Name: preparation and in vitro characterization of dendrimer-based contrast agents for magnetic resonance imaging
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The financial support of the Max-Planck Society, the Turkish Ministry of National Education (PhD fellowship to S. G.), and the German Exchange Academic Service (DAAD, PhD fellowship to T. S.) are gratefully acknowledged.

1. Preparation of DCA

<ol>
	<li>Synthesis of the monomeric unit 46.
	<ol>
		<li>Synthesis of 4-(4-nitrophenyl)-2-(4,7,10-tris-tert-butoxycarbonylmethyl-1,4,7,10-tetraazacyclododec-1-yl)butyric acid tert-butyl ester (2).
		<ol>
			<li>Dissolve (4,7-bis-tert-butoxycarbonylmethyl-1,4,7,10-tetraaza-cyclododec-1-yl)-acetic acid tert-butyl ester 1 (1.00 g, 1.94 mmol) in N,N-dimethylformamide (DM...

<ol>
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L., Faulkner, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+luminescence+properties+of+a+kinetically+stable+dinuclear+ytterbium+complex+with+differentiated+binding+sites.">Synthesis and luminescence properties of a kinetically stable dinuclear ytterbium complex with differentiated binding sites.</a> Chem. Commun. (13), 1550-1551 (2003).</li><li>Vibhute, S. 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=Synthesis+and+characterization+of+pH-sensitive,+biotinylated+MRI+contrast+agents+and+their+conjugates+with+avidin.">Synthesis and characterization of pH-sensitive, biotinylated MRI contrast agents and their conjugates with avidin.</a> Org. Biomol. Chem. 11 (8), 1294-1305 (2013).</li><li>Vogel, A. I., Furniss, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Vogel's textbook of practical organic chemistry. 5th ed. , (1989).</li><li>Lundanes, E., Reubsaet, L., Greibrokk, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Chromatography : basic principles, sample preparations and related methods. , (2013).</li><li>Barge, A., Cravotto, G., Gianolio, E., Fedeli, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+determine+free+Gd+and+free+ligand+in+solution+of+Gd+chelates.+A+technical+note.">How to determine free Gd and free ligand in solution of Gd chelates. A technical note.</a> Contrast Media Mol. Imaging. 1 (5), 184-188 (2006).</li><li>Keeler, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Understanding NMR spectroscopy. 2nd ed. , (2010).</li><li>Hillenkamp, F., Peter-Katalini&#263;, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> MALDI MS : a practical guide to instrumentation, methods and applications. , (2007).</li><li>Peters, J. A., Huskens, J., Raber, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lanthanide+induced+shifts+and+relaxation+rate+enhancements.">Lanthanide induced shifts and relaxation rate enhancements.</a> Prog. Nucl. Magn. Reson. Spectrosc. 28, 283-350 (1996).</li><li>Averill, D. J., Garcia, J., Siriwardena-Mahanama, B. N., Vithanarachchi, S. M., Allen, M. 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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=Synthesis,+characterization,+and+biological+evaluation+of+integrin+alpha(v)beta(3)-targeted+PAMAM+dendrimers.">Synthesis, characterization, and biological evaluation of integrin alpha(v)beta(3)-targeted PAMAM dendrimers.</a> Mol. Pharmaceut. 5 (4), 527-539 (2008).</li><li>Sherry, A. D., Caravan, P., Lenkinski, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primer+on+Gadolinium+Chemistry.">Primer on Gadolinium Chemistry.</a> J. Magn. Reson. Imaging. 30 (6), 1240-1248 (2009).</li><li>Caki&#263;, N., G&#252;nd&#252;z, S., Rengarasu, R., Angelovski, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthetic+strategies+for+preparation+of+cyclen-based+MRI+contrast+agents.">Synthetic strategies for preparation of cyclen-based MRI contrast agents.