Chirality-assisted synthesis (CAS) is a general approach to control the shapes of large molecular strips. CAS is based on enantiomerically pure building blocks that are designed to strictly couple in a single geometric orientation. Fully shape-persistent structures can thus be created, even in the form of linear chains. With CAS, selective recognition between large host and guest molecules can reliably be designed de novo. To demonstrate this concept, three C-shaped strips that can embrace a pillar[5]arene macrocycle were synthesized. The pillar[5]arene bound to the strips was a better host for electron-deficient guests than the free macrocycle. Experimental and computational evidence is provided for these unique cooperative interactions to illustrate how CAS could open the door towards the precise positioning of functional groups for regulated supramolecular recognition and catalysis.

The electrochemical oxidation of ferrocenes having an H- or Li-terminated ethynyl group has been studied, especially as it relates to their covalent anchoring to carbon surfaces. The anodic oxidation of lithioethynylferrocene (1-Li) results in rapid loss of Li(+) and formation of the ethynyl-based radical FeCp(η(5)-C5H4)(C≡C), (1, Cp = η(5)-C5H5), which reacts with the electrode. Chemically modified electrodes (CMEs) were thereby produced containing strongly bonded, ethynyl-linked monolayers and electrochemically controlled multilayers. Strong attachments of ethynylferrocenes to gold and platinum surfaces were also possible. The lithiation/anodic oxidation process is a mirror analogue of the diazonium/cathodic reduction process for preparation of aryl-modified CMEs. A second method produced an ethynylferrocene-modified electrode by direct anodic oxidation of the H-terminated ethynylferrocene (1-H) at a considerably more positive potential. Both processes produced robust modified electrodes with well-defined ferrocene-based surface cyclic voltammetry waves that remained unchanged for as many as 10(4) scans. Ferrocene derivatives in which the ethynyl moiety was separated from the cyclopentadienyl ring by an ether group showed very similar behavior. DFT calculations were performed on the relevant redox states of 1-H, 1-Li, and 1, with emphasis on the ferrocenyl vs ethynyl character of their high valence orbitals. Whereas the HOMOs of both 1-H and 1-Li have some ethynyl character, the SOMOs of the corresponding monocations are strictly ferrocenium in makeup. Predominant ethynyl character returns to the highest valence orbitals after loss of Li(+) from [1-Li](+) or loss of H(+) from [1-H](2+). These anodic processes hold promise for the controlled chemical modification of carbon and other electrode surfaces by a variety of ethynyl or alkynyl-linked organic and metal-containing systems.

We report an original catalytic molecular tetrahedron. By threading through the cavity of the tetrahedron, polymeric substrates are unfolded or broken apart. Our catalyst distinguishes between polymer chains of different lengths, functionalizing the shorter polymers selectively over the longer ones-as a proof of concept for selective catalysis to modify polymers. Our findings advance the fundamental understanding of the thermodynamic and kinetic phenomena controlling the interactions between molecular cages and synthetic polymers, offering valuable ability to create complex materials in the future.

