An improved procedure for phosphorous fractionation in plant materials exploiting sample preparation and monosegmented flow analysis

Sample treatment procedures were evaluated for fractionation of phosphorous in plant materials (determination of organic and inorganic, soluble and insoluble fractions). The procedures aimed the conversion of different species into orthophosphate, minimizing time, reagent amounts and waste generation. A monosegmented flow system with multicommutation was developed for the spectrophotometric determination of orthophosphate by the molybdenum blue method. Linear response within 0.5 and 25.0 mg L^− 1 P, detection limit of 24 μg L^− 1 P (99.7% confidence level), coefficient of variation of 3.5% (n = 10) and sampling rate of 38 measurements per hour were estimated. Each determination consumes 5.0 mg ascorbic acid and 0.60 mg of ammonium molybdate. Total phosphorous determination can be carried out after microwave-assisted acid digestion by employing 100 mg of plant material and 500 μL of concentrated HNO₃. Extraction of soluble phosphorous can be carried out with water by stirring for 10 min and organic soluble phosphorous can be determined either after microwave-assisted acid digestion or photodegradation in the presence of ammonium persulfate in acid medium. The results for the different fractions agreed with those obtained by ICP OES at the 95% confidence level.     

Towards Axially Chiral Pyrazole-Based Phosphorus Scaffolds by Dipeptide-Phosphonium Salt Catalysis

Given the comparatively lower rotational barriers, the catalytic asymmetric construction of axially chiral biaryl structures, especially those containing a five-membered heterocycle, still remains a challenge. Herein, we described a general and modular protocol to access atropisomeric arylpyrazole scaffolds containing a phosphorus unit by a dipeptide phosphonium salt catalyzed reaction involving an oxidative central-to-axial chirality conversion. This reaction features excellent yields and enantioselectivities, broad substrate scope, and a low catalyst loading, delivering axially chiral phosphine compounds.     

Melt stabilisation of Phillips type polyethylene, Part I: The role of phenolic and phosphorous antioxidants

The role of a phenolic and three phosphorous (phosphite, phosphonite and phosphine) antioxidants in the melt stabilisation of polyethylene was studied in a Phillips type polyethylene by multiple extrusions. The polyethylene was stabilised with a single antioxidant at 700 ppm and with phenolic/phosphorous antioxidant combinations containing 700 ppm of each component. The functional groups (methyl, vinyl, vinylidene, trans-vinylene and carbonyl) of polyethylene and the residual amount of phosphorous antioxidants were analysed quantitatively by FT-IR methods developed in our laboratory. The rheological characteristics, the colour and the residual thermo-oxidative stability of the polymer were determined and compared. Blown films were prepared and their mechanical strength measured by the Elmendorf and Dart-drop tests. The comparison of the different characteristics revealed that the chemical reactions taking place during the first processing of the nascent polymer powder, as well as the chemical composition of the antioxidants determine the reactions taking place in further processing operations. The changes in the characteristics of stabilised polyethylene during processing are controlled by the phosphorous stabiliser. The effect and final result depend on the chemical structure of the given antioxidant. The phenolic antioxidant itself does not hinder the formation of long chain branches. It reduces the rate of oxidation of the various phosphorous stabilisers, but does not modify the mechanism of stabilisation of the phosphonite and the phosphine. The reactions of the phosphite are significantly modified by the presence of a phenolic antioxidant.     

One‐Pot Four‐Component Synthesis of Tetrasubstituted Pyrroles

A convenient one‐pot four‐component synthesis of tetrasubstituted pyrroles was carried out through the reaction of butane‐2,3‐dione with α‐aminophosphorous ylides, obtained in situ from the 1 : 1 : 1 addition reaction between triphenylphosphine, dialkyl acetylenedicarboxylate, and ammonium acetate.     

The mechanical strength of polysilicon films: Part 1. The influence of fabrication governed surface conditions

In an effort to explain the considerable variations in measured mechanical strength of polysilicon films doped with phosphorous for use in MEMS applications, the influence of the specimen manufacturing processes on the mechanical properties has been examined in connection with varying exposure to 49% hydrofluoric acid (HF). It was found that surface roughness as characterized by groove formation along grain boundaries depends on the HF release time. Surface undulations and crevasses related to grain structure result thus in reduced fracture strength and, in addition, induce errors into the determination of the effective elastic modulus—especially when the latter is determined from flexure configurations. Extensive exposure to HF results in pervasive material degradation, as evidenced by a transition from transgranular to intergranular fracture, and a correspondingly precipitous drop of the film strength with attendant increase in grain boundary material removal. Short times of exposure to HF can result in delamination of a thin surface layer, which is sufficient to initiate an “early” failure. Longer exposure allows HF permeation into the intergranular domains, degrading the body of the material significantly. On the other hand, tests on material from a different source that has undergone different doping and post-processing demonstrated a suppression of this degradation resulting in film strengths that are higher by a factor of two or more. Thus, consideration of additional influences of doping and electro-chemical phenomena during the HF wet release, in association with silicon-metal contacts, is necessary.     

