Directed formation of micro- and nanoscale patterns of functional light-harvesting LH2 complexes

The precision placement of the desired protein components on a suitable substrate is an essential prelude to any hybrid "biochip" device, but a second and equally important condition must also be met: the retention of full biological activity. Here we demonstrate the selective binding of an optically active membrane protein, the light-harvesting LH2 complex from Rhodobacter sphaeroides, to patterned self-assembled monolayers at the micron scale and the fabrication of nanometer-scale patterns of these molecules using near-field photolithographic methods. In contrast to plasma proteins, which are reversibly adsorbed on many surfaces, the LH2 complex is readily patterned simply by spatial control of surface polarity. Near-field photolithography has yielded rows of light-harvesting complexes only 98 nm wide. Retention of the native optical properties of patterned LH2 molecules was demonstrated using in situ fluorescence emission spectroscopy.     

Formation of a True Molecular Composite using Optimal Hydrogen Bonding

Guidelines for creating miscible blends containing a liquid crystalline polymer and an amorphous polymer by optimizing intermolecular interactions between the two polymers are presented. It is shown that by controlling the spacing between the functional groups that participate in hydrogen bonding along the amorphous polymer chain, the extent of intermolecular interactions between the two polymers is optimized, and this induces miscibility in the systems studied.     

Low-Temperature Chemical Approaches for Synthesizing Sulfides and Nitrides of Reactive Transition Metals

The advent of the sol–gel technique over the past several decades and the recognition of its excellent flexibility for synthesizing a large variety of oxide ceramics and glasses in both bulk and thin-film forms has generated considerable interest in using solution-based processes to prepare ceramic materials. Because of the success of the sol–gel technique, a number of other chemical processes have been developed utilizing metalorganic/organometallic starting materials to create molecularly architectured precursors, which have proven effective in synthesizing both oxide and non-oxide materials. In the present study, two different chemical approaches have been implemented to synthesize non-oxides (sulfides and nitrides) of reactive transition-metal elements. Accordingly, a novel thio-sol–gel process for preparing TiS₂ and NbS₂ powders has been studied. In the case of TiS₂ synthesis, the chemical reaction has been examined in detail using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography (GC). The effects of modification of the titanium precursor on the morphology of the final sulfide have also been investigated and are discussed. A second, more generalized process has been developed for synthesizing homogeneous precursors in multicomponent systems. Its utilization in preparing ternary nitrides has been demonstrated, and is also presented. © 1997 by John Wiley & Sons, Ltd.     

Application of combined Monte Carlo and molecular dynamics method to simulation of dipalmitoyl phosphatidylcholine lipid bilayer

We describe a new equilibration procedure for the atomic level simulation of a hydrated lipid bilayer. The procedure consists of alternating molecular dynamics trajectory calculations in a constant surface tension and temperature ensemble with configurational bias Monte Carlo moves to different regions of the configuration space of the bilayer, in a constant volume and temperature ensemble. The procedure is described in detail and is applied to a bilayer of 100 molecules of dipalmitoyl phosphatidylcholine (DPPC) and 3205 water molecules. We find that the hybrid simulation procedure enhances the equilibration of the bilayer as measured by the convergence of the area per molecule and the segmental order parameters, as compared with a simulation using only molecular dynamics (MD). Progress toward equilibration is almost three times as fast in CPU time, compared with a purely MD simulation. Equilibration is complete, as judged by the lack of energy drift in three separate 200-ps runs of continuous MD started from different initial states. Results of the simulation are presented and compared with experimental data and with other recent simulations of DPPC. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1153–1164, 1999     

Characterisation of nickel silicide thin films by spectroscopy and microscopy techniques

This article discusses the formation and detailed materials characterisation of nickel silicide thin films. Nickel silicide thin films have been formed by thermally reacting electron beam evaporated thin films of nickel with silicon. The nickel silicide thin films have been analysed using Auger electron spectroscopy (AES) depth profiles, secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectroscopy (RBS). The AES depth profile shows a uniform NiSi film, with a composition of 49-50% nickel and 51-50% silicon. No oxygen contamination either on the surface or at the silicide-silicon interface was observed. The SIMS depth profile confirms the existence of a uniform film, with no traces of oxygen contamination. RBS results indicate a nickel silicide layer of 114 nm, with the simulated spectra in close agreement with the experimental data. Atomic force microscopy and transmission electron microscopy have been used to study the morphology of the nickel silicide thin films. The average grain size and average surface roughness of these films was found to be 30-50 and 0.67 nm, respectively. The film surface has also been studied using Kikuchi patterns obtained by electron backscatter detection.     

