Name: synthesis of cyclic polymers and characterization of their diffusive motion in the melt state at the single molecule level
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Description: Watch this Scientific Journal Video about Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level at JoVE.com

This work was supported by a Grant-in-Aid for Scientific Research No. 22750122 (S.H.), No. 26288099 (T.Y.), and No. 23350050 (Y.T.) of the Japan Society for the Promotion of Science. S.H. is grateful for The Kurata Memorial Hitachi Science and Technology Foundation. The research reported in this publication was supported by the King Abdullah University of Science and Technology (S.H.).

1. Synthesis of Monofunctional and Bifunctional Poly(THF)
<ol>
	<li>Monofunctional poly(THF)
	<ol>
		<li>Flame dry a 2-neck 100-ml round-bottom flask. Vacuum and fill the flask with nitrogen (3 cycles).</li>
		<li>Add distilled tetrahydrofuran (THF) (50 ml) to the flask. Put the flask in a water bath at 20 &#176;C and equilibrate the temperature.</li>
		<li>Add methyl triflate (0.5 mmol) to the flask by a syringe. Stir the mixture for 5-10 min at 20 &#176;C.</li>
		<li>Add N-phenyl pyrrolidine...

<ol>
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The 4-armed and 8-shaped polymers were prepared via the ESA-CF protocol (Figure 1), which is a critical step for the synthesis.12,24 Monofunctional and bifunctional linear poly(THF)s with N-phenylpiperidinium end groups were synthesized according to the previous procedure.11 The ion exchange was carried out by reprecipitation of an acetone solution of a polymer precursor with triflate counteranions into an aqueous solution containing an excess amount of carboxylate.
<p ...

Cyclic polymers are unique in that they do not have chain ends. They often exhibit unusual behaviors which is distinct from their linear counterpart, including increased thermal stability of polymer micelles by a linear-to-cyclic conversion,1,2 and spatial organization of DNA in bacterial cells by a loop formation.3 Topological interactions between the cyclic chains are believed to be the critical factor for such unusual behaviors.4,5 Therefore, characterizing the motion and relaxation of cyclic polymers under entangled conditions has been an important research topic in polymer science for decades.6
Cyclic polymer dynamics has been investigated using both synthetic and naturally occurring molecules by means of ensemble averaged experimental methods such as nuclear magnetic resonance (NMR), light scattering, and viscosity measurements.7-9 However, these studies often suffer from impurity molecules in the samples.10 Furthermore, spatiotemporal heterogeneities of the motion of individual molecules caused by inherent structural heterogeneity of entangled polymers are often hidden behind the ensemble averaging in these studies. In order to characterize molecular level dynamics of cyclic polymers, a synthesis method that provides high purity cyclic polymers and an experimental and analysis methods that allow for quantitative characterization of molecular motion at the single molecule level have to be developed. Here, we will show a method to synthesize high-purity cyclic and dicyclic poly(THF)s that incorporate a fluorophore unit using an electrostatic self-assembly and covalent fixation (ESA-CF) process11-13 and a method to analyze the motion of the individual fluorophore-incorporated polymer chains using a combination of mean-squared displacement (MSD) and cumulative distribution function (CDF) analyses.
A proper data processing has been shown to be essential for the accurate characterization of the diffusive motion. With an adequate MSD and CDF analyses, a multiple-mode diffusion of the cyclic and dicyclic polymers in the melt and semi-dilute solution of the linear polymer chains has been revealed,14-16 suggesting the significant effects of the topological states of the polymers on the diffusive motion of the chains under entangled conditions.17 While the experimental and analytical approaches to characterize the motion of the cyclic polymers are described in this protocol, the same method can be used to quantitatively characterize the diffusive motion in many other heterogeneous systems. The approach would be especially suitable when multiple diffusion components existing in the samples are to be analyzed.

