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The liquid-vapor-phase equilibrium properties of the previously developed TIP4P-Ew water model have been studied using thermodynamic integration free-energy simulation techniques in the temperature range of 274–400 K. We stress that free-energy results from simulations need to be corrected in order to be compared to the experiment. This is due to the fact that the thermodynamic end states accessible through simulations correspond to fictitious substances (classical rigid liquids and classical rigid ideal gases) while experiments operate on real substances (liquids and real gases, with quantum effects). After applying analytical corrections the vapor pressure curve obtained from simulated free-energy changes is in excellent agreement with the experimental vapor pressure curve. The boiling point of TIP4P-Ew water under ambient pressure is found to be at 370.3±1.9 K, about 7 K higher than the boiling point of TIP4P water (363.7±5.1 K; from simulations that employ finite range treatment of electrostatic and Lennard-Jones interactions). This is in contrast to the approximately +15 K by which the temperature of the density maximum and the melting temperature of TIP4P-Ew are shifted relative to TIP4P, indicating that the temperature range over which the liquid phase of TIP4P-Ew is stable is narrower than that of TIP4P and resembles more that of real water. The quality of the vapor pressure results highlights the success of TIP4P-Ew in describing the energetic and entropic aspects of intermolecular interactions in liquid water. [ABSTRACT FROM AUTHOR]

A re-parameterization of the standard TIP4P water model for use with Ewald techniques is introduced, providing an overall global improvement in water properties relative to several popular nonpolarizable and polarizable water potentials. Using high precision simulations, and careful application of standard analytical corrections, we show that the new TIP4P-Ew potential has a density maximum at ∼1 °C, and reproduces experimental bulk-densities and the enthalpy of vaporization, DHvap , from -37.5 to 127 °C at 1 atm with an absolute average error of less than 1%. Structural properties are in very good agreement with x-ray scattering intensities at temperatures between 0 and 77 °C and dynamical properties such as self-diffusion coefficient are in excellent agreement with experiment. The parameterization approach used can be easily generalized to rehabilitate any water force field using available experimental data over a range of thermodynamic points. [ABSTRACT FROM AUTHOR]

A guanidine-based catalyst, first involving acetyl transfer to the catalyst and the second involving only hydrogen bonding to the catalyst was used to study two alternative mechanisms for the ring-opening polymerization of L-lactide. The results showed that the hydrogen bonding pathway is favored over the acetyl transfer pathway.

ABSTRACT This study reports an application of trichloroethanol (TCE) as a bifunctional initiator for the synthesis of block copolymers (BCPs) by organocatalyzed ring-opening polymerization (OROP) and atom transfer radical polymerization (ATRP). TCE was employed to synthesize a low dispersity poly (valerolactone) macroinitiator, which was subsequently used for the ATRP of tert-butyl methacrylate. While it is known that TCE can serve as an initiator in ATRP, the ability to induce polymerization under OROP is reported for the first time. The formation of well-defined BCPs was confirmed by gel permeation chromatography and 1H NMR. Computational studies were performed to obtain a molecular-level understanding of the ring-opening polymerization mechanism involving TCE as initiator. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 563-569 [ABSTRACT FROM AUTHOR]

We describe investigations with B3LYP density functionaltheoryto probe mechanisms for the organocatalyzed depolymerization of poly(ethylene)terephthalate (PET) into ester and amide products. These investigationsutilize model systems involving the trans-esterification and amidationof methylbenzoate (MB) with ethylene glycol (EG), ethylenediamine(EDA), and ethanolamine (EA) organocatalyzed by 1,5,7-triazabicyclododecene(TBD) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Mechanisms forreactions in which TBD acts as the lone catalyst have been comparedwith pathways in which TBD and DBU catalyze these processes with anadditional molecule of the amine or alcohol acting as a cocatalyst.Calculations suggest that the combination of an organocatalyst witha molecule of an alcohol or amine cocatalyst is slightly more activatingthan a lone catalyst. Our results predict that nucleophilic attackis the rate-determining step in reactions involving EDA and EG andthat TBD is a better catalyst than DBU in the amidation of MB withEDA; in addition, both organocatalysts activate alcohols more thanamines during nucleophilic attack. Amidation and trans-esterificationpossess similar barriers for reactions involving EA; but the amide,which is the thermodynamic product, is preferentially formed insteadof the ester. [ABSTRACT FROM AUTHOR]

(-)-Sparteine is a proven organocatalyst for the ring-opening polymerization (ROP) of l-lactide, which affords polymers of controlled molecular weight and narrow polydispersity. The recent worldwide shortage of (-)-sparteine has necessitated the identification of simple and cost-effective replacement ROP catalysts. A series of commercially available molecules was first identified through molecular modeling and then subsequently investigated for polymerizing l-lactide. The modeling proved very useful at predicting spatial relationships and nitrogen geometries that greatly aided in the rapid identification of various alkyl amines as alternative organocatalysts.

Recognize this! A hydrogen-bonding motif based on hexafluorinated alcohol derivatives (see picture; O red, F yellow) activates electrophilic substrates. The catalytic activity of the hydrogen-bonded systems was demonstrated for the ring-opening polymerization of a variety of strained heterocycles. Narrowly dispersed polymers with predictable molecular weights were obtained with end-group fidelity.