Name: microfluidic-based synthesis of covalent organic frameworks (cofs): a tool for continuous production of cof fibers and direct printing on a surface
Uploaded: 2017-07-10T11:30:00
Description: Watch this Scientific Journal Video about Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface at JoVE.com

The authors acknowledge the Swiss National Science Foundation (SNF) for financial support through project no. 200021_160174.

1. Master Mold Fabrication
<ol>
	<li>Perform the photolithographic fabrication of a 4 inch silicon master mold as described in detail previously19; the master mold used in this study has been fabricated using the same protocol. 
	NOTE: Microfluidic devices are typically fabricated through a multi-step process. The first step is the design of the microfluidic channel using a conventional drawing software. Then, high-resolution film photomasks containing the microfluidic network are produced ...

<ol>
	<li>Cote, A. P., 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=Porous,+crystalline,+covalent+organic+frameworks.">Porous, crystalline, covalent organic frameworks.</a> Science. 310, 1166-1170 (2005).</li><li>Ding, S. Y., Wang, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Covalent+organic+frameworks+(COFs):+from+design+to+applications.">Covalent organic frameworks (COFs): from design to applications.</a> Chem Soc Rev. 42, 548-568 (2013).</li><li>Huang, N., Wang, P., Jiang, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Covalent+organic+frameworks:+a+materials+platform+for+structural+and+functional+designs.">Covalent organic frameworks: a materials platform for structural and functional designs.</a> Nat Rev Mater. 1, 16068 (2016).</li><li>Xu, H., Gao, J., Stable Jiang, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=crystalline,+porous,+covalent+organic+frameworks+as+a+platform+for+chiral+organocatalysts.">crystalline, porous, covalent organic frameworks as a platform for chiral organocatalysts.</a> Nat Chem. 7, 905-912 (2015).</li><li>Wan, S., Guo, J., Kim, J., Ihee, H., Jiang, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Belt-Shaped,+Blue+Luminescent,+and+Semiconducting+Covalent+Organic+Framework.">A Belt-Shaped, Blue Luminescent, and Semiconducting Covalent Organic Framework.</a> Angew Chem Int Edit. 47, 8826-8830 (2008).</li><li>Rodriguez-San-Miguel, 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=Crystalline+fibres+of+a+covalent+organic+framework+through+bottom-up+microfluidic+synthesis.">Crystalline fibres of a covalent organic framework through bottom-up microfluidic synthesis.</a> Chem Commun. 52, 9212-9215 (2016).</li><li>Bisbey, R. P., DeBlase, C. R., Smith, B. J., Dichtel, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-dimensional+Covalent+Organic+Framework+Thin+Films+Grown+in+Flow.">Two-dimensional Covalent Organic Framework Thin Films Grown in Flow.</a> J Am Chem Soc. 138, 11433-11436 (2016).</li><li>Spitler, E. L., Dichtel, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lewis+acid-catalysed+formation+of+two-dimensional+phthalocyanine+covalent+organic+frameworks.">Lewis acid-catalysed formation of two-dimensional phthalocyanine covalent organic frameworks.</a> Nat Chem. 2, 672-677 (2010).</li><li>Keskin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption,+Diffusion,+and+Separation+of+CH4/H-2+Mixtures+in+Covalent+Organic+Frameworks:+Molecular+Simulations+and+Theoretical+Predictions.">Adsorption, Diffusion, and Separation of CH4/H-2 Mixtures in Covalent Organic Frameworks: Molecular Simulations and Theoretical Predictions.</a> J Phys Chem C. 116, 1772-1779 (2012).</li><li>Tilford, R. W., Mugavero, S. J., Pellechia, P. J., Lavigne, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tailoring+microporosity+in+covalent+organic+frameworks.">Tailoring microporosity in covalent organic frameworks.</a> Adv Mater. 20, 2741-2746 (2008).</li><li>Hasegawa, S., 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=Three-dimensional+porous+coordination+polymer+functionalized+with+amide+groups+based+on+tridentate+ligand:+Selective+sorption+and+catalysis.">Three-dimensional porous coordination polymer functionalized with amide groups based on tridentate ligand: Selective sorption and catalysis.</a> J Am Chem Soc. 129, 2607-2614 (2007).