The effect of triethyl citrate on the dispersibility and water vapor sorption behavior of polylactic acid/zeolite composites

The aim of this study was to investigate the water vapor adsorption behavior and mechanical properties of poly (lactic acid) (PLA)/zeolite (5, 10, or 15 phr) composites prepared with triethyl citrate (TEC; 20 phr) via a melting process. TEC was used to improve the flexibility of the PLA and the dispersibility of the zeolite in TEC-zeolite suspensions that were ultra-sonicated. It was found that zeolite was uniformly dispersed in the PLA matrix, and the interfacial adhesion between the PLA matrix and zeolite was enhanced by TEC. In addition, the tensile strengths and Young's modulus of the composites improved with increasing zeolite content. The PLA/zeolite composites prepared with TEC had increased water vapor permeability and contact angles compared to neat PLA and standard PLA/zeolite due to the presence of TEC. In particular, TEC accelerated the hydrolysis of the PLA surface in a high humidity environment, resulting in an improvement in water vapor sorption capacity. At the same zeolite content of 15 phr, the equilibrium moisture content (EMC) values of PLA/zeolite films prepared with TEC increased by up to 39.25 mg/g whereas those prepared without TEC only increased by up to 24.33 mg/g. The results suggest the possibility of applying PLA/zeolite films prepared with TEC as a flexible active packaging material.     

Crystal structures of two isostructural compounds: a second polymorph of dipotassium hydrogen citrate,K2HC6H5O7, and potassium rubidium hydrogen citrate,KRbHC6H5O7

The crystal structures of a new polymorph of dipotassium hydrogen citrate, 2K⁺·HC₆H₅O₇^2?, and potassium rubidium hydrogen citrate, K⁺·Rb⁺·HC₆H₅O₇^2?, have been solved and refined using laboratory powder X‐ray diffraction and optimized using density functional techniques. In the new polymorph of the dipotassium salt, KO₇ and KO₈ coordination polyhedra share corners and edges to form a three‐dimensional framework with channels parallel to the a axis and [111]. The hydrophobic methylene groups face each other in the channels. The un‐ionized carboxylic acid group forms a strong charge‐assisted hydrogen bond to the central ionized carboxylate group. The hydroxy group forms an intermolecular hydrogen bond to a different central carboxylate group. In the potassium rubidium salt, the K⁺ and Rb⁺ cations are disordered over two sites, in approximately 0.72:0.28 and 0.28:0.72 ratios. KO₈ and RbO₉ coordination polyhedra share corners and edges to form a three‐dimensional framework with channels parallel to the a axis. The un‐ionized carboxylic acid group forms a strong charge‐assisted hydrogen bond to an ionized carboxylate group. The hydroxy group forms an intermolecular hydrogen bond to the central carboxylate group. Density functional theory (DFT) calculations on the ordered cation structures suggest that interchange of K⁺ and Rb⁺ at the two cation sites changes the energy insignificantly.     

Scale-Up Preparation of Crocins I and II from Gardenia jasminoides by a Two-Step Chromatographic Approach and Their Inhibitory Activity Against ATP Citrate Lyase

Crocins are highly valuable natural compounds for treating human disorders, and they are also high-end spices and colorants in the food industry. Due to the limitation of obtaining this type of highly polar compound, the commercial prices of crocins I and II are expensive. In this study, macroporous resin column chromatography combined with high-speed counter-current chromatography (HSCCC) was used to purify crocins I and II from natural sources. With only two chromatographic steps, both compounds were simultaneously isolated from the dry fruit of Gardenia jasminoides, which is a cheap herbal medicine distributed in a number of countries. In an effort to shorten the isolation time and reduce solvent usage, forward and reverse rotations were successively utilized in the HSCCC isolation procedure. Crocins I and II were simultaneously obtained from a herbal resource with high recoveries of 0.5% and 0.1%, respectively, and high purities of 98.7% and 99.1%, respectively, by HPLC analysis. The optimized preparation method was proven to be highly efficient, convenient, and cost-effective. Crocins I and II exhibited inhibitory activity against ATP citrate lyase, and their IC₅₀ values were determined to be 36.3 ± 6.24 and 29.7 ± 7.41 μM, respectively.     

The influence of 1-butyl-3-methyl-imidazolium bromide on the partitioning of l-tyrosine within the {polyethylene glycol 600 + potassium citrate} aqueous biphasic system at T = 298.15 K

Partitioning in aqueous biphasic systems (ABS) is widely recognized today as a rapid, gentle, and highly efficient technique for the separation of soluble as well as particulate biomaterials. This technique has gained increasing attention as the separation method of choice in biotechnology. In recent years, a new approach has been proposed based on the use of ionic liquids (ILs) as adjuvants for the separation and purification of bio-molecules using polymer-based ABS. In this regard, the influence of IL 1-butyl-3-methylimidazolium bromide ([C₄mim]Br) on the phase behavior and extraction capability of {PEG 600 + tri-potassium citrate (K₃C₆H₅O₇)} ABS for l-tyrosine (Tyr) is investigated here. For this purpose, phase diagrams and the liquid–liquid equilibrium (LLE) data for the {PEG 600 + K₃C₆H₅O₇} ABS with the addition of small quantities of IL were determined at T = 298.15 K. It was found that, for the studied polymer-based ABS, the addition of 5 wt% of [C₄mim]Br to ABS caused the expansion of two-phase area in the salt-rich region; while, for the PEG-rich region no change was observed. The partition coefficients of l-tyrosine (K_Tyr) within the studied system were determined at T = 298.15 K. The results obtained indicate that the addition of small quantities of [C₄mim]Br to the {PEG 600 + K₃C₆H₅O₇} ABS could enhance the extraction efficiency for l-tyrosine. In addition, the experimental data are correlated using the NRTL model. The comparisons between the correlation and the experimental data reveal a good agreement.     

