreenPt with BODIPY-based photosentitizer in the axial position with an incredible high light response and singlet oxygen generation ability. GreenPt demonstrated the ability to release cisplatin under low-dose green light irradiation up to 1 J/cm2. The investigation of the photoreduction mechanism of GreenPt prodrug using DFT modeling and ΔG0 PET estimation revealed that the anion-radical formation and substituent photoinduced electron transfer from the triplet excited state of the BODIPY axial ligand to the Pt(IV) center is the key step in the light-induced release of cisplatin. Green-light-activated BODIPY-based photosentitizers 5 and 8 demonstrated outstanding photosensitizing properties with an extraordinary phototoxicity index (PI) >1300. GreenPt prodrug demonstrated gradual intracellular accumulation and light-induced phototoxicity with PI > 100, thus demonstrating dual action through light-controlled release of both cisplatin and a potent BODIPY-based photosensitizer.

Tipping the balance between twist and chair ligand conformers in multinuclear ethylzinc cyclophosphazenates.

Hexaanionic cyclophosphazenate ligands [(RN)6P3N3]6- provide versatile platforms for the assembly of multinuclear metal arrays due to their multiple coordination sites and highly flexible ligand core structure. This work investigates the impact of incrementally increasing the steric demand of the ligand periphery on the coordination behavior of ethylzinc arrays. It shows that the increased congestion around the ligand sites is alleviated by progressive condensation with the elimination of diethylzinc. The condensation is accompanied by a switch in ligand conformation: the phosphazene ring of the methyl derivative adopts the chair conformer in the dimeric complex (EtZn)12[(RN)6P3N3]2, while the more sterically demanding isobutyl derivative exhibits twist conformers in both the monomeric complex (EtZn)6[(iBuN)6P3N3] and the condensed dimer (EtZn)8Zn2[(iBuN)6P3N3]2. Ethyl and propyl derivatives mark a tipping point: the dimeric complex (EtZn)12[(RN)6P3N3]2 exhibits the chair conformation and is observed in solution and within the stabilising environment of a co-crystal. However, when crystallising in pure form, it transforms with the loss of one equivalent of Et2Zn into the collapsed dimer (EtZn)10Zn[(RN)6P3N3]2 which features the twist conformer.

Design, development, and evaluation of the organic chemistry representational competence assessment (ORCA)

This paper describes the design and evaluation of the O̲rganic chemistry R̲epresentational C̲ompetence A̲ssessment (ORCA). Grounded in Kozma and Russell's representational competence framework, the ORCA measures the learner's ability to interpret, translate, and use six commonly used representations of molecular structure (condensed structures, Lewis structures, skeletal structures, wedge-dash diagrams, Newman projections, and chair conformations). Semi-structured interviews with 38 first-semester organic chemistry learners informed the development of the ORCA items. The ORCA was developed and refined through three pilot administrations involving a total of 3477 first-semester organic chemistry students from multiple institutions. The final version of the ORCA was completed by 1494 students across five institutions. Various analyses provided evidence for the validity and reliability of the data generated by the assessment. Both one-factor and three-factor correlated structures were explored via confirmatory factor analysis. The one-factor model better captured the underlying structure of the data, which suggests that representational competence is better evaluated as a unified construct rather than as distinct, separate skills. The ORCA data reveal that the representational competence skills are interconnected and should consistently be reinforced throughout the organic chemistry course.

Late Middle to Late Ordovician Phosphate Accumulation of the Moyero River Section (Siberia): A Record of Upwelling and Global Cooling

The phosphate-bearing rocks (phosphate rocks and phosphorites) were studied over a 45-meter interval of the Moyero river section, covering the upper part of the Darriwilian and the lower part of the Sandbian stages of the Ordovician. These rocks were investigated by field observations and laboratory methods, including optic and scanning electron microscopy, X-ray diffraction analyses. The accumulation of phosphatic matter is manifested in carbonates, sandstones, and aleurolites in the form of grains (ooids and peloids), intraclasts, phosphatic and phosphatized shells. In argillites, it is represented by cryptocrystalline matter. Phosphate matter consists of fluorapatite. The peaks of phosphate accumulation are associated with the formation of layers of physically reworked granular phosphorites (condensation horizons) directly above the depositional sequence boundaries. The formation of the studied phosphate-bearing rocks during the Darriwilian-Sandbian transition was influenced by a combination of global (Great Ordovician Biodiversification Event (GOBE), reduction in sea surface temperature, atmospheric CO2, high sea level, flooding of craton margins) and regional (equatorial position of Siberia, arid climate, facies) factors. Global conditions led to the enrichment of seawater with phosphorus and the effect of upwelling. Regional conditions determined the characteristics of phosphate formation. Studied phosphate-bearing rocks can be considered as a record of upwelling on the Siberian craton during the Middle-Late Ordovician transition and one of the manifestations of long-term global cooling started early in the Middle Ordovician.

