The role of organoaluminum and electron donors in propene insertion on the Ziegler-Natta catalyst.

Alkyl aluminium plays a primary role in activating Ti within Ziegler-Natta (ZN) catalysts for propylene polymerization. We performed density functional calculations to explore the additional roles of AlEt3 and AlEt2Cl, in conjunction with diisobutyl phthalate (DIBP) internal donor and dicyclopentyl dimethoxysilane (DCPDMS) external donor, to enhance the stereoselectivity of propene insertion. Based on our calculated adsorption energies on the (MgCl2)13/TiCl2iBu cluster model for the ZN catalyst, the presence of DIBP on the cluster essentially facilitated AlEt2Cl adsorption while AlEt2Cl also promoted the adsorption of DIBP. The reaction between AlEt3 and DIBP on the cluster led to the extraction of DIBP, creating an available site for DCPDMS adsorption. While the stereoselectivity, represented by the difference in the activation energies between 1,2-re and 1,2-si insertions of propene, was negligible on the cluster containing only DIBP, it became significant on the clusters containing both AlEt2Cl and DIBP (and DCPDMS). AlEt2Cl plays a pivotal role in imposing steric effects near the Ti active site, thereby increasing stereoselectivity. Our findings suggest the importance of including AlEt2Cl alongside DIBP (and DCPDMS) in the ZN cluster model to investigate stereoselective propene insertion. Considering AlEt2Cl adsorption and AlEt3 reaction with internal donors is essential in developing Ziegler-Natta catalysts.

Ag/Au-incorporated trimethyl chitosan-shell hybrid particles as reinforcing and antioxidant fillers for trimethyl chitosan hydrogel.

N,N,N-Trimethyl chitosan (TMC) is a quaternized chitosan with versatile biological features. However, low mechanical strength limits its uses, for example, as hydrogels for tissue engineering applications. This study illustrates a viable synthesis of metal/polymer hybrid, core-shell colloidal particles and their use as reinforcing and antioxidant fillers for TMC hydrogels. The core-shell particles were initially synthesized by surfactant-free emulsion polymerization, induced by a photo-redox initiating system of riboflavin assisted by a 3° amine and 2° alcohol co-initiators. The synthesized core-shell particles were based on two polymeric shells: TMC and chitosan, and two polymeric cores: poly (hydroxypropyl methacrylate) (PHPMA) and poly(2-hydroxy ethyl methacrylate) (PHEMA). The presence of both 3° amine on TMC and 2° alcohol on HPMA monomer enhanced the photopolymerization performance. The TMC-based particles had sizes of 122-154 nm and zeta potentials of 10-35 mV, bringing the colloidal stability in the 4-10 pH range. Furthermore, due to the presence of TMC on the shell layer, the core-shell particles could be used as templates to grow the Ag/Au bimetallic nanoparticles with alloy and core-shell types through a thermal reduction. The prepared hybrid particles were incorporated in TMC hydrogels as a multifunctional filler, improving their mechanical and antioxidant properties.

Caffeine-Containing Emulsion: Influence of the HLB and Mixing Proportions, the Oil's Chemical Composition, and the Existence of Caffeine on Emulsion Properties.

This study employs a low-energy emulsification method to prepare caffeine-containing emulsions, denoted as Caf-EM. Three different oils, including coconut, sesame, and grape seed oils, are utilized along with the surfactants Span 80 and Tween 80. We investigate the influence of various factors, including (i) the hydrophilic-lipophilic balance (HLB) and surfactant ratio, (ii) the chemical composition of the oils, and (iii) the presence of caffeine, on the stability and size of emulsions. The results indicate that the HLB value and surfactant ratio are the most crucial factors affecting the emulsions' stability. The most stable Caf-EM formulation is achieved by combining mixed surfactants of Span 80 and Tween 80 with an optimal HLB value of 6.4 at a concentration of 15% (S15 to 6.4) across all oil types. This specific ratio also leads to significantly smaller emulsion droplet sizes than other ratios and is the only ratio that produces stable emulsions even without caffeine (denoted as EM). Notably, formulation S15-6.4 additionally causes a phase inversion from oil-in-water (O/W) to water-in-oil (W/O). Furthermore, the presence of caffeine in the water phase contributes to the formation of smaller and more stable emulsions. The particle size of Caf-EM is approximately 1.5 times smaller than that of EM. Regarding the oil's chemical composition, while there is a discernible trend in emulsion droplet size (coconut oil > grape seed oil > sesame oil), the differences within this sequence are insignificant, suggesting that the oil's chemical composition does not have a pronounced effect.

Synergistic Reinforcement of Cellulose Microfibers from Pineapple Leaf and Ionic Cross-Linking on the Properties of Hydrogels.

