Presence Of 2-propanol Research Articles

Optimized Chiral Separation of 20 Amino Acids Derivatized with 9-Fluorenylmethyl Chloroformate Using Cyclodextrins as Chiral Selectors in Capillary Electrophoresis

Direct chiral separation of DL-amino acids derivatized with 9-fluorenylmethyl chloroformate (FMOC-amino acids) is accomplished with micellar electrokinetic capillary chromatography. Separation parameters such as sodium dodecyl sulfate (SDS) and cyclodextrin concentrations are optimized by factorial designs. The interaction and effect of these variables on chiral recognition of FMOC-amino acids are presented in optimization charts. The enantioseparations are performed under optimized conditions by using γ-cyclodextrin (γ-CD) or β-cyclodextrin (β-CD) as chiral selectors. By using β-CD as a chiral selector, baseline separation of 20 FMOC-amino acids is achieved under some different conditions ; 17 of the amino acids could be separated under the same conditions (50 mM phosphate, 50 mM SDS, 12 mM β-CD, and 15% 2-propanol). Application of γ-CD resulted in chiral separation of 12 FMOC-amino acids. For all FMOC-amino acids tested, the presence of 2-propanol was a prerequisite for a chiral separation when using β-CD as a chiral selector. Similarly, 2-propanol was needed in the majority of cases in which γ-CD was employed. Separation efficiencies are in the range of 10.7-0.9 x 10 5 theoretical plates per meter.

Enantioseparation of amino acids and dipeptides using vancomycin as chiral selector in capillary electrophoresis.

Vancomycin was applied as chiral selector for the enantiomeric separation of derivatized amino acids and dipeptides. The influence of vancomycin concentration, pH and presence of 2-propanol in the buffer were examined in order to find optimal separation conditions. Optimization was by factorial design. Further, chiral separation of derivatives prepared with three different reagents was compared. These reagents were 9-fluorenylmethyl chloroformate (FMOC), 2-(9-anthryl)ethyl chloroformate (AEOC) and dansyl chloride (dansyl). Optimum resolution was at high vancomycin concentrations, while optimum efficiency was at low vancomycin concentrations. As a consequence of the very high enantioselectivity of vancomycin, the vancomycin concentration below the amount necessary for maximal resolution can be used. Separation efficiency was relatively low, and this could be attributed to adsorption of the selector at the capillary wall. Three factors led to decreased adsorption: application of a pH above the zero mobility pH value, low vancomycin concentrations and the presence of 2-propanol. For amino acids, the resolutions of the different derivatives were: dansyl > AEOC > FMOC, while for dipeptides, the highest selectivity was with AEOC.

The photolysis ( λ = 254 nm) of tyrosine in aqueous solutions in the absence and presence of oxygen. The reaction of tyrosine with singlet oxygen

In the 254 nm photolysis of deoxygenated aqueous solutions of tyrosine (TYROH, 10 −3 mol dm −3) TYROH is consumed with a quantum yield of 9.1 × 10 −3 while the observed products (quantum yields in parentheses) are 2,2′-bityrosyl (BITYR, 3.1 × 10 −3) and 2-amino-4-ethenyl-hex-4-enic acid (AEHEA, 1.6 × 10 −3). In N 2O-saturated solutions, N 2 (1.8 × 10 −2), in the presence of 2-propanol, H 2 (1 × 10 −3) are formed. In air-saturated solutions the tyrosine consumption is increased (9.7 × 10 −2); in addition to increased yields of BITYR ({if1.4 × 10 −2}) but unaltered yields of AEHEA (1.6 × 10 −2), 3a-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indol-2-carboxylic acid (HOHICA,1.6 × 10 −2), 3,4-dihydroxyphenylalanine (DOPA, 3.8 × 10 −2) and 2,4-dihydroxyphenylalanine (2,4-DHPhe, 2.3 × 10 −3) are observed. The sum of the quantum yields of the O 2-dependent products increases with increasing O 2 and TYROH concentrations, approaching a plateau value of approximately 7 × 10 −2 at high reactant concentrations. In D 2O the quantum yields of BITYR, HOHICA and DOPA are increased considerably while those of AEHEA are decreased. Irradiation of Rose Bengal with visible light ( 1O 2 formation) in the presence of TYROH yields HOHICA (90%) and BITYR (10%). It is concluded that from the excited singlet state ( 1TYROH) photoionization and splitting of the phenolic OH bond occurs giving rise to tyrosine-derived phenoxyl radicals (TYRO) which are the precursors of BITYR. Also, from 1TYROH a 1,3-H-shift of the phenolic OH and concomitant ring-opening occurs. Addition of water and loss of carbon dioxide in subsequent thermal reactions yields AEHEA as the final product. Quenching of the TYROH triplet state ( 3TYROH) by O 2 yields 1O 2 which reacts with TYROH by H abstraction. The resulting intermediates TYRO . and HO 2 . are the precursors of BITYR and HOHICA. In addition, a reaction of O 2 with 3TYROH possibly yields 1,4- and 3,6-endoperoxides which are the precursors of further HOHICA and of DOPA and 2,4-DHPhe, respectively.

