Synthesis, structural and conformational studies of Z- and E-isomers of fluorinated C-6 isobutenyl N-methyl thymine derivatives

A new series of conformationally restricted pyrimidine derivatives bearing C-6 isobutenyl side-chain (2-9) has been prepared. The novel fluoroalkenyl pyrimidine nucleoside mimetic 3 as model compound for development of tracer molecule in positron emission tomography (PET) was synthesized by fluorination reaction of methoxytritylated pyrimidine derivative using diethylaminosulfur trifluoride (DAST). Conversion of one hydroxyl group to methoxytritylated, fluorinated, mesylated and acetylated pyrimidine derivatives (2, 3, 5-7 and 9) afforded a mixture of Z- and E-isomers in which Z-isomers were predominant. Conformational study of 1, and its fluorinated structural congeners 3 and 4 by the use of NOE experiments revealed predominant conformation of compounds where vinyl H-1′ proton is spatially close to N-1 methyl and H-3′b methylene protons and on the other hand H-3′a methylene protons are close to C-5 methyl protons. The stereostructure of 1,3-dihydroxyisobutenyl N-methyl thymine 1 was unambiguously confirmed by X-ray crystal structure analysis.     

Zeeman shift--a tool for assignment of 14N NQR lines of nonequivalent 14N atoms in powder samples

The use of Zeeman perturbed 14N nuclear quadrupole resonance (NQR) to determine the ν+ and ν-14N lines in polycrystalline samples with several nonequivalent nitrogen atoms was investigated. The 14N NQR line shift due to a weak external Zeeman magnetic field was calculated, assuming isotropic distribution of EFG tensor directions. We calculated the broad line distribution of the ν+ and ν- line shifts and experimentally confirmed the calculated Zeeman field dependence of singularities (NQR peaks) in cyclotrimethylenetrinitramine (RDX) and aminotetrazole monohydrate (ATMH). The calculated and measured frequency shifts agreed well. The proposed measurement method enabled determination of which 14N NQR lines in ATMH belong to ν+ and which to ν- transitions.     

Ni speciation in tea infusions by monolithic chromatography—ICP-MS and Q-TOF-MS

For humans, Ni is not considered to be an essential trace element. Its compounds, at levels present in foodstuffs and drinks, are generally considered to be safe for consumption, but for individuals who already suffer from contact allergy to Ni and may be subject to develop systemic reactions from its dietary ingestion, dietary exposure to Ni must be kept under control. Being the second most popular beverage, tea is a potential source of dietary Ni. Present knowledge on its speciation in tea infusions is poor. Therefore, complete speciation analysis, consisting of separation by liquid chromatography using a weak CIM DEAE-1 monolithic column, “on-line” detection by inductively coupled plasma mass spectrometry (ICP-MS) and “off-line” identification of ligands by hybrid quadrupole time-of-flight mass spectrometry (Q-TOF MS), was implemented for the first time to study Ni speciation in tea infusions. Total concentrations of Ni in dry leaves of white, green, oolong and black tea (Camellia sinensis) and flowers of herbal chamomile (Matricaria chamomilla) and hibiscus (Hibiscus sabdariffa) tea were determined after microwave digestion by ICP-MS. They lay between 1.21 and 14.4 mg?kg^?1. Good agreement between the determined and the certified values of the Ni content in the standard reference material SRM 1573a tomato leaves confirmed the accuracy of the total Ni determination. During the infusion process, up to 85 % of Ni was extracted from tea leaves or flowers. Separation of Ni species was completed in 10 min by applying aqueous linear gradient elution with 0.6 mol?L^?1 NH₄NO₃. Ni was found to be present in the chromatographic fraction in which quinic acid was identified by Q-TOF in all the tea infusions analysed, which had pH values between 5.6 and 6.0. The only exception was the infusion of hibiscus tea with a pH of 2.7, where results of speciation analysis showed that Ni is present in its divalent ionic form.     

Correlation-based method for improvement of NQR signals utilizing signal shape information

In the correlation method the signal shape information can be utilized for detection of weak signals, hidden in the noise. We tested the advantages, drawbacks and some practical features of the method applied to magnetic resonance detection. The influence of the signal width, shape and similarity to the template on the correlation function was studied by numerical simulation. The findings were applied to the optimization of the template for improved localization of a noisy¹⁴N nuclear quadrupole resonance (NQR) line in NaNO₂ during repetitive scans by a superregenerative spectrometer. The value of the correlation method in faster NQR intensity evaluation was also confirmed.     

