Structural and thermodynamic analysis of heteroassociation of daunomycin and flavin mononucleotide molecules in water by <Superscript>1</Superscript>H NMR spectroscopy

Heteroassociation of the antitumor antibiotic daunomycin (DAU) with flavin mononucleotide (FMN) has been investigated by one-and two-dimensional ¹H NMR spectroscopy (500 MHz) in a water solution to determine the molecular mechanism of the combined action of the antibiotic and vitamin in the FMN-DAU system. The equilibrium constants of the reactions, induced proton chemical shifts, and thermodynamic parameters (ΔH, ΔS) of heteroassociation were determined from the concentration and temperature dependences of the proton chemical shifts in the interacting aromatic molecules. Analysis of the results indicate that heterocomplexes of riboflavin mononucleotide and daunomycin are formed due to stacking interactions between aromatic chromophores. The most probable spatial structure of the 1:1 DAU-FMN heterocomplex was determined by the molecular dynamics method using the X-PLOR program and the results of the analysis of the induced proton chemical shifts in molecules. Calculation of the relative content of self-and hetero-complexes of daunomycin for different values of the ratio (r) between the concentrations of flavin mononucleotide and daunomycin demonstrated that for r > 3, the contribution of DAU-FMN heterocomplexes to the equilibrium distribution of associates in aqueous solution is dominant. It is concluded that the aromatic molecules of vitamins, in particular, riboflavin, can form energetically strong heteroassociates with antitumor antibiotics in water solution and can thereby affect their medical and biological activity.     

Formation of complexes of antimicrobial agent norfloxacin with antitumor antibiotics of anthracycline series

The formation of complexes in solutions of the norfloxacin antimicrobial agent (NOR) with daunomycin (DAU) and nogalamycin (NOG), antitumor anthracycline antibiotics, was studied using ¹H NMR spectroscopy. Based on the concentration and temperature dependences of the chemical shifts of the protons of interacting molecules, the equilibrium constants and thermodynamic parameters (enthalpy and entropy) of heteroassociation of the antibiotics were calculated. It was shown that NOR interacts with DAU (NOG) in aqueous solutions forming stacked heterocomplexes with parallel orientation of the molecular chromophores. The conclusion was drawn that such interactions should be taken into account when anthracyclines and quinolones are jointly administered during combined chemotherapy, since they can contribute to the medico-biological synergistic effect of these antibiotics.     

1H NMR study of self-association of actinomycin D in an aqueous solution

This paper presents the results of a proton magnetic resonance study (500 MHz) of self-association of actinomycin D (AMD) antibiotic in an aqueous solution. The equailibrium constants and thermo-dynamic parameters (ΔH, ΔS) of molecular association as well as the limiting values of proton chemical shifts of associate molecules were determined from the concentration and temperature dependences of¹H NMR chemical shifts of AMD. The results were analyzed using dimeric and infinite-dimensional cooperative models of molecular self-association. The value of the cooperativity parameter indicates that AMD self-association is anticooperative, i.e., formation of aggregates larger than dimers is energetically unfavorable. The values of induced proton chemical shifts were used to determine the most probable mutual orientation of chromophores in AMD structure. Sevastopol State Technical University. Berkbeck College, London University. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 1, pp. 81–88, January–February, 1995. Translated by L. Smolina     

Self-association of daunomycin antibiotic in various buffer solutions

The self-association of an antitumor antibiotic, daunomycin (DAU), in various buffer solutions, including water-salt solutions, phosphate buffer, HEPES, and TRIS, was studied by 1D and 2D ¹H NMR spectroscopy at 500 MHz. The two-dimensional NOESY spectra and the concentration and temperature dependences of the chemical shifts of antibiotic protons in the solvents studied showed that the self-association parameters of DAU were independent of the type of buffer solutions. The most probable two spatial structures of the dimer of DAU in solution were constructed by the method of molecular mechanics. The mutual orientation of the chromophores was parallel in one structure and antiparallel in the other.     

<Superscript>1</Superscript>H NMR Study of Heteroassociation of Ethidium Homodimer and Propidium Iodide in Water

1D and 2D ¹H NMR spectroscopy (500 MHz) was used to study heteroassociation of the bifunctional intercalator ethidium homodimer (EBH) with a phenanthridine dye propidium iodide (PI) in an aqueous salt (0.1 mol/l NaCl). A physical model of equilibrium between various associated forms of ethidium homodimer and propidium in solution is suggested, the most probable forms being 1:1 and 1:2 complexes of PI with the EBH monomer and dimer. The chemical shifts of the EBH molecule in heterocomplexes, as well as the equilibrium constants and the thermodynamic parameters (enthalpy, entropy) of heteroassociations, were calculated from the concentration and temperature dependences of the proton chemical shifts. It is concluded that the propidium molecule is built (intercalated) into the EBH monomer and dimer to form 1:1 and 1:2 complexes mainly stabilized by dispersive and hydrophobic interactions.Original Russian Text Copyright © 2004 by A. N.Veselkov, M. P. Evstigneev, S. A. Hernandez, O. V. Rogova, D. A. Veselkov, and D. B. Davies__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 837–843, September–October, 2004.     

