Back Conversion Research Articles

Identification and expression profiling of flax (Linum usitatissimum L.) polyamine oxidase genes in response to stimuli

AbstractPolyamine oxidases (PAOs) are known to be involved in either the terminal catabolism or the back conversion of polyamines, which affect a range of physiological processes, including growth, development, and stress responses. In this study, based on genome-wide analysis, we identified five putative PAO genes (LuPAO1toLuPAO5) in flax (Linum usitatissimumL.) that contain the amino-oxidase domain and FAD-binding-domain. The expression analysis using quantitative real-time PCR revealed spatial variations in the expression ofLuPAOsin different organs. In addition, the expression level ofLuPAOsin the flax cell suspension culture was increased by treatment with methyl-jasmonate (MeJA) or pectin, but not with salicylic acid or chitosan. This indicates that LuPAOs might be involved in the MeJA-mediated biological activities. Taken together, our genome-wide analysis of PAO genes and expression profiling of these genes provide the first step toward the functional dissection of LuPAOs.

Back Conversion from Product to Parent: Methyl Triclosan to Triclosan in Plants

Numerous man-made chemicals pass through wastewater treatment plants (WWTPs), where biological and chemical treatments often result in the formation of a wide range of transformation products via reactions such as conjugation and alkylation. Such transformation products may come into contact with plants when treated wastewater and biosolids are used in agricultural production or when plants are used for mitigation purposes (e.g., treatment wetlands). Using the high-volume antimicrobial triclosan as a model compound, we showed that its primary transformation product in the WWTPs, methyl triclosan, was readily converted back to the parent in plants. Upon exposure to environmentally relevant concentrations of methyl triclosan, triclosan was detected in Arabidopsis thaliana cells within 12 h, and the level of triclosan increased over time. The molar fraction of triclosan to methyl triclosan in the cells was estimated to be 0.17 at 144 h. When grown in a nutrient solution containing methyl triclosan, lettuce a...

Selective Etching of N‐Doped Graphene Meshes as Metal‐Free Catalyst with Tunable Kinetics, High Activity and the Origin of New Catalytic Behaviors

AbstractNew N‐doped reduced graphene oxide (N‐RGO) meshes are facile fabricated by selective etching of 3–5 nm nanopores, with controllable doping of N dopants at an ultrahigh N/C ratio up to 15.6 at%, from pristine graphene oxide sheets in one‐pot hydrothermal reaction. The N‐RGO meshes are illustrated to be an efficient metal‐free catalyst toward hydrogenation of 4‐nitrophenol, with new catalytic behaviors emerging in following three aspects: (i) tunable kinetics following pseudofirst order from commonly observed pseudozero order; (ii) strikingly improved activity with 26‐fold increased rate constant (1.0 s−1 g−1 L); (iii) no induction time required prior to reaction due to depressed back conversion, and dramatically decreased apparent activation energy (Ea) (17 kJ mol−1). The origin of these new catalytic properties can be assigned to the synergetic effects between graphitic N doping and structural defects arising from nanopores. Deeper understanding unveils that the concentration of graphitic N is inverse proportion to Ea, while the pyrrolic N has no impact on this reaction, and oxygenate groups hampers it. The porous nature allows the N‐RGO meshes to conduct catalyze reactions in continuous flow fashion.

Broadband, efficient, and robust quasi-parametric chirped-pulse amplification.

Quasi-parametric chirped pulse amplification (QPCPA) is a new scheme that enables the amplification of chirped signal pulses without back conversion by depleting the idler pulses. In this paper, we present a numerical study on the bandwidth, efficiency, and robustness of QPCPA. Self-locked phase among the interacting waves is found to be the underlying mechanism for the suppression of back conversion, which allows signal efficiency approaching to the quantum limit even under the phase-mismatch condition, and thus greatly increases the phase-mismatch tolerance of QPCPA. We demonstrate that QPCPA can break through the trade-off between the efficiency and bandwidth encountered in conventional optical parametric amplification, hence supporting highly efficient amplification of few-cycle pulses.