</li><li>Das, G., 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=Chemical+sensing+in+two+dimensional+porous+covalent+organic+nanosheets.">Chemical sensing in two dimensional porous covalent organic nanosheets.</a> Chem Sci. 6, 3931-3939 (2015).</li><li>Guo, 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=Conjugated+organic+framework+with+three-dimensionally+ordered+stable+structure+and+delocalized+pi+clouds.">Conjugated organic framework with three-dimensionally ordered stable structure and delocalized pi clouds.</a> Nat Commun. 4, 2736 (2013).</li><li>Furukawa, H., Yaghi, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Storage+of+Hydrogen,+Methane,+and+Carbon+Dioxide+in+Highly+Porous+Covalent+Organic+Frameworks+for+Clean+Energy+Applications.">Storage of Hydrogen, Methane, and Carbon Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy Applications.</a> J Am Chem Soc. 131, 8875-8883 (2009).</li><li>Xu, F., 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=Electrochemically+active,+crystalline,+mesoporous+covalent+organic+frameworks+on+carbon+nanotubes+for+synergistic+lithium-ion+battery+energy+storage.">Electrochemically active, crystalline, mesoporous covalent organic frameworks on carbon nanotubes for synergistic lithium-ion battery energy storage.</a> Sci Rep-Uk. 5, 8225 (2015).</li><li>El-Kaderi, H. 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=Designed+synthesis+of+3D+covalent+organic+frameworks.">Designed synthesis of 3D covalent organic frameworks.</a> Science. 316, 268-272 (2007).</li><li>Ruigomez, 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=Direct+On-Surface+Patterning+of+a+Crystalline+Laminar+Covalent+Organic+Framework+Synthesized+at+Room+Temperature.">Direct On-Surface Patterning of a Crystalline Laminar Covalent Organic Framework Synthesized at Room Temperature.</a> Chem Eur J. 21, 10666-10670 (2015).</li><li>Segura, J. L., Mancheno, M. J., Zamora, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Covalent+organic+frameworks+based+on+Schiff-base+chemistry:+synthesis,+properties+and+potential+applications.">Covalent organic frameworks based on Schiff-base chemistry: synthesis, properties and potential applications.</a> Chem Soc Rev. 45, 5635-5671 (2016).</li><li>Abrishamkar, 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=Microfluidic+Pneumatic+Cages:+A+Novel+Approach+for+In-chip+Crystal+Trapping,+Manipulation+and+Controlled+Chemical+Treatment.">Microfluidic Pneumatic Cages: A Novel Approach for In-chip Crystal Trapping, Manipulation and Controlled Chemical Treatment.</a> J Vis Exp. (113), e54193 (2016).</li><li>Duffy, D. C., McDonald, J. C., Schueller, O. J. A., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+prototyping+of+microfluidic+systems+in+poly(dimethylsiloxane).">Rapid prototyping of microfluidic systems in poly(dimethylsiloxane).</a> Anal Chem. 70, 4974-4984 (1998).</li><li>Rubio-Martinez, 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=Freezing+the+Nonclassical+Crystal+Growth+of+a+Coordination+Polymer+Using+Controlled+Dynamic+Gradients.">Freezing the Nonclassical Crystal Growth of a Coordination Polymer Using Controlled Dynamic Gradients.</a> Adv Mater. 28, 8150-8155 (2016).</li><li>Liu, 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=A+Catalytic+Chiral+Gel+Microfluidic+Reactor+Assembled+via+Dynamic+Covalent+Chemistry.">A Catalytic Chiral Gel Microfluidic Reactor Assembled via Dynamic Covalent Chemistry.</a> Chem Sci. 6, 2292-2296 (2015).</li><li>Puigmarti-Luis, 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=Stepwise+Template+Growth+of+Functional+Nanowires+from+an+Amino+Acid-Supported+Framework+in+a+Microfluidic+Chip.">Stepwise Template Growth of Functional Nanowires from an Amino Acid-Supported Framework in a Microfluidic Chip.</a> ACS Nano. 8 (1), 818-826 (2014).</li></ol>

The microfluidic-based synthetic method reported here provides a novel and simple approach for direct printing of COF materials on surfaces. Synthesis is performed using a single-layer microfluidic device, comprised of a microfluidic PDMS chip bonded to a glass coverslip. The fabrication of the microfluidic device can be achieved through conventional casting of PDMS against a silicon master mold and subsequently bonding the PDMS with the imprinted microchannels against a glass coverslip.
For t...

