Changes in Flavor Components of Onion by γ-Irradiation

The effect of γ-irradiation on the flavor of Onions (Senshu Yellow) associated with sprout-inhibition has been investigated. The relative amounts of propionaldehyde, n-propyl mercaptan and di-n-propyl disulfide in onions stored for 0, 5, 10, 20 and 30 days, respectively, after irradiation were estimated by measurement of peak areas of gas chromatograms. It was observed that the lachrymatory character and the pungent flavor had been decreased by γ-irradiation (remarkably at 70 and 700 Krads). In this connection, the amounts of propionaldehyde and di-n-propyl disulfide were decreased with increasing radiation dose and storage period at room temperature (20 to 25°C) and at low temperature (4°C). Moreover, it was observed that the sweetness had been decreased by γ-irradiation, but the amount of n-propyl mercaptan was increased with radiation dose and storage period. Therefore it seems that there is no correlation between the sweetness of onion and the amount of n-propyl mercaptan.     

A New Pyridoxamine 5′-Phosphate–α-Ketoglutaric Acid Transaminase (Pyridoxamine 5′-phosphate:2-Oxoglutarate Aminotransferase)

A thin-layer chromatographic method is described for the separation, identification and determination of 2,4-dinitrophenyl sulfides. The derivatives are easily obtained from mercaptan and dinitrofluorobenzene in the presence of sodium bicarbonate at room temperature. The sulfides are separated on silica gel plates using a solvent mixture of benzene-xylene-carbon tetrachloride (2:1:1, v/v). The individual sulfides are determined spectrophotometrically, at 330~335 mμ in ethanol, ε_max ca. 13,000, after washing out the plate with hexane and extraction from the adsorbent with acetone.     

UV-Photolysis of S-(cis-l-Propenyl)-L-cysteine in Oxygen-free Aqueous Solution

From the comparisons of mass spectral fragmentations and gas chromatographic retention times with reference compounds, volatile flavor products from UV-photolysis of S-(cis-l-propenyl)-L-cysteine in oxygen-free aqueous solutions were identical with propanal, 2-methyl-2-pentenal, n-propyl mercaptan, allyl mercaptan, 1-propenyl mercaptan, 2-methylthiophene, 3-methylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, 3,4-dimethylthiophene, n-propyl 1-propenyl sulfide and di- 1-propenyl sulfide. Moreover, from the comparison of two-dimentional thin-layer chromatograms with reference compounds, ninhydrin-positive products with interest in terms of the degradation mechanism were identical with alanine and cystine. It seems that above-mentioned thiophene derivatives are produced via 1-propenyl thiyl radicals.     

Conversion of furfural into furfuryl alcohol by saccharomyces cervisiae 354

The influence of aeration, stirring conditions, and the addition of furfural on the yield and productivity of furfural – furfuryl alcohol bioconversion by the yeast strain Saccharomyces cerevisiae 354 was investigated. The formation of furfuryl alcohol increases up to 32 hours of incubation corresponding to the addition of furfural, while the cell growth essentially ceased at 20 hours. The conversion of furfural into furfuryl alcohol under anaerobic and low aeration conditions was 70% and the productivity 0.5g · 1^?1 · h^?1, when the final concentrationof of furfural amounted to 35 g · 1^?1.     

