DOSY

Gebrauchs-anweisung, /. directions for use. -dosis, /. usual dose. 

Minimal-, lowest, minimum, -betrag, m. lowest amount lowest rate, -dosis,/. minimum dose, -gehalt, m. minimum content, -ober-fiache, /. minimum surface, -wert, m. minimum value. -zahl,/. minimum number. 

Todes-dosis, -gabe, /. fatal dose, lethal dose, -kampf, m. death struggle, agony, -stogg, m. 

The concept of dose response in pharmacology has been known and discussed for some time. A prescription written in 1562 for hyoscyamus and opium for sleep clearly states, If you want him to sleep less, give him less [13], It was recognized by one of the earliest physicians, Paracelsus (1493-1541), that it is only the dose that makes something beneficial or harmful All things are poison, and nothing is without poison. The Dosis alone makes a thing not poison. ... 

The sticking coefficient of H2 on a metal has been determined through an adsorption experiment. The metal surface is assumed to have No = 1.5 x 10 sites m and each adsorption site is assumed to be occupied by one hydrogen atom when the surface is saturated. The experiment was performed by exposing the surface to a known pressure of hydrogen over a well-defined period of time (dosis) and then sequentially determining how much was adsorbed by, for example, TPD. All adsorption experiments where performed at such low temperatures that desorption could be neglected. 

A detailed analysis of the proton high field NMR spectra of tomato juice and pulp has recently been acquired [15]. The combination of suitable selective and two-dimensional techniques (J-resolved, COSY, TOCSY, DOSY, etc.) was used for... 

J.-P. Salo and H. Salomies, Farmaseuttinen aikakaus-kirja-DOSIS 12, 152-64 (1996). 

Spectral width, dynamic range, resolution and sensitivity are expected to be pushed toward further limits. An emerging advancement in NMR spectroscopy is the DOSY technique (Section 5.4.1.1) which offers a separation capability as a function of the rates of steady state diffusion of molecules in solution. 

The study of molecular diffusion in solution by NMR methods offers insights into a range of physical molecular properties. Different mobility rates or diffusion coefficients may also be the basis for the separation of the spectra of mixtures of small molecules in solution, this procedure being referred to as diffusion-ordered spectroscopy (DOSY) [271] (Figure 5.11). In this 2D experiment, the acquired FID is transformed with respect to 2 (the acquisition time). 

DOSY was developed to provide useful displays of PFG-NMR data sets that incorporate all reliable information about the system under study obtained from PFG-NMR data and prior knowledge. Various pulse sequences for DOSY have been developed [273,274]. 

DOSY is a technique that may prove successful in the determination of additives in mixtures [279]. Using different field gradients it is possible to distinguish components in a mixture on the basis of their diffusion coefficients. Morris and Johnson [271] have developed diffusion-ordered 2D NMR experiments for the analysis of mixtures. PFG-NMR can thus be used to identify those components in a mixture that have similar (or overlapping) chemical shifts but different diffusional properties. Multivariate curve resolution (MCR) analysis of DOSY data allows generation of pure spectra of the individual components for identification. The pure spin-echo diffusion decays that are obtained for the individual components may be used to determine the diffusion coefficient/distribution [281]. Mixtures of molecules of very similar sizes can readily be analysed by DOSY. Diffusion-ordered spectroscopy [273,282], which does not require prior separation, is a viable competitor for techniques such as HPLC-NMR that are based on chemical separation. 

Linssen and de Vries [285] have examined 1 % di-f-butyl-p-cresol (DBPC) in low-MW poly(tetrahydro-furan) by means of DOSY (Figure 5.13). DOSY is a powerful tool for the analysis of polydisperse samples and complex mixtures, such as anionic surfactants. It is not to be expected that DOSY will rapidly become a standard tool in polymer/additive analysis. 

Figure 5.12 1K DOSY spectrum of (+) Tinuvin P, ( ) Irganox 1330 and (o) BHT in TCE-d2 showing resolution of the individual components along the chemical shift and diffusion dimensions. The single pulse lH NMR spectrum is shown on top of the 2D DOSY plot. After Jayawickrama et al. [284]. Reprinted from D.A. Jayawickrama et al. Magnetic Resonance Chemistry, 36, 755-760 (1998). Copyright 1998 John Wiley Sons, Ltd. Reproduced with permission...

Figure 5.13 DOSY 2D display for 1 % DBPC in PTHF-1500 (horizontal axis H NMR vertical axis diffusion coefficients). Reproduced by permission of DSM Research, Geleen...

An important technical development of the PFG and STD experiments was introduced at the beginning of the 1990s the Diffusion Ordered Spectroscopy, that is DOSY.69 70 It provides a convenient way of displaying the molecular self-diffusion information in a bi-dimensional array, with the NMR spectrum in one dimension and the self-diffusion coefficient in the other. While the chemical-shift information is obtained by Fast Fourier Transformation (FFT) of the time domain data, the diffusion information is obtained by an Inverse Laplace Transformation (ILT) of the signal decay data. The goal of DOSY experiment is to separate species spectroscopically (not physically) present in a mixture of compounds for this reason, DOSY is also known as "NMR chromatography."... 

More recently, three-dimensional (3D) pulse sequences with DOSY have been presented where a diffusion coordinate is added to the conventional 2D map. As in the conventional 2D spectra, these experiments reduce the probability of signal overlap by spreading the NMR frequency of the same species over a 2D plane, and distribute the diffusion coefficient. 

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