Showing papers on "Reagent published in 1974"

Determination of phosphorus

Abstract: A one step method for the spectrophotometric determination of phosphorus in the presence of protein using molybdic acid is disclosed. Protein precipitation is avoided by including a long chain amine ethylene oxide adduct in the sample reagent mixture being analyzed.

Reduction and inactivation of superoxide dismutase by hydrogen peroxide

Abstract: Reactions of H2O2 with superoxide dismutase were studied by e.p.r. (electron paramagnetic resonance) spectroscopy and other methods. In agreement with earlier work, the Cu2+ of the enzyme is reduced by H2O2, although the reaction does not go to completion and its kinetics are not simple. With dilute enzyme the time for half-reduction with 9mm-H2O2 is about 150ms. It is suggested that the reaction is a one-electron reduction, involving liberation of O2−. On somewhat more prolonged exposure to H2O2, the enzyme is inactivated. For enzyme in dilute solution and over a limited range of H2O2 concentrations, inactivation is first-order with respect to enzyme and reagent, with k=3.1m−1·s−1 at 20–25°C. Inactivation is accompanied by marked changes in the e.p.r. and visible spectra and appears to be associated with destruction of one histidine residue per subunit. It is suggested that this histidine is close to the metal in the native enzyme and essential for its enzymic activity.

Carbon-13 Magnetic Resonance Studies of Azoles. Tautomerism, Shift Reagent Effects, and Solvent Effects

Abstract: The effects of substitution, lanthanide-shift reagents, solvent changes, and tautomerism were investigated on the ^(13)C chemical shifts of pyrrole, pyrazole, imidazole, s- and v-triazole, and tetrazole. It was concluded that ^(13)C chemical shifts are of limited value to ascertain the positions of tautomeric equilibrium for rapidly interconverting azole tautomers.

Ferric chloride in acetic anhydide. Mild and versatile reagent for the cleavage of ethers

Abstract: Durch eine Losung von wasserfreiem Fe(III)-chlorid in Acetanhydrid werden Ather (I) uber die Zwischenstufen (III) zu den Acetaten (IV) bzw. (V) gespalten.

A simple, sensitive method for lipid phosphorus

Abstract: A method is described for quantitatively determining lipid phosphorus with a linear range from 0.7–10.0 μg. The method is simple and rapid, requiring one stable reagent and a single extraction with 1-butyl acetate after the phosphorus is converted to inorganic phosphate by means of a perchlorate digestion. The stable complex is read at 310 nm.

Chemical syntheses with a quenched flow reactor. Hydroxytrihydroborate and peroxynitrite

Abstract: The technique of mixing two streams of reactant solutions in a reaction tube with down stream injection of a solution containing a quenching reagent has been used for studying the kinetics of fast reactions. The method is ideal for a synthesis involving the formation of an intermediate species which (1) must be prepared under conditions such that its half-life is in the range between a millisecond and several seconds and (2) can be stabilized by rapid reaction with a quenching reagent. The method was verified by the successful use of this method for preparing solutions of two different compounds in high yield, sodium hydroxytrihydroborate and sodium peroxynitrite. The apparatus is described. 1 table.

Metathesis of alkynes by a molybdenum hexacarbonyl–resorcinol catalyst

Abstract: A mixture of molybdenum hexacarbonyl and a phenol reagent is an active and selective homogeneous catalyst for the metathesis of aromatic disubstituted alkynes.

Process for treating stack gases

Abstract: Stack gases containing pollutant gases and particulate matter are passed through a defined flow path into which at least one selected liquid reagent is introduced in a prescribed manner to intimately contact the stack gases therein. The liquid reagent scrubs the stack gases and thereby removes a substantial portion of the pollutant gases and particulate matter therefrom. One reagent may be used or several different reagents may be employed at different stages of the flow path to best effect removal of various different pollutants contained within the stack gases. Removal of sulfur dioxide is accomplished by a highly reactive and substantially non-abrasive reagent, such as a lime solution and such solution further effects removal of materials in trace amounts in the stack gases such as mercury, bergillium and vanadium. Removal of nitric oxide and other materials in trace amounts is also accomplished by the process which includes as a reagent an oxidant.

