Strong Acidic Conditions Research Articles

Effects of ligand and metal on the reductive elimination of dihydrogen by dinuclear complexes of chromium and manganese

Six new dinuclear complexes of the form ( η 6 , η 6 - C 6H 5C 6H 4R)Cr 2(CO) 4-μ-L 2, where R  H, L 2  (CH 3) 4P 2, [(CH 3) 2] 2CH 2, [(CH 3O) 2P] 2NCH 3, (F 2P) 2NCH 3, [(CF 3CH 2O) 2P] 2CH 2 and R  CH 3, L  [(C 6H 5) 2P] 2CH 2 have been prepared and are fully characterized by their elemental analyses and spectral properties. The reactions of several dinuclear chromium compounds and ( η 5 , η 5 -C 5H 4C 5H 4)Mn 2- (CO) 4-μ-[(C 6H 5) 2P] 2CH 2 with strong acids have been examined. Dihydrogen evolution has been observed with all but one of the dinuclear chromium compounds. The relative rate of dihydrogen formation by the chromium compounds was found to be dependent upon the metal basicity which is dictated by the electronic character of the diphosphine ligand. The manganese derivative slowly eliminates dihydrogen under strong acid conditions. Deuterated acids have been shown to react with the dinuclear compounds to liberate mostly, but not exclusively, D 2 suggesting that some hydrogen exchange with either the arene rings or with the ligands is occurring prior to dihydrogen elimination. In no case has it been possible to recover the dinuclear compound intact after the reductive elimination of dihydrogen.

The remarkable sensitivity to acid‐catalyzed peptolysis of peptide chains (endopeptolysis) having a succession of three N‐alkylated amino acid residues

An investigation on the resistance against acids of over 30 peptides containing a repetition of N‐alkylated amino acids has revealed the extremely facile cleavage of the peptide bond (endopeptolysis; ranking from a few minutes to 1 hour in Tfa) between the second and third residue in a sequence of three l‐imino acid residues (called “triad”)‐ This is pronouncedly so if Pro is the head member of the triad. Triads become resistant against hydrolysis, however, when both the first and second positions are occupied by Pro, and even more so if the second member is d‐MePhe. On the other hand, as an exception, diads of iminoacids preceded by Gly also are sensitive to hydrolysis. Two possible mechanisms are proposed, among which the one that is characterized by an intramolecular attack of the N‐nucleophilic site of the first residue on the peptide bond between the second and third unit and thus forming a diketopiperazine‐onium intermediate, is our preference. This sensitivity towards acidolysis and acid‐catalyzed hydrolysis should not be overlooked, not only during the planning of peptide syntheses (having especially implications during acidic deprotection protocols), but it will compromise any strategy that makes use of strong acid conditions, e.g. in chiral determinations of N‐alkylated amino acids in peptide hydrolysates, because acidic peptide breakdown is accompanied by appreciable stereo‐mutation. Finally, the weakened resistance of iminoacid peptide chains is obviously related to trans‐cis isomerization about the first peptide bond within the triads and suggests that endopeptidases may well act initially through a trans‐cis isomerase stage.

Aspartic proteinases in fishes and aquatic invertebrates

1. 1. The literature on molecular properties and physiological role of aspartic proteinases in fishes and aquatic in vertebrates has been reviewed. 2. 2. Pepsins have not been detected in invertebrates, and apparently cathepsin D, as well as other cathepsins, act both as digestive and lysosomal enzymes in many of these animals. The molecular properties of invertebrate cathepsin D correspond with cathepsin D in fishes and mammalians. 3. 3. Fishes with a true stomach have pepsinogen secretion. Fish pepsins have higher pH optimum and are less stable in strong acid conditions than mammalian pepsins. They are very efficient at low temperatures, but less thermostable than mammalian pepsins. 4. 4. Many fishes have two significantly different pepsins: Pepsin I and Pepsin II, which digest haemoglobin at a maximal rate in the pH ranges 3–4 and 2–3 respectively. Usually the pI of Pepsin I is in the range 6.5–7, whereas pI of Pepsin II is about 4. 5. 5. Fish Pepsin I and cathepsin D have very similar molecular properties, and a hypothesis proposing that cathepsin D is the ancestor enzyme of aspartic proteinases in higher animals is presented.

