An integrated AFM-Raman instrument for studying heterogeneous catalytic systems: a first showcase

The integration of Atomic Force Microscopy and Raman spectroscopy is tested for use in heterogeneous catalysis research by a preliminary investigation, the photo-oxidation of rhodamine-6G. Temperature and atmosphere were varied in an in situ cell to show compatibility with realistic reaction conditions.     

The natural DNA bending angle in the lac repressor headpiece-O1 operator complex is determined by protein-DNA contacts and water release

We performed molecular dynamics simulations of the lac repressor headpiece-O1 operator complex for natural, over and underbent DNA to assess the factors that determine the natural DNA bending angle. At the natural angle, the specific and nonspecific contacts between the protein and DNA are optimized. Protein-DNA contacts show different angle dependences in the right and left sites, with the left site generally getting weaker and the right site getting stronger as the bending angle increases. Two entropic factors were identified as well: at the natural bending angle, water release and the quasiharmonic protein configurational entropy are maximized. The gain in protein configurational entropy might stem from an entropy-entropy compensation mechanism, in which a reduction in protein fluctuations is offset by a loss in correlations between the right and left sites.     

Cisplatin nanoliposomes for cancer therapy: AFM and fluorescence imaging of cisplatin encapsulation, stability, cellular uptake, and toxicity

Cisplatin is the most effective cytotoxic agent against many cancers. Its usage, however, is limited due to inefficient uptake by the target cells. A liposomal formulation of cisplatin is reported to partly overcome this limitation. Physicochemical characteristics of the liposome-cisplatin preparation, including its size, stability, encapsulation efficiency, and cytoplasmic internalization efficiency, play a significant role in an effective usage of liposomal formulations. We have used atomic force microscopy (AFM) to determine physicochemical characteristics of cisplatin-encapsulated liposomes, AFM and fluorescence microscopy to examine their cytoplasmic internalization, and Live/Dead assay to examine their cell toxicity. Nonencapsulated cisplatin is globular and 10-50 nm in size. AFM force-dissection and stiffness measurements show that cisplatin-encapsulated liposomes are significantly stiffer ( approximately 100%) and more stable than liposomes without encapsulated cisplatin. Cisplatin-encapsulated liposomes of approximately 250 nm diameter (nanoliposomes) are most efficiently internalized and induce cell toxicity in a time-dependent manner. Liposomes without cisplatin of similar dimensions, although internalized in the cell cytoplasm, do not induce cell toxicity.     

Extremely strong self-assembly of a bimetallic salen complex visualized at the single-molecule level

A bis-Zn(salphen) structure shows extremely strong self-assembly both in solution as well as at the solid-liquid interface as evidenced by scanning tunneling microscopy, competitive UV-vis and fluorescence titrations, dynamic light scattering, and transmission electron microscopy. Density functional theory analysis on the Zn(2) complex rationalizes the very high stability of the self-assembled structures provoked by unusual oligomeric (Zn-O)(n) coordination motifs within the assembly. This coordination mode is strikingly different when compared with mononuclear Zn(salphen) analogues that form dimeric structures having a typical Zn(2)O(2) central unit. The high stability of the multinuclear structure therefore holds great promise for the development of stable self-assembled monolayers with potential for new opto-electronic materials.     

The activity of solutions of Ru3(CO)12 as catalysts for the fischer-tropsch reaction

Solutions of dodecacarbonyl-triangulo-triruthenium [Ru₃(CO)₁₂] have been shown to be catalyst precursors for the Fischer-Tropsch reaction; the catalyst formed under the reaction conditions is heterogeneous; no indication of homogeneous activity was found.     

Recent advances in microcontact printing

Microcontact printing is a remarkable surface patterning technique. Developed about 10 years ago, it has triggered enormous interest from the surface science community, as well as from engineers and biologists. The last five years have been rich in improvements to the microcontact printing process itself, as well as in new technical innovations, many designed to suit new applications. In this review, we describe the evolution of microcontact printing over the past five years. The review is categorized into three main sections: the improvements made to the technique, new variations, and new applications.     

