Thermal analysis characterization of PAAm-<Emphasis Type="Italic">co</Emphasis>-MC hydrogels

This paper reports the thermal characterization of polyacrylamide-co-methylcellulose hydrogels and the constituent monomers (acrylamide and methylcellulose). Polymeric materials can be used to produce hydrogels, which can be natural, synthetic, or a mixture. The hydrogels described here were obtained by free radical polymerization, in the presence of N,N′-methylene-bis-acrylamide as a cross-linker agent. Four acrylamide concentrations were used for the synthesis of hydrogels: 3.6, 7.2, 14.7, and 21.7% (w/v). The materials so obtained were analyzed by TG, DTG, DSC, and FT-IR. The TG curves of acrylamide and methylcellulose showed three mass loss events. In DSC curves, the acrylamide exhibited one melting peak at 84.5 °C, and methylcellulose indicated one exothermic event. Nevertheless, acrylamide was considered more stable than methylcellulose. The TG curves of the hydrogels exhibited three mass loss events, and on the DSC curves, three endothermic events were observed. It was verified that the different acrylamide proportions influenced the thermic behavior of hydrogels, and that the authors considered the 7.2% hydrogel a promising drug carrier system. The absorption bands were well defined, confirming the presence of the functional groups in the samples.     

Graphene Oxide Nanosheets Modified with Single‐Domain Antibodies for Rapid and Efficient Capture of Cells

Peripheral blood can provide valuable information on an individual’s immune status. Cell‐based assays typically target leukocytes and their products. Characterization of leukocytes from whole blood requires their separation from the far more numerous red blood cells. 1 Current methods to classify leukocytes, such as recovery on antibody‐coated beads or fluorescence‐activated cell sorting require long sample preparation times and relatively large sample volumes. 2 A simple method that enables the characterization of cells from a small peripheral whole blood sample could overcome limitations of current analytical techniques. We describe the development of a simple graphene oxide surface coated with single‐domain antibody fragments. This format allows quick and efficient capture of distinct WBC subpopulations from small samples (～30 μL) of whole blood in a geometry that does not require any specialized equipment such as cell sorters or microfluidic devices.     

Electron ionisation and fast-atom bombardment mass spectrometry study of diaryl carbonates

Electron ionisation mass spectrometry studies were performed previously for p-diphenyl carbonate and some monosubstituted diphenyl carbonates. In this work, p-diphenyl carbonate and p-methoxyphenylphenyl carbonate are re-examined, and p-chlorophenyl phenyl carbonate and two disubstituted diphenyl carbonates, bis (p-chlorophenyl) carbonate and p-methoxyphenyl-p-fluorophenyl carbonate, are studied for the first time. The previously established fragmentation routes were observed for all compounds investigated. Some other different sequences were observed, and a fragmentation path, other than decarboxylation, of the molecular ion is proposed. In the fast-atom bombardment study it was observed that the M(+*)/[MH](+) ion abundance ratio increased from 0.44 for compound 1 to 2.95 for compound 5. [MH](+) is not a dominant ion in most of compounds studied, in spite of the presence of a carbonyl group, a strong proton acceptor. The presence of two oxygen atoms bonded to the carbonyl group appears to induce delocalisation of the electron pairs, thus deactivating the carbonyl site for protonation. In addition, m-nitrobenzyl alcohol (NBA) being a relatively aprotic/hydrophobic matrix reinforces the deactivation for protonation. Because the carbonate group and NBA are common features to the study, the contributions of the substituents were taken into account to explain the different behaviour of the five compounds with respect to protonation.     

Ionization by pH and Anionic Surfactant Binding Gives the Same Thickening Effects of Crosslinked Polyacrylic Acid Derivatives

Physical properties of aqueous solutions of hydrophobically modified crosslinked polyacrylic acids change quite extensively as the polymer is charged up. A study is carried out concerning the similarities between two polymer ionization processes, that is, by pH increment and anionic surfactant addition. The two processes charge the polymer by distinctly different mechanisms. At sufficiently high pH the carboxylic groups of the polymer are virtually all ionized and the polymer is, therefore, fully charged. The effective repulsion among the charged groups due to the entropy of the counterions promotes an increased stiffness as well as an expansion of the polymer particles. We investigate here how the ionization and swelling will be if, instead of high pH, the polymer is at low pH conditions but associated to ionic surfactants. Surfactants associate to the polymer both in a noncooperative way by the binding of individual surfactant molecules and in a cooperative way as micelles since the polymer promotes surfactant self-assembly. This binding leads to a highly charged polymer-surfactant complex and leads to an osmotic swelling as well. The swelling and the gelation were monitored by rheology and dynamic light scattering, of polymer solutions by varying the pHs and adding ionic surfactants at low pH. The results show that ionization by surfactants and by pH lead to approximately the same gelation degree, as can be seen by similar viscosity values. Both processes result in dramatic viscosity increases, up to 8 orders of magnitude. More hydrophobic surfactants, with longer alkyl chain, are shown to be more efficient as enhancers of swelling and gelation. The network that is formed at high pH or at sufficiently high concentration of surfactant can be weakened or even disrupted if monovalent or divalent salts are added, demonstrating the role of counterion entropy.     

