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The binding mode of cationic porphyrin (trans-BMPyP) with poly[d(G-C)2] and poly[d(A-T)2] was examined according to the site of the periphery cationic methyl pyridine ion of the cationic porphyrin (o-, m-, p-) as well as the possibility of a B-Z transition depending on the binding modes by measuring the absorption spectrum and circular dichroism (CD). The negative band found in the soret region showed the intercalation mode of m- and p-trans-BMPyP-poly[d(G-C)2] to the DNA base pairs, but no B-Z transition was induced. On the other hand, the distinctive bisignate band found in the soret region of the CD spectrum for m- and p-trans-BMPyP-poly[d(A-T)2] suggests that m- and p-trans-BMPyP have an effective extensive stacking-based binding mode along with the skeleton of poly[d(A-T)2], wherein the B-Z transition was induced through extensive stacking. The difference in binding mode was attributed to the difference in the molecular structure depending on the site of the periphery cationic methyl pyridine ion in the cationic porphyrin. In other words, o-trans-BMPyP is nonplanar because of the steric hindrance of the cationic methyl pyridine ion at the o-site. In contrast, m- and p-trans-BMPyP are planar, but not all porphyrins with a planar structure undergo the B-Z transition. In conclusion, a B-Z transition is induced if the structure of a porphyrin is planar and the binding mode allows the porphyrins to be stacked effectively along the DNA skeleton, not in a binding mode where the porphyrin is intercalated to the DNA.Communicated by Ramaswamy H. Sarma.

The binding mode of cationic porphyrin (

This research focuses on the synergy of converting carbon dioxide (CO2) into methane (CH4) by simultaneously introducing light and heat as dynamic sources to activate the catalyst. A CaTiO3@Ni-Pt catalyst, loaded with 30.0 wt.% Ni and 1.0 wt.% Pt on a perovskite CaTiO3 support was introduced. The photo-thermal catalytic hybrid system has two features that distinguish it from other photo- or thermal-catalytic systems. First, unlike the CO2 thermal-methanation reaction where CO2 and H2 react at a molar ratio of 1:4, 2.0 mol of H2 was replaced with 2.0 mol H2O in the photo-thermal catalytic hybrid system compared to the thermal-methanation reaction requiring 4.0 mol of H2. Second, by loading Ni and Pt, which are catalytic active species with excellent CO2 and H2 adsorption abilities, the CO2 reduction (46.48%) was promoted and the CH4 selectivity (99.46%) in the product was increased compared to the photo-methanation reaction. The CaTiO3@Ni-Pt not only inhibited the recombination of the photo-generated charges, but also facilitated the adsorption of the reactants in the photo-thermal hybrid system. The quantum efficiency of the CaTiO3@Ni-Pt catalyst measured for the photo-thermal hybrid system steadily increased to 180 °C. Nevertheless, this study implies that a photo-thermal hybrid system can be useful to photo-reducing CO2 by adding a small amount of heat. From a thermal reaction standpoint, a photo-thermal hybrid system can be used to reduce the reaction temperature during CO2 thermal-methanation and to reduce the consumption of H2 in half.

The ultimate goal of this study was to synthesize core-shell hetero-nanostructures for efficient charge separation during photocatalytic reactions. This is expected to result in increased photocatalytic activity. A core@shell structured CuS@In2S3 was proposed for solar hydrogen production with CuInS2 as an interface between the CuS and In2S3 components. The formation of the CuInS2 interface was confirmed from the XRD and HRTEM analysis. The introduction of the CuInS2 interface resulted in sulfur vacancies on the surface of the photocatalyst, which in turn increased the reactant active sites. In particular, it behaved like an electron trap to retard electron-hole recombination, so that it could eventually improve the photocatalytic activity. The designed CuS@CuInS2:In2S3 photocatalyst exhibited a hydrogen production of 2000 μmol/g after 10 h. Photoluminescence, photocurrent and IMVS measurements validated the enhanced photoactivity which was due to both the reduced recombination rate between the excited electron and hole pairs (e−/h+), and the rapid electron transfer in the core@interface:shell structured CuS@CuInS2:In2S3 photocatalyst.

Carbon- and Rh-loaded strontium titanate (SrTiO3) nanoparticles (NPs) were synthesized respectively by the wet impregnation method and the aerobic and anaerobic ethanol oxidation methods, and characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction crystallography, UV–vis absorption, Raman spectroscopy, and X-ray photoelectron spectroscopy. Carbon was shown to be uniformly coated on SrTiO3 NPs by the aerobic and anaerobic ethanol oxidation methods Electrocatalytic activities of unmodified and modified SrTiO3 NPs were tested for water splitting and CO2 reduction. The aerobic C-coated and Rh-loaded SrTiO3 catalysts showed comparable activity that was increased by >10-fold of that of unmodified SrTiO3 catalyst. These results demonstrate that both metallic and nonmetallic surface modifications can highly improve the electrocatalytic activity of SrTiO3 NPs and point to highlight a more important role of the modifier in the electrocatalytic reactions than of the SrTiO3 structure.

