ARYL AZIDES AS PROTEIN PHOTOLABELS: ABSORPTION SPECTRAL PROPERTIES AND QUANTUM YIELDS OF PHOTODISSOCIATION

Abstract A series of ring-substituted phenyl and naphthyl azides have been prepared. Electronic absorption spectral properties and quantum yields of disappearance have been determined in aqueous solution. For phenyl azide derivatives, the wavelengths of maximum absorption vary systematically, correlating with electronic effects of the ring substituents. Quantum yield values of 0.1–0.7 are obtained and are independent of a number of experimental conditions, including concentration. There is no simple correlation of the quantum yields of azide disappearance with electronic effects, except that the naphthyl azides have higher photochemical efficiencies than the phenyl azide derivatives. A series of potential protein photolabels has been identified based on electronic absorption characteristics and photochemical efficiencies.     

Mainframes and Micros

This paper examines the business user and the problems of meeting his computing needs, particularly with regard to linking micros to mainframes.     

Excited-state electronic coupling and photoinduced multiple electron transfer in two related ligand-bridged hexanuclear mixed-valence compounds

The synthesis, characterization, electrochemical, photophysical, and photochemical properties of two hexanuclear mixed-valence compounds are reported. Each supramolecular species consists of two cyano-bridged [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(3)L-NC-Fe(II)(CN)(5)] triads that are linked to each other through a Pt(IV)-L-Pt(IV) bridge, where L = 4,4'-dipyridyl (bpy) or 3,3'-dimethyl-4,4'-dipyridyl (dmb). The major difference between the two compounds is the electronic nature of the bridging ligand between the two Pt atoms. Both species exhibit a broad Fe(II) --> Pt(IV) intervalent (IT) absorption band at 421 nm with an oscillator strength that is approximately four times that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(5)] and twice that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) When L = bpy, the resonance Raman spectrum obtained by irradiating the IT band at 488 nm exhibits several dipyridyl ring modes at 1604, 1291, and 1234 cm(-1) which are not present in the spectrum when L = dmb. In addition, femtosecond pump-probe spectroscopy performed at 400 nm yields a transient bleach of the IT absorption band with a single exponential decay of 3.5 ps for L = bpy, compared with only 1.8 ps for L = dmb and 2.1 ps for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) Last, prolonged irradiation of the complexes at 488 nm leads to the formation of 4 equiv of ferricyanide with a quantum efficiency of 0.0014 for L = bpy and 0.0011 for L = dmb. The transient absorption, resonance Raman, and photochemical data suggest that the degree of excited electronic coupling in these compounds is tunable by changing the electronic nature of the Pt-L-Pt bridging ligand.     

Microfluorometric study of oxygen dependence of (1"-pyrene butyl)-2-rhodamine ester probe in mitochondria of living cells

The access to oxygen concentration is of importance in various organelles of living cells, especially in mitochondria. A new probe, (1"-pyrene butyl)-2-rhodamine ester, was designed to target this organelle. We present here the properties of the probe in such an environment. Microspectrofluorometry confirms the localization of the probe in the mitochondrial environment at low doses (1 microM). At these doses, the cell toxicity experiments show no effect on the cell growth. The emission spectrum measured at an excitation wavelength of 340 nm (pyrene centered) indicates energy transfer from the pyrene to the rhodamine chromophore, as also observed in an ethanol solution. With excitation at 337 nm, the excited state decays biexponentially with lifetime decays of 6-9 ns and 90 ns. The first corresponds to the intrinsic fluorescence of the cell and the latter corresponds to the pyrene chromophore. In degassed conditions the pyrene lifetime decay increases up to 130 ns. Under an oxygen atmosphere the lifetime decays decrease to 62 ns. The lifetime changes with the oxygen concentration were compared with the range obtained during our previous study in ethanol solution (5-220 ns). The observed differences were interpreted by studying the lifetime of the probe in simplified environments, liposome suspensions and protein solutions. In this paper we show that the new probe can be used to measure the fluctuation of oxygen concentration in the surroundings of mitochondria.     

Structure and magnetism of the first strictly dinuclear compound containing paramagnetic 3d and 5f metal ions. Major influence of the Cu(II) ion coordination on the exchange Cu(II)-U(IV) interaction

The dinuclear compound [CuL2(py)U(acac)2] has been synthesized by treating [Cu(H2L2)] with U(acac)4 (L2 = N,N'-bis(3-hydroxysalicylidene)-2-methyl-1,2-propanediamine) and shows the antiferromagnetic Cu-U interaction; the distinct magnetic behaviour of the trinuclear complexes [(CuL2)2U] (antiferromagnetic) and [[CuL1(py)]U[CuL1]] (ferromagnetic) revealed the major influence of the Cu(II) ion coordination on the exchange interaction (L1 = N,N'-bis(3-hydroxysalicylidene)-2,2-dimethyl-1,3-propanediamine).     

