The authors would like to thank Dr. B. Ellen Scanley for her technical training and help using the TEM at the Connecticut State Colleges and University (CSCU) Center for Nanotechnology and Dr. Ishita Mukerji at Wesleyan University for access to her CD spectrophotometer. The work reported was in part supported by the Science Institute at Fairfield University, the NASA Connecticut Space Grant Consortium, and by the National Science Foundation under Grant Number CHE-1624774.

1. Synthesis and Purification of 1,2-Dithiolane Modified Peptide
<ol>
	<li>Synthesis of dithiolane precursor, 3-(acetylthio)-2-(acetylthiomethyl)propanoic acid19.
	<ol>
		<li>Add 1 g of 3-bromo-2-(bromomethyl)propionic acid (1 equiv.) dissolved in minimal amount of 1 M NaOH (approximately 4 mL) to a 25-mL round bottom reaction flask with stirring at 55 &#176;C. Seal the reaction flask with a septa and place under nitrogen atmosphere.</li>
		<li>Prepare a solution containing 1.49...

<ol>
	<li>Wang, J., Liu, K., Xing, R., Yan, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peptide+self-assembly:+Thermodynamics+and+kinetics.">Peptide self-assembly: Thermodynamics and kinetics.</a> Chemical Society Reviews. 45, 5589-5604 (2016).</li><li>Dong, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+supramolecular+polymers+for+biomedical+applications.">Functional supramolecular polymers for biomedical applications.</a> Advanced Materials. 27, 498-526 (2015).</li><li>Edwards-Gayle, C. J. C., Hamley, I. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembly+of+bioactive+peptides,+peptide+conjugates,+and+peptide+mimetic+materials.">Self-assembly of bioactive peptides, peptide conjugates, and peptide mimetic materials.</a> Organic and Biomolecular Chemistry. 15, 5867-5876 (2017).</li><li>Goor, O. J. G. M., Hendrikse, S. I. S., Dankers, P. Y. W., Meijer, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+supramolecular+polymers+to+multi-component+biomaterials.">From supramolecular polymers to multi-component biomaterials.</a> Chemical Society Reviews. 46, 6621-6637 (2017).</li><li>DiMaio, J. T. M., Doran, T. M., Ryan, D. M., Raymond, D. M., Nilsson, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modulating+supramolecular+peptide+hydrogel+viscoelasticity+using+biomolecular+recognition.">Modulating supramolecular peptide hydrogel viscoelasticity using biomolecular recognition.</a> Biomacromolecules. 18, 3591-3599 (2017).</li><li>DiMaio, J. T. M., Raymond, D. M., Nilsson, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Display+of+functional+proteins+on+supramolecular+peptide+nanofibrils+using+a+split-protein+strategy.">Display of functional proteins on supramolecular peptide nanofibrils using a split-protein strategy.</a> Organic and Biomolecular Chemistry. 15, 5279-5283 (2017).</li><li>Mahmoud, Z. N., Gunnoo, S. B., Thomson, A. R., Fletcher, J. M., Woolfson, D. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bioorthogonal+dual+functionalization+of+self-assembling+peptide+fibers.">Bioorthogonal dual functionalization of self-assembling peptide fibers.</a> Biomaterials. 32, 3712-3720 (2011).</li><li>Petkau-Milroy, K., Uhlenheuer, D. A., Spiering, A. J. H., Vekemans, J. A. J. M., Brunsveld, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+and+bio-orthogonal+protein+assembly+along+a+supramolecular+polymer.">Dynamic and bio-orthogonal protein assembly along a supramolecular polymer.</a> Chemical Science. 4, 2886-2891 (2013).</li><li>Li, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurofibrillar+tangle+surrogates:+Histone+H1+binding+to+patterned+phosphotyrosine+peptide+nanotubes.">Neurofibrillar tangle surrogates: Histone H1 binding to patterned phosphotyrosine peptide nanotubes.</a> Biochemistry. 53, 4225-4227 (2014).</li><li>Sadownik, A., Stefely, J., Regen, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymerized+liposomes+formed+under+extremely+mild+conditions.">Polymerized liposomes formed under extremely mild conditions.</a> Journal of the American Chemical Society. 108, 7789-7791 (1986).