Modeling and design of singly-resonant optical parametric oscillator with an intracavity idler absorber for enhanced conversion efficiency for the signal

We present modeling and design of continuous-wave (cw) singly-resonant optical parametric oscillator (SR-OPO) with an intracavity idler absorber to enhance the conversion efficiency for the signal by suppressing the back conversion of the signal and idler to the pump. Following plane wave analysis, we arrive at the optimum parameters of the OPO, with the intracavity idler absorber, to achieve high conversion efficiency for the signal. For a given pump intensity, we have analyzed the effect of position and number of absorbers required for optimum performance of the device. The model is also extended to the case in which the signal is absorbed, yielding higher conversion efficiency for the idler (in mid-IR region). The magnitude of absorption and the effect of intercrystal phase shift on the conversion efficiency are also discussed. We also present an analytical solution for twin-crystal SR-OPO with an absorber in between, taking into account the variation of signal amplitude inside the cavity, we reaffirm that the frequently used constant signal-wave approximation is valid if the reflectivity of the output coupler is high for the signal.

Identification of the actual coding region for polyamine oxidase 6 from rice (OsPAO6) and its partial characterization

ABSTRACTPolyamines (PA) in plant play roles in growth and development and in responses to environmental stresses. The family of polyamine oxidases (PAO) contributes to a balanced homeostasis of PAs catalyzing two different reactions, terminal catabolic (TC) and back-conversion (BC) pathway, in PA catabolism. From the seven PAOs encoded by the rice genome (OsPAO1 – OsPAO7) OsPAO6 could so far not be characterized due to failure in obtaining the coding cDNA based on accessions in the genomic databases. We report cloning and characterization of the correct OsPAO6 cDNA with a length of 1,742 bp. The 1,491 bp long open reading frame codes for a 497-amino acid protein from nine exons. The protein which has 92% identity to OsPAO7 localizes to plasma membrane.

Optical and dielectric properties of transparent ZrO2–TiO2–Li2B4O7 glass system

Abstract A new series of transparent zirconium titanium lithium diborate glasses of the nominal composition 85 Li 2 B 4 O 7 –(15–x) TiO 2 – x ZrO 2 (x = 0, 5, 10 and 15 mol %) was prepared using melt quenching method. The investigated glasses are characterized in an attempt to determine the effect of different zirconium ion concentrations on their structural, optical and dielectric properties. X-ray diffraction (XRD) patterns confirmed the amorphous nature of the present glass system. The main features concerning the local structure of the present glass system were determined by Fourier transform infrared (FTIR) spectroscopy. The addition of Zr ions to borate glass changed the coordination of borate matrix and consequently converted BO 4 to BO 3 (BO 4 →BO 3 back conversion effect). Optical transmission and reflection measurements were performed as a function of wavelength, showing highly transparent glasses. The optical constants such as refractive index, extinction coefficient, absorption coefficient and optical band gap were calculated. The actual value of the optical band gap energy for these glasses was established by studying the absorption band profile. The frequency and temperature dependent dielectric constant, dielectric loss and AC electrical conductivity measurements were carried out. Excellent structural and physical, optical and dielectric properties of the present glass system indicate prospects for various photonic devices.

Sensitive LC-MS/MS Method for the Determination of Ramipril in Human Plasma: Application to a Bioequivalence Study in Indian Volunteers

Sensitive and selective analytical method is required for the estimation of ramipril in human plasma as ramipril has been reported to have high intra-subject variability and phase II inactive metabolite (ramipril acyl glucuronide) back-converted to ramipril in an in vitro system. If this back conversion is not restricted, it could lead to pseudo estimation of ramipril in human plasma. A specific, sensitive, and reproducible high-performance liquid chromatography-tandem mass spectrometric method was developed and validated for determination of ramipril in human plasma, using ramipril-d5 as an internal standard. Ramipril and ramipril-d5 were extracted from human plasma using solid-phase extraction, and compounds are separated on a Luna C18 (2) 100A (150 × 4.6 mm, 5 μm) column with a mobile phase consisting of methanol and ammonium acetate buffer (pH 4.5; 5 mM) (85:15, v/v). Quantification was achieved by monitoring transitions of m/z 415.6 → 154.0 for ramipril and 420.3 → 154.0 for ramipril-d5 in multiple reaction monitoring, using a turbo ion source in negative polarity. No matrix effect was observed within the linearity range of 50.3–32,850.6 pg/mL (r > 0.999). The degree of the matrix effect for ramipril was determined as 3.5%, and it had no impact on incurred sample analysis with run time of 7.0 min. The intra- and inter-day precision values were within 5.2 and 5.0%, respectively, for ramipril at the lower limit of quantification level. Stability data indicated that ramipril and ramipril acyl glucuronide are stable under various handling conditions and back conversion was not taken place for ramipril acyl glucuronide. The method was successfully applied for the bioequivalence study of ramipril after oral administration of 2.5 mg capsule in healthy Indian volunteers.

