14 research outputs found
Determining Lennard-Jones Parameters Using Multiscale Target Data through Presampling-Enhanced, Surrogate-Assisted Global Optimization
Force field-based
models are a Newtonian mechanics approximation
of reality and are inherently noisy. Coupling models from different
molecular scale domains (including single, gas-phase molecules up
to multimolecule, condensed phase ensembles) is difficult, which is
also the case for finding solutions that transfer well between the
scales. In this contribution, we introduce a surrogate-assisted algorithm
to optimize Lennard-Jones parameters for target data from different
scale domains to overcome the difficulties named above. Specifically,
our approach combines a surrogate-assisted global evolutionary optimization
method with a presampling phase that takes advantage of one scale
domain being less computationally expensive to evaluate. The algorithm’s
components were evaluated individually, elucidating their individual
merits. Our findings show that the process of parametrizing force
fields can significantly benefit from both the presampling method,
which alleviates the need to have a good initial guess for the parameters,
and the surrogate model, which improves efficiency
Postsynthetic Modification of Metal–Organic Frameworks through Nitrile Oxide–Alkyne Cycloaddition
Postsynthetic modification
of metal–organic frameworks is an important method to tailor
their properties. We report on the nitrile oxide–alkyne cycloaddition
(NOAC) as a modification tool, a reaction requiring neither strained
alkynes nor a catalyst. This is demonstrated with the reaction of
nitrile oxides with PEPEP-PIZOF-15 and -19 at room temperature. PIZOF-15
and -19 are porous Zr-based MOFs (BET surface areas 1740 and 960 m<sup>2</sup> g<sup>–1</sup>, respectively) consisting of two mutually
interpenetrating UiO-type frameworks with linkers of the type <sup>–</sup>O<sub>2</sub>CÂ[PE-PÂ(R<sup>1</sup>,R<sup>2</sup>)-EP]ÂCO<sub>2</sub><sup>–</sup> (P, phenylene; E, ethynylene; R<sup>1</sup> and R<sup>2</sup>, side chains at the central benzene ring with
R<sup>1</sup> = R<sup>2</sup> = OCH<sub>2</sub>Cî—¼CH or R<sup>1</sup> = OCH<sub>2</sub>Cî—¼CH and R<sup>2</sup> = OÂ(CH<sub>2</sub>CH<sub>2</sub>O)<sub>3</sub>Me). Their syntheses, using benzoic
acid as a modulator, and their characterization are reported herein.
The propargyloxy (OCH<sub>2</sub>Cî—¼CH) side chains contain
the ethyne moieties needed for NOAC. Formation of nitrile oxides through
oxidation of oximes in aqueous ethanolic solution in the presence
of PEPEP-PIZOF-15 and -19 resulted in the reaction of 96–100%
of the ethyne moieties to give isoxazoles. Thereby the framework was
preserved. The type of nitrile oxide RCNO was greatly varied with
R being isopentyl, tolyl, 2-pyridyl, and pentafluorophenyl. A detailed
NMR spectroscopic investigation showed the formation of the 3,5-disubstituted
isoxazole to be clearly favored (≥96%) over that of the constitutional
isomeric 3,4-disubstituted isoxazole, except for one example