Hydration and dehydration of crystalline and amorphous forms of raffinose

Screening of Cyclodextrins in the Processing of Buserelin Dry Powders for Inhalation Prepared by Spray Freeze-Drying

Purpose

In this study, we prepared inhalable buserelin microparticles using the spray freeze-drying (SFD) method for pulmonary drug delivery. Raffinose as a cryoprotectant carrier was combined with two levels of five different cyclodextrins (CDs) and then processed by SFD.

Methods

Dry powder diameters were evaluated by laser light scattering and morphology was determined by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis were utilized for the determination of crystalline structures. The aerodynamic properties of the spray freeze-dried powders were evaluated by twin stage impinger (TSI) and the stability of prepared samples was assessed under normal and accelerated conditions.

Results

The prepared powders were mostly porous spheres and the size of microparticles ranged from 9.08 to 13.53 μm, which are suitable as spray-freeze dried particles. All formulations showed amorphous structure confirmed by DSC and XRD. The aerosolization performance of the formulation containing buserelin, raffinose and 5% beta-cyclodextrin (β-CD), was the highest and its fine particle fraction (FPF) was 69.38%. The more circular and separated structures were observed in higher concentrations of CDs, which were compatible with FPFs. The highest stability was obtained in the formulation containing hydroxypropyl beta-cyclodextrin (HP-β-16. CD) 5%. On the contrary, sulfobutylether beta-cyclodextrin (SBE-β-CD) 5% bearing particles showed the least stability.

Conclusion

By adjusting the type and ratio of CDs in the presence of raffinose, the prepared formulations could effectively enhance the aerosolization and stability of buserelin. Therefore, they can be proposed as a suitable career for lung drug delivery.

A strategy to promote the convenient storage and direct use of polyhydroxybutyrate-degrading Bacillus sp. JY14 by lyophilization with protective reagents

BACKGROUND

Bioplastics are attracting considerable attention, owing to the increase in non-degradable waste. Using microorganisms to degrade bioplastics is a promising strategy for reducing non-degradable plastic waste. However, maintaining bacterial viability and activity during culture and storage remains challenging. With the use of conventional methods, cell viability and activity was lost; therefore, these conditions need to be optimized for the practical application of microorganisms in bioplastic degradation. Therefore, we aimed to optimize the feasibility of the lyophilization method for convenient storage and direct use. In addition, we incoporated protective reagents to increase the viability and activity of lyophilized microorganisms. By selecting and applying the best protective reagents for the lyophilization process and the effects of additives on the growth and PHB-degrading activity of strains were analyzed after lyophilization. For developing the lyophilization method for protecting degradation activity, it may promote practical applications of bioplastic-degrading bacteria.

RESULTS

In this study, the polyhydroxybutyrate (PHB)-degrading strain, Bacillus sp. JY14 was lyophilized with the use of various sugars as protective reagents. Among the carbon sources tested, raffinose was associated with the highest cell survival rate (12.1%). Moreover, 7% of raffionose showed the highest PHB degradation yield (92.1%). Therefore, raffinose was selected as the most effective protective reagent. Also, bacterial activity was successfully maintained, with raffinose, under different storage temperatures and period.

CONCLUSIONS

This study highlights lyophilization as an efficient microorganism storage method to enhance the applicability of bioplastic-degrading bacterial strains. The approach developed herein can be further studied and used to promote the application of microorganisms in bioplastic degradation.

Desolvation induced crystal jumping: reversible hydration and dehydration of a spironolactone–saccharin cocrystal with water as the jumping-mate

We present a spironolactone–saccharin cocrystal hydrate as the first example of a crystal that jumps without changes in either the lattice parameter or the molecular conformation to highlight the unique advantages of the jumping-mate strategy.

Influence of Carbamazepine Dihydrate on the Preparation of Amorphous Solid Dispersions by Hot Melt Extrusion

Amorphous solid dispersions (ASDs) are commonly used in the pharmaceutical industry to improve the dissolution and bioavailability of poorly water-soluble drugs. Hot melt extrusion (HME) has been employed to prepare ASD based products. However, due to the narrow processing window of HME, ASDs are normally obtained with high processing temperatures and mechanical stress. Interestingly, one-third of pharmaceutical compounds reportedly exist in hydrate forms. In this study, we selected carbamazepine (CBZ) dihydrate to investigate its solid-state changes during the dehydration process and the impact of the dehydration on the preparation of CBZ ASDs using a Leistritz micro-18 extruder. Various characterization techniques were used to study the dehydration kinetics of CBZ dihydrate under different conditions. We designed the extrusion runs and demonstrated that: 1) the dehydration of CBZ dihydrate resulted in a disordered state of the drug molecule; 2) the resulted higher energy state CBZ facilitated the drug solubilization and mixing with the polymer matrix during the HME process, which significantly decreased the required extrusion temperature from 140 to 60 °C for CBZ ASDs manufacturing compared to directly processing anhydrous crystalline CBZ. This work illustrated that the proper utilization of drug hydrates can significantly improve the processability of HME for preparing ASDs.

