Dissolving pulp from eucalyptus sawdust for regenerated cellulose products

Cellulose - This study assesses the possibility of obtaining regenerated cellulose products (beads and films) from eucalyptus sawdust dissolving pulps produced by non-conventional processes,...     

An efficient route for the synthesis of chiral conduritol-derivative carboxamides via palladium-catalyzed aminocarbonylation of bromocyclohexenetetraols

A family of chiral conduritol-derivative carboxamides was synthesized through palladium-catalyzed aminocarbonylation of diastereoisomeric bromocyclohexenetetraols, previously prepared through biotransformation of bromobenzene by mutant strains of Pseudomonas putida F39/D.The coupling reactions of bromocyclohexenetetraols with CO and different amines, such as tert-butylamine, aniline, and piperidine, were performed in the presence of in situ generated Pd(0)/PPh₃ catalyst. The methodology was applied to the corresponding iodo-cyclohexenetetraol derivative, using (L)-alanine and (L)-valine methyl ethers as N-nucleophiles. The resulting carboxamides were obtained in highly chemoselective reactions, isolated, and fully characterized.     

Assembling wormlike micelles in tubular nanopores by tuning surfactant-wall interactions

Threadlike molecular assemblies are excluded from narrow pores unless attractive interactions with the confining pore walls compensate for the loss of configurational entropy. Here we show that wormlike surfactant micelles can be assembled in the 8 nm tubular nanopores of SBA-15 silica by adjusting the surfactant-pore-wall interactions. The modulation of the interactions was achieved by coadsorption of a surface modifier that also provides control over the partitioning of wormlike aggregates between the bulk solution and the pore space. We anticipate that the concept of tuning the interactions with the pore wall will be applicable to a wide variety of self-assembling molecules and pores.     

Optimization of ultrasound assisted-emulsification-dispersive liquid-liquid microextraction by experimental design methodologies for the determination of sulfur compounds in wines by gas chromatography-mass spectrometry

A new method was developed for analyzing sulfur compounds in the aroma of white wines using ultrasound assisted-emulsification-dispersive liquid-liquid microextraction coupled with gas chromatography-mass spectrometry detection. In the present work, the analytical method for simultaneous determination of seven sulfur compounds (methylmercaptoacetate, methyl(methylthio)acetate, 2-methylthioethanol, 3-methylthiopropanol, 3-methylthiohexanol, 4-methylthio-4-methyl-2-pentanone and hexanethiol) is reported. Parameters that affect the efficiency of the methodology such as extracting and dispersing solvents, sample volume, ion strength, cavitation time and centrifugation time were investigated using a fractionated factorial 2^6-1 (R = V) screening design. Then, the factors presenting significant positive effects on the analytical response (extracting volume, ion strength, cavitation time and centrifugation time) were considered in a further central composite design to optimize the operational conditions for the ultrasound assisted-emulsification-dispersive liquid-liquid microextraction procedure. Additionally, multiple response simultaneous optimization by using the desirability function was used to find the optimum experimental conditions. The best results were obtained using pH sample 4.25, extractant volume 150 μL, ionic strength 8.75% NaCl, cavitation time 20 s and centrifugation time 50 s. The use of the optimized ultrasound assisted-emulsification-dispersive liquid-liquid microextraction technique allowed to obtain the best extraction results with the minimum interference from other substances from the matrix, and it allowed to quantify the analytes in white wine samples by calibration graphs. Recoveries ranging from 91.99% to 125.87% for all sulfur compounds proved the accuracy of the proposed method in white wine samples. Method detection limits were in the range of 0.36-1.67 ng mL⁻¹ and limits of quantitation were between 0.63 and 3.02 ng mL⁻¹ for sulfur compounds in white wine samples. The proposed methodology was successfully applied for the determination concentrations of sulfur compounds in different commercial Chardonnay wine samples from Mendoza, Argentine.     

Target Visualization by MRI Using the Avidin/Biotin Amplification Route: Synthesis and Testing of a Biotin–Gd‐DOTA Monoamide Trimer

To design efficient targeting strategies in magnetic resonance (MR) molecular imaging applications, the formation of supramolecular adducts between (strept)avidin ((S)Av) and tribiotinylated Gd‐DOTA‐monoamide complexes (DOTA=1,4,7,10‐tetraazacyclododecane‐N,N′,N′′,N′′′‐tetraacetic acid) was explored. Two compounds based on the trivalent core of tris(2‐aminoethyl)amine each containing three biotin molecules and one ( L1 ) or three ( L2 ) DOTA‐monoamide (DOTAMA) ligands were synthesized. In these tribiotinylated derivatives the biotins are spaced far enough apart to allow the formation of the supramolecular adduct with the protein and to host the chelating units in between the (S)Av layers. Size exclusion HPLC analyses indicated complete formation of very high molecular weight polymers (>2 MDa) with (S)Av in solution. A ¹H NMR spectroscopy relaxometric study on the obtained polymeric adducts showed a marked increase of the relaxivity at 35–40 MHz as a consequence of the lengthening of the tumbling time due to the formation of Gd‐chelates/(S)Av polymers. The most efficient Gd₃ L2 /(S)Av polymeric system was used for a test in cell cultures. The target is represented by a neural cell adhesion molecule (NCAM), which is overexpressed in Kaposi’s sarcoma cells and tumor endothelial cells (TEC) and that is efficiently recognized by a biotinylated tetrameric peptide (C3d‐Bio). In vitro experiments showed that only cells incubated with both C3d‐Bio and Gd₃ L2 /SAv polymer were hyperintense with respect to the control. Relaxation rates of cell pellets incubated with Gd₃ L2 /SAv alone were not significantly different from the untreated cells demonstrating the absence of a specific binding.     

Exploring polymer solubility with thermally-responsive Diels-Alder monomers: Revisiting the monkey's fist

Thermo-responsive monomers were designed to contain a Diels-Alder (DA) adduct such that cyclo-reversion would yield either the maleimide or the furan unit attached to the polymer chain. These thermally responsive monomers were then copolymerized with N-isopropylacrylamide (NIPAM) via reversible addition-fragmentation chain-transfer (RAFT) polymerization to yield linear gradient-copolymer structures as a comparison to existing nanogel/starlike systems to understand how polymer topology and composition influence solution-state properties. Using UV–Vis spectroscopy, it was determined that solution-state properties were thermally dependent and influenced by a number of variables such as comonomer feed ratio, polymer chain end functionality, and polymer backbone length and composition. Manipulation of the feed ratio allowed for control over the cloud point, including the breadth and location of phase separation. Thermal treatment of these copolymers revealed tunable and predictable variations in previously observed transitions, directly correlated to cleavage of the DA adducts and change in polymer backbone composition. Finally, on cooling cycles, a double sigmoid was sometimes observed, indicating a complex globule to random coil transition correlated to polymer chain end composition. These studies help understand how to untie the “monkey's fist.”     

Revisiting Keteniminium Salts: More than the Nitrogen Analogs of Ketenes

Keteniminium salts are powerful electrophilic heterocumulene reagents well‐known for their selectivity and stereocontrol in [2+2] cycloadditions to olefins and carbonyl derivatives. Furthermore, they are readily accessible from stable and simple precursors under a variety of different conditions. Herein, we present the chemistry of keteniminium salts with the hindsight of time, describe preparation methods, recent [2+2] chemistry, mechanistic studies, and assorted applications that significantly extend the scope of utility of these unique electrophilic heterocumulenes.