Design of a smart drug delivery system is a topic of current interest. Under this perspective, polymer nanocomposites (PNs) of butyl acrylate (BA), methacrylic acid (MAA), and functionalized carbon ...nanotubes (CNTs
) were synthesized by in situ emulsion polymerization (IEP). Carbon nanotubes were synthesized by chemical vapor deposition (CVD) and purified with steam. Purified CNTs were analyzed by FE-SEM and HR-TEM. CNTs
contain acyl chloride groups attached to their surface. Purified and functionalized CNTs were studied by FT-IR and Raman spectroscopies. The synthesized nanocomposites were studied by XPS,
C-NMR, and DSC. Anhydride groups link CNTs
to MAA-BA polymeric chains. The potentiality of the prepared nanocomposites, and of their pure polymer matrices to deliver hydrocortisone, was evaluated in vitro by UV-VIS spectroscopy. The relationship between the chemical structure of the synthesized nanocomposites, or their pure polymeric matrices, and their ability to release hydrocortisone was studied by FT-IR spectroscopy. The hydrocortisone release profile of some of the studied nanocomposites is driven by a change in the inter-associated to self-associated hydrogen bonds balance. The CNTs
used to prepare the studied nanocomposites act as hydrocortisone reservoirs.
A simplified procedure to synthesize zwitterionic cellulose by means of N-protected aspartic anhydride under mild conditions was developed. The preparation of modified cellulose samples was carried ...out under heterogeneous, aqueous conditions by reacting NH
OH-activated cellulose with aspartic anhydrides N-protected with trifluoroacetyl (TFAc) and carbobenzyloxy (Cbz). Modified cellulose samples Cel-Asp-N-TFAc and Cel-Asp-N-Cbz were characterized by Fourier Transform Infrared (FTIR) and
C solid state Nuclear Magnetic Resonance (NMR) spectroscopy. The functionalization degree of each cellulose sample was determined by the
C NMR signal integration values corresponding to the cellulose C1 vs. the Cα of the aspartate residue and corroborated by elemental analysis. In agreement, both analytical methods averaged a grafting degree of 20% for Cel-Asp-N-TFAc and 16% for Cel-Asp-N-Cbz. Conveniently, Cel-Asp-N-TFAc was concomitantly partially N-deprotected (65%) as determined by the ninhydrin method. The zwitterion character of this sample was confirmed by a potentiometric titration curve and the availability of these amino acid residues on the cellulose was inspected by adsorption kinetics method with a 100 mg L
cotton blue dye solution. In addition, the synthesis reported in the present work involves environmentally related advantages over previous methodologies developed in our group concerning to zwitterionic cellulose preparation.
To design the properties of a copolymer using free radical polymerization, a semicontinuous process can be applied to vary the instantaneous copolymer composition along the conversion searching for a ...specific composition spectrum of copolymer chains, which can be termed as weight composition distribution (WCD) of copolymer chains. Here, the styrene-
-butyl acrylate (S/BA) system was polymerized by means of a semicontinuous emulsion process, varying the composition of the comonomer feed to obtain forced composition copolymers (FCCs). Five different feeding profiles were used, searching for a scheme to obtain chains rich in S (looking for considerable modulus), and chains rich in BA (looking for large deformation) as a technique to achieve synergy in copolymer properties; the mechanostatic and dynamic characterization discloses the correspondence between WCD and the bulk properties. ¹H-nuclear magnetic resonance (¹H-NMR) analysis enabled the determination of the cumulative copolymer composition characterization, required to estimate the WCD. The static test (stress-strain) and dynamic mechanical analysis (DMA) were performed following normed procedures. This is the first report that shows very diverse mechanostatic performances of copolymers obtained using the same chemical system and global comonomer composition, forming a comprehensive failure envelope, even though the tests were carried out at the same temperature and cross head speed. The principles for synergic performance can be applied to controlled radical copolymerization, designing the composition variation in individual molecules along the conversion.
A simple and direct method is described to prepare cationic bis(NHC)-Au(i) complexes containing N-alkyl or N-aryl NHC ligands to generate relevant gold complexes using metallic gold as the starting ...material.
LysCel is a cellulose-based material in which l-lysine molecules are grafted with their amino side chains to the cellulose hydroxyl groups. This modification increases considerably the mechanical ...strength and resistance of cellulosic structures toward water. It has been attributed to the formation of double salt bridges between lysine aminocarboxyl groups in the zwitterionic state. In order to characterize this unusual structure, we have performed high-resolution solid-state 15N and 13C CPMAS NMR experiments on LysCel samples labeled with 15N in the α-position or ε-position. Furthermore, 13C−15N REDOR experiments were performed on LysCel where half of the aminocarboxyl groups were labeled in 1-position with 13C and the other half in α-position with 15N. The comparison with the 13C and 15N chemical shifts of l-leucine lyophilized at different pH shows that the aminocarboxyl groups of LysCel are indeed zwitterionic. The REDOR experiments indicate distances of about 3.5 Å between the carboxyl carbon and the nitrogen atoms of different aminocarboxyl groups, indicating that the latter are in close contact with each other. However, the data are not compatible with isolated aminocarboxyl dimers but indicate the assembly of zwitterionic aminocarboxyl dimers either in a flat ribbon or as tetramers, exhibiting similar intra- and interdimer 13C···15N distances. This interaction of several aminocarboxyl groups is responsible for the zwitterionic state, in contrast to the gas phase, where amino acid dimers exhibiting two OHN hydrogen bonds are neutral.