The use of iodine staining for the quantitative analysis of lipids separated by thin layer chromatography

The method described for quantitative estimation of lipids separated on thin layer chromatography plates exploits the observation that most lipids can be stained by iodine vapor and that, in "controlled" conditions, the intensity of this staining is proportional to the actual amount of lipid in the spot. The method consists of exposing the developed plate to iodine vapor; spraying it with a suitable solvent to prevent halogen evaporation; collecting the stained lipids by scraping the spots off the plate; and determining by a rate-sensing method the absorbed iodine. The final determination is performed by measuring spectrophotometrically (at 410 nm) the rate of decolorization of a solution of Ce(IV) by As(III) in strong acidic conditions. The reaction rate, which is positively related to the concentration of iodine, is derived from the slope of the absorbance change plotted vs time. Providing that standards and samples are stained simultaneously, a quantitative estimation of lipid components of a mixture is possible in a reasonable time with excellent accuracy and reproducibility. In our hands, the method has been successfully applied to several common phospholipids, long chain fatty acids, cholesterol and deoxycholate, and triacylglycerols, in the range of 5-60 micrograms.

The mild and selective N-debenzylation of tertiary alkylamines using β-trimethylsilylethyl chloroformate.

Benzyl groups are efficiently and selectively cleaved from tertiary alkylamines using β-trimethylsilylethyl chloroformate. This general method is compatible with a wide range of functionality because it does not require strong hydrolytic or acidic solvolytic conditions.

Comparison of six genetically defined inhibitors from the silkworm haemolymph against fungal protease

1. 1. Haemolymph protein inhibitors against a fungal protease were partially purified and their properties were compared using silkworm strains having distinct electrophoretic bands. 2. 2. Great developmental changes in the inhibitory activity and electrophoretic patterns were observed. 3. 3. Inhibitor fractions separated on a DEAE-Sephacel column corresponded to the electrophoretic bands. 4. 4. Low molecular weight inhibitors, A and F were extremely heat stable but high molecular weight inhibitors, C and D were labile. 5. 5. The inhibitor C was stable at pH 5–8 but labile under strong acidic or basic conditions, whereas F was extremely stable over a wide range of pH.

Selectivity in secondary ion mass spectrometry. A study of pyrimidine derivatives

The influence of the molecular structure and surface environment on the secondary ion emission induced by keV ions was investigated for a series of compounds derived from 4(2′-hydroxyphenyl)-2,5-dimethylpyrimidine; the 2-methyl of the pyrimidine ring was substituted by different functional groups. The secondary ion mass spectra recorded under various experimental conditions are presented. A strong enhancement of the protonated molecular ion yield was correlated with an increase of the basicity of the functional group for samples prepared under strong acidic conditions; such a correlation has not been observed with aprotic solvents. The fixation of metal cations (Ag +, Li + and Na +) exhibits a complex behaviour. Ag + fixation is likely to occur on the phenolic moiety and therefore, is not selective. In contrast, Li + and Na + fixation strongly depends on the nature of the substituting group. The observed behaviour cannot be explained from simple chemical considerations such as the intrinsic base properties of the molecules; steric hindrance and matrix effects must be taken into consideration.

Proteolytic Activity in Anther Extracts of Fertile and Cytoplasmic Male Sterile Petunia

Proteolytic activity is compared in anther extracts from Petunia parodii fertile and cytoplasmic male sterile lines. It is characterized relative to developmental stage of the anthers, effect of variable incubation times, pH of isolation buffers, and degradation of marker proteins. In fertile anthers, proteolytic activity increases at the end of microsporogenesis and peaks early in microgametogenesis. Degradation is most severe in extracts of fertile anthers and in high molecular weight proteins and reaches its maximum within 20 minutes. Degradation of marker proteins is greatest at pH 5.6 to 8.0 in fertile anther extracts and is eliminated under strong acid conditions (pH 2.8 to 4.0) in both fertile and cytoplasmic male sterile anther extracts. Marker proteins degrade more severely in extracts of fertile anthers; however, the order of substrate sensitivity-myosin > phosphorylase b > bovine serum albumin and ovalbumin > beta-galactosidase-is the same in extracts from fertile and cytoplasmic male sterile anthers.

