Zone Method Research Articles

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er3+, Tm3+ and Yb3+ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm3+1G4→3H6 transition, 531 and 547 nm (green) from the Er3+2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, and 640 and 662 nm (red) from the Er3+4F9/2 → 4I15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er2O3, 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3, and this crystal is suitable for use in highly efficient white light emission devices.

Insecticidal and repellent activities of Azadirachta indica A. (Juss) oil against fifth instar larvae and adults of Sahlbergella singularis (Hemiptera:Miridae)

Sahlbergella singularis is one of the insects that causes the most damage to cocoa trees in Togo. The management of this pest is mainly based on chemical control, with its negative consequences for human health and the environment. In order to find an alternative to the use of synthetic pesticides, the insecticidal and repellent activities of neem oil were tested in vitro on fifth instar larvae and adults of S. singularis. Larvae were collected from a cocoa plot. The fifth instar larvae were separated from the other stages. Some of the larvae were reared in the laboratory until adult emergence. The concentrations of neem oil used were 0.5, 1, 1.5, 2 and 2.5 µl.ml-1. Insecticidal tests were carried out by spraying the solutions directly onto the insects. The repellency test was carried out using the preferential zone method on filter paper. The results showed an increasing mortality rate with increasing concentrations of neem oil for both fifth instar larvae and adults. The calculated LC50’s for larvae and adults were 0.89 and 0.98 µl.ml-1 respectively. Neem oil had a weak repellent effect on both fifth instar larvae and adults, with average repellency rates of 23.60% and 28.8% respectively. These results show that neem oil can be an alternative to the use of synthetic pesticides in the control of S. singularis.

Scintillation Properties of Ba3RE(PO4)3 Single Crystals (RE = Y, La, Lu)

Eulytite-type Ba3RE(PO4)3 (RE = Y, La, and Lu) single crystals were synthesized by the floating zone method, and their scintillation properties were investigated. The powder X-ray diffraction measurement revealed that the single phase of Ba3RE(PO4)3 samples were successfully synthesized. The samples exhibited a luminescence peak due to self-trapped exciton at around 400 nm under vacuum ultraviolet and X-ray irradiation. The X-ray-induced scintillation decay time constants of the samples were several microseconds at room temperature. In the 241Am α-ray irradiated pulse height spectra, all the samples showed a clear full energy peak, and the absolute light yields of the Ba3Y(PO4)3, Ba3La(PO4)3, and Ba3Lu(PO4)3 single crystals were estimated to be 960, 1160, and 1220 ph/5.5 MeV-α, with a typical error of ±10%, respectively. The scintillation light yields of the Ba3RE(PO4)3 have been quantitatively clarified for the first time.

Finite-element simulation of in-plane tear propagation in the dissected aorta: Implications for the propagation mechanism.

Computer modeling and numerical simulation are essential for understanding the progression of aortic dissection. However, tear propagation has not been properly modeled and simulated. The in-plane dissection propagation between concentrically distributed elastic lamellae is modeled using the cohesive zone method with a bilinear traction-separation law. The parameters of cohesive elements are calibrated for the three modes of interfacial damage in the media, enabling quantitative predictions of in-plane tear propagation. An idealized cylindrical tube-shaped bilayer thick-wall model of the aorta is employed to elucidate the influence of geometrical parameters, loading conditions and residual stress on the tear propagation. While the model is capable of replicating that deeper, larger tears are associated with lower critical pressure, new findings include: (i) Larger axial stretch leads to lower critical pressure; (ii) Increased magnitude of residual stress is associated with higher critical pressure; (iii) Pressure difference between true and false lumen alters the critical pressure; (iv) The interfacial damage is mostly opening mode in the axial direction, but shear-dominated in the circumferential direction; (v) Damage due to the opening mode is associated with smaller fracture energy, which makes it easier to propagate than the shear and the mixed modes. (vi) The deformed shape of the tear, which is related to its geometrical features and loading conditions, modulates the critical pressure via two pathways: (a) deformed shapes are associated with specific modes of damage, which influences the critical pressure, and (b) deformed shapes modulate the critical pressure directly via geometrical constraints.