A crystallographic and thermal study of pridinol mesylate and its monohydrated solvate

Herein are reported the crystal and molecular structures of the pridinol mesylate salt (C20H25NO+·CH3O3S−) (I) and its monohydrated solvate form (C20H25NO+·CH3O3S−·H2O) (II). A comparison of both with the already reported structure of pure pridinol [1,1-diphenyl-3-piperidino-1-propanol, C20H25NO; Tacke et al. (1980). Chem. Ber. 113, 1962–1980] is made. Molecular structures (I) and (II) are alike in bond distances and bond angles, but differ in their spatial conformation, and, more relevant still, in their hydrogen-bonding motifs. This gives rise to quite different packing schemes, in the form of simple dimers in (I) but water-mediated hydrogen-bonded chains in (II). The dehydration behaviour of form (II) is highly dependent on the heating rate, with slow rates leading to a clear endothermic dehydration step, towards anhydrous (I), with subsequent melting of this latter phase. Increased heating rates result in a more unclear behaviour ending in a structural collapse (melting of the hydrated phase), at temperatures significantly lower than the melting point of the anhydrous phase. The eventual relevance of the water link in the structure of (II) is discussed in regard to this behaviour.

Merits and Limitations of Dynamic Vapor Sorption Studies on the Morphology and Physicochemical State of Freeze-Dried Products

The goal of the present study was to assess the applicability of dynamic vapor sorption analysis of freeze-dried products. Water vapor sorption profiles of intact and ground cakes were recorded to determine the relevance of powder handling. Grinding prior to measurements appeared to be related with a more rapid uptake of water vapor and crystallization. Crystallization may be prevented when analyzing intact cakes. More hygroscopic materials appeared to require a longer time to achieve a constant mass. The specific surface area of different freeze-dried products was calculated from the sorption isotherms using water, organic solvents, and krypton. The specific surface areas calculated for mannitol with water and ethanol was in good agreement with krypton data. False high values were obtained from water vapor sorption of the investigated amorphous materials. The results were slightly improved by the application of vacuum. For trehalose and sucrose, no sorption and thus faulty results were detected with the studied organic solvents. The degree of crystallinity of mannitol within a binary formulation could not be determined by dynamic vapor sorption. Differences in sorption and crystallization tendencies of mannitol and sucrose that were freeze-dried separately and in a binary mixture were considered as the root cause.

Evaluation of excipients for enhanced thermal stabilization of a human type 5 adenoviral vector through spray drying

We have produced a thermally stable recombinant human type 5 adenoviral vector (AdHu5) through spray drying with three excipient formulations (l-leucine, lactose/trehalose and mannitol/dextran). Spray drying leads to immobilization of the viral vector which is believed to prevent viral protein unfolding, aggregation and inactivation. The spray dried powders were characterized by scanning electron microscopy, differential scanning calorimetry, Karl Fischer titrations, and X-ray diffraction to identify the effects of temperature and atmospheric moisture on the immobilizing matrix. Thermal stability of the viral vector was confirmed in vitro by infection of A549 lung epithelial cells. Mannitol/dextran powders showed the greatest improvement in thermal stability with almost no viral activity loss after storage at 20°C for 90days (0.7±0.3 log TCID50) which is a significant improvement over the current -80°C storage protocol. Furthermore, viral activity was retained over short term exposure (72h) to temperatures as high as 55°C. Conversely, all powders exhibited activity loss when subjected to moisture due to amplified molecular motion of the matrix. Overall, a straightforward method ideal for the production of thermally stable vaccines has been demonstrated through spray drying AdHu5 with a blend of mannitol and dextran and storing the powder under low humidity conditions.

Using containerless methods to develop amorphous pharmaceuticals

BACKGROUND

Many pipeline drugs have low solubility in their crystalline state and require compounding in special dosage forms to increase bioavailability for oral administration. The use of amorphous formulations increases solubility and uptake of active pharmaceutical ingredients. These forms are rapidly gaining commercial importance for both pre-clinical and clinical use.

