Name: synthesis and characterization of supramolecular colloids
Uploaded: 2016-04-22T14:00:00
Description: Watch this Scientific Journal Video about Synthesis and Characterization of Supramolecular Colloids at JoVE.com

The authors acknowledge The Netherlands Organization for Scientific research (NWO ECHO-STIP Grant 717.013.005, NWO VIDI Grant 723.014.006) for the financial support.

1. Synthesis of Core-shell Silica Particles
Note: Silica particles are synthesized according to the following procedure, which is based on the St&#246;ber method24,25.
<ol>
	<li>Synthesis of fluorescent silica seeds
	<ol>
		<li>Dissolve 105 mg (0.27 mmol) of fluorescein-isothiocyanate in 5 ml of ethanol.</li>
		<li>Add 100 &#181;l of (3-aminopropyl) triethoxysilane (APTES, 0.43 mmol) to the previous solution.</li>
		<li>Sonicate the solution durin...

<ol>
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Mater. 23 (1), 30-69 (2011).</li><li>Kim, H., 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=Structural+colour+printing+using+a+magnetically+tunable+and+lithographically+fixable+photonic+crystal.">Structural colour printing using a magnetically tunable and lithographically fixable photonic crystal.</a> Nat. Photonics. 3 (9), 534-540 (2009).</li><li>Dinsmore, A. D., 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=Colloidosomes:+Selectively+permeable+capsules+composed+of+colloidal+particles.">Colloidosomes: Selectively permeable capsules composed of colloidal particles.</a> Science. 298 (5595), 1006-1009 (2002).</li><li>Destribats, M., Rouvet, M., Gehin-Delval, C., Schmitt, C., Binks, B. 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J., 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=Surface+roughness+directed+self-assembly+of+patchy+particles+into+colloidal+micelles.">Surface roughness directed self-assembly of patchy particles into colloidal micelles.</a> PNAS. 109 (27), 10787-10792 (2012).</li><li>Rossi, L., 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=Cubic+crystals+from+cubic+colloids.">Cubic crystals from cubic colloids.</a> Soft Matter. 7 (9), 4139-4142 (2011).</li><li>Erb, R. M., Son, H. S., Samanta, B., Rotello, V. M., Yellen, B. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic+assembly+of+colloidal+superstructures+with+multipole+symmetry.">Magnetic assembly of colloidal superstructures with multipole symmetry.</a> Nature. 457 (7232), 999-1002 (2009).</li><li>Vutukuri, H. 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=Colloidal+analogues+of+charged+and+uncharged+polymer+chains+with+tunable+stiffness.">Colloidal analogues of charged and uncharged polymer chains with tunable stiffness.</a> Angew. Chem. Int. Edit. 51 (45), 11249-11253 (2012).</li><li>De Greef, T. F. A., 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=Materials+science:+Supramolecular+polymers.">Materials science: Supramolecular polymers.</a> Nature. 453 (7192), 171-173 (2008).</li><li>De Feijter, I., Albertazzi, L., Palmans, A. R. A., Voets, I. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stimuli-responsive+colloidal+assembly+driven+by+surface-grafted+supramolecular+moieties.">Stimuli-responsive colloidal assembly driven by surface-grafted supramolecular moieties.</a> Langmuir. 31 (1), 57-64 (2015).</li><li>Celiz, A. D., Lee, T. C., Scherman, O. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymer-mediated+dispersion+of+cold+nanoparticles:+using+supramolecular+moieties+on+the+periphery.">Polymer-mediated dispersion of cold nanoparticles: using supramolecular moieties on the periphery.</a> Adv. Mater. 21 (38-39), 3937-3940 (2009).</li><li>Cantekin, S., De Greef, T. F. A., Palmans, A. R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Benzene-1,3,5-tricarboxamide:+A+versatile+ordering+moiety+for+supramolecular+chemistry.">Benzene-1,3,5-tricarboxamide: A versatile ordering moiety for supramolecular chemistry.</a> Chem. Soc. Rev. 41 (18), 6125-6137 (2012).</li><li>Mes, T., Van Der Weegen, R., Palmans, A. R. A., Meijer, E. 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When cyclohexane, with a refractive index of 1.426, is used as a solvent to disperse the BTA-colloids, van der Waals interactions are very weak, since the refractive indices of colloids and solvent are nearly the same. Note that the concentration of functionalized colloids used for the SLS experiments in cyclohexane is much higher compared to the bare silica colloids in water. This is necessary to obtain a sufficiently strong scattering due to the low contrast as the refractive indices are almost matched. Trace amounts o...

