Narrow Results

The mechanisms of the photoelectretic effect appearing on Ni intercalation GaSe were studied. The presence of the photoelectretic effect for such an object of investigation can be explained by the estimation that in Ni intercalated GaSe, the nonequilibrium electrons and holes excited by light occurred on an asymmetric potential well.

In this investigation, the mechanical and thermal properties of the montmorillonite-epoxy nanocomposites were studied. The epoxy compounds were prepared by in situ polymerization and the intercalation dispersion were obtained as evidenced using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal remarkable stiffening effect and slight toughening effect of the MMT in the epoxy resin and an insight about the crack tip and notch tip toughening mechanism. According to the DMA, the glass transition temperature increases as increasing the MMT content.

The tungsten oxides and bronzes have been extensively studied since their discovery in the last century, because of their brilliant colors and high electrical conductivity. More recently the driving interest resulted from their potential use in electrochromic displays and other electrochemical systems. Their crystalline structures are generally based on the corner sharing of WO₆ octahedra giving tunnels of variable size and shape leading to exciting intercalation chemistry. These structures readily undergo redox reactions, and in the last quarter century these reactions have often involved soft chemistry. Most recently hydrothermal techniques have been used to prepare new sodium tungstates with the hexagonal tungsten bronze and the pyrochlore structures. The phase formed is a function of the pH of the reaction medium. The pyrochlore phase readily undergoes ion-exchange with a wide range of monovalent cations giving the compounds, M_xW₂O_6+x/2 · yH₂O; the value of y is strongly dependent on the identity of the cation, M. WO₃ with the pyrochlore structure could be formed from the hydronium and ammonium complexes. Lithium can be readily intercalated either chemically and electrochemically into both these phases, just as in the previously-known bronze phases. Surprisingly more lithium is incorporated in most cases in the hexagonal than in the pyrochlore phase. The ions in the pyrochlore structure show rapid ionic mobility, with the hydronium ion showing the greatest mobility.

In this paper, we present a novel method to study the electronic density-of-states of intercalation materials. We present evidence that electrochemical quasi-steady state potential curves of a number of materials exhibit fine structure in striking agreement with the density of electronic states, as obtained from ab initio calculations. The ability to probe the electronic structure by our electrochemical technique seems, in most cases, to be restricted to disordered materials. We suggest that localization of the band states is essential, in order for the technique to give a good picture of their density. The electrochemical density of states is often smaller than the computed one due to kinetic effects, i.e. very slow relaxations of the charge carriers. Our highly sensitive electrochemical method opens new vistas for studying the electronic structure of disordered materials, that can be intercalated with an ionic species.

The mechanism of formation of silica nano-plates by exfoliation of a phyllosilicate magnesium containing clay, Lucentite, in an aqueous solution of poly(acrylic acid) has been studied. Fourier transform infrared spectroscopy and MgK-edge near edge X-ray adsorption fine structure (NEXAFS) analysis shows that non-surface (bulk) Mg ions were not chemically involved in the poly(acrylic acid)/clay intercalation, but were substantially involved in the exfoliation resulting in the silica nano-plates. During intercalation, OK-edge NEXAFS shows that surface defects were formed which represent additional structural branches on the surface. During exfoliation, these increased significantly. Si L_3,2-edge NEXAFS measurements shows that this occurred by migration of SiO₄ groups within the exfoliated silica plates.

Scanning tunneling microscopy is used to study intercalation of cobalt underneath a graphene layer on Ru(0001). Deposition of cobalt on graphene/Ru(0001) at 873 K leads to the intercalation of cobalt between the graphene layer and the Ru(0001) substrate, and the intercalation is associated with Co diffusion at steps and defects. The morphology of graphene/Co/Ru(0001) shows moiré pattern, as same as that of graphene/Ru(0001). The bright areas where Co islands exist are hcp regions of graphene/Ru(0001). The intercalated Co islands have a pseudomorphic structure superimposed on Ru(0001).

Exfoliated silicate minerals have attracted great attentions because of the dramatic improvement in properties. This paper highlights the preparation of exfoliated silicate minerals, including physical, chemical, mixed physical and chemical methods. The mechanisms by which silicates are exfoliated and the important influential factors are also summarized. Finally, the instrumental techniques to characterize the exfoliated structure and exfoliation degree are presented.

