Weak Absorption Bands Research Articles

Comparison and Interpretation of Spectral Characteristics of the Leading and Trailing Hemispheres of Europa and Callisto

Europa and Callisto are two “extreme members” in a sequence of the Galilean ice satellites formed at different distances from Jupiter. The difference in their mean density probably reflects the material density gradient that appeared even in the subplanetary disk of Jupiter. At the same time, general peculiarities in the composition of the surfaces of Europa and Callisto apparently characterize the accumulated effect of all subsequent evolutionary processes, including current volcanic activity on the satellite Io and its ionized material transfer in Jovian magnetosphere, as well as chemical reactions taking place under low-temperature (within ~90–130 K) and irradiation conditions. In 2016–2017, we observed the leading and trailing hemispheres of Europa and Callisto in the spectral range of 1.0–2.5 μm at 2-m telescope of Caucasian Mountain Observatory (CMO) of Sternberg Astronomical Institute (SAI) of Moscow State University (MSU). We found that, on a global scale, Europa and Callisto exhibit similar spectral characteristics and, particularly, the maxima in the distributions of sulfuric acid hydrate in the trailing hemispheres of the both moons, which agrees with the data of previous measurements. This can be considered as evidence for general ion implantation on these and other moons in the radiation belts of Jupiter. Moreover, our spectral data suggest that water ice and hydrates (clathrates) of other compounds are dominant or abundant in the leading hemispheres of Europa and Callisto. Specifically, we detected a weak absorption band of CH4 clathrate centered at ~1.67 μm in the reflectance spectra of the leading (the band is more intense) and trailing (the band is less intense) hemispheres of Europa. Weak signs of the same absorption band are also in the reflectance spectra of Callisto measured at its different orientations.

Cyclic Voltammetric DNA Binding Investigations on Some Anticancer Potential Metal Complexes: a Review.

Cancer is developed by rapid, uncontrolled, and abnormal cell proliferation and one of the leading causes of deaths worldwide in human beings. For the remedial measures of preventing different types of cancers, one of the research domains that have gained substantial importance in medical science is the development of new metallo-drugs and their investigations as potential anticancer drug agents by using various analytical techniques. Since metal-based complexes show weak absorption bands, electrochemical methods are considered more feasible and preferable over spectroscopic methods for easy characterization. Due to closer resemblance of electrochemical and biological processes, cyclic voltammetry among different electrochemical methods is considered the most versatile for the study of in-vitro metal-based drug-DNA interactions in terms of changes in the redox activities. Current potential data of a metal complex leads to determine binding kinetics in terms of binding constant and binding site size that involve determining the binding mode of drug with DNA, i.e., electrostatic interactions, intercalation, or minor-major groove binding. Binding parameters and modes of interactions, further, help to develop the mechanism of action of drug with the DNA. In this review, we emphasize on cyclic voltammetric DNA binding studies on some metal complexes that have been carried out in the last three decades for the investigation of their anticancer potentials.

Raman and reflectance spectroscopy of serpentinites and related hydrated silicates: Effects of physical properties and observational parameters, and implications for detection and characterization on Mars

Raman and high-resolution reflectance spectrometers will play an increasingly important role in future surface exploration of Mars. We undertook a study of the 532 nm Raman and 0.35–2.5 μm reflectance spectral properties of a suite of terrestrial serpentinites and related rocks from the Southern Quebec Ophiolite Belt, Canada in order to: (1) determine what factors control the appearance of their Raman and reflectance spectra; and (2) enable more robust analysis of Raman and reflectance observational data for Mars to be provided by future Mars landed missions. We examined the effects of surface texture, presence of weathered surfaces, sample heterogeneity, grain size (whole rock versus powder) on Raman and reflectance spectra, and of integration time on the Raman spectra. The Raman spectra are characterized by strong induced fluorescence, however they usually still allow the strongest peaks of the major silicate phase (serpentine, tremolite-actinolite, or talc) to be identified. The different serpentine polymorphs (antigorite, chrysotile, lizardite) can also normally be identified by differences in some Raman peak positions. Only a few of the accessory phases are recognizable in the Raman spectra. There is no systematic difference relating the presence or absence of Raman peaks between whole rock and powder spectra. Increasing integration time can allow weak Raman peaks to be more confidently recognized. Reflectance spectra are dominated by the numerous absorption bands of serpentine or talc, making these phases easily identifiable, but also making accessory phases difficult to identify. Factors such as tetrahedrally-coordinated Fe3+, mixed valence Fe (Fe2+/Fe3+), and the presence of octahedrally coordinated Fe2+ in serpentine can also be recognized. As in the Raman spectra, accessory phases are generally not identifiable in the reflectance spectra due to low abundance, weak absorption bands, or because their absorption bands are overlapped by the stronger hydrated silicate absorption bands. In the reflectance spectra the presence of magnetite can be recognized by a lowering of reflectance and a negatively-sloped spectrum. The presence of other opaque phases may be inferred from a lowering of reflectance. Reflectance spectroscopy is generally superior to Raman spectroscopy for identifying the presence of serpentine because of the aforementioned induced fluorescence seen in some of the Raman spectra. Raman and reflectance spectra do not always allow for identification of the same accessory phases, demonstrating their complementarity for analysis of hydrated silicate-dominated rocks.

