Excess partial molar enthalpies,entropies, Gibbs energies,and volumes in aqueous dimethylsulfoxide

The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H₂O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H₂O. The values of the excess partial molar Gibbs energies for both DMSO and H₂O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H₂O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H₂O molecules from exposure to the nonpolar alkyl groups of DMSO.     

Preparation temperature dependence of size and polydispersity of alkylthiol monolayer protected gold clusters

The influence of preparation temperature on the size and size distribution of dodecylthiol monolayer protected gold clusters was studied. The monolayer protected clusters (MPCs) were synthesized by two different variations of the Brust-Schiffrin procedure. In all of the experiments, the stoichiometry of the reactants dodecylthiol, HAuCl(4), and sodium borohydride was kept constant, while the temperature was varied in the range of -18 to +90 degrees C. Two series were performed in which an aqueous solution of NaBH(4) was either added over 30 s or all in one portion. The size and size distribution of the MPCs were determined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It has been demonstrated that in general the MPC size increases with elevated preparation temperatures.     

Different Views on the Stability of Protein Conformations and Hydrophobic Effects

Apparently contradictory statements about the thermodynamics of aqueous protein solutions and of hydrophobic effect are quoted and discussed. Some credibility is found in the divergent points of view and it is pointed out that they focus attention on different aspects of the complicated conditions in aqueous solutions, some of which are more important than others for the stability of protein conformations.The importance of characteristics of solvent water is emphasized, in particular (1) the strong mutual cohesion of water molecules, and (2) structural changes of water induced by (nonpolar) solute molecules. It is stressed that consideration of only one of these effects and an inexpedient choice of standard states are origins of confusion in the literature about aqueous systems. A simple approach to hydrophobic effects considering both of the above mentioned effects, is proposed.     

Synthesis of linear and tripoidal oligo(phenylene ethynylene)-based building blocks for application in modular DNA-programmed assembly

Rigid linear and tripoidal organic modules based on the oligo(phenylene ethynylene) backbone having salicylaldehyde-derived termini are synthesized. A highly functionalized 5-iodosalicyl aldehyde was prepared and coupled to each ethynyl group of 1,4-diethynylbenzene or 1,3,5-triethynylbenzene in Sonogashira couplings. The two or three termini of the compounds are functionalized for incorporation in linear and branched oligonucleotide strands. For the linear module (LM), the two termini are equipped with amide spacers, and one of these was functionalized with a DMTr (dimethoxytrityl)-protected hydroxy group and the other with a phosphoramidite. One of the tripoidal modules is prepared with DMTr groups in two of its three termini. A tripoidal module is also synthesized with three different groups on its hydroxy termini: a phosphoramidite, a DMTr group, and an Fmoc group. Extended studies have shown that these rigid linear and tripoidal organic modules can be incorporated into short oligonucleotides. Several of these modules can be applied for DNA-directed assembly and covalent coupling into structures of predetermined connectivity. Such structures have potential application for molecular electronics and nanotechnology.     

Using the Donsker Delta Function to Compute Hedging Strategies

We use white noise calculus and the Donsker Delta Function to find explicit formulas for the replicating portfolios in a Black–Scholes market for a class of contingent T-claims.     

DNA origami: a quantum leap for self-assembly of complex structures

The spatially controlled positioning of functional materials by self-assembly is one of the fundamental visions of nanotechnology. Major steps towards this goal have been achieved using DNA as a programmable building block. This tutorial review will focus on one of the most promising methods: DNA origami. The basic design principles, organization of a variety of functional materials and recent implementation of DNA robotics are discussed together with future challenges and opportunities.     

Controlling chiral organization of molecular rods on Au(111) by molecular design

Chiral self-assembled structures formed from organic molecules adsorbed on surfaces have been the subject of intense investigation in the recent decade, owing both to relevance in applications such as enantiospecific heterogeneous catalysis or chiral separation as well as to fundamental interest, for example, in relation to the origin of biomolecular homochirality. A central target is rational design of molecular building blocks allowing transfer of chirality from the molecular to the supramolecular level. We previously studied the surface self-assembly of a class of linear compounds based on an oligo(phenylene ethynylene) backbone, which were shown to form a characteristic windmill adsorption pattern on the Au(111) surface. However, since these prochiral compounds were intrinsically achiral, domains with oppositely oriented windmill motifs and related conformational surface enantiomers were always realized in equal proportion. Here we report on the enantioselective, high yield chemical synthesis of a structurally related but intrinsically chiral compound in which two peripheral tert-butyl substituents are replaced by sec-butyl groups, each containing an (S) chiral center. Using scanning tunneling microscopy under ultrahigh vacuum conditions, we characterize the adsorption structures formed from this compound on the Au(111) surface. The perturbation introduced by the modified molecular design is found to be sufficiently small so structures form that are closely analogous to those observed for the original tert-butyl substituted compound. However, as demonstrated from careful statistical analysis of high-resolution STM images, the introduction of the two chiral (S)-sec-butyl substituents leads to a strong preference for windmill motifs with one orientation, demonstrating control of the chiral organization of the molecular backbones through rational molecular design.     

Chiral induction by seeding surface assemblies of chiral switches

It is demonstrated by scanning tunneling microscopy that coadsorption of a molecular chiral switch with a complementary, intrinsically chiral induction seed on the Au(111) surface leads to the formation of globally homochiral molecular assemblies.     

Synthesis of an elongated linear oligo(phenylene ethynylene)-based building block for application in DNA-programmed assembly

The synthesis of an elongated linear oligonucleotide-functionalised module (ELOM) is described. The ELOM structure is based on an oligo(phenylene ethynylene) backbone substituted with two decyloxy groups. The two termini constitute two salicylaldehyde moieties acting as chemical cross-linkers. Before incorporation into an oligonucleotide sequence the organic part of the module, the elongated linear module (ELM), is functionalised with a dimethoxytrityl group and a phosphoramidite group. This enables incorporation into the middle of 30-mer oligonucleotide sequences by automated DNA synthesis. The obtained ELOMs were characterised by polyacrylamide gel electrophoresis and MALDI-TOF mass spectrometry. In analogy with previously reported LOM and TOM structures the coupling reactions of the ELOM modules were tested.