Structural aspects, IR study, and molecular photophysics of the cumulene-bridged complexes with rhenium(I), ruthenium(II), and osmium(II) centers

The synthesis of a series of ReI, RuII, and OsII complexes that contain rigid polyphosphine/cumulene spacers is reported here. These cumulenic ligands, namely, 1,1',3,3'-tetrakis(diphenylphosphino)allene (C3P4) and 1,1',4,4'-tetrakis(diphenylphosphino)cumulene (C4P4), utilize diphenylphosphino linkage components to coordinate to the metal-polypyridyl or metal-carbonyl units. Characterization of all mono-, homo-, and heterobimetallic complexes is achieved using 31P(1H) NMR, IR, and fast atom bombardment mass spectroscopy (FAB/MS) and elemental analysis. The two ReI homobimetallic complexes were also characterized by single-crystal X-ray structure determination, which provided the structural evidence of a 90 degrees rotation between the C3 and C4 adducts causing a change in the electrochemical behavior. The ground-state electronic absorption and redox interactions, along with the excited-state photophysical characteristics, are also explored. Electrochemical studies showed that an increase in the carbon chain length resulted in a greater amount of sigma-donation from the ligand to the metal centers, as well as a greater amount of electronic communication between the metal termini of the bimetallic species. The electronic absorption and emission spectra of the new complexes were also determined and characterized. The lifetimes of the excited-state luminescence of the ReI mono- and homobimetallic complexes were found to be an order of magnitude shorter than the lifetimes of the heterobimetallic complexes containing the RuII and OsII moieties. Excited-state energy transfer was observed from the higher MLCT excited state of the ReI centers to the lower energy MLCT excited state of the RuII and OsII centers on the following basis: no ReI-based emission was detected in the steady-state emission measurements, the time-resolved decay traces were fitted to only single-exponential decays, and the quantum yields were identical for each compound at two different excitation wavelengths where different percentages of the metal-based chromophores were excited.     

Vibrational spectroscopy of Cs+ solvated by methylamine

We report the vibrational spectra of the cluster ions Cs⁺(CH₃NH₂)_N, N=3–22. Bands in the 1015–1050 cm^?1 region of the infrared are due to the v8 mode (CN stretch) of methylamine molecules displaying different degrees of interaction with the central ion. Monte Carlo simulations of the solvated Cs⁺ ion indicate that nine methylamine molecules fill the first solvation shell of Cs⁺ and that possible rearrangements in cluster structure occur at N=14?15. No absorptions due to bulklike methylamine molecules are observed through N=22.     

Radiometric flow injection analysis with an ASIA (Ismatec) analyzer

Radiometric Flow Injection Analysis of a radioactive (¹³¹I) sample is described. For analysis an ASIA (Ismatec) analyzer with a NaI (Tl) scintillation detector was used.     

Structure elucidation of unsaturated fatty acids after vicinal hydroxylation of the double bonds by negative electrospray ionisation low-energy tandem mass spectrometry

A method for determining the positions of double bonds in unsaturated fatty acids by use of negative electrospray ionisation low-energy tandem mass spectrometry is described. First, a vicinal hydroxylation of the double bonds of mono- and poly-unsaturated fatty acids was performed. Low-energy collision activation dissociation of the deprotonated molecules produced structurally informative ions formed by a-cleavages relative to the hydroxyl groups. Abundant fragment ions that confirmed the positions of all hydroxyl groups, and thus the positions of the double bonds in the native fatty acids, were observed in the spectra of derivatised mono-, di-, and tri-unsaturated fatty acids. Two types of ions were observed, called [alpha'(n)](-) and [alpha(n)](-). The letter n indicates the positions of the hydroxyl groups. The structurally diagnostic ions [alpha'(n)](-) were produced by cleavages distal to the hydroxyl-groups with the charge retained on the carboxylate. [alpha'(n)](-) ions originating from all hydroxyl-groups were observed in the spectra of modified mono-, di-, and tri-unsaturated fatty acids. Initial proton transfer of a hydroxyl proton to the carboxylate with subsequent cleavages proximal to the hydroxyl groups, relative to the carboxylate, resulted in the two structurally diagnostic [alpha(n)](-) ions. In hydroxylated fatty acids having two or more double bonds in their native structure, [alpha(n)](-) ions originating only from the two final hydroxyl-groups were observed. The formation of all ions of [alpha'(n)](-) and [alpha(n)](-) type can be rationalised by a six-membered transition state. Hydroxylated deprotonated tetra-, penta-, and hexa-unsaturated fatty acids also produced [alpha'(n)](-) ions indicating the positions of most of the hydroxyl-groups, whereas the [alpha(n)](-) ions were observed as described above. The method described offers a simple approach to the determination of the positions of double bonds in unsaturated fatty acids, and is an alternative to utilising di-lithiated fatty acids. The method should also be applicable when fatty acids are constituents of more complex molecules such as phospholipids.     

