Titration calorimetry of surfactant–drug interactions: Micelle formation and saturation studies

Isothermal titration calorimetry (ITC) was employed to monitor the addition of five model drugs to anionic surfactant based micelles, composed of sodium dodecyl sulfate (SDS), through to the point at which they were saturated with drug. Analysis of the resultant data using this newly developed method has confirmed the suitability of the technique to acquire such data with saturation limits established in all cases. Values for the point at which saturation occurred ranged from 17 molecules of theophylline per micelle at T = 298 K up to 63 molecules of caffeine per micelle at 310 K. Micellar systems can be disrupted by the presence of additional chemicals, such as the drugs used in this study, therefore a separate investigation was undertaken to determine the critical micellar concentration (CMC) for SDS in the presence of each drug at T = 298 K and 310 K using ITC. In the majority of cases, there was no appreciable alteration to the CMC of SDS with drug present.     

The role of water in the thermodynamics of drug binding to cyclodextrin

The thermodynamic parameters, Δ_BG^∘, Δ_BH^∘, Δ_BS^∘, and Δ_BC_p, of the drugs flurbiprofen (FLP), nabumetone (NAB), and naproxen (NPX) binding to β-cyclodextrin (βCD) and to γ-cyclodextrin (γCD) in 0.10 M sodium phosphate buffer were determined from isothermal titration calorimetry (ITC) measurements over the temperature range from 293.15 K to 313.15 K. The heat capacity changes for the binding reactions ranged from −(362 ± 48) J · mol⁻¹ · K⁻¹ for FLP and −(238 ± 90) J · mol⁻¹ · K⁻¹ for NAB binding in the βCD cavity to 0 for FLP and −(25.1 ± 9.2) J · mol⁻¹ · K⁻¹ for NPX binding in the larger γCD cavity, implying that the structure of water is reorganized in the βCD binding reactions but not reorganized in the γCD binding reactions. Comparison of the fluorescence enhancements of FLP and NAB upon transferring from the aqueous buffer to isopropanol with the maximum fluorescence enhancements observed for their βCD binding reactions indicated that some localized water was retained in the FLP–βCD complex and almost none in the NAB–βCD complex. No fluorescence change occurs with drug binding in the larger γCD cavity, indicating the retention of the bulk water environment in the drug–γCD complex. Since the specific drug binding interactions are essentially the same for βCD and γCD, these differences in the retention of bulk water may account for the enthalpically driven nature of the βCD binding reactions and the entropically driven nature of the γCD binding reactions.     

Use of hydrophobins in formulation of water insoluble drugs for oral administration

The poor water solubility of many drugs requires a specific formulation to achieve a sufficient bioavailability after oral administration. Suspensions of small drug particles can be used to improve the bioavailability. We here show that the fungal hydrophobin SC3 can be used to make suspensions of water insoluble drugs. Bioavailability of two of these drugs, nifedipine and cyclosporine A (CyA), was tested when administered as a SC3-based suspension. SC3 (in a 1:2 (w/w) drug:SC3 ratio) or 100% PEG400 increased the bioavailability of nifedipine to a similar degree (6 ± 2- and 4 ± 3-fold, respectively) compared to nifedipine powder without additives. Moreover, SC3 (in a 7:1 (w/w) drug:hydrophobin ratio) was as effective as a 20-fold diluted Neoral^® formulation by increasing bioavailability of CyA 2.3 ± 0.3-fold compared to CyA in water. Interestingly, using SC3 in the CyA formulation resulted in a slower uptake (p < 0.001 in T_max) of the drug, with a lower peak concentration (C_max 1.8 mg ml^?1) at a later time point (T_max 9 ± 2 h) compared to Neoral^® (C_max 2.2 mg ml^?1; T_max 3.2 ± 0.2). Consequently, SC3 will result in a more constant, longer lasting drug level in the body. Taken together, hydrophobins are attractive candidates to formulate hydrophobic drugs.     

