Maximum Extinction Coefficient Research Articles

Remote sensing measurements of the volcanic ash plume over Poland in April 2010

This work provides information on selected optical parameters related to volcanic ash produced during the eruption of the Eyjafjoll volcano in Iceland in 2010. The observations were made between 16 and 18 April 2010 at four stations representative for northern (Sopot), central (Warsaw, Belsk) and south-eastern (Strzyzow) regions of Poland. The largest ash plume (in terms of aerosol optical thickness) over Poland was observed at night of 16/17 April 2010 in the layer between 4 and 5.5 km a.s.l. The highest values of the aerosol extinction coefficient reached 0.06e0.08 km � 1 at 532 nm (based on lidar observations in Warsaw) and 0.02e0.04 km � 1 at 1064 nm (based on ceilometer observations in Warsaw). The corresponding optical thickness due to volcanic ash reached values of about 0.05 at 532 nm and about 0.03 at 1064 nm. These values are similar to those reported for the Belsk station based on lidar observations. The ash mass concentration estimated based on the maximum aerosol extinction coefficient reached 0.22 � 0.11 mg m � 3 . This value is significantly lower than the limit (2 mg m � 3 ) for the aircraft operation.

Determination of Astaxanthin and Canthaxanthin Triplet Properties in Different Polarities of the Solvent by Laser Flash Photolysis

AbstractTriplet‐triplet extinction coefficients for astaxanthin (I) and canthaxanthin (II) in different deaerated polarity solutions of MeCN and benzene were evaluated by laser flash photolysis at 298 K in the spectral region from 350 to 650 nm by energy transfer method, employing 2‐acetonaphthone as sensitizer. The triplet‐triplet extinction coefficients in MeCN and benzene were different in terms of the carotenoid present. The maximum triplet‐triplet extinction coefficient was 0.1–1.7×105 L·mol−1·cm−1 in different solvents. The rate constants of triplet decay were I: 1.25×1010 L·mol−1·s−1, II: 1.12×1010 L·mol−1·s−1 in MeCN; and I: 1.75×1010 L·mol−1·cm−1, II: 3.27×1010 L·mol−1·s−1 in benzene. The bimolecular rate constants of energy transfer from triplet excited 2‐acetonaphthone to carotenoids were determined from the linear regression of the decay rate constant of 2‐acetonaphthone triplet at varying carotenoid concentrations. The triplet lifetimes of 3AST* and 3CAN* in different solvents were also determined. The results indicated that triplet energy transfer was nearly diffusion‐controlled.

Characterization of the Eyjafjallajökull ash-plume: Potential of lidar remote sensing

Observations of the dispersion of volcanic ash clouds and their optical and microphysical characterization are essential for climate research and air traffic. This became obvious during the Eyjafjallajökull-eruption in April 2010. In this paper we report on continuous measurements with two EARLINET Raman- and depolarization lidars conducted at Maisach close to Munich, Germany. By means of range corrected signals the temporal development of the ash-plume could be documented in near real-time. They confirmed results from a chemistry transport model (MCCM). The optical characterization includes the backscatter coefficient at three wavelengths, and the extinction coefficient and particle linear depolarization ratio at two. The maximum extinction coefficient of the ash layer over Maisach was 0.75km−1 and wavelength independent, the particle linear depolarization ratio was about 37%. This is a strong indication of large non-spherical particles. An inversion of the optical data derived from the lidar measurements led to a maximum mass concentration of approximately 1.1mgm−3 over Maisach. As a consequence of the ambiguity of the inversion process and measurement-errors, relative uncertainties are between 30% and 50%.

