Characterization of activated carbon fibers using argon adsorption

In this paper, we present results of the internal structure (pore size and pore wall thickness distributions) of a series of activated carbon fibers with different degrees of burn-off, determined from interpretation of argon adsorption data at 87 K using infinite and finite wall thickness models. The latter approach has recently been developed in our laboratory. The results show that while the low bun-off samples have nearly uniform pore size (

The effects of parabens on the mechanosensitive channels of E. coli

Parabens are alkyl esters of p-hydroxybenzoic acid used as preservatives in a wide range of food, pharmaceutical, and cosmetic products (Soni et al. Food Chem. Toxicol. 39:513-532, 2001). Despite their common use for over 50 years, their mechanism of action is still unclear. In this study we examined the effects of ethyl and propyl paraben, on gating of the E. coli mechanosensitive channel of large conductance (MscL) reconstituted into azolectin liposomes. We found that propyl and ethyl paraben spontaneously activate MscL. Moreover, the addition of propyl paraben caused an increase in MscL activity and the lowering Of P-1/2, the pressure at which the MscL was opened 50% of the time, the AGO, the free energy required to open the MscL, and the parameter a, which describes the channel sensitivity to pressure. In addition, in silico studies showed that propyl paraben binds to the channel gate of the MscL. The mechanosensitive channel of small conductance was also found to be spontaneously activated by parabens. In summary, our study indicates that one of the previously unidentified mechanisms of action of parabens as antimicrobial agents is via an interaction with the mechanosensitive channels to upset the osmotic gradients in bacteria.

Hydrodynamics and mass transfer coefficient in activated sludge aerated stirred column reactor: Experimental analysis and modeling

The aerated stirred reactor (ASR) has been widely used in biochemical and wastewater treatment processes. The information describing how the activated sludge properties and operation conditions affect the hydrodynamics and mass transfer coefficient is missing in the literature. The aim of this study was to investigate the influence of flow regime, superficial gas velocity (U-G), power consumption unit (P/V-L), sludge loading, and apparent viscosity (pap) of activated sludge fluid on the mixing time (t(m)), gas hold-up (epsilon), and volumetric mass transfer coefficient (kLa) in an activated sludge aerated stirred column reactor (ASCR). The activated sludge fluid performed a non-Newtonian rheological behavior. The sludge loading significantly affected the fluid hydrodynamics and mass transfer. With an increase in the UG and P/V-L, the epsilon and k(L)a increased, and the t(m), decreased. The E, kLa, and tm,were influenced dramatically as the flow regime changed from homogeneous to heterogeneous patterns. The proposed mathematical models predicted the experimental results well under experimental conditions, indicating that the U-G, P/V-L, and mu(ap) had significant impact on the t(m) epsilon, and k(L)a. These models were able to give the tm, F, and kLa values with an error around +/- 8%, and always less than +/- 10%. (c) 2005 Wiley Periodicals, Inc.

Grand canonical Monte Carlo simulation study of methane adsorption at an open graphite surface and in slitlike carbon pores at 273 K

Grand canonical Monte Carlo (GCMC) simulation was used for the systematic investigation of the supercritical methane adsorption at 273 K on an open graphite surface and in slitlike micropores of different sizes. For both considered adsorption systems the calculated excess adsorption isotherms exhibit a maximum. The effect of the pore size on the maximum surface excess and isosteric enthalpy of adsorption for methane storage at 273 K is discussed. The microscopic detailed picture of methane densification near the homogeneous graphite wall and in slitlike pores at 273 K is presented with selected local density profiles and snapshots. Finally, the reliable pore size distributions, obtained in the range of the microporosity, for two pitch-based microporous activated carbon fibers are calculated from the local excess adsorption isotherms obtained via the GCMC simulation. The current systematic study of supercritical methane adsorption both on an open graphite surface and in slitlike micropores performed by the GCMC summarizes recent investigations performed at slightly different temperatures and usually a lower pressure range by advanced methods based on the statistical thermodynamics.

Adsorption of pure fluids in activated carbon with a modified lattice gas model

In this article we study the effects of adsorbed phase compression, lattice structure, and pore size distribution on the analysis of adsorption in microporous activated carbon. The lattice gas approach of Ono-Kondo is modified to account for the above effects. Data of nitrogen adsorption at 77 K onto a number of activated carbon samples are analyzed to investigate the pore filling pressure versus pore width, the packing effect, and the compression of the adsorbed phase. It is found that the PSDs obtained from this analysis are comparable to those obtained by the DFT method. The discrete nature of the PSDs derived from the modified lattice gas theory is due to the inherent assumption of discrete layers of molecules. Nevertheless, it does provide interesting information on the evolution of micropores during the activation process.