WO3/MoO3 hybrid nanostructures were first prepared by a two-step hydrothermal method and applied to photocatalytic coupled-dye degradation, photoelectrocatalytic water splitting and CO2 reduction. Methyl orange (MO), rhodamine B (RhB) and methylene blue (MB) were used to examine dye coupling effect for photodegradation. Poorly photodegraded MO was found to be easily removed by coupling with MB. W-rich oxide material was found to be efficient for removal of MO and MB while Mo-rich material was more efficient for RhB. The WO3/MoO3 hybrid structure showed a dramatically improved performance than those of pure WO3 and MoO3 for water splitting and CO2 reduction.

This study focuses on hydrogen production by methanol photolysis using zinc indium sulfide (ZnxInySz). The X-ray diffraction identified that the synthesized Zn2InS2.5 and ZnInS2.5 particles have a hexagonal Zn3In2S6 structure, but when In of twice amount against Zn is coexisted, the particle exhibits a perfect hexagonal ZnIn2S4 structure. The results in ultra-violet absorption and X-ray photoelectron spectroscopy analysis confirmed that the band-gaps of ZnxInySz particles decrease depend on the coexistence of In. However, the photocurrent which related to the life time of excited electrons was no correlation with the Zn/In molar ratio, and it was the highest on ZnInS2.5 particle with a ratio of Zn:In = 1:1. Eventually, the hydrogen production by methanol photolysis in aqueous solution was the best on ZnInS2.5 particle. This result gives ultimately relevant that the recombination between electrons and holes during methanol photolysis could be suppressed on bimetallic ZnInS2.5 particle.

In this work, the Cu (0.1, 0.5, 1.0, and 5.0 mol.-%)-incorporated ZnO nanoparticles (CuxZnyO) are prepared by a conventional hydrothermal method. Powder X-ray diffraction patterns confirm that Cu ion is stably inserted into the framework of ZnO, and the crystallite size decreases as the amount of Cu ion increases. With the insertion of Cu ions into ZnO, the recombination rate of photogenerated charge carriers is found to be low which in turn increases the photocatalytic activity. The H2 production activity of Cu-inserted ZnO catalysts is higher than the pure ZnO catalyst. Among the different samples, the Cu0.01Zn0.99O catalyst having a 1.0 mol.-% of Cu shows the higher H2 production activity. The enahanced H2 production activity of CuxZnyO catalysts is attributed to the longer life-time of excited electrons during the photocatalytic reaction and the decreased electron-hole recombination rate.

The oxidative DNA cleavage induced by the [Cu(2,2′-bipyridine)2(NO3)]NO3 (Cu(bpy)2) complex was examined using the linear dichroism (LD) technique. Using this method, the oxidative DNA cleavage by the Fenton mechanism was reported to occur through two sequential first-order reactions. As the Cu(bpy)2 concentration increased, the rate constant of both first order reactions increased, as expected. The activation energy of the second step was estimated to be 0.190 kJ mol−1. A similar method was applied for various synthetic polynucleotides. Poly[d(G-C)2], poly(dG)·poly(dC), and poly(dA)·poly(dT) produced a time-dependent decrease in LD, which could be elucidated by a single component exponential decay. This observation is in contrast to Fenton-type oxidative DNA cleavage. On the other hand, poly[d(A-T)2] produced a time-dependent decrease in the LD magnitude, which could be elucidated by two sequential first order reactions.

The binding modes of o-, m-, and p-trans-BMPyP with DNA were studied using their spectroscopic properties. Also, the binding modes were compared based on the location and number of periphery cationic methylpyridine ions of the cationic porphyrins. The optical absorption spectra of the o-, m-, and p-trans-BMPyP when bound to DNA presented red shifts and hypochromicity compared to the optical absorption spectrum of DNA-free cationic porphyrins. m-trans-BMPyP–DNA presented the largest red shifts and hypochromicity. The results of the circular dichroism spectral analysis indicated positive and negative bisignate absorption bands in the Soret band of the porphyrins in the case of all concentration ratios of o- and p-trans-BMPyP–DNA, and two negative absorption bands were observed in m-trans-BMPyP–DNA. Compared to the size of the absorption band of the DNA optical absorption spectrum, the results of the reduced linear (LDr) spectral analysis indicated mainly small sizes of Soret absorption bands (the absorption spectrum of porphyrins) and positive LDr values for o- and p-trans-BMPyP–DNA. In consideration of several of such spectroscopic properties, the binding of o- and p-trans-BMPyP with DNA can be said to be distant to insertion modes. Although the case of m-trans-BMPyP to DNA is an insertion mode, the m-trans-BMPyP molecular surface presented much tilt within the intercalation pocket. The results of comparing the binding modes of TMPyP having four periphery cationic methylpyridine ions of cationic porphyrin indicated that regardless of the number of periphery cationic methylpyridine ions of cationic porphyrin, in the case of the ortho-position, nonplanarity due to steric hindrance of the periphery cationic methylpyridine ions presented outside or groove-binding modes indicative of interaction with DNA phosphates. Unlike the ortho-position, the para-position presented different binding modes based on the number of periphery cationic methylpyridine ions. Only cationic porphyrins having four periphery cationic methylpyridine ions were inserted into the DNA. Lastly, regardless of the number of periphery cationic methylpyridine ions, all meta-positions were inserted into the DNA. This indicated that at the least the location and the number of periphery cationic methylpyridine ions of the porphyrins used in this experiment were important elements that determine insertion into DNA base pairs.