Determination of fracture toughness of 2.25Cr1Mo0.25V steel based on acoustic emission technique

The correct determination of fracture toughness is dependent on the accurate measurement of the point of crack initiation. In this research work, the AE technique is used to accurately detect the point of crack initiation and determine the initiation fracture toughness value JAE of 2.25Cr1Mo0.25V steel. Moreover, conventional standard procedures such as the J-R curve and stretch zone methods are also used to determine the fracture toughness JQ and JSZW values, respectively. Multiple AE parameters involving the entropy, peak amplitude, count, and energy are extracted from AE signals to identify the damage progression during fracture toughness tests. The results show several critical points associated with the point of plastic yielding, the onset of crack initiation, and the rapid crack growth and final fracture can be accurately identified by AE characteristics. Furthermore, the point of crack initiation recognized by AE is used to determine the JAE value. The fracture toughness JAE values of different specimens are also compared with the corresponding JQ and JSZW values. The JAE values are found to be about 20% lower than the JQ values but are significantly larger than the JSZW(2D) and JSZW(3D) values. It is believed that the fracture toughness parameter JAE determined by the AE technique can provide an important reference for evaluating the fracture toughness of engineering materials.

Quantum paramagnetism in a non-Kramers rare-earth oxide: Monoclinic Pr2Ti2O7

Little is so far known about the magnetism of the ${A}_{2}{B}_{2}{\mathrm{O}}_{7}$ monoclinic layered perovskites that replace the spin-ice supporting pyrochlore structure for ${r}_{A}/{r}_{B}>1.78$. We show that high quality monoclinic ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ single crystals with a three-dimensional network of non-Kramers ${\mathrm{Pr}}^{3+}$ ions that interact through edge-sharing superexchange interactions, form a singlet ground-state quantum paramagnet that does not undergo any magnetic phase transitions down to, at least, 1.8 K. The chemical phase stability, structure, and magnetic properties of the layered perovskite ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ were investigated using x-ray diffraction, transmission electron microscopy, and magnetization measurements. Synthesis of polycrystalline samples with the nominal compositions of ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2+x}{\mathrm{O}}_{7}$ ($\ensuremath{-}0.16\ensuremath{\le}x\ensuremath{\le}0.16$) showed that deviations from the ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ stoichiometry lead to secondary phases of related structures including the perovskite phase ${\mathrm{Pr}}_{2/3}{\mathrm{TiO}}_{3}$ and the orthorhombic phases ${\mathrm{Pr}}_{4}{\mathrm{Ti}}_{9}{\mathrm{O}}_{24}$ and ${\mathrm{Pr}}_{2}{\mathrm{TiO}}_{5}$. No indications of site disordering (stuffing and antistuffing) or vacancy defects were observed in the ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ majority phase. A procedure for growth of high-structural-quality stoichiometric single crystals of ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ by the traveling solvent floating zone method is reported. Thermomagnetic measurements of single-crystalline ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ reveal an isolated singlet ground state that we associate with the low-symmetry crystal electric-field environments that split the ($2J+1=9$)-fold degenerate spin-orbital multiplets of the four differently coordinated ${\mathrm{Pr}}^{3+}$ ions into 36 isolated singlets resulting in an anisotropic temperature-independent van Vleck susceptibility at low $T$. A small isotropic Curie term is associated with 0.96(2)% noninteracting ${\mathrm{Pr}}^{4+}$ impurities.

