Pim G. A. Janssen

pH-Switchable Helicity of DNA-Templated Assemblies†

Coming together: Oligothymine is used as a template to self-assemble complementary nonchiral naphthalene guests. Depending on the protonated state of the guest, left- or right-handed DNA-templated self-assemblies are formed (see picture). The templated assembly processes were studied in detail with temperature-dependent circular dichroism and UV/Vis spectroscopy.

Persistent, well-defined, monodisperse, pi-conjugated organic nanoparticles via G-Quadruplex self-assembly

Several oligo(p-phenylene-vinylene) oligomers capped with a guanosine or a guanine moiety have been prepared via a palladium-catalyzed cross-coupling reaction. Their self-assembly, in both the absence and presence of alkaline salts, has been studied by means of different techniques in solution (NMR, MS, UV-vis, CD, fluorescence), solid state (X-ray diffraction), and on surfaces (STM, AFM). When no salt is added, these pi-conjugated molecules self-associate in a mixture of hydrogen-bonded oligomers, among which the G-quartet structure may be predominant if the steric hindrance around the guanine base becomes important. In contrast, in the presence of sodium or potassium salts, well-defined assemblies of eight functional molecules (8mers) can be formed selectively and quantitatively. In these assemblies, the pi-conjugated oligomers are maintained in a chirally tilted (J-type) stacking arrangement, which is manifested by negative Cotton effects, small bathochromic absorption and emission shifts, and fluorescence enhancements. Furthermore, these self-assembled organic nanostructures, approximately 1.5-2.0 nm high and 8.5 nm wide, exhibit an extraordinary stability to temperature or concentration changes in apolar media, and they can be transferred and imaged over solid substrates as individual nanoparticles, showing no significant dissociation or further aggregation.

Encapsulation of DNA-templated chromophore assemblies within virus protein nanotubes

A beneficial virus: The hierarchical self-assembly of a three-component system consisting of single-stranded DNA (oligothymines; Tq), chromophores (G), and virus coat proteins (CP) leads to the formation of micrometer-long nanotubes (see picture). Tuning the interaction between the three components leads to the formation of structures with different length scales, and the chromophores within the nanotubes maintain the helical arrangement of the Tq–G template

Electrospray-Ionization Mass Spectrometry for Screening the Specificity and Stability of Single-Stranded-DNA Templated Self-Assemblies

Supramolecular complexes consisting of a single-stranded oligothymine (dTn) as the host template and an array of guest molecules equipped with a complementary diaminotriazine hydrogen-bonding unit have been studied with electrospray-ionization mass spectrometry (ESI-MS). In this hybrid construct, a supramolecular stack of guest molecules is hydrogen bonded to dTn. By changing the hydrogen-bonding motif of the DNA host template or the guest molecules, selective hydrogen bonding was proven. We were able to detect single-stranded-DNA (ssDNA)-guest complexes for strands with lengths of up to 20 bases, in which the highest complex mass detected was 15 kDa; these complexes constitute 20-component self-assembled objects. Gas-phase breakdown experiments on single- and multiple-guest-DNA assemblies gave qualitative information on the fragmentation pathways and the relative complex stabilities. We found that the guest molecules are removed from the template one by one in a highly controlled way. The stabilities of the complexes depend mainly on the molecular weight of the guest molecules, a fact suggesting that the complexes collapse in the gas phase. By mixing two different guests with the ssDNA template, a multicomponent dynamic library can be created. Our results demonstrate that ESI-MS is a powerful tool to analyze supramolecular ssDNA complexes in great detail.

ssDNA templated assembly of oligonucleotides and bivalent naphthalene guests

The hybridization of oligothymine templates with oligomeric adenine and naphthalene diaminotriazine guests has been studied by UV-vis and circular dichroism (CD) spectroscopy. First, the length of the oligothymine template and the oligoadenine guest has been systematically varied. The studies reveal that increasing the length of multivalent guests results in a stabilization of the templated assemblies. Hybridization studies also show that guest–guest interactions between the multivalent guests additionally enhance the stability. Based on these results, a bivalent naphthalene diaminotriazine guest has been synthesized, showing a higher stability than the monovalent naphthalene diaminotriazine guest; the host–guest interaction energy is higher while the guest–guest interaction remains the same.

Tuning the self-assembly of a ditopic crown ether functionalized oligo(p-phenylenevinylene)

A chiral ditopic crownether functionalized oligo(p-phenylenevinylene), COPV, has been synthesized and fully characterized. The binding properties and the organization of COPV have been studied in solution and in the solid state. In chloroform, due to the benzo-15-crown-5 moieties, COPV is able to bind cations. In case of K+ a strong 2 : 2 complex is formed in which two COPVs are sandwiched between two potassium ions. Na+ is bound following a two-step negative cooperative process to form a 2 : 1 Na+/COPV complex. When COPV in the presence of potassium ions is drop-cast on a silicon substrate, fibers are formed. In waterCOPV forms stable helical aggregates as can be concluded from the Cotton effect, the UV-vis and fluorescence spectroscopy. AFM and light scattering studies show that ellipsoidal aggregates are present in water.

Synthesis and properties of ?,?-phenyl-capped bithiophene derivatives

Nine different α,ω-phenyl-endcapped bithiophenes were synthesised, and the effect of the different side chains on the liquid crystalline properties, alignment ability and charge carrier mobility have been studied. An increase in chain length leads to a decrease in the liquid crystalline–isotropic phase (clearing) transition temperature. Remarkably, introduction of an asymmetric carbon centre close to the π-conjugated segment resulted in the loss of the liquid crystalline phase. Alignment on rubbed polyimide was obtained for the liquid crystalline thiophene derivatives lacking heteroatoms in the side chain and for the chiral α,ω-phenyl-endcapped bithiophene. Some bithiophenes showed bipolar charge transport in time-of-flight (TOF) measurements, with mobilities up to 3 × 10−3 cm2 V−1 s−1 in the liquid crystalline state. Field effect transistors revealed mobility for holes up to 1 × 10−3 cm2 V−1 s−1 (crystalline state). From the data set obtained, it can be concluded that the use of linear hydrocarbon chains as solubilising tails in these types of π-conjugated building blocks gives the best overall electronic performance.