Weak Absorption Bands Research Articles

The spin-forbidden vacuum-ultraviolet absorption spectrum of 14N15N

Photoabsorption spectra of 14N15N were recorded at high resolution with a vacuum-ultraviolet Fourier-transform spectrometer fed by synchrotron radiation in the range of 81-100 nm. The combination of high column density (3 × 1017 cm-2) and low temperature (98 K) allowed for the recording of weak spin-forbidden absorption bands' exciting levels of triplet character. The triplet states borrow intensity from 1Πu states of Rydberg and valence character while causing their predissociation. New predissociation linewidths and molecular constants are obtained for the states C3Πu(v = 7, 8, 14, 15, 16, 21), G3Πu(v = 0, 1, 4), and F3Πu(v = 0). The positions and widths of these levels are shown to be well-predicted by a coupled-Schrödinger equation model with empirical parameters based on experimental data on 14N2 and 15N2 triplet levels.

Full-physics carbon dioxide retrievals from the Orbiting Carbon Observatory-2 (OCO-2) satellite by only using the 2.06 µm band

Abstract. Passive remote sensing of atmospheric carbon dioxide uses spectroscopic measurements of sunlight backscattered by the Earth's surface and atmosphere. The current state-of-the-art retrieval methods use three different spectral bands, the oxygen A band at 0.76 µm and the weak and strong CO2 absorption bands at 1.61 and 2.06 µm, respectively, to infer information on light scattering and the carbon dioxide column-averaged dry-air mole fraction XCO2. In this study, we propose a one-band XCO2 retrieval technique which uses only the 2.06 µm band measurements from the Orbiting Carbon Observatory-2 (OCO-2) satellite. We examine the data quality by comparing the OCO-2 XCO2 with collocated ground-based measurements from the Total Carbon Column Observing Network (TCCON). Over land and ocean the OCO-2 one-band retrieval shows differences from TCCON observations with a standard deviation of ∼1.30 ppm and a station-to-station variability of ∼0.50 ppm. Moreover, we compare one-band and three-band retrievals over Europe, the Middle East, and Africa and see high correlation between the two retrievals with a SD of 0.93 ppm. Compared to the three-band retrievals, XCO2 retrievals using only the 2.06 µm band have similar retrieval accuracy, precision, and data yield.

INTERACTION OF HYDRIDE Σ-COMPLEX OF 5,7-DINITRO-8-HYDROXYQUINOLINE WITH SALTS OF AROMATIC DIAZO COMPOUNDS

Interaction between 5,7-dinitro-8-hydroxyquinoline hydride anionic σ-adduct and chlorides of substituted aryldiazonium in water yielded 5-arylazo-7-nitro-8-hydroxyquinolines, the substitution products of the nitro group at the C-5 σ-adduct position. The direction of the reaction agrees with the quantum-chemical calculations carried out earlier and the GMLA principle, which assumes that the mild acid, which is a diazocathione, will attack the reaction center to which the softest base corresponds, that is, the least negatively charged C-5 carbon atom, in contrast to the C-7 atom. It is shown that the yield of the product increases with the presence of an electron-withdrawing substituent in the diazocomponent. Also in this study, the synthesis of the hydride σ-adduct of 5,7-dinitro-8-hydroxyquinoline was optimized. It was found that the use of pure dimethylacetamide as a solvent, as well as the addition of sodium carbonate, increases the yield and purity of the synthesized σ-adduct. The structure of the obtained compounds was proved by the methods of NMR and IR spectroscopy. In the IR spectra of all synthesized azo compounds, weak absorption bands corresponding to the stretching vibrations of the azogroup (N = N) are fixed in the range of 1400-1465 cm-1, which also indirectly confirms the expected direction of the reaction. Otherwise, the bands of the azogroup vibrations would be shifted to the 1500-1600 cm-1 region as a result of azo-hydrazoic tautomerism. In 1H NMR spectra of synthesized compounds, there is no proton signal of intramolecular hydrogen bond at δ 14-15 ppm, characteristic of the hydrazine form. The proton signals of the arylazo group also confirm the presence of the latter. The use of anionic hydride σ-complexes of dinitroquinoline derivatives as azo-component in the reaction with aromatic diazo compound expands the synthetic possibilities of the azo coupling reaction and allows to obtaine new nitroazoquinolines.