Prediction of beef meat emulsion quality with apparent light backscatter extinction

Normalized light backscatter intensity ( I N ) response as a function of fat/lean ratio ( R FL ; 0.075, 0.25, and 0.33), chopping time (CT; 2, 5 and 8 min) and fiber separation distances ( d ; 2, 2.5 and 3 mm), were measured using a fiber optic spectrometer. Models based on the apparent light extinction coefficient (model I), fat/nonfat solid concentrations (model II), and the intensity ratio between optical distances (model III), were tested for I N 0 prediction ( I N at d = 0). Model I was significantly ( P < 0.0001) better than model II for prediction at 570 nm ( λ ), 8 min (CT), and 0.075 of R FL . Model III showed maximum geometry values and extinction coefficients for optical fiber separations of 2 and 2.5 mm, yielding the higher R 2 as R FL and wavelength increased. The results demonstrated a high correlation between functional properties of meat emulsion (i.e., R FL ) and optical wavebands that may have potential for predicting I N 0 using an optic sensor technology.

Core-Perfluoroalkylated Perylene Diimides and Naphthalene Diimides: Versatile Synthesis, Solubility, Electrochemistry, and Optical Properties

By a strategy featuring perfluoroalkylation of the highly soluble intermediates and their further efficient transformations to target compounds, a versatile synthesis of core-perfluoroalkylated perylene diimides (PDIs) and naphthalene diimides (NDIs) was developed, and PDIs perfluoroalkylated at 1-position or 1,6-positions and core-perfluoroalkylated NDIs were first obtained. By esterification, perfluoroalkylation, hydrolysis, and condensation with amine, 1-perfluorooctyl-PDIs (7b, 7c, and 7e), 1,7-bis(perfluorooctyl)-PDIs (8a-c and 8e-g), 1,6-bis(perfluorooctyl)-PDIs (8'e), a mixture of 1,7-bis(trifluoromethyl)-PDIs and 1,6-bis(trifluoromethyl)-PDIs (11b and 11'b, 11d and 11'd, in a ratio of 19:1), 2-perfluorooctyl-NDIs (20a-d), and 2,6-bis(perfluorooctyl)-NDIs (21a-21d) were efficiently synthesized. Five valuable intermediates--1-perfluorooctylperylene dianhydride (5), 1,7-bis(perfluorooctyl)perylene dianhydride (6) 1,6-bis(perfluorooctyl)perylene dianhydride (6'), 2-perfluorooctylnaphthalene dianhydride (18), and 2,6-bis(perfluorooctyl) naphthalene dianhydride (19)--were also obtained, and they can condense with many amines to produce PDIs containing different functional side chains on the imide nitrogen atoms. Solubility, electrochemistry, and optical properties of the above core-perfluoroalkylated PDIs and NDIs were investigated. Core-perfluoroalkylated 8e, 8f, 8'e, mixture of 11d and 11'd, 20b, and 20d with excellent solubility in common organic solvents are competitive as candidates as solution processable semiconductors. Core-perfluoroalkylated PDIs and NDIs with experimental LUMO energy of 4.04-4.34 eV demonstrate strong electron accepting ability. For core-perfluoroalkylated PDIs, the maximum absorptions display blue shifts of 6-18 nm and the maximum molar extinction coefficients decrease obviously relative to those of unsubstituted PDIs, and they inherit the strong fluorescence from the PDIs family, which makes them promising fluorescent dyes.

Fluorimetric quantitation of citalopram and escitalopram in plasma: developing an express method to monitor compliance in clinical trials

Selective serotonin reuptake inhibitors (SSRIs) in general, and citalopram/escitalopram in particular, are widely used to treat clinical depression. However, SSRI bioavailability and non-compliance represent major issues, especially in the clinical trials setting. In this context, frequent drug-level measurements for compliance monitoring would be a desirable tool to improve clinical outcomes with SSRIs. However, the liquid chromatography techniques available are expensive, requiring excessive sample preparation, and suffer from high complexity. We sought to develop a rapid method for the measurement of citalopram/escitalopram levels in human plasma by fluorimetry. A total of 34 frozen human plasma samples were thawed at room temperature and repeatedly centrifuged in cellulose to remove aggregates, proteins and solids. Fluorescence spectra were measured in the range 270-450 nm with excitation at 240 nm on a FluoroMax 3 spectrofluorimeter. Control samples contained known concentrations of SSRIs. SSRI absorbance spectra were recorded in the range 230-320 nm. The shape of the spectra and the absorbance of citalopram and escitalopram were very similar, with UV maximum absorbance at 239 nm. The maximum extinction coefficient was epsilon239=15,930 M-1 cm-1 for citalopram and epsilon239=13,630 M-1 cm-1 for escitalopram. The fluorescence spectra of SSRIs are unique and are characterized by the presence of two well-defined conjugated spectra with maxima at 300 and 382 nm. Fluorimetry is very suitable for assessment of plasma SSRI levels. This inexpensive and efficient technique can objectively and reliably quantify drug levels in biological fluids, thereby directly determining the level of patient adherence to the prescribed drug regimen. This method will be useful in a broad spectrum of applications, from compliance/bioavailability assessments in animal and human experiments to utilization in large-scale clinical trials.