Excited-state properties of the central-cis isomer of the carotenoid peridinin

The central-cis isomer of the carotenoid peridinin, presumably 13-cis, was separated and studied with spectroscopic methods including static absorption, fluorescence and femtosecond time-resolved absorption. The investigations exposed differences in the photophysical properties of this isomer in respect to all-trans peridinin. Steady-state absorption spectroscopy revealed the presence of an additional weak absorption band at the long wavelength tail of the main S0 → S2 transition. Modelling of the hypothetical vibronic progression of the S0 → S1 electronic transition demonstrated that this weak band can be associated with a higher (0–2) vibronic band of the transition and that lower vibronic bands have negligible intensities due to a large displacement between the S0 and S1 states energy curves as also suggested by the spectral shape of steady-state fluorescence emission. Transient absorption studies demonstrated that the lifetime of the S1 state of the central-cis isomer is shorter compared to the all-trans counterpart by 6–16%, depending on the polarity of the solvent. On the other hand, molecular isomerization negligibly affects the lifetime of intramolecular charge transfer (ICT), which for both isomers is ∼10 ps in the polar solvent methanol.

Anisotropic localized surface plasmon resonances in CuS nanoplates prepared by size-selective precipitation

CuS nanoplates were synthesized by a colloidal method and separated into four fractions of nanoplates with different aspect ratios by a size-selective precipitation. In addition to a strong near infrared absorption band ascribed to the in-plane mode of the localized surface plasmon resonance (LSPR), we found a weak absorption band on the high frequency tail of the in-plane LSPR band. The frequency of the weak absorption band was almost constant and independent of the aspect ratio, while the in-plane LSPR band exhibited a strong aspect ratio dependence. These characteristics suggested that the weak absorption band is ascribed to the out-of-plane LSPR. Although the out-of-plane LSPR was expected to be difficult to observe for CuS nanoplates due to its low intensity and overlap with the strong in-plane resonance, we could successfully identify the out-of-plane mode by reducing the width of the size distribution and spectral broadening caused thereby.

Radical Ions of 3-Styryl-quinoxalin-2-one Derivatives Studied by Pulse Radiolysis in Organic Solvents

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH3, -OCH3, and -N(CH3)2) or electron-withdrawing (R = -OCF3) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH3), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O2) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ•-) are characterized by two absorption maxima located at λmax = 470-490 nm and λmax = 510-540 nm, with the respective molar absorption coefficients ε470-490 = 8500-13 100 M-1 cm-1 and ε510-540 = 6100-10 300 M-1 cm-1, depending on the substituent (R). All 4R-SQ•- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 106 s-1. In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH•), which are characterized by weak absorption bands with λmax = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ•+) are characterized by a strong absorption with λmax = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN•+) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 105 s-1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ•+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 104 s-1 and, in principle, is not affected by the presence of O2, suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ•-) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ•+).

Emissive mononuclear Cu(I) triphenylphosphine complexes with functionalized 6-tert-butoxycarbonyl-2,2′-bipyridine

Two new emissive mononuclear copper(I) triphenylphosphine complexes with functionalized 6-tert-butoxycarbonyl-2,2′-bipyridine chelating ligands were prepared and characterized. Each Cu(I) cation has a markedly distorted P2N2 tetrahedral array with two different Cu—N bond distances, due to the addition of the bulky tert-butoxycarbonyl group at the 6-position of the 2,2′-bipyridyl ring. A weak low-energy broad absorption band appears at 330—500 nm in their CH2Cl2 solutions, which is influenced by the methylation of the 2,2′-bipyridyl ring. At room temperature, the photoluminescence can be clearly observed both in degassed CH2Cl2 solution and in the solid state, because of the introduction of the bulky tert-butoxycarbonyl substituent, and the emission properties are remarkably affected by both the methylation and the alkoxycarbonyl variation of the 2,2′-bipyridyl ring. It is shown that the introduction of the bulky tert-butoxycarbonyl group is favorable for improving the emission properties of the 6-alkoxycarbonyl-2,2′-bipyridine-based cuprous complexes.

