UV Absorption Band Research Articles

UV–visible and infrared absorption spectra of gamma irradiated CuO-doped lithium phosphate, lead phosphate and zinc phosphate glasses: A comparative study

Undoped and CuO-doped lithium phosphate, lead phosphate and zinc phosphate glasses were prepared. UV–visible and infrared absorption spectra of the prepared samples were measured before and after successive gamma irradiation. Experimental optical spectra of the undoped samples reveal strong UV absorption bands, which are attributed to the presence of trace iron impurities in both the lithium and zinc phosphate glasses while the lead phosphate glass exhibits broad UV bands due to combined absorption of trace iron impurities and divalent lead ions. The CuO-doped glasses reveal an extra broad visible band due to Cu 2+ ions in octahedral coordination. The effects of gamma irradiation have been analyzed for both the sharing of all constituent components including trace iron impurities. Infrared absorption spectra of the prepared samples were investigated by the KBr disk technique. The FTIR spectra reveal main characteristic absorption bands due to different phosphate groups. The IR spectra are observed to be slightly affected by the increase of CuO in the doping level (0.2–3%) indicating the stability of the main network units.

Kinetics of cyclobutane thymine dimer splitting by DNA photolyase directly monitored in the UV

CPD photolyase uses light to repair cyclobutane pyrimidine dimers (CPDs) formed between adjacent pyrimidines in UV-irradiated DNA. The enzyme harbors an FAD cofactor in fully reduced state (FADH(-)). The CPD repair mechanism involves electron transfer from photoexcited FADH(-) to the CPD, splitting of its intradimer bonds, and electron return to restore catalytically active FADH(-). The two electron transfer processes occur on time scales of 10(-10) and 10(-9)s, respectively. Until now, CPD splitting itself has only been poorly characterized by experiments. Using a previously unreported transient absorption setup, we succeeded in monitoring cyclobutane thymine dimer repair in the main UV absorption band of intact thymine at 266nm. Flavin transitions that overlay DNA-based absorption changes at 266nm were monitored independently in the visible and subtracted to obtain the true repair kinetics. Restoration of intact thymine showed a short lag and a biexponential rise with time constants of 0.2 and 1.5ns. We assign these two time constants to splitting of the intradimer bonds (creating one intact thymine and one thymine anion radical T(∘-)) and electron return from T(∘-) to the FAD cofactor with recovery of the second thymine, respectively. Previous model studies and computer simulations yielded various CPD splitting times between <1ps and <100ns. Our experimental results should serve as a benchmark for future efforts to model enzymatic photorepair. The technique and methods developed here may be applied to monitor other photoreactions involving DNA.

Solvothermal Synthesis of CeO&lt;sub&gt;2&lt;/sub&gt; Nanoparticles

Ultrafine CeO2 nanoparticles were synthesized directly via solvothermal treatment of Ce(NO3)3·6H2O powder in toluene at 180 °C for 48 h, and characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and UV-vis absorption spectrum. The results from XRD, Raman and XPS revealed the formation of pure cubic phase CeO2 with some oxygen vacancies. The TEM image disclosed that the as-synthesized CeO2 comprised nanoparticles of about 5–8 nm. The UV-vis absorption spectrum showed that the as-synthesized CeO2 nanoparticles had a wide UV absorption band centered at around 326 nm (3.8 eV).

DNA Binding Studies of Tartrazine Food Additive

The interaction of native calf thymus DNA with tartrazine in 10 mM Tris-HCl aqueous solution at neutral pH 7.4 was investigated. Tartrazine is a nitrous derivative and may cause allergic reactions, with a potential of toxicological risk. Also, tartrazine induces oxidative stress and DNA damage. Its DNA binding properties were studied by UV-vis and circular dichroism spectra, competitive binding with Hoechst 33258, and viscosity measurements. Tartrazine molecules bind to DNA via groove mode as illustrated by hyperchromism in the UV absorption band of tartrazine, decrease in Hoechst-DNA solution fluorescence, unchanged viscosity of DNA, and conformational changes such as conversion from B-like to C-like in the circular dichroism spectra of DNA. The binding constants (K(b)) of DNA with tartrazine were calculated at different temperatures. Enthalpy and entropy changes were calculated to be +37 and +213 kJ mol(-1), respectively, according to the Van't Hoff equation, which indicated that the reaction is predominantly entropically driven. Also, tartrazine does not cleave plasmid DNA. Tartrazine interacts with calf thymus DNA via a groove interaction mode with an intrinsic binding constant of 3.75 × 10(4) M(-1).