ChemInform Abstract: PROTECTION OF THE TRYPTOPHAN INDOLE RING IN PEPTIDE SYNTHESIS. USE OF A NEW DERIVATIVE, NIN‐2,2,2‐TRICHLOROETHOXYCARBONYLTRYPTOPHAN

AbstractDie IndoI‐NH‐Funktion des Tryptophans wird als TrichlorethoxycarbonyI‐Derivat (Troc) geschützt.

PROTECTION OF THE TRYPTOPHAN INDOLE RING IN PEPTIDE SYNTHESIS. USE OF A NEW DERIVATIVE, Nin-2,2,2-TRICHLOROETHOXYCARBONYLTRYPTOPHAN

Abstract The 2,2,2-trichloroethoxycarbonyl (Troc) group attached at the Nin function of tryptophan by acylation with Troc-Cl in the presence of a catalytic amount of tetra-n-butylammonium hydrogensulfate can be quantitatively removed either by cadmium dust in acetic acid or under basic conditions, e.g., hydrazine hydrate and NaOH, but is resistant to strong acidic conditions.

The pigments of Papilio graphium weiskei: Sarpedobilin and ommin responsible for a unique pattern in a butterfly wing membrane

1. 1. The pigments of the butterfly Papilio graphium weiskei have been separately extracted from the different coloured zones of the wing membrane and analyzed. 2. 2. Sarpedobilin 3, a neopterobilin, is present in all parts of the wing, at higher concentrations in the green and blue areas, in traces in the pink zones, the total amount being spectrophotometrically determined at 50 μg per individual. 3. 3. The pigment from the pink and mauve areas cannot be extracted in the usual conditions, but only after in-situ destruction of the membrane under strong acidic conditions. The substance thus obtained shows redox properties. It is identified with ommin on the basis of the already reported similar red pigment obtained in such conditions “Farbstoffe IV” from other insect species. 4. 4. In conclusion, the unique wing pattern of P. weiskei where green, blue, mauve and pink zones occur, is due to the superposition of two pigments, sarpedobilin (a derivative of pterobilin) and ommin, present within the membrane.

Selective elution of immunoadsorbed anti-(human prolactin) immunoglobulins with enhanced immunochemical properties.

Specific anti-(human prolactin) immunoglobulin, isolated by immunoadsorption from a resolubilized Na2SO4 precipitate of a sheep antiserum, has been fractionated into antibody populations with a 10-fold range of affinity for antigen by using a new elution procedure. The procedure utilized acetonitrile (20%, v/v) in a gradient of pH, decreasing from pH 7 to pH2. The recovered immunoglobulin (74.3%) was eluted as a single peak after chromatography on Sephacryl S-300 and on radioiodination retained high immunoreactivity (91%). One antibody population, of low abundance, had an affinity constant (Ka = 8.6 x 10(10) l/mol) 5.7 times that of the unfractionated antiserum and, when used in radioimmunoassay standard curves, resulted in a 3.8-fold increase in the sensitivity of the assay. The bulk of adsorbed immunoglobulin was eluted at pH 4.3, thereby avoiding exposure to strong acid conditions and maintaining the integrity of the immunoglobulin molecule. In contrast, elution of immunoglobulin in the absence of acetonitrile could only be achieved at low pH (pH2) with minimal fractionation, and resulted in a poor recovery (37.1%) and loss of immunoreactivity (53%).