METHODS

Synthesis of amorphous drugs was performed using an acoustic levitation containerless processing method and spray drying. The structure of the products was investigated using in-situ high energy X-ray diffraction. Selected solvents for processing drugs were investigated using acoustic levitation. The stability of amorphous samples was measured using X-ray diffraction. Samples processed using both spray drying and containerless synthesis were compared.

RESULTS

We review methods for making amorphous pharmaceuticals and present data on materials made by containerless processing and spray drying. It was shown that containerless processing using acoustic levitation can be used to make phase-pure forms of drugs that are known to be difficult to amorphize. The stability and structure of the materials was investigated in the context of developing and making clinically useful formulations.

CONCLUSIONS

Amorphous compounds are emerging as an important component of drug development and for the oral delivery of drugs with low solubility. Containerless techniques can be used to efficiently synthesize small quantities of pure amorphous forms that are potentially useful in pre-clinical trials and for use in the optimization of clinical products.

GENERAL SIGNIFICANCE

Developing new pharmaceutical products is an essential enterprise to improve patient outcomes. The development and application of amorphous pharmaceuticals to increase absorption is rapidly gaining importance and it provides opportunities for breakthrough research on new drugs. There is an urgent need to solve problems associated with making formulations that are both stable and that provide high bioavailability. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Dehydration of raffinose pentahydrate: structures of raffinose 5-, 4.433-, 4.289- and 4.127-hydrate at 93 K

Raffinose [or O-α-D-galactopyranosyl-(1→6)-α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside] pentahydrate, C18H32O16·5H2O, (I), and three lower hydrates, namely the 4.433-, (II), 4.289-, (III), and 4.127-hydrated, (IV), forms, obtained in the course of the dehydration of (I), have been studied. The unit cells in the space group P2₁2₁2₁ are of similar dimensions for all the crystals. The conformation of the raffinose molecules remains almost the same across the four crystal structures. The raffinose molecules are linked into a three-dimensional hydrogen-bonded network involving all the -OH groups, the ring and glycosidic O atoms, and the water molecules. Six water sites were identified in the structures of (II), (III) and (IV), of which W1, W4 and W6 (W = water) are partially occupied with their populations coupled. W1, W4 and one of the -OH groups of the galactose ring form an infinite hydrogen-bonding chain around a 2₁ axis parallel to the a axis (denoted chain A), and W6 and the same -OH group form a similar chain (chain A') disordered with chain A. The occupancy ratio of chain A to chain A' for N-hydrates (N is a hydration number between 4 and 5) is (N - 4):(5 - N). The transformation of chain A to chain A' as part of the dehydration process has little effect on the rest of the structure. Thus, the dehydration proceeds without significant impact on the crystal structure.

Solid-state characterization and transformation of various creatine phosphate sodium hydrates

Creatine phosphate sodium (CPS) salt is a first-line cardiovascular drug for severe diastolic heart failure. The drug exists in different hydrate forms. The marketed drug form was determined as CPS·4.5H2 O (H1); however, the reference standard was supplied as CPS·6H2 O (H2). In this work, we present two newly identified hydrate forms: a thermodynamically stable low hydrate form, CPS·1.5H2 O (H3), and a pressure-sensitive transit form, CPS·7H2 O (H4). The hydrate forms were discovered through a comprehensive solid-state screening experiment and fully characterized using a range of analytical techniques including X-ray powder diffraction (XRPD), FTIR, Raman spectroscopy, hot-stage microscopy (HSM), thermogravimetric analysis, and differential scanning calorimetry. Stability tests revealed that H3 was the most stable hydrate under thermal stimulation. H4 is a pressure-sensitive hydrate and easily transforms to H2 and then H1 upon grinding. The form transformation process was closely monitored using the HSM, variable-temperature XRPD (VT-XRPD), and VT-Raman spectroscopy techniques. Specifically, the transformation of H4 to H1 is characterized in a single-crystal-to-single-crystal transformation process. The newly discovered hydrate form H3 has superior physicochemical properties than the marketed forms and is worthy of further development.