</li><li>Zhang, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ATN-161+Peptide+functionalized+reversibly+cross-linked+polymersomes+mediate+targeted+doxorubicin+delivery+into+melanoma-bearing+C57BL/6+mice.">ATN-161 Peptide functionalized reversibly cross-linked polymersomes mediate targeted doxorubicin delivery into melanoma-bearing C57BL/6 mice.</a> Molecular Pharmaceutics. 14, 2538-2547 (2017).</li><li>Margulis, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+polymeric+nanocubes+by+self-assembly+and+crystallization+of+dithiolane-containing+triblock+copolymers.">Formation of polymeric nanocubes by self-assembly and crystallization of dithiolane-containing triblock copolymers.</a> Angewandte Chemie International Edition. 56, 16357-16362 (2017).</li><li>Zhang, X., Waymouth, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=1,2-Dithiolane-Derived+Dynamic,+Covalent+Materials:+Cooperative+Self-Assembly+and+Reversible+Cross-Linking.">1,2-Dithiolane-Derived Dynamic, Covalent Materials: Cooperative Self-Assembly and Reversible Cross-Linking.</a> Journal of the American Chemical Society. 139, 3822-3833 (2017).</li><li>Sakia, N., Matile, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stack+exchange+strategies+for+the+synthesis+of+covalent+double-channel+photosystems+by+self-organizing+surface-initiated+polymerization.">Stack exchange strategies for the synthesis of covalent double-channel photosystems by self-organizing surface-initiated polymerization.</a> Journal of the American Chemical Society. 133, 18542-18545 (2011).</li><li>Uji, H., Morita, T., Kimura, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+direction+dependence+of+single-molecule+conductance+of+a+helical+peptide+in+molecular+junction.">Molecular direction dependence of single-molecule conductance of a helical peptide in molecular junction.</a> Physical Chemistry Chemical Physics. 15, 757-760 (2013).</li><li>Liang, C., Ni, R., Smith, J. 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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disulfide+exchange:+Exposing+supramolecular+reactivity+through+dynamic+covalent+chemistry.">Disulfide exchange: Exposing supramolecular reactivity through dynamic covalent chemistry.</a> Chemical Society Reviews. 43, 1861-1872 (2014).</li><li>Vendetti, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dihydroasparagusic+acid:+Antioxidant+and+tyrosinase+inhibitory+activities+and+improved+synthesis.">Dihydroasparagusic acid: Antioxidant and tyrosinase inhibitory activities and improved synthesis.</a> Journal of Agricultural and Food Chemistry. 61, 6848-6855 (2013).</li><li>Stawikowski, M., Fields, G. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Introduction+to+peptide+synthesis.">Introduction to peptide synthesis.</a> Current Protocols in Protein Science. 26, (2002).</li><li>Canadell, J., Goossens, H., Klumperman, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-healing+materials+based+on+disulfide+links.">Self-healing materials based on disulfide links.</a> Macromolecules. 44, 2536-2541 (2011).</li><li>Lafont, U., van Zeijl, H., van der Zwaag, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+cross-linkers+on+the+cohesive+and+adhesive+self-healing+ability+of+polydisulfide-based+thermosets.">Influence of cross-linkers on the cohesive and adhesive self-healing ability of polydisulfide-based thermosets.</a> ACS Applied Materials and Interfaces. 4, 6280-6288 (2012).</li><li>Komaromy, D., Stuart, M. C. A., Santiago, G. M., Tezcan, M., Krasnikov, V. V., Otto, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembly+can+direct+dynamic+covalent+bond+formation+toward+diversity+or+specificity.">Self-assembly can direct dynamic covalent bond formation toward diversity or specificity.</a> Journal of the American Chemical Society. 139, 6234-6241 (2017).</li><li>McAvery, K. M., Guan, B., Fortier, C. A., Tarr, M. A., Cole, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-induced+oxidation+of+cholesterol+observed+during+MALDI-TOF+mass+spectrometry.">Laser-induced oxidation of cholesterol observed during MALDI-TOF mass spectrometry.</a> Journal of the American Society for Mass Spectrometry. 22, 659-669 (2011).