Covalent organic frameworks (COFs) are a well-established class of porous and crystalline material in which the organic building blocks are firmly held together by covalent bonds1,2,3,4,5. COFs are typically assembled following supramolecular chemistry principles, where the constituent molecular building blocks are selectively reacted to define a final and predetermined porous assembly. Such an approach allows the synthesis of materials with controlled and ordered structure (e.g.,with defined pore dimensions) and composition3,6,7,8. Compared to other porous materials, COFs are unique since they are comprised of light elements (C, H, B, N and O) and have tunable porosities1,5. Inspired by these unique and intrinsic characteristics, COFs have been assessed for potential application in chemical separations9, gas storage10and catalysis11, sensors12, optoelectronics13, clean energy technologies14 and electrochemical energy devices15.
To date, the vast majority of methods used for the preparation of COF materials are based on solvothermal self-condensation and co-condensation reactions, where high temperatures and pressures are the standard. Although COFs are thermally robust, they commonly suffer from limited processability, i.e., COFs are usually insoluble and unprocessable crystalline powders, and this significantly limits their use in a range of potential and practical applications2,6,8,16,17. Despite the remarkable progress made in COF synthesis, a major challenge in the field is to develop a method enabling the preparation of COFs in appropriate reaction conditions (e.g., temperature and pressure), which can then facilitate their processability on surfaces.
Recently, studies have shown that Shiff-base chemistry can be used to synthesize an imine-based COF at room temperature. The COF produced, named RT-COF-1, forms due to the fast and efficient reaction between 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 1,3,5-benzenetricarbaldehyde (BTCA)17 (Figure 1A). The efficacy of this synthetic method was demonstrated by the direct printing of micron and submicron patterns of RT-COF-1 on both rigid and flexible surfaces using lithography or inkjet printing techniques. More recently, and making use of microfluidics, we have demonstrated an effective approach for the continuous synthesis of fibers of the same imine-based COF hereafter called MF-COF6. Unlike other reported synthetic approaches for the generation of COFs18, this microfluidic-based synthetic method enabled the rapid synthesis of MF-COF fibers at ambient temperatures and pressures within a few seconds. Furthermore, and owing to the mechanical stability of the synthesized MF-COF fibers, we have demonstrated how such microfluidic-based method can enable the direct printing of 2D and 3D structures on surfaces. Herein, we demonstrate that this method can be used to draw COF structures on various surfaces having different chemical and physical properties. We believe that this novel method opens new avenues for the well-controlled patterning and direct printing of COFs in different orientations and on various surfaces.

<table border="0" cellpadding="0" cellspacing="0" width="1147">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">High resolution film masks</td>
			<td style="width:252px;">Microlitho, UK</td>
			<td style="width:189px;">-</td>
			<td style="width:371px;">Features down to 5um</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Silicon wafers</td>
			<td style="width:252px;">Silicon Materials Inc., Germany</td>
			<td style="width:189px;">4&#34; Silicon Wafers</td>
			<td>Front surface: polished, back surface: etched</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Silicone Elastomer KIT (PDMS)</td>
			<td style="width:252px;">Dow Corning, USA</td>
			<td style="width:189px;">Sylgard 184</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Chlorotrimethylsilane</td>
			<td style="width:252px;">Sigma-Aldrich, Switzerland</td>
			<td style="width:189px;">386529</td>
			<td>&#8805;97%, CAUTION: Handle it only under fume hood.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Biopsy puncher</td>
			<td style="width:252px;">Miltex GmBH, Germany</td>
			<td style="width:189px;">33-31A-P/25</td>
			<td>1.5 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Glass coverslip</td>
			<td style="width:252px;">Menzel-Glaser, Germany</td>
			<td style="width:189px;">BB024040SC</td>
			<td>24 mm &#215; 40 mm, #5</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Plasma generator instrument</td>
			<td style="width:252px;">Diener</td>
			<td style="width:189px;">Zepto B</td>
			<td>Frequency: 40 kHz and plasma generator power: 0-30 W</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">PTFE tubing</td>
			<td style="width:252px;">PKM SA, Switzerland</td>
			<td style="width:189px;">AWG-TFS-XXX</td>
			<td style="width:371px;">AWG 20TFS, roll of 100 m</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">neMESYS Syringe Pumps</td>
			<td style="width:252px;">Cetoni GmbH, Germany</td>
			<td style="width:189px;">Low Pressure (290N)</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Disposable Cup</td>
			<td style="width:252px;">Semadeni, Switzerland</td>
			<td style="width:189px;">8323</td>
			<td>PS, 200 ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Plastic Spatula</td>
			<td style="width:252px;">Semadeni, Switzerland</td>
			<td style="width:189px;">3340</td>
			<td>L &#215; W : 135 mm x 14 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Disposable Scalpels</td>
			<td style="width:252px;">B. Braun, Switzerland</td>
			<td style="width:189px;">233-5320</td>
			<td>Nr. 20</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Disposable Syringes</td>
			<td style="width:252px;">VWR, Switzerland</td>
			<td style="width:189px;">613-3951</td>
			<td>5 ml, Discardit II</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">Acetic Acid</td>
			<td style="width:252px;">Sigma-Aldrich, Switzerland</td>
			<td style="width:189px;">695092-500</td>
			<td>&#62;=99.7%, CAUTION: Handle it only under fume hood.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">1,3,5-benzenetricarbaldehyde</td>
			<td style="width:252px;">Aldrich-Fine Chemicals</td>
			<td style="width:189px;">753491</td>
			<td>97%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:336px;">1,3,5-Tris(4-aminophenyl)benzene</td>
			<td style="width:252px;">Tokyo Chemical Industry</td>
			<td style="width:189px;">T2728-5G</td>
			<td>&#62;93.0%</td>
		</tr>
	</tbody>
</table>

