Visible Spectral Changes Research Articles

In situ High-Temperature Visible Microspectroscopy for Volcanic Materials

In situ high-temperature visible microspectroscopy has been developed in order to study color change kinetics of volcanic materials. Olivine thin sections put on a synthetic alumina plate are heated on a heating stage at 600-800 degrees C under a visible microspectroscope. Changes in visible absorption spectra are monitored every 60 s for 5 hours. The obtained high-temperature visible spectra showed a gradual increase with time in absorbance in the shorter wavelength region (400-600 nm). The 430 nm absorbance (ligand field transition of Fe3+ increased more with time at higher temperatures. Assuming diffusional transport in plane sheets, apparent diffusion coefficients were determined at temperatures of 600-800 degrees C. The activation energy for this diffusion in olivine is 208 +/- 17 kJ/mol. This activation energy value is similar to those for the metal vacancy diffusion in olivine. This newly developed in situ high-temperature visible microspectroscopy can provide kinetic measurements of visible spectral change of materials at high temperatures such as volcanic materials.

The Three Nitric-oxide Synthases Differ in Their Kinetics of Tetrahydrobiopterin Radical Formation, Heme-Dioxy Reduction, and Arginine Hydroxylation

The nitric-oxide synthases (NOSs) make nitric oxide and citrulline from l-arginine. How the bound cofactor (6R)-tetrahydrobiopterin (H4B) participates in Arg hydroxylation is a topic of interest. We demonstrated previously that H4B radical formation in the inducible NOS oxygenase domain (iNOSoxy) is kinetically coupled to the disappearance of a heme-dioxy intermediate and to Arg hydroxylation. Here we report single turnover studies that determine and compare the kinetics of these transitions in Arg hydroxylation reactions catalyzed by the oxygenase domains of endothelial and neuronal NOSs (eNOSoxy and nNOSoxy). There was a buildup of a heme-dioxy intermediate in eNOSoxy and nNOSoxy followed by a monophasic transition to ferric enzyme during the reaction. The rate of heme-dioxy decay matched the rates of H4B radical formation and Arg hydroxylation in both enzymes. The rates of H4B radical formation differed such that nNOSoxy (18 s(-1)) > iNOSoxy (11 s(-1)) > eNOSoxy (6 s(-1)), whereas the lifetimes of the resulting H4B radical followed an opposite rank order. 5MeH4B supported a three-fold faster radical formation and greater radical stability relative to H4B in both eNOSoxy and nNOSoxy. Our results indicate the following: (i) the three NOSs share a common mechanism, whereby H4B transfers an electron to the heme-dioxy intermediate. This step enables Arg hydroxylation and is rate-limiting for all subsequent steps in the hydroxylation reaction. (ii) A direct correlation exists between pterin radical stability and the speed of its formation in the three NOSs. (iii) Uncoupled NO synthesis often seen for eNOS at low H4B concentrations may be caused by the slow formation and poor stability of its H4B radical.

Molecularly Imprinted Polymers with Signaling Function Based on the UV–Vis Spectral Change by Diastereoselective Binding Events

Abstract Signaling cinchonidine-imprinted polymers were prepared using a polymerizable iron(III) porphyrin and/or methacrylic acid as functional monomer(s), and evaluated by chromatographic tests, Scatchard analysis, and spectroscopic analysis. An imprinted polymer prepared with an equimolar amount of the iron(III) porphyrin monomer to cinchonidine and six equivalents of methacrylic acid gave the strongest binding (Ka = 5.7 × 105 M−1) and highest selectivity (α = 14.6) for cinchonidine against its diastereomer, cinchonine. Thus, it was concluded that the iron(III) porphyrin and methacrylic acid residues worked cooperatively at the imprinted binding site. There is also the added advantage that the porphyrin provides a signaling function proportional to the chiral binding event of cinchonidine. A linear relationship was observed between the UV–vis absorbance of the imprinted polymer and the logarithm of cinchonidine concentrations, indicating that the polymer may be used as a selective cinchonidine sensing material. Moreover, various metalloporphyrins can be used as functionalized monomers in order to prepare functional MIPs for a wide range of target compounds capable of coordination with such metalloporphyrins, even if the target compounds have no characteristic UV–vis absorption or fluorescence.