</li><li>Krimm, S., Bandekar, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrational+spectroscopy+and+conformation+of+peptides,+polypeptides,+and+proteins.">Vibrational spectroscopy and conformation of peptides, polypeptides, and proteins.</a> Advances in Protein Chemistry. 38, 181-364 (1986).</li><li>Halverson, K. J., Sucholeiki, I., Ashburn, T. T., Lansbury, P. 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K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Artificial+[FeFe]-hydrogenase:+On+resin+modification+of+an+amino+acid+to+anchor+a+hexacarbonyldiiron+cluster+in+a+peptide+framework.">Artificial [FeFe]-hydrogenase: On resin modification of an amino acid to anchor a hexacarbonyldiiron cluster in a peptide framework.</a> European Journal of Inorganic Chemistry. 2011, 1050-1055 (2011).</li><li>Van Duinen, S. G., Castano, E. M., Prelli, F., Bots, G. T. A. B., Luyendijk, W., Frangione, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hereditary+cerebral+hemorrhage+with+amyloidosis+in+patients+of+Dutch+origin+is+related+to+Alzheimer+disease.">Hereditary cerebral hemorrhage with amyloidosis in patients of Dutch origin is related to Alzheimer disease.</a> Proceedings of the National Academy of Sciences of the United States of America. 84, 5991-5994 (1987).</li><li>Barth, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+infrared+absorption+of+amino+acid+sidechains.">The infrared absorption of amino acid sidechains.</a> Progress in Biophysics and Molecular Biology. 74, 141-173 (2000).</li><li>Jayaraman, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Slow+amyloid+nucleation+via+&#945;-helix-rich+oligomeric+intermediates+in+short+polyglutamine-containing+Huntingtin+fragments.">Slow amyloid nucleation via &#945;-helix-rich oligomeric intermediates in short polyglutamine-containing Huntingtin fragments.</a> Journal of Molecular Biology. 415, 881-899 (2012).</li></ol>

The authors have nothing to disclose.

This article discusses the details of both the synthesis and the purification of an N-terminal 1,2-dithiolane modified self-assembling peptide and the characterization of the resulting supramolecular structures. The synthesis of the 1,2-dithiolane peptide reported here has the advantages, including a one-step synthesis to produce the dithiolane precursor, 3-(acetylthio)-2-(acetylthiomethyl)propanoic acid, and the on-resin microwave deprotection reaction of the precursor thioacetate protecting group to yield the oxidized ...

The robust peptide bond forming chemistry involved in solid-phase peptide synthesis and the ability to control sequence length and composition make the peptides that self-assemble into supramolecular structures a heavily researched field. The factors that control and stabilize peptide self-assembled structures, including side chain steric and electrostatic interactions, hydrogen bonding, and hydrophobic effects1, serve as a set of design rules. As the research into these fundamental design rules continues to progress, the logical next step in peptide self-assembly involves expanding the diversity of peptide-based structures and functions. While self-assembling peptides are a versatile biomaterial that have been used for many biomedical applications by tuning the peptide sequence or assembly conditions2,3,4, the development of strategies for post-assembly modifications to peptide nanofibers5,6,7,8,9 remains a relatively unexplored area.
Dynamic disulfide exchange and thiol chemistry at the surface of supramolecular structures is one area that has the potential to yield new and functional biomaterials. The incorporation of 1,2-dithiolane moieties (commonly a derivative of lipoic acid (la) or asparagusic acid (aa)) have been reported in liposome systems10,11, block copolymers12,13, and as organizing anchors at surfaces14,15. Herein, we report the synthesis and characterization of a self-assembling peptide derived from the nucleating core of the A&#946; peptide associated with Alzheimer&#39;s disease that is modified at the N-terminus with a 1,2-dithiolane functional group16,17. The resulting supramolecular fibers now serve as an experimental platform to study the disulfide-exchange and thiol reactivity at the supramolecular surface of amyloid fibers18.

