Experimental mole fraction solubilities of several carboxylic acids (2-methoxybenzoic acid, 4-methoxybenzoic acid, 4-nitrobenzoic acid, 4-chloro-3-nitrobenzoic acid, 2-chloro-5-nitrobenzoic acid,2-methylbenzoic acid and ibuprofen) and 9-fluorenone, thianthrene and xanthene were measured in a wide range of solvents of varying polarity and hydrogen-bonding characteristics. Results of these measurements were used to calculate gas-to-organic solvent and water-to-organic solvent solubility ratios, which were then substituted into known Abraham process partitioning correlations. The molecular solute descriptors that were obtained as the result of these computations described the measured solubility data to within an average absolute deviation of 0.2 log units. The calculated solute descriptors also enable one to estimate many chemically, biologically and pharmaceutically important properties for the ten solutes studied using published mathematical correlations.

The transdermal delivery route has become a popular alternative to more conventional routes, such as oral administration, but has not yet reached its full potential (Prausnitz & Langer, 2008:1261). Although the transdermal route proves to have several advantages over the conventional route, the greatest challenge is to overcome the effective barrier of the skin (Jepps et al., 2012:153). The permeation of the active pharmaceutical ingredient (API) through the skin is a complex, multi-step process and therefore predicting the permeability of the API is difficult (Jepps et al., 2012:153; Williams, 2003:30). Various approaches have been developed to overcome the skin barrier and it is recognised that the nature of the vehicle in which the API is applied plays a significant role in promoting transdermal delivery (Foldvari, 2000:417). It is important to consider the fate of the formulation ingredients and the API after application and how this changes the composition of the formulation on the skin when developing a vehicle for transdermal delivery (Lane et al., 2012:496; Otto et al., 2009:2). Wiechers (2012) proposed the Skin Delivery Gap (SDG) as an indicator for the permeability of an API. An API with a SDG < 1 will readily permeate the skin, whilst an SDG > 1 indicates a more complex delivery system is required. The partitioning of the API between the skin and the formulation is influenced by the formulation and by altering the formulation properties it is possible to manipulate the transdermal delivery of the API. The relative polarity index (RPI), based on the octanol-water partition coefficient (log P) of the stratum corneum, formulation and the API, was initially developed by Wiechers as a tool for developing formulations with an optimal polarity, to ensure the transdermal delivery of at least 50% of the API (Lane et al., 2012:498; Wiechers, 2008:94; Wiechers et al., 2004:174). The use of log P as an indicator of polarity was considered impractical by Hansen (2013) and acknowledged by both Wiechers and Abbott, who consequently developed the Formulating for Efficacy™ (FFE™) software which uses Hansen solubility parameters (HSP) instead of log P to indicate polarity (Hansen, 2013). The FFE™ calculates HSP distances, known as gaps, between the skin, API and the formulation to indicate the solubility of the different components in each other. A smaller HSP gap indicates a high solubility. The FFE™ enables the formulator to develop a formulation with a good balance between the active-formulation gap (AFG) and the skin-formulation gap (SFG) to ensure sufficient diffusion of the API into the skin. The FFE™ software was used to develop formulations containing 1.5% atropine as a model drug. Formulations of different polarity (optimised towards the stratum corneum, more hydrophilic and more lipophilic) were developed to determine the effect of the polarity of the formulation and the relevant HSP gaps on the transdermal delivery of the API. The same formulations were utilised for atropine sulphate to determine the effect the salt form has on the transdermal delivery of the API compared to the base compound. The log P and octanol-buffer partition coefficient (log D) of both atropine and atropine sulphate were determined. Log D is a more reliable indicator of distribution compared to log P, since, it considers the degree of ionisation of the API (Ashford, 2007:294). The log P and log D of atropine (0.22 and -1.26) and atropine sulphate (-1.32 and -1.23) both predicted poor skin penetration (Brown et al., 2005:177). The aqueous solubility of atropine (0.9 mg/ml) also predicted limited transdermal delivery, while the solubility of atropine in phosphate buffer solution (PBS pH 7.4) (5.8 mg/ml) indicated favourable permeation (Naik et al., 2000:321). The high degree of ionisation of the API (99.68 %), at pH 7.4, predicts only a small amount will penetrate the skin (Barry, 2007:576). The membrane release study confirmed the API was released from the different formulations and subsequently skin diffusion studies were conducted, followed by tape stripping after 12 h, to determine which formulation resulted in the highest transdermal delivery of the API. The atropine hydrophilic formulation released the highest percentage of API after 6 h (13.930%). This was explained by the low affinity the lipophilic atropine has towards the hydrophilic formulation (Otto et al., 2009:9). The highest percentage transdermal delivery (0.065%) was observed with the lipophilic formulation containing atropine. The higher SFG compared to the AFG of the lipophilic formulation initially predicted poor transdermal delivery, but when considering the HSP profile and molar volume of the different ingredients, it was observed the dimethyl isosorbide (DMI) penetrated and provided a desirable environment for the API in the skin. The residual formulation (containing less DMI and more polyethylene glycol 400 (PEG 8) and liquid paraffin) was less desirable for the API and was therefore forced out of the formulation (Abbott, 2012:219). Both these factors contributed to the high transdermal delivery of atropine from the lipophilic formulation. The atropine sulphate hydrophilic formulation had the highest percentage in the stratum corneum-epidermis (0.29 μg/ml) and the hydrophilic formulation of both atropine and atropine sulphate had the highest concentration in the epidermis-dermis (both 0.55 μg/ml). The hydrophilic formulations had the lowest driving force provided by the AFG and the only driving force for the API to leave the formulation was the concentration gradient. These formulations had the lowest transdermal delivery which indicates the API had not fully traversed through the skin after 12 h. According to Wiechers, a minimised SFG would indicate the formulation is optimised towards the stratum corneum and should essentially deliver the highest percentage of API through the skin. The results obtained are contrary to this belief and it is concluded that the total HSP profile and the molar volume of the formulation and the API should be considered when developing a formulation with optimal transdermal delivery rather than just the SFG. / MSc (Pharmaceutics), North-West University, Potchefstroom Campus, 2015

