A proteomic analysis of organelles from Arabidopsis thaliana

We introduce the use of Arabidopsis thaliana callus culture as a system for proteomic analysis of plant organelles using liquid-grown callus. This callus is relatively homogeneous, reproducible and cytoplasmically rich, and provides organelles in sufficient quantities for proteomic studies. A database was generated of mitochondrial, endoplasmic reticulum (ER), Golgi/prevacuolar compartment and plasma membrane (PM) markers using two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (2-D SDS-PAGE) and peptide sequencing or mass spectrometric methods. The major callus membrane-associated proteins were characterised as being integral or peripheral by Triton X-114 phase partitioning. The database was used to define specific proteins at the Arabidopsis callus plasma membrane. This database of organelle proteins provides the basis for future characterisation of the expression and localisation of novel plant proteins.     

Substitution and derivatization reactions of a water soluble iron(II) complex containing a self-assembled tetradentate phosphine ligand

Facile substitution reactions of the two water ligands in the hydrophilic tetradentate phosphine complex cis-[Fe{(HOCH2)P{CH2N(CH2P(CH2OH)2)CH2}2P(CH2OH)}(H2O)2](SO4) (abbreviated to [Fe(L1)(H2O)2](SO4), 1) take place upon addition of Cl-, NCS-, N3(-), CO3(2-) and CO to give [Fe(L1)X2] (2, X = Cl; 4, X = NCS; 5, X=N3), [Fe(L1)(kappa2-O(2)CO)], 6 and [Fe(L1)(CO)2](SO4), 7. The unsymmetrical mono-substituted intermediates [Fe(L1)(H2O)(CO)](SO(4)) and [Fe(L(1))(CO)(kappa(1)-OSO(3))] (8/9) have been identified spectroscopically en-route to 7. Treatment of 1 with acetic anhydride affords the acylated derivative [Fe{(AcOCH2)P{CH2N(CH2P(CH2OAc)2)CH2}2P(CH2OAc)}(kappa2-O(2)SO2)] (abbreviated to [Fe(L2)(kappa2-O(2)SO2)], 10), which has increased solubility over 1 in both organic solvents and water. Treatment of 1 with glycine does not lead to functionalisation of L1, but substitution of the aqua ligands occurs to form [Fe(L(1))(NH(2)CH(2)CO(2)-kappa(2)N,O)](HSO(4)), 11. Compound 10 reacts with chloride to form [Fe(L(2))Cl(2)] 12, and 12 reacts with CO in the presence of NaBPh4 to form [Fe(L2)Cl(CO)](BPh4) 13b. Both of the chlorides in 12 are substituted on reaction with NCS- and N3(-) to form [Fe(L2)(NCS)2] 14 and [Fe(L2)(N3)2] 15, respectively. Complexes 2.H2O, 4.2H2O, 5.0.812H2O, 6.1.7H2O, 7.H2O, 10.1.3CH3C(O)CH3, 12 and 15.0.5H2O have all been crystallographically characterised.     

Dihydrogen complexes of rhodium: [RhH2(H2)x (PR3)2]+ (R = Cy, iPr; x = 1, 2)

Addition of H2 (4 atm at 298 K) to [Rh(nbd)(PR3)2][BAr(F)4] [R = Cy, iPr] affords Rh(III) dihydride/dihydrogen complexes. For R = Cy, complex 1a results, which has been shown by low-temperature NMR experiments to be the bis-dihydrogen/bis-hydride complex [Rh(H)2(eta2-H2)2(PCy3)2][BAr(F)4]. An X-ray diffraction study on 1a confirmed the {Rh(PCy3)2} core structure, but due to a poor data set, the hydrogen ligands were not located. DFT calculations at the B3LYP/DZVP level support the formulation as a Rh(III) dihydride/dihydrogen complex with cis hydride ligands. For R = iPr, the equivalent species, [Rh(H)2(eta2-H2)2(P iPr3)2][BAr(F)4] 2a, is formed, along with another complex that was spectroscopically identified as the mono-dihydrogen, bis-hydride solvent complex [Rh(H)2(eta2-H2)(CD2Cl2)(P iPr3)2][BAr(F)4] 2b. The analogous complex with PCy3 ligands, [Rh(H)2(eta2-H2)(CD2Cl2)(PCy3)2][BAr(F)4] 1b, can be observed by reducing the H2 pressure to 2 atm (at 298 K). Under vacuum, the dihydrogen ligands are lost in these complexes to form the spectroscopically characterized species, tentatively identified as the bis hydrides [Rh(H)2(L)2(PR3)2][BAr(F)4] (1c R = Cy; 2c R = iPr; L = CD2Cl2 or agostic interaction). Exposure of 1c or 2c to a H2 atmosphere regenerates the dihydrogen/bis-hydride complexes, while adding acetonitrile affords the bis-hydride MeCN adduct complexes [Rh(H)2(NCMe)2(PR3)2][BAr(F)4]. The dihydrogen complexes lose [HPR3][BAr(F)4] at or just above ambient temperature, suggested to be by heterolytic splitting of coordinated H2, to ultimately afford the dicationic cluster compounds of the type [Rh6(PR3)6(mu-H)12][BAr(F)4]2 in moderate yield.     

