Characteristic UV Absorption Bands Research Articles

Solid-phase chemiluminescent reaction of Eu2(SO4)3 with XeF2 as a possible source of the Eu(IV) highest oxidation state

The highly exothermic solid-phase interaction of anhydrous europium (III) sulfate polycrystalline powder with xenon difluoride was found to be a potential source of the highest oxidation state (HOS) of europium, Eu4+. The reaction is accompanied by chemiluminescence (CL) in the visible spectral region and proceeds spontaneously at room temperature for ​~ ​20 ​h. Several photon emitters are established and identified, namely, atomic Xe and single-ionized xenon Xe+, emitting in the wavelength range 420–700 ​nm, as well as the electronically excited ion Eu3+ (590–700 ​nm). Absorption with a maximum of ~340 ​nm is registered in the diffuse reflectance spectrum of the reaction mixture during first few minutes of the reaction. This signal is tentatively assigned to the HOS of europium (+4). The reaction mechanism is proposed which includes a) Eu3+-assisted decomposition of xenon difluoride leading to atomic fluorine as well as highly reactive intermediates XeF+ and Xe+; b) oxidation of Eu3+ ion to the HOS by the latter; c) generation of excited species in the reduction stages followed by CL: Xe2+(Xe+) → Xe0 (blue-green emission) and Eu4+ → Eu3+ (red emission), sulfate environment is considered as the reductant; d) the F• ​+ ​SO4•- interaction and partial replacement of sulfate ligands with fluoride and fluorosulfate anions in the coordination sphere of the europium ion. Theoretical calculations using composite methods suggest the proposed mechanism and demonstrate the thermodynamic probability of ozone formation in the studied reaction, which was detected by the characteristic UV absorption band.

Isonicotinic acid hydrazide-based silver nanoparticles as simple colorimetric sensor for the detection of Cr3+

A simple colorimetric method for the detection of Cr3+ is proposed using silver nanoparticles (AgNPs) prepared with isonicotinic acid hydrazide (INAH) and sodium citrate. The AgNPs were synthesized via a one-step approach at room temperature using INAH as reducing agent in the presence of sodium citrate. As synthesized AgNPs showed a characteristic UV absorption band at 403nm. The AgNPs exhibited an excellent response with regard to colorimetric sensing of Cr3+ as a result of their surface modification. No such response was observed in case of AgNPs prepared in the absence of INAH. It is proposed that INAH as isonicotinic acid (INA) and citrate on the surfaces of AgNPs interact cooperatively with the Cr3+ ions, resulting in aggregation of AgNPs in the solution. The aggregation induced by the addition of Cr3+ to the AgNPs containing solution leads to turn the color of a solution from golden yellow to red along with a remarkable change in absorption band. The color change was readily detectable with the naked eye even at lower concentration of Cr3+. The spectral change was monitored by UV–vis spectroscopy. Under optimized conditions, the sensor demonstrated a good linear relationship between absorption ratios and the Cr3+ concentrations in the range of 1×10−6 to 5×10−5M with correlation coefficient (R2) of 0.993, and detection limit of 4.5×10−7M for the colorimetric assay. In addition, the developed sensor showed high selectivity for Cr3+ in the presence of other common heavy metal ions. This method enabled the rapid determination of Cr3+ in tap and river water samples within the acceptable range of recoveries.

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.

Optical spectroscopy of Yb2+ ions in YbF3-doped CaF2 crystals

Abstract Transparent colorless Ca1−xYbx F2+x (x=0.0007–0.016) crystals were grown using the vertical Bridgman technique. In order to obtain efficient Yb3+–Yb2+ conversion in the as-grown crystals, a special procedure has been developed. Room temperature optical absorption spectra reveal the characteristic UV absorption bands of the Yb2+ ions in the as-grown crystals, with intensities more than 10 times higher than those reported by other authors using various conversion procedures. The influence of YbF3 content and of codoping with Pb2+ ions on the absorption and emission spectra has been studied. Room temperature emission bands in the near UV (not reported before) and in the visible spectral domain have been observed. The emission intensity depends on the dopant concentration. A comparison of our results with those obtained by other authors is also given.

