Pyridine extinction coefficients

Methyl Red (4-dimethylaminoazobenzene-2 -carboxylic acid) [493-52-7] M 269.3, m 181-182 , Cl 13020, pK j 2.30, pK2 4.82. The acid is extracted with boiling toluene using a Soxhlel apparatus. The crystals which separated on slow cooling to room temperature are filtered off, washed with a little toluene and recrysld from glacial acetic acid, benzene or toluene followed by pyridine/waler. Alternatively, dissolved in aq 5% NaHC03 soln, and ppted from hot soln by dropwise addition of aq HCl. Repealed until the extinction coefficients did not increase. 

M 604.5, m >250"(dec). Cl 16255, X,max 506nm. Dissolved in the minimum quantity of boiling water, filtered and enough EtOH was added to ppte ca 80% of the dye. This process was repeated until a soln of the dye in aqueous 20% pyridine had a constant extinction coefficient. 

This ester is formed from the anhydride in pyridine and is quantitatively cleaved with H2NNH2-H2O, Pyr-AcOH. The sensitivity of detection of this ester is high with its absorbance maximum of 513 nm and extinction coefficient of 78,600 in 5% CI2CHCO2H/CH2CI2 where it forms the trityl cation. ... 

The specific surface area of the fresh and used catalysts was measured by nitrogen adsorption method (Sorptometer 1900, Carlo Erba Instruments). The catalysts were outgassed at 473 K prior to the measurements and the Dubinin equation was used to calculate the specific surface area. The acidity of investigated samples was measured by infrared spectroscopy (ATI Mattson FTIR) by using pyridine (>99.5%, a.r.) as a probe molecule for qualitative and quantitative determination of both Bronstcd and Lewis acid sites (further denoted as BAS and LAS). The amounts of BAS and LAS were calculated from the intensities of corresponding spectral bands by using the molar extinction coefficients reported by Emeis (23). Full details of the acidity measurements are provided elsewhere (22). 

The density of Bronstcd and Lewis acid sites was determined by IR spectroscopy (Nicolet 710) of adsorbed pyridine, after desorption at 250°C, using the molar extinction coefficients previously obtained by Emeis [11]. The acid strength distribution of selected zeolites was studied by NH3-TPD in an Autochem 2910 Equipment (Micromeritics) coupled to a quadrupole mass spectrometer. First, NH3 was adsorbed at 175°C until saturation and then desorbed by increasing the temperature up to 800°C at a heating rate of 10°C/min. 

Here, eM, Ml, and / Ml2 are the respective extinction coefficients of all participants of Eq. (1) and [Mb is the total concentration of 1. The values of Kl and K2]j are summarized in Table II. The solid line in the inset was calculated using the best-fit values of mt / Ml2, A l, and K2h, while the broken line is the calculated prediction if K2l 0. The broken line deviates systematically from the experimental points confirming the binding of the second pyridine-type ligand. Imidazole behaves similarly (27). 

Emeis, C.A. Determination of integrated molar extinction coefficients for infrared absorption bands of pyridine adsorbed on sohd acid catalysts. J. Catal. 1993,141, 347-354. 

Fig. 4. Visible spectra of catalase, compound I, and compound II 5 [xM (heme) beef liver catalase (Boehringer-Mannheim) in 0.1 M potassium phosphate buffer pH 7.4, 30°C. Compound I was formed by addition of a slight excess of peroxoacetic acid. Compound II was formed from peroxoacetic acid compound I by addition of a small excess of potassium ferrocyanide. Absorbance values are converted to extinction coefficients using 120 mM for the coefficient at 405 nm for the ferric enzyme (confirmed by alkaline pyridine hemochromogen formation). Spectra are corrected to 100% from occupancies of f 90% compound I, 10% ferric enzyme (steady state compound I) and 88% compound II, 12% compound I (steady state compound II). The extinction coefficients for the 500 to 720 nm range have been multiplied by 10. Unpublished experiments (P.N., 1999).

Thiosalicylic acid forms a green 2 1 complex with V02+ in aqueous ethanol442 (log K1 = 10.24, log K2 = 8.39). Addition of pyridine causes a more than 10-fold increase in the molar extinction coefficient and a yellow shift affording a chloroform extractable complex which can be used for the analysis of vanadium. The thermodynamic parameters for the 2 1 complex of furfurylmercaptan and V02+ are (35 °Q log K, 8.18 AH° = - 8.18 kcal mol"1, AG°, - 23.31 kcal mol"1 AS°, + 49.12 e.u 443 Stepwise formation constants of the V02+ complex of p-(mercaptoacetamide)chloro-benzene have been determined.444... 

As expected for silica-alumina as a mixed oxide (see also Section IV.B.5), the PyH+ and PyL species are observed simultaneously (160, 205,206,221-223). Two distinct types of Lewis acid sites could be detected (19b mode at 1456 and 1462 cm-1, respectively) on a specially prepared aluminum-on-silica catalyst (160). On water addition, the Lewis sites can be converted into Br nsted sites (160, 205, 221), The effect of Na+ ions on the acidity of silica-aluminas has been studied by Parry (205) and by Bourne et al. (160). It can be concluded from Parry s results that Na+ ions affect both types of acid sites, so that alkali poisoning does not seem to eliminate the Br nsted sites selectively. For quantitative determination of the surface density of Lewis and Br nsted acid sites by pyridine chemisorption, one requires the knowledge of at least the ratio of the extinction coefficients for characteristic infrared absorption bands of the PyH+ and PyL species. Attempts have been made to evaluate this ratio for the 19b mode, which occurs near 1450 cm-1 for the PyL species and near 1545 cm-1 for the PyH+ species (160,198,206,221,224,225). The most reliable value as calculated from the data given by Hughes and White (198) seems to be... 

