Studies on the Degradation Mechanisms of Proteins and their Derivatives in the Foods

Cysteine-aldehyde compounds were prepared by the reactions of l-cysteine with formaldehyde, acetaldehyde, n-butyraldehyde, benzaldehyde and furfural in 50% ethanol solutions. Hydrogen sulfide and ammonia liberated from cysteine-aldehyde compounds in heated aqueous solutions (oil bath : 120°C) were determined. Although thiazolidine derivatives were stable generally in boiling aqueous solution, l-cysteine-furfural compound was unstable and a large amount of hydrogen sulfide compared with other compounds was released.     

Chemical characterization of two extracts used in the determination of available soil nitrogen

Summary Two soil extracts used for chemical indexes for N availability, 0.01M NaHCO₃ and boiling 0.01M CaCl₂, were analyzed in effort to learn more about the nature of the extracted organic matter (O.M.). The two extracts appeared to remove different fractions of the soil O.M. A study of five soils showed that the C/N value of the NaHCO₃ extract (following decarbonation) was significantly higher than that of the total soil O.M.; while the C/N value in the boiling CaCl₂ extract was not significantly different from that in the soil O.M. There was also significant variation in C/N values among soils for the boiling CaCl₂ extract. The extracts of three soils were analyzed for apparent molecular weight distribution using gel filtration and the results compared to those for base-extracted humic substances. Almost all the molecules in the extracts had apparent molecular weights less than 21,000 daltons while 21 to 47% of the humic substances from the same soils (extracted with 0.5M NaOH) had molecular weights greater than 21,000 daltons. In the boiling CaCl₂ extract, 78 to 87% of the humic substances had apparent molecular weights less than 1,000 daltons, whereas with the NaHCO₃ extract, 42 to 83% of the humic substances were in the 1,000 to 21,000 dalton range. Forty-three to 92% of the N extracted by the NaHCO₃ was in protein form, and 8 to 30% was ninhydrin-detectable. In the boiling CaCl₂ extract 25 to 30% of the extracted N was ninhydrin-detectable. For the same 10 soils, ninhydrin-detectable N values of the boiling CaCl₂ extract appeared closely related to greenhouse and field relative N uptake, while the ninhydrin-detectable N values of the NaHCO₃ extract appeared unrelated to both. The protein N and protein in plus ninhydrin-detectable N values of the NaHCO₃ extract were closely related to greenhouse relative N uptake only. The results of this study indicated that specific fractions of the soil O.M. were being extracted by the two solutions and that significant differences existed in the chemical nature of the two extracts. Paper No. 6175 of the J. Ser. of the Pennsylvania Agric. Exp. Stn. Authorized for publication Jan. 26, 1981.     

Efficient Nanostructured TiO2/SnS Heterojunction Solar Cells

Tin sulfide (SnS) is one of the most promising solar cell materials, as it is abundant, environment friendly, available at low cost, and offers long‐term stability. However, the highest efficiency of the SnS solar cell reported so far remains at 4.36% even using the expensive atomic layer deposition process. This study reports on the fabrication of SnS solar cells by a solution process that employs rapid thermal treatment for few seconds under Ar gas flow after spin‐coating a precursor solution of SnCl₂ and thiourea dissolved in dimethylformamide onto a nanostructured thin TiO₂ electrode. The best‐performing cell exhibits power conversion efficiency (PCE) of 3.8% under 1 sun radiation conditions (AM1.5G). Moreover, secondary treatment using SnCl₂ results in a significant improvement of 4.8% in PCE, which is one of the highest efficiencies among SnS‐based solar cells, especially with TiO₂ electrodes. The thin film properties of SnS after SnCl₂ secondary treatment are analyzed using grazing‐incidence wide‐angle X‐ray scattering, and high‐resolution transmittance electron microscopy.     