Concentration distribution of Yb2+ and Yb3+ ions in YbF3:CaF2 crystals

Abstract Calcium fluoride crystals doped with YbF 3 were grown using the Bridgman technique. The optical absorption spectra reveal the characteristic UV-absorption bands of divalent Ytterbium. The absorption coefficient of divalent Yb is more than ten times higher than that of trivalent Ytterbium. This shows that the developed crystal growth process achieves a good Yb 3+ –Yb 2+ conversion. The concentration distribution of the Yb 2+ and Yb 3+ ions among two of the samples was investigated using the optical absorption method. Taking into account the relationship between the optical absorption coefficient and the concentration of the impurities in the sample, the segregation coefficient of the two types of ytterbium ions has been calculated. From our calculations, we obtained the results that the segregation coefficient of the Yb 3+ ions in a CaF 2 host is ≈1, and for Yb 2+ ions is

Preparation and oscillation of absorption bands of ZnS clusters

Electric-field-induced transient pore formation (electroporation) in DOPC vesicles is usedfor the preparation of molecular ZnS clusters. The absence of caps permits (a) continuedgrowth of the ZnS clusters formed, (b) the assessment of their true absorption spectraunaltered by stabilizing ligands, and (c) the previously inaccessible live observation of thegrowth of the clusters in the molecular-size regime. The ensuing self-aggregation of ZnS isslowed down to month timescales by its adsorption at the exterior surface of the vesicles.The growth of the clusters in the molecular size regime is found to exhibit novel,time-dependent, oscillating red- and blue-shifts of the characteristic UV absorption band ina certain special condition. On the basis of similarities between the oscillating trend of theexperimentally observed transition energy and that of the calculated HOMO–LUMO gap of(ZnS)n clusterswith n = 1–9,the wavelengths of the sequential spectral peaks can be assigned to the ZnS monomer (ZnS, 217 nm), dimer((ZnS)2, 253 nm),tetramer ((ZnS)4,225 nm), heptamer ((ZnS)7, ∼250 nm) andnonamer ((ZnS)9, 228 nm).

Crystal Structures and Spectroscopic Properties of Zinc(II) Ternary Complexes of Vitamin L, H′ and Their Isomer <i>m</i>-Aminobenzoic Acid with Bipyridine

The crystal structures of the three Zn(II) complexes, [Zn(bpy)(o-AB)2] (1) (bpy=2,2'-bipyridine, o-AB=o-aminobenzoic acid=Vitamin L), [Zn(bpy)(m-AB)Cl]2 (2) (m-AB=m-aminobenzoic acid), [Zn(bpy)(p-AB)Cl]*p-AB*H2O (3) (p-AB=p-aminobenzoic acid=Vitamin H'), have been determined and the basic coordination geometries and architectures organized by hydrogen-bonds and pi-pi interactions also characterized. The substitute amine group at ortho-, meta-, and para-position of AB plays an important role to produce completely different coordination motif of these complexes, further, in all complexes, aromatic amines are not coordinated to Zn(II) atom. While two different types of coordination modes of the carboxylate O atoms are present in these complexes: one mode consists of the usual Zn-O bond lengths (2.009(2)-2.251(2) A) in complex 1, 2 and 3; another consists of a very long Zn-O bond lengths (2.422(2) A) in complex 1. Each of the complexes has the characteristic UV absorption bands around 250-310 nm region, and the intense fluorescence band at near 325 nm.

Preparation of Ultrasmall, Uncapped PbS Quantum Dots via Electroporation of Vesicles

Electric-field-induced transient pore formation (electroporation) in synthetic unilamellar dioleoylphosphatidylcholine vesicles of 178-nm diameter is utilized for the preparation of subnanometer-size PbS quantum dots. With Pb2+ ions originally entrapped in the vesicles and S2- ions placed in the bulk, their reaction is initiated by the opening of pores and occurs in the bulk. The ensuing self-aggregation of PbS is slowed to the hour and day time scales by its adsorption at the exterior surface of the vesicles. The growth of the particles in the molecular size regime is found to exhibit novel, time-dependent, oscillating red and blue shifts of the characteristic UV absorption band. On the basis of similarities between the oscillating trend of the experimentally observed transition energy and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital gap of (PbS)n clusters with n = 1-9, the wavelengths of the sequential spectral peaks can be assigned to the PbS monomer (237.5 nm), dimer (282 nm), tetramer (232 nm), hexamer (281 nm), octamer (234.5 nm), and nonamer (278-280 nm). Growth beyond the octamer is associated with the customary monotonic red shift of the absorption band. Under the experimental conditions used, a stable system is reached with unchanging spectral features after 20 days. This solution is estimated to contain 1.82 x 10(-5) M (PbS)9 particles, each with a greatest dimension of <9 A.

