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When cholesterol is imbedded in the membrane, the alcohol group is oriented in order to interact with the head group of the phospholipids while the rigid Quattro cyclic system and the tail are parallel to the fatty acid chains. This ability can be exploited by using cholesterol to direct functionalities to the cell surface. The idea has been proven viable in experiments by Langecker et al. where a lipid membrane channel is bound to the cell surface using cholesterols affinity for the lipid membrane (Figure 2).  
When cholesterol is imbedded in the membrane, the alcohol group is oriented in order to interact with the head group of the phospholipids while the rigid Quattro cyclic system and the tail are parallel to the fatty acid chains. This ability can be exploited by using cholesterol to direct functionalities to the cell surface. The idea has been proven viable in experiments by Langecker et al. where a lipid membrane channel is bound to the cell surface using cholesterols affinity for the lipid membrane (Figure 2).  


[[Image:Biomod_Aarhus_Chem_Lipidbilayer.png|600x600px|center| thumb| Figure xx:Illustration of the lipid membrane channel. The cylinders are made of DNA, and the orange ellipses represent cholesterol. A: structure seen, at an angle, from the bottom. B: cross-section view when the channel is imbedded in the membrane.]]
[[Image:Biomod_Aarhus_Chem_Lipidbilayer.png|600x600px|center| thumb| Figure xx: Illustration of the lipid membrane channel. The cylinders are made of DNA, and the orange ellipses represent cholesterol. A: structure seen, at an angle, from the bottom. B: cross-section view when the channel is imbedded in the membrane.]]


The ability to attach to cell membranes is also exploited in this project in order to bind the origami plate to the cell surface. Thereby insuring a high local concentration of the photosensitizer at the cell surface. In order to conjugate cholesterol to DNA staple strands, the cholesterol is modified with an NHS-ester handle. This NHS-ester can be used in an amide coupling reaction with a beforehand amine modified DNA strand. In total 19 staple strands are modified with cholesterol for use in the origami plate.
The ability to attach to cell membranes is also exploited in this project in order to bind the origami plate to the cell surface. Thereby insuring a high local concentration of the photosensitizer at the cell surface. In order to conjugate cholesterol to DNA staple strands, the cholesterol is modified with an NHS-ester handle. This NHS-ester can be used in an amide coupling reaction with a beforehand amine modified DNA strand. In total 19 staple strands are modified with cholesterol for use in the origami plate.

Revision as of 07:16, 20 October 2013

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Preview

Cholesterol

Cholesterol (Figure 1) is a natural and important steroid in many living organisms. The steroid structure of cholesterol is the precursor for a number of important steroid hormones. Besides being the precursor for other compounds, cholesterol has important functions as a lipid. In cells cholesterol is imbedded in the lipid bilayer to control the permeability and the fluidity.

picture!

When cholesterol is imbedded in the membrane, the alcohol group is oriented in order to interact with the head group of the phospholipids while the rigid Quattro cyclic system and the tail are parallel to the fatty acid chains. This ability can be exploited by using cholesterol to direct functionalities to the cell surface. The idea has been proven viable in experiments by Langecker et al. where a lipid membrane channel is bound to the cell surface using cholesterols affinity for the lipid membrane (Figure 2).

Figure xx: Illustration of the lipid membrane channel. The cylinders are made of DNA, and the orange ellipses represent cholesterol. A: structure seen, at an angle, from the bottom. B: cross-section view when the channel is imbedded in the membrane.

The ability to attach to cell membranes is also exploited in this project in order to bind the origami plate to the cell surface. Thereby insuring a high local concentration of the photosensitizer at the cell surface. In order to conjugate cholesterol to DNA staple strands, the cholesterol is modified with an NHS-ester handle. This NHS-ester can be used in an amide coupling reaction with a beforehand amine modified DNA strand. In total 19 staple strands are modified with cholesterol for use in the origami plate.