Improving the Algorithm of Extracting Regional Total Precipitable Water Vapor Over Land From MODIS Images

Precise estimation of total precipitable water vapor (TPW) with high temporal and spatial resolutions is of great importance in different disciplines. Moderate-Resolution Imaging Spectroradiometer (MODIS) is one of the sensors which have absorption and nonabsorption bands of water vapor. There is a standard algorithm to produce TPW product of MODIS (MOD05/MYD05) which uses the ratios of reflectances in strong, moderate, and weak absorption bands of water vapor to nonabsorption ones (transmission). This paper aims to present a method based on this algorithm to optimize TPW estimation in local scale. To do so, the western part of Iran was chosen as the study region. Terra MODIS images and MOD05 in clear-sky conditions related to the 100 days in four seasons of 2015–2016 were provided as the selected data. To validate and improve the results, TPW measured in six radiosonde stations and interpolated for overpass time of Terra was utilized. Four procedures were performed. In the first procedure, the coefficients of transmissions were extracted using linear least-squares technique, separately. For the second procedure, the coefficients were calculated in terms of the highest atmospheric transmission sensitivity to TPW for each absorption band separately, and in the third procedure, they were calculated simultaneously. In the last procedure, the errors from third one were modeled with a linear relationship between reflectance ratios of absorption bands. Based on the results, in highest accuracy, the coefficient of determination ${{{\text{R}}}}^{2}$ and Root Mean Square Error was 0.878 and 2.702 mm, respectively, which were acceptable comparing those of other researchers.

High sensitivity cavity ring down spectroscopy of the 4ν3 band of NO2 near 1.59 µm

The very weak 4ν3 B-type absorption band of the nitrogen dioxide main isotopologue (14N16O2) is investigated between 6175 and 6350 cm−1. The absorption spectrum of this band was recorded by high sensitivity continuous wave-cavity ring down spectroscopy with noise equivalent absorption of αmin ≈ 1 × 10−10 cm−1. More than 1630 lines of the 4ν3 band are assigned with rotational quantum numbers N and Ka up to 55 and 7, respectively, what corresponds to 1731 spin-rotation-vibration transitions. The overall measured set of the line positions is used to fit the effective Hamiltonian parameters. The effective Hamiltonian takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,4) vibrational state and those of the nearby (0,2,3) bright state at 6183.61 cm−1 together with the electron spin-rotation interactions. The fitted set of the parameters reproduces the observed line positions with an rms of 2.2 × 10−3 cm−1. A selected set of the measured line intensities are used to determine the effective dipole moment parameters including the Herman–Wallis type parameters describing the line intensities of the 4ν3 band. The rms deviation of the fit is 5.7%.

Modeling and assessment of wavelength displacements of characteristic absorption features of common rock forming minerals encrusted by lichens

Arctic environments provide a challenging ground for geological mapping and mineral exploration. Inaccessibility complicates ground surveys and the presence of ice, vegetation, and lichens hinders supportive remote sensing surveys. Spectral mixing of lichens and bare rock can shift the wavelength position of characteristic absorption features, thereby complicating the spectral mapping of minerals and lithologies. The extent to which diagnostic rock features are preserved despite the presence of lichens is of major concern in remotely sensed geological studies and estimates of the critical level of lichen coverage, below which spectral features of the mineral substrate can still be identified, are needed. We investigated how surficial lichen cover affects the characteristics of shortwave infrared (SWIR) mineral absorption features and the efficacy of automated absorption feature extraction. For this purpose, mixed spectra were synthetically generated from laboratory spectra of common rock forming SWIR absorbing minerals and lichens. Wavelength displacements of characteristic absorption features for each mixed spectrum were then analyzed as a function of percentage lichen cover. Distinctive trends were identified that can be used in future analysis: The strong spectral features of mica group minerals around 2200 and 2340–2350nm maintain their integrity for up to 30% lichen cover, despite the related shift toward shorter wavelengths for higher percentage lichen cover. In contrast, very weak absorption bands around 2440nm in (white) micas spectra are completely obscured for a lichen cover of ≥50%. Our observations suggest that the chlorite feature around 2250nm is shifted toward longer wavelengths and the depth of this feature as well as the contrast between lichen and substrate spectra define the amount of lichen needed to mask it. Furthermore, lichens induce a spectral shift towards shorter wavelengths for the features around 2320nm for the rocks containing amphibole, chlorite, carbonate and serpentine group minerals. In addition, no wavelength displacement is observed for chlorite, biotite and phlogopite features around 2380nm in mixtures with lichens. By quantifying lichen cover effects on mineral absorption features, our study highlights the importance of being precautious in any interpretation in areas characterized by abundant lichen-covered outcrops. This can be of significant importance for mineral and deposit vectoring as the presence of abundant lichen coverage causing slightly shifted features for a given spectra can be erroneously identified as a path to a deposit.

