Iridium luminophore complexes for unimolecular oxygen sensors

In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)(2)(vacac), 1, Ir(ppy)(2)(vacac), 2, fac-Ir(ppy)(2)(vppy), 3, and mer-Ir(ppy)(2)(vppy), 4, where C6 = Coumarin 6, vacac = allylacetoacetate, ppy = 2-phenylpyridine, and vppy = 2-(4-vinylphenyl)pyridine, all have pendent vinyl or allyl groups for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements, elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray crystallography, and a series of 1-D ((1)H, (13)C) and 2-D ((1)H-(1)H, (1)H-(13)C) NMR experiments were used to resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and largest quantum efficiencies in solution (tau = 6.0 micros, phi = 0.22 for 1; tau = 0.4 micros, phi = 0.2 for 3) and, as result, are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies.     

Mass spectra of 3(2H)-cinnolinone and 2-substituted derivatives

The mass spectrum of 3(2H)-cinnolinone indicates that it undergoes fragmentation in a fashion similar to other heterocyclic systems containing two vicinal nitrogens. The initial fragmentation, loss of CO, gives a 1H-indazole radical cation, as was shown by deuterium labelling and metastable ion spectra. Four 2-substituted-3(2H)-cinnolinones were also studied and it was found that their fragmentation patterns are highly influenced by the substituent groups.     

Multipesticide residue method for fruits and vegetables: California Department of Food and Agriculture

Summary This procedure describes the CDFA method for multipesticide residue analysis of fresh fruits and vegetables. An aliquot of chopped sample is blended with acetonitrile. The resulting aqueous acetonitrile extract is filtered and cleaned up via reverse phase solid phase extraction apparatus. The pH of the filtrate is adjusted to neutral using phosphate buffer and the acetonitrile layer is separated from the aqueous layer by a salting out process. An aliquot of the acetonitrile layer is concentrated with a K-D evaporator by forming an azeotrope with n-hexane. The prepared sample is assayed for pesticide residues using GLC and HPLC. The performance of this method was evaluated by fortifying 6 representative fruits and vegetables with 7 chlorinated hydrocarbons, 7 organophosphate and 7 N-methylcarbamate pesticides at 0.1–0.2 ppm. No matrix interference was observed and the recovery of residues varied among different samples as well as different pesticides. Chlorothalonil results varied widely with irreproducible recoveries. In general, the method appears to be fast, rugged, and able to detect routinely at the 0.01 ppm level.     

A novel method for measuring initial-burst chemiluminescence in a liquid scintillation counter using the myeloperoxidase-H20Cl− reaction

These studies show that there is an initial quantifiable burst of luminol-enhanced CL associated with the interaction of MPO with H₂O₂ and Cl^?. They also confirm that the reaction is H₂O₂-concentration dependent (2). The novel method for quantifying initial-burst CL in a liquid scintillation counter introduced in this study provides many advantages over previous CL studies using the same counter, as noted above. This method provides for more efficient representation of CL associated with the MPO reaction, and allows for valid conclusions concerning the drug effects on this reaction. The ability to “see” the initial part of the reaction may also allow kinetic analysis of this (and other) enzyme CL reactions.     

Organic-free water for total organic carbon determination

Commercially available “organic-free” water is compared with water cleaned by ultraviolet (u.v.) radiation for applicability to total organic carbon determinations. The u.v.-treated water contains an organic carbon concentration less than the detection limit of the method used (0.056 mg C l^-1). The commercially processed water lacks the consistently low blank level required for use in TOC determinations.     

A recoverable enzymatic microgel based on biomolecular recognition

The enzyme beta-galactosidase has been immobilized through incorporation into a selectively soluble microgel, prepared from DNA, biotinylated peptide nucleic acid (PNA), and the protein avidin. The enzyme was conjugated to avidin, allowing it to be integrated directly into the microgel network. Efficient hydrolysis of a small-molecule substrate occurred at 37 degrees , but cooling and centrifuging led to precipitation of the microgels and product separation. The microgels were then reconstituted by adding fresh buffer and shaking. The enzymatic activity was completely recovered through repeated cycles. This method should be generalizable to a wide variety of other enzymes and substrates.     

2,7-DIIODO-9-DIAZOFLUORENE: A POTENTIAL REAGENT FOR PHOTOLABELING

Abstract— The photochemistry of 2,7-diiodo-9-diazofiuorene was studied to examine its suitability as a photolabeling agent of hydrophobic sites in biological assemblies. Irradiation of the diazo compound generates 2,7-diiodofluorenylidene. The carbene was detected by laser transient absorption spectroscopy and characterized by its chemical and physical properties. Like fluorenylidene, the triplet is the ground state of 2,7-diiodofluorenylidene. However, the substituted triplet carbene does not reform its higher energy, electrophilic singlet state fast enough for reactions of the upper state to compete with the irreversible consumption of the triplet. Thus, the products from the reactions of diiodofluorenylidene contain a higher proportion of those characteristic of the triplet carbene than occurs in the reactions of fluorenylidene. This will limit the utility of this diazocompound as a photolabeling agent.     