</a> Tetrahedron Lett. 56 (6), 759-765 (2015).</li><li>Polasek, M., Hermann, P., Peters, J. A., Geraldes, C. F. G. C., Lukes, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PAMAM+Dendrimers+Conjugated+with+an+Uncharged+Gadolinium(III)+Chelate+with+a+Fast+Water+Exchange:+The+Influence+of+Chelate+Charge+on+Rotational+Dynamics.">PAMAM Dendrimers Conjugated with an Uncharged Gadolinium(III) Chelate with a Fast Water Exchange: The Influence of Chelate Charge on Rotational Dynamics.</a> Bioconjugate Chem. 20 (11), 2142-2153 (2009).</li><li>Ali, M. 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=Synthesis+and+relaxometric+studies+of+a+dendrimer-based+pH-responsive+MRI+contrast+agent.">Synthesis and relaxometric studies of a dendrimer-based pH-responsive MRI contrast agent.</a> Chem. Eur. J. 14 (24), 7250-7258 (2008).</li><li>Jackson, C. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+of+dendrimer+molecules+by+transmission+electron+microscopy+(TEM):+Staining+methods+and+Cryo-TEM+of+vitrified+solutions.">Visualization of dendrimer molecules by transmission electron microscopy (TEM): Staining methods and Cryo-TEM of vitrified solutions.</a> Macromolecules. 31 (18), 6259-6265 (1998).</li><li>Jain, K., Kesharwani, P., Gupta, U., Jain, N. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dendrimer+toxicity:+Let's+meet+the+challenge.">Dendrimer toxicity: Let's meet the challenge.</a> Int. J. Pharm. 394 (1-2), 122-142 (2010).</li><li>Rudovsky, 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=PAMAM+dendrimeric+conjugates+with+a+Gd-DOTA+phosphinate+derivative+and+their+adducts+with+polyaminoacids:+The+interplay+of+global+motion,+internal+rotation,+and+fast+water+exchange.">PAMAM dendrimeric conjugates with a Gd-DOTA phosphinate derivative and their adducts with polyaminoacids: The interplay of global motion, internal rotation, and fast water exchange.</a> Bioconjugate Chem. 17 (4), 975-987 (2006).</li><li>Xu, 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=Toward+improved+syntheses+of+dendrimer-based+magnetic+resonance+imaging+contrast+agents:+New+bifunctional+diethylenetriaminepentaacetic+acid+ligands+and+nonaqueous+conjugation+chemistry.">Toward improved syntheses of dendrimer-based magnetic resonance imaging contrast agents: New bifunctional diethylenetriaminepentaacetic acid ligands and nonaqueous conjugation chemistry.</a> J. Med. Chem. 50 (14), 3185-3193 (2007).</li><li>Nwe, K., Bryant, L. H., Brechbiel, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(amidoamine)+Dendrimer+Based+MRI+Contrast+Agents+Exhibiting+Enhanced+Relaxivities+Derived+via+Metal+Preligation+Techniques.">Poly(amidoamine) Dendrimer Based MRI Contrast Agents Exhibiting Enhanced Relaxivities Derived via Metal Preligation Techniques.</a> Bioconjugate Chem. 21 (6), 1014-1017 (2010).</li><li>Livramento, J. B., 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=First+in+vivo+MRI+assessment+of+a+self-assembled+metallostar+compound+endowed+with+a+remarkable+high+field+relaxivity.">First in vivo MRI assessment of a self-assembled metallostar compound endowed with a remarkable high field relaxivity.</a> Contrast Media Mol. 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Preparation of the dendrimeric MRI contrast agent requires appropriate selection of the monomeric unit (i.e., the chelator for Gd(III)). They reduce the toxicity of this paramagnetic ion and, to date, a wide variety of acyclic and macrocyclic chelators serve this purpose1-3. Among these, macrocyclic DOTA-type chelators possess the highest thermodynamic stability and kinetic inertness and, hence, are the most preferred choice for the preparation of inert MRI contrast agents1,18. Furthermore,...