Zn(II)-salphen complexes as versatile building blocks for the construction of supramolecular box assemblies

Zn(II)-salphen complexes are readily accessible and interesting supramolecular building blocks with a large structural diversity. Higher-order supramolecular assemblies, such as molecular boxes based on a bis-Zn(II)-salphen building block and various ditopic bipyridine ligands, have been constructed by means of supramolecular, coordinative Zn(II)-N(pyr) interactions. The use of bipyridine ligands of differing sizes enables the construction of structures with predefined box diameters. The features of the 2:2 box assemblies were investigated in detail by (variable temperature) NMR spectroscopy, UV-visible spectroscopy, NMR titrations, and X-ray crystallographic studies. The spectroscopic studies reveal a high association constant for the Zn(II)-salphen-pyridyl motif, which lies in the range 10(5)-10(6) M(-1). The strong interaction between the Zn(II) center and pyridine donors was supported by PM3 calculations that showed a relatively high Lewis acid character of the metal center in the salphen complex. Titration curves monitored by UV-visible show a cooperative effect between the two bipyridine ligands upon complexation to the bis-Zn(II) template, suggesting the formation of 2:2 complexes. The crystal structures of two supramolecular boxes have been determined. In both examples such a 2:2 assembly is present in the solid state, and the box size is different because they consist of different building blocks. Interestingly, the box assemblies line up in the solid state to form porous channels that are potentially useful in a number of applications.     

Protonation Equilibria of Mononuclear Vanadate: Thermodynamic Evidence for the Expansion of the Coordination Number in VO(2)(+)

A spectrophotometric investigation of the protonation of HVO(4)(2-) has been conducted at vanadium(V) concentrations low enough (5 x 10(-5) mol dm(-3)) to prevent the formation of polynuclear ions. Equilibrium constants as well as enthalpy and entropy changes for the formation of H(2)VO(4)(-) and VO(2)(+) have been determined in ionic medium: 1.0 mol dm(-3) NaCl and NaClO(4), respectively. The percentage concentration of the neutral species, H(3)VO(4), is so low (apparently <1%) that the protonation of H(2)VO(4)(-) to form VO(2)(+) occurs virtually in a single step. The disproportionately great stability of VO(2)(+) relative to H(3)VO(4) is explained in terms of an increase in the coordination number of vanadium when the cationic species is formed. This explanation is based on a comparison of the thermodynamic quantities of the vanadium(V) species with those of various other oxyacids reported in the literature.     

Pd-catalyzed stereoselective tandem ring-opening amination/cyclization of vinyl γ-lactones: access to caprolactam diversity

A stereoselective amination/cyclization cascade process has been developed that allows for the preparation of a series of unsaturated and substituted caprolactam derivatives in good yields. This conceptually novel protocol takes advantage of the easy access and modular character of vinyl γ-lactones that can be prepared from simple precursors. Activation of the lactone substrate in the presence of a suitable Pd precursor and newly developed phosphoramidite ligand offers a stereocontrolled ring-opening/allylic amination manifold under ambient conditions. The intermediate (E)-configured ε-amino acid can be cyclized using a suitable dehydrating agent in an efficient one-pot, two-step sequence. This overall highly chemo-, stereo- and regio-selective transformation streamlines the production of a wide variety of modifiable and valuable caprolactam building blocks in an operationally attractive way.

A Pd-mediated stereoselective tandem process has been developed towards a large variety of functional caprolactam synthons.     

Synthesis and reactions of terminal osmium and ruthenium complexed phosphinidenes [(eta6-Ar)(L)Md=PMes*

Novel, very stable ruthenium and osmium containing terminal phosphinidene complexes [(eta(6)-Ar)(L)M=Mes*] (Ar=benzene, p-cymene; L=PR(3), CO, and RNC) have been prepared by dehydrohalogenation of novel [(eta(6)-Ar)MX(2)(PH(2)Mes*)] complexes in the presence of a stabilizing ligand. Xray crystal structures are reported for [(eta(6)-C(6)H(6))(PPh(3))Rud=PMes*] (9) and [(eta(6)-pCy)(PPh(3))Os=PMes*] (4). Dehydrohalogenation in the absence of a stabilizing ligand resulted in the new P-spiroannulated Ru(2)P(2)-ring structure 16. Dehydrohalogenation in the presence of but-2-yne gave a novel phosphaallyl complex [(eta(6)-Ar)Ru(eta(3)-R(2)PC(Me)CHMe)] 26, for which an X-ray crystal structure is reported. The mechanism by which 16 and 26 are obtained is presumed to involve the intermediate formation of the 16-electron (eta(6)-benzene)Rud=PMes* phosphinidene complex.