The interaction of Δ- and Λ-[Ru(phen)2DPPZ]2+ (DPPZ = dipyrido[3,2-a:2′, 3′-c]phenazine, phen = phenanthroline) with a G-quadruplex formed from 5′-G2T2G2TGTG2T2G2–3′(15-mer) was investigated. The well-known enhancement of luminescence intensity (the ‘light-switch’ effect) was observed for the [Ru(phen)2DPPZ]2+ complexes upon formation of an adduct with the G-quadruplex. The emission intensity of the G-quadruplex-bound Λ-isomer was 3-fold larger than that of the Δ-isomer when bound to the G-quadruplex, which is opposite of the result observed in the case of double stranded DNA (dsDNA); the light switch effect is larger for the dsDNA-bound Δ-isomer. In the job plot of the G-quadruplex with Δ- and Λ-[Ru(phen)2DPPZ]2+, a major inflection point for the two isomers was observed at x ≈ .65, which suggests a binding stoichiometry of 2:1 for both enantiomers. When the G base at the 8th position was replaced with 6-methyl isoxanthopterin (6MI), a fluorescent guanine analog, the excited energy of 6-MI transferred to...

This study examined the influence of the molecular crowding condition induced by polyethylene glycol (PEG) on the G-quadruplex structure of the thrombin-binding aptamer sequence, 5'-GGGTTGGGTGTGGGTTGGG (G3), in a solution containing a sufficient concentration of mono cations (K+ and Na+). Although the G3 sequence preferably formed the antiparallel type G-quadruplex structure in a Na+ solution, conversion to the parallel type occurred when PEG was added. The antiparallel type was maintained at low PEG concentrations. When the PEG concentration reached 30%, the antiparallel type and parallel type coexist. At PEG concentrations above 40%, the G-quadruplex structure adopted the parallel type completely. In the presence of K+ ions, G3 showed a parallel conformation and remained as a parallel conformation with increasing PEG concentration. The dissociation temperature increased with increasing PEG concentration in all cases, suggesting that the G-quadruplex conformation is more stable under molecular crowding conditions.Communicated by Ramaswamy H. Sarma.

Guanine is the most strongly oxidized base in DNA; generation of a guanine radical cation as an intermediate in an oxidation reaction leads to migration through a resulting cationic hole in the DNA π-stack until it is trapped by irreversible reaction with water or other free radicals. In the case of normal sequences, the primary position of Guanine oxidations by one-electron oxidants such as carbonate radical anions, BPT(7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene), and riboflavin are 5'-G in GG doublets and the central G in a GGG triplet. According to results, the properties of guanine oxidation on abasic site containing sequences are independent from the position of AP(apurinic/apyrimidinic) site in the presence of carbonate radical anions under a short irradiation time, although this radical is exposed to solvent by the existence of an abasic site. The lack of abasic site effect on guanine oxidative damage by the carbonate radical may be due to a sequence-independent property of the initial electron transfer rate in the hole injection step, or may relate to an electron transfer mechanism with large reorganization energy dependency. Consequently, the carbonate radical anions may easily migrate to another single G in the charge re-distribution step. Meanwhile, there is a strong dependency on the presence of an AP(apurinic/apyrimidinic) site in the cleavage patterns of guanine oxidations by physically large oxidizing agents, such as BPT(7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene) and riboflavin. These radicals show strong AP(apurinic/apyrimidinic) site dependency and clear G-site selectivity.Communicated by Ramaswamy H. Sarma.

The spectral properties of meso-tetrakis (N-methylpyridinium-4-yl)porphyrin (TMPyP) in the presence of parallel and antiparallel G-quadruplexes formed from a thrombin-binding aptamer G-quadruplex (...

trans-BMPyP induced the B-Z transition for alternated AT oligonucleotides as it was evident by inversed CD spectrum. The transition occurred simultaneously with appearance of the extensive stacking of porphyrin. Complete B-Z transition required at least 14 base-pairs long. Insertion of one or two GC base pairs prevented the B-Z transition.

Metallic indium (In) spheres were, for the first time, produced by the anaerobic ethanol oxidation of indium oxide. The changes in morphology and crystal structure were characterized by scanning electron microscopy, optical microscopy and X-ray diffraction crystallography. The surface oxidation of In metal was examined by X-ray photoelectron spectroscopy. This novel method for the production of In metal will increase the potential applications of In to areas, such as semiconductor alloys, organic synthesis, and photovoltaic devices.

This paper reports the synthesis of ZnS microspheres with cubic and hexagonal crystal phases using a solvothermal method. These materials were characterized by a range of techniques. The effects of Au and Ag-doping on ZnS were also examined. Hexagonal phase ZnO microspheres could be obtained by a CO oxidation process over the ZnS microspheres. The onset of CO oxidation occurred above 350 °C, which was increased by Au and Ag doping. The synthesized materials were used for the photocatalytic degradation of mixed dyes {methylene blue (MB) + methyl orange (MO) + rhodamine B (RhB)}. The observed photocatalytic degradation rate over the photocatalysts was in the order, RhB

Tailoring the exposed crystal facet of a material is a very important strategy for improving the application performance. Herein, cubic phase Co 3 O 4 with two different morphologies, nanoplates and nanologs, was synthesized, and CO oxidation, preferential oxidation of CO (CO-PROX) under H 2 -rich condition, water-gas shift (WGS) reaction, and supercapacitor properties were examined. The nanoplates with {112}-exposed facets showed better performance in all the test model systems. The {112} facets contained more active Co 3+ , which is responsible for the activation of CO oxidation (and H 2 production) at a lower temperatures. A facial ion transport on the facet increased the specific capacitance of the plates. The wider application tests and the design of Co oxide nanostructures provide a better strategy for the development of Co-based materials.