Synthesis, characterization and DNA binding of the complexes of rare earth with phenanthroline and demethylcantharate

Three novel rare earth complexes, [Ln 2(DCA) 2(phen) 2](NO 3) 2·6H 2O (Ln(III)=Sm(III)( 1), Er(III)( 2), Yb(III)( 3); DCA 2−=demethylcantharate, 7-oxabicyclo[2.2.1] heptane-2,3-dicarboxylate, C 8H 8O 5 2−; phen=1,10-phenanthroline, C 12H 8N 2) were synthesized. The structures were characterized by elemental analysis, molar conductance, IR and TGA. The results suggested that the structural features of the complexes were: in each DCA 2−, one carboxylate group, as bidentate bridging group, connected two rare earth ions; the other carboxylate group, as bidentate chelate group took part in the coordination with rare earth ion. And cyclic ether oxygen of DCA 2− and nitrogen atoms of phen took part in the coordination. The probable coordination number was seven. The interaction of the complexes with DNA was studied by UV-spectra, fluorescence spectra and viscosity measurements. Following increasing the concentration of DNA, the UV absorption bands nearby 265 nm of the three complexes appeared hypochromism and red-shift phenomena. And the values of binding constants K b were 1.89×10 5 L/mol ( 1), 3.54×10 4 L/mol ( 2) and 3.83×10 4 L/mol ( 3). The complexes could quench the fluorescence of EB-DNA system, and the values of equilibrium constants K sq were 1.72( 1), 0.56( 2) and 1.09( 3). The relative viscosity of DNA steadily decreased with increasing the concentration of complexes. So, we could infer that the complexes may partially insert into DNA. The study of agarose gel electrophoresis showed that the complexes could cleave plasmid DNA, and the process of the reaction was through unclassical redox mechanism.

Photodissociation Dynamics of Allyl Alcohol in UV: The Exit Channel Barrier for OH Production

Photodissociation dynamics of allyl alcohol (H2C=CH-CH2OH) has been investigated at 205 - 213 nm along the UV absorption band by measuring rotationally-resolved laser-induced fluorescence spectra of OH radicals. Observed energy partitioning of the available energy among products at all photon energies investigated was similar and the barrier energy for OH production is about 574.7 kJ/mol from the OH yield measurements. The potential energy surfaces for the S0, T1, and S1 excited states along the dissociation coordinate were obtained by ab initio quantum chemical calculations. The observed energy partitioning was successfully modeled by the barrier-impulsive model with the reverse barrier and the geometry obtained by the calculated potential energy surfaces. The dissociation takes place on the T1 excited state potential energy surface with an energy barrier in the exit channel and a large portion of the photon energy is distributed in the internal degrees of freedom of the polyatomic products.