Mesostructured colloidal materials find widespread application in science and technology, as model systems for fundamental studies on atomic and molecular materials1,2, as photonic materials3,4, as drug delivery systems5,6, as coatings7 and in lithography for surface patterning8,9. Since lyophobic colloids are metastable materials that eventually aggregate irreversibly due to the omnipresent van der Waals interactions, their manipulation into specific target structures is notoriously difficult. Numerous strategies have been developed to control colloidal self-assembly including the use of additives to tune the electrostatic10,11 or depletion interactions12,13, or external triggers such as magnetic14 or electric15 fields. A sophisticated alternative strategy to achieve control over the structure, dynamics and mechanics of these systems is their functionalization with molecules interacting through specific and directional forces. Supramolecular chemistry offers a comprehensive toolbox of small molecules exhibiting site-specific, directional and strong yet reversible interactions, which can be modulated in strength by solvent polarity, temperature and light16. Since their properties have been studied extensively in bulk and in solution, these molecules are attractive candidates to structure soft materials into exotic phases in a predictable manner. Despite the clear potential of such an integrated approach to orchestrate colloidal assembly via supramolecular chemistry, these disciplines have rarely interfaced to tailor the properties of mesostructured colloidal materials17,18.
A solid platform of supramolecular colloids must fulfill three main requirements. Firstly, coupling of the supramolecular moiety should be done under mild-conditions to prevent degradation. Secondly, surface forces at separations larger than direct contact should be dominated by the tethered motifs, which means that uncoated colloids should nearly exclusively interact via excluded-volume interactions. Therefore, the physico-chemical properties of the colloids should be tailored to suppress other interactions inherent in colloidal systems, such as van der Waals or electrostatic forces. Thirdly, characterization should allow for an unequivocal attribution of the assembly to the presence of the supramolecular moieties. To meet these three prerequisites, a robust two-step synthesis of supramolecular colloids was developed (Figure 1a). In a first step, hydrophobic NVOC-functionalized silica particles are prepared for dispersion in cyclohexane. The NVOC group can be easily cleaved, yielding amine-functionalized particles. The high reactivity of amines enables straightforward post-functionalization with the desired supramolecular moiety using a wide range of mild reaction conditions. Herein, we prepare supramolecular colloids by functionalization of silica beads with stearyl alcohol and a benzene-1,3,5-tricarboxamide (BTA) derivative20. The stearyl alcohol plays several important roles: it makes the colloids organophilic and it introduces short-range steric repulsions which aids to reduce the nonspecific interaction between colloids21,22. van der Waals forces are further reduced because of the close match between the refractive index of the colloids and the solvent23. Light-and thermoresponsive short-range attractive surface forces are generated by incorporation of o-nitrobenzyl protected BTAs20. O-nitrobenzyl moiety is a photo-cleavable group that blocks the formation of hydrogen bonds between adjacent BTAs when incorporated on the amides in the discotics (Figure 1b). Upon photocleavage by UV-light, the BTA in solution is able to recognize and interact with identical BTA molecules through a 3-fold hydrogen bond array, with a binding strength that is strongly temperature dependent17. Since the van der Waals attractions are minimal for stearyl coated silica particles in cyclohexane as well as light- and temperature-independent, the observed stimuli-responsive colloidal assembly must be BTA-mediated.
This detailed video demonstrates how to synthesize and characterize supramolecular colloids and how to study their self-assembly upon UV-irradiation by confocal microscopy. In addition, a simple image analysis protocol to distinguish colloidal singlets from clustered colloids and to determine the amount of colloids per clusters is reported. The versatility of the synthetic strategy allows to readily vary particle size, surface coverage as well as the introduced binding moiety, which opens up new avenues for the development of a large family of colloidal building blocks for mesostructured advanced materials.