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			<td height="21" style="height:21px;width:320px;">Materials</td>
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			<td height="21" style="height:21px;width:320px;">THF</td>
			<td style="width:240px;">Godo</td>
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			<td></td>
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			<td height="21" style="height:21px;width:320px;">Wakosil C-300</td>
			<td style="width:240px;">Wako Pure Chemical Industries</td>
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			<td height="21" style="height:21px;width:320px;">Acetone</td>
			<td style="width:240px;">Godo</td>
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			<td height="21" style="height:21px;width:320px;">Toluene</td>
			<td style="width:240px;">Godo</td>
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			<td height="21" style="height:21px;width:320px;">n-Hexane</td>
			<td style="width:240px;">Godo</td>
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			<td height="21" style="height:21px;width:320px;">CHCl3</td>
			<td style="width:240px;">Kanto Chemical</td>
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			<td height="21" style="height:21px;width:320px;">Bio-Beads S-X1</td>
			<td style="width:240px;">Bio-Rad</td>
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			<td height="21" style="height:21px;width:320px;">Methyl triflate</td>
			<td style="width:240px;">Nacalai Tesque</td>
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			<td height="21" style="height:21px;width:320px;">Triflic anhydride</td>
			<td style="width:240px;">Nacalai Tesque</td>
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			<td height="21" style="height:21px;width:320px;">Potassium Hydroxide</td>
			<td style="width:240px;">Wako Pure Chemical Industries</td>
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			<td height="21" style="height:21px;width:320px;">Ethanol</td>
			<td style="width:240px;">Wako Pure Chemical Industries</td>
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			<td height="21" style="height:21px;width:320px;">Poly(tetrahydrofuran)</td>
			<td style="width:240px;">Aldrich</td>
			<td style="width:119px;"></td>
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			<td height="21" style="height:21px;width:320px;">Chloroform</td>
			<td style="width:240px;">Wako Pure Chemical Industries</td>
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			<td height="21" style="height:21px;width:320px;">Immersion oil</td>
			<td style="width:240px;">Cargille</td>
			<td style="width:119px;">Type 37 / Type A</td>
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			<td height="21" style="height:21px;width:320px;">Equipment</td>
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			<td height="21" style="height:21px;width:320px;">2-Neck 100-mL round-bottom flask</td>
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			<td height="21" style="height:21px;width:320px;">Flask</td>
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			<td height="21" style="height:21px;width:320px;">Beaker</td>
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			<td height="21" style="height:21px;width:320px;">Funnel</td>
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			<td height="21" style="height:21px;width:320px;">Filter paper</td>
			<td style="width:240px;">Whatman</td>
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			<td height="21" style="height:21px;width:320px;">Reflux condenser</td>
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			<td height="21" style="height:21px;width:320px;">Syringe</td>
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			<td height="21" style="height:21px;width:320px;">Water bath</td>
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			<td height="21" style="height:21px;width:320px;">Magnetic stirrer</td>
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			<td height="21" style="height:21px;width:320px;">Rotary evaporator</td>
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			<td height="21" style="height:21px;width:320px;">Microscope cover slips (24 x 24 mm, No. 1)</td>
			<td style="width:240px;">Matsunami Glass</td>
			<td style="width:119px;">CO22241</td>
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			<td height="21" style="height:21px;width:320px;">Staining jar</td>
			<td style="width:240px;">AS ONE Corporation</td>
			<td style="width:119px;">1-7934-01</td>
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			<td height="21" style="height:21px;width:320px;">Ultrasonic cleaner</td>
			<td style="width:240px;">VWR International&#160;</td>
			<td style="width:119px;">142-0047</td>
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			<td height="21" style="height:21px;width:320px;">Inverted microscope</td>
			<td style="width:240px;">Olympus</td>
			<td style="width:119px;">IX71</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Ar-Kr ion laser</td>
			<td style="width:240px;">Coherent</td>
			<td style="width:119px;">Innova 70C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Berek compensator</td>
			<td style="width:240px;">Newport</td>
			<td align="right" style="width:119px;">5540</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Excitation filter</td>
			<td style="width:240px;">Semrock</td>
			<td style="width:119px;">LL01-488-12.5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Dichloric mirror</td>
			<td style="width:240px;">Omega optical</td>
			<td style="width:119px;">500DRLP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Emission filter</td>
			<td style="width:240px;">Semrock</td>
			<td style="width:119px;">BLP01-488R-25</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Lens and mirror</td>
			<td style="width:240px;">Thorlabs</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">EM-CCD camera</td>
			<td style="width:240px;">Andor Technology</td>
			<td style="width:119px;">iXon</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Objective lens (x100, N.A. = 1.3)</td>
			<td style="width:240px;">Olympus</td>
			<td style="width:119px;">UPLFLN 100XOP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Objective heater</td>
			<td style="width:240px;">Bioptechs</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:320px;">Preparative GPC</td>
			<td style="width:240px;">Japan Analytical Industry</td>
			<td style="width:119px;">LC-908</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