#5667 PULMONARY CONGESTION IN HEMODIALYSIS: PREVALENCE, DYNAMICS AND ASSOCIATED FACTORS

Abstract Background and Aims Lung ultrasound (LUS) helps detecting pulmonary congestion (PC) among haemodialysis (HD) patients. This study investigated the relation between PC, cardiac function parameters, volume status and ultrafiltration, as well as chronic inflammation in two consecutive HD sessions with different inter-dialytic intervals. Method Prospective observational study, where 18 HD patients underwent LUS to calculate the B Lines Score (BLS) using the 8 zone method, inferior vena cava (IVC) dimensions measurement, and echocardiography before and after their regular first (S1) and second (S2) HD sessions of the week. The cut-off for BLS was fixed as 0.54 line per zone. Total body volume using Bio-electrical Impedance Analysis (BIA) was measured before both HD sessions besides serum NT-pro BNP (N-Terminal Pro-Brain Natriuretic Peptide Type B) levels. Moreover, circulating markers of inflammation (soluble urokinase Plasminogen Activator Receptor [suPAR] and soluble Suppression of Tumorigenicity 2 [sST2]) were measured before each session. Results Interdialytic interval did not impact BLS, which was high before and after both sessions. There was no significant difference in BLS before and after S1, whereas the difference was significant in S2 (P: 0.03, ES: 0.54). BIA was correlated to PC only before S2 (R² = 0.374, P = 0.007). BLS and the systolic cardiac function represented by the ejection fraction were correlated only after S2. Nt-ProBNP levels and BLS were correlated before both sessions (R²: 0.421, P: 0.004; R² = 0.505, P = 0.001), respectively. Cardiac diastolic function was correlated with BLS before S1 (R² = 0.476, P = 0.002) and after S2 (R² = 0.193, P = 0.034). Mean levels (± SD, ng/ml) of suPAR (7.88 ± 3.07), (7.78 ± 3.02) remained significantly above the normal range (< 4 ng/ml), while sST2 levels reached 2-fold the upper normal value in some patients (27.4 ± 17.8). Conclusion PC is common in HD patients even after reaching their dry weight at the end of their two consecutive sessions. It is not only correlated to volume status and cardiac function. Chronic inflammation may be involved in PC pathophysiology. A better management strategy is thus needed to better reduce PC in HD patients.

Luminescence Properties of Epitaxial Cu2O Thin Films Electrodeposited on Metallic Substrates and Cu2O Single Crystals.

The luminescent properties of epitaxial Cu2O thin films were studied in 10-300 K temperature range and compared with the luminescent properties of Cu2O single crystals. Cu2O thin films were deposited epitaxially via the electrodeposition method on either Cu or Ag substrates at different processing parameters, which determined the epitaxial orientation relationships. Cu2O (100) and (111) single crystal samples were cut from a crystal rod grown using the floating zone method. Luminescence spectra of thin films contain the same emission bands as single crystals around 720, 810 and 910 nm, characterizing VO2+, VO+ and VCu defects, correspondingly. Additional emission bands, whose origin is under discussion, are observed around 650-680 nm, while the exciton features are negligibly small. The relative mutual contribution of the emission bands varies depending on the thin film sample. The existence of the domains of crystallites with different orientations determines the polarization of luminescence. The PL of both Cu2O thin films and single crystals is characterized by negative thermal quenching in the low-temperature region; the reason of this phenomenon is discussed.

Scintillation properties of Pr-doped CaWO4 single crystals synthesized by the floating zone method

Pr-doped CaWO4 single crystals with dopant concentrations of 0.05–1% were synthesized by the floating zone method, and the photoluminescence and scintillation properties were evaluated. Emissions due to the 4f–4f transitions of Pr3+ were observed in visible–near-infrared ranges under visible light and X-ray irradiation. The X-ray-induced scintillation decay times were typical values of the transitions of Pr3+ when monitored at 380–900 nm. The afterglow levels when 20 ms passed after X-ray irradiation were calculated to be 573–730 ppm and increased as the dopant concentrations increased. In the integration-type scintillation detector property, 0.05, 0.1, and 0.5% Pr-doped samples showed good linearity between X-ray exposure dose rate and scintillation signals from 0.05 to 5 Gy/h.

The Spatial Correlation and Anisotropy of β-(AlxGa1-x)2O3 Single Crystal.

The long-range crystallographic order and anisotropy in β-(AlxGa1-x)2O3 (x = 0.0, 0.06, 0.11, 0.17, 0.26) crystals, prepared by optical floating zone method with different Al composition, is systematically studied by spatial correlation model and using an angle-resolved polarized Raman spectroscopy. Alloying with aluminum is seen as causing Raman peaks to blue shift while their full widths at half maxima broadened. As x increased, the correlation length (CL) of the Raman modes decreased. By changing x, the CL is more strongly affected for low-frequency phonons than the modes in the high-frequency region. For each Raman mode, the CL is decreased by increasing temperature. The results of angle-resolved polarized Raman spectroscopy have revealed that the intensities of β-(AlxGa1-x)2O3 peaks are highly polarization dependent, with significant effects on the anisotropy with alloying. As the Al composition increased, the anisotropy of Raman tensor elements was enhanced for the two strongest phonon modes in the low-frequency range, while the anisotropy of the sharpest Raman phonon modes in the high-frequency region decreased. Our comprehensive study has provided meaningful results for comprehending the long-range orderliness and anisotropy in technologically important β-(AlxGa1-x)2O3 crystals.