Tracing the Early Emergence of Microbial Sulfur Metabolisms

Abstract

Hydrogen sulfide (nH₂S) and sulfur oxide (SO _n ; n?=?1, 2, 3) gases in early Earth’s globally anoxic atmosphere were subjected to gas-phase chemical transformations by UV light. A principal photolysis pathway at that time produced elemental sulfur aerosols with mass-independently fractionated (MIF) isotopic values carrying variable minor isotope (³³S, ³⁶S) compositions. These rained into the sulfate-deficient Archean (ca. 3.85–2.5 Ga) oceans to react with [Fe²⁺]_aq and form sedimentary sulfides. The MIF-bearing sulfides were incorporated into Archean sediments, including banded iron formations (BIF). Such aerosols may also have fueled microbial sulfur metabolisms, and thus are traceable by the MIF sulfur isotopes. Yet, data show that before ～3.5 Ga mass-dependent³⁴S/³²S values in Early Archean sediments tend to fall within a narrow (±0.1%) range even as they carry mass-independent values. By about 3.5 Ga, ³⁴S/³²S values show much greater changes (>1%) in range congruent with microbial metabolic processing. Here, we trace probable pathways of elemental sulfur aerosols into Archean sediments, and couple our study with analysis of the evolutionary relationships of enzymes involved in sulfur metabolism to explain the observed trends. Our model explains why elemental sulfur aerosols were apparently not utilized by the Eoarchean (pre-3.65 Ga) biosphere even though an immediate precursor to the required enzyme may have already been present.

• Highlights

• Evolution of microbial sulfur metabolisms is tracked by multiple sulfur isotopes

• Alkaline hydrothermal vents were an abode for early microbial life

• Sulfite detoxification prompted anaerobic respiration

• Reversal of respiratory electron transport chain (ETC) stimulated photothiotrophy

• Surplus e- acceptors permitted the emergence of elemental sulfur reduction

     

A Study on Low-boiling Chemical Constituents of Cryptotaenia japonica Hassk

Low-boiling compounds escaping during steam distillation of Cryptotaenia japonica Hassk were collected and examined with chromatographies and by the preparation of their derivatives.

The following compounds were identified. Six paraffin hydrocarbons: n-pentane, n-hexane, n-heptane, n-octane, isooctane, n-nonane; seven carbonyl compounds: formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isovaleraldehyde, acetone, 3-methyl-2-pentanone; three esters: n-propyl and isopropyl formates, n-propyl acetate; eight alcohols: methanol, ethanol, n-propanol, isopropanol, isobutanol, sec-butanol, isopentanol, n-octanol; two sulfides: dimethyl and methyl ethyl sulfides; six monoterpene hydrocarbons: α-pinene, camphene, β-pinene, sabinene, myrcene, limonene.     

Stabilities and rates in the laccase/TEMPO-catalyzed oxidation of alcohols

The influence of alcohol, 4-acetylamino,2,2,6,6′-tetramethylpiperidinyloxy (4-acetylamino-TEMPO) and laccase (from Trametes versicolor, TvL) concentration in the aerobic oxidation of furfuryl alcohol was investigated. Studies show that the K_m for 4-acetylamino-TEMPO is around 6.3 mM (V_max=0.18 mM min^?1) using 6.6 U mL^?1 of laccase and a furfuryl alcohol concentration of 140 mM. Under these optimized conditions, the reaction rate is still dependent on the concentration of enzyme in solution. Laccase can be reused, with a residual activity of around 25%. An important conclusion is that laccase is not stable in the presence of oxoammonium salts, presumably due to degradation via oxidation of essential amino acid residues or the glycosyl moieties on the periphery of the enzyme.     

Linear oligopeptides. 56. Critical size for development of β-and α-helical structures of monodispersed homo-l-oligomethionines in the solid state

The infrared absorption properties of monodispersed, chemically and optically pure ‘amino-PEG’-bound linear homooligopeptides having the general formula t-Bx(l-Met)_n NHPEG, n = 1–15 and H₂⁺(l-Met)_nNHPEG, n = 1–14 have been investigated in the solid state. The critical sizes for development of the β-structure and α-helix (n = 3 and n = 13, respectively), and the effect, on the latter, of the solvent from which the solid samples are cast, have been established.     

Metal-metal bonding and charge localisation in [Ru2X9], X=Cl or Br; n=1, 2, 3, 4. A spectroelectrochemical study

A spectroelectrochemical study of [Ru₂X₉]ⁿ⁻, X=Cl, Br; n=1, 2, 3, 4 has been undertaken. Stable solutions of n=4, 2, 1 can be formed by electrolysis at low temperatures. Analysis of the Vis-NIR spectra of the complexes indicate that the Ru^II---R^III dimers (n=4) have delocalised mixed valence and that the Ru^III---R^III (n=3) dimers have a strong Ru---Ru bond. The more oxidised materials do not form a Ru---Ru bond; the spectroscopic data indicates the Ru^III---R^IV dimers have localised valency.     

