Identification and synthesis of novel biomaterials based on spider structural silk fibers

The diversity in function and mechanical behavior of spider silks, and the ability to produce these silks recombinantly, have tremendous potential in creating a new class of biomimetic materials. Here we investigate the structural and mechanical properties of pyriform silks from the golden orb-weaver, Nephila clavipes. Nanoscale indentation measurements using atomic force microscopy on natural pyriform silk suggests that this biomaterial has high toughness that may be suitable for dissipating high amounts of mechanical energy. We also observed the occurrence of highly organized nanocrystals within the pyriform silk fibers that may contribute to the remarkable energy dissipation capability of these silks. It has been demonstrated that poly-(Gly–Ala) and poly-Ala stretches within the internal block repeat modules of dragline silk fibroins form nanocrystals, and these nanocrystalline structures may be responsible for the high extensibility of the dragline silks. In contrast, amino acid sequence analysis shows that PySp2 does not contain the same motifs. In the absence of poly-(Gly–Ala) and poly-Ala repeats, we hypothesized that PySp2 contains new protein motifs sufficient to polymerize into functional structures. To investigate the functional contributions of these novel motifs during pyriform fiber formation, we expressed different recombinant PySp2 fibroins with various segments spanning its block repeat units. We demonstrate that PySp2 recombinant proteins with the Pro-rich sub-block domain (PXP motifs, where X= sub-set of the amino acids A, L, or R) and/or the Ser + Gln + Ala-rich sub-block domain (QQSSVAQS motifs) are sufficient for artificial fiber formation. Moreover, we show that recombinant PySp2 proteins that contain a single block repeat unit can self-assemble into foam-like nanostructures. Collectively, our findings support the use of PySp2 recombinant proteins for a wide range of biomimetic materials with morphologies ranging from fibers to porous structures.     

Diastereoselective assembly of pentanuclear circular helicates

Reaction of a ligand which contains two N-donor and O-donor tridentate domains separated by a 1,3-phenylene spacer unit with Zn(2+) ions results in a pentanuclear circular helicate [Zn(5)(L)(5)](10+) and this structure persists in both the solid and solution state. The formation of this high nuclearity species is governed by unfavourable steric interactions between the phenyl units which destabilize the simple linear helicate. Incorporation of enantiopure units within the ligand strand controls the diastereoselectivity with up to 80% d.e.     

Bond bundles and the origins of functionality

We briefly review the method by which the electron charge density of atomic systems is decomposed into unique volumes called bond bundles, which are characterized by well-defined and additive properties. We then show that boundaries of bond bundles topologically constrain their chemical reactivity. To illustrate this fact, we model the response of the bond bundles of ethane and ethene to electrophilic attack and from the results of these models posit that functional group properties can be inferred from the shapes of their bond bundles. By relating functionality to bond bundle shape, it is possible to see subtle changes in chemical reactivity that are otherwise difficult to explain, as is illustrated by comparing bond bundles through a series of impact sensitive polynitroaromatic molecules.     

Importance of dynamic hydrogen bonds and reorientation barriers in proton transport

The dynamic nature of hydrogen bonds in phenolic polymers, where the hydrogen bond donor/acceptor reorientation can occur in a single site, presents lower barriers for proton transport.     

An energy efficient and facile synthesis of high molecular weight polyesters using ketenes

A facile, ketene-based strategy for the synthesis of polyesters from stable Meldrum's acid monomers has been developed which overcomes many issues associated with traditional step-growth procedures. A significant increase in polymerization efficiency is observed with only 10 min reaction time at 220 °C being needed to obtain high molecular weight polymers.     

In vivo characterization of nonribosomal peptide synthetases NocA and NocB in the biosynthesis of nocardicin A

Two nonribosomal peptide synthetases (NRPS), NocA and NocB, together comprising five modules, are essential for the biosynthesis of the D,L,D configured tripeptide backbone of the monocyclic β-lactam nocardicin A. We report a double replacement gene strategy in which point mutations were engineered in the two encoding NRPS genes without disruption of the nocABC operon by placing selective markers in adjacent genes. A series of mutants was constructed to inactivate the thiolation (T) domain of each module and to evaluate an HHxxxDR catalytic motif in NocA and an atypical extended histidine motif in NocB. The loss of nocardicin A production in each of the T domain mutants indicates that all five modules are essential for its biosynthesis. Conversely, production of nocardicin A was not affected by mutation of the NocB histidine motif or the R828G mutation in NocA.     

A parallel dual-electrode detector for capillary electrophoresis

An approach to on-capillary dual-electrode detection for CE using a parallel electrode configuration has been developed. The parallel configuration provides two operating modes. In the first mode, one working electrode is held at an oxidizing potential and the second working electrode is held at a reducing potential. This results in redox cycling of analytes between the oxidized and reduced forms, enhancing sensitivity compared to single-electrode detection. In the second mode, both working electrodes are held at different oxidizing potentials. This mode provides electrochemical characterization of electrophoretic peaks. In the redox cyclying mode, signal enhancement of up to twofold was observed for the dual-electrode detection of phenolic acid standards compared to single-electrode detection. Variation in response of less than 10% from electrode to electrode was determined (at a concentration of 60 nM) indicating reproducible fabrication. LODs were determined to be as low as 5.0 nM for dual-electrode configuration. Using the dual-potential mode peak identification of targeted phenolic acids in whiskey samples were confirmed based on both migration time and current ratios.     

Neutron activation analysis of concrete for cross-border nuclear security

The dissolution of the Soviet Union coupled with the growing sophistication of international terror organizations has brought about a desire to ensure that a sound infrastructure exists to interdict smuggled nuclear material prior to leaving its country of origin. To combat the threat of nuclear trafficking, radiation portal monitors (RPMs) are deployed around the world to intercept illicit material while in transit by passively detecting gamma and neutron radiation. Portal monitors in some locations have reported abnormally high background counts. The higher background data has been attributed, in part, to the naturally occurring radioactive materials (NORM) in the concrete surrounding the portal monitors. Higher background increases the minimum detectable activity (MDA) and can ultimately lead to more material passing through the RPMs undetected. This work employed two different neutron activation analysis (NAA) methods for the purpose of developing a process to characterize the concrete surrounding the RPMs. Thermal neutron instrumental NAA (INAA) and fast NAA (FNAA) were conducted on six samples from three different composition concrete slabs. Comparator standards and quality control materials were used to help ensure that the methods were both precise and accurate. The combination of INAA and FNAA accounted for 84–100% of the total elemental composition of the samples. Knowing the composition of the concrete will allow RPM customers to choose suitable materials prior to installation, thereby increasing the ability of the monitors to detect radiological and nuclear materials.