Methanol model compounds

Fig. 9.10 Absorption spectra of K-1 (a model compound) and its chemiluminescent methylamine-activation products KM-1 and KM-2. All in methanol.

Anchimeric assistance in the solvolysis of /3-arylthiovinyl sulfonates was demonstrated by means of kinetic studies on model compounds (182). In a variety of solvents ranging from nitromethane and methanol to acetic acid, the /3-arylthiovinyl sulfonate 216 was shown to react 20 to 33 times faster than the triphenylvinyl sulfonate 217. Different accelerating factors were... 

Omura, K. Iodine oxidation of alpha -tocopherol and its model compound in alkaline methanol unexpected isomerization of the product quinone monoketals. J. Org. Chem. 1989, 54, 1987-1990. 

Purification. The commercial LDPE was dissolved in hot toluene and precipitated in methanol. The resulting small chips were dried in a vacuum oven overnight at 80° C. HDPE was purified in the same manner, except that in this case much of the commercial material was insoluble in toluene, and so significant fractionation apparently occurs during t.he purification. The model compounds were purified by the flash chromatographic technique of Still et al. (10). 

The use of surface-enhanced resonance Raman spectroscopy (SERRS) as an identification tool in TLC and HPLC has been investigated in detail. The chemical structures and common names of anionic dyes employed as model compounds are depicted in Fig. 3.88. RP-HPLC separations were performed in an ODS column (100 X 3 mm i.d. particla size 5 pm). The flow rate was 0.7 ml/min and dyes were detected at 500 nm. A heated nitrogen flow (200°C, 3 bar) was employed for spraying the effluent and for evaporating the solvent. Silica and alumina TLC plates were applied as deposition substrates they were moved at a speed of 2 mm/min. Solvents A and B were ammonium acetate-acetic acid buffer (pH = 4.7) containing 25 mM tributylammonium nitrate (TBAN03) and methanol, respectively. The baseline separation of anionic dyes is illustrated in Fig. 3.89. It was established that the limits of identification of the deposited dyes were 10 - 20 ng corresponding to the injected concentrations of 5 - 10 /ig/ml. It was further stated that the combined HPLC-(TLC)-SERRS technique makes possible the safe identification of anionic dyes [150],... 

Absorption studies of the model compound in polar and nonpolar solvents support the finding that the dimer is present in a form which allows for close proximity between the two porphyrin rings. The absorption spectra of the dimer and the monomer are shown in Fig. 9. The spectra in methanol show a significant blue-shift of the Soret peak and a small red-shift in the visible bands for the diporphyrin, consistent with the spectral properties of previously synthesized cofacial diporphyrins(16,17) wherein exciton interactions can take place. ( 18) In methylene chloride, the Soret blue shift appears to be much less (<5 nm with reference to 4). 

Model compounds in seawater (>10 L) (1) wash with 2 L of distilled water (2) 8-h Soxhlet extraction with mixture of 150 mL of methanol and 100 mL of water 6... 

Model compounds and drinking water (>10 L) sequential Soxhlet extraction with methanol, pyridine, and ethyl ether, 8 h each see ref 5 and 7 17... 

Desorption of the model compounds isolated on the quaternary XAD-4 (QXAD-4) resin column was accomplished by sequential elution with ethyl ether, methanol, ethyl ether, 0.1 N HCl/ether, 0.1 N HCl/methanol, and saturated HCl/methanol. The acidified organic solvents were used for acidic solute removal. 

Preparation of Model Compound Test Solutions. Individual stock solutions containing 500 mg/L were prepared by dissolving quinaldic acid, glycine, and glucose in OFW 5-chlorouracil in 2 N NH4OH phenanthrene, 1-chlorododecane, 2,4 -dichlorobiphenyl, and 2,2, 5,5 -tetrachlorobiphenyl in hexane and the remaining compounds in methanol. Humic acid stock solution was prepared in 0.02 N NaOH. The composition of the test solutions is reported in Table I. Test solutions (500 mL) were prepared by adding salts and the required volumes of stock solutions in OFW. Phenanthrene, 1-chlorododecane,... 

This paper reports on the oxygen tolerance of a series of catalyst systems, by subjecting two different substrates to oxidation (i) methanol as an easily oxidizable model compound and (ii) HMF, a versatile intermediate, as a more difficult substrate with the advantage of the presence of two different oxidizable groups. Catalyst variables included the metal as well as the support. 

Fusion with Alkali and Cupric Oxide in Nonaqueous Solvents. Alkali lignin was fused with potassium hydroxide and cupric oxide in methanol under conditions suggested by Tiemann (20) and in n-amyl alcohol as suggested by Klages (4). These procedures were very effective in earlier model compound studies in our laboratories (12). Ether extracts obtained were less than those from corresponding experiments in aqueous solution, and qualitative compositions were essentially the same. In the case of the amyl alcohol experiments, artifacts with the cupric oxide were obtained. Again, experiments were conducted under more dilute conditions in a bomb under superatmospheric conditions, but results were no better. 

To prepare the oxidized form of MDH, the isolated preparation has to be treated with electron acceptor in order to remove substrate and finally to oxidize the enzyme. However, the enzyme is very labile in its oxidized form (the inactivation concomitantly leading to destruction of PQQ, as deduced from the rapid disappearance of its absorption band) the only way to keep it active is to perform the oxidation in the presence of cyanide or hydroxylamine [71], Most probably, the reason for this is adduct formation between the stabilizer and PQQ at the C-5 position, in line with the maximum of the stable oxidized form with that of the methanol adduct of the model compound (Table 2). Since sGDH is perfectly stable in its oxidized form, the origin of the instability of PQQ and the stability of PQQH in MDH could be the special residues (discussed earlier) surrounding the cofactor in MDH (PQQH has not been observed so far in sGDH). However, in view of the small red shift induced by Ca on PQQ in the enzymes and model... 

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