Comments on "Two-mass models of the vocal cords for natural sounding voice synthesis"

Koizumi et al. [J. Acoust. Soc. Am. 82, 1179-1192 (1987)] have proposed a way to incorporate mucosal waves into previous two-mass mechanical models of the vocal folds. This was accomplished by allowing the mass of the masses to vary with time. The equations of motion Koizumi et al. used to mathematically describe this model neglected terms from the time rate of change of momentum of Newton's second law. In this letter, approximations of the magnitude of this term indicate that it must not be neglected.     

Tandem addition beta-lithiation-alkylation sequence on alpha,beta-unsaturated aldehydes

A tandem reaction between (E)-cinnamaldehyde, 1a, and phenyllithium affording beta-substituted dihydrochalcones was recently reported. NMR spectroscopic studies on the reaction mixture, as well as isotopic exchange reactions and trapping of two intermediates, provide clues on the several mechanistic steps of this new reaction. Extended studies revealed that beta-alkyl-substituted alpha,beta-unsaturated aldehydes and aliphatic lithium reagents did not afford good yields of the tandem reaction products, while aromatic lithium reagents gave good results. The aggregation features of the aryllithium reagents and the extended charged delocalization effects are considered to promote beta-selectivity. This approach provides a convenient route for the synthesis of a wide variety of beta-alkyl-substituted dihydrochalcones.     

Biodegradable polymers derived from natural fatty acids

A new class of polyanhydrides synthesized from nonlinear hydrophobic fatty acid esters, based on ricinoleic, maleic acid, and sebacic acid, possessed desired physico-chemical and mechanical properties for use as drug carriers. The polymers were synthesized by melt condensation to yield film-forming polymers with molecular weights exceeding 100,000. Their rate of elimination from rats in the course of about 2 months was faster than that found for similar polyanhydrides previously tested. In vitro studies showed that these polymers underwent rapid degradation in the first 10 days. The drug release followed first-order kinetics, showing a rapid drug release rate in the first 10 days which correlated with the degradation of the polymers. The fatty acid ester monomers underwent in vitro enzymatic degradation to the natural starting acids. Tests in rats demonstrated their toxicological inertness and biodegradability. © 1995 John Wiley & Sons, Inc.     

Entrapped energy in chiral solutions: quantification and information capacity

A homogeneous solution of a chiral substance stores a residual chemical potential, related to its overall anisotropy. Therefore, by mixing solutions of opposite enantiomers, heat release may take place, corresponding to the mutual anisotropy annulment. In the following study we present proofs for this fundamental, yet unexplored, prediction by measuring the heat released upon mixing of aqueous solutions of D-proline with L-proline, as well as D-alanine with L-alanine, using isothermal titration calorimetry. Heat release in the range of 0.6-6 cal/mol was detected in these intermolecular racemizations at 30 degrees C. Its magnitude varied linearly with the apparent optical rotation, which complied with the possibility that the hydration envelope coating the chiral molecule is of a long-range condensed and asymmetrical configuration that can expand by integration with adjacent hydration envelopes. The ordered water in such hydration layers constitutes regions of "negative entropy", a basic medium for information storage. On the basis of our findings, a fundamental expression which combines entropy, information capacity, and thermal energy is proposed.     

[(Ph)2(NMe2)C(OLi)⋅THF]2: Crystal Structure of the Tetrahedral Intermediate Formed in the Reaction of N,N-Dimethylbenzamide and Phenyllithium

Information on the reaction path for the 1,2-eliminiation of LiNMe₂ to form benzophenone is provided by the X-ray crystal structure analysis of the tetrahedral adduct [(Ph)₂(NMe₂)C(OLi)⋅THF]₂ (a portion of the structure is shown schematically), which is prepared from N,N-dimethylbenzamide and phenyllithium. A N1−Li1 interaction, which is not observed, would lead to loss of the anomeric effect (n_N→σ^*_C−O) as well as high conformational strain along the C1−N1 bond.     

Effect of PLGA block molecular weight on gelling temperature of PLGA‐PEG‐PLGA thermoresponsive copolymers

Thermoresponsive, biodegradable polymeric hydrogel networks are used widely in medicinal applications. Poly(d ,l ‐lactic acid‐co‐glycolic acid)‐b‐poly(ethylene glycol)‐b‐poly(d ,l ‐lactic acid‐co‐glycolic acid) (PLGA‐PEG‐PLGA) triblock copolymers exhibit a sol–gel transition upon heating. The effect of PLGA block and PEG chain molecular weights (MWs) on the gelling temperature of polymer aqueous solution (20% w/w) is described. All polymer solutions convert into a hard gel within 2 °C of the gelling temperature. The release properties of the gels were displayed using paracetamol as a representative drug. A linear relation is described between the gelling temperature and PLGA block MW. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 35–39     

An Apparatus for Production of Isotopically and Spin-Enriched Hydrogen for Induced Polarization Studies

An apparatus for the production of hydrogen for hydrogenation-induced polarization studies was developed. The apparatus provides hydrogen gas from a solid source, thereby simplifying the requirement for siting of the apparatus. The produced hydrogen can be either isotopically enriched (with deuterium) or spin-enriched (with parahydrogen). These specialty gases were produced at small predetermined quantities and ambient pressure. The properties of the hydrogen mixtures were characterized by gas-phase nuclear magnetic resonance. The T ₁ of the hydrogen mixtures (3.7 ms) was not affected by para-enrichment. The line width of the hydrogen signal in the para-enriched mixture was 34% larger. The reaction of ethyl propiolate hydrogenation served to evaluate the performance in terms of the ability to create hyperpolarized states. In this reaction, a polarization of 11.2% was measured for protons. Consecutive alkene hydrogenations as well as hydrogenations of the catalyst ligand resulted in additional hyperpolarized signals which were systematically assigned.