Thermal Data (thermal + data)

Distribution by Scientific Domains

Selected Abstracts

A solid-state approach to enable early development compounds: Selection and animal bioavailability studies of an itraconazole amorphous solid dispersion

David Engers
Abstract A solid-state approach to enable compounds in preclinical development is used by identifying an amorphous solid dispersion in a simple formulation to increase bioavailability. Itraconazole (ITZ) was chosen as a model crystalline compound displaying poor aqueous solubility and low bioavailability. Solid dispersions were prepared with different polymers (PVP K-12, K29/32, K90; PVP VA S-630; HPMC-P 55; and HPMC-AS HG) at varied concentrations (1:5, 1:2, 2:1, 5:1 by weight) using two preparation methods (evaporation and freeze drying). Physical characterization and stability data were collected to examine recommended storage, handling, and manufacturing conditions. Based on generated data, a 1:2 (w/w) ITZ/HPMC-P dispersion was selected for further characterization, testing, and scale-up. Thermal data and computational analysis suggest that it is a possible solid nanosuspension. The dispersion was successfully scaled using spray drying, with the materials exhibiting similar physical properties as the screening samples. A simple formulation of 1:2 (w/w) ITZ/HPMC-P dispersion in a capsule was compared to crystalline ITZ in a capsule in a dog bioavailability study, with the dispersion being significantly more bioavailable. This study demonstrated the utility of using an amorphous solid form with desirable physical properties to significantly improve bioavailability and provides a viable strategy for evaluating early drug candidates. 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3901,3922, 2010 [source]

Order-disorder enantiotropy, monotropy, and isostructurality in a tetroxoprim-sulfametrole 1:1 molecular complex: Crystallographic and thermal studies

Mino R. Caira
Abstract Two enantiotropic polymorphs of a tetroxoprim (TXP)-sulfametrole (SMTR) 1:1 molecular complex monohydrate and two isostructural TXP-SMTR 1:1 molecular complex solvates with methanol and ethanol were grown and studied by X-ray diffraction and thermal methods (thermogravimetric analysis and differential scanning calorimetry). Interconversion of the polymorphic hydrates is essentially an order/disorder transition involving a substituent on the TXP molecule. These hydrated phases may be described as "nearly isostructural" with the methanol and ethanol solvates. Thermal data for decomposition of the solvates were rationalized on the basis of the location and topologies of solvent crystallographic sites. Solid-state properties of two monotropic polymorphs of the unsolvated TXP-SMTR 1:1 molecular complex were also investigated and the theoretical and experimental phase diagrams of the individual components were assessed. The existence of polymorphic and pseudopolymorphic forms is determined by conformational flexibility of the TXP-SMTR bimolecular complex components, a tendency for molecular disorder in TXP, the ability of the drug complex to form intricate, highly stabilized hydrogen-bonded frameworks, and the competition between nonspecific van der Waals and specific hydrogen bond interactions. 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2164,2176, 2003 [source]

An unexpected co-crystal with a variable degree of order: 1:1 rac -1,2-cyclohexanediol/triphenylphosphine oxide

Maxime A. Siegler
A 1:1 co-crystal of rac - trans -1,2-C6H10(OH)2 and (C6H5)3PO has been found that is unusual because there are no strong interactions between the two kinds of molecules, which are segregated into layers. Furthermore, neither pure rac -1,2-cyclohexanediol (CHD) nor pure triphenylphosphine oxide (TPPO) has any obvious packing problem that would make the formation of inclusion complexes likely. The TPPO layers are very much like those found in two of the four known polymorphs of pure TPPO. The hydrogen-bonded ribbons of CHD are similar to those found in other vic -diol crystals. The co-crystals are triclinic (space group P), but the deviations from monoclinic symmetry (space group C2/c) are small. The magnitudes of those deviations depend on the solvent from which the crystal is grown; the deviations are largest for crystals grown from acetone, smallest for crystals grown from toluene, and intermediate for crystals grown from ethanol. The deviations arise from incomplete enantiomeric disorder of the R,R and S,S diols; this disorder is not required by symmetry in either space group, but occupancy factors are nearly 0.50 when the structure is refined as monoclinic. When the structure is refined as triclinic the deviations of the occupancy factors from 0.50 mirror the deviations from monoclinic symmetry because information about the partial R,R/S,S ordering is transmitted from one diol layer to the next through the very pseudosymmetric TPPO layer. Analyses suggest individual CHD layers are at least mostly ordered. The degree of order seems to be established at the time the crystal is grown and is unlikely to change with heating or cooling. Thermal data suggest the existence of the co-crystal is a consequence of kinetic rather than thermodynamic factors. [source]

