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N Purdie

Publications and source records attributed to N Purdie.

At least 19 recordsLinked to original sources
PubMed1999

Algorithms for validating chiral properties of insulins.

The combination of chiral ligand exchange on Cu(II) complexes in aqueous base with circular dichroism spectropolarimetric detection provides excellent avenues to validate the chirality properties of oligopeptides and proteins. The method is quick and simple and has the potential for development into an automated, routine procedure for quality control applications. Target analytes used for this first study of a protein system are human, porcine, and bovine insulins prepared by different procedures and obtained from different sources, production lots, and manufacturers. The analytical specificity of the test makes the method a potentially useful technique for validating the chirality properties of many peptide and protein forms.

Algorithms↗
PubMed1999

Algorithms for the quantitative validation of chiral properties of peptides.

Complexation with Cu(II) ion in strong aqueous base, combined with visible range circular dichroism detection, were used to quantitatively differentiate among the L-enantiomers of the GG, GA, GY, AG, AA, AY, YG, YA, and YY dipeptides and the D-enantiomer of GA. Using ellipticity data at all (n = 1500) wavelengths in the measured spectra, and two novel data reduction procedures, quantitative determinations were made of the compositions of binary mixtures. For mixtures made with the L-GA and D-GA enantiomers, the accuracy of the measured enantiomeric purities was better than 0.17 % over the 1-48 % range for the minor component. The method has considerable potential for use in quality control of peptide and protein biotechnological drug forms.

Algorithms↗
PubMed1999

Tripeptide discriminations using circular dichroism detection.

A general spectroscopic method is described that might be applied to validating amino acid sequences in peptides and protein fragments with a view to it becoming a routine procedure with which to characterize biotechnology drug products. The tripeptides are the L-enantiomers of GGA, GGH, GGI, GGL, GGF, GHG, LGG, and YGG. The simple procedure calls for their complexation with Cu(II) ion in strong aqueous base. Binding the first three residues in the sequence, beginning at the amine terminus, completes the coordination sphere of the Cu(II) ion, so duplication of the initial sequence from peptide to peptide could be an important limiting factor in determining the extent of differentiation that is possible. The analytical focus is the selectivity associated with the chirality properties of the peptides. Detection is by circular dichroism operating in the visible range. The eight analytes were chosen as representative of a series where the sequences are most similar and therefore potentially the most difficult to discriminate spectroscopically. All have just one chiral center. Using ellipticity data at all (n = 1500) wavelengths in the measured spectra, and two novel data reduction procedures, total discrimination among all eight analytes is achieved. The method has considerable potential for use in quality control of peptide and protein biotechnological drug forms, especially their enantiomeric purities.

Algorithms↗
PubMed1999

A convenient assay method for the quality control of peptides and proteins.

The development of a convenient and very accurate procedure with which to discriminate among subsets of structurally similar peptides and proteins, and measure enantiomeric purities with very good accuracy, has been described in a series of recent articles. A factor preventing its general application to all peptide forms is that comparisons were originally limited to closed subsets of structurally similar types, e.g., dipeptides, tripeptides, and insulin drug forms. In the most recent of these articles, a modification to the method was described which did enable the comparisons to be extended between sets, in particular the di-and tripeptides. That same modification is extended even further in this article to include additional di- and tripeptides, glycylglycine oligomers, insulin drug forms, and neuropeptides. The same principal component analysis treatment used for data reduction and statistical comparisons in prior work enables the discrimination among 49 of the total of 51 analytes investigated.

Circular Dichroism↗
PubMed1999

Clustering of CD spectral data as a prototype QSAR model for neuropeptides.

An analytical method that might eventually qualify as a general quality control assay procedure for polypeptide drug forms was described in the companion article to this paper. The detector is visible range circular dichroism spectroscopy. Multivariate data analysis reduced the spectral data to essentially four principal components (or factors) that are characteristic of each analyte. The level of analytical selectivity achieved among 51 analytes is very high. Using an alternative factor analysis algorithm, the selectivity is even more conveniently accomplished in the form of a 2-D cluster diagram presentation that has the potential of being a prototypical predictive in vitro model for correlating experimental data with structure-activity or structure-function relationships. Clustering of the analytes is a consequence not only of the chiral interactions associated with ligand exchange in the immediate primary coordination sphere of the host derivatizing reagent, but also of long-range intermolecular interactions between the coordination architecture of the host and the chiral polypeptides.

Circular Dichroism↗
PubMed1994

Induced circular dichroism study of the aqueous solution complexation of cello-oligosaccharides and related polysaccharides with aromatic dyes.

