: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for ‘one-pot’ chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules.

Modular and predictable assembly of porous organic molecular crystals

Developing a comprehensive method to compute bond orders is a problem that has eluded chemists since Lewis's pioneering work on chemical bonding a century ago. Here, a computationally efficient method solving this problem is introduced and demonstrated for diverse materials including elements from each chemical group and period. The method is applied to non-magnetic, collinear magnetic, and non-collinear magnetic materials with localized or delocalized bonding electrons. Examples studied include the stretched O2 molecule, 26 diatomic molecules, 3d and 5d transition metal solids, periodic materials with 1 to 8748 atoms per unit cell, a biomolecule, a hypercoordinate molecule, an electron deficient molecule, hydrogen bound systems, transition states, Lewis acid–base complexes, aromatic compounds, magnetic systems, ionic materials, dispersion bound systems, nanostructures, and other materials. From near-zero to high-order bonds were studied. Both the bond orders and the sum of bond orders for each atom are accurate across various bonding types: metallic, covalent, polar-covalent, ionic, aromatic, dative, hypercoordinate, electron deficient multi-centered, agostic, and hydrogen bonding. The method yields similar results for correlated wavefunction and density functional theory inputs and for different SZ values of a spin multiplet. The method requires only the electron and spin magnetization density distributions as input and has a computational cost scaling linearly with increasing number of atoms in the unit cell. No prior approach is as general. The method does not apply to electrides, highly time-dependent states, some extremely high-energy excited states, and nuclear reactions.

/pdf/introducing-ddec6-atomic-population-analysis-part-3-2apvo8oc0k.pdf

Introducing DDEC6 atomic population analysis: part 3. Comprehensive method to compute bond orders

Reversible addition–fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are the two most common controlled radical polymerization methods. Both methods afford functional polymers with a predefined length, composition, dispersity and end group. Further, RAFT and ATRP tame radicals by reversibly converting active polymeric radicals into dormant chains. However, the mechanisms by which the ATRP and RAFT methods control chain growth are distinct, so each method presents unique opportunities and challenges, depending on the desired application. This Perspective compares RAFT and ATRP by identifying their mechanistic strengths and weaknesses, and their latest synthetic applications. Reversible addition–fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are evaluated in terms of their mechanistic strengths and weaknesses, versatility and latest synthetic advances.

A comparison of RAFT and ATRP methods for controlled radical polymerization

Density functional theory (DFT) is the most widely-used electronic structure approximation across chemistry, physics, and materials science. Every year, thousands of papers report hybrid DFT simulations of chemical structures, mechanisms, and spectra. Unfortunately, hybrid DFT's accuracy is ultimately limited by tradeoffs between over-delocalization and under-binding. This review summarizes these tradeoffs, and introduces six modern attempts to go beyond them while maintaining hybrid DFT's relatively low computational cost: DFT+U, self-interaction corrections, localized orbital scaling corrections, local hybrid functionals, real-space nondynamical correlation, and our rung-3.5 approach. The review concludes with practical suggestions for DFT users to identify and mitigate these tradeoffs' impact on their simulations.

Replacing hybrid density functional theory: motivation and recent advances

A facile and efficient two-step synthesis of p-substituted tris(2-pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis, p-Cl substituents in tris(4-chloro-2-pyridylmethyl)amine (TPMA3Cl ) were replaced in one step and high yield by electron-donating cyclic amines (pyrrolidine (TPMAPYR ), piperidine (TPMAPIP ), and morpholine (TPMAMOR )) by nucleophilic aromatic substitution. The [CuII (TPMANR2 )Br]+ complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [CuII (TPMA)Br]+ , indicating >3 orders of magnitude higher ATRP activity. [CuI (TPMAPYR )]+ exhibited the highest reported activity for Br-capped acrylate chain ends in DMF, and moderate activity toward C-F bonds at room temperature. ATRP of n-butyl acrylate using only 10-25 part per million loadings of [CuII (TPMANR2 )Br]+ exhibited excellent control.

p-Substituted Tris(2-pyridylmethyl)amines as Ligands for Highly Active ATRP Catalysts: Facile Synthesis and Characterization.

Orbitals and orbital overlap are important concepts in chemistry but are seldom incorporated into medicinal chemistry analyses of drug–target interactions. Our orbital overlap distance D(r) quantifies the size of the “test orbital” that best overlaps with a system’s computed orbitals at point r. The overlap distance provides information about all of the occupied orbitals across a molecule, extending frontier orbital (Fukui) analysis and complementing widely used maps of the surface electrostatic potential. We present the first tests of the overlap distance for problems in medicinal chemistry. The overlap distance quantifies the different coordination chemistries of pairs of metal cations possessing similar charges and ionic radii. Combining the overlap distance and electrostatic potential provides a rich picture of the binding sites for chemically “hard” versus “soft” cations in formylglycine-generating enzyme and extends frontier orbital analysis in quantifying the chemistry of promiscuous binders. We co...

Arshad Mehmood

Papers

p-Substituted Tris(2-pyridylmethyl)amines as Ligands for Highly Active ATRP Catalysts: Facile Synthesis and Characterization.

An Orbital-Overlap Complement to Ligand and Binding Site Electrostatic Potential Maps

Crystal engineering and electrostatic properties of co-crystals of pyrimethamine with benzoic acid and gallic acid

Experimental and theoretical charge density analysis of skin whitening agent kojic acid

The electron delocalization range in stretched bonds