Hydrolytic behavior of two β-lactams and their corresponding imidate salts. New evidence for stereoelectronic control

The basic hydrolysis and the concurrent carbonyl–oxygen exchange of 18O-labelled N-phenyl-4-phenyl-2-azetidinone (5*) and N-2,6-dimethylphenyl-2-azetidinone (6*) have been studied. β-Lactam 5* was easily hydrolysed and showed no carbonyl–oxygen exchange with 0.1 N sodium hydroxide (dioxane–water, 9:1). Under the same conditions, β-lactam 6* gave no exchange and was found resistant to basic hydrolysis. Hydrolysis and exchange was observed when 6* was refluxed with 0.1 N and 1 N sodium hydroxide in water.The hydrolysis of the corresponding imidate salts 7 and 8 was also investigated. Under basic conditions, salt 7 gave an 8:2 mixture of ester amine 9 and β-lactam 5, while under acidic conditions the hydrochloride salt of ester amine 9 was the only product. Under basic conditions, the imidate salt 8 produced only the β-lactam 6, and under acidic conditions, a 3:7 mixture of the hydrochloride salt of 10 and β-lactam 6. Under stronger acidic conditions (≥3 N HCl), 8 gave only the starting β-lactam 6.The results of these hydrolysis reactions are easily explained on the basis of the stereoelectronic theory for the cleavage of tetrahedral intermediates, and by taking into account that the nitrogen of tetrahedral intermediates must be either protonated under acidic conditions, or hydrogen bonded with the solvent under basic conditions in order to observe the cleavage of the C—N bond.

A reinvestigation of the bamberger‐ham phenazine. Synthesis: A limitation

AbstractThe Bamberger‐Ham condensation of 4‐substituted nitrosobenzenes in concentrated sulfuric acid reported as a method of synthesis for phenazine N‐oxides has been found to be limited to electron donating substituents. Methyl 4‐nitrosobenzoale has been found to react under these conditions to give dimethyl 2‐nitrodiphenylamine‐4, 5‐diearboxylate (2). Compounds of unknown structure previously reported to arise from acid treatment of 4‐bromo‐ and 4‐chloronilrosobenzene have been shown to be 4, 5‐dibromo‐2‐nitrosophenylamine (10) and the analogous dichloro compound. Treatment under stronger acidic conditions (oleum) converted 10 but not 2 into the corresponding phenazine N‐oxide. Mechanistic implications are discussed.

Molecular organization in bacterial cell membranes: IV. Isolation by preparative electrophoresis in sodium dodecylsulphate and properties of the two major polypeptide groups of a “soluble” fraction from Streptomyces albus membranes

Two polypeptide fractions have been purified from a “soluble” fraction of n-butanol-extracted Streptomyces albus membranes by preparative electrophoresis in sodium dodecylsulphate. They accounted for approx. 80% of the protein of the fraction (i.e. 20% of the total membrane protein). The ultraviolet spectrum of Group 1 (relative mobility 1.0) revealed the presence of nucleotide material, while that of Group 3 (relative mobility 0.65±0.05) showed the presence of a possibly aggregated protein-like material. About 100 and 30% of the protein contents (Lowry method) of Groups 3 and 1, respectively, were recovered as amino acid residues. These results confirm the protein nature of both fractions and suggest an overestimation of the protein value in Group 1. Both polypeptide groups can be classified as “extrinsic” membrane proteins on the basis of their similar amino acid composition (Vanderkooi, G. and Capaldi, R. A. (1972) Ann. N.Y. Acad. Sci. 195, 135–138). Three N-terminal amino acids were found in each fraction: one common (alanine), methionine, leucine or isoleucine (Group 3) and glutamic acid, lysine (Group 1). The sedimentation coefficients calculated were 2.46 S for Group 3 and 1.54 S for Group 1. Analysis of the isolated groups by gel electrophoresis under non-dissociating conditions or with Triton X-100, gave aggregate-like patterns. Sodium dodecylsulphate electrophoresis revealed an anomalous staining behaviour of Group 3 depending upon the dissociating conditions. The whole “soluble” fraction bound 0.40 mg dodecylsulphate /mg protein (0.55 mg detergent/mg protein corrected for overestimation). After dialysis, the fraction retained 10% of the bound dodecylsulphate. Circular dichroism of the isolated groups after exhaustive dialysis showed similar spectra, although of lower dichroism, to those obtained by other authors on soluble enzymes treated with sodium dodecylsulphate. Strong acid conditions were required to change the CD spectra of the polypeptides.