A fast and accurate vector radiative transfer model for simulating the near-infrared hyperspectral scattering processes in clear atmospheric conditions

This study develops a Weighting Featured Monochromatic Radiance (WFMR) method to efficiently and accurately compute the vector radiance, including multiple scattering at the near-infrared band. The monochromatic radiances within a spectral band that are of a high correlation are grouped to represent the average band radiance. The simulated radiance from WFMR is validated against a large variety of OCO-2 (the Orbiting Carbon Observation 2) profiles. It is shown that the dominant errors introduced by the WFMR method are below 0.1%, 0.025%, and 0.12% for O2 A band, weak and strong CO2 absorption bands, respectively, and the computational speed is, however, about 80 times faster than that of the reference line-by-line calculation. The technique performs very well and captures the realistic characteristics of the atmospheric radiation distribution. Besides, for the WFMR method, its numerical accuracy can be defined, and its linearization to form the Jacobians matrix is very straightforward. These advantages are particularly well suited for remote sensing applications.

Changes in Performance Characteristics of Transformer Oil by the Action of Ionizing Radiation

Changes in physicochemical parameters, such as resistivity, viscosity, and density, and the formation of gaseous products (Н2, СН4, С2Н4, С2Н6, С3Н8, С4Н10, С5Н12, and С6Н14) depending on the absorbed dose in the range of 29.7–237.6 kGy have been studied. It has been found that the chemical composition of transformer oil is changed by γ-irradiation and this change is accompanied by changes in the resistivity, viscosity, and density of the oil. The degree of conversion depends on the absorbed dose and increases with it. The IR spectra exhibit =С–Н stretching vibrations, –С=С in-plane bending vibrations, and –СН out-of-plane bending vibrations in aromatic compounds. In addition, –С–Н stretching vibrations and–С–СН3 bending vibrations (antisymmetric and symmetric) in alkanes are observed. The IR absorption spectra have been observed in the ranges of $${\Delta }{{\lambda }_{1}} = 2800 - 3300\,{\text{c}}{{{\text{m}}}^{{ - 1}}},$$$${\Delta }{{\lambda }_{2}} = 2000~\,{\text{c}}{{{\text{m}}}^{{ - 1}}},$$$${\Delta }{{\lambda }_{3}} = 1350 - 1450\,\,{\text{c}}{{{\text{m}}}^{{ - 1}}}$$, and $${\Delta }{{\lambda }_{4}} = 600 - 1200~\,\,{\text{c}}{{{\text{m}}}^{{ - 1}}}.$$ The absorption band at $${\Delta }{{\lambda }_{4}} = 600 - 1200~\,{\text{c}}{{{\text{m}}}^{{ - 1}}}$$ is a diffuse part of the spectrum, which includes a number of weak absorption bands.

Toward a Molecular Reorganization Energy-Based Analysis of Third-Order Nonlinear Optical Properties of Polymethine Dyes and J-Aggregates.

This work demonstrates the feasibility and applicability of the theory of extended multiphonon electron transitions for the description of nonlinear optical properties of polymethine dyes using quantum chemistry and model calculations. The transformation of a strong one-photon absorption band in dye monomers to a weak two-photon absorption band is rationalized from the electron-nuclear resonance condition. The power law fitting of the results of quantum chemical computations of nonlinear optical properties allows the predicting of the shift of the corresponding Egorov-like resonance curve to the shortest dye in the vinylogous series of dye monomers. The results presented provide an insight and guide for the rational molecular design and application of polymethine dyes.