Microbial acceleration of aerobic pyrite oxidation at circumneutral pH

Pyrite (FeS₂) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro‐organisms in pyrite oxidation under acidic‐pH conditions is well known, to date there is very little known about the capacity for aerobic micro‐organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite‐bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin–Benson–Bassham CO₂ fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30–50 nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X‐ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro‐organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral‐pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite‐associated metals.     

A theoretical approach to the link between oxidoreductions and pyrite formation in the early stage of evolution

There are two fundamental axioms of surface metabolism theory: (i) pyrite formation from H₂S and FeS is proposed as a source of energy for life, and (ii) archaic reductive citric acid cycle is put into the center of a metabolic network. However, the concept fails to indicate how sulfide oxidation ought to be coupled to processes driven by free energy change occurring during pyrite production, and secondly, how reductive citric acid cycle ought to be supplied with row material(s). Recently, the non-enzymatic methylglyoxalase pathway has been recommended as the anaplerotic route for the reductive citric acid cycle. In this paper a mechanism is proposed by which the oxidation of lactate, the essential step of the anaplerotic path, becomes possible and a coupling system between sulfide oxidation and endergonic reaction(s) is also presented. Oxidoreduction for other redox pairs is discussed too. It is concluded that the S^o/H₂S system may have been the clue to energy production at the early stage of evolution, as hydrogen sulfide produced by the metabolic network may have functioned as a coupling molecule between endergonic and exergonic reactions.     

Decomposition in presence of nitrate of amino acids,especially tyrosine,during acid hydrolysis of plant material and standard amino acid solution

Summary Nitrate present in or added to ryegrass samples considerably decomposed tyrosine during hydrolysis. Addition of 30 mg stannous chloride to 250 mg ryegrass in 250 ml 6N HCl had only a small preventing effect, whereas 480 mg SnCl₂.2H₂O or 0.17 ml thioglycollic acid, entirely prevented decomposition. Other amino acids remained unaffected by nitrate. Additions of nitrate to standard amino acid solutions completely decomposed tyrosine. Other amino acids, except proline, progressively decomposed with increasing nitrate additions. Effects from stannous chloride and thioglycollic acid were the same as on ryegrass     

Alterations in surfaces and textures of minerals during the bacterial leaching of a complex sulfide ore

Abstract

The purpose of the work was to characterize changes in surface textures of minerals during the biological leaching of a complex sulfide ore. The ore contained pyrrhotite (Fe_I__xS), pyrite (FeS₂), sphalerite (ZnS), pentlandite [(Ni,Fe,Co)₉S₈], and chalcopyrite (CuFeS₂). Several mixed cultures were initially screened using the ore material as the sole substrate. Shake flask leaching experiments showed no major differences among test cultures, which were all derived by enrichment techniques using environmental samples collected from a mine site. Leached pyrrhotite surfaces were invariably surrounded by a dark rim of elemental S. A reaction zone was also associated with leached sphalerite grains. Chemical analyses of leach solutions indicated that the relative ranking of biological leaching of the sulfide minerals was Zn > Ni > Co > Cu. Microscopic observations were in keeping with this rankin     

Dedication

Mixed cultures derived from Boston Harbor sediments, which gave evidence of methylating tin compounds, yielded two isolates, each a Bacillus sp., which methylated CH₃SnCl₃ to form (CH₃)₃SnX in coculture. Neither organism alone gave evidence of methylation. SnCl₄ and (CH₃)₂SnCl₂ were not methylated. Transfer of either organism to filtered medium containing CH₃SnCl₃ in which the other had grown did not lead to methylation. Therefore methylation by the coculture is not simply a matter of cross‐feeding.     

