Selection and characterization of a newly isolated thermotolerant Pichia kudriavzevii strain for ethanol production at high temperature from cassava starch hydrolysate

Pichia kudriavzevii DMKU 3-ET15 was isolated from traditional fermented pork sausage by an enrichment technique in a yeast extract peptone dextrose (YPD) broth, supplemented with 4 % (v/v) ethanol at 40 °C and selected based on its ethanol fermentation ability at 40 °C in YPD broth composed of 16 % glucose, and in a cassava starch hydrolysate medium composed of cassava starch hydrolysate adjusted to 16 % glucose. The strain produced ethanol from cassava starch hydrolysate at a high temperature up to 45 °C, but the optimal temperature for ethanol production was at 40 °C. Ethanol production by this strain using shaking flask cultivation was the highest in a medium containing cassava starch hydrolysate adjusted to 18 % glucose, 0.05 % (NH₄)₂SO₄, 0.09 % yeast extract, 0.05 % KH₂PO₄, and 0.05 % MgSO₄·7H₂O, with a pH of 5.0 at 40 °C. The highest ethanol concentration reached 7.86 % (w/v) after 24 h, with productivity of 3.28 g/l/h and yield of 85.4 % of the theoretical yield. At 42 °C, ethanol production by this strain became slightly lower, while at 45 °C only 3.82 % (w/v) of ethanol, 1.27 g/l/h productivity and 41.5 % of the theoretical yield were attained. In a study on ethanol production in a 2.5-l jar fermenter with an agitation speed of 300 rpm and an aeration rate of 0.1 vvm throughout the fermentation, P. kudriavzevii DMKU 3-ET15 yielded a final ethanol concentration of 7.35 % (w/v) after 33 h, a productivity of 2.23 g/l/h and a yield of 79.9 % of the theoretical yield.     

Biohydrogen production from wheat straw hydrolysate by dark fermentation using extreme thermophilic mixed culture

Hydrolysate was tested as substrate for hydrogen production by extreme thermophilic mixed culture (70°C) in both batch and continuously fed reactors. Hydrogen was produced at hydrolysate concentrations up to 25% (v/v), while no hydrogen was produced at hydrolysate concentration of 30% (v/v), indicating that hydrolysate at high concentrations was inhibiting the hydrogen fermentation process. In addition, the lag phase for hydrogen production was strongly influenced by the hydrolysate concentration, and was prolonged from approximately 11 h at the hydrolysate concentrations below 20% (v/v) to 38 h at the hydrolysate concentration of 25% (v/v). The maximum hydrogen yield as determined in batch assays was 318.4 ± 5.2 mL‐H₂/g‐sugars (14.2 ± 0.2 mmol‐H₂/g‐sugars) at the hydrolysate concentration of 5% (v/v). Continuously fed, and the continuously stirred tank reactor (CSTR), operating at 3 day hydraulic retention time (HRT) and fed with 20% (v/v) hydrolysate could successfully produce hydrogen. The hydrogen yield and production rate were 178.0 ± 10.1 mL‐H₂/g‐sugars (7.9 ± 0.4 mmol H₂/g‐sugars) and 184.0 ± 10.7 mL‐H₂/day L_reactor (8.2 ± 0.5 mmol‐H₂/day L_reactor), respectively, corresponding to 12% of the chemical oxygen demand (COD) from sugars. Additionally, it was found that toxic compounds, furfural and hydroxymethylfurfural (HMF), contained in the hydrolysate were effectively degraded in the CSTR, and their concentrations were reduced from 50 and 28 mg/L, respectively, to undetectable concentrations in the effluent. Phylogenetic analysis of the mixed culture revealed that members involved hydrogen producers in both batch and CSTR reactors were phylogenetically related to the Caldanaerobacter subteraneus, Thermoanaerobacter subteraneus, and Thermoanaerobacterium thermosaccharolyticum. Biotechnol. Bioeng. 2010;105: 899–908. © 2009 Wiley Periodicals, Inc.     