A novel deep red emission phosphor BaAl2Ge2O8:Mn4+ for plant growth LEDs

The luminescence properties of BaAl2Ge2O8:Mn4+ are investigated in this paper. The excitation spectrum of BaAl2Ge2O8:Mn4+ shows two broad bands. The absorption band centred at 288 nm is attributed to the overlap of the Mn4+-O2− charge transfer transition and the 4A2 → 4T1 transition of the Mn4+ ions. The weak absorption band centred at 435 nm is attributed to the 4A2 → 4T2 transition of the Mn4+ ions. The luminescence spectrum shows two emission peaks at 652 nm and 668 nm due to the 2E → 4A2 transition of the Mn4+ ions. As the concentration of the Mn4+ ions increases, the lifetime of the phosphor decreases from 1.766 ms to 1.595 ms. The chromaticity coordinates are (0.720, 0.279), which is a deep red emission. The luminescence of BaAl2Ge2O8:Mn4+ contributes to plant growth and can be applied to plant illumination sources.

Managing intramolecular energy transfer in well-defined polyfluorenes grafting one/two orange emissive groups on central or terminal fluorene unit

Three sets of polyfluorenes grafting one/two orange emissive groups on central or terminal fluorene unit have been synthesized successfully through the catalyst-transfer polymerization. The molecular weights linearly increase with increase in the feed ratios of [monomer]/[catalyst] in a certain molecular weight range. The initiators with bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) (IPr) as the ancillary ligand show better catalytic activity, leading to higher molecular weight of up to 126.3 kDa. All polymers in toluene have the similar absorption spectra to polyfluorene homopolymer, while the weak absorption bands of 420–500 nm are observed only in the polymers with low molecular weight. Photoluminescence spectra display a dominant blue emission from the polyfluorene backbone and a weak orange emission (508–661 nm) from the orange group. The clearly enhanced orange emission in the polymers with low molecular weight is mainly ascribed to the intramolecular Förster energy transfer from the polyfluorene segment to the orange group, which is further confirmed by the electroluminescent behavior of the polymers.

Sensitization of upconverting nanoparticles with a NIR-emissive cyanine dye using a micellar encapsulation approach

Photon upconversion nanomaterials have a wide range of applications, including biosensing and deep-tissue imaging. Their typically very weak and narrow absorption bands together with their size dependent luminescence efficiency can limit their application potential. This has been addressed by increasingly sophisticated core–shell particle architectures including the sensitization with organic dyes that strongly absorb in the near infrared (NIR). In this work, we present a simple water-dispersible micellar system that features energy transfer from the novel NIR excitable dye, 1859 SL with a high molar absorption coefficient and a moderate fluorescence quantum yield to oleate-capped NaYF4:20%Yb(III), 2%Er(III) upconversion nanoparticles (UCNP) upon 808 nm excitation. The micelles were formed using the surfactants Pluronic F-127 and Tween 80 to produce a hydrophilic dye-UCNP system. Successful energy transfer from the dye to the UCNP could be confirmed by emission measurements that revealed the occurrence of upconversion emission upon excitation at 808 nm and an enhancement of the green Er(III) emission compared to direct Er(III) excitation at 808 nm.

Phaethon variability during December 2017 closest approach to Earth

In the course of its last close encounter with the Earth in December 2017, the peculiar Near Earth Object (NEO) 3200 Phaethon has been the target of an international observational campaign in particular connected with the proposed mission Destiny+ (Demonstration and Experiment of Space Technology for INterplanetary voYage Phaethon fLyby dUSt science) by JAXA (Japan Aerospace Exploration Agency) to be launched in 2022. The nature of 3200 Phaethon is still debated because of its asteroidal dynamical behavior as opposed to its connection with the Geminid meteor shower, typical cometary residuals. Owing to its vicinity to our planet (Minimum Orbit Intersection Distance MOID = 0.0206 AU) it has been included also in the class of Potentially Hazardous objects and it has been extensively investigated also during its previous perihelion passages. It has been classified as B-type asteroid (Binzel et al., 2001), with different spectral slopes found by several authors in the wavelength region shortward 0.55 μm. Many issues remain to be explored regarding the nature of this object and in this context we observed 3200 Phaethon in the course of 24 h during its last closest approach to the Earth. Low-resolution spectra at very high elevation angles (airmass <1.15) were acquired with the 1.22–m Asiago telescope on 2017-Dec-16 and 2017-Dec-17. The variation of the viewing geometry during these observations was also derived. We found a significant variation in Phaethon spectral slope in the wavelength range [0.33–0.64] μm during its perigeon passage. The slope varies from −9.1±0.2%(/0.1μm) on 2017-Dec-16 to −2.0±0.1%(/0.1μm) on 2017-Dec-17. This variation seems to be related to a disappearing bluer region at high latitudes (>70∘, close to the North pole). The spectra show also a weak absorption band around 0.43 μm and lack the reflectance downturn at least until ∼0.33μm. The comparison with meteorites suggests compositional similarities with CI/CM unusual chondrites. We propose several scenarios that could be responsible for the variability recorded, such as possible surface variations in composition, grain-size, or the level of space weathering and thermal metamorphism. A strong and sudden variation of dust production is also discussed.

