Ynol ethers from dichloroenol ethers: mechanistic elucidation through 35Cl labeling

The mechanism of ynol ether formation from dichloroenol ethers, a decades-old transformation, has been studied by experimental and theoretical techniques to determine the relative importance of the Fritsch-Buttenberg-Wichell rearrangement (alpha-elimination) and beta-elimination in the evolution of the intermediate carbenoid.     

Biophysical and structural characterization of a robust octameric beta-peptide bundle

Proteins composed of alpha-amino acids are essential components of the machinery required for life. Stanley Miller's renowned electric discharge experiment provided evidence that an environment of methane, ammonia, water, and hydrogen was sufficient to produce alpha-amino acids. This reaction also generated other potential protein building blocks such as the beta-amino acid beta-glycine (also known as beta-alanine); however, the potential of these species to form complex ordered structures that support functional roles has not been widely investigated. In this report we apply a variety of biophysical techniques, including circular dichroism, differential scanning calorimetry, analytical ultracentrifugation, NMR and X-ray crystallography, to characterize the oligomerization of two 12-mer beta3-peptides, Acid-1Y and Acid-1Y*. Like the previously reported beta3-peptide Zwit-1F, Acid-1Y and Acid-1Y* fold spontaneously into discrete, octameric quaternary structures that we refer to as beta-peptide bundles. Surprisingly, the Acid-1Y octamer is more stable than the analogous Zwit-1F octamer, in terms of both its thermodynamics and kinetics of unfolding. The structure of Acid-1Y, reported here to 2.3 A resolution, provides intriguing hypotheses for the increase in stability. To summarize, in this work we provide additional evidence that nonnatural beta-peptide oligomers can assemble into cooperatively folded structures with potential application in enzyme design, and as medical tools and nanomaterials. Furthermore, these studies suggest that nature's selection of alpha-amino acid precursors was not based solely on their ability to assemble into stable oligomeric structures.     

Photoionization of C(4) molecular beam: ab initio calculations

Large computations are performed on the C(4) (+) cation in order to characterize its stable isomers and its lowest electronic excited states using configuration interaction methods and large basis sets. Several stable isomers are found including a linear C(4) (+)(l-C(4) (+)), a rhombic C(4) (+)(r-C(4) (+)) (or cyclic), and a branched (d-C(4) (+)) structure. Our calculations show a high density of electronic states for all of these isomers favoring their interactions. By combining the present ab initio data and those on neutral C(4), the l-C(4)(X)+hnu-->l-C(4) (+)(X(+))+e(-), d-C(4)(X)+hnu-->d-C(4) (+)(X(+))+e(-), and r-C(4)(X)+hnu-->r-C(4) (+)(X(+))+e(-) vertical photoionization transition energies are computed at 10.87, 10.92, and 10.77 eV, respectively. Photoionizing a C(4) molecular beam results on an onset at 10.4-10.5 eV and then to a linear increase of the signal due to the opening of several ionization channels involving most of the C(4) and C(4) (+) isomers and electronic states.     

Terminal olefins from aldehydes through enol triflate reduction

The transformation of aldehydes into terminal olefins through reduction of the corresponding enol triflates is described. The method is effective with both linear and alpha-branched aldehydes.     

Copper‐Mediated Formation of Aryl,Heteroaryl, Vinyl and Alkynyl Difluoromethylphosphonates: A General Approach to Fluorinated Phosphate Mimics

A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF₂PO(OEt)₂, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates.     

The Application of Ultrasound in the Enzymatic Hydrolysis of Switchgrass

In a series of experiments, untreated and ammonium hydroxide pretreated Klenow lowland variety switchgrasses are converted to reducing sugars using low-frequency (20 kHz) ultrasound and commercially available cellulase enzyme. Results from experiments using untreated and pretreated switchgrasses with and without ultrasound are presented and discussed. In untreated switchgrass experiments, the combination of ultrasound and enzymes resulted in an increase of 7.5% in reducing sugars compared to experiments using just enzymes. In experiments using ammonium hydroxide pretreated switchgrass, the combination of ultrasound and enzymes resulted in an increase of 9.3% in reducing sugars compared to experiments using just enzymes. Experimental evidence indicates that there is a synergistic effect from the combination of ultrasound and enzymes which lowers the diffusion-limiting barrier to enzyme/substrate binding and results in an increase in reaction rate. Scanning electron microscopic images provide evidence that ultrasound-induced pitting increases substrate surface area and affects reaction rate and yield.     

Miniemulsion polymerizations of n-butyl cyanoacrylate via two routes: towards a control of particle degradation

This study aimed at determining the influence of the mechanism of polymerization on the molar mass and degradation of poly(n-butyl cyanoacrylate) (PBCA) nanoparticles obtained by miniemulsion polymerization. Therefore, nanoparticles of poly(n-butyl cyanoacrylate) were synthesized via radical and/or anionic miniemulsion polymerization stabilized by Brij?78, a POE based surfactant. Polymerization conditions had little influence on the final diameter while it severely affected the final molar masses of PBCA. An increase of the temperature and of the pH of the continuous phase led to higher molar masses. A further increase was observed when a radical initiator was added in the monomer. The evolution of the molar mass of the synthesized poly(n-butyl cyanoacrylate) was followed as a function of time at pH 7.4 by Size Exclusion Chromatography. As expected, the degradation kinetics strongly depended on the polymerization mechanism (anionic or radical).     

Synthesis and characterization of a novel phosphorus–nitrogen‐containing flame retardant and its application for textile

The economic and environmentally friendly flame‐retardant compound, tetramethyl (6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(oxy)bis(methylene) diphosphonate ( CN‐1 ), was synthesized by a simple two‐step procedure from dimethyl phosphate, and its chemical structure was characterized by ¹H, ¹³C, and ³¹P nuclear magnetic resonance and gas chromatography mass spectroscopy. Using the traditional pad–dry–cure method, we obtained several different add‐ons (wt%) by treating cotton twill fabric with flame retardant ( CN‐1 ). Thermogravimetric analysis, in an air and nitrogen atmosphere, of the modified cotton showed that decomposition occurred ~230°C with 16% residue weight char yield at 600°C, indicating high thermal stability for all treated levels. Limiting oxygen index (LOI) and the vertical flammability test were employed to determine the effectiveness of the flame‐retardant treatments on the fabrics. LOI values increased from ~18 vol% oxygen in nitrogen for untreated fabric to maximum of 34 vol% for the highest treatment level. Fabrics with higher levels of flame retardant also easily passed the vertical flammability test. Furthermore, Fourier transform infrared and scanning electron microscopy were utilized to characterize the chemical structure as well as the surface morphology of the flame‐retardant treated twill fabrics, including char area and the edge between unburned fabric and char area. Copyright © 2011 John Wiley & Sons, Ltd.     

Femtosecond dynamics of cyclopropenylidene, c-C3H2

The photophysics of the B (1)B(1) state of isolated cyclopropenylidene, c-C(3)H(2), has been studied by femtosecond time-resolved photoionisation and photoelectron spectroscopy. The carbene was produced by flash pyrolysis of 3-chlorocycloprop-1-ene. The bands at 266.9 nm and 264.6 nm have been investigated. The excited state deactivates in a two step process. The first time constant of less than 50 fs corresponds most likely to a nonradiative transition to the A-state, the second one on the order of 200 fs describes the internal conversion to the electronic ground state. The data are compared to those measured for the chlorinated carbene c-C(3)HCl. In the photoelectron spectrum of c-C(3)H(2) resonances were observed which can be assigned to members of a Rydberg d-series.