Predicting plasticization efficiency from three-dimensional molecular structure of a polymer plasticizer

Spectroscopic characterization of radicals formed by hydrogen-atom abstraction from γ-valerolactone and γ-butyrolactone

γ-valerolactone (GVL) and its unmethylated counterpart, γ-butyrolactone (GBL), are important compounds with a wide range of potential uses. For example, GVL is proposed as an ideal alternative renewable energy source, while GBL can be utilized as an electrolyte. Understanding the combustion mechanisms of these compounds is crucial for optimizing their use as energy sources and monitoring the products formed during combustion. During pyrolysis, reactions with hydrogen atoms play a key role. Although the reactions of lactones with hydrogen atoms have been studied at higher temperatures using theoretical and computational methods, the spectroscopic data for the radicals produced during these reactions remain incomplete. Such data could, however, be valuable for tracking radical mechanisms. This study investigated these reactions at 3.1 K using the para-H2 matrix-isolation technique. The conditions provided by this method are particularly well-suited for studying radicals, in contrast to the conditions used in pyrolysis studies. IR spectroscopy was employed to monitor the reactions, enabling us to observe the vibrational spectra of the resulting radicals. These spectroscopic data could offer valuable insights for further exploring the combustion processes of GVL and GBL.

Ceftriaxone-Loaded Polymeric Microneedles, Dressings, and Microfibers for Wound Treatment

The objective of this study was to create polymeric dressings, microfibers, and microneedles (MN) loaded with ceftriaxone, using PMVA (Poly (Methyl vinyl ether-alt-maleic acid), Kollicoat^® 100P, and Kollicoat^® Protect as polymers to treat diabetic wounds and accelerate their recovery. These formulations were optimized through a series of experiments and were subsequently subjected to physicochemical tests. The results of the characterization of the dressings, microfibers, and microneedles (PMVA and 100P) were, respectively, a bioadhesion of 281.34, 720, 720, 2487, and 510.5 gf; a post-humectation bioadhesion of 186.34, 831.5, 2380, and 630.5 gf, tear strength of 2200, 1233, 1562, and 385 gf, erythema of 358, 8.4, 227, and 188; transepidermal water loss (TEWL) of 2.6, 4.7, 1.9, and 5.2 g/h·m²; hydration of 76.1, 89.9, 73.5, and 83.5%; pH of 4.85, 5.40, 5.85, and 4.85; and drug release (Peppas kinetics release) of n: 0.53, n: 0.62, n: 0.62, and n: 0.66). In vitro studies were performed on Franz-type diffusion cells and indicated flux of 57.1, 145.4, 718.7, and 2.7 µg/cm²; permeation coefficient (Kp) of 13.2, 19.56, 42, and 0.00015 cm²/h; and time lag (t_L) of 6.29, 17.61, 27. 49, and 22.3 h, respectively, in wounded skin. There was no passage of ceftriaxone from dressings and microfibers to healthy skin, but that was not the case for PMVA/100P and Kollicoat^® 100P microneedles, which exhibited flux of 194 and 0.4 µg/cm², Kp of 11.3 and 0.00002 cm²/h, and t_L of 5.2 and 9.7 h, respectively. The healing time of the formulations in vivo (tests carried out using diabetic Wistar rats) was under 14 days. In summary, polymeric dressings, microfibers, and microneedles loaded with ceftriaxone were developed. These formulations have the potential to address the challenges associated with chronic wounds, such as diabetic foot, improving the outcomes.

Structural Characterization of the Plasticizers' Role in Polymer Inclusion Membranes Used for Indium (III) Transport Containing IONQUEST® 801 as Carrier