Integral Method Analysis of Electroabsorption Spectra and Electrophotoluminescence Study of (C4H9NH3)2Pbl4 Organic–Inorganic Quantum Well

Electric-field-induced changes in absorption and photoluminescence (PL) spectra and in PL decay profile have been measured for two-dimensional hybrid organic–inorganic halide perovskite semiconductor, ((C4H9NH3)2Pbl4) (N1). Electroabsorption (E-A) spectra observed at room temperature and at a low temperature of 45 K were analyzed by assuming the Stark shift, and the magnitudes of the change in electric dipole moment and polarizability following photoexcitation were determined. The strong signal observed in the E-A spectra at 45 K was interpreted in terms of the weak absorption band which shows extremely large Stark shift resulting from the large change in polarizability following photoexcitation. Electrophotoluminescence spectra of this compound, that is, field-induced change in PL spectra, show that PL of N1 is quenched by the application of electric field. Field effects on PL decay profiles show that the quenching results both from the field-induced decrease of the population of the emitting state follo...

Ammonia in Jupiter’s Atmosphere: Spatial and Temporal Variations of the NH3 Absorption Bands at 645 and 787 Nm

Based on the material of long-term spectrophotometric observations of Jupiter, we studied the weak absorption bands of ammonia at 645 and 878 nm, whose behavior had previously been little studied. A clearly expressed depression of ammonia absorption in the 787-nm band was found in the Northern Equatorial Belt (NEB) of Jupiter. In the Great Red Spot, this band also exhibits substantial weakening. The position of the depression in the NEB is similar to that of the enhanced brightness temperature detected in the observations of the millimeter-wave radio emission, which is considered to be a result of the reduced ammonia content in this belt. At the same time, the weakening of the 787-nm band in the Red Spot is most likely caused by the enhanced bulk density of clouds, which influences the formation of absorption bands in the multiple scattering by cloud particles. The brightness temperature in the Red Spot is relatively low, as seen from observations in the radio and thermal IR ranges. We studied the spatial and temporal variations of the 645- and 787-nm bands in five belts of Jupiter: the Equatorial Zone (EZ), both Equatorial Belts (SEB and NEB), and both Tropical Zones (STZ and NTZ). The observations covered the time interval from 2005 to 2015, i.e., almost a complete orbital period of Jupiter. These observations confirmed the systematic character of the depression of the 787-nm band in the NEB and the difference in the latitudinal variations of the 645- and 787-nm bands. The latter can be related to features of the vertical distribution of the cloud density, which has a different influence on bands of different intensity.

Color mechanisms in spinel: a multi-analytical investigation of natural crystals with a wide range of coloration

