Electric Dichroism Measurements Research Articles

Orientation Tuning of a Polypyridyl Ru(II) Complex Immobilized on a Clay Surface toward Chiral Discrimination

The present work reports an attempt to elucidate a stereoselective energy-transfer system by immobilizing a chiral metal complex on a clay surface. The metal complex used was [Ru(bpy)2L(i)]2+ with L1 = bpy (2,2'-bipyridine), L2 = 4,4'-diundecyl-2,2'-bipyridine, and L3 = 5,5'-diundecyl-2,2'-bipyridine. The adsorption structure of [Ru(bpy)2L(i)]2+ was studied by means of electric dichroism measurements on an aqueous dispersion of a colloidal clay. It was found that the molecular orientation of the adsorbed Ru(II) complex was affected remarkably by the positions of the alkyl chains on the bpy ligand; that is, the angle of the 3-fold or pseudo-3-fold symmetry axis of the Ru(II) complex with respect to the surface normal was obtained to be 24 degrees, 30 degrees, and 52 degrees for i = 1, 2, and 3, respectively. The efficiency of the energy-transfer was determined by photoluminescence quenching measurements between the adsorbed Ru(II) complex and [Ru(acac)3] (acac = acetylacetonate) in solution. As a result, stereoselectivity appeared most for the case of [Ru(bpy)2L3]2+ in which its two helically twisted bpy ligands were projected in an outward direction.

Electric Dichroism Studies on an Aqueous Dispersion of Unilamellar Titanium Oxides: Optical Anisotropy near the Absorption Edge

Electric dichroism measurements have been performed on an aqueous dispersion of unilamellar titanium oxides produced by the exfoliation of the following three kinds of titanium oxides: (A) lepidocrocite-type titanate (Cs0.7Ti1.825□0.175O4), (B) tetratitanate (K2Ti4O9), and (C) pentatitanate (Cs2Ti5O11). The AFM images showed that these exfoliated titanium oxides consisted of flakelike particles with an average diameter ranging from 0.1 to 2 μm. Under the applied voltage pulse [(1−20) × 103 V cm-1], an aqueous dispersion of titanium oxides exhibited orientational dichroism in the UV region with a maximum around 300 nm. From the reduced linear dichroism at complete orientation, the orientation of the effective transition moment (μeff) was determined with respect to the oriented axis of a particle. Here μeff was defined as the vector sum of three orthogonal transition moments of a particle. As a result, an angle (α) between μeff and the oriented axis of a particle was determined to be α = 41.6°, 24.6°, and 23.6° at 300 nm for samples A−C, respectively. The results were compared with the recent theoretical calculations of these samples. Electric dichroism was also measured for an aqueous dispersion containing sample A and a cationic molecule, [Ru(phen)3]2+. From the reduced linear dichroism in the visible region, an [Ru(phen)3]2+ ion was concluded to be adsorbed with its 3-fold symmetry axis nearly perpendicular to a surface.

Induction of Circular Dichroism by Coadsorption of Chiral and Achiral Metal Complexes on a Colloidal Clay

Two kinds of metal complexes, an achiral metal complex, [Fe(terpy)]2+ (terpy = 2,2‘,2‘ ‘-terpyridyl), and a chiral metal complex, Δ-[Ni(phen)3]2+ (phen = 1,10-phenanthroline), were coadsorbed by colloidally dispersed sodium saponite clay. Interaction between these molecules on a clay surface was investigated by electric dichroism and circular dichroism measurements. The molecular orientation of an adsorbed [Fe(terpy)]2+ ion was determined in the absence or presence of Δ-[Ni(phen)3]2+ by electric dichroism measurements. The angle of the C2 axis of [Fe(terpy)]2+ with respect to a clay surface changed from 35.4° to 44.4° when the complex was coadsorbed with Δ-[Ni(phen)3]2+. The circular dichroism spectrum of a clay dispersion containing [Fe(terpy)]Cl2 and Δ-[Ni(phen)3]Cl2 was measured in the wavelength region of 350−600 nm. Δ-[Ni(phen)3]2+ had no electronic absorption in this region. Circular dichroism due to adsorbed [Fe(terpy)]2+ appeared when Δ-[Ni(phen)3]Cl2 was added to the ratio of [Fe(terpy)]Cl2/Δ-[Ni...

