Influence of the morphology of poly(EGDMA-co-HEMA) on the chemical modifications and retention of O-phosphothreonine

The influence of the morphology of ethylene glycol dimethacrylate-hydroxyethyl methacrylate copolymer [poly(EGDMA-co-HEMA)] base support to obtain different Fe(3+)-containing sorbents and their properties in retention of O-phosphothreonine [Thre(P)] is examined in this paper. Three base supports poly(EGDMA-co-HEMA) (I-III) were obtained using different quantities of initiator in suspension polymerization reactions. These products were submitted to chemical modifications using 1,4-butanediol diglycidyl ether (BDGE) in activation reactions and different chelating agents (iminodiacetic acid, IDA; disodium ethylenediamine tetraacetate, EDTA; and hexamethylenediamine tetrapropanoic acid, HMDTP) in coupling reactions to attain Fe(3+)-containing sorbents. Properties such as specific surface area (S(s)), specific pore volume (V(p)), scanning electron microscopy (SEM), IR spectroscopy, quantity of functional groups (oxirane and carboxyl), amount of chelated metal ion, ligand occupation (L), swelling studies as well as quantity of O-phosphoamino acid retained were used as comparative parameters for matrices. In general, the derivatization reactions proved to be more efficient when higher S(s) of macropores (50-400,000 nm) were available in the matrix. In our case, it was observed when highest percentage of initiator was used. On the other hand, the effect of accessibility of surface area on the yield of coupling reactions was noticed when comparing the different chelating agents since the number of carboxyl groups present in products was higher when the molecular size of the chelating agent was lower. Although all Fe(3+)-containing sorbents resulted efficient to retain Thre(P), the values of retention of the amino acid were slightly higher when IDA-containing matrices were used irrespective of the quantity of metal chelated. This could be probably due to the fact that the IDA ligand could be bounded to the matrix in sites that though accessible for the center of adsorption were hard for Thre(P) to access.     

Dye-incorporated poly(EGDMA-HEMA) microspheres as specific sorbents for aluminum removal

Aluminum [Al(III)] adsorption onto dye-incorporated poly(ethylene glycol dimethacrylate-hydroxyethyl methacrylate) [poly(EGDMA-HEMA)] microspheres was investigated. Poly(EGDMA-HEMA) microspheres, in the size range of 150–200 μm, were produced by a modified suspension polymerization of EGDMA and HEMA. The reactive dyes (i.e., Congo Red, Cibacron Blue F3GA and Alkali Blue 6B) were covalently incorporated to the microspheres. The maximum dye load was 14.5 μmol Congo Red/g, 16.5 μmol Cibacron Blue F3GA/g and 23.7 μmol Alkali Blue 6B/g polymer. The maximum Al(III) adsorption on the dye microspheres from aqueous solutions containing different amounts of Al(III) ions were 27.9 mg/g, 17.3 mg/g and 12.2 mg/g polymer for the Congo Red, Cibacron Blue F3GA and Alkali Blue 6B, respectively. The maximum Al(III) adsorption was observed at pH 7.0 in all cases. Non-specific Al(III) adsorption was about 0.84 mg/g polymer under the same conditions. High desorption ratios (95%) were achieved in all cases by using 0.1 M HNO₃. It was possible to reuse these dye-incorporated poly(EGDMA-HEMA) microspheres without significant losses in the Al(III) adsorption capacities.     

Effect of the matrix structure and concentration of polymer-immobilized Ni2+-iminodiacetic acid complexes on retention of IgG1

