Synthesis and characterization of nanocomposites based on polylactide/silver nanoparticles, obtained by thermochemical reduction of Ag+ ions by natural or synthetic polymers

The addition of silver ions or nanoparticles to impart antimicrobial properties to polymeric or other materials is a widely used method. However, it should be noted that the antiviral and antimicrobial effect of silver nanoparticles that come into contact with the environment, associated with their size, with a decrease in the size of nanoparticles, their effectiveness increases sharply. In the present work, we used a biodegradable polymer polylactide (PLA), which is obtained by condensation of lactic acid or ring-opening polymerization of lactide. These studies will further contribute to the development of new safe materials, in particular for food packaging, which is undoubtedly an urgent problem. The work aims is to obtain the silver-containing polymer composites based on polylactide by thermochemical reduction of Ag+ ions using natural (chitosan) and synthetic (polyethyleneimine (PEI)) polymers and to study the structure, morphology, thermomechanical and antimicrobial properties of the obtained nanocomposites. Thermochemical reduction of Ag+ ions in the bulk of polymer films, containing PLA, silver palmitate as a precursor of Ag NP and reducing agent (PEI or chitosan), has been performed by keeping them at 100–170 °C within 5 minutes. The polymeric film composites, cast from chloroform solution, were heated in an oven using precise thermal regulator VRT-3. As a result of reduction, the films get attained silver color, the Ag content in the bulk of films varied from 1 to 4 wt. %, and the thickness of the films was 110 μm. Structure, morphology, thermomechanical and antimicrobial properties of two types of nanocomposites – PLA-Ag-PEI and PLA-Ag-chitosan, formed by the thermochemical reduction of Ag+ in polymer films have been studied using wide-angle X-ray scattering (WAXS) (a DRON-4-07 diffractometer), a transmission electron microscope (TEM) (JEM-1230 JEOL, Japan), and thermomechanical analysis (a UIP-70M device). Antimicrobial activity of the obtained nanocomposites was investigated applying reference strains of opportunistic bacteria Staphylococcus aureus and Escherichia coli. It has been found that thermochemical reduction of Ag+ ions in the bulk of polymer films, when using synthetic or natural polymers (PEI or chitosan) as a reducing and stabilizing agent of silver nanoparticles occurs at 160 °C during 5 minutes. It has been found that the average size of Ag nanoparticles in the polymeric matrix is equal to ~ 7 and ~ 4 nm for PEI and chitosan, respectively. It has been shown that PLA-Ag-chitosan nanocomposites have much higher antimicrobial activity against S. aureus and E. coli strains as compared to PLA-Ag-PEI nanocomposites.

INHIBITORY EFFICIENCY AND PHYSICOCHEMICAL PROPERTIES OF LIPIDS FROM LEAVES AND JUICE OF ALOE ARBORESCENS Mill.

The composition of lipids isolated from leaves and juice of A. arborescens (7 years ago) and the inhibitory efficiency of lipids from leaves of A. arborescens were studied. The phospholipid (PL) fractions were divided by means of TLC method. The quantitative proportion of PL fractions was determined by spectrophotometrically. The more substantial differences in the composition of PL from leaves and juice of A. arcorescens are revealed in the proportion of the more poorly oxidizable fractions of PL. The more low relative content of PL in the total lipid composition from leaves compared with than in lipids from juice, and shares of sterols are the same for lipids from leaves and juice cause 16% diminution of the molar ratio of [sterols]/[PL] in lipids from juice of A. arborescens. Lipids from leaves are known to characterize the high inhibitory efficiency that is demonstrated by model of the low temperature autoxidation of methyl oleate in the thin layer. Using UV-spectroscopy and the mathematic analysis of spectra by Gauss method the presence of the biologically active substances which contain in lipids was analysed. There are only flavonoids in the chloroform solution of lipids from juice and flavonoids and carotenoids in the small quantity in the chloroform solution of lipids from the leaves of A. arborescens.

