Absorption Spectra Of CO Research Articles

Optical absorption spectra of substitutional Co 2+ ions in Mg x Cd 1– x Se alloys

Optical absorption spectra of substitutional Co2+ ions in Mgx Cd1–x Se alloys were investigated in the composition region of 0.0 ≤ x ≤ 0.4 and in the wavelength region of 300 to 2500 nm at 4.8 K and 290 K. We observed several absorption bands in the wavelength regions corresponding to the 4A2(4F) → 4T1(4P) transition and the 4A2(4F) → 4T1(4F) transition of Co2+ at a tetrahedral Td point symmetry point in the host crystals, as well as unknown absorption bands. The several absorption bands were analyzed in the framework of the crystal-field theory along with the second-order spin-orbit coupling. The unknown absorption bands were assigned as due to phonon-assisted absorption bands. We also investigated the variations of the crystal-field parameter Dq and the Racah parameter B with composition x in the Mgx Cd1–x Se system. The results showed that the crystal-field parameter (Dq ) increases, on the other hand, the Racah parameter (B ) decreases with increasing composition x, which may be connected with an increase in the covalency of the metal-ligand bond with increasing composition x in the Mgx Cd1–x Se system. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The detection of carbon monoxide by cavity enhanced absorption spectroscopy with a DFB diode laser

It has been proven that cavity enhanced absorption spectroscopy is a high sensitive spectral technique. The aim of our study was to apply this spectral technique to the detection of carbon monoxide with a narrow line width tunable DFB diode laser and high Q factor optical cavity. Absorption signals were extracted from a measurement recording the average of 20 highest light intensities that leak out of the cavity. The absorption spectrum of CO centered at 6354.18 cm −1 was recorded; the experiment results indicate that cavity enhanced absorption spectroscopy could produce accurate high resolution spectrum. A detection sensitivity about 5.687 × 10 −7 cm −1 has been achieved in a 45 cm-long cell.

A Zinc(II)/Lead(II)/Cadmium(II)-Inducible Operon from the Cyanobacterium Anabaena Is Regulated by AztR, an α3N ArsR/SmtB Metalloregulator

A novel Zn(II)/Pb(II)/Cd(II)-responsive operon that consists of genes encoding a Zn(II)/Pb(II) CPx-ATPase efflux pump (aztA) and a Zn(II)/Cd(II)/Pb(II)-specific SmtB/ArsR family repressor (aztR) has been identified and characterized from the cyanobacterium Anabaena PCC 7120. In vivo real time quantitative RT-PCR assays reveal that both aztR and aztA expression are induced by divalent metal ions Zn(II), Cd(II), and Pb(II) but not by other divalent [Co(II), Ni(II)] or monovalent metal ions [Cu(I) and Ag(I)]. The introduction of a plasmid containing the azt operon into a Zn(II)/Cd(II)-hypersensitive Escherichia coli strain GG48 functionally restores Zn(II) and Pb(II) resistance with a limited effect on Cd(II) resistance. Gel mobility shift assays and aztR O/P-lacZ induction experiments confirm that AztR is the metal-regulated repressor of this operon. In vitro biochemical and mutagenesis studies indicate that AztR contains a sole metal-binding site, designated the alpha3N site, that binds Zn(II), Cd(II), and Pb(II) with a high affinity. Optical absorption spectra of Co(II)- and Cd(II)-substituted AztR and (113)Cd NMR spectroscopy of (113)Cd(II)-substituted AztR reveal that the sole alpha3N site in AztR is a CadC-like distorted tetrahedral S(3)(N,O) metal site. The first metal-coordination shell in the AztR alpha3N site differs from other alpha3N family members that sense Cd(II)/Pb(II) and those alpha5 repressors that sense Zn(II)/Co(II). Our results reveal that the alpha3N site in AztR mediates derepression of the azt operon in the presence of Zn(II), as well as Cd(II) and Pb(II); this might have provided Anabaena with an evolutionary advantage to adapt to heavy-metal-rich environments, while maintaining homeostasis of an essential metal ion, Zn(II).

