(11)C] Carbon monoxide in selenium-mediated synthesis of (11)C-carbamoyl compounds

Using either amines, amino alcohols, or alcohols in selenium-mediated synthesis with [(11)C]carbon monoxide, 3 ureas, 6 carbamates, and 1 carbonate were labeled. Tetrabutylammonium fluoride ((TBA)F) was discovered to form a soluble and reactive complex with selenium and drastically increase the radiochemical yields. Of the selected carbamoyl compounds, one was a receptor ligand, one was an enzyme inhibitor, and one was a muscular relaxant pharmaceutical. The (11)C-target compounds were obtained in radiochemical yields ranging from low to almost quantitative and with specific radioactivity up to 1300 GBq/micromol. The radiochemical purity of the final products exceeded 98%. In one case, the corresponding (13)C-substituted compound was produced to verify the position of the (11)C-label. In a typical experiment starting with 16.4 GBq [(11)C]carbon monoxide, 7.0 GBq of LC-purified 5-phenyl-1,3-oxazolidin-[2-(11)C]-2-one was obtained within 20 min from start of the carbonylation reaction (84% decay-corrected radiochemical yield). The presented approach is an interesting alternative to the use of [(11)C]phosgene in labeling chemistry.     

Ru(II) and Os(II) nucleosides and oligonucleotides: synthesis and properties

A general and versatile method for the site-specific incorporation of polypyridine Ru(II) and Os(II) complexes into DNA oligonucleotides using solid-phase phosphoramidite chemistry is reported. Novel nucleosides containing a [(bpy)(2)M(3-ethynyl-1,10-phenanthroline)](2+) (M = Ru, Os) metal center covalently attached to the 5-position in 2'-deoxyuridine are synthesized, and their electrochemical as well as photophysical properties are studied. The Ru(II) nucleoside exhibits a rather long-lived excited state in phosphate buffer pH 7.0 (tau = 1.08 micros) associated with a relatively high emission quantum efficiency (phi = 0.051). The solvent dependence of the absorption and emission spectra is consistent with an emissive MLCT state where charge localization takes place on the extended heterocycle-linked phenanthroline. In contrast, the Os(II)-containing nucleoside is quite nonemissive in aqueous environment (tau = 0.027 micros, phi = 1 x 10(-4)). The metal-containing nucleosides are converted into their phosphoramidites and are utilized for the high-yield preparation of modified oligonucleotides. The novel oligonucleotides, characterized by absorption and emission spectroscopy, enzymatic digestion, and electrophoresis, form stable duplexes. Circular dichroism spectra confirm that the global conformation of the double helix is not altered by the presence of these polypyridyl complexes in the major groove. Metal-containing phosphoramidites with predetermined absolute configuration at the octahedral coordination center are synthesized and utilized for the synthesis of diasteromerically pure metal-containing DNA oligonucleotides. Emission spectroscopy suggests a higher protection of the Delta metal center from the bulk solvent and better accommodation within the major groove.     

A comparative ab initio study of some molecular systems based on hydrazine and formamide

A series of ab initio calculations has been performed on formamide and its hydrogen bonded dimer, s-diformylhydrazine, s-dimethylhydrazine and hydrazine. All systems were assumed planar. The CO, CN and NN bond lengths were optimized in all cases, in order to study the changes of these bonds with variations in the environment. Gross atomic populations and force constants were also considered, and in some calculations the effect of basis enlargements was studied. Significant changes were found in the formamide unit upon dimerization via hydrogen bonds or a NN bond. And, also, a systematic variation was found for the NN bond by going from hydrazine via dimethylhydrazine to diformylhydrazine. The results of this study indicate that the effect of substitution within the framework used is well simulated by ab initio calculations.     

The effect of hydrogen bonding on structural parameters I: An ab initio study of the keto and enol tautomers of formamide and their hydrogen bonded dimers

In order to study the variation of CO and CN bond lengths as functions of the hydrogen bond length, a series of ab initio calculations have been performed on the keto and enol tautomers of formamide. The formation of hydrogen bonds leads to an increase in the conjugation of the NCO fragment. This increase is expressed as a lengthening of the double bonds and a corresponding shortening of the single bonds. These changes are found to vary with the length of the hydrogen bonds and analytical expressions for these variations of the bond lengths have been derived. The potential functions for dimerization, i.e. formation of, respectively, two N-H ·· O and two O-H ·· N hydrogen bonds have also been found. The results obtained indicate significant differences between the two types of hydrogen bonds.     