Electric dichroism of a multiwell spectral hole as an indicator of anisotropy in the distribution of stark moments of impurity molecules

Burning of multiwell holes in impurity-absorption spectra of glasses and polymers in an alternating electric field was theoretically studied. A case of circularly polarized burning radiation with a spectrum consisting of a series of close equidistant lines that shift synchronously with the variation of the electric field across the sample was considered. It was shown that an electric field applied to the sample after hole burning changes the optical density in the hole center, and that this change depends on the orientation of the plane of polarization of the probing radiation. Centrosymmetric impurity molecules, whose Stark moments (with randomly distributed magnitudes and directions) are governed only by their interaction with matrix molecules, and molecules with small intrinsic permanent Stark moments were considered. It was shown that the measurements of electric dichroism of a multiwell spectral hole make it possible to study both the anisotropy of matrix-induced moments and additional moments that arise, for example, when a metal atom leaves the plane of a metalloporphyrin molecule. It was also shown that the sensitivity and selectivity of the suggested method exceed those of known methods.

Synthesis, cytotoxicity, DNA interaction and topoisomerase II inhibition properties of tetrahydropyrrolo[3,4- a]carbazole-1,3-dione and tetrahydropyrido-[3,2- b]pyrrolo[3,4- g]indole-1,3-dione derivatives

Three tetrahydropyrrolo[3,4- a]carbazole-1,3-diones ( 6– 8) and two tetrahydropyrido[3,2- b]pyrrolo[3,4- g]indole-1,3-diones ( 11– 12) have been synthesized. Their interaction with DNA was probed by absorption and thermal melting studies. Compounds 8 and 12 both equipped with a hydroxyethyl–aminoethyl side-chain demonstrated higher affinities for poly(dA-dT) 2 than compounds 6, 7 and 11 bearing a dimethylaminoethyl side-chain. Circular and electric linear dichroism measurements showed that all five drugs behave as typical DNA intercalating agents. A plasmid cleavage assay was used to evaluate the capacity of the drugs to inhibit human topoisomerase II. Compounds 8 and 12 which bind strongly to DNA were found to stabilize DNA-topoisomerase II covalent complexes but their topoisomerase II inhibitory properties do not correlate with their cytotoxic potential. Compounds 6 and 7 are essentially inactive whereas compounds 8, 11 and 12 exhibit a high toxicity to P388 murine leukemia cells and provoke a marked accumulation in the G2/M phase of the cell cycle. These compounds form a new class of DNA-targeted antitumor agents.

Rebeccamycin analogues from Indolo[2,3-c]carbazole

Glycosylated indolocarbazoles related to the antibiotic rebeccamycin represent an important series of antitumor drugs. In the course of structure–activity relationship studies, we report the synthesis of two new derivatives containing an indolo[2,3-c]carbazole chromophore instead of the conventional indolo[2,3-a]carbazole unit found in the natural metabolites. The N-methylated compound 8 containing one glucose residue behaves as a typical DNA intercalating agent, as judged from circular and electric linear dichroism measurements with purified DNA. In contrast, the bis-glycosylated derivative 7 containing a glucose residue on each indole nitrogen has lost its capacity to form stable complexes with DNA. DNA relaxation experiments reveal that the two drugs 7 and 8 have weak effects on human DNA topoisomerase I. The modified conformation of the indolocarbazole chromophore is detrimental to the stabilization of topoisomerase I–DNA complexes. The lack of potent topoisomerase I inhibition leads to decreased cytotoxicity but, however, we observed that the DNA-intercalating mono-glycosyl derivative 8 is about 5 times more cytotoxic than the bis-glycosyl analogue 7. The study suggests that the naturally-occurring indolo[2,3-a]carbazole skeleton should be preserved to maintain the topoisomerase I inhibitory and cytotoxic activities.

Turbulence Decay in Stopped Flow Experiments by Measurements of Electric Dichroism