Terpolymer bead particles (100-350 microm in diameter) were prepared by suspension radical polymerization from methacrylate esters [2,3-epoxypropyl methacrylate (GMA), 2-(2-hydroxyethoxy)ethyl methacrylate (DEGMA) and ethylene dimethacrylate (EDMA)] and subsequently derivatized affording iminodiacetic acid (IDA) chelating sorbents. The sorbents differed in pore volumes (0-0.7 cm3/g) and specific surface areas (0.03-9.8 m2/g) of their matrices as well as in the amounts of immobilized Ni2+-IDA complexes (0.03-1.58 mmol/g). The binding of imidazole was studied by frontal chromatography to evaluate the accessibility of Ni2+-IDA complexes. It was found that an increase in the bonded imidazole content with increasing immobilized Ni2+-IDA concentration was strongly dependent on the matrix morphology. A higher pore volume of the matrix significantly improved the utilizability of Ni2+-IDA complexes for imidazole binding. The performance of the sorbents based on two porous matrices with immobilized Ni2+-IDA concentration (0.1-1.58 mmol/g) differing in pore size distributions was compared in immobilized metal affinity chromatography (IMAC) of monoclonal mouse immunoglobulin IgG1 specific against human choriogonadotropic hormone (GTH-spec IgG1). The results have shown that sorbents based on matrix with large pores (up to 20 microm in diameter) exhibited high protein binding capacities. The GTH-spec IgG1 (Mw=158,000) was eluted from all the sorbents in its native form as was confirmed by MALDI-TOF.     

Iron(III) complexing ability of carbohydrate derivatives

A solution study on the coordinative ability of galactaric acid (GalAH(2)), d-glucosamine (GlcN) and d-glucosaminic acid (GlcNAH) toward Fe(3+) ion is reported. UV spectroscopic study provides useful information to identify complex species formation and their stability constants are determined by means of potentiometric measurements. GalAH(2) behaves as chelating ligand through carboxylic oxygen and alpha-hydroxylic oxygen in the protonated or dissociated form depending on pH value. Two complex species [Fe(2)GalA(OH)(4)] and Na[FeGalAH(-2)] .2H(2)O are also isolated in the solid state and characterised through IR spectroscopy. GlcNAH also binds the Fe(3+) ion through carboxylic and hydroxylic groups, while NH(2) group is probably involved in metal coordination up to pH 4. GlcN demonstrates low ligating ability at acidic pH and does not prevent metal hydroxyde precipitation.     

Real-time detection of Fe.EDTA/H2O2-induced DNA cleavage by linear dichroism

The conditions for the measurement of linear dichroism (LD) can be adjusted so as to solely reflect the length and the flexibility of DNA. The real-time detection of the EDTA.Fe(2+)-induced oxidative cleavage of double-stranded native and synthetic DNAs was performed using LD. The decrease in the magnitude of the LD at 260 nm, which reflects an increase in the flexibility and a decrease in the length of the DNA, can be described by the sum of two or three exponential curves in relation to the EDTA.Fe(2+) concentration. The fast component was assigned to the cleavage of one of the double strands, inducing an increase in the flexibility, while the other slower component was assigned to the cleavage of the double strand, resulting in the shortening of DNA. The decrease in the magnitude of the LD of poly[d(A-T)(2)] was similar to that of poly[d(I-C)(2)], while that of poly[d(G-C)(2)] was found to be the slowest, indicating that the resistance of poly[d(G-C)(2)] against the Fenton-type reagent was the strongest. This observation suggests that the amine group in the minor groove of the double helix may play an important role in slowing the EDTA.Fe(2+)-induced oxidative cleavage.     

Design, synthesis, and metal binding of novel Pseudo- oligopeptides containing two phosphinic acid groups

Phosphinic compounds have potential as amide-bond mimetics in the development of novel peptidomimetics, enzyme inhibitors, and metal-binding ligands. Novel pseudo-oligopeptides with two phosphinic acid groups embedded in the peptide backbone serving as amide-bond surrogates, Psi[P(O,OH)--CH(2)], were targeted. A series of linear and cyclic pseudo-oligopeptides with two phosphinic acid groups arrayed at different positions in the peptide sequence were designed, including Ac--Phe--{(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly}(2)--NH(2) (P2), Ac--NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--NH(2) (P3), Ac--NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe--Phe--(R,S) --AlaPsi[P(O,OH)--CH(2)]Gly--NH(2) (P4), cyclo{NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe}(2) (P5), and cyclo[NH--(R,S)--AlaPsi[P(O,OH)--CH(2)]Gly--Phe--Phe](2) (P6). They were synthesized via conventional Fmoc chemistry on solid support utilizing Fmoc-protected phosphinic acid-containing pseudo-dipeptide fragment, i.e. Fmoc--(R,S)--AlaPsi[P(O,OCH(3))--CH(2)]Gly--OH. The pseudo-peptides containing two phosphinic acid groups exhibited the highest binding affinity and selectivity for Fe(III) among the 10-metal ions screened by ESI-MS analysis--Cu(II), Zn(II), Co(II), Ni(II), Mn(II), Fe(II), Fe(III), Al(III), Ga(III), and Gd(III). P4 and P6 with 11-atom linkages between the two phosphinic acids preferred intramolecular metal binding to form 1:1 ligand/metal complexes. As revealed by competition experiments, P4 showed the highest relative binding affinity among the six compounds tested. Noteworthy, P4 also showed higher relative binding affinity than similar dihydroxamate-containing pseudo-peptides reported previously. The novel structural prototype and facile synthesis along with selective and potent Fe(III) binding strongly suggest that pseudo-peptides containing the two or more phosphinic groups as amide-bond surrogates deserve further exploration in medicinal chemistry.     