<table>
	<tbody>
		<tr>
			<td>Rink amide MBHA resin, high load</td>
			<td>Gyros Protein Technologies</td>
			<td>RAM-5-HL</td>
			<td>Avoid contact with skin and eyes; do not inhale</td>
		</tr>
		<tr>
			<td>N,N-Dimethylformamide</td>
			<td>Fisher Scientific</td>
			<td>D119-4</td>
			<td>Flammable liquid and vapor; irritating to eyes and skin; Use personal protective equipment; keep away from open flame</td>
		</tr>
		<tr>
			<td>Fmoc-L-Val-OH</td>
			<td>Gyros Protein Technologies</td>
			<td>FLA-25-V</td>
			<td>Wear personal protective equipment; do not inhale</td>
		</tr>
		<tr>
			<td>Fmoc-L-Leu-OH</td>
			<td>Gyros Protein Technologies</td>
			<td>FLA-25-L</td>
			<td>Wear personal protective equipment; do not inhale</td>
		</tr>
		<tr>
			<td>Fmoc-L-Lys(Boc)-OH</td>
			<td>Gyros Protein Technologies</td>
			<td>FLA-25-KBC</td>
			<td>Wear personal protective equipment; do not inhale</td>
		</tr>
		<tr>
			<td>Fmoc-L-Phe-OH</td>
			<td>Gyros Protein Technologies</td>
			<td>FLA-25-F</td>
			<td>Wear personal protective equipment; do not inhale</td>
		</tr>
		<tr>
			<td>Fmoc-L-Ala-OH</td>
			<td>Gyros Protein Technologies</td>
			<td>FLA-25-A</td>
			<td>Wear personal protective equipment; do not inhale</td>
		</tr>
		<tr>
			<td>Fmoc-L-Gln(Trt)-OH</td>
			<td>Gyros Protein Technologies</td>
			<td>FLA-25-QT</td>
			<td>Wear personal protective equipment; do not inhale</td>
		</tr>
		<tr>
			<td>N,N,N&#8242;,N&#8242;-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate</td>
			<td>Gyros Protein Technologies</td>
			<td>26432</td>
			<td>Causes skin, eye and respiratory irritation; do not inhale; use under hood or in well ventilated area</td>
		</tr>
		<tr>
			<td>0.4 M N-methylmorpholine in DMF</td>
			<td>Gyros Protein Technologies</td>
			<td>PS3-MM-L</td>
			<td>highly flammable; wear personal protective equipment; keep away from heat and keep container tightly closed; do not inhale or swallow; wash skin thoroughly after handling</td>
		</tr>
		<tr>
			<td>20% piperidine in DMF</td>
			<td>Gyros Protein Technologies</td>
			<td>PS3-PPR-L</td>
			<td>Causes severe eye and skin burns; Flammable Liquid and vapor; Do not inhale</td>
		</tr>
		<tr>
			<td>dichloromethane</td>
			<td>Fisher Scientific</td>
			<td>D37-4</td>
			<td>May cause cancer; Do not inhale; Wear personal protective equipment; use under hood only; if contacted rise with water for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>acetonitrile</td>
			<td>Fisher Scientific</td>
			<td>A998-4</td>
			<td>Flammable; irritating to eyes; Use personal protective equipment; Use only under a fume hood; keep away from open flame or hot surface; if contacted rinse wiith water for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>trifluoroacetic acid</td>
			<td>Fisher Scientific</td>
			<td>A116-50</td>
			<td>Causes severe burns; do not inhale; harmful to aquatic life; use personal protective equipment; use only under fume hood; if contacted rinse with water for at least 15 minutes and obain immediate medical attention</td>
		</tr>
		<tr>
			<td>4% uranyl acetate</td>
			<td>Electron Microscopy Sciences</td>
			<td>22400-4</td>
			<td>Do not inhale; harmful to aquatic life</td>
		</tr>
		<tr>
			<td>4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid</td>
			<td>Acros Organics</td>
			<td>AC172571000</td>
			<td>Do not inhale; use outdoors or in well-ventilated area</td>
		</tr>
		<tr>
			<td>nitrogen Gas</td>
			<td>TechAir</td>
			<td></td>
			<td>Contents under pressure, may explode if heated</td>
		</tr>
		<tr>
			<td>3-bromo-2-(bromomethyl)propionic acid</td>