Water clusters in amorphous pharmaceuticals

Amorphous materials, although lacking the long-range translational and rotational order of crystalline and liquid crystalline materials, possess certain local (short-range) structure. This paper reviews the distribution of one particular component present in all amorphous pharmaceuticals, that is, water. Based on the current understanding of the structure of water, water molecules can exist in either unclustered form or as aggregates (clusters) of different sizes and geometries. Water clusters are reported in a range of amorphous systems including carbohydrates and their aqueous solutions, synthetic polymers, and proteins. Evidence of water clustering is obtained by various methods that include neutron and X-ray scattering, molecular dynamics simulation, water sorption isotherm, concentration dependence of the calorimetric Tg , dielectric relaxation, and nuclear magnetic resonance. A review of the published data suggests that clustering depends on water concentration, with unclustered water molecules existing at low water contents, whereas clusters form at intermediate water contents. The transition from water clusters to unclustered water molecules can be expected to change water dependence of pharmaceutical properties, such as rates of degradation. We conclude that a mechanistic understanding of the impact of water on the stability of amorphous pharmaceuticals would require systematic studies of water distribution and clustering, while such investigations are lacking.

Glass transition and time-dependent crystallization behavior of dehydration bioprotectant sugars

It has been suggested that the crystallization of a sugar hydrate can provide additional desiccation by removing water from the amorphous phase, thereby increasing the glass transition temperature (T(g)). However, present experiments demonstrated that in single sugar systems, if relative humidity is enough for sugar crystallization, the amorphous phase will have a short life. In the conditions of the present experiments, more than 75% of amorphous phase crystallized in less than one month. The good performance of sugars that form hydrated crystals (trehalose and raffinose) as bioprotectants in dehydrated systems is related to the high amount of water needed to form crystals, but not to the decreased water content or increased T(g) of the amorphous phase. The latter effect is only temporary, and presumably shorter than the expected shelf life of pharmaceuticals or food ingredients, and is related to thermodynamic reasons: if there is enough water for the crystal to form, it will readily form.

Solid state amorphization of pharmaceuticals

Amorphous solids are conventionally formed by supercooling liquids or by concentrating noncrystallizing solutes (spray-drying and freeze-drying). However, a lot of pharmaceutical processes may also directly convert compounds from crystal to noncrystal which may have desired or undesired consequences for their stability. The purpose of this short review paper is (i) to illustrate the possibility to amorphize one compound by several different routes (supercooling, dehydration of hydrate, milling, annealing of metastable crystalline forms), (ii) to examine factors that favor crystal to glass rather than crystal to crystal transformations, (iii) to discuss the role of possible amorphous intermediates in solid-solid conversions induced by milling, (iv) to address the issue of chemical stability in the course of solid state amorphization, (v) to discuss the nature of the amorphous state obtained by the nonconventional routes, (vi) to show the effect of milling conditions on glasses properties, and (vii) to attempt to rationalize the observed transformations using the concepts of effective temperature introduced in nonequilibrium physics.

Studies of the crystallization of amorphous trehalose using simultaneous gravimetric vapor sorption/near IR (GVS/NIR) and "modulated" GVS/NIR

The purpose of this research was to investigate the influence of changes in the amorphous state on the crystallization of trehalose. Amorphous trehalose is known to stabilize biomaterials; hence, an understanding of crystallization is vital. Amorphous trehalose, prepared by spray-drying, was exposed to either a single step (0-75%) in relative humidity (RH) or to modulated 0-75-0% RH to cause crystallization. For the single-step experiment, two samples crystallized in a predictable manner to form the dihydrate. One sample, while notionally identical, did not crystallize in the same way and showed a mass loss throughout the time at 75% RH, with a final mass less than that expected for the dihydrate. The idiosyncratic sample was seen to have a starting near infrared (NIR) spectra similar to that exhibited by anhydrous crystalline trehalose, implying that short-range order in the amorphous material (or a small amount of crystalline seed, not detectable using powder X-ray diffraction) caused the sample to fail to form the dihydrate fully when exposed to high RH. The modulated RH study showed that the amorphous material interacted strongly with water; the intensity of the NIR traces was not proportional to mass of water but rather the extent of hydrogen bonding. Subsequent crystallization of this sample clearly was a partial formation of the dihydrate, but with the bulk of the sample then shielded such that it was unable to show significant sorption when exposed to elevated RH. It has been shown that the nature of the amorphous form will alter the way in which samples crystallize. With oscillation in RH, it was possible to further understand the interactions between water and amorphous trehalose.

