Spectrophotometric studies of the thermodynamics of sitting-atop complexation between free base meso-tetraarylporphyrins and titanium(IV) chloride

Titanium(IV) chloride reacts with free base meso-tetraarylporphyrin and its ortho, meta and para-substituted derivatives (H₂T(X)PP; X: OCH₃, CH₃ and Cl) for formation of sitting-atop (SAT) complexes, [TiCl₄(H₂T(X)PP)]. The computer fitting of the variation of the absorbance versus mole ratio by KINFIT program was used for calculation of the formation constants of these complexes in chloroform. Thermodynamic parameters, ΔG°, ΔH°, ΔS°, have been determined and the influence of the temperature and the substituted aryl groups (electronic and steric effects) in the free base porphyrins on the stability of the SAT complexes was studied.     

Grafting of poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-dimethylacrylamide] copolymer onto siliceous support for preconcentration and determination of lead (II) in human plasma and environmental samples

A method is reported for surface grafting of polymer containing a functional monomer for metal chelating, poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-dimethylacrylamide] (poly(AGE/IDA-co-DMAA) onto silica modified by silylation with 3-mercaptopropyltrimethoxysilane. Monomer 1-(N,N-bis-carboxymethyl)amino-3-allylglycerol (AGE/IDA) was synthesized by reaction of allyl glycidyl ether with iminodiacetic acid. The resulting sorbent has been characterized using FT-IR, elemental analysis, thermogravimetric analysis (TGA), FT-Raman and scanning electron microscopy (SEM) and evaluated for the preconcentration and determination of trace Pb(II) in human biological fluid and environmental water samples. The optimum pH value for sorption of the metal ion was 5.5. The sorption capacity of functionalized resin was 15.06 mg g⁻¹. The chelating sorbent can be reused for 15 cycles of sorption–desorption without any significant change in sorption capacity. A recovery of 96.2% was obtained for the metal ion with 0.5 M nitric acid as eluting agent. The profile of lead uptake by the sorbent reflects good accessibility of the chelating sites in the poly(AGE/IDA-co-DMAA)-grafted silica gel. Scatchard analysis revealed that the homogeneous binding sites were formed in the polymers. The equilibrium adsorption data of Pb(II) by modified resin were analyzed by Langmuir, Freundlich, Temkin and Redlich–Peterson models. On the basis of equilibrium adsorption data the Langmuir, Freundlich and Temkin constants were determined as 0.70, 1.35 and 2.7, respectively at pH 5.5 and 20 °C. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of adsorption.     

New anion-exchange solid-phase extraction support used for preconcentration and determination of lead in water samples by flame atomic absorption spectrometry

A new chelating resin was prepared by coupling Amberlite XAD-2 with Brilliant Green through an azo spacer. The resulting resin has been characterized by FTIR spectrometry, elemental analysis, and thermogravimetric analysis and studied for the preconcentration and determination of trace Pb(II) ions from solution samples. The anionic complex of Pb(II) and iodide was retained on the resin by the formation of an ion associate with Brilliant Green on Amberlite XAD-2 in weak acidic medium. The optimum pH value for sorption of the metal ion was 5.5. The sorption capacity of the functionalized resin is 53.8 mg/g. The chelating resin can be reused for 20 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 103% was obtained for the metal ion with 0.1 M EDTA as the eluting agent. Scatchard analysis revealed that the homogeneous binding sites were formed in the polymers. The resin was subjected to evaluation through batch binding and column chromatography of Pb(II). The equilibrium adsorption data of Pb(II) on modified resin were analyzed by Langmuir, Freundlich, and Temkin models. Based on equilibrium adsorption data, the Langmuir, Freundlich, and Temkin constants were determined to be 0.192, 13.189, and 3.418 at pH 5.5 and 25 degrees C. The method was applied for lead ion determination in tap water samples.     

Acetone extracted propolis as a novel membrane and its application in phenol biosensors: the case of catechol

A novel biosensor for catechol has been constructed by immobilizing polyphenol oxidase (PPO) into acetone-extracted propolis (AEP) composite modified with gold nanoparticles (GNPs) and attached to multiwalled carbon nanotube (MWCNTs) on a gold electrode surface. The propolis for AEP was obtained from honeybee colonies. Under the optimum conditions, this method could be successfully used for the amperometric determination of catechol within a concentration range of 1 × 10⁻⁶ to 5 × 10⁻⁴ M, with a detection limit of 8 × 10⁻⁷ M (S/N = 3). The effects of pH and operating potential are also explored to optimize the measurement conditions. The best response was obtained at pH 5, while an optimum ratio of signal-to-noise (S/N) was obtained at −20 mV (versus Ag/AgCl), which was selected as the applied potential for the amperometric measurements. All subsequent experiments were performed at pH 5. Cyclic voltammetry and electrochemical impedance spectroscopy was used to characterize the PPO/CNTs/GNPs/AEP/Au biosensor. The biosensor also exhibited good selectivity, stability, and reproducibility.