Analysis of Phenomenon of Plasticity Loss of Steel Core Made by Selective Laser Melting Method in Zone of Pressure Mould Conformal Cooling Channel.

This paper presents the results of testing the mechanical properties of maraging steel 1.2709 that were obtained by the SLM method under uniaxial and triaxial states of stress. The triaxial state of stress was realised by making circumferential notches in the samples with different radii of rounding. The specimens were subjected to two types of heat treatment, which consisted of ageing at 490 °C and 540 °C for 8 h. The results of the tests that were conducted on the samples were considered as references and compared with the results of the strength tests that were conducted directly on the SLM-made core model. Differences were found between the results of these tests. Based on the experimental results, the relationship between the equivalent strain of the specimen in the bottom of notch εeq and triaxiality factor η was determined. Function εeq = f(η) was proposed as a criterion for the decrease in the plasticity of the material in the area of the pressure mould cooling channel. Using the FEM method, equivalent strain field εeq and triaxiality factor η were determined in the conformal channel cooled core model. Based on the proposed criterion of plasticity loss and the results of numerical calculations, it was shown that the values of equivalent strain εeq and triaxiality factor η in the core that was aged at 490 °C did not meet this criterion. On the other hand, the values of strain εeq and triaxiality factor η did not exceed the safety limit when ageing was carried out at 540 °C. The plasticity loss method presented in this paper assumes that the value of the triaxiality factor in the vicinity of the channel is influenced by the shape, cross-sectional dimensions and trajectory of the channel axis. Using the methodology proposed in this paper, it is possible to determine the value of allowable deformations in the cooling channel zone and to determine whether the heat treatment applied to the SLM steel does not cause an excessive reduction in the plastic properties.

Er-Doped Mg4Ta2O9 Single-Crystal Scintillators Emitting Near-Infrared Photons for High-Dose Field Monitoring

Mg4Ta2O9 single crystals doped with 0.01, 0.1, and 1% Er were grown using the floating zone method, and their photoluminescence and scintillation properties were studied. X-ray diffraction analysis confirmed that all samples had a hexagonal structure of Mg4Ta2O9. The samples showed that the emission peak at 1550 nm was due to 4f−4f transitions of Er3+ ions, with quantum yields of 32.9, 46.6, and 18.0% for 0.01, 0.1, and 1% doping concentrations, respectively. All samples showed scintillation with a broad emission band at 350 nm due to charge transfer from Ta5+ to O2− ions and emission peak at 1550 nm due to 4f−4f transition of Er3+ ions. The dose rate response functions showed that the detection limit for all samples was 0.06 Gy/h for scintillation detector applications.

Microstructure-based crack formation in tungsten exposed to cyclic transient heating

The performance of plasma facing material (PFM) in nuclear fusion reactor is dramatically influenced by the synergy between steady heat loading and transient events. The negative and positive thermal stresses induced by a temperature gradient can trigger crack damage and even complete failure. Deep understanding the cracking mechanism is of great significance to optimize structure design and to improve service capability of PFM. Herein we combine the extended finite element method (XFEM) with the cohesive zone method (CZM) in order to unravel the characteristics of inter-granular micro-cracking formation in polycrystalline tungsten (W) by taking account of topological microstructure and external loading condition. From the macro component to the mesoscopic structure, the temperature and stress distributions of W/Cu/CuCrZr monoblock under steady state coupled with cyclic transient event is first numerically investigated and compared with the results from experimental measurement. Then, by using the displacement rate estimated from the heat-energy-variation-induced accumulated plastic strain on the surface of monoblock as a bridge, the inter-granular crack propagation behaviors in the equiaxial grain (EG), gradient grain (GG) and heterogeneous grain (HG) structures of the cross-sectional component and in different surface grain sizes of component are predicted, respectively. It is found that higher heat loading with longer duration time leads to the increment of cumulative plastic strain level so that crack extension rate is accelerated. The GG structure exhibits a remarkable improvement on crack development since the change of inter-granular crack path at the triple point is influenced by the inclined boundary with respect to the loading direction. These results provide valuable insights into the correlation of grain morphology and brittle crack growth, especially focusing on further improvement of PFM.

