Solution- and solid-phase, modular approaches for obtaining different natural product-like polycyclic architectures from an aminoindoline scaffold for combinatorial chemistry

With the goal of developing a modular approach leading to different indoline alkaloid natural-product-like tricyclic derivatives having an unsaturated lactam (see compounds 13, 14, and 16), an aminoindoline-based bicyclic scaffold 10 was obtained from 9. The selective deprotection of the indoline NTeoc or benzylic NHAlloc in compound 10, followed by N-acryloylation and then subjection to a ring-closing metathesis reaction, successfully led to obtaining two different architectures (13/14 and 16) having an unsaturated lactam functionality. This modular solution-phase methodology was then developed on solid phase. To achieve this objective, the aminoindoline bicyclic scaffold having an additional hydroxyl group could be immobilized onto the solid support using alkylsilyl linker-based polystyrene macrobeads, giving 18. By applying a ring-closing metathesis approach, 20 (tricyclic derivative with seven-membered-ring unsaturated lactam) and 23 (tricyclic derivative with eight-membered-ring unsaturated lactam) were then obtained from 18 in a number of steps.     

Photo-oxidation of diglycine in confined media Relaxation of longitudinal magnetization in spin correlated radical pairs

Time-resolved electron paramagnetic resonance spectra (X-band) of correlated radical pairs created in AOT reverse micelles are presented and simulated using the microreactor model. They are discussed in terms of the two-site model with a particular emphasis on longitudinal relaxation mechanisms. The geminate radical pair is created by photo-oxidation of dyglicine by the excited triplet states of an anthraquinone salt. The strong chemically induced electron spin polarization observed is due to three mechanisms: TM, RPM, and SCRPM. Relative contributions from these mechanisms depend on the water pool volume and the time of observation. There are three types of longitudinal relaxation in radical pairs. The first is relaxation of the RPM induced longitudinal magnetization in spin correlated radical pairs. The second is the longitudinal relaxation in radical pairs which are not correlated (with a zero value of the double quantum coherence). In such pairs, the generation of longitudinal magnetization due to RPM is impossible, and the spin-selective recombination of the pairs is ineffective. Under all experimental conditions, the first type of relaxation is slower than the second type. For both, the physical mechanism leading to relaxation is modulation of the Heisenberg electron spin exchange interaction. This is an internal relaxation process. The third relaxation type occurs in radical pairs due to ordinary longitudinal relaxation in non-interacting radicals. Normally, relaxation of the third type is the slowest of the three. This explains time and micelle size dependence of the relative contribution of RPM into TREPR spectra. It seems reasonable to suggest that the creation of the initial spin state populations is partially adiabatic.     

Aryl-substituted sulfonium betaines: preparation and use in the epoxidation of aldehydes

Thermally induced decarboxylation of carboxymethylsulfonium betaines results in formation of the corresponding sulfur ylides in situ. Decarboxylation rates for a range of arylcarboxymethylsulfonium betaine salts have been determined using NMR spectroscopy, and the efficiency of ylide generation and trapping has been evaluated via methylidene transfer to a range of aldehydes to form epoxides.     

Further 6-sparse Steiner Triple Systems

We give a construction that produces 6-sparse Steiner triple systems of order v for all sufficiently large v of the form 3p, p prime and p ≡ 3 (mod 4). We also give a complete list of all 429 6-sparse systems with v < 10000 produced by this construction.     

Development of a theoretical model describing sonoporation activity of cells exposed to ultrasound in the presence of contrast agents

Sonoporation uses ultrasound, with the aid of ultrasound contrast agents (UCAs), to enhance cell permeabilization, thereby allowing delivery of therapeutic compounds noninvasively into specific target cells. The objective of this study was to determine if a computational model describing shear stress on a cell membrane due to microstreaming would successfully reflect sonoporation activity with respect to the peak rarefactional pressure. The theoretical models were compared to the sonoporation results from Chinese hamster ovary cells using Definity(?) at 0.9, 3.15, and 5.6 MHz and were found to accurately describe the maximum sonoporation activity, the pressure where a decrease in sonoporation activity occurs, and relative differences between maximum activity and the activity after that decrease. Therefore, the model supports the experimental findings that shear stress on cell membranes secondary to oscillating UCAs results in sonoporation.     

影响频谱分析仪频率分辨率的因素

频率分辨率是频谱分析仪的一项重要技术指标,在介绍频谱分析仪原理的基础上,对频谱分析仪的分辨率带宽、频率选择性、本振残余调频和本振相位噪声参数进行了解析,从而使读者掌握各参数与频谱分析仪频率分辨率之间的关系,在选购频谱仪和实际测量时合理地考虑以上参数。     

Density Functional Theory Guided Investigation of Ligand-Induced Neptunyl-Neptunyl Interactions

Actinyl-actinyl interactions are particularly prevalent for the pentavalent neptunyl cation (Np(V)O₂)⁺ where these interactions appear either as a T - or D -shape (diamond-shape). T -shaped interactions have been previously identified in high concentration Np(V) solutions containing simple anions (NO₃⁻, ClO₄⁻, Cl⁻) whereas D -shaped have only been isolated in the solid-state in the presence of carboxylate ligands. In this study, Density Functional Theory (DFT) calculations were paired with Raman spectroscopy to evaluate the formation of D -shaped interactions in the presence of aliphatic (R=H (formate), CH₃ (acetate), CH₂CH₃ (propionate)) and aromatic (R=C₆H₅ (benzoate), C₆H₄OH (4-hydroxybenzoate), C₅H₄N (isonicotinate)) carboxylate ligands. DFT studies indicate that the ΔG to form hydrated T - and D -shaped forms are not spontaneous but become so with the addition of the carboxylate ligands. Raman spectra of the Np(V) carboxylate solutions contained vibrational modes associated with the D -shaped interactions, but spectral changes observed over time indicate a dynamic system. Crystallization experiments from the Np(V) carboxylate systems confirmed the presence of D- shaped dimers for the aromatic carboxylates, suggesting that the choice of the anion in solution favors actinyl-actinyl interactions even at low concentrations (≤20 mM) of Np(V).     

Modulating Photochemical Properties to Enhance the Stability of Electronically Dimmable Eye Protection Devices†

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole-based stabilizers were evaluated for stabilizing the liquid crystals. Based on spin trapping experiments, radicals generated upon UV exposure is likely responsible for the degradation of the system. The radical generation is competitively inhibited by the addition of stabilizers.