     

Lipid Nanoparticles Containing siRNA Synthesized by Microfluidic Mixing Exhibit an Electron-Dense Nanostructured Core

Lipid nanoparticles (LNP) containing ionizable cationic lipids are the leading systems for enabling therapeutic applications of siRNA; however, the structure of these systems has not been defined. Here we examine the structure of LNP siRNA systems containing DLinKC2-DMA(an ionizable cationic lipid), phospholipid, cholesterol and a polyethylene glycol (PEG) lipid formed using a rapid microfluidic mixing process. Techniques employed include cryo-transmission electron microscopy, (31)P NMR, membrane fusion assays, density measurements, and molecular modeling. The experimental results indicate that these LNP siRNA systems have an interior lipid core containing siRNA duplexes complexed to cationic lipid and that the interior core also contains phospholipid and cholesterol. Consistent with experimental observations, molecular modeling calculations indicate that the interior of LNP siRNA systems exhibits a periodic structure of aqueous compartments, where some compartments contain siRNA. It is concluded that LNP siRNA systems formulated by rapid mixing of an ethanol solution of lipid with an aqueous medium containing siRNA exhibit a nanostructured core. The results give insight into the mechanism whereby LNP siRNA systems are formed, providing an understanding of the high encapsulation efficiencies that can be achieved and information on methods of constructing more sophisticated LNP systems.     

A bioinspired self assembled dimeric porphyrin pocket that binds electron accepting ligands

A binding pocket consisting of two zinc porphyrins self assembled by Watson-Crick base pairing is presented. The porphyrin binding pocket is located in the confined environment of a lipid membrane whereas the DNA is located in the water phase. Bidentate electron accepting ligands are shown to coordinate in-between the two porphyrins.     

How an enzyme tames reactive intermediates: positioning of the active-site components of lysine 2,3-aminomutase during enzymatic turnover as determined by ENDOR spectroscopy

Lysine 2,3-aminomutase (LAM) utilizes a [4Fe-4S] cluster, S-adenosyl-L-methionine (SAM), and pyridoxal 5'-phosphate (PLP) to isomerize L-alpha-lysine to L-beta-lysine. LAM is a member of the radical-SAM enzyme superfamily in which a [4Fe-4S]+ cluster reductively cleaves SAM to produce the 5'-deoxyadenosyl radical, which abstracts an H-atom from substrate to form 5'-deoxyadenosine (5'-Ado) and the alpha-Lys* radical (state 3 (Lys*)). This radical isomerizes to the beta-Lys* radical (state 4(Lys*)), which then abstracts an H-atom from 5'-Ado to form beta-lysine and the 5'-deoxyadenosyl radical; the latter then regenerates SAM. We use 13C, 1,2H, 31P, and 14N ENDOR to characterize the active site of LAM in intermediate states that contain the isomeric substrate radicals or analogues. With L-alpha-lysine as substrate, we monitor the state with beta-Lys*. In parallel, we use two substrate analogues that generate stable analogues of the alpha-Lys* radical: trans-4,5-dehydro-L-lysine (DHLys) and 4-thia-L-lysine (SLys). This first glimpse of the motions of active-site components during catalytic turnover suggests a possible major movement of PLP during catalysis. However, the principal focus of this work is on the relative positions of the carbons involved in H-atom transfer. We conclude that the active site facilitates hydrogen atom transfer by enforcing van der Waals contact between radicals and their reacting partners. This constraint enables the enzyme to minimize and even eliminate side reactions of highly reactive species such as the 5'-deoxyadensosyl radical.     

Ultrasound mediated efficient ring opening of epoxides by in situ generated dithiocarbamates in green reaction media

Ultrasound accelerated a safe, clean and environmentally benign one-pot, three-component synthesis of 2-hydroxy dithiocarbamate, from amine, carbon disulfide and epoxide in good to excellent yields and short reaction time with excellent chemo-, regio-, and stereoselectivities in green reaction media (water, deep eutectic solvent [DES] and polyethylene glycol [PEG]). The one-pot, three-component condensation of primary and secondary amine with carbon disulfide and epoxides under ultrasonic irradiation was developed as a green and fast protocol for the rapid high-yielding preparation of 2-hydroxy dithiocarbamate in green reaction media without organic solvent and tedious workup.     

Electrochemical Detection of Persulfate at the Modified Glassy Carbon Electrode with Nanocomposite Containing Nano‐Ruthenium Oxide/Thionine and Nano‐Ruthenium Oxide/Celestine Blue

The present study describes the fabrication of a sensitive amperometric sensor for the determination of persulfate. The immobilization surface was prepared by modifying a glassy carbon (GC) electrode with a nanocomposite containing ruthenium oxide (RuOx) nanoparticles and thionine (TH) or celestin blue (CB). The modified electrodes indicated excellent electrocatalytic activity toward persulfate reduction at a potential of +0.1 V. The proposed sensor showed detection limits of 1.46 µM for the GC/RuOx/TH modified electrode and 2.64 µM for the GC/RuOx/CB modified electrode. The sensitivities were obtained as 3 nA µM^?1 at a concentration range of 10 µM to 11 mM for the GC/RuOx/TH modified electrode and 1 nA µM^?1 at a concentration range of 10 µM to 6 mM for the GC/RuOx/CB modified electrodes.     

The daily radon dose in body organs caused by drinking milk and water

Milk is considered as the richest nutrition, being used by people. When drinking milk or water the radon gas will transfer from air to them rapidly. Since milk is majorly composed of water, probably radon existence in livestock consumable water could be the main cause of its presence in milk. Different portion of milk changed by radon gamma ray and consumption of radon included water or milk has its effects on the human body. For investigation the effect of radon in water or milk on human organs, this study has been done in two phases with MCNPX software. In the first phase, the dose rate of absorbed gamma ray by different portion of milk which is indoctrinated by 1 Bq/m³ of radon during a day is calculated. Moreover, the effects shown by milk and its components in radon gamma spectrum, which is demonstrator of milk absorption spectrum, are also surveyed. In the second phase as well, according to the human body phantom, the absorbed gamma dose caused by daily consumption of indoctrinated water or milk with 1 Bq/m³ radon is calculated. The production rate of free radicals in milk and its different components are derived according to escape data of MCNPX code.