Gamma ray interactions with MoO3-doped lead phosphate glasses

The UV–Visible, Fourier transform infrared (FTIR) and Raman and electron spin resonance (ESR) spectra of undoped lead phosphate and MoO3-doped glassy samples have been investigated. The UV–VIS absorption spectra were re-measured after successive gamma irradiation. Before irradiation, undoped sample exhibited strong ultraviolet absorption, which was attributed to co-absorption due to trace iron impurities (mainly Fe3+ ions) and lead Pb2+ ions. With the introduction of MoO3 in progressive amounts, extra visible bands were recorded at about 400–440, 540, 750 and 870 nm. These bands are most likely correlated with the presence of Mo3+, Mo4+ and Mo5+ ions in the host glass. In the undoped specimen, gamma irradiation produced UV absorption bands that increased slightly with irradiation but no visible bands were recorded. Samples containing high MoO3 content showed some resistance to irradiation with no bands in the visible region being observed. FTIR absorption spectra of the undoped and MoO3-doped samples revealed the formation of metaphosphate and pyrophosphate structural units. Highly MoO3-doped samples exhibited additional bands due to molybdate groups. Raman and ESR spectra were in agreement with UV–VIS and IR data, indicating the presence of molybdenum ions in lead phosphate glass, as Mo3+, Mo4+ and Mo6+ with different ratios. However, such glassy systems favor the trivalent species.

Synthesis, Photophysical and Electrochemical Characterization of the Heteroleptic Iridium Complexes with Modified Ancillary Ligand by Carrier‐transporting Groups

AbstractTwo heteroleptic iridium complexes with a general formulation of (piq)2Ir(G‐pic) were synthesized and characterized by 1H NMR, 13C NMR and element analysis, in which piq is 1‐phenylisoquinoline, G‐pic is picolinic acid derivative containing carrier‐transporting group by a non‐conjugated connection of 1,6‐dioxyhexane. Both (piq)2Ir(G‐pic) complexes exhibited an enhanced UV absorption band at 310–400 nm, an increased HOMO energy level and an identical red emission peaked at 612 nm with higher fluorescence quantum efficiency (øf), compared to (piq)2Ir(pic) in dichloromethane solution. Interestingly, this iridium complex containing both hole‐transporting triphenylamine and electron‐transporting oxadiazole moieties exhibited the best Фf of 0.58 using Ru(bpy)3(PF6)2 as the reference (øf=0.062 in acetonitrile). This work indicates that incorporating carrier‐transporting groups into ancillary ligand by a non‐conjugated connection is available for improving the optophysical properties of their iridium complexes.

UV–visible and infrared spectroscopy of gamma-irradiated lithium diborate glasses containing SeO 2

UV–visible spectroscopic studies of a base lithium diborate glass together with samples containing SeO 2 substituting B 2O 3 have been measured before and after successive gamma irradiation. The optical absorption spectra of the base and SeO 2-containing samples show charge transfer UV absorption bands which are related to the unavoidable contamination with trace iron impurities [mainly Fe 3+ ions] within the raw materials used for the preparation of such glasses. The progressive introduction of SeO 2 causes some changes in the intensity of the two UV bands which are identified at 235 and 285 nm instead of the three peaks already observed in the base glass at 235, 275, 310 nm. Gamma irradiation produces induced bands which are assumed to be generated from the intrinsic defects in the lithium diborate base glass together with the sharing of trace iron impurities through suggested photochemical reactions. The UV induced bands are observed to be highly intensified showing continuous growth with progressive irradiation and are identified at about 230, 285 and 310 nm together with a further induced broad visible band centered at about 550 nm. Infrared absorption measurements of the base lithium diborate glass reveal characteristic bands due to stretching and bending vibrations of both BO 3 and BO 4 units together with the far-infrared bands due to the modifier Li + ions. The introduction of SeO 2 causes some changes in the IR spectra due either to the sharing of SeO 3 units and/or the polymerization of the borate network.

Synthesis, Crystal Structure and Spectroscopic Property of [Cu(C20H10Cl4O2N2)]&amp;middot;DMF

