Synthesis and characterization of potential multifunctional methacrylate-based dental monomers

Research on Chemical Intermediates - We describe synthesis and characterization of a series of novel multifunctional methacrylate-based dental monomers. Triethanolamine was reacted with glycidyl...     

On the resilience of nitrogen assimilation by intact roots under starvation,as revealed by isotopic and metabolomic techniques

The response of root metabolism to variations in carbon source availability is critical for whole‐plant nitrogen (N) assimilation and growth. However, the effect of changes in the carbohydrate input to intact roots is currently not well understood and, for example, both smaller and larger values of root:shoot ratios or root N uptake have been observed so far under elevated CO₂. In addition, previous studies on sugar starvation mainly focused on senescent or excised organs while an increasing body of data suggests that intact roots may behave differently with, for example, little protein remobilization. Here, we investigated the carbon and nitrogen primary metabolism in intact roots of French bean (Phaseolus vulgaris L.) plants maintained under continuous darkness for 4 days. We combined natural isotopic ¹⁵N/¹⁴N measurements, metabolomic and ¹³C‐labeling data and show that intact roots continued nitrate assimilation to glutamate for at least 3 days while the respiration rate decreased. The activity of the tricarboxylic acid cycle diminished so that glutamate synthesis was sustained by the anaplerotic phosphoenolpyruvate carboxylase fixation. Presumably, the pentose phosphate pathway contributed to provide reducing power for nitrate reduction. All the biosynthetic metabolic fluxes were nevertheless down‐regulated and, consequently, the concentration of all amino acids decreased. This is the case of asparagine, strongly suggesting that, as opposed to excised root tips, protein remobilization in intact roots remained very low for 3 days in spite of the restriction of respiratory substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectral studies of solutions at elevated temperatures and pressures. IX. Acetic acid

Raman spectra of glacial acetic acid from 350 to 3700 cm^–1 have been measured at temperatures up to 275°C and at a pressure of 9 MPa. Raman spectra of aqueous solutions of acetic acid from 3.9 to 16 molar have been measured up to 200°C at a pressure of 7 MPa. The spectral region 800 to 1850 cm^–1 for both glacial acetic acid and its aqueous solutions have been studied in detail since this region is significantly affected by variations in temperature and concentration. An interpretation of the bands in this spectral region was made with the aid of factor analysis, difference spectroscopy, band resolution techniques and the existing extensive literature. The results suggest that the major equilibrium in glacial acetic acid is between cyclic and linear dimers; however, in aqueous solutions in the concentration range studied, mono- and di-hydrated dimers and cyclic dimers are the predominant species.     

Preparation of starch and soluble sugars of plant material for the analysis of carbon isotope composition: a comparison of methods

Starch and soluble sugars are the major photosynthetic products, and their carbon isotope signatures reflect external versus internal limitations of CO₂ fixation. There has been recent renewed interest in the isotope composition of carbohydrates, mainly for use in CO₂ flux partitioning studies at the ecosystem level. The major obstacle to the use of carbohydrates in such studies has been the lack of an acknowledged method to isolate starch and soluble sugars for isotopic measurements. We here report on the comparison and evaluation of existing methods (acid and enzymatic hydrolysis for starch; ion‐exchange purification and compound‐specific analysis for sugars). The selectivity and reproducibility of the methods were tested using three approaches: (i) an artificial leaf composed of a mixture of isotopically defined compounds, (ii) a C₄ leaf spiked with C₃ starch, and (iii) two natural plant samples (root, leaf). Starch preparation methods based on enzymatic or acid hydrolysis did not yield similar results and exhibited contaminations by non‐starch compounds. The specificity of the acidic hydrolysis method was especially low, and we therefore suggest terming these preparations as HCl‐hydrolysable carbon, rather than starch. Despite being more specific, enzyme‐based methods to isolate starch also need to be further optimized to increase specificity. The analysis of sugars by ion‐exchange methods (bulk preparations) was fast but produced more variable isotope compositions than compound‐specific methods. Compound‐specific approaches did not in all cases correctly reproduce the target values, mainly due to unsatisfactory separation of sugars and background contamination. Our study demonstrates that, despite their wide application, methods for the preparation of starch and soluble sugars for the analysis of carbon isotope composition are not (yet) reliable enough to be routinely applied and further research is urgently needed to resolve the identified problems. Copyright © 2009 John Wiley & Sons, Ltd.     

An investigation on polycaprolactone/chitosan/Fe3O4 nanofibrous composite used for hyperthermia

Hyperthermia is considered as an effective supplementary cancer treatment. However, the uneven temperature distribution is the major challenge in hyperthermia. Nanotechnology could solve this problem by applying magnetic nanoparticles directly or in nanofibers as implants. Low solubility, poor cancer targeting, and leakage are limitations of free magnetic nanoparticles. In this work, Fe₃O₄ nanoparticles were loaded into polycaprolactone/chitosan blended nanofibers in various contents. Magnetic, chemical, physical, and morphology of the derived nanofibrous composites were then studied. The results showed the magnetic properties of the nanocomposite had low coercivity, which was close to superparamagnetic particles. Chemical analysis showed that components had no interaction with each other. Nevertheless, Fe₃O₄ was slightly transformed to other iron oxides. However, the magnetic analysis showed this transformation had no significant effect on final magnetic content of the nanofibers. The results of X‐ray diffraction (XRD) (19.5 nm), transmittance electron microscopy (TEM) (21.6 nm), and vibration sample magnetometer (VSM) (17 nm) suggested that the magnetic nanoparticles were single domain. Thermal analysis results showed that 7% Fe₃O₄ nanofibers had more heat increase as oppose to other nanofibrous composites in the alternative magnetic field (AMF). Nonetheless, the heat performance of 3% Fe₃O₄ nanofibers was more than others according to its specific power absorption (SPA). Therefore, due to the importance of using nanoparticles in the least possible content, this method can be used as a postsurgical treatment by applying these nanofibrous composites as implants on the tumor site. Moreover, these nanofiber composites could carry anticancer drugs, which are applied as a multi‐mode treatment system.     

UV-degradation effect on optical and surface properties of polystyrene-TiO<Subscript>2</Subscript> nanocomposite film

Thin films of polystyrene and polystyrene-TiO₂ nanocomposite were prepared by spin coating from a polystyrene solution in which TiO₂ nanoparticles were dispersed by mechanical mixing. Thin films of polystyrene (PS) and polystyrene-TiO₂ nanocomposite were exposed to UV irradiation for varied time intervals. The effect of UV radiation on the optical properties, crystallinity, surface energy and degradation of PS-TiO₂ nano-composite has been studied. X-Ray diffraction analysis (XRD), UV-Vis and FTIR spectroscopy, Atomic Force Microscopy (AFM) and contact angle measurement were used to study the induced changes of the properties of the irradiated PS-TiO₂ nanocomposite. Optical band gaps and hydrophilicity in UV-irradiated samples were altered by destruction processes. The optical band gap values were found to reduce from 4.54 eV in pure PS to 4.45 eV for PS-TiO₂ nanocomposite prior to irradiation. This value is further reduced to 3.46 after UV irradiation for 45 h.