Optical and Microphysical Properties of Upper Clouds Measured with the Raman Lidar and Hydrometeor Videosonde: A Case Study on 29 March 2004 over Tsukuba, Japan

AbstractOptical and microphysical properties of the upper clouds at an altitude range of 5–11 km were measured over Tsukuba, Japan, on 29–30 March 2004 using a ground-based Raman lidar and a balloon-borne hydrometeor videosonde (HYVIS). The Raman lidar measured the vertical distributions of the particle extinction coefficient, backscattering coefficients, depolarization ratio, and extinction-to-backscatter ratio (lidar ratio) at 532 nm; further, it measured the water vapor mixing ratio. The HYVIS measured the vertical distributions of the particle size, shape, cross-sectional area, and number concentration of the cloud particles by taking microscopic images. The HYVIS measurement showed that the cloud particles were ice crystals whose shapes were columnar, bulletlike, platelike, and irregular, and 7–400 μm in size. The Raman lidar measurement showed that the depolarization ratio ranged from 0% to 35% and the lidar ranged from 0.3 to 30 sr for the clouds in ice-saturated air. The comparison between the measured data and theoretical calculations of the cloud optical properties suggests that the observed variations in the depolarization ratio and lidar ratio were primarily due to the variation in the proportion of the horizontally oriented ice crystals in the clouds. The optical thickness of the cloud obtained from the lidar was about 2 times lower than that calculated from the HYVIS data, and the maximum extinction coefficient was about 5 times lower than the HYVIS data. The most probable reason for the differences is the horizontal inhomogeneities of the cloud properties between the measurements sites for the two instruments.

On the temperature dependence of the primary yield and the product Gεmax of hydrated electrons in the low-LET radiolysis of liquid water

Monte-Carlo simulations are performed to calculate the temperature dependence of the primary hydrated electron yield (Geaq-) for liquid water irradiated by low linear-energy-transfer radiation (LET ~ 0.3 keV µm–1) in the range 25–325°C. Calculations are carried out by taking properly into account the effect of the time and temperature dependencies of the water dielectric constant on the electron–cation geminate recombination. Our computed Geaq- values slightly increase with increasing temperature, in good agreement with experiment. The product Geaq- εmax(eaq-), estimated by using existing experimental data of the maximum molar extinction coefficient εmax(eaq-), remains nearly constant or slightly increases, depending on the temperature dependence chosen for εmax. Our Geaq-εmax(eaq-) values compare generally well with most experimental data, as well as with the predictions of deterministic diffusion-kinetic model calculations. Moreover, our results indicate that the static dielectric constant of water (εs) does not play any significant role on the electron–cation recombination at early times. Such a finding is inconsistent with the interpretation, proposed by certain authors in the literature, that Geaq- should in fact decrease as temperature is increased because of an increased electron–cation geminate recombination due to a lowering of εs. Finally, the temperature dependence of the hydrated electron yields, calculated at various times between 10 ps and 1 µs, shows that at low LET, the time required to establish homogeneous chemistry in the bulk of the solution is ~10–6 s in the range ~25–100°C, and that this time diminishes to ~10–7 s at higher temperatures. Key words: liquid water, radiolysis, temperature, hydrated electron (eaq-), radiolytic yields, electron–cation geminate recombination, dielectric constant, molar extinction coefficient of eaq-, homogenization time.