A Schiff base ligand,N,N'-bis(3,5-dichlorosalicylaldehyde)-o-phenylenediamine,and its copper complex was synthesized.The compound was characterized by elemental analysis,FTIR,TG-DTG,single crystal X-ray diffraction,UV-Vis absorption spectroscopy,and fluorescence excitation and emission spectra.The high thermal decomposition temperature of 384 ℃ for the complex showed that it had high thermal stability.In its infrared spectrum,a strong band was observed at about 1616 cm-1.This band was due to the conjugated C N stretching vibration,and was shifted to higher frequency compared with the free ligand of 3,5-dichlorosalicylaldehyde and o-phenylenediamine.The new band at 530 cm-1 was assigned to Cu—O stretching vibration.The crystal of the copper(Ⅱ) complex belongs to monoclinic system with space group,P2(1)/n,a = 0.81316(8) nm,b = 1.53101(18) nm,c = 1.87819(19) nm,β = 92.4530(10) °,Z = 4,the final R1 = 0.058,and ωR2 = 0.148.The central copper ion of the complex coordinated with the two O and two N of the Schiff base to form a five-membered ring and two six-membered rings,which constituted a fourcoordinated planar conformation.The complex's UV absorption bands were at about 268,310 and 435 nm,where the absorption band at about 435 nm can be assigned to the intrinsic absorption of C N.Its fluorescence excitation is in the range of 360 ～ 480 nm,and its DMF solution emitted intensive blue-green fluorescence at the peak wavelength of 507 nm.Its optical gap was about 2.59 eV,which was determined by the intrinsic absorption band edge of the complex in DMF solution.

Fluorescence Properties of Colour Centres Produced by Ultrashort Laser Irradiation in LiF Crystals

LiF is a nonhygroscopic alkali halide crystal which possesses good optical and physical properties, and can host different species of colour centres at room temperature. Colour centres in LiF present broad absorption and emission bands in the near UV, visible and near IR regions of the spectrum. In this paper we study spectroscopic properties of colour centres produced in LiF by ultrashort laser pulses. The absorption and emission properties of these materials were measured showing that during the irradiation F, F2, F2+, F3+ and F2− colour centres were created in the crystals. A colour centres formation dose-like curve as a function of the ultrashort pulse energy was determined using fluorescence spectroscopy.

Synthesis and applications of 2,7-carbazole-based conjugated main-chain copolymers containing electron deficient bithiazole units for organic solar cells

A series of low-band-gap (LBG) donor-accepor con- jugated main-chain copolymers (P1-P4) containing planar 2,7- carbazole as electron donors and bithiazole units (4,4 0 -dihexyl- 2,2 0 -bithiazole and 4,4 0 -dihexyl-5,5 0 -di(thiophen-2-yl)-2,2 0 -bithia- zole) as electron acceptors were synthesized and studied for the applications in bulk heterojunction (BHJ) solar cells. The effects of electron deficient bithiazole units on the thermal, optical, electrochemical, and photovoltaic (PV) properties of these LBG copolymers were investigated. Absorption spectra revealed that polymers P1-P4 exhibited broad absorption bands in UV and visible regions from 300 to 600 nm with opti- cal band gaps in the range of 1.93-1.99 eV, which overlapped with the major region of the solar emission spectrum. More- over, carbazole-based polymers P1-P4 showed low values of the highest occupied molecular orbital (HOMO) levels, which provided good air stability and high open circuit voltages (Voc) in the PV applications. The BHJ PV devices were fabricated using polymers P1-P4 as electron donors and (6,6)-phenyl-C61- butyric acid methyl ester (PC61BM) or (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptors in different weight ratios. The PV device bearing an active layer of polymer blend P4:PC71BM (1:1.5 w/w) showed the best power conver- sion efficiency value of 1.01% with a short circuit current den- sity (Jsc) of 4.83 mA/cm 2 , a fill factor (FF) of 35%, and Voc ¼ 0.60 V under 100 mW/cm 2 of AM 1.5 white-light illumination.

