The high-performance mechanical properties of certain spider silks can be radically altered by the addition of water. For example, unconstrained silk fibers from the major ampullate gland of the golden orbweaving spider, Nephila claVipes, contract to about half of their original length when immersed in water. In this paper we use solid-state 13 C and 2 H NMR to study N. claVipes silk fibers, so as to address the molecular origins of supercontraction in the wet silk. Using 13 C NMR, we study backbone dynamics and demonstrate that, when in contact with water, a substantial fraction of the glycine, glutamine, tyrosine, serine, and leucine residues in the protein backbone show dramatic increases in the rate of large-amplitude reorientation. 2 H NMR of silk samples that incorporate leucine deuterated at one terminal methyl group provides a probe for dynamics at specific side chains along the fiber. Only a subset of these leucine residues is strongly affected by water. We suggest that the highly conserved YGGLGS(N)QGAGR blocks found in the silk protein play a major role in the supercontraction process. Amino acid sequences are proposed to produce artificial spider silk with similar mechanical properties, but without the undesired phenomenon of supercontraction. A possible use of the "supercontracting sequence" is also suggested.

Spider dragline silk is Nature's high-performance protein fiber. This biomaterial has attracted much interest from scientists in various disciplines since it has become feasible to produce spider silk proteins by means of biotechnology. This article reports on research directed toward the regeneration of spider silk. A procedure is describedsincluding spinning and postspinning processings that produces fibers with promising mechanical properties from dissolved natural spider dragline silk. Tensile tests and structural characterization of the regenerated fibers illustrate correlations between the macroscopic and microscopic properties of the final material and between these properties and the fiber's processing history. Results point to the importance of an aqueous environment in the annealing of structure. The revealed structure-property relationships are expected to be of fundamental importance for the future design of man-made protein products.

A microfabricated spinneret is described that is capable of spinning meters of fibers from solutions containing as little as 10 mg of purified protein. Using the spinneret, regenerated Bombyx mori fibers were made using various processing parameters. A log-linear relationship was found between the maximum stress sustained by the regenerated fibers and their diameters. Solid state 13 C NMR was used to determine the effects of spinneret diameter and postspinning draw ratio on the secondary structure of the alanine residues in the silk protein. The relationship between the secondary structure of the alanine residues and the maximum stress of the silks was also examined. The results suggest that a relatively high fraction of the alanine residues in the silks must be in the -sheet conformation (>65%) in order to produce the highest stress fibers. However, the fraction of alanine residues in the -sheet conformation does not uniquely determine the maximum stress of a fiber; it is suggested that orientation of these -sheets is also an important parameter.

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Solid state 13 C NMR is used to identify the conformation of alanine residues in minor ampullate gland silk from Nephila clavipes and in a genetically engineered protein based on the consensus sequence of MaSp2, a protein present in low concentrations in major ampullate gland silk. The results of the NMR on minor ampullate gland silk are compared to previous NMR data on major ampullate gland silk, and the results on the genetically engineered protein are compared to previous NMR data on the gland fibroin from the major ampullate gland. Differences in the secondary structure of major and minor ampullate gland silk are correlated with mechanical properties. The alanine residues of major ampullate gland silk have previously been shown to consist almost entirely of β-sheet conformations. In contrast, the conformations of the alanine residues of minor ampullate gland silk are more heterogeneous, with a larger fraction of the alanine residues in non-β-sheet conformations. It is hypothesized that these non-β-sheet structures in minor ampullate gland silk are part of the cause for its lower tensile strength. In addition, both unprocessed genetically engineered silk and lyophilized major ampullate gland fibroin, have similar alanine Cβ carbon chemical shifts yet differ in their alanine CR carbon chemical shifts. This suggests that this genetically engineered protein is good starting material for biofiber synthesis but that it does not exactly mimic the gland fibroin.

Current experiments in liquid-state nuclear magnetic resonance quantum computing are limited by low initial polarization. To address this problem, we have investigated the use of optical pumping techniques to enhance the polarization of a 2-qubit NMR quantum computer ( 13 C and 1 H in 13 CHCl3). To efficiently use the increased polarization, we have generalized the procedure for effective pure state preparation. With this new, more flexible scheme, an effective pure state was prepared with polarization-enhancement of a factor of 10 compared to the thermal state. An implementation of Grover's quantum search algorithm was demonstrated using this new technique.Intensive experimental efforts have been made to implement quantum computing since Shor [1] and Grover [2] developed their respective algorithms. So far, the only experimental demonstrations of quantum computing algorithms have been based on nuclear magnetic resonance (NMRQC) [3]. However, the low polarization of hightemperature nuclear spin systems is a major limitation of this approach. To cope with the corresponding highly mixed spin state, schemes have been developed which produce an effective pure state [4,5]. Unfortunately, all of these techniques require exponential resources to implement and improved scalable procedures for fully polarizing an embedded spin system [6] are not practical with the very low initial polarizations found in NMRQC. In addition to the experimental challenges, recent theoretical work has called into question the boundary between classical and quantum computing in the case of highly mixed systems [10]. A crucial parameter in determining where this boundary lies is the initial polarization of the quantum system. It is therefore highly relevant to explore existing techniques used to enhance polarization for NMR and to investigate their application to quantum computing [11].One recently developed technique is based on laserpolarized Xenon. It is known that the high electron polarization in optically pumped alkali metals like rubidium can be transferred to the nuclear spins of noble gases such as 3 He or 129 Xe via a spin-exchange mechanism [7]. More recently, it was found that hyperpolarized liquid 129 Xe could be used to enhance the polarization of nuclei of other molecules in solution via the spin polarizationinduced nuclear Overhauser effect (SPINOE) [8,9]. The focus of our work is the coupling of optical pumping with NMRQC. We have developed a temporal labeling scheme which is more flexible than the existing ones and which allows efficient use of the polarization enhancements. To validate this technique, we have created an effective pure state with an order of magnitude polarization enhancement. The flexibility of our scheme is further illustrated by applying this approach to perform Grover's search algorithm. Polarization-enhancements up to a factor of 7 are achieved.In a typical optical pumping experiment, we start by pressurizing a glass cell (pyrex, 200 cc) containing solid Rb to 3.5 Atm with a mixture of ultrapure gases: 1...

Rotational Echo DOuble Resonance (REDOR) NMR is an oft-demonstrated tool for measuring distance between isolated IS spin pairs. Its application to more complex ISn spin networks (n>1), however, is rare, as in these systems the interpretation of the results is model-dependent–while it is precisely the measurement of multiple distances which is required for molecular structure elucidation. Recently, Θ-REDOR was introduced and was shown to improve interpretability at the cost of signal intensity. In this paper we analyze generalizations to the REDOR pulse sequence, and present a new experimental procedure which allows for simultaneous distance determinations in larger spin systems with improved signal intensity. Experimental data are presented for the IS2 spin system glycine-C213-N15.