skip to main content

Title: Screw dislocation-induced pyramidal crystallization of dendron-like macromolecules featuring asymmetric geometry
We report herein that dendron-shaped macromolecules AB n crystallize into well-ordered pyramid-like structures from mixed solvents, instead of spherical motifs with curved structures, as found in the bulk. The design of the asymmetric molecular architecture and the choice of mixed solvents are applied as strategies to manipulate the crystallization process. In mixed solvents, the solvent selection for the Janus macromolecule and the existence of dominant crystalline clusters contribute to the formation of flat nanosheets. Whereas during solvent evaporation, the bulkiness of the asymmetric macromolecules easily creates defects within 2D nanosheets which lead to their spiral growth through screw dislocation. The size of the nanosheets and the growth into 2D nanosheets or 3D pyramidal structures can be regulated by the solvent ratio and solvent compositions. Moreover, macromolecules of higher asymmetry generate polycrystals of lower orderliness, probably due to higher localized stress.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Chemical Science
Page Range / eLocation ID:
12130 to 12137
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    ABSTRACT: The dosing of peptide and protein therapeutics is complicated by rapid clearance from the blood pool and poor cellular membrane permeability. Encapsulation into nanocarriers such as liposomes or polymersomes has long been explored to overcome these limitations, but manufacturing challenges have limited clinical translation by these approaches. Recently, inverse Flash NanoPrecipitation (iFNP) has been developed to produce highly loaded polymeric nanocarriers with the peptide or protein contained within a hydrophilic core, stabilized by a hydrophobic polymer shell. Encapsulation of proteins with higher-order structure requires understanding how processing may affect their conformational state. We demonstrate a combined experimental/simulation approach to characterize protein behavior during iFNP processing steps using the Trp-cage protein TC5b as a model. Explicit-solvent fully atomistic molecular dynamics simulations with enhanced sampling techniques are coupled with two-dimensional heteronuclear multiple-quantum coherence nuclear magnetic resonance spectroscopy (2D-HMQC NMR) and circular dichroism to determine the structure of TC5b during mixed-solvent exposure encountered in iFNP processing. The simulations involve atomistic models of mixed solvents and protein to capture the complexity of the hydrogen bonding and hydrophobic interactions between water, dimethylsulfoxide (DMSO), and the protein. The combined analyses reveal structural unfolding of the protein in 11 M DMSO but confirm complete refolding after release from the polymeric nanocarrier back into an aqueous phase. 
    more » « less
  2. null (Ed.)
    Data informatics approaches were applied to the Cambridge Structural Database (CSD) in an effort to discern fundamental trends related to the preparation, occurrence, and general properties of organic solvates. Foremost, the 50 most abundant solvate classes in the CSD were identified through SMILES string matching implemented through CSD Python API, and their relative occurrence rates were compared against data reported 20 years prior. These two sets of data suggest that solvate preparation methods have become less diverse over that time period with an increasing fraction derived from a smaller subset of solvents, though the relative abundance of hetero-solvates containing more than one type of solvent molecule simultaneously increased. A subsequent SMILES string matching facilitated the identification of ∼2700 pairs of solvate and solvent-free structures from the top 10 solvate classes. Data from the two related groups showed statistical differences in both the lattice symmetries and packing fractions. Solvates exhibited an inherent bias favoring triclinic lattice symmetry, which is likely related to the larger number of unique molecular components in the asymmetric unit. More surprising was the fact that solvates that do not exhibit disorder statistically had lower packing fractions than their solvent-free analogues. While solvate formation may in fact be a means to achieve phases with higher packing efficiency for some organic molecules, the data indicate this is not a general trend. 
    more » « less
  3. Abstract