Manipulation of pyrite colonization and leaching by iron-oxidizing <Emphasis Type="Italic">Acidithiobacillus</Emphasis> species

In this study, the process of pyrite colonization and leaching by three iron-oxidizing Acidithiobacillus species was investigated by fluorescence microscopy, bacterial attachment, and leaching assays. Within the first 4–5 days, only the biofilm subpopulation was responsible for pyrite dissolution. Pyrite-grown cells, in contrast to iron-grown cells, were able to oxidize iron(II) ions or pyrite after 24 h iron starvation and incubation with 1 mM H₂O₂, indicating that these cells were adapted to the presence of enhanced levels of reactive oxygen species (ROS), which are generated on metal sulfide surfaces. Acidithiobacillus ferrivorans SS3 and Acidithiobacillus ferrooxidans R1 showed enhanced pyrite colonization and biofilm formation compared to A. ferrooxidans ^T. A broad range of factors influencing the biofilm formation on pyrite were also identified, some of them were strain-specific. Cultivation at non-optimum growth temperatures or increased ionic strength led to a decreased colonization of pyrite. The presence of iron(III) ions increased pyrite colonization, especially when pyrite-grown cells were used, while the addition of 20 mM copper(II) ions resulted in reduced biofilm formation on pyrite. This observation correlated with a different extracellular polymeric substance (EPS) composition of copper-exposed cells. Interestingly, the addition of 1 mM sodium glucuronate in combination with iron(III) ions led to a 5-fold and 7-fold increased cell attachment after 1 and 8 days of incubation, respectively, in A. ferrooxidans ^T. In addition, sodium glucuronate addition enhanced pyrite dissolution by 25 %.     

Hydrogen Gas Production by an Ectothiorhodospira vacuolata Strain

A hydrogen gas (H₂)-producing strain of Ectothiorhodospira vacuolata isolated from Soap Lake, Washington, possessed nitrogenase activity. Increasing evolution of H₂ with decreasing ammonium chloride concentrations provided evidence that nitrogenase was the catalyst in gas production. Cells were grown in a mineral medium plus 0.2% acetate with sodium sulfide as an electron donor. Factors increasing H₂ production included addition of reduced carbon compounds such as propionate and succinate, increased reducing power by increasing sodium sulfide concentrations, and increased energy charge (ATP) by increasing light intensity.     

Measurement of bacterial sulfate reduction in sediments: Evaluation of a single-step chromium reduction method

A procedure which includes the Total Reduced Inorganic Sulfur (TRIS) in a single distillation step is described for the radiotracer measurement of sulfate reduction in sediments. The TRIS includes both Acid Volatile Sulfide (AVS: H₂S + FeS) and the remaining Chromium Reducible Sulfur (CRS: S⁰, FeS₂). The single-step distillation was simpler and faster than the consecutive distillations of AVS and CRS. It also resulted in higher (4–50%) sulfate reduction rates than those obtained from the sum of³⁵S in AVS and CRS. The difference was largest when the sediment had been dried after AVS but before CRS distillation. Relative to the³⁵S-AVS distillation alone, the³⁵S-TRIS single-step distallation yielded 8–87% higher reduction rates. The separation and recovery of FeS, S⁰ and FeS₂ was studied under three distillation conditions: 1) cold acid, 2) cold acid with Cr²⁺, and 3) hot acid with Cr²⁺. The FeS was recovered by cold acid alone while pyrite was recovered by cold acid with Cr²⁺. A smaller S⁰ fraction, presumably of the finer crystal sizes, was recovered also in the cold acid with Cr²⁺ while most of the S⁰ required hot acid with Cr²⁺ for reduction to H₂S.     

A modified method for amino acid analysis with ninhydrin of Coomassie-stained proteins from polyacrylamide gels

Triton X-100 (from three different suppliers) and Brij 35, substituted ethers of polyoxyethylene alcohols, were found to contain variable amounts of powerful oxidizing impurities representing a range of 0.04-0.22% H₂O₂ equivalents. These detergents contain also a considerable quantity of carbonyl compounds (0.5-2%) originating from carboxylic acids and ketones or aldehydes. Tween 20, also a polyoxyethylene detergent, and sodium dodecyl sulfate were free from oxidizing contamination. Aqueous solutions of Triton X-100 and Brij 35 (1–4%) reacted readily with SH groups of protein and nonprotein molecules as well as with Fe²⁺ ion. Both detergents were purified from the oxidizing impurities by treating aqueous solution of detergent with either NaHSO₃ or SnCl₂ followed by an extraction procedure. The present findings may clarify as well as complicate the interpretation of previous studies where these detergents were used for biological purposes, especially in enzyme and protein purifications, or when present in assay procedures that are based on the formation or consumption of reducing reagents.     

