Fluorescence Quenching Study on the Interaction of Some Schiff Base Complexes with Bovine Serum Albumin

The interaction of Schiff base ligand A and its three metal complexes [A‐Fe(II), A‐Cu(II), and A‐Zn(II)] with bovine serum albumin (BSA) was investigated using a tryptophan fluorescence quenching method. The Schiff base ligand A and its three metal complexes all showed quenching of BSA fluorescence in a Tris‐HCl buffer. Quenching constants were determined for quenching BSA by the Schiff base ligand A and its metal complexes in a Tris‐HCl buffer (pH=7.4) at different temperatures. The experimental results show that the dynamic quenching constant (K_SV) was increased with increasing temperature, whereas the association constant (K) was decreased with the increase of temperature. The thermodynamic parameters ΔH, ΔG and ΔS at different temperatures were calculated. The ionic strength of the Tris‐HCl buffer had a great influence on the wavelength of maximum emission of BSA. Under low ionic strength, the emission spectra of BSA influenced by A‐Zn(II) had a small blue shift. Compared to A‐Zn(II), the emission spectra of BSA in the presence of the Schiff base ligand A and A‐Cu(II) had no significant λ_em shift. At high ionic strength, the emission spectra of BSA upon addition of the Schiff base A, A‐Fe(II), and A‐Zn(II) all had a red shift, but the emission spectra of BSA had λ_em shift neither at low ionic strength, nor at high ionic strength in the presence of A‐Cu(II). Furthermore, the temperature did not affect the λ_em shift of BSA emission spectra.     

New details in the polarized spectrum of naphthalene by means of linear dichroism studies in oriented polymer matrices

Linear dichroism (LD) spectra are presented for naphthalene oriented in stretched polyethylene and polypropylene matrices at 77 K and 296 K. From the calculated spectrum LD(λ)/A(λ), where A(λ) is the corrected absorbance spectrum of the sample by unpolarized light, orientational parameters are calculated and component spectra, 235–315 nm, are resolved corresponding to polarization parallel to the long (B_3u = x) and the short (B_2u = y) axes in the molecular plane (D_2h). The orientational parameters indicate different orientational mechanisms in polyethylene and polypropylene, but the resolving procedure yields mainly identical component spectra. It is suggested that the polarization (B_3u) predominating in the 245–275 nm region isdue to a B_1g vibronic perturbation of the ¹B_2u state.     

Use of the vanadium(V)-xylenol orange mixture as an improved reagent for the spectrophotometric determination of traces of hydrogen peroxide

The reaction in V(V)-xylenol orange (XO)-H₂O₂ system was studied by spectrometry. On the addition of hydrogen peroxide to the mixture of vanadium(V) and XO (V-XO reagent), the absorption peak of V(V)-XO complex (λ_max = 582 nm) decreased significantly. The decrease in the absorbance (denoted as ΔA) was proportional to the concentration of hydrogen peroxide. The constant values of ΔA were obtained under the condition of [XO]/[V(V)] = 0.5 ~ 1.2 and in the pH 3.5 ~ 4.5 region. Based on these results, the conditions for the use of the V-XO reagent in the colorimetric determination of hydrogen peroxide were examined in detail. The V-XO reagent was found to be useful for the trace analysis of hydrogen peroxide with high sensitivity, and the data were little affected by the presence of some inorganic and organic substances. The lower limit of the determination is about 1 × 10^?6M.     

Effect of proton irradiation on structure and optical property of PTFE film

Effects of protons on chemical structure and optical properties of polytetrafluoroethylene (PTFE) film were investigated in the energy range of 60 to 170 keV to simulate the effects of space proton irradiation environment. The results show that for PTFE film irradiated with protons, the change in C_1s spectrum, along with those in F_1s and the FT‐IR spectrum after irradiation, demonstrates that two processes take place simultaneously. One is substitution in which carbon to fluorine bonds can be broken by the protons and some positions of fluorine are occupied by active protons; the other is the carbonification, which results in the change of surface color and an increase of carbon percentage on the irradiated surface. For the PTFE film irradiated with 150 keV protons, the spectral absorbance ΔA_λ in the wavelengths longer than 300 nm increase unmonotonously with proton fluence, and an abnormally recovery decrease of the ΔA_λ with the increase of fluence in the range of 5×10¹³ cm^?2 to 10¹⁵ cm^?2 is observed. The change of the ΔA_λ could be related to the competition of the carbonification and the substituting effect. The carbonification increases the ΔA_λ, while the substituting increases the amorphousness amount, leading to an increase in the transparency of the film. In addition, the creation of radicals can also contribute to the increase in absorbance. Copyright © 2003 John Wiley & Sons, Ltd.     