Polymer inclusion membranes containing cellulose triacetate as support, Ionquest^® 801 ((2–ethylhexyl acid) -mono (2–ethylhexyl) phosphonic ester) as extractant, and 2NPOE (o–nitrophenyl octyl ether) or TBEP (tri (2–butoxyethyl phosphate)) as plasticizers were characterized using several instrumental techniques (Fourier Transform Infrared Spectroscopy (FT–IR), Reflection Infrared Mapping Microscopy (RIMM), Electrochemical Impedance Spectroscopy (EIS), Differential Scanning Calorimetry (DSC)) with the aim of determining physical and chemical parameters (structure, electric resistance, dielectric constant, thickness, components’ distributions, glass transition temperature, stability) that allow a better comprehension of the role that the plasticizer plays in PIMs designed for In(III) transport. In comparison to TBEP, 2NPOE presents less dispersion and affinity in the PIMs, a plasticizer effect at higher content, higher membrane resistance and less permittivity, and a pronounced drop in the glass transition temperature. However, the increase in permittivity with In (III) sorption is more noticeable and, in general, PIMs with 2NPOE present higher permeability values. These facts indicate that In (III) transport is favored in membranes with chemical environment of high polarity and efficiently plasticized. A drawback is the decrease in stability because of the minor affinity among the components in 2NPOE–PIMs.

Plasticization of Polylactide after Solidification: An Effectiveness and Utilization for Correct Interpretation of Thermal Properties

Polylactide/triethyl citrate (PLA/TEC) systems were prepared in two ways by introducing TEC to solidified polymer matrix (SS) and by blending in a molten state (MS) to investigate the effectiveness of the plasticization process after solidification of polylactide. The plasticization processes, independently of way of introducing the TEC into PLA matrix, leads to systems characterized by similar stability, morphology and properties. Some differences in mechanical properties between MS and SS systems result primarily from the difference in the degree of crystallinity/crystal thickness of the PLA matrix itself. Based on the presented results, it was concluded that the plasticization process after solidification of polylactide is an alternative to the conventional method of modification-blending in a molten state. Then, this new approach to plasticization process was utilized for interpretation of thermal properties of PLA and PLA/TEC systems. It turned out that double melting peak observed at DSC thermograms does not result from the melting of a double population of crystals with different lamellar thickness, or the melting of both the α' and α crystalline phase (commonly used explanations in literature), but is associated with the improvement of perfection of crystalline structure of PLA during heating process.

A Strategy for Nonmigrating Highly Plasticized PVC

Nonmigrating highly plasticized PVC was prepared based on a new compound that acts as a plasticizer that was derived from di(2-ethylhexyl) 4-hydrophthalate and chlorinated paraffin-52. The as-prepared PVC has a plasticizing efficiency as high as DOP and its migration is totally suppressed. Unlike other reported methods, this approach increases the interaction between phthalate and PVC to suppress its migration, not simply to enlarge its molecular size (or molecular weight). This methodology is highly versatile for producing the desired non-leaching PVC with a permanent plasticizer effect.

Toward the low actuation temperature of flexible shape memory polymer composites with room temperature deformability via induced plasticizing effect

Room temperature deformable PLA/TPU/PEG blends demostrate superior shape memory properties under low temperature environments due to the induced plasticizing effect.

The use of rheology to elucidate the granulation mechanisms of a miscible and immiscible system during continuous twin-screw melt granulation

Twin-screw hot melt granulation (TS HMG) is a valuable, but still unexplored alternative to granulate temperature and moisture sensitive drugs in a continuous way. Recently, the material behavior of an immiscible drug-binder blend during TS HMG was unraveled by using a rheometer and differential scanning calorimetry (DSC). Additionally, vibrational spectroscopic techniques proved the link between TS HMG and rheology since equal interactions at molecular level did occur in both processes. This allowed to use a rheometer to gain knowledge of the material behavior during hot melt processing of an immiscible drug-binder blend. However, miscibility of a drug-binder formulation and drug-binder interactions appear to influence the rheological properties and, hence conceivably also the granulation mechanism. The aim of this research was to examine if the TS HMG process of a miscible formulation system is comparable with the mechanism of an immiscible system and to evaluate whether rheology still serves as a useful tool to understand and optimize the hot melt granulation (HMG) process. The executed research (thermal analysis, rheological parameters and spectroscopic data) demonstrated the occurrence of a high and broad tan(δ) curve without a loss peak during the rheological temperature ramp which implies a higher material deformability without movement of the softened single polymer chains. Spectroscopic analysis revealed drug-polymer interactions which constrain the polymer to flow independently. As a result, the binder distribution step, which generally follows the immersion step, was hindered. This insight assisted the understanding of the granule properties. Inhomogeneous granules were produced due to large initial nuclei or adhesion of multiple smaller nuclei. Consequently, a higher granulation temperature was required in order to get the binder more homogeneously distributed within the granules.

