Change In Absorption Intensity Research Articles

THE EFFECT OF TYPE ZEOLITE ON THE GAS TRANSPORT PROPERTIES OF POLYIMIDE-BASED MIXED MATRIX MEMBRANES

The permeation rates of O2, N2, CO2 and CH4 has been studied for polyimide-polyethersulfone (PI/PES) blends-zeolite mixed matrix membranes synthesized in our laboratory. The study investigated the effect of zeolite loading and different zeolite type on the gas separation performance of these mixed matrix membranes. Frequency shifts and absorption intensity changes in the FTIR spectra of the PI/PES blends as compared with those of the pure polymers indicate that there is a mixing of polymer blends at the molecular level. Differential scanning calorimetry measurements of pure and PI/PES blends membranes have showed one unique glass transition temperature that supports the miscible character of the PI/PES mixture. The PI/PES-zeolite 4A mixed matrix membrane with 25 wt % zeolite loading produced the highest O2/N2 and CO2/CH4 selectivity of around 7.45 and 46.05, respectively.

Characterization of Alq3 thin films by a near-field microwave microprobe

We observed tris-8-hydroxyquinoline aluminum (Alq3) thin films dependence on substrate heating temperatures by using a near-field microwave microprobe (NFMM) and by optical absorption at wavelengths between 200 and 900 nm. The changes of absorption intensity at different substrate heating temperatures are correlated to the changes in the sheet resistance of Alq3 thin films.

Distributions of copper and CuBr in CuBr nanocrystallite-dispersed glasses prepared by copper staining

CuBr nanocrystallite-dispersed glasses were prepared by incorporation of copper into bromide ion-containing borosilicate glass using the technique of copper staining. The copper ion incorporation process was mainly controlled by ionic diffusion from the surface to the interior of the glass. The depth profiles of Cu and CuBr concentration were examined by energy dispersive X-ray analysis and by reference to the change in absorption intensity assigned to the CuBr exciton band along the depth. While the Cu concentration was found to decrease monotonically, the CuBr concentration profile showed a maximum at a distance of 10–50μm from the glass surface. Although the depth reached by the copper ions became greater with increasing heat-treatment time, the depth at which CuBr was precipitated was found to be saturated. This means that regions were found in the glasses in which no CuBr crystallites precipitated, although migration of Cu ions to these regions had taken place.

Color centers in Yb:YAG crystals grown by temperature-gradient techniques

Yb:YAG (Yb:Y3Al5O12) crystals have been grown by temperature-gradient techniques (TGT) and their color centers and impurity defects were investigated by means of gamma irradiations and thermal treatment. Two color centers located at 255 and 290 nm were observed in the as-grown TGT-Yb:YAG. Analysis shows that the 255 nm band may be associated with Fe3+ ions. Absorption intensity changes of the 290 nm band after gamma irradiation and thermal treatment indicate that this band may be associated with oxygen-vacancy defects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Quantitative Analyses of Absorption-Sensitive Surface Plasmon Resonance Near-Infrared Spectra

Surface plasmon resonance near-infrared (SPR-NIR) spectroscopy provides 10-100 times absorption enhancement compared with the absorption in the corresponding attenuated total reflection (ATR) NIR spectra. However, analysis of the enhanced SPR-NIR spectra is not straightforward because of the substantial contribution from SPR. This paper proposes two analysis methods for concentration-dependent changes of SPR-NIR spectra from a viewpoint of change in absorption intensity. One is based on rapid scans of the SPR-NIR spectra with a fixed incident angle, and the other is based on multi-angle sequential scans. A concentration of methanol in water has successfully been determined by both methods. From the measurement of the light intensity within an absorption band of water (5230-5120 cm(-1)) at a fixed incident angle, the concentration was calibrated to an accuracy of 0.02 wt. %. In the latter multi-angle method, it has been proved that computed bottom ridges of the envelope curve of the SPR-NIR spectra are not only enhanced 30 times compared with the corresponding ATR-NIR spectra, but are also equivalent to the conventional transmittance NIR spectra in quality. The bottom ridges allow us to analyze SPR-NIR spectra in the same manner as conventional spectral analyses based on Beer's law.