<table border="0" cellpadding="0" cellspacing="0" width="1805">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">APTES</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">FTIC</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">TEOS</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">LUDOX AS-40</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td>Silica particles of 13 nm in radius</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">MilliQ</td>
			<td style="width:128px;">---</td>
			<td style="width:119px;">---</td>
			<td style="width:1035px;">18.2 M&#937;&#183;cm at 25 &#176;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Ethanol</td>
			<td style="width:128px;">SolvaChrom</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Ammonia (25% in water)</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Chloroform</td>
			<td style="width:128px;">SolvaChrom</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Cyclohexane</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Dimethylformamide (DMF)</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Stearyl alcohol</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">N,N-Diisopropylethylamine (DIPEA)</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP)</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Succinimidyl 3-(2-pyridyldithio)propionate (SPDP)</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dithiothreitol (DTT)&#160;</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td style="width:1035px;">---</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">NVOC-C11-OH</td>
			<td style="width:128px;">Synthesized</td>
			<td style="width:119px;">---</td>
			<td style="width:1035px;">I. de Feijter, 2014 Responsive materials from adaptive supramolecular constructs, Doctoral thesis, Technical University of Eindhoven, The Netherlands</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">BTA</td>
			<td style="width:128px;">Synthesized</td>
			<td style="width:119px;">---</td>
			<td style="width:1035px;">I. de Feijter, 2014 Responsive materials from adaptive supramolecular constructs, Doctoral thesis, Technical University of Eindhoven, The Netherlands</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Centrifuge</td>
			<td style="width:128px;">Thermo Scientific</td>
			<td style="width:119px;"></td>
			<td>Heraeus Megafuge 1.0</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Ultrasound bath</td>
			<td style="width:128px;">VWR</td>
			<td style="width:119px;"></td>
			<td>Ultrasonic cleaner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Peristaltic pumps</td>
			<td>Harvard Apparatus</td>
			<td></td>
			<td>PHD Ultra Syringe Pump</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:524px;">UV-oven</td>
			<td style="width:128px;">Luzchem</td>
			<td style="width:119px;"></td>
			<td>LZC-a V UV reactor equipped with 8x8 UVA light bulbs (&#955;max=354 nm)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Stirrer-heating plate</td>
			<td style="width:128px;">Heidolph</td>
			<td style="width:119px;"></td>
			<td>MR-Hei Standard</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Light Scattering</td>
			<td style="width:128px;">ALV</td>
			<td style="width:119px;"></td>
			<td>CGS-3 MD-4 compact goniometer system, equipped with a Multiple Tau digital real time correlator (ALV-7004) and a solid-state laser (&#955;=532 nm, 40 mW)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">UV-Vis spectrophotometer</td>
			<td style="width:128px;">Thermo Scientific</td>
			<td style="width:119px;"></td>
			<td>NanoDrop 1000 Spectrophotometer</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Confocal microscope</td>
			<td style="width:128px;">Nikon</td>
			<td style="width:119px;"></td>
			<td>Ti Eclipse with an argon laser with &#955;excitation=488 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Slide spacers</td>
			<td style="width:128px;">Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td>Grace BioLabs Secure seal imaging spacer (1 well, diam. &#215; thickness 13 mm &#215; 0.12 mm)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Syringes</td>
			<td style="width:128px;">BD Plastipak</td>
			<td style="width:119px;"></td>
			<td>20 mL syringe</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Plastic tubing</td>
			<td style="width:128px;">SCI</td>
			<td style="width:119px;">BB31695-PE/5</td>
			<td>Ethylene oxide gas sterilizable micro medical tubing</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:524px;">Pulsating vortex mixer</td>
			<td style="width:128px;">VWR</td>
			<td style="width:119px;"></td>
			<td>Electrical: 120V, 50/60Hz, 150W Speed Range: 500&#8211;3000 rpm</td>
		</tr>
	</tbody>
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synthesis and characterization of supramolecular colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

&#160;Given that the two-step procedure used to synthesize the supramolecular colloids (Figure 1a), couples the BTA- derivatives (Figure 1b) in a second step at room temperature and in mild-reaction conditions, its stability is ensured.
<img alt="Figure 1" src="/files/ftp_upload/53934/53934fig1.jpg" /> 
Figure 1. Scheme of the synthesis of supramolecular colloids. A) Coupli...

