Depolarization Technique Research Articles

Temperature-dependent Rotational Dynamics of a 3-(benzo[d]Thiazol-2-yl)-7-diethylamino)-2H-chromen-2-one non-polar Probe in n-pentanol, n-nonanol, and n-decanol Solvents.

Rotational dynamics of non-polar probe 3-(benzo[d]thiazol-2-yl)-7-(diethylamino)-2H-chromen-2-one (3BT7D2H-one) and in n-pentanol, n-nonanol, and n-decanol alcohol solvents is studied using steady-state fluorescence depolarization and time-correlated single photon counting technique with varying temperature. Experimental observations indicate that 3BT7D2H-one rotates slowly in n-decanol solvent compared to other chosen solvents. Rotational motion is analyzed using the Stoke 's-Einstein-Debye (SED) model. 3BT7D2H-one solute rotational dynamics is satisfactorily described by the SED slip boundary limit in all three solvents.

Temperature-Dependent Rotational Dynamics of a Polar Probe in Non-Polar Aprotic Solvents: Interplay of Solvent Viscosity and Size Effect.

Rotational dynamics of 3-(benzo[d]thiazol-2-yl)-7-(diethylamino)-2H-chromen-2-one (3BT7D2H-one) probe in non-polar aprotic 1,4 dioxane, toluene and cyclohexane solvents of different and comparable viscosity are studied with varying temperature using steady-state and fluorescence depolarization technique. The experimental reorientation time is compared with the hydrodynamic Stoke's-Einstein-Debye(SED). The experimentally measured rotational reorientation times are higher in 1,4 dioxane attributed to its solvent viscosity. In cyclohexane, the solute rotational dynamics behavior shows a transition from sub-slip to SED slip boundary conditions with varying temperatures. Solvent viscosity, size, and subtle changes in the molecular shape of solute play an important role in the rotational dynamics of polar probes in non-polar aprotic solvents.

Influence of Temperature on Rotational Dynamics of 3B7D2HC-2-one Molecule in Non-polar, Polar, and Polar Aprotic Solvents.

Rotational dynamics of 3-(3H-2l4-benzo[c]isothiazol-2-yl)-7-(diethylamino)-2H-chromen-2-one (3B7D2HC-2-one) is studied using steady-state fluorescence depolarization and time-resolved fluorescence techniques in non-polar, polar and polar aprotic solvents by varying temperatures. Computational calculations are performed using Gaussian 09 software. Over the general solvatochromic method, an advanced thermochromic shift method is used to estimate dipole moments. Experiment rotational diffusion of 3B7D2HC-2-one in methanol indicates slow rotation over the other two solvents. Further, experiment rotational diffusion is analyzed using hydrodynamic and Quasi-hydrodynamic theories. The observed reorientation time follows the trend as predicted by quasi-hydrodynamic models.

Rotational dynamics study of structurally similar (medium sized) coumarin dyes in aqueous mixtures of DMSO and DMA

The rotational diffusion dynamics of four medium sized, structurally similar, polar Coumarin dyes namely, Coumarin-478 (C478), Coumarin-480 (C480), Coumarin-519 (C519), and Coumarin-523 (C523) has been studied at room temperature in aqueous DMSO and aqueous DMA by using steady state and time resolved fluorescence depolarization techniques. All the probes exhibited faster rotation in organic solvent rich zone than in water rich zone that resulted in a downward bent “hook profile” of rotational reorientation time as a function of viscosity. A faster rotational diffusion is observed for C523 in contrast to the other three solutes in both the aqueous solvent mixtures. The difference between τr values at iso-viscous points is smaller in case of aqueous DMA than in aqueous DMSO which reveals the importance of dielectric friction. Since both solutes and solvents are polar in nature, the Nee-Zwanzig (NZ) and van der Zwan and Hynes (ZH) dielectric friction theories have been used along with Stokes-Einstein-Debye (SED) hydrodynamic theory to assess the experimental results and understand the microfriction experienced by the solute. An important aspect of this work is to establish a relation between viscosity and hydrogen bond strengths at varying compositions of solvent mixtures as well as hydrogen bond strength between solute and solvents with the help of Gaussian 09 software. The H-bond strength thus calculated is found to be higher at a composition where the viscosity is the maximum. It provides an additional support to the experimental results.