Degradation of Single Stranded Nucleic Acids by the Chemical Nuclease Activity of the Metal Complex [Cu(phen)(nal)]+

The chemical design of metal complexes of the type [Cu(phen)(antib)]⁺ (where antib is a quinolone or a fluoroquinolone) has been carried out in an approach to better understand how the coordination of their components affect the activity of quinolones. The ability of [Cu(phen)(nal)]⁺ to interact with DNA in vivo and its capacity to promote the degradation of plasmid and chromosomal DNA, under reductive conditions has been previously reported. However whether this compound utilizes other intracellular targets to promote bacterial killing was a question that deserved to be answered. In this paper, the studies of the chemical nuclease properties encoded by the metal complex [Cu(phen)(nal)]⁺ were extended by using different types of single chain nucleic acids, i.e, ribosomal and tumor mosaic virus RNAs as well as poly-dA-dT. Our results showed that degradation of the nucleic acids occurred only under reductive conditions. Although MPA and [3-mercaptoethanol were the chemical reducers that best assisted the nuclease reaction, other biological compounds such as citric and succinic acid also were shown to act like reducers in that reaction. All.hough the nuclease activity of [Cu(phen)(nal)]⁺ was comparable to that exhibited by bis copper phenanthroline [Cu(phen)z]²⁺our results showed that none of the individual components of [Cu(phen)(nal)]⁺ was able to promote the degradation of either the RNAs or poly(dA-dT). These results strongly support the hypothesis that the metal complex [Cu(phen)(nal)] uses not only DNA but also RNA as targets to promote bacterial killing.     

Zinc-substituted Desulfovibrio gigas desulforedoxins: resolving subunit degeneracy with nonsymmetric pseudocontact shifts

Desulfovibrio gigas desulforedoxin (Dx) consists of two identical peptides, each containing one [Fe-4S] center per monomer. Variants with different iron and zinc metal compositions arise when desulforedoxin is produced recombinantly from Escherichia coli. The three forms of the protein, the two homodimers [Fe(III)/Fe(III)]Dx and [Zn(II)/Zn(II)]Dx, and the heterodimer [Fe(III)/Zn(II)]Dx, can be separated by ion exchange chromatography on the basis of their charge differences. Once separated, the desulforedoxins containing iron can be reduced with added dithionite. For NMR studies, different protein samples were prepared labeled with (15)N or (15)N + (13)C. Spectral assignments were determined for [Fe(II)/Fe(II)]Dx and [Fe(II)/Zn(II)]Dx from 3D (15)N TOCSY-HSQC and NOESY-HSQC data, and compared with those reported previously for [Zn(II)/Zn(II)]Dx. Assignments for the (13)C(alpha) shifts were obtained from an HNCA experiment. Comparison of (1)H-(15)N HSQC spectra of [Zn(II)/Zn(II)]Dx, [Fe(II)/Fe(II)]Dx and [Fe(II)/Zn(II)]Dx revealed that the pseudocontact shifts in [Fe(II)/Zn(II)]Dx can be decomposed into inter- and intramonomer components, which, when summed, accurately predict the observed pseudocontact shifts observed for [Fe(II)/Fe(II)]Dx. The degree of linearity observed in the pseudocontact shifts for residues >/=8.5 A from the metal center indicates that the replacement of Fe(II) by Zn(II) produces little or no change in the structure of Dx. The results suggest a general strategy for the analysis of NMR spectra of homo-oligomeric proteins in which a paramagnetic center introduced into a single subunit is used to break the magnetic symmetry and make it possible to obtain distance constraints (both pseudocontact and NOE) between subunits.     

