Blue transitions

Blue transitions are also observed with IR excitation at 1.064 m in Tm3+-doped fluorozirconate fibers. Depending on the pumping power, different up-conversion pathways are identified. For low pumping powers, a four-fold up-conversion process leads to excitation of 1D2 ... 

Most Investigations have concentrated on two of the nBCMU series of polymers (R=-(CH2)j 0C0NHCH2C02C/Hg) with n = 3 and i, 3BCMU has a yellow to blue transition and. BCMU a yellow to red transition in chloroform/hexane solvent mixtures and when hot toluene solutions are cooled. 

Recently the higher homologue, 9BCMU, has been synthesised and characterised (27). This polymer shows yellow to blue, yellow to red, yellow to red and blue and red to blue transitions. These transitions are observed using the same solvent/non-solvent mixture, chloroform/hexane, as for 3 and /.BCMU (28). Examples of these transitions are shown in Figure 3. 

Fig. 87 At range corresponding to a fixed pH range of the transition of an indicator (here bromthymol blue transition range from pH 6.0 to 7.7) (a) for the case of a titration curve which is very steep in that pH range, and (b) for a titration curve which is less steep in that range...

This limit corresponds to fig Fg (blue transition not saturated). We suppose the blue laser tuned at resonance (Ag 0) and we consider first Ar=0. The system (14) has 3 time constants, two short Xx and X2 and one long X3 ... 

Figure 6. Kinetics of the yellow to blue transition. The concentration of the yellow component is monitored at 465 nm the point for the color transition. The inset shows the absorption spectra for the two phases with arrows indicating the monitoring points ...

Wegner and co-workers questioned these results and on the basis of their light scattering results believe that the obseirved yellow to blue transition is intimately linked to the precipitation of the PDA (3). According to their data isolated rod-like molecules of Poly-3BCMCJ do not exist in solution. The spectral shift under debate is shown by Figure 3. 

Figure 1.5 Comparison of 63 organic-only and transition metal HAT rate constants measured experimentally ( obs) those determined from the cross relation (eqn (1.8), caic)- The line indicates perfect agreement. The reactions (Tables 1.2 and 1.4) involve oxyl radicals+ 0-H bonds (blue ), oxyl radicals + C-H bonds (blue ), transition metal complexes -h O-H bonds (red ) and transition metal complexes + C-H bonds (red O). Error bars are omitted for clarity (see Figures 1.2 and 1.4). The correlation coefficient for all data is 0.94.

An alternative approach is to replace the native metal cations in the protein with synthetic organic cations known as bolaforms (see Birge et al. for examples). Removal of native cations results in a purple to blue transition in the protein, caused by protonation of Asp-85. Cations are removed using EDTA (Sigma E 9884) or cation-exchange resins (BioRad AG MP-50 Resin).Bolaforms are then added to the solution or the polymer matrix. Some bolaforms are capable of regenerating the purple form of BR and show an increased lifetime of the O-state intermediate. Glycerol and other poly-hydroxyl compounds may enhance the O — P transition (results not shown). 

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