Sensitization experiments

Maier-Reimer, E., Mikolajewicz, U. and Crowley, T. J. (1990). Ocean general circulation model sensitivity experiment with an open American Isthmus. Paleoceanography, 5,349-366. 

Anaphylaxis most commonly starts with symptoms on the skin or the respiratory tract (table 2). The symptomatology is variable there is no obligatory involvement of all organ systems. A major characteristic of anaphylaxis is the rather rapid onset of symptoms after contact with the elicitor. The interval varies between a few seconds or minutes until 1 or 2 h, partly dependent upon the route of application (rapid onset after intravenous allergen exposure) and degree of sensitization. Experience in insect sting anaphylaxis in... 

In Section IV we quantify the relation of the information-rich phase of the scattering wavefunction to the observable 8(E) of Eq. (5). Here we proceed by connecting the two-pathway method with several other phase-sensitive experiments. Consider first excitation from g) into an electronically excited bound state with a sufficiently broad pulse to span two levels, Ea and ),... 

Figures 16 and 17. Covariance processing methods can thus reduce data acquisition times for lower sensitivity experiments such as 1,1- or INADEQUATE when these data are going to be interrogated following covariance processing.50 Alternatively, when the increased s /n of...

Figure 16 Comparison of the F projections of the multiplicity-edited GHSQC, 60 Hz 1,1-ADEQUATE, the UIC calculated HSQC-1,1-ADEQUATE, and GIC calculated HSQC-1,1-ADEQUATE spectra (power 0.5) of strychnine (1). While Snyder and Bruschweiler have noted52 that signal-to-noise (s/n) measurements of covariance spectra may not be the most viable means of making comparisons, in the present example, the differences are so dramatic that they still allow valid conclusions to be drawn. The C12 (77.6 ppm) resonance provides a convenient s/n comparator. The region from 80 to 100 ppm, which is devoid of responses in the spectrum of strychnine, was used to define the "noise" region for the measurement. There is certainly no question that multiplicity-edited GHSQC is a high-sensitivity experiment as attested by a s/n for the C12/H12 correlation response of 290 1. In comparison, the C12 resonance of the 60 Hz 1,1-ADEQUATE spectrum is a much more modest 22 1. In contrast, the s/n for the C12 resonance in the HSQC-1,1-ADEQUATE spectra calculated using UIC and GIC methods was 293 1 and 257 1, respectively.

Like unsaturated ketones, a,0-unsaturated carboxylic acid derivatives, e.g. lactones and anhydrides, undergo cycloadditions to alkenes. As for the preparative conditions (direct irradiation or sensitized experiments) these compounds are situated somewhere in between enones on the one side and olefins on the other. 

The simple reaction scheme outlined in Scheme 2 easily accommodates the results obtained in the investigation of XA. The basic scheme is just the same as it is for BA except that the relative energies of the singlet and triplet states of the carbene are reversed. All of the evidence points to a singlet ground state for XA. This includes the absence of an epr signal, the nearly diffusion-controlled formation of ether in direct and sensitized experiments, the stereospecific cyclopropanation, and the absence of a rapid reaction of the carbene with 02. 

This paper describes the successful synthesis and examination of polyfr-(amino /9-thiosulfate) ether] (PATE), a water soluble photolabile polymer. Evidence has been presented that the PATE polymer is zwitterionic and forms weak associations in aqueous solutions. Heat treatment of PATE films result in extensive crosslinking, presumably through a disulfide bond. This work presents strong evidence that PATE is activated by deep UV radiation, and that a disulfide crosslink is formed. Sensitization experiments demonstrate that the crosslinking reaction can be induced by a triplet sensitizer. Finally, preliminary results point out the potential for application of PATE films as active photoimaging systems. 

Self-sensitization experiment of an aqueous Ag+ zeolite A suspension. 1 nAs corresponds to 3.94 nl of oxygen. 

Thus for instance, in the sensitization experiments carried out with ethoxy-carbonyl-carbene, dimethoxy-carbonylcarbene, and carbene A, the light capture was generally more than 80% 35> Jn the case of phenyl-cyclopentadienyhdenes the nonstereospecificity clearly depends on the fight capture by the sensitizer... 

The effects of an absorption edge are shown in an important case for semiconductors in Figure 4.4. This shows the real and imaginary parts of the scattering factors for gallium and arsenic near the K absorption edges. The exchanges in values, and resultant intensities, that are shown can and have been used for composition- sensitive experiments such as the determination of stoichiometry in III-V semiconductors. However, the tunabihty of a synchrotron radiation source is required for such experiments in most cases. 

The next set of experiments were designed to compare chlorine with bromine and iodine in terms of membrane sensitivity. Experiments with A-2 and X-2 were run for forty hours but U-1 was exposed for only 16 hours because of rapid deterioration on exposure to bromine. Concentrations of all halogens were equivalent to 3 ppm CI2 on a molar basis. Performance profiles for membranes U-1, A-2 and X-2 are shown in Figures 8, 9, and 10 respectively. Only product flux is reported in this case since it appears to be a more sensitive indicator of performance changes. 

The lifetime of the triplet excited molecule with energy 1 eV below the Si energy is probably extremely short the triplet excitations are suggested to take place to dissociative states [90]. Such conclusion can be obtained from the biphotonic sensitization experiments mentioned in connection with the energy of the triplet states (Sec. 2.1) if the decomposition had not been fast enough (t < 10 sec) due to the back transfer of energy, the sensitization could not have been observed [29]. 