Extension–bending coupling phenomena and residual hygrothermal stresses effects on the Energy Release Rate and mode mixity of generally layered laminates

This article presents a novel analytical solution to the delamination problem of interface deformable generally layered (asymmetric and unbalanced) composite laminates. The governing equation describing the interface forces and moments is obtained for the reduced form of the first-order shear deformation theory of plates (FSDT) under plane strain assumptions and accounts for the extension–bending coupling phenomena and residual hygrothermal stresses, both of which have been neglected in the past. The interface forces and moments are included in a novel generalization of the J-integral which is used for the estimation of the Energy Release Rate (ERR). The analytical results of the ERR and the mode mixity exhibit a great agreement with the results of Finite Element (FE) models developed using the Cohesive Zone Method (CZM) and the Virtual Crack Closure Technique (VCCT) for a Double Cantilever Beam (DCB) test of a generally layered fibre metal laminate.

Effects of Temperature Difference and Heat Loss on Oscillation Characteristics of Thermo-Solutocapillary Convection in Toluene/N-Hexane Mixed Solution

During the crystal growth process using the floating zone method, the uneven distribution of impurities on the surface of the melt can trigger a coupling mechanism between solutocapillary convection driven by the concentration gradient and thermocapillary convection driven by the temperature gradient, resulting in the Marangoni convection at the free surface. When the temperature and concentration gradients reach certain values, the crystal surface and interior exhibit time-dependent, periodic oscillations, leading to the formation of micrometer-scale impurity stripes within the crystal. This study focuses on the effects of temperature difference and heat loss in a liquid bridge under microgravity on the structure and interface oscillation characteristics of thermo-solutocapillary convection, aiming to explore the coupling phenomenon of this oscillation and provide valuable information for crystal growth processes. An improved level set method is employed to accurately track every displacement of the interface, while the surface tension is addressed using the CSF model. In addition, the area compensation method is used to maintain simulation quality balance. A comprehensive analysis is performed on the oscillation characteristics of thermo-solutocapillary convection at the free surface, ranging from the temperature, concentration, deformation, and velocity distributions at the upper and middle heights of the liquid bridge. The results indicate that under small temperature differences (ΔT = 1 − 3), the transverse velocity at the upper end exhibits a single-periodic oscillation, while the longitudinal velocity presents a double-periodic oscillation. At the intermediate height, both the transverse and longitudinal velocities display a single-periodic oscillation. Under a large temperature difference (ΔT = 6), the oscillation of velocities at the upper end and the middle position become multi-periodic. In addition, heat loss has certain regular effects on the oscillatory flow of thermo-solutocapillary convection within a certain range. The velocity, amplitude, and frequency of the upper end and the middle position at the free surface decrease gradually, and the oscillation intensity also weakens with the increase in heat loss (Bi = 0.2 − 0.6). These new discoveries can provide a valuable reference for optimizing the crystal growth process, thereby enhancing the quality and performance of crystal materials.

Growth and phase transition of Sr3Zr2O7 single crystals

The melting behavior of Ruddlesden-Popper type hybrid improper ferroelectric Sr3Zr2O7 phase in the ZrO2–SrO pseudo-binary system was investigated, and its single crystals were successfully grown. A series of the slow-cooling floating zone experiments revealed that Sr3Zr2O7 melts incongruently into SrZrO3 phase and a liquid and that the compositional range where Sr3Zr2O7 and a liquid coexist is located around 70 mol% SrO composition. Based on the results, we attempted to grow Sr3Zr2O7 single crystals by the traveling solvent floating zone method using SrO-excess solvent and feed. Consequently, many small single crystals of Sr3Zr2O7 phase with several millimeters in size were discovered in the as-grown boules covered with SrO phase. The phase transition behavior of the grown crystals was investigated by differential thermal analysis with polarizing optical microscopy as well as by optical second harmonic generation measurements. We directly observed a reconstruction of orthorhombic twin domains in Sr3Zr2O7 single crystals accompanied by the first-order ferroelectric transition at about 410 °C.