Investigation of optical properties of Ce3+-doped Gd2SiO5 crystal irradiated by a femtosecond laser

We report on the optical property changes for Ce3+-doped Gd2SiO5 crystal irradiated by a femtosecond (fs) laser. Absorption spectra showed that Ce-related color centers were formed in this crystal after an 800nm fs laser irradiation. The annealing temperature-dependence of the refractive index and absorption intensity changes have been investigated. Furthermore, a new way of writing overlapped gratings inside the crystal by use of birefringence of fs laser beam in this crystal was proposed.

Time-Dependent Density Functional Theory Investigation of Electric Field Effects on Absorption Spectra of Meso−Meso-Linked Zinc Porphyrin Arrays: Role of Charge-Transfer States

By using time-dependent density functional theory, we calculated the transition energies of a zinc porphyrin monomer and its meso-meso-linked arrays. In line with the prediction of the molecular exciton model, the calculated splitting energy of the Soret band increased as the number of linked porphyrins increased. We then examined how the transition energies of the dimer array were shifted by an applied electric field. For reproduction of an electroabsorption spectrum (EA), i.e., the field-induced change in absorption intensity, a model Hamiltonian constructed from five states is proposed. It is concluded for the dimer that the field-induced coupling between the lower-energy Soret band Se and the lower-lying ionic character (charge-transfer) states is responsible for the experimentally observed blue shift of Se as well as the second-derivative profile in the EA spectrum.

Surface‐enhanced resonance Raman scattering using pulsed and continuous‐wave laser excitation

AbstractPulsed and continuous‐wave (CW) lasers were compared as excitation sources for surface‐enhanced resonance Raman scattering (SERRS). CW excitation provided SERRS spectra with a greater signal‐to‐noise ratio and more sensitive detection by a factor of ∼50 compared with the high peak power, low repetition rate pulsed configuration used. The SERRS intensity using a pulsed laser produced a non‐linear response with respect to changes in power of the laser. At powers of less than ∼0.012 mW, the absolute intensity under the peaks of the CW and pulsed SERRS spectra converged, suggesting that lower peak power, high repetition rate systems may be more effective excitation sources for SERRS. Transmission electron microscopy of pulsed laser‐irradiated silver particles showed significant sample damage and morphological changes. This problem was overcome with the use of a recirculating large‐volume flow cell system, providing a fresh sample for each measurement. A picosecond‐resolved time delay experiment found that SERRS intensity decreased by ∼60% when exposed to a 400 nm pump pulse and probed with a 529 nm pulse. As the time delay between pump and probe increased the system recovered gradually to ∼60% of the original SERRS intensity after 50 ps, where it remained constant. This suggests that the surface bonding between the silver and the dye is significantly perturbed, with some nanoscale diffusion occurring of the dye away from the metal surface. Hence chemical enhancement is temporarily prevented and electromagnetic enhancement is reduced as a function of 1/r3 as the dye moves away from the surface. Additionally, transient heating of the colloidal particles caused by the pulsed laser may also lead to plasmon shifts and changes in absorption intensity. Other factors such as surface annealing or decomposition of the silver particle or dye due the extreme temperature conditions may account for the permanent loss in SERRS intensity. Copyright © 2005 John Wiley & Sons, Ltd.

Cytochrome b5 Reductase: Role of the si-Face Residues, Proline 92 and Tyrosine 93, in Structure and Catalysis