Recombinant human activated protein C improves pulmonary function in ovine acute lung injury resulting from smoke inhalation and sepsis

Objective: To investigate the effects of recombinant human activated protein C (rhAPC) on pulmonary function in acute lung injury (ALI) resulting from smoke inhalation in association with a bacterial challenge. Design: Prospective, randomized, controlled, experimental animal study with repeated measurements. Setting: Investigational intensive care unit at a university hospital. Subjects: Eighteen sheep (37.2 +/- 1.0 kg) were operatively prepared and randomly allocated to either the sham, control, or rhAPC group (n = 6 each). After a tracheotomy had been performed, ALI was produced in the control and rhAPC group by insufflation of 4 sets of 12 breaths of cotton smoke. Then, a 30 mL suspension of live Pseudomonas aeruginosa bacteria (containing 2-5 x 10(11) colony forming units) was instilled into the lungs according to an established protocol. The sham group received only the vehicle, i.e., 4 sets of 12 breaths of room air and instillation of 30 mL normal saline. The sheep were studied in the awake state for 24 hrs and were ventilated with 100% oxygen. RhAPC (24 mu g/kg/hr) was intravenously administered. The infusion was initiated 1 hr post-injury and lasted until the end of the experiment. The animals were resuscitated with Ringer's lactate solution to maintain constant pulmonary artery occlusion pressure. Measurements and Main Results., In comparison with nontreatment in controls, the infusion of rhAPC significantly attenuated the fall in PaO2/FiO(2) ratio (control group values were 521 +/- 22 at baseline [BL], 72 +/- 5 at 12 hrs, and 74 +/- 7 at 24 hrs, vs. rhAPC group values of 541 +/- 12 at BL, 151 +/- 29 at 12 hours [p < .05 vs. control], and 118 +/- 20 at 24 hrs), and significantly reduced the increase in pulmonary microvascular shunt fraction (Qs/Qt; control group at BL, 0.14 +/- 0.02, and at 24 hrs, 0.65 +/- 0.08; rhAPC group at BL, 0.24 +/- 0.04, and at 24 hrs, 0.45 +/- 0.02 [p < .05 vs. control]) and the increase in peak airway pressure (mbar; control group at BL, 20 +/- 1, and at 24 hrs, 36 +/- 4; rhAPC group at BL, 21 +/- 1, and at 24 hrs, 28 +/- 2 [p < .05 vs. control]). In addition, rhAPC limited the increase in lung 3-nitrotyrosine (after 24 hrs [%]: sham, 7 +/- 2; control, 17 +/- 1; rhAPC, 12 +/- 1 [p < .05 vs. control]), a reliable indicator of tissue injury. However, rhAPC failed to prevent lung edema formation. RhAPC-treated sheep showed no difference in activated clotting time or platelet count but exhibited less fibrin degradation products (1/6 animals) than did controls (4/6 animals). Conclusions. Recombinant human activated protein C attenuated ALI after smoke inhalation and bacterial challenge in sheep, without bleeding complications.

New method to determine PSD using supercritical adsorption: Applied to methane adsorption in activated carbon

Adsorption of supercritical fluids is increasingly carried out to determine the micropore size distribution. This is largely motivated by the advances in the use of supercritical adsorption in high energy applications, such as hydrogen and methane storage in porous media. Experimental data are reported as mass excess versus pressure, and when these data are matched against the theoretical mass excess, significant errors could occur if the void volume used in the calculation of the experimental mass excess is incorrectly determined [Malbrunot, P.; Vidal, D.; Vermesse, J.; Chahine, R.; Bose, T. K. Langmuir 1997, 13, 539]. 1 The incorrect value for the void volume leads to a wrong description of the maximum in the plot of mass excess versus pressure as well as the part of the isotherm over the pressure region where the isotherm is decreasing. Because of this uncertainty in the maximum and the decreasing part of the isotherm, we propose a new method in which the problems associated with this are completely avoided. Our method involves only the relationship between the amount that is introduced into the adsorption cell and the equilibrium pressure. This information of direct experimental data has two distinct advantages. The first is that the data is the raw data without any manipulation (i.e., involving further calculations), and the second one is that this relationship always monotonically increases with pressure. We will illustrate this new method with the adsorption data of methane in a commercial sample of activated carbon.