Twenty natural spinel single crystals displaying colors almost representative for the entire spinel variability were investigated by electron microprobe and UV–VIS–NIR–MIR and FTIR spectroscopies. Eight of them, selected among the Fe-bearing ones, were also analyzed by X-ray diffraction, and five by Mossbauer spectroscopy to obtain information on the oxidation state and site distribution of Fe. The adopted multi-analytical approach was successful in revealing that the color displayed by aluminate spinel crystals is due to a combination of two or more minor transition elements acting as chromophore, such as V3+, Cr3+, Fe2+, Fe3+, Mn2+ and Mn3+, variably distributed in the tetrahedrally and octahedrally coordinated sites of the spinel structure. Iron-poor orange, red and magenta spinel crystals owe their color mainly to the presence of V3+ and Cr3+ at the M sites (with predominance of V3+ for orange and of Cr3+ for red color). Iron-rich pink, blue and green spinel crystals, in spite of exhibiting very different colors, have relatively similar optical absorption spectra characterized by a strong UV-edge absorption and a series of weak absorption bands in the visible range. From pink to blue and green spinel samples, color differences depend on the increase of Fetot (primarily) and Fe3+ contents (secondarily), which are responsible for both the intensification of UV-edge absorption and the different intensity, width and position of the prominent absorption bands occurring in the range 18,000−15,000 cm−1. The scarcity in nature of yellow spinel is explained by the rarity of conditions necessary to obtain the yellow color, such as the exclusive presence of Mn acting as a chromophore or at least the absence of Fe2+, to avoid masking of the weak electronic transitions in Fe3+, Mn2+ and Mn3+.

Laboratory spectral calibration of the TanSat atmospheric carbon dioxide grating spectrometer

Abstract. TanSat is a key satellite mission in the Chinese Earth Observation program and is designed to measure the global atmospheric column-averaged dry-air CO2 mole fraction by measuring the visible and near-infrared solar-reflected spectra. The first Chinese super-high-resolution grating spectrometer for measuring atmospheric CO2 is aboard TanSat. This spectrometer is a suite incorporating three grating spectrometers that make coincident measurements of reflected sunlight in the near-infrared CO2 band near 1.61 and 2.06 µm and in the molecular oxygen (O2) A-band at 0.76 µm. The spectral resolving power (λ∕Δλ) values are ∼19 000, ∼12 800, and ∼12 250 in the O2 A-band, and the weak and strong absorption bands of CO2, respectively. This paper describes the prelaunch spectral calibration of the atmospheric carbon dioxide grating spectrometer aboard TanSat. Several critical aspects of the spectrometer, including the spectral resolution, spectral dispersion, and the instrument line shape function of each channel, which are directly related to producing the Level 1 products are evaluated in this paper. The instrument line shape function of the spectrometer is notably symmetrical and perfectly consistent across all channels in the three bands. The symmetry is better then 99.99 %, and the consistency in the worst case is better then 99.97 %, 99.98 %, and 99.98 % in the O2 A, WCO2, and SCO2 bands, respectively. The resulting variations in the spectral calibrations and the radiometric response errors are negligible. The spectral resolution characterizations meet the mission requirements. The spectral dispersions have excellent consistency in the spatial dimension of each band, and there is good linearity in the spectral dimension of each band. The RMS errors of the fitting residuals are 0.9, 1, and 0.7 pm in the O2 A-band, the WCO2 band, and the SCO2 band, respectively. Taken together, these results suggest that the spectral characterizations of the spectrometer aboard TanSat meet the mission requirements.

Nature, distribution and origin of CO2 on Enceladus

We present the first map of CO2 at the surface of Enceladus using data obtained by the Cassini Visible-Infrared Mapping Spectrometer (VIMS). In order to measure the weak and narrow CO2 absorption band depths around 4.26 µm, we improved: (1) the calibration of VIMS spectra; (2) the calculation of geographic coordinates; and (3) the projection techniques. We averaged multiple observations of a given area to obtain a signal to noise ratio high enough to map the CO2 abundances. CO2 is reliably detected mostly in the South Polar Region. This region includes active faults (Tiger Stripes), the highest observed surface temperatures, and locations of active plume eruptions. The occurrence here of CO2 is consistent with an endogenic origin controlled by tectonics. Both pure CO2 ice and complexed CO2 are detected from the positions of absorption bands between 4.27 and 4.24 µm. The highest concentrations of CO2 are between the main active faults of the South Polar Region, where the surface temperature is low. Pure CO2 ice deposits at the surface of Enceladus are best modeled by the formation of gas pockets below the icy crust and above the surface of the internal ocean. These pockets eventually release cold CO2 gas (∼70 to ∼119 K) at low-velocity (seeping) between the Tiger Stripes [Matson et al., 2018, Icarus, 302, 18–26]. CO2 clathrate hydrates may form in the ocean and may be subsequently released when a CO2 gas pocket blows out and erupts. Other mechanisms may contribute to reinforcing the anti-correlation of the CO2 distribution (of any type) with respect to the location of the Tiger Stripes, such as successive sublimation of CO2 and condensation on colder areas, and partial frost cover by H2O releases from plume eruptions.

