Electric magnetic resonance and spectrophotometry evidence on the photodynamic activity of a new perylenequinonoid pigment

Di-cysteine substituted hypocrellin B (DCHB) is a new water-soluble photosensitizer with significantly enhanced red absorption at wavelengths longer than 600 nm over the parent compound hypocrellin B (HB). The photosensitizing properties (Type I and/or Type II mechanisms) of DCHB have been investigated in dimethylsulfoxide (DMSO) and aqueous solution (pH 7.4) using electron paramagnetic resonance (EPR) and spectrophotometric methods. In anaerobic DMSO solution, the semiquinone anion radical of DCHB (DCHB^•−) is predominantly photoproduced via self-electron transfer between excited- and ground-state DCHB species. The presence of an electron donor significantly promotes the formation of the reduced form of DCHB. When a deoxygenated aqueous solution of DCHB and an electron donor are irradiated with 532 nm light, the hydroquinone of DCHB (DCHBH₂) is formed via the disproportionation of the first-formed DCHB^•− and second electron transfer to DCHB^•− from the electron donor. When oxygen is present, singlet oxygen (¹O₂), superoxide anion radical (O₂^•−) and hydroxyl radical (^•OH) are produced. The quantum yield of ¹O₂ generation by DCHB photosensitization is estimated to be 0.54 using Rose Bengal as a reference, a little lower than that of HB (0.76). The superoxide anion radical is also significantly enhanced by the presence of electron donors. Moreover, (O₂^•−) upon disproportionation generated H₂O₂ and ultimately the highly reactive ^•OH via the Haber-Weiss reaction pathway. The efficiency of (O₂^•−) generation by DCHB is obviously enhanced over that of HB. These findings suggest that the photodynamic actions of DCHB may proceed via Type I and Type II mechanisms and that this new photosensitizer retains photosensitizing activity after photodynamic therapy-oriented chemical modification.     

Alkyl capped carbonates ofβ-cyclodextrin

The synthesis is described of alkyl capped carbonates of-cyclodextrin, obtained from diols activated with carbonyldiimidazole. The reaction preferentially gave monocapped derivatives which were characterized by HPLC, TLC, FT-IR and¹³C-NMR. These compounds are stable at pH <7, and methyl orange was found to form stronger inclusion compounds with capped-cyclodextrin than with the parent-cyclodextrin. Paramagnetic Gd(III) complexes were also studied, but they were found to be included into capped-cyclodextrin as well as into-cyclodextrin.Part of this work was presented at the 7th International Symposium on Cyclodextrins, 1994, Tokyo, April 25–28, Book of Abstract, page 54.     

Paramagnetic surface active ionic liquids: synthesis,properties, and applications

Paramagnetic surface active ionic liquids (PMSAILs) classify task-specific ionic liquids with magnetic properties by incorporating metal into the cationic or anionic part of the ionic liquid. Paramagnetic ionic liquids had long-chain either in cations or anions and showed excellent surface activity and magnetic properties without any need for the magnetic nanoparticles. These PMSAILs have inherent unique ionic liquid properties and self-assembled into various nano-aggregates such as micelles, vesicles, rod-like micelles, and etc., by modification in the structure of cations or anions. PMSAILs provide stimuli-responsive properties, which is one of the essential aspects of targeted applications. The appropriate functional tunability of anions and cations in PMSAILs leads to various multifaceted chemical and biological applications. A new emerging trend in PMSAIL research is hybridization with flexible materials. This review will mainly deal with the synthesis, characterization, and brief history of PMSAILs and their potential advantages in the various applications in micellar catalysis, purification and separation of biomolecules, compaction and decompaction of DNA, drug delivery, and other biomedical applications.     

Synthesis of a new stable and water-soluble tris(4-hydroxysulfonyltetrachlorophenyl)methyl radical with selective oxidative capacity

A new stable organic free radical of the PTM (perchlorotriphenylmethyl) series very soluble in water is reported. This free radical is sensitive to electron transfer processes, and the selectivity of these reactions in the presence of ascorbic acid, pyrogallol, and catechol as reducing species is described. The electron paramagnetic resonance spectrum and the electrochemical behavior are also presented.     

Fabrication of superhydrophobic surfaces based on ZnO-PDMS nanocomposite coatings and study of its wetting behaviour

Superhydrophobic surfaces based on ZnO-PDMS nanocomposite coatings are demonstrated by a simple, facile, time-saving, wet chemical route. ZnO nanopowders with average particle size of 14 nm were synthesized by a low temperature solution combustion method. Powder X-ray diffraction results confirm that the nanopowders exhibit hexagonal wurtzite structure and belong to space group P63mc. Field emission scanning electron micrographs reveal that the nanoparticles are connected to each other to make large network systems consisting of hierarchical structure. The as formed ZnO coating exhibits wetting behaviour with Water Contact Angle (WCA) of ∼108°, however on modification with polydimethylsiloxane (PDMS), it transforms to superhydrophobic surface with measured contact and sliding angles for water at 155° and less than 5° respectively. The surface properties such as surface free energy (γ_p), interfacial free energy (γ_pw), and the adhesive work (W_pw) were evaluated. Electron paramagnetic resonance (EPR) studies on superhydrophobic coatings revealed that the surface defects play a major role on the wetting behaviour. Advantages of the present method include the cheap and fluorine-free raw materials, environmentally benign solvents, and feasibility for applying on large area of different substrates.     