Studies on the Stability of Chlortetracycline in Mixed Feeds: Epimerization of Chlortetracycline

Abstract Chlortetracycline is known to degrade in aqueous solution by four pathways: anhydrochlortetracycline formation under strong acid conditions, epimerization under weakly acid conditions, isochlortetracycline formation under strongly basic conditions (usually anaerobic), and formation of a desdimethylamino chlortetracycline compound under aerobic conditions at pH values greater than 5. Studies on feeds decomposed to 50% of activity indicated that isochlortetracycline and anbydrochlortetracycline were not formed in the decomposition, while epichlortetracycline and a highly fluorescent unknown compound were formed. Epimerization occurs rapidly in feeds, reaching an equilibrium in a few hours. In several types of feed, protein, fat, fiber, moisture contents, and pH did not affect the degree of epimerization. Temperature of storage appears to be significant. Data suggest that an equilibrium is established between the chlortetracycline and epichlortetracycline followed by breakdown of either chlortetracycline or its epimer or both to as yet unidentified products.

The reaction of reduced pyridine nucleotides with acid

Reduced pyridine nucleotides and related compounds react with acid to yield a primary product that absorbs at 290 mμ. Evidence is presented that suggests that this product is formed by opening the heterocyclic ring yielding an aldehyde. Under strong acid conditions (pH 1), the 290-mμ chromophore is cleaved from the nucleotide giving adenosinediphosphate ribose and a pyridine derivative. The acid product is discussed and related to a postulated mechanism of oxidative phosphorylation at the pyridine nucleotide level.

Chemical Resistance of Phenolic Laminates

Abstract Eight representative types of phenolic laminates were immersed in various aqueous chemical solutions for 6 months and tested periodically for weight change, dimensional change, and strength losses. On the whole, any laminate which has the desired properties after prolonged immersion in water alone would also be satisfactory for other field conditions, with the exception of a strong acid condition or any alkaline condition. Where alkaline or strong acid conditions are involved, special care must be taken in the selection of laminates to be used.

The Interaction of Light Intensity and pH Values of Nutrient Medium in the Growth, Yield, and Chemical Composition of Rice Plants.

In order to ascertain the physiological roles of the hydrogen-ion concentration of nutrient medium and the intensity of daylight upon growth, yield, and chemical composition of rice plant, these experiments were carried out under the condition of water culture. Two varieties, namely Kameno-o and Husaku sirazi were cultured with two modiffed Kasigai's solutions, which were prepared to be kept at 3.1 and 5.8 pH values respectively. The nutrient solutions were renewed every other day, so that no significant change of pH values and of the chemcal forms of compounds would occure in the experiments. The pots, in which the materials were growing, were classfied into three groups and they were placed under the different conditions of solar radiation in the following plan. Three cubical wooden frames (2X3.7X3 m, ) were set on field; and two of them were covered with one or two laycrs of white cotton cloth and the other had no cover as control. The growth of plant was markedly affected by the difference of both by the reaction of the culture solutions and the light intensities. Under the conditions of decreasing light the plants apted to grow in elongation rapidly. ln some experiments, however in the strong acidic condition the light effect was marked, since growth was lirnited by hydrogen-ion concentration. The number of tillers increased directly proportional to the light intensity in the case of pH 5.8., but such a tendency was not clear in the higher acidity. Lowering the intensity to 0.65 of day light produced rather more dry matter of plant, but a further diminishing light intensity, made it to fell off considerablly. The yield of grains increased almost proportional to the amount of solar radiation in the case of pH 5.8 but in the higher acidity a reversible relation, even a slight, was found. Muchs sugars and starch were contained in the plants cultured with strong acidic solutions when the light was insufficiemt, while, they were less in the case of pH. 5.8. The amount of chlorophyll in leaves was directly proportional to the decreasing light intensities at both reaction of culture media within the limits of these experiments. In the slightly decreasring of light, carotine and xanthophyll increased exceptionally. A partial parallelism was found between the amount of nitrogen in plants and the decreasing of light intensity. Similar results were also obtained concernning to phosphorus and potassium, while less iron, on the contrary, was found, especially in the strong scidity of medium. From the fact above mentioned, it may be concluded that rice plants grow favorablly in the lack of solar radiations under the strong acidic conditions.