Proton transfer from exogenous donors in catalysis by human carbonic anhydrase II

In the site-specific mutant of human carbonic anhydrase in which the proton shuttle His64 is replaced with alanine, H64A HCA II, catalysis can be activated in a saturable manner by the proton donor 4-methylimidazole (4-MI). From 1H NMR relaxivities, we found 4-MI bound as a second-shell ligand of the tetrahedrally coordinated cobalt in Co(II)-substituted H64A HCA II, with 4-MI located about 4.5 Å from the metal. Binding constants of 4-MI to H64A HCA II were estimated from: (1) NMR relaxation of the protons of 4-MI by Co(II)-H64A HCA II, (2) the visible absorption spectrum of Co(II)-H64A HCA II in the presence of 4-MI, (3) the inhibition by 4-MI of the catalytic hydration of CO 2, and (4) from the catalyzed exchange of 18O between CO 2 and water. These experiments along with previously reported crystallographic and catalytic data help identify a range of distances at which proton transfer is efficient in carbonic anhydrase II.

Temperature dependence of the polarized electronic absorption spectra of olivines. Part II?Cobalt-containing olivines

Polarized electronic absorption spectra of single crystalline Co2[SiO4] and (Co0.64Mg0.36)2[SiO4] (E|| a (|| Z), E || b (|| X), E || c (|| Y)) have been studied in the temperature range 293 ≤ T/K ≤ 1273. The three polarized spectra show a total of 15 bands. Five bands are caused by spin-allowed transitions in Co2+ ions at M1 sites which appear in all polarization directions. Seven polarization-dependent bands can be ascribed to spin-allowed transitions in Co2+ ions at M2 sites and three bands may be assigned to spin-forbidden transitions. The assignment of bands due to Co2+ ions at M1 and M2 sites has been made on the basis of transition energies and intensity ratios. Further arguments have been derived from the comparison of spectra of crystals with different cobalt content, from the analysis of the polarization dependence of the spectra, and from the evolution of band intensities with temperature.

Cobalt(II) Chloride Complex Formation in Acetamide–Calcium Nitrate Tetrahydrate Melts

The absorption spectra of Co(II) chloride complexes, containing variable concentrations of chloride ligand, in a molten mixture of 80 mol% acetamide–20 mol% calcium nitrate tetrahydrate, were studied at 313, 333, 353, and 363 K, in the wavelength range 400-800 nm. The melt contains three possible ligands (CH3CONH2, H2O, and NO3 -) for competition with added chloride ligand. Addition of chloride caused a shift of the absorption maximum of octahedral cobalt(II) nitrate towards lower energies and pronounced changes in the shape of the initial spectrum of cobalt(II) nitrate. The effect of temperature changes on the molar absorption coefficient of the Co(II) species was dependent on the chloride concentration and was attributed to the structural changes occurring in the cobalt(II) species. The STAR and STAR FA programs were applied to identify the complex ionic species and to calculate the stability constants of Co(II) complexes formed in this solvent. The results indicate the highest probability of formation of the following complex species: Co(NO3)4 2-, Co(NO3)2Cl2 2-, and CoCl4 2-. Stability constants of each complex were presented for the equilibria occurring at 313, 333, 353, and 363 K. Distribution of the Co(II) species was also calculated over the ranges of chloride concentration and temperature investigated.

Electronic absorption spectrum and low-lying electronic states of Co2 isolated in solid neon

We report electronic absorption spectra in the mid-, near infrared and visible regions for cobalt dimers isolated in neon matrices. In addition to the already reported transition near 2.8 eV and above, ten states can be observed spanning a wide energy range from 0.068 to 2.49 eV. For four excited states in the IR range and two states in the visible, analysis of the vibronic systems leads to estimates of electronic energies, vibrational parameters and bond length variations. The data are compared to results of photodetachment experiments and recent theoretical predictions.