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose (HMHEC) solutions are investigated experimentally. Weak shear thickening at intermediate shear rates takes place for HMHEC at moderate concentrations and becomes more significant at lower temperatures. While this amphiphilic polymer in surfactant-free solution does not turn turbid by heating to 95 degrees C, its mixture with nonionic surfactant shows a lower cloud point temperature than does a pure surfactant solution. For some mixture cases, phase separation takes place at temperatures as low as 2 degrees C. The drop of cloud point temperature is attributed to an additional attractive interaction between mixed micelles via chain bridging. With increasing temperature, the viscosity of an HMHEC-surfactant mixture in aqueous solution first decreases but then rises considerably until around the cloud point. The observed viscosity increase can be explained by the interchain association because of micellar aggregation.     

Vicinal hydroxylation of unsaturated fatty acids for structural characterization of intact neutral phospholipids by negative electrospray ionization tandem quadrupole mass spectrometry

We report a novel method allowing the complete structural characterization of intact species of the phospholipid classes phosphatidylcholine and phosphatidylethanolamine by utilizing negative electrospray ionization quadrupole tandem mass spectrometry (MS/MS). Information on the molecular weight of the intact phospholipid species, the class to which it belongs, the molecular mass of the fatty acid substituents and their regioisomerism, is easily revealed by MS/MS. Throughout our investigations the R2COO- ions were more abundant than the R1COO- ions, and this observation is used for regioisomeric assignment of the two fatty acids. However, for phospholipid species containing an unsaturated fatty acid, information on the position of the double bond is not achieved in this way. By converting the olefinic sites to their 1,2-dihydroxylated derivatives, information on the position of the hydroxyl groups (and hence of the double bond) is obtained by performing a second MS/MS experiment. Thus, a complete structural characterization of intact phosphatidylcholine and phosphatidylethanolamine species is obtained by performing these two MS/MS experiments. In order to ensure structural distinction of isobaric species, a number of phosphatidylethanolamine and phosphatidylcholine species were synthesized from lyso-phosphatidylcholine and analyzed by the present method. The applicability of the method to real samples is also demonstrated by the complete structural elucidation of the two phosphatidylcholine species 16:0/18:1Delta9 and 16:0/18:1Delta11 from egg yolk.     

Profiling mechanisms of alkane hydroxylase activity in vivo using the diagnostic substrate norcarane

Mechanistically informative chemical probes are used to characterize the activity of functional alkane hydroxylases in whole cells. Norcarane is a substrate used to reveal the lifetime of radical intermediates formed during alkane oxidation. Results from oxidations of this probe with organisms that contain the two most prevalent medium-chain-length alkane-oxidizing metalloenzymes, alkane omega-monooxygenase (AlkB) and cytochrome P450 (CYP), are reported. The results--radical lifetimes of 1-7 ns for AlkB and less than 100 ps for CYP--indicate that these two classes of enzymes are mechanistically distinguishable and that whole-cell mechanistic assays can identify the active hydroxylase. The oxidation of norcarane by several recently isolated strains (Hydrocarboniphaga effusa AP103, rJ4, and rJ5, whose alkane-oxidizing enzymes have not yet been identified) is also reported. Radical lifetimes of 1-3 ns are observed, consistent with these organisms containing an AlkB-like enzyme and inconsistent with their employing a CYP-like enzyme for growth on hydrocarbons.     

Sequence comparison and environmental adaptation of a bacterial endonuclease

The periplasmic/extracellular bacterial enzyme endonuclease I was chosen as a model system to identify features that might be responsible for temperature- and salt adaptation. A statistical study of amino acid sequence properties belonging to endonuclease I enzymes from three mesophilic habitats (non-marine, brackish water and marine), and three marine temperature groups (psychrophile, intermediate and mesophile) has been conducted. Ten new endonuclease I genes have been sequenced in order to increase the sample size. A bioinformatical method of property dependent statistical analysis of alignments has been applied. To our knowledge this is the first time these methods have been used in order to investigate environmental adaptation of enzymes. Adaptation to low temperature seems to involve increased surface isoelectric point and hydrophobicity in contrast to salt adaptation in which the isoelectric point and hydrophobicity at the surface decreases. Redistribution of charge and hydrophobicity might be the most important signature for cold adaptation and salt adaptation of this enzyme class. The results indicate that general trends of adaptation are possible to elucidate from the amino acid sequences. Also in this paper a new scale of stratified B-factors, derived from the Protein Data Bank, is presented.     

Polydimethylsiloxane‐coated partitioning sample collection device for the precise quantification of polycyclic aromatic hydrocarbons in air

A novel partitioning collection device comprising a glass cartridge packed with poly(dimethylsiloxane)‐coated macroporous silica particles was developed for the precise quantification of polycyclic aromatic hydrocarbons in air. The analyte collection and elution performances achieved using different amounts of poly(dimethylsiloxane) coating were quantitatively evaluated. The sample retention power increased with increasing the coating, and more than 250 L of air could be collected without analyte breakthrough at a sampling temperature of 35°C. During the air collection, the moisture in the air was not retained on the particles due to the hydrophobic surface of the sorbent. A complete and rapid elution of the collected analytes from the device was accomplished by the passage of only 10 mL of acetone with ultrasonication for 1 min. The proposed method was successfully applied for the determination of airborne polycyclic aromatic hydrocarbons in tunnel air.