Effects of Enhanced Flexibility and Pore Size Distribution on Adsorption-Induced Deformation of Mesoporous Materials.

Here, we present a new model of adsorption-induced deformation of mesoporous solids. The model is based on a simplified version of local density functional theory in the framework of solvation free energy. Instead of density, which is treated as constant here, we used film thickness and pore radius as order parameters. This allows us to obtain a self-consistent system of equations describing simultaneously the processes of gas adsorption and adsorbent deformation, as well as conditions for capillary condensation and evaporation. In the limit of infinitely rigid pore walls, when the film becomes several monolayers thick, the model reduces to the well-known Derjaguin-Broekhoff-de Boer theory for pores with cylindrical geometry. We have investigated the effects of enhanced flexibility of the solid as well as the influence of pore size distribution on the adsorption/deformation process. The formulation of the theory allows to determine the average pore size and its width from the desorption branch of the strain isotherm only. The model reproduces the nonmonotonic behavior of the strain isotherm at low relative pressure. Furthermore, we discuss the effect of rigidity of the adsorbent on the pore size distribution, showing qualitatively different results of the adsorption isotherms for rigid and highly flexible materials, in particular, the shift of evaporation pressure to lower values and the absence of a limiting value of the loading at high relative pressure. We also discuss the results of the theory with respect to experimental data obtained from the literature.

Evaluation of sympathetic blockade after intrathecal and epidural lidocaine in rats by laser Doppler perfusion imaging.

The widespread use of neuraxial anaesthesia increases the need for animal models to evaluate therapeutic prospects, mechanisms and risks of this technique. As a methodological prerequisite, we characterised the sympathetic blockade after different modes of neuraxial anaesthesia with regard to segments supplying the splanchnic region. Under haemodynamic monitoring, lidocaine 2% or saline were infused via intrathecal (10 microl), lumbar epidural (10 and 30 microl) or thoracic epidural (10 and 30 microl) catheters. Segmental spread of neuraxially infused local anaesthetic was assessed using methylene blue. Mean arterial blood pressure decreased more severely after neuraxial lidocaine in thoracic epidural (10 and 30 microl) compared to high-volume (30 microl anaesthesia animals. Determination of the sympathetic blockade by means of laser Doppler perfusion imaging was restricted to the paws due to a higher density of subcutaneous blood vessels as compared to the abdominal wall (mean +/- SD: 3.93 +/- 0.06 vs. 1.35 +/- 0.05/384 mm(2), p < 0.05). Only high-volume (30 microl) lumbar and thoracic epidural anaesthesia (10 and 30 microl) increased skin perfusion in both hind and front paws. This extensive sympathetic blockade was demonstrated to include splanchnic segments using thermography. Segmental spread of methylene blue did not closely correspond to laser Doppler findings and should be interpreted as minimum rather than exact epidural spread of local anaesthetic.

Isotherms of Capillary Condensation Influenced by Formation of Adsorption Films.

Isotherms of capillary condensation are often used to determine the vapor sorption capacity of porous adsorbents as well as the pore size distribution by radii. In this paper, for calculating the volume of capillary condensate and of adsorption films in a porous body, an approach based on the theory of surface forces is used. Adsorption isotherms and disjoining pressure isotherms of wetting films are presented here in an exponential form discussed earlier. The calculations were made for straight cylindrical capillaries of different radii and slit pores of different width. The mechanisms of capillary condensation differ in cylindrical and slit pores. In cylindrical pores capillary condensation occurs due to capillary instability of curved wetting films on a capillary surface, when film thickness grows. In the case of slit pores, coalescence of wetting films formed on opposite slit surfaces proceeds under the action of attractive dispersion forces. Partial volumes of liquid in the state of both capillary condensate and adsorbed films are calculated dependent on the relative vapor pressure in a surrounding media. Copyright 2000 Academic Press.

Description of Gas Adsorption Isotherms on Porous and Dispersed Systems with the Excess Surface Work Model.

We introduced in (2) and (3) the excess surface work (ESW) to describe adsorption isotherms of nonporous materials and of a single phase over the complete pressure range. In this paper this model is extended successfully to adsorption isotherms of porous and finely dispersed materials. In this case capillary condensation may occur and the excess surface work yields more than one minimum. By linearizing the corresponding integral form and calculating the parameters, it is now possible to describe the complete adsorption isotherm as for the simple case of nonporous systems. Copyright 1998 Academic Press.