Theoretical Investigation of Infrared Spectra and Pocket Dynamics of Photodissociated Carbonmonoxy Myoglobin

Molecular dynamics simulations of the photodissociated state of carbonmonoxy myoglobin (MbCO) are presented using a fluctuating charge model for CO. A new three-point charge model is fitted to high-level ab initio calculations of the dipole and quadrupole moment functions taken from the literature. The infrared spectrum of the CO molecule in the heme pocket is calculated using the dipole moment time autocorrelation function and shows good agreement with experiment. In particular, the new model reproduces the experimentally observed splitting of the CO absorption spectrum. The splitting of 3–7 cm −1 (compared to the experimental value of 10 cm −1) can be directly attributed to the two possible orientations of CO within the docking site at the edge of the distal heme pocket (the B states), as previously suggested on the basis of experimental femtosecond time-resolved infrared studies. Further information on the time evolution of the position and orientation of the CO molecule is obtained and analyzed. The calculated difference in the free energy between the two possible orientations (Fe···CO and Fe···OC) is 0.3 kcal mol −1 and agrees well with the experimentally estimated value of 0.29 kcal mol −1. A comparison of the new fluctuating charge model with an established fixed charge model reveals some differences that may be critical for the correct prediction of the infrared spectrum and energy barriers. The photodissociation of CO from the myoglobin mutant L29F using the new model shows rapid escape of CO from the distal heme pocket, in good agreement with recent experimental data. The effect of the protein environment on the multipole moments of the CO ligand is investigated and taken into account in a refined model. Molecular dynamics simulations with this refined model are in agreement with the calculations based on the gas-phase model. However, it is demonstrated that even small changes in the electrostatics of CO alter the details of the dynamics.

Kinetic and spectroscopic characterization of the H178A methionyl aminopeptidase from Escherichia coli.

To gain insight into the role of the strictly conserved histidine residue, H178, in the reaction mechanism of the methionyl aminopeptidase from Escherichia coli (EcMetAP-I), the H178A mutant enzyme was prepared. Metal-reconstituted H178A binds only one equivalent of Co(II) or Fe(II) tightly with affinities that are identical to the WT enzyme based on kinetic and isothermal titration calorimetry (ITC) data. Electronic absorption spectra of Co(II)-loaded H178A EcMetAP-I indicate that the active site divalent metal ion is pentacoordinate, identical to the WT enzyme. These data indicate that the metal binding site has not been affected by altering H178. The effect of altering H178 on activity is, in general, due to a decrease in k(cat). The k(cat) value for Co(II)-loaded H178A decreased 70-fold toward MGMM and 290-fold toward MP-p-NA compared to the WT enzyme, while k(cat) decreased 50-fold toward MGMM for the Fe(II)-loaded H178A enzyme and 140-fold toward MP-p-NA. The K(m) values for MGMM remained unaffected, while those for MP-p-NA increased approximately 2-fold for Co(II)- and Fe(II)-loaded H178A. The k(cat)/K(m) values for both Co(II)- and Fe(II)-loaded H178A toward both substrates ranged from approximately 50- to 580-fold reduction. The pH dependence of log K(m), log k(cat), and log(k(cat)/K(m)) of both WT and H178A EcMetAP-I were also obtained and are identical, within error, for H178A and WT EcMetAP-I. Therefore, H178A is catalytically important but is not required for catalysis. Assignment of one of the observed pK(a) values at 8.1 for WT EcMetAP-I was obtained from plots of molar absorptivity at lambda(max(640)) vs pH for both WT and H178A EcMetAP-I. Apparent pK(a) values of 8.1 and 7.6 were obtained for WT and H178A EcMetAP-I, respectively, and were assigned to the deprotonation of a metal-bound water molecule. The data reported herein provide support for the key elements of the previously proposed mechanism and suggest that a similar mechanism can apply to the enzyme with a single metal in the active site.

