Drying cellulose nanofibrils: in search of a suitable method

Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.     

An Asymmetric Synthesis of 1,2,4-Trioxane Anticancer Agents via Desymmetrization of Peroxyquinols through a Brønsted Acid Catalysis Cascade

The desymmetrization of p-peroxyquinols using a Br?nsted acid-catalyzed acetalization/oxa-Michael cascade was achieved in high yields and selectivities for a variety of aliphatic and aryl aldehydes. Mechanistic studies suggest that the reaction proceeds through a dynamic kinetic resolution of the peroxy hemiacetal intermediate. The resulting 1,2,4-trioxane products were derivatized and show potent cancer cell-growth inhibition.     

Molecular methods to measure intestinal bacteria: a review

The intestine is an exceptionally rich ecosystem encompassing a complex interaction among microorganisms, influenced by host factors, ingested food, and liquid. Characterizing the intestinal microbiota is currently an active area of research. Various molecular-based methods are available to characterize the intestinal microbiota, but all methods possess relative strengths, as well as salient weaknesses. It is important that researchers are cognizant of the limitations of these methods, and that they take the appropriate steps to mitigate weaknesses. Here, we discuss methodologies used to monitor intestinal bacteria including: (i) traditional clone libraries; (ii) direct sequencing using next-generation parallel sequencing technology; (iii) denaturing gradient gel electrophoresis and temperature gradient gel electrophoresis; (iv) terminal restriction fragment length polymorphism analysis; (v) fluorescent in situ hybridization; and (vi) quantitative PCR. In addition, we also discuss experimental design, sample collection and storage, DNA extraction, gene targets, PCR bias, and methods to reduce PCR bias.     

Relationship between viscous dynamics and the configurational thermal expansion coefficient of glass-forming liquids

We propose a model to describe the relationship between the viscosity of a glass-forming liquid and its configurational contribution to liquid state thermal expansion. The viscosity of the glass-forming liquids is expressed in terms of three standard parameters: the glass transition temperature (T_g), the liquid fragility index (m), and the extrapolated infinite temperature viscosity (η_∞), which are obtained by fitting of the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) expression to measured viscosity data. The model is tested with experimental data for 41 different glass-forming systems. A good correlation is observed between our model viscosity parameter,h(T_g, m, η_∞), and the configurational coefficient of thermal expansion (i.e., the configurational CTE). Within a given class of glass compositions, the model offers the ability to predict trends in configurational CTE with changes in viscosity parameters. Since viscosity is governed by glass network topology, the model also suggests the role of topological constraints in governing changes in configurational CTE.     

The effect of dissipation on the resistive admittance of an elastic medium

The effect of dissipation on the real part of the admittance of an elastic half-space is typically thought to be unimportant if the loss factor ζ of the elastic medium is small. However, dissipation induces losses in the near field of the source and, provided the size of the source is small enough, this phenomenon can be more important than elastic wave radiation. Such losses give rise to a fundamental limit in the quality factor of an oscillator attached to a substrate. Near field losses associated with strains in the elastic substrate can actually be larger than intrinsic losses in the oscillator itself if the internal friction of the substrate is larger than the internal friction of the oscillator. For a uniform stress applied to a disk of radius a, a monopole source, such phenomena become significant for k(L)a<ζ, while for higher order multipole sources of order l, near field losses are important for (k(L)a)(l+1)<ζ, a far less restrictive constraint.     

Constructions for retransmission permutation arrays

Li et al. (Retransmission ≠ repeat: simple retransmission permutation can resolve overlapping channel collisions, 2009) introduced a technique for resolving overlapping channel transmissions that used an interesting new type of combinatorial structure. In connection with this problem, they provided an example of a 4 × 4 array having certain desirable properties. We define a class of combinatorial structures, which we term retrans mission permutation arrays, that generalise the example that Li et?al. provided. We show that these arrays exist for all possible orders. We also define some extensions having additional properties, for which we provide some partial results.     

The impact of sampling methods on bias and variance in stochastic linear programs

Stochastic linear programs can be solved approximately by drawing a subset of all possible random scenarios and solving the problem based on this subset, an approach known as sample average approximation (SAA). The value of the objective function at the optimal solution obtained via SAA provides an estimate of the true optimal objective function value. This estimator is known to be optimistically biased; the expected optimal objective function value for the sampled problem is lower (for minimization problems) than the optimal objective function value for the true problem. We investigate how two alternative sampling methods, antithetic variates (AV) and Latin Hypercube (LH) sampling, affect both the bias and variance, and thus the mean squared error (MSE), of this estimator. For a simple example, we analytically express the reductions in bias and variance obtained by these two alternative sampling methods. For eight test problems from the literature, we computationally investigate the impact of these sampling methods on bias and variance. We find that both sampling methods are effective at reducing mean squared error, with Latin Hypercube sampling outperforming antithetic variates. For our analytic example and the eight test problems we derive or estimate the condition number as defined in Shapiro et al. (Math. Program. 94:1–19, 2002). We find that for ill-conditioned problems, bias plays a larger role in MSE, and AV and LH sampling methods are more likely to reduce bias.     