H atom elimination is of lower importance from this state, 81 82 IC in the mechanism suggested by Wichramaaratchi et al. is practically identical with 8i 8x used in the terminology of Orlandi s group. The authors of Refs. 55, 83, 121, and 122 all agree that there is a dissociative triplet state, T , which can easily be populated by ISC from 81. We show the potential energy curve of this state (T ) as it has been suggested by Orlandi et al. [83,121]. This state gives only radical decomposition products. In order to explain the results of the biphotonic sensitization experiments (Sec. 2.1) another triplet state —1 eV below 81 (Ti) is also needed. Most probably, this triplet is also dissociative. 

A basic problem of the energy-transfer experiments is that the quenchers used may also react with electron or cationic species, in addition to the excited molecules. If the excited molecules also form after charge recombination (which is now unambiguously established), the quenchers may considerably hinder the formation of excited molecules [8]. Comparison of the results obtained in this manner with those obtained via other techniques shows that the solute technique strongly underestimates the G(Si) value. It should be mentioned that in most of the sensitization experiments unrealistically high K Stern-Volmer constants were obtained [141,142]. 

An interesting example where erroneous mechanistic conclusions were drawn from sensitization experiments is the photoreduction of acridine (17). Although irradiation of acridine in a variety of hydrogen containing solvents gave measurable reduction to acridan and diacridan, addition of benzophenone or acetophenone greatly enhanced the rate of this reaction.113... 

The photocyclodimerization of coumarin (2//-l-benzo[b]pyran-2-one) in direct and sensitized experiments is known to proceed rather inefficiently in the absence of Lewis acids and in better yields in their presence.42,43 In contrast, 2-quinolone (22, X = NH)44 or 1-thiocoumarin (2//-l-benzo[b]thiopyran-2-one 22, X = S)45 afford anti head-to-head dimers 23 on direct irradiation in very good yields. Psoralens (7//-furo[3,2-g][l]benzopyran-7-ones) usually exhibit a behavior similar to that of coumarins.46... 

Among the 1,3-linked bichromophoric anthracenes listed in Table 3, 1,3-di-9-anthryl-l-propanone 21a, l,3-di-9-anthryl-l-butanone 21b, and l,3-di-9-anthryl-2-methyl-l-propanone 21c are exceptional because their photochemical isomerization by intramolecular 4n+4n cycloaddition to give 22 is characterized by high quantum yields, viz. 0.65, 0.40, and 0.72, respectively. For photochemical cycloadditions of linked anthracenes, the quantum yield of 0.72 is the highest ever observed. Oxygen quenching and sensitization experiments indicate that 21a, 21b, and 21c undergo the 4n+4n cycloaddition in the excited triplet state (see Section II.C). 

Fig. 5 Ozone isopleth diagram for 18th July 2006 at the EMEP GB0036R Harwell station plotted from the results of VOC and NOx emission sensitivity experiments performed with a Photochemical Trajectory Model [23]...

Me and co-workers studied the intramolecular photocycloaddition of naphthyl groups in poly(l-vinylnaphthalene) (335) in cyclohexane, benzene, and dichloromethane [338], In cyclohexane, the reaction proceeds via first-order kinetics to a high conversion of 70%, whereas in dichloromethane, the reaction levels off at a very low conversion of 20%. Quenching and sensitizing experiments proved that the Mplet mechanism is predominant in cyclohexane, whereas in dichloromethane, a singlet mechanism is predominant. The addition of trifluo-roacetic acid to the illuminated sample restores the initial absorbance. 

McMurry and co-workers have reported that irradiation of the epimeric hydroxycy-clopentenones 37a, b yields the stereoisomeric lactones 38a, b most likely via an intermediate hydroxycyclopropyl ketene37. The stereospecificity of the reaction may result from hydrogen bonding between the hydroxyl group and the incipient carbonyl in the transition state. The results of quenching and sensitization experiments implicate a reactive singlet state. 

On the basis of triplet sensitization experiments, this rearrangement was shown to occur from the excited singlet state and to involve the biradical intermediate 111. Interestingly, vinyl cyclopropane esters 113-114 underwent geometric isomerization at a much faster rate than rearrangement on direct excitation (Scheme 8.34) [57, 58]. However, the triplet-sensitized reaction of these esters give both cyclopentene and isomerization products. 

The photoreduction of 2- and 3-chloroanisole in alcoholic solvents has been studied and is considered to be best accounted for by invoking methoxyphenyl radicals which abstract hydrogen atoms from the solvent378.4-Chloroanisole probably reacts partly via a homolytic cleavage, but in view of the results of quenching and sensitization experiments, another pathway consists of electron transfer from the solvent (ROH) to excited aryl halide, followed by dissociation of the radical anion into chloride ion and aryl radical. 

The photonucleophilic substitution of the monochloroanisoles in alcoholic solvents had been studied earlier378 and it was then concluded that 4-chloroanisole reacts via a radical anion formed by electron transfer from the solvent to an excited molecule, whereas 3-chloroanisole undergoes substitution via an aryl cation. In another study379, it was found, on the basis of quenching and sensitization experiments and on the basis of the ratios of... 

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