Experimental verification of gas spectra calculated for high temperatures using the HITRAN/HITEMP database

The knowledge of absorption coefficients of the gases CO, CO2 and H2O at high temperatures is important for the in situ determination of the concentration of these gases in combustion system. These coefficients can be calculated using molecular data form the HITRAN database. The 1996 edition of this database contains a special high temperature database for CO, CO2 and H2O. Based on these data absorption coefficients and spectra of CO, CO2 and H2O have been calculated for different concentrations and temperatures. Additionally, measurements were carried out using a high temperature calibration gas cell and in situ Fourier transform infrared spectroscopy absorption spectroscopy. A comparison between the spectra calculated and measured showed a good agreement. At temperatures of 1100°C large deviations between these results of theory and experiment could be found for certain spectral regions of CO2. Based on these results the measuring system was used for the quantitative analysis of the combustion gases in a pilot-scale horizontally moving grate furnace as well as in a laboratory scale furnace using wood chips, waste wood and fibreboard as fuels.

Far-infrared broadband measurements with Hilbert spectroscopy

A principal possibility of broadband far-infrared (FIR) spectral measurements with Hilbert-transform technique, based on ac Josephson effect, has been experimentally studied. High-pressure 200 W mercury arc lamp was used as a source of FIR broadband radiation. The grain-boundary YBaCuO thin-film Josephson junctions (JJ) with the normal-state resistance R n =1–3 Ω and the I c R n-product up to 1 mV were used in the experiments. Broadband spectra with different FIR mesh-type filters have been measured by this technique. First results on the detection of gas absorption spectra in FIR range with Hilbert spectroscopy (HS) were obtained. Several lines of CO absorption spectrum in the range from 300 up to 1000 GHz have been resolved, when broadband blackbody radiation passed through a gas cell.

X α –DV Modeling of Photoionization and Electronic Absorption Spectra of Cobalt tris –Acetylacetonate

Ionization energies, excited state energies, and oscillator strengths of electron–dipole transitions are calculated within the framework of the SCF–Xα–DV quantum–chemical model of the Co(HCOCHHCO)3 model complex in order to interpret the photoionization and electronic absorption spectra of cobalt tris–β–diketonate. It is shown that the sequences of ionization and excitation energies calculated in the transition state approximation do not significantly differ from the sequence of energies estimated in the frozen MO approximation. The model absorption spectrum with a correction of 1.9 eV applied to the energy of the vacant π4 * orbital is in good agreement with our gas–phase absorption spectrum of Co(acac)3.

Characterization of the metal-substituted dipeptidyl peptidase III (rat liver).

Dipeptidyl peptidase III (DPP III) (EC 3.4.14.4), which has a HELLGH-E (residues 450-455, 508) motif as the zinc binding site, is classified as a zinc metallopeptidase. The zinc dissociation constants of the wild type, Leu(453)-deleted, and E508D mutant of DPP III at pH 7.4 were 4.5 (+/-0.7) x 10(-13), 5.8 (+/-0.7) x 10(-12), and 3.2 (+/-0.9) x 10(-10) M, respectively. The recoveries of the enzyme activities by the addition of various metal ions to apo-DPP III were also measured, and Co(2+), Ni(2+), and Cu(2+) ions completely recovered the enzyme activities as did Zn(2+). The dissociation constants of Co(2+), Ni(2+), and Cu(2+) ions for apo-DPP III at pH 7.4 were 8.2 (+/-0.9) x 10(-13), 2.7 (+/-0.3) x 10(-12), and 1.1 (+/-0.1) x 10(-14) M, respectively. The shape of the absorption spectrum of Co(2+)-DPP III was very similar to that of Co(2+)-carboxypeptidase A or Co(2+)-thermolysin, in which the Co(2+) is bound to two histidyl nitrogens, a water molecule, and a glutamate residue. The absorption spectrum of Cu(2+)-DPP III is also very similar to that of Cu(2+)-thermolysin. The EPR spectrum and the EPR parameters of Cu(2+)-DPP III were very similar to those of Cu(2+)-thermolysin but slightly different from those of Cu(2+)-carboxypeptidase A. The five lines of the superfine structure in the perpendicular region of the EPR spectrum in Cu(2+)-DPP III suggest that nitrogen atoms should coordinate to the cupric ion in Cu(2+)-DPP III. All of these data suggest that the donor set and the coordination geometry of the metal ions in DPP III, which has the HExxxH motif as the metal binding site, are very similar to those of the metal ions in thermolysin, which has the HExxH motif.