Watch this Scientific Journal Video about Synthesis and Characterization of Supramolecular Colloids at JoVE.com

Synthesis and Characterization of Supramolecular Colloids

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

The overall goal of this protocol is to describe how to direct colloidal self-assembly by anchoring supramolecular moieties onto the colloids whose interactions are strong, directional, and reversible. This method can help to answer key questions in the material science field, such as how to accurately control the colloidal self-assembly to create complex and mesostructured materials with interesting properties. The main advantage of this technique is that colloidal association is driven by the supramolecular moieties that remain responsive to light and to temperature upon surface immobilization.Therefore, colloids self-assemble upon photoactivation of the hydrogen bonds of the molecules by UV light. To synthesize the florescent silica seeds, first mix 2.5 milliliters of dye-functionalized aptes with 25 millileters of 25%ammonia and 250 milliliters of ethanol in a one liter round-bottom flask. To obtain monodisperse silica seeds it is really important to add the tetraethyl orthosilicate under the meniscus of the reaction mixture.Using a glass pipette, add 10 milileters of TEOS while stirring with a magnetic stirrer. Similarly, after five hours, add another 1.75 milliliters of TEOS and stir the mixture overnight under an argon atmosphere. The following day, wash the seeds as described in the text protocol.To synthesize the core-shell silica particles, first add ethanol, deionized water, 25%ammonia, and the seed dispersion to a one liter round-bottom flask. Then, fill a plastic syringe with five milliliters of TEOS and 10 milliliters of ethanol. Fill a second plastic syringe with 1.34 milliliters of 25%ammonia, 3.4 milliliters of deionized water, and 10.25 milliliters of ethanol.Connect both syringes to the round-bottom flask with plastic tubing. Equip the flask with an argon flow. The argon inlet has to be next to the outlet of the second syringe to avoid contact between ammonia gases from the TEOS droplets and prevent secondary nucleation.Add the content of both syringes at the same time at 1.7 milliliters per hour using peristaltic pumps while stirring the mixture. Ensure to obtain free-falling droplets to avoid colliding on the walls and therefore secondary nucleation. Stop the addition after seven hours to obtain core-shell particles of approximately 300 nanometers in radius before washing the particles as described in the text protocol.For the synthesis of NVOC-functionalized colloids, disperse 10 milligrams of core-shell silica particles in one milliliter of ethanol together with 12 milligrams of the NVOC-protected linker molecule and 31 milligrams of stearyl alcohol in a 50 milliliter round-bottom flask. Sonicate the mixture for 10 minutes to ensure that all molecules are disolved and the particles are well dispersed. Add a magnetic stir bar to the mixture and evaporate the ethanol with a steady stream of argon at room temperature.Before proceeding, ensure that there is no ethanol left, otherwise it could react with the silanol groups of the particles. Next, heat the flask up to 180 degrees Celsius for six hours under continuous stirring and under a steady stream of argon, before washing the silica colloids as described in the text protocol. To synthesize the BTA colloids, disperse 10 milligrams of the functionalized particles in three milliliters of chloroform.To cleave the NVOC group homogeneously, place the sample in the UV oven and stir it gently with a magnetic stirrer while deprotecting. Irradiate the dispersion for one hour to yield the amine functionalized particles. Then, dissolve nine milligrams of BTA, 8.7 microliters of DIPEA, and 5.2 milligrams of PyBOP in one milliliter of chloroform.Add the solution to the amine functionalized particle dispersion and stir overnight at room temperature