Insight into the negative magnetization and anomalous exchange-bias in DyFe5Al7 through neutron depolarization and neutron diffraction studies

We have provided the mesoscopic and microscopic understandings of polarity reversal of the magnetization or negative magnetization (NM) below T COMP = 93 K in an exotic magnetic material containing three magnetic sublattices, viz., DyFe5Al7 crystallizing in ThMn12 structure, using neutron depolarization and neutron diffraction techniques. A full recovery of the neutron beam polarization at the T COMP in a neutron depolarization experiment reveals a total compensation of magnetization inside the magnetic domains in the sample. The temperature-dependent neutron diffraction study under zero magnetic field has provided temperature dependencies of antiparallelly coupled Dy (M Dy(2a)) and Fe (M Fe(8f) and M Fe(8j)) sublattice magnetic moments along [100] direction. The dominance of |M Dy(2a)| over total Fe moment, , below T COMP leads to the NM in the compound. The magnetization versus magnetic field curves below the T COMP indicate the presence of field-induced spin reorientation in the compound. The magnetic field required for spin reorientation (H SR) is maximum at the lowest temperature and it decreases to zero as the temperature is increased to T COMP. Interestingly, the compound shows a finite exchange-bias (H EB) below the T COMP only, as evident from the field-cooled hysteresis loops, while at T > T COMP, H EB is almost zero. The cooling-field (H COOL) dependent study of H EB shows a slope change at H COOL ∼ H SR indicating a correlation of exchange-bias with spin-reorientation in the compound. This study, apart from revealing microscopic understanding of magnetic behavior of an exotic three magnetic sublattice system, provides a correlation among exchange-bias, magnetic compensation, and spin-reorientation phenomena.

A toy Monte Carlo simulation for the transverse polarization of high-energy electron beams

Transversely-polarized beams are heuristic to the mechanism of CP violation and explore new physics. Besides, the transverse-polarization monitoring is a key point for the beam energy calibration by the resonant depolarization technique. In the article, the transverse polarization measurement of a high-energy electron beam is performed by Monte Carlo simulation on the circular electron-positron collider. The principle based on the Compton back-scattering combining a deflection magnetic field is discussed in detail. The physical presentation of the analyzing power is used to fit the asymmetric distribution of scattered electrons, which is proportional to the transverse polarization. Furthermore, we develop an efficient algorithm that obtain this analyzing power function and use different strategies to measure the transverse polarization for cross-check. Our measurement method is theoretically suitable with a statistical error 1% within few tens of seconds in Z pole on the circular electron-positron collider. The total systematic uncertainties are controlled to be about 0.6% related to the magnetic field, the drift distance, the laser polarization, the beam energy spread and the related uncertainties of a position sensitive detector.

Resonant depolarization technique at VEPP-4M in Novosibirsk

Resonant depolarization technique at VEPP-4M in Novosibirsk

Rotational Diffusion Dynamics of Fluorescein Derivatives in Binary Mixtures of Solvents: An Experimental and Computational Study

With a view to understand the nature of solute solvent interactions, rotational reorientation times (τr) of three medium sized dipolar laser dyes viz., dichlorofluorescein (DCF), sodium fluorescein (SF) and kiton red (KR) in two binary mixtures namely, aqueous-DMSO and aqueous-1-propanol have been determined employing steady state fluorescence depolarization technique. The experimental results are analyzed in the light of SED hydrodynamic and of Gierer and Wirtz (GW) and Dote, Kivelson and Schwartz (DKS) quasihydrodynamic models. Rotational reorientation times (τr) are plotted as function of viscosity (η) on the binary solvent mixtures. An interesting hook shaped profile is observed in both the binary mixtures of solvents that is likely to shed light on solute-solvent interactions. Further, theoretical study has been carried out using Gaussian 09 software. The optimized geometry, HOMO-LUMO, energy gap and molecular electron potential map (MEPM) were extracted from DFT/B3LYP 6-311g(d) basis set. The hyper conjugation or intra-molecular delocalization was estimated from NBO analysis. Strong interactions were observed between nO33→σ*C31, πN38→σ*C12 and πO32→π*(C31- O33) with E(2) energies of 203.58, 121.89 and 39.92 kJ/mol for SF, KR and DCF.