Spin Echo Attenuation of Restricted Diffusion as a Discord of Spin Phase Structure

By using the particle probability density we analyze the spin echo attenuation of particles, diffusing in a bounded region. It provides a means to expand a nonuniform spin phase distribution into a series of waves that characterize the geometry and boundary conditions of confinement. Random motion disrupts the initial phase structure created by applied gradients and consequently discords its structure waves. By assuming the spin phase fluctuation and/or the randomness of spin phase distribution in the subensemble as a Gaussian stochastic process, we derive a new analytical expression for the echo attenuation related to the particle velocity correlation. For a diffusion in porous structure we get the expression featuring the same “diffusive diffraction” patterns as those being found and explained by P. T. Callaghan and A. Coy (“Principles of Nuclear Magnetic Resonance Microscopy,” Oxford Univ. Press, Oxford (1991);J. Chem. Phys.101, 4599–4609 (1994)) with the use of propagator theory. With the new approach we cast a new light on the phenomena and derive analitically how the diffusive diffractions appear when the sequence of finite or even modulated gradients are applied. The method takes into account the non-Markovian character of restricted diffusion, and therefore the echo dependence on the diffusion lengths and on the strength of applied gradient differs from the results of authors assuming the Markovian diffusion either by dealing with the diffusion propagators or by the computer simulation of Fick's diffusion.     

Examples of Analysis of Stochastic Processes Based on Time Series Data

Time series data from stochastic processes described by the Langevin equation are analyzed. Analysis is based on estimation of the deterministic and random terms of the Langevin equation from data. The terms are presented as fields and inspected visually. Forming a model of the process, the terms are also used to reconstruct the deterministic and stochastic process trajectories. The deterministic term is approximated by an analytical ansatz. The equations obtained by the approximation are used to generate deterministic process trajectories and to study their linear stability. Influence of measurement noise on the estimates is also discussed.     

Oxidative ring opening of 3-hydroxyquinoline-2,4(1H,3H)-diones into N-(α-ketoacyl)anthranilic acids

N-(α-Ketoacyl)anthranilic acids were prepared by oxidative ring opening of 3-hydroxyquinoline-2,4(1H,3H)-diones by using paraperiodic acid (H₅IO₆) or sodium periodate (NaIO₄). The optimisation of the reaction conditions is described as well as the utilisation of N-(α-ketoacyl)anthranilic acids in the preparation of anthranilic acid hydrochlorides.     

A New Pathway of DNA G‐Quadruplex Formation

A new folding intermediate of Oxytricha nova telomeric Oxy‐1.5 G‐quadruplex was characterized in aqueous solution using NMR spectroscopy, native gel electrophoresis, thermal differential spectra (TDS), CD spectroscopy, and differential scanning calorimetry (DSC). NMR experiments have revealed that this intermediate (i‐Oxy‐1.5) exists in two symmetric bimolecular forms in which all guanine bases are involved in GG N1‐carbonyl symmetric base pairs. Kinetic analysis of K⁺‐induced structural transitions shows that folding of Oxy‐1.5 G‐quadruplex from i‐Oxy‐1.5 is much faster and proceeds through less intermediates than folding from single strands. Therefore, a new folding pathway of Oxy‐1.5 G‐quadruplex is proposed. This study provides evidence that G‐rich DNA sequences can self‐assemble into specific pre‐organized DNA structures that are predisposed to fold into G‐quadruplex when interacting with cations such as potassium ions.     

RuII,OsII, and IrIII Complexes with Chelating Pyridyl–Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis

Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir^III–Cp*‐ and Os^II–Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p‐cymene=4‐isopropyl‐toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4‐substituted phenylacetylene building blocks have been used to introduce electronic fine‐tuning in the ligands. The ligands thus can be generally described as 4‐(4‐R‐phenyl)‐3‐methyl‐1‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐5‐ylidene (with R being H (L¹), Me (L²), OMe (L³), CN (L⁴), CF₃ (L⁵), Br (L⁶) or NO₂ (L⁷)). The corresponding complexes (Ir‐ 1 to Ir‐ 7 and Os‐ 1 to Os‐ 7 ) were characterized by standard spectroscopic methods, and the expected three‐legged, piano‐stool type coordination was unambiguously confirmed by X‐ray diffraction analysis of selected compounds. Together with Ru^II analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented.