Mukaiyama–Michael Reactions with trans‐2,5‐Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions,Not from Steric Hindrance

The scope of the enantioselective Mukaiyama–Michael reactions catalyzed by trans‐2,5‐diphenylpyrrolidine has been expanded to include both α‐ and β‐substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C?C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals that the enantioselectivity is mostly due to stabilizing noncovalent interactions between the reacting partners, not due to steric hindrance. The role of attractive noncovalent interactions in enantioselective catalysis may be underappreciated.     

7‐(2‐Oxoalkoxy)coumarins: Synthesis and Anti‐Inflammatory Activity of a Series of Substituted Coumarins

A series of 7‐(2‐oxoalkoxy)coumarins have been synthesized by conjugating substituted 7‐hydroxycoumarins with different chloroketones. The anti‐inflammatory properties of 7‐(2‐oxoalkoxy)coumarins were studied in LPS‐induced inflammatory response in J774 macrophages. Western blot was used to determine the expression of iNOS and COX‐2, NO was determined by measuring its metabolite nitrite by Griess reaction and IL‐6 was measured by ELISA. Seventeen of the studied compounds inhibited NO and IL‐6 production over 50% at 100 μM concentrations. IC₅₀ values of the best inhibitors were 21 μM/24 μM (NO/IL‐6) for compound 12 and 30 μM/10 μM (NO/IL‐6) for compound 20 . The main result was that the substitution with 7‐(2‐oxoalkoxy) group improved the anti‐inflammatory properties of most of the investigated 7‐hydroxycoumarins.     

Capillary zone electrophoresis of lipoarabinomannan by multi-layered concentration

The present article describes a capillary zone electrophoresis method which relies on a multilayered water-alkali solvent stacking with online ionization to enhance detection of mannose, arabinose, and their oligosaccharides, which are used as the migration profile standards but are also the distinctive structural components of lipoarabinomannan. Lipoarabinomannan is detected in patients having tuberculosis. The capillary electrophoresis method with ionization of the whole saccharides without degradation in alkaline solution inside the capillary is based on the structural deprotonation of the molecules under ultrahigh pH conditions. The validation of the capillary electrophoresis parameters revealed that the 15-fold electrolyte–water-injection plug allowed detection of one-third lower concentrations than detected without online concentration. For the first time, the better detectability was seen especially for highly polymerized, but otherwise poorly ionized, arabinooctaose. The applicability of the method for detecting whole large biological saccharide complexes was confirmed by the glycolipid lipoarabinomannan. For the first time also, the migration of the indestructible lipoarabinomannan was detected together with oligosaccharides used representing the capping units, namely mannose, mannobiose, and mannotriose. The myo-inositol-phosphate-lipid unit was seen to migrate separately from the arabinomannan, since it was hydrolyzed from one lipoarabinomannan product under alkaline conditions in capillary electrophoresis.     

In vitro degradation of porous poly(dl-lactide-co-glycolide) (PLGA)/bioactive glass composite foams with a polar structure

In vitro degradation of porous 50/50, 70/30 and 90/10 PLGA (poly(dl-lactide-co-glycolide)) foams and PLGA/bioactive glass (20 wt%) composite foams was studied up to 16 weeks in TRIS (pH 7.4; 37 °C). Polar PLGA/bioactive glass composite films were prepared by applying the bioactive glass (S53P4) on one side of the composite. Porous foams were made by solvent casting and pressure quenching with CO₂. The fabricated foams had an initial pore size of 50-500 μm and thickness of 2-2.5 mm. In vitro degradation of the prepared foams was evaluated after 1, 2, 4, 6, 8, 12 and 16 weeks. Weight loss, water uptake, molecular mass and the amount of dissolved bioactive glass were measured after each time period. Changes in pore morphology were analysed with SEM. The present in vitro results will be evaluated and compared with the results from ongoing animal studies where comparable implants are used for bone defect treatment under non-load-bearing conditions.     