Specificity of the Binding of fd Gene 5 Protein to Polydeoxyribonucleotides

Abstract

The long-wavelength circular dichroism (CD) changes induced by binding of fd gene 5 protein to the alternating DNA sequences poly[d(A-C)] and poly [d(C-T)] were similar to those induced by the protein complexed with the homopolymers poly[d(A)], poly[d(C)], and poly[d(T)]. The fd gene 5 protein showed different binding affinities for the various polymers. The affinity for the alternating sequences was not compositionally weighted with respect to the affinities for the homopolymers, indicating that both base composition and base sequence of the template are important for the binding of fd gene 5 protein.     

Fluorescence study of the interaction of Suwannee River fulvic acid with metal ions and Al3+-metal ion competition

In this study emission and synchronous-scan fluorescence spectroscopy have been used to investigate the interaction of the class A (oxygen seeking 'hard acid') metal Al(3+), with Suwannee River fulvic acid (SRFA), as well as competition between Al(3+) and several other metal ions (Ca(2+), Mg(2+), Cu(2+), Pd(2+), La(3+), Tb(3+) and Fe(3+)) for binding sites on SRFA. Of the four metal ions possessing very similar (and relatively low) ionic indices (Ca(2+), Mg(2+), Cu(2+) and Pd(2+)) only the latter two paramagnetic ions significantly quenched SRFA fluorescence emission intensity. Of the four metal ions possessing very similar (and relatively low) covalent indices (Ca(2+), Mg(2+), La(3+) and Tb(3+)) only the last paramagnetic ion (Tb(3+)) significantly quenched SRFA fluorescence. None of these metals was able to significantly compete with SRFA-bound Al(3+).Fe(3+), which differs substantially from all of the other metals examined in this study in that it possesses a relatively high ionic index (but not as high as Al(3+)) and a relatively low covalent index (but not as low as Al(3+)), was able not only to quench SRFA fluorescence but also to compete (at least to some extent) with SRFA-bound Al(3+). Synchronous-scan fluorescence SRFA spectra taken in the absence and presence of Fe(3+) and/or Al(3+) support the view that these two metal ions can compete for sites on SRFA. The results of these fluorescence experiments further confirm the Al(3+), and metal ions that have electronic properties somewhat similar to Al(3+) (such as Fe(3+)) are somewhat unique in their ability to interact strongly with binding sites on fulvic acids.     

Specificity of the binding of fd gene 5 protein to polydeoxyribonucleotides

The long-wavelength circular dichroism (CD) changes induced by binding of fd gene 5 protein to the alternating DNA sequences poly[d(A-C)] and poly[d(C-T)] were similar to those induced by the protein complexed with the homopolymers poly[d(A)], poly[d(C)], and poly[d(T)]. The fd gene 5 protein showed different binding affinities for the various polymers. The affinity for the alternating sequences was not compositionally weighted with respect to the affinities for the homopolymers, indicating that both base composition and base sequence of the template are important for the binding of fd gene 5 protein.     

Mechanism of non-enzymic transamination reaction between histidine and α-oxoglutaric acid

Non-enzymic transamination reactions at 85 degrees between various amino acids and alpha-oxoglutaric acid are catalysed by metal ions, e.g. Al(3+), Fe(2+), Cu(2+) and Fe(3+). The reaction is optimum at pH4.0. Of the 14 amino acids studied histidine is the most active. In the presence of Al(3+) histidine transaminates with alpha-oxoglutaric acid, forming glutamic acid and Al(3+)-imidazolylpyruvic acid complex as the end products. However, in the presence of Fe(2+) or Cu(2+) the products are glutamic acid and a 1:2 metal ion-imidazolylpyruvic acid chelate. The greater effectiveness of histidine in these reactions is attributed to the presence of the tertiary imidazole nitrogen atom, which is involved in the formation of stable sparingly soluble metal ion-imidazolylpyruvic acid complexes or chelates as end products of these reactions. Of the metal ions studied only Al(3+), Fe(2+), Fe(3+) and Cu(2+) are effective catalysts for the transamination reactions, and EDTA addition completely inhibits the catalytic effect of the Al(3+). Spectrophotometric evidence is presented to demonstrate the presence of metal ion complexes of Schiff bases of histidine as intermediates in the transamination reactions. These results may contribute to understanding the role of histidine in enzyme catalysis.     