Assessment of Defects and Amorphous Structure Produced in Raffinose Pentahydrate upon Dehydration

The progressive conversion of crystalline raffinose pentahydrate to its amorphous form by dehydration at 60 degrees C, well below its melting temperature, was monitored by X-ray powder diffraction over a period of 72 h. The presence of defects within the crystal structure and any amorphous structure created was determined computationally by a total diffraction method where both coherent long-range crystalline order and incoherent short-range disorder components were modeled as a single system. The data were analyzed using Rietveld, pair distribution function (PDF), and Debye total diffraction methods. Throughout the dehydration process, when crystalline material was observed, the average long-range crystal structure remained isostructural with the original pentahydrate material. Although the space group symmetry remained unchanged by dehydration, the c-axis of the crystal unit cell exhibited an abrupt discontinuity after approximately 2 h of drying (loss of one to two water molecules). Analysis of diffuse X-ray scattering revealed an initial rapid build up of defects during the first 0.5 h with no evidence of any amorphous material. From 1-2 h of drying out to 8 h where the crystalline structure is last observed, the diffuse scattering has both amorphous and defect contributions. After 24 h of drying, there was no evidence of any crystalline material remaining. It is concluded that the removal of the first two waters from raffinose pentahydrate created defects, likely in the form of vacancies, that provided the thermodynamic driving force and disorder for subsequent conversion to the completely amorphous state.

Rapid Assessment of the Structural Relaxation Behavior of Amorphous Pharmaceutical Solids: Effect of Residual Water on Molecular Mobility

PURPOSE

Use RH-perfusion microcalorimetry and other analytical techniques to measure the interactions between water vapor and amorphous pharmaceutical solids; use these measurements and a mathematical model to provide a mechanistic understanding of observed calorimetric events.

MATERIALS

Isothermal microcalorimetry was used to characterize interactions of water vapor with a model amorphous system, spray-dried raffinose. Differential scanning calorimetry was used to measure glass transition temperature, T (g). High-sensitivity differential scanning calorimetry was used to measure enthalpy relaxation. X-ray powder diffraction (XRPD) was used to confirm that the spray-dried samples were amorphous. Scanning electron microscopy (SEM) was used to examine particle morphology. Gravimetric vapor sorption was used to measure moisture sorption isotherms. Thermogravimetric analysis (TGA) was used to measure loss on drying.

RESULTS

A moisture-induced thermal activity trace (MITAT) provides a rapid measure of the dependence of molecular mobility on moisture content at a given storage temperature. At some relative humidity threshold, RH(m), the MITAT exhibits a dramatic increase in the calorimetric rate of heat flux. Simulations using calorimetric data indicate that this thermal event is a consequence of enthalpy relaxation.

CONCLUSIONS

RH-perfusion microcalorimetry is a useful tool to determine the onset of moisture-induced physical instability of glassy pharmaceuticals and could find a broad application to determine appropriate storage conditions to ensure long-term physical stability. Remarkably, thermal events measured on practical laboratory timescales (hours to days) are relevant to the stability of amorphous materials on much longer, pharmaceutically relevant timescales (years). The mechanistic understanding of these observations in terms of enthalpy relaxation has added further value to the use of RH-perfusion calorimetry as a rapid means to characterize the molecular mobility of amorphous solids.

Analytical techniques for quantification of amorphous/crystalline phases in pharmaceutical solids

The existence of different solid-state forms such as polymorphs, solvates, hydrates, and amorphous form in pharmaceutical drug substances and excipients, along with their downstream consequences in drug products and biological systems, is well documented. Out of these solid states, amorphous systems have attracted considerable attention of formulation scientists for their specific advantages, and their presence, either by accident or design is known to incorporate distinct properties in the drug product. Identification of different solid-state forms is crucial to anticipate changes in the performance of the material upon storage and/or handling. Quantitative analysis of physical state is imperative from the viewpoint of both the manufacturing and the regulatory control aimed at assuring safety and efficacy of drug products. Numerous analytical techniques have been reported for the quantification of amorphous/crystalline phase, and implicit in all quantitative options are issues of accuracy, precision, and suitability. These quantitative techniques mainly vary in the properties evaluated, thus yielding divergent values of crystallinity for a given sample. The present review provides a compilation of the theoretical and practical aspects of existing techniques, thereby facilitating the selection of an appropriate technique to accomplish various objectives of quantification of amorphous systems.

Thermodynamic and dynamic factors involved in the stability of native protein structure in amorphous solids in relation to levels of hydration

The internal, dynamical fluctuations of protein molecules exhibit many of the features typical of polymeric and bulk small molecule glass forming systems. The response of a protein's internal molecular mobility to temperature changes is similar to that of other amorphous systems, in that different types of motions freeze out at different temperatures, suggesting they exhibit the alpha-beta-modes of motion typical of polymeric glass formers. These modes of motion are attributed to the dynamic regimes that afford proteins the flexibility for function but that also develop into the large-scale collective motions that lead to unfolding. The protein dynamical transition, T(d), which has the same meaning as the T(g) value of other amorphous systems, is attributed to the temperature where protein activity is lost and the unfolding process is inhibited. This review describes how modulation of T(d) by hydration and lyoprotectants can determine the stability of protein molecules that have been processed as bulk, amorphous materials. It also examines the thermodynamic, dynamic, and molecular factors involved in stabilizing folded proteins, and the effects typical pharmaceutical processes can have on native protein structure in going from the solution state to the solid state.

