Since Seemans pioneering work, [1a-c] DNA has been recognized as a building material for programmable hollow 3D nanoobjects. DNA nanoconstruction benefits from the structural rigidity of short DNA double strands, scalability, good accessibility of synthetic and chemically modified DNA, and the option for enzymatic amplification and processing. Four strategies for the construction of nanoobjects such as polyhedra exist so far. Strategy I is vertex-centered and goes from noncovalent junctions to covalent objects: Noncovalent three-way junctions are assembled from three linear oligonucleotides. Each arm contains a sticky end sequence which is hybridized to its complement in another junction and then covalently connected by DNA ligases.[1] Strategy II is the reverse of strategy I and makes use of trisoligonucleotides, in other words covalent junctions are noncovalently assembled to give the target nanoobjects.[2d, e] Non-natural modes of copying [2a] and amplifying [2b] were proposed to enable the replication of junctions and nanoconstructs from the latter.[2c]Strategy III is a face-centered approach, employing as many oligonucleotides as there are faces on the object while each oligonucleotide is composed of as many segments as there are edges surrounding the faces.[3a-d] Strategy IV first defines the longest path through the object by connecting all vertices using a very long DNA single strand; a set of shorter oligonucleotides generates suitable rigid motifs such as double crossovers, while additional connectivities are expressed by means of paranemic crossover motifs. [4] Recently the assembly of triangular prisms, cubes, pentameric and hexameric prisms, heteroprisms, and biprisms was reported. A set of single-stranded linear and cyclic DNA building blocks was used, and in the latter case rigid organic linker molecules were used as vertices.[5]Herein we report on a new generation of trisoligonucleotides and their employment in benchmark experiments to evaluate strategy II. We selected a dodecahedron, as polyhedra with a smaller number of vertices have been described already. [1][2][3][4][5] The feasibility of constructing a dodecahedron that reflects the basic symmetry of a virus was forseen for strategy III, [1d] but so far this has not been achieved by any strategy.Previously prepared trisoligonucleotides with three different arms were based on asymmetric linker constructs, [2a, e, f, 6] so that in principle a set of three different sequences could be connected in three different ways. Linker scaffolds with C 3h symmetry are thought to be advantageous because all vertices are expected to be subject to the same conformational constraints. Moreover, diastereomeric mixtures obtained by the utilization of commercially available racemic linker amidites [6b, 7] are avoided here. Until now trisoligonucleotides with C 3h linkers were synthesized by chemical copying of connectivity, that is the usage of a 3'-connected trisoligonucleotide template for the trislinking of suitable 5'-functionalized linear oligonucleo...
Seit den bahnbrechenden Arbeiten von Seeman [1a-c] wird DNA als Konstruktionsmaterial für programmierbare hohle 3D-Nanoobjekte untersucht und genutzt. Nanokonstrukte aus DNA profitieren von der Rigidität kurzer DNA-Doppelstränge, der Skalierbarkeit, der guten Verfügbarkeit synthetischer und chemisch modifizierter DNA und der Mög-lichkeit, DNA enzymatisch zu amplifizieren und zu prozessieren. Bisher sind vier Strategien zur Konstruktion von Objekten wie Polyedern beschrieben worden. Strategie I beruht auf einer eckenzentrierten Verknüpfung und führt ausgehend von nichtkovalenten DNA-Verzweigungspunkten zu kovalenten Objekten. Nichtkovalente Dreiwegekreuzungen (three-way junctions) entstehen durch Selbstorganisation von drei linearen Oligonucleotiden; jeder Arm hat ein kohäsives einzelsträngiges Ende (sticky end), das mit einem komplementären einzelsträngigen Ende einer weiteren Dreiwegekreuzung hybridisiert und anschließend durch DNA-Ligase kovalent verknüpft wird.[1] Strategie II verläuft entgegengesetzt zu Strategie I und verwendet Trisoligonucleotide, d. h. kovalent verknüpfte DNA-Verzweigungspunkte, die sich nichtkovalent zu den Zielstrukturen selbstorganisieren. [2d, e] Nichtnatürliche Kopier- [2a] und Amplifikationsverfahren [2b] wurden vorgeschlagen, um die Replikation und Amplifikation von Trisoligonucleotiden oder der daraus entstehenden Nanostrukturen zu ermöglichen.[2c] Strategie III ist ein flä-chenzentrierter Ansatz, bei dem die Zahl der eingesetzten Oligonucleotide der Zahl der Flächen des zu synthetisierenden Objektes entspricht. Jedes Oligonucleotid besteht aus Segmenten, die für je eine Kante der Flächen stehen. [3a-d] Strategie IV bestimmt als erstes den längsten Pfad durch das Objekt, der alle Eckpunkte durch einen sehr langen DNAStrang verbindet. Ein Satz kürzerer Oligonucleotide ermög-licht dann die Bildung starrer Double-Crossover-Strukturen, während zusätzliche Verknüpfungen mithilfe von ParanemicCrossover-Motiven erzeugt werden.