and under an argon atmosphere. Following centrifugation of the dispersion, remove the supernatant and add three milliliters of fresh chloroform. Sonicate the new dispersion for three minutes before centrifuging again and removing the supernatant.Dry the particles at 70 degrees Celsius in vacuo for 48 hours. Disperse 20 milligrams of the small functionalized particles in one milliliter of chloroform and irradiate the dispersion in a UV oven for one hour to cleave the NVOC group. Stir the dispersion gently with a magnetic stir bar while deprotecting.Spin down the resulting amine functionalized particles and remove the supernatant. Then, dry the particles at 70 degrees Celsius for two hours. Next, dissolve 0.5 milligrams of SPDP in 200 microliters of DMF.Add the SPDP solution to the 20 milligrams of dried amine functionalized particles and vortex the system for 30 minutes. Wash the particles with one milliliter of DMF, six times. In the last washing step, try to remove as much supernatant as possible.Then, dissolve 0.53 milligrams of DTT in 50 microliters of DMF. Add the DTT solution to the particles and vortex the dispersion for 30 minutes, within this time, the pyridine 2 thione group is cleaved. Determine the absorbence of the free pyridine 2 thione liberated in the supernatant at a wave length of 233 nanometers with a microvolume UV-Vis spectrophotometer.To monitor the colloidal assembly by confocal microscopy, first prepare 400 microliters of a dispersion of 0.1 weight percent of BTA functionalized particles in cyclohexane and sonicate the sample for 20 minutes. Then irradiate the sample vial in the UV oven to cleave off the ortho-nitrobenzyl group of the BTA. Take 25 microliter aliquots at different times of irradiation, for example, from zero up to 30 minutes, to monitor the clustering process.Place the different aliquots on different glass slides with the help of a spacer, and close the chambers with a cover slip. After closing the chamber, turn the cover slip upside-down to let the particles sediment and absorb onto the glass, which facilitates the imaging. Take several images of each sample with the confocal microscope as soon as possible after sample preparation for each irradiation time.To produce supramolecular colloids, first silica colloids are hydrophobized by functionalization with stearyl alcohol, and the NVOC-protected linker. The NVOC-protective group is then cleaved, and colloids can be post-functionalized with the supramolecular moiety. Static light scattering measurements allow for calculation of the refractive index of the colloids.By fitting the date, values of 1.391 for the bare colloid and 1.436 for the stearyl alcohol coated colloids were determined. This clearly shows how the functionalization of the colloids has an impact on their refractive index. To assess the amount of active sites per particle, the amount of cleaved pyridine 2 thione groups are directly related to the number of amines per particle.Here, one amine per 46.4 square nanometers was found. confocal image analysis allows for quantification of the number of singlets as a function of the UV irradiation time. Before UV irradiation to photocleave the ortho-nitrobenzyl moiety, 80%of the colloids are present as singlets.Irradiation at a maximum wavelength of 354 nanometers initiates colloidal aggregation as the hydrogen bonds of the BTA are activated. While attempting this procedure, it's important to keep the system water-free, as colloids might cluster due to capillary forces. Therefore, water traces should be illiminated from all synthesis steps.This work demonstrates that bridging the gap between colloidal and supramolecular science paves the way for researchers in the field of material science to create complex materials sensitive to external stimuli. After watching this video, you should have a good understanding on how to direct colloidal self-assembly using hydrogen bonds by anchoring supramolecular motifs on colloidal particles.