    2D nanosheets have been widely explored as electrode materials owing to their extraordinarily high electrochemical activity and fast solid‐state diffusion. However, the scalable electrode fabrication based on this type of material usually suffers from severe performance losses due to restricted ion‐transport kinetics in a large thickness. Here, a novel strategy based on evaporation‐induced assembly to enable directional ion transport via forming vertically aligned nanosheets is reported. The orientational ordering is achieved by a rapid evaporation of mixed solvents during the electrode fabrication process. Compared with conventional drop‐cast electrodes, which exhibit a random arrangement of the nanosheets and obvious decrease of rate performance with increasing thickness, the electrode based on the vertically aligned nanosheets is able to retain the original high rate capability even at high mass loadings and electrode thickness. Combined electrochemical and structural characterization reveals the electrode composed of orientation‐controlled nanosheets to possess lower charge‐transfer resistances, leading to more complete phase transformation in the active material.

    more » « less
  4. Liquid phase exfoliation (LPE) is a method that can be used to produce bulk quantities of two-dimensional (2D) nanosheets from layered van der Waals (vdW) materials. In recent years, LPE has been applied to several non-vdW materials with anisotropic bonding to produce nanosheets and platelets, but it has not been demonstrated for materials with strong isotropic bonding. In this paper, we demonstrate the exfoliation of boron carbide (B 4 C), the third hardest known material, into ultrathin nanosheets. B 4 C has a structure consisting of strongly bonded boron icosahedra and carbon chains, but does not have anisotropic cleavage energies to suggest that it can be readily cleaved into nanosheets. B 4 C has been widely studied for its very high melting point, high mechanical strength, and chemical stability, as well as its zero- and one-dimensional nanostructured forms. Herein, ultrathin nanosheets are successfully prepared by sonication of B 4 C powder in organic solvents and are characterized by microscopy and spectroscopy. Density functional theory (DFT) simulations reveal that B 4 C can be cleaved along several different crystallographic planes with similar energetic favourability, facilititated by an unexpected mechanism of breaking boron icosahedra and forming new boron-rich cage structures at the surface. Atomic force microscopy (AFM) shows that the nanosheets produced by LPE are as thin as 5 nm, with an average thickness of 31.4 nm and average area of 16 000 nm 2 . Raman spectroscopy shows that many of the nanosheets exhibit additional carbon-rich peaks that change with laser irradiation, which are attributed to atomic rearrangements and amorphization at the nanosheet surfaces, consistent with the diverse cleavage planes. High-resolution transmission electron microscopy (HRTEM) demonstrates that many different cleavage planes exist among the exfoliated nanosheets, in agreement with DFT simulations. This work elucidates the exfoliation mechanism of 2D B 4 C and suggests that LPE can be applied to generate nanosheets from a variety of non-layered and non-vdW materials. 
    more » « less
  5. Two-dimensional infrared (2D IR) spectroscopy, infrared pump–infrared probe spectroscopy, and density functional theory calculations were used to study vibrational relaxation by ring and carbonyl stretching modes in a series of methylated xanthine derivatives in acetonitrile and deuterium oxide (heavy water). Isotropic signals from the excited symmetric and asymmetric carbonyl stretch modes decay biexponentially in both solvents. Coherent energy transfer between the symmetric and asymmetric carbonyl stretching modes gives rise to a quantum beat in the time-dependent anisotropy signals. The damping time of the coherent oscillation agrees with the fast decay component of the carbonyl bleach recovery signals, indicating that this time constant reflects intramolecular vibrational redistribution (IVR) to other solute modes. Despite their similar frequencies, the excited ring modes decay monoexponentially with a time constant that matches the slow decay component of the carbonyl modes. The slow decay times, which are faster in heavy water than in acetonitrile, approximately match the ones observed in previous UV pump–IR probe measurements on the same compounds. The slow component is assigned to intermolecular energy transfer to solvent bath modes from low-frequency solute modes, which are populated by IVR and are anharmonically coupled to the carbonyl and ring stretch modes. 2D IR measurements indicate that the carbonyl stretching modes are weakly coupled to the delocalized ring modes, resulting in slow exchange that cannot explain the common solvent-dependence. IVR is suggested to occur at different rates for the carbonyl vs ring modes due to differences in mode-specific couplings and not to differences in the density of accessible states.

    more » « less