Shear-Induced and Nanofiber-Nucleated Crystallization of Novel Aliphatic-Aromatic Copolyesters Delineated for In Situ Generation of Biodegradable Nanocomposites.

The shear-induced and cellulose-nanofiber nucleated crystallization of two novel aliphatic–aromatic copolyesters is outlined due to its significance for the in situ generation of biodegradable nanocomposites, which require the crystallization of nanofibrous sheared inclusions at higher temperatures. The shear-induced non-isothermal crystallization of two copolyesters, namely, poly(butylene adipate-co-succinate-co-glutarate-co-terephthalate) (PBASGT) and poly(butylene adipate-co-terephthalate) (PBAT), was studied following a light depolarization technique. To have a deep insight into the process, the effects of the shear rate, shear time, shearing temperature and cooling rate on the initiation, kinetics, growth and termination of crystals were investigated. Films of 60 μm were subjected to various shear rates (100–800 s−1) for different time intervals during cooling. The effects of the shearing time and increasing the shear rate were found to be an elevated crystallization temperature, increased nucleation density, reduced growth size of lamella stacks and decreased crystallization time. Due to the boosted nucleation sites, the nuclei impinged with each other quickly and growth was hindered. The effect of the cooling rate was more significant at lower shear rates. Shearing the samples at lower temperatures, but still above the nominal melting point, further shifted the non-isothermal crystallization to higher temperatures. As a result of cellulose nanofibers’ presence, the crystallization of PBAT, analyzed by DSC, was shifted to higher temperatures.

Solvation, rotational dynamics, photophysical properties study of aromatic asymmetric di-ketones: An experimental and theoretical approach

In this article we have investigated the solvation, rotational dynamics and photo physics of diketone derivatives DK-2 and DK-3 in alcohols and alkanes at room temperature through both a time-resolved fluorescence depolarization technique and steady state. Viscosity of dissolvable varies linearly with respect to rotational times of the molecule. Outcomes are investigated by utilizing the theory of hydrodynamic (SED) Stokes- Einstein-Debye to evaluate the friction with stick and slip limiting conditions. In addition, using the solvatochromic shift and quantum chemical technique aromatic di-ketone derivatives, 1-(4′-dodecyl-[1,1′-biphenyl]-4-yl)-3-(4-ethoxyphenyl) propane-1,3-dione (DK-2) and 1-(4′-dodecyl-[1,1′-biphenyl]-4-yl)-3-(4-(nonyloxy)phenyl)propane-1,3-dione (DK-3) estimated properties of fluorescence. The excitation and emission spectra of DK-2 and DK-3 have been observed in several solvents. The dipole moments calculated using DFT theory and solvatochromic correlations. Estimated (μg) value by DFT theory is relatively greater than the solvatochromic shift techniques. The dipole moments of excited state (μe) are found to be more prominent than dipole moment of ground states (μg) which approves π → π* transition. The variance of dipole moments (Δμ) was determined from microscopic solvent polarity parameter (ETN) and solvatochromic shift technique and outcomes are compared.

Investigation of magnetic ordering and origin of exchange-bias effect in doped manganite, Sm0.4Ca0.6MnO3

We have carried out detailed investigations of magnetic ordering and the origin of exchange-bias phenomenology in polycrystalline 154Sm0.4Ca0.6MnO3 perovskite compound by employing dc and ac magnetizations, neutron depolarization, and neutron diffraction techniques. The neutron diffraction study reveals a broad charge ordering transition in the temperature range of 275–150 K, manifested by gradually varying structural distortions. DC magnetization and neutron diffraction studies infer a magnetic ordering around 110 K. Below ∼40 K, this compound exhibits a large enhancement of the magnetization and an exchange-bias effect (∼18 kOe at 5 K). The exchange-bias effect shows a characteristic temperature and cooling field dependence and a training effect. The compound undergoes a CE-type (checker-board type) antiferromagnetic (AFM) ordering of Mn3+/Mn4+ spins below 110 K. The large magnetization below ∼40 K arises from the ferrimagnetic (FIM) ordering of a minority (∼5 vol. %) non-perovskite phase of Mn3O4. The appearance of exchange bias is ascribed due to the presence of an interface, formed between the FIM (Mn3O4) phase and the main AFM perovskite phase. Our study has implications in giving new directions in the search of large exchange-bias effects in mixed FIM/AFM bulk systems.