Preparation of Porous Poly(Lactic Acid)/Tricalcium Phosphate Composite Scaffolds for Tissue Engineering

The development of bioactive and composite materials for tissue engineering applications is being investigated worldwide. Many approaches have been published by including combinations of resorbable polymers with hydroxyapatite (HA), tricalcium phosphate (TCP), bioactive glasses and glass-ceramics in different scaffolds architectures. Taking into account these antecedents, porous polylactic acid (PLA)/TCP composites were fabricated by employing dissolution-leaching technic from PLA/chloroform solution (10, 15, and 20 wt % of TCP). Composite scaffolds exhibited porosity values 1.3 times higher when compared to PLA foams. Their bioactive response of the composite foams after immersion in a simulated body fluid (SBF) was studied by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR-ATR). By XRD analysis, diffraction peaks attributed to hydroxyapatite deposition were observed; and by FTIR-ATR, new absorption bands corresponding to HA were detected. Regarding mechanical properties, an increasing tendency on elastic Young's modulus values was observed at higher TCP concentrations. These results envision the feasibility of using these composites as precursors for bone tissue materials engineering.

Transient Absorption of DNA bases in the gas phase and in chloroform solution: a comparative quantum mechanical study

We study the excited state absorption (ESA) properties of the four DNA bases (thymine, cytosine, adenine, and guanine) by different single reference quantum mechanical methods, i.e. equation of motion coupled cluster singles and doubles (EOM-CCSD), singles, doubles and perturbative triples (EOM-CC3), and time-dependent density functional theory (TD-DFT), with the long-range corrected CAM-B3LYP functional. Preliminary results at the Tamm-Dancoff (TDA) CAM-B3LYP level using the maximum overlap method (MOM) are reported for Thymine. In the gas phase, the three methods predict similar One Photon Absorption (OPA) spectra, which are also consistent with the experimental results and with the most accurate computational studies available in the literature. The ESA spectra are then computed for the pp states (one for pyrimidine, two for purines) associated with the lowest energy absorption band, and for the close-lying np state. The EOM-CC3, EOM-CCSD and CAM-B3LYP methods provide similar ESA spectral patterns, which are also in qualitative agreement with literature RASPT2 results. Once validated in the gas phase, TD-CAM-B3LYP has been used to compute the ESA in chloroform, including solvent effect by the polarizable continuum model (PCM). The predicted OPA and ESA spectra in chloroform are very similar to those in the gas phase, most of the bands shifting by less than 0.1 eV, with a small increase of the intensities and a moderate destabilization of the np state. Finally, ESA spectra have been computed from the minima of the lowest energy pp state, and are consistent with the available experimental transient absorption spectra of the nucleosides in solution, providing a final validation of our computational approach.

Dielectric Relaxation and Thermodynamic Study of Caffeine-Chloroform Solution using TDR

The Complex permittivity of caffeine – Chloroform solution for different temperature and various concentrations have been measured in the range of 10MHZ to 30 GHz using Time Domain Reflectometry. From complex permittivity spectra, Static dielectric constant (εo) and relaxation time (τ) were determined using nonlinear least square fit method. Using Erying rate equation, for different molar concentration of caffeine Enthalpy of Activation ∆H and Entropy of Activation ∆S were determined.

Electrospun Hybrid Microfibers of Polylactic Acid with Plasma Polypyrrole Particles with Ultrahydrophobic Surface for Biomedical Applications

This work presents a study on the formation of hybrid electrospun fibers of polylactic acid (PLA) with insoluble polypyrrole (PPy) particles inside with the objective to prepare ultrahydrophobic fibers for biomedical applications. Krebs-Ringer and phosphate-buffered saline solutions were used as test solutions of human fluids. The PPy particles were synthesized by plasma with diameter in the 60-1000 nm range and were suspended in a PLA-chloroform solution with a PPy/PLA = 0.027 mass ratio. PLA fibers with PPy particles inside were formed electrospinning this suspension obtaining diameters in the 0.12-9.0 µm range with average between 1.65 and 1.85 µm. Contact angles of the fibers with the test solutions were measured in the 113°-147° interval, most of them in the ultrahydrophobic (120°-150°) region. The lowest angles were obtained with particles synthesized at the lowest power (20 W) and were like those obtained on PLA fibers. The highest angles were measured on the fibers with the particles synthesized at the highest synthesis power (100 W), with difference up to 15°. This difference in the angles was correlated with the resonant ≈ C ≈ groups of the particles through the fiber ultraviolet absorption.