Various macromolecules of widely different chemistry and structure show unusual rotational diffusion time constants in stopped flow experiments. These effects have been characterized by measurements of electric dichroism in a combined stopped-flow−electric-field-jump instrument. DNA restriction fragments in the range of chain lengths up to 179 base pairs do not show anything unusual yet: the dichroism decay times correspond to the standard values reflecting unperturbed rotational diffusion. For fragments with more than 200 base pairs, the dichroism measured directly after stop of the flow revealed decay time constants clearly smaller than the corresponding values found without flow. The reduction of the time constants for overall rotational diffusion is ∼10% for a fragment with 256 bp and increases to ∼70% for DNA with 800 bp. The decay time constants return to the usual values within a few ms after stop of flow. The limiting electric dichroism of the flow induced state is virtually identical with that of standard DNA and, thus, the local secondary structure remains in the B-form. However, the polarizability of the flow induced state is clearly reduced. These results seem to indicate a flexible state of DNA induced by shear stress, resulting from breaking of stacking interactions. The kinetics can be described by a model with parallel reactions leading to the native state with a time constant of ∼1 ms. Effects observed for single stranded poly(A) are virtually identical to those of double stranded DNA for samples of corresponding hydrodynamic dimensions. The time constants for the transition to the standard state are again ∼1 ms, although stacking reactions of poly(A) occur in the time range ≤ 1 μs. Further experiments with other macromolecules or macromolecular aggregates indicate that acceleration of rotational motion is a general phenomenon under stopped flow conditions: for example bacteriorhodopsin membrane disks and colloidal suspensions of the fibrous claylike silicate attapulgite show very high accelerations of their rotational diffusion time constants after stopped flow by factors of about 3000. The return to the usual state both for bacteriorhodopsin and for attapulgite extends over a broad time range up to ∼100 ms. Although it cannot be excluded that these effects are partly due to kinking of the structures, the similarity of the data for materials of very different structures indicates that the acceleration of rotational diffusion is mainly due to the existence of turbulence. The rotational motion of small molecules, such as 95 bp DNA, is much faster than rotational motion of corresponding volume elements of the solvent and, thus, these molecules do not indicate turbulence. The data demonstrate that turbulence decays over a broad time range: small vortices with high rates of rotational motion decay first, merge into larger ones with lower rotation rates, until finally the largest ones compatible with the dimension of the observation chamber are reflected only by particles with relatively large dimensions and slow rotational diffusion. These results demonstrate the mode of turbulence in stopped flow observation cells, the scaling of its decay, and the utility of electrooptical techniques for the characterization of turbulence.

Fifty years of electro-optics: An overview of research in the field of macromolecules

The paper presents the most prominent developments in the field of electro-optical methods applied to macromolecular solutions since the advent of pulsed electro-optics in the fifties. References to appropriate review articles and books on this subject are given. Recent works from the author's laboratory on the effect of osmotic effectors on DNA condensation by multivalent cations are briefly described. They are based on circular and electric dichroism measurements, together with precipitation experiments. These observations are interpreted in the frame of counterion condensation theory.

Measurement and Computation of the Dipole Moment of Globular Proteins. 4. α- and γ-Chymotrypsins

The dipole moments of α- and γ-chymotrypsins are determined using the dielectric constant measurement. The results are roughly comparable to those of electric dichroism measurements despite the principle and methodology of these two techniques are entirely different. Nevertheless, the differences which exist between them seem to be beyond the experimental error. The cause of disagreement appears to be, at least partially, due to the difficulty of finding the correct internal field. A new theory which is based on an ellipsoidal particle surrounded by a hydration shell is discussed. The model was found to improve the agreement markedly. Additionally, in order to corroborate the observed dipole moments with numerical computations, the dipole moments of α- and γ-chymotrypsins were calculated using protein data bases. The dipole moment of small proteins consists of two major components, the moment due to fixed surface charges and the core moment due to polar chemical bonds. The calculation of the surface charg...

Measurement and computation of the dipole moment of globular proteins III: Chymotrypsin

The dipole moments of α- and γ-chymotrypsin are determined experimentally using the dielectric constant measuring method. The values thus obtained are compared with the results of the electric dichroism measurements for α-chymotrypsins by other investigators. The agreement is reasonably good, if not satisfactory. The cause of difference appears to be due to the difficulty of finding the correct internal field. The interaction between two neighboring dipoles is found to be a minor component of the local fields. Secondly, the dipole moment of α-chymotrypsin was computed using Protein Data Bases. The dipole moment of proteins consists of two major components, the moment due to fixed surface charges and the core moment due to polar chemical bonds. The method of calculation was described in detail in previous papers. The p K shifts of polar side chains were calculated using the methods of Tanford et al. and its modification by Warshel et al. The agreement between measured and calculated dipole moments is satisfactory.