Acetobacter xylinum, grown in the presence of low levels of the water-soluble dye Calcofluor White ST produces a pellicle of cellulose that has no detectable crystallinity. Biological factors of this sort are probably more important than physical factors in controlling the higher order structures of celluloses. Circular dichroism (CD) is induced by complexes that are formed by specific interactions between chiral oligosaccharides and dye molecules. Using CD, equilibrium constants were measured for the association reactions between various dyes with a series of cello-oligosaccharides (n = 2-6), methylcellulose, hydroxypropylcellulose (HPC), amylose, cyclomalto-oligosaccharides (cyclodextrins), and the linear malto-oligosaccharides (n = 3-7). Possible structural features of the complexes are discussed. Dyes that are capable of binding to the higher cello-oligomers in aqueous solutions are the same dyes that modify the solid structure of bacterial cellulose. An analogy between the binding of water-soluble dyes to cello-oligosaccharides and the binding of the cellulose-degrading enzyme, cellobiohydrolase I, to cellulose is discussed.

Acetobacter↗
PubMed1994

Determination of enantiomers in ephedrine mixtures by polarimetry.

Enantiomeric purities have been measured with precisions that are equivalent to those obtained from chiral chromatography by a simple ligand substitution reaction into the first coordination sphere of Cu(II)-tartrate complexes. The model systems are binary mixtures of the ephedrines. Ligand exchange reactions are done in bulk aqueous media. The detector is polarimetry. Multivariate regression analyses of optical rotation data measured at five wavelengths are used to prepare calibration and prediction models for binary mixtures of the enantiomers.

Algorithms↗
PubMed1992

On the helix sense of gramicidin A single channels.

In order to resolve whether gramicidin A channels are formed by right- or left-handed beta-helices, we synthesized an optically reversed (or mirror image) analogue of gramicidin A, called gramicidin A-, to test whether it forms channels that have the same handedness as channels formed by gramicidin M- (F. Heitz et al., Biophys. J. 40:87-89, 1982). In gramicidin M- the four tryptophan residues have been replaced with phenylalanine, and the circular dichroism (CD) spectrum therefore reflects almost exclusively contributions from the polypeptide backbone. The CD spectrum of gramicidin M- in dimyristoylphosphatidylcholine vesicles is consistent with a left-handed helical backbone folding motif (F. Heitz et al., Biophys. Chem. 24:149-160, 1986), and the CD spectra of gramicidins A and A- are essentially mirror images of each other. Based on hybrid channel experiments, gramicidin A- and M- channels are structurally equivalent, while gramicidin A and A- channels are nonequivalent, being of opposite helix sense. Gramicidin A- channels are therefore left-handed, and natural gramicidin A channels in phospholipid bilayers are right-handed beta 6.3-helical dimers.

Amino Acid Sequence↗
PubMed1991

Direct measure of the low-density fractions of serum cholesterol.

Data on total cholesterol (TC) and its distribution among the three solubilizing lipid fractions in human serum have been obtained from three independent laboratories, and binary linear correlations between TC and each of the various fractions are compared. Two sources used the approved double-enzymatic multistep Allain-Trinder reaction with absorption detection. In the third method, which is entirely new, a nonenzymatic chromogenic reaction and circular dichroism (CD) detection were used. TC results from all three sources are in excellent agreement. HDL-C values measured by both enzymatic methods also agree in their correlations with TC but these are quite different from the correlation observed between HDL-C and TC values obtained by the new nonenzymatic procedure. Reasons are given which suggest that the nonenzymatic method is more accurate for the measurement of the low-density lipid fractions and why health risk determinations that are based upon calculated values for this variable should be deemphasized until a more dependable procedure is approved for use.

Cholesterol↗
PubMed1989

Analytical applications of circular dichroism.

The goal of the present research has been to develop a selective analytical detection procedure for the easy identification and assay of drugs and related substances present in complex mixtures, without a chromatographic separation step or other work up. The detector of choice is circular dichroism (CD) spectropolarimetry which has the appropriate balance between degree of analytical selectivity and breadth of application. Applications that are described are selected from work carried out in the context of forensic, clinical, and pharmaceutical chemistries, and specifically include discussions of the analyses of enantiomeric mixtures of nicotine and cocaine, the D and E vitamins, and cholesterol and other steroids.

Animals↗
PubMed1984

Determination of "Brompton's cocktails" by circular dichroism.

Circular dichroism spectropolarimetry has been applied to the simultaneous determination of chiral compounds in binary mixtures without separation or sample preparation steps. A strategy which uses data measured at equivalent wavelength pairs simplifies the calculations. Correspondence is within +/- 2% of the compositions of prepared standard mixtures.

Chloroform↗