Binding neutral guests to concave surfaces of molecular hosts. Rigid structural model for complexation between two lipophilic entities

The 1:2 compound formed between a new cavitand C₄₀H₄₈Si₄O₈ [chemical name: 5,10;12,17;19,24;26,3-tetrakis(dimethylsiladioxa)-1,8,15,22-tetramethyl[1₄]metacyclophane] and CS₂ (M _r =921.42) provided a suitable structural model for a rigid inclusion complex between uncharged lipophilic molecules. The detailed structure of this compound has been determined by single crystal X-ray diffraction at 128 K (Crystal data:a=11.233,b=20.018,c=10.069 Å, =90.84^o,Z=2, space groupP2₁/m). Anisotropic refinement converged atR=0.040 for 3768 reflections above the intensity threshold, leading to positional and thermal parameters of a relatively high precision. The cavitand has an enforced cavity appropriately sized to include only slim linear guests. The crystallographic analysis revealed a 1:1 molecular inclusion complex with CS₂, the guest species being almost entirely encapsulated within the basket-shaped cavity of the host. The complex is stabilized by dispersion forces. All the guest atoms lie within van der Waals distances from the surrounding sections of the host and are well ordered. The second CS₂ molecule is located in the crystal lattice between molecules of the complex and is slightly disordered. Mirror plane symmetry characterizes the entire structure. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82032 (22 pages).     

Interrelation between hydration and interheadgroup interaction in phospholipids

The stability and the ionic conductivity of biological membranes and of lipid bilayers depend on their hydration. A small number of water molecules adhere strongly to the different residues of the lipid headgroups and are oriented by them. An additional number of water molecules adhere more weakly, preserving their freedom of rotation, but are essential for bestowing the thermodynamic properties of hydrated bilayers and of biological membranes. Around six water molecules are attached so strongly to the headgroups of different phospholipids (PL) that they are rendered unfreezable, or their freezing is extended over such a wide range of temperatures that it cannot be detected by differential scanning calorimetry (DSC). If cholesterol is added to the PL above the concentration at which phase separation of the cholesterol phase occurs, the number of unfreezable water molecules per PL increases, indicating that the PL molecules on the border line between the two phases attach nearly twice as many water molecules as those in the middle of the phase. The orientation of about seven or eight water molecules attached to PL headgroups (seven to phosphatidyl serine (PS)) can be detected by polarized FTIR. The dichroic ratio of the successively adhering water molecules to the headgroup of PS fluctuates between 2.6 and 2.9, with the cumulative value of about 2.8 for the seven water molecules adhering to the headgroup of PS. In addition, in this case, the number of water molecules oriented by PL molecule residues on the border line of the two phases is much larger ( approximately 13 for PS). Interaction between two opposite negatively charged layers containing PS approaching each other may lead, after correlated electrostatic attraction, to change in the conformation of the headgroups with concomitant dehydration. This process is enhanced by Ca(+) and by Li(+), but it may also occur with Na(+) and K(+) as counter-ions if the layers are mutually aligned. This process may be important in the fusion mechanism of biological membranes, and its molecular modeling has been carried out.     

Dual emission probe for luminescence oxygen sensing: a critical comparison between intensity, lifetime and ratiometric measurements

The characterization of a dual emission sensing luminescence material for water-dissolved oxygen sensing is presented in this paper. The oxygen-sensitive material is based on a dual-emitting luminescent molecule immobilized onto an adequate solid support. The metal chelate formed between the 8-hydroxy-7-iodo-5-quinolinesulphonic acid (Ferron) and aluminium (Al-Ferron) was the selected oxygen-sensitive dual-emitting luminescent complex, while the anionic exchanger Dowex 1X2-200 resin was the selected solid support.When the Al-ferron metal chelate is adsorbed onto the anionic exchanger resin it displays two largely different emission bands. The first is a fluorescence emission band, possessing a decay time in the nanosecond range, and which is insensitive to the oxygen presence (the “reference” signal). The second emission is a long-lived highly sensitive oxygen-quenchable phosphorescent emission. Under some optimised experimental conditions both emissions can be simultaneously measured when the metal chelate is excited with a 390 nm light. Under these conditions, and using the same experimental set-up, oxygen concentration can be obtained by measuring the intensity of the phosphorescent emission, the triplet lifetime of the phosphorescence emission or the ratio between the intensity of the phosphorescence emission and the self-reference signal (fluorescence emission from the immobilized metal chelate).The reliability, the operational characteristics, the stability and the analytical performance characteristics for water-dissolved oxygen sensing are evaluated and critically compared for each measurement principle. Advantages and disadvantages of each measurement scheme for reliable optical sensing will be finally discussed.     

FORMATION AND MICROSTRUCTURE OF POLYETHYLENE MICROPOROUS MEMBRANES THROUGH THERMALLY INDUCED PHASE SEPARATION*

Microporous membranes of low-high density polyethylene and their blends were prepared bythermally-induced phase separation of polymer/long-aliphatic chain alcohol (diluent) mixtures.The microstructures of this particular membrane, which depends on the diluent properties,polymer concentration and cooling rate, were observed by scanning electron microscopy."Beehive-type,"leafy-like, and lacy porous structure morphologies can be formed,depending onthe blend composition and phase separation conditions, which were discussed by the polymer anddiluent crystallization processes.     