Dynamic properties of molecular chains with variable stiffness

The dynamics of a free-draining chain of variable stiffness in a dilute solution is investigated. The chain is considered as a differentiable space curve with stretching and bending elasticity. Second moments, like the mean square end-to-end distance, the radius of gyration, and the pair correlation function of the equilibrium distribution exactly agree with those of the well-known Kratky–Porod wormlike chain. The equation of motion of the chain is derived and solved by a normal mode analysis. In the limit of a flexible chain the model exhibits the well-known Rouse dynamics, whereas in the rod limit the eigenfunctions correspond to bending motion only. In addition, the rotational motion in the latter limit is naturally obtained within the model. The relaxation times obtained by the model are compared with experimental transient birefringence and dynamic light scattering data. In addition, electric dichroism measurements are interpreted in terms of the model. All of these experiments are in good agreement with the theoretical predictions.

Interactions of Enantiomeric Ruthenium (II) Complexes with Polynucleotides as Studied by Circular Dichroism, Electric Dichroism Measurements, and Photolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInteractions of Enantiomeric Ruthenium (II) Complexes with Polynucleotides as Studied by Circular Dichroism, Electric Dichroism Measurements, and PhotolysisKyaw Naing, Masayuki Takahashi, Masahiro Taniguchi, and Akihiko YamagishiCite this: Inorg. Chem. 1995, 34, 1, 350–356Publication Date (Print):January 1, 1995Publication History Published online1 May 2002Published inissue 1 January 1995https://doi.org/10.1021/ic00105a054RIGHTS & PERMISSIONSArticle Views278Altmetric-Citations55LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Interactions of Chiral Ru(II) Complexes with Calf Thymus DNA as Studied by Circular Dichroism and Electric Dichroism Measurements

Abstract The interactions of the enantiomers of [Ru(bpy)2(phi)]Cl2 and [Ru(phen)2(phi)]Cl2 (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, and phi = 9,10-phenanthrenequinone diimine) with calf thymus DNA were studied by spectroscopic titrations, circular dichroism, and electric linear dichroism methods. These complexes bound to DNA with binding constants greater than 104 M−1. From the CD and LD spectra, the phi ligands of both complexes are concluded to be intercalated between the basepairs of DNA.

Electric dichroism evidence for intercalation of optically active [Ru(bpy)2(phi)]2+(phi = 9,10-phenanthrenequinone diimine, bpy = 2,2′-bipyridyl) by DNA

Electric dichroism measurements on a solution containing DNA and enantiomeric [Ru(bpy)2(phi)]2+(phi = 9,10-phenanthrenequinone diimine, bpy = 2,2′-bipyridyl) at pH 7.0 have revealed that the phi ligand of the bound metal complex orients perpendicularly to the helical axis of DNA, supporting a structure where the metal complex is bound to DNA with the phi ligand intercalated between the base pairs.

Condensation and Precipitation of Chromatin By Multivalent Cations

The condensation and the precipitation of rat liver chromatin upon addition of spermine4+, spermidine3+, hexamminecobalt(III)3+ and Mg2+ cations have been studied using solubility, fluorescence, circular dichroism, melting curves, electric dichroism and spermidine binding measurements, made on both soluble and precipitated complexes. The soluble complexes obtained with tetra- and trivalent cations were depleted from all histones and enriched in other proteins, particularly high mobility group proteins 1 and 2, which brings about an important enhancement of tryptophan fluorescence without modification of its two lifetimes 5.1 and 1.2 ns. In the precipitates the non-histone proteins are eliminated. Under precipitation by Mg2+ ions, the distribution of proteins remains practically unchanged. The electric dichroism and the melting curves indicate that the soluble complexes between polyamines and chromatin undergo important condensation and, at high ratios of cation over phosphate, are constituted by heterogeneous assemblies of non-histone proteins and DNA. On the contrary, the insoluble complexes seem to retain the main features of original chromatin. Precipitation by Mg2+ ions reveal much less drastic changes than those produced by polyamines. Precipitation by spermidine occurs when one cation is bound per eight nucleotides, which in addition to the histone positive charges brings about a complete neutralization of chromatin phosphates.