Direct photolithographic deforming of organomodified siloxane films for micro-optics fabrication.

Direct photolithographic deforming of hybrid glass films is used to fabricate optical structures. The structure is fabricated in polyethylene-oxide-acrylate modified hybrid glass films with (1) binary and gray-scale photomasks using a mercury UV-lamp exposure and (2) maskless UV-laser patterning. Fabrication of isolated lenslets, lens arrays, and gratings is presented, including the associated exposure patterns. The hybrid glass material yields light-induced deformation peak-to-valley (p.v.) heights up to 12.8 microm with mercury UV-lamp exposure and p.v. deformation heights up to 6.8 microm with 365-nm UV-laser exposure. The fabricated lenslets' surface data are presented as Zernike-polynomial fit coefficients. Material synthesis and processing-related aspects are examined to understand and control the material's deformation under exposure. The hybrid glass material exhibits a maximum spectral extinction coefficient of 1.6 x 10(-3) microm(-1) at wavelengths ranging from 450 to 2,200 nm and has a refractive index of 1.52 at 632.8 nm. The fabricated structures exhibit rms surface roughness between 1 and 5 nm.

Fabrication of micro-optical structures by applying negative tone hybrid glass materials and greyscale lithography

Direct lithographic patterning of lenslet arrays with lens sags up to 75 µm and opto-mechanical structures with thickness up to 118 µm is demonstrated, using negative tone hybrid glass materials and greyscale and binary photomasks. The hybrid glass material features a maximum extinction coefficient of 2.0×10−4 µm−1 between 450 and 1600 nm, a refractive index of 1.531 at 632.8 nm and an estimated Abbe number of 45. The patterned structures exhibit rms surface roughness between 10 to 45 nm.

Stability of 5-acetamido-6-formylamino-3-methyluracil in buffers and urine

The caffeine metabolite 5-acetamido-6-formylamino-3-methyluracil (AFMU) and its product of spontaneous deformylation 5-acetamido-6-amino-3-methyluracil (AAMU) were synthesized. Their ultraviolet absorption spectra differed significantly from each other and wavelengths of absorption maximum and molar extinction coefficients varied with pH. The changes of the absorption spectrum parameters of AFMU and AAMU with pH indicated that they ionized with p K a of 5.7 and 8.3, respectively. The spontaneous deformylation of AFMU in solutions of different pH and urine were investigated spectrophotometrically and by high-performance liquid chromatography. The data showed the following: (a) AFMU transformed uniquely to AAMU; (b) deformylation obeyed first-order kinetics under the different conditions tested; (c) the half-life of AFMU varied between 7.8 and 36 h between pH 9.0 and 2.0 at 24 °C, with a maximum of 150 h at pH 3.0; (d) AFMU deformylated below pH 2.0 and above pH 10.0 with a half-life of less than 4.6 h; (e) half-lives of AFMU in urine were 57 and 12.5 h at 24 and 37 °C, respectively, comparable to those in buffers at equivalent pH and temperature. The results are discussed in relation to the mechanism of deformylation and the use of caffeine as a probe drug for NAT2 phenotyping.

Preparation of a Novel Infrared Photoinitiator and Kinetic Monitoring of Photopolymerization by Real Time FT-IR Spectroscopy

In this paper, a novel cationic cyanine dye-borate complex, 1,3,3,1′,3′,3′-hexamethyl-11-chloro- 10,12 propylenetricarbocyanine triphenylbutylborate was prepared and used as the photoinitiator in infrared laser-induced photopolymerization of acrylates. It had a maximum electron absorption at 786 nm, which matched well with the output wavelength of the adopted infrared laser diode, with a maximum molar extinction coefficient of 1.4×105 L mol−1 cm−1 in chloroform solution. Under the irradiation of infrared laser the polymeric samples based on phthalicdiglycol diacrylate (PDDA), binder, photoinitiator and solvent polymerized and the polymerizing process was monitored through Real Time FT-IR spectroscopy (RTFT-IR). The double bond conversion was determined from the reduction of the absorption of acrylate monomer at 1635 cm−1 and 1620 cm−1 (CH2=CH strentching) in FT-IR spectra during laser irradiation. As the concentration of photoinitiator rose, the polymerization rate (Rp) increased rapidly but then decreased when the concentration reached a critical value. Rp and the ultimate double bond conversion of sample increased when the infrared laser power was enhanced, whereas they fell greatly as the thickness of the polymeric sample layer increased.

