Conductometric behaviour of alkali metal halides in non-aqueous solvents containing crown-ethers

The conductometric behaviour of NaCl, KCl and RbCl in ethanol solutions, in the presence of dicyclohexyl-18-crown-6, and of KI in acetonitrile solutions, in the presence of 12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6 and dicyclohexyl-18-crown-6, has been investigated. The analysis of data has been performed by means of the Fuoss-Onsager-Skinner equations and the results compared with the parameters of the same salts in pure solvents. The addition of crown-ether to the ethanol solutions gives rise to a greater decrease in conductivity for KCl and RbCl than for NaCl, so that the maximum difference in the Λ_o values which is 4.7 Λ unit in pure ethanol, decreases to 0.9 Λ unit. Also the association constant to ion pairs of the three salts which is appreciable in pure ethanol, decreases to zero when the crown-ether is added. In acetonitrile the difference in the Λ_o values for systems with and without crowns is small for 12-crown-4 (～2.9 Λ unit); it increases according to the complexity of the added crown (～21 Λ unit for the 15-crown-5, ～24 Λ unit for the 18-crown-6, ～ 30 Λ unit for the dicyclo- and dibenzo-18-crown-6). A small association constant value was found for the systms KI with 12-crown-4 and with 15-crown-5 in this solvent. The results of the above systems are discussed in terms of competitive interaction forces of the crown-ethers and the solvent molecules on the ionic species present in solution.     

Pseudopterosin Content Variability of the Purple Sea Whip Pseudopterogorgia elisabethae at the Islands of San Andres and Providencia (Sw Caribbean)

To determine pseudopterosin composition and concentration in colonies of Pseudopterogorgia elisabethae from the islands of San Andres and Providencia, we collected fragments of individual colonies at various sites and depth ranges around the islands. Chromatographic profiles of the polar fraction, particularly those obtained by HPLC-MS analyses, allowed us to recognize two different chemotypes. Chemotype 1 characterized samples from Providencia whereas chemotype 2 characterized samples from San Andres. A complex pseudopterosin mixture (compounds 1-13) characterized chemotype 1. These compounds were isolated by a combination of chromatographic methods and identified by spectroscopic methods (MS, UV, 1H, and 13C NMR). We identified the known pseudopterosins G and K and seco-pseudopterosin A. We also isolated and identified seven new compounds, pseudopterosins P-V, isomers of known pseudopterosins. Pseudopterosins G and K were found at concentrations ranging between 1 and 3% of the animal dry mass. Pseudopterosins Q and U were the major compounds reaching up to 6% of the animal dry mass at some locations. Major metabolites in chemotype 2 had a molecular weight and fragmentation pattern different from that observed in the pseudopterosins, as determined by HPLC-MS. Total pseudopterosin concentration in this chemotype was below 3% dry mass at all sites. Total pseudopterosin concentration was significantly higher in chemotype 1, with concentrations ranging between 4 and 20% dry mass. At most locations on Providencia, however, total pseudopterosin concentration ranged between 11 and 15% dry mass. Concentrations exceed reports from other locations in the Caribbean. Furthermore, pseudopterosin composition in our samples is quite different from those in specimens of P. elisabethae from the Bahamas and Bermuda. Pseudopterosins G, K, and P-V are characteristic of P. elisabethae colonies from the island of Providencia, while pseudopterosins A-D are characteristic of colonies of P. elisabethae from the Bahamas islands, and pseudopterosins E-L have been isolated from P. elisabethae from the Bahamas and Bermuda. The overall morphology of P. elisabethae can be variable, and chemical differences are not correlated to specific morphs. We confirmed the species identity of each colony by morphological and sclerite analysis and found no significant differences in sclerite dimensions among different colonies and chemotypes.     

Molecular adsorption: early stage surface exploration

In this study, the atomic force microscope has been employed in force spectroscopy mode to gain information on the interaction between long mucin molecules and a positively charged surface during the first few seconds of interaction. Recent studies have revealed that negatively charged mucin molecules introduced to a positively charged surface are kinetically trapped and bind very rapidly, assuming non-equilibrium conformations. This systematic study of surface dwell times has revealed that significant differences exist in mucin adsorption during the first three seconds of introduction to the surface and provides direct evidence of molecular rearrangement for several seconds before trapping occurs. Limited interactions were recorded at dwell times of less than one second, with increased molecular rearrangement observed between 1.5 and 2.25 s. Increasing the surface dwell time beyond this critical limit caused rupture of the tip-tethered mucin molecules during the retract cycle of the cantilever. All subsequent recorded events, at increased dwell times up to 3 s, revealed events at much reduced distances from the point of contact between the mucin functionalised-cantilever and the positively charged surface.     

Assessing blood flow control through a bootstrap method

In order to assess blood flow control, the relationship between blood pressure and blood flow can be modeled by linear filters. We present a bootstrap method, which allows the statistical analysis of an index of blood flow control that is obtained from constrained system identification using an established set of pre-defined filters.     