Quantitative analysis of prostaglandins in cell culture medium by high-resolution gas chromatography with electron-capture detection

Prostaglandins have been shown to be important modulators of haemostatis , immune responses, and growth of normal and neoplastic cells. In order to investigate the cell origin and metabolic profile of the endogenous prostaglandins in human tumours, a convenient extraction and gas chromatographic method for measuring the various classes of prostaglandins was developed. Infiltrating macrophages from human tumours were isolated using adherence to plastic. Macrophage-enriched and macrophage-depleted cell populations were then cultured in vitro and the media supernatant was studied for the presence of prostaglandins E1, E2, F2 alpha, and 6-keto-F1 alpha (the spontaneous breakdown product of prostacyclin, PGI2). Routinely, 1 ml of medium containing 10(6) cells was studied. The eicosanoids were extracted using commercially available octadecylsilyl silica reversed-phase columns prior to derivatization. Standards and samples were prepared as pentafluorobenzyl ester (methoxime) trimethylsilyl ether derivatives for analysis on an OV-101 (25 m X 0.2 mm) fused-silica capillary column. Recovery of standards ranged from 93% to 37%, with linear recovery in all instances (regression coefficients greater than 0.98). Detection limits were 20 pg for each of the prostaglandins. Analysis of cell subpopulations from six human tumours revealed that infiltrating macrophages produce various prostaglandin profiles and are largely responsible for the prostaglandin production in human cancer. The described analytical method is the first application of high-resolution gas chromatography with electron-capture detection to the quantitative profiling of prostaglandins from human cell culture.     

Measurements of calcium with a fluorescent probe Rhod-5N: Influence of high ionic strength and pH

We describe a new method for the spectroscopic determination of high calcium concentration using a fluorescent probe Rhod-5N. This method was investigated in order to be utilized in high ionic strength solution, such as seawater. The probe is fluorescent when bound to calcium, LM, but not as the free form L. The dissociation constant of the equilibrium (0.14 mM) was determined at several ionic strengths, i.e. in the absence and in the presence of additional ions (0.7 M NaCl). The influence of pH was studied. In order to correctly model the experimental data, we included a new fluorescent compound: LHM (calcium bound protonated probe). The first acidity constant (0.02 μM) and the second dissociation constant (4.5 mM) were calculated. A useful range for the determination of calcium concentration is provided. Such a method is fast and easy to carry out.     

Pulse radiolysis studies on galactose oxidase

Single-Cu-containing galactose oxidase in the GOase(semi) state (Cu(II), no Tyr(*) radical) reacts with pulse radiolysis generated formate radicals CO(2)(*-) to give an intermediate UV-vis spectrum assigned as RSSR(*-), peak at 450 nm (epsilon = 8100 M(-1) cm(-1)). From a detailed kinetic analysis at 450 nm, pH 7.0, the following steps have been identified. First the strongly reducing CO(2)(*-) (-1.9V) reduces GOase(semi) (k(0) > or = 6.5 x 10(8) M(-1) s(-1)) to a species GOase(semi)(*-). This is followed by biphasic reactions (i) GOase(semi)(*-) + GOase(semi) (k(1) = 1.6 x 10(7) M(-1) s(-1)) to give GOase(semi) + P(*-) and (ii) P(*-) + GOase(semi) (k(2) = 6.7 x 10(6) M(-1) s(-1)) to give GOase(semi)RSSR(*-). There are no significant absorbance changes for the formation of GOase(semi)(*-) and P(*-), which are Cu(I) (or related) species. However, GOase(semi)RSSR(*-) has an absorption spectrum which differs significantly from that of GOase(semi). The 450 nm peak is characteristic of an RSSR(*-) radical with two cysteines in close sequence proximity and is here assigned to Cys515-Cys518, which is at the GOase surface and 10.2 A from the Cu. On chemical modification of the RSSR group with HSPO(3)(2-) to give RSSPO(3)H(-) and RS(-), absorbance changes are approximately 50% of those previously observed. The decay of RSSR(*-) (0.17 s(-1)) results in the formation of GOase(red). No RSSR(*-) formation is observed in the reaction of GOase(semi) Tyr495Phe with CO(2)(*-), and a single process giving GOase(red)Tyr495Phe occurs. Similarly in the reaction of GOase(ox) with CO(2)(*-), a single-stage reaction gives GOase(semi).     

Multifunctional Redox Polymers: Electrochrome,Polyelectrolyte, Sensor,Electrode Modifier,Nanoparticle Stabilizer,and Catalyst Template

Simple “click” polycondensation metallopolymers of redox‐robust bis(ethynyl)biferrocene (biFc) and di(azido) poly(ethylene glycol) (PEG400 and PEG1000) were designed for multiple functions including improvement of water solubility and biocompatibility, the introduction of mixed valency and sensing capabilities, and as nanoparticle stabilizers for catalysis.