UV Absorption Band Research Articles

Growth and spectroscopic characterization of Pb2+:CaF2 crystals

CaF2 crystals doped with various concentrations of PbF2 (0.4, 0.5, 1 and 2 mol%) were grown in vacuum, in a shaped graphite furnace using the vertical Bridgman method. The optical absorption spectra reveal the four characteristic UV absorption bands (labeled A, B, C and D) of the Pb2+ ions. As the PbF2 concentration increases, the structure of the bands become clearly visible, that is characteristic for the ns2 ions in various hosts. High intensity emission bands in the near UV spectral region have been observed. The dependence on the Pb2+ concentration of the optical absorption and emission of the Pb2+:CaF2 crystals were not reported before.

Resonance Raman Spectra of TNT and RDX Using Vibronic Theory, Excited-State Gradient, and Complex Polarizability Approximations

Geometries, UV absorption bands, and resonance Raman (RR) cross sections of TNT and RDX are investigated using density functional theory (DFT) in conjunction with the Coulomb attenuated B3LYP exchange-correlation functional. The absorption and RR spectra are determined with use of vibronic (VB) theory, excited-state gradient, and complex polarizability (CPP) approximations. We examined low-energy isomers (two for TNT and four for RDX) whose energies differ by less than 1 kcal/mol, such that they would appreciably be populated at room temperature. The two TNT isomers differ by an internal rotation of the methyl group, while the four conformers of RDX differ by the arrangements of the nitro group relative to the ring. Our theoretical optical properties of the TNT and RDX isomers are in excellent agreement with experimental and recent CCSD-EOM results, respectively. For the two TNT isomers, the ultraviolet RR (UVRR) spectra are similar and in good agreement with recently measured experimental results. Additionally, the UVRR spectra computed using the excited-state and CPP approaches compare favorably with the VB theory results. On the other hand, the RR spectra of the RDX conformers differ from one another, reflecting the importance of the positioning of the NO2 groups with respect to the ring. In the gas phase or in solution, RDX would give a spectrum associated with a conformationally averaged structure. It is encouraging that the computed spectra of the conformers show similarities to recent measured RDX spectra in acetonitrile solution, and reproduce the 10-fold decrease in the absolute Raman cross sections of RDX compared to TNT for the observed 229 nm excitation. We show that in TNT and RDX vibrational bands that couple to NO2 or the ring are particularly resonance enhanced. Finally, the computed RDX spectra of the conformers present a benchmark for understanding the RR spectra of the solid-phase polymorphs of RDX.

Multi-spectroscopic DNA interaction studies of sunset yellow food additive

The use of food dyes is at least controversial due to their essential role. Synthetic color food additives occupy an important place in the food industry. Moreover many of them have been related to health problems mainly in children that are considered the most vulnerable group. The purpose of this work is to present spectrophotometric methods to analyze the interaction of native calf thymus DNA (CT-DNA) with sunset yellow (SY) at physiological pH. Considerable hyperchromism and no red shift with an intrinsic binding constant of 7 × 10(4 )M(-1) were observed in UV absorption band of SY. Binding constants of DNA with complex were calculated at different temperatures. Slow increase in specific viscosity of DNA, induced circular dichroism spectral changes, and no significant changes in the fluorescence of neutral red-DNA solutions in the presence of SY suggest that this molecule interacts with CT-DNA via groove binding mode. Furthermore, the enthalpy and entropy of the reaction between SY and CT-DNA showed that the reaction is exothermic and enthalpy favored (∆H = -58.19 kJ mol(-1); ΔS = -274.36 kJ mol(-1) ) which are other evidences to indicate that van der Waals interactions and hydrogen bonding are the main running forces in the binding of the mentioned molecule and mode of interaction with DNA.

