Rapid biomass analysis

New, rapid, and inexpensive methods that monitor the chemical composition of corn stover and corn stover-derived samples are a key element to enabling the commercialization of processes that convert stover to fuels and chemicals. These new techniques combine near infrared (NIR) spectroscopy and projection to latent structures (PLS) multivariate analysis to allow the compositional analysis of hundreds of samples in 1 d at a cost of about $10 each. The new NIR/PLS rapid analysis methods can also be used to support a variety of research projects that would have been too costly to pursue by traditional methods.     

Use of solid-phase microextraction-capillary-gas chromatography (SPME-CGC) for the varietal characterization of wines by means of chemometrical methods

The extraction of wine aroma compounds was studied by direct-SPME (DI/SPME), headspace-SPME (HS/SPME) and multiple-headspace-extraction-SPME (MHE/SPME). The aromagrams obtained by HS/SPME-CGC were evaluated with chemometrical methods for the varietal classification of wines. Received: 25 July 1997 / Revised: 24 September 1997 / Accepted: 7 October 1997     

The synthesis of dicationic extended bis-benzimidazoles

The synthesis of extended dicationic bis-benzimidazoles starting from trans-1,2-bis(4-cyanophenyl)ethene and trans-1,2-bis(4-cyanophenyl)cyclopropane is reported. The target diamidines show significant in vitro activity against B. subtilis.     

The preparation of 2,6-diaminopyrazine, 2,6-diazidopyrazine and some of their derivatives

A much improved synthesis of the heretofore difficultly obtainable 2,6-diaminopyrazine (4) was afforded by the low-pressure catalytic hydrogenation (palladium on carbon) of 2,6-diazido-pyrazine (2) ; reaction of 2,6-dichloropyrazine (1) and sodium azide gave 2 in 84% yield. The outcome of the reduction was found to be solvent dependent: 1,2-dimethoxyethane containing aqueous ammonia gave 4 in 83% yield; 1,2-dimethoxyethane alone gave 5-aminotetrazolo[1,5-a]-pyrazine (3) in 26% yield. Additional alternative syntheses of 3 and 4 are described. A number of acyl and azo derivatives of 4 were prepared. Reactions of 2 with dimethyl acetylenedicarboxylate and ethyl acetate (base catalyzed) leading to vic-triazole derivatives are also described.     

Role of the spacer in the singlet-singlet energy transfer mechanism (Förster vs Dexter) in cofacial bisporphyrins

The cofacial bisporphyrins H4DPS (DPS = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene), H4DPO (DPO = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran), H4DPX (DPX = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene), H4DPA (DPA = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene), and H4DPB (DPB = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene) have been monometalated by Zn(OAc)2.2H2O and by GaCl3 to explore the singlet-singlet energy transfer from the photoexcited metal porphyrin center to the linked free base porphyrin. The spectroscopic (UV-vis and fluorescence) and photophysical properties (fluorescence lifetimes, tauF, and quantum yields, phiF) have been investigated at 298 and 77 K in degassed 2-MeTHF for the donor-acceptor systems, (Zn)H2DPS, (Zn)H2DPO, (Zn)H2DPA, (Zn)H2DPX, and (Zn)H2DPB, as well as for the bis-zinc complexes, (Zn)2DPS, (Zn)2DPO, (Zn)2DPX, and (Zn)2DPB, respectively, and the monoporphyrin derivatives, H2P, (Zn)P, and (Ga-OMe)P (P2- = 5-phenyl-2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrin-dianion). The singlet-singlet energy transfer rate constants (KET) were obtained using KET = (1/tauF -1/tauFo), where tauFo is the fluorescence lifetime of the corresponding bis-zinc(II) systems (or (Zn)P and (Ga-OMe)P) where no energy transfer occurs. The tauF value for three bis-zinc(II) compounds varies from 1.69 to 2.01 ns and is 1.84 (at 298 K) and 3.20 ns (at 77 K) for (Ga-OMe)P. In the donor-acceptor bismacrocycles, depending on the spacer and the temperature, the fluorescence lifetimes decrease down to 50-240 ps. The KET values range from approximately 4 to approximately 21 (ns(-1)) and have been analyzed considering both the F?rster and the Dexter mechanisms. Using the C(meso)-C(meso) distance parameters in the calculations, the F?rster and Dexter mechanisms operate for DPS and DPO, and for DPA, DPX, and DPB spacer systems, respectively. The limit distance where one mechanism dominates over the other is estimated to be around 5-6 A.     