The binding property of 1-pyrenyl-tris(N-methyl-p-pyridino)porphyrin (a pyrene-porphyrin dyad; Py-TMPyP) to various G-quadruplexes formed from 5′-G3TnG3TGTG3TnG3 (n = 2 and 3, designated as S1 and S2, respectively) and conformation-dependent stability of the Py-TMPyP–quadruplex complexes were investigated via thermal melting profiles and circular dichroism (CD) spectral analyses. Upon binding to parallel (in the presence of K+) and antiparallel (in the presence of Na+) S1 and S2 quadruplexes, a bisignate CD signal in the Soret region was induced for all four G-quadruplexes, indicating that the direction of interaction of the electric transition moments of the porphyrins differed. This suggested that the porphyrin binding site in the G-quadruplex is highly unsymmetric. Py-TMPyP induced a moderately negative CD signal in the pyrene absorption region when binding to the parallel S1 quadruplex and parallel/antiparallel mixed S2 quadruplex. In contrast, a strongly negative CD signal was observed for the Py-TMPyP bound to antiparallel S1 quadruplex, while no CD signal appeared for the antiparallel S2 quadruplex. Considering that two and three thymine bases are present in the loops of S1 and S2, respectively, the number of the thymines in the loop is important for the interaction of pyrene and the G-quadruplex. The thermal melting study showed that the antiparallel form of the G-quadruplex was generally less stable compared to the corresponding parallel conformation. The presence of Py-TMPyP caused destabilization of the G-quadruplexes.

Ruthenium(II) polypyridyl dimer containing large planar aromatic bridging ligands [μ-(tpphz)(phen)4Ru2]4+ (phen = 1,10-phenanthroline, tpphz = tetrapyrido[3,2-a:2′,3′-c:3″, 2″-h:2‴, 3‴-j]phenazine, bis-Ru-tpphz) were synthesized and characterized by elemental analysis, and 1H nuclear magnetic spectroscopy. The binding mode of the synthesized bis-Ru-tpphz to DNA was compared with those of the bis-Ru-bip, and bis-Ru-tatpp complexes. The structures of the connecting bridge of bis-Ru complexes were different. The absorption and reduced linear dichroism spectrum showed that the planar linker moiety of the bis-Ru-tatpp complex is inserted between the DNA base-pairs despite the steric hindrance originating from its large ruthenium ligand part, whereas the bis-Ru-bip complex has flexible linker binds at the groove of the DNA. The binding mode of the bis-Ru-tpphz complex, which has fused shorter bridge ligands than the bis-Ru-tatpp complex, was in contrast with the other two complexes. The bis-Ru-tpphz complex binds either at the groove of the DNA or to the negatively charged phosphate group; intercalative binding was prevented by either short bridge structure or steric hindrances from the phenanthroline ligand. In conclusion, the structure of the bridge of the bis-Ru(II) complex plays an important role in determining the binding mode of these compounds to DNA. To have the mode of insertion, the bridge ligand structure must be fused and have a sufficiently long distance.

The binding modes of a pyrene–porphyrin dyad, (1-pyrenyl)-tris(N-methyl-p-pyridino)porphyrin (PyTMpyP), to various DNAs (calf thymus DNA (Ct-DNA), poly[d(G–C)2], and poly[d(A–T)2]) have been investigated using circular dichroism and linear dichroism measurements. Based on the polarization spectroscopic results, it can be shown that the pyrenyl and porphryin planes are skewed to a large extent for PyTMPyP in an aqueous environment and in the binding site of poly[d(G–C)2]. In this complex, a photoinduced electron transfer (PET) process between the pyrenyl and porphyrin moieties occurs. On the other hand, PET was not observed in the PyTMPyP–poly[d(A–T)2] complex, whereas the fluorescence intensity of TMPyP was enhanced. The molecular planes of the pyrene and porphyrin moieties are almost parallel in the poly[d(A–T)2] and Ct-DNA adducts. Moreover, the generation of 1O2 species occurs only for the PyTMPyP–Ct-DNA and PyTMPyP–poly[d(A–T)2] complexes. We discuss the photophysical properties of PyTMPyP which are attributed to the binding patterns and the sequence of DNA bases.