Potent antiviral effect of green synthesis silver nanoparticles on Newcastle disease virus

Newcastle disease virus (NDV) causes serious infectious diseases in birds, affecting poultry production. In addition to adverse side effects, almost all conventional drugs targeting viral proteins have drug resistance mutations. This study aimed to evaluate the antiviral activity of green silver nanoparticles using green tea leaf extract as a new strategy to control NDV in ovo. The Log embryo infective dose₅₀ (EID₅₀) virucidal reduction was used to measure the antiviral activity of silver nanoparticles against NDV. The treatment of Vero cells with the silver nanoparticles (AgNPs) at a noncytotoxic concentration significantly therapeutic value by inhibiting NDV entry and reduced viral replication, which led to a great reduction in the viral titer in ovo. In conclusion, silver nanoparticles are effective as a therapeutic antiviral agent against NDV and inhibit microbial resistance by making it difficult for the microbe to adapt.     

Highly atom economical uncatalysed and I2-catalysed silylation of phenols,alcohols and carbohydrates,using HMDS under solvent-free reaction conditions (SFRC)

An uncatalysed silylation of phenols, regardless on the aggregate state and nature of the substituents with 0.55 equiv of HMDS under solvent-free reaction conditions (SFRC) at room temperature is reported. Sterically hindered phenols, carbohydrates and most of the alcohols additionally required a catalytic amount (up to 2 mol %) of iodine. The reaction protocol is very simple; obtaining a pure product, particularly of uncatalysed reactions, was frequently a completely solvent-free process.     

Thermodynamic study of three pharmacologically significant drugs: Density,viscosity, and refractive index measurements at different temperatures

Measurements of density, viscosity, and refractive index of three pharmacologically significant drugs, i.e. diclofenac sodium, cetrizine, and doxycycline have been carried in aqueous medium at T = (293.15 to 313.15) K. An automated vibrating-tube densimeter, viscometer, and refractometer are used in a concentration range from (7.5) · 10^?3 to 25 · 10^?3) mol · kg^?1. The precise density results are used to evaluate the apparent molar volume, partial molar volume, thermal expansion coefficient, partial molar expansivity, and the Hepler’s constant. Viscosity results are used to calculate the Jones–Dole viscosity B-coefficient, free energy of activation of the solute and solvent, activation enthalpy, and activation entropy. The molar refractive indices of the drug solutions can be employed to calculate molar refraction. It is inferred from these results that the above mentioned drugs act as structure-making compounds due to hydrophobic hydration of the molecules in the drugs.     

Measurement and correlation of antifungal drugs solubility in pure supercritical CO2 using semiempirical models

In the present study the solubilities of two antifungal drugs of ketoconazole and clotrimazole in supercritical carbon dioxide were measured using a simple static method. The experimental data were measured at (308 to 348) K, over the pressure range of (12.2 to 35.5) MPa. The mole fraction solubilities ranged from 0.2 · 10^?6 to 17.45 · 10^?5. In this study five density based models were used to calculate the solubility of drugs in supercritical carbon dioxide. The density based models are Chrastil, modified Chrastil, Bartle, modified Bartle and Mendez-Santiago and Teja (M–T). Interaction parameters for the studied models were obtained and the percentage of average absolute relative deviation (AARD%) in each calculation was displayed. The correlation results showed good agreement with the experimental data. A comparison among the five models revealed that the Bartle and its modified models gave much better correlations of the solubility data with an average absolute relative deviation (AARD%) ranging from 4.8% to 6.2% and from 4.5% to 6.3% for ketoconazole and clotrimazole, respectively. Using the correlation results, the heat of drug–CO₂ solvation and that of drug vaporization was separately approximated in the range of (?22.1 to ?26.4 and 88.3 to 125.9) kJ · mol^?1.     