The superstructure of chromatin and its condensation mechanism

Electric dichroism and X-ray scattering measurements on solutions of uncondensed and condensed chicken erythrocyte chromatin were interpreted on the basis of model calculations. Information about the state of uncondensed fibers in the conditions of electric dichroism measurements was obtained from scattering patterns recorded as a function of pH, in the presence of spermine and at very low monovalent cation concentrations. Electric dichroism measurements on a complex of uncondensed chromatin with methylene blue were made to determine the contribution of the linker and of the nucleosomes to the total dichroism. A new approach to calculate the dichroism from realistic structural models, which also yields other structural parameters (radius of gyration, radius of gyration of the cross-section, mass per unit length) was used. Only a restricted range of structures is simultaneously compatible with all experimental results. Further, it is shown that previous interpretations of dichroism measurements on chromatin were in contradiction with X-ray scattering data and failed to take into account the distribution of orientation of the nucleosomes in the fibers. When this is done, it is found that the linker DNA in chicken erythrocyte and sea urchin chromatin must run nearly perpendicularly to the fibre axis. Taken together with the dependence of the fibre diameter on the linker length, these results provide the strongest evidence hitherto available for a model in which the linker crosses the central part of the fibre.

Polyamine addition to preparation media induces chromatin condensation, irreversibly at low ionic strength

Polyamines (spermine, spermidine) are commonly used as stabilizing cations in the chromatin preparation media. Their residual binding to chromatin is not easily reversed at low ionic strength, even after extensive dialysis, as evidenced by the use of labelled spennidine. Electric dichroism measurements show that their presence interferes with the physico-chemical characterization of chromatin by maintaining a condensed structure. These results give a definite answer to the controversy about the sign of optical anisotropy of chromatin determined by electric and flow dichroism techniques. Chromatin; Polyamine; Electric dichroism

Orientation of the Chromophore Plane in Purple Membrane

Excitation of bacteriorhodopsin (BR) in its beta absorption band drives a photocycle identical in the millisecond range, to that excited in the alpha band of BR. The relative contribution of the two transition dipoles distinguished in the beta band to the initiation of the photocycle was established by photoselection experiments. Having this information the orientation of the chromophoric plane was specified by electric dichroism measurements.

Comparative Study of the Condensation of Chicken Erythrocyte and Calf Thymus Chromatins by Di- and Multivalent Cations

The condensation of chicken erythrocyte (CE) and calf thymus (CT) chromatins upon addition of di- and multivalent cations has been studied using turbidity, precipitation and electric dichroism measurements. For all the cations investigated (Mg2+, Tb3+, Co(NH3)6(3+), spermidine Spd2+ and spermine Sp4+) condensation of CE chromatin occurred before the onset of aggregation, while aggregation of CT chromatin started before condensation with all cations except Mg2+ and Tb3+. Precipitation of CE chromatin required lower di- and multivalent cations concentrations than CT chromatin. The electric dichroism data for both chromatins, at low ionic strength in the absence of di- or multivalent cations, indicated that the nucleoprotein molecules were not totally decondensed but that a "precondensed" state was already present. A positive electric dichroism was observed for the most condensed chromatin fibers, in agreement with the "cross-linker" models. Tb3+ led to less compact condensed particles as judged from the electric dichroism observations, but electron microscopy revealed that "30 nm fibers" were formed. Very little aggregation was produced by Tb3+. On the contrary, spermine produced very large networks of condensed molecules, but large spheroidal particles were also observed. The condensation of CE chromatin happened without changes of solution conductivity upon cation salt addition, regardless of the condensing cation, indicating a cooperative uptake of the ions during this process.

Influence of DNA length on spermine-induced condensation: Importance of the bending and stiffening of DNA

Using DNA restriction fragments of 258 to 4362 base-pairs, we have investigated the influence of the DNA length on the condensation process induced by spermine, with the aid of electric dichroism measurements. The 258- and 436 bp fragments condensed into rod-like particles, while the fragments of 748 bp or more condensed into torus-shaped particles. Our results suggest that a DNA molecule longer than the circumference of the toroids observed previously (680 bp) is required to serve as a nucleus for the growth of the condensed particles. The toroids were more stable in the electric field than the rod-shaped particles, suggesting that rapid fluctuations of the bound spermine counterions can provide one of the main attractive forces yielding to the condensation process. Relaxation time data for the 436 bp fragment revealed that the structure of DNA was altered at a spermine concentration as low as one-tenth of that required for condensation: the DNA became bent in the presence of spermine. Moreover, the field strength dependence of the relaxation times, as well as the fitting of the decay curves at 12.5 kV/cm, showed an increase of the stiffness of the DNA double helix upon spermine addition. We estimated that, in the case of DNA condensation by spermine, a decrease in the measured persistence length may occur, irrespective of the DNA flexibility, owing to the bending of the DNA molecule.