Isothermal titration calorimetry experiments

In 2001, a possibility of detectable differences in chiroptical and achiral physicochemical experiments between an enantiomeric pair of poly[bis (S)-3,7-dimethyloctyl silylene] (33-SS) and poly[bis (R)-3,7-dimethyloctyl silyl-ene] (33-RR) (Scheme 10) was reported [119]. The polymers bearing two identical chiral side groups with 96% ee have nearly degenerate doublewell energy potentials, leading to PM-transition at - 65 °C in isooctane. Recently, Shinitzky et al. reported positive experimental results that show distinct differences in helix-coil transition behavior between synthetic d-and L-oligopeptides with 24 identical residues dissolved in water by CD and isothermal titration calorimetry experiments [120]. They assumed that ortho-water in the triplet state (75% of bulk water) is responsible for the LD-differences [121]. 

Recently, Lee and co-workers have shown that abinol-strapped calix[4]pyr-role (49) can be used in the enantioselective recognition of carboxylate anions [66]. Both the R- and S-enantiomers of the strapped calixpyrrole were isolated and characterized. Detailed studies of the enantioselectivity of the S enantiomer were carried out by isothermal titration calorimetry experiments in acetonitrile with the chiral anions (R)-2-phenylbutyrate and (S)-2-phenylbutyrate. Stability constants were determined and revealed... 

As shown throughout these results on dual protein systems, the experimental conditions for optimum cross-assembly are specific for each system because of the required charge and size compensation. This could explain the earlier results reported in 1990 that showed that Lf interacts and forms complexes with p-Lg and BSA but not with a-La [141], A specific optimum pH value favouring Lf/a-La cross-assembly was probably missing in this work. We have recently confirmed this assumption by showing that, once the conditions are optimised, LF interacts with a-La as well as with P-Lg, as revealed by isothermal titration calorimetry experiments (unpublished data). Indeed, we also observed self-assemblies into microspheres of p-Lg/LF, a-La/LF and p-Lg/LYS binary mixtures at specific, system-dependent pH values (unpubhshed data). 

Instrumentation. H and NMR spectra were recorded on a Bruker AV 400 spectrometer (400.2 MHz for proton and 100.6 MHz for carbon) at 310 K. Chemical shifts (< are expressed in ppm coupling constants (J) in Hz. Deuterated DMSO and/or water were used as solvent chemical shift values are reported relative to residual signals (DMSO 5 = 2.50 for H and 5 = 39.5 for C). ESl-MS data were obtained on a VG Trio-2000 Fisons Instruments Mass Spectrometer with VG MassLynx software. Vers. 2.00 in CH3CN/H2O at 60°C. Isothermal titration calorimetry (ITC) experiments were conducted on a VP isothermal titration calorimeter from Microcal at 30°C. 

Further experiments focused therefore on [RuCl(en)(r 6-tha)]+ (12) and [RuCl(rj6-p-cym)(en)]+ (22), which represent the two different classes, and their conformational distortion of short oligonucleotide duplexes. Chemical probes demonstrated that the induced distortion extended over at least seven base pairs for [RuCl(rj6-p-cym)(en)]+ (22), whereas the distortion was less extensive for [RuCl(en)(rj6-tha)]+ (12). Isothermal titration calorimetry also showed that the thermodynamic destabilization of the duplex was more pronounced for [RuCl(r 6-p-cym)(en)]+ (22) (89). DNA polymerization was markedly more strongly inhibited by the monofunctional Ru(II) adducts than by monofunctional Pt(II) compounds. The lack of recognition of the DNA monofunctional adducts by HMGB1, an interaction that shields cisplatin-DNA adducts from repair, points to a different mechanism of antitumor activity for the ruthenium-arenes. DNA repair activity by a repair-proficient HeLa cell-free extract (CFE) showed a considerably lower level of damage-induced DNA repair synthesis (about six times) for [RuCl(en)(rj6-tha)] + compared to cisplatin. This enhanced persistence of the adduct is consistent with the higher cytotoxicity of this compound (89). 

The enthalpy change associated with formation of a thermodynamically ideal solution is equal to zero. Therefore any heat change measured in a mixing calorimetry experiment is a direct indicator of the interactions in the system (Prigogine and Defay, 1954). For a simple biopolymer solution, calorimetric measurements can be conveniently made using titra-tion/flow calorimeter equipment. For example, from isothermal titration calorimetry of solutions of bovine P-casein, Portnaya et al. (2006) have determined the association behaviour, the critical micelle concentration (CMC), and the enthalpy of (de)micellization. 

Isothermal titration calorimetry (ITC) dilution experiments were used to measure association constants and thermodynamic parameters for the formation of dimers 15-15 (cf. Section 14.09.3.1) <20010L3221>. Aggregates 15-15 are highly associated at 298K and entropically driven. The change in heat capacity (ACp) for the formation of dimer 15-15 was determined by ITC measurements from 288 to 328 K yielding the negative value (ACp = — 185 6 cal mol-1 K 1). It was concluded that the dimerization process is driven by hydrophobic effect. 

Both heparin and heparan sulfate interact with CS protein and help in the binding of the parasite to liver cells. Surface plasmon resonance (SPR) experiments indicate that heparin has fast on-rate k and slow off-rate (kd) kinetics for CS protein with a of 41 nM. Isothermal titration calorimetry shows that the minimum sequence within the heparin polymer capable of a strong interaction with the CS protein is a decasaccharide. High concentrations of exogenous heparin or heparan sulfate can inhibit the binding of CS protein to HepG2 cell, a human hepatoma cell line. However, at low concentrations, heparin or heparan sulfate can also act as a... 

The binding parameters of both hosts with chloride were determined using isothermal titration calorimetry. The microcalorimetry experiments re-... 

Several amino acids were utilized as a template during polymerization (Phe, Tyr, Ala, Val, Leu, He), by complexation to the copper structure (Fig. 17). The association constants for the amino acids are of the order of 10 -10" M whereas ida is of the order of 10 This assures that the amino acids are not capable of displacing the IDA ligand from the copper center. Experimental conditions called for greater than twofold excess amino acid during polymerization procedures in order to ensure a 1 1 complex between the amino acid and the copper center. Isothermal titration calorimetry (ITC) experiments indicate that the binding between Cu-IDA and L-phenylalanine reaches saturation after two equivalents of amino acid. 

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