The effects of surface lactone hydrolysis and temperature on the specific and nonspecific interactions between phenobarbital and activated carbon surfaces

The effect of hydrolyzing lactone functional groups on the surfaces of different activated carbons upon the specific and nonspecific interactions between phenobarbital and activated carbon surfaces was studied. The effect of temperature on both specific and nonspecific interactions was also studied. The increase in OH groups on the surfaces of activated carbons, as a result of hydrolyzing surface lactone groups, caused an increase in the specific adsorption capacity (K(2)) for phenobarbital without having a significant effect on the hydrophobic bonding capacity (K(HB)). Increasing the temperature at which the adsorption experiment was carried out, on the other hand, resulted in a decrease in K(HB) without having a significant effect on K(2). The decrease in K(HB) per unit temperature increase was the same regardless of the activated carbon. These results are in very good agreement with the modified-Langmuir-like equation (M-LLE).     

Surface Characterization of Activated Charcoal by X-Ray Photoelectron Spectroscopy (XPS): Correlation with Phenobarbital Adsorption Data

X-ray photoelectron spectroscopy (XPS) was used to identify the functional states of carbon existing on the surfaces of various activated charcoals. The relative percentages of carbon, oxygen, and detectable trace elements comprising the activated charcoal surfaces were determined. Analysis of the carbon core-electron binding energy region revealed the existence of one hydrocarbon state (C–H, C–C are indistinguishable) and three oxygen-containing functional states. These states were hydroxyls or ethers (C–O), carbon-yls (C = O), and carboxylic acids or esters (O–C = O). The C–O functional state contributed approximately 60–70% to the total percentage of oxygen-containing states. A very good correlation existed between the apparent areas occupied on the adsorbent surface per phenobarbital molecule and the relative percentages of the C–O functional state. Previously reported heat of displacement results for phenobarbital adsorption are now explained since the C–O state appears to be the primary site involved in the binding of phenobarbital by the activated charcoals.     

Model Selection for the Adsorption of Phenobarbital by Activated Charcoal

Activated charcoal is known to adsorb a wide variety of substances from solution, and several equations have been used to fit the resulting adsorption data. The determination of the correct model to fit phenobarbital adsorption onto activated charcoal was made using a calorimetric method. The differential heats of displacement of water by phenobarbital for four activated charcoals were determined and found to be linearly related to the amount of phenobarbital adsorbed. The activated charcoals studied had statistically similar heats of displacement. The linear relationship between heat evolved and the amount of phenobarbital adsorbed is consistent with the assumptions implicit in the Langmuir model.     

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption: A New Langmuir-like Model to Account for the Effect of Solvent Displacement Stoichiometry

The reported inconsistencies between calorimetry and the van't Hoff equation hinder the utility of thermodynamics in pharmaceutical research. In ligand binding or adsorption assays, it is believed that the van't Hoff equation falls short because of the lack of stoichiometric treatment in the equilibrium constant. A new modified Langmuir-Like equation that accounts for the stoichiometry of solute adsorption and solvent displacement is proposed in this work. The performance of the model was evaluated by studying the adsorption of phenobarbital from aqueous solutions by commercial activated carbon. The amount of water occupying the adsorption sites was estimated by graphical analysis of the ‘knee point’ of water-vapor adsorption isotherms and was found to correlate well with the relative percentage of hydroxyl and carbonyl surface groups. It was found that one phenobarbital molecule displaces 2-6 water molecules from the adsorption site. It is shown that adsorption enthalpy was not affected by the adjustment for stoichiometry, supporting the notion that the van't Hoff enthalpy is intrinsic and is independent of the stoichiometry of solvent displacement in Langmuir-based binding. The widely reported disparities between the van't Hoff and calorimetric enthalpies are unlikely to be from a stoichiometric origin.     