			<td>Alfa Aesar</td>
			<td>AAA1963014</td>
			<td>Do not inhale; causes irritation to skin and eyes; corrosive</td>
		</tr>
		<tr>
			<td>sodium hydroxide</td>
			<td>Fisher Scientific</td>
			<td>S318-100</td>
			<td>Use personal protective equipment; use only under fume hood; if contact rinse area for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>potassium thioacetate</td>
			<td>Acros Organics</td>
			<td>AC221300250</td>
			<td>Causes skin and eye irritation; do not inhale; use personal protective equipment</td>
		</tr>
		<tr>
			<td>sulfuric acid</td>
			<td>Fisher Scientific</td>
			<td>SA213</td>
			<td>Causes burns; keep away from water; keep away from combustible material; do not inhale; use personal protective equipment; if contact rinse area for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>chloroform-d</td>
			<td>Acros Organics</td>
			<td>AC320690075</td>
			<td>Possible cancer hazard; irritating to skin and eyes; do not inhale; Use personal protective equipment; use only under fume hood; If contact rinse area for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>chloroform</td>
			<td>Fisher Scientific</td>
			<td>C298-4</td>
			<td>Possible cancer hazard; irritating to skin and eyes; do not inhale; Use personal protective equipment; use only under fume hood; If contact rinse area for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>N,N-diisopropylethylamine</td>
			<td>Acros Organics</td>
			<td>AC367841000</td>
			<td>Highly flammable; harmful to aquatic life; wear personal protective equipment; do not swallow</td>
		</tr>
		<tr>
			<td>ammonium hydroxide</td>
			<td>Fisher Scientific</td>
			<td>A669S-500</td>
			<td>Corrosive; do not inhale</td>
		</tr>
		<tr>
			<td>methanol</td>
			<td>Fisher Scientific</td>
			<td>A452-4</td>
			<td>Flammable liquid and vapor; use personal protective equipment; do not inhale; If contact rinse area for at least 15 minutes and obtain medical attention</td>
		</tr>
		<tr>
			<td>triisopropylsilane</td>
			<td>Sigma Aldrich</td>
			<td>233781</td>
			<td>Flammable; use personal proctective safety equipment; keep container tightly closed</td>
		</tr>
		<tr>
			<td>diethyl ether</td>
			<td>Fisher Scientific</td>
			<td>E138-1</td>
			<td>Extremely flammable; Irritating to skin and eyes; Use personal protective equipment</td>
		</tr>
		<tr>
			<td>2,5-dihydroxybenzoic acid</td>
			<td>Sigma Aldrich</td>
			<td>39319-10x10MG-F</td>
			<td>do not inhale; irritating to skin and eyes</td>
		</tr>
		<tr>
			<td>alpha-cyano-4-hydroxycinnamic acid</td>
			<td>Alfa Aesar</td>
			<td>AAJ67635EXK</td>
			<td></td>
		</tr>
		<tr>
			<td>c18 zip-tip</td>
			<td>Millipore</td>
			<td>ZTC18S096</td>
			<td></td>
		</tr>
		<tr>
			<td>tris(2-carboxyethyl) phospine hydrochloride</td>
			<td>Thermo Scientific</td>
			<td>PI20490</td>
			<td></td>
		</tr>
		<tr>
			<td>silica gel 60 F254 coated aluminum-backed TLC sheets</td>
			<td>EMD Millipore</td>
			<td>1.05549.0001</td>
			<td></td>
		</tr>
		<tr>
			<td>Thin walled Precision NMR tubes</td>
			<td>Bel-Art</td>
			<td>663000585</td>
			<td>5mm O.D.</td>
		</tr>
		<tr>
			<td>All-plastic Norm-Ject syringes</td>
			<td>Air Tite</td>
			<td>AL10</td>
			<td></td>
		</tr>
		<tr>
			<td>single-use needle</td>
			<td>BD PrecisionGlide</td>
			<td>BD 305185</td>
			<td>used needles get disposed on in sharps waste container</td>
		</tr>
		<tr>
			<td>disposable fritted syringe</td>
			<td>Torviq</td>
			<td>SF1000LL</td>
			<td>10mL fritted syringes were used in the report, but larger syringes are avaibale if needed for larger scale synthesis.</td>
		</tr>
		<tr>