Solvent Effects on Chemical Processes. 10. Solubility of α-Cyclodextrin in Binary Aqueous-Organic Solvents: Relationship to Solid Phase Composition

□ The equilibrium solubility at 25 °C of α-cyclodextrin was measured in several binary aqueous-organic solvent mixtures, the organic cosolvents being methanol, 2-propanol, ethylene glycol, and acetone. Solubility maxima were observed as the solvent composition was varied from pure water to pure cosolvent. The maximum in methanol systems was hardly detectable, but it was very pronounced in 2-propanol and acetone, and two maxima were seen in the ethylene glycol system. Karl Fischer analysis of the solid phase isolated from 2-propanol/water equilibrium systems showed that α-cyclodextrin hexahydrate is the stable form in water, whereas a solid phase containing three water molecules per molecule of α-cyclodextrin is the stable form in the presence of 2-propanol. The appearance of a solubility maximum in this system, and by extension presumably in the other cosolvent systems, is attributed to the existence of more than one stable solid phase of α-cyclodextrin.

Enantiomer Discrimination by Continuous Precipitation

A continuous turbidimetric method for the discrimination of enantiomers (L- and D-lysine) by the inhibitory action of L-lysine on the crystallization of L-glutamic acid is proposed. A multidetection flow system including an open-closed loop and a single detector permits the determination of kinetic parameters for the crystallization of L-glutamic acid in the presence of 2-propanol. L-Lysine can thus be determined in the presence of a 20 times higher D-lysine concentration. The proposed method was applied to the determination of L-lysine in pharmaceutical preparations with good results.

Rhodium-carbenoid mediated O-H insertion reactions. O-H insertion vs. H-abstraction and effect of catalyst

The synthesis and rhodium mediated O-H insertion reactions of a wide range of diazo compounds are described. The rate at which the diazo compounds decompose in the presence of 2-propanol and the rhodium catalyst is strongly dependent on the electron withdrawing group(s) attached to the diazo carbon, with diazophosphonates being the least reactive. Insertion into the O-H bond of methanol, t-butanol and phenols was also investigated, as well as the effect of catalyst. In some cases ‘reduction’ of the diazo group to the corresponding CH 2 group competes with O-H insertion, although this is highly catalyst and substrate dependent. Of the catalysts used, rhodium(II) trifluoroacetamide is the most effective for O-H insertion reactions.

On the syntheses and photochemical properties of heterocyclic ketones as photosensitizers

The syntheses, and the electrochemical and photochemical properties of the fluorenone analogues 9H-pyrrolo[1,2-a]indole-9-one (1), and 9H-pyrido[3,4,b] pyrrolizin-9-one (2), which absorb in the visible region (ε400nm = 4711 mol−1 cm−1 for 1 and ε400nm = 872 1 mol cm−1 for 2), are described. 9-Fluorenone as well as compounds 1 and 2 were able to reduce methyl viologen in the presence of 2-propanol under irradiation with UV light (λ⪢ 280 nm). Compounds 1 and 2 showed an interesting absorption and fluorescence behavior depending on concentration, solvent and pH value. Aqueous solutions of compound 1 gave two fluorescence maxima at 395 and 478 nm, when excited by λEX = 302 and 368 nm, respectively. In contrast, aqueous solutions of compound 2 showed only one emission maximum at 417 nm (excited by λEX = 296 or 378 nm). Fluorescence quantum yields (solvent: propanol, excitation wavelength λEx = 436 nm) for compounds 1 and 2 were 0.2%. Compounds 1 and 2 showed irreversible reduction potentials at −850 and −560 mV (vs NHE), respectively. The results were compared with benzophenone and 9-fluorenone.