microfluidic-based synthesis of covalent organic frameworks (cofs): a tool for continuous production of cof fibers and direct printing on a surface

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The first COF was reported in 2005 with much effort centered on the establishment of new synthetic routes for its preparation. To date, most available synthetic methods for COF synthesis are based on bulk mixing under solvothermal conditions. Therefore, there is increasing interest in developing systematic protocols for COF synthesis that provide for fine control over reaction conditions and improve COF processability on surfaces, which is essential for their use in practical applications. Herein, we present a novel microfluidic-based method for COF synthesis where the reaction between two constituent building blocks, 1,3,5-benzenetricarbaldehyde (BTCA) and 1,3,5-tris(4-aminophenyl)benzene (TAPB), takes place under controlled diffusion conditions and at room temperature. Using such an approach yields sponge-like, crystalline fibers of a COF material, hereafter called MF-COF. The mechanical properties of MF-COF and the dynamic nature of the approach allow the continuous production of MF-COF fibers and their direct printing onto surfaces. The general method opens new potential applications requiring advanced printing of 2D or 3D COF structures on flexible or rigid surfaces.

The microfluidic device used in our investigations is fabricated using conventional PDMS replica molding20 and incorporates four microfluidic inlet channels that merge into a main microchannel. The final microfluidic device consists of a structured PDMS layer and a glass coverslip used to close the imprinted microchannels, as shown in Figure 1B.
<img alt="Figure 1" class="xfi...

Watch this Scientific Journal Video about Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface at JoVE.com

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

We present a novel microfluidic-based method for synthesis of covalent organic frameworks (COFs). We demonstrate how this approach can be used to produce continuous COF fibers, and also 2D or 3D COF structures on surfaces.

Microfluidic-based Synthesis of Covalent Organic Frameworks (COFs): A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The ...