Interactions of mammalian cytochrome P450, NADPH-cytochrome P450 reductase, and cytochrome b5 enzymes

An immobilized system was developed to detect interactions of human cytochromes P450 (P450) with the accessory proteins NADPH-P450 reductase and cytochrome b 5 ( b 5) using an enzyme-linked affinity approach. Purified enzymes were first bound to wells of a polystyrene plate, and biotinylated partner enzymes were added and bound. A streptavidin–peroxidase complex was added, and protein–protein binding was monitored by measuring peroxidase activity of the bound biotinylated proteins. In a model study, we examined protein–protein interactions of Pseudomonas putida putidaredoxin (Pdx) and putidaredoxin reductase (PdR). A linear relationship ( r 2 = 0.96) was observed for binding of PdR-biotin to immobilized Pdx compared with binding of Pdx-biotin to immobilized PdR (the estimated K d value for the Pdx · PdR complex was 0.054 μM). Human P450 2A6 interacted strongly with NADPH-P450 reductase; the K d values (with the reductase) ranged between 0.005 and 0.1 μM for P450s 2C19, 2D6, and 3A4. Relatively weak interaction was found between holo- b 5 or apo- b 5 (devoid of heme) with NADPH-P450 reductase. Among the rat, rabbit, and human P450 1A2 enzymes, the rat enzyme showed the tightest interaction with b 5, although no increases in 7-ethoxyresorufin O-deethylation activities were observed with any of the P450 1A2 enzymes. Human P450s 2A6, 2D6, 2E1, and 3A4 interacted well with b 5, with P450 3A4 yielding the lowest K d values followed by P450s 2A6 and 2D6. No appreciable increases in interaction between human P450s with b 5 or NADPH-P450 reductase were observed when typical substrates for the P450s were included. We also found that NADPH-P450 reductase did not cause changes in the P450 · substrate K d values estimated from substrate-induced UV–visible spectral changes with rabbit P450 1A2 or human P450 2A6, 2D6, or 3A4. Collectively, the results show direct and tight interactions between P450 enzymes and the accessory proteins NADPH-P450 reductase and b 5, with different affinities, and that ligand binding to mammalian P450s did not lead to increased interaction between P450s and the reductase.

Microperoxidase-8 Associated to CTAB Micelles: A New Catalyst with Peroxidase Activity

Literature data have pointed to microperoxidase-8 (MP-8) as an attractive water-soluble model for studying the reaction mechanism of peroxidases because this heme peptide is able to form the same enzyme intermediates during reaction with peroxides. In this work, we have demonstrated that the association of Fe(III)MP-8 with CTAB micelles provides a microenvironment with an alkaline interface and a hydrophobic core that gives special characteristics to the Fe(III)MP-8/peroxide (tert-butyl hydroperoxide or hydrogen peroxide) reaction as compared with homogeneous medium. EPR spin-trapping studies using 5,5-dimethyl-1-pyrroline N-oxide and computer simulations of the experimental spectra were performed to determine the reaction mechanism. From the analysis of the results, alkoxyl and hydroxyl radicals of t-BuOOH and HOOH, respectively, were identified as the initial radicals produced, presumably by homolytic scission of the O−O bond by Fe(III)MP-8/CTAB. The UV−vis spectral changes for Fe(III)MP-8 pointed to th...

Three-way-output response system by electric potential: UV–vis, CD, and fluorescence spectral changes upon electrolysis of the chiral ester of tetracyanoanthraquinodimethane

The newly prepared tetracyanoanthraquinodimethane (TCNAQ) derivatives 1a, b with a chiral auxiliary are good electron acceptors and exhibit weak circular dichroism (CD) based on the absorption of TCNAQ. The twin-type electron acceptor 1c with two TCNAQ units shows larger ellipticity by exciton coupling. UV–vis, CD, and fluorescence spectra were changed drastically upon electrochemical reduction of 1c , which demonstrates the unprecedented three-way-output response system.

