Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Chemical syntheses of biodegradable polymers

Silk fibroin biomaterials for tissue regenerations.

We report a study of self-assembled beta-pleated sheets in B. mori silk fibroin films using thermal analysis and infrared spectroscopy. B. mori silk fibroin may stand as an exemplar of fibrous proteins containing crystalline beta-sheets. Materials were prepared from concentrated solutions (2−5 wt % fibroin in water) and then dried to achieve a less ordered state without beta-sheets. Crystallization of beta-pleated sheets was effected either by heating the films above the glass transition temperature (Tg) and holding isothermally or by exposure to methanol. The fractions of secondary structural components including random coils, alpha-helices, beta-pleated sheets, turns, and side chains were evaluated using Fourier self-deconvolution (FSD) of the infrared absorbance spectra. The silk fibroin films were studied thermally using temperature-modulated differential scanning calorimetry (TMDSC) to obtain the reversing heat capacity. The increment of the reversing heat capacity ΔCp0(Tg) at the glass transition fo...

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Determining Beta Sheet Crystallinity in Fibrous Proteins by Thermal Analysis and Infrared Spectroscopy

Biogenic calcium carbonate forms the inorganic component of seashells, otoliths, and many marine skeletons, and its formation is directed by an ordered template of macromolecules. Classical nucleation theory considers crystal formation to occur from a critical nucleus formed by the assembly of ions from solution. Using cryotransmission electron microscopy, we found that template-directed calcium carbonate formation starts with the formation of prenucleation clusters. Their aggregation leads to the nucleation of amorphous nanoparticles in solution. These nanoparticles assemble at the template and, after reaching a critical size, develop dynamic crystalline domains, one of which is selectively stabilized by the template. Our findings have implications for template-directed mineral formation in biological as well as in synthetic systems.

The initial stages of template-controlled CaCO3 formation revealed by Cryo-TEM

The objective of the present study is to investigate the possibility of preparing pure protein microspheres from regenerated silk fibroin (RSF). It is found that RSF microspheres, with predictable and controllable sizes ranging from 0.2 to 1.5 µm, can be prepared via mild self-assembling of silk fibroin molecular chains. The merits of this novel method include a rather simple production apparatus and no potentially toxic agents, such as surfactants, initiators, cross-linking agents, etc. The results show that the particle size and size distribution of RSF microspheres are greatly affected by the amount of ethanol additive, the freezing temperature and the concentration of silk fibroin. Finally, the mechanism of RSF microspheres formation is also discussed based on our experimental results.

The preparation of regenerated silk fibroin microspheres

The pollution of water resources has become a worldwide concern because of the indiscriminate disposal of heavy metal ions and toxic organics in the past few decades. In this study, we use a sustainable, low cost, and abundant plant protein, soy protein isolate (SPI) as a matrix, polyethyleneimine (PEI) as a functional component to prepare the SPI/PEI composite hydrogels through a facile chemical crosslinking method. The results show that the SPI/PEI composite hydrogels can effectively adsorb Cu(II) ions from aqueous solution. In particular, the SPI/PEI composite hydrogel with a 50% PEI content demonstrates an excellent selectivity for the removal of Cu(II) ions when co-existing competitive heavy metal ions, including Zn(II), Cd(II), and Pb(II), especially the selectivity coefficient for Cu(II)/Zn(II), reaches about 250. Furthermore, the adsorbed Cu(II) ions in the composite hydrogel can be reduced easily in situ by NaBH4 to form uniformly dispersed copper nanoparticles (Cu NPs), which gives a Cu NP-loaded-SPI/PEI composite hydrogel. Such a material is found to be able to act as a catalyst to catalyse the model reaction, i.e., the reduction of 4-nitrophenol with a high efficiency. These results suggest that such a SPI-based hydrogel is a good candidate to selectively adsorb and recycle copper element for the waste disposal industry. In addition, we also provide a strategy to keep the natural resources sustainable, i.e., to select a natural and sustainable material (SPI) to protect the environment (wastewater treatment), and to recycle metals (copper and possibly others).

Soy protein-based polyethylenimine hydrogel and its high selectivity for copper ion removal in wastewater treatment

Collagen hydrogel has been regarded as an excellent biomaterial because it is an abundant and sustainable resource and has good biocompatibility and controllable cell-based biodegradability. However, the poor mechanical properties of collagen hydrogel are the main disadvantage preventing it from having wide applications. In this communication, we use aldehyde-functionalized dextran, which is prepared from the oxidation of another natural polymer dextran, as a macromolecular cross-linker to enhance the strength of the collagen hydrogel. The resulting collagen/aldehyde-functionalized dextran (Col/DAD) hydrogels are much stronger and show better thermostability than the pristine collagen hydrogel, as expected. The maximum compressive strength of the Col/DAD hydrogel is 32.5 ± 1.6 kPa, which is about 20 times more than that of the pristine collagen hydrogel. We also prove that our method maintains the good biocompatibility of the collagen hydrogel and does not bring the cytotoxicity often observed from conven...

Strong Collagen Hydrogels by Oxidized Dextran Modification

Protein adsorption and separation with chitosan-based amphoteric membranes

Silk protein is a promising natural material applied in various fields, but the application of silk protein-based hydrogel is quite limited because of its long gelation time and poor mechanical properties. Here, we present a facile way to prepare strong silk protein hydrogels simply by adding surfactant into silk fibroin aqueous solution and incubating at 60 °C. The resulting silk protein hydrogels demonstrate fairly good mechanical properties; for example, the silk protein hydrogel made by adding sodium dodecyl sulfate (SDS) has the compressive and tensile moduli of 3.0 and 3.3 MPa, respectively, which are close to some tissues in the body, such as cartilages, tendons, and ligaments. The effect of different types of surfactant on the formation of strong silk protein hydrogel, and the possible reason for the improvement of the mechanical properties of the hydrogel are also discussed. In addition, we show that such a strong silk protein hydrogel maintains good biocompatibility when adding a proper amount o...

Jinrong Yao

Papers

The preparation of regenerated silk fibroin microspheres

Soy protein-based polyethylenimine hydrogel and its high selectivity for copper ion removal in wastewater treatment

Strong Collagen Hydrogels by Oxidized Dextran Modification

Protein adsorption and separation with chitosan-based amphoteric membranes

Robust Protein Hydrogels from Silkworm Silk