Acid-base and copper (II) complexation equilibria of poly(inosinic)-poly(cytidylic)

Abstract

The acid‐base and copper (II) complexing properties of the heteropolynucleotide poly(inosinic)‐poly(cytidylic) acid were studied by means of potentiometric, spectrophotometric, CD, and molecular fluorescence titrations in a working aqueous medium of 0.15 M ionic strength at 37°C. The study of the acid‐base equilibria has proved the existence of four different species in the pH interval 2–11. Two new species are detected in the presence of copper(II) ion, at acidic and neutral pH values. Spectrophotometric, CD, melting, and fluorescence data were treated with a multivariate curve resolution procedure that allowed the determination of the number of species simultaneously present in each system [acid‐base equilibria, copper(II) complexation equilibria], and the estimation of their concentration profiles and of the pure spectra for each species. From the concentration profiles an unambiguous assignment of which species are present at any pH conditions can be made. Furthermore, the knowledge of the pure uv‐visible, fluorescence, and CD spectra recovered by the proposed resolution method for each species brings important structural information. When this mathematical approach was applied to the thermal denaturation data, the melting profile and the uv pure spectra for all the different species or conformations formed in the melting process, were calculated. © 1997 John Wiley & Sons, Inc. Biopoly 42: 271–283, 1997

Noise propagation and error estimations in multivariate curve resolution alternating least squares using resampling methods

“…The mean and standard deviation for each pK a value were obtained from the eight estimations of the pK a values obtained in the MCR-ALS analysis of each individual pH titration data set. Results obtained were in good agreement with those obtained previously [19]. Lack of fit values were in the range between 0.4% and 1.6%.…”

“…Eight acid-base titrations of the polynucleotide poly(I)poly(C) were performed. More details about how to perform one of these titrations were described in an earlier work [19]. One experiment consisted in a titration in the pH range between 2 and 8.1.…”

“…First the set of theoretical concentration, C, and spectral, S T , profiles was obtained from resolution of the experimental data obtained in the earlier work [19]. A simulated data matrix D sim was then built up assuming the fulfillment of a bilinear model (as in the generalized Beer law [21] in matrix form (Scheme 1a)):…”

“…See References [6,7,11,14] for explanations of the use of the ALS iterative optimization procedure. MCR-ALS has been extensively used to analyze spectroscopic data obtained in biochemical and biophysical process monitoring [3,4,19] and other data systems [1,2].…”

“…The data example in this work is the acid-base titration of a polynucleotide monitored by UV absorption spectroscopy. This is a three-component acidbase equilibrium system with highly overlapping spectral profiles and some selectivity in concentration profiles at the beginning and end of the titration [19].…”