Argentomctric coulomelric titration of thioacetamide

The coulometric determination of thioacetamide (TAA) with electrogenerated silver is described. The titration is done in a solution 0.1M in both ammonia and sodium hydroxide, and the end-point is detected potentiometncally with a silver-silver sulphide electrode. On repeat analyses of approx. 2-mg samples of TAA an average error of -04% (relative standard deviation 0.25%) was obtained. Important steps in the procedure include cleaning the silver generating electrode in nitric acid before each titration, purging well with nitrogen to remove oxygen, and not using too large a sample.     

Mesoporous silica-supported uranyl: synthesis and photoreactivity

A mesoporous silica-supported uranyl material (U(aq)O(2)(2+)-silica) was prepared by a co-condensation method. Our approach involves an I(-)M(+)S(-) scheme, where the electrostatic interaction between the anionic inorganic precursor (I(-)), surfactant (S(-)), and cationic mediator (M(+)) provides the basis for the stability of the composite material. The synthesis was carried out under acidic conditions, where the anionic sodium dodecyl sulfate provided the template for the uranyl cation and silicate to condense. Excitation with visible or near-UV light of aqueous suspensions of U(aq)O(2)(2+)-silica generates an excited state that decays with k(0) = 1.5 x 10(4) s(-1). The reaction of the excited state with aliphatic alcohols exhibits kinetic saturation and concentration-dependent kinetic isotope effects. For 2-propanol, the value of k(C)3(H)7(OH)/k(C)()3(D)7(OH) decreases from 2.0 at low alcohol concentrations to 1.0 in the saturation regime at high alcohol concentrations. Taken together, the data describe a kinetic system controlled by chemical reaction at one extreme and diffusion at the other. At low [alcohol], the second-order rate constants for the reaction of silica-U(aq)O(2)(2+) with methanol, 2-propanol, 2-butanol, and 2-pentanol are comparable to the rate constants obtained for these alcohols in homogeneous aqueous solutions containing H(3)PO(4). Under slow steady-state photolysis in O(2)-saturated suspensions, U(aq)O(2)(2+)-silica acts as a photocatalyst for the oxidation of alcohols with O(2).     

Syntheses of gold-manganese and gold-rhenium clusters, [(Ph3PAu)3M(CO)4] and [(Ph3PAu)4M(CO)4] (M = Mn, Re), and the crystal structure of [(Ph3PAu)4Mn(CO)4]BF4

The specific additions of one, three or four Ph₃PAu groups to [M(CO)₅]⁻ (M=Mn, Re) are described. Thus [M(CO)₅] ⁻ in THF reacts with [(Ph₃PAu)₃O]BF₄ to give [(Ph₃PAu)₄Mn(CO)₄]BF₄. An X-ray crystal structure of the M = Mn example shows the cation to have a trigonal bipyramidal Au₄Mn core with the Mn in an equatorial site. The previously known neutral (Ph₃PAu)₃M(CO)₄ clusters are formed by addition of two Ph₃PAu groups, using the mixed reagent [(Ph₃PAu) ₃O]BF₄/[ppn][Co(CO)₄], to Ph₃PAuM(CO)₅, which itself is readily prepared from [M(CO)₅]⁻ and Ph₃PAuCl.     

Synthesis and Characterisation of a Thiocarbonyl containing Osmium Cluster

Reaction of CS₂ with H₂Os₃(CO)₈(MeCN)S in cyclohexane yields a product H₂Os₃(CO)₇(CS)S₂. this has been characterised by NMR and mass spectroscopy, and by X-ray analysis, and has been shown to contain a terminal thiocarbonyl ligand.     

Mono-cyclopentadienyl complexes of lanthanum: synthesis and characterization of anilido derivatives

Use of the bulky cyclopentadienyl ligand [η⁵-C₅H₂(SiMe₃)₃-1,2,4]⁻ (Cp?) allows for the isolation of monomeric, mono-ring lanthanide species. As previously reported, (Cp?)K reacts with LaI₃(THF)₄ (THF=tetrahydrofuran) in THF/pyridine to form the mono-ring complex (Cp?)LaI₂(py)₃ (1) (py=pyridine); a minor product of this reaction is the bis-ring species (Cp?)₂LaI(py) (2). The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual intramolecular contacts. Addition of one equiv of KNHAr (Ar=2,6-ⁱPr₂C₆H₃) to complex 1 in THF generates the mono-anilido compound (Cp?)LaI(NHAr)(THF)₂ (3), which may be converted to the more stable pyridine adduct (Cp?)LaI(NHAr)(py)₂ (4) by the addition of pyridine to 3. An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group oriented trans to the iodide atom (N1-La1-I1=123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar C_s-symmetric structure with a slightly increased N_anilido-La-I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct (Cp?)LaI₂(bipy)(py) (5), in which the two iodide atoms are cis-disposed, yields the mono-anilido complex (Cp?)LaI(NHAr)(bipy)(py) (6) (bipy=2,2^′-bipyridine); this compound may also be prepared by the addition of bipy to (Cp?)LaI(NHAr)(py)₂ (4). An X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp? ring, an iodide, an anilido group, a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis fashion (N_anilido-La-I=111.2(2)°), resulting in a complex with C₁ symmetry. Both (Cp?)LaI(NHAr)(py)₂ (4) and (Cp?)LaI(NHAr)(bipy)(py) (6) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.     

