Induced circular dichroism of DNA-dye complexes

The binding of methylene blue, proflavine, and ethidium bromide with DNA has been studied by spectrophotometric titration. Methylene blue and proflavine or methylene blue and ethidium bromide were simultaneously titrated by DNA. The results indicate that all of these dyes compete for the same bindine sites. The binding properties are discussed in terms of symmetry. The optical properties of the dye–DNA complexes have been studied as a function of DNA/dye ratio. The induced circular dichriosm due to dye–dye interaction was measured at low dye/DNA ratios for cases involving both the same dye and different dyes. A positive Cotton effect for DNA–proflavine complex may be induced at 465 mμ by eithr proflavine or ethidium bromide, whereas a netgative Cotton effect at 465 mμ may be induced by methylene blue. The limiting circular dichroism, with no dye–dye interaction, and the induced circular dichroism spectra are discussed in terms of symmetry rules.     

Effect of chemical structures of acridine and triphenylmethane dyes on the induced optical activity of DNA-dye complexes

Fifteen symmetrically substituted acridine dyes, all of which are interrelated by their chemical structures, each belonging to a C_2v symmetry, and three triphenylmethane dyes with amino or dimethylamino substituents are utilized to study necessary conditions for the appearance of extrinsic Cotton effects upon their binding to native and heat-denatured deoxyribonucleic acid (DNA). Three different kinds of the DNA–dye complexes, i.e., (1) dye added to native DNA, (2) heat-denatured DNA–dye complex, and (3) dye added to preheated DNA, were examined for each dye at a fixed P/D value of about 4. Optical activity was always observed for the compelexes of type (1) in each absorption band of the dyes in the visible and near-ultraviolet region. Two exceptions are 9-acetamido- and 9-hydroxyacridine, both being nonionic in aqueous solution at a pH range of 6. Acridinium chloride was unable to exhibit any definite extrinsic Cotton effect for complexes (2) and (3). Thus, the monocationic form of a dye due to the protonation or quaternization of the ring nitrogen in acridines or exonuclear amino nitrogen in triphenylmethane dyes is concluded to be an essential factor for extrinsic Cotton effect to appear. Changes in the absorption spectra upon complex formation are also related to the structure of dyes. Hypochromism and bathochromism are associated with the induced optical activity in all cases in the presence of native and denatured DNA.     

Dielectric behaviour of frozen DNA in solution

In this article, measurements are reported on ice and frozen DNA solutions between 100 Hz–10 MHz. Pure ice is shown to exhibit single relaxation behaviour, which confirms previous work taken over a more restricted frequency range. The frozen DNA solution displays double‐dispersion behaviour. One dispersion centred around 3 kHz is due to a defect mechanism while the other, centred around 2 MHz, may be attributed to counterion flow through the water immediately adjacent to the DNA molecule. Bioelectromagnetics 20:40–45, 1999. © 1999 Wiley‐Liss, Inc.     

Polarized fluorescence studies of electrically oriented DNA-dye solutions

Transient changes have been recorded in each of the four polarized components of fluorescence, when dilute solutions of dye-tagged DNA are subjected to short electric pulses. The directions of the absorption and emission transition moments, and hence of the plane of the dye molecules, relative to the DNA geometry have been estimated for eleven dyes. Data obtained for ethidium bromide and five acridine derivatives are consistent with the intercalation model generally accepted for these dyes. In addition, it is shown that neutral red, acridine red and probably auramine O also bind with their molecular planes essentially perpendicular to the long helical axis. The remaining two, hydroxystilbamidine and the bibenzimidazole derivative Hoechst 33258, give rise to effects which indicate that these molecules bind in such a manner that the absorption and emission transitions are closely associated with the grooves of the DNA helix.     

Dielectric behaviour and conformational stability of collagen on interaction with DNA

Collagen-DNA interaction studies will aid in improving the stability of DNA against nucleases. In the present study, the effect of DNA on different physico-chemical properties of collagen like viscosity, conformation and dielectric behaviour has been studied. Increase of DNA concentration leads to the increment of viscosity of collagen at the pH 4 and 5, but the trend is reversed at the pH of 6 and 7 due to the formation of collagen fibrils. The temperature dependent CD spectroscopic studies for collagen-DNA conjugate showed that thermal stability of collagen is modulated with increasing molar concentration of DNA. It also shows that DNA interactions with collagen did not result in change in the triple helical structure of collagen. Impedance measurements show that the strength of ion pairs for different molar concentrations of collagen-DNA conjugates has changed. Nyquist plot for collagen-DNA conjugate posses higher Y″ at DNA concentration of 1:25 and 1:50 whereas at 1:1 and 1:10 lower Y″ than the native collagen have been observed. An understanding of this nature of the collagen-DNA interactions is helpful for gene delivery applications.     

Ligand redox non-innocent behaviour in ruthenium complexes of ethynyl tolans

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(CCC₆H₄CCSiMe₃)(L₂)Cp′] and [Ru(CCC₆H₄CCC₆H₄R-4)(L₂)Cp′] (R = OMe, Me, CO₂Me, NO₂; L₂ = (PPh₃)₂, Cp′ = Cp; L₂ = dppe; Cp′ = Cp^∗) have been synthesised. One-electron oxidations of these complexes gave the corresponding radical cations, which were significantly more chemically stable in the case of the Ru(dppe)Cp^∗ derivatives. The representative complex [Ru(CCC₆H₄CCC₆H₄OMe-4)(dppe)Cp^∗] was further examined by spectroelectrochemical (IR and UV-Vis-NIR) methods. The results of the spectroelectrochemical studies, supported by DFT calculations, indicate that the hole is largely supported by the ‘RuCCC₆H₄’ moiety in a manner similar to that described previously for simple aryl ethynyl complexes, rather than being more extensively delocalized along the entire conjugated ligand.     

Electric behaviour of natural and demineralized bones. Dielectric properties up to 1 GHz

In this paper we have measured the dielectric spectrum of water-saturated bones in native and demineralized states up to 1 GHz in the time domain. A novel method of analysis of the time domain spectroscopy data has been used. The results show a dielectric dispersion centered around 400 MHz for native samples and around 200 MHz for demineralized ones. The proposed mechanism for this dispersion is the movement of polar side chains, which is in agreement with what happens in hydrated collagen fibres.     

Calorimetry of DNA-dye interactions in aqueous solution: I. Proflavine and ethidium bromide

The results of an investigation on the interaction of proflavine and of ethidium bromide with DNA (calf thymus) in dilute aqueous solution are reported. The binding of the two dyes by DNA has been studied by means of microcalorimetric and of equilibrium dialysis measurements. Data on the thermodynamics of dimerization of both proflavine and ethidium bromide in aqueous solution obtained on the basis of spectroscopic and/or calorimetric experiments are also reported.The enthalpy data show that dye-dimerization and dye “strong” interaction with DNA are energetically favourable and quite similar while only in the latter case the phenomenon is also entropy driven. This is taken as further evidence in support of the concept that “strong” interaction-of both proflavine and ethidium bromide with DNA means dye molecules intercalation into the native, double helical structure of the biopolymer.     

Synthesis, structures and luminescent behaviour of tridentate salicylaldiminato-type borate complexes

Treatment of the ligands 3,5-tBu₂-2-(OH)C₆H₂CHNR [R = 2-(CO₂H)C₆H₄ (1a) and 2-(CO₂H)C₁₀H₆ (1b)] with trimethylborate, B(OMe)₃, in toluene yields, after work-up, the yellow crystalline complexes {[3,5-tBu₂-2-(O)C₆H₂CHNR]B(OMe)} [R = 2-(CO₂)C₆H₄ (2a) and 2-(CO₂)C₁₀H₆ (2b)], respectively. Further treatment of these complexes with trifluoromethanesulfonic (triflic) acid, CF₃SO₃H, followed by recrystallisation from tetrahydrofuran (thf) afforded the triflate salts [{3,5-tBu₂-2-(O)C₆H₂CHNR}B(thf)][CF₃SO₃] [R = 2-(CO₂)C₆H₄ (3a) and 2-(CO₂)C₁₀H₆ (3b)]. An electroluminescent device was constructed using 2a, which produced orange-green light with broad emission spectra (maximum brightness of 5 cd/m² being observed at 13 V). Compounds 1a and 2b·2MeCN have been characterised by single crystal X-ray structure determinations.     

