Wavefunction-based electron correlation methods for solids

In this article we provide an overview of the most common ways of treating electron correlation effects in 3D-periodic systems with some emphasize on wavefunction-based correlation methods such as the method of increments and the local MP2 method implemented in the Cryscor program. We discuss strengths and weaknesses of the different approaches and give examples for their application. Additionally, for the method of increments we discuss recent developments for its application to open shell systems and problems related to the treatment of graphene sheets.     

Silylation products of cyclic tri-aminal carbanions and their lithiation

The structure of 1,3,5-trimethyl-1,3,5-triaza-cyclohexane (TMTAC) was determined by single crystal X-ray diffraction and compared with earlier gas-phase data. It shows a preference for an aee-conformation in all phases. Lithiated TMTAC, [(RLi)(2)·(RH)] (1) (R = 2,4,6-trimethyl-2,4,6-triaza-cyclohex-1-yl), was reacted with Et(3)SiCl, Ph(3)SiCl and PhMe(2)SiCl to afford the substituted silanes Et(3)SiR (1), Ph(3)SiR (2) and PhMe(2)SiR (3) in moderate yields. They were characterised by NMR spectroscopy ((1)H, (13)C, (29)Si). 1 reacts with Me(2)SiCl(2) and Ph(2)SiCl(2) to give Me(2)SiR(2) (5) and Ph(2)SiR(2) (6) which were characterised by NMR spectroscopy. 5 was also identified by crystal structure determination. Analogous triple substitution could not be observed by employing trichlorosilanes. Quantumchemical calculations explain this by sterical overcrowding of the silicon atom. The reaction of 1 with SiCl(4) did not yield fourfold substitution but a formal insertion product of SiCl(2) into a C-N bond of the TMTAC ring (2,4,6-trimethyl-2,4,6-triaza-1,1-dichloro-1-sila-cycloheptane, 7) in very small quantities. It was identified by X-ray crystallography and shows an intramolecular Si···N dative bond. The reactions of (3) and (5) with n-butyl lithium afforded lithiation of the silicon bound methyl groups in both cases. The products, 8 and 9, were characterised by NMR spectroscopy ((1)H, (13)C, (29)Si), 8 was also characterised by X-ray crystallography.     

Non-specific interactions of CdTe/Cds Quantum Dots with human blood mononuclear cells

In order to study biological events, researchers commonly use methods based on fluorescence. These techniques generally use fluorescent probes, commonly small organic molecules or fluorescent proteins. However, these probes still present some drawbacks, limiting the detection. Semiconductor nanocrystals - Quantum Dots (QDs) - have emerged as an alternative tool to conventional fluorescent dyes in biological detection due to its topping properties - wide absorption cross section, brightness and high photostability. Some questions have emerged about the use of QDs for biological applications. Here, we use optical tools to study non-specific interactions between aqueous synthesized QDs and peripheral blood mononuclear cells. By fluorescence microscopy we observed that bare QDs can label cell membrane in live cells and also label intracellular compartments in artificially permeabilized cells, indicating that non-specific labeling of sub-structures inside the cells must be considered when investigating an internal target by specific conjugation. Since fluorescence microscopy and flow cytometry are complementary techniques (fluorescence microscopy provides a morphological image of a few samples and flow cytometry is a powerful technique to quantify biological events in a large number of cells), in this work we also used flow cytometry to investigate non-specific labeling. Moreover, by using optical tweezers, we observed that, after QDs incubation, zeta potentials in live cells changed to a less negative value, which may indicate that oxidative adverse effects were caused by QDs to the cells.     

Fluorescent conjugated block copolymer nanoparticles by controlled mixing

Monitoring of the formation of stable fluorescent nanoparticles from controlled mixing of a THF solution of poly(fluorene ethynylene)-block-poly(ethylene glycol) in a microfluidic laminar flow crossjunction by spatially resolved fluorescence spectroscopy reveals the time scale of particle formation as well as incorporation of small molecule guests and the role of solvent mixing.     

Mapping the location of grafted PNIPAAM in mesoporous SBA-15 silica using gas adsorption analysis

The thermoresponsive polymer poly-N-isopropylacrylamide (PNIPAAM) was grafted in mesoporous SBA-15 silica. The grafting process consists of three steps: (i) increasing the amount of surface silanol groups of SBA-15 by hydroxylation, (ii) attachment of an anchor (1-(trichlorosilyl)-2-(m/p-(chloromethylphenyl)ethane) and finally (iii) the polymerization of the monomers (NIPAAM) onto the anchor. After each step, the materials were characterized regarding the porosity, using inert gas (argon, nitrogen) physisorption measurements. Also, the structure was investigated by small-angle X-ray diffraction analysis and thermogravimetric analysis was used for determination of the amount of grafted material. A total of 17% by weight of organic material was introduced in the porous host and the structure was preserved during the grafting process. Physisorption measurements revealed that the anchor is mainly located in the intrawall pores present in SBA-15. Consequently, the polymer is preferentially located in the intrawall pores or in the vicinity thereof. The final mesopore volume is 0.47 cm(3) g(-1) as compared to 0.96 cm(3) g(-1) for the pure SBA-15. The surprisingly large loss of mesopore volume and an almost constant mesopore diameter is consistent with a partial sealing of the mesopore volume in the composite materials. The potential thermocontrol combined with the large mesoporosity and the possible "storage space" provided by the sealed mesopore volume leads to a material with possibilities for various applications.     

How Post‐Translational Modifications Influence Amyloid Formation: A Systematic Study of Phosphorylation and Glycosylation in Model Peptides

A reciprocal relationship between phosphorylation and O‐glycosylation has been reported for many cellular processes and human diseases. The accumulated evidence points to the significant role these post‐translational modifications play in aggregation and fibril formation. Simplified peptide model systems provide a means for investigating the molecular changes associated with protein aggregation. In this study, by using an amyloid‐forming model peptide, we show that phosphorylation and glycosylation can affect folding and aggregation kinetics differently. Incorporation of phosphoserines, regardless of their quantity and position, turned out to be most efficient in preventing amyloid formation, whereas O‐glycosylation has a more subtle effect. The introduction of a single β‐galactose does not change the folding behavior of the model peptide, but does alter the aggregation kinetics in a site‐specific manner. The presence of multiple galactose residues has an effect similar to that of phosphorylation.     

Catalytically Active Peptide–Gold Nanoparticle Conjugates: Prospecting for Artificial Enzymes

The self‐assembly of peptides onto the surface of gold nanoparticles has emerged as a promising strategy towards the creation of artificial enzymes. The resulting high local peptide density surrounding the nanoparticle leads to cooperative and synergistic effects, which result in rate accelerations and distinct catalytic properties compared to the unconjugated peptide. This Minireview summarizes contributions to and progress made in the field of catalytically active peptide–gold nanoparticle conjugates. The origin of distinct properties, as well as potential applications, are also discussed.