Synthesis Of Po Research Articles

Microorganisms drive stabilization and accumulation of organic phosphorus: An incubation experiment

At the earliest stage of pedogenesis, microorganisms are the main biological drivers of nutrient transformation and mobilization from rock minerals. However, this driving process is not yet well understood despite its importance for the formation and fertility of soil. The aim of this study was to determine the microbial accumulation of organic phosphorus (Po) and microbial release of bioavailable phosphorus (bio-P) from rock minerals and to analyse which factors control these processes. We hypothesized that microorganisms contribute to stabilization and accumulation of Po. For this purpose, we carried out a series of incubation experiments with model soils (with soil Po removed) and soil extracts of natural soil from the earliest stage of pedogenesis in the newest retreat area of the Hailuogou glacier. A modified Hedley fractionation method was used to characterize the P forms in soils. Microbial synthesis of Po was clearly observed in this study. In view of the fact that carbon (C) and nitrogen (N) are the main energy and material sources of microorganisms and that their stoichiometry plays an important role in microbial metabolism, we hypothesized that the C and N (ratio and level) play a regulatory role in microbial transformation of P. Therefore, the different C/N gradients were constructed in our incubation experiments. Results showed addition of C and N resulted in an accumulation of stable Po and decrease in pH in soils. These results suggest that not all microbial biomass P is easily degraded. Along two C/N ratio gradients (same ratio but keeping C vs N constant), opposite patterns of total Po (TPo) changes was observed. Opposite patterns were also observed for bio-P along the two C/N ratio gradients. Regardless of the C/N ratio, high CN additions always led to lower TPo accumulations, higher bio-P releases and higher phosphatase activity compared to low CN additions. We conclude that microbial synthesis of Po contributed to the P fractions in soil stable residual pools and that microbial release of bioavailable P was driven by two modes (i.e., N-driven mode and C-driven mode). Our study highlights that microorganisms drive the accumulation of soil Po during the earliest stage of pedogenesis in our study area.

General Synthetic Strategy for Pomegranate-like Transition-Metal Phosphides@N-Doped Carbon Nanostructures with High Lithium Storage Capacity

Pomegranate-like nanostructured materials promise extensive applications in various fields due to their unique properties derived from special architectures. However, the controlled synthesis of po...

Propylene epoxidation with hydrogen peroxide in acidic conditions

In the present work, the epoxidation of propylene with hydrogen peroxide in the presence of acids and halides is studied. The presence of acids and halides is indispensable for increasing the selectivity of the direct synthesis of hydrogen peroxide, the first step of the direct propylene oxide production from hydrogen, oxygen and propylene. Therefore, we focus on the systematic study of the effect of these compounds on the epoxidation of propylene with hydrogen peroxide in prospective of its future integration with hydrogen peroxide in-situ formed. Indeed, the epoxidation of propylene with hydrogen peroxide is the second step of the direct PO synthesis from hydrogen, oxygen and propylene. The acid concentration and type were shown to have an effect on the PO selectivity. Sulphuric and hydrochloric acids, typical compounds used to stabilize the hydrogen peroxide, are not suitable for the direct propylene oxide due to their fast dissociation in the solution. This leads to a fast ring opening reaction of the epoxide. Phosphoric acid was shown to have a much milder effect on the propylene oxide selectivity, therefore being an option for the direct propylene oxide synthesis. Also, the amount of halides (NaBr) needed to stabilize the hydrogen peroxide, does not have an effect on the epoxidation step. Therefore phosphoric acid and NaBr can be implemented in the direct propylene oxide synthesis from hydrogen, oxygen and propylene.

Synthesis and Properties of Peroxy Oligomers Obtained by Telomerization Effects of the Presence of Bases

