Pretreatment of yellow poplar sawdust by pressure cooking in water

The pretreatment of yellow poplar wood sawdust using liquid water at temperatures above 220°C enhances enzyme hydrolysis. This paper reviews our prior research and describes the laboratory reactor system currently in use for cooking wood sawdust at temperatures ranging from 220 to 260°C. The wood sawdust at a 6–6.6% solid/liquid slurry was treated in a 2 L, 304 SS, Parr reactor with three turbine propeller agitators and a proportional integral derivative (PID) controller, which controlled temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 60–70 min. Hold time at the final temperature was less than 1 min. A serpentine cooling coil, through which tap water was circulated at the completion of the run, cooled the reactor’s contents within 3 min after the maximum temperature was attained. A bottoms port, as well as ports in the reactor’s head plate, facilitated sampling of the slurry and measuring the pH, which changes from an initial value of 5 before cooking to a value of approx 3 after cooking. Enzyme hydrolysis gave 80–90% conversion of cellulose in the pretreated wood to glucose. Simultaneous saccharification and fermentation of washed, pretreated lignocellulose gave an ethanol yield that was 55% of theoretical. Untreated wood sawdust gave less than 5% hydrolysis under the same conditions.     

High-frequency EPR study of the ferrous ion in the reduced rubredoxin model

High-frequency (94-371 GHz) EPR data are reported for powdered samples of [PPh4]2[Fe(SPh)4], an accurate model for the reduced site of rubredoxins. This is the first HFEPR investigation of an S = 2 ferrous complex, illustrating the utility of this technique for the investigation of integer-spin systems. A full-matrix diagonalization approach is used to simulate spectra over the 94-371 GHz frequency range, providing the spin-Hamiltonian parameters g, D, and E. It is observed that g is anisotropic, characterized by gx = gy = 2.08 and gz = 2.00, and that D = +5.84 cm(-1) and E = +1.42 cm(-1), where the uncertainty in each parameter is estimated as +/- 2%. The spin-Hamiltonian for [PPh4]2[Fe(SPh)4] is related to fundamental properties, such as the crystal-field splitting and the spin-orbit coupling of Fe2+. It is shown that the conventional spin-Hamiltonian accurately represents the electronic structure of the Fe2+ ion in this molecule. Through a comparison with Fe(SPh)4(PPh4)2, the zero-field splitting of the Fe2+ site in reduced rubredoxin is estimated to be D = +5.3 cm(-1) and E = +1.5 cm(-1). This is one of the few HFEPR investigations of a rhombic, high-spin system; as such, it is a step toward the eventual investigation of similar Fe2+ sites in proteins.     

Tetranuclear manganese complexes with dimer-of-dimer and ladder structures from the use of a bis-bipyridyl ligand

The reaction of the bis-chelating ligand 1,2-bis(2,2'-bipyridine-6-yl)ethane (L) with the trinuclear species of formula [Mn(3)O(O(2)CR)(6)(py)(3)](ClO(4)) (R = Me (1); R = Et (2); R = Ph (3)) has afforded the new tetranuclear mixed-valent complexes [Mn(4)O(2)(O(2)CR)(4)L(2)](ClO(4))(2) (R = Me (4); R = Et (5); R = Ph (6)) and [Mn(4)O(2)(OMe)(3)(O(2)CR)(2)L(2)(MeOH)](ClO(4))(2) (R = Me (7); R = Et (8); R = Ph (9)). Complexes 4-6 were obtained in yields of 20%, 44%, and 37%, respectively. They are mixed-valent, with an average Mn oxidation state of +2.5. Complexes 7-9 were obtained in yields of 57%, 65%, and 70%, respectively. They are also mixed-valent, but with an average Mn oxidation state of +2.75. Complexes 4 x 2THF and 9 x 3MeOH x H(2)O crystallize in the triclinic space group P1 macro and contain [Mn(4)(mu(3)-O)(2)](6+) and [Mn(4)(mu(3)-O)(2)(mu-OMe)(2)](5+) cores, respectively, the latter being a new structural type in the family of Mn(4) complexes. Reactivity studies of 4-9 have shown that 4-6 can be converted into 7-9, respectively, and vice versa. The magnetic properties of 5 and 9 have been studied by dc and ac magnetic susceptibility techniques. Complex 5 displays antiferromagnetic coupling between its Mn ions resulting in a spin ground state of S = 0. Complex 9 also displays antiferromagnetic coupling, but the resulting ground state is S = (7)/(2), as confirmed by fitting magnetization versus field data collected for 9 at low temperatures, which gave S = (7)/(2), D = -0.77 cm(-1), and g = 1.79. Complex 9 exhibits a frequency-dependent out-of-phase ac susceptibility peak, indicative of the slow magnetization relaxation that is diagnostic of single-molecule magnetism behavior.     