Quaternary Stereogenic Centers through Enantioselective Heck Arylation of Acyclic Olefins with Aryldiazonium Salts: Application in a Concise Synthesis of (R)‐Verapamil

We describe herein a highly regio‐ and enantioselective Pd‐catalyzed Heck arylation of unactivated trisubstituted acyclic olefins to provide all‐carbon quaternary stereogenic centers. Chiral N,N ligands of the pyrimidine‐ and pyrazino‐oxazoline class were developed for that purpose, providing the desired products in good to high yields with enantiomeric ratios up to >99:1. Both linear and branched substituents on the olefins were well‐tolerated. The potential of this new method is demonstrated by the straightforward synthesis of several O‐methyl lactols and lactones containing quaternary stereocenters, together with a concise enantioselective total synthesis of the calcium channel blocker verapamil.     

Spironolactone and its Complexes with β-cyclodextrin: Modern NMR Characterization and Structural DFTB-SCC Calculations

In the present work, inclusion complexes of spironolactone (SP) with β-cyclodextrin (β-CD) in solid phase and aqueous solution were studied by solubility methods, NMR spectroscopy and thermal analysis. The results showed different kinds of complexations when freeze-drying and kneading methods were used. The freeze-drying product (1:1, SP:β-CD) showed lower degree of complexation and stability than the (1:2, SP:β-CD) compound obtained by kneading method. The spironolactone molecule was also studied by NMR spectroscopy at 400 MHz. The chemical shifts of all spironolactone atoms and their inclusion compounds were assigned. Extensive use of 1D and 2D NMR techniques, including ROESY experiment, allowed verifying the position of the spironolactone molecule inside the cyclodextrin cavity in both situations. In addition, DFTB-SCC quantum mechanical calculations of the inclusion compounds were performed. The predicted structural properties are in good agreement with ROESY NMR results.     

Loading of Exponentially Grown LBL Films with Silver Nanoparticles and Their Application to Generalized SERS Detection

Feature film : Thin films made by exponential layer‐by‐layer growth display high diffusivity and can be readily infiltrated with inorganic nanoparticles. They can sequestrate molecular systems from solution as a function of the composition of their layers, while providing intense surface‐enhanced Raman scattering (SERS) signals (see picture).

     

Identification of the optically active vibrational modes in the photoluminescence of MEH-PPV films

The temperature dependence of the photoluminescence properties of a thin film of poly[2-methoxy-5-(2(')-ethylhexyloxy)-p-phenylene-vinylene], MEH-PPV, fabricated by spin coating, is analyzed. The evolution with temperature of the peak energy of the purely electronic transition, of the first vibronic band, of the effective conjugation length, and of the Huang-Rhys factors are discussed. The asymmetric character of the pure electronic transition peak and the contribution of the individual vibrational modes to the first vibronic band line shape are considered by a model developed by Cury et al. [J. Chem. Phys. 121, 3836 (2004)]. The temperature dependence of the Huang-Rhys factors of the main vibrational modes pertaining to the first vibronic band allows us to identify two competing vibrational modes. These results show that the electron coupling to different vibrational modes depends on temperature via reduction of thermal disorder.     

Purification of plasmid DNA vectors by aqueous two-phase extraction and hydrophobic interaction chromatography

The current study explores the possibility of using a polyethyleneglycol(PEG)-ammonium sulphate aqueous two-phase system (ATPS) as an early step in a process for the purification of a model 6.1 kbp plasmid DNA (pDNA) vector. Neutralised alkaline lysates were fed directly to ATPS. Conditions were selected to direct pDNA towards the salt-rich bottom phase, so that this stream could be subsequently processed by hydrophobic interaction chromatography (HIC). Screening of the best conditions for ATPS extraction was performed using three PEG molecular weights (300, 400 and 600) and varying the tie-line length, phase volume ratio and lysate load. For a 20% (w/w) lysate load, the best results were obtained with PEG 600 using the shortest tie-line (38.16%, w/w). By further manipulating the system composition along this tie-line in order to obtain a top/bottom phase volume ratio of 9.3 (35%, w/w PEG 600, 6%, w/w NH4)2 SO4), it was possible to recover 100% of pDNA in the bottom phase with a three-fold increase in concentration. Further increase in the lysate load up to 40% (w/w) with this system resulted in a eight-fold increase in pDNA concentration, but with a yield loss of 15%. The ATPS extraction was integrated with HIC and the overall process compared with a previously defined process that uses sequential precipitations with iso-propanol and ammonium sulphate prior to HIC. Although the final yield is lower in the ATPS-based process the purity grade of the final pDNA product is higher. This shows that it is possible to substitute the time-consuming two-step precipitation procedure by a simple ATPS extraction.     

Directed lattices: site-to-bond conversion and its uses for the percolation and dilute polymer transitions

A method for conversion of directed site animals to their bond counterparts is used to significantly extend the number of such configurations in 2, 3, 4 dimensions, obtain their loop partition and study the singularity structure (for both dominant and subdominant singularities) of the corresponding dilute polymer transitions. A special property of bond directed configurations (equivalence lence of loop and bond perimeter partition) is exploited to obtain longer susceptibility series in 3 and 4 dimensions and the gap exponent estimate is refined into the intervals TANOPartly funded by SBF 341 (Aachen-Julich-Koln) and Reitoria Uni. Porto (Project 1-87)