Structural evaluation and shielding behavior of gamma irradiated vanadium doped silicophosphate glasses

Ultraviolet and visible spectroscopic studies of base undoped and V2O5-doped sodium silicophosphate glasses were carried out in order to characterize the valence states of vanadium ions in such host mixed glass forming oxides. The same spectroscopic measurements were repeated after subjecting the glass to gamma irradiation with a dose of 8Mrad (8×104Gy). The base glass without V2O5 reveals an UV absorption band which is related to the presence of unavoidable trace iron impurities within the chemicals used for the preparation of this glass. V2O5-doped glasses exhibit extended UV–visible absorption spectra which are attributed to the collective presence of vanadium ions in three possible valencies V3+, V4+ and V5+ with the lower valence predominating.Infrared absorption spectra of the prepared samples indicate the combined presence of vibrational bands due to the sharing of both phosphate and silicate networks in the IR spectra. The addition of V2O5 in the doping level (0.1–3%) did not cause obvious changes in the IR spectra. Gamma irradiation produces noticeable but limited UV–visible spectral variations which show some shielding behavior in some cases. X-ray diffraction technique was applied to confirm the amorphous nature of the prepared glasses. ESR spectral data confirm the optical spectra results indicating the presence of both V3+ and V4+ ions in measurable percent.

Electronic polarization effects in the photodissociation of Cl2

Velocity mapped ion imaging and resonantly enhanced multiphoton ionization time-of-flight methods have been used to investigate the photodissociation dynamics of the diatomic molecule Cl(2) following excitation to the first UV absorption band. The experimental results presented here are compared with high level time dependent wavepacket calculations performed on a set of ab initio potential energy curves [D. B. Kokh, A. B. Alekseyev, and R. J. Buenker, J. Chem. Phys. 120, 11549 (2004)]. The theoretical calculations provide the first determination of all dynamical information regarding the dissociation of a system of this complexity, including angular momentum polarization. Both low rank K = 1, 2 and high rank K = 3 electronic polarization are predicted to be important for dissociation into both asymptotic product channels and, in general, good agreement is found between the recent theory and the measurements made here, which include the first experimental determination of high rank K = 3 orientation.

DNA Binding Studies of 3, 5, 6-Trichloro-2-Pyridinol Pesticide Metabolite

3, 5, 6-Trichloro-2-pyridinol (TCP) is a stable metabolite of two major pesticides, Chlopyrifos insecticide and Triclopyr herbicide, which are widely used in the world. The potential health hazard associated with TCP is identified due to its high affinity to the DNA molecule. Therefore, in this study, the interaction of native calf thymus DNA with TCP has been investigated using spectrophotometric, circular dichroism (CD), spectrofluorometric, viscometric and voltametric techniques. It was found that TCP molecules could interact with DNA via a groove-binding mode, as evidenced by hyperchromism, with no red shift in the UV absorption band of TCP, no changes in K(b) values in the presence of salt, no significant changes in the specific viscosity and CD spectra of DNA, and a decrease in peak currents with no shift in the voltamogram. In addition, TCP is able to release Hoechst 33258, a strong groove binder, in the DNA solutions. The results are indicative of the groove-binding mode of TCP to DNA.

DNA-Binding Studies of Fluoxetine Antidepressant

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) antidepressant that is widely prescribed. The DNA-binding behavior of fluoxetine antidepressant and calf thymus DNA was investigated in Tris-HCl buffer at physiological pH 7.4 with a series of techniques, including UV-Vis and circular dichroism spectroscopies, competitive study with Hoechst 33258, viscometry, and cyclic voltammetry. Fluoxetine molecules bind to DNA via groove mode as illustrated by hypochromism with no red shift in the UV absorption band of fluoxetine, decrease in Hoechst-DNA solution fluorescence, and no significant changes in viscosity of DNA. The CD spectra of DNA molecules show a little change in stacking mode of base pair but no modification changes in DNA conformation, for example, from B-DNA to A or C-DNA. The binding constant (K(b)) of DNA with fluoxetine was calculated to be 6.7 × 10(4) M(-1), which is in the range of reported and known groove binders, such as distamycin. All results showed the groove-binding mode of interaction of fluoxetine with DNA.