Magnetic resonance imaging (MRI) is a powerful and non-ionizing imaging technique widely used in biomedical research and clinical diagnostics due to its noninvasive nature and excellent intrinsic soft-tissue contrast. The most commonly used MRI methods utilize the signal obtained from water protons, providing high-resolution images and detailed information within the tissues based on differences in the density of the water signals. The signal intensity and the specificity of the MRI experiments can be further improved using contrast agents (CAs). These are paramagnetic or superparamagnetic species that affect the longitudinal (T1) and transverse (T2) relaxation times, respectively1,2.
Complexes of the lanthanide ion gadolinium with polyamino polycarboxylic acid ligands are the most commonly used T1 CAs. Gadolinium(III) shortens the T1 relaxation time of water protons, thus increasing the signal contrast in MRI experiments3. However, ionic gadolinium is toxic; its size approximates that of calcium(II), and it seriously affects calcium-assisted signaling in cells. Therefore, acyclic and macrocyclic chelates are employed to neutralize this toxicity. Various multidentate ligands have been developed so far, resulting in gadolinium(III) complexes with high thermodynamic stability and kinetic inertness1. Those based on the 12-membered azamacrocycle cyclen, in particular its tetracarboxylic derivative DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) are the most investigated and applied complexes of this CA class.
Nevertheless, GdDOTA-type CAs are low molecular weight systems, displaying certain disadvantages such as low contrast efficiency and fast renal excretion. Macromolecular and multivalent CAs may be a good solution to these problems4. Since CA biodistribution is mainly determined by their size, macromolecular CAs display much longer retention times within tissues. Equally important, the multivalency of these agents results in an increased local concentration of the monomeric MR probe (e.g., GdDOTA complex), substantially improving the acquired MR signal and the measurement quality.
Dendrimers are amongst the most preferred scaffolds for the preparation of multivalent CAs for MRI4,5. These highly branched macromolecules with well-defined sizes are prone to various coupling reactions on their surface. In this work, we report the preparation, purification, and characterization of a dendrimeric CA for MRI consisting of a generation 4 (G4) poly(amidoamine) (PAMAM) dendrimer coupled to GdDOTA-like chelates (DCA). We describe the synthesis of the reactive DOTA derivative and its coupling to the PAMAM dendrimer. Upon complexation with Gd(III), the standard physicochemical characterization procedure of DCA was performed. Finally, MRI experiments were performed to demonstrate the ability of DCA to produce MR images with a stronger contrast than those obtained from low molecular weight CAs.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Cyclen</td>
			<td style="width:275px;">CheMatech</td>
			<td style="width:136px;">C002</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">tert-Butyl bromoacetate&#160;</td>
			<td style="width:275px;">Alfa Aesar</td>
			<td style="width:136px;">A14917</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">N,N-Dimethylformamide</td>
			<td style="width:275px;">Fluka</td>
			<td style="width:136px;">40248</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Potassium carbonate</td>
			<td style="width:275px;">Sigma-Aldrich</td>
			<td style="width:136px;">209619</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">4-(4-Nitrophenyl)butryic acid</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">335339</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Thionyl chloride&#160;</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">382662500</td>
			<td style="width:259px;">Note: Corrosive substance; toxic if inhaled</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Bromine</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">402841000</td>
			<td style="width:259px;">Note: causes severe skin burns, fatal if inhaled&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Diethyl ether</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Sodium sulphate</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">196640010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Chloroform&#160;</td>
			<td style="width:275px;">VWR Chemicals</td>
			<td style="width:136px;">22711.29</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">tert-Butyl 2,2,2-trichloroacetimidate</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">364789</td>
			<td style="width:259px;">Note: flammable substance; irritrant to skin and eyes</td>
		</tr>
		<tr height="67">
			<td height="67" style="height:67px;width:251px;">Boron trifluoride etherate</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">174560250</td>
			<td style="width:259px;">48 % BF3. Note: Flammable substance; causes skin burns, fatal if inhaled&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Sodium bicarbonate</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">424270010</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Ethyl-acetate</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td>For column chromatography</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">n-Hexane</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td>For column chromatography</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Bulb-to-bulb (Kugelrohr) distillation apparatus</td>
			<td style="width:275px;">B&#252;chi</td>
			<td style="width:136px;"></td>
			<td>Model type: Glass oven B-585</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Silicagel</td>
			<td style="width:275px;">Carl Roth GmbH</td>
			<td style="width:136px;">P090.2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Methanol</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td>For column chromatography</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Dichloromethane&#160;</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td>For column chromatography</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Ethanol</td>
			<td style="width:275px;">VWR Chemicals</td>
			<td style="width:136px;">20821.296</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Ammonia</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">428381000</td>