The perylene diimide-incorporated 4-armed star and 8-shaped dicyclic poly(THF)s were synthesized using the electrostatic self-assembly and covalent fixation (ESA-CF) process (Figure 1, Figure 2). Time-lapse single-molecule fluorescence images were measured for the 4-armed (Figure 3a) and 8-shaped (Figure 3b) polymers. The time-lapse fluorescence images (Figure 3) show spatially isolated bright and sharp s...

Watch this Scientific Journal Video about Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level at JoVE.com

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

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 ...

The overall goal of this experiment is to characterize diffusional motion of topological polymers, especially cyclic polymers, under entangled conditions at the single molecule level. This method can help answer key questions in the field of polymer physics, such as topology-dependent spacio-temporal dynamics of polymers. The main advantage of this technique is that heterogeneous diffusion can be quantitatively characterized at the single-chain level, which is usually hidden behind on some level.To begin this procedure, dissolve perylene diimide salt in 150 milliliters of water, then dissolve monofunctional poly(THF)in four millimeters of acetone. Add the acetone solution drop-wise to the vigorously stirred aqueous solution. Collect the formed precipitate by vacuum filtration.Next, prepare a five milligram per milliliter solution of the precipitate in toluene. Reflux the solution for four hours. After allowing the solution to cool, completely remove the solvent under reduced pressure by rotary evaporation.When finished, dissolve the residue in a 2:1 mixture of n-hexane:acetone and filter the resulting solution through a plug of silica gel. Then add the filtered solution to ice cold water to precipitate the product. To prepare the polymer melt sample, add 100 microliters of non-labeled linear poly(THF)to a glass bottle and heat it to approximately 25 degrees celsius using a hair dryer.Prepare a 10 to the minus six molars solution of the fluorophore incorporated polymer solution in chloroform. Then add one microliter of this solution to 100 microliters of the non-labeled linear poly(THF)melt. After thoroughly mixing the sample with a pipette tip, evaporate the chloroform by heating with a hair dryer.Using a micro-pipette place 10 microliters of the sample on a cleaned cover slip. Place another cleaned cover slip on the sample and gently press the two cover slips together using plastic tweezers. Next, attach an objective heater to the objective lens of an inverted microscope and set the temperature to 30 degrees celsius.Place one drop of immersion oil on the lens and mount the sample on the microscope stage. Ensure that a sample thickness of approximately 10 micrometers is obtained by checking the axial position of the bottom and top surface of the sample. Then adjust the focus of the microscope to a few micrometers above the bottom surface of the sample.Following this, apply an electron multiplying or EM gain to a CCD camera in order to obtain a high quality fluorescent image of the single fluorophore. Now set a region of interest using the software controlling the camera. To optimize the experimental conditions, adjust the illumination area of the sample to approximately 20 micrometers in diameter using the diaphragm inserted in the excitation beam path.Set the excitation laser power at the sample to four to eight milliwatts by manually selecting an appropriate neutral density filter inserted in the excitation beam path. Finally, record 500 to 1000 fluorescence image sequences of the fluorophore incorporated polymer in the melt state at a 100 to 200 hertz frame rate. Time-lapse single molecule florescence images were measured for the four-armed and eight-shaped polymers and show spatially isolated bright and sharp spots due to the incorporation of the highly fluorescent perylene diimide fluorophore into the chains.The frequency histograms of the diffusion coefficient determined by mean-squared displacement analysis display broad distributions resulting from both the statistical error of the analysis and heterogeneity of the diffusion. The frequency histograms show clear deviations from the homogeneous diffusion model, which demonstrates heterogeneous diffusion of the polymer molecules. The single and double Gaussian models hit the experimentally obtained cumulative distribution functions well and demonstrate that the diffusion of the formed polymer is described by the broad distribution of the diffusion coefficient, whereas the eight-shaped polymer displays two distinct diffusion modes.Once mastered, the synthesis of polymers can be done in six hours and the single molecule immersion experiment can be done in several hours if they are performed properly. After it's development, this technique paved the way for researchers in the field of polymer science to explore polymer dynamics in crowded environments. After watching this video, you should have a good understanding of how to characterize diffusive motion of topological polymers under entangled condition at the single-chain level.Don't forget that working with lasers and organic solvents can be extremely hazardous and precautions such as laser safety and review of the MSDS should always be taken while performing this procedure.

