Thermal analysis on phase behavior of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) interacting with aliphatic polyesters

Abstract  

Thermal behavior, miscibility, and crystalline morphology in blends of low-molecular-weight poly(l-lactic acid) (LM_w-PLLA) or high-molecular-weight PLLA (HM_w-PLLA) with various polyesters such as poly(butylene adipate) (PBA), poly(ethylene adipate) (PEA), poly(trimethylene adipate) (PTA), or poly(ethylene succinate) (PESu), respectively, were explored using differential scanning calorimeter (DSC), and polarized-light optical microscopy (POM). Phase behavior in blends of PLLA with other polyesters has been intriguing and not straight forward. Using a low- and high molecular weight PLLA, this study aimed at mainly using thermal analyses for probing the phase behavior, phase diagrams, and temperature dependence of blends systems composed of PLLA of two different molecular weights (low and high) with a series of aliphatic polyesters of different structures varying in the (CH₂/CO) ratio in main chains. The blends of LM_w-PLLA/PEA and LM_w-PLLA/PTA show miscibility in melt and amorphous glassy states. Meanwhile, the LM_w-PLLA/PESu blend is immiscible with an asymmetry-shaped upper critical solution temperature (UCST) at 220–240 °C depending on the blend composition. In contrast to miscibility in LM_w-PLLA/PTA and LM_w-PLLA/PEA blends, HM_w-PLLA with polyesters are mostly immiscible; and HM_w-PLLA/PTA blend is the only one showing an asymmetry-shaped UCST phase diagram with clarity points at 195–235 °C (depending on composition). Reversibility of UCST behavior, with no chemical transreactions, in these blends was proven by solvent recasting, gel permeation chromatography, and Fourier transform infrared spectroscopy (FT-IR). Crystalline morphology behavior of the LM_w-PLLA/PEA and LM_w-PLLA/PTA blends furnishes addition evidence for miscibility in the amorphous phase between LM_w-PLLA and PTA or PEA.     

Synthesis and Characterization of Cationic Glycidyl-Based Poly(aminoester)-Folic Acid Targeting Conjugates and Study on Gene Delivery

A new poly(aminoester) (EPAE-FA) containing folic acid and amino groups in the backbone and side chain was synthesized. EPAE-FA self-assembled readily with the plasmid DNA (pCMV-βgal) in HEPES buffer and was characterized by dynamic light scattering, zeta potential, fluorescence images, and XTT cell viability assays. To evaluate the transfection effect of graft ratio of FA on the EPAE system, EPAE-FA polymers with two different graft ratios (EPAE-FA12k and EPAE-FA14k) were also prepared. This study found that all EPAE-FA polymers were able to bind plasmid DNA and yielded positively charged complexes with nano-sized particles ( < 200 nm). To assess the transfection efficiency mediated by EPAE and EPAE-FA polymers, we performed in vitro transfection activity assays using FR-negative (COS-7) and FR-positive (HeLa) cells. The EPAE-FA12k/DNA and EPAE-FA14k/DNA complexes were able to transfect HeLa cell in vitro with higher transfection efficiency than PEI25k/DNA at the similar weight ratio. These results demonstrated that the introduction of FA into EPAE system had a significant effect on transferring ability for FR-positive cells (HeLa). Examination of the cytotoxicity of PEI25k and EPAE-FA system revealed that EPAE-FA system had lower cytotoxicity. In this paper, EPAE-FA seemed to be a novel cationic poly(aminoester) for gene delivery and an interesting candidate for further study.     

Synthesis of Iso-condensed Heteroaromatic Pyrroles and Their Application in the Preparation of Conducting Polymers

Iso-condensed heteroaromatic pyrroles 1 are 10 -electron aromatic compounds. They are of interest from both theoretical and synthetic points of view. They are the cyclic analogues of heteroaromatic ortho-quinodimethanes 2, and can react with dienophiles in a Diels-Alder reaction to give the synthetically useful cycloadducts 3. Many of them are also of potential pharmaceutical importance because they are isosteric with indoles. Iso-condensed heteroaromatic pyrroles 1 can be used also as the monomers for the synthesis of new conducting polymers 5 with special properties and characteristics. However, the methods for the efficient preparation of the iso-condensed heteroaromatic pyrroles are quite limited. Iso-condensed heteroaromatic pyrroles are generally unstable in acidic conditions and are easily oxidized by air. In our laboratories, we developed three methods for the preparation of this labile heterocyclic ring system under acidic, neutral, and basic conditions.1 Synthesis of the conjugated systems such as 6 for OLED applications will also be discussed.     

Absorption and foaming of plastics using carbon dioxide

In this study, carbon dioxide was used as a foaming agent for common plastics, such as acrylonitrile–butadiene–styrene (ABS) polymer, polystyrene (PS), polypropylene (PP), high-density polyethylene (HDPE), and high impact polystyrene (HIPS). Carbon dioxide was first absorbed by the sample plastics placed within a pressure vessel at various pressure levels and absorption time intervals. The Henry’s constant of the absorbed carbon dioxide in the plastics was determined. The diffusion coefficient of carbon dioxide in polymer was also identified by curve-fitting with the relationship between the absorbed amount and time. The results showed that ABS, PS, and HIPS absorbed more gas than did PP and HDPE, because PP and HDPE exhibit higher crystallinity. Generally, a polymer can take up saturation absorption of gas under higher pressure. After absorption, the foaming process occurred at various temperatures and time intervals. The cell structure, density, and size of the plastic foams were then investigated using scanning electron microscopy. A longer foaming period and higher temperature increase the size of the cell and decrease the cell density (the number of bubbles per unit volume). A dense skin layer without bubbles appeared directly adjacent to the surface of the foamed plastics. Its thickness decreased if the foaming process took place at higher temperatures.     

Nickel-catalyzed, cascade cycloadditions of 1-ethynyl-8-halonaphthalenes with nitriles: synthesis, structure, and physical properties of new pyrroloarenes

The reaction of 1-ethynyl-8-halonaphthalenes 1 with nitriles in the presence of the catalytic system [NiBr(2)(dppe)]/Zn (dppe=1,2-bis(diphenylphosphino)ethane) is found to produce unusual pyrroloarenes 2. The carbon-nitrogen triple bond in nitrile is activated twice, and five new bonds are formed in a one-pot transformation, which causes a pyrrole and two six-membered rings to be generated simultaneously. The scope and limitations of this reaction are examined. Similarly, alkyl-bridged diynes also furnish the corresponding polycycles. Diaryl-substituted cycloadducts 2 (R(1)=Ar) are fluxional, because of the restriction in rotation of the aryl groups. The rotational barrier is studied by performing (1)H NMR experiments at various temperatures. The structures of several compounds are determined by X-ray crystallographic analysis. The photophysical and electrochemical properties of the pyrroloarenes are also investigated.     

Two New Saturated Sesquiterpene Diols—Cadinan-3β, 9β-Diol and Cadinan-3β, 9α-Diol from Taiwania Cryptomerioides Hayata

From the wood of Taiwania cryptomerioides Hayata, two new sesquiterpenes, cadinan-3β, 9β-diol and cadinan-3β, 9α-diol were isolated as minor components. Their structures were elucidated as (I) and (II), respectively.     

Isolation of sesquiterpenoids from sponge Dysidea avara and chemical modification of avarol as potential antitumor agents

The marine sponge Dysidea avara contained avarol (1) and avarone (2). Avarol on acylation yielded 2',5'-O-dibenzoylavarol (3); 2,5'-O-(4-chlorobenzoyl)avarol (4); 2,5'-O-dicinnamoylavarol (5); 2,5'-O-(4-bromobenzoyl)avarol(6); 2',5'-O-dioctanoylavarol (7); 2',5'-O-(4-fluorobenzoyl)avarol (8) and diacetylavarol (9). The structural elucidation of all the compounds 1-9 have been done by spectral analysis. The cytotoxicity of these compounds were also determined and evaluated. Compounds 6 and 9 showed selective cytotoxicity against Hepa (human hepatoma) and KB cell lines respectively.     

Evaluation of surface charge density and surface potential by electrophoretic mobility for solid lipid nanoparticles and human brain-microvascular endothelial cells

Electrophoretic mobility, zeta potential, surface charge density, and surface potential of cacao butter-based solid lipid nanoparticles (SLN) and human brain-microvascular endothelial cells (HBMEC) were analyzed in this study. Electrophoretic mobility and zeta potential were determined experimentally. Surface charge density and surface potential were evaluated theoretically via incorporation of ion condensation theory with the relationship between surface charge density and surface potential. The results revealed that the lower the pH value, the weaker the electrostatic properties of the negatively charged SLN and HBMEC. A higher content of cacao butter or a slower stirring rate yielded a larger SLN and stronger surface electricity. On the contrary, storage led to instability of SLN suspension and weaker electrical behavior because of hydrolysis of ionogenic groups on the particle surfaces. Also, high H+ concentration resulted in excess adsorption of H+ onto HBMEC, rendering charge reversal and cell death. The largest normalized discrepancy between surface potential and zeta potential occurred at pH = 7. For a fixed biocolloidal species, the discrepancy was nearly invariant at high pH value. However, the discrepancy followed the order of electrical intensity for HBMEC system at low pH value because mammalian cells were sensitive to H+. The present study provided a practical method to obtain surface charge properties by capillary electrophoresis.     

Briarenolide E: the first 2-ketobriarane diterpenoid from an octocoral Briareum sp. (Briareidae)

A novel 2-ketobriarane diterpenoid, briarenolide E (1), was isolated from an octocoral Briareum sp. The structure of briarane 1 was elucidated by interpretations of spectral data. Compound 1 displayed modestly inhibitory effects on the generation of superoxide anions and the release of elastase by human neutrophils.