Mixed-ligand lanthanide complexes—II : Complexes of β-diketone and heterocyclic amine. Synthesis and spectroscopic studies

The imidazole adducts of tris(heptafluorooctanedionato)lanthanide(III), [Ln(fod)₃ · im] have been synthesized and characterized. The electronic spectra in the visible region have been analysed and spectral parameters ($\text{β}$, b^1/2, δ and T_λ) and oscillator strengths calculated and discussed. These complexes are more covalent than the analogous [Ln(fod)₃ · pz] complexes, pz = pyrazole. The covalency is more in solution than in the solid state. The experimental and the calculated oscillator strengths are in good agreement. The band shape for the hypersensitive transition in the solid and solution spectra is compared with the other known systems and discussed. The difference in the band shape of the hypersensitive transition in the solid and in solution is indicative of solvent molecule coordination. The Mössbauer spectrum of [Eu(fod)₃ · im] is reported. The dipolar shift produced in the NMR spectrum of [Eu(fod)₃ · im] is upfield in comparison to the signal of the organic moiety itself as well as in its diamagnetic analogues. The coordinated base does not dissociate even in DMSO solution. Due to their poor solubility these compounds are not suitable for use as induced NMR shift reagents.     

Determination of rates of collision-induced vibrational and intramultiplet transitions for YO(A2II) molecules in Ar- and N2-diluted flames

Rate contants for single-step collisional transitions between specified vibrational and electronic-doublet levels of YO(A²II) molecules were determined under multiple-collision conditions at constant total gas pressure. We recorded simultaneously the thermal emission spectrum and the fluorescence spectra induced by a cw dye laser tuned successively at various vibronic transitions. We used premixed N₂-diluted or Ar-diluted H₂-O₂ flames at 1 atm and = 2350 K, containing YO vapour. Relative rate constants (normalized to the quenching plus radiative de-excitation rate constants) were obtained by solving a set of simultaneous master equations involving the stationary laser-induced population increments. Absolute rate constants were derived therefrom by determining indirectly the fluorescence efficiency. Exoergic doublet-mixing collisions appeared to have greater probabilities than Δv = ?1 or ?2 transitions and were about equally probable as quenching collisions. Ar and N₂ were about equally efficient as collision partner. The rate constants of each process and of its reverse were compared with detailed-balance. The rotational levels in the pumped band appeared to preserve the e/f symmetry index partially.     

Overhauser shift in single crystals of FA2PF6

The shift ΔB_ov of the ESR line due to the saturation of the NMR of hyperfine-coupled nuclei (Overhauser shift) was measured for single crystals of the organic conductor (FA₂)^±PF₆^?. ΔB_ov is proportional to AP, where A is the average hyperfine interaction between the conduction electrons and the nuclei in resonance and P is the dynamic nuclear polarization. The proton spin relaxation times were measured from the time dependence of the Overhauser shift, ΔB_ov(t), after rf pulses.     

Three-dimensional derivative spectrochimatograms in high-performance liquid chromatography and their implications for peak homogeneity validation

The full ultraviolet spectra generated by a photodiode-array detector are transformed to the nth derivative (dⁿA/dλⁿ). The bipolar, three-dimensional data matrix (dⁿA/dλⁿ, λ, t) is presented with computer-aided graphics as an extension of the spectrochromatogram concept to aid peak validation. Existing display algorithms are modified to yield several presentations which reveal the full topography of the elution profile. These include rotation in three-dimensional space and inspection of the positive and negative data planes. A novel contour-plot representation is proposed to enable the derivative spectrochromatographic data to be presented in a two-dimensional format. Two planes of data (i.e., positive and negative amplitudes of (dⁿA/dλⁿ) in the (λ, t) plane) can be displayed as required for derivative data presentation. The technique is used to assess the homogeneity of overlapping peaks of ethynyloestradiol and norethisterone.     