The use of several types of metal cations--a new approach to the study of the metallophilia of Ranvier's nodes of nerve fibers]

Mechanisms of metal affinity of Ranvier's nodes of myelinated nerve fibers in the peripheral nerve system have been investigated. It is indicated that Fe(3+)-ions are able to reduce to Fe(2+)-ions. Ag(+)-ions compete with Fe(3+)-ions for places of adsorption in a gap [correction of chick] between myelinated segments of Ranvier's node. It is demonstrated that Fe(3+)- and Fe(2+)-ions are adsorbed in the gap [correction of chink], while Ag(+)-ions are adsorbed in the gap [correction of chink] and axon in the bulbs of the node. One can increase ferrocyanide of ferrous sediment by several times by ferricyanide of ferrous sediment as well as by ferrocyanide of silver and of metal silver ones. A possibility to use several kinds of metal ions for demonstration of cytochemical heterogeneity of nerve fibre membrane is discussed.     

Right- and left-handed helixes of poly[d(A-T)].poly[d(A-T)] investigated by infrared spectroscopy

The secondary structures of double-stranded poly[d(A-T)].poly[d(A-T)] in films have been studied by IR spectroscopy with three different counterions (Na+, Cs+, and Ni2+) and a wide variety of water content conditions (relative humidity between 100 and 47%). In addition to the A-, B-, C-, and D-form spectra, a new IR spectrum has been obtained in the presence of nickel ions. The IR spectra of Ni2+-poly[d(A-T)].poly[d(A-T)] films are analyzed by comparison with previously assigned IR spectra of left-handed poly[d(G-C)].poly[d(G-C)] and poly[d(A-C)].poly[d(G-T)], and it is possible to conclude that they reflect a Z-type structure for poly[d(A-T)].poly[d(A-T)]. The Z conformation has been favored by the high polynucleotide concentration, by the low water content of the films, and by specific interactions of the transition metal ions with the purine bases stabilized in a syn conformation. A structuration of the water hydration molecules around the double-stranded Ni2+-poly[d(A-T)].poly[d(A-T)] is shown by the presence of a strong sharp water band at 1615 cm-1.     

Comparison of measured and modelled copper binding by natural organic matter in freshwaters

Fifteen freshwater samples containing significant concentrations of dissolved organic carbon-[DOC]-were titrated with copper under standardised conditions (pH 6 and 7), and concentrations of Cu(2+)-[Cu(2+)]-were measured with an ion-selective electrode. Measured values of [Cu(2+)], which were in the range 10(-11)-10(-5) moll(-1), were compared with those simulated using Humic Ion-Binding Models V and VI. It was assumed that copper speciation was controlled by the organic matter, represented by fulvic acid (FA), together with inorganic solution complexation (calculated with an inorganic speciation model). The models were calibrated by adjusting a single quantity, the concentration of FA. The optimised value-[FA](opt)-was that giving the best agreement, according to least squares, between measured and simulated [Cu(2+)]. The calculations took into account competition by other dissolved (filterable) metals (Mg, Al, Ca, Fe(II), Fe(III), Zn); in the case of Fe(III) it was assumed either that all the dissolved metal was truly in solution, or that the activity of Fe(3+) was controlled by equilibrium with Fe(OH)(3). The assumption about Fe(III) had relatively small effects on the fitting of Model V, but was significant for Model VI, because Model VI represents low-abundance, high-affinity binding sites in humic matter, which are sensitive to Fe(III) competition. Because of its inclusion of the high-affinity sites, Model VI provided better fits of the data than did Model V. Furthermore, Model VI with Fe(3+) activity controlled by Fe(OH)(3) gave smaller variation in the ratio of [FA](opt) to [DOC] than Model VI with all Fe(III) assumed to be in solution. The average [FA](opt)/[DOC] found from the Cu titrations was 1.30, which implies that 65% of the organic matter is 'active' with respect to metal binding. The average ratio of 1.30 is in reasonable agreement with ratios obtained by applying the model to field data sets for charge balance (1.22), Al speciation (1.56) and base titrations of Cu-amended waters (1.45). It is concluded that Model VI/Fe(OH)(3) provides the most reliable predictions of dissolved metal speciation in natural waters; at a total Cu concentration of 1 microM, the predicted concentration of Cu(2+) is expected to be correct to within a factor of 3.6 in 95% of cases.     