Thermal transitions in mixtures of polydeoxyribodinucleotides

Oligo d(C-A) and oligo d(T-G) of known average lengths, prepared by a combination of chemical and enzymatic procedures, have been mixed in 0.02 M and 0.07 M Na⁺, and absorbance has been studied as a function of increasing temperature. The transitions have been analyzed for the temperature of maximum slope T_m, the breadth of the transition, the value of the slope at T_m, and the maximum hyperchromicity. Linear expressions have been found relating the inverse of the length in nucleotide units (n^?1) of the shorter oligomer, irrespective of its identity, to T_m and also to the transition breadth. From a difference in slope between the T_m versus n^?1 expressions for the two molarities, the entropy and enthalpy of melting have been calculated as a function of n^?1.     

Studies on the Sunlight Flavor of Beer

Three synthetic lupulone analogues, i.e., 1-acetyl-3,3,5-tri-allyl-, 1-acetyl-3,3,5-tri-n-propyl-and 1-acetyl-3,3,5-tri-n-butyl-hexadiene- (1,5) -diol- (2,6) -on- (4) did not cause sunlight flavor of beer when they were added to a fermented solution of sucrose and exposed to sunlight.

When methanol solutions of humulone and acetolupuphenonen were exposed to sunlight, changes in the UV-absorption spectra were observed. This fact indicates that humulone and acetolupuphenone underwent some photochemical reaction upon exposure to sunlight.

Prenyl (γ,γ-dimethylallyl) mercaptan was synthesized, which gave a typical sunlight flavor when it was added, in a trace amount, to a fermented solution of sucrose.     

Infrared spectra of isotopic polyglycines

For infrared absorption measurements, the following five isotopic polyglycines have been prepared: ordinary polyglycine (—NHCH₂CO—)_n, N-deuterated polyglycine (—NDCH₂CO—)_n, C-deuterated polyglycine (—NHCD₂CO—)_n, completely deuterated polyglycine (—NDCD₂CO—)_n, and N¹⁵-substituted polyglycine (—¹⁵NHCH₂CO—)_n. Infrared spectra have been observed both in the I and II forms of each of these five isotopic polyglycines in the spectral region of 4000–300 cm.^?1. On the basis of the comparison of these spectra with each other, a nearly complete set of assignments of the observed bands of polyglycines has been given.     

A simple, practical and complete O-time Algorithm for RNA folding using the Four-Russians Speedup

Background  

The problem of computationally predicting the secondary structure (or folding) of RNA molecules was first introduced more than thirty years ago and yet continues to be an area of active research and development. The basic RNA-folding problem of finding a maximum cardinality, non-crossing, matching of complimentary nucleotides in an RNA sequence of length n, has an O(n ³)-time dynamic programming solution that is widely applied. It is known that an o(n ³) worst-case time solution is possible, but the published and suggested methods are complex and have not been established to be practical. Significant practical improvements to the original dynamic programming method have been introduced, but they retain the O(n ³) worst-case time bound when n is the only problem-parameter used in the bound. Surprisingly, the most widely-used, general technique to achieve a worst-case (and often practical) speed up of dynamic programming, the Four-Russians technique, has not been previously applied to the RNA-folding problem. This is perhaps due to technical issues in adapting the technique to RNA-folding.     

