UV-vis Emission Research Articles

Role of the Salt Bridge Between Arg176 and Glu126 in the Thermal Stability of the Bacillus amyloliquefaciens α-Amylase (BAA)

In the Bacillus amyloliquefaciens α-amylase (BAA), the loop (residues 176-185; region I) that is the part of the calcium-binding site (CaI, II) has two more amino acid residues than the α-amylase from Bacillus licheniformis (BLA). Arg176 in this region makes an ionic interaction with Glu126 from region II (residues 118-130), but this interaction is lost in BLA owing to substitution of R176Q and E126V. The goal of the present work was to quantitatively estimate the effect of ionic interaction on the overall stability of the enzyme. To clarify the functional and structural significance of the corresponding salt bridge, Glu126 was deleted (ΔE126) and converted to Val (E126V), Asp (E126D), and Lys (E126K) by site-directed mutagenesis. Kinetic constants, thermodynamic parameters, and structural changes were examined for the wild-type and mutated forms using UV-visible, atomic absoption, and fluorescence emission spectroscopies. Wild type exhibited higher k(cat) and K(m) but lower catalytic efficiency than the mutant enzymes. A decreased thermostability and an increased flexibility were also found in all of the mutant enzymes when compared with the wild type. Additionally, the calcium content of the wild type was more than ΔE126. Thus, it may be suggested that ionic interaction could decrease the mobility of the discussed region, prevent the diffusion of cations, and improve the thermostability of the whole enzyme. Based on these observations, the contribution of loop destabilization may be compensated by the formation of a salt bridge that has been used as an evolutionary mechanism or structural adaptation by the mesophilic enzyme.

Fluorescent and colorimetric magnetic microspheres as nanosensors for Hg2+ in aqueous solution prepared by a sol–gel grafting reaction and host–guest interaction

Fluorescent sensing TSRh6G-β-cyclodextrin fluorophore/adamantane-modified inclusion complex magnetic nanoparticles (TFIC MNPs) have been synthesized via the cooperation of a host-guest interaction and sol-gel grafting reaction. Powder X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-visible absorption and emission spectroscopy have been employed to characterize the material. Fluorescence and UV-visible spectra have shown that the resultant multifunctional nanoparticle sensors exhibit selective 'turn-on' type fluorescent enhancements and a clear color change from light brown to pink with Hg(2+). Owing to a larger surface area and high permeability, TFIC MNPs exhibit remarkable selectivity and sensitivity for Hg(2+), and its detection limit measures up to the micromolar level in aqueous solution. Most importantly, magnetic measurements have shown that TFIC magnetic nanoparticles are superparamagnetic and they can be separated and collected easily using a commercial magnet. These results not only solve the limitations in practical sensing applications of nanosensors, but also enable the fabrication of other multifunctional nanostructure-based hybrid nanomaterials.

Photo-induced electron transfer in a pyrenylcarbazole containing polymer–multiwalled carbon nanotube composite

A polymer incorporated with a pyrenylcarbazole pendant poly(12-(3-(pyren-1-yl)-carbazol-9-yl)dodecyl methacrylate, denoted as PCP) was synthesized and applied in the functionalization of multi-walled carbon nanotubes (MWCNTs) by noncovalent π–π interaction. The PCP–MWCNT hybrids were isolated and characterized by SEM, TEM, and UV-visible absorption and emission spectroscopies. The strong interaction between PCP and the MWCNT in a 1,1,2,2-tetrachloroethane (TCE) solution was studied. It demonstrated an effective quenching effect on emission from PCP by the MWCNTs. DFT calculations showed electron delocalization between the pyrene and carbazole moieties. The LUMO of PCP is mainly located on the pyrene moiety while the LUMO + 1 is predominantly positioned on the carbazole moiety. Femtosecond transient absorption (TA) experiments determined the characteristic TA peaks of the excited states, which have contributions from both the pyrene and carbazole moieties. The excited state lifetime of the polymer PCP was measured to be 659 ps and the photo-excited electrons were injected into the MWCNTs very effectively on a time scale of 420 fs.

