Derivatisation Derivative

The AMAPs (2-[ arylmethyl amino]-l,3-propanediols) are a class of planar polycyclic aromatic derivatives, which contain polar side-chains. They are known to be DNA intercalators and possess broad spectrum antitumour activity. An approach to C-radiolabelled AMAP derivative 40 used the Bucherer reaction as an initial starting reaction. 2-Naphthol was reacted with 4-bromophenylhydrazine 38 in the presence of sodium metabisulfite and HCl to afford 39. Subsequent derivatisation of 39 afforded 40. 

In liquid chromatography, in contrast to gas chromatography [see Section 9.2(2)], derivatives are almost invariably prepared to enhance the response of a particular detector to the substance of analytical interest. For example, with compounds lacking an ultraviolet chromophore in the 254 nm region but having a reactive functional group, derivatisation provides a means of introducing into the molecule a chromophore suitable for its detection. Derivative preparation can be carried out either prior to the separation (pre-column derivatisation) or afterwards (post-column derivatisation). The most commonly used techniques are pre-column off-line and post-column on-line derivatisation. 

Reagents which form a derivative that strongly absorbs UV/visible radiation are called chromatags an example is the reagent ninhydrin, commonly used to obtain derivatives of amino acids which show absorption at about 570 nm. Derivatisation for fluorescence detectors is based on the reaction of non-fluorescent reagent molecules (fluorotags) with solutes to form fluorescent... 

Various types of derivatisation have now been developed for both gas and liquid chromatography. For more detailed information regarding the choice of a suitable derivative for a particular analytical problem, the appropriate works of reference should be consulted.62,63... 

Deposit character of, (eg) 509 Deposition completeness of, 507 potentials of metals, 508 Derivative spectrofluorimetry 733 Derivative spectrophotometry 668 Derivatisation in chromatography, gas, 236 liquid, 228 in fluorimetry, 735 Desiccants 99 Desiccators 98 cooling of crucible in, 100 desiccants for, 99 Scheibler type, 99 uses of, 100 vacuum, 100... 

Transformation of bromocriptine free base 2 into water soluble salt -mesylate, is the only way to obtain a suitable therapeutical form. Crystallization of mesylate using alcohol as a solvent in the presence of excess of strong acid, e.g. methanesulphonic acid can induce formation of 12 -0-alkyl-derivative 2. Until now this derivatisation of ergot molecule has been practically unknown. In continuation we developed the preparative method for obtaining these compounds, (using tetrafluoroboric acid as a catalyst) (ref. 20). 

A similar procedure was adopted for synthesis of nanoparticles of cellulose (CelNPs). The polysaccharide nanoparticles were derivatised under ambient conditions to obtain nanosized hydrophobic derivatives. The challenge here is to maintain the nanosize even after derivatisation due to which less vigorous conditions are preferred. A schematic synthesis of acetyl and isocyanate modified derivatives of starch nanoparticles (SNPs) is shown in scheme 3. The organic modification was confirmed from X-ray diffraction (XRD) pattern which revealed that A- style crystallinity of starch nanoparticles (SNPs) was destroyed and new peaks emerged on derivatisation. FT-IR spectra of acetylated derivatives however showed the presence of peak at 3400 cm- due to -OH stretching indicating that the substitution is not complete. 

Lyim and co-workers carried out smdies of the Ap(io 35) peptide - derived from residues 10-35 of the p-amyloid responsible for Alzheimer s disease - which forms fibrils composed of parallel p-sheets [62]. The peptide was compared to its C-terminal PEG-derivatised analogue. TEM experiments showed that both formed fibrils [63] (Fig. 21) but the uranyl acetate stain was not found inside the peptide-PEG fibrils, indicating that PEG was at the outer edge of the fibril. 

HPLC has also been used for analysing fatty acid mixtures [708] and for the characterisation of fatty acids and their derivatives [709]. Fatty acids are commonly analysed on polymeric RPLC columns. Only multiple unsaturated fatty acids can be detected by UV in HPLC the others require derivatisation into UV-absorbing or fluorescing derivatives. Simultaneous determination of saturated and unsaturated fatty acids (C12-C24) by means of RPLC has been reported [710]. Derivatisation is necessary. 

It has proved to be very useful, providing both qualitative and quantitative information derived from mathematical processing of UV/VIS spectra. The principles of derivative spectrophotometry were discussed [15,16]. Obviously, derivatisation of spectra does not provide any additional information to that acquired during the measurement, but allows for easier interpretation. In particular, the possibility of resolving overlapping peaks makes derivative spectrophotometry a valuable tool for multicomponent analysis. Typically, derivative spectrophotometry is useful for the simultaneous determination of two additives in polymeric materials with very closely positioned absorption maxima. In quantitative analysis, derivative spectrophotometry leads to an increase in selectivity. 