A novel redox switch for fluorescence: drastic UV–vis and fluorescence spectral changes upon electrolysis of a hexaphenylethane derivative of 10,10′-dimethylbiacridan

The newly prepared title donor 1 has a very long CC bond [1.635(2) Å], which was readily cleaved upon oxidation to give dication 2 2+ containing two 10-methylacridinium chromophores. Colorless donor 1 ( E ox +0.18 V) is non-fluorescent whereas orange dication 2 2+ ( E red −0.27 V) emits strong green fluorescence, so that, this pair can be considered as a novel redox switch for fluorescence with high electrochemical bistability.

Photoluminescence switching of azobenzene-conjugated Pt(II) terpyridine complexes by trans-cis photoisomerization.

Pt(II) complexes with a terpyridylazobenzene ligand (tpyAB) were newly synthesized, and their photoluminescence properties by trans-cis isomerization of the azo moiety were investigated. In these complexes, upon excitation with 366-nm light in polar solvents such as DMF, DMSO, and propylene carbonate, trans-to-cis isomerization with significant UV-vis spectral changes occurred almost completely. Cis-to-trans isomerization was observed both by irradiation with visible light and by heat. The reduction peaks due to the terpyridine and the azo group in the cyclic voltammograms of the Pt complexes were shifted in the positive direction by trans-to-cis isomerization. Emission spectral changes due to trans-cis isomerization were observed for both the tpyAB and the Pt complexes. The significant differences in the emission properties of the complex compared to tpyAB include the observation that both the excitation and emission wavelengths were shifted to lower energy, located in the visible region. Moreover, the change in emission intensity between the trans and cis forms was more significant upon excitation with UV light, because the trans form of the complexes showed absolutely no emission. Accordingly, the azobenzene-conjugated Pt(II) terpyridine complexes promise to be doubly photofunctional materials, showing complete off-on switching of emission linked to the trans-cis conformation change.

Anion sensor based on the indoaniline–thiourea system

A new chromogenic indoaniline–thiourea-based sensor was designed to recognize anions in an organic solvent through complementary intermolecular hydrogen bonding. Complexed anions cause significant disturbance to the intramolecular hydrogen-bonded structure of the sensor, which then induces color and UV–vis spectral changes. This sensor allows for selective colorimetric detection of tetrahedral oxoanions (HSO 4 − and H 2PO 4 −).

Two-photon photochromism of two simple chromene derivatives

Two kinds of typical chromene derivatives, 5a,9-dimethyl-5aH-benzo[b]chromene (1) and 7a,11-dimethyl-7aH-dibenzo[b,f]chromene (2), were synthesized to understand the relationship between molecular structures and two-photon photochromism for chromene derivatives. The photochromic performances of 1 and 2 in hexane were investigated by measuring ultraviolet (UV)–visible absorption and 1H nuclear magnetic resonance spectral changes upon UV irradiation. The results indicate that 1 showed the two-photon photochromic reaction, whereas the main photochemical reaction of 2 was the isomerization between the open-E and open-Z isomers. Density functional theory (DFT) calculations suggest that these different photochromic performances are attributed to the differences in relative stabilities of closed, open-Z and open-E isomers for 1 and 2. Combined with DFT calculations for 12aH-12a-methyl-naphtho[3,2]chromene (3), the most typical chromene derivative well exhibiting two-photon photochromism, we conclude that chromene derivatives show the best two-photon photochromic performances only if closed isomers are more stable than open-Z and open-E isomers.

Specific visible spectral changes induced by guanine binding to cytosine-derivatized porphyrin

The interaction of the free nucleic acid bases adenine, cytosine, and thymidine with meso-tri(4-sulfonatophenyl) meso 4-phenyl porphyrin cytosine amide (TPSC) trisodium salt at pH 5.9, 7.4, and 9.3 results is a decrease in the absorbance of the Soret (B-band) at 413 nm of TPSC. A decrease in Soret band absorbance is observed with guanine below pH 8; at higher pH values a new absorbance band at 424 nm is observed. The appearance of the band is consistent with hydrogen bonding between the cytosine-functionalized porphyrin and guanine and the resulting perturbation of the electron orbitals of the porphyrin.

