DNA-Functionalized Nanoceria for Probing Oxidation of Phosphorus Compounds

Chemical reactions without an obvious optical signal change, such as fluorescence or color, are difficult to monitor. Often, more advanced analytical techniques such as high-performance liquid chromatography and mass spectroscopy are needed. It would be useful to convert such reactions to those with changes in optical signals. In this work, we demonstrate that fluorescently labeled DNA oligonucleotides adsorbed on nanomaterials can probe such reactions, and oxidation of phosphorus-containing species was used as an example. Various metal oxides were tested, and CeO2 nanoparticles were found to be the most efficient for this purpose. Among phosphate, phosphite, and hypophosphite, only phosphate produced a large signal, indicating its strongest adsorption on CeO2 to displace the DNA. This was further used to screen oxidation agents to convert lower oxidation-state compounds to phosphate, and bleach was found to be able to oxidize phosphite. Canonical discriminant analysis was performed to discriminate various phosphorus species using a sensor array containing different metal oxides. On the basis of this, glyphosate was studied for its adsorption and oxidation. Although this method is not specific enough for selective biosensors, it is useful as a tool to produce sensitive optical signals to follow important chemical transformations.

Palladium-phosphinous acid complexes catalyzed Suzuki cross-coupling reaction of heteroaryl bromides with phenylboronic acid in water/alcoholic solvents

Highly active, air-stable and water-soluble palladium-phosphinous acid complexes have been applied to Suzuki cross-coupling reaction of heteroaryl bromides under mild conditions in water/alcoholic solvents. Suzuki cross-coupling reaction of heteroaryl bromides with phenylboronic acid occurred efficiently using palladium phosphinous acid complexes (POPd) and phase transfer catalyst (tetrabutylammonium bromide and polyethylene glycol) in water/ethanol mixture, water/propanol mixture and neat water respectively, the corresponding yields of cross-coupling heteroaryl-aryls were satisfied. The tert-butyl substituted ligand di-tert-butylphosphino in combination with POPd was found to be more active than the same family derived catalysts dipalladium complexes POPd1 and POPd2, and other two kinds of Pd-catalysts Pd(PPh3)4 and Pd2(dba)3. The mechanism of Suzuki cross-coupling reaction between heteroaryl bromides and phenylboronic acid in water was proposed with respect to the key role of phase transfer catalyst on the transmetallation step. Compared with other solid phase transfer catalysts, TBAB was tested as the ideal one. The alkalinity of base and the molar proportion between POPd and TBAB were investigated in water and alcoholic solvents. Notably, in the presence of TBAB adding alcoholic solvents into water enhanced the yields of target products. However in terms of the liquid phase transfer catalyst of PEGs, mixing water into PEGs could slightly decrease the yields with respect to the water free PEGs bulk phase, which was probably due to the homogenous liquid conditions in pure PEGs and weak interactions between PEGs and heteroaryl bromide molecules in water depending on their molecular chain lengths.

Textural properties and surface chemistry of lotus stalk-derived activated carbons prepared using different phosphorus oxyacids: adsorption of trimethoprim

The preparation of activated carbons (AC-H(x)P(y)O(z)) by four kinds of oxyacids of phosphorus (H(3)PO(4), H(4)P(2)O(7), HPO(3) and H(3)PO(3)) activation of lotus stalk (LS) was studied, with a particular focus on the effect of these H(x)P(y)O(z) on both surface chemistry and porous texture. The XRD analysis of the samples after H(x)P(y)O(z) impregnation showed H(4)P(2)O(7) had the strongest influence on the crystallinity of LS. Thermo gravimetric studies of the pyrolysis of LS-H(x)P(y)O(z) indicated that these H(x)P(y)O(z) had a very different influence on the thermal degradation of LS. The prepared activated carbons were characterized by SEM, N(2) sorption/desorption isotherms, XRD, FTIR and Boehm's titration. Batched sorption studies were performed to compare adsorptive properties of the carbons toward trimethoprim (TMP). The surface area and pore volume of AC-H(3)PO(4) and AC-H(4)P(2)O(7) were much higher than AC-HPO(3) and AC-H(3)PO(3). Boehm's titration results indicated that AC-H(4)P(2)O(7) and AC-H(3)PO(3) possessed more acidic oxygen functionalities than AC-H(3)PO(4) and AC-HPO(3). The structure of the AC-HPO(3) was kept as its starting material after activation. Activation with H(3)PO(3) would result in the aromatization of the carbon. The sorption affinities of TMP follows an order of AC-H(4)P(2)O(7)>AC-H(3)PO(4)>AC-H(3)PO(3)>AC-HPO(3).