Influence of Surface Wettability on Adsorption Isotherms of Water Vapor

Using an exponential form of an isotherm of adsorption the excess surface free energy of a solid surface covered with an adsorption or wetting film Deltagammasv was calculated on the basis of Gibbs equation starting from the state of an infinitely thick film. Isotherms of adsorption and of excess surface free energy were calculated for different values of two parameters that characterize the range of action of surface forces and corresponding decay length. In the case of partial wetting of a solid surface, isotherms consisting of two exponential terms were used, as was proposed earlier by A. Adamson. Equilibrium contact angles that are formed with droplets of bulk liquid were calculated using the Frumkin-Derjaguin approach in dependence on the parameters of isotherms. Calculations of contact angles that are formed between convex capillary menisci in thin pores, at relative vapor pressure lower than 1, have shown that a transition from partial wetting of a lone solid surface (at p/ps = 1) to complete wetting in thin pores (at p/ps < 1) may occur. Corresponding threshold values of relative vapor pressure and pore radii were calculated. In the case of complete wetting, corrections for capillary pressures that arise due to formation of a transition zone between wetting films and curved meniscus surfaces were estimated. The calculations are limited by the values of relative vapor pressure near saturation when thick enough wetting films are formed on pore surfaces. Due to the application of model isotherms with some adopted parameters, the results obtained are qualitative in nature. However, the methods of calculation developed for the excess free energy of solid surfaces covered with thin adsorption of thicker wetting films and of contact angles outside and inside thin pores may be of general interest. Copyright 1998 Academic Press. Copyright 1998Academic Press

Construction of a gene map of the nephronophthisis type 1 (NPHP1) region on human chromosome 2q12-q13.

A gene for the autosomal recessive kidney disorder juvenile nephronophthisis (NPH) is located on chromosome 2q between markers D2S1893 and D2S1888. Recently, the presence of large homozygous deletions was described in the majority of NPH patients. We constructed an integrated YAC/PAC contig of 54 markers and 30 PAC clones that encompasses this deletion and the flanking inverted duplication. Thirty-six novel sequence-tagged site markers were generated for this region of 2-3 Mb, 22 of which represent PAC ends. Ten of 18 multiplex NPH families show a homozygous deletion for 8 consecutive markers. BlastN database search and expressed sequence tag (EST) mapping led to the localization of 18 EST clones to the integrated contig, representing 11 putative transcribed sequences. Seven EST clones were localized to the NPHP1 region between D2S1893 and D2S1888. Two EST clones, zc07a11 from a human parathyroid tumor library and yy63e10 from a multiple sclerosis lesion library, are located in the deletion region. PCR amplification experiments indicate that zc07a11 represents a chimeric cDNA. Through FISH analysis the NPHP1 deletion region was localized to 2q12-q13. In summary, our study provides a high-resolution physical map of the NPHP1 region with 7 precisely localized expressed sequences, 2 of which have recently been shown to be part of a gene for NPH. These data will alleviate the identification of further genes of a homozygous gene deletion syndrome in patients with NPH and oculomotor apraxia and will be instrumental in the characterization of the molecular mechanism leading to the large homozygous deletion in this region. The data furthermore provide an important step toward the construction of a sequence-ready PAC contig of this region.

A novel gene encoding an SH3 domain protein is mutated in nephronophthisis type 1.

Juvenile nephronophthisis (NPH), an autosomal recessive cystic kidney disease, is the primary genetic cause of chronic renal failure in children. About two thirds of patients with NPH carry a large homozygous deletion at the gene locus NPH1 on 2q13. We here identify a novel gene. NPHP1, which extends over most of this common deletion. The 4.5-kb transcript encodes a protein with an SH3 domain, which is highly conserved throughout evolution. The 11-kb interval between the 3' end of NPHP1 and an inverted repeat containing the distal deletion breakpoint was found to contain the first exon of a second gene, MALL. In patients with a hemizygous deletion of the NPH1 region, additional point mutations were found in NPHP1 but not in MALL.

Energetic Classification of Adsorption Isotherms

The new model describes adsorption isotherms with a two-parameter function. The parameters are easy and precise to calculate from the excess surface work of the adsorbed layer. The excess surface work is defined as the product of adsorbed amount and the change of the chemical potential. The differential form yields a minimum at the first layer. It is possible to linearize the corresponding integral form. The physical meanings of the two parameters are the monolayer capacity and the chemical potential, which is necessary for adsorption. The new model allows an energetic classification of adsorption phenomena of surface films in the energetic range from weak physisorption to chemical adsorption