CHEMILUMINESCENCE AND ENERGY TRANSFER FROM SINGLET OXYGEN PAIRS

Abstract— Chemiluminescence and photochemiluminescence of systems generating excited (singlet) molecular oxygen has been studied at low temperature in fluid media. A possible interpretation is proposed: that dimers of singlet oxygen are directly or indirectly responsible for the observed emission, the species [¹δg +¹σg⁺] predominating. Energy transfer to a fluorescent molecule is possible only when conditions of spectral overlap, required for transfer by inductive resonance, are fulfilled. Evidence is also presented for the formation of a transient complex between oxygen and a sensitiser or acceptor molecule [S…O₂], which is the precursor of singlet oxygen in these systems. However, other possible mechanisms cannot be excluded.     

Thermostability of landscape phage probes

Immunoassays have traditionally relied on antibodies as diagnostic probes. Their use outside of a laboratory, however, may be problematic because antibodies are often unstable in severe environmental conditions. Environmental monitoring requires thermostable probes, such as landscape phage, that carry thousands of foreign peptides on their surfaces, are superior to antibodies, and can operate in non-controlled conditions. While parent wild-type phage are known to be extremely stable in various media at high temperatures, no work has been done to demonstrate the stability of landscape phage probes. We examined the thermostability of a landscape phage probe and a monoclonal antibody specific for -galactosidase in parallel in an enzyme-linked immunosorbent assay (ELISA) format. They were both stable for greater than six months at room temperature, but at higher temperatures the antibody degraded more rapidly than the phage probe. Phage retained detectable binding ability for more than six weeks at 63 °C, and three days at 76 °C. The activation energy of phage degradation was determined to be 1.34×10⁵ J/mol. These results confirm that phage probes are highly thermostable and can function even after exposure to high temperatures during shipping, storage and operation.     

Investigating bidentate and tridentate carbamoylmethylphosphine oxide ligand interactions with rare-Earth elements using electrospray ionization quadrupole ion trap mass spectrometry

Electrospray ionization (ESI) quadrupole ion trap mass spectrometry (QIT-MS) and collisionally activated dissociation (CAD) were used to evaluate the rare-earth binding properties of two hydrophobic carbamoylmethylphosphine oxide (CMPO) ligands, the normal bidentate variety, (t-BuC6H4)2P(O)CH2C(O)N(i-Bu)2 (A), a new potentially tridentate extractant, (t-BuC6H4)2P(O)CH[CH2C(O)N(i-Bu)2]C(O)N(i-Bu)2 (B), and tributyl phosphate. The mass spectral results obtained from analysis of 1% HNO3/methanol solution containing the ligands and dissolved lanthanide salts reveal that the favorable stoichiometries of the ligand/metal/nitrate complexes are 2:1:2 for the bidentate ligand A, 1:1:2 for the tridentate ligand B, and 3:1:2 for the monodentate tributyl phosphate. These observed stoichiometries correlate with the number of available binding sites on each ligand as well as with potential steric effects. Energy-variable collisionally activated dissociation experiments showed that for the 2:1:2 complexes involving ligand A or B, as the ionic radius of the bound metal decreased, the removal of nitric acid required less energy and resulted in less extensive spontaneous solvent coordination. This experimental trend suggests that, as the ionic radius of the lanthanide ion decreases, a pair of the carbamoylmethylphosphine ligands is able to more completely solvate the bound metal ion thereby weakening the nitrate-metal interaction.     

Covalent attachment of a nickel nitrilotriacetic acid group to a germanium attenuated total reflectance element

The surface of a germanium internal reflectance element (IRE) was modified to bind 6X-histidine (his)-tagged biomolecules. The step-by-step surface modification was monitored via single-pass attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR). Initially an adlayer of 7-octenyltrimethoxysilane (7-OTMS) was formed on the Ge crystal through the surface hydroxyl groups, which were produced via ozonolysis of the Ge surface. The vinyl moiety of 7-OTMS was oxidized to a carboxylic acid, which was activated by 1,1'-carbonydiimidazole (CDI) to produce a labile imidazole. The labile imidazole that resulted from the CDI coupling was then displaced by the primary amine of nitrilotriacetic acid (NTA). Nickel sulfate was added to the system, and it coordinated with the three carbonyl groups and the nitrogen on NTA, thus leaving the ability of Ni to coordinate with two adjacent histidine residues. Binding of his-tagged biotin to nickel nitrilotriacetic acid (Ni-NTA) was observed by ATR-FT-IR spectroscopy. The surface modification method presented in this paper had minimal nonspecific binding, the Ni-NTA surface was reusable if stored properly, and complete removal of the organic surface was achievable.     