Improving probiotic spore yield using rice straw hydrolysate

Spore-forming Bacillus sp. has been extensively studied for their probiotic properties. In this study, an acid-treated rice straw hydrolysate was used as carbon source to produce the spores of Bacillus coagulans. The results showed that this hydrolysate significantly improved the spore yield compared with other carbon sources such as glucose. Three significant medium components including rice straw hydrolysate, MnSO₄ and yeast extract were screened by Plackett–Burman design. These significant variables were further optimized by response surface methodology (RSM). The optimal values of the medium components were rice straw hydolysate of 27% (v/v), MnSO₄ of 0·78 g l⁻¹ and yeast extract of 1·2 g l⁻¹. The optimized medium and RSM model for spore production were validated in a 5 l bioreactor. Overall, this sporulation medium containing acid-treated rice straw hydrolysate has a potential to be used in the production of B. coagulans spores.     

Immobilization of whole cells ofStreptomyces kanamyceticus containing glucose isomerase by a combination of heat treatment in the presence of minerals and entrapment in calcium alginate gels

A method of immobilization of whole cells ofStreptomyces kanamyceticus containing glucose isomerase was devised, based on techniques of heat fixation in the presence of minerals and, entrapment in calcium alginate gels. The optimum activity of the enzyme was obtained when the cells were heat-fixed at 60°C for 10 min in the presence of 50 mmol/L MgSO₄·7H₂O and 5 mmol/L CoCl₂·6H₂O and then cast into calcium alginate beads using 2% sodium alginate.     

A new medium for spore production of <Emphasis Type="Italic">Blakeslea trispora</Emphasis> using response surface methodology

Optimization of the medium components which enhance sporulation of the two mating types of the fungus Blakeslea trispora ATCC 14271 and ATCC 14272 (a heterothallic Zygomycota producing carotene) was achieved with the aid of response surface methodology (RSM). Glucose, corn steep liquor, yeast extract, and ammonium sulfate were investigated as carbon and nitrogen sources in a basal medium. RSM was adopted to optimize the medium in order to obtain a good growth of the fungus as a prerequisite for enhanced sporulation. In the second step, the basal medium was supplemented with different trace elements which significantly affect sporulation (i.e. CuSO₄·5H₂O, FeCl₃·6H₂O, Co(NO₃)₂·6H₂O, and MnCl₂·4H₂O). Central composite design proved to be valuable in optimizing a chemically defined solid medium for spore production of B. trispora. The composition of the new solid medium to enhance spore production by B. trispora (ATCC 14271) is as follows (per liter): 7.5 g glucose, 3.2 g corn steep liquor, 1.7 g yeast extract, 4.1 g ammonium sulfate, 6 mg CuSO₄·5H₂O, 276 mg FeCl₃·6H₂O, 2 mg Co(NO₃)₂·6H₂O, and 20 g agar (pH 6.0). Practical validation of this optimum medium gave spore number of 1.2 × 10⁸ spores/dish which is 77% higher than that produced in Potato Dextrose Agar (PDA). In the case of B. trispora (ATCC 14272) the new solid substrate for enhanced sporulation consists of (per l) 6.4 g glucose, 3.3 g corn steep liquor, 1.4 g yeast extract, 4.3 g ammonium sulfate, 264 mg CuSO₄·5H₂O, 485 mg FeCl₃·6H₂O, 223 mg MnCl₂^.4H₂O, and 20 g agar (pH 6.0). Spore numbers of 2 × 10⁷ spores/dish were obtained on the new medium by B. trispora (ATCC 14272), which is 95% higher than that produced on PDA. The results corroborated the validity and the effectiveness of the models. The new media considerably improved sporulation of both strains of B. trispora compared to the production of spores on PDA, which is the medium usually used for sporulation of the fungus.     

Production of <Emphasis Type="SmallCaps">l</Emphasis>-phenylacetylcarbinol by microbial transformation in polyethylene glycol-induced cloud point system

Microbial transformation of benzaldehyde into l-phenylacetylcarbinol by whole cell Saccharomyces cerevisiae has been carried out in a novel polyethylene glycol (PEG)-induced cloud point system. The system is composed of 80 g PEG 20,000, 75 ml Triton X-100, 20 g peptone, 10 g yeast extract, 25 g glucose, 1 g MgSO₄·7H₂O, 0.05 g CaCl₂·2H₂O, 35 g Na₂HPO₄·12H₂O, and 10.7 g citric acid per liter of tap water. The microbial transformation is conducted at 0.6 ml of acetaldehyde (35% volume content), 0.9 ml of benzaldehyde, and 7 g of wet cell per 100 ml of the PEG-induced cloud point system. Under the conditions, a relatively longer-term bioactivity of whole cell microorganism in the PEG-induced cloud point system has been achieved. A fed-batch microbial transformation process with a discrete addition of glucose and substrate gets a high final product concentration of about 8 g/l.     