Numerical approximations and regularizations of Riccati equations arising in hyperbolic dynamics with unbounded control operators

This paper provides an approximation theory for numerical computations of the solutions to algebraic Riccati equations arising in hyperbolic, boundary control problems. One of the difficulties in the approximation theory for Riccati equations is that many attractive numerical methods (such as standard finite elements) do not satisfy a uniform stabilizability condition, which is necessary for the stability of the approximate Riccati solutions. To deal with these problems, a regularizationapproximation technique, based on the introduction of special artificial terms to the dynamics of the original model, is proposed. The need for this regularization appears to be a distinct feature of hyperbolic (hyperbolic-like) equations, rather than parabolic (parabolic-like) problems where the smoothing effect of the dynamics is beneficial for the convergence and stability properties of approximate solutions to the associated Riccati equations (see [14]). The ultimate result demonstrates that the regularized, finite-dimensional feedback control yields near optimal performance and that the corresponding Riccati solution satisfies all the desired convergence properties. The general theory is illustrated by an example of a boundary control problem associated with the Kirchoff plate model. Some numerical results are provided for the given example.     

Periodic sequence distribution of product ion abundances in electron capture dissociation of amphipathic peptides and proteins

The rules for product ion formation in electron capture dissociation (ECD) mass spectrometry of peptides and proteins remain unclear. Random backbone cleavage probability and the nonspecific nature of ECD toward amino acid sequence have been reported, contrary to preferential channels of fragmentation in slow heating-based tandem mass spectrometry. Here we demonstrate that for amphipathic peptides and proteins, modulation of ECD product ion abundance (PIA) along the sequence is pronounced. Moreover, because of the specific primary (and presumably secondary) structure of amphipathic peptides, PIA in ECD demonstrates a clear and reproducible periodic sequence distribution. On the one hand, the period of ECD PIA corresponds to periodic distribution of spatially separated hydrophobic and hydrophilic domains within the peptide primary sequence. On the other hand, the same period correlates with secondary structure units, such as α-helical turns, known for solution-phase structure. Based on a number of examples, we formulate a set of characteristic features for ECD of amphipathic peptides and proteins: (1) periodic distribution of PIA is observed and is reproducible in a wide range of ECD parameters and on different experimental platforms; (2) local maxima of PIA are not necessarily located near the charged site; (3) ion activation before ECD not only extends product ion sequence coverage but also preserves ion yield modulation; (4) the most efficient cleavage (e.g. global maximum of ECD PIA distribution) can be remote from the charged site; (5) the number and location of PIA maxima correlate with amino acid hydrophobicity maxima generally to within a single amino acid displacement; and (6) preferential cleavage sites follow a selected hydrogen spine in an α-helical peptide segment. Presently proposed novel insights into ECD behavior are important for advancing understanding of the ECD mechanism, particularly the role of peptide sequence on PIA. An improved ECD model could facilitate protein sequencing and improve identification of unknown proteins in proteomics technologies. In structural biology, the periodic/preferential product ion yield in ECD of α-helical structures potentially opens the way toward de novo site-specific secondary structure determination of peptides and proteins in the gas phase and its correlation with solution-phase structure.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Conductivities and transport properties of gelled electrolytes with and without an ionic liquid for Li and Li-ion batteries

Conductivity and transport properties have been determined for gelled polymer electrolytes of three compositions: a base PVdF-polymer gel with organic carbonate solvents as plasticizers and LiN(SO(2)C(2)F(5))(2) electrolyte, a second polymer electrolyte with 5 mass % 1-ethyl-3-methylimidazolium bisperfluoroethylsulfonyl imide (EMI-BETI) added to the base polymer electrolyte, and a third PVdF polymer electrolyte using only EMI-BETI as the plasticizer. Conductivities were studied over the temperature range +25 to -40 degrees C, and for all three gels, the temperature dependence of the conductivities was found to follow the VTF equation, which is consistent with the free volume model for ion transport. For the gel containing 5 mass % EMI-BETI, transport numbers were determined from +50 to -20 degrees C and were found to decrease as the temperature decreased. Although there are no theoretical models to treat and interpret the temperature dependence of transport numbers, we found that a modified VTF equation resulted in an excellent fit to the temperature dependence of the transport number, which is another confirmation of a free volume model for transport in these gelled polymer electrolytes.