Function Of Concentration Gradient Research Articles

Excellency of pyrimidinyl moieties containing α-aminophosphonates over benzthiazolyl moieties for thermal and structural stability of stem bromelain

An efficient approach has been made for the synthesis of a series of novel di α-aminophosphonates by the reaction of terephthalaldehyde with various pyrimidine/benzthiazole amines and diethyl phosphite using sulfonated graphitic carbon nitride – SA@g-C3N4 as catalyst under room temperature and solvent free conditions. Later, the different effects of these newly synthesized α-aminophosphonates as a function of concentration gradient has been scrutinized on the thermal and structural stability of stem bromelain (SBM) through combining the results of various spectroscopic techniques like UV–vis, steady state fluorescence and circular dichroism (CD). Lastly the competitive and distinctive behaviour of α-aminophosphonates towards the stability of SBM has been envisaged using molecular docking simulations which suggest that nature of α-aminophosphonates plays a crucial role for their interactions with SBM. Molecular docking results clearly show that α-aminophosphonates with pyrimidine ring are having more number of hydrogen bonding interaction with amino acid residues of SBM than α-aminophosphonates with benzthiazolyl ring. Sequentially for thermal and structure stability of SBM, concentration of α-aminophosphonates plays an inexorable role and through these results it must be concluded that most of the α-aminophosphonates are stabilizing the SBM upto the 0. 1 mM concentration.

Calibration of Big Bottle RAD H2O set-up for radon in water using HDPE bottles

Glass bottles are generally employed for water sampling because glass is impervious to radon and is not lost during sample storage. On the other hand, glass is fragile and may break, so 1 L High Density PolyEthylene (HDPE) bottles (Thermo Scientific Nalgene) are tested in place of glass vessels employing Big Bottle RAD H2O device (Durridge Company) coupled with RAD7 monitor. The purpose of this calibration is to quantify radon loss during storage in HDPE bottles, evaluate possible radon uptake by known volume of desiccant (Drierite, granular CaSO4) and quantify radon interaction with the rubber and plastic parts of the experimental circuit. These processes have been separately investigated, performing proper experiments for the assessment of their influence on resulting radon data using seven series of solutions at known activity concentrations in the range from 27 to 194 Bq/L. Percent radon loss during storage in 1 L HDPE bottles has been estimated at 0.0045 min−1. Radon absorption by desiccant, expressed as ‘equivalent’ volume of Drierite is 0.673±0.092 L and is somehow independent, within errors, from i) the amount of water already absorbed in Drierite, ii) a recirculation time greater than 30 min and iii) radon concentrations. Radon absorption/desorption from rubber and plastic parts of the experimental device has been assessed as a function of concentration gradient between the inner volume of the circuit and the pores of polymer's. A final algorithm accounting for the above described physical processes has been developed for long runs (2–3 h). A simplified calculation method for short measurements (30 min) is also provided.

In silico assay development for screening of tetracyclic triterpenoids as anticancer agents against human breast cancer cell line MCF7.

Experimental activity of a compound on cancer cell line/target is mostly analyzed in the form of percentage inhibition at different concentration gradient and time of incubation. In this study a statistical model has been developed referred as in silico assay using support vector regression model, which can act with change in concentration gradient and time of incubation. This model is a function of concentration gradient, treatment hour and independent components; which calculate the percentage inhibition in combination of above three components. This model is designed to screen tetracyclic triterpenoids active against human breast cancer cell line MCF7. The model has been statistically validated, checked for applicability domain and predicted results were reconfirmed by MTT assay, for example Oenotheranstrol derivatives, OenA & B. Computational SAR, target and docking studies were performed to understand the cytotoxic mechanism of action of Oenotheranstrol compounds. The proposed in silico assay model will work for specific chemical family for which it will be optimized. This model can be used to analyze growth kinetics pattern on different human cancer cell lines for designed compounds.