Thermodynamic Estimate of the Number of Solvent Molecules Displaced by a Solute Molecule for Enthalpy-Driven Adsorption: Phenobarbital and Activated Carbons as the Model System

A Modified Crisp Equation, describing the differential Gibbs free energy of the adsorption process, is being proposed, which considers multiple sites available on the surface for adsorption and their relative fractions. The differential Gibbs free energy can be calculated by the van't Hoff Equation, which depends on the affinity constant in the Langmuir-like equation. To consider the number of solvent molecules displaced by a solute molecule in the adsorption process, a new derivative of the Langmuir-like equation is being proposed as well. By comparing the differential Gibbs free energies obtained from the 2 thermodynamic relationships, it can be determined that a phenobarbital molecule displaces 5 water molecules on the activated carbon surface for site-specific adsorption from solution. For the series of experimental conditions studied, including 4 activated carbons, pH effects, temperature effects, and solvent effects, the corrected differential Gibbs free energies using n₁ = 5 for site-specific adsorption are quite consistent between the 2 thermodynamic relationships. The difference between the estimates of the differential Gibbs free energies by the Modified Crisp Equation and the van't Hoff Equation provides a new experimental method to calculate the number of solvent molecules displaced by an adsorbing solute molecule.     

Phenobarbital Removal Characteristics of Three Brands of Activated Charcoals: A System Analysis Approach

The in vivo phenobarbital removal characteristics of three brands of activated charcoal (Actidose, Charcoaid, Superchar) were studied in normal volunteers using a system analysis approach. The subjects received a 200-mg dose of oral or intravenous phenobarbital followed by a single oral dose of 30 g of one of the three charcoals in a randomized crossover design. The relative merits of the three charcoals in enhancing the removal of oral and intravenous phenobarbital were assessed using a system analysis approach. The removal clearance, time to peak (t _p), peak removal clearance (R _max), percentage of dose removed (PCT), and phenobarbital removal clearance (CL_r) were calculated for the oral and intravenous treatments. Superchar had a pulse-like effect, with the shortest t _p and the largest R _max. Actidose and Charcoaid had similar effects, with Actidose inducing slightly greater phenobarbital removal. Superchar has the highest surface area and relative percentage of surface hydroxyl groups, whereas Actidose has the lowest surface area and relative percentage of surface hydroxyl groups of the three charcoals studied. Although correlations between the in vitro and the in vivo phenobarbital adsorption characteristics of the three charcoals may be difficult due to the presence of preservatives and palatibility enhancers in the commercial preparations, it appears that the in vivo effectiveness decreases as the surface area and the concentration of surface hydroxyl groups decrease. The proposed system analysis approach requires fewer assumptions than methods based on compartmental or physiologic approaches and has the advantage of describing the phenobarbital removal in a dynamic manner.     

Adsorptive removal of Bisphenol A by biomass activated carbon and insights into the adsorption mechanism through density functional theory calculations

Activated carbon was synthesized from Tithonia diversifolia biomass using potassium hydroxide as the chemical activating reagent. Taguchi's experimental design approach was applied to determine the best preparation conditions. An optimum 2:1 impregnation ratio and 700 °C activation temperature produced the best carbon with a high 854.44 m²g^-1 surface area, 0.445 cm³g^-1 total pore volume and 18.3% yield. From the analysis of variance (ANOVA), the impregnation ratio was found to be the most influential factor in preparing activated carbon with the maximum surface area. SEM and XRD studies revealed the porous microcrystallite structure of the obtained activated carbon. Batch adsorption studies were performed to test the efficiency of Tithonia diversifolia activated carbon for the removal of Bisphenol A (BPA) from aqueous solution. A maximum 98.2% removal percentage was attained at optimum conditions of 0.2 g adsorbent dose, pH 7, 80 min contact time and 40 mg L^?1 initial BPA concentration. The Langmuir isotherm model described the equilibrium adsorption of BPA well with a maximum adsorption capacity(q_m) of 15.69 mg g^?1 while the kinetic adsorption study indicated a pseudo second order model. A theoretical investigation suggested that the adsorption of BPA onto the activated carbon mainly proceeds via chemisorption and the presence of a carboxyl functional group on the activated carbon surface yielded a greater adsorptive impact on BPA. This study indicates that Tithonia diversifolia could be used as a potential raw material for preparing activated carbon for removing of BPA from water.     