The Bis(pentafluoroethyl)phosphinous acid (C2F5)2POH

The industrial product (C(2)F(5))(3)PF(2) is transformed into the phosphinic acid chloride (C(2)F(5))(2)P(O)Cl, which reacts with an excess of Bu(3)SnH in a clean, multistep reaction to give the stannyl derivative (C(2)F(5))(2)POSnBu(3). Subsequent treatment with gaseous HBr leads to the formation of (C(2)F(5))(2)POH, which is isolated in 70 % yield. Besides (CF(3))(2)POH, bis(pentafluoroethyl)phosphinous acid, (C(2)F(5))(2)POH, represents the second known example of a phosphinous acid that is predicted by using density functional theory calculations at the B3PW91/6-311G(3d,p) level to be more stable than the phosphane oxide tautomer, the energy difference being 11.7 kJ mol(-1). Only the phosphinous acid isomer is detectable in the gas phase and in solution. However, investigations of the neat liquid reveal a temperature-dependent tautomeric equilibrium with the phosphane oxide isomer (C(2)F(5))(2)P(O)H, which is characterized by vibrational and multinuclear NMR spectroscopic methods in combination with quantum-chemical calculations.

An expeditious aqueous Suzuki-Miyaura method for the substituted aryl heterocyclics

Palladium-catalyzed cross-coupling reactions utilizing aryl halides have become a widely used strategy for the formation of new carbon-carbon bonds and in particular for the synthesis of biaryls. The replacement of expensive, toxic, and flammable organic solvents by water is highly desirable for reducing costs and for developing environmentally benign synthetic reactions that facilitate catalyst recycling. Herein, we report an efficient Suzuki-Miyaura cross-coupling reaction using a variety of heterocyclic halides in neat water. Employing air- and moisture-stable palladium-phosphinous acid catalyst [(t-Bu)2P(OH)]2PdCl2(POPd) allows formation of substituted aryl heterocyclics in moderate to high yields. The organic cosolvents are not required. The feasibility of catalyst recycling has also been demonstrated.

Hydrogen and copper ion-induced molecular reorganizations in scorpionand-like ligands. A potentiometric, mechanistic, and solid-state study

Two aza scorpionand-like macrocycles (L2 and L3) have been prepared. L2 consists of a tren amine with two of its arms cyclizized with a 2,6-bis(bromomethyl)pyridine. In L3, the remaining pendant arm has been further functionalized with a fluorophoric naphthalene group. X-ray data on the compounds [H(L3)]ClO4.H2O (1) and [H3(L3)](H2PO4)3.H2O (2) as well as solution studies (pH-metry, UV-vis, and fluorescence data) show the movement of the pendant arm as a result of the protonation degree of the macrocycles and of the formation of intramolecular hydrogen bonds. X-ray data on the complexes [Cu(L2)](ClO4)2]2.H2O (3) and [Cu(L3)](ClO4)2 (4) and solution studies on Cu2+ coordination show the implication of the nitrogen of the arm in the binding to the metal ion. Kinetic studies on the decomposition and formation of the Cu2+ complexes provide additional information about the pH-dependent molecular reorganizations. Moreover, the obtained information suggests that the kinetics of the tail on/off process is essentially independent of the lability of the metal center.