The influence of the side-chain sequence on the structure-activity correlations of immunomodulatory branched polypeptides. Synthesis and conformational analysis of new model polypeptides

New branched polypeptides were synthesized for a detailed study of the influence of the side-chain structure on the conformation and biological properties. The first subset of polypeptides were prepared by coupling of tetrapeptides to poly[L-Lys]. These polymers contain either DL-Ala3-X [poly[Lys-(X-DL-Ala3)n]] or X-DL-Ala3 [poly[Lys-(DL-Ala3-X)n] (n less than or equal to 1)] tetrapeptide side chains. Another group of branched polymers comprise a mixture of DL-Alam and of DL-Alam-X oligomeric branches in a random distribution [poly[Lys-(DL-Alam-Xi)] (i less than 1, m approximately 3)]. In each subset the X = Leu or Phe derivatives were prepared. The N-protected tetrapeptides were synthesized by conventional liquid phase methods and were coupled as active esters. The degree of racemization was found relatively high both for active esters and coupled derivatives, when optically active amino acids were in the C-terminal position of the tetrapeptides. In the case of the poly[Lys-(Leu-DL-Ala3)n] derivative, comparative experiments were carried out using various methodical alterations. The highest stereochemical homogeniety could be achieved when the tetrapeptide active ester was synthesized by the "backing off" method. CD spectra of poly[Lys-(Xi-DL-Alam)] (i less than 1, m approximately 3) and of poly[Lys-(X-DL-Ala3)n] were analyzed and compared to those of poly[Lys-(DL-Alam-Xi)] and of poly[Lys-(DL-Ala3-X)n]. All measurements were performed in water solutions of varying pH values and ionic strengths. The data obtained suggest that branched polypeptides containing a mixture of two different types of oligomeric side chains (DL-Alam and DL-Alam-Xi or Xi-DL-Alam) distributed randomly adopt an almost identical conformation to those that comprise only the respective tetrapeptide (DL-Ala3-X or X-DL-Ala3) branches. The results also indicate that the tendency to form an ordered structure is determined by the identity and the position of the chiral amino acid X (Phe or Leu) in the side chain.     

Interactions of bismuth complexes with metallothionein(II).

Bismuth complexes are widely used as anti-ulcer drugs and can significantly reduce the side effects of platinum anti-cancer drugs. Bismuth is known to induce the synthesis of metallothionein (MT) in the kidney, but there are few chemical studies on the interactions of bismuth complexes with metallothionein. Here we show that Bi(3+) binds strongly to metallothionein with a stoichiometry bismuth:MT = 7:1 (Bi(7)MT) and can readily displace Zn(2+) and Cd(2+). Bismuth is still bound to the protein even in strongly acidic solutions (pH 1). Reactions of bismuth citrate with MT are faster than those of [Bi(EDTA)](-), and both exhibit biphasic kinetics. (1)H NMR data show that Zn(2+) is displaced faster than Cd(2+), and that both Zn(2+) and Cd(2+) in the beta-domain (three metal cluster) of MT are displaced by Bi(3+) much faster than from the alpha-domain (four metal cluster). The extended x-ray absorption fine structure spectrum of Bi(7)MT is very similar to that for the glutathione and N-acetyl-L-cysteine complexes [Bi(GS)(3)] and [Bi(NAC)(3)] with an inner coordination sphere of three sulfur atoms and average Bi-S distances of 2.55 A. Some sites appear to contain additional short Bi-O bonds of 2.2 A and longer Bi-S bonds of 3.1 A. The Bi(3+) sites in Bi(7)MT are therefore highly distorted in comparison with those of Zn(2+) and Cd(2+).     