The crystalline semiconductor material (MnPS₃) has interlayer d-spacing gap of 6.4 Å. The main advantage of this gap is the ability to accommodate organic and inorganic compounds. Pyridine was intercalated in the MnPS₃ interlayer gap under specific conditions. Four phases (d-spacing = 12.48 Å, 10.8 Å, 9.7 Å and 7.3 Å) were observed and the corresponding lattice expansions were determined, 5.8 Å, 4.4 Å, 3.3 Å and 1 Å, respectively. X-ray diffraction patterns of the samples after the experiment were stopped to reveal the presence of three phases together. The phase transformation occurred for the aforementioned phases. The crystallite size of certain phases is within nanorange. The magnetic properties of the materials are affected by the phase transformation. Complete intercalation was confirmed by the XRD and infrared (IR) measurements.

Double-matrix hierarchical structure of the 〈molecular-lattice matrix MCM-41〈hydroquinone〉〉 is synthesized. Its use in the cathode process in the Li⁺-intercalation current generation showed a significant improvement in the structure of the discharge curve and the practical constancy of diffusion coefficient throughout the discharge process. Theoretical model describing the peculiarities of observed characteristics in the structure is presented.

Intercalation of salicylate (Sal) into layered zinc hydroxide nitrate (ZHN) nanohybrid materials was successfully synthesized by the coprecipitation method. The effect of pH, crystallization method, temperature and time of hydrothermal treatment on preparation was investigated in detail and compared. The products were confirmed by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), and scanning electron microscope (SEM). The results revealed that ZHN–Sal with pure phase and good crystallinity was obtained at pH = 6.0–6.5, 60${}^{\circ }$C and 3h of temperature and time of hydrothermal treatment. The TG-DTA data indicated that the intercalated Sal had a high stability compared to the isolated. And the phases and compositions of the sample calcined at increasing temperatures were also identified by XRPD and FTIR techniques. Furthermore, ZHN–Sal exhibited an improved UV-blocking ability, showing it can be used as a potential alternative matrix for the UV blocker.

Molecular dynamics simulation and minimization process were carried out to study the structure properties of α-zirconium phosphate (α-ZrP) loaded with aniline molecules. Two minimum-energy configurations of α-ZrP with interlayer distances 14.14 and 19.0 Å were found for the systems of molar ratios of aniline to ZrP = 1:1 and 2:1. The structure properties of aniline and α-ZrP and also the interaction between aniline and α-ZrP were analyzed. The phase behavior was analyzed by calculated diffraction patterns, power spectra, and various distribution functions.

A series of nucleobase appended tri-cationic porphyrins (AT4, TT4, GT4 and CT4) have been synthesized and their binding and cleaving ability of DNA were investigated in this present study. UV-vis, fluorescence, circular dichroism and thermal melting studies were carried out to investigate binding of the porphyrin with calf thymus DNA (CTDNA). The apparent binding constant (K_app) and the intrinsic binding constant (K_b) values calculated from UV-vis and fluorescence titrations, respectively, were comparable to 5,10,15,20-tetra(N-methylpyridinium-4-yl) porphyrin (H₂T4) or slightly more for few compounds. Circular dichroism spectra of these porphyrins with DNA show variation in their mode of binding. Among the nucleobase appended tri-cationic porphyrins, the porphyrin in GT4 and TT4 exhibit strong intercalating ability in the DNA duplex whereas the porphyrin in AT4 and CT4 exhibit very less ability for intercalation. The intercalating efficiency of the porphyrin in GT4 is even stronger than that of the H₂T4. The steric strain exists between the tri-cationic porphyrin moiety and the DNA may decrease depending on (a) the ease to exhibit keto-enol tautomerism due to the more acidic protons in guanine and thymine, (b) extended conjugation and (c) hydrogen bonding capability of the nucleobase moieties. Photocleavage proclivities with pBR322 DNA in the presence of light reveal that AT4, TT4 and CT4 show same amount of cleavage but GT4 shows more cleaving efficiency than H₂T4 due to the stacked guanine moieties those are more reducing than a single guanine residue. The singlet oxygen mechanism that is responsible for the photocleavage was confirmed with various inhibitors and interestingly with Tiron (disodium salt of 1,2-dihydroxy-3,5-benzenedisulfonic acid) the photocleaving efficiency increases due to the inhibition of superoxide formation.

