Assessment of ethanol and acetonitrile in 18F-FDG preparations by means of liquid chromatography

Introduction Acetonitrile (ACN) and ethanol (EtOH) are common solvents used in radiopharmaceutical production. In accordance to official compendia, the concentration of these solvents should be assessed by gas chromatography. In the present paper, an optimized method, based on Koziorowski (2010), is validated. Methods ACN and EtOH concentrations and retention times (Rt) were obtained by a HPLC system equipped with a refractive index detector (RID), an ion exclusion column and ultrapure water as mobile phase. The methodology was validated following the ICH Q2(R1) requirements. Results The solvents EtOH and ACN were eluted at 23.22 and 26.32 minutes, respectively, with a final run time of 30 minutes. The validation parameters (accuracy, precision, linearity, specificity, robustness, detection and quantification limits) were obtained. Conclusions A reproducible HPLC method for the quantification of residual solvents in preparations of 2-deoxy-2-[fluorine-18]fluoro-D-glucose (¹⁸F-FDG) was described and validated. The method was precise, accurate, selective, robust and linear over a wide range. In addition, this method showed a high sensitivity, with limits of detection and quantitation comparable to the usual methods by gas chromatography.     

Tunable Crystallinity and Charge Transfer in Two‐Dimensional G‐Quadruplex Organic Frameworks

DNA G‐quadruplex structures were recently discovered to provide reliable scaffolding for two‐dimensional organic frameworks due to the strong hydrogen‐bonding ability of guanine. Herein, 2,7‐diaryl pyrene building blocks with high HOMO energies and large optical gaps are incorporated into G‐quadruplex organic frameworks. The adjustable substitution on the aryl groups provides an opportunity to elucidate the framework formation mechanism; molecular non‐planarity is found to be beneficial for restricting interlayer slippage, and the framework crystallinity is highest when intermolecular interaction and non‐planarity strike a fine balance. When guanine‐functionalized pyrenes are co‐crystallized with naphthalene diimide, charge‐transfer (CT) complexes are obtained. The photophysical properties of the pyrene‐only and CT frameworks are characterized by UV/Vis and steady‐state and time‐resolved photoluminescence spectroscopies, and by EPR spectroscopy for the CT complex frameworks.     

Congestion game scheduling for virtual drug screening optimization

In virtual drug screening, the chemical diversity of hits is an important factor, along with their predicted activity. Moreover, interim results are of interest for directing the further research, and their diversity is also desirable. In this paper, we consider a problem of obtaining a diverse set of virtual screening hits in a short time. To this end, we propose a mathematical model of task scheduling for virtual drug screening in high-performance computational systems as a congestion game between computational nodes to find the equilibrium solutions for best balancing the number of interim hits with their chemical diversity. The model considers the heterogeneous environment with workload uncertainty, processing time uncertainty, and limited knowledge about the input dataset structure. We perform computational experiments and evaluate the performance of the developed approach considering organic molecules database GDB-9. The used set of molecules is rich enough to demonstrate the feasibility and practicability of proposed solutions. We compare the algorithm with two known heuristics used in practice and observe that game-based scheduling outperforms them by the hit discovery rate and chemical diversity at earlier steps. Based on these results, we use a social utility metric for assessing the efficiency of our equilibrium solutions and show that they reach greatest values.     

Isolation of methylammonium room temperature reactive polyiodide melt into a new starch complex

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The preparation, characterization, and X-ray structural analysis of dichlorobis[1-methyl-3-(2-propyl) -2(3H)-imidazolethione]mercury(II)

A new compound of mercury(II) chloride complexed to 1-methyl-3-(2-propyl) -2(3H)-imidazolethione (mipit) has been prepared and characterized via standard methods and X-ray crystallography. The structural significance of this study is that it shows one of the few monomeric examples of a mercury(II) chloride thione complex reported to date. The compound crystallizes in space group P2₁/c with a = 17.143(6) Å, b = 17.047(6) Å, c = 14.759(5) Å, = 105.899(5)°, V = 4148(2) ų, Z = 8. The coordination sphere is distorted tetrahedral with Hg–S bonds and Hg–Cl bond distances falling within the normally expected ranges. Bond angles ranged from 108.11(4)° to 115.51(4)° with the widest angle being observed for the S–Hg–S linkage. Ligand bond distances and angles including the C=S distance are within the normally expected values observed for this compound.     

Identification of 2,3-butanedione (diacetyl) as the compound causing odor events at trace levels in the Llobregat River and Barcelona's treated water (Spain)

A study of organic compounds imparting sweet and buttery odor problems in the Llobregat River (northeast Spain) and in treated water was conducted. Solid-phase microextraction (SPME), gas chromatography-olfactometry, and flavor profile analysis (FPA) were used as analytical methodologies to identify the compound responsible for odor incidents. 2,3-Butanedione (diacetyl) with a concentration range of 0.90-26 microg/l in river water samples entering the water treatment plant was identified as the compound causing the odor events. Flavor profile analysis establishes 0.05 microg/l as its odor threshold concentration (OTC) in water, with an odor recognition concentration of 0.20 microg/l. The analyses were carried out with SPME-GC-MS and parameters affecting SPME extraction such as selection of the fiber (carboxen-polydimethylsiloxane), extraction time (30 min), temperature (60 degrees C), and ionic strength were evaluated. Quality parameters of the optimized method gives good linearity (r2 > 0.999), a limit of detection (0.08 microg/l) similar to the OTC of the compound, and good reproducibility (R.S.D. < 20%). The SPME method was applied to identify the compound causing the odor.     