Reversal Potential of a Wide Ion Channel. Nonuniform Charge Distribution Effects

A theory for the reversal potential Vr in a wide, charged ion channel (i.e., with radius comparable to channel length and Debye's length) embedded in a planar membrane is developed. We analyze the influence of a nonuniform channel charge distribution along the channel axis on Vr. The analysis is performed in the framework of the space charge model, which is generalized for axial nonuniform charge distributions. Two kinds of nonhomogeneity are considered: (1) a symmetrical nonhomogeneous distribution when channel charge is uniformly smeared over the inner surface of channel wall, but it does not extend over the whole surface, and (2) an asymmetrical nonhomogeneous distribution corresponding to some part of the total charge uniformly smeared over the channel wall and some other located on one of the channel entrances. For the first distribution it is shown that even a small deviation from a uniform distribution leads to a significant change in the reversal potential. In particular, the experimentally observed nonmonotonic behavior of Vr for the voltage-dependent anion channel from mitochondria (VDAC) as a function of concentration gradient [Zambrowicz, E. B.; Colombini, M.; Biophys. J. 1993, 65, 1093.] is explained by invoking the axial nonhomogeneity of channel charge. For the second kind of distribution (which resembles that in VDAC closed states) it is shown that the sign and value of the reversal potential depends on the location of the mobile part of the channel charge. Theoretical results are compared with previously reported experimental data for VDAC but they are valid for any charged multiionic channel where the Nernst−Planck formalism can be applied.

Microdialysis probes calibration: Gradient and tissue dependent changes in No Net Flux and reverse dialysis methods

Probe calibrations are required for accurate estimations of extracellular concentrations in microdialysis experiments. Several methods have been developed and validated for in vivo determination of dialysis membrane recovery such as the perfusion rate method and the No Net Flux method. In this study, the No Net Flux and the reverse dialysis methods were investigated. Both measure the net transport of drug across the dialysis membrane. The recovery was defined as R = (Cin - Cout)/Cin, where Cin and Cout were the concentrations of a compound in the perfusate and in the dialysate, respectively. First, the accuracy of the No Net Flux method to estimate in vivo recovery was compared in two situations: diffusion from the probe into the dialysis medium and diffusion from the outer medium into the probe. The point of no net transport was used to estimate the concentration surrounding the probe. Neither difference between extracellular concentrations (intercept values) nor difference between recoveries were observed. Then the reverse dialysis method was tested to estimate the relative loss of drug from the perfusate when the probe was placed in a drug-free medium. Finally comparisons of the behavior of the drug diffusion across the membrane under increasing gradient conditions have shown an asymptotic profile, specific of the tissue: blood, muscle, and adipose tissue. The faster a drug was removed by microvascular transport (blood>muscle>adipocytes), the higher was the recovery, until the perfusate concentration reached a threshold value where the transport process became gradient limited and no more tissue limited. The usefulness of the reverse dialysis method has allowed us (a) to estimate the recovery of a dialysis probe in vivo without a systemic administration of a drug and (b) to characterize the diffusion process as a function of concentration gradient and tissue.

The mechanism of cation permeation in rabbit gallbladder

The experimental measurements of passive ion permeation in rabbit gallbladder presented in this paper include: single-salt dilution potentials as a function of concentration gradient; comparison of dilution potentials for different alkali chlorides; comparison of biionic potentials for different alkali chlorides; and biionic mixture potentials as a function of cation concentration gradient. Both dilution potentials and biionic potentials yield the permeability sequence K(+)>Rb(+)>Na(+)>Li(+)>Cs(+), a sequence consistent with simple considerations of ion-site interactions and ion hydration energies. Construction of empirical selectivity isotherms for alkali cation permeation in epithelia shows that permeability ratios are nearer one in the gallbladder and other epithelia than in most other biological membranes, indicating a relatively hydrated permeation route. Evaluation of the results of this and the preceding paper suggests the following: that cations permeate gallbladder epithelium via channels with fixed neutral sites; that the rate-controlling membrane is thick enough that microscopic electroneutrality must be obeyed; that virtually all anion conductance is in a shunt which develops with time after dissection; that apparent permeability changes with solution composition are due to the non-ideal activity factorn being less than 1.0; that effects of pH, Ca(++), and ionic strength may involve changes in the anion/cation mobility ratio owing to changes in wall charges or dipoles; and that the permeation route may reside in the tight junctions. A similar mechanism may be applicable to cation permeation in other epithelia.