Interaction of N,N′,N″,N‴-tetramethyltetra-2,3-pyridinoporphyrazinatonickel(II), ([Ni(2,3-tmtppa)]⁴⁺) and N,N′,N″,N‴-tetramethyltetra-2,3-pyridinoporphyrazinatoiron(II), ([Fe(2,3-tmtppa)]⁴⁺) with calf thymus DNA (CT-DNA) have been studied in 1mM phosphate buffer and low ionic strength (5 mM NaCl) using several spectroscopic techniques: absorbance, fluorescence and circular dichroism. The 2:1 porphyrazine/DNA mole ratio, existence of moderate hypochromicity, moderate and progressive red shift and conservative ICD in the visible part of [Fe(2,3-tmtppa)]⁴⁺ spectra suggested an outside binding with self-stacking mode. Analysis of the dramatic hypochromicity, small blue shift and bisignate ICD in the Q-band absorption region of [Ni(2,3-tmtppa)]⁴⁺ spectra and 1:1 porphyrazine/DNA mole ratio possibly led us to the dual binding mode of this complex, i.e. at the minor and major grooves of DNA. The influence of the ionic strength on the porphyrazine-DNA binding confirmed this suggestion. The fluorescence quenching of DNA-ethidium bromide complex by porphyrazines was investigated. The values of quenching constants (K_sv) and the rate constants of the quenching (K_q) were determined by Stern-Volmer equation. The values of K_sv have been obtained (2.07 ± 0.11) × 10⁶ and (0.48 ± 0.01) × 10⁶ M⁻¹ for [Fe(2,3-tmtppa)]⁴⁺ and [Ni(2,3-tmtppa)]⁴⁺, respectively, at 27°C. The higher affinity of [Fe(2,3-tmtppa)]⁴⁺ for the quenching of EB-DNA fluorescence with respect to Ni complex was attributed to self-stacking of the former along DNA helix and favorable energy transfer between EB⁺ and cationic porphyrazine. ΔG₂₅ (the difference between the free energy of the native (N) and the denatured (D) form of DNA at 25°C), ΔH_m and ΔS_m (difference between enthalpy and entropy at T_m) were extracted from thermal curves. The decline in the melting temperature of DNA following the addition of porphyrazine complexes confirms that the substantial mode of Ni and Fe interaction is not intercalation. The thermodynamic results imply that both Ni and Fe complexes have a slight destabilizing effect on the DNA. A comparison between [Ni(tmtppa)]⁴⁺ and [Fe(tmtppa)]⁴⁺ indicates that the latter is more effective than the former.

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 influence of water soluble cationic meso-tetra(4N-hydroxyethyl)pyridyl porphyrin (H₂THOEtPyP4) and it's metal complexes with Ni(II), Cu(II), Co(II) and Zn(II) on hydrodynamic and spectral behavior of DNA solutions has been studied by viscometry and UV-vis absorption methods. It was shown that the presence of planar porphyrins, such as H₂THOEtPyP4, NiTHOEtPyP4 and CuTHOEtPyP4 leads to an increase in viscosity at relatively small concentrations, and then decreases to stable values. Such behavior corresponds to intercalation of these porphyrins in DNA structure, which results in a decrease of helical twist and lengthening of the DNA molecule. In the case of porphyrins with axial ligands, such as ZnTHOEtPyP4 and CoTHOEtPyP4, the relative viscosity decreases, which is explained by self-stacking of these porphyrins on DNA surface. Calculation and interpretation of binding parameters (K_b and n) demonstrated good agreement of viscometric and spectrophotometric measurements.

The influence of porphyrin molecules configuration on their ability to affect on DNA structure were investigated for water-soluble cationic meso-tetra-(3N-hydroxyethylpyridyl) porphyrin (H₂THOEtPyP3) and its metal complexes with Cu, Ni, Co, Zn using viscometry and UV-vis absorption spectroscopy. A comparative analysis was performed with the results of previously conducted similar studies of meso-tetra-(4N-hydroxyethylpyridyl) porphyrin (H₂THOEtPyP4). Viscosity measurements show that the change in position of peripheral radicals on pyridylic ring has absolutely no effect on the laws of interaction of investigated porphyrins with DNA in case of outside binders such as CoTHOEPyP3 and ZnTHOEPyP3. In the presence of planar porphyrins, such as CuTHOEPyP3 and NiTHOEPyP3 the laws of structural changes of DNA are the same as in the case of H₂THOEtPyP3, with some differences. Comparison of different locations of peripheral radicals on pyridylic rings leads to the conclusion that H₂THOEtPyP3 and its metal complexes bind to DNA preferably more than H₂THOEtPyP4 and its metal complexes. This fact may be explained only suggesting that porphyrins with hydroxyethyl groups at 3N-position are favorably located relative to the DNA helix axis than at 4N-position.