International audience; Mg 2+ ion stimulates the DNA strand exchange reaction catalyzed by RecA, a key step in homologous recombination. To elucidate the molecular mechanisms underlying the role of Mg 2+ and the strand exchange reaction itself, we investigated the interaction of RecA with Mg 2+ and sought to determine which step of the reaction is affected. Thermal stability, intrinsic fluorescence, and native mass spectrometric analyses of RecA revealed that RecA binds at least two Mg 2+ ions with K D ≈ 2 mM and 5 mM. Deletion of the C-terminal acidic tail of RecA made its thermal stability and fluorescence characteristics insensitive to Mg 2+ and similar to those of full-length RecA in the presence of saturating Mg 2+. These observations, together with the results of a molecular dynamics simulation, support the idea that the acidic tail hampers the strand exchange reaction by interacting with other parts of RecA, and that binding of Mg 2+ to the tail prevents these interactions and releases RecA from inhibition. We observed that binding of the first Mg 2+ stimulated joint molecule formation, whereas binding of the second stimulated progression of the reaction. Thus, RecA is actively involved in the strand exchange step as well as bringing the two DNAs close to each other.

Background In stabilization of the G-quadruplex, formation of a Hoogsteen base-pair between the guanine (G) bases is essential. However, the contribution of each Hoogsteen base-pair at different positions to whole stability of the G-quadruplex has not been known. In this study, the effect of a deficiency of the Hoogsteen type hydrogen bond in the G-quadruplex stability was investigated. Spectral properties of meso-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) associated with various G-quadruplexes were also examined. Methods The thermal stability of the thrombin-binding DNA aptamer 5′G1G2TTG5G6TG8TG10G11TTG14G15 G-quadruplex, in which the guanine (G) base at 1, 2, 5, 6 and 8th positions was replaced with an inosine (I) base, one at a time, was investigated by circular dichroism (CD). The absorption, CD and fluorescence decay curve for the G-quadruplex associated TMPyP were also measured. Results The transition from the G-quadruplex to a single stranded form was endothermic and induced by an increase in entropy. The order in stability was 0>8>6>2>5>1, where the numbers denote the position of the replacement and 0 represents no replacements of the G base, suggesting the significant contribution of the G1 base in the stability of the G-quadruplex. Alteration in the spectral property of TMPyP briefly followed the order in thermal stability. Conclusions Replacement of a G base with an I base resulted in destabilization of the G-quadruplex. The missing hydrogen bond at position 1 destabilized the G-quadruplex most efficiently. TMPyP binds near the I base-replaced location namely, the side of the G-quadruplex. General significance The Hoogsteen base-pairing is confirmed to be essential in stabilization of G-quadruplex. When G is replaced with I, the latter base is mobile to interact with cationic porphyrin., Graphical abstract, Highlights • Thermal stability of a quadruplex, 5´G1G2TTG5G6TG8TG9G10TTG11G12 was investigated. • Replacement of G by I base decreases melting temperature. • The stability decreased 0>8>6>2>5>1, where numbers denotes the position replaced. • Replaced I base interacts with a cationic porphyrin, TMPyP.

Complexes of dipyridylamine based ligand with an anthracene moiety containing divalent metal ions Co(II), Cu(II), Ni(II), Zn(II) and Cd(II) were characterized structurally. The experimental results showed that they can induce considerable oxidative DNA cleavage in the presence of hydrogen peroxide and dioxygen. The Zn(II) complex did not show any appreciable cleavage activity, whereas the Cd(II) and Ni(II) complexes were moderately active. On the other hand, Cu(II) and Co(II) complex showed the formation of a significant quantity of linear DNA resulting from the double-strand breaks. Mechanistic studies revealed the involvement of HO˙ and the superoxide anion to be the reactive species in the scission process in aerobic media. A mechanism involving either the Fenton or the Haber–Weiss reaction was proposed for the DNA cleavage mediated by these complexes. The Cu(II) complex could also cleave the double stranded calf thymus DNA (ds DNA) in the presence of activators, most likely via an oxidative mechanism, whereas the activity of the other complexes was negligible under similar reaction conditions. The kinetic aspects of ds DNA cleavage with the Cu(II) are detailed. The interaction of the five metal complexes with ds DNA was investigated by UV absorption and linear dichroism studies, and the mode of complexes binding to ds DNA is proposed.

The binding modes of a pyrene–porphyrin dyad, (1-pyrenyl)-tris(N-methyl-p-pyridino)porphyrin (PyTMpyP), to DNA and its photophysical properties have been investigated using various spectroscopic techniques. The circular dichroism (CD) spectrum of PyTMpyP bound to DNA (PyTMpyP–DNA) showed one negative and two positive bands in the Soret region. The CD signal in the pyrene absorption region was positive. The shape of the CD spectrum does not support an intercalative binding mode of TMpyP, which would typically afford a negative CD band in the absence of the pyrene moiety. Linear dichroism (LD) experiments revealed a very small signal in the Soret region, which also challenges the intercalation of TMpyP into DNA. Upon excitation of the pyrene moiety, the emission intensity of porphyrin in aqueous solution was quenched due to a photoinduced electron transfer (PET) process between the pyrenyl and porphyrin moieties. On the other hand, the emission of porphyrin was markedly enhanced upon binding to DNA, as the PET process from the excited pyrene moiety to TMpyP was suppressed when bound to DNA. The PET process occurs in the timescale of 65 ps, and could be detected by femtosecond transient absorption spectroscopic methods. Two fluorescence decay times were observed for PyTMpyP in aqueous solution (0.78 and 4.8 ns). Both decay times increased upon binding to DNA owing to environment and/or conformational changes in PyTMpyP. The driving force (ΔG) of the PET process was evaluated under conditions of minor and major groove binding. The PET process and photophysical properties of the PyTMpyP dyad were concluded to be influenced by the binding mode.