四氯化碳诱导大鼠肝硬化腹水模型的改进与优化

目的应用四氯化碳（CCl4）联合苯巴比妥及乙醇的方法,以期建立稳定性、均一性、重复性良好且成模率较高的大鼠肝硬化腹水模型,为相关血浆蛋白制品的药效学评价等研究奠定基础。方法将90只雄性Wistar大鼠随机分为5组：正常对照组10只,腹腔注射橄榄油,正常饮水;模型组分为CCl4组、CCl4＋苯巴比妥组、CCl4＋乙醇组、CCl4＋苯巴比妥＋乙醇组,每组20只,给予不同饮用水处理,腹腔注射40%CCl4橄榄油混合液。各实验组腹腔注射剂量均为2 ml/kg,每周注射2次,共12周。建模过程中,定期测量体质量和腹围,采集静脉血监测肝功能指标和血浆胶体渗透压（COP）。建模结束后,随机处死各组大鼠,取肝右叶组织进行病理学鉴定。应用统计学方法对数据进行分析。结果各模型组在建模的第8～12周先后出现符合筛选标准的模型。其中,第8周时,CCl4＋苯巴比妥＋乙醇组大鼠开始出现腹水阳性体征,个别达到建模标准;第9周时,CCl4＋苯巴比妥组和CCl4＋乙醇组均有符合要求的模型产生;CCl4组至第10周时开始出现建模成功的大鼠。至12周建模结束时,与正常对照组相比,各模型组体质量、腹围、肝功能指标、COP等差异均具有统计学意义,以CCl4＋苯巴比妥＋乙醇组的差异最为明显。各模型组的成模率分别是65%、75%、75%和80%。镜下观察模型组大鼠的肝组织病理学切片,可见假小叶形成等典型的肝硬化形成特征。结论四氯化碳联合苯巴比妥与乙醇诱导大鼠肝硬化腹水动物模型较传统的方法可以有效提高实验动物的成模率,缩短建模周期。     

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption II: Effect of pH and pH Buffers on Phenobarbital Adsorption to Activated Carbon

The reported inconsistencies between the van't Hoff equation and calorimetry hinder the utility of thermodynamics in biochemical and pharmaceutical research. A novel thermodynamic approach is developed herein for ligand adsorption with a focus on the interpretation of calorimetric data in the presence of concurrent proton exchange reactions. Such exchange reactions typically result in a pH-dependence of calorimetric measurements that obscures intrinsic binding enthalpies. It is shown that for the adsorption of phenobarbital to activated carbon, the measured calorimetric enthalpy is a result of three linked acid/base equilibria. A model was established to predict the intrinsic binding enthalpy using 1) the adsorbate's pKa and 2) the adsorbate's enthalpy of protonation. The observed calorimetric enthalpy of binding exhibited both pH and buffer-dependence and was between -5 and -42 kJ/mol. Meanwhile, the predicted intrinsic enthalpy (-25.1 kJ/mol) of binding was in excellent agreement with the measured intrinsic enthalpy (-25.6 kJ/mol). Corrections to the observed calorimetric enthalpies allowed comparisons with enthalpies obtained from the van't Hoff method. It is shown that the predicted intrinsic calorimetric enthalpy agrees well with the van't Hoff enthalpies in instances where observed enthalpies significantly deviated. This treatment is general and is not specific to phenobarbital or activated carbon.     

Effects of food type on the extent of drug-drug interactions between activated charcoal and phenobarbital in rats

Activated charcoal is known to decrease the intestinal absorption of co-administered drug by adsorption. The extent of this drug-drug interaction (DDI) is attenuated by food intake. The aim of this study was to quantitatively evaluate the effects of food type on the extent of DDI between phenobarbital and activated charcoal using a rat model. Phenobarbital was orally administered at a dose of 1.5 mg/kg with or without 33 mg/kg of activated charcoal under fasted or fed conditions, and the plasma concentration profile of phenobarbital was monitored. Several fed conditions, such as a standard breakfast, high-fat meal or enteral nutrient used in human studies, were examined. Under the fasted conditions, activated charcoal significantly decreased the area under the plasma concentration - time curve (AUC) of phenobarbital by 45.2%. When the standard breakfast or high-fat meal was fed, this DDI was reduced to 28.3 and 18.0%, respectively, as assessed by the reduction in the AUC. On the contrary, enteral nutrient did not significantly attenuate the DDI. In conclusion, the influence of food intake on the extent of DDI between phenobarbital and activated charcoal was found to differ among the types of food concomitantly ingested.     