Synthesis and crystal chemistry of NH3(MoO3)3

NH₃(MoO₃)₃ crystallizes with hexagonal symmetry, space group $\text{P6}{}_3\text{m}$, lattice constants a = 10.568 Å, c = 3.726 Å, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted MoO₆ octahedra, parallel to the [001] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MoO distances range from 1.645 to 2.378 Å and OMoO angles from 74.3 to 114.3°. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordination with terminal oxygens.     

Adsorption of Molybdenum on Titania from Aqueous Solutions

The adsorption of Mo from dilute aqueous solutions (10(-3) to 3x10(-2) M) is effected on three samples of titania, two are anatase and the third is P25, which is composed of rutile and anatase. The adsorption isotherms at 298, 318, and 338 K are analyzed using a Langmuir linear equation. The isotherms on P25 showed a distinct inflection point that is reproduced by two linear portions, indicating different adsorption regimes. This adsorption behavior is explained as follows: with low amount adsorbed the adsorption is initiated by protonation of the basic hydroxyls on which the negatively charged MoO(4)(2-')s are adsorbed, and this is accompanied by an increase in the pH of the impregnating solution. At higher adsorption the coordinatively unsaturated Ti(4+) sites participate in the process, leading to a decline in the initial increase in pH. In the case of the two anatase samples the low surface area resulted in poor distribution of adsorption sites; consequently, the distinction between the two modes of adsorption was not entirely clear. The higher adsorption site density in the case of anatase is accompanied by a lower surface coverage, θ, than that for P25. The heat of adsorption, Q, on the three titania samples showed a linear increase with θ, which is represented by the regression equation: -Q=95.77θ-4.25 (R(2)=0.993). Copyright 2001 Academic Press.     

Formation of disubstituted beta-lactones using bifunctional catalysis

[reaction: see text] Acid chlorides and aromatic aldehydes react in the presence of a stoichiometric amount of a tertiary amine and catalytic amounts of a cinchona alkaloid derivative and a Lewis acid to produce beta-lactones in high diastereo- and enantioselectivity. The sense of the diastereoselectivity depends on the substitution of the acid chloride, with the reactions of aliphatic acid chlorides giving predominantly the trans-isomer and those of alkoxyacetyl chlorides favoring formation of the cis-isomer.     

Minimization of water vapor interference in the analysis of non-methane volatile organic compounds by solid adsorbent sampling

Water vapor can be a significant interference in the analysis of air for non-methane volatile organic compounds (NMVOCs) using solid-adsorbent sampling techniques. The adsorbent materials used in sampling cartridges have different hydrophobic characteristics, and it is therefore necessary to characterize solid-adsorbent cartridges over a wide range of humidity. Controlled humidity experiments were performed to assess the extent of water vapor interference when samples are collected onto AirToxics solid-adsorbent cartridges. It was found that elevating the temperature of the cartridge to 10 degrees C above the temperature of the air sample greatly reduced water vapor adsorption and interferences and resulted in > or = 90% recovery of NMVOCs, biogenic VOCs and chlorofluorocarbons. Similar collection efficiencies were obtained at ambient temperature by reducing the relative humidity to > or = 60% in the sample by dilution with dry, scrubbed ambient air. A procedure also was developed and optimized for dry-purging cartridges prior to analysis. However, under optimized conditions, significant losses of C3-C5 compounds still occurred under highly humid conditions. It was determined that these losses were due to reduced retention during sampling rather than loss during the dry purge procedure. The dry purge method was shown to be adequate at high humidities for sampling NMVOCs with retention indices greater than 500.     

Gravity-induced convective flow in microfluidic systems: electrochemical characterization and application to enzyme-linked immunosorbent assay tests

A way of using gravity flow to induce a linear convection within a microfluidic system is presented. It is shown and mathematically supported that tilting a 1 cm long covered microchannel is enough to generate flow rates up to 1000 nL.min(-1), which represents a linear velocity of 2.4 mm.s(-1). This paper also presents a method to monitor the microfluidic events occurring in a covered microchannel when a difference of pressure is applied to force a solution to flow in said covered microchannel, thanks to electrodes inserted in the microfluidic device. Gravity-induced flow monitored electrochemically is applied to the performance of a parallel-microchannel enzyme-linked immunosorbent assay (ELISA) of the thyroid-stimulating hormone (TSH) with electrochemical detection. A simple method for generating and monitoring fluid flows is described, which can, for instance, be used for controlling parallel assays in microsystems.