CdSe nanocrystals (NCs) capped by organic ligands are studied at the atomistic level using classical molecular simulations. We show for the first time that the NC−ligand bond strength can be explained using a simple model based on electrostatic interactions. The computed binding energies in vacuum for amine, thiol, thiolate, and phosphine oxide ligands are 86.8, 34.7, 1283, and 313.6 kJ/mol, respectively. These values are in good agreement with available quantum chemical calculations and experiments. It is crucial that one corrects for the dielectric constant of the solvent used in the experiment. We also show that the amine capping layer is formed in two stages: first, amine molecules binds to a single surface cation each, and then additional amines bind to less favorable sites forming hydrogen bonds with already adsorbed ligands. The crossover between these mechanisms can occur at ambient conditions. We speculate that this crossover may be responsible for transitions in optical properties reported earlier. The calculated adsorption isotherms show that amine ligands desorb from the nanocrystal surface under ultra-high vacuum at ambient temperatures.

Human α-synuclein (αS) has been shown to be N terminally acetylated in its physiological state. This modification is proposed to modulate the function and aggregation of αS into amyloid fibrils. Using bacterially expressed acetylated-αS (NTAc-αS) and endogenous αS (Endo-αS) from human erythrocytes, we show that N-terminal acetylation has little impact on αS binding to anionic membranes and thus likely not relevant for regulating membrane affinity. N-terminal acetylation does have an effect on αS aggregation, resulting in a narrower distribution of the aggregation lag times and rates. 2D-IR spectra show that acetylation changes the secondary structure of αS in fibrils. This difference may arise from the slightly higher helical propensity of acetylated-αS in solution leading to a more homogenous fibril population with different fibril structure than non-acetylated αS. We speculate that N-terminal acetylation imposes conformational restraints on N-terminal residues in αS, thus predisposing αS toward specific interactions with other binding partners or alternatively decrease nonspecific interactions.

Coiled-coil leucine zipper domains are well-studied molecular recognition motifs that are attractive candidates for incorporation into engineered self-assembly systems due to their modular nature and wide range of binding affinities. Here, we investigate the ability of this peptide family to induce and control the specific association of micron-sized building blocks. Individual microparticles are functionalized with multiple copies of one particular leucine zipper motif which is capable of selfassembling through dimerization. We find that the dissociation temperature of the peptidefunctionalized microparticles is considerably higher than the melting temperature of free peptide dimers in solution, which is a signature of the multivalent nature of the peptide-mediated particle interactions. We further demonstrate that titrating in freely soluble peptides to the peptide-coated bead suspensions can tune the particle association at constant temperature, pH, and ionic strength.While the high dissociation temperature of peptide-functionalized micro-objects may make global temperature control challenging, this 'competition control' with freely soluble peptides offers an attractive alternative to fine-tune the colloidal self-assembly with additional particle-specificity.

We imprint plasmonic near field enhancements as nanoscale topography in SU8 photoresist using two-photon absorption from a spectrally filtered broadband supercontinuum light source. Imprinted patterns smaller than 50 nm across are obtained localized at positions of high local field enhancements in gold bow tie antennas, and gold split rings resonant in the visible and near-infrared. Enhanced exposure only occurs at wavelengths and polarizations that exactly match the plasmonic resonances. Hence our work demonstrates that wavelength selective addressing of hot spots for nanolithography using an inexpensive, low peak-power picosecond pulsed source is freely tunable throughout the visible and infrared to match any desired plasmon resonance.

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