The interaction of Δ- and Λ-[Ru(phen)

In this study, the binding mode of porphyrin-free single-stranded poly[d(AT)] and trans-BMPyP was observed in the Z-form trans-BMPyP-poly[d(A-T)

The interaction of Δ- and Λ-[Ru(phen)2DPPZ]2+ (DPPZ = dipyrido[3,2-a:2′, 3′-c]phenazine, phen = phenanthroline) with a G-quadruplex formed from 5′-G2T2G2TGTG2T2G2–3′(15-mer) was investigated. The well-known enhancement of luminescence intensity (the ‘light-switch’ effect) was observed for the [Ru(phen)2DPPZ]2+ complexes upon formation of an adduct with the G-quadruplex. The emission intensity of the G-quadruplex-bound Λ-isomer was 3-fold larger than that of the Δ-isomer when bound to the G-quadruplex, which is opposite of the result observed in the case of double stranded DNA (dsDNA); the light switch effect is larger for the dsDNA-bound Δ-isomer. In the job plot of the G-quadruplex with Δ- and Λ-[Ru(phen)2DPPZ]2+, a major inflection point for the two isomers was observed at x ≈ .65, which suggests a binding stoichiometry of 2:1 for both enantiomers. When the G base at the 8th position was replaced with 6-methyl isoxanthopterin (6MI), a fluorescent guanine analog, the excited energy of 6-MI transferred to bound Δ- or Λ-[Ru(phen)2DPPZ]2+, which suggests that at least a part of both Ru(II) enantiomers is close to or in contact with the diagonal loop of the G-quadruplex. A luminescence quenching experiment using [Fe(CN)6]4- for the G-quadruplex-bound Ru(II) complex revealed downward bending curves for both enantiomers in the Stern–Volmer plot, which suggests the presence of Ru(II) complexes that are both accessible and inaccessible to the quencher and may be related to the 2:1 binding stoichiometry.

Meso-tetrakis(N-methyl pyridinium-4-yl)porphyrin (TMPyP) intercalates between the base-pairs of DNA at a low [TMPyP]/[DNA base] ratio in aqueous solutions and molecular crowding conditions, which is induced by the addition of Poly(ethylene glycol) (PEG). Studied DNA-binding drugs, including TMPyP, 9-aminoacridine, ethidium bromide, and DAPI (4′,6-diamidino-2-phenylindole) showed similar binding properties in the presence or absence of PEG molecules which is examined by circular and linear dichroism. According to the LDr (reduced linear dichroism) results of the binding drugs examined in this work, PEG molecules induced no significant change compared to their binding properties in aqueous buffering systems. These results suggest that the transition moments are not expected to be perturbed significantly by PEG molecules. In this study, the experimental conditions of PEG 8000 were maintained at 35% (v/v) of total reaction volume, which is equal to the optimal molar concentration (0.0536 M as final concentration for PEG 8000) to maintain suitable cell-like conditions. Therefore, there was no need to focus on the conformational changes of the DNA helical structure, such as forming irregular aggregate structures, induced by large quantities of molecular crowding media itself at this stage.

We doped (M) and codoped (MM’) Co, Cu, and Ni into CeO 2 support, and tested their gas-phase CO oxidation performance by temperature-programmed reaction mass spectrometry for the as-prepared, thermal H 2 - and N 2 -treated samples. Additionally, fundamental characteristics of doped CeO 2 were revealed by transmission electron microscopy, optical microscopy, X-ray diffraction crystallography, UV–visible absorption, Brunauer–Emmett–Teller (BET) surface area measurements, and temperature-programmed reduction experiments. The CO oxidation performance was greatly improved upon metal-doping and thermal pre-treatment in H 2 and N 2 condition. It was found that Cu-contained samples showed higher CO performance while Ni, Co and CoNi-doped samples showed poor performances. The T 10% (the temperature at 10% CO conversion) was lowered by 140 °C upon Cu-doping. Upon N 2 (or H 2 -thermal treatment), the T 10% was lowered by 80 and 110 °C for Cu-doped and undoped CeO 2 catalyst, respectively. Overall, this study provides deeper information of surface treatment effects useful to development of efficient catalysts.

The effects of the central metal ion on complex formation between meso-tetrakis(N-methylpyridium-4-yl)porphyrin (TMPyP) and the thrombin-binding aptamer G-quadruplex, 5'G2T2G2TGTG2T2G2, were examined in this study. The central metal ions were vanadium and zinc. At a [porphyrin]/[G-quadruplex] ratio of less than one, the absorption and CD spectra were unaffected by the mixing ratio for all three porphyrins, suggesting that the binding mode is homogeneous. Relatively small changes in the absorption spectrum when forming the complexes with the G-quadruplex, the positive CD signal, and the large accessibility of the I(-) quencher, suggested that all these porphyrins are not intercalated between the G-quartet. Stabilization of the G-quadruplex by ZnTMPyP was most effective. The effect of VOTMPyP on G-quadruplex stabilization was moderate, whereas TMPyP slightly destabilized G-quadruplex. From this observation, the involvement of the ligation of one G-quartet component to the central metal ion in G-quadruplex stabilization by metallo-TMPyP is suggested.