Influence of the structure of medium-sized aromatic precursors on the reactivity of their dications towards rare gases

The gas-phase reactivity of dications generated by dissociative electron ionization of several aromatic C_mH_nN_o precursors with 4 ≤ m ≤ 13, 4 ≤ n ≤ 21, and 0 ≤ o ≤ 2 with rare gases is investigated. Whereas most of these reactions lead to monocations via simple electron transfer, proton transfer, or Coulomb explosion, the formation of organo rare-gas dications is observed in a few cases. Specifically, dications generated from 2,4,6-trimethylpyridine react with krypton and xenon to form organo rare-gas species as major products and under maintenance of the two-fold positive charge. Such a reactivity is not observed in the presence of lighter rare gases. The formation of organo rare-gas dications are also observed for dications generated from 3-vinylpyridine, N,N-dimethylaniline, isopropylbenzene, and 4-ethyltoluene as neutral precursors. In some cases, isomeric dications are characterized by very different reactivity toward rare gases, suggesting that the structure of the precursors is crucial and that electron ionization does not lead to a total scrambling of the structures of the doubly charged ions obtained.     

DNA binding of benzophenanthridine compounds sanguinarine versus ethidium: Comparative binding and thermodynamic profile of intercalation

There is compelling evidence that cellular DNA is the target of many small molecule anticancer agents. Consequently, elucidation of the molecular nature governing the interaction of small molecules to DNA is paramount to the progression of the rational drug design strategies. In this study, we have compared the binding and thermodynamic aspects of two known DNA binding agents, ethidium and sanguinarine with calf thymus DNA. The study revealed non-cooperative binding phenomena for both the drugs to DNA with an affinity similar for ethidium and sanguinarine as observed from different techniques. The binding phenomena analyzed from isothermal titration calorimetry showed exothermic binding for both compounds that was favoured by negative enthalpy and positive entropy changes typical of intercalative binding. The binding of both the drugs was further characterized by strong stabilization of DNA against thermal strand separation in optical melting as well as differential scanning calorimetry studies. The data of the salt dependence of binding of sanguinarine and ethidium from the plot of log K versus log [Na⁺] revealed a slope of ?0.711 and ?0.875, respectively, consistent with the values predicted by the theories for the binding of monovalent cations and the binding free energy has been analyzed for contributions from polyelectrolytic and non-polyelectrolytic forces. The salt dependence of the binding was also evident from the conformational changes in the circular dichroism where both extrinsic and induced changes were lowered on increasing the salt concentration. The heat capacity changes obtained from temperature dependence of enthalpy change gave values of (?590 and ?670) J · mol^?1 · K^?1, respectively for the binding of sanguinarine and ethidium to DNA. Overall the DNA binding of ethidium was slightly more favoured over sanguinarine.     

Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh₂)₂N(R) (R = ⁱPr, H, Ph and –CH₂–C₆H₄–CHCH₂) complexes at 40 °C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = ⁱPr > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile “copper–olefin” complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper–phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism.     

Quantitative aspects of recognition of the antibiotic drug oxytetracycline by bovine serum albumin: Calorimetric and spectroscopic studies

A quantitative understanding of the mode of interaction of drugs with target proteins provides a guide for the synthesis of new drug molecules. The binding of the antibiotic drug oxytetracycline with serum albumin has been studied by a combination of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), steady-state and time-resolved fluorescence spectroscopy, and circular dichroism spectroscopy. The values of the binding constant (K), enthalpy change (ΔH), entropy (ΔS), and stoichiometry of binding have been determined along with the associated conformational changes in the protein. Oxytetracycline binds to bovine serum albumin with a 1:1 stoichiometry and with a weakly temperature dependent association constant of 1.8 · 10⁴ at T = 298.15 K. The effect of ionic strength, tetrabutylammonium bromide, and sucrose on the thermodynamic parameters obtained from ITC and DSC measurements indicate involvement of predominantly ionic and hydrophobic interactions with a minor hydrogen bonding contribution in the drug-protein complexation. The DSC results on the binding of oxytetracycline with bovine serum albumin in the absence and presence of these additives provide quantitative information on the effect of drugs on the stability of bovine serum albumin, and suggest preferential complexation of one of the domains of the protein. The results further indicate that the drug occupies binding site II on bovine serum albumin.     