Exogenous bridging and nonbridging in Cu(II) complexes of Mannich base ligands: Synthesis and physical properties

Preparation of pentadentate ligands L¹, L², L³ and L⁴, where L¹ = 4-chloro-3-methyl-2[(prolin-1-yl)methyl]-6-[N-phenyl piperazin-1-yl)methyl]phenol, L² = 4-ethyl-2-[(prolin-1-yl)methyl]-6-[(N-phenyl piperazin-1-yl)methyl]phenol, L³ = 4-chloro-3-methyl-2-[(prolin-1-yl)methyl]-6-[N-methyl piperazin-1-yl]methyl phenol, L⁴ = 4-methoxy-2-[(prolin-1-yl)methyl]-6-[(N-phenyl piperazin-1-yl)methyl]phenol is described together with that of the corresponding Cu(II) complexes with various bridging motifs like OH, OAc and NO₂. The complexes are characterized by elemental analysis, electrochemical and electron paramagnetic spectral studies. Redox properties of the complexes in acetonitrile are highly quasireversible due to the chemical or/and stereochemical changes subsequent to electron transfer. The complexes show resolved copper hyperfine EPR at room temperature, indicating the presence of weak antiferromagnetic coupling between the copper atoms. Strengths of the antiferromagnetic interactions are in the order NO₂>OAc>OH.     

Modeling techniques for analysis and interpretation of electron magnetic resonance (EMR) data for transition ions at low symmetry sites in crystals—A primer for experimentalists

Electron magnetic resonance (EMR) studies of paramagnetic centers exhibiting monoclinic and triclinic local site symmetry have gained renewed importance, since such centers occur often in various technologically important materials and biological systems. The intricate low symmetry aspects, which arise for such centers, bear on meaningful interpretation of EMR data and their correlation with structural data. This review provides a primer for experimentalists who wish to utilize efficiently the modeling techniques for analysis and interpretation of EMR data for transition ions, especially ions located at low symmetry sites in crystals. This requires proper understanding of the low symmetry effects observable in EMR spectra as well as related theoretical questions concerning, e.g., (i) existence of physically equivalent zero-field splitting (ZFS) parameter sets, (ii) clear definitions of the axis systems, (iii) proper forms of spin Hamiltonians, and (iv) distinction between apparent and actual low symmetry cases. The question (i) involves consideration of the orthorhombic standardization, which provides basis for standardization of monoclinic and triclinic ZFS parameters. Thus, the aspects pertaining to orthorhombic site symmetry are also outlined. To solve other questions several modeling techniques have been utilized and related computer packages have recently been developed in our group: (1) the superposition model calculations of the zero-field splitting parameters (ZFSPs) in arbitrary symmetry, (2) the procedure for diagonalization of the 2nd-rank ZFSPs and transformation of respective 4th- and 6th-rank ZFSPs, (3) the pseudosymmetry axes method for approximation of the 4th- and 6th-rank ZFSPs to higher symmetry, and (4) the closeness factors and norm ratios for quantitative comparisons of various ZFSP sets. These modeling techniques enable deeper analysis and interpretation of the low symmetry aspects involved in the fitted and theoretical ZFSPs. The computer packages facilitate extracting useful structural information inherent in monoclinic and triclinic ZFSP sets. Illustrative examples taken from recent studies of low symmetry ion-host systems are discussed.     

Electronic, magnetic and structural properties of A2VMoO6 perovskites (A=Ca, Sr)

The perovskites Sr₂VMoO₆ and Ca₂VMoO₆ have been synthesized by liquid-mix technique in citrate melts, and their electronic, magnetic and structural properties have been investigated. No signs of V/Mo ordering are seen by synchrotron X-ray powder diffraction, but despite the chemical disorder both oxides are highly conductive and Pauli paramagnetic. Electrical conductivities of these solid solutions are comparable or higher than those reported for polycrystalline AMoO₃ end members. It is suggested that the delocalized metallic conductivity of these compounds with two different transition-metal atoms implies valence equilibrium between the degenerate oxidation-state couples V⁴⁺Mo⁴⁺ and V³⁺Mo⁵⁺.     

Simple data acquisition method for multi-dimensional EPR spectral-spatial imaging using a combination of constant-time and projection-reconstruction modalities

A combination of the constant-time spectral-spatial imaging (CTSSI) modality and projection-reconstruction modality was tested to simplify data acquisition for multi-dimensional CW EPR spectral-spatial imaging. In this method, 3D spectral-spatial image data were obtained by simple repetition of conventional 2D CW imaging process, except that the field gradient amplitude was incremented in constant steps in each repetition. The data collection scheme was no different from the conventional CW imaging system for spectral-spatial data acquisition. No special equipment and/or rewriting of existing software were required. The data acquisition process for multi-dimensional spectral-spatial imaging is consequently simplified. There is also no “missing-angle” issue because the CTSSI modality was employed to reconstruct 2D spectral-spatial images. Extra reconstruction processes to obtain higher spatial dimensions were performed using a conventional projection-reconstruction modality. This data acquisition technique can be applied to any conventional CW EPR (spatial) imaging system for multi-dimensional spectral-spatial imaging.