Comparison of the X-ray crystal structures of four closely related Mo(CO)5(R2PXR′) (R2 = OCH2CMe2CH2O, XR′ = S-2-Pr, NHC6H4-4-Me; R2 = Ph2, XR′ = NHC6H4-2-Me, OC6H4-4-SMe) complexes

The X-ray crystal structures of four closely related Mo(CO)₅(R₂PXR) (R₂ = OCH₂CMe₂CH₂O, XR = S-2-Pr, NHC₆H₄-4-Me; R₂ = Ph₂, XR = NHC₆H₄-2-Me, OC₆H₄-4-SMe) complexes have been determined. The R₂PXR ligands are oriented so that the P—X bond and one of the Mo—C bonds are nearly eclipsed. This results in the distortion of the octahedral coordination geometry via tilting of the Mo(CO)₅ group away from the XR group. As observed in related complexes, the Mo—C bond of the carbonyl trans to the phosphorus-donor group is shorter than are the Mo—C bonds of the carbonyls trans to carbonyls. In contrast, no significant differences were observed between the Mo—C bonds of carbonyls trans to phosphites and the Mo—C bonds of carbonyls trans to phosphinites. The conformations of the 1,3,2-dioxaphosphorinanes were distorted chairs with the P end of the chair significantly flattened relative to the seat of the chair. This conformation is similar to that which has been observed for 1,3,2-dioxaphosphorinanes in other transition metal complexes.     

X-ray crystal structures ofcis-bis(diphenylphosphinamide)tetracarbonylmolybdenum(0) andtrans-bis(N-methyl diphenylphosphinamide)tetracarbonylmolybdenum(0)

The X-ray crystal structures ofcis-Mo(CO)₄(Ph₂PNH₂)₂,I, andtrans-Mo(CO)₄(Ph₂PNHMe)₂,II, are presented. ComplexI crystallizes in the monoclinic space groupP2₁/c(a=13.433(1),b=12.2719(8),c=17.318(2)Å;=109.79(1)°;V=2686.1(8)ų;Z=4). ComplexII crystallizes in the triclinic space groupP¯1 (a=6.9986(8),b=10.328(1),c=11.241(2)Å,=107.58(1)°,=91.76(1)°, =101.28(1)°,V=756.1(4)ų,Z=1). The molybdenum coordination geometry in each complex is a slightly distorted octahedron. The molybdenum-carbon bond lengths for the carbonyls trans to phosphorus in complexI are shorter than those the carbonyls trans to other carbonyls. The average molybdenum-phosphorus distance inI (2.525(5)Å) is similar to those in other diphenylphosphinamide complexes and longer than the molybdenum-phosphorus distance inII in 2.4585(7)Å). The distance between two nitrogen atoms incis Mo(CO)₄(Ph₂PNH₂)₂ (3.74(3)Å) is significantly larger than the sum of their van der Waals radii (3.10 Å) indicating that the two nitrogens are not hydrogen bonded.     

Ultraviolet Photolysis Studies on XeO4 in Noble‐Gas and F2 Matrices and the Formation and Characterization of a New XeVIII Oxide, (η2‐O2)XeO3

The photolytic behavior of the thermochemically unstable xenon(VIII) oxide XeO₄ was investigated by UV irradiation in noble‐gas and F₂ matrices. Photolysis of Xe¹⁶O₄ or Xe¹⁸O₄ in noble‐gas matrices at 365 nm yielded XeO₃ and a new xenon(VIII) oxide, namely, (η²‐O₂)XeO₃, which, along with XeO₄, was characterized by matrix‐isolation IR spectroscopy and quantum‐chemical calculations. Calculations of the UV spectrum showed that the photodecomposition is induced by an n→σ* transition, but the nature of the excitation differs when different light sources are used. There is strong evidence for the formation of mobile ¹D excited O atoms in the case of excitation at 365 nm, which led to the formation of (η²‐O₂)XeO₃ by reaction with XeO₄. Matrix‐isolation IR spectroscopy in Ne and Ar matrices afforded the natural‐abundance xenon isotopic pattern for the ν₃(T₂) stretching mode of Xe¹⁶O₄, and ¹⁸O enrichment provided the ¹⁶O/¹⁸O isotopic shifts of XeO₄ and (η²‐O₂)XeO₃.