Infrared studies of CO2 doped Xe solutions in gas, liquid and solid phases. The fundamental ν3 band and the Coriolis perturbed Fermi doublet (ν1+ν21, ν1+ν211)

The IR absorption spectra of CO2 doped Xe solutions have been recorded in the range of the fundamental ν3(Σu) band and of the Coriolis perturbed ν1+ν21, ν1+ν211(πu) Fermi doublet (ν1+ν2≈3ν2) in gas, liquid and solid phases. The characteristic transformation and rapid narrowing of the ν3 band, observed in the gas to liquid phase transition, shows marked hindering of the rotational motion of the CO2 molecule in dense Xe mixtures. It was found that the liquid to solid phase transition is accompanied by noticeable broadening of the ν3 band. The rotational motion of CO2 is not frozen in solid Xe at least near the freezing point. This is in contrast with sharp narrowing of the vibrational bands and so with blocking up rotations in the case of a heavier CS2 guest in the solid Xe host just below the freezing point. The intensity ratio A(ν1+ν21)/A(ν1+ν211) of the Coriolis perturbed ν1+ν21, ν1+ν211 doublet reveals the noticeable increase from 8±1 in a low density gas to 18±2 in the liquid phase. The results obtained suggest remarkable modification of the second-order Coriolis coupling in the case of CO2 doped dense liquid Xe.

Superposition model analysis from polarized electronic absorptionspectra of Co2+ in trigonally distorted octahedra in brucite-typeCo(OH)2

Polarized electronic absorption spectra of Co2+ in trigonally compressedoctahedra in brucite-type Co(OH)2 have been measured at 290 and 90 K bymicroscope-spectrometric techniques and analysed in terms of the superpositionmodel (SM) of crystal fields. The resulting SM and interelectronic repulsionparameters are B̄4 = 5260, B̄2 = 4920, Racah B = 825, Racah C = 3550 cm-1 at 290 K andB̄4 = 5320, B̄2 = 3900, Racah B = 830,Racah C = 3500 cm-1 at 90 K (R0 = 2.1115 Å; fixed exponentialand spin-orbit parameters t4 = 5, t2 = 3, ζ = 500 cm-1). Togetherwith a recent SM analysis of Li2Co3(SeO3)4, theB̄krefined for Co(OH)2 further confine the magnitude of the hitherto unknown`correct' SM parameters of Co2+ for future application to structurallyand/or chemically less well defined systems.

In situ combustion measurements of CO_2 by use of a distributed-feedback diode-laser sensor near 20 µm

High-resolution absorption measurements of CO(2) were made in a heated static cell and in the combustion region above a flat-flame burner for the development of an in situ CO(2) combustion diagnostic based on a distributed-feedback diode laser operating near 2.0 mum. Calculated absorption spectra of high-temperature H(2)O and CO(2) were used to find candidate transitions for CO(2) detection, and the R(50) transition at 1.997 mum (the nu(1) + 2nu(2) + nu(3) band) was selected on the basis of its line strength and its isolation from interfering high-temperature water absorption. Measurements of spectroscopic parameters such as the line strength, the self-broadening coefficient, and the line position were made for the R(50) transition, and an improved value for the line strength is reported. The combustion-product populations of CO(2) in the combustion region above a flat-flame burner were determined in situ to verify the measured spectroscopic parameters and to demonstrate the feasibility of the diode-laser sensor.