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Research

JoVE Journal

Chemistry

Isolation and Chemical Characterization of Lipid A from Gram-negative Bacteria

Lipopolysaccharide (LPS) is the major cell surface molecule of gram-negative bacteria, deposited on the outer leaflet of the outer membrane bilayer. LPS can be subdivided into three domains: the distal O-polysaccharide, a core oligosaccharide, and the lipid A domain consisting of a lipid A molecular species and 3-deoxy-D-manno-oct-2-ulosonic acid residues (Kdo). The lipid A domain is the only component essential for bacterial cell survival. Following its synthesis, lipid A is chemically modified in response to environmental stresses such as pH or temperature, to promote resistance to antibiotic compounds, and to evade recognition by mediators of the host innate immune response. The following protocol details the small- and large-scale isolation of lipid A from gram-negative bacteria. Isolated material is then chemically characterized by thin layer chromatography (TLC) or mass-spectrometry (MS). In addition to matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) MS, we also describe tandem MS protocols for analyzing lipid A molecular species using electrospray ionization (ESI) coupled to collision induced dissociation (CID) and newly employed ultraviolet photodissociation (UVPD) methods. Our MS protocols allow for unequivocal determination of chemical structure, paramount to characterization of lipid A molecules that contain unique or novel chemical modifications. We also describe the radioisotopic labeling, and subsequent isolation, of lipid A from bacterial cells for analysis by TLC. Relative to MS-based protocols, TLC provides a more economical and rapid characterization method, but cannot be used to unambiguously assign lipid A chemical structures without the use of standards of known chemical structure. Over the last two decades isolation and characterization of lipid A has led to numerous exciting discoveries that have improved our understanding of the physiology of gram-negative bacteria, mechanisms of antibiotic resistance, the human innate immune response, and have provided many new targets in the development of antibacterial compounds.

Isolation and characterization of the lipid A domain of lipopolysaccharide (LPS) from gram-negative bacteria provides insight into cell surface based mechanisms of antibiotic resistance, bacterial survival and fitness, and how chemically diverse lipid A molecular species differentially modulate host innate immune responses.

Lipopolysaccharide (LPS) is the major cell surface molecule of gram-negative bacteria, deposited on the outer leaflet of the outer membrane bilayer. LPS ...