Multiple isotope effect study of the acid-catalyzed hydrolysis of methyl formate

Multiple isotope effects have been measured for the acid-catalyzed hydrolysis of methyl formate in 0.5 M HCl at 20 degrees C. The isotope effects in the present investigation include the carbonyl carbon (13k = 1.028 +/- 0.001), the carbonyl oxygen (18k = 0.9945 +/- 0.0009), the nucleophile oxygen (18k = 0.995 +/- 0.001), and the formyl hydrogen ((D)k = 0.81 +/- 0.02). Determination of the carbonyl carbon, carbonyl oxygen, and formyl hydrogen isotope effects was performed via isotopic analysis of residual substrate. However, determination of the oxygen nucleophile isotope effect required analysis of the oxygen atoms of the product (formic acid), which exchange with the solvent (water) under acid conditions. This necessitated measurement of the rate of exchange of these oxygen atoms under the conditions for hydrolysis (k(ex) = 0.0723 min(-1)) and correction of the raw isotope ratios measured during the nucleophile-O isotope effect experiment. These results, along with the previously reported isotope effect for the leaving oxygen (18k = 1.0009) and the ratio of the rate of hydrolysis to that of exchange of the carbonyl oxygen with water (k(h)/k(ex) = 11.3), give a detailed picture of the transition-state structure for the reaction.     

Photoinduced axial ligation and deligation dynamics of nonplanar nickel dodecaarylporphyrins

The ground- and excited-state metal-ligand dynamics of nonplanar nickel(II) 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (NiDPP) and two fluorinated analogues (NiF(20)DPP and NiF(28)DPP) have been investigated using static and time-resolved absorption spectroscopy in toluene and in ligating media that differ in basicity, aromaticity, and steric encumbrance. Because of the electronic and steric consequences of nonplanarity, NiDPP does not bind axial ligands in the ground state, but metal coordination does occur after photoexcitation with multistep dynamics that depend on the properties of the ligand. Following the structural relaxations that occur in all nickel porphyrins within approximately 10 ps, ligand binding to photoexcited NiDPP is progressively longer in pyridine, piperidine, and 3,5-lutidine (25-100 ps) but does not occur at all in 2,6-lutidine in which the ligating nitrogen is sterically encumbered. The transient intermediate that is formed, which nominally could be either a five- or six-coordinate species, also has a ligand-dependent lifetime (200-550 ps). Decay of this intermediate occurs partially via ligand release to re-form the uncoordinated species, in competition with binding of the second axial ligand and/or conformational/electronic relaxations (of a six-coordinate intermediate) to give the ground state of the bis-ligated photoproduct. The finding that the photoproduct channel principally depends on ligand characteristics along with the time-evolving spectra suggests that the transient intermediate may involve a five-coordinate species. In contrast to NiDPP, the fluorinated analogues NiF(20)DPP and NiF(28)DPP do coordinate axial ligands in the ground state but eject them after photoexcitation. Collectively, these results demonstrate the sensitivity with which the electronic and structural characteristics of the macrocycle, substituents, and solvent (ligands) can govern the photophysical and photochemical properties of nonplanar porphyrins and open new avenues for exploring photoinduced ligand association and dissociation behavior.     

Observation and interpretation of HH coupling in 1H187Os satellite NMR spectra

The single hydride resonance observed for each of the compounds H₃Os₃(CO)₉CX (X = OMe, Br, H) has one set of ¹⁸⁷Os satellites which are further split into doublets by HH coupling. The implications of this observation for structural assignments based on ¹⁸⁷Os satellites are discussed.     

A strain-promoted [3 + 2] azide-alkyne cycloaddition for covalent modification of biomolecules in living systems

Selective chemical reactions that are orthogonal to the diverse functionality of biological systems have become important tools in the field of chemical biology. Two notable examples are the Staudinger ligation of azides and phosphines and the Cu(I)-catalyzed [3 + 2] cycloaddition of azides and alkynes ("click chemistry"). The Staudinger ligation has sufficient biocompatibility for performance in living animals but suffers from phosphine oxidation and synthetic challenges. Click chemistry obviates the requirement of phosphines, but the Cu(I) catalyst is toxic to cells, thereby precluding in vivo applications. Here we present a strain-promoted [3 + 2] cycloaddition between cyclooctynes and azides that proceeds under physiological conditions without the need for a catalyst. The utility of the reaction was demonstrated by selective modification of biomolecules in vitro and on living cells, with no apparent toxicity.     

A mass spectrometric investigation of non-covalent interactions between ruthenium complexes and DNA

Electrospray ionisation mass spectrometry was used to investigate reactions between six ruthenium compounds and three different non self-complementary duplex oligonucleotides containing 16 base pairs. Each of the compounds studied formed non-covalent complexes containing between one and five ruthenium molecules bound to DNA. Competition experiments involving duplex 16mers and pairs of ruthenium compounds were used to determine the order of relative binding affinities of the metal compounds. Other competition experiments involving ruthenium compounds, and the organic DNA binding agents daunomycin and distamycin, provided information about the sites and modes of DNA binding of the ruthenium compounds.     

Pyridine-containing m-phenylene ethynylene oligomers having tunable basicities

Incorporation of a pyridine monomer into the backbone of a m-phenylene ethynylene oligomer allows functionalization of the interior binding cavity of the folded oligomer. The basicity of the inwardly directed pyridine moiety was modulated by changing the substituents on the pyridine ring and through oligomer folding, granting access to a pK(a) range of 5-14 in acetonitrile. [reaction: see text]