The overall goal of this approach is to demonstrate how a microfluidic-based platform can be used to produce continuous fibers of covalent organic frameworks that can be printed on surfaces to create 2D and 3D structures. Despite the remarkable progress in the synthesis of covalent and organic frameworks, developing a method to facilitate the process ability of these materials remains a challenge, which makes this approach very promising. This method effectively contributes to the field of crystalline materials through introduction of a noble, synthetic approach to produce continuous fibers of covalent and organic frameworks, thereby enhancing their process ability.To begin the device fabrication, in a fume hood, place a silicon master mold fabricated from a four inch silicon wafer in a vacuum desiccator. Dispatch 100 microliters of trimethylsilyl chloride into a glass vial and place the vial in the vacuum desiccator. Close the desiccator and put it under vacuum.Allow the trimethylsilyl chloride vapor to deposit on the master mold surface for one hour. Then, slowly vent the desiccator. Remove the silanised master mold and close the desiccator.Store the silanised mold in a closed container or in a laminal flow hood. Next, in a disposable cup, use a plastic spatula to mix together PDMS elastomer and curing agent in a 10:0.9 weight ratio. De-gass the mixture in a vacuum desiccator for 30 minutes.Then, carefully place four PTFE frames on the master mold, so that each frame encloses a single pattern on the mold. Pour the PTMS mixture into the frames and over the mold until full. Cure the PDMS in an oven at 70 degrees celsius for two hours, then remove the mold from the oven and allow the PDMS chips to cool to room temperature in the laminar flow hood.Once cool, carefully separate the frames from the mold by hand. Gently slide the PDMS chips from the frame. Use a 1.5 millimeter biopsy puncture to punch inlet and outlet holes at the end to the micro-fluidic channels in the chips.Trim excess PDMS from the chips and clean the chip and cover slip surfaces with adhesive tape. Place the clean chips in a plasma generator with the open channels facing up, along with four glass cover slips. Evacuate the sample chamber and run the generator for one minute.Then, vent the chamber and remove the plasma treated chips and cover slips. Bond each chip to a treated cover slip with the open channels faced down by gently pressing the chip onto the cover slip. Place the resulting micro-fluidic chips in an oven at 70 degree celsius for at least four hours to strengthen the bonding between the PDMS and the glass.To begin preparing for the synthesis, draw three milliliters of 40 milli molar BTCA in acetic acid into a five milliliter syringe. Draw three milliliters of 40 milli molar TAPB in acetic acid into another five milliliter syringe. Use PTFE tubing with an inner diameter of 0.8 millimeters and connect the tubings from one side to the syringes.Mount both syringes on a syringe pump. Next, fill two five milliliters syringes with acetic acid, use PTFE tubing with an inner diameter of 0.8 millimeters and connect the tubings from one side to the syringes. Secure these syringes into syringe pumps.Then, obtain a single layer four channel micro-fluidic chip. Connect the other side of the PTFE tubing to the inlets of the micro-fluidic device and connect the syringes to the outer channel inlets. Connect the 15 centimeter length of PTFE tubing to the chip outlet.Fix the end of the tubing in a 60 millimeter petri dish containing 10 milliliters of acetic acid. Place a glass cover slip next to the petri dish. Set each syringe pump to a flow rate of 100 microliters per minute and start the pumps.Wait one minute for the flows to stabilize while monitoring the MF-COF fiber formation in the chip. Change the flow rates of the acetic acid and check the outlet tubing. If the sheath flows of acetic acid are too high relative to the BTCA and TAPB flows, the MF-COF fiber's microstructure suspension will be too dilute to form a continuous fiber.If the sheath flows of acetic acid are too low relative to the reagent flows, the high concentration of MF-COF fibers will clog the outlet tubing. Set each syringe to a flow rate of 100 microliters per minute and wait one minute for the flows to stabilize. Once the flows have stabilized and the continuous MF-COF fiber reaches the end of the outlet tube, hold the end of the tube, a few millimeters above the surface.Slowly move the tube to draw an MF-COF structure. The suitable mechanical properties drive from the microscopic organization of MF-COF, allow the use of MF-COF fibers for conformal creating of 2D and 3D structures on saraphasis. Slowly raise the tube two to three centimeters from the surface to produce a free standing stable MF-COF fiber.Slowly lower the tube to continue drawing a 2D or 3D structure directly on the cover slip. MF-COF fibers were synthesized from TAPB and BTCA, using a four channel micro-fluidic device. Scanning electron microscopy showed that the fibers consisted of inter-connected micro and nano fibers in 3D sponge-like, porous structures that grant the mechanical properties needed to print 2D and 3D structures.2D MF-COF structures were printed on glass surfaces by drawing shapes as the fiber was continuously generated. The relative precision of the printing process was further highlighted in writing experiments on glass. The fibers did not merge when patterned over each other, allowing printing of 3D structures.In addition to glass, MF-COF structures were printed on tissue paper, cardboard, aluminum foil and polystyrene. While attempting this procedure, remember to perform all the steps for the fabrication of the micro-fluidic device inside the laminar flow hood and all the synthesis steps that involve handling of acetic acid under a fume hood. After its development, this technique paves the way for the researchers in the field of crystalline materials to explore new technological applications requiring advance patterning of 2D and 3D structures made of crystalline fibers and various seraphasis.After watching this video, you should have a good understanding of how to synthesize the continuous fiber of covalent, organic frameworks using a micro-fluidic platform and how to print a produced fiber and seraphasis to make 2D and 3D structures.

