Calixarenes as second-sphere ligands for transition metal ions. Synthesis and crystal structure of [(H2O)5 Ni(NC5H5)]2(Na)[calix[4]arene sulfonate] · 3.5 H2O and [(H2O)4Cu(NC5H5)2]-(H3O)3 [calix[4]arene sulfonate] · 10 H2O

The title compounds crystallize such that bilayers of calixarenes are separated by hydrophilic layers. In each case the transition metal has, in addition to a primary sphere of ligands, a second-sphere coordination by a calixarene. [(H₂O)₅Ni(NC₅H₅)]₂(Na)[calix[4]arene sulfonate]·3.5 H₂O,1, crystallizes in the triclinic space groupP \(\bar 1\) witha = 12.487(4),b = 14.281(2),c = 15.055(5) Å, α = 85.66(2), β = 80.07(2), γ = 80.48(2)°, andD _c = 1.64 g cm^?3 forZ = 2. Refinement based on 2441 observed reflections led to a finalR value of 0.066. There are two different environments for the nickel-containing cations: one is positioned within the hydrophilic layer with the pyridine ligand intercalated into the hydrophobic calixarene bilayer and the other is also positioned within the hydrophilic layer, but the pyridine ligand is inserted into the hydrophobic cavity of the calix[4]arene. [(H₂O)₄Cu(NC₅HS)₂](H₃O)₃[calix[4]arene sulfonate]·10 H₂O,2, crystallizes in the triclinic space groupP \(\bar 1\) witha = 15.438(4),b = 15.727(6),c = 12.121(9) Å, α = 112.74(4), β = 102.02(4), γ = 85.34(4)°, andD _c = 1.57 g cm^?3 forZ = 2. Refinement based on 3925 observed reflections led to a finalR value of 0.107. The structure is similar to that of 1 except that the one copper-containing cation spans the hydrophilic layer and is intercalated into the bilayer of calixarenes on one side and positioned into the calixarene cavity on the other.     

Particle size analysis of perfluorocarbon emulsions in a complex whole blood matrix by sedimentation field-flow fractionation

The goal of this study was to show that sedimentation field-flow fractionation (SdFFF) could be used to study changes in the particle size distribution of perfluorocarbon (PFC) emulsion droplets in ex vivo whole blood samples. A PFC emulsion containing 40% w/v perfluorooctyl bromide (PFOB), 20% w/v perfluorodecyl bromide (PFDB), and 6% w/v egg yolk phospholipid (EYP) was manufactured by high pressure homogenization. The emulsion was infused intravenously to rats at a dose of 2.7 g PFC/kg body weight. Blood samples were collected at 0, 3, 6, and 24 h and analyzed (without additional sample manipulation) by SdFFF. Excellent chromatographic separation between the blood components and PFC emulsion droplets was achieved. After infusion, the particle size distribution broadened slightly. With time, the larger sized droplets were selectively removed by circulating monocytes and tissue resident macrophages of the reticuloendothelial system, causing the particle size distribution to shift to lower median diameters. SdFFF is an excellent technique for studying the in vivo stability of colloidal drug particles following intravenous administration.     

Observation and modelling of clamshell droplets on vertical fibres subjected to gravitational and drag forces

Extensive experimental investigation of the wetting processes of fibre-liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment of drops from fibres as airflow velocity increases, and also movement or flow of droplets along fibres. A detailed experimental study of the processes was conducted using stainless steel filter fibres and H2O aerosol, which coalesce on the fibre to form clamshell droplets. The droplets were predominantly observed in the Reynolds transition flow region, since this is the region where most of the above features occur. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as the increasing droplet size increases Reynolds number for the flow around the droplet. Two-dimensional flow in this region is usually modelled using the classical Karman vortex street, however there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is very good for both the radial and transverse oscillations.     