Al(OTf)3 as a new efficient catalyst for the direct nucleophilic substitution of ferrocenyl alcohol substrates. Convenient preparation of ferrocenyl-PEG compounds

The use of Al(OTf)₃ as a new efficient catalyst for the direct nucleophilic substitution of the hydroxy group of ferrocenyl alcohols is described. This catalyst, originally developed for the mono-substitution of ethylene glycol nucleophiles of different length has shown a high activity with other carbon-, nitrogen-, and sulfur-based nucleophiles. In all the studied cases, no more than 1 mol % of catalyst was needed to allow fast and clean reactions.     

In vitro evaluation of Radachlorin® sensitizer for photodynamic therapy

This paper reports the evaluation of a new photosensitizer, Radachlorin® in comparison with one of its well known components but used solely, Chlorin e₆. The photodynamic properties and cell uptake and localisation of the two drugs were compared. In vitro studies were conducted on human adenocarcinoma cells (HT29) and lung carcinoma cell line (A549). Both dyes showed an absorption maximum between 640 and 650 nm, but those absorption peaks are enhanced by interactions with serum, with a shifted maximum at 661 and 664 nm, and much higher absorbance. As Radachlorin® is constituted of different products and as photoreactivity is dependent on absorbed light energy, we chose to adapt concentrations so that both drugs had the same absorption at the irradiation wavelength (664 nm) for photoreactivity tests, and express concentrations in optical density at 664 nm. The capacity of the two drugs to generate Reactive Oxygen Species was identical, but on HT29 cells, Radachlorin® reaches its optimal LD50 sooner than Chlorin e₆. Radachlorin® LD50 on HT29 cells was 0.0251 OD_664nm after 2 h and 0.0672 OD_664nm for Chlorin e₆ for a 20 J cm^?2 irradiation. Radachlorin® gave very similar results on A549 cells, LD50 being 0.05 for 5 J irradiation, and 0.026 for 10 and 20 J cm^?2. Pharmacokinetics using fluorescence showed that, even if Radachlorin® quickly crossed HT29 (a human colonic cancer line) cell membrane, cellular distribution evolved from a diffuse cytoplasmic repartition 1 hour after Radachlorin® addition to a delimited localisation into organelles all around the nucleus. Radachlorin® intracellular fluorescence decreased after 4 h, whereas we did not observe a decrease of Chlorin e₆ intracellular fluorescence for times up to 24 h. In both case, a quick decline was observed as soon as the culture medium was replaced with a drug-free one. Radachlorin® appears to be an excellent photosensitizer, with similar phototoxicity to Chlorin e₆ on cell cultures, but with quicker kinetics, which could be an improvement if confirmed on further in vivo studies.     

Self-microemulsifying and microemulsion systems for transdermal delivery of indomethacin: Effect of phase transition

This study investigated the transdermal delivery of indomethacin (model drug) from self-microemulsifying system, microemulsions and their phase transition systems. The study selected five formulations with fixed surfactant–oil ratio and increasing water content. These included a water free self-microemulsifying drug delivery system (SMEDDS), microemulsions containing water at 5% (w/w) (ME 5%) or at 10% (w/w) (ME 10%), a liquid crystalline formulation containing water at 30% (w/w) (LC) and coarse emulsion containing water at 80% (w/w) (EM). To clarify the results the study evaluated a microemulsion containing 10% (w/w) of receptor fluid (30%, v/v ethanol in phosphate buffered saline, PBS) (MEEB 10%) and a supersaturated system of ME 10% (MESS 10%). The viscosity increased with increasing water content up to certain limit above which the viscosity started to reduce. These formulations increased the transdermal drug flux compared to saturated drug solution in PBS (control) with formulation being ranked as SMEDDS > MEEB 10% ≈ ME 10% ≈ ME 5% > LC > EM > control. SMEDDS produced the longest lag time. The MESS 10% produced a flux value similar to that of SMEDDS but with shorter lag time suggesting transformation of SMEDDS into microemulsion after topical application with possible supersaturation. These systems can provide the formula with high flexibility in selecting the optimum viscosity as the tested preparations were able to enhance transdermal delivery in the range between SMEDDS, ME and the LC preparations with some enhancing ability for the EM.     

