Enhancement of cellulose acetate degradation under accelerated weathering by plasticization with eco-friendly plasticizers

Cellulose acetate (CA) with a degree of substitution (DS) of 2.5 has been plasticized using eco-friendly plasticizers such as triacetin, tripropionin, triethyl citrate, tributyl citrate, tributyl 2-acetyl citrate and poly(ethylene glycol) of low molecular weight. Thermo-mechanical properties and hydrophilicity of the modified CA have been measured and correlated with the content and nature of the plasticizer used and compared with unplasticized CA. The increase in toughening and the change in the hydrophilicity by the plasticization were evaluated in terms of aging and weathering stability under accelerated conditions. Samples were exposed to UV-degradation with water spray periods. The treated samples were removed periodically and characterized by several analytical techniques. The results are discussed with particular emphasis toward the effects of plasticization on enhancement of the degradation rate of CA. The plasticization of CA triggered an increase of the weight loss between 50 and 90%, where low molecular weight plasticizers were shown to be more effective. A right balance between hydrophilicity and plasticization efficiency (reduction of T_g) is needed to increase the degradation rate of CA.     

Synthesis and Characterization of the Crystal Structure and Magnetic Properties of the New Fluorophosphate LiNaCo[PO(4)]F

The new compound LiNaCo[PO(4)]F was synthesized by a solid state reaction route, and its crystal structure was determined by single-crystal X-ray diffraction measurements. The magnetic properties of LiNaCo[PO(4)]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO(4)]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) ?, and Z = 8. The structure consists of edge-sharing CoO(4)F(2) octahedra forming CoFO(3) chains running along the b axis. These chains are interlinked by PO(4) tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The magnetic susceptibility follows the Curie-Weiss behavior above 60 K with θ = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO(4)]F undergoes a three-dimensional magnetic ordering at T(mag) = 10.2(5) K. The neutron powder diffraction measurements at 3 K show that the spins in each CoFO(3) chain along the b-direction are ferromagnetically coupled, while these FM chains are antiferromagnetically coupled along the a-direction but have a noncollinear arrangement along the c-direction. The noncollinear spin arrangement implies the presence of spin conflict along the c-direction. The observed magnetic structures are well explained by the spin exchange constants determined from density functional calculations.     

Computational studies of 1:2 complex between retinol propionate and β cyclodextrin

[M05-2X/6-31G*:PM3MM] and [B3LYP/6-31G*:PM3] ONIOM2 methods have been used to investigate the vitamin A propionate/β cyclodextrin complex with 1:2 stoichiometry. Both methods give almost the same lowest energy minimum. The minimum energy structure of the complex is found in good agreement with experimental data. In this configuration, the major structure of propionate of vitamin A (PVA) is embedded inside the two cavities of βCD while the propionate group is kept outside. However, the three methyl groups of PVA are positioned in the free space between both βCD molecules. The driving forces for complexation are dominated by Van der Waals interactions between PVA and the βCD molecules assisted with multiple hydrogen bond interactions between the two cyclodextrin molecules. These interactions were investigated using the natural bond orbital approach.     

DFT and quantum chemical investigation of molecular properties of substituted pyrrolidinones

The DFT, quantum-chemical calculations and thermodynamics parameters of 1-{2-[(2-hydroxyethyl)thio]ethyl}pyrrolidin-2-one (HTEP); [2-(2-oxo-pyrrolidin-1-yl)-ethyl]-phosphonic acid diethyl ester (EOEP); {[2-(2-oxopyrrolidin-1-yl)ethyl]thio}acetic acid (OETA); (2-pyridin-4-yl-ethyl]thio}acetic acid (PTA) and pyridine (PY) have been calculated with Gaussian 94 and Hybrid B3LYP functional density with 6-31G* basis set. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied orbital (LUMO) energy and molecular densities have been investigated.     

Conduction mechanism and the dielectric relaxation process of a-Se75Te25−xGax (x=0, 5, 10 and 15 at wt%) chalcogenide glasses

Se₇₅Te_25−xGa_x (x=0, 5, 10 and 15 at wt%) chalcogenide compositions were prepared by the well known melt quenching technique. Thin films with different thicknesses in the range (185–630 nm) of the obtained compositions were deposited by thermal evaporation technique. X-ray diffraction patterns indicate that the amorphous nature of the obtained films. The ac conductivity and the dielectric properties of the studied films have been investigated in the frequency range (10²–10⁵ Hz) and in the temperature range (293–333 K). The ac conductivity was found to obey the power low ω^s where s≤1 independent of film thickness. The temperature dependence of both ac conductivity and the exponent s can be well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant ε₁ and dielectric loss ε₂ are frequency and temperature dependent. The maximum barrier height W_m calculated from the results of the dielectric loss according to the Guintini equation, and agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The density of localized state was estimated for the studied film compositions. The variation of the studied properties with Ga content was also investigated. The correlation between the ac conduction and the dielectric properties were verified.     