Quantitative trace-level speciation of arsenite and arsenate in drinking water by ion chromatography

We describe an improved method for the determination of inorganic arsenic in drinking water. The method is based on comprehensive optimization of the anion-exchange ion chromatographic (IC) separation of arsenite and arsenate with post-column generation and detection of the arsenate-molybdate heteropoly acid (AMHPA) complex ion. The arsenite capacity factor was improved from 0.081 to 0.13 by using a mobile phase (2.0 mL min(-1)) composed of 2.5 mM Na2CO3 and 0.91 mM NaHCO3 (pH 10.5). A post-column photo-oxidation reactor (2.5 m x 0.7 mm) was optimized (0.37 microM potassium persulfate at 0.50 mL min(-1)) such that arsenite was converted to arsenate with 99.8 +/- 4.2% efficiency. Multi-variate optimization of the complexation reaction conditions yielded the following levels: 1.3 mM ammonium molybdate, 7.7 mM ascorbic acid, 0.48 M nitric acid, 0.17 mM potassium antimony tartrate, and 1.0% (v/v) glycerol. A long-path length flow cell (Teflon AF, 100-cm) was used to measure the absorption of the AMHPA complex (818 +/- 2 nm). Figures of merit for arsenite/arsenate include: limit of detection (1.6/0.40 microg L(-1)): standard error in absorbance (5.1 x 10(-3)/3.5 x 10(-3)); and sensitivity (2.9 x 10(-3)/2.2 x 10(-3) absorbance units per ppb). Successful application of the method to fortified surface and ground waters (100 microL samples) is also described.     

Synthesis and interaction with copper(II) cations of cyano- and aminoresorcin[4]arenes

Following our studies on resorcin[4]arenes, we synthesized new macrocycles containing cyanomethyl and aminomethyl side chains. Three stereoisomers (2a-c) of the former were obtained by BF3*Et2O tetramerization of the corresponding trans-cinnamic acid derivative and were shown to be in the 1,2-alternate, cone, and 1,3-alternate conformations. Conversely, the tetraamino derivative 6a in the cone conformation was prepared from the corresponding tetrabromide 3a. The interactions with Cu(II) cations of the new compounds were analyzed by measurements of 1H NMR and EPR spectra in parallel with molecular modeling calculations.     

Protonation-induced stereoisomerism in nicotine: Conformational studies using classical (AMBER) and <Emphasis Type="Italic">ab initio</Emphasis> (Car–Parrinello) molecular dynamics

A variety of biologically active small molecules contain prochiral tertiary amines, which become chiral centers upon protonation. S-nicotine, the prototypical nicotinic acetylcholine receptor agonist, produces two diastereomers on protonation. Results, using both classical (AMBER) and ab initio (Car–Parrinello) molecular dynamical studies, illustrate the significant differences in conformational space explored by each diastereomer. As is expected, this phenomenon has an appreciable effect on nicotines energy hypersurface and leads to differentiation in molecular shape and divergent sampling. Thus, protonation induced isomerism can produce dynamic effects that may influence the behavior of a molecule in its interaction with a target protein. We also examine differences in the conformational dynamics for each diastereomer as quantified by both molecular dynamics methods.     

Automated analysis of 13C/12C ratios in CO2 and dissolved inorganic carbon for ecological and environmental applications

Stable carbon isotope ratios (13C/12C) are a valuable tool for studying a wide range of environmental processes, including carbon cycling and subsurface microbial activity. Recent advances in automated analysis provide the opportunity to increase greatly the ease and consistency of isotopic analysis. This study evaluated an automated headspace sampler linked to a commercially available CO2 preconcentration system and continuous flow isotope ratio mass spectrometer. Field sampling and analysis methods are illustrated for delta13C of soil respired CO2, from both tracer and natural abundance experiments, and dissolved inorganic carbon from contaminated groundwater. The automated system demonstrated accuracy, precision, and linearity, with standard errors below 0.1 per thousand for replicate gas standards run at concentrations varying five-fold. It measured 40 samples per 10-hour run, with concentrations ranging from ppb to percentage levels. In the field, gas samples were injected into nitrogen-filled autosampler vials, thereby allowing use of small sample volumes, control of analyte concentration, and direct analysis by the automated system with no further preparation. A significant linear relationship between standard concentrations and peak area allows for accurate estimates of sample CO2 concentration from the mass spectrometric data. The ability to analyze multiple small-volume samples with minimal off-line preparation should enhance the application of isotopes to well-replicated field experiments for process-level studies and spatial and temporal scaling.     