Probing low temperature non-equilibrium magnetic state in Co2.75Fe0.25O4+δ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments

The low temperature lattice structure and magnetic properties of Co2.75Fe0.25O4 ferrite have been investigated using experimental results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac susceptibility, neutron diffraction and neutron depolarization techniques. The samples have been prepared by chemical co-precipitation of the Fe and Co nitrates solution in high alkaline medium and subsequent thermal annealing of the precipitates in the temperature range of 473–1173 K. Rietveld refinement of the SXRD patterns at room temperature indicated two-phased cubic spinel structure for the samples annealed at temperatures 473–873 K. The samples annealed at temperatures 973 K and 1173 K (CF90) have shown single phased lattice structure. Refinement of the neutron diffraction patterns in the measurement temperature range 5–300 K confirmed the antiferromagnetic (AFM) Co3O4 and ferrimagnetic (FIM) Co2.75Fe0.25O4 phases for the sample annealed at 873 K and single FIM phase of Co2.75Fe0.25O4 for the CF90 sample. Magnetic measurements have shown a non-equilibrium magnetic structure, consisting of high temperature FIM phase and low temperature AFM phase. The magnetic phases are sensitive to magnetic fields, where high temperature phase is suppressed at higher magnetic fields by enhancing the low temperature AFM phase, irrespective of annealing temperature of the samples.

The GEM-based detector for tracking the Compton-scattered photons in the Laser Polarimeter facility at VEPP4-M collider

The Laser Polarimeter is being developed at VEPP-4M collider for beam energy calibration by Resonant Depolarization technique. The essential part of this facility is a photon-tracking detector measuring coordinates of backscattered gammas. The detector is based on triple-GEM cascade with pad readout. Its design and the first results of the measurements with radioactive source are described in the paper.

The triple-GEM detector for the Laser Polarimeter facility at VEPP4-M collider

The Laser Polarimeter is being developed at VEPP-4M collider for beam energy calibration by Resonant Depolarization technique. The essential part of this facility is a photon-tracking detector measuring coordinates of backscattered gammas.

Shear-induced non-isothermal crystallization of poly(butylene adipate-co-terephthalate)

The influence of shear on non-isothermal crystallization of commercial poly(butylene adipate-co-terephthalate) (PBAT) was investigated. PBAT melt was sheared at 130 and 150 °C at rates of 10–100/s, and then cooled. The crystallization was followed by a light depolarization technique, whereas the crystallized specimens were analyzed by DSC, 2D-SAXS, 2D-WAXS, PLM and SALS. Shear flow shifted crystallization to higher temperature, and the effect was augmented by lower temperature of shearing as well as by higher shear rate and strain. Crystallization peak rate temperature of PBAT, sheared at 130 °C for 5 min at 100/s, increased by up to 12 °C. However, no evidence of crystal orientation due to shear was found, indicating that the shear induced the point-like nucleation. Only a small increase of melting peak temperatures, by up to 2–5 °C, was observed for the specimens sheared at the highest rates (≥50/s).

Lipidated α/Sulfono-α-AA heterogeneous peptides as antimicrobial agents for MRSA

Though antibiotics have been used for decades to treat bacterial infections, there is a great need for new treatment methods. Bacteria are becoming resistant to conventional antibiotics, as is the case with Methicillin resistant Staphylococcus aureus (MRSA). Herein we report the design of a series of lipidated α/Sulfono-α-AA heterogeneous peptides as mimics for Host Defense Peptides (HDPs). Utilizing fluorescence microscopy and depolarization techniques, our compounds demonstrate the ability to kill Gram-positive bacteria through cell membrane disruption. This mechanism of action makes it difficult for bacteria to develop resistance. Further time kill studies and hemolytic assays have also proven these compounds to be efficient in their ability to eradicate bacteria cells while remaining non-toxic to human red blood cells. This new class of peptidomimetics shows promise for the future antibiotic treatment of MRSA.