Protease-activated receptor-2 peptides activate neurokinin-1 receptors in the mouse isolated trachea

Protective roles for protease-activated receptor-2 (PAR2) in the airways including activation of epithelial chloride (Cl-) secretion are based on the use of presumably PAR(2)-selective peptide agonists. To determine whether PAR(2) peptide-activated Cl- secretion from mouse tracheal epithelium is dependent on PAR(2), changes in ion conductance across the epithelium [short-circuit current (I-SC)] to PAR(2) peptides were measured in Ussing chambers under voltage clamp. In addition, epithelium and endothelium-dependent relaxations to these peptides were measured in two established PAR(2) bioassays, isolated ring segments of mouse trachea and rat thoracic aorta, respectively. Apical application of the PAR(2) peptide SLIGRL caused increases in I-SC, which were inhibited by three structurally different neurokinin receptor-1 (NK1R) antagonists and inhibitors of Cl- channels but not by capsaicin, the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP(8-37), or the nonselective cyclooxygenase inhibitor indomethacin. Only high concentrations of trypsin caused an increase in I-SC but did not affect the responses to SLIGRL. Relaxations to SLIGRL in the trachea and aorta were unaffected by the NK1R antagonist nolpitantium (SR 140333) but were abolished by trypsin desensitization. The rank order of potency for a range of peptides in the trachea I-SC assay was 2-furoyl-LIGRL &gt; SLCGRL &gt; SLIGRL &gt; SLIGRT &gt; LSIGRL compared with 2-furoyl-LIGRL &gt; SLIGRL &gt; SLIGRT &gt; SLCGRL (LSIGRL inactive) in the aorta relaxation assay. In the mouse trachea, PAR(2) peptides activate both epithelial NK1R coupled to Cl- secretion and PAR(2) coupled to prostaglandin E-2-mediated smooth muscle relaxation. Such a potential lack of specificity of these commonly used peptides needs to be considered when roles for PAR(2) in airway function in health and disease are determined.

Substance P preferentially inhibits large conductance nicotinic ACh receptor channels in rat intracardiac ganglion neurons

The effects of substance P (SP) on nicotinic acetylcholine (ACh)-evoked currents were investigated in parasympathetic neurons dissociated from neonatal rat intracardiac ganglia using standard whole cell, perforated patch, and outside-out recording configurations of the patch-clamp technique. Focal application of SP onto the soma reversibly decreased the peak amplitude of the ACh-evoked current with half-maximal inhibition occurring at 45 mu M and complete block at 300 mu M SP. Whole cell current-voltage (I-V) relationships obtained in the absence and presence of SP indicate that the block of ACh-evoked currents by SP is voltage independent. The rate of decay of ACh-evoked currents was increased sixfold in the presence of SP (100 mu M), suggesting that SP may increase the rate of receptor desensitization. SP-induced inhibition of ACh-evoked currents was observed following cell dialysis and in the presence of either 1 mM 8-Br-cAMP, a membrane-permeant cAMP analogue, 5 mu M H-7, a protein kinase C inhibitor, or 2 mM intracellular AMP-PNP, a nonhydrolyzable ATP analogue. These data suggest that a diffusible cytosolic second messenger is unlikely to mediate SP inhibition of neuronal nicotinic ACh receptor (nAChR) channels. Activation of nAChR channels in outside-out membrane patches by either ACh (3 mu M) or cytisine (3 mu M) indicates the presence of at least three distinct conductances (20, 35, and 47 pS) in rat intracardiac neurons. In the presence of 3 mu M SP, the large conductance nAChR channels are preferentially inhibited. The open probabilities of the large conductance classes activated by either ACh or cytisine were reversibly decreased by 10- to 30-fold in the presence of SP. The single-channel conductances were unchanged, and mean apparent channel open times for the large conductance nAChR channels only were slightly decreased by SP. Given that individual parasympathetic neurons of rat intracardiac ganglia express a heterogeneous population of nAChR subunits represented by the different conductance levels, SP appears to preferentially inhibit those combinations of nAChR subunits that form the large conductance nAChR channels. Since ACh is the principal neurotransmitter of extrinsic (vagal) innervation of the mammalian heart, SP may play an important role in modulating autonomic control of the heart.

Activation of calcium-sensitive potassium channels in L6 skeletal myocytes by arginine vasopressin requires extracellular calcium

The effects of extracellular application of arginine vasopressin (AVP) upon membrane currents in L6 skeletal myocytes was investigated using the whole-cell configuration of the patch-clamp technique. At O mV AVP produced large amplitude, transient outward currents that reversed when the clamping potential was changed to -100 mV (negative to EK) The effects of alterations in the extracellular K+ concentration upon the current reversal potential suggested that the current elicited by AVP was carried mainly by K+ ions. Intracellular dialysis with 10 μM inositol 1,4,5-trisphosphate (InsP3) elicited similar currents but only in 6/14 cells. Inclusion of 5 mg ml-1 heparin in the intracellular solutions was ineffective at inhibiting the current responses to AVP. The AVP-induced current was totally abolished when the intracellular EGTA concentration was increased from 0.05 mM to 10 mM or Ca2+ was removed from the extracellular perfusing solution. These results suggest that AVP produces activation of a Ca2+-sensitive K+ conductance in L6 skeletal myocytes by a process dependent upon extracellular Ca2+ and not intracellular Ca2+ release. © 1995 Academic Press. All rights reserved.