A Versatile Drift‐Free Super‐Resolution Imaging Method via Oblique Bright‐Field Correlation

AbstractHigh‐resolution optical microscopy, particularly super‐resolution localization microscopy, requires precise real‐time drift correction to maintain constant focus at nanoscale precision during the prolonged data acquisition. Existing methods, such as fiducial marker tracking, reflection monitoring, and bright‐field image correlation, each provide certain advantages but are limited in their broad applicability. In this work, a versatile and robust drift correction technique is presented for single‐molecule localization‐based super‐resolution microscopy. It is based on the displacement analysis of bright‐field image features of the specimen with oblique illumination. By leveraging the monotonic relationship between the displacement of image features and axial positions, this method can precisely measure the drift of the imaging system in real‐time with sub‐nanometer precision in all three dimensions, over a broad axial range, and for various samples, including those with closely matched refractive indices. The performance of this method is validated against conventional marker‐assisted techniques and demonstrates its high precision in super‐resolution imaging across various biological samples. This method paves the way for fully automated drift‐free super‐resolution imaging systems.

Supramolecular Dimeric MnIII Complexes: Synthesis, Structure, Magnetic Properties, and Catalytic Oxidation Studies.

In this study, a tetradentate Schiff-base ligand (H2L), synthesized by the condensation of ethylenediamine with 2-hydroxy-3-methoxy-5-methylbenzaldehyde, was reacted with either manganese salts or manganese salts in the presence of various pseudohalides in methanol. This reaction resulted in the formation of five mononuclear MnIII complexes: [Mn(L)(H2O)2](NO3)·1/2H2O·1/2CH3OH (1), [Mn(L)(H2O)2](ClO4)·H2O (2), [Mn(L)(N3)(H2O)]·1/3H2O (3), [Mn(L)(NCS)(H2O)] (4), and [Mn(L)(H2O)2](dca) (5) (where dca is dicyanamide ion). X-ray crystallography revealed that the MnIII centers adopt a hexa-coordinate pseudo-octahedral geometry, where the equatorial plane is constructed with phenoxo oxygen and imine nitrogen atoms from the Schiff base ligand, while the axial positions are occupied by water molecules or a combination of water and pseudohalides. Supramolecular interactions, primarily π-π stacking and hydrogen bonding, contribute to the formation of pseudodimeric structures in the solid state. Magnetic susceptibility measurements indicated antiferromagnetic coupling within quasi-dimers, primarily through hydrogen bonds. Catalytic studies showed that the complexes effectively catalyze the aerobic oxidation of substrates such as 2-aminophenol and 3,5-di-tert-butylcatechol to yield 2-aminophenoxazin-3-one and 3,5-di-tert-butylquinone, respectively. They also catalyze the oxidation of styrene to its corresponding oxirane, demonstrating their versatile catalytic proficiency. Mechanistic insights, supported by ESI mass spectrometry and EPR studies, suggest that catalysis involves the formation of a complex-substrate aggregate, followed by an intramolecular electron transfer.

Deciphering the Influence of Alkylene Bridged and Chelating Mode on Pd—C and Pd—X (X = Cl, Br, and I) Bonding Interaction Within Bis‐(NHC)‐Palladium Complexes Using Quantum Chemistry Tools

ABSTRACTIn this paper, we have explored the influence of alkylene‐bridged length and coordination mode on the reactivity of a series of 24 alkylene‐bridged palladium complexes using computational tools (B3PW91/LANL2DZ//6‐31G(d) level) in gas phase and DMSO. These palladium complexes prefer a boat and chair configuration for methylene and ethylene bridge length, respectively. In addition, phenyl and nitro complexes present a higher activation for Pd—C bonds while the most stable Pd⋯C interactions are observed for abnormal mode with methylene bridge. According to the energy decomposition analysis (EDA), hydrogen and phenyl complexes in both chelation modes present a better electrostatic character. Moreover, Pd⋯C interactions are stronger compared to the Pd⋯X ones for ethylene‐bridged abnormal complexes (in gas phase). Finally, the donation/back‐donation ratio (d/b) values reveal the Fischer carbene character of these [bis(NHC)]⋯[PdX2] interactions. Concerning the hybridization around the metal cation for the Pd—C bond, the sp2d type is observed for methylene‐bridged palladium complexes while the sp3 one is observed for ethylene bridge complexes.