Development of a vaginal delivery film containing EFdA, a novel anti-HIV nucleoside reverse transcriptase inhibitor

The aim of this work was to develop a fast-dissolving film formulation containing EFdA for potential use as a topical vaginal microbicide for prevention of HIV sexual transmission. Solid state compatibility approaches were used to screen commonly used polymers for formulation development. Factorial design and desirability function were used to investigate the effect of two variables, the ratio of the polymers and the concentration of selected plasticizer on four mechanical responses including tensile strength, elongation at break, toughness and elastic modulus for optimization of the film formulation. Assessments of EFdA-loaded films included physicochemical characteristics, in vitro cytotoxicity, epithelia integrity, ex vivo permeability and bioactivity test. The optimal placebo film was composed of PVA, HPMC E5 and propylene glycol (7:3:3, w/w), and its mechanical characteristics were comparable to those of VCF(®) film (a commercial vaginal film product). Permeability studies using human ectocervical explants showed that there was no significant difference in cumulative permeated amount of EFdA between EFdA film and free EFdA. The results of in vitro cytotoxicity and bioactivity testing showed that 50% cytotoxic concentration (CC50) was several orders of magnitude higher than 50% effective concentration (EC50) of EFdA. Furthermore, epithelial integrity study showed that EFdA-loaded film had a much lower toxicity to HEC-1A cell monolayers as compared to VCF(®). Therefore, EFdA-loaded vaginal film may be considered as a promising vaginal microbicide for HIV prevention.

Towards better process understanding: chemometrics and multivariate measurements in manufacturing of solid dosage forms

The manufacturing of tablets involves many unit operations that possess multivariate and complex characteristics. The interactions between the material characteristics and process related variation are presently not comprehensively analyzed due to univariate detection methods. As a consequence, current best practice to control a typical process is to not allow process-related factors to vary i.e. lock the production parameters. The problem related to the lack of sufficient process understanding is still there: the variation within process and material properties is an intrinsic feature and cannot be compensated for with constant process parameters. Instead, a more comprehensive approach based on the use of multivariate tools for investigating processes should be applied. In the pharmaceutical field these methods are referred to as Process Analytical Technology (PAT) tools that aim to achieve a thorough understanding and control over the production process. PAT includes the frames for measurement as well as data analyzes and controlling for in-depth understanding, leading to more consistent and safer drug products with less batch rejections. In the optimal situation, by applying these techniques, destructive end-product testing could be avoided. In this paper the most prominent multivariate data analysis measuring tools within tablet manufacturing and basic research on operations are reviewed.

Deproteinized natural rubber film forming polymeric solutions for nicotine transdermal delivery

Film forming polymeric solutions were prepared from DNRL blended with MC, PVA, or SAG, together with dibutylphthalate or glycerine used as plasticizers. These formulations were easily prepared by simple mixing. In a preliminary step, in situ films were prepared by solvent evaporation in a Petri-dish. Their mechanical and physicochemical properties were determined. The in vitro release and skin permeation of nicotine dissolved in these blended polymers were investigated by a modified Franz diffusion cell. The formulations had a white milky appearance, and were homogeneous and smooth in texture. Their pH was suitable for usage in skin contact. The mechanical property of in situ films depended on the ingredients but all compatible films were in an amorphous phase. The DNRL/PVA was shown to be the most suitable mixture to form completed films. The in vitro release and skin permeation studies demonstrated a biphasic release that provided an initial rapid release followed by a constant release rate that fitted the Higuchi's model. Nicotine loaded DNRL/PVA series were selected for the stability test for 3 months. These formulations needed to be kept at 4°C in tight fitting containers. In conclusion, film forming polymeric solutions could be developed for transdermal nicotine delivery systems.