Effects of prolonged oral reading on F0, SPL, subglottal pressure and amplitude characteristics of glottal flow waveforms

The effects of prolonged (5x45 minute) reading (vocal loading) on fundamental frequency (F0), sound pressure level (SPL), subglottal (intraroral) pressure (p), and two glottal flow waveform parameters (AC amplitude of glottal flow, f, and negative peak amplitude of differentiated flow (d) of normal female and male subjects (N = 80) were studied. Two rest (morning and noon) and three loading (two in the morning and one in the afternoon) samples were recorded and analyzed. The glottal waveforms were obtained by inverse filtering of the acoustic pressure waveforms of speaking voice samples. The analyses were based on measurement and inverse filtering of the first stressed syllable of "paappa" words repeated 3x5 times for normal, as soft as possible, and as loud as possible phonation. In normal phonation the parameter values changed statistically significantly due to loading. In many cases the values obtained in the morning samples changed after the first loading session. This is interpreted as a vocal "warming-up effect." Especially in soft phonation p, d, and f were sensitive indicators of vocal loading. In both normal and soft phonation, the SPL, p, d, and f values tended to rise due to prolonged reading in the morning and afternoon samples, indicating increased effort (normal phonation) and a rise in the phonatory threshold (soft phonation). The lunch break vocal rest ("rest effect") considerably affected the parameter values in many cases.     

Channel selective scanning tunneling spectroscopy

In this paper we simulate STM and STS experiments for CO monomers and dimers on Cu(1 1 1) surface. We show that the contrast of STM images can be attributed to interference effects between tunneling channels, and suggest that functionalizing the microscope tip improves the channel selectivity of STM. Furthermore, we show that voltage and position dependent tunneling spectra also reflect the same interference effects, but adds the energy resolution to the channel analysis. Especially in the case of nonresonant tunneling, STS measures local density of states only indirectly. The present study suggests that STS in constant height mode can be used in investigating the phase and energy sensitivity of tunneling channels in adsorbate molecules and nanostructures.     

A comparison of the prevalence of vocal symptoms among teacher students and other university students

Studies focusing on different groups of students show that the prevalence of vocal symptoms and voice disorder vary depending on the study populations. A previous study of vocal symptoms and voice disorders among teacher students has shown that 20% of the students studying to become teachers in comprehensive schools and upper secondary schools reported frequently occurring vocal symptoms, ie, two symptoms or more occurring weekly or more often during the past year, and that most of these students had an organic voice disorder. This raised the question of whether other university students would also report similar, frequently occurring vocal symptoms. A questionnaire was distributed to 220 students of several faculties at the University of Turku, Finland. The results were compared with the results of a study of vocal symptoms reported by 175 students studying to become teachers. This comparison showed that students in general reported frequently occurring vocal symptoms, whereas the students studying to become teachers reported a greater number of frequently occurring symptoms than did other students at the university.     

Cooperative Ligands in Dissolution of Gold

Development of new, environmentally benign dissolution methods for metallic gold is driven by needs in the circular economy. Gold is widely used in consumer electronics, but sustainable and selective dissolution methods for Au are scarce. Herein, we describe a quantitative dissolution of gold in organic solution under mild conditions by using hydrogen peroxide as an oxidant. In the dissolution reaction, two thiol ligands, pyridine-4-thiol and 2-mercaptobenzimidazole, work in a cooperative manner. The mechanistic investigations suggest that two pyridine-4-thiol molecules form a complex with Au⁰ that can be oxidized, whereas the role of inexpensive 2-mercaptobenzimidazole is to stabilize the formed Au^I species through a ligand exchange process. Under optimized conditions, the reaction proceeds vigorously and gold dissolves quantitatively in two hours. The demonstrated ligand-exchange mechanism with two thiols allows to drastically reduce the thiol consumption and may lead to even more effective gold dissolution methods in the future.