Hydrogels contain a large amount of water; thus, they are jelly-like, soft, and fragile. Although hydrogels' stiffness and strength can be improved by introducing another network to form a double or interpenetrating network, these mechanical properties are still not enough as many applications demand even stiffer and stronger hydrogels. Different methods of reinforcing hydrogels have been proposed and published. In this research, cellulose microfiber isolated from pineapple leaf was used as the reinforcement for hydrogels. The reinforcing efficiency of the fiber was studied for both single and double networks through the compression test. Other properties such as morphology and swelling behavior of the reinforced hydrogels were also studied. A synergistic effect of the second network and the fiber on the reinforcement was observed. The improvement due to the effect of fiber loading of only 0.6 wt % was found to be as high as 150%. This is greater than that observed in some nanofiller systems. Thus, the fiber can be used as a green reinforcement for similar hydrogel systems.

Enhanced degradation of chitosan by applying plasma treatment in combination with oxidizing agents for potential use as an anticancer agent.

Solution plasma (SP) treatment in combination with oxidizing agents, i.e., hydrogen peroxide (H2O2), potassium persulfate (K2S2O8) and sodium nitrite (NaNO2) were adopted to chitosan degradation in order to achieve fast degradation rate, low chemicals used and high yield of low-molecular-weight chitosan and chitooligosaccharide (COS). Among the studied oxidizing agents, H2O2 was found to be the best choice in terms of appreciable molecular weight reduction without major change in chemical structure of the degraded products of chitosan. By the combination with SP treatment, dilute solution of H2O2 (4-60mM) was required for effective degradation of chitosan. The combination of SP treatment and dilute solution of H2O2 (60mM) resulted in the great reduction of molecular weight of chitosan and water-soluble chitosan was obtained as a major product. The resulting water-soluble chitosan was precipitated to obtain COS. An inhibitory effect against cervical cancer cell line (HeLa cells) of COS was also examined.

Sericin-binded-deprotenized natural rubber film containing chitin whiskers as elasto-gel dressing.

Here, we aims to demonstrate a simple concept in biomaterials design by using natural resources solely as raw materials to fabricate elastic wound care dressing. Elasto-gel films comprise of silk sericin (SRC), natural rubber (NR), and chitin whisker (CTW) were developed. A glue-like protein SRC found in silk cocoons is beneficial for the treatment of wounds due to its superior skin moisturizing ability. However, the pure SRC film is generally difficult to be fabricated because of its weak structural feature. This limitation was overcome by using NR as a binder which consecutively rendered elasticity and strength of the films. CTW was chosen as another component to promote ability of the films for tissue restoration. Before the film formation, protein in the natural rubber latex (NRL) was removed to avoid allergic and cytotoxic problems. The enzyme-treated NR/SRC (ETNR/SRC) films having different blend compositions were fabricated by solution casting technique. The highest amount of the SRC to gain an easy to handle ETNR/SRC film was 30%. The ETNR/SRC/CTW films having 20% SRC were fabricated and studied in comparison. Essential properties of the films as elastic wound care dressings were investigated and effect of the materials chemistry on the observed properties were discussed.

Accelerated nanoparticles synthesis in alcohol-water-mixture-based solution plasma.

An extraordinary high-speed synthesis of gold nanoparticles (AuNPs) was discovered by synthesizing the AuNPs in ethanol-water mixtures using a solution plasma process (SPP). The influence of the ethanol mole fraction (χethanol) in the ethanol-water mixtures on the reduction rate of gold chloride ions to AuNPs under the SPP system was studied. The results indicated that the reaction rate of the AuNPs synthesis exhibited a maximum value (i.e. 35.2 times faster than in a pure water system) at the significant point where the partial molar volumes of ethanol and water changed drastically.

Verification of Radicals Formation in Ethanol-Water Mixture Based Solution Plasma and Their Relation to the Rate of Reaction.

Our previous research demonstrated that using ethanol-water mixture as a liquid medium for the synthesis of gold nanoparticles by the solution plasma process (SPP) could lead to an increment of the reaction rate of ∼35.2 times faster than that in pure water. This drastic change was observed when a small amount of ethanol, that is, at an ethanol mole fraction (χethanol) of 0.089, was added in the system. After this composition, the reaction rate decreased continuously. To better understand what happens in the ethanol-water mixture-based SPP, in this study, effect of the ethanol content on the radical formation in the system was verified. We focused on detecting the magnetic resonance of electronic spins using electron spin resonance spectroscopy to determine the type and quantity of the generated radicals at each χethanol. Results indicated that ethanol radicals were generated in the ethanol-water mixtures and exhibited maximum quantity at the xethanol of 0.089. Relationship between the ethanol radical yield and the rate of reaction, along with possible mechanism responsible for the observed phenomenon, is discussed in this paper.

Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity.

Black titania spheres (H-TiO2-x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO2-x, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO2-x can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti(3+) sites.

Preparation of chitosan-coated polyethylene packaging films by DBD plasma treatment.

Polyethylene (PE) packaging films were coated with chitosan in order to introduce the antibacterial activity to the films. To augment the interaction between the two polymers, we modified the surfaces of the PE films by dielectric barrier discharge (DBD) plasma before chitosan coating. After that the plasma-treated PE films were immersed in chitosan acetate solutions with different concentrations of chitosan. The optimum plasma treatment time was 10 s as determined from contact angle measurement. Effect of the plasma treatment on the surface roughness of the PE films was investigated by atomic force microscope (AFM) while the occurrence of polar functional groups was observed by X-ray photoelectron spectroscope (XPS) and Fourier transformed infrared spectroscope (FTIR). It was found that the surface roughness as well as the occurrence of oxygen-containing functional groups (i.e., C═O, C-O, and -OH) of the plasma-treated PE films increased from those of the untreated one, indicating that the DBD plasma enhanced hydrophilicity of the PE films. The amounts of chitosan coated on the PE films were determined after washing the coated films in water for several number of washing cycles prior to detection of the chitosan content by the Kjaldahl method. The amounts of chitosan coated on the PE films were constant after washing for three times and the chitosan-coated PE films exhibited appreciable antibacterial activity against Escherichia coli and Staphylococcus aureus. Hence, the obtained chitosan-coated PE films could be a promising candidate for antibacterial food packaging.

Chitosan whiskers from shrimp shells incorporated into dimethacrylate-based dental resin sealant.

A resin-based sealant containing chitosan whiskers was developed for use as a pit and fissure sealer. Chitosan whiskers were synthesized and then characterized using Fourier transform infrared spectrometry and transmission electron microscopy. The whiskers were next incorporated into dimethacrylate monomer at various ratios by weight and subsequently analyzed for their antimicrobial and physical properties. The dimethacrylate-based sealant containing chitosan whiskers had a greater antimicrobial activity than control sealant and they were comparable with antimicrobial commercial resin sealants. The inclusion of the whiskers did not reduce the curing depth or degree of double bond conversion and the reduction in hardness was minimal. In conclusion, a resin-based sealant containing chitosan whiskers can be considered an effective antimicrobial pit and fissure sealant.

Novel chitosan-spotted alginate fibers from wet-spinning of alginate solutions containing emulsified chitosan-citrate complex and their characterization.

The major problem associated with the production of alginate/chitosan hybridized fibers by wet spinning is the formation of gels due to ionic interactions of the oppositely charged molecules of alginate and chitosan when these two polymers are directly mixed. Here, we proposed a novel method of using chitosan in the form of an emulsion. The emulsion was prepared by adding a primary emulsion of olive oil in a sodium dodecyl sulfate (SDS) aqueous solution into a chitosan-citrate complex. The complexation of chitosan with citric acid is the key of this method. The citrate ions neutralize the positive charges of chitosan, rendering the chitosan-citrate complex to readily penetrate into the core of the SDS/olive oil micelles. The obtained emulsified chitosan-citrate complex (hereafter, the chitosan-citrate emulsion) of varying amount was then added into an alginate aqueous solution to prepare the alginate/chitosan spinning dope suspensions. The alginate/chitosan hybridized fibers showed spotty features of the emulsified chitosan-citrate complex particles locating close to the surface and the inside of the hybridized fibers. At the lowest content of incorporated chitosan (i.e., 0.5% w/w chitosan), both the tenacity and the elongation at break of the obtained chitosan-spotted alginate fibers were the greatest. Further increase in the chitosan content resulted in a monotonous decrease in the property values. Lastly, preliminary studies demonstrated that the obtained chitosan-spotted alginate fibers showed great promises as carriers for drug delivery.

Benzopyran, biphenyl, and tetraoxygenated xanthone derivatives from the twigs of Garcinia nigrolineata.

One new benzopyran, nigrolineabenzopyran A (1), two new biphenyls, nigrolineabiphenyls A and B (2, 3), and four new tetraoxygenated xanthones, nigrolineaxanthones T-W (4-7), were isolated from the crude methanol extract of the twigs of Garcinia nigrolineata along with 11 known xanthones. The xanthones isolated from the twigs as well as those from the stem bark were evaluated for antibacterial activity against methicillin-resistant Staphylococcus aureus. Nigrolineaxanthone F, latisxanthone D, and brasilixanthone showed significant activity, with an equal MIC value of 2 microg/mL.