Molecular Mobility in Raffinose in the Crystalline Pentahydrate Form and in the Amorphous Anhydrous Form

PURPOSE

The aims of the study are to characterize the slow molecular mobility in solid raffinose in the crystalline pentahydrate form, as well as in the anhydrous amorphous form (Tg = 109 degrees C at 5 degrees C/min), and to analyze the differences and the similarities of the molecular motions in both forms.

METHODS

Thermally stimulated depolarization current (TSDC) is used to isolate the individual modes of motion present in raffinose, in the temperature range between -165 and +60 degrees C. From the experimental output of the TSDC experiments, the kinetic parameters associated with the different relaxational modes of motion were obtained, which allowed a detailed characterization of the distribution of relaxation times of the complex relaxations observed in raffinose. The features of the glass transition relaxation in raffinose were characterized by differential scanning calorimetry (DSC).

RESULTS

A complex mobility was found in the crystalline form of raffinose. From the analysis of the TSDC data, we conclude that these molecular motions are local and noncooperative. A sub-Tg relaxation, or secondary process, was also detected and analyzed by TSDC in the amorphous phase. It has low activation energy and low degree of cooperativity. The glass transition was studied by DSC. The fragility index (Angell's scale) of raffinose obtained from DSC data is m = 148.

CONCLUSIONS

TSDC proved to be an adequate technique to study the molecular mobility in the crystalline pentahydrate form of raffinose. In the amorphous form, on the other hand, the secondary relaxation was analyzed by TSDC, but the study of the glass transition relaxation was not possible by this experimental technique as a consequence of conductivity problems. The DSC study of the glass transition indicates that raffinose is an extremely fragile glass former.

Partially Crystalline Systems in Lyophilization: I. Use of Ternary State Diagrams to Determine Extent of Crystallization of Bulking Agent

Two model ternary systems: water-glycine-raffinose and water-glycine-trehalose were investigated to determine the extent of glycine crystallization in frozen solutions. The use of such partially crystalline systems allows primary drying to be carried out substantially above the collapse temperature. Differential scanning calorimetry (DSC) and variable temperature X-ray diffractometry (XRD) were used to monitor phase transitions in frozen systems as well as to determine the T'g. Aqueous solutions containing different glycine to carbohydrate weight ratios were first cooled to -60 degrees C and then warmed to room temperature. In both raffinose and trehalose systems, when the initial glycine to sugar (raffinose pentahydrate or trehalose dihydrate) ratio was <1, glycine crystallization was not detected. When the ratio was >or=1, partial glycine crystallization was observed during warming. The presence of amorphous glycine caused the T'g to be substantially lower than that of the solution containing only the carbohydrate. To determine the extent of glycine crystallization, the solutions were annealed for 5 h just above the temperature of glycine crystallization. The T'g observed in the second warming curve was very close to that of the carbohydrate solution alone, indicating almost complete glycine crystallization. These studies enabled the construction of the water-rich sections of the raffinose-glycine-water and trehalose-glycine-water state diagrams. These diagrams consist of a kinetically stable freeze-concentrated solution and a doubly unstable glassy region, which readily crystallizes during cooling or subsequent warming. In addition, there is an intermediate region, where during the experimental timescale, there appears to be hindered glycine nucleation but unhindered crystal growth. To obtain substantially crystalline glycine in the frozen solutions, the glycine to carbohydrate ratios should be >or=1.

Raffinose Crystallization During Freeze-Drying and Its Impact on Recovery of Protein Activity

PURPOSE

To study i) phase transitions in raffinose solution in the frozen state and during freeze-drying and ii) evaluate the impact of raffinose crystallization on the recovery of protein activity in reconstituted lyophiles.

METHODS

X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC) were used to study the frozen aqueous solutions of raffinose pentahydrate. Phase transitions during primary and secondary drying were monitored by simulating the entire freeze-drying process, in situ, in the sample chamber of the diffractometer. The activity of lactate dehydrogenase (LDH) in reconstituted lyophiles was determined spectrophotometrically.