microfluidic-based-synthesis-covalent-organic-frameworks-cofs-tool

Research

JoVE Journal

Chemistry

Preparation and Use of Samarium Diiodide (SmI2) in Organic Synthesis: The Mechanistic Role of HMPA and Ni(II) Salts in the Samarium Barbier Reaction

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of molecular iodine to samarium metal in THF.1,2-3 It is a mild and selective single electron reductant and its versatility is a result of its ability to initiate a wide range of reductions including C-C bond-forming and cascade or sequential reactions. SmI2 can reduce a variety of functional groups including sulfoxides and sulfones, phosphine oxides, epoxides, alkyl and aryl halides, carbonyls, and conjugated double bonds.2-12 One of the fascinating features of SmI-2-mediated reactions is the ability to manipulate the outcome of reactions through the selective use of cosolvents or additives. In most instances, additives are essential in controlling the rate of reduction and the chemo- or stereoselectivity of reactions.13-14 Additives commonly utilized to fine tune the reactivity of SmI2 can be classified into three major groups: (1) Lewis bases (HMPA, other electron-donor ligands, chelating ethers, etc.), (2) proton sources (alcohols, water etc.), and (3) inorganic additives (Ni(acac)2, FeCl3, etc).3
Understanding the mechanism of SmI2 reactions and the role of the additives enables utilization of the full potential of the reagent in organic synthesis. The Sm-Barbier reaction is chosen to illustrate the synthetic importance and mechanistic role of two common additives: HMPA and Ni(II) in this reaction. The Sm-Barbier reaction is similar to the traditional Grignard reaction with the only difference being that the alkyl halide, carbonyl, and Sm reductant are mixed simultaneously in one pot.1,15 Examples of Sm-mediated Barbier reactions with a range of coupling partners have been reported,1,3,7,10,12 and have been utilized in key steps of the synthesis of large natural products.16,17 Previous studies on the effect of additives on SmI2 reactions have shown that HMPA enhances the reduction potential of SmI2 by coordinating to the samarium metal center, producing a more powerful,13-14,18 sterically encumbered reductant19-21 and in some cases playing an integral role in post electron-transfer steps facilitating subsequent bond-forming events.22 In the Sm-Barbier reaction, HMPA has been shown to additionally activate the alkyl halide by forming a complex in a pre-equilibrium step.23
Ni(II) salts are a catalytic additive used frequently in Sm-mediated transformations.24-27 Though critical for success, the mechanistic role of Ni(II) was not known in these reactions. Recently it has been shown that SmI2 reduces Ni(II) to Ni(0), and the reaction is then carried out through organometallic Ni(0) chemistry.28
These mechanistic studies highlight that although the same Barbier product is obtained, the use of different additives in the SmI2 reaction drastically alters the mechanistic pathway of the reaction. The protocol for running these SmI2-initiated reactions is described.

Preparation and Use of Samarium Diiodide SmI2 in Organic Synthesis: The Mechanistic Role of HMPA and NiII Salts in the Samarium Barbier Reaction

A straightforward procedure for the preparation of samarium diiodide (SmI2) in THF is described. The role of two main additives namely hexamethylphosphoramide (HMPA) and Ni(acac)2 in Sm mediated reactions is demonstrated in the Sm-Barbier reaction.

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of ...

Covalent Binding of BMP-2 on Surfaces Using a Self-assembled Monolayer Approach

Bone morphogenetic protein 2 (BMP-2) is a growth factor embedded in the extracellular matrix of bone tissue. BMP-2 acts as trigger of mesenchymal cell differentiation into osteoblasts, thus stimulating healing and de novo bone formation. The clinical use of recombinant human BMP-2 (rhBMP-2) in conjunction with scaffolds has raised recent controversies, based on the mode of presentation and the amount to be delivered. The protocol presented here provides a simple and efficient way to deliver BMP-2 for in vitro studies on cells. We describe how to form a self-assembled monolayer consisting of a heterobifunctional linker, and show the subsequent binding step to obtain covalent immobilization of rhBMP-2. With this approach it is possible to achieve a sustained presentation of BMP-2 while maintaining the biological activity of the protein. In fact, the surface immobilization of BMP-2 allows targeted investigations by preventing unspecific adsorption, while reducing the amount of growth factor and, most notably, hindering uncontrolled release from the surface. Both short- and long-term signaling events triggered by BMP-2 are taking place when cells are exposed to surfaces presenting covalently immobilized rhBMP-2, making this approach suitable for in vitro studies on cell responses to BMP-2 stimulation.