PH luminescence switch, DNA binding and photocleavage, and cytotoxicity of a dinuclear ruthenium complex

The ground- and excited-state acid-base properties of [Ru2(bpy)4(H2bipt)]Cl4 1 {bpy = 2,2'-bipyridine, H2bipt = 2,5-bis[1,10]phenanthrolin[4,5-f]-imidazol-2-yl)thiophene} are investigated by emission and UV-visible absorption spectrophotometric pH titrations. The DNA binding properties of 1 are studied by means of DNA viscosity and optical spectroscopic techniques of UV-visible absorption and emission spectral titrations, steady-state emission quenching with ferrocyanide, ethidium bromide competitive binding, and DNA thermal denaturation as well as density functional theoretical calculations. The DNA photocleavage and singlet oxygen generation properties as well as in vitro anticancer activities against five cancer cell lines are studied as well. The results demonstrated that pH-induced luminescence switching, DNA binding, and anticancer properties of 1 are much improved with respect to those of the mononuclear analog [Ru(bpy)2(Htip)]Cl2 {Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}.

A kinetic and mechanistic study into the formation of the Cu–Cr layered double hydroxide

The formation of the layered double hydroxide [Cu2Cr(OH)6]Cl·yH2O from the reaction between CuO and aqueous CrCl3·6H2O was explored using synchrotron X-ray diffraction and ex situ analyses. The use of hard X-rays permitted time-resolved in situ studies to be performed as the reaction proceeded under a range of conditions. Additional information was obtained from ex situ experiments in which aliquots of the reaction mixture were removed, quenched, and subsequently analysed by laboratory X-ray diffraction, IR, UV-visible, and atomic emission spectroscopies. On the basis of these data, it is proposed that the reaction involves three steps. First, the solid CuO starting material is hydrolysed to give Cu(OH)2 chains, releasing Cu(2+) ions into solution. The Cu hydroxide chains subsequently condense with aqueous Cr(3+) species, Cl(-) ions and water molecules to give a hydrated form of the LDH. This material then extrudes some water to form a phase with a reduced interlayer spacing.

Spectral and luminescent properties of new Pt(II) complexes with bis(salicylidene)ethylenediamine ligands

The results of synthesis of new Pt(II) complexes with N,N′-ethylene-bis(3-methoxysalicylideneiminate) and N,N′-2,3-dimethylbutane-2,3-diyl-bis(3-methoxysalicylideneiminate) ligands and their investigation by X-ray photoelectron spectroscopy and UV-visible absorption and emission spectroscopy are discussed. The degradation channels of excited electronic states of the complexes are determined.

Arrangement effect of the di-μ-oxo dimanganese catalyst and Ru(bpy)32+ photoexcitation centers adsorbed on mica for visible-light-derived water oxidation

A photosynthetic photosystem II (PS II) model was developed by adsorbing [(OH2)(terpy)MnIII(μ-O)2MnIV(terpy)(OH2)]3+ (1, terpy = 2,2′:6′,2′′-terpyridine) as an oxygen evolving center and Ru(bpy)32+ (bpy = 2,2′-bipyridine) as a photoexcitation center onto mica. The mica adsorbates were prepared by three different methods; Adsorbate A was prepared by adsorption of 1 followed by Ru(bpy)32+ on mica, and Adsorbates B and C were prepared by the opposite adsorption order and co-adsorption of 1 and Ru(bpy)32+, respectively. The UV-visible diffuse reflectance (DR) spectroscopic data and emission decay measurements of the photoexcited Ru(bpy)32+ suggested the different arrangements of 1 and Ru(bpy)32+ among the three adsorbates in a mica interlayer. For Adsorbate A, Ru(bpy)32+ could be adsorbed near the mica surface, being shallowly intercalated relative to 1. For Adsorbate B, 1 is adsorbed near the mica surface, Ru(bpy)32+ being deeply intercalated relative to 1. For Adsorbate C, either 1 or Ru(bpy)32+ could be randomly intercalated relative to the other adsorbates. In photochemical water oxidation experiments, a significant amount of O2 was evolved when visible light was used to irradiate an aqueous suspension of Adsorbate A containing a S2O82− electron acceptor in a liquid phase, whereas O2 was not evolved under the same conditions when using Adsorbates B and C. 1 is considered to work for photochemical water oxidation in Adsorbate A due to an efficient electron transport from deeply intercalated 1 to S2O82− ions in a liquid phase via Ru(bpy)32+ photoexcitation near the mica adsorbate surface.