Preparation of Nonmetallic Silver Clusters in Aqueous Solutions Using UV Lasers

Abstract Nonmetallic silver clusters (λmax = 275 nm) were prepared by UV laser irradiation of aqueous solutions of silver perchlorate in the presence of 2-propanol and sodium polyphosphate. They were transformed into silver colloids (λmax = 380 nm) obeying second-order kinetics. Effects of added electrolytes on the kinetics were studied.

On the syntheses and photochemical properties of novel pyrrolizinone derivatives as photosensitizers

The syntheses of the pyrrolizinone derivatives 8H-6-methyl-7-phenylthieno[2,3-b]-pyrrolizin-8-one (1), 10H-6,7,8,9-tetrahydro(1)benzothieno[2,3-b]pyrrolizin-10-one (2), 8H-6-phenylthieno[2,3-b]pyrrolizin-8-one (3), 8H-methylthieno[2,3-b]pyrrolizin-8-one (4), are described. In contrast to benzophenone, compounds 1 – 4 absorb in the visible light region (ε 436 nm = 400, 420, 450, and 320 l mol −1 cm −1 for compounds 1 – 4, respectively). 9-Fluorenone as well as compounds 1 – 4 were able to reduce methylviologen in the presence of 2-propanol under irradiation with UV light (λ > 280 nm). Compounds 1 – 4 showed an interesting fluorescence behavior depending on solvent and on Ph - value, which will be discussed in detail.

Acetone-sensitized photolysis of 5-iodouracil and 5-iodouridine in aqueous solution in the presence of alcohols: free radical chain mechanism

The photolysis of 5-iodouracil (IU) and 5-iodouridine (IUd) in deoxygenated aqueous solution was studied as a function of pH and in the presence of alcohols. UV and high performance liquid chromatography (HPLC) analysis shows that uracil and I − are the photoproducts of IU. The quantum yield Φ IU→HU of uracil formation from IU in the presence of 2-propanol (1.4 M), using continuous 254 nm radiation, increases with pH from 0.058 in neutral solution to 0.4 at pH 13. The conversion is significantly enhanced by acetone (0.12 M); for an intensity of I 254=2.2 mW cm -2, Φ IU→HU-0.9 and 10 at pH 7 and 12 respectively. Linear dependences of Φ IU→HU vs. I 254 − 1 2 were obtained and, at fixed pH and I 254, Φ IU→HU values decrease with decreasing concentrations of acetone or 2-propanol. The chain reaction is initiated by hydrogen-atom abstraction by triplet acetone from 2- propanol. The suggested propagation sequence is electron transfer from (CH 3) 2 COH/(CH 3) 2 CO − radicals to IU, thereby yielding acetone, I − and the uracilyl radical, which regenerates the alcohol radical by hydrogen- atom abstraction from 2-propanol. The increase in Φ IU→HU with increasing pH is mainly ascribed to a higher efficiency of electron transfer from the (CH 3) 2 .CO − radical to the IU anion than from the (CH 3) 2 .COH radical and to the slower termination reaction of (CH 3) 2 .CO −. Similar dependences and comparable Φ values were obtained for IUd. The chain reaction is suppressed by traces of oxygen. An indication for a chain reaction also in the absence of acetone is based on the linear dependence of Φ IU→HU vs. I 254 − 1 2 at pH 13.

Lactobacillus kefir alcohol dehydrogenase: a useful catalyst for synthesis

The alcohol dehydrogenase from Lactobacillus kefir simultaneously catalyzes carbonyl reductions and NADPH regeneration in the presence of 2-propanol. Representative synthesis of a number of chiral alcohols was accomplished in good yield and high enantiomeric excess (94-99%). This NADPH-requiring enzyme tranfers the pro-R hydride from the cofactor to the si face of carbonyls to give (r) alcohols

Site-directed mutagenesis of glycine-14 and two "critical" cysteinyl residues in Drosophila alcohol dehydrogenase