Role of laser pre-pulse wavelength and inter-pulse delay on signal enhancement in collinear double-pulse laser-induced breakdown spectroscopy

Dual-pulse (DP) laser-induced breakdown spectroscopy (LIBS) provides significant improvement in signal intensity as compared to conventional single-pulse LIBS. We investigated collinear DPLIBS experimental performance using various laser wavelength combinations employing 1064 nm, 532 nm, and 266 nm Nd:YAG lasers. In particular, the role of the pre-pulse laser wavelength, inter-pulse delay times, and energies of the reheating pulses on LIBS sensitivity improvements is studied. Wavelengths of 1064 nm, 532 nm, and 266 nm pulses were used for generating pre-pulse plasma while 1064 nm pulse was used for reheating the pre-formed plasma generated by the pre-pulse. Significant emission intensity enhancement is noticed for all reheated plasma regardless of the pre-pulse excitation beam wavelength compared to single pulse LIBS. A dual peak in signal enhancement was observed for different inter-pulse delays, especially for 1064:1064 nm combinations, which is explained based on temperature measurement and shockwave expansion phenomenon. Our results also show that 266 nm:1064 nm combination provided maximum absolute signal intensity as compared to 1064 nm:1064 nm or 532 nm:1064 nm.     

Changes in Secondary Metabolite Contents Following Crude Drug Preparation

Crude drug is commonly prepared by directly drying of freshly harvested plant organ or after slicing. These processes may decrease or maintain the content of the desired metabolites presence in the crude drug. Plant rhizome can be directly sliced followed by drying or after storage at certain period. Certain rhizome can maintain the secondary metabolites after being stored for three months (12 weeks), while others decreased just after being stored for two weeks. Drying process can be performed under the sun or in an air circulated oven with temperature not higher than 60 °C. Phenolic content of crude drugs on the other hand is the lowest if it is dried at 60 °C. Drying at 40 °C, 80 °C and 100 °C produce crude drug with higher phenolic content compared to those dried at 60 °C. This may associated with the activity of peroxidase that has optimal activity at 60° C. At above 60 °C, the activity of peroxidase may decrease due to the degradation of the enzyme. Moist treatment of fresh material may increase the content of the secondary metabolites. Boiling of Cosmos caudatus leaves increased the content of the flavonoid glycoside. However, part of the flavonoid was presence in the aliquot that hamper further step of crude drug preparation. Steaming of potato peels increased the chlorogenic acid content. From these observations, steaming can be considered as one of pre-treatment steps in the preparation of crude drugs prior drying process. The increase of flavonoid glycoside in Cosmos caudatus leaves upon boiling has been confirmed not due to the increase the extractability of the flavonoid. The increase of key enzyme activity that involved in the biosynthetic pathway upon moist-heat treatment need to be further studied     

Study of immobilized candida rugosa lipase for biodiesel fuel production from palm oil by flow microcalorimetry

Enzymatic transesterification of palm oil with methanol and ethanol was studied. Of the four lipases that were tested in the initial screening, lipase Candida Rugosa (CR) resulted in the highest yield of mono alkyl esters. Lipase CR was further investigated in immobilized form within an activated carbon as support. The activated carbon was prepared by activation physical. Using the immobilized lipase CR, the effects of water and alcohol concentration, enzyme loading and enzyme thermal stability in the transesterification reaction were investigated. The optimal conditions for processing 50 g of palm oil were: 37 °C, 1:14.5 oil/methanol molar ratio, 1.0 g water and 500 mg lipase for the reactions with methanol, 35 °C, 1:15.0 oil/ethanol molar ratio, 1.0 g water, 500 mg lipase for the reactions with ethanol, and 35 °C, 1:10.0 oil/n-butanol molar ratio, 1.0 g water, 500 mg lipase for the reactions with ethanol. Subject to the optimal conditions, methyl and ethyl esters formation of 70 and 85 mol% in 1 h of reaction were obtained for the immobilized enzyme reactions. The flow microcalorimetry is an important and novel techniques is used in evaluation of biodiesel production.     