Synergistic Taste Effects of Some New Ribonucleotide Derivatives

Taste effects of six newly synthesized ribonucleotide derivatives, i.e., disodium salts of 2-methyl-5′-inosinic acid · 6H₂O, 2-ethyl-5′-inosinic acid · 1.5H₂O, 2-N-methyl-5′-guanylic acid · 5.5H₂O, 2-N-dimethyl-5′-guanylic acid · 2.5H₂O, 2-methylthio-5′-inosinic acid · 6H₂O and 2-ethylthio-5′-inosinic acid · 2H₂O, were studied. Stimulus thresholds (detection thresholds) of these derivatives ranged from about 0.02 to 0.006 g/100ml. Flavor-enhancing activities of them were 2.3 to 8.0 times larger than that of disodium 5′-inosinate · 7.5H₂O IMP) in the synergistic effect with monosodium glutamate. Furthermore, the quality of taste of all the derivatives was recognized to be the same kind to that of IMP.     

Development of meridic and oligidic diets for rearing the aphid Myzus persicae

Meridic and oligidic diets suitable for the continuous culture of the aphid Myzus persicae were developed through modifications of a holidic diet. These included the addition of various amounts of crude nutrients and the replacement of defined nutrients by crude nutrients. The highest level of aphid growth (mean weights of 600 to 800 μg) was maintained (for 45 successive generations) on a meridic diet made by supplementing a holidic diet with 2.0% yeast extract (NBC).Continuous culture, at a level of growth (400 to 600 μg) comparable to that on the unsupplemented holidic diet (formulated with 34 defined nutrients), was supported by an oligidic diet containing only 10 weighed ingredients: 15 g sucrose, 2.5 g enzymatic casein hydrolysate (NBC), 2 g yeast extract, 123 mg MgSO₄·7H₂O, 100 mg ascorbic acid, 10 mg niacin, 5 mg Ca pantothenate, 2.5 mg pyridoxine, 2.5 mg thiamine, and appx. 1.5 gm K₂HPO₄·3H₂O (pH 6.8) per 100 ml of diet.Yeast extract at 2.0% provided adequate amounts of choline chloride, biotin, folic acid and inositol, but not of niacin, pantothenate, pyridoxine, and thiamine. Enzymatic casein hydrolyzate at 2.5% could replace the 20 defined amino acids of the holidic diet. Diets with both yeast extract and casein hydrolysate did not have to be supplemented with trace minerals (Cu, Fe, Mn and Zn). Yeast extract at 2.5% provided sufficient amounts of trace minerals, amino acids, and B-vitamins to sustain numerous successive generations, albeit at a low level of growth (200 to 300 μg). The simplicity and low cost of oligidic diets makes them attractive for aphid studies in which nutrition is not the primary consideration.     

Kinetics of Inhibition of Rabbit Intestine Alkaline Phosphatase by Heteroligand Peroxo Complexes of Vanadium(V) and Tungsten(VI)

The present work was undertaken to examine and compare some biologically important properties of peroxo compounds of V(V) and W(VI) containing biogenic species as ancillary ligand. New anionic peroxovanadate(V) complex of the type Na[VO(O₂)₂(triglycine)]·3H₂O (pV1) and a molecular peroxotungstate(VI) [WO(O₂)₂(triglycine)]·3H₂O (pW1) were synthesized and characterized for the purpose and their stability in solution was ascertained. Studies on kinetics of inhibition of alkaline phosphatase activity by the newly synthesized compounds and series of dipeptide and amino acid containing peroxo complexes of vanadium and tungsten synthesized previously by us viz., Na[VO(O₂)₂(gly-gly)(H₂O)]·H₂O (gly-gly = glycyl-glycine), Na[VO(O₂)₂(asn)]·H₂O (asn = asparagine), Na[VO(O₂)₂(gln)]·H₂O (gln = glutamine), and [WO(O₂)₂(gly-gly)(H₂O)]·3H₂O, revealed that each of these species is a potent mixed-type inhibitor of the enzyme. Significant difference was noted between the peroxovanadium (pV) and peroxotungsten (pW) compounds in terms of their oxidant activity with reduced glutathione.     

