Coupling shifts

When an equimolar mixture of Ni2+, Cu2+ and Zn2+ was added to aqueous electrochemical solutions of [29] and [30] the ferrocene-ferrocenium redox couple shifted anodically by an amount approximately the same as that induced by the Cu2+ cation alone. This result suggests that [29] and [30] are... 

The novel results of electrochemical experiments with receptor [92] are particularly interesting. When an equimolar mixture of H2PO4, HSOJ and Cl- (each 5 x 10 4 mol dm 3) was added to an acetonitrile solution of [92] (5 x 10-4 mol dm-3), the ligand-centred reduction couple shifted cathodically by 175 mV (a shift similar to that caused by the presence of H2PO4 alone). 

MII(bpy )3] is observed (30,31) via cyclic voltammetry in nonaqueous solvents as three 170 mV-separated peaks at -1.2 to -1.3 V vs SCE. The reducibility of the ligand depends on the metal charge and E1/2 for the metal-bound bpy/bpy" couple shifts to less negative potentials as the metal-center charge increases. Thus the first reduction of Ir(bpy)3 +, which occurs at -0.83 V vs SCE in acetonitrile, though 400 mV positive of the MII(bpy)3 +/[MII(bpy)2(bpy )]+ potential, is ascribed to ligand, rather than metal, reduction (41). The... 

Electrochemical studies Adducts undergo similar electrochemical processes, with reduction couples shifted to slightly more negative potentials owing to the lower electron affinity of the cage. This is due to... 

While solvent effects are small for the ring redox ( 0.2 V), the effect of donor solvents which stabilize the higher oxidation state is marked for the metal redox, especially so for those of low-spin d6/d7 and d1jd%. There is a linear relationship between E° for the Feu/I couple and the Gutmann donicity number. The Com u and Cou/I couples shift positively as the pof substituted pyridine, as solvent, decreases and the ring oxidation precedes the CoIII/n couple in noncoordinating solvents such as CH2C12. 

Figure 8. Dipole coupling shifts (experimental points) as function of coverage in Stage 1, compared with theoretical shifts for random (S ) and regular (S oc 3/2) distributions assuming free molecule polarizabilities...

Figure 10. (Top) experimental values (X) of the relative IR band intensity compared with Q2 X , where Q is based on ay = 0.18A3 and d = 1.85A (bottom,) coverage dependence of the dipole coupling shift (experimental points) compared with theoretical shifts for random (S a ) and regular (S a 3/2) distributions, assuming the same values of ay and d, and with at = 2086 cm 1...

It is important, therefore, to consider the rate at which the dipole coupling shift at a reference molecule increases towards its limiting value as nearest neighbours, next nearest neighbours, etc., are successively taken into account. Ihe model system used here consists of a small hexagonal island of the (/T x i/Tj-lO0 overlayer of CO on Cu(lll). 

Figure 11. The dependence on island size D of the dipole coupling shift relative to that in an infinite layer of (y/ 3 X y/ 3)-30° structure...

The E° values of these redox couples shift cathodically with increase in pH. The Pourbaix diagram for cis-[RuVI(bpy)2(0)2]2+ is given in Fig. 20. 

The behaviour of the glass electrode has also been examined.42-43 The glass-calomel electrode system yields stable and reproducible potentials which vary in the normal way with changes in hydrogen ion concentration. However, the EMF of the couple shifts several hundred millivolts as the solution composition changes from water to hydrogen peroxide. Table 1.2 summarizes the apparent and true pH of aqueous solutions of hydrogen peroxide. 

An important constraint that leads to a complete re-evaluation of the degassing models described above comes from consideration of fissiogenic Xe and Xe together (Ozima et al., 1985). Coupled shifts in Xe/ Xe and Xe/ °Xe are proportional to the Pu/ I ratio of the source reservoir. On a Xe/ Xe... 

If combinatorial libraries consist of compound mixtures (e.g., after cleavage from the resin beads), a reliable analytical characterization is difficult. In this case the utilization of mass spectrometry for analysis is based on the prediction of mass distribution of the library. Computer-generated distribution profiles can be compared with the actual profile obtained from the compound library [93,94]. Evaluation of mass distribution detects synthetic problems based on incomplete coupling (shift toward lower molecular masses), incomplete deprotection, or unwanted library modification, such as oxidation, acylation, or alkylation (shift toward higher molecular masses). However, for a larger library of compound mixtures many different compounds will have the same molecular mass. This greatly complicates structural determination and even makes it impossible at a certain mixture complexity. 

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