<p>New bifunctional oligomers bearing peroxy groups have been synthesized by telomerization in one step reaction. For obtaining oligoperoxides (PO) by telomerization method, epoxide compounds will react with substances containing labile hydrogen atom. Using the principle of stochiometric imbalance between diepoxy compounds and substances with mobile hydrogen atoms and employing a functional peroxide as telogen, the synthesis of PO was studied. 2,2–Di[4–(2,3–epoxy–1-propoxy)phenyl]–propane (diglycidyl ether of diphenylol propane - DGEDPP), 1,2–Di (2,3–epoxy–1-propoxy) ethane (diglycidyl ether of ethylene glycol - DGEEG) and 1,2–Epoxy–3–tert–butylperoxypropane (EP) have been synthesized by methods reported in the literature. Chemical structures have been confirmed by NMR and FTIR, number-average molecular weights M<sub>n</sub> of PO<sub>s</sub> by cryoscopy, active oxygen content [O]<sub>act</sub>. for PO<sub>s</sub> was determined by iodometry and epoxy number (<em>e.n</em>.) for PO<sub>s</sub> was measured via direct titration of PO samples. A 50% solution of potassium or sodium isopropylates in 2-propanol is used to catalyze the telomerisation. Different parameters such as ratio of components, temperature, reaction time have been optimized in vu to get well defined peroxy oligomers. The presence of peroxy groups in synthesized POs allows us to employ these compounds as curing agents for polymers containing unsaturated double bonds and may be used to improve performance of unsaturated polyester GFR systems.</p>

Propene epoxidation with O 2 and H 2: Identification of the most active gold clusters

Gold was deposited on alkaline-treated TS-1 (TS-1-Na1) to prepare Au/TS-1-Na1(DP) by deposition–precipitation (DP) and Au/TS-1-Na1(SG) by solid grinding (SG). 129Xe NMR technique has detected that tiny Au clusters have been incorporated into the microporous channels of Au/TS-1-Na1(DP), while they were absent inside the microporous channels of Au/TS-1-Na1(SG). On the other hand, HAADF-STEM observation showed that the amount of Au clusters (1.0–2.0 nm) over the exterior surfaces was much larger in Au/TS-1-Na1(SG) than in Au/TS-1-Na1(DP). In propene epoxidation with O 2 and H 2, Au/TS-1-Na1(SG) exhibited much higher PO formation rate (127 g PO kg cat - 1 h −1) than Au/TS-1-Na1(DP) (74 g PO kg cat - 1 h −1), indicating that Au clusters with diameters of 1.0–2.0 nm are more active for PO synthesis than tiny Au clusters incorporated inside the microporous channels.

Propene epoxidation with in‐site H2O2 produced by H2/O2 non‐equilibrium plasma

AbstractA novel in‐site H2O2 strategy is proposed for the liquid‐phase epoxidation of propene catalyzed by titanium silicalite (TS‐1). Said in‐site H2O2 strategy is based on the direct synthesis of H2O2 from H2 and O2 under atmospheric pressure via nonequilibrium plasma reactions. Methanol is used to absorb H2O2 from the dielectric barrier discharge (DBD) reactor. Methanol also serves as the desired solvent for the liquid‐phase epoxidation reactor. The efficiency of the integrated process for in‐site synthesis of H2O2 reached 69% selectivity, and 62% yield with a nonexplosive H2/O2 mixture when the DBD reactor worked at an input power of 3.5 W (energy consumption 12.4 kWh/kg H2O2). The liquid‐phase epoxidation of propene using the in‐site H2O2 successfully proceeded over an 18 h time course under the conditions of 50 °C and 3.0 MPa, more than 92% H2O2 conversion and more than 93% PO selectivity were obtained. The two‐reactor integrated process worked smoothly during continuous operation, no performance decay was observed for both the DBD reactor and the epoxidation reactor. These facts mean that our in‐site H2O2 strategy for PO synthesis is promising. © 2007 American Institute of Chemical Engineers AIChE J, 2007

The synthesis of glycoprotein Po and peripheral myelin protein 22 in sciatic nerve of male rats is modulated by testosterone metabolites

Glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22) are two proteins playing a crucial physiological role in the maintenance of the multilamellar structure of peripheral myelin. We here demonstrate that the removal of circulating androgens by orchidectomy induces a significant decrease of the synthesis of Po and PMP22 in the rat sciatic nerve. In case of Po, this effect may be counteracted by the subsequent treatment with testosterone metabolites, dihydrotestosterone or 5α-androstan-3α,17β-diol (3α-diol). Experiments have been consequently performed in order to evaluate the role of androgen receptor (AR) in the control of Po synthesis. In vivo treatment with flutamide (i.e., an antagonist of AR) induces a decrease of the synthesis of this myelin protein in the sciatic nerve of intact male rats confirming a role for this steroid receptor. On the contrary, PMP22 seems not to be under the control of AR, but a role for GABA A receptor may be proposed. This concept is based on the findings that: (a) only 3α-diol, which is able to interact with GABA A receptor, is effective in stimulating the synthesis of PMP22 in the sciatic nerve of castrated male rats, and (b) flutamide treatment is ineffective in decreasing the protein levels in intact male rats. The observations here reported clearly show similarities and dissimilarities with the effects exerted by other members of neuroactive steroid family, like for instance progesterone derivatives, which will be discussed in text.