Enhanced detection efficiency of genetically encoded tag allows the visualization of monomeric proteins by electron microscopy

A cadmium-binding, genetically encoded protein tag, consisting of three repeats of metallothionein (3MT), can be used in electron microscopy for the visualization of multimeric- but not monomeric-tagged proteins due to insufficient electron density in monomeric proteins. Here, we present a technique for detecting monomeric 3MT-tagged green fluorescent protein (GFP-3MT) using a platinum compound to intensify the electron density. Substitution of cadmium by platinum as a result of incubating purified cadmium-binding 3MT-tagged GFP (GFP-Cd-3MT) with cis-diamminedichloroplatinum(II) (cisDDP) was assessed by a UV absorption band centered at 284nm thereby indicating platinum-sulfhydryl bonds. The incubation time and the concentration of cisDDP to reach maximal absorption were 2h and 36-fold molar equivalent of cisDDP, respectively. GFP-Pt-3MT isolated by gel filtration chromatography contained 29 platinum atoms per single GFP-3MT molecule. Electron-dense particles were observed in a GFP-Pt-3MT sample by electron microscopy without negative staining. Further image processing and image analysis demonstrated that particles with higher density relative to their surroundings were detectable in both GFP-Cd-3MT and GFP-Pt-3MT samples. These results demonstrate that replacement of cadmium with platinum, together with proper image analyses, improve detection efficiency and enable the visualization of 3MT-tagged monomeric protein by electron microscopy.

Gamma rays interactions with WO3-doped lead borate glasses

Optical and FT infrared spectral properties of tungsten ions in a host lead borate glass with composition PbO 55%, B2O3 45% (wt%) were studied. The same spectral properties were re-measured after subjecting the samples to successive gamma irradiation. The work was undertaken to justify the state of tungsten ions in such glass system by combined spectral investigations. Optical and FTIR spectral studies were confirmed by investigating electron spin resonance (ESR) of the undoped and WO3-doped samples before and after gamma irradiation. The optical spectrum of the undoped glass exhibits strong and wide UV absorption bands, which are related to the combined UV spectra of trace iron impurities (Fe3+ ions) and that from divalent lead (Pb2+) ions. Optical studies of WO3-doped sample indicate the presence of tungsten ions mostly in the hexavalent W6+ state. The presence of tungsten ions as structural groups was obtained by comparing the FTIR spectra of the undoped and WO3-doped samples. ESR spectra confirm the optical and FTIR spectral studies. The studied host lead borate glass has been found to show obvious shielding behavior towards successive gamma irradiation as revealed by the constancy of optical absorption spectral curves.

Low-temperature electrolytic coloration and spectral properties of sucrose crystals

Sucrose crystals are colored electrolytically at low temperatures and various voltages by using a pointed cathode and a flat anode. Caramels, carbonyl compounds, glycosylamines and free radicals are produced in colored sucrose crystals. No obvious characteristic absorption band in UV and visible wavelength regions is observed in absorption spectrum of uncolored sucrose crystal. Intense characteristic absorption bands of glycosylamines, carbonyl compounds and caramels are observed in absorption spectra of colored sucrose crystals. Production of caramels, carbonyl compounds, glycosylamines and free radicals are explained. Current–time curve for electrolytic coloration of sucrose crystal and its relationship with electrolytic coloration process are given.

On the photochromic properties of dithienylethenes grafted on gold clusters

Using ab initio spectroscopic tools, we have investigated the structural and electronic properties of a photochromic molecule grafted on a Au13 cluster. To simulate the electronic absorption spectra of this hybrid system, we relied on a (Time-Dependent) Density Functional Theory protocol. It is shown that this TD-DFT procedure combined with an analysis of the virtual molecular orbitals implied in the UV absorption bands provide insights into the loss or preservation of the photochromic properties of the organic switch after attachment to the metallic cluster.