Synthesis, structural characterization and antibacterial activity of 2,6-diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases and their copper(II) complexes

2,6-Diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases (L¹, L² and L³) and their Cu(II) complexes of the general formula [CuL·H₂O] were synthesized and characterized by various spectroscopic techniques. The crystal structure of [CuL³·(py)]·py was investigated by single crystal X-ray structure analysis. The Cu(II) cation has near square pyramidal, penta-coordinate geometry. The binegatively charged tetradentate Schiff base is asymmetrically coordinated to the Cu(II) ion via the pyridine N atom, the azomethine N atom, the sulfonyl O atom and the deprotonated hydrazine N atom. There is a pyridine molecule apically coordinated to the Cu(II) ion. All the Schiff bases and their copper(II) complexes were screened by the disc diffusion method against multi-drug resistant (MDR) gram-negative and gram-positive bacteria. The minimum inhibitory concentration (MIC) values were also determined. These results show that the antibacterial activity of the Schiff bases against Methicillin-resistant Staphylococcus aureus (MRSA) is enhanced when they are chelated with the copper(II) ion.     

Synthesis, characterization and radiolytic properties of bis(oxalato)borate containing ionic liquids

Previously unreported bis(oxalato)borate (BOB) ionic liquids (ILs) containing imidazolium, pyridinium, and pyrrolidinium cations were prepared from the corresponding halide salts by reaction with sodium bis(oxalato)borate (NaBOB), and their properties are reported. Pulse radiolysis experiments revealed that the BOB anion scavenges solvated electrons with rate constants of 3×10⁸ M⁻¹ s⁻¹ in the ionic liquid C₄mpyrr NTf₂ and 2.8×10⁷ M⁻¹ s⁻¹ in water. This reactivity indicates that BOB ILs may be too sensitive to be used as neat solvents for nuclear separations processes in high radiation fields but may still be useful for preventing criticality while processing relatively “cold” fissile actinides.     

Single-molecule spectroscopy of fluorescent proteins

The discovery and use of fluorescent proteins has revolutionized cellular biology. Despite the widespread use of visible fluorescent proteins as reporters and sensors in cellular environments the versatile photophysics of fluorescent proteins is still subject to intense research. Understanding the details of the photophysics of these reporters is essential for accurate interpretation of the biological and biochemical processes illuminated by fluorescent proteins. Some aspects of the complex photophysics of fluorescent proteins can only be observed and understood at the single-molecule level, which removes averaging inherent to ensemble studies. In this paper we review how single-molecule emission detection has helped understanding of the complex photophysics of fluorescent proteins.

Controlling the Structure of Manganese(II) Phosphates by the Choice and Ratio of Organophosphate and Auxiliary Ligands

Tetranuclear manganese(II) phosphates [Mn(dipp)(bpy)]₄?4 H₂O ( 1 ) and [Mn₄(dmpp)₂(dmppH)₄(bpy)₄(H₂O)₂]?H₂O ( 2 ) have been prepared from Mn(OAc)₂?4 H₂O and 2,6‐diisopropylphenyl phosphate (dippH₂) or 2,6‐dimethylphenyl phosphate (dmppH₂) in the presence of 2,2′‐bipyridine (bpy). In contrast, the reaction between [Mn(bpy)₂(OAc)(ClO₄)]?H₂O and dippH₂ affords [Mn(bpy)₂(dippH)]₂?2 ClO₄?2 CH₃OH ( 3 ). The reactions of Mn(OAc)₂?4 H₂O, dippH₂, and pyridine (py) or 3,5‐dimethylpyrazole (dmpz) in CH₃CN under reflux afford hexanuclear complexes [Mn₆(dipp)₆(py)₈]?2CH₃CN ( 4 ) and [Mn₆(dipp)₆(dmpz)₆(AcOH)₂]?2 H₂O ( 5 ), respectively. Although compounds 1 and 2 are tetrameric, the former is a closed cubane‐like structure resembling the D4R secondary building unit of zeolites, whereas the latter exists in a staircase structure with fused Mn₂O₄P₂ rings. The core structure of 3 contains a Mn₂O₄P₂ eight‐membered ring that resembles the S4R building block of zeolites. Single‐crystal X‐ray diffraction studies reveal that compounds 4 and 5 have a similar core structure and differ from each other by the neutral ligands coordinated to manganese ions. All six phosphate ligands exist in a doubly deprotonated [(RO)PO₃^2?] form and exhibit two types of binding modes [5.222] and [3.111]. An interesting feature of compounds 1 – 5 is that although they are oligonuclear complexes, there is an absence of oxido bridges. The magnetic properties of compounds 1 – 5 have been investigated in the temperature range 5–298 K, and it was found that all the compounds obey the Curie law.