The zwitterion functionalization of cellulose with lysine was achieved in a two-step synthesis. The cellulose modification in each step of the synthesis was corroborated by FTIR and solid state 13C ...NMR spectroscopy. The zwitterionic character in the modified cellulose was determined by its isoelectric point using a titration curve vs. pH. The dye adsorption performance of the modified cellulose was evaluated with malachite green and indigo carmine solutions. Cellulose modification increases laccase immobilization almost 10-fold compared to unmodified cellulose. Ionic and hydrophobic interactions are involved in immobilization, stabilizing laccase and the zwitterionic cellulose system. A novel theoretical approach of this immobilization is also proposed involving the interaction energies of the specific ionic moieties and supported by hydrophobic interactions shared between the enzyme and the zwitterionic cellulose interface. Moreover, immobilization did not affect the bioactivity of the enzyme, but on the contrary increased it by 29%. The laccase and zwitterionic cellulose system (Laccase-Lys-Cel) was tested against malachite green and indigo carmine in a 96-h experiment. The best removal results of about 93% from aqueous solution were observed for indigo carmine after 1 h and 99% after 72 h. Finally, Laccase-Lys-Cel combines two mechanisms: (1) dye adsorption in the early stages and (2) final dye degradation by the enzyme.
Display omitted
A family of water soluble gold(I) complexes with NHC carbene ligands derived from amino acids were prepared via the direct transmetalation reaction of the respective silver NHC complexes. The ...oxidative addition of Br2 to Au(I)-NHC complexes was studied and the crystal structure of AuBr3(NHC) compound derived from alanine is presented.
A series of Au(NHC)2 (1a–4a) complexes supported by NHC ligands derived from glycine, alanine, methionine and phenylalanine (1–4 respectively) were prepared via a direct transmetalation reaction of their respective silver complexes. The Au complexes were characterized by ESI-MS and NMR spectroscopy in solution. These compounds exhibit instability when the solvent is removed; they displayed a strong tendency to form colored solutions in the order 4a>3a>2a>1a, which is associated with gold nanoparticles. 1a and 2a undergo oxidative addition of elemental bromine, yielding Au(NHC)2Br2 (1b) for 1a and a mixture of Au(NHC)2Br2 (2b) and Au(NHC)Br3 (2c) for 2a. 2b and 2c were characterized by single crystal X-ray diffraction.
The synthesis and characterization of Cp∗Ir complexes containing ortho-functionalized 1,3-bis(aryl)triazenide ligands has been carried out. The molecular structures of all of the complexes confirm ...the bonding of the triazenide ligands as chelates. Display omitted
•Bis(aryl)triazene including hydroxymethyl groups was synthesized and characterized.•Iridium (III) bis(aryl)triazenide complexes were synthesized and characterized.•Molecular structures of the four iridium triazenide complexes were obtained.•Triazenide coordination as monoanionic bidentate ligands was confirmed.
Iridium (III) 1,3-bis(aryl)triazenide complexes Cp∗IrCl(ArNNNAr′) (Cp∗=C5Me5, Ar=Ar′=C6H5, 1; Ar=Ar′=o-CF3-C6H4, 2; Ar=Ar′=o-HOCH2-C6H4, 3; Ar=o-HOCH2-C6H4, Ar′=p-CH3-C6H4, 4) have been obtained by reaction of iridium dimer Cp∗IrCl22 with the corresponding triazenes in the presence of NEt3 in CH3CN. The iridium complexes 1–4 were characterized by IR, ESI-MS and NMR spectroscopy. In all of the complexes, the triazenes are coordinated to iridium (III) as monoanionic bidentate N,N′-donor ligands. Compounds 1–4 are the first examples studied by single crystal X-ray diffraction of mononuclear bis(aryl)triazenide iridium complexes, where the N-N-N fragment effectively chelates the Ir (III) central atom.
Using a semicontinuous seeded emulsion polymerization process with a gradual variation in feed composition, butyl acrylate (BA)/styrene copolymers were obtained (variable composition copolymers, ...VCCs). BA seed particles of two different diameters were used to prepare copolymer materials with 50-85 wt.% styrene. In each reaction, cumulative copolymer composition was followed by
1
H-NMR; with such data, a histogram showing the relative content of copolymer chains corresponding to each composition interval was built. The VCCs presented higher moduli and ultimate mechanostatical properties than their equivalent core-shell type polymers. The mechanical performance of VCC materials was explained considering the respective histograms.
PDF