Photodissociation dynamics of tert-butylnitrite following excitation to the S1 and S2 states. A study by velocity-map ion-imaging and 3D-REMPI spectroscopy

Excitation of tert-butylnitrite into the first and second UV absorption bands leads to efficient dissociation into the fragment radicals NO and tert-butoxy in their electronic ground states (2)Π and (2)E, respectively. Velocity distributions and angular anisotropies for the NO fragment in several hundred rotational and vibrational quantum states were obtained by velocity-map imaging and the recently developed 3D-REMPI method. Excitation into the well resolved vibronic progression bands (k = 0, 1, 2) of the NO stretch mode in the S1← S0 transition produces NO fragments mostly in the vibrational state with v = k, with smaller fractions in v = k- 1 and v = k- 2. It is concluded that dissociation occurs on the purely repulsive PES of S1 without barrier. All velocity distributions from photolysis via the S1(nπ*) state are monomodal and show high negative anisotropy (β≈-1). The rotational distributions peak near j = 30.5 irrespective of the vibronic state S1(k) excited and the vibrational state v of the NO fragment. On average 46% of the excess energy is converted to kinetic energy, 23% and 31% remain as internal energy in the NO fragment and the t-BuO radical, respectively. Photolysis via excitation into the S2← S0 transition at 227 nm yields NO fragments with about equal populations in v = 0 and v = 1. The rotational distributions have a single maximum near j = 59.5. The velocity distributions are monomodal with positive anisotropy β≈ 0.8. The average fractions of the excess energy distributed into translation, internal energy of NO, and internal energy of t-BuO are 39%, 23%, and 38%, respectively. In all cases ∼8500 cm(-1) of energy remain in the internal degrees of freedom of the t-BuO fragment. This is mostly assigned to rotational energy. An ab initio calculation of the dynamic reaction path shows that not only the NO fragment but also the t-BuO fragment gain large angular momentum during dissociation on the purely repulsive potential energy surface of S2.

Theoretical study of the radiationless deactivation mechanisms of photo-excited thiophene

The radiationless deactivation mechanisms of photo-excited thiophene have been studied using the multi-reference second-order perturbation theory and linear response coupled cluster methods. The electronic spectrum has been established and various minimum energy structures and conical intersections involving the ground and lowest singlet excited states have been characterized. Simplified reaction paths connecting the optimized geometries have been calculated as well. Based on these investigations, several deactivation mechanisms have been identified leading from the lowest bright 1ππ∗ states back to the electronic ground state. The excited state depletion in each case is possible due to the existence of low-lying conical intersections formed by either cleavage of one of the CS bonds or out-of-plane deformations of the aromatic ring. The deactivation mechanisms suggested in this work should provide some very efficient decay channels after excitation into the first UV absorption band of thiophene, and are good candidates to explain why this compound is non-fluorescent.

DNA binding, DNA cleavage and cytotoxicity studies of a new water soluble copper(II) complex: The effect of ligand shape on the mode of binding

The interaction of native calf thymus DNA (CT-DNA) with [Cu(ph 2phen)(phen-dione)Cl]Cl was studied at physiological pH by spectrophotometric, spectrofluorometric, circular dichroism, and viscometric techniques. Considerable hypochromicity and red shift are observed in the UV absorption band of the Cu complex. Binding constants ( K b) of DNA with the complex were calculated at different temperatures. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van’t Hoff equation, which indicated that reaction is predominantly enthalpically driven. All these results indicate that Cu(II) complex interacts with CT-DNA via intercalative mode. Also, this new complex induced cleavage in pUC18 plasmid DNA as indicated in gel electrophoresis and showed excellent antitumor activity against K562 (human chronic myeloid leukemia) and human T lymphocyte carcinoma-Jurkat cell lines.