Is salivary histatin 5 a metallopeptide?

Histatins are small histidine-rich salivary polypeptides which exhibit antimicrobial activity against Candida albicans. This antimicrobial activity has been ascribed in part to a high content of basic amino acids. However, unlike most other antimicrobial proteins histatins have a high content of histidine, tyrosine and acidic amino acids known to participate in metal ion coordination. This study was conducted to test whether histatin 5 could bind zinc and copper which are metals present in salivary secretions and whole saliva. Physical binding parameters and spectral properties of zinc- and copper-histatin complexes were investigated in order to obtain direct evidence of these interactions. A spectrophotometric competition assay using the metallochromic indicator murexide showed that histatin 5 dissociates metal indicator complexes containing zinc or copper ions. Absorption spectra of histatin 5 at increasing copper chloride concentrations resulted in higher absorbance in the 230–280 nm wavelength range and this spectral change was saturated at a peptide:metal molar ratio of approx. 1:1. A corresponding band was observed in the visible range of the spectrum with a maximum and molar extinction coefficient corresponding to that of copper binding to an ATCUN motif. Quantitative assessment of zinc and copper binding to histatin 5 using isothermal titration calorimetry revealed at least one high affinity site for each metal, with binding constants of 1.2×105 and 2.6×107 M−1, respectively. These results indicate that histatin 5 exhibits metallopeptide-like properties. The precise biological significance of this has not yet been established but histatins may contribute significantly to salivary metal binding capacity.

Effects of a thiolate axial ligand on the pi-->pi* electronic states of oxoferryl porphyrins: a study of the optical and resonance Raman spectra of compounds I and II of chloroperoxidase.

Optical absorption and resonance Raman spectra have been investigated for enzymatic intermediates, compounds I and II, of chloroperoxidase (CPO) which contains a thiolate-ligated iron porphyrin. Compound I of CPO (CPO-I), an oxoferryl porphyrin pi cation radical, gave an apparently asymmetric single-peaked Soret band at 367 nm, for which band fitting analyses revealed the presence of two transition bands around 365 and 415 nm. Compound II of CPO (CPO-II), an oxoferryl neutral porphyrin, gave a split Soret spectrum with two bands (blue and red Soret bands) at 373 and 436 nm. Thus both CPO-I and CPO-II can be categorized as hyperporphyrins. The maximum extinction coefficients (epsilon(b) and epsilon(r)) and energies (Eb and Er) of the blue and red Soret bands of CPO-II were found to fall on an epsilon(b)/epsilon(r) versus Eb-Er correlation line derived from data reported for six-coordinate ferrous derivatives of cytochrome P450 and CPO. Corresponding data for CPO-I did not fall on the correlation line. Resonance enhancement of the FeIV=O stretching (vFeO) Raman band was found for CPO-I when Raman scattering was excited at wavelengths within both transition bands around 365 and 415 nm, while the vFeO Raman band was not identified for CPO-II at any of the excitation wavelengths examined here. These findings suggest that the thiolate axial ligand causes Soret band splitting of CPO-II through configuration interaction between the sulfur-->porphyrin e(g)* charge transfer and porphyrin a1u,a2u-->e(g)* transitions, while the FeO portion is important in determining the shape of the Soret band of CPO-I.

New ways of determining structural groups in brown coals and their bioconversion products by FT IR spectroscopy.