A New Series of Proton/Charge Transfer Molecules: Synthesis and Spectral Studies of 2-(5-Aryl-1-carbomethoxy-1H-pyrazol-3-yl)phenols

Abstract. The carbomethoxyhydrazone of 2'-hydroxyacetophenone was trilithiated with excess lithium diisopropylamide and C-acylated with a variety of benzoate esters followed by acid cyclization of the intermediates to 2-(5-aryl-l-car-bomethoxy-lHpyrazol-3-yl)phenols [3-(2-hydroxyphen-yl)-lH-pyrazoles]. The products were characterized by Fourier transform-IR, ^lH NMR, ¹³C NMR, UV-visible absorption and fluorescence. All the derivatives in n -heptane have an absorption maximum at ˜304 nm and an extremely weak (φ_r= 10 ⁴) fluorescence with maxima in the range of 335–460 nm. The broad range of fluorescence maxima and fluorescence quantum yields is attributed to varying contributions of charge transfer that are dependent on both the identity of the substituent and solvent polarity. A phenomenally large Stokes-shifted fluorescence maximum at 620 nm was observed for 2-(l-car-bomethoxy-5-[4-dimethylaminophenyl]-lff-pyrazol-3-y1)phenol in n-heptane and attributed to excited-state intramolecular proton transfer. As a result, competitive excited-state proton/charge transfer properties have been observed in the pyrazoles studied, of which the spectral properties can be fine tuned by substituent as well as solvent effects.     

Synthesis of bis-3-alkyl-5-arylhydantoins and bis-3-alkyl-5-arylthiohydantoins separated by two and four carbon atoms

Synthesis of 1,2- and 1,4-bis-thiohydantoins and hydantoins employing ethylenediamine and 1,4-diaminobutane as spacers is described. Compounds containing a two carbon bridge were synthesized by alkylation of ethylenediamine with two equivalents of N-t-butyl-α-(p-toluenesulfonyloxy)phenylacetamide 3 . The phenyl isothiocyanate adduct of 3 cyclized in refluxing toluene to form 1a . Other isothiocyanate or isocyanate adducts derived from alkylation product 4 required hydrolysis to induce cyclization. Compounds 1b-1f were obtained in this way. Compounds with a four carbon bridge were obtained by reaction of two equivalents of methyl α-bromophenyl acetate and 1,4-diaminobutane to produce N,N'-bis-[(α-phenyl-α-methoxycarbonyl)methyl]butylenediamine 6 . The isothiocyanate or isocyanate adducts from 6 cyclized, without hydrolysis, to form compounds 2a-2e .     

Synthesis, characterization and antifungal activity of group 12 metal complexes of 2-acetylpyridine-N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-N-ethylthiosemicarbazone (H4ELO)

Reaction of group 12 metal halides in ethanol with the thiosemicarbazones 2-acetylpyridine-⁴N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-⁴N-ethylthiosemicarbazone (H4ELO) produced the compounds [M(H4EL)X₂] and [M(H4ELO)X₂] [M=Zn(II), Cd(II) or Hg(II), X=Cl, Br or I]. The ligands and complexes were characterized by elemental analysis and by IR and NMR (¹H, ¹³C, ¹¹³Cd, ¹⁹⁹Hg) spectroscopy, and the structures of H4ELO·H₂O and the complexes [Cd(H4EL)I₂]·2DMSO, [Hg(H4EL)Br₂]–DMSO, [Zn(H4ELO)Cl₂] and [Zn(H4ELO)Br₂] were determined by X-ray diffraction. The metal centers in the complexes have coordination number five, H4EL and H4ELO behaving as neutral NNS- and ONS-tridentate ligands, respectively. The coordination polyhedra are close to tetragonal pyramids, the degree of distortion towards trigonal bipyramids was estimated by τ calculation. Against the pathogenic fungi Aspergillus niger and Paecilomyces variotii, the mercury complexes of H4ELO had activities that at some doses exceeded that of nystatin.