A new method of synthesis of some 2-aryl and 2-heterocyclic benzimidazole,benzoxazole and benzothiazole derivatives

A new one-step facile method for the synthesis of some benzimidazole, benzoxazole and benzothiazole derivatives is described. The method involves the action of aromatic and heterocyclic selenoamides on some o-phenylenediamine, o-aminophenol and o-aminothiophenol and their derivatives.     

Hydrogen‐bonded assemblies of 20‐(4‐pyridyl)porphyrin‐54,104,154‐tribenzoic acid with dimethyl sulfoxide and 4‐acetylpyridine in their dimethyl sulfoxide and tetrahydrofuran solvates

Crystals of the title compounds, 20‐(4‐pyridyl)porphyrin‐5⁴,10⁴,15⁴‐tribenzoic acid–dimethyl sulfoxide (2/5), C₄₆H₂₉N₅O₆·2.5C₂H₆OS, (I), and 20‐(4‐pyridyl)porphyrin‐5⁴,10⁴,15⁴‐tribenzoic acid–4‐acetylpyridine–tetrahydrofuran (1/2/10), C₄₆H₂₉N₅O₆·2C₇H₇NO·10C₄H₈O, (II), consist of hydrogen‐bonded supramolecular chains of porphyrin units solvated by molecules of dimethyl sulfoxide [in (I)] and 4‐acetylpyridine [in (II)]. In (I), these chains consist of heterogeneous arrays with alternating porphyrin and dimethyl sulfoxide species, being sustained by COOH...O=S hydrogen bonds. They adopt a zigzag geometry and link on both sides to additional molecules of dimethyl sulfoxide. In (II), the chains consist of homogeneous linear supramolecular arrays of porphyrin units, which are directly connected to one another via COOH...N(pyridyl) hydrogen bonds. As in the previous case, these arrays are solvated on both sides by molecules of the 4‐acetylpyridine ligand via similar COOH(porphyrin)...N(ligand) hydrogen bonds. The two crystal structures contain wide interporphyrin voids, which accommodate disordered/diffused solvent molecules, viz. dimethyl sulfoxide in (I) and tetrahydrofuran in (II).     

Individual cell migration analysis using fiber-optic bundles

In this paper we describe a novel optical fiber-based technology for analyzing cell migration. Cells were labeled with a membrane-bound fluorescent dye and distributed onto a polished optical fiber bundle. When a cell passes over one of the individual fibers in the bundle, the membrane-bound dye causes a large intensity increase, which stays for a given residence time until the cell departs from the fiber. Residence time increases significantly upon exposure to an antimigratory drug, indicating a decrease in cell migration. This approach provides a simple migration assay and does not require sophisticated tracking software. By using optical fiber bundles containing smaller individual fibers with higher spatial resolution, this approach was employed to develop a migration assay based on subcellular imaging. The subcellular imaging platform allows for rapid analysis of migratory potential, reducing experimental time from several hours in a standard assay to 5 min using this technology.Electronic Supplementary Material Supplementary material is available for this article at     

Biological sensing using transmission surface plasmon resonance spectroscopy

Ultrathin gold island films evaporated on transparent substrates offer promising transducers for chemical and biological sensing in the transmission surface plasmon resonance (T-SPR) mode. In the present work, the applicability of T-SPR-based systems to biosensing is demonstrated, using a well-established biological model system. Au island films were evaporated on polystyrene slides and modified with a biotinylated monolayer via a multistep surface reaction, the latter assisted by the good adhesion of metal islands to polystyrene. The biotin-derivatized Au island film was then used as a biological recognition surface for selective sensing of avidin binding, distinguishing between specific and nonspecific binding to the substrate. Transduction of the binding event into an optical signal was achieved by T-SPR spectroscopy, using plasmon intensity measurements, rather than wavelength change, for maximal sensitivity and convenience. T-SPR spectroscopy of Au island films is shown to be an effective tool for monitoring the binding of biological molecules to receptor layers on the Au surface and a promising approach to label-free optical biosensing.     

Novel carbamoyl phosphonate monomers and polymers from unsaturated isocyanates

Carbamoyl phosphonate derivatives of methacrylic acid and α-methyl styrene were synthesized in good yield by reacting dimethyl and diethylphosphite with isocyanato ethylmethacrylate (IEM) or with meta-isopropenyl-α,α-dimethylbenzylisocyanate (m-TMI). The IEM derivatives yield soluble homopolymers with common radical initiators. The m-TMI carbamoyl phosphonates were copolymerized with styrene and with acrylates yielding soluble materials with better than 50 mol % incorporation of the phosphonate monomer. The side chain carbamoyl phosphonate group drastically lowers the T_g relative to those of the parent polymers. Thermogravimetric studies suggest the NHC(O)? P(O)(OR)₂ bond to be stable to about 225°C. The radiopacifying salt UO₂(NO₃)₂6 H₂O yields transparent films with the phosphonate-containing polymers. The T_g increases with uranyl content. © 1993 John Wiley & Sons, Inc.