Prediction of the adsorption of diazepam by activated carbon in aqueous media

Adsorption isotherms for the diazepam-activated carbon system in simulated intestinal fluid (SIF), without pancreatin, and in SIF with different percentages of ethanol were determined as were the solubilities of diazepam in SIF and in SIF with different percentages of ethanol. The surface area of the activated carbon was also evaluated. The results from the experimental work provided information on the relationship between adsorption and solubility. An excellent logarithmic relationship was observed between the adsorption affinity and the solubility of diazepam in the ethanol-SIF mixtures. This relationship was explained by a linear relationship between the differential free energy of displacement and the differential free energy of solution. Excellent correlations were also observed between the amounts of diazepam adsorbed by activated carbon and the solubilities of diazepam in the ethanol-SIF mixtures. This relationship was used to predict the complete isotherm, which was in excellent agreement with the experimental work.     

Use of activated charcoal to reduce elevated serum phenobarbital concentration in a neonate

The course of a neonate administered activated charcoal orally for elevated phenobarbital concentration is described. The neonate required a serum concentration of phenobarbital eventually exceeding 80 micrograms/mL for seizure control. However, due to the severe CNS injury as a result of the asphyxia at birth, a diagnosis of cerebral death by electroencephalogram and apnea test was pursued. This required the phenobarbital concentration to be less than 30 micrograms/mL. Serial phenobarbital concentrations during this time indicated a 250 hour half-life, which would require two weeks for the phenobarbital to drop below 30 micrograms/mL. With the administration of six doses of activated charcoal at 0.7 g/kg/dose, the phenobarbital serum concentration decreased to 22 micrograms/mL, giving an estimated phenobarbital half-life of 22 hours. This, and two other subsequent cases, indicates repeated doses of activated charcoal are effective in augmenting the clearance of certain drugs in the neonatal age group.     

Thermodynamic Evaluation of the Interaction Driven by Hydrophobic Bonding in the Aqueous Phase

In the present study, the interaction between phenobarbital and activated carbons which is driven by hydrophobic bonding was evaluated. The Two-Mechanism Langmuir-Like Equation was proposed to describe the isotherms for phenobarbital adsorbing to activated carbons. The parameters in the Two-Mechanism Langmuir-Like Equation obtained from the nonlinear fitting of isotherms were used in the calculations of the differential Gibbs free energy for the hydrophobic bonding-driven interaction. Two thermodynamic models, the Modified Crisp Model and the van't Hoff Equation, were adopted to estimate the differential Gibbs free energy. And, comparing the differential Gibbs free energy obtained from the 2 thermodynamic relationships, it can be determined that an adsorbing phenobarbital molecule displaces 12 water molecules on the hydrocarbon surfaces of the activated carbons (hydrophobic bonding case). The difference between the estimates of the differential Gibbs free energy obtained by the Modified Crisp Model and by the van't Hoff Equation provides a new experimental method to calculate the number of solvent molecules displaced by an adsorbing solute molecule. This is a completely general technique for the hydrophobic bonding-driven interaction and is not limited to the systems studied. The calculated positive differential entropy confirmed that the adsorption process was entropy driven.     