Derivative preparation can be performed either prior to the separation (pre-column derivatisation) or after (post-column derivatisa-tion), and can be done either on-line or off-line. The two techniques most commonly used are pre-column off-line and post column online. 

Post-column on-line derivatisation is carried out in a reactor located between the column and the detector. With this technique, the derivatisation reaction does not need to go to completion, provided it can be done reproducibly, and the reaction does not produce any chromatographic interferences. The reaction needs to take place in a fairly short time at moderate temperatures, and the reagent should not be detectable under the same conditions at which the derivative is detected. The mobile phase may not be the best medium in which to carry out the reaction, and the presence of the reactor after the column will increase the extra-column dispersion. 

Analytical methods for the detection of residues of semicarbazide use derivatisation with 2-nitrobenzaldehyde and LC-MS detection. Figure 18 shows the positive ESI response for a 1 ppm solution of semicarbazide after derivatisation and concentration. The main peak 2 at 16 min shows the expected 209 (M+H)+ ion of the 2-nitrobenzaldehyde derivative of semicarbazide together with its sodium adduct ion at m/z 231 (Figure 19). 

GC of aqueous simulant or water extract of olive oil using cold on-column injector. 1,4 butane diol internal standard Solvent extraction with dichloromethane and concurrent derivatisation with 9-(methylaminomethyl)anthracene. Fluorescent derivatives analysed by HPLC with fluorescence detection... 

Chloro-1,3,2-oxazaphospholanc (chlorophosphoramidite) 43 derived from (IR, 25)-(-)-cphedrine 42 was prepared for the first time as early as 1977 by its reaction with phosphorus trichloride (Scheme 15) [32, 33], Later, similar procedures were reported for its isolation as a single epimer which, on the basis of spectroscopic and derivatisation studies, has been assigned configuration [34-36],... 

Another way for covalent immobilisation is to synthesise indicator chemistry with polymerizable entities such as methacrylate groups (Figure 4). These groups can then be copolymerized with monomers such as hydrophobic methyl methacrylate or hydrophilic acryl amide to give sensor copolymers. In order to obtain self-plasticized materials, methacrylate monomers with long alkyl chains (hexyl or dodecyl methacrylate) can be used. Thus, sensor copolymers are obtained which have a Tg below room temperature. Similarly, ionophores and ionic additives (quaternary ammonium ions and borates) can be derivatised to give methacrylate derivatives. 

A GC analysis of amino acids requires a derivatisation step to increase the volatility of the amino acids. Generally, norleucine and/or norvaline are the internal standards added to the hydrolysate to check the derivatisation yield. According to the experimental method applied, the limits of detection (LOD) vary in the range 10 100 pg for each amino acid. Regarding the chromatographic columns, as most of the derivatives are esters barely polar compounds the most commonly used are fused-silica capillary columns with a low... 

If no KIE is present, the contribution of the derivative atom to the measured 8 value of the derivatised compound can be calculated using a simple mass balance equation (14.2), where n is number of moles of the isotope of interest, F is the fractional abundance of the isotope of interest, c refers to the compound of interest, d refers to the derivative group and... 

The precision associated with the determination of 8 values is derived from the errors associated with the correction factors and is also dependent on the molar ratio of the element of interest between the sample and derivative. Therefore in order to minimise the final error it is preferable to employ a derivatisation reaction with no associated KIE and to minimise the amount of derivative atoms added. 

Derivatisation is often substance-specific, and thus although volatile derivatives of the expected compounds will be produced according to the... 

The high water-solubility of surfactants and their, often more polar, metabolites prevents direct application of gas chromatographic separation (GC) with appropriate detection. The necessary volatilisation without thermal decomposition can be achieved by derivatisation of the analytes, but these manipulations are time- and manpower-consuming and can be susceptible to discrimination. Additionally, each derivatisation step in environmental analysis is normally target-directed to produce volatile derivatives of the compounds to be determined. Unknown surfactants that are simultaneously present, but differ in structure and therefore cannot react with the derivatisation reagent, are discriminated under these conditions. 

Analyses of derivatives of NPEOs have been carried out with a large number of derivatisation reagents. Among them, polyfluorinated reagents, such as pentafluorobenzoyl chloride and heptafluorobutyric... 

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