Spectral Narrowing of UV-Visible Absorption and Emission Spectra of Anthracene-Derivatives in β-Cyclodextrin Nanocavity: Effects of Host/Guest Stoichiometry

Cyclodextrins (CD) are cyclic oligosaccharides consisting of six or more D-glucopyranose units, the interior of which forms a hydrophobic cavity. In the present study, we employed the CD confinement effects as a tool to suppress an electronic decoherence of guest wavefunction by reducing intermolecular interactions between a guest molecule and the surrounding environment. Effects of host/guest stoichiometry on the decoherence suppresion were investigated by comparing native β-CD with trimethyl-β-CD that should form only a 1:1 complex. Both fluorecence and fluorecence-excitation spectra of inclusion complexes exhibited spectral narrowings only for the β-CD host, suggesting that the formation of barrel-type β-CD dimer plays a key role for the pronounced spectral narrowings.

Photochemistry of fac‐[Re(bpy)(CO)3Cl

The photochemistry of fac-[Re(bpy)(CO)3Cl] (1 a; bpy=2,2′-bipyridine) initiated by irradiation using <330 nm light has been investigated. Isomerization proceeded in THF to give the corresponding mer-isomer 1 b. However, in the presence of a small amount of MeCN, the main product was the CO-ligand-substituted complex (OC-6-24)-[Re(bpy)(CO)2Cl(MeCN)] (2 c; bpy=2,2′-bipyridine). In MeCN, two isomers, 2 c and its (OC-6-34) form (2 a), were produced. Only 2 c thermally isomerized to produce the (OC-6-44) form 2 b. A detailed investigation led to the conclusion that both 1 b and 2 c are produced by a dissociative mechanism, whereas 2 a forms by an associative mechanism. A comparison of the ultrafast transient UV-visible absorption, emission, and IR spectra of 1 a acquired by excitation using higher-energy light (e.g., 270 nm) and lower-energy light (e.g., 400 nm) gave detailed information about the excited states, intermediates, and kinetics of the photochemical reactions and photophysical processes of 1 a. Irradiation of 1 a using the higher-energy light resulted in the generation of the higher singlet excited state with τ≤25 fs, from which intersystem crossing proceeded to give the higher triplet state (3HES(1)). In THF, 3HES(1) was competitively converted to both the triplet ligand field (3LF) and metal-to-ligand charge transfer (3mLCT) with lifetimes of 200 fs, in which the former is a reactive state that converts to [Re(bpy)(CO)2Cl(thf)]+ (1 c) within 10 ps by means of a dissociative mechanism. Re-coordination of CO to 1 c gives both 1 a and 1 b. In MeCN, irradiation of 1 a by using high-energy light gives the coordinatively unsaturated complex, which rapidly converted to 2 c. A seven-coordinate complex is also produced within several hundred femtoseconds, which is converted to 2 a within several hundred picoseconds.