Relationship between collagen autofluorescence of the human cervix and menopausal status

The goal of this study was to evaluate the effect of different menopausal states (pre- and post-) on the endogenous fluorescence of normal cervical tissues. In particular, the average fluorescence as well as the interpatient and intrasample variability in the average fluorescence of the epithelium and stroma were evaluated as a function of pre- and postmenopausal states. High-resolution fluorescence images at excitation-emission wavelengths of 440, 520 nm and 365, 465 nm were obtained from epithelia and stroma of freeze-trapped cervical tissue blocks maintained at -196 degrees C. The fluorescence images were recorded using a low temperature optical scanner. Fluorescence images from a normal sample population (n = 27) were quantitatively analyzed, and the average epithelial and stromal fluorescence intensities were obtained. Data grouped according to menopausal status (pre- vs post-) showed statistically significant differences (P < 0.002) in stromal fluorescence. In particular, the cervical stroma of postmenopausal women showed (1) significantly greater average fluorescence and (2) greater interpatient and intrasample variability in the fluorescence, relative to that of premenopausal women. These results provide evidence for changes in collagen cross-linking with menopause.     

Long periodic ripple in a 2D hybrid halide perovskite structure using branched organic spacers

Two-dimensional (2D) halide perovskites have great promise in optoelectronic devices because of their stability and optical tunability, but the subtle effects on the inorganic layer when modifying the organic spacer remain unclear. Here, we introduce two homologous series of Ruddlesden–Popper (RP) structures using the branched isobutylammonium (IBA) and isoamylammonium (IAA) cations with the general formula (RA)₂(MA)_n−1Pb_nI_3n+1 (RA = IBA, IAA; MA = methylammonium n = 1–4). Surprisingly, the IAA n = 2 member results in the first modulated 2D perovskite structure with a ripple with a periodicity of 50.6 Å occurring in the inorganic slab diagonally to the [101] direction of the basic unit cell. This leads to an increase of Pb–I–Pb angles along the direction of the wave. Generally, both series show larger in-plane bond angles resulting from the additional bulkiness of the spacers compensating for the MA''s small size. Larger bond angles have been shown to decrease the bandgap which is seen here with the bulkier IBA leading to both larger in-plane angles and lower bandgaps except for n = 2, in which the modulated structure has a lower bandgap because of its larger Pb–I–Pb angles. Photo-response was tested for the n = 4 compounds and confirmed, signaling their potential use in solar cell devices. We made films using an MACl additive which showed good crystallinity and preferred orientation according to grazing-incidence wide-angle scattering (GIWAXS). As exemplar, the two n = 4 samples were employed in devices with champion efficiencies of 8.22% and 7.32% for IBA and IAA, respectively.

Using branched spacer cations results in a modulated rippled 2D perovskite structure and materials for solar cells.     

Hydrogen bonding and cooperativity in isolated and hydrated sugars: mannose, galactose, glucose, and lactose

The conformation of phenyl-substituted monosaccharides (mannose, galactose, and glucose) and their singly hydrated complexes has been investigated in the gas phase by means of a combination of mass selected, conformer specific ultraviolet and infrared double resonance hole burning spectroscopy experiments, and ab initio quantum chemistry calculations. In each case, the water molecule inserts into the carbohydrate at a position where it can replace a weak intramolecular interaction by two stronger intermolecular hydrogen bonds. The insertion can produce significant changes in the conformational preferences of the carbohydrates, and there is a clear preference for structures where cooperative effects enhance the stability of the monosaccharide conformers to which the water molecule chooses to bind. The conclusions drawn from the study of monosaccharide-water complexes are extended to the disaccharide lactose and discussed in the light of the underlying mechanisms that may be involved in the binding of carbohydrate assemblies to proteins and the involvement, or not, of key structural water molecules.