			<td style="width:259px;">7N Solution in Methanol</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Palladium&#160;</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">643181</td>
			<td style="width:259px;">15 % wet</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Hydrogenation apparatus PARR</td>
			<td style="width:275px;">PARR Instrument Company</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Celite 503</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">22151</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Sintered glass funnel</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Thiophosgen</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">115150</td>
			<td style="width:259px;">Note: irritrant to skin; toxic if inhaled</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Triethylamine</td>
			<td style="width:275px;">Alfa Aesar</td>
			<td style="width:136px;">A12646</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Dichloromethane&#160;</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">348460010</td>
			<td style="width:259px;">Extra dry&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Magnetic stirrer</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">PAMAM G4 Dendrimer</td>
			<td style="width:275px;">Andrews ChemService</td>
			<td style="width:136px;">AuCS - 297</td>
			<td style="width:259px;">&#160;10 % wt. solution in MeOH</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Lipophylic Sephadex LH-20</td>
			<td style="width:275px;">Sigma</td>
			<td style="width:136px;">LH20100</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Thin-layer chromatography plates</td>
			<td style="width:275px;">Merck Millipore</td>
			<td style="width:136px;">1.05554.0001</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Formic acid</td>
			<td style="width:275px;">VWR Chemicals</td>
			<td style="width:136px;">20318.297</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Lophylizer&#160;</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Gadollinium(III) chloride hexahydrate</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">G7532</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Sodium hydroxide</td>
			<td style="width:275px;">Acros Organics</td>
			<td style="width:136px;">134070010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">pH meter</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Ethylenediaminetetraacetic acid disodium salt dihydrate</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">E5134</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Mass spectrometer (ESI)</td>
			<td style="width:275px;">Agilent</td>
			<td style="width:136px;"></td>
			<td>Ion trap SL 1100&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Acetate buffer</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td>pH 5.8</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Xylenol orange</td>
			<td style="width:275px;">Aldrich</td>
			<td style="width:136px;">52097</td>
			<td>20 &#956;M in acetate buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Hydrophylic Sephadex G-15</td>
			<td style="width:275px;">GE Healthcare</td>
			<td style="width:136px;">17-0020-01</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Amicon Ultra-15 Centrifugal Filter Unit</td>
			<td style="width:275px;">Merck Millipore</td>
			<td style="width:136px;">UFC900324</td>
			<td style="width:259px;">Ultracel-3 membrane (MWCO 3000)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Centrifuge</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">NMR spectrometer&#160;</td>
			<td style="width:275px;">Bruker</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">Avance III 300 MHz</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Topspin</td>
			<td style="width:275px;">Bruker</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">version 2.1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Combustion analysis instrument</td>
			<td style="width:275px;">EuroVector SpA</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">EuroEA 3000 Elemental Analyser&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">MALDI-ToF MS instrument</td>
			<td style="width:275px;">Applied Biosystems</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">Voyager-STR</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Deuteriumoxid</td>
			<td style="width:275px;">Carl Roth GmbH</td>
			<td style="width:136px;">6672.3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">tert-Butyl alcohol</td>
			<td style="width:275px;">Carl Roth GmbH</td>
			<td style="width:136px;">AE16.1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Vortex mixer</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Norell NMR tubes</td>
			<td style="width:275px;">Deutero GmbH</td>
			<td style="width:136px;">507-HP-7</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">NMR coaxial tube</td>
			<td style="width:275px;">Deutero GmbH</td>
			<td style="width:136px;">coaxialb-5-7</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">DLS instrument</td>
			<td style="width:275px;">Malvern</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">Zetasizer Nano ZS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">0.20 &#956;m PTFE filter&#160;</td>
			<td style="width:275px;">Carl Roth GmbH</td>
			<td style="width:136px;">KC94.1</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">HEPES</td>
			<td style="width:275px;">Fisher BioReagents</td>
			<td style="width:136px;">BP310</td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Plastic tube vials</td>
			<td style="width:275px;">any source</td>
			<td style="width:136px;"></td>
			<td style="width:259px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Dotarem</td>
			<td style="width:275px;">Guerbet</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">NDC 67684-2000-1</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:251px;">MRI scanner</td>
			<td style="width:275px;">Bruker</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">BioSpec 70/30 USR magnet (7 T). Note: potential hazards related to high magnetic fields</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">RF coil</td>
			<td style="width:275px;">Bruker</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">dual frequency volume coil (RF RES 300 1H/19F 075/040 LIN/LIN TR)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Paravision (software)</td>
			<td style="width:275px;">Bruker</td>
			<td style="width:136px;"></td>
			<td style="width:259px;">Version 5.1</td>
		</tr>
	</tbody>
</table>