Synthesis and Opto‐electronic Properties of a Red‐Emitting Heteroleptic Platinum Complex Using Pyrazol‐based Diketone Derivative as Ancillary Ligand

AbstractA red‐emitting heteroleptic cyclometalated platinum(II) complex containing an ancillary ligand of pyrazol‐based diketone derivative was synthesized. Its optophysical and electroluminescent properties were studied. Compared to the reported (piq)Pt(acac) complex, this platinum(II) complex exhibited a blue‐shifted UV absorption band at 300–450 nm, a low LUMO energy level and improved electroluminescent property. Using this platinum(II) complex as a single doping emitter and a blend of ploy(9,9‐dioctylfluorene) and 2‐tert‐butylphenyl‐5‐phenyl‐1,3,4‐oxadiazole as a host matrix, the fabricated polymer light‐emitting devices displayed saturated red emission with a peak at 648 nm and a shoulder at 601 nm. Furthermore, the emission quenching of the platinum(II) complex was significantly suppressed in these devices at high current density due to an introduction of the non‐planar pyrazol group into the ancillary ligand.

Biofunctional Silicon Nanoparticles by Means of Thiol‐Ene Click Chemistry

The preparation and characterization of butylene-terminated silicon nanoparticles (SiNPs) and their functionalization using thiol-ene chemistry is described, as well as the coupling of DNA strands. Bromide-terminated SiNPs were prepared by means of the oxidation of magnesium silicide and functionalized with butylene chains through treatment with the corresponding Grignard reagent. The successful coupling was confirmed by NMR and FTIR spectroscopy. TEM measurements revealed a silicon-core diameter of (2.4±0.5) nm. The fluorescence emission maximum is at λ(max)=525 nm when excited at λ(exc)=430 nm. The conjugation of these alkene-terminated SiNPs by means of thiol-ene chemistry is described for a variety of functional thiols. Efficient coupling was evidenced by NMR and FTIR spectroscopy. Moreover, the characteristic fluorescence properties of the SiNPs remained unaltered, thus demonstrating the value of this approach towards functional oxide-free SiNPs. Activation of the attached carboxylic acid moieties allowed for conjugation of NH(2)-terminated oligo-ssDNA (ss=single strand) to the SiNPs. Successful coupling was confirmed by a characteristic new UV absorption band at 260 nm, and by the still-present distinctive fluorescence of the SiNPs at 525 nm. Gel electrophoresis confirmed coupling of 2 to 3 DNA strands onto the SiNPs, whereas no uncoupled DNA was observed.

Fabrication and ultraviolet-shielding properties of silica-coated titania-doped ceria nanoparticles

A series of well-dispersed titania-doped ceria nanoparticles Ce 1- x Ti x O 2 were rapidly prepared by a novel salt-assisted solution combustion process using correspondent metal nitrates as oxidizers and ethyl glycol as fuel, and then coated with amorphous silica by seeded polymerization using tetraethyl orthoslicate (TEOS). The as-prepared samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible light (UV-Vis) diffuse reflectance spectroscopy. The results indicated that compared with the as-prepared pure ceria nanoparticles, the red-shift phenomenon occurred for Ti-doped ceria nanoparticles with Ti incorporation. Meanwhile, the absorption intensity in the UV light region slightly decreased and transmission rate in visible light region was somewhat enhanced. In comparison with the silica-coated CeO 2 nanopowders, the silica-coated Ce 0.95Ti 0.05O 2 nanopowders displayed the same absorption intensity in the UV light region, broader UV absorption band and higher transmission rate in visible light region.

Synthesis and characterization of novel conjugated polymers based on 3-cyclobutene-1,2-dione moiety

Abstract T hree novel conjugated polymers bearing 3,4-bis(4-hexylthiophen-2-yl)-3-cyclobutene-1,2-dione unit in their main chain have been synthesized successfully in good yields through Suzuki or Stille coupling reaction. Their molecular structures have been confirmed by FT-IR, 1H NMR and 13C NMR. All these copolymers exhibit broad and strong absorption bands in UV–vis region, and their optical band gaps are calculated to be 1.6–2.0 eV, suggesting that they have good coverage with the solar spectrum. These polymers have good thermostability and solubility in common organic solvents. Moreover, all these objective macromolecules possess high electron affinity of ∼3.8 eV determined from cyclic voltammetry measurement, implying that they are potential n-type polymeric photovoltaic materials.