Three amino acid residues (glycine-14, cysteine-135, and cysteine-218) previously speculated to be important for the structure and function of Drosophila melanogaster alcohol dehydrogenase have been investigated by using site-directed mutagenesis followed by kinetic analysis and chemical modification. Mutating glycine-14 to valine (G14V) virtually inactivates Drosophila ADH, and substitution of alanine at this position (G14A) causes a 31% decrease in activity. Thermal denaturation and kinetic and inhibition studies further demonstrate that replacing glycine-14 with either alanine or valine leads to structural changes in the NAD binding domain. These results provide direct evidence for the role played by glycine-14 in maintaining the correct conformation in the NAD binding domain. On the other hand, changing of cysteine-135, -218, or both to alanine (C135A, C218A, and C135A/C218A) causes no decrease in the catalytic activity of the enzyme, indicating that neither of the cysteinyl residues is essential for catalysis. C135A and wild-type enzyme are both inactivated by DTNB. In contrast, C218A and C135A/C218A are unaffected by DTNB treatment. DTNB modification of cysteine-218 can be prevented by the substrates NAD and 2-propanol, suggesting that cysteine-218 may be in the vicinity of the active site. Cysteine-135 which is normally insensitive to DTNB becomes accessible in the presence of 2-propanol and/or NAD, suggesting a conformational change induced by binding of these substrates.

Photochemistry of a benzophenone-containing bisimide: a model for inherently photosensitive polyimides

The photochemistry of bisimide II has been studied in solution by conventional means as well as by time-resolved laser techniques. Compound II, the adduct of benzophenonetetracarboxylic dianhydride and 2 equivalents of 2-isopropylaniline, was designed as a model for inherently photosensitive, solvent-soluble polyimides — whose photochemistry is not well understood. A low temperature phosphorescence spectrum of matrix-isolated II, along with other results, indicates that the reactivity of II following photon absorption (300 – 365 nm) is due to its lowest n,π * triplet state. Triplet II behaves in a similar fashion to triplet benzophenone, being efficiently quenched by 1,3-dienes and photoreduced by compounds containing labile CH bonds. The absorption spectrum of the intermediate ketyl in the photoreduction was observed, and phosphorescence quenching rate constants for excited II determined in the presence of 2-propanol or triethylamine. The equation for determining quenching rate constants in a “gated” quenching experiment was derived and differs from that used in normal Stern-Volmer studies.

光触媒を使用した石炭への光照射効果

The studies of influence on irradiation of coals with ultra-high pressure mercury lamp were carried out in the presence of 2-propanol and Rh complex catalyst. The yields of benzene soluble fractions increased by photo-irradiation compared with non-irradiated. The average molcular weight of benzene soluble fractions decreased using Nakayama coaland increased using Yubari coal by photo-irradiation. These tendencies were also found in molcular distribution from gel permeation chromatograms. These changes of benzene fractionsof irradiated coals more increased using photocatalyst. These results suggest that the coals decomposed partially by photo-irradiation.

Effect of water concentration on photoreduction of anthraquinone-2-sulfonate by 2-propanol in aqueous acetonitrile solution

Irradiation of anthraquinone-2-sulfonate (AQS) in the presence of 2-propanol (0.08 M) in aqueous acetonitrile solution with nitrogen laser (337 nm) gave AQS radical anion (AQS/sup .-/) in a yield depending very much on water content, the highest yield being obtained in the solution of 40-60 vol% water content. This is attributable to exponential increase with water concentration of the decay rate of triplet AQS and of the deprotonation rate of AQSH/sup ./ resulting from hydrogen abstraction of triplet AQS from 2-propanol. The dependence of these rates on water concentration was treated satisfactorily with Perrin's equation to give an average value of 3.3 A for the radius of the solvation sphere surrounding triplet AQS and AQSH/sup ./ in which a water molecule must exist to quench triplet AQS and to accept a proton from AQSH/sup ./, respectively. Laser exciation and continuous irradiation gave apparently different pK/sub a/ values of AQSH/sup ./. The meaning of this observation was also discussed

Amino acid sequence analysis of the glycopeptides from human complement component C3

Human complement component C3 has been cleaved completely by trypsin in the presence of 2-propanol. The hydrolysate was fully solubilized and fractionated by reversed-phase HPLC. Two peptides only contained glucosamine, Unambiguous sequence analyses identified Asn-63 of the β-chain and Asn-268 of the α-chain as the sites of carbohydrate attachment. A third potential Asn-Xaa-Thr/Ser glycosylation site, Asn-946 of the α-chain, is not modified. The different states of glycosylation of the three sites cannot be explained by differences in exposure or secondary structure. All three are predicted reverse turn.