The conserved sequence motif "RxY(T)(S)xx(S)(N)" coordinates flavin binding in NADH:cytochrome b(5) reductase (cb(5)r) and other members of the flavin transhydrogenase superfamily of oxidoreductases. To investigate the roles of Y93, the third and only aromatic residue of the "RxY(T)(S)xx(S)(N)" motif, that stacks against the si-face of the flavin isoalloxazine ring, and P92, the second residue in the motif that is also in close proximity to the FAD moiety, a series of rat cb(5)r variants were produced with substitutions at either P92 or Y93, respectively. The proline mutants P92A, G, and S together with the tyrosine mutants Y93A, D, F, H, S, and W were recombinantly expressed in E. coli and purified to homogeneity. Each mutant protein was found to bind FAD in a 1:1 cofactor:protein stoichiometry while UV CD spectra suggested similar secondary structure organization among all nine variants. The tyrosine variants Y93A, D, F, H, and S exhibited varying degrees of blue-shift in the flavin visible absorption maxima while visible CD spectra of the Y93A, D, H, S, and W mutants exhibited similar blue-shifted maxima together with changes in absorption intensity. Intrinsic flavin fluorescence was quenched in the wild type, P92S and A, and Y93H and W mutants while Y93A, D, F, and S mutants exhibited increased fluorescence when compared to free FAD. The tyrosine variants Y93A, D, F, and S also exhibited greater thermolability of FAD binding. The specificity constant (k(cat)/K(m)(NADH)) for NADH:FR activity decreased in the order wild type > P92S > P92A > P92G > Y93F > Y93S > Y93A > Y93D > Y93H > Y93W with the Y93W variant retaining only 0.5% of wild-type efficiency. Both K(s)(H4NAD) and K(s)(NAD+) values suggested that Y93A, F, and W mutants had compromised NADH and NAD(+) binding. Thermodynamic measurements of the midpoint potential (E degrees ', n = 2) of the FAD/FADH(2) redox couple revealed that the potentials of the Y93A and S variants were approximately 30 mV more positive than that of wild-type cb(5)r (E degrees ' = -268 mV) while that of Y93H was approximately 30 mV more negative. These results indicate that neither P92 nor Y93 are critical for flavin incorporation in cb(5)r and that an aromatic side chain is not essential at position 93, but they demonstrate that Y93 forms contacts with the FAD that effectively modulate the spectroscopic, catalytic, and thermodynamic properties of the bound cofactor.

Synthesis of bipyridine polymer linked with cyanostyryl groups for colorimetric and fluorescent anion sensing

We have synthesized a novel conjugated polymer composed of bipyridine and cyanostyryl groups. The polymer solution in DMF exhibited absorption maximum at 404 nm and emission maximum at 535 nm. Once the polymer in DMF solution was added a hydroxide anion, UV-visible and fluorescence spectra exhibited considerable changes in absorption intensity, absorption wavelength, and emission intensity. These optical changes of polymer solution with hydroxide anion show potential application in chemosensory material for anion.

Heterogeneous photocatalysed degradation of a herbicide derivative, isoproturon in aqueous suspension of titanium dioxide

Heterogeneous photocatalysed degradation of a herbicide derivative, N-(4-isopropylphenyl)- N′, N′-dimethylurea (Isoproturon, 1) was investigated in aqueous suspensions of titanium dioxide by monitoring the change in absorption intensity and depletion in Total Organic Carbon content as a function of irradiation time. The degradation kinetics was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO 2 and in the presence of electron acceptors such as hydrogen peroxide (H 2O 2), potassium bromate (KBrO 3) and potassium persulphate (K 2S 2O 8) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts. An attempt was made to identify the degradation product through GC-MS analysis technique.

Semiconductor mediated photocatalysed degradation of an anthraquinone dye, Remazol Brilliant Blue R under sunlight and artificial light source

Semiconductor mediated photocatalysed degradation of an anthraquinone dye Remazol Brilliant Blue R under sunlight and artificial light source has been investigated in aqueous suspensions of titanium dioxide by monitoring the change in absorption intensity as a function of irradiation time under a variety of conditions. The degradation kinetics were studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO 2 and in the presence of electron acceptors such as hydrogen peroxide (H 2O 2), potassium bromate (KBrO 3) and ammonium persulphate (NH 4) 2S 2O 8 besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient under UV light, whereas Hombikat UV100 was better under sunlight as compared with other photocatalysts. The degradation products were analysed by GC–MS technique and probable pathways for the formation of products are proposed.