Adaptive fast nonsingular terminal sliding mode tracking control for quadrotor with disturbances compensation and actuator saturation

This paper designs the double closed-loop control system combining nonlinear disturbances observers (NDOB) and an adaptive fast nonsingular terminal sliding mode (AFNTSM) for the tracking control problem of quadrotor under external disturbances, actuator saturation and unmodeled dynamics. The NDOB-AFNTSM method avoids the singularity problem. To compensate for disturbances, an adaptive strategy estimates the unknown bound of NDOB errors and the unknown bound of disturbances. Besides, new fast reaching law shortens convergence times. The dead zone method is chosen to avoid over-estimation and system divergence. Considering actuator saturation, this paper uses an anti-saturation auxiliary compensator to compensate for unknown saturation errors. System stability is confirmed by the Lyapunov direct method. The simulation results reveal that the proposed method improves convergence speed and accuracy, which is more robuster than similar methods. Finally, two comparative studies for performance indexes in simulation demonstrate the preferable performance of the proposed method.

An Open-Source ABAQUS Plug-In for Delamination Analysis of 3D Printed Composites.

This article presents the development and implementation of the Delamination Plug-in, an open-source tool for modeling delamination tests in the ABAQUS software. Specifically designed for stochastic modeling of 3D printed composites, the plug-in combines the benefits of the graphical user interface (GUI) and the programming of commercial finite element (FE) software. The Delamination Plug-in offers an effortless alternative to the time-consuming analytical modeling and GUI work involved in delamination tests and includes algorithms for several tests, such as the double cantilever beam, end-loaded split, end-notched flexure, and modified end-loaded split tests, solved using the virtual crack closure technique and the cohesive zone method. It enables the user to develop simulations for both simple symmetric laminates and generally layered laminates with additional thermal stresses. The applicability of the tool is demonstrated through its use in two distinct delamination problems, one for conventional and one for 3D printed composite laminates, and its results are compared to analytical models and experimental data from the open literature. The results demonstrate that the Delamination Plug-in is efficient and applicable for such materials. This establishes the tool as an important means of automating delamination analysis and for the development and testing of 3D printed composites, making it a valuable tool for both researchers and industry professionals.

Investigation of radio-photoluminescence properties in Sm-doped Al4SiO8 single crystals

We report radio-photoluminescence (RPL) properties of Sm-doped Al4SiO8 single crystals as a new RPL material. The Sm-doped Al4SiO8 single crystals were synthesized by the floating zone method. In PL emission spectra, the emission peaks due to the 4f-4f transitions of Sm3+ ions and 2EJ–4A2 transitions of Cr3+ ions were observed before X-ray irradiation, and the ones due to the 4f-4f transitions of Sm2+ appeared as well as Sm3+ after X-ray irradiation. The RPL dose response functions showed linear response from 1 mGy to 10 Gy for the 2.0% Sm-doped sample and from 10 mGy to 10 Gy for the others. Sm2+ ions of the new emission center completely disappeared by heat treatment at 500 °C for 10 min.

Synthesis, Characterization, and Antibacterial Activity of New Isatin Derivatives.

1H-indol-2,3-dione (isatin) class of biologically active compounds have analgesic, anti-microbial, anti-inflammatory, anti-tubercular, anti-proliferative properties, and is also useful for the treatment of SARS-CoV. Schiff bases containing isatin moiety are known to have broad spectrum of biological activities like anti-viral, anti-tubercular, anti-fungal, and anti-bacterial. In this work, several Schiff base derivatives have been synthesized using two methods (synthetic and microwave) by reacting isatin with o-phenylenediamine. The synthesized compounds were structurally characterized and their in-vivo antimicrobial activity was tested against Gram-negative and Gram-positive bacteria using the inhibition zone method. Several newly synthesized isatin derivatives were found effective as antimicrobial agents and showed good potency (compounds 3c, 3d, 6a, 6b, 6d). Compound 3c displayed higher antimicrobial activity than standard drug (Amoxicillin) against Staphylococcus aureus at higher concentration (16 μg/mL) and against Escherichia coli at lower concentration (1 μg/mL).