Tafoni development in a cryotic environment: an example from Northern Victoria Land, Antarctica

Andrea Strini
Abstract Tafoni are a type of cavernous weathering widespread around the world. Despite the extensive distribution of the tafoni, their genesis is not clear and is still a matter of debate, also because they occur in such different climatic conditions and on so many different types of substrate. Geomorphological characterization of more than 60 tafoni in three different Antarctic sites (two coastal and one inland) between 74 and 76 S with sampling of weathering products and salt occurrences are described together with thermal data (on different surfaces) and wind speed recorded in different periods of the year in a selected tafone close to the Italian Antarctic station. The aim of this present study is to provide further information to help understand the processes involved in the growth of tafoni in a cryotic environment, and the relationship of these processes to climate, with particular attention to the thermal regime and the role of wind. The new data presented in this paper suggest that there is no single key factor that drives the tafoni development, although thermal stress seems the most efficient process, particularly if we consider the short-term fluctuations. The data also confirm that other thermal processes, such as freezing,thawing cycles and thermal shock, are not really effective for the development of tafoni in this area. The wind speed measured within the tafoni is half that recorded outside, thus favouring snow accumulation within the tafoni and therefore promoting salt crystallization. On the other hand, the wind effect on the thermal regime within the tafoni seems negligible. While both salt weathering and thermal stress appear active in this cryotic environment, these are azonal processes and are therefore active in other climatic areas where tafoni are widespread (such as the Mediterranean region). Copyright 2007 John Wiley & Sons, Ltd. [source]

Rock albedo and monitoring of thermal conditions in respect of weathering: some expected and some unexpected results

Kevin Hall
Abstract Broadly speaking, there is, at least within geomorphic circles, a general acceptance that rocks with low albedos will warm both faster and to higher temperatures than rocks with high albedos, reflectivity influencing radiative warming. Upon this foundation are built notions of weathering in respect of the resulting thermal differences, both at the grain scale and at the scale of rock masses. Here, a series of paving bricks painted in 20 per cent reflectivity intervals from black through to white were used to monitor albedo-influenced temperatures at a site in northern Canada in an attempt to test this premise. Temperatures were collected, for five months, for the rock surface and the base of the rock, the blocks being set within a mass of local sediment. Resulting thermal data did indeed show that the dark bricks were warmer than the white but only when their temperatures were equal to or cooler than the air temperature. As brick temperature exceeded that of the air, so the dark and light bricks moved to parity; indeed, the white bricks frequently became warmer than the dark. It is argued that this ,negating' of the albedo influence on heating is a result of the necessity of the bricks, both white and black, to convect heat away to the surrounding cooler air; the darker brick, being hotter, initially convects faster than the white as a product of the temperature difference between the two media. Thus, where the bricks become significantly hotter than the air, they lose energy to that air and so their respective temperatures become closer, the albedo influence being superceded by the requirement to equilibrate with the surrounding air. It is argued that this finding will have importance to our understanding of weathering in general and to our perceptions of weathering differences between different lithologies. Copyright 2005 John Wiley & Sons, Ltd. [source]

Earth hummocks (thfur): new insights to their thermal characteristics and development in eastern Lesotho, southern Africa