A theoretical investigation of the structure and vibrational frequencies of CH3CN–BF3 and CH3CN–BCl3

Ab initio calculations have been performed at MP2/6-31+G(2d,p) level to study the structures, vibrational frequencies, binding energies, and barriers to internal rotation of the complexes, CH3CN–BF3 and CH3CN–BCl3. Internal rotation of the complexes is predicted to be essentially barrierless. The vibrational frequencies and force constants of the complexes have been calculated and compared with experimental values, including those of CH3CN. The force constants are later used to calculate the frequencies of other isotopomers. The large frequency changes of the CN and C–C stretches upon complexation are well reproduced. The distinctive hypsochromic shift of the CN stretch of the complex is originated from the increase in force constant, whereas the frequency shift of the C–C stretch from the change in vibrational coupling upon complexation. The CN stretch also shows a dramatic change in absorption intensity due to higher charge separation in the complex. The shorter N–B bond length and higher stretch frequency of CH3CN–BCl3 along with the higher binding energy indicate that BCl3 is a more effective electron pair acceptor than BF3.

Electric field effects on absorption and fluorescence spectra of pyrene doped in a PMMA polymer film

Electric field modulated absorption, fluorescence and fluorescence excitation spectra of pyrene doped in a PMMA polymer film were measured with excitation from 220 to 380 nm. The observed spectra of the field-induced change in absorption intensity or fluorescence intensity for each electronic transition agree well with the first derivatives of the corresponding absorption or fluorescence spectrum, indicating that the field effect results from the Stark shift induced by a change in molecular polarizability between the ground state and the excited state. The magnitude of the change in polarizability was evaluated for the first, S 1( 1L b), the second, S 2( 1B a), the third, S 3( 1B b), and the fourth, S 4( 1L a), optically spin-allowed absorption bands. The change in average polarizability following excitation is found to be in the order of S 1<S 4<S 3<S 2, and all the polarizabilities in the excited states are larger than in the ground state. The third nonlinear order susceptibility ( χ (3)) of a pyrene-doped PMMA film was also calculated on the basis of the electroabsorption and electrofluorescence excitation spectra.

Dynamic Infrared Linear Dichroic Spectra of Prestretched Polypropylene

DIRLD (dynamic infrared linear dichroic) spectra of prestretched isotactic polypropylene have been recorded. The line shape features in the in-phase spectra are described on the basis of frequency shifts and absorption amplitude variations during the stretching cycle. Details such as the dichroism of the bands, direction of the shift, and changes in the absorption intensities must be considered to explain signs and shapes of the DIRLD bands. Evidence for chain reorientations under stress has not been found. The general principle of frequency shifts and changes in absorption intensities as the origin of DIRLD bands is demonstrated by spectral simulations.

Gas permeation through PSF-PI miscible blend membranes

The permeation rates of He, H 2, CO 2, N 2 and O 2, are reported for a series of miscible polysulfone-polyimide (PSF-PI) blend membranes synthesized in our laboratory. For gases which do not interact with the polymer matrix (such as He, H 2, N 2 and O 2), gas permeabilities in the miscible blends vary monotonically between those of the pure polymers and can be described by simple mixture equations. In the case of CO 2, which interacts with PI, blend permeabilities decrease somewhat, compared to pure PSF and PI. This, however, is accompanied by a two-fold improvement in the critical pressures of plasticization vs. polyimide. Permselectivities of CO 2 N 2 and H 2 CO 2 in the blends deviate from mixing theory predictions, in contrast to selectivities of gas pairs which do not interact with PI. Differential scanning calorimetry measurements of pure and PSF/PI blend membranes show one unique glass transition temperature, supporting the miscible character of the PSF/PI mixture. Optical micrographs of the blend membranes clearly indicate perfect homogenization and no phase separation. Frequency shifts and absorption intensity changes in the FTIR spectra of the blends, as compared with those of the pure polymers, indicate mixing at the molecular level. This compatibility in mixing PSF and PI, results essentially in a new blend polymer material, suitable for the preparation of gas separation membranes. Such membranes combine satisfactory gas permeation properties, reduced cost, advanced resistance to harsh chemical and temperature environments, and improved tolerance to plasticizing gases.

