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Bing Gong

Publications and source records attributed to Bing Gong.

8 recordsLinked to original sources
PubMed2004

Highly efficient, one-step macrocyclizations assisted by the folding and preorganization of precursor oligomers.

Highly efficient, one-step macrocyclizations leading to the formation of macrocyclic hexa(aramides) in high yields (69-82%) are described. The one-step macrocyclizations were facilitated by the preorganization or folding of the backbones of uncyclized precursors in the course of macrocyclization. The preorganization of backbones was achieved by the presence of localized three-centered hydrogen bonds that were adopted in the design of a class of closely related, backbone-rigidified foldamers. The macrocyclization involved reactions between diacid chloride 1 and diamine 2. The crude reaction mixtures and products were conveniently examined by mass spectrometric method (MALDI-TOF). Compared to most traditional one-step macrocyclizations that usually require high dilution conditions and often lead to very low overall yields of the desired products, cyclic hexamers 3 were obtained as the overwhelmingly major product under a variety of reaction conditions, suggesting the generality of this approach.

Cyclization↗
PubMed2004

Backbone-rigidified oligo(m-phenylene ethynylenes).

Oligo(m-phenylene ethynylenes) (oligo(m-PE)) with backbones rigidified by intramolecular hydrogen bonds were found to fold into well-defined conformations. The localized intramolecular hydrogen bond involves a donor and an acceptor from two adjacent benzene rings, respectively, which enforces globally folded conformations on these oligomers. Oligomers with two to seven residues have been synthesized and characterized. The persistence of the intramolecular hydrogen bonds and the corresponding curved conformations were established by ab initio and molecular mechanics calculations, 1D and 2D (1)H NMR spectroscopy, and UV spectroscopy. Pentamer 5, hexamer 6, and heptamer 7 adopt well-defined helical conformations. Such a backbone-based conformational programming should lead to molecules whose conformations are resilient toward structural variation of the side groups. These m-PE oligomers have provided a new approach for achieving folded unnatural oligomers under conditions that are otherwise unfavorable for previously described, solvent-driven folding of m-PE foldamers. Stably folded structures based on the design principle described here can be developed and may find important applications.

Hydrogen Bonding↗
PubMed2004

Well-defined secondary structures.

Molecules and assemblies of molecules with well-defined secondary structures have been designed and characterized by controlling noncovalent interactions. By specifying intermolecular interactions, a class of information-storing molecular duplexes have been successfully developed. These H-bonded molecular duplexes demonstrate programmable, sequence-specificity and predictable, tunable stabilities. Based on these highly specific molecular zippers (or glues), a systematic approach to designing self-assembled structures is now feasible. Duplex-directed formation of beta-sheets, block copolymers and templated organic reactions have been realized. By specifying intramolecular noncovalent interactions, a backbone-rigidification strategy has been established, leading to unnatural molecular strands that adopt well-defined, crescent or helical conformations. The generality of this backbone-rigidification strategy has been demonstrated in three different classes of unnatural oligomers: oligoaramides, oligoureas and oligo(phenylene ethynylenes). Large nanosized cavities have been created based on the folding of these helical foldamers. Tuning the size of the nanocavities has been achieved without changing the underlying helical topology. These helical foldamers can serve as novel platforms for the systematic design of nanostructures.

Biopolymers↗
PubMed2003

Duplex foldamers from assembly induced folding.

Oligoamide strands 1, 2, and 3, consisting of 4-H-bond units, were originally designed to form noncovalent polymers based on the expectation that they would adopt an extended conformation. Instead of assembling into the expected supramolecular polymer through their 4-H-bond units, the 1:1 mixture of 1 and 2 was found to form a highly stable dimeric species. To dimerize, the H-bonding sequences of 1 and 2 can only adopt a folded (stacked) conformation. The self-assembly of 3 was also found to adopt a similar folded duplex conformation. These novel duplex foldamers are very stable. They were characterized by 1D and 2D 1H NMR, VPO, and mass spectral (ESI) studies.

Biomimetic Materials↗
PubMed2002

Creating nanocavities of tunable sizes: hollow helices.

A general strategy for creating nanocavities with tunable sizes based on the folding of unnatural oligomers is presented. The backbones of these oligomers are rigidified by localized, three-center intramolecular hydrogen bonds, which lead to well-defined hollow helical conformations. Changing the curvature of the oligomer backbone leads to the adjustment of the interior cavity size. Helices with interior cavities of 10 A to >30 A across, the largest thus far formed by the folding of unnatural foldamers, are generated. Cavities of these sizes are usually seen at the tertiary and quaternary structural levels of proteins. The ability to tune molecular dimensions without altering the underlying topology is seen in few natural and unnatural foldamer systems.

Hydrogen Bonding↗
PubMed2002

A noncovalent approach to antiparallel beta-sheet formation.

Four tripeptide chains, when attached to the same end of a hydrogen-bonded duplex (1.2) with the unsymmetrical, complementary sequences of ADAA/DADD, have been brought into proximity, leading to the formation of four hybrid duplexes, 1a.2a, 1a.2b, 1b.2a, and 1b.2b, each of which contains a two-stranded beta-sheet segment. The extended conformations of the peptide chains were confirmed by 1D and 2D NMR. The peptide strands stay registered through hydrogen bonding and the beta-sheets are stabilized by side chain interactions. Two-dimensional NMR data also indicate that the duplex template prevents further aggregation in the peptide segment. When the peptide chains are attached to the two different termini of the duplex template, NMR studies show the presence of a mixture with no clearly defined conformations. In the absence of the duplex template, the tripeptides are found to associate randomly. Finally, isothermal titration calorimetry studies revealed that the hybrid duplex 1a.2a was more stable than either the duplex template or the peptides alone.

Calorimetry↗