Stefan W. Grab
Abstract The aspect-controlled variations in soil freezing within earth hummocks of eastern Lesotho (southern Africa) are analysed. Ground thermal data were measured for an earth hummock from late autumn to early spring in 1995 and 1996, using Tinytalk data loggers. During 1995, ground temperatures were recorded at 15 and 20 cm depth on the hummock north, east, south and west aspects, whilst in 1996 temperatures were recorded at 1 cm, 5 cm and 10 cm on the north and south aspects. The data from 1995 indicate that soil freezing commences on the hummock southern aspects and gradually progresses towards the western and northern aspects, whilst the eastern aspect remained unfrozen throughout winter. The data from 1996 indicate that a thick snow cover almost nullifies the temperature differences between the hummock northern and southern aspects. However, given the relative absence of snow during contemporary winters, freeze intensity and duration is longest on the hummock southern and western aspects, which helps explain earth hummock deformation (elongation and coalescence) in a southwesterly direction on slope gradients ,3. Copyright 2005 John Wiley & Sons, Ltd. [source]

Rock thermal data at the grain scale: applicability to granular disintegration in cold environments

Kevin Hall
Abstract Consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data. In most instances, both the size of the transducer and the nature of the study have negated any applicability of the resulting data to the understanding of grain-to-grain separation within rock. The application of microthermocouples (,015 mm diameter) and high-frequency logging (20 s intervals) at a taffoni site on southern Alexander Island and from a rock outcrop on Adelaide Island (Antarctica) provide new data pertaining to the thermal conditions, at the grain scale, of the rock surface. The results show that thermal changes (,T/t) can be very high, with values of 22 C min,1 being recorded. Although available data indicate that there can be differences in frequency and magnitude of ,uctuations as a function of aspect, all aspects experienced some large magnitude (,2 C min,1) ,uctuations. Further, in many instances, large thermal changes in more than one direction could occur within 1 min or in subsequent minutes. These data suggest that the surface grains experience rapidly changing stress ,elds that may, with time, effect fatigue at the grain boundaries; albedo differences between grains and the resulting thermal variations are thought to exacerbate this. The available data failed to show any indication of water freezing (an exotherm) and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions, and that in this dry, Antarctic region thermal stress may play a signi,cant role. Copyright 2003 John Wiley & Sons, Ltd. [source]

Phytoplankton communities and antecedent conditions: high resolution sampling in Esthwaite Water

Summary 1. The succession of a phytoplankton community was investigated through an intensive period of sampling and related to physical, chemical and biological conditions sampled at an equal, or higher, temporal resolution. 2. Phytoplankton samples were taken on a weekly basis from June to September 2004 and analysed for diversity, species composition, and contribution of different functional groups to total biomass. Physical and chemical data were collected on the sampling days, and physical environmental factors were also logged continuously throughout the period by automatic measuring stations. This continuous logging allowed community structure to be compared with physical data averaged over periods from a day to a week before each sampling date. 3. The Schmidt stability of the lake, a measure of the strength of stratification calculated from thermal data, showed a negative correlation with phytoplankton species diversity. This is consistent with the hypothesis that mixing was preventing exclusion by species that would otherwise dominate in stratified conditions. 4. At a functional level, stress tolerant (S-type) species dominated during the stratified summer conditions, with small, colonising species (C types) and ruderal, disturbance tolerant species (R types) contributing little to the overall biomass. Of the stress tolerant species, the faster growing (SC) phytoplankters were significantly favoured by more stable, stratified conditions and higher solar radiation. Increased abundance of this group resulted in decreased species diversity. Correlations were generally strongest when using the 6- to 7-day averaged physical data, stressing the importance of continuous measurements of these drivers in phytoplankton studies. [source]