Chemiluminescence microfluidic system of gold nanoparticles enhanced luminol-silver nitrate for the determination of vitamin B12

A rapid and sensitive chemiluminescence (CL) system coupled with a microfluidic chip has been presented to determine vitamin B12 (VB12) based on the reaction of luminol and silver nitrate (AgNO(3)) in the presence of gold nanoparticles (AuNPs). A microfluidic chip was fabricated by a soft-lithographic procedure using polydimethyl siloxane (PDMS) having four inlets and one outlet with a 200μm wide, 250μm deep, and 100mm long microchannel. Ag(+) was used as a chemiluminogenic oxidant in this CL reaction which oxidized luminol to produce strong CL signal in the presence of AuNPs. Luminol reacted with AgNO(3) under the catalysis of AuNPs to produce luminol radicals which reacted with dissolved oxygen and emitted CL light. The proposed CL system was applied to determine the amount of VB12 in VB12 tablets and multivitamin. Under the optimum conditions, the CL intensity of the system was increased with the concentration of VB12 in the range of 0.25-100ng mL(-1) with the correlation coefficient of 0.9982. The limit of detection was found to be 0.04ng mL(-1) with the relative standard deviation of 1.56% for five replicate determinations of 25ng mL(-1) of VB12. The CL reaction mechanism was demonstrated by UV-visible spectra and CL emission spectra.

Experimental Study Coupled With Electrical Modeling for the Consideration of DBD-Based Plasma Jet

In this paper, a dielectric-barrier discharge (DBD) of Ar:N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures at atmospheric pressure is studied in relation to plasma jet production. The discharge takes place in a capillary dielectric tube, and it is sustained by positive high-voltage pulses. It is herein claimed that, apart from the traditional DBD (which is developed perpendicularly to the gas flow and can produce afterglows), plasma jet propagates simultaneously parallel to the gas flow due to ionization waves guided by the dielectric tube. A quite simple electrical model is applied to simulate the proposed DBD and plasma jet coexistence. The concept of capacitive behavior of both barrier discharge and jet is taken into account. This model in combination with UV-visible optical emission spectroscopy and conventional photography supports the aforementioned statements. The dependence of the jet domination against the afterglow on the gas mixture is demonstrated, and the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> additive at 2.5 %-3% in Ar is found to be the most efficient for jet production. The model runs with the measured interelectrode voltage as input and yields the circuit total current as output. Matching between the measured current and the model output is attempted by adjusting two free parameters. This tuning of the free parameters provides reliable values for the electrical components of the model. Thus, a simple mean for realistic representation of both DBD and jet is achieved. This tool could be applied to the design of plasma jet reactors.

Structural Photodynamic Behavior of Topotecan, a Potent Anticancer Drug, in Aqueous Solutions at Different pHs

In this work, we report on photophysical studies of the anticancer drug topotecan (TPT) in aqueous solutions at different pHs. We used steady-state (UV-visible absorption and emission) and time-resolved picosecond (ps) emission spectroscopies to investigate the role of the H-bonding interactions as well as the proton concentration (pH = 0.48-7.40) on the behavior of topotecan (TPT) in its ground- (S0) and electronically first (S1) excited-states. At physiological conditions (pH = 7.40), the drug exists at S0 in equilibrium between the enol (E), cation (C), and zwitterion (Z) forms. The photoformation of Z* (τZ = 5.83 ns) occurs from directly excited (λexc = 371 nm) E as the two-step reaction: E*→C*→Z*. In this process, a very fast (less than 10 ps) protonation of E* leads to C*, which subsequently undergoes fast (580 ps) deprotonation to give Z* as the final photoproduct. At higher proton concentrations (pH = 0.48-1.31), a ground-state equilibrium exists between three different cationic species (C1, C2, and C3). The proton motion from the acidic solution to the C forms of TPT to give the reactions C1*→C2*→C3* is governed by the proton diffusion. In these conditions, both dynamic and static quenching occurs. The rate constant values k*(DPT1) and k*(DPT2) for the direct protonation of C1* and C2*, respectively, depend on the pH of the surrounding. The number of protons implicated in the reaction changes from ∼2 (pH = 0.48-0.78) to ∼1 (pH = 0.78-1.31), thus indicating the existence of two different reactions and proton-transfer dynamics. These results evidence the conformational, structural, and dynamical changes of aqueous solutions of TPT with the pH of the environment. They should help to understand the molecular structure/activity of TPT at cellular level.

