Experimental Techniqnes

New experimental techniqnes for the direct measurement of interparticle forces are now available and can be nsed to nnderstand the physicochemical factors that control adhesion, coating phenomena, tribology, and others. 

Whereas theoretical studies of dihydrogen bonding where dihydrogen-bonded complexes are isolated, approximating the gas phase, are very numerons, gas-phase experiments with these complexes are relatively rare. This circumstance is probably connected with the nontrivial experimental techniqnes used for gas-phase investigations. 

The small 110 a.a. ribonuclease from B. amyloliquefaciens, bamase, has been studied extensively in A.R.Fersht s laboratory (Sali, Bycroft and Fersht, 1988 Matouschek et al, 1990 Bycroft et al., 1990 Serrano and Fersht, 1989) using NMR as an essential experimental techniqne. The df-helices of bamase have been studied with respect to stability and it was found that mutation of the THR and THR residnes located at the N-terminal of the helix (Serrano and Fersht, 1989) could destabilize the protein with up to 2.5 kcal mol b The THR and SER residnes are capable of facilitating the formation of an additional hydrogen bond in the first him of the df-helix. If THR is snbstitnted with ASP or GLU no marked change in stability was observed, probably dne to the known charge-dipole interaction between the negative charge of the ASP or GLU and the positive end of the helix macro-dipole. 

To determine the concentration, or the nnmber of moles present, of a snbstance by an experimental techniqne called titration... 

H2O molecules in the hydration spheres with the bnlk H2O solvent varies by many orders of magnitude depending on the metal ion. This, combined with the use of many different experimental techniqnes, has resulted in discrepancies in the literatnre, particnlarly for metal ions with a weakly bonnd, rapidly exchanging hydration sphere. The Na+ cation, for example, has had qnoted values for the primary solvation number ranging from 2 to 13, although a value close to six is generally accepted." ... 

In the following we will illnstrate, with the help of several examples deahng with the electro-oxidation of alcohols, how the use of coupled experimental techniqnes will be able to elncidate most of the reaction pathways. 

C. P. Poole, Jr, Electron-Spin Resonance A Comprehensive Treatise on Experimental Techniqnes , Dover Pnblishing, 1997. 

Direct structural analysis of transition states is difficult due to their short lifetimes. Only relatively recently, ultrafast spectroscopy has started to provide direct insights into the nature of transition states, albeit mostly for rather simple reactions. However, indirect information regarding stereoelectronic factors in the transition state can be glimpsed from a variety of experimental techniqnes inclnding effects of substituents, solvents, isotopic perturbations, and structural constraints. Introduction of snbstituents often leads to well-defined stereochemical outcomes. The enhancement of either rate or selectivity can provide insights into reaction mechanisms and transition state structures. 

Halpaap [2] discusses in some detail the experimental techniqne of preparative layer chromatography with sample quantities between 0.1 and 100 mg, nsing plates up to 100 cm X 20 cm in area and adsorbent layers up to 2 mm thick. 

The experimental techniqnes used to measure the diffusion are based upon chromatographic methods, " NMR (for self-diffusion), and photon correlation spectroscopy. The so-called chromatographic method for the measurement of diffusion coefficients, strictly speaking, is not a chromatographic method since no adsorption/desorption or retention... 

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