Polyelectrolyte complexes of glycol chitosan with some mucopolysaccharides: Dielectric properties and electrical conductivity

The dielectric properties, DC electrical conductivity, and I-V characteristics of thin films of polyelectrolyte complexes formed by glycol chitosan (GlChi) with mucopolysaccharides chondroitin sulfate A (CSA), chondroitin sulfate C (CSC), and hyaluronic acid (HA) have been studied at different temperatures. The dielectric constant and the loss factor were measured at frequencies ranging from 1 to 100 kHz at all temperatures. The behavior of GlChi–CSA and GlChi–CSC complexes resembles that of the GlChi–dextran sulfate complex reported earlier. The GlChi–HA complex behaves differently and is similar to the GlChi–alginic acid complex reported [Srinivasan, R. & Kamalam, R. (1982) Biopolymers 21 , 251–263, 265–275].     

Structure and solution behaviour of cyclooctadiene complexes of platinum(II)

The substitution behaviour of [PtCl(R)(COD)] (R⁻ = Me and Fc) complexes, by the stepwise addition of phosphine ligands, L (L = PPh₃, PEt₃ and P(NMe₂)₃), were investigated in situ by ¹H and ³¹P NMR spectroscopy. Addition of less than two equivalents of the phosphine ligand results in the formation of dimeric molecules with the general formula trans-[Pt(R)(μ-Cl)(L)]₂ for the sterically demanding systems where R⁻ = Me/L = P(NMe₂)₃ and R⁻ = Fc/L = PEt₃, PPh₃ and P(NMe₂)₃ while larger quantities resulted in cis- and trans mixtures of mononuclear complexes being formed. In the case of the relatively small steric demanding, strongly coordinating, PEt₃ ligand the trans-[PtCl(R)(PEt₃)₂] mononuclear complexes were exclusively observed in both cases. The crystal structures of the two substrates, [PtCl(R)(COD)] (R⁻ = Me or Fc), as well as the cis-[PtCl(Fc)(PPh₃)₂] substitution product are reported.     

Synthesis, characterisation and solution behaviour of fluoroalkyl phosphoryl complexes of tin tetrachloride

The synthesis, characterisation and solution behaviour of a series of octahedral complexes SnCl₄·2L (L = R₂NP(O)(OCH₂CF₃)₂; R = Me (1); Et (2) or L = P(O)(OCH₂R_f)₃; R_f = CF₃ (3); C₂F₅ (4)) are described. Complexes 1-4 were prepared from SnCl₄ and 2 equiv. of the ligand, L, in anhydrous CH₂Cl₂ solution. The adducts have been characterised by multinuclear (¹H, ³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analysis. In dichloromethane solution, the NMR data showed the presence of a mixture of cis and trans isomers for 1 and 2 and only the cis isomer for 3 and 4. The difference could be interpreted in terms of the electronic effects of the substituents on the phosphorus atom of the ligand. In addition, the solution structure of the complexes studied by variable temperature ³¹P-{¹H} and ¹H NMR in the presence of excess ligand indicated that the ligand exchange on the cis isomer dominates the chemistry. The metal-ligand exchange barriers were estimated to be 13.38 and 11.39 kcal/mol for 1 and 3, respectively. The results are discussed and compared with those previously reported for the related hexamethylphosphoramide adduct, SnCl₄·2HMPA.     