Ascorbic Acid as a Free Radical Scavenger in Porcine and Bovine Aqueous Humour

Aim: To study the antioxidant activity, UV absorption, concentration and stability of ascorbic acid (AA) in porcine and bovine aqueous humour (AH). Methods: Porcine and bovine AH was taken within 5 min after death and frozen at –70°C. The characteristic UV absorption band of AA and the concentration of AA in AH was determined by UV spectrophotometry. The antioxidant activity of AA to serve as a free radical scavenger in AH has been determined by using a novel fluorescent probe for antioxidants, the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO). The fluorescence lifetime and intensity of this probe reflect the concentration of dissolved antioxidants. The time-resolved fluorescence of DBO (laser excitation at 351 nm) in AH and in a neutral phosphate-buffered saline (PBS) solution containing only the natural amount of AA as an additive were measured. Results: The characteristic UV absorption band of AA has its maximum at 266 nm in AH. The concentration of AA in porcine and bovine AH was found to be 0.547 ± 0.044 and 1.09 ± 0.16 mM, respectively, by spectrophotometry. The fluorescence lifetime of the probe DBO was reduced from 320 ± 5 ns in pure aerated PBS to 205 ± 5 ns in porcine AH and 165 ± 3 ns in bovine AH. A detailed kinetic analysis of the lifetime shortening suggests that AA contributes approximately 75 and 85% to the antioxidant activity of porcine and bovine AH, respectively. Conclusions: Our experiments suggest that AA is the major contributor to the antioxidant activity of porcine and bovine AH. The role of AA to serve as an antioxidant in AH is discussed. In addition, UV spectrophotometry is established as an alternative method to determine the concentration of AA in AH.

Chemical behaviour of zirconium oxychloride octahydrate and acetic acid in precursor solution for zirconia film formation on glass

Precursor solutions for zirconia films on soda lime silica glass substrate were prepared from zirconium oxychloride octahydrate (ZOO) and acetic acid (HOAC) maintaining the mol ratios, [HOAC]/[ZOO]=2, 4, 6, 8 and 10. A characteristic UV absorption band at ∼280 nm in the ∼120h aged precursor solutions was identified for acetate group of the zirconium acetato complexed species. The presence of acetate ligand coordinated with either ZrOOH+ or [Zr4(OH)8]8+ or with both was predicted by the studies of UV spectra of aged solutions and FTIR spectra of unbaked films on silicon wafer. Dipping technique was followed for film formation. Thicknesses and refractive indices of the baked (450°±5°C) films were in the ranges 1818±20 A and 1.702–1.762 respectively. The positive SIMS experiment on two typical films baked at 450°±5°C derived from the precursors with [HOAC]/[ZOO]=2 and 6, detected the ionic species, Zr+, ZrO+, ZrO2+, Na+, Ca+, Fe+, H+ while the negative SIMS detected O− and Cl−. The relative contents of the ionic species with respect to Zr+ were dependent on the acid content of the precursors. Reflection (%) of the baked films in the UV region was also dependent on the acid content of the precursors. Electron diffraction pattern of the typical baked film derived from the precursor with [HOAC]/[ZOO]=2 exhibited meta-stable cubic phase of zirconia and the grains were found to be elongated (aspect ratio, 2.00–2.33).

Polyurethanes and polyurethane cationomers bearing nitroaromatic groups and their photobehavior

AbstractElastomer‐type polyether urethanes and polyether urethane cationomers with nitroaromatic groups were prepared and the effect of UV irradiation on their characteristics was evaluated comparatively with a model compound. The photobehavior by UV irradiation with a high‐pressure Hg lamp was studied in solution, following the change of absorption bands characteristic for nitro structures as a function of irradiation time. UV irradiation causes diminution of the intensity of characteristic UV absorption bands and a decrease of molecular weight.

Host–Guest Complexation of Mono[6-(1-pyridinio)-6-deoxy]-α-cyclodextrin with Several Inorganic Anions

Abstract Mono[6-(1-pyridinio)-6-deoxy]-α-cyclodextrin (1) formed 1:1 charge-transfer complexes with such inorganic anions as I−, SCN−, and Br− in an aqueous solution to afford characteristic UV absorption bands. The binding constant (Ka) for a I− complex with 1 was ca. 45 times as large as that with a nonmacrocyclic analog of 1, ca. 10 times that with native α-cyclodextrin, and 4.4 times that with a β-cyclodextrin analog. The I− ion was bound to a dipyridinio analog of 1 more strongly than to 1 by a factor of 10. The Ka values decreased with an increase in the ionic strength of the medium. The complexation was competitively inhibited by ClO4−. Hydrophobic, van der Waals, electrostatic, and charge-transfer interactions were supposed to take part in the complexation co-operatively.