Energy transfer in ZnO-anthracene hybrid structure

Anthracene dispersed in Polyphenylsiloxane (PPS) glass was synthesized on epitaxially grown zinc oxide (ZnO) to realize organic/inorganic hybrid semiconductors for efficient energy transfer. The photoluminescence (PL) from ZnO was modified by the presence of anthracene molecules due to resonant energy transfer. The UV-visible emission from anthracene molecule was also influenced due to resonant coupling with the excitonic and defect bound excitonic states in ZnO. Temperature dependence of PL of the hybrid system showed quenching of the defect bound emission of the ZnO to be due to energy transfer from anthracene. The PL lifetime in ZnO-anthracene/PPS hybrid structure at 4 K is relatively shorter and becomes comparable to the PL lifetimes in ZnO at 77 K. However, at room temperatures the PL lifetime of the hybrid structure is significantly longer than in ZnO and is comparable to the recombination lifetime in anthracene.

Photocatalytic reduction of methyl orange on Au/TiO2 semiconductors

Abstract The photocatalytic reduction of Methyl Orange (MO) in aqueous solution by gold nanoparticles deposited by deposition–precipitation (DP) method on Degussa P25 was studied as a function of gold content. A shift to the red region on the UV spectra from 3.2 (Degussa P25) to 2.9–2.8 eV on the Au/TiO 2 materials was observed by the presence of gold. High photocatalytic activity for the MO reduction using lamps of low energy UV–Vis emission (λ = 365, 418, 435 nm) was obtained for the Au/TiO 2 semiconductors, improving the rate constant of reduction in a factor up to 3.2 times compared to TiO 2 P25 used as reference. These results evidence a very important role of gold in photoreduction reactions for organic compounds, in this particular case for the reduction of MO.

PH triggered switching dye sensor based on furan and pyrone units

pH triggered dye sensor based on pyrone unit as a donor group and furan unit as an acceptor grouphave resulted in very promising optical switches, when dye was applied by alkali-induced nucleophilic additionreaction. The dye displayedclear UV-Visible absorption changes and new fluorescence emission behaviors, which are based on intramolecular charge transfer (ICT) system of the dye molecular structure. The levels of energy potential and the electron density distributions of this dye chemosensor were also simulated and discussed using computational modelcalculation.

The first structural and spectroscopic study of a paramagnetic 5f DO3A complex

A 5f(2) uranium(IV) complex of the macrocycle DO3A (DO3A = [4,7,10-tris-carboxymethyl-,1,4,7,10-tetraaza-cyclododec-1-yl]-acetic acid) has been prepared and characterised in the solid state and in solution. The DO3A scaffold containing no strongly absorbing chromophores enables the facile detection of relatively long-lived (8-13 ns) UV-visible emission that possesses significant charge transfer character tentatively assigned to deactivation of the excited (3)F(2) 5f(1) 6d(1) electronic configuration. This study demonstrates, for the first time, that luminescence of simple U(iv) chelates is detectable in the absence of an antenna, potentially serving as a diagnostic tract for environmental U(IV) species.

Multifunctional and Reactive Enantiopure Organometallic Helicenes: Tuning Chiroptical Properties by Structural Variations of Mono‐ and Bis(platinahelicene)s

Acetylacetonato-platina[6]- and -platina[7]helicenes have been prepared from 2-pyridyl-substituted benzophenanthrene ligands by following a two-step cycloplatination reaction. The photophysical properties (UV-visible absorption and emission behavior) and chiroptical properties (circular dichroism and molar rotation) of the resolved enantiomers have been measured. These metallahelicenes constitute a novel family of easily accessible helicene derivatives that exhibit large and tuneable chiroptical properties that can be rationalized theoretically and compared to the parent [6]- and [7]carbohelicenes. Furthermore, they are red phosphors at room temperature and their large chiroptical properties can be modulated by oxidation of the metal center to Pt(IV). Hetero- and homochiral diastereomeric bis(metallahelicene)s that possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands have also been prepared. It is shown that the heterochiral (P,M)-bis(Pt(III)-[6]helicene) 9a(1) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene) 9a(2). Spectral assignments and an analysis of the optical rotation of these systems were made with the help of time-dependent density functional theory. The calculations highlight the contributions of the metal centers to the chiroptical properties. For 9a(1) and 9a(2), σ-π conjugation between the helicenes and the Pt-Pt moiety may contribute strongly to the optical rotation and electronic circular dichroism.