<Emphasis Type="Italic">Cupriavidus necator</Emphasis> JMP134 rapidly reduces furfural with a Zn-dependent alcohol dehydrogenase

Ethanol is a renewable biofuel, and it can be produced from lignocellulosic biomass. The biomass is usually converted to hydrolysates that consist of sugar and sugar derivatives, such as furfural. Yeast ferments sugar to ethanol, but furfural higher than 3 mM is inhibitory. It can take several days for yeast cells to reduce furfural to non-inhibitory furfuryl alcohol before producing ethanol. Bioreduction of furfural to furfuryl alcohol before fermentation may relieve yeast from furfural toxicity. We observed that Cupriavidus necator JMP134, a strict aerobe, rapidly reduced 17 mM furfural to less than 3 mM within 14 min with cell turbidity of 1.0 at 600 nm at 50°C. The rapid reduction consumed ethanol. The “furfural reductase” (FurX) was purified, and it oxidized ethanol to acetaldehyde and reduced furfural to furfuryl alcohol with NAD⁺ as the cofactor. The protein was identified with mass spectrometry fingerprinting to be a hypothetical protein belonging to Zn-dependent alcohol dehydrogenase family. The furX-inactivation mutant of C. necator JMP134 lost the ability to rapidly reduce furfural, and Escherichia coli producing recombinant FurX gained the ability. Thus, an alcohol dehydrogenase enabled bacteria to rapidly reduce furfural with ethanol as the reducing power.     

Co-oligopeptides of aromatic amino acids and glycine with a variable distance between the aromatic residues. III. Co-oligopeptides of L-phenylalanine, L-tryptophan, and Glycine: synthesis and ultraviolet absorption properties.

The preparation of the co-oligopeptides of the series H-Gly-Phe-(Gly)_n-Trp-Gly-OH (n = 0, 1, 2) and of other free peptides of glycine, L -tryptophan, and L -phenylalanine is reported. The syntheses have been carried out by conventional methods, using N-hydroxysuccinimide esters for the coupling steps. The ultraviolet absorption properties of the free peptides have been investigated in water. No hypo- or hyperchromicity was found for the aromatic chromophores, with the exception of H-Gly-Phe-Trp-OH, which shows a small but significant hypochromicity. The contribution of the peptide bond to the molar absorptivity in the far ultraviolet has been separated from that of the side chain plus the ? COO^? group by plotting the measured molar absorptivity ? of the farthest accessible uv maximum as a function of the number of peptide bonds (n_A). The peptide bond contribution proved to be independent of n_A in the range n_A = 1–5, thus ruling out the onset of helical conformations in the longer chain peptides.     

Far-infrared spectra of poly(-α-amino acids) with basic alkyl group side chains

Far-infrared spectra in the region from 700 to 60 cm^?1 have been measured for the α-helix structures of poly(L -α-amino-n-butyric acid), poly-L -norvaline, poly-L -norleucine, and poly-L -leucine and for the β-form structures of poly(L -α-amino-n-butyric acid), poly-L -valine, poly(DL -amino-n-butyric acid), poly-DL -norvaline, and poly-DL -norleucine. The changes of the spectra on N-deuteration have been measured in the region between 700 and 400 cm^?1. It is concluded that, the α-helix has characteristic bauds near 690, 650, 610, 380, 150, and 100 cm^?1, and that the β-form has characteristic bands near 700, 240, and 120 cm^?1. The main-chain vibrations in the region from 600 to 200 cm^?1 are strongly coupled with the side-chain deformation vibrations.     

Biochemical characterization of ethanol-dependent reduction of furfural by alcohol dehydrogenases