New methods of determining the structural groups -COOH and -CH2- have been developed. The investigation of carboxyl groups is possible both after derivatization with p-fluorophenacylbromide and by quantitative interpretation of the Fourier transform infrared (FT IR) spectra. There exists a linear relationship between the results of these two methods that is generally valid for the analysis of all brown coal components. The maximum extinction coefficient of the symmetric stretching vibration band of the CH2 groups has been determined using model substances. This allows quantification of this structural group directly from the FT IR spectrum. The results agree with the contents of methylene groups as determined by 13C-cross polarization-magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy. Using these methods, the COOH and CH2 groups contained in brown coals of the North Rhine region and in their bioconversion products have been quantified.

A Comparative Study of the Kinetics of Cytarabine Hydrolytic Deamination in Aqueous Solutions

Cytarabine (1-D-arabinofuranosylcytosine, I) is a drug belonging to the group of nucleoside antimetabolites [1]. At present, the drug is produced abroad both in dry (lyophilized) and liquid forms. The production of liquid forms is less labor-consuming and more economically effective. At the same time, it was reported [2 – 8] that cytarabine is subject to hydrolytic deamination in aqueous media with the formation of a therapeutically inactive 1-D-arabinosyluracil (II) and ammonia (Fig. 1). Our task was to study the stability of cytarabine in aqueous solutions during a preset storage time. For this purpose, it was necessary to select a method that would be (i) capable of studying the kinetics and rate of the cytarabine hydrolytic deamination reaction and (ii) sufficiently simple and optimum from the standpoint of sensitivity and reproducibility. Various methods were developed for determination of the content of I in medicinal preparations and for the study of hydrolytic deamination of this compound. These include TLC [9], RIA [10 – 13], mass spectrometry [14], gas chromatography in various modes, including those combined with other techniques [15, 16], UV spectrophotometry [17], extraction methods [18], and liquid chromatography at low [19] and high pressures [20 – 35]. The method of direct UV spectrophotometry [17] is based on the difference between the absorption spectra of I and its decomposition product II (having absorption peaks at 280 and 260 nm, respectively, in 0.1 N HCl). This technique is most simple and was widely used in the early investigations of the hydrolytic deamination reaction [2 – 4, 6 – 8]. In recent years, compounds I and II are more frequently determined by HPLC techniques offering some advantages over the other methods. Compounds belonging to arabinosyl nucleosides were predominantly studied by inversed-phase HPLC (IPHPLC) [20 – 22], although ion-exchange HPLC [23] and combined techniques can be used as well [27]. In application to nucleosides, IPHPLC can be used in several different modes [36], including chromatography under socratic conditions (most frequently used for the analysis of arabinosyl nucleosides) [20 – 22], gradient-elution chromatography, and ion-pair chromatography [29, 34, 35]. As is known [3], the maximum extinction coefficient of cytosine nucleosides is observed at low pH. Therefore, using these conditions we may reach a maximum sensitivity of spectrophotometric detection. At the same time, all the molecules of cytosine nucleosides studied under these conditions are ionized and, hence, exhibit weak adsorption on the immobile (nonpolar) phase that results in lower resolution. Thus, optimum possibilities for controlling the interaction of partitioned components with the immobile phase are provided by the method of ion-pair chromatography.

One-Electron Reduction Potential and the β-Fragmentation of Acetylthiyl Radical, Comparisons with Benzoylthiyl Radical and the Oxygen Counterparts

One-electron oxidation of acetyl thiolate (CH3C(O)S-) was achieved by hydroxyl (OH•) and azide (N3•) radicals in aqueous solution. The resulting acetylthiyl radical (CH3C(O)S•) absorbs in the wavelength region 300−550 nm, with a maximum extinction coefficient of 3900 M-1 cm-1 at 440 nm. With N3•/N3- as a reference couple, the reduction potential E°(CH3C(O)S•/CH3C(O)S-) was measured to be 1.22 V vs NHE. Using a pKa of 3.35 for thioacetic acid (CH3C(O)SH), the standard reduction potential E°(CH3C(O)S•, H+/CH3C(O)SH) is calculated to be 1.42 V vs NHE. This reduction potential implies that the S−H bond energy of CH3C(O)S−H is 88.6 kcal/mol (370.8 kJ/mol). The β-fragmentation of the CH3C(O)S• radical, i.e., CH3C(O)S• → CH3• + COS, was observed. Its kinetics was found to follow the Arrhenius equation, log(k2/s-1) = (12.3 ± 0.1) − (10.1 ± 0.2)/θ, where θ = 2.3RT kcal/mol. At 22 °C, the CH3C(O)S• radical decays with a rate constant of 6.6 × 104 s-1. The thermochemical properties of the CH3C(O)S• radical and its β-fragmentation reaction are compared with those of the benzoylthiyl radical (PhC(O)S•), as well as the corresponding oxygen counterparts, the acetyloxyl (CH3C(O)O•) and benzoyloxyl (PhC(O)O•) radicals.