Nanostructured titanium dioxide film preparation using inorganic nanoparticles instead of organic precursor materials.

Carbon dioxide is a major contributor to global warming. A promising method of reducing the concentration of atmospheric carbon dioxide is by photocatalytic conversion of carbon dioxide into renewable fuels, which has to be done using a photocatalytic film. The nanostructured film preparation method proposed in this study is a preparation of colloidal solution followed by film deposition using manual coating methods, mostly vertical dip-coating. Deposited films were calcined to forma crystalline film on the glass substrate. This method was adopted in case of film preparation from titanium dioxide. Comprehensive study on impact of different factors including temperature, type of surfactants, type of solvents, concentration of surfactants, and concentration of solvents on quality of thin film including band gap, particle size, strength and homogeneity was performed in this work. Material characterisation tests including UV-visible spectroscopy and field emission scanning electron microscopy were carried out to analyse the film characteristics. Mechanical tests including wipe test, rinse test, acetone test, scratch test and scotch tape test were performed to analyse the mechanical strength of obtained thin film. Nanostructured films were successfully prepared with controlled particle size in the range of 70 - 100 nm for TiO2. Films obtained in this study demonstrate acceptable durability and partial uniformity. The film preparation method used in this study was markedly economical, facile and reproducible.

Composition-Dependent Ultraviolet up-Conversion Luminescence in Yb&lt;sup&gt;3+&lt;/sup&gt;-Ho&lt;sup&gt;3+&lt;/sup&gt; Co-Doped Germanium- Phosphate Glasses

Yb3+-Ho3+ co-doped germanium-phosphate glasses have been prepared and characterized for its optical properties through measuring photoluminescence and Raman spectra. UV-visible up-conversion emission of holmium ion in Yb3+-Ho3+ co-doped germanium-phosphate glasses has been observed on 980nm excitation. As phosphate was substituted for germanium the red emission Red I decreased at first and then increased later while the green emission Green I decreased and the ratio of Red I to Green I increased. Interestingly, the value of ultraviolet emission intensity was larger than that of the blue and green emission intensity in phosphate glass sample. We believe that Yb3+-Ho3+ co-doped germanium-phosphate glasses might be a potential host material for developing ultraviolet all–solid compact lasers. The possible excitation mechanisms involved in these emissions were discussed, too.

Synchrotron UV−Visible Multispectral Luminescence Microimaging of Historical Samples

UV-visible luminescence techniques are fre-quently used for the study of cultural heritage materials, despite their limitations for identification and discrimination in the case of complex heterogeneous materials. In contrast to tabletop setups, two methods based on the vacuum ultraviolet (VUV)-UV-visible emission generated at a bending magnet of a synchrotron source are described. The main advantages of the source are the extended wavelength range attained, the continuous tunability of the source, and its brightness, leading to a submicrometer lateral resolution. Raster-scanning microspectroscopy and full-field microimaging were implemented and tested at the DISCO beamline (synchrotron SOLEIL, France). Investigative measurements were performed on a sample from a varnished musical instrument and a paint sample containing the pigment zinc white (ZnO) in order to illustrate some of the challenges analyzing heterogeneous cultural heritage cross-section samples with the novel imaging approach. The data sets obtained proved useful for mapping organic materials at the submicrometer scale and visualizing heterogeneities of the semiconductor pigment material. We propose and discuss the combined use of raster-scanning microspectroscopy and full-field microimaging in an integrated analytical methodology. Synchrotron UV luminescence appears as a novel tool for identification of craftsmen's and artists' materials and techniques and to assess the condition of artifacts, from the precise identification and localization of luminescent materials.