3D Printing of Silk Protein Structures by Aqueous Solvent‐Directed Molecular Assembly

Hierarchical molecular assembly is a fundamental strategy for manufacturing protein structures in nature. However, to translate this natural strategy into advanced digital manufacturing like three‐dimensional (3D) printing remains a technical challenge. This work presents a 3D printing technique with silk fibroin to address this challenge, by rationally designing an aqueous salt bath capable of directing the hierarchical assembly of the protein molecules. This technique, conducted under aqueous and ambient conditions, results in 3D proteinaceous architectures characterized by intrinsic biocompatibility/biodegradability and robust mechanical features. The versatility of this method is shown in a diversity of 3D shapes and a range of functional components integrated into the 3D prints. The manufacturing capability is exemplified by the single‐step construction of perfusable microfluidic chips which eliminates the use of supporting or sacrificial materials. The 3D shaping capability of the protein material can benefit a multitude of biomedical devices, from drug delivery to surgical implants to tissue scaffolds. This work also provides insights into the recapitulation of solvent‐directed hierarchical molecular assembly for artificial manufacturing.     

Voltammetric behaviour of rhenium(I) complexes with phosphine and carbon monoxide ligands in acetonitrile solvent

Summary The anodic and cathodic behaviour of the complexesmer-[ReCl(CO)₃(PMe₂Ph)₂],fac[ReCl(CO)₃(PMe₂Ph)₂],mer-[ReCl(CO)₃(PPh₃)₂], and [ReCl(CO)₂(PMe₂Ph)₃] in acetonitrile solvent were studied using platinum and mercury electrodes. Cyclic voltammetry and controlled potential coulometry were the main electroanalytical techniques employed. The nature of the electrolysis products and of the electrode oxidation and reduction processes were investigated. In particular, [ReCl(CO)(MeCN)₂(PMe₂Ph)₃][ClO₄]₂, [ReCl₃(CO)₂(PMe₂Ph)₂], and a not completely defined rhenium(-I) complex were electrochemically synthesized and characterized by means of i.r. and¹H n.m.r. spectroscopy, and by elemental analysis.     

Palladium(II) and platinum(II) halide complexes with 2,6-dimethyl-4H-pyran-4-thione

Summary 2,6-Dimethyl-4H-pyran-4-thione (DMTP) acts as a sulphur donor towards Pt^II and Pd^II halides yielding adducts of general formula [M(DMTP)₂X₂] (M=Pd or Pt; X=Cl, Br or I). When complex syntheses are performed in benzene, the solvated species [M(DMTP)₂X₂]·C₆H₆ (M=Pd or Pt; X=Cl or Br) are obtained. The compounds have been characterized by i.r. and n.m.r. (¹H and¹³C) spectroscopy and by thermogravimetric data. The adduct geometry and the influence of benzene are discussed.     

Identification of an unusual naturally occurring apolar fatty acid amide in mammalian brain and a method for its quantitative determination

Fatty acid amides (FAAs), such as the N-acylamides, N-acylethanolamides, N-acyldopamines and N-acylamino acids, are now emerging as an important new class of lipid-signalling molecules. This paper provides evidence, based on high-performance liquid chromatography/electrospray ionisation mass spectrometry (HPLC/ESI-MS/MS), gas chromatography/mass spectrometry (GC/MS) and 1H-NMR, of the occurrence in mouse and bovine brain extracts of a compound characterised by a mass spectrum attributable to a FAA not previously described, namely, the isopropyl-amide of stearic acid (SIPA). A highly sensitive GC/MS method was developed for quantification of naturally occurring SIPA and, also, for purposes of comparison, that of palmitoylethanolamide (PEA), a structurally related compound commonly determined in animal tissues. The results obtained show that SIPA levels in mouse brain are 8-10-fold higher than those of PEA. Moreover, SIPA was found in human neuroblastoma cell (SHSY-5Y) extracts, at significantly higher levels following exposure of the cells to the mitochondrial inhibitor rotenone. All this evidence not only shows surprisingly that SIPA may be found naturally in mammalian biological extracts despite the unusual functional group (i.e. isopropylamide) implicated, but also raises many important questions concerning its biological origin.     

Optically induced birefringence and holography in silk

In this study, we demonstrated that thin films of azobenzene‐modified Bombyx mori silk showed optically induced effects similar to those found in other polymers incorporating azobenzene moieties. Optically induced anisotropy in refractive index reached 7 × 10^?3 with 18 J cm^?2 required to reach 50% of steady state. Holograms were formed with diffraction efficiencies reaching 2.5%. The holograms were accompanied by surface relief gratings and measurements of the mechanical properties of films with surface relief gratings showed that the raised areas were more adhesive than the lower areas. We also demonstrated the fidelity of holographic images. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

A family of 16 isomolecular salts (3‐XpyH)₂[MX′₄] (3‐XpyH=3‐halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X′=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X‐ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non‐covalent interactions: N? H???X′? M hydrogen bonds, C? X???X′? M halogen bonds and π–π stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C? X???X′? M halogen bonds, whereas an analogous change of the inorganic halogen (X′) weakens both halogen bonds and N? H???X′? M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C? F???X′? M) halogen bonds are absent. The structure is directed by N? H???X′? M hydrogen bonds and π‐stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X′), long (weak) C? X???X′? M interactions are observed with type I halogen–halogen interaction geometries (C? X???X′ ≈ X???X′? M ≈155°), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X′), stronger halogen bonds are formed with a type II halogen–halogen interaction geometry (C? X???X′ ≈180°; X???X′? M ≈110°) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.     

Development and Investigation of Ultrastable PbS/CdS/ZnS Quantum Dots for Near‐Infrared Tumor Imaging

Achieving bright, reliable, robust, and stable probes for in vivo imaging is becoming extremely urgent for the cancer imaging research community. To date very few works have reported on elucidating in the varied and chemically complex biological milieu. The authors report detailed investigations of the synthesis of near‐infrared, water dispersive, strongly luminescent, and highly stable PbS/CdS/ZnS core/shell/shell quantum dots (QDs). These QDs are extremely stable, they could keep their initial morphology, dispersion status, and photoluminescence (PL) in phosphate buffered saline buffer for as long as 14 months. The QDs also show excellent photostability and could keep ≈80% of their initial PL intensity after 1 h continuous, strong UV illumination. More interestingly, they show negligible toxicity to cultured cells even at high QDs concentration. Given these outstanding properties, the QDs are explored for in vivo, tumor imaging in mice. With one order of magnitude lower QD concentration (0.04 mg mL^–1), significantly weaker laser intensity (0.04 W cm^–2 vs ≈1 W cm^–2), and considerably shorter signal integration time (≤1 ms vs hundreds of ms) as compared to the best reported rare earth doped nanoparticles, the QDs show high emission intensity even at injection depth of ≈2.5 mm.