Complexation of the antibiotic daunomycin with desoxytetraribonucleoside triphosphate 5’-d(CpGpCpG) in aqueous solution

This paper presents the results of our study of the complexation of the antibiotic daunomycin with desoxytetranucleotide 5’-d(CpGpCpG) in aqueous salt solution by one- and two-dimensional (2D-TOCSY and 2D-NOESY)¹H NMR spectroscopy (500 MHz). The concentration and temperature dependences of the proton chemical shifts of molecules were measured and used to calculate the equilibrium reaction constants, the relative contents of different types of complex as functions of concentration and temperature, the limiting values of the proton chemical shifts of daunomycin in various complexes, and the thermodynamic parameters of complexation δH and δS. It is concluded that the triplet nucleotide sequences are the preferable sites at which daunomycin is attached. The binding of the second daunomycin molecule to both single-stranded and duplex forms of tetramer is markedly anticooperative. This is explained by the presence in the antibiotic of a positively charged amino sugar residue creating steric hindrances for the attachment of the second antibiotic molecule to the short tetranucleotide sequence. The most plausible spatial structure of the 1:2 complex of antibiotic with desoxytetranucleotide is constructed using the calculated values of the induced proton chemical shifts of daunomycin and 2D-NOE data. Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 276–286, March–April, 1999.     

Structural and Thermodynamic Analysis of Daunomycin Binding with Desoxyhexanucleotides with Different Base Sequences by NMR Spectroscopy

Complexation of the anthracycline antibiotic daunomycin (DAU) with self-complementary desoxyhexanucleotides with different base sequences in the chain, 5-d(CGTACG) and 5-d(CGCGCG), is studied in aqueous solution. Homonuclear 2D-¹H NMR spectroscopy (TOCSY and NOESY) and heteronuclear ¹H–³¹P NMR spectroscopy (HMBC) are used for complete assignment of the nonexchangeable proton resonances and the phosphorus signals and for qualitative determination of preferable DAU binding sites, respectively. Daunomycin is preferably intercalated into the first d(CG)-site of each hexanucleotide, and the aminosaccharide ring of DAU lies in the minor groove of the hexamer duplex, partly overlapping the third base pair. Quantitative analysis of DAU complexation with desoxyhexanucleotides was done by analyzing the concentration and temperature dependences of the DAU proton chemical shifts; the equilibrium reaction constants and the thermodynamic parameters of the formation of the 1:1, 1:2, 2:1, and 2:2 DAU complexes with hexamers, as well as the limiting values of the DAU proton chemical shifts were determined in aqueous solution. The antibiotic preferably binds with the triplet sections of the nucleotide sequence containing two neighboring CG-pairs of nitrogen bases flanked by the AT-pair in 5-d(CGTACG) compared to the triplets consisting of a sequence of three CG-pairs in the 5-d(CGCGCG) hexamer. The specific binding of daunomycin depends on the character of the hydrophobic interactions of the aminosaccharide ring of the antibiotic in the minor groove of the DNA double helix. Calculations have been carried out to determine the most probable spatial structures of the 1:2 DAU–desoxyhexanucleotide complexes; the results agree well with X-ray diffraction data.     

1H NMR Analysis of Heteroassociation of Caffeine with Mitoxanthrone in Aqueous Solution

Heteroassociation of caffeine (CAF) with the antibiotic mitoxanthrone (novatrone, NOV) in aqueous solution was studied by one-dimensional (1D) and two-dimensional (2D) ¹H NMR spectroscopy (500 MHz). The concentration and temperature dependences of the proton chemical shifts of the molecules in aqueous solution have been measured. The equilibrium constants of heteroassociation between CAF and NOV and the limiting proton chemical shifts of the aromatic ligands of the associates have been determined. The most plausible structure of the 1:1 CAF–NOV heterocomplex in aqueous solution was inferred from the calculated values of the induced proton chemical shifts and quantum-mechanical screening curves for CAF and NOV. The thermodynamic parameters of the formation of the CAF–NOV heterocomplex have been calculated. The relatively high heteroassociation constant (K = 256 ± 31 M^–1, T = 318 K), the positive value of entropy for heteroassociation [ S = 15.3 ± 4.0 J/(moleK)], and the structural features of the chromophore of the novatrone molecule indicate that hydrophobic interactions play a significant role in stabilization of the CAF–NOV heterocomplex.     