Gold sputtered electrode surfaces enhance direct electron transfer reactions of human cytochrome P450s

We immobilized human cytochrome P450 (CYP), a membrane-bound enzyme, onto both smooth and nanostructured surfaces of gold electrodes via a naphthalene thiolate monolayer film. Rapid electron transfer of CYP with an electrode as a redox partner took place when the enzyme was immobilized onto an electrode surface with nanostructures. This structure was easily prepared by conventional sputtering techniques. A well-defined pair of peaks was observed at ? 0.175 V (vs. SHE) with the largest heterogeneous electron transfer rate constant of 340 s^? 1 for human CYP. The positive redox potential shift of 45 mV upon drug (testosterone) binding was clearly detected, which corresponded to a change in the spin states of heme iron in CYP. The present study showed that gold sputtered surfaces are very useful for direct electron transfer reactions of human CYP isoforms.     

Insertion of the p-complex structure of silylenoid H2SiLiF into X–H bonds (X = C,Si, N,P, O,S, and F)

The insertion reactions of the p-complex structure (A) of silylenoid H₂SiLiF into XH_n molecules (X = C, Si, N, P, O, S, and F; n = 1–4) have been studied by ab initio calculations at the G3(MP2) level. The results indicate that the insertion reactions of A into X–H bonds proceed via three reaction paths, I, II, and III, forming the same products, substituted silanes H₃SiXH_n − 1 with dissociation of LiF, respectively, and all insertion reactions are exothermic. All the seven X–H bonds can undergo insertion reactions with A via path I and II, but only four of them, C–H, Si–H, P–H, and S–H, undergo insertion reactions via path III. The following conclusions emerge from this work: (i) the X–H insertion reactions of A occur in a concerted manner via a three-membered ring transition state; (ii) for path I and II, the stabilization energies of the A–XH_n complexes decrease in the order HF > H₂O > H₂S > NH₃ > SiH₄ > CH₄; (iii) for path I and II, the greater the atomic number of heteroatom (X) in a given row, the easier the insertion reaction of XH_n hydrides and the larger the exothermicity, and for the second-row hydrides, the reaction barriers are lower than for the first-row hydrides; (iv) The barriers of path I are lowest in those of three pathways with the exception of A + SiH₄ system, which barrier of path III is lowest. Moreover, the present study demonstrates that both electronic and steric effects play major roles in the course of insertion reactions of A into X–H bonds.     

Development and validation of a stability-indicating LC method for simultaneous determination of related compounds of guaifenesin,terbutaline sulfate and ambroxol HCl in cough syrup formulation

A new liquid chromatographic method has been developed and validated for the determination of terbutaline sulfate (TLS), guaifenesin (GFN) and ambroxol HCl (AML), for its potential impurities in drug substances and drug products. Efficient chromatographic separation was achieved on X-Terra RP-18 column with a simple mobile phase combination containing a gradient mixture of solvents A and B at a flow rate of 1.0 mL min⁻¹ and quantitation was carried out using ultraviolet detection at 222 nm with column temperature of 35 °C. The resolution between TLS, GFN and AML, its associated impurities was found to be greater than 1.5. Regression analysis shows an r value (correlation coefficient) greater than 0.998. This method was capable to detect all the process impurities of TLS, GFN and AML, at a level below 0.015% with respect to a test concentration of 0.125, 5.0 and 1.5 mg mL⁻¹, respectively. The % RSD for the inter-day and intra-day precisions for all the impurities of TLS, GFN and AML were found to be less than 3.0. The method has shown good, consistent recoveries. The drugs were subjected to stress conditions of acid, base, water hydrolysis, oxidation, photolysis and thermal degradation, as prescribed by international conference on harmonization (ICH).