Infrared spectroscopic study of sulfate-bearing calcite from deep-sea bamboo coral

The powder infrared spectra of a sulfate-bearing calcitic coral sample are recorded at room temperature in attenuated total reflectance (ATR) geometry and at low temperature in transmission geometry. The comparison of ATR spectra recorded with diamond or Ge crystal confirms that the width and the shape of the prominent absorption bands, related to CO 3 groups, are dominantly affected by macroscopic electrostatic interactions. In contrast, the temperature-dependence of the position and width of weak and narrow absorption bands, related to CO 3 or SO 4 groups, can be interpreted in terms of thermal expansion, anharmonic coupling, and local strain fluctuations. The three SO 4 stretching bands display a contrasted thermal behavior, the frequency of one of them increasing with temperature. Based on first-principles calculation, this unusual temperature dependence is traced back to the anisotropy of calcite thermal expansion. These results sustain the previously proposed atomic-scale model of sulfate in calcite and attest to a dominantly structural nature of sulfate in the investigated sample. Accordingly, structurally substituted sulfur in deep-sea calcitic bamboo coral could be used as proxy of seawater sulfate.

Hydrothermally crystallized Sr-containing bioactive glass film and its cytocompatibility

Abstract Sr-containing bioactive glass film with the Sr/(Ca+Sr) atomic ratio of 20% was sol-gel coated on titanium substrate, followed by hydrothermal treatment in a mixed phosphate solution (8 mM CaHPO 4 and 2 mM SrHPO 4 ) and other media at 120 or 140 °C. X-ray diffraction (XRD) analysis confirms amorphous nature of the gel powder calcined at 610 °C, but small peaks of Ca 1.8 Sr 0.2 SiO 4 or Ca 1.5 Sr 0.5 SiO 4 are also present. The absorption bands of Si-O-Si, PO 4 and OH groups and a weak absorption band of NO 3 groups appear in FT-IR spectrum of the calcined gel powder. Hydroxyapatite (HA) is detected for the hydrothermally treated sample by XRD and Raman analyses. Sr-containing HA nanocrystallites are formed on the film through a dissolution and precipitation mechanism in the hydrothermal treatment. The appearant bonding strength is 21±1 MPa for the both samples. In the test with MC3T3-E1 cells, the two coated samples exhibit larger viability, higher ALP levels and better cell morphology than the polished sample.

Luminescence and energy transfer of Tb3 +–doped BaO–Gd2O3–Al2O3–B2O3–SiO2 glasses

Transparent Tb3+–doped BaO–Gd2O3–Al2O3–B2O3–SiO2 glasses with the greater than 4g/cm3 were prepared by high temperature melting method and its luminescent properties have been investigated by measured UV–vis transmission, excitation, emission and luminescence decay spectra. The transmission spectrum shows there are three weak absorption bands locate at about 312, 378 and 484nm in the glasses and it has good transmittance in the visible spectrum region. Intense green emission can be observed under UV excitation. The effective energy transfer from Gd3+ ion to Tb3+ ion could occur and sensitize the luminescence of Tb3+ ion. The green emission intensity of Tb3+ ion could change with the increasing SiO2/B2O3 ratio in the borosilicate glass matrix. With the increasing concentration of Tb3+ ion, 5D4→7FJ transitions could be enhanced through the cross relaxation between the two nearby Tb3+ ions. Luminescence decay time of 2.12ms from 546nm emission is obtained. The results indicate that Tb3+–doped BaO–Gd2O3–Al2O3–B2O3–SiO2 glasses would be potential scintillating material for applications in X-ray imaging.