Spectroscopic Studies on the Interaction of Isatin with Calf Thymus DNA

The interaction of native calf thymus DNA (CT-DNA) with isatin was studied at physiological pH by spectrophotometric, spectrofluorometric, competition experiment, circular dichroism, and viscometric techniques. No red shift and isobestic points are observed in UV absorption band of isatin. A strong fluorescence quenching reaction of DNA to isatin was observed, and the binding constants (Kf) of DNA with isatin and corresponding numbers of binding sites (n) were calculated at different temperatures. Thermodynamic parameters enthalpy change (ΔH) and entropy change (ΔS) were calculated to be +27.42 kJ mol⁻¹ and +201 J mol⁻¹ K⁻¹ according to Van't Hoff's equation, which indicated that the reaction is predominantly entropically driven. DNA viscosity and iodide quenching results suggest that isatin does not intercalate into the DNA base pairs. Circular dichroism spectra of CT-DNA indicated deep conformational changes in the DNA double helix. These results indicate that isatin interacts with CT-DNA via groove binding mode.

Coated Hydrophilic Thin Film on Glasses Using Freeze Drying-Assisted Sol-Gel Technique for Self-Cleaning Building Materials

Titanium dioxide thin film has been successfully synthesized deposited on ITO glass substrates by the sol–gel dip-coating method using freeze drying technique. The precursor and TiO2 film were characterized using XRD, AFM and UV-vis absorption spectra analysis technologies. The XRD result demonstrates that the TiO2 film is well crystallized and consists of anatase phase only with (101) plane. The morphology of the nanoparticles of TiO2 thin film is spherical shape with grain size of 30.1 nm in average diameter and the surface of the TiO2 film is smooth. There is a strong wide UV absorption band around 387 nm and the calculated band gap (Eg) value of the TiO2 thin film is about 3.18 eV. The water contact angles for the thin film was only about 12°. The freeze drying-assisted sol-gel technique offers a novel process route in treating hydrophilic glasses for self-cleaning building materials and would be widely application for building energy saving.

The improvement of the amorphous environment of the germanate–tellurate glasses in the presence of the gadolinium ions

Glasses in the system xGd2O3·(100 − x)[TeO2·GeO2] with 0 ≤ x ≤ 50 mol% have been prepared from melt quenching method. In this paper, we investigated changes of the coordination numbers of germanium, tellurium, and gadolinium ions by investigations of FTIR, EPR, and UV–VIS spectroscopy. By analyzing the structural changes resulted from the IR spectra we found that the bending modes of [GeO4] structural units and the deformed modes of the Te–O–Te linkages produce intercalation of the [GdOn] entities in the germanate–tellurate chain network and densification of the glasses by increasing the number of [GeO6] structural units. EPR spectra of the studied samples reveal that the gadolinium ions play a role of network former. The UV–VIS spectra show broad UV absorption bands located in the 250–350 nm region. Their intensity increase with the increasing of Gd2O3 content showing that these stronger transitions can be due to the presence of the O=Ge bonds (n–π* excitations) of [GeO5] structural units. The [GeO5] structural units are more stable thermodynamically than their analogues and the [GeO6] structural units produce the improvement of the amorphous character of these glasses.

Probing the molecular and electronic structure of the lichen metabolite usnic acid: A DFT study

The molecular structure of usnic acid was investigated by the density functional theory (DFT). Two keto-enol tautomers are nearly isoenergetic and more stable than other tautomers. Noteworthy is the energy difference among the three intramolecular O–H⋯O hydrogen bonds. The DFT/PCM calculated dissociation constants account for the acidic sequence of the three OH-groups. The electronic structure was also studied by calculating IR/Raman, NMR, and absorption features. A reliable assignment of the ‘fingerprint’ carbonyl stretching modes was supported by calculations on related molecules. The calculated NMR chemical shifts fit expectation in terms of a fast interconversion between the two most preferred tautomers. A variety of π → π ∗ and n → π∗ excitations, localized on a single ring or involving a charge-transfer between the two lateral rings of the molecule, gives rise to the broad UV-absorption bands. This property accounts for the efficient protection against damaging solar radiation provided by usnic acid for lichens.