1H nmr study of heteroassociation of caffeine with acridine orange in aqueous solution

The molecular mechanism of the action of caffeine (CAF) as a complexing interceptor of aromatic ligands intercalated in DNA is considered using a typical intercalant — acridine orange (AO) dye. Hetero-association of CAF and AO was investigated by one- and two-dimensional H NMR spectroscopy (500 MHz). The concentration (at 298 and 308 K) and temperature dependences of the proton chemical shifts of molecules in aqueous solution were measured. The equilibrium constants of the CAF-AO hetero-association reactions at different temperatures and the limiting chemical shifts of the protons of the aromatic ligands of the associates were determined. The most plausible structure of the 1:1 CAF-AO helerocomplex in aqueous solution is suggested based on the calculated values of the induced proton chemical shifts of the molecules and the quantum mechanical screening curves for CAF and AO. The thermodynamic parameters of CAF-AO helerocomplex formation art calculated. The structural and thermodynamic analyses indicate that dispersion forces and hydrophobic interactions play a significant role in heterocomplex formation in aqueous salt solution. The relative contents of different types of associate in a mixed solution containing CAF and AO are estimated. The equilibrium of CAF-AO heteroassociates in solution is characterized in relation to temperature. Heteroassociation of CAF and AO molecules leads to decreased effective concentration of intercalant in solution and hence to decreased mutagenic activity of the dye. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 86-96, January–February, 2000.     

Peracetylated cellulose: end group modification and structural analysis by means of <Superscript>1</Superscript>H-NMR spectroscopy

A homologous series of partially hydrolyzed celluloses (level-off-DP cellulose) with weight-average molecular weight (DP_w) < 150 were peracetylated and characterized by ¹H-NMR spectroscopy. The results demonstrate the utility of ¹H-NMR spectroscopy to assign the chemical shifts of all end groups of the peracetylated cellulose. On the one hand, the chemical shifts of all methine and methylene protons of the non-reducing terminal end group (TEG) as well as the - and -anomer of the reducing end group (REG) could be determined by two-dimensional NMR techniques (COSY-DQF) and by selective excitation of isolated proton signals (1D-TOCSY) of these end groups. On the other hand, the spectral resolution was high enough to determine the number-average molecular weight (DP_n) of peracetylated level-off-DP cellulose (LODP cellulose acetates) as shown in comparison with the data of gel permeation chromatography (GPC). This molecular weight determination of cellulose using end group analysis by means of ¹H-NMR spectroscopy was demonstrated for the first time. Furthermore, a specific modification of hydroxyls in end groups could be exemplified in case of 1-OH-deacetylation of the REG of peracetylated LODP cellulose.     

The thermodynamic characteristics of retention of tricyclo[5.2.1.0<Superscript>2,6</Superscript>]decane isomer molecules on different sorbents in gas chromatography

The thermodynamic characteristics of sorption of the isomeric tricyclo[5.2.1.0^2.6]decane (tetrahydrodicyclopentadiene, TDCPD) molecules were for the first time determined experimentally and by molecular statistical methods under the conditions of gas-adsorption chromatography on graphitized thermal carbon black and gas-liquid chromatography on stationary liquid phases of different polarities (Apiezon L and Carbowax 20M). The effects of the chemical nature of sorbents on the retention of the TDCPD isomers are considered. A procedure for calculating the thermodynamic characteristics of adsorption of molecules with a complex structure is suggested within the framework of the atom-atom approximation of the semiempirical molecular statistical theory of adsorption for the example of isostructural norbornane molecules. The procedure involves simultaneous variation of geometric parameters and refinement of the parameters that determine the special features of the electronic structure. This method was used to determine several geometric parameters of the TDCPD molecules for the first time. The results were in close agreement with the quantum-chemical data.     

Investigation of the association of aromatic dyestuff molecules in aqueous solution by1H NMR

We have studied experimentally the proton chemical shifts of the molecules of Acridine Orange and proflavine in aqueous solution as a function of the.concentration of the aromatic ligands. A method is proposed for determining the chemical shifts of the protons in associations from the observed concentration dependence of the proton chemical shifts of dyestuff molecules in solution, which can be used at fairly high concentrations of the interacting molecules. The association constants of the dyestuff molecules and the proton chemical shifts in the association have been calculated. The proton shifts obtained have been used toether with a model of the ring currents to determine the most probable structure for the 1:1 molecular complexes of Acridine Organce and proflavine in aqueous solution.Sevastopol Institute for Instrument Construction. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 83–89, January–February, 1991. Original article submitted February 2, 1988.     