Carbon-13 NMR spectra of retinal1 and its related compounds

Carbon-13 NMR spectra of all-trans retinal₁ and vitamin A₁ were measured by the pulse Fourier transform method in CCl₄. All peaks in these spectra were assigned from considerations of chemical shifts, half proton-decoupled spectra, spin-lattice relaxation times and induced chemical shift by the addition of shift reagent. The carbon-13 NMR spectrum was also measured for all-trans retinal₁ which had been exposed to the sunlight for three hours, and the induced isomer was proposed to be 11-s-cis retinal₁.     

Study on spectroscopic characterization of Pd porphyrin and its interaction with ctDNA

The fluorescence and solid substrate room temperature phosphorescence (SS-RTP) properties of Pd(II) meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (Pd(II)TMPyP) were studied. The factors influencing the SS-RTP emission, such as filter type, inorganic salt sort, drying temperature, pre-drying time and drying time were investigated in detail. Strong SS-RTP signal can be induced on the slow speed filter paper in the presence of the external inorganic salt, Ca(NO₃)₂, with the maximum excitation and emission wavelengths at 421 nm and 675 nm, respectively. The interaction between calf thymus DNA (ctDNA) and Pd(II)TMPyP was investigated at pH 7.2 using SS-RTP, fluorescence and UV-vis spectroscopy. The SS-RTP intensity of Pd(II)TMPyP was enhanced efficiently with the increasing amount of ctDNA. This phenomenon demonstrates that the intercalated porphyrin is shielded by ctDNA to avoid collision quenching. This result was supported by SS-RTP lifetime measurement, SS-RTP anion quenching experiment and fluorescence polarization measurement. Furthermore, with the addition of ctDNA, the UV-vis spectra of Pd(II)TMPyP shows apparent hypochromicity (40%) at the Soret maximum of 417 nm and a red shift of Δλ = 15 nm, also indicating that Pd(II)TMPyP intercalates into ctDNA bases. The binding constant of Pd(II)TMPyP to ctDNA was calculated to be 4.41 × 10⁵ L/mol based on the derivative McGhee-von Hippel plots.     

Photocatalytic inhibitory effect of immobilized TiO2 semiconductor on the growth of Escherichia coli studied by acoustic wave impedance analysis

The effect of immobilized TiO₂ photocatalyst on the growth of Escherichia coli was investigated with acoustic wave impedance (AWI) analysis technique for the first time. The motional resistance variation (ΔR₁) curves under different growth conditions were obtained and compared. By fitting ΔR₁ versus time curves toward the impedance response model, three growth kinetic parameters (A, μ_m and λ) for different growth situations were gained. The results showed the lag time (λ) was prolonged, and the maximum specific growth rate (μ_m) and the asymptote (A) were decreased in the presence of UV light and TiO₂ photocatalyst. In addition, the quantificational relationships between the growth parameters and TiO₂ dosage were also investigated, which reflect the inhibitory effect of TiO₂ under a certain light intensity on the growth of E. coli. The three kinetic growth parameters (A, μ_m and λ) obtained from the impedance response model are close to those obtained from the Gompertz popular growth model. These results showed that the AWI analysis technique adapts to study the effect of TiO₂ photocatalyst on the growth of bacteria on the qualitative and quantificational level.     

Infrared and electronic absorption spectra of some trisubstituted benzenes

The electronic absorption spectra of 2,3-, 2,4-, 2,5-, 2,6- and 3,4-difluorobenzonitriles, 3,4-difluoroaniline and 3,4-difluoroanisole in the ultraviolet region in vapour phase have been recorded on medium quartz and Hilger large quartz spectrographs and on a Hitachi model 150-20 UV-VIS ratio recording spectrophotometer. All the molecules investigated have exhibited two π* ← π band systems corresponding to ¹B_2u ← ¹A_1g (λ2600 Å) and ¹B_1u ← ¹A_1g (λ2100 Å) systems of benzene. The infrared absorption spectra of all the molecules studied have also been recorded and analysed. These infrared data have been taken to help analyse the u.v. spectra of the molecules studied.     