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Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid phase by using combinatorial chemistry. One of the most well studied classes of peptidomimetics is peptoids. Peptoids are easy to synthesize and have been shown to be proteolysis-resistant and cell-permeable. Over the past decade, many useful protein ligands have been identified through screening of peptoid libraries. However, most of the ligands identified from peptoid libraries do not display high affinity, with rare exceptions. This may be due, in part, to the lack of chiral centers and conformational constraints in peptoid molecules. Recently, we described a new synthetic route to access peptide tertiary amides (PTAs). PTAs are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. With side chains on both &#945;-carbon and main chain nitrogen atoms, the conformation of these molecules are greatly constrained by sterical hindrance and allylic 1,3 strain. (Figure 1) Our study suggests that these PTA molecules are highly structured in solution and can be used to identify protein ligands. We believe that these molecules can be a future source of high-affinity protein ligands. Here we describe the synthetic method combining the power of both split-and-pool and sub-monomer strategies to synthesize a sample one-bead one-compound (OBOC) library of PTAs.

Peptide tertiary amides (PTAs) are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. Here we describe a synthetic method which combines&#160;both split-and-pool and sub-monomer strategies to synthesize a one-bead one-compound library of PTAs.

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid ...

Nucleoside Triphosphates - From Synthesis to Biochemical Characterization

The traditional strategy for the introduction of chemical functionalities is the use of solid-phase synthesis by appending suitably modified phosphoramidite precursors to the nascent chain. However, the conditions used during the synthesis and the restriction to rather short sequences hamper the applicability of this methodology. On the other hand, modified nucleoside triphosphates are activated building blocks that have been employed for the mild introduction of numerous functional groups into nucleic acids, a strategy that paves the way for the use of modified nucleic acids in a wide-ranging palette of practical applications such as functional tagging and generation of ribozymes and DNAzymes. One of the major challenges resides in the intricacy of the methodology leading to the isolation and characterization of these nucleoside analogues.
	
	In this video article, we present a detailed protocol for the synthesis of these modified analogues using phosphorous(III)-based reagents. In addition, the procedure for their biochemical characterization is divulged, with a special emphasis on primer extension reactions and TdT tailing polymerization. This detailed protocol will be of use for the crafting of modified dNTPs and their further use in chemical biology.

The protocol described herein aims to explain and abridge the numerous obstacles in the way of the intricate route leading to modified nucleoside triphosphates. Consequently, this protocol facilitates both the synthesis of these activated building-blocks and their availability for practical applications.

The  traditional strategy for the introduction of chemical functionalities is the  use of solid-phase synthesis by appending suitably modified ...

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the hydroxylmethylene phosphine precursor with ammonia in methanol under a nitrogen atmosphere. The N-triphosPh ligand precipitates from the solution after approximately 1 hr of reflux and can be isolated analytically pure via simple cannula filtration procedure under nitrogen. Reaction of the N-triphosPh ligand with [Ru3(CO)12] under reflux affords a deep red solution that show evolution of CO gas on ligand complexation. Orange crystals of the complex [Ru(CO)2{N(CH2PPh2)3}-&#954;3P] (2) were isolated on cooling to RT. The 31P{1H} NMR spectrum showed a characteristic single peak at lower frequency compared to the free ligand. Reaction of a toluene solution of complex 2 with oxygen resulted in the instantaneous precipitation of the carbonate complex [Ru(CO3)(CO){N(CH2PPh2)3}-&#954;3P] (3) as an air stable orange solid. Subsequent hydrogenation of 3 under 15 bar of hydrogen in a high-pressure reactor gave the dihydride complex [RuH2(CO){N(CH2PPh2)3}-&#954;3P] (4), which was fully characterized by X-ray crystallography and NMR spectroscopy. Complexes 3 and 4 are potentially useful catalyst precursors for a range of hydrogenation reactions, including biomass-derived products such as levulinic acid (LA). Complex 4 was found to cleanly react with LA in the presence of the proton source additive NH4PF6 to give [Ru(CO){N(CH2PPh2)3}-&#954;3P{CH3CO(CH2)2CO2H}-&#954;2O](PF6) (6).

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Ruthenium phosphine complexes are widely used for homogeneous catalytic reactions such as hydrogenations. The synthesis of a series of novel tridentate ruthenium complexes bearing the N-triphos ligand N(CH2PPh2)3 is reported. Additionally, the stoichiometric reaction of a dihydride Ru&#8211;N-triphos complex with levulinic acid is described.

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

Preparation of Carbon Nanosheets at Room Temperature

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into defined aggregates in aqueous media and at the air-water interface. In the aggregated state, the oligoynes can then be carbonized under mild conditions while preserving the morphology and the embedded chemical functionalization. This novel approach provides direct access to functionalized carbon nanomaterials. In this article, we present a synthetic approach that allows us to prepare hexayne carboxylate amphiphiles as carbon-rich siblings of typical fatty acid esters through a series of repeated bromination and Negishi-type cross-coupling reactions. The obtained compounds are designed to self-assemble into monolayers at the air-water interface, and we show how this can be achieved in a Langmuir trough. Thus, compression of the molecules at the air-water interface triggers the film formation and leads to a densely packed layer of the molecules. The complete carbonization of the films at the air-water interface is then accomplished by cross-linking of the hexayne layer at room temperature, using UV irradiation as a mild external stimulus. The changes in the layer during this process can be monitored with the help of infrared reflection-absorption spectroscopy and Brewster angle microscopy. Moreover, a transfer of the carbonized films onto solid substrates by the Langmuir-Blodgett technique has enabled us to prove that they were carbon nanosheets with lateral dimensions on the order of centimeters.