Present research continues the development of viscometry method for studying porphyrin–DNA interactions.Water soluble cationic meso-tetra-(3$N$-alylpyridyl) porphyrin (H₂TAlPyP3) and its Cu-, Co- and Zn-containing derivatives were studied using UV-vis absorption spectroscopy and viscometry in order to clarify the effect of chemical structure (presence of double bond in structure of a side radical) of porphyrins and ability to affect the DNA structure. Their binding constant ($K_b)$ and stoichiometry ($n)$ were determined based on the absorbance spectra for each DNA–porphyrin complex. The results were compared with results of previously conducted similar studies with meso-tetra-(3$N$-hydroxyethylpyridyl) porphyrins. It was shown, that the planar porphyrins H₂TAlPyP3 and CuTAlPyP3 interact with DNA predominantly by intercalation at low relative concentrations of $r$(($r$$=$ [Porphyrin]/[DNA])) and by external binding mode at high values of $r$, whereas the change of chemical structure of peripheral radicals of porphyrins does not absolutely affect on the mechanism of interaction of outside binders CoTAlPyP3 and ZnTAlPyP3 with DNA.

The influence of water soluble cationic meso-tetra-(4N-allylpyridyl) porphyrin (H₂TAlPyP4) and its metal complexes with Cu, Co and Zn on hydrodynamic and spectral behavior of DNA solutions has been studied by viscometry, CD and UV-vis spectroscopy methods. The results were compared with the results of previously conducted similar studies on meso-tetra-(3N-allylpyridyl) porphyrin (H₂TAllPyP3). It has been shown that the change in position of peripheral radicals on the pyridylic ring has absolutely no effect on the rules of interaction of investigated porphyrins with DNA in the case of outside binders CoTAllPyP4 and ZnTAllPyP4. Planar porphyrin H₂TAllPyP4 interacts with DNA predominantly by the intercalation mode at low relative concentrations of $r$ ($r=$ [Porphyrin]/[DNA]) and by external binding mode at high values of $r$. CuTAllPyP4 shows unusual behavior by interacting with DNA via a non-classical (partial) intercalation binding mode. It was shown that H${}_{\mathrm{\text{2}}}$TAllPyP3 and its metal complexes bind to DNA much more intensely than H₂TAllPyP4 and its metal complexes.

In current work we investigate the interaction between polyguanylic acid and Ethidium Bromide (EtBr) and the changes of thermodynamic parameters due to those interactions by spectrophotometric methods. From the binding isotherms, binding constants were calculated for three different temperatures and the changes of Gibbs free energy, entropy and enthalpy for complex-formation were determined. Complex-formation with four-stranded poly(G) structure needs less conformational changes in contrast with poly(G)poly(C), and due to that, EtBr binds with 5 and not 4 nucleotides. Obtained results confirm the concept that polyguanylic acids may form four-stranded complex structures with intercalating ligand EtBr in the aqueous solution.

In the present study, the interaction of 5-Fluorouracil with herring sperm DNA is reported using spectroscopic and molecular modeling techniques. This binding study of 5-FU with hs-DNA is of paramount importance in understanding chemico–biological interactions for drug design, pharmacy and biochemistry without altering the original structure. The challenge of the study was to find the exact binding mode of the drug 5-Fluorouracil with hs-DNA. From the absorption studies, a hyperchromic effect was observed for the herring sperm DNA in the presence of 5-Fluorouracil and a binding constant of 6.153 × 10³ M^-1 for 5-Fluorouracil reveals the existence of weak interaction between the 5-Fluorouracil and herring sperm DNA. Ethidium bromide loaded herring sperm DNA showed a quenching in the fluorescence intensity after the addition of 5-Fluorouracil. The binding constants for 5-Fluorouracil stranded DNA and competitive bindings of 5-FU interacting with DNA–EB systems were examined by fluorescence spectra. The Stern–Volmer plots and fluorescence lifetime results confirm the static quenching nature of the drug-DNA complex. The binding constant K_b was 2.5 × 10⁴ L mol^-1 and the number of binding sites are 1.17. The 5-FU on DNA system was calculated using double logarithmic plot. From the Forster nonradiative energy transfer study it has been found that the distance of 5-FU from DNA was 4.24 nm. In addition to the spectroscopic results, the molecular modeling studies also revealed the major groove binding as well as the partial intercalation mode of binding between the 5-Fluorouracil and herring sperm DNA. The binding energy and major groove binding as -6.04 kcal mol^-1 and -6.31 kcal mol^-1 were calculated from the modeling studies. All the testimonies manifested that binding modes between 5-Fluorouracil and DNA were evidenced to be groove binding and in partial intercalative mode.