The transdermal delivery route has become a popular alternative to more conventional routes, such as oral administration, but has not yet reached its full potential (Prausnitz & Langer, 2008:1261). Although the transdermal route proves to have several advantages over the conventional route, the greatest challenge is to overcome the effective barrier of the skin (Jepps et al., 2012:153). The permeation of the active pharmaceutical ingredient (API) through the skin is a complex, multi-step process and therefore predicting the permeability of the API is difficult (Jepps et al., 2012:153; Williams, 2003:30). Various approaches have been developed to overcome the skin barrier and it is recognised that the nature of the vehicle in which the API is applied plays a significant role in promoting transdermal delivery (Foldvari, 2000:417). It is important to consider the fate of the formulation ingredients and the API after application and how this changes the composition of the formulation on the skin when developing a vehicle for transdermal delivery (Lane et al., 2012:496; Otto et al., 2009:2). Wiechers (2012) proposed the Skin Delivery Gap (SDG) as an indicator for the permeability of an API. An API with a SDG < 1 will readily permeate the skin, whilst an SDG > 1 indicates a more complex delivery system is required. The partitioning of the API between the skin and the formulation is influenced by the formulation and by altering the formulation properties it is possible to manipulate the transdermal delivery of the API. The relative polarity index (RPI), based on the octanol-water partition coefficient (log P) of the stratum corneum, formulation and the API, was initially developed by Wiechers as a tool for developing formulations with an optimal polarity, to ensure the transdermal delivery of at least 50% of the API (Lane et al., 2012:498; Wiechers, 2008:94; Wiechers et al., 2004:174). The use of log P as an indicator of polarity was considered impractical by Hansen (2013) and acknowledged by both Wiechers and Abbott, who consequently developed the Formulating for Efficacy™ (FFE™) software which uses Hansen solubility parameters (HSP) instead of log P to indicate polarity (Hansen, 2013). The FFE™ calculates HSP distances, known as gaps, between the skin, API and the formulation to indicate the solubility of the different components in each other. A smaller HSP gap indicates a high solubility. The FFE™ enables the formulator to develop a formulation with a good balance between the active-formulation gap (AFG) and the skin-formulation gap (SFG) to ensure sufficient diffusion of the API into the skin. The FFE™ software was used to develop formulations containing 1.5% atropine as a model drug. Formulations of different polarity (optimised towards the stratum corneum, more hydrophilic and more lipophilic) were developed to determine the effect of the polarity of the formulation and the relevant HSP gaps on the transdermal delivery of the API. The same formulations were utilised for atropine sulphate to determine the effect the salt form has on the transdermal delivery of the API compared to the base compound. The log P and octanol-buffer partition coefficient (log D) of both atropine and atropine sulphate were determined. Log D is a more reliable indicator of distribution compared to log P, since, it considers the degree of ionisation of the API (Ashford, 2007:294). The log P and log D of atropine (0.22 and -1.26) and atropine sulphate (-1.32 and -1.23) both predicted poor skin penetration (Brown et al., 2005:177). The aqueous solubility of atropine (0.9 mg/ml) also predicted limited transdermal delivery, while the solubility of atropine in phosphate buffer solution (PBS pH 7.4) (5.8 mg/ml) indicated favourable permeation (Naik et al., 2000:321). The high degree of ionisation of the API (99.68 %), at pH 7.4, predicts only a small amount will penetrate the skin (Barry, 2007:576). The membrane release study confirmed the API was released from the different formulations and subsequently skin diffusion studies were conducted, followed by tape stripping after 12 h, to determine which formulation resulted in the highest transdermal delivery of the API. The atropine hydrophilic formulation released the highest percentage of API after 6 h (13.930%). This was explained by the low affinity the lipophilic atropine has towards the hydrophilic formulation (Otto et al., 2009:9). The highest percentage transdermal delivery (0.065%) was observed with the lipophilic formulation containing atropine. The higher SFG compared to the AFG of the lipophilic formulation initially predicted poor transdermal delivery, but when considering the HSP profile and molar volume of the different ingredients, it was observed the dimethyl isosorbide (DMI) penetrated and provided a desirable environment for the API in the skin. The residual formulation (containing less DMI and more polyethylene glycol 400 (PEG 8) and liquid paraffin) was less desirable for the API and was therefore forced out of the formulation (Abbott, 2012:219). Both these factors contributed to the high transdermal delivery of atropine from the lipophilic formulation. The atropine sulphate hydrophilic formulation had the highest percentage in the stratum corneum-epidermis (0.29 μg/ml) and the hydrophilic formulation of both atropine and atropine sulphate had the highest concentration in the epidermis-dermis (both 0.55 μg/ml). The hydrophilic formulations had the lowest driving force provided by the AFG and the only driving force for the API to leave the formulation was the concentration gradient. These formulations had the lowest transdermal delivery which indicates the API had not fully traversed through the skin after 12 h. According to Wiechers, a minimised SFG would indicate the formulation is optimised towards the stratum corneum and should essentially deliver the highest percentage of API through the skin. The results obtained are contrary to this belief and it is concluded that the total HSP profile and the molar volume of the formulation and the API should be considered when developing a formulation with optimal transdermal delivery rather than just the SFG. / MSc (Pharmaceutics), North-West University, Potchefstroom Campus, 2015