Persistent sensory dysfunction in pain-free herniotomy

Background: Persistent post-herniotomy pain may be a neuropathic pain state based on the finding of a persistent sensory dysfunction. However, detailed information on the normal distribution of sensory function in pain-free post-herniotomy patients hinders identification of exact pathogenic mechanisms. Therefore, we aimed to establish normative data on sensory function in pain-free patients >1 year after a groin herniotomy. Methods: Sensory thresholds were assessed in 40 pain-free patients by a standardized quantitative sensory testing (QST). Secondary endpoints included comparison of sensory function between the operated and the nave side, and correlation between sensory function modalities. Results: QST showed that on the operated side, thermal data were normally distributed, but mechanical pressure and pinch thresholds were normalized only after log-transformation, and cold pain and pressure tolerance could not be normalized. Comparison of QST results revealed significant (P<0.01) cutaneous hypoesthesia/hyperalgesia, but also significant pressure hyperalgesia (P<0.01) and decreased pressure tolerance (P=0.02) on the operated vs. the nave side. Wind-up was seen in 6 (15%) but with a low pain intensity. Conclusion: Persistent sensory dysfunction is common in pain-free post-herniotomy patients. Future studies of sensory function in persistent post-herniotomy pain should compare the findings to the present data in order to characterize individual patients and potentially identify subgroups, which may aid in allocation of patients to pharmacological or surgical treatment. [source]

Trends in solubility of polymorphs

Madhu Pudipeddi
Abstract Polymorphism of drug substances has been the subject of intense investigation in the pharmaceutical field for over 40 years. Considering the multitude of reports on solubility or dissolution of polymorphs in the literature, an attempt is made in this study to answer the question: How big is the impact of polymorphism on solubility? A large number of literature reports on solubility or dissolution of polymorphs were reviewed and the data were analyzed for trends in solubility ratio of polymorphs. The general trend reveals that the ratio of polymorph solubility is typically less than 2, although occasionally higher ratios can be observed. A similar trend is also observed for anhydrate/hydrate solubility ratios, although anhydrate/hydrate solubility ratios appear to be more spread out and higher than the typical ratio for nonsolvated polymorphs. An attempt is also made in this commentary to estimate the ratio of solubilities of polymorphs from thermal data. The trend in estimated solubility ratio shows good agreement with the one observed with experimentally determined solubility values. 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:929,939, 2005 [source]

Permafrost distribution in talus slopes located within the alpine periglacial belt, Swiss Alps

Christophe Lambiel
Abstract The extent of permafrost in nine talus slopes located within the alpine periglacial belt in the western Swiss Alps was investigated using ground surface temperature measurements and one- dimensional geoelectrical profiles. Based on the thermal data, permafrost appears likely in the lower parts of the slopes. At the same locations, an electrically resistive layer, interpreted as frozen sediments, was identified beneath 3,5,m of surface materials. Further upslope, resistivities were lower and ground surface temperatures were warmer, suggesting that permafrost was absent. The cooling of the ground in the lower parts of some of the talus slopes investigated was apparently due to the chimney effect. It is inferred that this mechanism plays an important role in permafrost development in the lower half of talus slopes located within the discontinuous mountain permafrost belt. Copyright 2008 John Wiley & Sons, Ltd. [source]

Percutaneous permeation of enantiomers and racemates of chiral drugs and prediction of their flux ratios using thermal data: A pharmaceutical perspective

CHIRALITY, Issue 5 2003
Mohsen I. Afouna
Abstract Albeit pharmacological, pharmacokinetic, and toxicological differences between enantiomeric pairs or between the pure enantiomers and racemate of chiral drugs are known to exist for decades, we are just beginning to realize that there are apparent differences between these species with respect to their percutaneous permeation as well. Such differences in permeation are likely to be enhanced when chiral drugs are formulated with chiral excipients, necessitating a careful assessment of the effect of formulation excipients on the permeation as well as the overall therapeutic outcomes. The in vitro transport data from the preclinical investigations, using laboratory animal models and/or in vitro cell culture systems, must be carefully validated in vivo as there are differences between these models and the human skin. Mathematical models such as MTMT that utilize the interdependence of certain physicochemical characteristics and percutaneous permeability have a predictive value in assessing the flux behavior of enantiomers and racemates. Chirality 15:456,465, 2003. 2003 Wiley-Liss, Inc. [source]