Synthesis of cholesterol derivative

The cholesterol derivative 5 is synthesized in a three step procedure (Scheme 2). The linker and cholesterol are envisioned to react in a simple SN2 reaction. The oxyanion, from the deprotonated alcohol, performs a nucleophilic attack on the α-carbon with bromide as the leaving group. The second step is an acidic deprotection of the ester and the third step is an activation of the acid with N-hydroxysuccinimide (NHS).

picture!

The synthesis of 3 resulted in a low yield (8%), when using the procedure described by Simeone et al. and an optimization was as a consequence tried. However the optimization did not result in a significant improvement as the highest obtained yield was 12% in a time-consuming reaction procedure.

The synthesis of 4 is a deprotection of the tert-butyl ester with acid. Compound 3 was dissolved and left to react in formic acid at room temperature. After the reaction was judged to be finished by TLC, the formic acid was evaporated under reduced pressure after which the product could be extracted from the organic phase with aq. saturated solution of sodium hydrogen carbonate. Hereafter the water phase was made acidic with 2 M hydrochloric acid and the product was back-extracted using dichloromethane (DCM). This method of purification results in the pure product in 76% yield after evaporation in vacuo.

To heighten the reactivity of the carboxylic acid it is converted into an NHS-ester, compound 5. The acid 4 was mixed with the coupling reagent N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide (EDC) and NHS after which the reaction was left to stir for 3 h. An NHS-ester is easily hydrolyzed as NHS is a very good leaving group. The inherent reactivity, which makes it useful as a coupling intermediate, also renders it hard to handle without the functionality decomposes. Therefore, the work-up had to be performed quickly. The desired product 5 was synthesized in 80% yield, which was deemed successful.

Photosensitizer

Preview

Results And Discussion

Conclusion

ddUTP shizzle

Conclusion

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</style> </head> <body> <div id="indexing"> <div id="sitemap"> <p id="sitemapTitle">SITEMAP | BIOMOD 2013 NANO CREATORS | Aarhus University</p> <div id="footer-contents"> <div class="footer-section"> <p class="footer-section-title">INTRODUCTION</p> <ul> <li><a href="/wiki/Biomod/2013/Aarhus">Home, abstract, animation and video</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Introduction">Introduction</a></li </ul> </div> <div class="footer-section"> <p class="footer-section-title">RESULTS AND DISCUSSION</p> <ul> <li><a href="/wiki/Biomod/2013/Aarhus/Results_And_Discussion/Origami">Origami</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Results_And_Discussion/Peptide_lock">Peptide lock</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Results_And_Discussion/Chemical_Modification">Chemical modification</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Results_And_Discussion/sisiRNA">sisiRNA</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Results_And_Discussion/System_In_Action">System in action</a></li> </ul> </div> <div class="footer-section"> <p class="footer-section-title">MATERIALS AND METHODS</p> <ul> <li><a href="/wiki/Biomod/2013/Aarhus/Materials_And_Methods/Origami">Origami</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Materials_And_Methods/Peptide_lock">Peptide lock</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Materials_And_Methods/Chemical_Modification">Chemical modification</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Materials_And_Methods/sisiRNA">sisiRNA</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Materials_And_Methods/System_In_Action">System in action</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Materials_And_Methods/Methods">Methods</a></li> </ul> </div> <div class="footer-section"> <p class="footer-section-title">SUPPLEMENTARY</p> <ul> <li><a href="/wiki/Biomod/2013/Aarhus/Supplementary/Team_And_Acknowledgments">Team and acknowledgments</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Supplementary/Optimizations">Optimizations</a></li> <li><a href="/wiki/Biomod/2013/Aarhus/Supplementary/Supplementary_Data">Supplementary data</a></li> 

                                               <li><a

href="/wiki/Biomod/2013/Aarhus/Supplementary/Supplementary_Informations">Supplementary informations</a> <li><a href="/wiki/Biomod/2013/Aarhus/Supplementary/References">References</a></li> </ul> </div> </div> <div> <p id="copyright">Copyright (C) 2013 | BIOMOD Team Nano Creators @ Aarhus University | Programming by: <a href="mailto:pvskaarup@gmail.com?Subject=BIOMOD 2013:">Peter Vium Skaarup</a>.</p> </div> </div>

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