Electrochemical Detection of MS2 Phage Using a Bead‐based Immunoassay and a NanoIDA

A microbead based sandwich immunoassay for MS2 bacteriophage was developed using an interdigitated array (IDA) electrode with nanoscale dimensions (220 nm electrode width, 620 nm gap). The IDA was fabricated using an electron beam lithographic lift‐off technique. After an antibody‐assisted capture of MS2 using paramagnetic microbeads, a β‐galactosidase labeled secondary antibody was used to convert p‐aminophenyl‐β‐D ‐galactopyranoside (PAPG) into the redox active p‐aminophenol (PAP). Amperometric detection of PAP with IDA electrodes at +300 and ?200 mV vs. a Ag/AgCl reference electrode was used to measure the result, detecting MS2 concentrations as low as 10 ng/mL.     

Cluster chemistry: XXXIX. Gold—ruthenium clusters with sulphur ligands: Synthesis and structure of HRu3Au(μ3-S)(CO)9(PPh3), Ru3Au(μ3-SBut)(CO)9(PPh3) and Ru3Au2(μ3-S)(CO)9(PPh3)2

H₂Ru₃(μ₃-S)(CO)₉ is deprotonated by K[HBBu^s₃] to give cluster anions which react with [O{Au(PPh₃)}₃]⁺ or with AuCl(PPh₃)/T1⁺ to give HRu₃Au(μ₃-S)(CO)₉(PPh₃) (1) and Ru₃Au₂(μ₃-S)(CO)₉(PPh₃)₂ (3). A similar sequence with HRu₃(μ₃-SBu^t)(CO)₉ leads to Ru₃Au(μ₃-SBu^t)(CO)₉(PPh₃) (2) as the main product although some 1 also forms, indicating SC cleavage competes with deprotonation of HRu₃(μ₃-SBu^t)(CO)₉ by [HBBu^s₃]^?. The X-ray crystal structures of 1, 2 and 3 are described; (1) and (2) have “butterfly” AuRu₃ cores with markedly different hinge angles of 119 and 148° respectively, while 3 has a trigonal-bipyramidal Au₂Ru₃ skeleton. All three clusters have the sulphur atom symmetrically bridging the Ru₃ triangular face.     

Synthesis of a novel prostaglandin H2(pgH2) analogue

We describe a five-step synthesis of a PGH₂ analogue from (R)-glyceraldehyde acetonide via formation of 1,2(S)-0-isopropylidene-hex-3(E)-en-5-one, conjugate addition of prostanoid C₁₃- C₂₀ side-chain as the cuprate with C₁-C₇ side-chain used to quench the resultant enolate, and finaily acid-catalysed ketal exchange to provide the desired analogue.     

Negative ion photoelectron spectroscopy of solvated electron cluster anions, (H2O) n − and (NH3) n −

The photodetachment spectra of (H₂O) _n ^=2?69/? and (NH₃) _n ^=41?1100/? have been recorded, and vertical detachment energies (VDEs) were obtained from the spectra. For both systems, the cluster anion VDEs increase smoothly with increasing sizes and most species plot linearly withn ^?1/3, extrapolating to a VDE (n=∞) value which is very close to the photoelectric threshold energy for the corresponding condensed phase solvated electron system. The linear extrapolation of this data to the analogous condensed phase property suggests that these cluster anions are gas phase counterparts to solvated electrons, i.e. they are embryonic forms of hydrated and ammoniated electrons which mature with increasing cluster size toward condensed phase solvated electrons.     

Tuning the singlet oxygen quantum yield of near-IR-absorbing porphyrazines

We report the quantum yields for singlet oxygen production by a series of porphyrazines (pz) of the form M[pz(An;B4-n)] (Scheme 1), where the peripheral substituent A is [S-R]2 with R = (CH2CH2O)3H, B is a fused alpha,alpha'-dialkoxybenzo group and M = 2H, Mg or Zn. These compounds show intense near-IR absorbance/emission (longest wavelength emission, approximately 830 nm). Their solubilities vary with R, whereas their optical properties do not. We show that singlet oxygen sensitization by these luminescent compounds can be "tuned" from essentially off to on by varying n and selection among M = 2H, Mg or Zn. The quantum yields vary ca 60-fold within the set of compounds studied, from phidelta = 0.007 for compound 3 to phidelta = approximately 0.4 for compound 11.