[4] Kürzlich wurde über den Aufbau von Prismen mit drei-, fünf-und sechseckigen Grundflächen sowie Würfeln berichtet. Hierfür wurde ein Satz von einzelsträngigen linearen und cyclischen DNA-Elementen verwendet, wobei letztere starre organische Linkermoleküle als Ecken enthalten. [5] Wir berichten hier über eine neue Generation von Trisoligonucleotiden und deren Verwendung in Benchmark-Experimenten, um die Leistungsfähigkeit von Strategie II zu überprüfen. Wir wählten als Zielstruktur ein Dodekaeder, da Polyeder mit einer geringeren Zahl von Ecken bereits beschrieben wurden. [1][2][3][4][5] Der mögliche Aufbau eines DNA-Dodekaeders, das die einem Virus zugrundeliegende Symmetrie hat, wurde bereits für Strategie III vorhergesehen, [1d] ist aber bislang durch keine Strategie realisiert worden.Früher verwendete Trisoligonucleotide mit drei unterschiedlichen Armen basierten auf asymmetrischen Linkerkonstrukten, [2a, e, f, 6] sodass die drei unterschiedlichen Sequenzen auf drei verschiedene Arten verknüpft werden konnten. Linkergerüste mit C 3h -Symmetrie soll...
The Schmid cluster, [1] [Au 55 (PPh 3 ) 12 Cl 6 ], has stimulated many different areas of technology ranging from catalysis research [2] to the concept of quantum electronics. [3,4] Monofunctionalized water-soluble derivatives of this cluster [5] have become commercially available and found numerous applications. [6][7][8][9][10][11][12][13][14] Recently, gold clusters have been employed as universal fluorescence quenchers in molecular beacons [15] and as nanoscale antennas for the reception of radio radiation in the GHz frequency region, which causes local and selective inductive heating of cluster-labeled biomolecules.[16] These applications as well as current experiments in DNA nanotechnology [17][18][19][20][21][22][23] point to the need for the increased thermostability of these gold clusters. We have shown that replacement of the monopodal triphenylphosphane ligands in such clusters with water-soluble tripodal thioethers based on 1,3,5-tris(thiomethyl)benzene leads to gold clusters with improved stability. [24] Herein, we report a new generation of biocompatible gold clusters that are surrounded by a single dodecadentate, nanoscale thioether-based "gripper". This method allows nanoparticles to be singly functionalized without the otherwise necessary step of purification of mixtures by HPLC.[ 25] We demonstrate that "gripped" clusters in oligonucleotide conjugates can survive the temperature conditions of polymerase chain reaction (PCR) and hybridization experiments.The concept behind our ligand is sketched in Figure 1. The Au 55 cluster was proposed to possess a cuboctahedral core, the surface of which is composed of eight corner-sharing triangles (111) and six squares (110).[1] Although there is an ongoing debate [26,27] about the cluster geometry, we decided to adopt this proposal as a working hypothesis. Au 55 is expected to bind four tripodal ligands provided that the binding mode of the ligands is comparable to that of the Schmid cluster, in which the 12 triphenylphosphanes most likely occupy the corners of the cuboctahedron. If the four tripodal ligands are connected by suitable linkers, a dodecadentate ligand will result. The synthesis was also designed so that the final material carries a single functional group to allow conjugation to (bio)molecules.Scheme 1 shows the synthesis of the target ligand 8. We selected a monomaleimido group as the monoconjugable unit to ensure functional comparability with the commercially available variant of the Schmid cluster. Thioether 2 was generated from trisbromide 1 as a key precursor that allowed the synthesis of 8 by a divergent-convergent route in only six steps with an overall yield of 31 %. The gold cluster was synthesized from ligand 8 by phase-transfer synthesis, as previously described for the tristhioether derived from lcysteine.[24] High-resolution transmission electron microscopy revealed a narrow size distribution of the clusters with a mean diameter of 1.4 nm, which is as expected for Au 55 particles. The cluster was conjugated with a 5'-thiol-modifi...
Fest im Griff: Ein einzelner, maßgeschneiderter Ligand mit zwölf Thioethergruppen kann als Greifer für Au55‐Cluster eingesetzt werden und führt zu thermisch hoch stabilen monofunktionalisierten Markierungen für Biomoleküle (siehe Schema). Konjugate der Goldcluster mit DNA‐Strängen dienen als effektive Fluoreszenzlöscher, die mit den drastischen thermischen Bedingungen bei Polymerasekettenreaktionen kompatibel sind.
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