Adsorption of local anesthetics on activated carbon: Freundlich adsorption isotherms

We have shown that adsorbability of local anesthetics onto activated carbon, expressed by the partition coefficients at infinite dilution, correlated well with the pharmacological activity. However, there is no parameter that can singly express the tendency to be adsorbed. Adsorbability is a loosely defined term and its meaning varies with the adsorption model. This study showed that the logarithm of the adsorbed amount of drugs was linearly related to the logarithm of the free drug concentration, in conformity to the Freundlich adsorption isotherms. The slope of the double logarithmic plot is expressed by 1/N in the Freundlich equation and is considered to be inversely related to the drug affinity to the adsorbent. The slope was used to evaluate the tendency to be adsorbed, or "adsorbability" of seven aromatic amine local anesthetics. Phenobarbital was included to compare anionic drugs in contrast to the cationic local anesthetics. The slopes were nearly equal between the cationic and neutral local anesthetics. Apparently, the lower hydrophobicity of the cationic forms is compensated by the electrostatic attraction from the negative charges present on the activated carbon surface. With phenobarbital, the slope value of the anionic form was larger than the neutral form. The lower affinity of the anionic form may be caused by the electrostatic repulsion. The molecular size parameters (i.e., molecular weight, molar refraction, and parachor) showed a linear relationship to the slope values. It may be possible to estimate the affinity-related slope values from these parameters.     

Effects of alpha-carbon substituents on the N-demethylation of N-methyl-2-phenethylamines by rat liver microsomes

The effects of methyl, ethyl, isopropyl, isobutyl, and benzyl substituents at the alpha-carbon of N-methyl-2-phenethylamine on the kinetics of its N-demethylation in liver microsomes from both control and phenobarbital pretreated rats were studied. In control microsomes, the kinetic studies indicated that more than one enzyme was active for N-demethylation of N-methyl-alpha-methylphenethylamine (methamphetamine) while the other N-methyl-2-phenethylamines appeared to be demethylated by a single enzyme. In microsomes from phenobarbital pretreated animals, there appeared to be more than one enzyme system which was active for N-demethylation of all compounds except N-methyl-alpha-benzylphenethylamine. One of these had a much higher affinity for alpha-ethyl, isopropyl, and isobutyl N-methylphenethylamines while another exhibited affinities for substrates similar to the constitutive enzyme in control microsomes. A correlation was observed between the octanol-buffer or heptane-buffer distribution ratios of the compounds and the negative logarithm of the Michaelis constant (pKm) for the enzyme in control microsomes and for each of the enzyme systems in microsomes from phenobarbital-pretreated animals. Therefore, it is indicated that the concentration of a substrate at the active site of these microsomal enzymes is a function of its lipid solubility.     

Does sorbinil bind to the substrate binding site of aldose reductase?

With benzyl alcohol as the varied substrate, sorbinil was found to be a competitive inhibitor of aldose reductase, an enzyme implicated in the etiology of secondary diabetic complications. The K(is sorbinil) and the Vmax/Km (V/K) benzyl alcohol decreased at low pH with a pK of 7.5 and 7.7, respectively. These observations suggest that both sorbinil and benzyl alcohol bind to the same site on the enzyme. Active site inhibition by sorbinil is consistent with non-competitive inhibition patterns of sorbinil with nucleotide coenzyme or aldehyde as the varied substrate in the direction of aldehyde reduction.     

Biosorption of ibuprofen using functionalized bean husks

The ability of bean husk, an agricultural waste, as a promising adsorbent for sequestering Ibuprofen from aqueous solution was investigated. Bean husk waste was modified using ortho-phosphoric acid. The prepared adsorbent was further characterized using FTIR, SEM, EDX and pH_pzc techniques respectively. FTIR revealed prominent functional groups for IBP adsorption, SEM showed several pores on activated bean husk making it suitable for trapping IBP molecules. EDX results of acid activated bean husk has the highest percentage of carbon by weight (84.21%) and (89.02%) by atom, respectively. pH_pzc studies revealed that the surface of the prepared adsorbent contains predominantly acidic groups: carboxyl (0.531 mmol/g), phenolic (0.845 mmol/g) and lactonic (0.021 mmol/g) totalling 1.397 mmol/g while basic group has 0.700 mmol/g. Operational parameters such as: contact time, pH, temperature, initial IBP concentrations and adsorbent dose were studied. Optimum IBP adsorption took place at a pH of 4.75. Isotherm studies were conducted using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models respectively. Langmuir isotherm aligned best with the adsorption data. The maximum monolayer adsorptive capacity of the modified adsorbent was 50.00 mg/g at 50 °C. Four different kinetic models viz; pseudo first order, pseudo second order, Elovich, and Intraparticle-diffusion were used to investigate the kinetic process. Adsorption data fitted the pseudo second order kinetic model most. Thermodynamic parameters revealed that the process is spontaneous and endothermic. The study revealed that bean husk is a good precursor for activated carbon preparation; it is an efficient, readily available, economically friendly alternative for the sequestration of ibuprofen from aqueous solution.     