RESULTS

Raffinose formed a kinetically stable amorphous freeze-concentrated phase when aqueous solutions were frozen at different cooling rates. When these solutions were subjected to primary drying without annealing, raffinose remained amorphous. Raffinose crystallized as the pentahydrate when the solutions were annealed at a shelf temperature of -10 degrees C. Primary drying of these annealed systems resulted in the dehydration of raffinose pentahydrate to an amorphous phase. The phase separation of the protein from the amorphous raffinose in these two systems during freeze-drying resulted in a significant reduction in the recovery of LDH activity, even though the lyophile was amorphous.

CONCLUSIONS

Annealing of frozen aqueous raffinose solutions can result in solute crystallization, possibly as the pentahydrate. The crystalline pentahydrate dehydrates during primary drying to yield an amorphous lyophile. Raffinose crystallization during freeze-drying is accompanied by a significant loss of protein activity.

De- and rehydration behavior of α,α-trehalose dihydrate under humidity-controlled atmospheres

Effects of humidity were investigated on de- and rehydration behavior of alpha,alpha-trehalose dihydrate (T(h)) throughout simultaneous measurements of differential scanning calorimetry and X-ray diffractometry (DSC-XRD) and simultaneous thermogravimetry and differential thermal analysis (TG-DTA). When T(h) was heated from room temperature under dry nitrogen atmosphere, a metastable anhydrous crystal (T(alpha)) was formed at 105 degrees C after dehydration of T(h). The resulting T(alpha) melted at 125 degrees C and became amorphous, followed by cold crystallization from 150 degrees C giving rise to a stable anhydrous crystal T(beta). Under a highly humid atmosphere, on the other hand, T(beta) was formed at 90 degrees C directly as a result of T(h) dehydration. T(alpha) was readily rehydrated and turned back to T(h) when nitrogen gas with low water vapor pressure of 2.1kPa was admitted, whereas high water vapor pressure up to 7.4kPa was required for rehydration of T(beta) into T(h). This study provided a picture of pathways that link various solid forms of trehalose, taking into account the effects of a humid environment.

Crystalline to amorphous transition of disodium hydrogen phosphate during primary drying

PURPOSE

To monitor the phase transitions during freeze-drying of disodium hydrogen phosphate.

METHODS

The variable temperature sample stage of the X-ray diffractometer (XRD) was attached to a vacuum pump, which enabled the entire freeze-drying process to be carried out in the sample chamber. The phase transitions during the freeze-drying cycle were monitored in real time by XRD. Aqueous buffer solution (containing disodium hydrogen phosphate and sodium dihydrogen phosphate) was cooled at 2 degrees C/min from room temperature to -70 degrees C. It was then heated to -25 degrees C and subjected to primary drying for 2 h at a chamber pressure of approximately 100 mTorr, followed by secondary drying at -10 degrees C.

RESULTS

In the frozen solution, disodium hydrogen phosphate had crystallized as the dodecahydrate (Na2HPO4 x 12H2O) as was evident from its characteristic lines at approximately 5.37, 4.27, and 2.81 angstroms. Primary drying for 2 h resulted in ice sublimation, and the complete disappearance of the dodecahydrate peaks.

CONCLUSION

The dehydration of the crystalline dodecahydrate resulted in an amorphous anhydrate. Thus the amorphous nature of the end product is a result of phase transitions during the process and do not reflect the solid-state of the ingredients during the entire process.

Characterization of physical state of mannitol after freeze-drying: effect of acetylsalicylic acid as a second crystalline cosolute

Freeze-drying of mixed solutes is a preparative technique widely used in the pharmaceutical industry. The presence of an amorphous form or changes in the crystalline form can affect solid state stability. In this work, acetylsalicylic acid (AAS) was chosen as a model drug, and was mixed with mannitol, a commonly used bulking agent in formulation of tablets. Variations in the final freeze-dried crystalline forms were found after changing the ratios of the two co-solutes. Samples were analysed by powder X-ray diffractometry and differential scanning calorimetry. A major amorphous form and a minor crystalline delta-mannitol form were produced during the mannitol freeze-drying process. The crystal form of mannitol in the two-component system depended on the AAS:mannitol ratio. The AAS was mostly crystalline, regardless of the amount of mannitol present. A major delta-mannitol and a minor amorphous form were obtained when AAS was present in a high percentage (75% w/w). When AAS percentages of 50 and 25% (w/w) were present during the drying process, the mannitol was found in a highly crystalline form.