The Influence of Different Plasticizers and Polymers on the Mechanical and Thermal Properties, Porosity and Drug Permeability of Free Shellac Films

The effect of triethyl citrate (TEC) and different molecular weights and concentrations of polyethylene glycol (PEG), in addition to the effect of different water-soluble polymers and dispersions at different levels, hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), carbomer 940, polyvinyl alcohol (PVA), ethyl cellulose (EC), on the mechanical and thermal properties, drug permeability, and porosity of free shellac films were investigated. Shellac films were cast from aqueous solutions, and their mechanical properties were studied by tensile test. Thermal analyses were performed using differential scanning calorimetry (DSC). The results showed that the addition of plasticizer caused a decrease in both elastic modulus and glass transition temperature (T(g)) and an increase in elongation at break of free shellac films. This effect was related to the concentrations of plasticizers. Different molecular weights of PEGs have different plasticization mechanisms.Moreover, the incorporation of different amounts of HPMC, MC, or carbomer in free shellac films caused an increase in the flexibility, decrease in T(g), and a marked increase in drug permeability of free shellac films, whereas the addition of PVA caused a decrease in flexibility and drug permeability and an increase in T(g). Addition of EC resulted in a slight decrease of the elasticity and a small decrease in drug permeability. However it does not show a considerable effect on the T(g). In addition, it was found that the drug permeability is directly related to the mechanical properties and T(g) of shellac films.

A QSPR for the plasticization efficiency of polyvinylchloride plasticizers

A simple quantitative structure property relationship (QSPR) for correlating the plasticization efficiency of 25 polyvinylchloride (PVC) plasticizers was obtained using molecular modeling. The plasticizers studied were-aromatic esters (phthalate, terephthalate, benzoate, trimellitate), aliphatic esters (adipate, sebacate, azelate), citrates and a phosphate. The low temperature flex point, Tf, of plasticized polyvinylchloride resins was considered as an indicator of plasticization efficiency. Initially, we attempted to predict plasticization efficiency of PVC plasticizers from physical and structural descriptors derived from the plasticizer molecule alone. However, the correlation of these descriptors with Tf was not very good with R=0.78 and r2=0.613. This implied that the selected descriptors were unable to predict all the interactions between PVC and plasticizer. Hence, to account for these interactions, a model containing two polyvinylchloride (PVC) chain segments along with a plasticizer molecule in a simulation box was constructed, using molecular mechanics. A good QSPR equation correlating physical and structural descriptors derived from the model to Tf of the plasticized resins was obtained with R=0.954 and r2=0.909.

Ketoprofen poly(lactide-co-glycolide) physical interaction

The aim of this work was to provide an understanding of the interaction occurring between ketoprofen and poly(lactic-co-glycolic acid) (PLGA) that leads to polymer plasticization. Experimental glass transition temperature (Tg) values were fitted with the theoretical ones predicted by the Fox and Gordon-Taylor/Kelley-Bueche equations. PLGA films containing different amounts of ketoprofen (KET) were prepared by solvent casting and characterized by scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry evidenced that KET acted as a plasticizer in a similar biphasic way in both end-capped and uncapped PLGA. At KET contents of 20% to 35%, depending on the investigated polymer, the Tg was around 23 degrees C. Higher KET amounts did not lower further the Tg, and the excess of drug was found to crystallize into the polymeric matrix. Experimental Tg's deviated negatively from the predicted ones probably because of hydrogen bonding. The FTIR spectra of the films, loaded with different amounts of KET, showed a shift to higher wavenumbers for the peaks at 1697 and 1655 cm(-1) confirming the presence of some interactions, probably hydrogen bonds between the ketoprofen carboxylic group and the PLGA carbonyl groups along the polymer backbone. The hydrogen bonding between KET and PLGA is probably responsible for KET plasticizing effect. KET behaving as a lubricant may disrupt polymer chain-chain interactions, removing additional barriers to bond rotation and chain mobility.

Reengineering the pharmaceutical industry by crash-testing molecules

The recent decline in drug approvals and the increase in late-stage failures indicate that the ability to generate and screen large numbers of molecules has not improved the drug pipeline. Perhaps the pharmaceutical industry should follow the example of the automotive industry and agree upon a shared modeling language with vendors and academics to enable integration of predictive computational tools across the industry. This will then enable the virtual 'crash-testing' of drugs before synthesis, biological testing and, most importantly, clinical trials. This represents an ambitiously progressive approach using the models for simulating every stage of the drug discovery and development process. Combining the relevant computational algorithms into a grand unified model would enable prioritization of the best ideas before pursuing a discovery program, selecting a target or synthesizing a molecule. The successful application of these virtual crash-testing principles by any of its current proponents could revitalize the pharmaceutical industry so that failure is avoided.