Solution behaviour and biological activity of bisamidine complexes of platinum(II)

A series of platinum(II) amidine complexes were previously prepared with the aim of obtaining a new class of platinum-based antitumour drugs. This series includes compounds of the type cis--[PtCl2{Z-HN=C(NHMe)Me}2] and trans-[PtCl2{Z-HN=C(NHMe)Me}2] (1, 2), cis-[PtCl2{E-HN=C(NMe2)Me}2] and trans-[PtCl2{E-HN=C(NMe2)Me}2] (3, 4), cis-[PtCl2{Z-HN=C(NHMe)Ph}2] and trans-[PtCl2{Z-HN=C(NHMe)Ph}2] (5, 6), and cis-[PtCl2{HN=C(NMe2)Ph}2] and trans-[PtCl2{HN=C(NMe2)Ph}2] (7, 8). The reactions with dimethyl sulfoxide were studied for complexes 5-8; the formation of cationic species containing coordinated dimethyl sulfoxide was demonstrated by NMR experiments and electrospray ionization mass spectrometry. In this work, the amidine platinum(II) complexes were tested for their in vitro cytotoxicity on a panel of various human cancer cell lines. The results indicate that the benzamidine complex 8 was the most effective derivative also circumventing acquired cisplatin resistance as demonstrated by chemosensitivity tests performed on cisplatin-sensitive and cisplatin-resistant cell lines. The studies concerning the cellular DNA damage on both parental chemosensitive and resistant sublines suggest for the new trans-amidine complex a different mechanism of action compared with that exhibited by cisplatin.     

The oxygenation of cyclohexane under Gif conditions - The catalytic behaviour of iron complexes

The catalytic oxygenation of cyclohexane to cyclohexanol (-ol) and cyclohexanone (-one) using a series of di- and trivalent iron-picolinate complexes under Gif^IV conditions (10:1 v/v pyridine-acetic acid, zinc powder at room temperature under aerobic atmosphere) proceeds with turnover numbers [defined as (moles of oxygenated products)/(moles of catalyst)] of 161-184 and -one:-ol ratios of 4.2-4.7. The corresponding values for the binuclear picolinate complex [Fe₂(μ-OMe)₂(pic)₄] (237 turnovers, -one:-ol ratio 7.2) are significantly higher. Iron complexes bearing functionalised pyridyl ligands exhibit turnover numbers and ketone selectivities of similar magnitude to, and in some cases higher than, the picolinate complexes.     

Comparison of the sedimentation and gel-filtration behaviour of human apotransferrin and its copper and iron complexes

Equilibrium-dialysis experiments showed that Tris or citrate in the solution prevented copper from occupying completely the specific metal-binding sites on human transferrin. Differential measurements of sedimentation velocity under conditions where two atoms of copper per molecule of protein were bound showed an increase in s(0) (20,w), relative to that of the apoprotein, practically the same as that produced by two atoms of iron. Gel-filtration experiments made under the same conditions to investigate the effect of copper binding on the Stokes radius of the protein showed merely that it lost most of the metal as it passed down the column.     

Copper complexes of glycyl-histidyl-lysine and two of its synthetic analogues: chemical behaviour and biological activity

Copper complex formation equilibria of glycyl-L-histidyl-L-lysine (Gly-His-Lys, GHK) and of two synthetic analogues, where the histidine residue was replaced with a synthetic amino acid (L-spinacine or L-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid), have been carefully investigated using different experimental techniques: potentiometry, solution calorimetry, UV-VIS spectrophotometry, circular dichroism and electron paramagnetic resonance spectroscopies. All the ligands formed complexes having different stoichiometries and stabilities; evidence for the formation of binuclear species is also shown. The structures of the main complexes are discussed. It is suggested that the lateral lysine amino group participates in complex formation, but only at alkaline pH values: at physiological pH this group is protonated and available for possible interactions with cellular receptors. The above tripeptides have been tested for their enzymatic stability in human serum: the synthetic compounds showed no significant degradation for at least 3 h. Finally, their activity as growth factor has been studied in vitro. The two synthetic analogues showed an activity comparable to or even higher than that of GHK, thus suggesting their possible use as additives in cell culture media, even in the presence of serum. Relevant information on the GHK action mechanism as cell growth factor has been obtained: the formation of copper complexes, driven by the first (Gly) residue, appears necessary while the second residue (His) does not appear to play a specific role; the presence of the free side chain of the third residue (Lys) appears to be of fundamental importance.