1. Spatial and temporal evolution of the optical thickness of the Pinatubo aerosol cloud in the northern hemisphere from a network of ship‐borne and stationary lidars

The vertical profiles of the extinction coefficient and the total optical thickness of the Pinatubo aerosol layer obtained from a network of 5 Rayleigh‐Mie lidars are presented here. Three ship‐borne lidars (PROFESSOR ZUBOV†, PROFESSOR VIZE†, HENRI POINCARE*) and two fixed lidar stations (OHP* and CEL*) are operated respectively by the Roscomhydromet†, of Russia and of the Service d'Aeronomie du CNRS* of France. The measurements presented are in the altitude range 15–35 km. They were obtained between July 1991 ‐ April 1992 and cover 8°S–60°N latitude and 80°W–6°E longitude. This represents extensive coverage of the western sector of the northern hemisphere, which is partly coincident with UARS satellite coverage. Optical depths of up to 0.2 were observed and maximum extinction coefficient values of 0.08 km−1 were obtained at 24 km and 18°N latitude.

Stoichiometry and spectroscopic identity of copper centers in phenoxazinone synthase: A new addition to the blue copper oxidase family

Phenoxazinone synthase catalyzes the oxidative condensation of two molecules of substituted o-aminophenols to the phenoxazinone chromophore of actinomycin. Cyclization occurs with the concomitant reduction of molecular oxygen to water. We have shown that the enzyme requires 4-5 copper atoms/monomer for full activity and the additional copper inhibits the enzyme. The optical absorption spectrum of phenoxazinone synthase is also dependent on the Cu per monomer ratio, and the absorption peak at 598 nm has a maximum extinction coefficient of 4000 +/- 150 M-1 cm-1 at a ratio of 4-5 Cu atoms per monomer. The electron paramagnetic resonance (EPR) spectrum of enzyme as isolated with low copper content (0.8 Cu/monomer) only shows the presence of type 1 (blue) copper centers (g parallel = 2.24, A = 0.0067 cm-1, and g perpendicular = 2.07). Enzyme incubated with 4-5 Cu per monomer demonstrates the presence of both type 1 and type 2 copper centers with a stoichiometry of one type 1 center per monomer and the remainder bound as type 2 Cu2+. Anaerobic incubation of substrate with enzyme containing five Cu atoms per subunit results in bleaching of the blue center. The EPR spectrum of the enzyme reduced under these conditions suggests that one of the type 2 Cu2+ centers with a g parallel = 2.34, A = 0.016 cm-1, and g perpendicular = 2.07 remains oxidized and is not involved in catalysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature dependence of the equilibrium constant for iodine hydrolysis at temperatures between 25 and 120 °C

The equilibrium constant for iodine hydrolysis at elevated temperatures has been investigated using absorption spectroscopy and a simulation computer program. The temperature dependence of the aqueous I2 maximum extinction coefficient for visible light (at 460 nm) was first evaluated in a preliminary experiment using saturated I2 solution. The time dependence of I2 concentrations in dilute solution has subsequently been measured using the temperature-dependent extinction coefficient. The results were analysed by the simulation program, in which 11 normally accepted reactions were considered, and the equilibrium constant, K, was estimated. It was concluded that the K value at temperatures ranging between 25 and 120 °C may be expressed by log K(T)= 13880/T– 0.2445T+ 308.4 log T– 749.1, where the units of K and T are mol2 dm–6 and K, respectively.