Thermodynamics and kinetics for base-pair opening in the P1 duplex of the Tetrahymena group I ribozyme

The thermodynamics and kinetics for base-pair opening of the P1 duplex of the Tetrahymena group I ribozyme were studied by NMR hydrogen exchange experiments. The apparent equilibrium constants for base pair opening were measured for most of the imino protons in the P1 duplex using the base catalysts NH₃, HPO42− or TRIS. These equilibrium constants were also measured for several modified P1 duplexes, and the C-2·G23 base pair was the most stable base pair in all the duplexes. The conserved U-1·G22 base pair is required for activity of the ribozyme and the data here show that this wobble base pair destabilizes neighboring base pairs on only one side of the wobble. A 2′-OMe modification on the U-3 residue stabilized its own base pair but had little effect on the neighboring base pairs. Three base pairs, U-1·G22, C-2·G23 and A2·U21 showed unusual equilibrium constants for opening and possible implications of the opening thermodynamics of these base pairs on the undocking rates of the P1 helix with catalytic core are discussed.

Ligand-Dependent Catalytic Cycle and Role of Styrene in Nickel-Catalyzed Anhydride Cross-Coupling: Evidence for Turnover-Limiting Reductive Elimination

Results from a mechanistic study on the Ni(COD)2-bipy-catalyzed alkylation of anhydrides are consistent with turnover-limiting reductive elimination at high Et2Zn concentrations. While the presence of styrene does not affect the initial rate of alkylation, it appears to inhibit catalyst decomposition and provides higher product yield at long reaction times. In contrast, Ni(COD)2-iPrPHOX-catalyzed anhydride alkylation proceeds through two competing catalytic cycles differentiated by the presence of styrene. The presence of styrene in this system appears to accelerate rate-limiting oxidative addition and promotes the cycle which proceeds 4 times more rapidly and with much higher enantioselectivity than its styrene-lacking counterpart.

Air-stable Ir-(P-Phos) complex for highly enantioselective hydrogenation of quinolines and their immobilization in poly(ethylene glycol) dimethyl ether (DMPEG)

An air-stable catalyst system Ir-(P-Phos) catalyst was found to be highly effective in the asymmetric hydrogenation of quinoline derivatives. The catalyst immobilized in DMPEG was efficiently recovered and reused eight times, retaining reactivity and enantioselectivity.

Palladium–phosphinous acid-catalyzed Sonogashira cross-coupling reactions in water

A palladium--phosphinous acid-catalyzed Sonogashira cross-coupling reaction that proceeds in water under air atmosphere in the absence of organic co-solvents has been developed. Disubstituted alkynes have been prepared in up to 91% yield by POPd-catalyzed coupling of various aryl halides including chlorides in the presence of tetrabutylammonium bromide and pyrrolidine or NaOH.

Catalytic enantioselective addition of dialkylzinc to N-diphenylphosphinoylimines. A practical synthesis of alpha-chiral amines

The enantioselective addition of dialkylzinc reagents to N-diphenylphosphinoylimines derived from aryl-, furyl-, and cyclopropylaldehydes is efficiently catalyzed by a copper(II) triflate/(R,R)-MeDUPHOS complex. The yields are high (51-98%), and the enantiomeric excesses vary from 85 to 96%. This route provides a practical route to alpha-chiral amines.

Evaluation of several economical computational methods for geometry optimization of phosphorus acid derivatives

Several economical methods for geometry optimisation, applicable to larger molecules, have been evaluated for phosphorus acid derivatives. MP2/cc-pVDZ and B3LYP/6-31+G(d) geometry optimizations are used as reference points, results from geometry optimizations for other methods and their subsequent single point energy calculations are compared to these references. The geometries from HF/MIDI! optimizations were close to those of the references and subsequent single point energies with B3LYP/6-31+G(d,p) or EDF1/6-31+G(d) gave a mean average deviation (MAD) of less than 0.5 kcal mol-1 from those obtained with the reference geometries.