Light-induced coloration and transformation process in YAlO 3 crystal

The nature of point defects in YAlO 3 (YAP) which brings great influence on the crystal properties has not been fully established. The UV-irradiated crystal exhibits broad additional absorption bands in the range of 200–800 nm while the additional absorption bands 200–800 nm can be reduced, with a re-irradiation of a 457 nm green laser. The light-induced coloration and transformation mechanism is studied and it is found that the increase or decrease of both UV and visible absorption bands are related to the creation and annihilation of anion vacancies (V O 2+ and F +) and cation vacancies (V Al 3− and V Y 3−). It is proposed that the creation and annihilation of V O 2+, F +, V Al 3− and V Y 3− may be caused by the separation and recombination of the vacancy clusters [V O 2+–V Al 3−–F +] and [V O 2+–V Y 3−–F +], which play important roles in the formation and transformation process of light-induced color centers in YAP crystal.

Synthesis, optophysical and electrochemical properties of bipolar-transporting europium(III) complexes with carbazole and oxadiazole units

A series of bipolar-transporting europium(III) complexes containing carbazole and oxadiazole units were synthesized and characterized. Two intense UV absorption bands at around 286 nm and 352 nm, and sharply red emissions peaked at 614 nm were observed for these europium complexes in dichloromethane. Importantly, the bipolar-transporting europium(III) complexes exhibited higher thermal stability, more intense UV absorption at 286 nm and twofold increased photoluminescent quantum yield compared to the reported red chromophore of tri(dibenzoylmethane) (1,10-phenanthroline) europium(III).

Density functional theory calculation on the promotion effect of H 2 in the selective catalytic reduction of NO x over Ag–MFI zeolite

Density functional theory (DFT) calculation was used to study the hydrogen promotion effect for the selective catalytic reduction (HC-SCR) of NO x over Ag–MFI zeolite. The nature of the bond between an Ag atom and MFI is ionic. One of the roles of hydrogen addition is to neutralize the cationic Ag atom by forming an AgH molecule. We propose that the formation of a Ag 4 cluster is achieved by the AgH diffusion as follows: 2AgH + Ag-Z-Ag → HAg 4H-Z → Ag 4-Z + H 2. With the presence of oxygen, the HAg 4H cluster prefers the formation of HOO − adsorbate to the desorption of H 2. O 2 is physisorbed on the Ag 4 cluster. Thus, the HAg 4H cluster is important for the activation of oxygen. Another role of hydrogen addition is to reproduce the HAg 4H cluster from the Ag 4 cluster which is generated by the SCR reaction from HOOAg 4H species. Since time dependent DFT (TD-DFT) calculation shows that the UV absorption bands of the HAg 4H cluster are weak, UV–vis measurements are not adequate for the study of the reaction mechanisms of HC-SCR.

Speciation of Fe in Fe-modified zeolite catalysts

Fe-modified zeolites (ferrierite and MFI) were prepared by four impregnation methods followed by calcination and tested as catalysts in oxidative dehydrogenation of ethane by nitrous oxide at 350 °C. The Fe cationic and Fe oxidic species were identified by combination of UV–Vis spectroscopy and voltammetry. Monomeric or dimeric Fe ions have only UV absorption bands and some of them evolve voltammetrically identifiable [Fe(OH) x ] (3− x )+ ions in contact with acetic acid-sodium acetate buffer. Fe oxide nanoclusters characterised by UV band at about 28,000 cm −1 are not detected by voltammetry under chosen conditions because they are situated inside the zeolite channels. Amorphous, nanocrystalline, and crystalline Fe(III) oxides were distinguished sensitively by their specific voltammetric reduction peaks at potentials −0.1 to −0.8 V/SCE in acetate buffer (pH 4.7) and by phase-specific electron pair transitions responsible for Vis absorption band centred at 17,500–21,000 cm −1. The proposed method to differentiation between these ferric oxides is novel in materials analysis and solid state speciation. The monomeric and dimeric ferric ions are active in oxidative dehydrogenation of ethane to ethene with selectivity about 40–60% under used conditions, while Fe oxide nanoclusters are too active and over-oxidise ethane and/or ethene to C, CO and CO 2. Oppositely to general expectations, ferric oxides are indifferent in the catalytic reaction and do not decrease reaction selectivity.