Biochemical and kinetic evaluation of lipase and biosurfactant assisted ex novo synthesis of microbial oil for biodiesel production by Yarrowia lipolytica utilizing chicken tallow

The present study explores the production of biodiesel, a sustainable replacement for depleting fossil fuel by utilizing microbial oil, which was procured from Yarrowia lipolytica employing chicken tallow as the carbon substrate. Chicken tallow, yeast extract, and MgSO₄·7H₂O were screened for biomass production through Plackett–Burman design. Further, Box–Behnken design analysis was performed, and the optimal concentration of the medium variables was found to be 20 g/L of chicken tallow, 7.0 g/L of yeast extract, and 0.45 g/L of MgSO₄·7H₂O.The various parameters viz., pH (6), temperature (30 °C), RPM (150), inoculum volume (5%, v/v), and C/N ratio (100) were optimized for maximal biomass and lipid yield, and lipid content. Nile red-stained cells were observed for intracellular lipid bodies using fluorescence microscopy, and its fluorescence intensity was measured bythe flow cytometer. The dimorphic transition and substrate assimilation of Y. lipolytica were analyzed using scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). Batch kinetic studies revealed the concomitant synthesis of microbial lipid (4.16 g/L), lipase (43 U/mL), and biosurfactant (1.41 g/L). The GC-MS analysis of microbial oil presented the fatty acid profile as oleic acid (49.15%), palmitic acid (29.83%), stearic acid (11.43%), linoleic acid (3.83%), palmitoleic acid (3.77%), and myristic acid (1.32%).     

Infrared and raman spectra of metal 1,2,4,5-benzenetetracarboxylates: Evidence for very short,strong hydrogen bonds

Salts of 1,2,4,5-benzenetetracarboxylic acid with copper, aluminum, ammonium, cobalt(II), thallium(I), tin(II), uranyl ion, zinc, manganese, iron(II), nickel, potassium and sodium have been prepared and characterized by their IR spectra. The salts of aluminum, ammonium, thallium(I), tin(II), zinc, iron(II), nickel, potassium and sodium had not been reported before with adequate characterization. Raman spectra of selected compounds also aided structural interpretation. The IR spectra of Na₂C₁₀H₄O₈·2H₂O, Fe(C₁₀H₅O₈)₂·12H₂O, Zn(C₁₀H₅O₈)₂·12H₂O, Ni(C₁₀H₅O₈)₂·12H₂O, (NH₄)₃C₁₀H₃O₈·H₂O and CoC₁₀H₄O₈·6H₂O indicate very short, strong hydrogen bonds in these compounds. The IR and Raman spectra can be used to determine the mode of coordination (if any) of the carboxylate groups of 1,2,4,5- benzenetetracarboxylate to metal ions.     

Iron and nickel complexes with heterocyclic ligands: Stability,synthesis, spectral characterization,antimicrobial activity,acute and subacute toxicity