Prediction of Contact Angle for Pharmaceutical Solids from Their Molecular Structure

Three methods for modeling and predicting water contact angle for a heterogeneous series of pharmaceuticals using computed molecular descriptors and statistical analysis were developed. A number of theoretical molecular descriptors that were related to the structure and physicochemical properties were computed for compounds (n=34) whose experimental water contact angle was known. Thereafter, the descriptors were subjected to partial least squares projections to latent structures analysis. Three multivariate models were derived that allowed theoretical prediction of water contact angle for structurally heterogeneous materials. The R2 and Q2 values of the models ranged from 0.57 to 0.80 and 0.42 to 0.66, respectively. The models had moderate predictive ability and provided useful information about the molecular and physicochemical properties that affect material water contact angle. Increases in the bulkiness and hydrophobic molecular surface area of a molecule increased material water contact angle, whereas the greater presence of hydrophilic surfaces, which are not capable for hydrogen bonding, decrease materials water contact angle. Water contact angle can be predicted well for pharmaceutical solids using theoretical molecular descriptors that reflect the interaction potential of crystal/particle surfaces with water.

Enhanced film-forming properties for ethyl cellulose and starch acetate using n-alkenyl succinic anhydrides as novel plasticizers

PURPOSE

The aim of this study was to investigate the ability of n-alkenyl succinic anhydrides (n-ASAs) to improve the film-forming characteristics of a novel coating polymer, potato starch acetate degree of substitution 2.8 (SA). n-ASAs were also applied to improve the otherwise brittle properties of ethyl cellulose (EC) aqueous dispersion (Aquacoat) and EC solvent-based films.

METHODS

The effectiveness of two n-ASAs, 2-octenyl succinic anhydride (OSA) and 2-dodecen-1-ylsuccinic anhydride were evaluated as plasticizers. Mechanical properties, both water vapor and drug permeabilities, and glass transition temperatures of the cast free films were measured. Triethyl citrate and dibutyl sebacate were used as reference plasticizers.

RESULTS

The long hydrocarbon chain of n-ASA, with its accessible carbonyl groups, enabled a strong plasticization effect on the tested polymers. Due to the excellent mechanical properties (i.e., a tough film structure with considerable flexibility) and low permeability of the plasticized films, n-ASAs, and especially OSA proved to be an ideal plasticizer particularly for EC based coatings. Also, the EC aqueous dispersion plasticized with n-ASAs resulted in a markedly enhanced coalescence of the colloidal polymer particles, even at low drying temperatures.

CONCLUSIONS

In applications where a coating with high flexibility is required, n-ASAs can be used as plasticizers at moderately high concentrations (up to 60-70%, w/w) without losing the high tensile strength, excellent toughness and low permeability of EC and SA films.

3D QSAR studies on binding affinities of coumarin natural products for glycosomal GAPDH of Trypanosoma cruzi

Drug design strategies based on Comparative Molecular Field Analysis (CoMFA) have been used to predict the activity of new compounds. The major advantage of this approach is that it permits the analysis of a large number of quantitative descriptors and uses chemometric methods such as partial least squares (PLS) to correlate changes in bioactivity with changes in chemical structure. Because it is often difficult to rationalize all variables affecting the binding affinity of compounds using CoMFA solely, the program GRID was used to describe ligands in terms of their molecular interaction fields, MIFs. The program VolSurf that is able to compress the relevant information present in 3D maps into a few descriptors can treat these GRID fields. The binding affinities of a new set of compounds consisting of 13 coumarins, for one of which the three-dimensional ligand-enzyme bound structure is known, were studied. A final model based on the mentioned programs was independently validated by synthesizing and testing new coumarin derivatives. By relying on our knowledge of the real physical data (i.e., combining crystallographic and binding affinity results), it is also shown that ligand-based design agrees with structure-based design. The compound with the highest binding affinity was the coumarin chalepin, isolated from Rutaceae species, with an IC50 value of 55.5 microM towards the enzyme glyceraldehyde-3-phosphate dehydrogenase (gGAPDH) from glycosomes of the parasite Trypanosoma cruzi, the causative agent of Chagas' disease. The proposed models from GRID MIFs have revealed the importance of lipophilic interactions in modulating the inhibition, but without excluding the dependence on stereo-electronic properties as found from CoMFA fields.