The solubility of diuron was determined in binary and ternary cosolvent-water systems. The binary systems were composed of a completely miscible organic solvent (CMOS) and water while the ternary systems incorporate partially miscible organic solvents (PMOS) into the binary systems. Due to the low aqueous solubilities of trichloroethylene and toluene, the PMOS's do not behave as cosolvents and they do not play an important role in altering solubility.

Milling and co-milling are well known techniques that have potential to enhance the solubility and/or dissolution rate of poorly soluble drugs. There are broadly two aims for this project. The first was to develop an understanding of how individual and combination of techniques may be used to explore the impact of milling on particle characteristics (including phase changes, fractures and change in particle size) as a function of milling time/speed, for a range of single powder materials. Anhydrous (lactose, sucrose), monohydrate (lactose) and dihydrate (trehalose) excipients and a poorly soluble drug (ibuprofen), were chosen as model substrates. Each material was micronized by ball-milling (for various time durations and milling speeds) and then characterized by a range of techniques, specifically, SEM, DSC, TGA, THz and dielectric spectroscopy. The second aim of the project was to investigate the impact of milling and co-milling on the solubility and dissolution rate of ibuprofen after co-milling with a variety of excipients (polymer and surfactants). The principle findings of this programme of work can be summarized as follows: i) ball milling of lactose monohydrate produces nano-structured systems with a mixture of damaged crystals and amorphous phase, that can be characterised by dielectric relaxation spectroscopy (DRS), ii) THz spectroscopy provides estimates for residual crystallinity in lactose monohydrate that were much lower than the estimates from the thermal techniques. Such estimates of residual crystallinity are considered to be more reliable given the fact that the spectroscopic measurement characterizes the material in its native state, whereas thermal techniques require a heating process, which tend to induce de-vitrification and mutarotation of lactose. In case of anhydrous materials, while there was agreement between thermal and THz techniques at long milling times, it was shown that the THz technique was susceptible to moisture absorption and crystallization at short milling times, iii) In the molecular dynamics of milled sugars studied by DRS, the structural relaxation is not visible in the vicinity of glass transition, however the secondary relaxation (β) process is equally capable and provided molecular dynamics in term of activation energy changes. The activation energies of beta process of both lactose and sucrose are least affected by milling time, but the higher activation energies for sucrose as compared with lactose show that sucrose has lower propensity to re-crystallize than lactose during post milling storage, iv) Ibuprofen can be assayed by UV-method in the presence of interfering (in absorption) substance by applying multivariate method involving the calculation of concentration factors and v) Co-milling with soluplus has increased the in the solubility of ibuprofen by ~20% and dissolution rate ~50% in 30 min, while these values are ~5% and 30%, respectively in case of co-milling with HPMC.