preparation and in vitro characterization of dendrimer-based contrast agents for magnetic resonance imaging

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance imaging (MRI). Their purpose is to enhance the relaxation rate of water protons in tissue, thus increasing the MR image contrast and the specificity of the MRI measurements. Current clinically approved contrast agents are low molecular weight molecules that are rapidly cleared from the body. The use of dendrimers as carriers of paramagnetic chelators can play an important role in the future development of more efficient MRI contrast agents. Specifically, the increase in local concentration of the paramagnetic species results in a higher signal contrast. Furthermore, this CA provides a longer tissue retention time due to its high molecular weight and size. Here, we demonstrate a convenient procedure for the preparation of macromolecular MRI contrast agents based on poly(amidoamine) (PAMAM) dendrimers with monomacrocyclic DOTA-type chelators (DOTA &#8211; 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate). The chelating unit was appended by exploiting the reactivity of the isothiocyanate (NCS) group towards the amine surface groups of the PAMAM dendrimer to form thiourea bridges. Dendrimeric products were purified and analyzed by means of nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis. Finally, high resolution MR images were recorded and the signal contrasts obtained from the prepared dendrimeric and the commercially available monomeric agents were compared.

The preparation of DCA consisted of two stages: 1) synthesis of the monomeric DOTA-type chelator (Figure 1) and 2) coupling of the chelator with the G4 PAMAM dendrimer and subsequent preparation of the dendrimeric Gd(III) complex (Figure 2). In the first stage, a cyclen-based DOTA-type chelator containing four carboxylic acids and an orthogonal group suitable for further synthetic modifications was prepared. The preparation commenced from...

Watch this Scientific Journal Video about Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging at JoVE.com

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging

This protocol describes the preparation and characterization of a dendrimeric magnetic resonance imaging (MRI) contrast agent that carries cyclen-based macrocyclic chelates coordinating paramagnetic gadolinium ions. In a series of MRI experiments in vitro, this agent produced an amplified MRI signal when compared to the commercially available monomeric analogue.

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance ...

Research

JoVE Journal

Chemistry

Synthesis, Cellular Delivery and In vivo Application of Dendrimer-based pH Sensors

Synthesis, Cellular Delivery and In vivo Application of Dendrimer-based pH Sensors

The development of  fluorescent indicators represented a revolution for life sciences. Genetically  encoded and synthetic fluorophores with sensing ...

Preparation and Characterization of SDF-1&#945;-Chitosan-Dextran Sulfate Nanoparticles

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Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under ...

Preparation and Characterization of Individual and Multi-drug Loaded Physically Entrapped Polymeric Micelles

Amphiphilic block copolymers like polyethyleneglycol-block-polylactic acid (PEG-b-PLA) can self-assemble into micelles above their critical micellar ...

Sequencing of Plant Wall Heteroxylans Using Enzymic, Chemical (Methylation) and Physical (Mass Spectrometry, Nuclear Magnetic Resonance) Techniques

Sequencing of Plant Wall Heteroxylans Using Enzymic, Chemical Methylation and Physical Mass Spectrometry, Nuclear Magnetic Resonance Techniques

This protocol describes the specific techniques used for the characterization of reducing end (RE) and internal region glycosyl sequence(s) of ...

Synthesis and Characterization of Supramolecular Colloids

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

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors

Low-energy Cathodoluminescence for OxyNitride Phosphors

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and ...

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

A method is demonstrated to monitor macroscopic translational diffusion using electron paramagnetic resonance (EPR) imaging. A host-guest system with ...

DNA-magnetic Particle Binding Analysis by Dynamic and Electrophoretic Light Scattering

Isolation of DNA using magnetic particles is a field of high importance in biotechnology and molecular biology research. This protocol describes the ...

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We ...

Technical Aspect of the Automated Synthesis and Real-Time Kinetic Evaluation of [11C]SNAP-7941

Technical Aspect of the Automated Synthesis and Real-Time Kinetic Evaluation of [11C]SNAP-7941

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