Origin and suppression of back conversion in a phase-matched nonlinear frequency down-conversion process

Back conversion is an intrinsic phenomenon in nonlinear frequency down-conversion processes. However, the physical reason for its occurrence is not well understood. Here, we theoretically reveal that back conversion is the result of a π-phase jump associated with the depletion of one interacting wave. By suppressing the idler phase jump through a deliberate crystal absorption, the back conversion can be inhabited, thus enhancing the conversion efficiency from the pump to the signal. The results presented in this Letter will further the understanding of nonlinear parametric processes and pave the way toward the design of highly efficient down-conversion systems.

Gamma rays interactions with Eu2O3 doped lead fluoroborate glasses

The research article concentrates on the effects of gamma rays [150 kGy] over lead fluoroborate glass systems doped with Europium (Eu2O3) ions synthesized through melt-quench technique. FTIR measurements confirmed the conversion of three-fold borate units (BO3) to tetrahedral borate units (BO4) before irradiation and a back conversion was studied post irradiation, with addition of Eu2O3 ions; which was cross verified through N4 and N3 coordination numbers. Effects of gamma rays have been confirmed through ESR spectra where, resonance paramagnetic centers were perceived. Decrease in the intensities and red shift in the absorption peaks (UV-VIS-NIR absorption spectra) indicates the formation of the color centers in the glass matrices after high energetic gamma exposure. Stability of the samples were calculated using different characteristic temperatures (Tg, Tx, Tc, Tm) which was employed through DSC technique. Different elastic moduli (E, K, G, μ) of the samples were calculated and studied using standard Makishima-Mackenzie's model. Hardness (H) number of the samples have also been measured which showed decrease in the H values after irradiation with increase in Fragility (F) parameter. The unusual trend observed in the Eg values of the samples were validated through the Molar Volume (Vm), Oxide ion polarizability (αe) and optical basicity (Λ) values. The samples could be recommended for solid state lighting devices because of its semiconducting nature energy band gap values (Eg: 2.34–2.83 eV). The competitive stability factors (Dietzel factor (ΔT) ∼ 160–270 °C; Hruby's number (Hr): 1.130–4.237), high densities (ρ: 3.8501–4.1944 g/cm3), hardness parameter (H: 3.32–4.46 GPa) and low poisson's ratio (μ: 0.241–0.257) with supportive αe values motivates the samples to be proposed as radiation shielders and in space applications.

The Bone Sparing Effects of 2-Methoxyestradiol Are Mediated via Estrogen Receptor-α in Male Mice.

2-Methoxyestradiol (2ME2), a metabolite of 17β-estradiol (E2), exerts bone sparing effects in animal models. We hypothesized that the underlying mechanism is back conversion of 2ME2 to E2, which subsequently acts via estrogen receptor (ER)α. We measured serum E2 levels in orchidectomized wild-type (WT) mice treated with 2ME2 66.6 μg/d or placebo. In placebo-treated animals, E2 was below the detection limit. In 2ME2-treated mice, the serum E2 level was 4.97 ± 0.68 pg/mL. This corresponds to the level found in diesterus in cycling female mice. Next, we investigated bone parameters in orchidectomized WT and ERα knockout mice treated with 2ME2 or placebo for 35 days. 2ME2 (6.66 μg/d) preserved trabecular and cortical bone in WT mice. Trabecular volumetric-bone mineral density was 64 ± 20%, and trabecular bone volume/total volume was 60 ± 20% higher in the metaphyseal region of the femur in the 2ME2 group, compared with placebo (P < .01). Both trabecular number and trabecular thickness were increased (P < .01). Cortical bone mineral content in the diaphyseal region of the femur was 31 ± 3% higher in the 2ME2 group, compared with placebo (P < .001). This was due to larger cortical area (P < .001). Three-point bending showed an increased bone strength in WT 2ME2-treated animals compared with placebo (maximum load [Fmax] +19±5% in the 2ME2 group, P < .05). Importantly, no bone parameter was affected by 2ME2 treatment in ERα knockout mice. In conclusion, 2ME2 treatment of orchidectomized mice results in increased serum E2. ERα mediates the bone sparing effects of 2ME2. The likely mediator of this effect is E2 resulting from back conversion of 2ME2.

Numerical investigation of output beam quality in efficient broadband optical parametric chirped pulse amplification

We theoretically analyzed output beam quality of broad bandwidth non-collinear optical parametric chirped pulse amplification (NOPCPA) in LiB3O5 (LBO) centered at 800nm. With a three-dimensional numerical model, the influence of the pump intensity, pump and signal spatial modulations, and the walk-off effect on the OPCPA output beam quality are presented, together with conversion efficiency and the gain spectrum. The pump modulation is a dominant factor that affects the output beam quality. Comparatively, the influence of signal modulation is insignificant. For a low-energy system with small beam sizes, walk-off effect has to be considered. Pump modulation and walk-off effect lead to asymmetric output beam profile with increased modulation. A special pump modulation type is found to optimize output beam quality and efficiency. For a high-energy system with large beam sizes, the walk-off effect can be neglected, certain back conversion is beneficial to reduce the output modulation. A trade-off must be made between the output beam quality and the conversion efficiency, especially when the pump modulation is large since. A relatively high conversion efficiency and a low output modulation are both achievable by controlling the pump modulation and intensity.

Applications of ortho-para hydrogen catalyst

The underlying theory of hydrogen Ortho-Para conversion has long been known, but the specifics of non-linear heat of conversion from normal to para hydrogen have not been widely disseminated in the cryogenic literature. These factors are reviewed and thermally efficient applications in liquefiers and back conversion cooling systems are illustrated.

Experimental study of multiple optical parametric oscillator based on MgO:APLN and its evolution analysis of back conversion

In this paper, a multiple optical parametric oscillator based on MgO:APLN is reported. The polarization structure of MgO:APLN and output coupler transmittance are optimized, with a high repetition rate of 200 kHz and 1064 nm laser pumping. The 1.57 μm and 3.84 μm cross period parameters light output can be achieved by a single poled crystal for the first time. The maximum average output powers of 2.4 W at 1.57 μm and 1.31 W at 3.84 μm are obtained, corresponding to optical-optical conversion efficiency of 11.54% and 6.25%, respectively. For the phenomenon of energy back conversion appearing in the multiple optical parametric oscillation process, the numerical evolution of multi-wave coupling process through the coupled wave equations is investigated, and the concept of “back conversion in energy transmission area” is induced, and indicates that the existence of back conversion in energy transmission area causes the weak gain parameters of optical parametric oscillator to be enhanced twice. The theoretical analyses are basically in agreement with the experimental results.

Progress in terahertz sources based on difference-frequency generation [Invited

We review our previous results on efficient, high-power, and compact terahertz (THz) sources based on parametric processes. By reversely stacking GaP plates, we have improved photon conversion efficiency from 25% to 40%, which corresponds to the maximum value. As the number of the plates is increased from 4 to 5, the output power is decreased due to back conversion. The corresponding peak power of the THz output reaches 4 kW. We have investigated THz generation by mixing two frequencies generated by a single Nd:YLF solid-state laser. The average output power reaches 1 μW. By introducing two Nd:YLF crystals, we significantly improved the output power to 4.5 μW. Such a configuration allows us to generate different output frequencies. We review our progress for making our THz source further compact by taking advantage of passively Q-switched laser pulses. We have demonstrated that an intracavity can be utilized to enhance the THz output powers by two orders of magnitude.

Structural and spectroscopic characterization of E- and Z-isomers of azobenzene

Monomers of azobenzene were isolated in argon matrices at 15 K and characterized by infrared spectroscopy and theoretical calculations. When the equilibrium vapors existing over the azobenzene crystals at room temperature were trapped in the matrix, only the thermodynamically most stable E-azobenzene was detected. In an attempt to convert E-azobenzene into the Z isomer, the matrix-isolated E-monomers were irradiated either by broad-band or narrow-band UV-visible light of different wavelengths, in the 600-200 nm range. However, no E-to-Z transformation was observed under these conditions. In an alternative experiment, E-azobenzene was irradiated by UV-visible broad-band light in the gas phase prior to trapping in a matrix. In this case, the E-to-Z photoisomerization occurred, and both E- and Z-azobenzene monomers were detected in the matrix sample. Subsequent irradiation of the matrix with narrow-band tunable visible or UV light (λ < 550 nm) resulted in back conversion of Z-azobenzene into the E-form. The observed photoinduced E-to-Z isomerizations allowed for the reliable vibrational characterization of both azobenzene isomers. The two-dimensional potential energy surfaces of Z- and E-azobenzene were explored as functions of the torsional movement of the two phenyl rings. They exhibit large flat areas around the minima, for both isomers, allowing for large-amplitude zero-point torsional vibrations. For the Z-form, these vibrations were found to be responsible for significant changes in the equilibrium NN bond length (up to 0.3 pm). This also allowed to explain the experimentally observed frequency smearing of the N=N stretching vibration in this isomer.