Prebiotic phosphorus chemistry reconsidered

The available evidence indicates that the origin of life on Earth certainly occurred earlier than 3.5 billion years ago and perhaps substantially earlier. The time available for the chemical evolution which must have preceded this event is more difficult to estimate. Both endogenic and exogenic contributions to chemical evolution have been considered; i.e., from chemical reactions in a primitive atmosphere, or by introduction in the interiors of comets and/or meteorites. It is argued, however, that the phosphorus chemistry of Earth's earliest hydrosphere, whether primarily exogenic or endogenic in origin, was most likely dominated by compounds less oxidized than phosphoric acid and its esters. A scenario is presented for the early production of a suite of reactive phosphonic acid derivatives, the properties of which may have foreshadowed the later appearance of biophosphates.

Aging of phosphylated human acetylcholinesterase: catalytic processes mediated by aromatic and polar residues of the active centre

We have examined the effects of 11 substitutions of active centre gorge residues of human acetylcholinesterase (HuAChE) on the rates of phosphonylation by 1,2,2-trimethylpropyl methyl-phosphonofluoridate (soman) and the aging of the resulting conjugates. The rates of phosphonylation were reduced to as little as one-seventieth, mainly in mutants of the hydrogen-bond network (Glu-202, Glu-450, Tyr-133). These recombinant enzymes as well as the F338A, W86A, W86F and D74N mutant HuAChEs varied in their resistance to aging (15-3300-fold relative to the wild type). The most dramatic resistance to aging was observed for the phosphonyl conjugate of the mutant W86A enzyme (1850-3300-fold relative to the wild type). It is proposed that Trp-86 contributes to the aging process by stabilizing the evolving carbonium ion on the 1,2,2-trimethylpropyl moiety, via charge-pi interaction. The rate-enhancing effect of Trp-86 provides a rationale for the unique facility of aging in soman-inhibited cholinesterases, compared with the corresponding conjugates in other serine hydrolases. Replacements of Glu-202 by aspartic acid, glutamine or alanine residues resulted in a similar (1/130-1/300) decrease of the rates of aging. A comparable decrease was also observed for the conjugate of the F338A mutant. These results, and the similar pH dependence of aging rates for the wild-type and E202Q and F338A mutant HuAChEs, indicate that Glu-202 is not involved in proton transfer to the phosphonyl moiety. On the basis of these findings and of molecular modelling we suggest that Glu-202 and Phe-338 contribute to the aging process by stabilizing the imidazolium of the catalytic triad His-447 via charge-charge and charge-pi interactions respectively, thereby facilitating an oxonium formation on the phosphonyl moiety.

Study by 31P NMR spin echo mapping of vanadium phosphorus oxide catalysts

Vanadium phosphorus oxides (VPO) containing vanadium ions in the +3 and +4 oxidation states, namely VPO4, (VO)2P2O7, VOHPO4.0.5H2O and VO(H2PO4)2 have been characterized using 31P solid state NMR spectroscopy. Because of couplings between the unpaired electrons of V4+ or V3+ ions and 31P nuclei, 31P NMR lines are drastically broadened and shifted by more than 4500 ppm in the case of the V3+ phases. It is therefore necessary to use the Spin Echo Mapping technique to obtain the complete NMR information. The technique has proved to be particularly interesting as it permits us to distinguish between various V4+ phases. The observed frequency shift is proportional to the atomic magnetic susceptibility of the material and, therefore, changes with temperature. For V4+ phases, we have observed that the inverse shift was proportional to temperature in the working temperature range and that good estimations of the Weiss temperatures could be obtained. Moreover, at low temperature, the 31P NMR spin echo mapping of the pyrophosphate (VO)2P2O7 showed four distinct peaks that could be assigned to various unpaired electron spin densities on the phosphorus atoms. This has been correlated with previous structural determinations, particularly the oxidation state of vanadium ions in these solids. We have also observed that the inverse of the line width increased linearly with temperature in the working range. Special attention was given to VPO4 where both the evolution with temperature of the observed shift and the line width were very different from those observed on V4+ phases.