Evaluation of Global Conformation of Polydialkylsilane Using Correlation between Persistence Length and Excitonic Absorption

An empirical relationship between persistence length (q) and molar absorptivity (ε) of poly(dialkylsilane)s (PSis) was developed. Here the q value was estimated by a touched-bead wormlike-chain model with the relationship between the intrinsic viscosity and the molecular weight, which were obtained from a size exclusion chromatography equipped with a viscometer. The resulting ε–q plot showed an apparent saturation curve, which could be formulated as ε = 105/(2.16 + 21.3q–1.23) with a high correlation coefficient, r = 0.99. Furthermore, using this empirical ε–q relational equation, changes in the q value of the PSis among thermochromism with (i) abrupt transition, (ii) gradual transition, and (iii) nontransition were estimated. (i) Abrupt type of thermochromism: poly(n-decylmethylsilane) exhibited an UV absorption band at 308 nm above transition temperature (Tc). This band drastically decreased in the relatively narrow range of transition temperature (ca. −35 to −50 °C), accompanied by an appearance of a new UV absorption band at λmax: 334 nm. In this case, the q value above Tc at 308 nm and below Tc at λmax: 334 nm was nearly identical, at ca. 1.5 nm. (ii) Gradual type of thermochromism: poly(n-hexyl-n-propylsilane) showed a gradual bathochromic shift from λmax: 320 to 350 nm in the relatively wide range of trandition temperature between −20 and −55 °C, involving conformation change from 73 helix to all-trans. Here the q value for the all-trans conformation with 5 nm increased approximately twice than that for the 73 helix conformation. (iii) Nontransition type: poly(n-hexylmethylsilane) showed a bathochromic shift of ca. 11 nm in the ranges of observation temperature (+25 to −80 °C) without an apparent transition. Here the q values were gradually and contiuously increased from ca. 1.2 to 1.4 nm. These results allowed to estimate the q value of PSis under various conditions, leading to a novel approach of investigation of the conformation-dependent chromic behavior of PSis, such as thermochromism, solvatochromism, piezochromism, and electrochromism.

Molecular aspects on the interaction of isatin-3-isonicotinylhydrazone to deoxyribonucleic acid: model for intercalative drug-DNA binding.

Isatin-3-isonicotinylhydrazone was synthesized and characterized. The interaction of native calf thymus DNA with isatin-3-isonicotinylhydrazone (IINH) in 10mM Tris-HCl aqueous solutions at neutral pH 7.4 has been investigated by spectrophotometric, circular dichroism (CD), melting temperature (T ( m )), spectrofluorimetric, and viscometric techniques. It is found that IINH molecules could intercalate between base pairs of DNA as are evidenced by: hypochromism in UV absorption band of IINH, induced CD spectral changes, sharp increase in specific viscosity of DNA, and increase in the fluorescence of methylene blue (MB)-DNA solutions in the presence of increasing amounts of IINH, which indicates that it is able to release the intercalated MB completely. The binding constants of IINH-DNA complex at four different temperatures (277, 288, 298, and 310K) were calculated to be 4.7×10(4), 2.2×10(4), 1.75×10(4) and 1.1×10(4)M(-1), respectively. Furthermore, the enthalpy and entropy of the reaction between IINH and CT-DNA showed that the reaction is enthalpy-favored and entropy- disfavored (∆H=-30.187kJmol(-1); ∆S=-20.46Jmol(-1)K(-1)) which are other evidences to indicate the IINH is able to be intercalated in the DNA base pairs.