Partial purification and properties of putrescine oxidase from Candida guilliermondii.

Putrescine oxidase ([PO]; E.C. 1.4.3.4), which catalyzes the oxidative deamination of putrescine into gamma-aminobutyraldehyde, has been partially purified from Candida guilliermondii. Among the substrates tested, putrescine has the highest reaction rate, followed by spermidine and cadaverine. The K(m) values for putrescine, spermidine, and cadaverine were 20, 200, and 1.1 mM, respectively. The optimum pH and the temperature for PO were 8.0 and 37 degrees C, respectively. Growth of Candida species on putrescine as the sole nitrogen source induced the synthesis of PO that converts putrescine into delta 1-pyrroline and gamma-aminobutyric acid. These two products were detected and identified from the culture medium. The enzyme was not activated by divalent cations. Among the species of Candida tested, the highest enzyme activity was found in cell-free extracts of C. guilliermondii. The pathway of putrescine degradation was identified by substrate analysis to be along the nonacetylated pathway in C. guilliermondii.

Synthesis of PO(OR)2- and PR3+-Disubstituted Pyridines via N-(Trifluoromethylsulfonyl)pyridinium Triflates

Synthesis of PO(OR)2- and PR3+-Disubstituted Pyridines via N-(Trifluoromethylsulfonyl)pyridinium Triflates

Biosynthesis and compartmentalization of Po, apolipoprotein A-I, and lipids in the myelinating chick sciatic nerve.

Myelin deposition in developing chick sciatic nerve is associated with rapid synthesis of lipids, the major myelin protein Po and apo A-I, a major constituent of plasma lipoproteins. In order to understand possible roles of apo A-I in myelin assembly the synthesis and appearance of Po, apo A-I and lipids was studied in an intracellular fraction, an intralamellar fraction thought to be related to, or derived from, myelin and compact myelin from rapidly myelinating sciatic nerve of 1 day chicks. Incorporation with methionine or pulse-chase experiments indicated that initial synthesis of Po occurs in the intracellular fraction followed by movement to the intralamellar fraction and myelin. Incorporation of labelled oleate into phospholipids suggested that initial synthesis occurs in the intracellular and intralamellar fractions with slow movement to myelin. Incorporation of labelled galactose into cerebrosides suggested that initial synthesis occurs partially in myelin with slow loss from this fraction to the intralamellar fraction. However, incorporation of methionine into apo A-I indicated that initial synthesis occurred in the intracellular fraction with some transfer to the intralamellar fraction and secretion of a major portion into the incubation medium. It is concluded that the subcellular distribution of nascent apo A-I is not well coordinated with the distribution of other nascent constituents of the myelin membrane. The accumulation of nascent Po, phospholipids and cerebrosides in the intralamellar fraction compared to compact myelin suggests that this fraction may play a role as a precursor membrane or as a storage site for assembly of myelin constituents into compact myelin.

Biosynthesis of the major integral protein of rat peripheral nerve myelin

Schwann cells produce myelin as an extension of their plasma membrane and ensheath nerve fibres in the peripheral nervous system (PNS). Several myelin proteins are common to both central nervous system (CNS) and PNS myelin but the major integral protein (Po) of PNS myelin is peculiar to this membrane (Greenfield et al . , 1973). Po comprises around 60% of the total protein of PNS myelin. SDS/polyacrylamide-gel analysis indicates an apparent M , of 28 00@30 000 and the protein is known to have a single N-linked oligosaccharide chain (Ishaque et al., 1980). Other post-translational modifications include acylation (Agrawal et al . , 1982). phosphorylation (Wiggins & Morell, 1980) and sulphation (Matthieu et al., 1975). The purpose of this work was to identify the subcellular site of synthesis of Po in Schwann cells and determine the mechanisms by which this protein is inserted into membranes before transport to the Schwann cell plasma membrane. mRNA isolated from sciatic nerves of 15-day-old rats was translated in a wheatgerm system and Po was immune precipitated and analysed on SDS-gels (Colman et ul., 1982). The primary translation product had a M , of 30700 compared with an M , of 28500 for the mature protein. This result indicated a cleavable signal sequence in the primary translation product of P,, mRNA. Removal of the single oligosaccharide from mature P,, with endoglycosidase F