Spectra and structure of organophosphorus compounds—XXXVII. Infrared and Raman spectra,conformational stability,vibrational assignment and normal coordinate analysis of ethyldichlorophosphine-d0 and -d5

The infrared (3500 to 40 cm⁻¹) and Raman (3500 to 10 cm⁻¹) spectra have been recorded for the gaseous and solid phases of ethyldichlorophosphine, CH₃CH₂PCl₂, and CD₃CD₂PCl₂. Additionally, the Raman spectra of the liquids were recorded and qualitative depolarization values were obtained. In the spectrum of the gas the gauche conformer is predominant with about 65% abundance whereas in the spectrum of the liquid at ambient temperature the amount of gauche conformer is reduced compared to the gas phase and at −100°C the trans conformer predominates. The trans conformer is the more stable species in the solid. A variable temperature study was carried out on the Raman spectrum of the liquid and ΔH and ΔS values of 190 ± 30 cm⁻¹ (543 ± 87 cal/mol) and 2.86 ± 0.3 eu were determined, respectively, with the trans conformer being more stable. Similar variable temperature studies have been carried out on a number of conformer peaks in the infrared spectrum of the gas and a ΔH value of 53 ± 38 cm⁻¹ (152 ± 110 cal/mol) was obtained, again with the trans conformer being more stable. All the fundamental modes of both conformers have been assigned utilizing band contours, depolarization values, isotopic shift factors and group frequencies. A normal coordinate calculation has been carried out utilizing a modified valence force field to calculate the frequencies and potential energy distribution for both conformers. The barriers to methyl rotation of the trans and gauche conformers are 2.2 ± 0.1 and 2.3 ± 0.1 kcal/mol, respectively. These results are compared to similar quantities for some corresponding molecules.     

Triphenylamine and quinoline-containing polyfluorene for blue light-emitting diodes

A novel blue light-emitting polyfluorene-based copolymer PTHD containing electron-rich triphenylamine and electron-poor phenylquinoline side chains in the C-9 position of fluorene unit is described. By comparison of the solution and thin film photoluminescence (PL) spectra of PTHD, a considerable red-shift of Δλ = 10-15 nm was observed in the thin film PL spectrum. The emission intensity of the shoulder peak appeared in dilute solution was also significantly enhanced in the thin film. In contrast to the reference polymer poly{[9,9-dihexylfluorene]-alt-[9,9-di(2,4-diphenylquinoline)fluorene]}, PTHD exhibits higher HOMO energy level, and higher maximum brightness with the PLED device configuration of ITO/PEDOT:PSS/polymer_70% + PBD_30%/TPBI/LiF/Al.     

OBSERVATION OF THE PICOSECOND TIME-RESOLVED SPECTRUM OF SQUID BATHORHODOPSIN AT ROOM TEMPERATURE

Difference spectra between squid rhodopsin and its bathorhodopsin at room temperature were measured ca. 150 ps and ca. 500 ps after the excitation at 347.2 nm by a double-beam picosecond time-resolved spectrometer. The spectra measured showed a red shift of the isosbestic point between squid rhodopsin and its bathorhodopsin and a lower ΔA_max/ΔA_min value compared with those measured at low temperatures by conventional spectrophotometry.     