Photoreaction generating active oxygens of In(3+)-tetrakis(4-methylpyridyl)-porphine in the presence of albumins.

The complex formation of In(3+)-tetrakis(4-N-methylpyridyl)-porphine (In-TMPyP) with albumin was studied by resonance Raman spectroscopy. Albumin coordinated to In(3+) through the -S(-) group(s). The photoreaction was investigated using the visible spectral change and In-TMPyP-thiourea complex was used as a model. It was demonstrated that the complex in a weak basic solution (pH 8.5) is excited by light and the excited complex converts oxygen to superoxide anion, which finally cleavages the porphine ring of In-TMPyP.

Intercalation of water-soluble bis-Porphyrins into Poly(dA)-Poly(dT) double helix

The association constants ( K) of nucleic acid monomers with a series of water-soluble bis-porphyrins (bisMC1, bisMC3, bisMC5, bisMC7, and bisMC11) in which two porphyrin units were linked by a methylene chain of various lengths were estimated spectrophotometrically. Among the bis-porphyrins, the K values are similar for each nucleic acid monomer, indicating that the bridging chain length does not affect the association of the bis-porphyrins with the nucleic acid monomers. The melting curves of poly(dA)-poly(dT) in the presence of bisMC3 or bisMC5 were found to be biphasic, suggesting that bisMC3 and bisMC5 are bound to poly(dA)-poly(dT) with a binding mode different from the groove binding exhibited by the corresponding porphyrin monomers. A negative-induced CD peak in the Soret region of bisMC3 and bisMC5 with poly(dA)-poly(dT) is observed and the visible spectral changes of bisMC3 and bisMC5 upon addition of poly(dA)-poly(dT) are accompanied by a large red shift of the Soret band (bisMC3: 21 nm, bisMC5: 23 nm) with substantial hypochromicity (bisMC3: 49%, bisMC5: 40%). Therefore, it is reasonable to conclude that both of the porphyrin units of bisMC3 and bisMC5 intercalate into poly(dA)-poly(dT). In contrast to poly(dA)-poly(dT), the melting curves of poly(dA·dT) 2 in the presence of the bis-porphyrins did not show such biphasic behavior. Together with the CD and visible absorption data, it is certain that these bis-porphyrins do not intercalate into poly(dA·dT) 2.

Fluoride-binding to the Escherichia coli bd-type ubiquinol oxidase studied by visible absorption and EPR spectroscopies.

Cytochrome bd-type ubiquinol oxidase in the aerobic respiratory chain of Escherichia coli contains two hemes b (b558 and b595) and one heme d as redox metal centers. To clarify the structure of the reaction center, we analyzed the fully oxidized enzyme by visible and EPR spectroscopies using fluoride ion as a monitoring probe. The visible spectral changes upon fluoride-binding were typical of ferric iron-chlorine species, indicating heme d as a primary binding site. The negative peak at 645 nm in the difference spectrum indicates that heme b595 also provides the low-affinity fluoride-binding site. Fluoride-binding caused a complete disappearance from the EPR spectra of the low-spin signals ascribable to heme d and spectral changes in both rhombic and axial high-spin signals. After fluoride-binding, each component of the rhombic high-spin signal showed superhyperfine splitting arising from the interaction of the unpaired spin of the heme d iron with the nuclear magnetic moment of 19F. The axial high-spin species was converted to a new rhombic high-spin species assignable to heme b595-fluoride. The g = 2 component of this new species also gave 19F-superhyperfine splitting. These results indicate that both heme d and heme b595 can coordinate with a fluoride ion with different affinities in the fully oxidized state.