			<td>carbon grid</td>
			<td>Ted Pella, Inc.</td>
			<td>CF200-CU</td>
			<td>Make sure to prepare samples and staining on the carbon grid side, not the shiny copper side of grid</td>
		</tr>
		<tr>
			<td>self-closing tweezers</td>
			<td>Electron Microscopy Sciences</td>
			<td>78318-3X</td>
			<td>very sharp tips, length: 120 mm</td>
		</tr>
		<tr>
			<td>0.1 mm short path length cell</td>
			<td>Starna Cells, Inc.</td>
			<td>20/C-Q-0.1</td>
			<td>Fragile</td>
		</tr>
		<tr>
			<td>10mL Vessel Caps</td>
			<td>CEM</td>
			<td>909210</td>
			<td></td>
		</tr>
		<tr>
			<td>10mL Pressure Vessels</td>
			<td>CEM</td>
			<td>908035</td>
			<td></td>
		</tr>
		<tr>
			<td>Aeris Semi-Prep HPLC column</td>
			<td>Phenomenex</td>
			<td>00F-4632-N0</td>
			<td>150 x 10mm</td>
		</tr>
		<tr>
			<td>cell holder</td>
			<td>Starna Cells, Inc.</td>
			<td>CH-2049</td>
			<td>Needed when using short pathlength cells</td>
		</tr>
		<tr>
			<td>PS3 peptide synthesizer</td>
			<td>Gyros Protein Technologies</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DiscoverSP Microwave Reactor</td>
			<td>CEM</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>centrifuge</td>
			<td>HERMLE</td>
			<td>Z 206 A</td>
			<td>used a fixed 6x50 mL rotor</td>
		</tr>
		<tr>
			<td>HPLC</td>
			<td>Shimadzu</td>
			<td></td>
			<td>UV Detector</td>
		</tr>
		<tr>
			<td>nuclear magnetic resonance spectrometer</td>
			<td>Avance, Bruker</td>
			<td></td>
			<td>300 MHz</td>
		</tr>
		<tr>
			<td>MALDI-TOF mass spectrometer</td>
			<td>Axima Confidence, Shimadzu</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>lyophilizer</td>
			<td>Millrock Technology</td>
			<td>BT85A</td>
			<td></td>
		</tr>
		<tr>
			<td>Fourier-Transform Infrared Spectrometer</td>
			<td>Alpha Tensor, Bruker</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Transmission Electron Microscope</td>
			<td>Tecnai Spirit, FEI</td>
			<td></td>
			<td>Used with Gatan Orius Fiberoptic CCD digital camera. Accessed at CSCU Center for Nanotechnology</td>
		</tr>
		<tr>
			<td>Circular Dichroism Spectropolarimeter</td>
			<td>J-810, JASCO</td>
			<td></td>
			<td>Used with a six-cell Peltier temperature controller. Accessed at Wesleyan University.</td>
		</tr>
	</tbody>
</table>

synthesis and characterization of 1,2-dithiolane modified self-assembling peptides

This report focuses on the synthesis of an N-terminus 1,2-dithiolane modified self-assembling peptide and the characterization of the resulting self-assembled supramolecular structures. The synthetic route takes advantage of solid-phase peptide synthesis with the on-resin coupling of the dithiolane precursor molecule, 3-(acetylthio)-2-(acetylthiomethyl)propanoic acid, and the microwave-assisted thioacetate deprotection of the peptide N-terminus before final cleavage from the resin to yield the 1,2-dithiolane modified peptide. After the high-performance liquid chromatography (HPLC) purification of the 1,2-dithiolane peptide, derived from the nucleating core of the A&#946; peptide associated with Alzheimer&#39;s disease, the peptide is shown to self-assemble into cross-&#946; amyloid fibers. Protocols to characterize the amyloid fibers by Fourier-transform infrared spectroscopy (FT-IR), circular dichroism spectroscopy (CD) and transmission electron microscopy (TEM) are presented. The methods of N-terminal modification with a 1,2-dithiolane moiety to well-characterized self-assembling peptides can now be explored as model systems to develop post-assembly modification strategies and explore dynamic covalent chemistry on supramolecular peptide nanofiber surfaces.