30]Hexaphyrin(2.1.2.1.2.1) as Aromatic Planar Ligand and Its Trinuclear Rhodium(I) Complex.

Expanded porphyrins are attractive research targets because of their large and flexible structures, optical and electrochemical properties, and diverse coordination abilities. We are interested in the use of double bonds within expanded porphyrins because double bonds could conduct isomerization, expansion of π-conjugation, and giving different molecular geometry. We, thus, report [30]hexaphyrin(2.1.2.1.2.1) 3H-1, which was synthesized by a simple condensation reaction of 1,2-di(pyrrol-2-yl)ethene and pentafluorobenzaldehyde under an acidic condition. The compound 3H-1 exhibited 30π aromatic property with a highly planar structure, displaying intense Soret- and weak Q-like absorption bands. The compound 3H-1 has a sufficient space and dipyrrin-like coordination sites in its cavity. Trinuclear rhodium(I) complex 3Rh-1 was obtained with [Rh(CO)2Cl]2 and exhibited six redox potentials.

Ultrafast Charge Transfer and Relaxation Dynamics in Polymer-Encapsulating Single-Walled Carbon Nanotubes: Polythiophene and Coronene Polymer

We investigate the photophysical properties of polymer-encapsulating single-walled carbon nanotubes (SWNTs) using absorption spectroscopy, photoconductivity spectroscopy, and femtosecond pump–probe spectroscopy. In a polythiophene (PT)-encapsulating SWNT film, one or two PT layers are encapsulated within SWNTs, depending on the tube diameter. For single encapsulated PT layers, the photoconductivity action spectrum shows a large photocurrent signal corresponding to absorption bands associated with PT exciton and continuum states, indicating charge transfer between the PT and the small-diameter SWNT. Pump–probe measurements show that electron transfer to the SWNT occurs in 0.53 ps and electrons then recombine with holes remaining in the PT in 11 ps. In a coronene-polymer-encapsulating SWNT film, weak absorption bands at 1.7 and 3.4 eV are observed in addition to the SWNT spectrum. Band calculations allow these to be assigned to optical transitions between the electronic states originating from the coronene ...

Prelaunch Radiometric Calibration of the TanSat Atmospheric Carbon Dioxide Grating Spectrometer

TanSat is an important satellite in the Chinese Earth Observation Program which is designed to measure global atmospheric CO2 concentrations from space. The first Chinese superhigh-resolution grating spectrometer for measuring atmospheric CO2 is aboard TanSat. This spectrometer is a suite of three grating spectrometers that make coincident measurements of reflected sunlight in the near-infrared CO2 band near 1.61 and $2.06~\mu \text{m}$ and in the molecular oxygen A-band (O2A) at $0.76~\mu \text{m}$ . Their spectral resolving power ( $\lambda /\Delta \lambda$ ) is ~19 000, ~12 800, and ~12 250 in the O2A, weak absorption band of molecular carbon dioxide band, and strong absorption of carbon dioxide band, respectively. This paper describes the laboratory radiometric calibration of the spectrometer suite, which consists of measurements of the dark current response, gain coefficients, and signal-to-noise ratio (SNR). The SNRs of each channel meet the mission requirements for the O2A and weak CO2 band but slightly miss the requirements in a few channels in the strong CO2 band. The gain coefficients of the three bands have a negligible random error component and achieve very good stability. Most of the R-squared of gain coefficients model consist of five numbers of nine (e.g., 0.99999) after the decimal point, suggesting that the instrument has significant response linearity. The radiometric calibration results meet the requirements of an absolute calibration uncertainty of less than 5%.

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.