Synthesis of phosphocyclic 2,2′,7,7′-tetrahydroxydinaphthylmethane derivatives

Two types of phosphocyclic derivatives were synthesized by phosphorylation of 2,2′,7,7′-tetrahydroxydinaphthylmethane with triamidophosphites: triphosphorus containing compounds with a phosphocine ring and two acyclic diamidophosphite fragments, and tetraphosphorus-containing macrocycles with a 24-membered ring and two eight-membered phosphorus rings. It was shown that interaction of triphosphorus compounds with resorcinarene gives tetraphosphorus macrocycles.     

Rational Utilization of Black Phosphorus Nanosheets to Enhance Palladium-Mediated Bioorthogonal Catalytic Activity for Activation of Therapeutics

Pd-catalyzed chemistry has played a significant role in the growing subfield of bioorthogonal catalysis. However, rationally designing Pd nanocatalysts that show outstanding catalytic activity and good biocompatibility poses a great challenge. Herein, we propose an innovative strategy through exploiting black phosphorous nanosheets (BPNSs) to enhance Pd-mediated bioorthogonal catalytic activity. Firstly, the electron-donor properties of BPNSs enable in situ growth of Pd nanoparticles (PdNPs) on it. Meanwhile, due to the superb capability of reducing Pd^II, BPNSs can act as hard nucleophiles to accelerate the transmetallation in the decaging reaction process. Secondly, the lone pair electrons of BPNSs can firmly anchor PdNPs on their surface via Pd−P bonds. This design endows Pd/BP with the capability to retard tumor growth by activating prodrugs. This work proposes new insights into the design of heterogeneous transition-metal catalysts (TMCs) for bioorthogonal catalysis.     

Reductive Asymmetric Aza-Mislow-Evans Rearrangement by 1,3,2-Diazaphospholene Catalysis**

1,3,2-diazaphospholene hydrides (DAP−H) enable smooth conjugate reduction of polarized double bonds. The transiently formed phosphorus-enolate provides a potential platform for reductive α-functionalizations. In this respect, asymmetric C-heteroatom bond forming processes are synthetically appealing but remain elusive. We report a 1,3,2-diazaphospholene-catalyzed three-step cascade reaction of N-sulfinyl acrylamides comprised of conjugate reduction, [2,3]-sigmatropic aza-Mislow-Evans rearrangement and subsequent S−O bond cleavage. The obtained enantio-enriched α-hydroxy amides are formed in good yields and excellent enantiospecificity. The stereo-defined P-bound N,O-ketene aminal ensures an excellent transfer of chirality from the sulfur stereocenter to α-carbon. The transformation operates under mild conditions at ambient temperature. Moreover, DAP−H is a competent reductant for the cleavage of formed sulfenate ester, eliminating the extra step in traditional Mislow-Evans processes.     

Melt stabilisation of Phillips type polyethylene, Part II: Correlation between additive consumption and polymer properties

Phillips type polyethylene stabilised with combinations of 700 ppm phenolic antioxidant and different amounts of various phosphorous stabilisers (sterically hindered aryl phosphite [Hostanox PAR 24], phosphonite [Sandostab P-EPQ], and aryl–alkyl phosphine [PEPFINE]) was processed by six consecutive extrusions. The polymer was characterised by FT-IR spectroscopy, rheological (melt flow index, creep compliance), colour and oxidation induction time measurements. Films were prepared by blowing and their mechanical strength was determined by Elmendorf and dart drop tests. The consumption of the antioxidants was compared to the characteristics of the polymer and to the strength of the films. The consumption rate of both the phenolic and the phosphorous antioxidants is reduced in their combinations compared to single antioxidants. The chemical structure of the polymer is modified considerably in the first extrusion even at high antioxidant levels. The mechanism of stabilisation is determined by the type of the antioxidant(s) in further processing steps. The phenolic antioxidant does not prevent the formation of long chain branches. The phosphonite and the phosphine hinder efficiently hydrogen abstraction from the polymer chain and long chain branching. Their efficiency is similar, but the phosphonite is consumed fast, while the phosphine oxidises slowly. The investigated phosphite is less reactive; the contribution of the phenolic antioxidant to the inhibition reactions is significant in phenol/phosphite combinations, therefore long chain branching increases continuously with increasing number of processing steps.     

Double-quantum NMR spectroscopy of P species submitted to very large CSAs

We introduce an original pulse sequence, , which is a block super-cycled sequence employing as basic element a π pulse sandwiched by ‘window’ intervals. This homonuclear dipolar recoupling method allows the efficient excitation of double-quantum coherences between spin-1/2 nuclei submitted to very large chemical shift anisotropy. We demonstrate that this technique can be employed in double-quantum ↔ single-quantum ³¹P homonuclear correlation experiment at high magnetic field (B₀  14 T) and high MAS frequencies (ν_R  30 kHz). The performances of are compared to those of the double-quantum recoupling methods, such as BABA and bracketed fp-RFDR, which were already employed at fast MAS rates. The sequence displays a higher robustness to CSA and offset than the other existing techniques.