The catalytic effect of [M(2,2′-bipyridine) 2 (NO 3 )](NO 3 ) (M(bpy) 2 , M = Cu(II), Zn(II) and Cd(II)) on the super-coiled and double stranded DNA (scDNA and dsDNA) was examined by electrophoresis and a real-time detection linear dichroism (LD) technique. Although the Cu(bpy) 2 complex effectively cleaved both types of DNA, the other two complexes were inactive. This was explained by the electrochemical properties of the metal complexes. The Cu(bpy) 2 complex exhibited a redox potential at − 0.222 V with a peak to peak separation of 0.201 V, whereas the other two metal complexes did not undergo any redox reaction. Both electrophoresis and LD measurements revealed the superoxide radical, ·O 2 − , to be responsible for DNA cleavage. A kinetic study using the LD technique showed that the cleavage of dsDNA consisted of two first order reactions. The fast reaction is believed to reflect the cleavage of one strand, whereas the slow reaction involves the cleavage of the complementary strand at or near the first cleaved site.

The interactions of anionic oxo-titanium (IV) meso -tetrakis(4-sulfonatophenyl)porphyrin and cationic oxo-titanium(IV) meso -tetrakis(1-methylpyridium-4-yl)porphyrin with anionic and cationic micelles were examined by Raman spectroscopy and transient absorption spectroscopy. The Raman bands of O Ti IV porphyrins in the presence of surfactants with same charge were similar to those observed in a pure water solution. The characteristic Raman band was observed at 915 cm −1 , which was assigned to the O Ti stretching mode of the 6-coordinated complex, O Ti (H 2 O) porphyrins. On the other hand, in the presence of oppositely charged surfactants, a markedly up-shifted Raman band was observed at 945 cm −1 , which was assigned to the O Ti stretching mode of a 5-coordinated complex, O Ti porphyrins. O Ti porphyrins interact with oppositely charged surfactant micelles by losing the sixth axial ligand (H 2 O). The 5-coordinate complexes showed a shorter lifetime of the exited triplet state due to the lower lying quenching state.

The photoreduction of water-soluble cationic manganese(III) meso-tetrakis(1-methylpyridium-4-yl)porphyrin (Mn(III)(TMPyP)(4+)) bound to a synthetic polynucleotide, either poly[d(A-T)2] or poly[d(G-C)2], was examined by conventional absorption and circular dichroism (CD) spectroscopy, transient absorption, and transient Raman spectroscopy. Upon binding, Mn(III)(TMPyP)(4+) produced a positive CD signal for both polynucleotides, suggesting external binding. In the poly[d(A-T)2]-Mn(III)(TMPyP)(4+) adduct case, an interaction between the bound porphyrin was suggested. The transient absorption spectral features of Mn(III)(TMPyP)(4+) in the presence of poly[d(A-T)2] and poly[d(G-C)2] were similar to those of the photoreduced products, Mn(II)(TMPyP)(4+), whereas Mn(III)(TMPyP)(4+) in the absence of polynucleotides retained its oxidation state. This indicated that both poly[d(A-T)2] and poly[d(G-C)2] act as electron donors, resulting in photo-oxidized G and A bases. The transient Raman bands (ν2 and ν4) that were assigned to porphyrin macrocycles exhibited a large downshift of ~25 cm(-1), indicating the photoreduction of Mn(III) to Mn(II) porphyrins when bound to both polynucleotides. The transient Raman bands for pyridine were enhanced significantly, suggesting that the rotation of peripheral groups for binding with polynucleotides is the major change in the geometry expected in the photoreduction process. These photoinduced changes do not appear to be affected by the binding mode of porphyrin.

The binding properties and sequence selectivities of - and (bip = 4,4'-biphenylene (imidazo [4,4-f][1,10]phenanthroline) complexes with and were investigated using conventional spectroscopic methods. When bound to , a large positive circular dichroism (CD) spectrum was induced in absorption region of the bridging moiety for both the - and complexes, which suggested that the bridging moiety sits in the minor groove of the polynucleotide. As luminescence intensity increased, decay times became longer and complexes were well-protected from the negatively charged iodide quencher compared to that in the absence of . These luminescence measurements indicated that Ru(II) enantiomers were in a less polar environment compared to that in water and supported by minor groove binding. An angle of between the molecular plane of the bridging moiety of the complex and the local DNA helix axis calculated from reduced linear dichroism () spectrum further supported the minor groove binding mode. In the case of complex, this angle was , suggesting a tilt of DNA stem near the binding site and bridging moiety sit in the minor groove of the . In contrast, neither -nor complex produced significant CD or signal in the absorption region of the bridging moiety. Luminescence measurements revealed that both the - and complexes were partially accessible to the quencher. Furthermore, decay times became shorter when bis-Ru(II) complexes bound to . These observations suggest that both the - and complexes bind at the surface of , probably electrostatically to phosphate group. The results indicate that - and are able to discriminate between AT and GC base pairs.