Fe(II) spin-crossover in 2-D Hofmann-like coordination polymers with different sized pyridine derivatives: syntheses, crystal structures, and magnetic properties

The syntheses, crystal structures, and magnetic properties of 2-D Hofmann-like motif {FeII(alkyl-pyridine)2[AuI(CN)2]2} (alkyl = 3,4-dimethyl (1), 4-ethyl (2), 4-isopropyl (3)), {FeII(alkyl-pyridine)2[AuI(CN)2]2}∙1/2(alkyl-pyridine) (alkyl = 3,5-dimethyl (4)), and {FeII(X-Isonicotinate)2[AuI(CN)2]2} (X = allyl (5), phenyl (6)) have been investigated. In spite of a wide range of substituent sizes, the structures of 1-3, 5, and 6 are almost crystallographically identical. The 2-D layer consists of an octahedral FeII ion coordinated with the nitrogen atoms in [AuI(CN)2] linear units at equatorial positions and monodentate py derivatives at axial positions. The adjacent two layers interact via intermetallic Au–Au interactions, forming a bilayer structure. The distance between stacking bilayers is associated with bulky substituent ligands. With increasing bulkiness, the interlayer distance expands without any transformation in the crystal structure. Compound 4 possesses guest space where uncoordinated 3,5-dimethyl-pyridine is present. Compounds 1-4 and 6 undergo spin transitions. Only 5 retains the high-spin state characteristic. These constant structures are similar to formerly reported Ag derivatives {FeII(alkyl-pyridine)2[AgI(CN)2]2}. The related Ag and Au families are compared and discussed.

Experimental investigation of unsteady nature of shock waves induced by various ramps

The ramp induced shock wave boundary layer interaction (RI-SWBLI) has been investigated experimentally at different ramp angles in a Ma = 3 flow. The shock unsteady nature has been examined in detail by using a semi-quantitative processing of Schlieren images. The shock-wave locations are extracted to allow spectral analysis of the shock-wave oscillations. Results show that the shock motion is associated with the state of separation, which has been categorized into three classifications based on semi-quantitative Schlieren measurements, namely, unseparated, initially separated, and fully separated. The statistical analysis of the shock oscillation illustrates that the probability distribution function and power spectral density (PSD) along two locations of a certain height follow almost the same principles in the time–frequency domain. The PSD results show that significant variations of shock motion of lower location occur at 30° ramp interaction flow according to the PSD, which is characterized by a lower energy, wide range, and uniformly distributed motion. The probability of the reattachment shock events first rises at 24° ramp interaction flow. With increase in ramp angle, the axial position at the peak of the probability of shock events slowly transfers to upstream positions. Moreover, a conceptual model of the shock motion is proposed to preliminarily reveal the unsteady nature of shock induced by a RI-SWBLI, including three scenarios: In nonseparating interaction flows, the shock motion is mainly affected by the upstream turbulent boundary layer and the shear layer on the ramp. During the initial separation process, the shock wave motion is mainly affected by the pulsations of separation bubble. With full separation, impact movement is primarily controlled by newly designed aerodynamic ramp.