The synthesis and characterization by elemental analysis, emission atomic spectroscopy, TG measurements, magnetic measurements, FTIR, ¹H NMR, UV–visible spectra and conductivity of a series of iron (II) and nickel (II) complexes with two heterocyclic ligands (L¹(SMX): sulfamethoxazole and L²(MIZ): metronidazole) used in pharmaceutical field and with a new ligand derived benzoxazole (L³(MPBO): 2-(5-methylpyridine-2-yl)benzoxazole), were reported. The formulae obtained for the complexes are: [M(L¹)₂ Cl₂]·nH₂O, [M(L²)₂Cl₂(H₂O)₂]·H₂O and [M(L³)₂(OH)₂]·nH₂O. Stability constants of these complexes have been determined by potentiometric methods in water–ethanol (90:10, v/v) mixture at a 0.2 mol L^?1 ionic strength (NaCl) and at 25.0 ± 0.1 °C. Sirko program was used to determine the protonation constants as well as the binding constants of three species [ML₂H₂]²⁺, [ML₂] and [ML]²⁺. The antimicrobial activity of the ligands and complexes was evaluated in vitro against different human bacteria and fungi using agar diffusion method.Iron sulfamethoxazole complex showed a remarkable inhibition of bacteria growth especially on Staphylococcus aureus and P. aeruginosa. The iron metronidazole complex is active against yeasts especially on Candida tropicalis strain. Nickel complexes presented different antibacterial and antifungal behavior's against bacteria and fungal.The acute toxicity study revealed that the iron complexes are not toxic at 2000 mg/kg dose orally administrated.LD₅₀ for nickel complexes was determined using graphical method.No significant differences in the body weights between the control and the treated groups of both rat sexes in subacute toxicity study using for iron complexes. Hematological and clinical blood chemistry analysis revealed no toxicity effects of the iron complexes. Pathologically, neither gross abnormalities nor histopathological changes were observed for these complexes.     

Interguanine hydrogen-bonding patterns in adducts with water and Zn–purine complexes (purine is 9-methyladenine and 9-methylguanine). Unexpected preference of Zn(II) for adenine-N7 over guanine-N7

Guanine–guanine hydrogen bonding involving the Watson–Crick edge [N(1)H, N(2)H₂] of one base and the Hoogsteen edge (N7, O6) of the other is the dominant association pattern in the solid-state structures of two hydrates of 9-ethylguanine (9-EtGH), and in adducts of 9-methylguanine (9-MeGH) with the Zn compounds [ZnCl₂(H₂O)(9-MeGH-N7)]·(9-MeGH) as well as [ZnCl₂(H₂O)(9-MeA-N7)]·2(9-MeGH) (9-MeA is 9-methyladenine). The structures of 9-EtGH·2H₂O and 9-EtGH·3.5H₂O are dominated by polymeric tape structures of the guanine and extended water clusters. In [ZnCl₂(H₂O)(9-MeGH-N7)]·(9-MeGH) the metalated guanine is involved in hydrogen bonding (GG3 motif) with a free 9-MeGH, which in turn is centrosymmetrically related to itself via hydrogen bonds involving N(2)H₂ and N3 (GG4 motif). In [ZnCl₂(H₂O)(9-MeA-N7)]·2(9-MeGH) the metalated adenine base interacts via its Watson–Crick edge [N1, N(6)H₂] with the sugar edge [N(2)H₂, N3] of one of the guanine nucleobases of the GG pair. Crystallization of [ZnCl₂(H₂O)(9-MeA-N7)]·2(9-MeGH) from an aqueous solution containing 9-MeGH, 9-MeA, and ZnCl₂ is fully unexpected in that the anticipated preference of Zn(II) for guanine-N7 is not realized and instead coordination to adenine-N7 is observed. The relevance of [ZnCl₂(H₂O)(9-MeGH-N7)]·(9-MeGH) and [ZnCl₂(H₂O)(9-MeA-N7)]·2(9-MeGH) for metal-containing nucleic acid triplex structures is discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The New Basic Triple Salt Containing Magnesium Hydroxide

The quaternary system K₂SO₄–MgSO₄–Mg(OH)₂–H₂O and the associated systems (a) K₂SO₄–Mg(OH)₂–H₂O and (b) MgSO₄–Mg(OH)₂–H₂O were investigated at 100° Though isotherm (a) exhibited nothing new, isotherm (b) exhibited basic magnesium sulfate, MgSO₄ · 5Mg(OH)₂·3H₂O, as the solid phase. The solid phases of quaternary isotherm were the new basic triple salt K₂SO₄ · 2MgSO₄ · Mg(OH)₂ · 2H₂O, langbeinite, basic magnesium sulfate, kieserite and potassium sulfate.     

Growth of the Peritrich Opercularia coarctata in Axenic Culture*

A synthetic medium for Opercularia coarctata was developed that contains 20 amino acids, 10 vitamins, an 8-component balanced salt solution, Fe₂(SO₄)₃·(NH₄)₂SO₄·24H₂O, Tween 80, stigmasterol, a 7-component nucleic acid mixture, phenol red as an indicator, and 2,500 U.S.P. units/ml penicillin to maintain sterility. This medium supported axenic survival for 96 hr. Multiple supplements of thioctic acid, niacin, niacinamide, inositol, PABA, oleic acid, and Fe(NO₃)₂·9H₂O instead of Fe₂(SO₄)₃·(NH₄)₂SO₄·24H₂O coverted the survival medium into a growth medium, which permitted 36–45 days continuous cultivation of populations in excess of 4 × 10³ cells/3.0 ml final volume. Five generations were produced during the 48 hr logarithmic growth period. Serial transfers at 72 hr and during periods of greatest cell density produced a maximum of 8 generations 96 hr after initiation but the medium failed to sustain growth through more than 6 serial transfers. Extension of this investigation to formulating a minimal axenic medium is discussed.     

Statistical optimization of medium components for avilamycin production by <Emphasis Type="Italic">Streptomyces viridochromogenes</Emphasis> Tü57-1 using response surface methodology

A fermentation medium for avilamycin production by Streptomyces viridochromogenes Tü57-1 has been optimized. Important components and their concentrations were investigated using fractional factorial design and Box–Behnken Design. The results showed that soybean flour, soluble starch, MgSO₄·7H₂O and CaCl₂·2H₂O are important for avilamycin production. A polynomial model related to medium components and avilamycin yield had been established. A high coefficient of determination (R ² = 0.92) was obtained that indicated good agreement between the experimental and predicted values of avilamycin yield. Student’s T-test of each coefficient showed that all the linear and quadratic terms had significant effect (P > |T| < 0.05) on avilamycin yield. The significance of tested components was related to MgSO₄·7H₂O (0.37 g/L), CaCl₂·2H₂O (0.39 g/L), soybean flour (21.97 g/L) and soluble starch (37.22 g/L). The yield of avilamycin reached 88.33 ± 0.94 mg/L (p < 0.05) that was 2.8-fold the initial yield.     

The coordination chemistry of N-(2-pyridyl)pyridine-2′-carboxamide; A potentially tridentate ligand containing one secondary amide and two 2-pyridyl donor groups

New complexes of the general compositions M(LH)X₂ (M = Co, Zn; X = Cl, Br, I), Zn(LH)(NCS)₂, Zn(LH)(NO₃)₂ ·H₂O, Cu(LH)X₂ (X = Cl, Br, ONO₂), Ni(LH)Cl₂·H₂O, Co(LH)₂X₂ (X = NCS, ONO ₂), Ni(LH)₂X₂ (X = Cl, Br, NCS, ONO₂), Pt(LH)₂Cl₂ and MLCl·nH₂O (M = Ni, Cu, Pd; n = 2, 3), where LH = N-(2-pyridyl)pyridine-2′-carboxamide, have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods, magnetic susceptibilities and spectroscopic (IR, ligand field, ¹H NMR) studies. Pseudotetrahedral, square planar, square pyramidal and distorted octahedral stereochemistries are tentatively assigned in the solid state. Most complexes appear to be monomeric, while polymeric structural types are attributed for Ni(LH)Cl₂·H₂O and CuLCl·2H₂O. The neutral amide group of LH is coordinated to Co(II), Ni(II), Cu(II) and Zn(II) through oxygen, while N-coordination is observed for PdLCl·2H₂O. The amide group of L⁻ is bound to different Cu(II) atoms in CuLCl·2H₂O through both its nitrogen and oxygen. The rare O-coordination of the deprotonated amide bound is proposed for NiLCl· 3H₂O. The N(1) atom is not involved in coordination except in the complexes Ni(LH)Cl₂·H₂O, NiLCl· 3H₂O and CuLCl·2H₂O, where both pyridine residues are coordinated. The variation in structural types observed is believed to be a consequence of the stereochemical adaptability of the ligand to the electronic demands of the metal ions.     