Mechanism of Redox Reaction on Polypyrrole

A concentration of bipolarons in doped polypyrrole (PPy) decreases on elec trochemical reduction at an early stage while that of polarons increases. Further reduction increases the absorption intensity at 800 nm on expense of the peak intensity at 550 nm. Prolonged reduction produces a strong absorption at 400 nm and diminishes the intensities both at 550 nm and 800 nm. The trend of changes in absorption intensity at 800 nm repeats when the reduction system is fixed to pH = 3 by adding acetic acid. However, adding 0.01 mol of hydroquinone in the system lowers monotonically the absorption intensity at 800 nm on reduction. Cyclic voltammograms of the PPy change little after 7,000 cycles if hydroquinone is added to the system. Polarons are so reactive that PPy transforms into irreversible changes in the structure on the reduction process and the reactivity is retarded by adding hydroquinone in the system.

Intensity enhancement of symmetry forbidden transitions in solid solutions of benzene and naphthalene

Intensity enhancement of symmetry forbidden transitions in solid solutions of benzene and naphthalene has been measured at various temperatures. The effect, which consists essentially in allowing electronically forbidden transitions as a result of intermolecular interactions is attributed to two factors: ‘self-borrowing’ and ‘solvent borrowing’. Their relative contribution depends on the site symmetry of the solvent, thus explaining the marked intensity change in absorption of the ‘forbidden bands’ observed in phase transitions. ‘Forbidden bands’ were detected in the 1 A 1 g → 1B 2 u transition and not in the 1 A 1 g → 1B 1 u transition and a qualitative explanation for this difference is presented.

Dimer formation of bromocresol purple anions on the phosphorylated intermediate of sarcoplasmic reticulum.

The mechanism of spectral shift and absorption intensity change of the divalent bromocresol purple (BCP) anion was further investigated and it was characterized as a spectrophotometric membrane probe. At high concentrations (1-40 mM), the absorption intensity of th BCP anion at 590 nm (monomer band) decreased markedly with increase of the dye concentration, while another absorption band appeared at 554 nm. Analysis of the change of absorption intensity showed that the mared decrease resulted from dimer formation of BCP (polymer formation at concentrations higher than 20 mM). Wavelengths of maximum absorption (lambdamax) of the BCP anion were determined in various solvents and comparison of these lambdamax's with lambdamax of the BCP anion bound to SR showed that the hydrophobicity of the area of BCP anion binding to SR corresponded to a refractive index of 1.429. While the BCP anion bound to SR showed a monomer spectrum, a dimer band appeared for the BCP anion bound to SR-Pi (phosphorylated protein) with a marked decrease in the absorption intensity at the monomer band, indicating that two polar groups, binding sites for the BCP anions, closely approached each other in the SR-Pi configuration.

Two Types of Sarcoplasmic Reticulum-Orthophosphate Interactions Observed with Dye Probe1

The interaction of Pi with sarcoplasmic reticulum (SR) isolated from rabbit skeletal muscle was studied using bromocresol purple (BCP) as a probe and a dual-wavelength spectrophotometer. Two kinds of absorption-intensity changes controlled by a low concentration of Ca2+ (greater than 10(-6)M) were observed after addition of Pi; an increase phase (in the presence of Ca2+), and a decrease phase (in the presence of EGTA). The increase phase was rapid, Ca2+-dependent, Mg2+-enhanced (depressed by high Mg2+ concentration) and not inhibited by PCMB and was suggested to reflect the formation of an SR-Pi complex. The decrease phase was slower than the increase phase, and was strongly inhibited by the low concentration of Ca2+. It required Mg2+, and was completely inhibited by p-chloromercuribenzoate or deoxycholate. It was suggested to reflect the formation of SR-Pi (phosphorylated protein). ATP inhibited this phase by converting it completely to an SR-MgATP phase. PPi was effective for inducing the decrease phase but PPPi was not. From measurements of these phases, the association constants of the SR-Pi complex and SR-Pi at pH 8.8 in the reaction scheme, SR + Pi in equilibrium SR-Pi in equilibrium SR-Pi, were calculated as 5.4 X 10 M-1 and 1.8 X 10(3) M-1, respectively. From the completely different responses of SR-Pi and SR-Pi observed with BCP a marked difference in the conformations of these enzyme states was suggested.