We present the synthesis of an amphiphilic hexayne and its use in the preparation of carbon nanosheets at the air-water interface from a self-assembled monolayer of these reactive, carbon-rich molecular precursors.

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

Synthesis and Characterization of Fe-doped Aluminosilicate Nanotubes with Enhanced Electron Conductive Properties

The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe aims at lowering the band gap of imogolite, an insulator with the chemical formula (OH)3Al2O3SiOH, and at modifying its adsorption properties towards azo-dyes, an important class of organic pollutants of both wastewater and groundwater.
Fe-doped nanotubes are obtained in two ways: by direct synthesis, where FeCl3 is added to an aqueous mixture of the Si and Al precursors, and by post-synthesis loading, where preformed nanotubes are put in contact with a FeCl3&#8226;6H2O aqueous solution. In both synthesis methods, isomorphic substitution of Al3+ by Fe3+ occurs, preserving the nanotube structure. Isomorphic substitution is indeed limited to a mass fraction of ~1.0% Fe, since at a higher Fe content (i.e., a mass fraction of 1.4% Fe), Fe2O3 clusters form, especially when the loading procedure is adopted. The physicochemical properties of the materials are studied by means of X-ray powder diffraction (XRD), N2 sorption isotherms at -196 &#176;C, high resolution transmission electron microscopy (HRTEM), diffuse reflectance (DR) UV-Vis spectroscopy, and &#950;-potential measurements. The most relevant result is the possibility to replace Al3+ ions (located on the outer surface of the nanotubes) by post-synthesis loading on preformed imogolite without perturbing the delicate hydrolysis equilibria occurring during nanotube formation. During the loading procedure, an anionic exchange occurs, where Al3+ ions on the outer surface of the nanotubes are replaced by Fe3+ ions. In Fe-doped aluminosilicate nanotubes, isomorphic substitution of Al3+ by Fe3+ is found to affect the band gap of doped imogolite. Nonetheless, Fe3+ sites on the outer surface of nanotubes are able to coordinate organic moieties, like the azo-dye Acid Orange 7, through a ligand-displacement mechanism occurring in an aqueous solution.

Here, we present a protocol to synthesize and characterize Fe-doped aluminosilicate nanotubes. The materials are obtained by either sol-gel synthesis upon addition of FeCl3&#8226;6H2O to the mixture containing the Si and Al precursors or by post-synthesis ionic exchange of preformed aluminosilicate nanotubes.

The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe ...

Phase Behavior of Charged Vesicles Under Symmetric and Asymmetric Solution Conditions Monitored with Fluorescence Microscopy

Phase-separated giant unilamellar vesicles (GUVs) exhibiting coexisting liquid-ordered and liquid-disordered domains are a common biophysical tool to investigate the lipid raft hypothesis. Numerous studies, however, neglect the impact of physiological solution conditions. On that account, the current work presents the effect of high-salinity buffer and trans-membrane solution asymmetry on liquid-liquid phase separation in charged GUVs grown from dioleylphosphatidylglycerol, egg sphingomyelin, and cholesterol. The effects were studied under isothermal and varying temperature conditions.
We describe equipment and experimental strategies applicable for monitoring the stability of coexisting liquid domains in charged vesicles under symmetric and asymmetric high-salinity solution conditions. This includes an approach to prepare charged multicomponent GUVs in high-salinity buffer at high temperatures. The protocol entails the option to perform a partial exchange of the external solution by a simple dilution step while minimizing the vesicle dilution. An alternative approach is presented utilizing a microfluidic device that allows for a complete external solution exchange. The solution effects on phase separation were also studied under varying temperatures. To this end, we present the basic design and utility of an in-house built temperature control chamber. Furthermore, we reflect on the assessment of the GUV phase state, pitfalls associated with it and how to circumvent them.

Experiments on phase separated giant unilamellar vesicles (GUVs) frequently neglect physiological solution conditions. This work presents approaches to study the effect of high-salinity buffer on liquid-liquid phase separation in charged multicomponent GUVs as a function of trans-membrane solution asymmetry and temperature.

Phase-separated giant unilamellar vesicles (GUVs) exhibiting coexisting liquid-ordered and liquid-disordered domains are a common biophysical tool to ...

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.

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.