Time‐resolved spectroscopy of luminescence in a wide gap Si‐doped β‐Ga2O3

Optical properties of Si‐doped β‐Ga2O3 have been investigated by the time‐resolved spectroscopy, as well as by the conventional cw‐spectroscopy. The green photoluminescence is observed for photo‐excitations below the optical band gap Eg. The excitation spectrum of the green photoluminescence indicates a weak absorption band, presumably induced by Si‐doping, located at 0.2–0.3 eV below the conduction band minimum. The time‐resolved spectroscopy has revealed that the green photoluminescence manifests itself as the slower decay component. On the other hand, the fastest decay component, which is distributed from the UV to green regions, can be characterized by a time constant of ∼100 ns, comparable to that for un‐doped β‐Ga2O3.

Correlations between Structural and Optical Properties of Peroxy Bridges from First Principles

This work aims at addressing the issue of the optical signature of peroxy bridges by using first-principles methods that combine density functional theory, GW (where G and W stand for one-particle Green function and screened Coulomb potential, respectively), and the solution of a Bethe–Salpeter equation on a bulk amorphous SiO2 model. We demonstrate that the presence of bridges induces broad and weak absorption bands between 3.2 and 7.5 eV. By analyzing the Si–O–O–Si dihedral angle distributions and the corresponding electronic structure, we show that the low overlap between O 2p states involved in the optical transitions together with the dihedral angle site-to-site disorder are at the origin of this weak and broad absorption. Moreover, the energy difference between the two first optical transitions depends linearly on the energy difference between the two first occupied defect-induced electronic states, i.e., depends on the dihedral angle of the bridge. This behavior may explain the longstanding controv...

Absorption Tails of Donor:C60 Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation.

In disordered organic semiconductors, the transfer of a rather localized charge carrier from one site to another triggers a deformation of the molecular structure quantified by the intramolecular relaxation energy. A similar structural relaxation occurs upon population of intermolecular charge-transfer (CT) states formed at organic electron donor (D)-acceptor (A) interfaces. Weak CT absorption bands for D-A complexes occur at photon energies below the optical gaps of both the donors and the C60 acceptor as a result of optical transitions from the neutral ground state to the ionic CT state. In this work, we show that temperature-activated intramolecular vibrations of the ground state play a major role in determining the line shape of such CT absorption bands. This allows us to extract values for the relaxation energy related to the geometry change from neutral to ionic CT complexes. Experimental values for the relaxation energies of 20 D:C60 CT complexes correlate with values calculated within density functional theory. These results provide an experimental method for determining the polaron relaxation energy in solid-state organic D-A blends and show the importance of a reduced relaxation energy, which we introduce to characterize thermally activated CT processes.

An efficient synthetic method for organometallic radicals: structures and properties of gold(i)-(nitronyl nitroxide)-2-ide complexes.

One-pot synthesis of (nitronyl nitroxide)-gold(i)-phosphine (NN-Au-P) complexes has been developed using chloro(tetrahydrothiophene)gold(i), phosphine ligands, nitronyl nitroxide radicals, and sodium hydroxide. The NN-Au-P complexes can be easily handled because they were quite stable under aerated conditions in both solution and crystalline states. They showed weak absorption bands with vibrational structures in the 450-650 nm region. The oxidation potentials assigned to the NN moieties of NN-Au-P complexes with aromatic phosphines were observed around -0.1 V vs. Fc/Fc+ (-0.11 V for NN-Au-1, -0.08 V for NN-Au-2, -0.13 V for NN-Au-5, and -0.07 V for NN-Au-6), somewhat lower than that of NN-Au-P complexes with aliphatic phosphines (-0.25 V for NN-Au-3 and -0.17 V for NN-Au-4).