Many properties of polymers can be affected by dissolving gases and supercritical fluids at high temperatures and pressures. Solubility and diffusivity are crucial parameters in polymer processing applications that indicates the content of gases and supercritical fluids in a polymer. Hence, different devices for measuring solubility and diffusivity have been researched, but most of the devices used today are very complex, expensive, and requires long experiment time. In this final thesis, the feasibility of fiber optic sensors as measurement devices for solubility and diffusivity of gas/SCF in polymers have been investigated. Many of the polymers used in polymer processing have high refractive index, from 1.40 to 1.60. However, most of the refractive index sensors based on fiber optics only operate in refractive index ranges of 1 to 1.44 because once the surrounding refractive index becomes greater than that of cladding, the total internal reflection is lost and only small portion of the light propagation occurs. This final thesis first reviews the current methods to measure solubility and diffusivity of gases and supercritical fluids in polymers. In addition, different types of fiber optics sensors used for sensing the refractive index are reviewed. Then, the thesis presents cost efficient, but effective fiber optic refractive index sensors, which are the silver nanoparticle coated LPG sensor, uncoated PCF MZI sensor, silver nanoparticle PCF MZI sensor, and the transmission intensity based gap sensor, to sense the surrounding refractive index in the region greater than the cladding, for the future application of solubility and diffusivity measurement. Moreover, future works that would help in sensing solubility and diffusivity of gas in polymers are also proposed. / Graduate

No description available.

Oral drug administration remains the most popular route of drug delivery. Absorption of the dissolved drug through the intestinal epithelial membrane is a prerequisite to systemic bioavailability and drug efficacy. In efforts to reduce the long lead times, attrition rates, and costs of drug discovery and development, computational models have been developed to predict the membrane permeability and absorption efficiency of a dosed drug. Many models utilize various molecular descriptors to correlate with in vitro permeability or human intestinal absorption data. It is widely accepted that the two most significant physicochemical properties that control a compound's passive transport process are its aqueous solubility and lipophilicity characteristics.This work will discuss the theoretical background of passive transport, a number of computational models developed to predict in vitro permeability, other models that predict human fraction of dose absorbed, and predicting absorption efficiency relative to a maximum dose. A newly developed prediction method is also presented, that reveals an interesting relationship between fraction absorbed and the melting point of the drug.

No description available.

Gasoline spills are sources of groundwater contamination. In the event of a spill, timely remediation efforts can advert most of the potential groundwater contamination due to the immiscibility of gasoline in water. Ethanol functions as a cosolvent that can increase the solubility of gasoline in water. Therefore, the risk of groundwater contamination in the event of a fuel spill increases as the ethanol content in automobile fuels increases. This study examines the effect fuel spill size and ethanol content has on the quantities of toluene, ethylbenzene, m-xylene and o-xylene (TEMO) that dissolve into the aqueous phase at equilibrium. Laboratory experiments were preformed to determine the mass fractions of TEMO in waters that were in contact with various volumes of gasoline and ethanol. UNIFAC is a model capable of predicting the concentrations of TEMO in the aqueous phase of a gasoline-ethanol-water system at equilibrium. In this study, the generalized UNIFAC-LLE method, designed for chemical engineering applications, was used to model the laboratory experiments. New UNIFAC-LLE parameters were developed to improve the model's accuracy in predicting the solubilities of aromatic species in ethanol-water mixtures. The new UNIFAC-LLE parameters were also used to model the laboratory experiments. The modeled results were compared to the analogous laboratory experiments. The UNIFAC-LLE parameters developed in this study improved the model's accuracy in predicting the solubilities of TEMO when the aqueous ethanol mass fraction was between 0.114 and 0.431.