Two-Dimensional Nitrogen-Enriched Carbon Nanosheets with Surface-Enhanced Raman Scattering

We have fabricated two-dimensional nitrogen-enriched carbon nanosheets (2D-NECNs) through the pyrolysis of cross-linked poly­(4-vinylpyridine) homopolymers as a platform for detecting physically absorbed dye molecules using Raman-scattering spectra. Upon pyrolysis, a polymeric layer consisting of pyridinic rings was converted into a carbonized nanosheet enriched with pyridinic nitrogen (N₆), pyrrolic nitrogen (N₅), graphitic nitrogen (GN), and nitrogen oxide (NO) groups, the fractions of which were finely controlled through pyrolysis at temperatures selected in the range of 430–550 °C. The effects of temperature on the formation of nitrogen- and carbon-containing species in 2D-NECN were examined by XPS, which showed that N₆ and N₅ were the dominant species over GN and NO at 430 °C. Increasing the temperature of pyrolysis produced carbonized nanosheets containing more GN and NO generated at the expense of pyridinic groups. Using rhodamine 6G (R6G) and crystal violet (CV) molecules as probes for Raman measurements, we found that the Raman enhancement on 2D-NECN is due to a chemical mechanism (CM) and that the observed enhancement of the Raman intensity of molecules adsorbed on 2D-NECN hence shows a clear dependence on the nitrogen configuration of the four types. Among the nitrogen species, GN dominates the large enhancement. The chemical Raman enhancement is ascribed to the ability of GN to improve the π-conjugated domains and narrow the energy gap in 2D-NECN

Tailoring Carbon Nanostructure with Diverse and Tunable Morphology by the Pyrolysis of Self-Assembled Lamellar Nanodomains of a Block Copolymer

The pyrolysis of a block copolymer thin film, the free surface of which was in contact with air or a capping layer of SiO₂, produced four carbon nanostructures. Thin films of a diblock copolymer having perpendicularly oriented lamellar nanodomains served as carbon and nitrogen precursors. Before pyrolysis, the lamellar nanodomains were cross-linked with UV irradiation under nitrogen gas (UVIN). Without a capping layer, pyrolysis caused a structural transformation from lamellar nanodomains to short carbon nanowires or to dropletlike nanocarbons in a row via Rayleigh instability, depending on the duration of pyrolysis. When capped with a layer of SiO₂ followed by pyrolysis, the lamellar nanodomains were converted to pod-like, spaghetti-like, or long worm-like carbon nanostructures. These carbon nanostructures were driven by controlling the surface or interface tension and the residual yield of solid carbonaceous species

PEGylation Site-Dependent Structural Heterogeneity Study of MonoPEGylated Human Parathyroid Hormone Fragment hPTH(1–34)

The structures of C- and N-terminally monoPEGylated human parathyroid hormone fragment hPTH(1–34) as well as their unmodified counterparts, poly­(ethylene glycol) (PEG) and hPTH(1–34), have been studied by small-angle neutron scattering (SANS). The scattering results show that free hPTH(1–34) in 100 mM phosphate buffer (pH 7.4) aggregates into clusters. After conjugation with PEG, the PEG–peptide conjugates self-assemble into a supramolecular core–shell structure with a cylindrical shape. The PEG chains form a shell around the hPTH­(1–34) core to shield hPTH(1–34) from the solvent. The detailed structural information on the self-assembled structures is extracted from SANS using a model of the cylindrical core with a shell of Gaussian chains attached to the core surface. On the basis of the data, because of the charge–dipole interactions between the conjugated PEG chain and the peptide, the conjugated PEG chain forms a more collapsed conformation compared to free PEG. Moreover, the size of the self-assembled structures formed by the C-terminally monoPEGylated hPTH­(1–34) is about 3 times larger than that of the N-terminally monoPEGylated hPTH(1–34). The different aggregation numbers of the self-assembled structures, triggered by different PEGylation sites, are reported. These size discrepancies because of different PEGylation sites could potentially affect the pharmacokinetics of the hPTH(1–34) drug

Live Templates of a Supramolecular Block Copolymer for the Synthesis of Ordered Nanostructured TiO₂ Films via Guest Exchange

In this work, we introduce a facile method based on host–guest chemistry to synthesize a range of nanostructured TiO₂ materials using supramolecular templates of a dendron-jacketed block copolymer (DJBCP). The DJBCP is composed of amphiphilic dendrons (4′-(3,4,5-trido­decyl­oxy­benzoyl­oxy)­benzoic acid, TDB) selectively incorporated into a P4VP block of polystyrene-<i>block</i>-poly­(4-vinyl­pyridine) (PS-<i>b</i>-P4VP) via hydrogen bonding. The PS-<i>b</i>-P4VP host acts as a structure-directing template, while the guest molecules (TDB) assist the self-assembly nanostructures and zone-axis alignment, resulting in the nanostructured template of vertically oriented cylinders formed via successive phase transformations from <i>Im</i>3̅<i>m</i> to <i>R</i>3̅<i>m</i> to <i>P</i>6<i>mm</i> upon thermal annealing in the doctor-blade-cast film. The guest molecules subsequently direct the titania precursors into the P4VP domains of the templates via supramolecular guest exchange during immersion of the film in a designated precursor solution containing a P4VP-selective solvent. The subsequent UV irradiation step leads to the formation of PS-<i>b</i>-P4VP/​TiO₂ hybrids. Finally, removal of the host template by calcination leaves behind mesoporous channels and makes sacrifices to be a carbon source for carbon-doping TiO₂ materials. Various TiO₂ nanoarchitectures, namely, vertical and wiggly micrometer-length channels, inverse opals, fingerprint-like channels, heterogeneous multilayers, and nanotubes, have been fabricated by highly tunable DJBCP nanostructures