The 1-hydro-2,6-dimethyl-3,5-dicyanopyridinyl radical in solution: mechanisms of photochemical formation and kinetics of disappearance by self-combination

The 1-hydro-2,6-dimethyl-3,5-dicyanopyridinyl radical (HDCP·) has been identified by electron spin resonance spectroscopy (ESR) in solution at room temperature as an intermediate during both the 280–300 nm photoreduction of 2,6-dimethyl-3,5-dicyanopyridine (DCP) in 2-propanol and the 270–300 nm photo-oxidation of the corresponding 1,4-dihydropyridine (H 2DCP) in oxygenated aqueous acetone. The hyperfine couplings and the g value of HDCP· are reported. The rate constant for the second-order self-combination of HDCP· as determined by time-resolved ESR is 2 k = (1.6 ± 0.4) × 10 9 M −1 s −1 in 2-propanol at 20 °C. In addition to the HDCP· radical dimer (yield, 24%), combination products of the (CH 3) 2ĊOH and the HDCP· radicals (total yield, 32%) have been identified among the products of the photoreduction of DCP in 2-propanol. Also reported are the quantum yields of DCP disappearance (0.07 and 0.15 at 280 nm and 300 nm respectively) and fluorescence quenching studies of aqueous solutions of DCP in the presence of 2-propanol. The various results are rationalized in terms of a mechanism proposed for the photoreduction of DCP in 2-propanol. It is suggested that the radical and product formation originates from the lowest excited 1(n-π *) state of DCP. The formation of the HDCP· radical by photo-oxidation of H 2DCP in oxygenated aqueous acetone is thought to proceed via singlet oxygen.

The elongation factor G carries a catalytic site for GTP hydrolysis, which is revealed by using 2-propanol in the absence of ribosomes.

In the absence of ribosomal particles, elongation factor G (EF-G) promotes very little GTP hydrolysis. After the addition of some aliphatic alcohols to EF-G, the rate of nucleotide cleavage was significantly increased and GTPase activity was easily detectable. The highest stimulation, nearly 16-fold, occurred with 2-propanol at a 20% (v/v) concentration. The reaction showed the characteristics of an enzymatic catalysis, but the rate was three orders of magnitude lower than that of the ribosome-dependent EF-G GTPase activity. Striking similarities between the two activities indicated that the catalysis stimulated by the alcohol was due to EF-G itself. We found that EF-G GTPase activity in the presence of 2-propanol displayed an absolute specificity for GTP as in the presence of ribosomes; the two activities copurified to a constant ratio and exhibited coincident chromatographic and electrophoretic patterns; the temperature for the half-inactivation of EF-G was 59.3 degrees C for both GTPase systems, as well as the kinetic constant for the thermal inactivation process which was found to be 0.05 min-1; and the Km for the GTP in the presence of 2-propanol (59 microM) was similar to that found in the presence of ribosomes. These results indicate that the EF-G molecule carries a catalytic site for GTP hydrolysis, which in the absence of ribosomal particles is activated by an appropriate alcohol/water surrounding medium.

A flash photolytic study of the kinetics and mechanism of the reduction of halocobaloximes by 1-hydroxy-1-methylethyl radicals

A study was undertaken to develop a method of formation of a radical and to evaluate the kinetics of the reduction of some cobalt complexes by this aliphatic radical. The hydroxy-isopropyl radical was prepared by the uv irradiation of acetone in the presence of 2-propanol. The steady-state photolysis of a solution of acetone, 2-propanol, and the desired cobalt(II) complex produced the absorption spectrum of the cobalt(II) cobaloxime. The kinetic data for the reaction are tabulated. The reaction could occur by either an inner-sphere or outer-sphere reaction, but the data seem to favor the outer-sphere electron-transfer process. However, the data are not entirely definitive. 21 references, 1 figure, 2 tables.

Free-radical redox reactions of uranium ions in sulphuric acid solutions

The radiolytic reduction of uranyl ions in degassed sulphuric acid solutions containing various organic solutes was studied. It was shown that while ĊOOH, CO2−, and α-hydroxy-alkyl radicals reduced uranyl ions, the β-hydroxy-alkyl radicals and those derived from gluconic acid could not affect the reduction. The oxidation of uranium(IV) by hydrogen peroxide at pH 0.7 involves hydroxyl radicals in a chain mechanism but at pH 2.0 the oxidation proceeds by a non-radical reaction pathway. From the enhancement of the rate of oxidation of uranium(IV) by oxygen in the presence of 2-propanol, a mechanism involving the perhydroxyl radical, which reconciles earlier published data on kinetics and oxygen tracer studies, is proposed for the oxygen-uranium(IV) reactions.