Hybrid Microporous Polymeric Materials with Outstanding Permeability and Increased Gas Transport Stability: PTMSP Aging Prevention by Sorption of the Polymerization Catalyst on HCPS

The influence of hyper-crosslinked polystyrene (HCPS) MacronetTM MN200 on the gas transport properties and aging of the highly permeable glassy polymer poly(1-trimethylsilyl-1-propyne) (PTMSP) was studied and analyzed in detail. The gas transport characteristics of dense PTMSP membranes containing 0–10.0 wt % HCPS were studied. It was shown that the introduction of a small amount of HCPS into the PTMSP matrix led to a 50–60% increase of the permeability coefficients of the material for light gases (N2, O2, CO2) and slowed down the deterioration of polymer transport properties over time. The lowest reduction in gas permeability coefficients (50–57%) was found for PTMSP containing HCPS 5.0 wt % after annealing at 100 °C for 300 h. It was found that HCPS sorbed residues of tantalum-based polymerization catalyst from PTMSP. In order to investigate the influence of catalysts on transport and physical properties of PTMSP, we purified the latter from the polymerization catalyst by addition of 5 wt % HCPS into polymer/chloroform solution. It was shown that sorption on HCPS allowed for almost complete removal of tantalum compounds from PTMSP. The membrane made of PTMSP purified by HCPS demonstrated more stable transport characteristics compared to the membrane made of the initial polymer. HCPS has a complex effect on the aging process of PTMSP. The introduction of HCPS into the polymer matrix not only slowed down the physical aging of PTMSP, but also reduced chemical aging due to removal of active reagents.

The Effect of Blood Contained in the Samples on the Metabolomic Profile of Mouse Brain Tissue: A Study by NMR Spectroscopy

(1) Recently, metabolic profiling of the tissue in the native state or extracts of its metabolites has become increasingly important in the field of metabolomics. An important factor, in this case, is the presence of blood in a tissue sample, which can potentially lead to a change in the concentration of tissue metabolites and, as a result, distortion of experimental data and their interpretation. (2) In this paper, the metabolomic profiling based on NMR spectroscopy was performed to determine the effect of blood contained in the studied samples of brain tissue on their metabolomic profile. We used 13 male laboratory CD-1® IGS mice for this study. The animals were divided into two groups. The first group of animals (n = 7) was subjected to the perfusion procedure, and the second group of animals (n = 6) was not perfused. The brain tissues of the animals were homogenized, and the metabolite fraction was extracted with a water/methanol/chloroform solution. Samples were studied by high-frequency 1H-NMR spectroscopy with subsequent statistical data analysis. The group comparison was performed with the use of the Student’s test. We identified 36 metabolites in the brain tissue with the use of NMR spectroscopy. (3) For the major set of studied metabolites, no significant differences were found in the brain tissue metabolite concentrations in the native state and after the blood removal procedure. (4) Thus, it was shown that the presence of blood does not have a significant effect on the metabolomic profile of the brain in animals without pathologies.

Reductive coupling synthesis of a soluble poly(9,10-anthrylene ethynylene)

A fully soluble poly(9,10-anthrylene ethynylene), poly[2,6-(2-octyldecyl)-9,10-anthrylene ethynylene] PAAE, with moderate degrees of polymerization Pn of ca. 10 is generated in a reductive, dehalogenative homocoupling scheme, starting from a 2,6-dialkylated 9,10-bis(dibromomethylene)-9,10-dihydroanthracene monomer and n-BuLi/CuCN as reducing agent. PAAE shows surprisingly broad and unstructured absorption and photoluminescence emission bands peaking at 506 nm and 611 nm, respectively, both in chloroform solution. The long absorption tail ranging into the 600-700 nm region and the large Stokes shift point to a high degree of geometrical disorder in the arrangement of the 9,10-anthrylene chromophores along the distorted polymer backbone. This disorder is borne out in the unusually strong wavelength dependence of fluorescence depolarisation, both with regards to the excitation and the emission wavelengths. Picosecond fluorescence depolarisation spectroscopy provides clear evidence for the presence of orthogonal transition dipole moments, presumably arising from the off-axis transition of the anthracene unit and the on-axis transition of the polymer backbone.