Lignocellulosic biomass is usually converted to hydrolysates, which consist of sugars and sugar derivatives, such as furfural. Before yeast ferments sugars to ethanol, it reduces toxic furfural to non-inhibitory furfuryl alcohol in a prolonged lag phase. Bioreduction of furfural may shorten the lag phase. Cupriavidus necator JMP134 rapidly reduces furfural with a Zn-dependent alcohol dehydrogenase (FurX) at the expense of ethanol (Li et al. 2011). The mechanism of the ethanol-dependent reduction of furfural by FurX and three homologous alcohol dehydrogenases was investigated. The reduction consisted of two individual reactions: ethanol-dependent reduction of NAD⁺ to NADH and then NADH-dependent reduction of furfural to furfuryl alcohol. The kinetic parameters of the coupled reaction and the individual reactions were determined for the four enzymes. The data indicated that limited NADH was released in the coupled reaction. The enzymes had high affinities for NADH (e.g., K _d of 0.043 μM for the FurX-NADH complex) and relatively low affinities for NAD⁺ (e.g., K _d of 87 μM for FurX-NAD⁺). The kinetic data suggest that the four enzymes are efficient “furfural reductases” with either ethanol or NADH as the reducing power. The standard free energy change (ΔG°′) for ethanol-dependent reduction of furfural was determined to be −1.1 kJ mol⁻¹. The physiological benefit for ethanol-dependent reduction of furfural is likely to replace toxic and recalcitrant furfural with less toxic and more biodegradable acetaldehyde.     

Microbial transformation of furfural to furfuryl alcohol by saccharomyces cerevisiae

Biotransformation of furfural by Saccharomyces cerevisiae 354 was performed in a sugar cane molasses medium containing salts. The furfural added was rapidly reduced to furfuryl alcohol until a final addition of 3%, without inhibition in the cells growth. An efficient conversion of 96% was obtained by feeding 6 g · l^?1 every 6 hours.     

An Investigation of the Structural Diversities of Lithiated HMPA Complexes of o-Mercaptopyridine and Trithiocyanuric Acid: Syntheses, Crystal structures and Model Molecular Orbital Calculations

Reaction of o-mercaptopyridine (o-MPH) and trithiocyanuric acid (TTCyH₃) with one equivalent of BuⁿLi in the presence of HMPA yields the mono-lithiated salts MPLi.HMPA (1) and TTCyH₂Li.2HMPA (2) respectively, which have been characterised by NMR spectroscopy and X-ray crystallography. Reaction of three equivalents of BuⁿLi with anhydrous TTCyH₃ in THF yields the tri-lithiated species TTCyLi₃.4THF (3). In all three compounds the lithium centres have N,S-bridged coordination modes. Whereas 1 is dimeric in the solid state, 2 has an unusual monomeric structure and 3, which is a very rare example of a structurally characterised tri-lithiated compound, has an unprecedented polymeric structure incorporating (NCSLi) _n (n = 1, 2) rings. The structural diversities displayed by 1 and 2 have been probed, and thereby in part rationalised, by ab initio (6-31G*/RHF, 6-31G**/RHF and 6-31G*/MP2 levels) MO calculations on both their thio-keto and thiol isomers and on their uncomplexed and complexed lithiated derivatives. In particular, the optimised structures predict and reproduce the N,S-bridging coordination modes found for lithium and explain why structure 1 is dimeric whereas 2 is monomeric.Electronic Supplementary Material available.     

Identification and structural characterisation of novel trehalose dinocardiomycolates from n-alkane-grown Rhodococcus opacus 1CP

Rhodococcus opacus 1CP, a potent degrader of (chloro-) aromatic compounds was found to utilise C₁₀–C₁₆ n-alkanes as sole carbon sources. Highest conversion rates were observed with n-tetradecane and n-hexadecane, whereas the utilisation of n-dodecane and n-decane was considerably slower. Thin-layer chromatography of organic extracts of n-alkane-grown 1CP cultures indicated the growth-associated formation of a glycolipid which was characterised as a trehalose dimycolate by ¹H-NMR spectroscopy and mass spectrometry. Total chain lengths between 48 and 54 carbons classify the fatty acid residues as nocardiomycolic acids. The presence of two double bonds in each mycolic acid is another feature that distinguishes the corresponding trehalose dinocardiomycolates from trehalose dicorynomycolates reported for Rhodococcus erythropolis DSM43215 and Rhodococcus ruber IEGM231. R. opacus 1CP was not found, even under nitrogen limitation, to produce anionic trehalose tetraesters which have previously been reported for R. erythropolis DSM43215.