Water diffusion in hydrated crystalline and amorphous sugars monitored using H/D exchange

Water interacts with pharmaceutical materials in a number of different ways. The aim of this study was to investigate if exchange experiments with D(2)O can provide useful insights into the structure of hydrated materials. Raffinose pentahydrate, trehalose dihydrate, and sucrose were used as model compounds in conjunction with their amorphous counterparts. Following exposure to D(2)O vapor, the exchange of water of hydration and/or hydroxyl groups was monitored using Raman spectroscopy. For the amorphous materials, all of the sugar hydroxyl groups were found to exchange on exposure to D(2)O, providing evidence that water has no fixed site in amorphous materials, nor is access to different parts of the molecule restricted. For raffinose pentahydrate and trehalose dihydrate, exchange of both hydrate water and hydroxyls was incomplete, suggesting that there are specific pathways for diffusion into and within the crystal structure. The results are rationalized based on the known crystal structures. Using exchange experiments to investigate hydrates thus appears to be a useful probe of structure.

Water sorption/desorption--near IR and calorimetric study of crystalline and amorphous raffinose

Mass loss at elevated RH is an established method for determining the occurrence of crystallisation of an amorphous material. Through the combination of near infrared spectroscopy and gravimetric vapour sorption, it has been possible to show the transition of raffinose from its spray-dried amorphous form to a crystalline form without this characteristic mass loss. It has also been possible to observe changes in the crystalline material for a period of 30 h subsequent to exposure to elevated relative humidity by near infrared spectroscopy that are not associated with changes in mass, but are related to repacking of hydrate molecules. Drying of the crystalline pentahydrate in the DVS-NIR was seen to show changes in the NIR peak related to -OH. From this, NIR peaks were tentatively ascribed as relating to a penta-, tetra-, tri- and a di-hydrate form, but the sample returned to the amorphous response by the time the water content fell to the equivalent of the monohydrate, indicating that crystallinity had been lost. These observations would be compatible with the hypothesis that lower hydrates of raffinose exist. Due to the absence of mass loss in association with crystallisation, it was found that the enthalpy of crystallisation of amorphous raffinose, as determined by isothermal microcalorimetry, is similar to the enthalpy of fusion determined by differential scanning calorimetry. Finally, it was observed that the early part of the response in the isothermal microcalorimeter was related to mobility of molecules when Tg was above T. This mobility was able to give the bulk morphology of a crystal before the sample developed long range order and crystalline properties.

Amorphous pharmaceutical solids: preparation, characterization and stabilization

The importance of amorphous pharmaceutical solids lies in their useful properties, common occurrence, and physicochemical instability relative to corresponding crystals. Some pharmaceuticals and excipients have a tendency to exist as amorphous solids, while others require deliberate prevention of crystallization to enter and remain in the amorphous state. Amorphous solids can be produced by common pharmaceutical processes, including melt quenching, freeze- and spray-drying, milling, wet granulation, and drying of solvated crystals. The characterization of amorphous solids reveals their structures, thermodynamic properties, and changes (crystallization and structural relaxation) in single- and multi-component systems. Current research in the stabilization of amorphous solids focuses on: (i) the stabilization of labile substances (e.g., proteins and peptides) during processing and storage using additives, (ii) the prevention of crystallization of the excipients that must remain amorphous for their intended functions, and (iii) the selection of appropriate storage conditions under which amorphous solids are stable.

Effect of sucrose/raffinose mass ratios on the stability of co-lyophilized protein during storage above the Tg

PURPOSE

To examine the potential of raffinose as an excipient in stabilizing protein and to study the effect of sucrose/raffinose mass ratios on the stability of co-lyophilized protein and amorphous solids during storage at an elevated temperature.

METHODS

Glucose-6-phosphate dehydrogenase (G6PDH) was colyophilized with sucrose and raffinose mixed at different mass ratios. The activity of dried G6PDH was monitored during storage at 44 degrees C. Thermal properties of sucrose/raffinose matrices were determined by differential scanning calorimetry (DSC).

RESULTS

Mass ratios of sucrose to raffinose did not affect the recovery of G6PDH activity after freeze-drying, but significantly affected the stability of freeze-dried G6PDH during storage. The sucrose-alone formulation offered the best enzyme stabilization during storage. With increasing fraction of raffinose, the G6PDH stability decreased, sugar crystallization inhibited, and crystal-melting temperature increased.

CONCLUSIONS

Despite the higher Tg of the formulations with higher fraction of raffinose, they provided less protection for G6PDH than did sucrose alone during storage. Our data do not support the prediction from recent thermophysical studies that raffinose should be superior to sucrose and trehalose as a potential excipient or stabilizer.