Metal cofactor requirement of β-lactamase II

Abstract: 1. The apoenzyme obtained on removal of Zn2+ from β-lactamase II from Bacillus cereus 569/H/9 showed less than 0.001% of the activity of the Zn2+-containing enzyme. 2. Removal of Zn2+ led to a conformational change in the enzyme and partial unmasking of a thiol group. 3. Replacement of Zn2+ by Co2+, Cd2+, Mn2+ or Hg2+ gave enzymes with significant, but lower, β-lactamase activity. No activity was detected in the presence of Cu2+, Ni2+, Mg2+ or Ca2+. 4. Equilibrium dialysis indicated that the enzyme had at least two Zn2+ binding sites. With benzylpenicillin as substrate the variation in activity with concentration of Zn2+ indicated that activity paralleled binding of Zn2+ to the site of highest affinity. 5. Replacement of Zn2+ by Co2+ and Cd2+ gave enzymes with absorption bands at 340 and 245nm respectively, and raised the question of whether the thiol group in the enzyme is a metal-ion ligand. 6. Reduction of the product obtained by reaction of denatured β-lactamase II with Ellman's reagent [5,5′-dithiobis-(2-nitrobenzoic acid)] gave a protein which could refold to produce β-lactamase II activity in high yield.

Trifluoromethanesulphonic acid, as a deprotecting reagent in peptide chemistry

Abstract: Trifluoromethanesulphonic acid was found to cleave, in the presence of anisole, a number of protecting groups currently employed in peptide chemistry without significant side reactions.

Diagonal polyacrylamide-dodecyl sulfate gel electrophoresis for the identification of ribosomal proteins crosslinked with methyl-4-mercaptobutyrimidate.

Abstract: A diagonal polyacrylamide-dodecyl sulfate gel electrophoresis procedure is described. Its utility is related to the use of the reagent methyl-4-mercaptobutyrimidate as a protein-protein crosslinking reagent. Crosslinking with this reagent occurs through the formation of intermolecular disulfide bonds. Oxidized proteins are separated in one dimension by electrophoresis under non-reducing conditions and in the second dimension under reducing conditions. All proteins except those derived from crosslinked species fall on a diagonal. Methods are described for the identification of the separated monomeric components of crosslinked species. The technique has been applied to the 30S ribosomal subunit of Escherichia coli, and the new crosslinked dimer, S4-S13, has been identified.

The Use of N-Hydroxy-5-norbornene-2, 3-dicarboximide Active Esters in Peptide Synthesis

Abstract: N-Hydroxy-5-norbornene-2, 3-dicarboximide (HONB) was found to be an excellent reagent to be used in couple with N, N'-dicyclohexylcarbodiimide (DCC) for the peptide synthesis. Various racemization tests by the use of this reagent were conducted to see the degree of racemization during the peptide synthesis. The newly employed reagent (HONB) decreases racemization, prohibits formation of N-acylurea and affords peptides in excellent yields and a high state of purity. To evaluate this new reagent, luteinizing hormone releasing hormone (LH-RH) was prepared by the new active ester method.

Location of energy barriers. VI. The dynamics of endothermic reactions, ab + c

Abstract: A systematic 3D classical-trajectory study has been made of the effect of reagent energy distribution and mass combination on the dynamics of endothermic reaction. The potential-energy hypersurface was endothermic by 35.7 kcal mole−1. Reagent translation, T′, and vibration, V′, was varied in the range up to T′ + V′ = 90 kcal mole−. Among the principal findings for the equal-mass case were the following. (i) There is an orders-of-magnitude increase in reaction cross section when energy is transferred from T′ to V′, until an optimal distribution over T′ and V′ is achieved at V′ ⪖, T′. There is a qualitative difference between the forms of the reactive cross section dependences S(T′) V′ and S(V′)T′. (ii) The greater efficacy of V′ than T′ in promoting endothermic reaction is marked even at total reagent energies ≈ 3 x the endothermic barrier height. (iii) The total reactive cross section for endothermic reaction increases to large values (≈ gas kinetic) as V′ increased to several times the barrier height. (iv) Reagent energy in excess of that required to cross the endothermic barrier is subject to the same “adiabatic” transformation into product energy as was previously observed for exothermic reactions: ΔT′ → ΔT + ΔR (where R is enhanced product rotational energy), and ΔV′ → ΔV. This is explained in terms of induced repulsive energy release in the former case, and induced attractive energy release in the latter. (v) The molecular product is backwards or sideways scattered. Enhanced V′ at constant T′ diminishes product repulsion, giving rise to more-forward scattering. (vi) These findings remain qualitatively unchanged when extreme mass combinations H H + L and L H + H (L = 1 amu, H = 80 amu) are substituted for the equal-mass combination, L L + L. Effects ascribable to a “late” barrier are accentuated for HH + L. and diminished for L H + H. (vii) The total reactive cross section at a given reagent energy increases in the sequence H H + L, L L + L, L H + H, for simple kinematic reasons. (viii) The dynamics on this endothermic potential-energy surface resemble, in all the points listed above, the dynamics on a thermoneutral surface which has its barrier crest in the coordinate of separation (surface II of part I of this series).