Determination of the solar calibration constant for a sun-sky radiometer: proposal of an in-situ procedure

A new procedure is presented for determining in situ the solar calibration constant, i.e., the Sun-sky radiometer counts for a direct normal solar flux extrapolated to the top of the atmosphere. The method makes use of a modified version of the Langley plot based on the use of an inversion code of column-integrated aerosol size distribution, and it is ordinarily applied to calibrate Prede Sun-sky radiometers. To analyze how such an in situ method can work accurately, the technique has been applied to a five-month dataset obtained from measurements taken in Rome, Italy, by a Prede Sun-sky radiometer from 22 April to 5 November 2001. The precision of the in situ method has been estimated to within 1-2.5%, depending on the wavelength.     

Quality control of Aspergillus flavus and A. parasiticus agar and comparison with dichloran 18% glycerol agar: a collaborative study

AFPA culture medium, which is used for recognition of Aspergillus flavus and A. parasiticus, has been validated in a collaborative study including nine laboratories located in Australia, Brazil, Denmark, The Netherlands, Sweden and United Kingdom. Three freeze-dried fungal mixtures, containing A. flavus/A. parasiticus and background fungi, were produced and checked for homogeneity. The coefficients of variance were low, ranging from 0.81% to 1.09% for total fungal counts and between 2.50% and 2.72% for counts of A. flavus/A. parasiticus. The laboratories analysed the contents of two vials of each mixture on commercial A. flavus and A. parasiticus agar (AFPA), in-house-made AFPA, and on a standard media, dichloran 18% glycerol agar (DG18). Reproducibility values for counts of A. flavus/A. parasiticus indicated no differences between the commercial AFPA and the in-house-made AFPA. Variation between laboratories was low, indicating that the medium was effective in use. Reproducibility values for DG18 were higher. There were no differences in counts of A. flavus/A. parasiticus on AFPA and DG18. However, DG18 gave slightly higher total fungal counts compared to AFPA.     

Adaptive Correction of Errors in Residue Coupled MASH ΔΣ Modulators

MASH delta-sigma () modulators consist of a cascade of several lower order single-loop modulators. In an ideal cascade, the quantization error from all but the last stage are digitally canceled. The drawback with a cascaded design is the requirement of precise matching of contributions from different quantizers to cancel lower order quantization noise from intermediate delta-sigma stages. This paper presents a new, adaptive improvement to the residue coupled MASH delta sigma modulator. The adaptive corrections significantly reduce the sensitivity to analog imperfections. The result is a simple MASH delta-sigma modulator with high precision. Simulations of a 1-1 MASH circuit structure with errors and corrections are included to confirm the theory.     

Congruence in the performance of model nitrifying activated sludge plants located in Germany,Scotland and Spain

A laboratory model nitrifying activated sludge plant treating OECD synthetic sewage was designed and constructed by each of three laboratories in Germany, Scotland and Spain in order to produce a sludge inoculum for 5 rapid toxicity bioassays. The plants were run for 3 years and produced sludge for the microbially based bioassays Vibrio fischeri bioluminescence, ATP luminescence and respiration, and, nitrification and enzyme inhibition. Although the initial sludge inoculum for the plants differed, as did some of the running conditions such as temperature regime, the sludge produced within the different countries had similar characteristics with respect to sludge age, total suspended solids and volatile suspended solids. Nitrification was generally maintained over the 3-year period although there were occasions when the process was inconsistent. Nitrification recovery was afforded by reseeding with a nitrifying sludge from a local wastewater treatment works (WWTW) or imposition of starvation conditions for a period of time. The sludge produced was used to carry out toxicity testing and results compared well with those using sludge from a WWTW. Overall, the use of sludge generated in the laboratory could be used for toxicity testing negating the need to resort to the use of natural WWTW sludge, which may contain a range of toxic substances due to uncontrolled industrial and domestic inputs and an unbalanced microbial consortium.     

Biomimetic Concealing of PLGA Microspheres in a 3D Scaffold to Prevent Macrophage Uptake

Scaffolds functionalized with delivery systems for the release of growth factors is a robust strategy to enhance tissue regeneration. However, after implantation, macrophages infiltrate the scaffold, eventually initiating the degradation and clearance of the delivery systems. Herein, it is hypothesized that fully embedding the poly(d,l ‐lactide‐co‐glycolide acid) microspheres (MS) in a highly structured collagen‐based scaffold (concealing) can prevent their detection, preserving the integrity of the payload. Confocal laser microscopy reveals that non‐embedded MS are easily internalized; when concealed, J774 and bone marrow‐derived macrophages (BMDM) cannot detect them. This is further demonstrated by flow cytometry, as a tenfold decrease is found in the number of MS engulfed by the cells, suggesting that collagen can cloak the MS. This correlates with the amount of nitric oxide and tumor necrosis factor‐α produced by J774 and BMDM in response to the concealed MS, comparable to that found for non‐functionalized collagen scaffolds. Finally, the release kinetics of a reporter protein is preserved in the presence of macrophages, only when MS are concealed. The data provide detailed strategies for fabricating three dimensional (3D) biomimetic scaffolds able to conceal delivery systems and preserve the therapeutic molecules for release.