Aside from the initial one-step synthesis of the dithiolane precursor molecule, the rest of the 1,2-dithiolane modified peptide synthesis occurs on solid support (Figure 1A). The conversion of 3-bromo-2-(bromomethyl)propionic acid to 3-(acetylthio)-2-(acetylthiomethyl)propanoic acid, the dithiolane precursor, is confirmed by 1H and 13C NMR (Figure 1B and C) before it is coupled to the free N...

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Synthesis and Characterization of 1,2-Dithiolane Modified Self-Assembling Peptides

A protocol for the synthesis of a 1,2-dithiolane modified peptide and the characterization of the supramolecular structures resulting from the peptide self-assembly.

This report focuses on the synthesis of an N-terminus 1,2-dithiolane modified self-assembling peptide and the characterization of the resulting ...

As structures to increase the functionality of supermolecular structures grows, this method of incorporating 1, 2-dithiolane groups with self-assembling peptides can help answer key questions about reactivity on supermolecular surfaces. The main advantage of this technique is that the coupling and deprotection of the 1, 2-dithiolane precursor molecule occurs on resin with only a single purification step of the final modified peptide. As the time it takes the assemblies to mature into their final supermolecular structures varies, visual demonstration of the characterization methods and results for the supermolecular assemblies is critical.To synthesize the dithiolane precursor, first dissolve one gram of 3-bromo-2-proprionic acid in approximately four milliliters of one-molar sodium hydroxide in a 50-milliliter round-bottomed reaction flask at 55 degrees Celsius with stirring. When all of the reagent has been suspended in solution, seal the reaction flask with a septa and place the flask under nitrogen atmosphere. Next, add 1.49 grams of potassium thioacetate and three milliliters of two-molar sulfuric acid to four milliliters of deionized water to create thioacetic acid in situ.Aspirate the thioacetic acid solution into a plastic, disposable 10-milliliter syringe and equip the syringe with an 18-gauge needle, then pierce the septa with the needle to add the mixture dropwise to the reaction flask and continue the reaction overnight at 55 degrees Celsius. The next morning, monitor the reaction by thin-layer chromatography on silica gel 60 F254 plates using a mixture of methanol and dichloromethane and visualizing the reaction progress by bromocresol green stain. When the completed reaction has cooled to room temperature, acidify the mixture with two-molar sulfuric acid to a pH of one.A yellow oil should separate out of solution, then extract the product with three 40-milliliter additions of cold chloroform and combine the organic layers for drying over magnesium sulfate, removing the chloroform under reduced pressure. The product should be a yellow oil with an overall yield of 83%and can be used without further purification. To couple the dithiolane precursor to the N-terminus of the on-resin peptide, add four equivalents of dithiolane precursor to five milliliters of dimethylformamide, four equivalents of HBTU, and 10 equivalents of DIPEA.Allow the coupling mixture to preactivate for 10 minutes at room temperature before adding the sample to the N-terminus-resin-containing fritted syringe. Shake the coupling reaction for two hours, followed by three five-milliliter washes in fresh dimethylformamide and repeat the coupling reaction and overnight shaking. After the second coupling, wash the resin with three five-milliliter dimethylformamide washes followed by three five-milliliter dichloromethane resin washes and transfer the dried resin to a 10-milliliter microwave reaction tube.Then, to deprotect the thioacetate group from the N-terminus dithiolane precursor, add two milliliters of dimethylformamide to the tube. Allow the resin to swell, add a small magnetic stir bar to the vessel, and resuspend the resin with low-speed magnetic stirring. After 15 minutes, add two milliliters of concentrated ammonium hydroxide to the tube, cap the reaction vessel with a silicone septa, and place the vessel in a microwave reactor for 45 minutes at 75 degrees Celsius with stirring.When the microwave reaction is complete, transfer the resin into a clean, disposable, fritted syringe and wash the resin with two five-milliliter dimethylformamide