Modulation of Organic Cation Transport and Lipid Fluidity by Benzyl Alcohol in Rat Renal Brush-border Membranes

Purpose. Organic cations are actively transported in renal brush-border membranes (BBM) by the H⁺/organic cation antiport system. In the present study, we investigated the relationship between membrane fluidity and organic cation transport in the BBM. Methods. The effects of benzyl alcohol, a membrane fluidizing agent, on the organic cation tetraethylammonium (TEA) uptake were studied using renal BBM vesicles isolated from rat kidney. BBM fluidity was assessed by fluorescence polarization technique. Results. H⁺ gradient-dependent uptake of TEA in BBM vesicles was inhibited by benzyl alcohol in a dose-dependent manner, with an apparent half inhibitory concentration of 18mM. The decrease in fluorescence anisotropy of l,6-diphenyl-l,3,5-hexatriene in BBM, which represents the increase in membrane fluidity, was correlated with the decrease in TEA transport activity. The dissipation rate of H⁺ gradient, a driving force for organic cation transport in BBM, was increased by benzyl alcohol. In addition, H⁺ gradient-independent TEA-TEA exchange was also inhibited by benzyl alcohol. These findings indicate that benzyl alcohol inhibits the uptake of TEA by affecting the intrinsic activity of the organic cation transporter and the H⁺ gradient dissipation rate. Conclusions. The membrane fluidity should be an important determinant for organic cation transport in renal BBM.     

Prevention of benzyl alcohol-induced aggregation of chymotrypsinogen by PEGylation

Objectives Addition of the antimicrobial preservative benzyl alcohol to reconstitution buffer promotes the formation of undesirable aggregates in multidose protein formulations. Herein we investigated the efficiency of PEGylation (attachment of poly(ethylene glycol)) to prevent benzyl alcohol‐induced aggregation of the model protein α‐chymotrypsinogen A (aCTgn). Methods Various PEG‐aCTgn conjugates were prepared using PEG with a molecular weight of either 700 or 5000 Da by varying the PEG‐to‐protein ratio during synthesis and the formation of insoluble aggregates was studied. The effect of benzyl alcohol on the thermodynamic stability and tertiary structure of aCTgn was also examined. Key findings When the model protein was reconstituted in buffer containing 0.9% benzyl alcohol, copious amounts of buffer‐insoluble aggregates formed within 24 h (>10%). Benzyl alcohol‐induced aggregation was completely prevented when two or five molecules of PEG with a molecular weight of 5000 Da were attached to the protein, whereas two or four molecules of bound 700 Da PEG were completely inefficient in preventing aggregation. Mechanistic investigations excluded prevention of structural perturbations or increased thermodynamic stability by PEGylation from being responsible for the prevention of aggregation. Simple addition of PEG to the buffer was also inefficient and PEG had to be covalently linked to the protein to be efficient. Conclusions The most likely explanation for the protective effect of the 5000 Da PEG is shielding of exposed hydrophobic protein surface area and prevention of protein–protein contacts (molecular spacer effect).     

混凝法以及混凝-吸附组合法对制药废水的处理

分别采用混凝法以及混凝—吸附组合法对制药废水进行了处理试验,研究了硫酸铁混凝剂的用量及溶液pH值对混凝效果的影响。混凝实验表明,硫酸铁的最佳混凝pH值为8.3,此时硫酸铁的最佳投药量为50g.L-1。在最佳pH和投药量条件下,CODcr和浊度去除率分别是45.5%、96.2%。通过混凝—吸附的组合实验,CODcr去除率最高可达到95.5%。比较了颗粒状活性炭和粉末状活性炭两种吸附剂对制药废水的吸附效果。实验表明,颗粒状活性炭的吸附效果好于粉末状活性炭。