Theoretical study of the electronic structure of carbon dioxide: Bending potential curves and generalized oscillator strengths

The electronic spectrum of carbon dioxide is predicted by means of multireference single- and double-excitation configuration interaction (MRD–CI) calculations. Bending potential curves for a large number of electronic states are calculated and the generalized oscillator strengths (GOS) obtained for the corresponding transitions are compared with recent electron energy loss spectra (EELS) obtained by Tanaka and co-workers as well as with optical intensity data. The CO2 absorption spectrum is dominated by vertical Rydberg transitions from the linear ground state but valence excited states with bent equilibrium geometries are also found to be important. Emphasis is placed on the intense spectral features in the 11.0–11.4 eV region of the spectrum. The two most intense peaks are both found to originate from π–3pπ transitions, one of which only becomes allowed upon molecular bending. Good agreement with the EELS results is obtained for the variation of the GOS with K2 and for the associated transition energies.

Difference-frequency generation in PPLN at 4.25 μm: an analysis of sensitivity limits for DFG spectrometers

We report difference-frequency generation (DFG) in periodically poled lithium niobate (PPLN) around 4.25 μm using a cw Nd:YAG and an injection-locked diode laser. This system provides a narrow linewidth source at 4.25 μm with near-shot-noise-limited operation. A conversion efficiency close to the theoretical limit is obtained. Detection of CO2 absorption spectra is demonstrated and further improvements and applications to high sensitivity spectroscopy are discussed.

Submillimeter-Wave Spectroscopy of CO in the a3Π State

Submillimeter-wave absorption spectrum of CO in electronically excited a3Π state was observed in the 540–830 GHz region by using a phase-locked BWO spectrometer. New rotational transitions up to J = 9–8 in the vibrational excited states up to v = 5 were analyzed accompanied with previous observations in the RF and millimeter-wave regions. A multivibrational states fit among a′ 3Σ+ (v = 0–3) and a3Π (v = 0–7) states was performed in order to analyze overall perturbation between the a3Π and a′ 3Σ+ states. As a result, the deperturbed rotational parameters were derived precisely to improve the RKR potential.

Divalent metal binding properties of the methionyl aminopeptidase from Escherichia coli.

The metal-binding properties of the methionyl aminopeptidase from Escherichia coli (MetAP) were investigated. Measurements of catalytic activity as a function of added Co(II) and Fe(II) revealed that maximal enzymatic activity is observed after the addition of only 1 equiv of divalent metal ion. Based on these studies, metal binding constants for the first metal binding event were found to be 0.3 +/- 0.2 microM and 0.2 +/- 0.2 microM for Co(II)- and Fe(II)-substituted MetAP, respectively. Binding of excess metal ions (>50 equiv) resulted in the loss of approximately 50% of the catalytic activity. Electronic absorption spectral titration of a 1 mM sample of MetAP with Co(II) provided a binding constant of 2.5 +/- 0.5 mM for the second metal binding site. Furthermore, the electronic absorption spectra of Co(II)-loaded MetAP indicated that both metal ions reside in a pentacoordinate geometry. Consistent with the absorption data, electron paramagnetic resonance (EPR) spectra of [CoCo(MetAP)] also indicated that the Co(II) geometries are not highly constrained, suggesting that each Co(II) ion in MetAP resides in a pentacoordinate geometry. EPR studies on [CoCo(MetAP)] also revealed that at pH 7.5 there is no significant spin-coupling between the two Co(II) ions, though a small proportion ( approximately 5%) of the sample exhibited detectable spin-spin interactions at pH values > 9.6. EPR studies on [Fe(III)_(MetAP)] and [Fe(III)Fe(III)(MetAP)] also suggested no spin-coupling between the two metal ions. (1)H nuclear magnetic resonance (NMR) spectra of [Co(II)_(MetAP)] in both H(2)O and D(2)O buffer indicated that the first metal binding site contains the only active-site histidine residue, His171. Mechanistic implications of the observed binding properties of divalent metal ions to the MetAP from E. coli are discussed.