Synthesis, exploring the structural, non covalent interaction effects, biological assessment, molecular docking and quantum chemical properties of functionalized new N-nitrosopiperidin-4-one: An experimental and theoretical study

The synthesis of 3-benzyl-1-nitroso-2,6-di-p-tolylpiperidin-4-one 2 has been carried via the nitrosation of 3-benzyl-2,6-di-p-tolylpiperidin-4-one 1 with sodium nitrite and dilute hydrochloric acid at room temperature. This work deals with the synthesis, characterization (1H and 13C NMR, 1H–1H-COSY, 1H–13C-COSY, and X-ray diffraction analysis), and stereochemical characterization of functionalized N-nitrosopiperidin-4-one. The molecular level behaviors of the compounds were determined by computational chemistry methods. It is to be noted that at room temperature, 3-benzyl-2,6-di-p-tolylpiperidin-4-one 1 preferentially exists in chair conformation with all substituents in equatorial orientation, whereas its nitroso derivative, 3-benzyl-1-nitroso-2,6-di-p-tolylpiperidin-4-one 2, exists in syn and anti isomers. The observed coupling constant data for 2 suggests that the syn isomer is an equilibrium mixture of two boat forms B1 and B2, and that the predominant conformer of the anti-isomer is boat form B1. Conformational analysis carried out through DFT calculation using Gaussian 09 program supported that B1 is the more stable conformer of compound 2 with minimum energy for both syn and anti isomers. Good correlations were obtained between the predicted boat conformation B1 from theoretical study (DFT calculation) and the corresponding experimental (1H NMR spectrum) ones. This was complemented by single-crystal X-ray analysis, which revealed that compound 2 exists as the anti-isomer with the piperidine ring adopting the B1 boat structure. Here, the phenyl group at C(2) and the benzyl group at C(3) are in axial orientation, and the phenyl group at C(6) are in equatorial orientation. Hirshfeld surface analysis of the molecule showed H⋯H (59.0 %), C⋯H/H⋯C (22.9 %), O⋯H/H⋯O (14.3 %), N⋯H/H⋯N (2.4 %), and O⋯O (0.5 %) interactions. Energy framework analysis revealed that among the components of the framework energies, electrostatic repulsion (Erep) is dominant. Finally, the molecular docking and dynamics simulation studies of the title ligand with 6LVM protein have shown better binding affinity, and stability. Further, ADME prediction of the compound 2 has exhibited excellent drug-likeness.

Experimental investigation of the characteristics of direct injection nozzle sprays in an afterburner environment

This study examined the atomization characteristics of direct injection nozzles under high-temperature, large-Mach inflow conditions using a high-speed camera. The effect of inflow conditions on fuel breakup length, fuel concentration field, and particle size spatial distribution was quantitatively analyzed by using image processing techniques. Experimental results indicate the following: 1) When the liquid-to-gas momentum ratio and inflow Mach number (Ma) are equal, the breakup length, fuel field boundary, and droplet distribution in the jet core region remain consistent for the same nozzle under room-temperature air and high-temperature gas conditions. 2) A breakup length model based on the breakup time of the liquid column is proposed. 3) The logarithmic fuel trajectory formula can effectively predict the physical phenomenon of the movement of fuel particles with the gaseous flow downstream of the injection point after their kinetic energy is depleted, with a prediction error of no >10 %. 4) The spatial distribution of particle sizes reveals that within the selected range of liquid-phase jet velocity, the distribution range of the Sauter mean diameter (SMD) of the jet core area in gas-flow environments with large Ma is similar. At the same axial position, a positive correlation exists between SMD and nozzle diameter. The results of this study have guiding importance for the design of integrated afterburner nozzles.

Substitution of the Axial Type 1 Cu Ligand Affords Binding of a Water Molecule in Axial Position Affecting Kinetics, Spectral, and Structural Properties of the Small Laccase Ssl1.

Multicopper oxidases use Cu ions as cofactors to oxidize various substrates. High reduction potential at Type 1 Cu is considered as crucial for effective catalysis. Previous studies have shown that replacing the axial methionine ligand of the Type 1 Cu with leucine or phenylalanine leads to an increased reduction potential, but not always to higher enzyme activity. Here we present a study on six variants of the small laccase Ssl1 from Streptomyces sviceus, where the axial methionine ligand was substituted, and the effect of the axial ligand on reduction potential, activity, spectral properties and structure was investigated. Absorption, electronic circular dichroism and EPR spectra revealed the presence of a stronger coordinating axial ligand like oxygen, which influences the electronic and catalytic properties more than the nature of the amino acid side chain. The crystal structures of the Ssl1 variants were solved, which show that none of the amino acid side chains coordinate to the Cu. Instead, a water molecule is found in the axial coordination site, which support the spectroscopic data. Our findings highlight the importance of combining structural and spectroscopic methods to investigate the effect of amino acid exchange on multicopper oxidases.