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent reactions with azides to form cyanocarbene intermediates. The synthesis of hypervalent iodonium alkynyl triflates can be facile, but difficulties stem from their isolation and reactivity. In particular, the necessity to use filtration under inert atmosphere at -45 &deg;C for some HIATs requires special care and equipment. Once isolated, the compounds can be stored and used in reactions with azides to form cyanocarbene intermediates. 
The evidence for cyanocarbene generation is shown by visible extrusion of dinitrogen as well as the characterization of products that occur from O-H insertion, sulfoxide complexation, and cyclopropanation. A side reaction of the cyanocarbene formation is the generation of a vinylidene-carbene and the conditions to control this process are discussed. There is also potential to form a hypervalent iodonium alkenyl triflate and the means of isolation and control of its generation are provided. The O-H insertion reaction involves using a HIAT, sodium azide or tetrabutylammonium azide, and methanol as solvent/substrate. The sulfoxide complexation reaction uses a HIAT, sodium azide or tetrabutylammonium azide, and dimethyl sulfoxide as solvent. The cyclopropanations can be performed with or without the use of solvent. The azide source must be tetrabutylammonium azide and the substrate shown is styrene.

Herein is described the synthesis, isolation, and reactions of hypervalent iodonium alkynyl triflates (HIATs) with azides to generate cyanocarbenes. The procedures will involve air-sensitive and cryogen techniques, including cold filtration under an inert atmosphere. Handling and safety of the synthesized compounds will also be discussed.

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent ...

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 ...

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

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 ...

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of trifluoromethoxylated aromatic compounds remains a formidable challenge in organic synthesis. Conventional approaches often suffer from poor substrate scope, or require use of highly toxic, difficult-to-handle, and/or thermally labile reagents. Herein, we report a user-friendly protocol for the synthesis of methyl 4-acetamido-3-(trifluoromethoxy)benzoate using 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one (Togni reagent II). Treating methyl 4-(N-hydroxyacetamido)benzoate (1a) with Togni reagent II in the presence of a catalytic amount of cesium carbonate (Cs2CO3) in chloroform at RT afforded methyl 4-(N-(trifluoromethoxy)acetamido)benzoate (2a). This intermediate was then converted to the final product methyl 4-acetamido-3-(trifluoromethoxy)benzoate (3a) in nitromethane at 120 &#176;C. This procedure is general and can be applied to the synthesis of a broad spectrum of ortho-trifluoromethoxylated aniline derivatives, which could serve as useful synthetic building blocks for the discovery and development of new pharmaceuticals, agrochemicals, and functional materials.

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

An operationally simple procedure for the synthesis of ortho-trifluoromethoxylated aniline derivatives via a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxyacetamide followed by thermally induced intramolecular OCF3-migration is reported.

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Insights into the Interactions of Amino Acids and Peptides with Inorganic Materials Using Single-Molecule Force Spectroscopy

The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals leads to the formation of composite materials with unique properties. In addition, the undesirable process of biofouling is initiated by the adsorption of biomolecules, mainly proteins, on surfaces. This organic layer is an adhesion layer for bacteria and allows them to interact with the surface. Understanding the fundamental forces that govern the interactions at the organic-inorganic interface is therefore important for many areas of research and could lead to the design of new materials for optical, mechanical and biomedical applications. This paper demonstrates a single-molecule force spectroscopy technique that utilizes an AFM to measure the adhesion force between either peptides or amino acids and well-defined inorganic surfaces. This technique involves a protocol for attaching the biomolecule to the AFM tip through a covalent flexible linker and single-molecule force spectroscopy measurements by atomic force microscope. In addition, an analysis of these measurements is included.

Here we present a protocol to measure the force of interactions between a well-defined inorganic surface and either peptides or amino acids by single-molecule force spectroscopy measurements using an atomic force microscope (AFM). The information obtained from the measurement is important to better understand the peptide-inorganic material interphase.

The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals ...

Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance (EPR) or ultraviolet-visible and near-infrared (UV-Vis-NIR) spectroscopies, we obtain useful information such as electron affinity, ionization potential, band-gap energies, the type of charge carriers, and degradation information that can be used to synthesize stable organic electronic devices. In this study, we present electrochemical and spectroelectrochemical methods to analyze the processes occurring in active layers of an organic device as well as the generated charge carriers.

In this article, we describe electrochemical, electron paramagnetic resonance, and ultraviolet-visible and near-infrared spectroelectrochemical methods to analyze organic compounds for application in organic electronics.

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance ...