The Influence of Initial Xylose Concentration, Agitation, and Aeration on Ethanol Production by Pichia stipitis from Rice Straw Hemicellulosic Hydrolysate

Rice straw hemicellulosic hydrolysate was used as fermentation medium for ethanol production by Pichia stipitis NRRL Y-7124. Shaking bath experiments were initially performed aiming to establish the best initial xylose concentration to be used in this bioconversion process. In the sequence, assays were carried out under different agitation (100 to 200 rpm) and aeration (V _flask/V _medium ratio varying from 2.5 to 5.0) conditions, and the influence of these variables on the fermentative parameters values (ethanol yield factor, Y _P/S; cell yield factor, Y _X/S; and ethanol volumetric productivity, Q _P) was investigated through a 2² full-factorial design. Initial xylose concentration of about 50 g/l was the most suitable for the development of this process, since the yeast was able to convert substrate in product with high efficiency. The factorial design assays showed a strong influence of both process variables in all the evaluated responses. The agitation and aeration increase caused a deviation in the yeast metabolism from ethanol to biomass production. The best results (Y _P/S?= 0.37 g/g and Q _P?=?0.39 g/l.h) were found when the lowest aeration (2.5 V _flask/V _medium ratio) and highest agitation (200 rpm) levels were employed. Under this condition, a process efficiency of 72.5% was achieved. These results demonstrated that the establishment of adequate conditions of aeration is of great relevance to improve the ethanol production from xylose by Pichia stipitis, using rice straw hemicellulosic hydrolysate as fermentation medium.     

Estrogen fluoroimmunoassay with a fluorimeter designed for low-intensity light detection

A small, highly sensitive, inexpensive fluorimeter for the detection of very low fluorescence intensities for analytical and clinical purposes is described. High sensitivity is achieved by use of an inexpensive continuous wave laser with a power of a few milliwatts. The optical arrangement of the instrument has been thoroughly designed so that the effects of Rayleigh and Raman scattering are minimized. Fluorescence is dected through optical filters with a side-on photomultiplier. Concentrations of rhodamine B in ethanol as low as 10^?11 M can be measured. To use this instrument for a fluoroimmunoassay of urinary estrogens (10^?9?10^?7 M), a purified monoclonal IgG, raised against estradiol, was labelled with RITC (rhodamine isothiocyanate) in a 1:1 molar ratio. It was possible to measure IgG-RITC concentrations between 10^?9 and 10^?10 M with good accuracy and reproducibility.     

2,3‐Dihydro‐3,3‐dimethylspiro[1H‐4‐oxanthracene‐5,2′‐oxiran]‐10(5H)‐one

The central six‐membered ring in the title compound, C₁₆H₁₆O₃, is almost planar (and almost coplanar with the aromatic ring), despite one of its C atoms being formally sp³ hybridized. The planarity is a consequence of the C atom at the centre of the spiro­cyclic system also being part of the three‐membered epoxide ring. The mol­ecules are linked by π–­π and C—H?π interactions.     

Synthesis, characterization, and SAMs electroactivity of ruthenium complexes with sulfur containing ligands

The vibrational and ¹H NMR data hints that the coordination of the 2,2′-dithiodipyridine (2-pySS) ligand to the [Ru(CN)₅]³⁻ metal center occurs through the sulfur atom instead of the nitrogen atoms which is usually observed for N-heterocyclic ligands. Electrochemical results show that this coordination mode implies an additional thermodynamic stabilization of the Ru^II over Ru^III oxidation state due to a relative stronger π-back-bonding interaction with the empty low-lying dπ orbitals of the sulfur atom. Computational data reinforce the experimental results showing that the 2-pySS Lewis base centers are located on the sulfur atoms. Ligands containing only sulfur atoms as coordination sites (2,2′-dithiodipyridine N-oxide (2-pySSNO), 1,4-dithiane (1,4-dt), and 2,6-dithiaspiro[3.3]heptane (asp)) were also coordinated to the [Ru(CN)₅]³⁻ metal center to undoubtedly correlate the electrochemical results with the ligand coordination atom. Among the synthesized compounds, the [Ru(CN)₅(1,4-dt)]³⁻ and [Ru(CN)₅(asp)]³⁻ complexes showed to be able to form self-assembled monolayers (SAMs) on gold. These SAMs, which were characterized by SERS (surface-enhanced Raman scattering) spectroscopy, successfully assessed the heterogeneous electron transfer reaction of the cytochrome c metalloprotein in physiological medium.     

Phase matching second harmonic generation at 0.8716 μm in a Na2SeO4·H2SeO3·H2O crystal

Na₂SeO₄·H₂SeO₃H₂O are transparent orthorhombic (class group mm2) crystals which exhibit interesting second order nonlinear optical properties in the blue region of the visible spectrum. We demonstrate here the efficient generation at λ_ω=0.8716 μm of the second harmonic in a peculiar crystal configuration where type I phase matching occurs.     

(Aroxymethyl)triphenyltin compounds: Crystal and molecular structure of triphenyl(p-toloxymethyl)tin

Compounds, Ph₃SnCH₂OAr, are available from Ph₃SnCH₂I and NaOAr in EtOH. The crystal and molecular structure of Ph₃SnCH₂OC₆H₄Me-p (II) has been determined by X-ray crystallography. The molecule in the crystal contains a slightly distorted tetrahedral tin atom [C-Sn-C valency angles varying from 106.9(5) to 114.1(6)°] with an intramolecular Sn---O distance of 2.900(11) Å. NMR spectral data for (II) and for Ph₃SnCH₂OC₆H₃Br₂-2,4 are reported.     

Synthesis and structural study of 1-(N,N-diethylamino)-2,2-bis(2-nitrophenylthio)ethene

The synthesis, variable temperature NMR spectra, and crystal structures of two crystalline forms, 2a and 2b, of the enamine 1-(N,N-diethylamino)-2,2-bis(2-nitrophenylthio)ethene have been obtained. Both forms crystallize in the monoclinic space group P2₁/a. The two phases have similar molecular structures but possess different intermolecular C–H······O hydrogen bonding interactions. Both forms exhibit disorder within the NEt₂ fragment at 298 K: sufficient disorder persisted with 2a (orange needles) down to 100 K to make the geometric parameters pertaining to the enamine fragment unreliable. The disorder was effectively eliminated on cooling 2b down (red colored blocks) to 150 K. Cell dimensions for the 2a-phase are at 100 K: a = 11.1030(4) Å, b = 15.1325(7) Å, c = 12.4504(7) Å, β = 114.606(3)°, while for the 2b-phase at 150 K, a = 15.5206(4) Å, b = 7.6958(2) Å, c = 15.7137(3) Å, β = 92.580(7)°. The C–N bond length in the β-form at 150 K of 1.335(3) Å indicates considerable double bond character: the rotational barrier of the C–N bond in CDCl₃ was calculated to be 52.4 kJ mol^?1.     

Synthesis and structure of 1,12-bis-(N-naphthalamido)-4,9-bis-(2,4,6-trimethylbenzenesulfonyl)-4,9-diaza-dodecane

1,12-Bis-(N-naphthalamido)-4,9-bis-(2,4,6-trimethylbenzenesulfonyl)-4,9-diaza-dodecane 1 was obtained from 1,8-naphthalic anhydride on successive reactions with 3-aminopropanol, 4-methylbenzenesulfonyl chloride and 1,4-bis-(2,4,6-trimethylbenzenesulfonamido)butane. The molecular structure of 1 was investigated by X-ray crystallography, NMR, and mass spectrometry. The molecule crystallizes in the triclinic space group, . The cell parameters are a = 8.1548(12), b = 15.878(3), c = 18.005(3) Å, = 97.685(10), = 93.260(15), and = 101.754(11)°. The asymmetric unit consists of the halves of two independent molecules, with Z = 2.     

Hydrogen-Bonding Interactions in the Crystal Structure of Bis( N -propyl- N -(2-hydroxyethyl)dithiocarbamato- S , S ′)nickel(II): Ni[S2CN(nPr)(CH2CH2OH)]2

Two independent molecules of Ni(S₂CN(Pr)CH₂CH₂OH)₂, each located about a center of inversion, comprise the asymmetric unit. The molecules differ from each other in terms of the relative orientation of the terminal hydroxyl groups. A square planar geometry is found for each nickel atom defined by four sulfur atoms derived from two symmetrically chelating dithiocarbamate ligands. The crystal packing is dominated by O–H···O interactions that lead to extensive cross linking in all directions. The compound crystallizes in the triclinic space group P-1 with a = 6.4008(11) ?, b = 11.480(2) ?, c = 12.517(2) ?, α = 88.021(2)°, β = 82.491(2)°, γ = 89.986(2)°, and Z = 2.     

Analysis of Powdered Coffee and Milk by ICP OES after Sample Treatment with Tetramethylammonium Hydroxide

 A simple method for the solubilization of powdered milk and soluble coffee using tetramethylammonium hydroxide (TMAH) is proposed. While 500 μL of the reagent was used for the solubilization of 350 mg of coffee samples, milk samples required 1000 μL of TMAH. Solubilization at 80 °C takes place within 10, 20 and 30 min for soluble coffee, whole and skim powdered milk, respectively. Subsequently, the volume was topped up to 25 mL with deionized water. Thereafter, the concentrations of Ca, Cu, Fe, K, Mg, Mn, Na, P, Se, Sn and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP OES). When applied to standard reference material and to commercial samples the proposed method showed good results, and it was also compared with two other preparation methods. Limits of detection calculated for Ca, Cu, Fe, K, Mg, Mn, Na, P, Se, Sn and Zn were 2.1, 0.065, 0.11, 103, 0.088, 0.011, 1.5, 2.1, 1.1, 0.66 and 0.11 μg g⁻¹, respectively. The RSD values were less than 10% for the certified reference materials (IAEA A-11 and BCR 63R). Statistical tests showed that the results for the metal concentrations do not vary significantly with the different methods or with the certified reference values, considering a confidence limit of 95%. Correspondence: Departamento de Química Analítica, Instituto de Química, UNICAMP, 13083-862, Campinas, Brazil. e-mail: codore@igm.unicamp.br Received August 5, 2002; accepted October 30, 2002