Uptake of phenolic compounds from plant foods in human intestinal Caco-2 cells

In continuation of our studies on the bioaccessibility of phenolic compounds from food grains as influenced by domestic processing, we examined the uptake of phenolics from native/sprouted finger millet (Eleucine coracana) and green gram (Vigna radiata) and native/heat-processed onion (Allium cepa) in human Caco-2 cells. Absorption of pure phenolic compounds, as well as the uptake of phenolic compounds from finger millet, green gram, and onion, was investigated in Caco-2 monolayer model. Transport of individual phenolic compounds from apical compartment to the basolateral compartment across Caco-2 monolayer was also investigated. Sprouting enhanced the uptake of syringic acid from both these grains. Open-pan boiling reduced the uptake of quercetin from the onion. Among pure phenolic compounds, syringic acid was maximally absorbed, while the flavonoid isovitexin was least absorbed. Apparent permeability coefficient P_(app) of phenolic compounds from their standard solutions was 2.02 × 10^?6 cm/s to 8.94 × 10^?6 cm/s. Sprouting of grains enhanced the uptake of syringic acid by the Caco-2 cells. Open-pan boiling drastically reduced the uptake of quercetin from the onion. The permeability of phenolic acids across Caco-2 monolayer was higher than those of flavonoids.     

Effect of anions on selective solubilization of zinc and copper in bacterial leaching of sulfide ores

Bacterial leaching of sulfide ores using Thiobacillus ferrooxidans, Thiobacillus thiooxidans, or a combination of the two was studied at various concentrations of specific anions. Selective zinc and copper solubilization was obtained by inhibiting iron oxidation without affecting sulfur/sulfide oxidation. Phosphate reduced iron solubilization from a pyrite (FeS(2))-sphalerite (ZnS) mixture without significantly affecting zinc solubilization. Copper leaching from a chalcopyrite (CuFeS(2))-sphalerite mixture was stimulated by phosphate, whereas chloride accelerated zinc extraction. In a complex sulfide ore containing pyrite, chalcopyrite, and sphalerite, both phosphate and chloride reduced iron solubilization and increased copper extraction, whereas only chloride stimulated zinc extraction. Maximum leaching obtained was 100% zinc and 50% copper. Time-course studies of copper and zinc solubilization suggest the possibility of selective metal recovery following treatment with specific anions.     

Antitumor activity of organotin compounds. Reaction,synthesis and structure of Et2SnCl2(phen) with 5-fluorouracil

The antitumor agent Et₂SnCl₂(phen) (phen = phenanthroline) reacts with 5-fluorouracil (UF) to form Et₂Sn(phen)UF)Cl by a basic catalytic process. The reaction may be characterized as nucleophilic attack on H⁺N(3) in the 5-fluorouracil ring by the cis-chloro in Et₂SnCl₂(phen). The product has been identified by microanalysis, IR, UV and NMR spectra and these results are consistent with the expected complex. The binding of the 5-fluorouracil ligand to the cis-chloro in Et₂SnCl₂(phen) not only enhances the antitumor activity of the complex, but also promotes studied aimed at understanding the mechanism of drug action.     