Electrical and magnetic properties of GdCrxMn1−xO3 (x = 0.0, 0.1) multiferroic nanoparticles

Gadolinium manganate (GdMnO3) and chromium doped gadolinium manganate (GdCr0.1Mn0.9O3) nanoparticles have been prepared using co-precipitation method. The effects of chromium (10% Cr+3) doping on structural, vibrational, optical, electrical and room temperature magnetic properties of GdMnO3 have been carried out. The structural characterization analysed through X-ray diffraction (XRD) shows the formation of orthorhombic structure with Pbnm space group. The morphology was examined by scanning electron microscopy (SEM). Raman and Fourier transform infrared spectroscopy has been employed for the vibrational investigations of GdMnO3 and doped GdMnO3. The Jahn–Teller modes observed at ~482 cm−1 (Ag) and 610 cm−1 (B1g) in Raman spectrum of GdMnO3 have not shifted with Cr3+ ions doping, which shows that the Cr3+ ions are not active to Jahn–Teller distortions. The UV–Vis absorption peak at 461 nm attributed to Mn (d-d) transition has shifted ~10 nm in GdCr0.1Mn0.9O3. The weaker absorption band at 725 nm (1.7 eV) is attributed to the dipole forbidden 5Eg–5T2g transition of the Mn3+ ion. The detailed investigation on the dielectric properties like dielectric constant, dissipation factor, ac conductivity has been carried out in the temperature range of 20–400 °C and in the frequency range of 1 kHz–1 MHz. The temperature dependent dielectric constant shows two dielectric anomalies which get shifted towards high temperature side with increase in frequency, thereby indicating relaxor type behaviour of the material. The dissipation curves also show the similar trend, suggesting the temperature dependent dielectric relaxation. The Cr doping enhances the dielectric properties of GdMnO3. The room temperature magnetic behaviour analyzed from the magnetic field dependent magnetization curves suggests paramagnetic behavior for both the composition; however Cr doping does enhance the magnetization.

Influence of transannular interaction over absorption and fluorescent properties of [2.2] paracyclophane and its phenyl derivatives

A significant bathochromic shift of the fluorescent and long-wavelength absorption bands of [2.2] paracyclophane comparing to corresponding bands of alkyl-benzenes is due to a strong transannular interaction, resulting in formation of a principally new excited state of lower energy. It is concluded that the fluorescent levels for alkylbenzene excimers and for the macrocycle are of the same nature. Analysis of [2.2] paracyclophane mono- and diphenylderivatives spectra shows that their intensive absorption bands (230–310 nm) are originated from electron transitions of biphenyl groups and weak long wavelength absorption (310–340 nm) and fluorescent bands are governed by the same electron transitions between ground and excimer-like excited states as in the case of non-substituted macrocycle.

Synthesis and characterization of novel rhenium(I) complexes towards potential biological imaging applications.

BackgroundRe(I) tricarbonyl complexes exhibit immense potential as fluorescence imaging agents. However, only a handful of rhenium complexes have been utilized in biological imaging. The present study describes the synthesis of four novel rhenium complexes, their characterization and preliminary biological studies to assess their potential as biological imaging agents.ResultsFour facial rhenium tricarbonyl complexes containing a pyridyl triazine core, (L1 = 5,5′(3-(2-pyridyl)-1,2,4-triazine-5,6-diyl)-bis-2-furansulfonic acid disodium salt and L2 = (3-(2- pyridyl)-5,6-diphenyl-1,2,4-triazine-4′,4′′-disulfonic acid sodium salt) have been synthesized by utililzing two different Re metal precursors, Re(CO)5Br and [Re(CO)3(H2O)3]OTf in an organic solvent mixture and water, respectively. The rhenium complexes [Re(CO)3(H2O)L1]+ (1), Re(CO)3L1Br (2), [Re(CO)3(H2O)L2]+ (3), and Re(CO)3L2Br (4), were obtained in 70–85% yield and characterized by 1H NMR, IR, UV, and luminescence spectroscopy. In both H2O and acetonitrile, complexes display a weak absorption band in the visible region which can be assigned to a metal to ligand charge transfer excitation and fluorescent emission lying in the 650–710 nm range. Cytotoxicity assays of complexes 1, 3, and 4 were carried out for rat peritoneal cells. Both plant cells (Allium cepa bulb cells) and rat peritoneal cells were stained using the maximum non-toxic concentration levels of the compounds, 20.00 mg ml−1 for 1 and 3 and 5.00 mg ml−1 for 4 to observe under the epifluorescence microscope. In both cell lines, compound concentrated specifically in the nuclei region. Hence, nuclei showed red fluorescence upon excitation at 550 nm.ConclusionsFour novel rhenium complexes have been synthesized and characterized. Remarkable enhancement of fluorescence upon binding with cells and visible range excitability demonstrates the possibility of using the new complexes in biological applications.Graphical abstractMicrograph of rat peritoneal cells incubated with novel rhenium complex under epifluorescence microscope. Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-016-0218-4) contains supplementary material, which is available to authorized users.