Graphene Nanocomposites Based Electrochemical Sensing Platform for Simultaneous Detection of Multi-drugs

Three reduced graphene oxide nanocomposites were employed to achieve the simultaneous electrochemical determination of multi-drugs including acetaminophen (ACTM), carbendazim (CB) and ciprofloxacin (CFX). All nanocomposite modified electrodes showed improved current responses for three drugs. Notably cauliflower-like platinum nanoparticles decorated reduced graphene oxide modified electrode (or Pt−RGO/GCE) exhibited the best performance in terms of electrochemical stability. Using Pt−RGO/GCE, the linear detect ranges of 30–120 μM, 25–115 μM and 10–25 μM, and detection limit values of 3.49, 2.96, and 1.53 μM were achieved for ACTM, CB and CFX respectively. The electrode was further used for the successful determination of above drugs in tap and river water using differential pulse voltammetry. From the obtained results, we believe that Pt-RGO/GCE is highly promising for the fabrication of robust electrochemical sensors for simultaneously determining ACTM, CB and CFX or similar types of drugs in the future.     

[Ni(NHC)2] as a Scaffold for Structurally Characterized trans [H−Ni−PR2] and trans [R2P−Ni−PR2] Complexes

The addition of PPh₂H, PPhMeH, PPhH₂, P(para-Tol)H₂, PMesH₂ and PH₃ to the two-coordinate Ni⁰ N-heterocyclic carbene species [Ni(NHC)₂] (NHC=IiPr₂, IMe₄, IEt₂Me₂) affords a series of mononuclear, terminal phosphido nickel complexes. Structural characterisation of nine of these compounds shows that they have unusual trans [H−Ni−PR₂] or novel trans [R₂P−Ni−PR₂] geometries. The bis-phosphido complexes are more accessible when smaller NHCs (IMe₄>IEt₂Me₂>IiPr₂) and phosphines are employed. P−P activation of the diphosphines R₂P−PR₂ (R₂=Ph₂, PhMe) provides an alternative route to some of the [Ni(NHC)₂(PR₂)₂] complexes. DFT calculations capture these trends with P−H bond activation proceeding from unconventional phosphine adducts in which the H substituent bridges the Ni−P bond. P−P bond activation from [Ni(NHC)₂(Ph₂P−PPh₂)] adducts proceeds with computed barriers below 10 kcal mol⁻¹. The ability of the [Ni(NHC)₂] moiety to afford isolable terminal phosphido products reflects the stability of the Ni−NHC bond that prevents ligand dissociation and onward reaction.     

Photosensitized DNA cleavage promoted by amino acids

A novel class of DNA cleavage agents are reported that derive activity from amino acids tethered to a photoactive intercalator.     

1,2,4,5‐Tetrazines vs. Carboxylic Acid Dimers: Molecular Chemistry vs. Supramolecular Chemistry

The structures of six new tetrazines have been determined and their molecular packing has been compared to the supermolecular architecture observed in related carboxylic acid dimers. In the tetrazines, covalent N? N bonds are considered to replace the intermolecular O? H???O hydrogen bonds of the carboxylic acids. In the systems investigated, it is apparent that, in the majority of cases, the covalent six‐membered ring of the tetrazine is an appropriate replacement for the carboxylic acid synthon. This apparent interplay between molecular and supramolecular units may have applications in the crystal engineering of new materials.     

Selective cleavage of P-N bonds and the conversion of rhodium N-pyrrolyl phosphine complexes into diphosphoxane-bridged dimers

Rhodium(I) complexes trans-[RhCl(CO)(PR(2)[NC(4)H(3)C(O)Me-2])(2)] (R = Ph, NC(4)H(4)) react with water to give the diphosphoxane-bridged dimers [Rh(2)Cl(2)(CO)(2)(mu-PR(2)OPR(2))(2)] following cleavage of the P-N bonds to the 2-acetyl-N-pyrrolyl groups. The two dimers have been crystallographically characterized and show a number of structural differences, with the PPh(2)OPPh(2) compound possessing semibridging chloride and carbonyl ligands whereas the P(NC(4)H(4))(2)OP(NC(4)H(4))(2) compound contains only terminal chlorides and carbonyls. No evidence for cleavage of the P-N bonds involving the unfunctionalized N-pyrrolyl groups in trans-[RhCl(CO)(P[NC(4)H(4)](2)[NC(4)H(3)C(O)Me-2])(2)] was observed.