Polyamine Oxidase 7 is a Terminal Catabolism-Type Enzyme in Oryza sativa and is Specifically Expressed in Anthers

Polyamine oxidase (PAO), which requires FAD as a cofactor, functions in polyamine catabolism. Plant PAOs are classified into two groups based on their reaction modes. The terminal catabolism (TC) reaction always produces 1,3-diaminopropane (DAP), H2O2, and the respective aldehydes, while the back-conversion (BC) reaction produces spermidine (Spd) from tetraamines, spermine (Spm) and thermospermine (T-Spm) and/or putrescine from Spd, along with 3-aminopropanal and H2O2. The Oryza sativa genome contains seven PAO-encoded genes termed OsPAO1-OsPAO7. To date, we have characterized four OsPAO genes. The products of these genes, i.e. OsPAO1, OsPAO3, OsPAO4 and OsPAO5, catalyze BC-type reactions. Whereas OsPAO1 remains in the cytoplasm, the other three PAOs localize to peroxisomes. Here, we examined OsPAO7 and its gene product. OsPAO7 shows high identity to maize ZmPAO1, the best characterized plant PAO having TC-type activity. OsPAO7 seems to remain in a peripheral layer of the plant cell with the aid of its predicted signal peptide and transmembrane domain. Recombinant OsPAO7 prefers Spm and Spd as substrates, and it produces DAP from both substrates in a time-dependent manner, indicating that OsPAO7 is the first TC-type enzyme identified in O. sativa. The results clearly show that two types of PAOs co-exist in O. sativa. Furthermore, OsPAO7 is specifically expressed in anthers, with an expressional peak at the bicellular pollen stage. The physiological function of OsPAO7 in anthers is discussed.

The role of iron(ii) dilution in the magnetic and photomagnetic properties of the series [FexZn1−x(bpp)2](NCSe)2

The effects of metal dilution on the spin-crossover behavior of iron(II) in the mixed crystal series [Fe(x)Zn(1-x)(bpp)2](NCSe)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) have been studied using magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. For each mixed-crystal system, the thermal spin transition temperature, T(1/2), and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T(1/2) decreases with the metal dilution while T(LIESST) remains unchanged. Dilution also tends to decrease the hysteresis width and smooth the transition curves. These effects were discussed first qualitatively and then quantitatively on the basis of a kinetic study governing the photo-induced back conversion taking into account the relative sizes of Zn(II) and Fe(II) ions. Interestingly, single crystals were obtained for [Fe(0.6)Zn(0.4)(bpp)2](NCSe)2 allowing the X-ray diffraction crystal-structure determination.

Structural and optical properties of 60B2O3–(20−x)Na2O–10PbO–10Al2O3:xTiO2:yNd2O3 glasses

In this work we investigate the effect of replacing Na2O by TiO2 on the structural and spectroscopic characteristics of the Nd2O3-doped 60B2O3–(20−x)Na2O–10PbO–10Al2O3:xTiO2:yNd2O3 borate glass matrix. Measurements of X-ray patterns, glass temperatures (Tg), vibrational (Raman and infrared (IR)) and optical (absorption and emission) spectra were carried out. The trend of Tg, the Judd–Ofelt parameters and Nephelauxetic ratio as the TiO2 and Nd2O3 concentration increases was interpreted quantitatively and qualitatively in terms of the network bonds and coordination numbers. Measurements of Tg across the Nd-doped glass series for different levels of Ti suggests changes in the rigidity of the matrix due to change of coordination of boron oxide resulting from the BO4–BO3 back conversion effect. The changes observed in the Raman and IR spectra are related to the BO3→BO4 conversion effect. The variation of the Judd–Ofelt parameters Ω(2) and Ω(6) indicates that the average rare earth-ligand radius decreases establishing an electronic density distribution when Nd3+ concentration increases. This effect is interpreted in terms of Judd–Ofelt parameters and by the bonding parameter b1/2 due to Nephelauxetic effect.

Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.