Synthesis and characterisation of mono-acetylide and unsymmetrical bis-acetylide complexes of ruthenium and osmium: X-ray structure determinations on [(dppe) 2Ru(Cl)(CC–C 6H 4- p-NO 2)], [(dppe) 2Ru(Cl)(CC–C 6H 3- o-CH 3- p-NO 2)] and [(dppm) 2Os(CC–C 6H 4- p-CH 3)(CC–C 6H 4- p-NO 2)

The synthesis of a series of metal mono-acetylides trans-[(dppe) 2Ru(Cl)(CC–R)] (R=C 6H 4- p-C 6H 5, C 6H 4- p-CH 3, C 6H 4- p-NO 2, C 6H 3- o-CH 3- p-NO 2, dppe=Ph 2PCH 2CH 2PPh 2), and unsymmetrical metal bis-acetylides trans-[(dppm) 2M(CC–R)(CC–R′)]; (M=Ru, Os; R=C 6H 4- p-NO 2, R′=C 6H 5, C 6H 4- p-CH 3; R=C 6H 5, R′=C 6H 4- p-CH 3) using a variety of σ-acetylide coupling reactions is reported. Three compounds have been structurally characterised, including the unsymmetrical trans-[(dppm) 2Os(CC–R)(CC–R′)] (R=C 6H 4- p-CH 3, R′=C 6H 4- p-NO 2] which shows the ‘rigid-rod’ nature of the acetylide-metal-acetylide linkage. The electrochemistry of symmetrical and unsymmetrical Ru(II) complexes demonstrates the role of the acetylide and the auxiliary ligands in determining the ease of oxidation at the metal centre whilst UV–vis spectral changes illustrate the influence of electron-withdrawing and -donating ligands.

Effects of Cyclodextrins on Fading of Azo Dyes with Sodium Sulfite

Effects of cyclodextrins (CyD) on fading of various azo dyes such as 1-arylazo-2-naphthols, 1-arylazo-4-naphthols, and 2-arylazo-1-naphthols with sodium sulfite at 30°C were investigated. Fading was found to occur as a result of adding of sulfite to a conjugate enone moiety (C-addition) or to a conjugate iminone moiety (N-addition) in the hydrozone tautomer. In the case of C-addition mainly conducted for 1-arylazonaphthols, the addition of β-CyD lessened the rate of fading through formation of an inclusion complex at the naphthol site of the dye. α-CyD had only limited effect on the fading rate since the cavity was too small to permit dye inclusion. Inclusion complexes were confirmed by vis-spectral change in the dyes subsequent to the addition of CyD. α-CyD caused remarkable retardation of fading for 2-arylazo-1-naphthols following N-addition. Inclusion of the dyes at the aryl site that would promote complexation was considered as explanation for this. β-CyD acted as an efficient retarding agent in the N-addition process. Retarding efficiency of fading due to CyD is discussed based on substituent effects, disposition of dyes in CyD cavities, reaction sites of the dyes, and the binding constant (Ka).

Binding of 2-azaanthraquinone derivatives to DNA and their interference with the activity of DNA topoisomerases in vitro.

We have investigated the binding ability to DNA of compounds belonging to the 2-azaanthraquinone-type structure and have examined the effect on the activity of DNA gyrase as well as on mammalian topoisomerases in vitro. Using different biophysical techniques it was found that one of these ligands, 9-((2-dimethylamino)ethyl)amino)-6-hydroxy-7-methoxy-5, 10-dihydroxybenzo[g]isoquinoline-5,10-dione (TPL-I), is an intercalating DNA binding agent, whereas the parent compound tolypocladin (TPL) and a derivative (TPL-II) showed almost no similar affinity to DNA. CD measurements demonstrated a significant and selective binding tendency of TPL-I to alternating purine/pyrimidine sequences with some preference for poly(dA-dT). poly(dA-dT). Tm values were increased of the ligand complex with the alternating AT-containing duplex polymer. The binding to various DNAs was characterized by CD and visible absorption spectral changes. From the latter, different binding constants of 6.2 x 10(5) and 1.5 x 10(5) M-1 were obtained for poly(dA-dT).poly(dA-dT) and poly(dA). poly(dT), respectively. Sedimentation measurements with supercoiled pBR322 plasmid DNA clearly indicated an intercalative binding mechanism associated with an unwinding angle of about 18 degrees. These results suggest that the intercalative binding of TPL-I is promoted by the 2-(dimethylamino)ethylamino group substituted on carbon 9 of the anthraquinone system. The cytotoxic compound TPL-I, but not TPL or TPL-II, effectively inhibited the DNA supercoiling reaction of DNA gyrase and the activity of mammalian topoisomerases I and II as measured by the relaxation assay. TPL-I affects the cleavage reaction of topoisomerases on a single site located in alternating purine-pyrimidine sequence regions. The inhibitory potency of TPL-I can be ascribed to a blocking of cleavage sites on the DNA substrate, which correlates with the sequence preference of the ligand.