Emissive Synthetic Cofactors: A Highly Responsive NAD+ Analogue Reveals Biomolecular Recognition Features

Apart from its vital function as a redox cofactor, nicotinamide adenine dinucleotide ( NAD⁺ ) has emerged as a crucial substrate for NAD⁺ -consuming enzymes, including poly(ADP-ribosyl)transferase 1 (PARP1) and CD38/CD157. Their association with severe diseases, such as cancer, Alzheimer's disease, and depressions, necessitates the development of new analytical tools based on traceable NAD⁺ surrogates. Here, the synthesis, photophysics and biochemical utilization of an emissive, thieno[3,4-d]pyrimidine-based NAD⁺ surrogate, termed N^thAD⁺ , are described. Its preparation was accomplished by enzymatic conversion of synthetic ^th ATP by nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1). The new NAD⁺ analogue possesses useful photophysical features including redshifted absorption and emission maxima as well as a relatively high quantum yield. Serving as a versatile substrate, N^thAD⁺ was reduced by alcohol dehydrogenase (ADH) to N^thADH and afforded ^thADP-ribose ( ^th ADPr ) upon hydrolysis by NAD⁺ -nucleosidase (NADase). Furthermore, N^thAD⁺ was engaged in cholera toxin A (CTA)-catalyzed mono(^thADP-ribosyl)ation, but was found incapable in promoting PARP1-mediated poly(^thADP-ribosyl)ation. Due to its high photophysical responsiveness, N^thAD⁺ is suited for spectroscopic real-time monitoring. Intriguingly, and as an N7-lacking NAD⁺ surrogate, the thieno-based cofactor showed reduced compatibility (i.e., functional similarity compared to native NAD⁺ ) relative to its isothiazolo-based analogue. The distinct tolerance, displayed by diverse NAD⁺ producing and consuming enzymes, suggests unique biological recognition features and dependency on the purine N7 moiety, which is found to be of importance, if not essential, for PARP1-mediated reactions.     

Permutation polynomials with low differential uniformity over finite fields of odd characteristic

In this paper, we propose a construction of functions with low differential uniformity based on known perfect nonlinear functions over finite fields of odd characteristic. For an odd prime power q, it is proved that the proposed functions over the finite field Fq are permutations if and only if q≡3(mod 4).     

Determination of polycyclic aromatic hydrocarbons in waters by ultrasound-assisted emulsification-microextraction and gas chromatography-mass spectrometry

An ultrasound-assisted emulsification-microextraction (USAEME) procedure was developed for the extraction of US EPA 16 polycyclic aromatic hydrocarbons (PAHs) in 10 mL of water samples, with subsequent determination by gas chromatography-mass spectrometry (GC-MS). After determination of the most suitable solvent and solvent volume, several other parameters (i.e., extraction time, centrifugation time and ionic strength of the sample) were optimized using a 2³ factorial experimental design. Limits of detection ranged from 0.001 to 0.036 μg L⁻¹. The developed procedure was applied to fortified distilled water with different fortification levels (0.5, 2 and 5 μg L⁻¹). Recoveries were over 92% and relative standard deviations of the recoveries were below 8%. The efficiency of the USAEME was compared with traditional liquid-liquid extraction (LLE) and solid-phase extraction on real water samples (i.e., tap water, well water and surface (lake) water as well as domestic and industrial wastewaters). The USAEME showed comparable efficiencies especially with LLE. The developed USAEME was demonstrated to be robust, viable, simple, rapid and easy to use for the determination of PAHs in water samples by GC-MS.     

Determination of selected polychlorinated biphenyls in soil by miniaturised ultrasonic solvent extraction and gas chromatography-mass-selective detection

Miniaturised ultrasonic solvent extraction procedure was developed for the determination of selected polychlorinated biphenyls (PCBs) in soil samples by gas chromatography-mass-selective detection by using 2³ factorial experimental design. Recoveries of PCBs from fortified soil samples are over 90% for three different fortification levels between 40 and 120 μg kg⁻¹, and relative standard deviations of the recoveries are below 7%. The limits of detection (LODs) ranged from 0.003 to 0.006 μg kg⁻¹. The performance of the proposed method was compared to traditional shake flask extraction method on the spiked real soil sample and extraction methods showed comparable efficiencies. Proposed miniaturised ultrasonic solvent extraction offers several advantages, i.e., reducing sample requirement for measurement of target compound, less solvent consumption and reducing the costs associated with solvent purchase and waste disposal.     

Five-dimensional -optimal lattice rules

A major search program is described that has been used to determine a set of five-dimensional -optimal lattice rules of enhanced trigonometric degrees up to 12. The program involved a distributed search, in which approximately 190 CPU-years were shared between more than 1,400 computers in many parts of the world.