No abstract

Enantioselective electrophilic aromatic nitration methodology is needed to advance chirality-assisted synthesis (CAS). Reported here is an enantioselective aromatic nitration strategy operating with chiral diester auxiliaries,and it provides an enantioselective synthesis of aC 3v -symmetric tribenzotriquinacene (TBTQ). These axially-chiral structures are much sought-after building blocks for CAS, but they were not accessible prior to this work in enantioenriched form without resolution of enantiomers.T his nitration strategy controls the stereochemistry of threefold nitration reactions from above the aromatic rings with chiral diester arms.Dicarbonyl-to-arenium chelation rigidifies the reaction systems,s ot hat remote stereocenters position the ester-directing groups selectively over specific atoms of the TBTQ framework. Closely guided by computational design, am ore selective through-space directing arm was first predicted with density functional theory (DFT), and then confirmed in the laboratory,t o outperform the initial structural design. This enantio-and regioselective TBTQ synthesis opens anew pathwaytoaccess building blocks for CAS.Classical electrophilic aromatic nitration reactions are among the best known and most frequently employed aromatic transformations. [1] They readily proceed [2] with unactivated aromatic substrates and provide exquisite control over the number of NO 2 groups introduced, unlike for instance most Friedel-Crafts alkylations and aromatic brominations. [1b-d, 3] Nevertheless,r esolution-free,e nantioselective electrophilic aromatic nitration processes (even with chiral auxiliaries) have yet to be reported. While enantioselective Friedel-Crafts-type reactions [4] and enantioselective aromatic brominations [5] have been studied extensively,o nly the enantioselective nitration of crotylsilanes, [6] but not of aromatic substrates,h as been described.To advance the growing field of chirality-assisted synthesis [7] (CAS), we now describe an enantioselective nitration strategy which makes use of chiral diester auxiliaries with remote stereocenters to induce axial chirality upon trifold nitration. We employ our chiral auxiliaries to achieve the first enantioselective synthesis of a C 3v -symmetric tribenzotriqui-nacene (TBTQ) [8] derivative,w hich is not based on either ak inetic, [9] crystallization-based, [10] or chromatographic [11] resolution. Directing arms with remote stereocenters are positioned at equal distances from the favored and disfavored sites of reactivity to provide for an enantioselective nitration methodology after removal (Figure 1b)ofthe through-space directing groups.T he success of our strategy stems from 1) chelation (Figure 1b)o ft wo ester carbonyl groups to the cationic Wheland intermediates positioned underneath these diester directing arms as well as 2) A 1, 3 strain (Figure 3b), which can be controlled by the size of the alkyl substituents attached to the remote chirality centers of the through-space directing groups.T his combination of A 1,3 strain with ...

Crystal-packing forces can have a significant impact on the relative stabilities of different molecules and their conformations. The magnitude of such effects is, however, not yet well understood. Herein we show, that crystal packing can completely overrule the relative stabilities of different stereoisomers in solution. Heating of atropoisomers (i.e. "frozen-out" conformational isomers) in solution leads to complex mixtures. In contrast, solid-state heating selectively amplifies minor (<25 mole %) components of these solution-phase mixtures. We show that this heating strategy is successful for compounds with up to four rotationally hindered σ bonds, for which a single stereoisomer out of seven can be amplified selectively. Our results demonstrate that common supramolecular interactions-for example, [methyl⋅⋅⋅π] coordination and [C-H⋅⋅⋅O] hydrogen bonding-can readily invert the relative thermodynamic stabilities of different molecular conformations. These findings open up potential new avenues to control the folding of macromolecules.

Antimicrobial peptides (AMPs) are peptides with promising applications for healthcare, veterinary, and agriculture industries. Despite prior success in AMP design using physics- or knowledge-based approaches, there is still a critical need to create new methodologies to design peptides with a low false positive rate and high AMP activity and selectivity. Toward this goal, we invented a cost-effective approach which utilizes a generative model to produce AMP-like sequences and molecular simulations to select peptides based on their structures and interactions. For a proof of concept, we curated a dataset that comprises 500,000 non-AMP peptide sequences and 8,000 labeled AMP sequences to train the generative model, which generated novel and diverse AMP candidates to potentially target a wide variety of microbes. Following a screening process to select peptides that are cationic and likely helical, we assessed 12 candidates by simulating their membrane-binding tendency to a lipid bilayer model. With the umbrella sampling technique, we determined the free energy change during transfer from the solution to the membrane environments for each peptide. Accordingly, we selected the six peptides with the best membrane-binding tendency, synthesized them, and characterized through spectroscopies and biological assays. Three novel peptides were validated with activity to inhibit bacterial growth. In aggregate, the combination of AMP generator and molecular simulations afford an enhanced accuracy in AMP design. Towards future precision AMP design, our methodology and results demonstrate the viability to design novel AMP-like peptides to target selected pathogens and mechanisms.

Chirality-assisted synthesis (CAS) is ag eneral approach to control the shapes of large molecular strips. CASisbased on enantiomerically pure building blocks that are designed to strictly couple in as ingle geometric orientation. Fully shape-persistent structures can thus be created, even in the form of linear chains.W ithC AS,s elective recognition between large host and guest molecules can reliably be designed de novo.T od emonstrate this concept, three C-shaped strips that can embrace ap illar[5]arene macrocycle were synthesized. The pillar [5]arene bound to the strips was ab etter host for electron-deficient guests than the free macrocycle.E xperimental and computational evidence is provided for these unique cooperative interactions to illustrate how CAS could open the door towards the precise positioning of functional groups for regulated supramolecular recognition and catalysis.