As in the human genome there are numerous repeat DNA sequences to adopt into non-B DNA structures such as hairpin, triplex, Z-DNA, G-quadruplex, and so on, an understanding of the interaction between DNA repair proteins and a non-B DNA forming sequence is very important. In this regard, the interaction between RecA protein and human telomeric 5'-TAGGG-(TTAGGG)3-TT-3' sequence and the G-quadruplex formed from this sequence has been investigated in bulk phase and at the single-molecule level. The RecA@ssDNA filament, which is formed by the interaction between RecA protein and a G-rich sequence, was dissociated by the addition of K(+) ions, and the dissociated G-rich sequence was quickly folded to a G-quadruplex structure, indicating that the G-quadruplex structure is more favorable than the RecA@ssDNA filament in the presence of K(+) ions. In addition, we demonstrate that the conformation of the G-quadruplex, which is heterogeneous in the absence of RecA, converged to the specific G-quadruplex with one double-chain-reversal loop upon association of RecA protein.

Four new Ru(II) complexes [RuHCl(bpy)(PPh(3))(CO)] (1), [RuHCl(bpy)(AsPh(3))(CO)] (2) (bpy = 2,2'-bipyridine), [RuCl(HL)(PPh(3))(2)(CO)] (3) and [RuCl(HL)(AsPh(3))(2)(CO)] (4) (HL = 2,2'-bipyridine-4,4'-dicarboxylic acid) were synthesized and characterized. X-ray diffraction was used to characterize 3 in solid state. The interactions of these complexes with DNA were explored by different techniques which revealed that the complexes could bind to CT-DNA through non-intercalation. The in vitro cytotoxic and antioxidant activities of the complexes validated against a panel of cancer cell lines and free radicals showed that 3 and 4 possess quite high anticancer and antioxidant activities over 1, 2 and standard drugs. An apparent dependence of biological activities on incorporation of COOH in bipyridine moiety was noticed: Inclusion of COOH caused significant differences in DNA binding, cytotoxicity and antioxidant activity.

One of the porphyrin moieties of the porphyrin dimer intercalates rapidly between the DNA base-pairs, followed by the slow intercalation of the other. The slow intercalation of the second porphyrin moiety of porphyrin dimer to poly[d(G-C)2] was investigated by normal absorption and circular dichroism spectroscopy. The change in absorbance in the Soret band of porphyrin upon association with poly[d(G-C)2] can be best elucidated by the combination of the two single exponential curves, suggesting the intercalation occurred via two independent first order reactions. Activation energies of these two first order reactions were calculated to be 0.37 kcal/mol and 3.19 kcal/mol, respectively. The intercalation associated with lower activation energy can be assigned to the intercalation of second porphyrin moiety to 5′CG3′ site while that with higher activation energy to 5′GC3′ intercalation site. Increasing the flexibility of poly[d(G-C)2] by adding Na+ ion resulted in an enhancement of the reaction rate for both steps in an exponential manner.

The binding mode of a porphyrin dimer to double stranded native DNA was investigated in this study using normal electric absorption, circular dichroism (CD) and linear dichroism (LD) spectroscopies. At the time of mixing, the spectral properties of the porphyrin dimer upon its association with DNA were characterized by hypochromism and a red shift in the absorption spectrum and by complicated CD and negative LD in the Soret region. As time elapsed, the CD spectrum became a negative single band and the negative LD signal increased. These spectral changes suggested that the majority of both porphyrin moieties of the dimer intercalated between the DNA base-pairs. The changes in the spectral characteristics of the DNA bound porphyrin-dimer were similar when the minor groove of DNA was saturated by 4′,6-diamidino-2-phenylindole (DAPI), which is well-known minor groove binding molecule. The spectral properties of DAPI, which can be summarized by a large positive induced CD in the DAPI absorption region (300~400 nm) and wavelength-independent positive reduced LD, remained intact when the porphyrin dimer was present. These observations indicated that both DAPI and porphyrin bind to DNA simultaneously, and furthermore, the bis-intercalation of the porphyrin dimer occurs in the major groove.

Solvent-to-polymer chirality transfer was examined using conjugated polymer with intramolecular stack structure (IaSS). When achiral poly(diphenylacetylene)s (PDPAs) dissolved in limonene, the solvent chirality was successfully transferred to the side phenyl stack structure, leading to intramolecular axial chirality. The phenyl–phenyl IaSS was under thermodynamic control to readily undergo asymmetric changes in chiral limonene, leading to optical activity in the isotropic structure between the main chain and resonant side phenyl rings. The axial chirality was significantly affected by the chain length and substitution position of the side alkyl groups. The longer alkyl chains and bulkier alkyl group prevented direct intermolecular interactions between the side phenyl rings and the chiral limonene molecules. PDPA with sterically congested, highly stable, and regulated IaSS was not favorable for efficient solvent-to-polymer chirality transfer.

Department of Gas-Energy Engineering, Kundong University, Gyeongbuk 760-833, KoreaReceived November 22, 2011, Accepted December 29, 2011The fluorescence intensity of DNA-intercalated ethidium with [ethidium]/[DNA base] being 0.005 wasquenched upon the binding of another intercalating ligand, meso-tetrakis(N-methylpyridinium-4-yl)porphyrin(TMPyP). Addition of Ca