Binding of ethidium ion to left-handed Z-RNA induces a cooperative transition to right-handed RNA at the intercalation site

The equilibrium binding of the ethidium cation (Etd+) to the right-handed A-form of poly-[r(C-G)], the B-form of poly[d(C-G)], and the left-handed Z-forms of Br-poly[r(C-G)] and Br-poly[d(C-G)] was investigated in 0.22 M NaCl by optical methods. Scatchard analysis indicates that Etd+ intercalates into right-handed forms of poly[r(C-G)] and poly[d(C-G)] in a noncooperative manner. Correlation of Etd+ absorbance binding isotherms and polynucleotide circular dichroism data indicates that drug binding to Br-poly[r(C-G) and Br-poly[d(C-G)] results in cooperative conversion from left-handed Z-forms to right-handed intercalated conformations. Approximate stoichiometries necessary to induce the left- to right-handed transitions are 1 Etd+/9 base pairs (bp) for Z-RNA and 1 Etd+/6 bp for Z-DNA. The apparent limiting binding stoichiometries are approximately 1 Etd+/3 bp for RNA and 1 Etd+/2 bp for DNA. The equilibrium binding constants for binding to the right-handed forms decrease in the order Br-poly[d(C-G)], Br-poly[r(C-G)], poly[d(C-G)], and poly[r(C-G)]. Thermodynamic parameters are obtained by van't Hoff analysis of Etd+ absorbance thermal dissociation data. Enthalpy values for all four polynucleotides are negative and of similar magnitude. Negative entropy values indicate that the binding processes are primarily enthalpically driven.(ABSTRACT TRUNCATED AT 250 WORDS)     

The light switch effect upon the association of [Ru(1,10-phenanthroline)2dipyrido[3,2-a:2',3'-c]phenazine]2+ with single stranded poly(dA) and poly(dT)

Large enhancement in the luminescence intensity of the Delta- and Lambda-Ru(phenanthroline)(2)dipyrido[3,2-a:2',3'-c]phenazine](2+) ([Ru(phen)(2)DPPZ](2+)) complexes upon their association with single stranded poly(dA) and poly(dT) is reported in this work. As the mixing ratio ([[Ru(phen)(2)DPPZ](2+)]/[DNA base]) increases, the luminescence intensity increase in a sigmoidal manner, indicating that the enhancement involves some cooperativity. At a high mixing ratio, the luminescence properties are affected by the nature of the DNA bases and not by the absolute configuration of the [Ru(phen)(2)DPPZ](2+) complex, indicating that the single stranded poly(dA) and poly(dT) do not recognize the configuration of the metal complex. In the case of the Lambda-[Ru(phen)(2)DPPZ](2+)-poly(dT) complex, the manner of the enhancement is somewhat different from the other Ru(II) complex-polynucelotide combinations: the luminescence intensity reached a maximum at an intermediate mixing ratio of 0.32, and gradually decreased as the mixing ratio increased. In contrast to other complexes at high mixing ratios, an upward bending curve was found in the Stern-Volmer plot, which indicates that the micro-environment of the Lambda-[Ru(phen)(2)DPPZ](2+) is heterogeneous. In the Delta-[Ru(phen)(2)DPPZ](2+)-poly(dT) complex case, formation of this highly luminescent species at an intermediate mixing ratio is far less effective.     

Sequence-dependant polymorphism of DNA duplex in solutions

Raman spectra of six synthetic polydeoxyribonucleotide duplexes with different base sequences have been examined in aqueous solutions with different salt or nucleotide concentrations. Detailed conformational differences have been indicated between B and Z forms of poly[d(G-C)] X poly[d(G-C)], between B forms of poly[d(G-C)] X poly[d(G-C)] and poly[d(G-m5C)] X poly[d(G-m5C)], between A and B forms of poly(dG) X poly(dC), between B and "CsF" forms of poly[d(A-T)] X poly[d(A-T)], between B forms of poly[d(A-U)] X poly[d(A-U)] and poly[d(A-T)] X poly[d(A-T)], and between low- and high-salt (CsF) forms of poly(dA) X poly(dT). The Raman spectrum of calf-thymus DNA in aqueous solution was also observed and was compared with the Raman spectra of its fibers in A, B, and C forms.