Chemical analysis for small amounts of horseradish peroxidase using “porphyrinogen” as a chromogenic reagent

The properties of porphyrinogen as a new chromogenic reagent were examined. 5,10,15,20-Tetrahydro-tetraphenylporphyrinogen (TPPN) is changed to 5,10,15,20-tetraphenylporphine (TPP) by the oxidative reaction involving six electrons, and its formation of the porphine ring significantly increased the absorbance in the Soret band.The horseradish peroxidase (HRP) accelerated the oxidative reaction as a catalyst and the increment of absorbance depended upon the increase in the concentration of HRP. The reaction proceeded in the presence of dissolved oxygen and in the neighborhood of pH 7. Based on these findings, a chemical analysis by catalytic action using HRP was developed.In the procedure for this determination, the difference in absorbance at 419 nm (ΔA₄₁₉=A_s−A_b, where A_s and A_b are the absorbances of the sample solution containing HRP and the blank solution without HRP after 30 min, respectively), was measured. The determination range of HRP, which was obtained from the ΔA₄₁₉—HRP concentration curve, was 0.05-1.0 mg/l. The relative standard deviation in the median of the calibration curve was 3.19% (seven determinations), and the detection limit (S/N=3) was 29 ng/l. Furthermore, when the proposed method was applied to the enzyme immunoassay, bisphenol A (BPA) was selectively and sensitivity determined.     

Observed adiabatic corrections to the born-oppenheimer approximation for diatomic molecules with ten valence electrons

Using millimeter-wave (mw) spectroscopy pure rotational transitions were measured with very high precision in several vibrational states for many compounds of the group III/VII and IV/VI diatomic molecules. The spectra were fitted to the usual Dunham expansion adopting the normal mass relations for the Y_lk except for Y₀₁ in order to combine all data of different isotopes for the same compound. For Y₀₁ the atomic mass relation given by Watson is used which introduces phenomenological parameters Δ₀₁^A, Δ₀₁^B for molecule AB taking the adiabatic and nonadiabatic corrections to the Born-Oppenheimer approximation into account. All observed spectra are well described by such a procedure. From these calculations the correction parameters Δ₀₁^A, Δ₀₁^B were obtained with an accuracy of ≈ 10% or better. Using known values of the rotational gJ factor and of the electric dipole moment the nonadiabatic part was calculated and with this result the adiabatic part was evaluated from Δ₀₁ for each atom. The adiabatic correction does not change very much for one specific atom by varying the chemical counterpart and in general it is less than 30% of the total correction for this class of molecules. The only exceptions are InI and the Tl and Pb compounds for which the adiabatic corrections are obtained ten to hundred times larger than those of the other compounds. No explanation is known for this behavior in the published literature.     

13C NMR spectral assignment of ribonuclease S-peptide. Some new structural information about its low-temperature folding

The ¹³C NMR spectrum of S-peptide (Ribonuclease 19 residue N-terminal fragment) (pH 5.4, 32°C, 12 mM in D₂O has been assigned with a basis on characteristic values for ¹³C signals of amino acids included in short peptides, SFOR multiplicities, ¹J_CH reduced values and spectral pH variations. The shift vs. temperature changes have been followed in the range 0°C–50°C and the corresponding curves analyzed by using the ΔH° and ΔS° values for the helix-coil transition obtained from ¹H NMR spectra. Values for chemical shifts in the coil and in the helix have been obtained in this way. Transition shifts are largest for CO and C_α resonances in the fragment 3–13, confirming that isolated S-peptide folds in a manner closely ressembling the native structure.     

Highly resolved electron spectra for resonantly enhanced four-photon ionization of no

Electron energy spectra of (2 + 2)-photon ionization of NO are reported. The intermediate resonance is ^A2⁺ and scans are made over the rotational width of u = 0 and 1. A new type of spectrometer is used accepting 2π sr at a resolution of 15 meV. The vibrational distribution peaks at Δ_v = 0 (Franck-Condon for direct ionization) but also at the highest energetically allowed Δ_v. We present evidence for pre-ionization via a dissociative channel.     

High resolution measurement of the3 P 1–3 P 0 transition isotopic shift between24Mg and26Mg

The isotopic frequency shift for the³ P ₁–³ P ₀ Δm _J =0 fine structure transition in the metastable triplet of²⁴Mg and²⁶Mg is reported. The transitions corresponding to the two even isotopes of Mg (λ?498 µm) are observed in a metastable atomic beam through a two-zones Ramsey interaction technique with a transit time limited full width at half maximum of 1.2 kHz (Q=5×10⁸). The isotopic shift turned out to be 1712.5±0.2 kHz.