The compound [Pt(terpy)(SCH2CH20H)]N03 is a dark red-purple microcrystalline material that is extremely water soluble. The complex is stable in cold aqueous solution for periods up to several weeks. High pH or heating (T >60°) leads to decomposition, however. The electronic absorption spectra of the ter-pyridine thiolato compounds are characteristically definitive in the 300-350 nm region and may be used to determine product purity. Solutions of [Pt(terpy)-(SCH2 CH2 OH)] N03 of less than 15 pM obey Beer s law and exhibit the following absorption maxima and molar extinction coefficients 475 (890), 342 (12,900), 327 (10,700), 311 (10,300), 277 (20,300), and 242 (28,700) nm. 

This esterified hemin is soluble in ligating solvents such as pyridine and also halogenated hydrocarbons, ethers such as tetrahydrofuran, and benzene. It is slightly soluble in alcohols and insoluble in water. In the presence of traces of water in a solution it will slowly convert to the n-oxo form. It can also dehydrate to the proto forms i under specific conditions. Other chemical, physical, and biological properties are similar to those for the protoporphyrin IX com-plex.i Extinction coefficients for the various characteristic spectra of this material are not well defined, as the solutions are generally unstable with time, going to mixtures of the various ligated and jx-oxo forms. 

The level of substitution of the antibody after reaction with SPDP is determined spectrophotometrically. A sample the derivatized antibody is treated with DTT at a final concentration of 5 mM, and the optical density measured at 280 nm and 343 nm. The pyridine-2-thione released by reduction has a molar extinction coefficient at 343 nm of 8.08 X 10 Af" cm (12). This product also absorbs at 280 nm with a molar extinction coefficient of 5.1 x 10 Af" cm . The true protein absorbance is determined from the formula ... 

As can be seen in Fig. 5, N conversion using H-ZSM-11 zeolite seems to be correlated with the number of Bronsted sites on the external surface (deduced from measurements of methylene blue adsorption capacity) and not with the total niunber of Bronsted sites (determined by the total pyridine adsorbed on Bronsted sites and desorbed at 150°C by FT-IR spectroscopy), using the literature data on the integrated molar extinction coefficients [17], (for infrared absorption bands of pyridine adsorbed on solids acid catalyst [17], providing no dependence of the integrated coefficients on the catalyst or strength of the sites). 

The acidity distribution was obtained by pyridine adsorption-desorption (Table 3). The presence in the IR spectrum of a band at 1455 cm was assigned to the pyridine coordinatively bonded to Lewis acid sites, while a band at 1545 cm was attributed to the pyridinium ion using the known values of the extinction coefficient of the two IR signals [12] it was possible to determine the Lewis and Bronsted acid sites densities. The number of acid sites observed in the used catalyst was about half of that present in... 

Calculate number of sulfhydryl groups (molar extinction coefficient of 19800 for the modified, pyridine-4-thione, thiol groups). 

The surface concentration of Bronsted and Lewis sites was evaluated by integration of the absorption bands at 1545 and 1455 cm due to adsorbed pyridinium ion and pyridine, with integrated molar extinction coefficients values 813 = 1-67 and Sij, = 2.22 cm pmol" [15]. Although absolute concentration of surface acid sites obtained by this method is affected by a 10 - 15% error [12], reliable and valuable information can usually be obtained on a relative scale. Moreover, in the present case pyridine is an ideal probe molecule. Indeed, being very similar in structure to the reactant involved in the present reaction, it is able to titrate exactly those acidic sites which can be reached also by HEP. 

The solubility of H2-tpyp in 17 solvents and the extinction coefficients in CHC13, pyridine, acetic acid, water (pH 2.3), and 1.0W HC1 [443 nm (e = 332,000), 590 nm (e = 14,300) and 639 nm (e = 18,200)] have been tabulated.12 Metal complexes have been prepared in acetic and formic acids.7 This porphyrin is relatively insoluble in DMF. 

Brpnsted acidity (mmol pyridine (g catalyst) ) of the different zeolites was measured at 623 K and calculated by use of the extinction coefficients given in Ref. 64. 

M) in pyridine (7 mL) for 24 h at 25°C. The carboxylic derivative is then washed with methanol (four times) and ether. Analysis for the extent of carboxylation involves a two-step procedure. An accurately weighed aliquot is treated with DCC and p-nitrophenol in pyridine. After several washings with THF to remove uiu eacted p-nitrophenol, piperidine-pyridine (1 9) is added to the silica gel, and the amount of p-nitrophenol released is measured at A = 410 nm by using 1.57 X lO" cm as the extinction coefficient of p-nitrophenoxide. The incorporation of carboxylic acid is 200 /u-mol/g. 

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