Semi‐interpenetrating polymer networks of methyl cellulose and polyacrylamide prepared by frontal polymerization

In this study, the feasibility of frontal polymerization (FP) as an alternative and convenient technique for the preparation of semi‐interpenetrating polymer networks made of methyl cellulose (MC) and cross‐linked polyacrylamide (PAAm) is demonstrated. FP was performed in water and glycerol, as largely available, nontoxic solvents. Although FP occurred in both media, differences were found by comparing the samples made in the two solvents. In particular, those prepared in water are characterized by larger inhomogeneity and less reproducibility, thus accounting for the boiling effects that influence propagating polymerization fronts when water was used. The effects of the ratio among MC and PAAm, the amount of cross‐linker and solvent medium were studied in terms of influence on temperature and velocity of FP fronts, glass transition temperature (dried samples), swelling behavior, dynamic‐mechanical properties (gels swollen in both water or glycerol), and tensile behavior. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1268–1274     

Thermoresponsive super water absorbent hydrogels prepared by frontal polymerization of N‐isopropyl acrylamide and 3‐sulfopropyl acrylate potassium salt

Super water absorbent polymer hydrogels were synthesized by frontal polymerization. These materials were obtained by copolymerizing N‐isopropyl acrylamide (NIPAAm) and 3‐sulfopropyl acrylate potassium salt (SPAK) in the presence of N,N′‐methylene‐bis‐acrylamide as a crosslinker. It was found that their swelling behavior in water can be easily tuned by using either the appropriate monomer ratio or the amount of the crosslinker used. Namely, the swelling ratio was found to range from about 1000% for the NIPAAm homopolymer in the presence of 5.0 mol % of crosslinker, up to 35,000% for the sample containing 87.5 mol % of SPAK and 1.0 mol % of crosslinker. The affinity toward water was also confirmed by contact angle analysis. Moreover, the obtained hydrogels exhibit a thermoresponsive behavior, with a lower critical solution temperature of about 28–30 °C. This value is close to that of poly(NIPAAm) but with a swelling capability that dramatically increases as the amount of SPAK increases. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Allosteric regulation of protein kinase PKCζ by the N-terminal C1 domain and small compounds to the PIF-pocket

Protein kinases are key mediators of cellular signaling, and therefore, their activities are tightly controlled. AGC kinases are regulated by phosphorylation and by N- and C-terminal regions. Here, we studied the molecular mechanism of inhibition of atypical PKCζ and found that the inhibition by the N-terminal region cannot be explained by a simple pseudosubstrate inhibitory mechanism. Notably, we found that the C1 domain allosterically inhibits PKCζ activity and verified an allosteric communication between the PIF-pocket of atypical PKCs and the binding site of the C1 domain. Finally, we developed low-molecular-weight compounds that bind to the PIF-pocket and allosterically inhibit PKCζ activity. This work establishes a central role for the PIF-pocket on the regulation of PKCζ and allows us to envisage development of drugs targeting the PIF-pocket that can either activate or inhibit AGC kinases.     

Frontal polymerization of diurethane diacrylates

This work deals with the preparation of poly(urethane acrylates) by using two different polymerization techniques. Namely, the classical batch procedure has been compared with frontal polymerization (FP). A thorough study on the effect of initiator type, concentration, and on the velocity of the front and its maximum temperature has been carried out. Moreover, two different synthetic ways have been studied: the one step poly(urethane acrylate) preparation starting directly from 1,6 diisocyanato hexane and 2‐hydroxyethyl acrylate, and the two step procedure consisting of the synthesis of the corresponding diurethane diacrylate and of its subsequent polymerization. The first method has the advantage of being faster but some caution is necessary due to the excessive heat that is generated if the reaction conditions are not properly chosen. The second approach requires a further step but has the advantage of being more controlled. DSC analysis did not show any significant difference by comparing the thermal properties of the materials obtained by the two techniques (batch and FP). However, since FP runs are very easy and fast to be performed, FP should be seriously taken into proper account when these materials have to be prepared. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3344–3352, 2008     

Hybrid organic/inorganic epoxy resins prepared by frontal polymerization

The syntheses of hybrid epoxy resins made from different ratios among bisphenol‐A diglycidyl ether, 3‐glycidoxypropyltrimethoxysilane (GPTMS), and diethylenetriamine were successfully performed by using frontal polymerization. Conversions were always almost quantitative, and, because of the use of this alternative convenient technique, materials were prepared in very short times. Samples were characterized by DSC, TGA, IR spectroscopy, and solvent extraction. It was found that those materials containing a relatively high‐Si amount exhibit two different transition temperatures, with the highest one that increases as the content of GPTMS raises. The analogies and the differences with the analogous samples prepared by the classical batch technique are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Multistimuli-responsive hydrogels of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) containing graphene

Nanocomposite hydrogels of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) containing graphene were prepared by radical polymerization. Their swelling properties in response to ionic strength and electrical stimuli were assessed. Graphene was obtained through an easy and convenient method lately developed by our research group, which consists in the exfoliation of graphite by sonicating it in a proper solvent medium. It was found that the graphene content influences the swelling properties of hydrogels; in particular, those containing graphene swell more than the filler-free ones; graphene content influences also the swelling ratio variation between the swollen and deswollen states.     

Trypanosoma cruzi trans-sialidase operates through a covalent sialyl-enzyme intermediate: tyrosine is the catalytic nucleophile

Modified sialic acid substrates have been used to label Trypanosoma cruzi trans-sialidase, demonstrating that the enzyme catalyses the transfer of sialic acid through a covalent glycosyl-enzyme intermediate, a mechanism common to most retaining glycosidases. Peptic digestion of labeled protein, followed by LC-MS/MS analysis of the digest, identified Tyr342 as the catalytic nucleophile. This is the first such example of a retaining glycosidase utilizing an aryl glycoside intermediate. It is suggested that this alternative choice of nucleophile is a consequence of the chemical nature of sialic acid. A Tyr/Glu couple is invoked to relay charge from a remote glutamic acid, thereby avoiding electrostatic repulsion with the sialic acid carboxylate group.     

Double responsive copolymer hydrogels prepared by frontal polymerization

Frontal polymerization was successfully used to synthesize copolymer hydrogels of poly(N‐vinylcaprolactam‐co‐itaconic acid). All materials were characterized by response to stimuli (pH and/or temperature), depending on the itaconic acid content. Namely, relatively low amounts of this latter were found to be crucial for determining the degree of swelling. In particular, hydrogels behave differently if swollen at pH values that are higher or lower of 7–8, and exhibit temperature response as well (lower critical solution temperature at ca. 30 °C), which makes these materials potentially interesting for biomedical applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2166–2170     

Organic–inorganic interpenetrating polymer networks and hybrid polymer materials prepared by frontal polymerization

Novel polyacrylamide‐based hydrogels containing 3‐(trimethoxysilyl)propyl methacrylate and/or tetraethoxy silane were synthesized by means of frontal polymerization, using ammonium persulfate as initiator, N,N′‐methylene bisacrylamide as crosslinking agent and dimethyl sulfoxide as solvent. The obtained samples were treated at pH of 2 or 5 to induce the sol–gel reaction and evaluate their swelling behavior in the conditions. The occurrence of this reaction was assessed by solid‐state NMR. Moreover, the thermal properties of the dry materials were studied by differential scanning calorimetry and thermal gravimetric analysis, and their water‐contact angles were measured. It was found that the amount of Si affects the extent of swelling and the hydrophilicity of the resulting materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4618–4625