We describe a method for accomplishing efficient immobilization of BMP-2 on surfaces. Our approach is based on the formation of a self-assembled monolayer to achieve the covalent binding of BMP-2 via its free amine residues. This method is a useful tool to study signaling at the cell membrane.

Bone morphogenetic protein 2 (BMP-2) is a growth factor embedded in the extracellular matrix of bone tissue. BMP-2 acts as trigger of mesenchymal cell ...

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 ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Mass Spectrometry-Guided Genome Mining as a Tool to Uncover Novel Natural Products

The chemical space covered by natural products is immense and widely unrecognized. Therefore, convenient methodologies to perform wide-ranging evaluation of their functions in nature and potential human benefits (e.g., for drug discovery applications) are desired. This protocol describes the combination of genome mining (GM) and molecular networking (MN), two contemporary approaches that match gene cluster-encoded annotations in whole genome sequencing with chemical structure signatures from crude metabolic extracts. This is the first step towards the discovery of new natural entities. These concepts, when applied together, are defined here as MS-guided genome mining. In this method, the main components are previously designated (using MN), and structurally related new candidates are associated with genome sequence annotations (using GM). Combining GM and MN is a profitable strategy to target new molecule backbones or harvest metabolic profiles in order to identify analogues from already known compounds.

A mass spectrometry-guided genome mining protocol is established and described here. It is based on genome sequence information and LC-MS/MS analysis and aims to facilitate identification of molecules from complex microbial and plant extracts.

The chemical space covered by natural products is immense and widely unrecognized. Therefore, convenient methodologies to perform wide-ranging evaluation ...

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Here, we demonstrate a protocol for the two-step synthesis of single-crystalline core-shells using a non-isostructural metal-organic framework (MOF) pair, HKUST-1 and MOF-5, which have well-matched crystal lattices.

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural tunability. However, the progression of MOF-based photochemistry has been hindered by the difficulty in spectrally characterizing these materials. Given that MOFs are typically larger than 100 nm in size, they are prone to excessive light scatter, thereby rendering data from valuable analytical tools like transient absorption and emission spectroscopy nearly uninterpretable. To gain meaningful insights of MOF-based photo-chemical and physical processes, special consideration must be taken toward properly preparing MOFs for spectroscopic measurements, as well as the experimental setups that garner higher quality data. With these considerations in mind, the present guide provides a general approach and set of guidelines for the spectroscopic investigation of MOFs. The guide addresses the following key topics: (1) sample preparation methods, (2) spectroscopic techniques/measurements with MOFs, (3) experimental setups, (3) control experiments, and (4) post-run stability characterization. With appropriate sample preparation and experimental approaches, pioneering advancements toward the fundamental understanding of light-MOF interactions are significantly more attainable.

Here, we use a polymer stabilizer to prepare metal-organic framework (MOF) suspensions that exhibit markedly decreased scatter in their ground-state and transient absorption spectra. With these MOF suspensions, the protocol provides various guidelines to characterize the MOFs spectroscopically to yield interpretable data.

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

Synthesis of Low-Valent MOFs from Multitopic Phosphine Linkers

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, energy, and catalysis. Recently, low-valent MOFs (LVMOFs) have been explored for their potential use as heterogeneous catalysts, and multitopic phosphine linkers have been shown to be a useful building block for the formation of LVMOFs. However, the synthesis of LVMOFs using phosphine linkers requires conditions that are distinct from those in the majority of the MOF synthetic literature, including the exclusion of air and water and the use of unconventional modulators and solvents, making it somewhat more challenging to access these materials. This work serves as a general tutorial for the synthesis of LVMOFs with phosphine linkers, including information on the following: 1) the judicious choice of the metal precursor, modulator, and solvent; 2) the experimental procedures, air-free techniques, and required equipment; 3) the proper storage and handling of the resultant LVMOFs; and 4) useful characterization methods for these materials. The intention of this report is to lower the barrier to this new subfield of MOF research and facilitate advancements toward novel catalytic materials.

Author Spotlight: Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers  

Here, we describe a protocol for the synthesis of low-valent metal-organic frameworks (LVMOFs) from low-valent metals and multitopic phosphine linkers under air-free conditions. The resulting materials have potential applications as heterogeneous catalyst mimics of low-valent metal-based homogeneous catalysts.

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...