Storage stability studies for tributyltin determination in human urine samples using headspace solid‐phase microextraction and gas chromatography mass spectrometry

A headspace solid‐phase micro‐extraction (HS‐SPME) method was employed in order to study the effect of storage conditions of human urine samples spiked with tributyltin (TBT) using gas chromatography and mass spectrometry. To render the analyte more volatile, the derivatization (ethylation) was made in situ by sodium tetraethylborate (NaBEt₄), which was added directly to dilute unpreserved urine samples and in buffers of similar acidity. The stability of TBT in human urine matrix was compared with the stability of TBT in buffer solutions of similar pH value. Critical parameters of storage conditions such as temperature and time, which affect the stability of TBT in this kind of matrix, were examined extensively. The tests showed that the stability of TBT remains practically satisfactory for a maximum of 2 days of storage either at +4 or 20°C. Greater variations were observed in the concentration of TBT in human urine samples at +4°C and lower ones at ?20°C over a month's storage. The freeze–thaw cycles have negative effect on the stability and should be kept to a minimum. The results from spiked urine samples are also discussed in comparison to those acquired from buffer solutions of equal TBT concentration. Copyright © 2012 John Wiley & Sons, Ltd.     

A CARBON-13 NMR STUDY OF POLAR-(NITRO)TRIMETHYLENEDIAMINE-N,N,N′-TRIACETATOCOBALTATE(III) ION

Abstract

The complex ion [Co(1,3-pd3a)NO₂]^? (pd3a=trimethylenediamine-N,N,N′-triacetate ion) was prepared from equatorial-skew-[Co(1,3-pd3a)H₂ O]. The absorption spectrum and the ¹³C NMR spectrum show the nitro product to be a polar isomer. The diamine backbone ring is believed to have the chair conformation.     

可见光光催化剂AgNbO3：柠檬酸络合法制备及其性能

以草酸铌铵和硝酸银为反应物,采用柠檬酸络合法成功的制备了钙钛矿型化合物AgNbO3可见光光催化剂,并运用X射线衍射、紫外-可见漫反射、扫描电镜、透射电镜和X射线光电子能谱等手段对催化剂进行了表征。同时以可见光为照射光源,以有机染料亚甲基蓝为模拟探针,考察其光催化性质。结果表明800℃所制备的样品具有最佳的光催化性能,其主要降解途径是以脱甲基的形式进行的,与固相法合成的样品相比,柠檬酸络合法所制备的样品具有较好的光催化性能。     

Functionalized carbon dots as sensors for gold nanoparticles in spiked samples: Formation of nanohybrids

This paper reports the synthesis, passivation and functionalization of luminescent carbon dots (CDs) possessing surface thiol ending groups. A simple procedure involving amidation of passivated carbon dots (p-CDs) with cysteamine boosts their photoluminescent properties and enables their use as easily controlled fluorescent nanosensors for determining citrate–gold nanoparticles (AuNPs). The mechanism behind the quenching phenomenon was established from fluorescence measurements at high temperatures and lifetime tests, and found to involve static quenching leading to the formation of CD–AuNP nanohybrids. A method for determining AuNPs in complex matrices was developed and validated by application to spiked drinking water and mussel tissues. The limits of detection and quantitation for AuNPs thus obtained were 0.20 and 0.66 nmol L^–1, respectively.     

Decorating graphene sheets with Pt nanoparticles using sodium citrate as reductant

In this paper, we proposed a novel and green approach for the synthesis of graphene nanosheets (GNS) and Pt nanoparticles-graphene nanosheets (Pt/GNS) hybrid materials, employing graphene oxide (GO) as precursor and sodium citrate as environmentally friendly reducing and stabilizing agent. The microstructures of GO and Pt/GNS were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and electrochemical measurements. The results confirmed that the uniform size distribution of Pt nanoparticles on the surface of GNS without agglomerates could be easily obtained via using sodium citrate as reductant, moreover the Pt/GNS hybrids exhibited high electrochemical activity.     

锌—柠檬酸氢二铵还原体系用于氢化偶氮苯的合成

采用锌-柠檬酸氢二铵溶液还原体系,以偶氮苯为原料合成出氢化偶氮苯.合成反应的最佳反应条件：当偶氮苯用量是0.625 mmol时,偶氮苯与锌的物质的量之比为1：5,0.2 g/mL柠檬酸氢二铵溶液用量5.0 mL,室温,时间约3 min,平均收率90.63％.