Understanding of the low temperature anomalous magnetic and lattice properties in Co1.25Fe1.75O4 ferrite using dc magnetization and neutron diffraction experiments

Abstract The present work has demonstrated the experimental results of dc magnetization and neutron diffraction measurements for Co1.25Fe1.75O4 ferrite. The material has been prepared by chemical route, and annealed at different temperatures to study its effect on the stabilization of Co and Fe ions in tetrahedral and octahedral sites. Magnetic measurements have been carried out to study the temperature variation of magnetization, coercivity and effective anisotropy constant of the samples. Neutron diffraction pattern has been used to calculate the lattice parameter, site distribution of Co and Fe ions, and site magnetic moments as the function of measurement temperature and annealing temperature of the samples. In this work, specific attempt has been made to understand the lattice and magnetic correlation by employing the neutron diffraction and neutron depolarization techniques. The experimental results suggest the possibility of an inverse relation between anomalous lattice expansion and decrement of high field magnetization at lower temperatures, typically below 150 K.

Microscopic and mesoscopic understanding of magnetization compensation phenomenon in ferrimagnetic Li0.5FeCr1.5O4 spinel

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices.

Neutron as a probe to study magnetization reversal in a spinel compound, CoCr1.9Fe0.1O4

Neutron depolarization and neutron diffraction techniques have been employed to investigate the origin of magnetization reversal in CoCr1.9Fe0.1O4 spinel compound. The spinel compound crystallizes in a face centered cubic (space group: Fd-3m) structure where Co2+ and (Cr/Fe)3+ ions occupy the tetrahedral 8a and octahedral 16d sites, respectively. The temperature dependent magnetization curves for magnetic fields ≤ 1 kOe show a magnetization reversal below the compensation temperature (Tcomp ∼ 40 K). The neutron depolarization measurements infer that the average magnetization of each domain becomes negligibly small at the TComp. Temperature dependent neutron diffraction study, a microscopic tool to understand sublattice magnetization, infers an antiparallel coupling between the tetrahedral (Co) and octahedral (Cr/Fe) site moments with ordered magnetic moments of −3.1(1) and 1.0(1) μB, respectively, at 30 K. Our neutron diffraction study also reveals that the unequal growth of the antiferromagnetically coupled tetrahedral and octahedral site moments across the TComp plays an important role in realizing the magnetization reversal in this spinel compound.

Egg activation-triggered shape change in the Dictyota dichotoma (Phaeophyceae) zygote is actin-myosin and secretion dependent.

Cellular morphogenesis in land plants and brown algae is typically a slow process involving growth established by an interplay of turgor pressure and cell wall rigidity. However, a recent study showed that zygotes of the brown alga Dictyota dichotoma undergo a rapid shape change from a sphere to an elongated spheroid in about 90 s, establishing the first body axis. Using a combination of pharmacology, staining techniques, membrane depolarization and microscopy techniques (brightfield, transmission electron microscopy and confocal laser scanning microscopy), egg activation and the shape change of the egg cell of D. dichotoma was studied. It was established that elongation of the zygote does not involve growth, i.e. a positive change in size. The elongation is dependent on F-actin and myosin but independent of microtubules. Secretion was also found to be necessary for elongation after addition of brefeldin A. Moreover, a temporal correlation between extracellular matrix secretion and elongation was observed. Ionomycin and high potassium seawater are capable of triggering the onset of elongation, suggesting a role for membrane depolarization and calcium influx in the signalling mechanism. The elongated cells are shorter in the presence of ionomycin, suggesting a role for calcium in elongation. A model is proposed in which the fast elongation of the fertilized egg in Dictyota is accomplished by a force generated by F-actin and myosin, regulated by cytoplasmic calcium concentrations and by secretion during elongation lowering the antagonistic force. The finding of early extracellular matrix secretion, membrane depolarization and ionophore-triggered egg activation suggest significant differences in the mechanism of egg activation signalling between D. dichotoma and the oogamous brown algal model system Fucus .