Application of Millimeter Wave in Verification of Scale Model Measurement for Radar Cross Section

According to the physical optic approximation, a physical scale factor is suggested for scale model measurement of radar cross section (RCS). By this factor, the models of radar targets can be tested at the same frequency as prototype. This is significant for the lack of experimental equipment required or the problem of frequency dependency of radar absorbing materials on the objects. For the purpose of further verification and comparison, millimeter-wave is used to measure the model at the wavelength scaling down proportionally to the prototype. And the measurements of the models are also carried out at microwave band (same working wavelength with prototype). The computed results from models agree well with the data by prototype itself.     

Streptomyces griseus KJ623766: A Natural Producer of Two Anthracycline Cytotoxic Metabolites β- and γ-Rhodomycinone

Background: This study aimed to produce, purify, structurally elucidate, and explore the biological activities of metabolites produced by Streptomyces (S.) griseus isolate {"type":"entrez-nucleotide","attrs":{"text":"KJ623766","term_id":"655350460"}}KJ623766, a recovered soil bacterium previously screened in our lab that showed promising cytotoxic activities against various cancer cell lines. Methods: Production of cytotoxic metabolites from S. griseus isolate {"type":"entrez-nucleotide","attrs":{"text":"KJ623766","term_id":"655350460"}}KJ623766 was carried out in a 14L laboratory fermenter under specified optimum conditions. Using a 3-(4,5-dimethylthazol-2-yl)-2,5-diphenyl tetrazolium-bromide assay, the cytotoxic activity of the ethyl acetate extract against Caco2 and Hela cancer cell lines was determined. Bioassay-guided fractionation of the ethyl acetate extract using different chromatographic techniques was used for cytotoxic metabolite purification. Chemical structures of the purified metabolites were identified using mass, 1D, and 2D NMR spectroscopic analysis. Results: Bioassay-guided fractionation of the ethyl acetate extract led to the purification of two cytotoxic metabolites, R1 and R2, of reproducible amounts of 5 and 1.5 mg/L, respectively. The structures of R1 and R2 metabolites were identified as β- and γ-rhodomycinone with CD₅₀ of 6.3, 9.45, 64.8 and 9.11, 9.35, 67.3 µg/mL against Caco2, Hela and Vero cell lines, respectively. Values were comparable to those of the positive control doxorubicin. Conclusions: This is the first report about the production of β- and γ-rhodomycinone, two important scaffolds for synthesis of anticancer drugs, from S. griseus.     

Low thrombogenicity coating of nonwoven PET fiber structures for vascular grafts

Vascular PET grafts (Dacron) have shown good performance in large vessels (≥6 mm) applications. To address the urgent unmet need for small‐diameter (2–6 mm) vascular grafts, proprietary high‐compliance nonwoven PET fiber structures were modified with various PEG concentrations using PVA as a cross‐linking agent, to fabricate non‐thrombogenic mechanically compliant vascular grafts. The blood compatibility assays measured through platelet adhesion (SEM and mepacrine dye) and platelet activation (morphological changes, P‐selectin secretion, and TXB2 production) demonstrate that functionalization using a 10% PEG solution was sufficient to significantly reduce platelet adhesion/activation close to optimal literature‐reported levels observed on carbon‐coated ePTFE.

     

Optical constants for Ge30− x Se70Ag x (0 ≤ x ≤ 30 at%) thin films based only on their reflectance spectra

In this paper, different homogenous compositions of Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30 at%) thin films were prepared by thermal evaporation. Reflection spectra, R(λ), for the films were measured in the wavelength range 400–2500?nm. A straightforward analysis proposed by Minkov [J. Phys. D: Appl. Phys. 22 (1989) p.1157], based on the maxima and minima of the reflection spectra, allows us to derive the real and imaginary parts of the complex index of refraction and the film thickness of the studied films. Increasing Ag content at the expense of Ge atoms is found to affect the refractive index and the extinction coefficient of the films. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing Ag content, the refractive index increases while the optical band gap decreases. The compositional dependence of the optical band gap for the Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30) thin films is discussed in terms of the chemical bond approach.