Mechanism of proton conductivity in polyvinyl alcohol-phenolsulfonic acid membranes from <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR data

With line narrowing during magic angle spinning in solid-state NMR, molecular mobility and hydration in composite membranes based on polyvinyl alcohol (PVA) and phenol-2,4-disulfonic acid (PSA) were studied as functions of the ratio of the acidic and polymeric components, the degree of cross-linking in the polymeric matrix, and the moisture content. It is shown that at high relative humidity proton transport takes place by means of the network of hydrogen bonds, which are formed by the H⁺ counterions, sulfonate groups, and water molecules. At low moisture content, the hydroxyl groups in PVA play an active role in proton transport.     

A <Superscript>1</Superscript>H NMR study of Nile Red solvation

In order to evaluate the capabilities of NMR spectroscopy for investigation of the solvatochromic effect in luminophore solutions, the ¹H NMR chemical shifts of Nile Red in mixtures of solvents with different polarities (benzene, toluene, methanol) has been determined. Their dependence upon the solvent mixture composition has been revealed and binding sites for luminophore and solvent component molecules have been determined. The results of the NMR study are consistent with data on the fluorescence of Nile Red solutions in toluene-ethanol mixtures.     

Evaluation of <Superscript>13</Superscript>C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

A convenient methodology was developed for a very accurate calculation of ¹³C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of ¹³C NMR chemical shifts. In addition, the particular dependencies of ¹³C chemical shifts on the geometry of cyclopropane ring were investigated.     

Computational <Superscript>19</Superscript>F NMR. 1. General features

Fluorine-19 NMR chemical shifts have been calculated for a wide variety of fluorine-containing inorganic and organic molecules by relativistic DFT methods. The agreement with experimental values, spanning the whole range from ClF to FOOF, is satisfactory but somewhat less accurate than for comparable light nuclei. ¹⁹F shifts in uranium chlorofluorides have been analyzed in detail, and the poor agreement with experiment is partly rationalized.     

Some observations on the stereospecificity of weakly bound complexes of organic molecules

Vinyl bromide-benzene/p-xylene and acrylonitrile-benzene/p-xylene complexes have been studied by measuring the ¹H chemical shifts induced in the vinyl protons by the aromatic molecules. Evidence is presented that indicates that the complexes are 1:1, and values for the equilibrium quotient, K_x, and the full induced shift Δ_c, are deduced for each proton; similar values of K_x are obtained for each of the three viny] protons. It is shown that the molecular interactions are specific. However, the complexes cannot be considered to have fixed geometry, but molecules involved take up a variety of relative orientations.     

NMR chemical shift substituent effects: 2-α-monosubstituted N,N-diethylacetamides

¹H NMR chemical shifts for some α-hetero-substituted N,N-diethylacetamides were recorded. The resonance assignments for the syn- and anti-methylene and -methyl protons have been made unambiguously through their aromatic solvent induced shifts and are opposed to the literture assignments for the N-methylene protons. An empirical relationship between the Charton polar (σ_L) and steric (V) parameters and the α-methylene proton resonances was found. The N-methylene proton chemical shifts also showed a qualitative dependence on the α-substituent electronegativity, while the N-ethyl methyl proton chemical shifts were related to the α-substituent steric effects. The Paulsen and Todt anisotropic model and the more populated rotamers proposed seem to explain the results very well.     

Non-empirical and DFT calculations of <Superscript>19</Superscript>F and <Superscript>13</Superscript>C chemical shifts in the NMR spectra of substituted pentafluorobenzenes

Chemical shifts in ¹⁹F and ¹³C NMR spectra of substituted pentafluorobenzenes are calculated by Hartree-Fock and density functional theory methods. The calculated values are compared with the experimental data known from the literature. It is shown that chemical shifts in non-polar solvents can be predicted sufficiently accurately by the GIAO-DFT(PBE/L22) method. This method is used to predict the ¹⁹F and ¹³C chemical shifts of a heptafluorobenzyl cation in the SbF₅ medium. The best agreement between the calculated and experimental values is achieved when the counterion effect is taken into account.     

[1-B<Subscript>10</Subscript>H<Subscript>9</Subscript>N<Subscript>2</Subscript>]<Superscript>−</Superscript> and [1-CB<Subscript>9</Subscript>H<Subscript>10</Subscript>]<Superscript>−</Superscript> anions: an attempt of quantum chemical calculations

Comparative quantum chemical calculations of structural parameters, chemical shifts of ¹¹B NMR spectra, and atomic charges in 10-vertex boron hydride anions [1-CB₉H₁₀]⁻ and [1-B₁₀H₉N₂]⁻ were performed using the restricted Hartree-Fock method with the 6-31++G(D,P) basis set. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1853–1855, September, 2007.