Spectroscopic titrations,

Mossbauer spectroscopic titration of [Me2Sn(IV)] and [MesSnflV)] hydroxides with ligands mimicking nucleic acid phosphate sites and with native DNA was the aim of work by Barbieri et al. A series of aqueous solutions of each system, formed by the organotin(IV) hydroxides and the phosphate ligands used... 

Spectroscopic titration of (Ph3P)2(CO)IrCl with B(CftF5)3 shows a weak affinity between the two compounds leading to an equilibrium ... 

Determination of the catalytically active species derived from 1 in solution. Spectrophotoraetric titration of the backbone ligand 5 with copper(II) acetate in methanol revealed formation of a dinuclear copper(ll) complex species Cu2L.3h(OAc) above a 1 2 molar ratio. A mononuclear copper(ll) species CuL 2h (6) dominates at a 1 1 molar ratio of 5 and copper(ll) acetate. Control experiments for the assignment of putative structures based on the obtained spectroscopic data included a UVA is spectroscopic titration of 5 with anhydrous sodium acetate in the presence of copper(ll) chloride and revealed that acetate is necessary for the formation of a copper (11) complex in methanol. The composition of 1 in methanol is the same as determined by elemental analysis for the sohd state. 

The kinetics of reactions of NO with ferri- and ferro-heme proteins and models under ambient conditions have been studied by time-resolved spectroscopic techniques. Representative results are summarized in Table I (22-28). Equilibrium constants determined for the formation of nitrosyl complexes of met-myoglobin (metMb), ferri-cytochrome-c (Cyt111) and catalase (Cat) are in reasonable agreement when measured both by flash photolysis techniques (K= konlkQff) and by spectroscopic titration in aqueous media (22). Table I summarizes the several orders of magnitude range of kon and kQs values obtained for ferri- and ferro-heme proteins. Many k0f[ values were too small to determine by flash photolysis methods and were determined by other means. The small values of kQ result in very large equilibrium constants K for the... 

UV/Vis spectroscopic titrations were used to determine association constant data for the calix[4]arenediquinone ligands with metal and ammonium cations and the results are summarized in Table 11. For both [54] and [55], Na+ and Ba2+ cations form very stable complexes. It is noteworthy that the diamide calix[4]arenediquinone [55] exhibits a larger association constant for BUNH3 than for NH, whereas with the bis(ethyl ester) derivative [54] the reverse... 

Further support for the contention that conjugate 13 can act as an amino acid binding agent came from quantitative visible spectroscopic titrations carried out in dichloromethane. It was determined that compound 13 forms 1 1 complexes with both phenylalanine and tryptophan with relatively high association constants (K = 4.86 X 10 M- (L-Phe), 5.35 x 10 NT (D-Phe),0.83 x 10 M" (L-Trp), and 0.94 X 10 M- (D-Trp)). 

Spectroscopic titration with pyridine reveal strong Bronsted acid groups... 

Spectral methods, spectroscopic titration and NMR data (chemical shifts on binding, intermolecular Nuclear Overhauser Effects, relaxation and correlation... 

A discussion of the fundamentals of the NMR technique is beyond the scope of this work, but may be found in the key reference. However, there are one or two aspects of NMR that are of particular interest to supramolecular chemists, as well as the obvious general need for a technique for characterising new chemical compounds. We have already seen in Section 1.4 the use of the NMR spectroscopic titration technique for the measurement of host-guest association constants in dilute solutions. However, more information may be gained from NMR spectroscopy than just binding constants. 

There is a caveat in using Eq. (21.34), illustrated by the simulated titration curve at 10 [iM Mg2+ (Fig. 21.5). This titration curve shows a significant fraction of folded RNA in the absence of Mg2+, where. C0bs 0.15. Spectroscopic titrations and most other methods used to assess Kohs assume a baseline value of 9 = 0 when [Mg2 = 0 and normalize the titration curve accordingly. Two of the calculated curves in Fig. 21.5 have been fit to a modified Hill equation that incorporates this assumption. The apparent value of Ar 2+ at the midpoint of one curve (1.99) is larger than the value used to calculate the titration curve (1.45 see legend to Fig. 21.5). 

Instead, a wide variety of spectroscopic and electrochemical titration methods are often employed to determine the equilibrium constants for a molecular recognition process at several different temperatures, which are then analyzed by the van t Hoff equation to give the thermodynamic parameters for the process. However, there is a critical tradeoff between the accuracy of the value obtained and the convenience of the measurement since the thermodynamic parameters, evaluated through the van t Hoff treatment, do not take into account the possible temperature dependence of the enthalpy change, i.e. heat capacity, and are less accurate in principle. In fact, it has been demonstrated with some supramolecular systems that the van t Hoff treatment leads to a curved plot and therefore the thermodynamic parameters deviated considerably from those determined by calorimetry.3132 Hence one should be cautious in handling thermodynamic parameters determined by spectroscopic titration and particularly in comparing the values for distinct systems determined by different methods. 

The anion templated syntheses by Beer afforded receptors 60-62 by reacting the chloride salt of the starting pyridinium precursor with an appropriately chosen 1,3-diamidobenzene derivative. Based on 1H NMR spectroscopic titrations carried out in acetone-d6, the structure Cl 60 was found to form with a 1 1 stoichiometry and with an association constant of 2400 M-1. 

Tauler, R., Izquierdo-Ridorsa, A., and Casassas, E., Simultaneous analysis of several spectroscopic titrations with self-modeling curve resolution, Chemom. Intell. Lab. Sys., 18, 293-300, 1993. 

The compounds form 1 1 complexes with all alkali ions and with a large number of other metal ions in organic solvents267,268,307. Among the alkali ions, K+ is bound most strongly, but K+-complex stability as well as K+ > Na+ selectivity are much less pronounced than with valinomycin. In concentrated enniatin solutions, non-equimolar complexes are formed. NMR- und CD-spectroscopic titrations have demonstrated that 2 1 enniatin-cation complexes are formed with a stability order of K+ > Cs+ > Na+. Evidence for formation of a 3 2 complex with Cs+ was also obtained133,216 ... 

A particularly powerful application of FTIR is the study of the sites on solid catalysts via probe molecules. The technique is often referred to as spectroscopic titration. UV-visible spectroscopy and MAS NMR spectroscopy can also be used to titrate the sites on catalyst surfaces.15,46,47 Applications include ... 

Table 4.5 IR absorption band values (cm ) for pyridine (py) in the spectroscopic titration of acids...

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