Chalcogen- and halogen-bonds involving SX<Subscript>2</Subscript> (X = F,Cl, and Br) with formaldehyde

The capacity of SX₂ (X = F, Cl, and Br) to engage in different kinds of noncovalent bonds was investigated by ab initio calculations. SCl₂ (SBr₂) has two σ-holes upon extension of Cl (Br)?S bonds, and two σ-holes upon extension of S?Cl (Br) bonds. SF₂ contains only two σ-holes upon extension of the F?S bond. Consequently, SCl₂ and SBr₂ form chalcogen and halogen bonds with the electron donor H₂CO while SF₂ forms only a chalcogen bond, i.e., no F···O halogen bond was found in the SF₂:H₂CO complex. The S···O chalcogen bond between SF₂ and H₂CO is the strongest, while the strongest halogen bond is Br···O between SBr₂ and H₂CO. The nature of these two types of noncovalent interaction was probed by a variety of methods, including molecular electrostatic potentials, QTAIM, energy decomposition, and electron density shift maps. Termolecular complexes X₂S···H₂CO···SX′₂ (X = F, Cl, Br, and X′ = Cl, Br) were constructed to study the interplay between chalcogen bonds and halogen bonds. All these complexes contained S···O and Cl (Br)···O bonds, with longer intermolecular distances, smaller values of electron density, and more positive three-body interaction energies, indicating negative cooperativity between the chalcogen bond and the halogen bond. In addition, for all complexes studied, interactions involving chalcogen bonds were more favorable than those involving halogen bonds.

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Graphical Abstract Molecular electrostatic potential and contour map of the Laplacian of the electron density in Cl₂S···H₂CO···SCl₂ complex

     

Optimization of culture media for L-asparaginase production by newly isolated bacteria,Bacillus sp. GH5

The enzyme L-asparaginase has been extensively studied by many researchers mainly because of its considerable therapeutic properties. Producing a convenient quantity of L-asparaginase can be conducted either by discovering new microbial sources with higher enzyme production or by manipulating the medium components for known microbial sources. The present paper discusses the studies carried out in order to enhance the production of L-asparaginase by newly isolated bacteria, Bacillus sp. GH5. Based on the results obtained from media optimization studies, a modified media was developed for optimal L-asparaginase production. Concisely, screening of the nutrients using a proper statistical design showed that tapioca starch, gelatin, ammonium oxalate, CaCO₃, and L-asparagine were respectively the most important sources for carbon, organic nitrogen, inorganic nitrogen, mineral salt, and amino acids. The composition of the optimized medium was the following (per 1 L): 5.0 g L-asparagine; 0.5 g MgSO₄ · 7H₂O; 6.0 g NaHPO₄ · 2H₂O; 3.0 g (NH₄)₂C₂O₄; 0.5 g CaCO₃; 0.014 g CaCl₂ · 2H₂O; 2.0% w/v tapioca starch; 5.0 g gelatin; and 15.0 g agar.     

Upgrading of straw hydrolysate for production of hydrogen and phenols in a microbial electrolysis cell (MEC)

In a microbial electrolysis cell (MEC), hydrolysate produced by hydrothermal treatment of wheat straw was used for hydrogen production during selective recovery of phenols. The average H₂ production rate was 0.61 m³ H₂/m³ MEC·day and equivalent to a rate of 0.40 kg COD/m³ MEC·day. The microbial community in the anode biofilm was adapted by establishment of xylose-degrading bacteria of the Bacteriodetes phylum (16%) and Geobacter sulfurreducens (49%). During the process, 61% of the chemical oxygen demand was removed as hydrogen at 64% yield. The total energy production yield was 78% considering the energy content in the consumed compounds and the cell voltage of 0.7 V. The highest hydrogen production was equivalent to 0.8 kg COD/m³ MEC·day and was obtained at pH 7–8 and 25°C. Accumulation of 53% w/v phenolic compounds in the liquor was obtained by stepwise addition of the hydrolysate during simultaneous production of hydrogen from consumption of 95% for the hemicellulose and 100% of the fatty acids. Final calculations showed that hydrolysate produced from 1 kg wheat straw was upgraded by means of the MEC to 22 g hydrogen (266 L), 8 g xylan, and 9 g polyphenolics for potential utilization in biobased materials.