Toxicity of organotins towards the marine yeastDebaryomyces hansenii

Of nine organotin compounds tested towards the marine yeastDebaryomyces hansenii, only triphenyltin chloride (Ph₃SnCl) and mono-, di-, and tributyltin chloride induced significant K⁺ release from cells which was symptomatic of viability loss. The general order of toxicity of the butylated compounds was tributyltin chloride (Bu₃SnCl) > monobutyltin chloride (BuSnCl₃) dibutyltin chloride (Bu₂SnCl₂). The overall toxicity of Ph₃SnCl was similar to BuSnCl₃. Release of K⁺ induced by butylated tin compounds or by Ph₃SnCl was strongly dependent on the external pH. Maximal toxicity occurred at pH 6.5 for Bu₃SnCl, BuSnCl₃, and Ph₃SnCl, whereas maximal toxicity of Bu₂SnCl₂ occurred at pH 5.0. Toxicity was decreased above or below these values. The toxicity of BuSnCl₃, Bu₃SnCl, and Ph₃SnCl was reduced at salinity levels approximating to sea water conditions. Prior growth ofD. hansenii in 3% (w/v) NaCl also resulted in reduced sensitivity to Bu₃SnCl as evidenced by a decreased rate and extent of K⁺ efflux. Bu₃SnCl-induced Na⁺ release from cells grown in the absence or presence of 3% (w/v) NaCl was low and similar in both cases. It appeared that the monovalent cation was important in the reduction of Bu₃SnCl toxicity since Na₂SO₄ had a similar protective effect as NaCl while CsCl completely prevented K⁺ efflux. Thus, the effects of external NaCl were related both to Na⁺ and to Cl^–. These results emphasize that cellular and environmental factors influence the toxic effects of organotins and suggests that these compounds may be more effective antimicrobial agents in some environmental niches than in others.     

Sulfur colloids as temporary energy reservoirs for Thiobacillus ferrooxidans during pyrite oxidation

Thiobacillus ferrooxidans was cultivated on 100-nm-thick synthetic pyrite (FeS₂) films. The steps of biooxidation were studied with high-resolution transmission electron microscopy. The crystallized sulfide was transformed into colloidal sulfur (4–70 nm, depending on the age of the cell and the degree of substrate oxidation; 70nm initially and 4nm after oxidation of the pyrite substrate), which was taken up and distributed over an organic capsule around the bacteria. This colloidal sulfur acted as intermediate energy storage and was transferred by contact to daughter cells not directly attached to the sulfide substrate.     

Synthesis, characterization, crystal structures and in vitro antistaphylococcal activity of organotin(IV) derivatives with 5,7-disubstituted-1,2,4-triazolo[1,5-a]pyrimidine

New organotin(IV) complexes of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp) with 1:1 and/or 1:2 stoichiometry were synthesized and investigated by X-ray diffraction, FT-IR and ¹¹⁹Sn Mössbauer in the solid state and by ¹H and ¹³C NMR spectroscopy, in solution. Moreover, the crystal and molecular structures of Et₂SnCl₂(dbtp)₂ and Ph₂SnCl₂(EtOH)₂(dptp)₂ are reported. The complexes contain hexacoordinated tin atoms: in Et₂SnCl₂(dbtp)₂ two 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine molecules coordinate classically the tin atom through N(3) atom and the coordination around the tin atom shows a skew trapezoidal structure with axial ethyl groups. In Ph₂SnCl₂(EtOH)₂(dptp)₂ two ethanol molecules coordinate tin through the oxygen atom and the 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine molecules are not directly bound to the metal center but strictly H-bonded, through N(3), to the OH group of the ethanol moieties; Ph₂SnCl₂(EtOH)₂(dptp)₂ has an all-trans structure and the C-Sn-C fragment is linear. On the basis of Mössbauer data, the 1:2 diorganotin(IV) complexes are advanced to have the same structure of Et₂SnCl₂(dbtp)₂, while Me₂SnCl₂(dptp)₂ to have a regular all-trans octahedral structure. A distorted cis-R₂ trigonal bipyramidal structure is assigned to 1:1 diorganotin(IV) complexes. The in vitro antibacterial activities of the synthesized complexes have been tested against a group of reference pathogen micro-organisms and some of them resulted active with MIC values of 5 μg/mL, most of all against staphylococcal strains, which shows their inhibitory effect.