Epitaxially Grown Mechanically Robust 2D Thin Film of Secondary Interactions Led Molecularly Woven Material

Molecularly woven materials with striking mechanical resilience, and 2D controlled topologies like textiles, fishing nets, and baskets are highly anticipated. Molecular weaving exclusively apprehended by the secondary interactions expanding to laterally grown 2D self-assemblies with retained crystalline arrangement is stimulating. The interlacing entails planar molecules screwed together to form 2D woven thin films. Here, secondary interactions led 2D interlaced molecularly woven material (2° MW) built by 1D helical threads of organic chromophores twisted together via end-to-end CH···O connections, held strongly at inter-crossing by multiple OH···N interactions to prevent slippage is presented. Whereas, 1D helical threads with face-to-face O-H···O connections sans interlacing led the non-woven material (2° NW). The polarity-driven directionality in 2° MW led the water-actuated epitaxial growth of 2D-sheets to lateral thin films restricted to nano-scale thickness. The molecularly woven thin film is self-healing, flexible, and mechanically resilient in nature, while maintaining the crystalline regularity is attributed to the supple secondary interactions (2° ).

On the Coexistence of the Carbene⋯H-D Hydrogen Bond and Other Accompanying Interactions in Forty Dimers of N-Heterocyclic-Carbenes (I, IMe2, IiPr2, ItBu2, IMes2, IDipp2, IAd2; I = imidazol-2-ylidene) and Some Fundamental Proton Donors (HF, HCN, H2O, MeOH, NH3)

The subject of research is forty dimers formed by imidazol-2-ylidene (I) or its derivative (IR2) obtained by replacing the hydrogen atoms in both N-H bonds with larger important and popular substituents of increasing complexity (methyl = Me, iso-propyl = iPr, tert-butyl = tBu, phenyl = Ph, mesityl = Mes, 2,6-diisopropylphenyl = Dipp, 1-adamantyl = Ad) and fundamental proton donor (HD) molecules (HF, HCN, H2O, MeOH, NH3). While the main goal is to characterize the generally dominant C⋯H-D hydrogen bond engaging a carbene carbon atom, an equally important issue is the often omitted analysis of the role of accompanying secondary interactions. Despite the often completely different binding possibilities of the considered carbenes, and especially HD molecules, several general trends are found. Namely, for a given carbene, the dissociation energy values of the IR2⋯HD dimers increase in the following order: NH3< H2O < HCN ≤ MeOH ≪ HF. Importantly, it is found that, for a given HD molecule, IDipp2 forms the strongest dimers. This is attributed to the multiplicity of various interactions accompanying the dominant C⋯H-D hydrogen bond. It is shown that substitution of hydrogen atoms in both N-H bonds of the imidazol-2-ylidene molecule by the investigated groups leads to stronger dimers with HF, HCN, H2O or MeOH. The presented results should contribute to increasing the knowledge about the carbene chemistry and the role of intermolecular interactions, including secondary ones.

Molecular Interaction of Protein-Pigment C-Phycocyanin with Bovine Serum Albumin in a Gomphosis Structure Inhibiting Amyloid Formation

Accumulation of amyloid fibrils in organisms accompanies many diseases. Natural extracts offer an alternative strategy to control the process with potentially fewer side effects. In this study, the inhibition of C-phycocyanin from Spirulina sp. on amyloid formation of bovine serum albumin (BSA) during a 21-day incubation was investigated using fluorescence and circular dichroism (CD), and mechanisms were explored via kinetic fitting and molecular docking. C-phycocyanin (0-50 µg/mL) hindered the amyloid formation process of BSA with increased half-lives (12.43-17.73 days) based on fluorescence intensity. A kinetic model was built and showed that the k₁ decreased from 1.820 × 10^-2 d^-1 to 2.62 × 10^-3 d^-1 with the increase of C-phycocyanin, while k₂ showed no changes, indicating that the inhibition of BSA fibrillation by C-phycocyanin occurred in a spontaneous process instead of self-catalyzed one. CD results show that C-phycocyanin inhibited conformational conversion (α-helices and β-sheets) of BSA from day 6 to day 18. Molecular docking suggested that C-phycocyanin may hinder BSA fibrillation by hydrogen-bonding > 6 of 27 α-helices of BSA in a gomphosis-like structure, but the unblocked BSA α-helices might follow the self-catalytic process subsequently.

Secondary interaction between MDMX and p53 core domain inhibits p53 DNA binding

The MDMX oncoprotein is an important regulator of tumor suppressor p53 activity during embryonic development. Despite sequence homology to the ubiquitin E3 ligase MDM2, MDMX depletion activates p53 without significant increase in p53 level, implicating a degradation-independent mechanism. We present evidence that MDMX inhibits the sequence-specific DNA binding activity of p53. This function requires the cooperation between MDMX and CK1α, and phosphorylation of S289 on MDMX. Depletion of MDMX or CK1α increases p53 DNA binding without stabilization of p53. A proteolytic fragment release assay revealed that in the MDMX-p53 complex, the MDMX acidic domain and RING domain interact stably with the p53 DNA binding domain. These interactions are referred to as secondary interactions because they only occur after the canonical-specific binding between the MDMX and p53 N termini, but exhibit significant binding stability in the mature complex. CK1α cooperates with MDMX to inhibit p53 DNA binding by further stabilizing the MDMX acidic domain and p53 core domain interaction. These results suggest that secondary intermolecular interaction is important in p53 regulation by MDMX, which may represent a common phenomenon in complexes containing multidomain proteins.