and two five-milliliter methanol washes. After the last wash, add five milliliters of cleavage cocktail to the resin-containing syringe for a 1 1/2 hour incubation with gentle shaking at room temperature. To prepare one milliliter of crude peptide for high-performance liquid chromatography or HPLC purification, add 400 microliters of concentrated peptide stock in acetonitrile to 600 microliters of water supplemented with 0.1%of trifluoroacetic acid and filter the solution through a 22-micrometer syringe filter into an HPLC vial.To purify the peptide, use a C18 semi-preparative column at a three-milliliters-per-minute flow rate over a linear gradient of 15 to 55%acetonitrile in 20 minutes with the UV-detectors set to 222 nanometers and 330 nanometers. Then collect and combine the peaks of interest. For peptide product confirmation by matrix-assisted laser desorption/ionization time of flight or MALDI-TOF mass spectrometry, mix 0.5 microliters of the collected peak on a matrix-assisted laser desorption/ionization plate containing 0.5 microliters of 2, 5-dihydroxybenzoic acid matrix.To prepare a self-assembly solution, dissolve one milligram of the lyophilized peptide powder in a mixture of 20%acetonitrile and 10-millimolar HEPES in a 1.5-milliliter microcentrifuge tube, then vortex the assembly solution and leave the sample to assemble at room temperature. When the peptide assembly reaches maturation, dry eight to 10 microliters of the assembly solution as a thin film on the attenuated total-reflection diamond crystal and monitor the disappearance of a large and broad water peak from 1640 to 1631 inverse centimeters as the dry film forms. Acquire background and infrared spectra from 1500 to 1800 inverse centimeters averaging 50 scans with a two inverse centimeter resolution, subtracting the background scans prior to each sample scan.The infrared signature for beta sheet assembly should be observed as a sharp peak between 1625 and 1635 inverse centimeters. When the peptide samples have matured into beta-sheet-rich supermolecular structures, load 10 microliters of the peptide assembly solution onto the surface of a transmission electron microscope carbon grid and allow the assemblies to adsorb onto the grid's surface for one to two minutes. Touch filter paper to the edge of the grid to remove the excess sample, and add 10 microliters of freshly-prepared 2%uranyl acetate stain to the grid surface for a two to three-minute incubation, then remove excess stain with filter paper and place the grid in a vacuum desiccator overnight before next-day imaging by transmission electron microscopy.Aside from the initial one-step synthesis of the dithiolane precursor molecule, the rest of the 1, 2-dithiolane-modified peptide synthesis occurs on solid support. The conversion of 3-bromo-2-proprionic acid to 3-2-propanoic acid, the dithiolane precursor, is confirmed by proton and Carbon-13 nuclear magnetic resonance before it is coupled to the free N-terminus amine of a peptide still on resin. After deprotection, the crude peptide is purified by reverse-phase HPLC and the product's mass is confirmed by MALDI-TOF mass spectrometry.Fourier-transform infrared and circular dichroism spectroscopy can be used to monitor the self-assembly of the purified 1, 2-dithiolane peptide into mature amyloid fibers to characterize their extended beta sheet conformation. The fibers can then be imaged by transmission electron microscopy. While these methods can be used to modify the N-terminus of any peptide sequence still on resin, it's important to remember that the peptide-self-assembly conditions should be optimized for each peptide.These techniques, which add 1, 2-dithiolane groups to self-assembling peptides, will allow researchers in the field of biomaterials to explore supermolecular surface reactivity.

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7.1K visualizações.  Fairfield University. As structures to increase the functionality of supermolecular structures grows, this method of incorporating 1, 2-dithiolane groups with self-assembling peptides can help answer key questions about reactivity on supermolecular surfaces. The main advantage of this technique is that the coupling and deprotection of the 1, 2-dithiolane precursor molecule occurs on resin with only a single purification step of the final modified peptide. As the time it takes the assemblies to mature into their fi...