Stefan Paszyc

1H NMR studies of gossypol and its complexes with some organic compounds

Abstract The 1H NMR spectra of gossypol and its complexes with some organic compounds in various solvents have been analyzed. In CDCl3 solution gossypol exists as the (±) aldehyde tautomer. In other solvents, aldehyde and lactol tautomers are in equilibrium, depending on the nucleophilicity of solvent (B). In the case of complexes of gossypol with organic compounds, the equilibrium is shifted to the aldehyde form, and the (±) diastereoisomers were observed in the 1H NMR spectrum due to asymmetric nonspecific interactions. Two types of tetrabutylammonium complexes of gossypol, 2:1 and 4:1 have been prepared. The spectrum of the 2:1 salt points to a very complex equilibrium in solution without a ketol tautomer. In this case a new type of intramolecular hydrogen bond is formed. Ketol is the main tautomeric form of the 4:1 salt, which shows a very strong intermolecular OHO− type hydrogen bond.

Spectroscopic and semiempirical studies of gossypol complexes with Fe2+ and Fe3+ cations

Abstract The complexes of gossypol with Fe2+ and Fe3+ cations were studied in acetonitrile by UV–Vis and FT-IR spectroscopy. Very complex equilibria and structural changes were observed for various ratios of gossypol–iron cation mixtures. With the formation of complexes, the ketol–ketol tautomer form of gossypol was favored. With increasing concentration of iron cation in the mixture, the deprotonation of hydroxyl groups was indicated. The semiempirical studies show that the most stable complexes of gossypol with iron cations are 1:4, 1:1 and 2:1. The structures of these complexes are discussed.

1H AND 13C NMR Studies of Tetrabutylammonium Salts of Gossypol in Chloroform Solution

Abstract Gossypol and its two 2:1 and 4:1 tetrabutylammonium salts were investigated by 1H and 13C NMR spectroscopy in CDCl3 solution. In this solution gossypol exists as a symmetrical aldehyde-aldehyde tautomer. In the case of the two 2:1 and 4:1 tetrabutylammonium salts of gossypol in chloroform the anhydrogossypol form was observed, instead of the ketol form which was determined in CD3 CN solution.

Fourier transform infrared study on the identification of gossypol tautomers

Abstract Gossypol and its adducts with some organic compounds, as well as its two tetrabutylammonium salts (2:1 and 4:1), were studied in various solutions by Fourier transform IR (FTIR) spectroscopy. In CH 2 Cl 2 solution gossypol exists as the aldehyde tautomer. In the DMSO-d 6 solution an equilibrium between the aldehyde and lactol tautomers was observed in which the predominant form is the latter. The IR spectrum of the 2:1 tetrabutylammonium salt indicates that a very complex equilibrium occurs in CD 3 CN solution. In the case of the 4:1 salt the ketol tautomeric form is associated via very strong intermolecular (O⋯⋯H⋯⋯O) − hydrogen bonds with large proton polarizability.

The tautomerization of gossypol as a function of the presence of Ni2+, Cu2+ or Zn2+ cations

Abstract 1 : 1 Complexes of gossypol with Ni(AuCl 4 ) 2 , Cu(AuCl 4 ) 2 and Zn(AuCl 4 ) 2 were studied in acetonitrile using FT-IR spectroscopy. With this complexation the tautomeric equilibrium of gossypol is completely shifted from the aldehyde-aldehyde to the lactol-lactol tautomer in the case of Ni 2+ and Cu 2+ complexes, and to the ketol-ketol tautomer with the Zn 2+ complex. The nature of the interaction of these ions with gossypol, especially that of the Zn 2+ ion, is explained in detail. Furthermore, all changes concerning hydrogen bond formation and the reasons for it are discussed.

The influence of temperature on the proton polarizability of an intramolecular hydrogen-bonded system within the gossypol molecule

Abstract The gossypol molecule was studied in CH 2 Cl 2 solution as a function of temperature using FTIR spectroscopy. With decreasing temperature some molecules associate via phenol-phenol hydrogen bonds. Furthermore, with decreasing temperature the hydrogen-bonded system O 6 H...O 7 H...OC⇌O 6 − ...HO 7 ...HOC + gains a large proton polarizability caused by collective proton motion within this system.

The structure of Gossypol as a function of the presence of HAuCl4 and of Be2+ ions

Abstract Solutions of gossypol with HAuCl 4 and Be(AuC1 4 ) 2 have been studied by FT-IR spectroscopy. Addition of HAuCl 4 shifts the tautomeric equilibrium of gossypol completely from the aldehyde—aldehyde to the ketol-ketol tautomer. On addition of Be(AuCl 4 ) 2 , 1:1 Be 2+ gossypol complexes are formed. With this complexation the tautomeric equilibrium of gossypol is completely shifted from the aldehyde—aldehyde to the lactol—lactol form. An IR continuum in the region 1100-500 cm −1 indicates that the Be 2+ ion fluctuates within the gossypol molecule between four O acceptor atoms. A four minima Be 2+ potential is present with steep slopes at the acceptor O atoms. The complex shows so-called “Be 2+ polarizability” since the Be 2+ can easily be shifted within this potential.

Photophysical studies of luminarosine: a new, highly fluorescent ribonucleoside with pteridine-like betaine as the aglycone

The solvent and pH dependence of the absorption and fluorescence spectra, fluorescence quantum yields and lifetimes, and fluorescence quenching behaviour of 4-(2,3,5-tri-O-acetyl-β-D-ribofuranosylamino)pyrido[2,1-h]pteridin-11-ium-6-olate, its α-anomer, the parent ribonucleoside 4-(β-D-ribofuranosylamino)-pyrido[2,1-h]-pteridin-11-ium-5-olate (luminarosine) and the aglycone 4-aminopyrido[2,1-h]-pteridin-11-ium-5-olate (luminarine) are reported. Spectroscopic properties of these compounds in solvents of different polarities are characterized by evidence of the occurrence of a highly dipolar, charge-transfer excited state within the heterocyclic betaine system. The pH dependence of the absorption spectra of luminarosine and luminarine infer the occurrence of ground state prototropic equilibria in solution involving protonation of the negatively charged oxygen atom followed by tautomerism to a lactam. The excited state prototropic equilibria, as shown by fluorescence properties, seem to be more complex and suggest the possible occurrence of proton-transfer and/or phototautomerization reactions.

Emission properties of gossypol in solution

Abstract Steady-state emission properties of gossypol in acetonitrile at room temperature have been studied using a HPLC system equipped with a specially improved highly sensitive fluorescence detector (ΦF⩾10−7). The fluorescence lifetimes (τ) have been determined using a time-correlated single photon counting system. At room temperature gossypol shows weak fluorescence with the overall quantum yield of ΦF=5×10−5. On the basis of a comparison of the excitation emission spectra with the absorption spectrum and the radiative properties of gossypol, the origin of gossypol fluorescence from two tautomeric forms: aldehyde in S 1 (n, π ∗ ) (τ=300 ps ) and S 2 ( π , π ∗ ) (τ=10 ps ) and lactol in S 1 (n, π ∗ ) (τ=18 ps ) state was suggested.

POSTSYNTHETIC TRANSFORMATIONS OF OLIGODEOXYNUCLEOTIDES ORIGINATED AT 6-METHYLTHIO-PURINE SITE

Abstract New route to oligodeoxynucleotides labeled with fluorescent luminarine was explored. Regioselective oxidation of 6-methylthio-purines to 6-methylsulphoxides reactive toward pyridine was achieved. Upon UV irradiation of 6-pyridinium-purines oligonucleotide cleavage instead of phototransformation to luminarine was observed.