The Organic Chemistry of Copper

Abstract: Publisher Summary This chapter discusses the organic chemistry of copper. Organocopper compounds have been obtained by many methods; the one commonly employed is the metathetical reaction between an organometallic reagent, wherein the metal is higher than copper in the electromotive series, and a copper salt. A general method for the preparation of organocopper compounds of the type RCu is the reaction of a Grignard or lithium reagent with an excess of a copper salt. Organocopper compounds, such as methyl–, phenyl–, tolyl–, and ethynylcopper are easily isolated by the virtue of their insolubility in the media employed in their preparations. The structures of some copper compounds have been determined either by X–ray crystallography or by a combination of nuclear magnetic resonance (NMR) and mass spectroscopic data and the degree of association. Ultraviolet spectral data have been reported for a few organocopper compounds. Organocopper–isocyanide complexes are assumed to be intermediates in certain organic syntheses. Perfluoroalkylcopper and perfluoroarylcopper compounds are noticeably more thermally stable than the corresponding alkyl and aryl compounds. The thermal decomposition of aryl– and vinylcopper compounds is an alternative method of obtaining dimeric products from organocopper compounds. Organocopper compounds are useful reagents for coupling reactions with organic halides. A noticeable feature of the majority of reactions of diorganocuprates with alkyl halides is that the molar ratios of up to 5: 1, respectively, are employed for most effective coupling.

Übergangsmetall‐Carben‐Komplexe, LXXVII. Abspaltung des Carbenliganden aus Pentacarbonyl(methoxyalkylcarben)chrom(0)‐Komplexen in einigen tertiären Stickstoffbasen, p‐Dioxan und Decalin. Synthese von Enoläthern

Abstract: Bei den Umsetzungen von (CO)5CrC(OCH3)CHR1R2 (R1 = H, R2 = H, CH3, C2H5 und R1 = R2 = CH3) 1–4 mit verschiedenen tertiaren Stickstoffbasen wurden in guten Ausbeuten Enolather vom Typ CH3OCHCR1R2 erhalten. Diese Beobachtungen werden durch die Spaltung der Chrom-Carbenkohlenstoff-Bindung durch das freie Elektronenpaar des Stickstoffs der Base und eine 1,2-Wasserstoffverschiebung eines zum Carbenkohlenstoff-Atom α-standigen H-Atoms verstandlich. Da die entsprechenden Umsetzungen mit p-Dioxan und 1-Methyl-2-pyrrolidon keine eindeutigen Reaktionsprodukte ergeben, hangt diese 1,2-H-Verschiebung offenbar masgeblich von der Basizitat des Reagens ab. Dagegen gab die thermische Abspaltung des Carbenliganden in Decalin das Dimere des Carbenliganden. Transition Metal Carbene Complexes, LXXVII. Cleavage of the Carbene Ligands from Pentacarbonyl(methoxyalkylcarbene)chromium(0) Complexes in some Tertiary Nitrogen Bases, p-Dioxan and Decalin (CO)5CrC(OCH3)CHR1R2 (R1 = H, R2 = H, CH3, C2H5, C2H5, and R1 = R2 = CH3) 1 — 4 reacts with various tertiary nitrogen bases to give enolethers of the type CH3OCHCR1 R2 in good yields. An explanation for these observations is the cleavage of the chromium-carbene-C-bond by the lone electron pair of the nitrogen base and a 1,2-shift of an H-atom in an α-position to the carbene C-atom. Analogous reactions with p-dioxan and 1-methyl-2-pyrrolidone give no definite products. Therefore the 1,2-H-shift seems to depend on the basicity of the reagent. On the other hand the thermal cleavage of the carbene ligand in decalin gave the dimer of the carbene ligand.

System for detecting the particular chemical constituent of a fluid

Abstract: A system for detecting the particular constituent of a fluid which comprises a cassette for holding a plurality of chemical reaction-testing strips each provided with a plurality of carriers containing reagents; means for drawing out said chemical reaction-testing strips one after another from the cassette and bringing a test fluid filled in a container into contact with the respective reagent carriers of the strip; means for producing an electric signal corresponding to the degree of a chemical reaction between the test fluid and any of said reagent carriers; and means for printing out data denoting the degree of said chemical reaction.