Effects of π bond type,backbone size,and halogen on structural and spectroscopic properties of hydrogen‐bonded complexes of the X?H … π type between alkenes or alkynes and haloacids (HF and HCl)

The effects of CC bond type (double or triple), substituent (H or methyl), and halogen (F and Cl) on three properties of hydrogen‐bonded complexes formed between unsaturated hydrocarbons and HX (X?F, Cl) are studied. The properties comprise hydrogen bond distances (R_H), stabilization energies (SE), and frequency shifts (Δν). A 2³ factorial design technique, along with ab initio (HF and MP2) and DFT (B3LYP and PBE1PBE) calculations, has been employed. All three responses are mainly affected by the halogen, and when it is changed from F to Cl, R_H tends to increase, while SE tends to decrease. Surprisingly, the type of substituent is more important than the type of CC bond, for all three responses. Both effects tend to decrease R_H. Significant interaction effects are obtained for the type of CC bond along with the type of substituent, and for the type of substituent along with the type of halogen. Both interaction effects are smaller than the main effects and also tend to decrease R_H. The greatest SE values are obtained with PBE1 functional (BSSE + ZPE corrected values). Again, the next more important effect is due to the type of substituent, and the replacement of H by CH₃ group tends to increase SE. The effect due to the CC bond type is not significant, at all computational levels. The only interaction effect that is significant for SE (corrected) and Δν is between factors 1 (CC bond type) and 2 (substituent), but only at HF and B3LYP levels, and it tends to increase both properties. As the halogen changes from F to Cl, Δν tends to decrease. In contrast, changing the substituent from H to CH₃ leads to greater values of Δν. The effect of CC bond type is not significant at HF level, and when it is changed from double to triple Δν is decreased, at B3LYP and PBE1 levels. A suggestion as to how the results may point toward a better experimental detection of similar (π‐type) complexes is also given. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Oxidation of Dibenzothiophene Catalyzed by Hemoglobin and Other Hemoproteins in Various Aqueous-Organic Media

Biocatalytic oxidation of dibenzothiophene (a model of organic sulfur in coal) with hydrogen peroxide was investigated. It was found that various hemoproteins, both enzymic (e.g., horseradish peroxidase) and nonenzymic (e.g., bovine blood hemoglobin), readily oxidized dibensothiophene to its S-oxide and, to a minor extent, further to its S-dioxide (sulfone). This process catalyzed by hemoglobin (a slaughterhouse waste protein) was studied in a number of monophasic aqueousorganic mixtures. Although hemoglobin was competent as an oxidation catalyst even in nearly dry organic solvents (with protic, acidic solvents being optimal), the highest conversions were observed in predominantly aqueous media. The hemoglobin-catalyzed oxidation of dibenzothiophene at low concentrations of the protein stopped long before all the substrate was oxidized. This phenomenon was caused by inactivation of hemoglobin by hydrogen peroxide that destroyed the heme moiety. The maximal degree of the hemoglobin-catalyzed dibenzothiophene oxidation was predicted, and found, to be strongly dependent on the reaction medium composition.     

Biomimetic Mineralization of the Alginate/Gelatin/Calcium Oxalate Matrix for Immobilization of Pectinase: Influence of Matrix on the Pectinolytic Activity

Pectinases catalyze the degradation of pectic substances and are used in several processes, mainly in food and textile industries. In this study, a biomimetic matrix of alginate/gelatin/calcium oxalate (AGOCa) was synthesized for the in situ immobilization via encapsulation of crude pectinase from Aspergillus niger ATCC 9642, obtaining an immobilization efficiency of about 61.7 %. To determine the performance of AGOCa matrix, this was compared to control matrices of alginate/calcium oxalate (AOxal) and alginate/water (ACa). By the evaluation of pH and temperature effects on the enzyme activity, it was observed an increase on pectinolytic activity for both three tested matrices with an increase on pH and temperature. The kinetic parameters for pectinase immobilized in the three matrices were determined using citric pectin as substrate. Values of K _m of 0.003, 0.0013, and 0.0022 g mL^?1 and V _max of 3.85, 4.32, and 3.17 μmol min^?1 g^?1 for AGOCa, AOxal, and ACa matrices were obtained, respectively. After 33 days of storage, the pectinase immobilized in the three different matrices kept its initial activity, but that immobilized in AGOCa presented high stability to the storage with a relative activity of about 160 %. The enzyme immobilized in AGOCa, AOxal, and ACa could be used in 10, 8, and 7 cycles, respectively, keeping 40 % of its initial activity.