Visible and near-infrared spectral changes in plasma of psychiatric patients

In the present study, the possible difference in visible and near-infrared (Vis-NIR) spectra of plasma in psychiatric patients compared to healthy control subjects was investigated. Mean Vis-NIR spectra of 60 psychiatric patients showed several specific peaks in the 630- to 930-nm region. Principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) were applied to manifest the spectral characteristics of each group. The PCA and SIMCA models demonstrated successful discrimination of the two groups using a score plot of the third versus fourth principal component and a Coomans plot, respectively. The PCA loadings were generally consistent with the discriminating power of the SIMCA model, indicating a specific pattern of Vis-NIR spectra in the plasma of psychiatric patients. The specific pattern possibly indicates altered superoxide, amine, and primary and secondary amides in plasma and may provide a possible indicator for the diagnosis of heterogeneous psychiatric disorders. This is the first step toward a clinical tool which has the potential to be applied in the diagnosis of psychiatric disease. Yet, there remain obstacles to its practical usage.

Electrocatalytic CO 2 reduction by cobalt octabutoxyphthalocyanine coated on graphite electrode

Electrocatalytic CO 2 reduction was studied by using a modified graphite electrode coated with cobalt octabutoxyphthalocyanine (CoPc(BuO) 8) and dipped in an aqueous electrolyte. The CoPc(BuO) 8 worked as a catalyst to produce CO with higher activity and selectivity than the non-substituted CoPc. Under typical conditions at pH 4.4, the most active and selective CO 2 reduction was achieved at −1.30 V with turnover number of the catalyst ∼ 1.1 × 10 6 h −1 and the selectivity of the produced CO H 2 ∼ 4.2 . The high activity was ascribed to the electron-donating BuO substituents of the complex, which would facilitate the coordination of CO 2 as well as the electron transfer from the complex to the coordinated CO 2 molecule. The use of a poly(4-vinylpyridine) membrane to disperse the complex decreased the activity. The mechanism was investigated by the use of in situ potential-step chronoamperospectroscopy (PSCAS) in a homogeneous CoPc(BuO) 8/pyridine solution. In the absence of CO 2, distinct two-steps visible spectral changes were observed following the first and second reductions of the complex. However, under CO 2 atmosphere, only the one-electron reduced species was present under steady state. It was proposed that the third reduction of a CO 2-coordinated CoPc(BuO) 8 should take place for CO production.

Theoretical Analysis of the IR and Visible Absorption Spectral Change by the Phase Transition of the Crystals of 2,3-Diphenylthio- and 2,3-Di(p-chlorothiophenyl)-1,4-Naphthoquinones

Abstract The isomerization mechanism of 2,3-Diphenylthio- and 2,3-Di(p-chloro thiophenyl)-1,4-Naphthoquinones was determined by using ab initio calculations and compared IR and visible absorption spectra. The optimized geometries using RHF/3–21G* method were determined with C2 symmetry for the violet form, and with C, symmetry for the red one. Visible spectra were identified by the charge transfers from thiophenyl group to naphthoquinone ring of these two isomers. The lowest allowed excitated states of these isomers were characterized by the the charge transfer (CT) from next-HOMO to LUMO in the violet form, and from HOMO to LUMO in the red form. The IR active CO stretching mode in the naphthoquinone ring appear as the symmetric type on the violet form, and anti-symmetric type on the red one.