Physical characterization studies

Cornelius CJ, Marand E. Hybrid inorganic-organic materials based on a 6FDA-6FpDA-DABA polyimide and silica physical characterization studies. Polymer 2002 43(8) 2385 00. 

Work on phosphazene high polymers continues to attract increased interest. Advances in the study of the ring-opening polymerization, and physical characterization in the solid state, of the materials produced by these reactions have been reported. 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

It may be envisioned that a protocol for the complete physical characterization of a solid material could easily be developed. At the early stages in drug development, each lot of active drug, excipients, and formulated blends would be characterized as fully as possible. A feedback loop would be established after each formulation run, in which the physical characteristics of the input materials were correlated with the quality of formulated product. Out of these studies would come an understanding of what particular properties were essential to the production of an acceptable formulation. 

Infrared (IR) spectroscopy, especially when measured by means of the Fourier transform method (FTIR), is another powerful technique for the physical characterization of pharmaceutical solids [17]. In the IR method, the vibrational modes of a molecule are used to deduce structural information. When studied in the solid, these same vibrations normally are affected by the nature of the structural details of the analyte, thus yielding information useful to the formulation scientist. The FTIR spectra are often used to evaluate the type of polymorphism existing in a drug substance, and they can be very useful in studies of the water contained within a hydrate species. With modem instrumentation, it is straightforward to obtain FTIR spectra of micrometer-sized particles through the use of a microscope fitted with suitable optics. 

Within various pharmaceutical laboratories (industrial and academic), the mul-tinuclear technique of solid state NMR has primarily been applied to the study of polymorphism at the qualitative and quantitative levels. Although the technique ideally lends itself to the structure determination of drug compounds in the solid state, it is anticipated that in the future, solid state NMR will become routinely used for method development and problem solving activities in the analytical/materials science/physical pharmacy area of the pharmaceutical sciences. During the past few years, an increasing number of publications have emerged in which solid state NMR has become an invaluable technique. With the continuing development of solid state NMR pulse sequences and hardware improvements (increased sensitivity), solid state NMR will provide a wealth of information for the physical characterization of pharmaceutical solids. 

In the present work, such a systematic approach to the physical characterization of pharmaceutical solids is outlined. Techniques available for the study of physical properties are classified as being associated with the molecular level (properties associated with individual molecules), the particulate level (properties pertaining to individual solid particles), and the bulk level (properties associated with an ensemble of particulates). Acquisition of this range of physical information yields a total profile of the pharmaceutical solid in question, whether it is an active drug, an excipient, or a blend of these. The development of a total profile is a requirement for successful manufacture of any solid dosage form. 

The EPA GLPs include a paragraph under Subpart G ( 160.135) that deals with physical and chemical characterization studies. This paragraph states that all provisions of GLP standards apply to certain specific physical and chemical characterization studies of test, control, and reference substances. These studies are listed. It also states that certain specified paragraphs do not apply to studies other than those listed. 

The physical characterization of ribosomal proteins has presented an exceptional challenge since they are difficult to purify, are relatively insoluble in aqueous solutions, and have a great propensity to aggregate. Polydispersity is an especially severe problem that has not been well addressed in most studies to date. Aggregation can cause substantial... 

During the last 15 years of ribosomal protein study, enormous progress has been made. Each of the proteins from E. coli ribosomes has been isolated, sequenced, and immunologically and physically characterized. Ribosomal proteins from other sources (e.g., from some bacteria, yeast, and rat) have been isolated and studied as well. 

In the following section, we restrict our discussion to templated mesoporous solids that are of potential interest as battery electrodes, including many transition-metal oxides and carbon. This slice of the literature still points the interested reader to many articles on the synthesis and physical characterization of relevant mesoporous materials. A much smaller number of electrochemical studies with templated mesoporous electrodes have been published, and these studies in particular will be noted. 

Campbell, W. J., C. W. Huggins, and A. G. Wylie. Chemical and physical characterization of amosite, chrysotile, crocidolite, and nonfibrous tremolite for oral ingestion studies by the National Institute of Environmental Health Services. Bureau of Mines RI. 8452. U.S. Department of the Interior, Report of Investigations. Washington, D.C. 

The purpose of model bioinorganic studies is to establish the relevant coordination chemistry, providing evidence for the reasonable existence of hypothesized biologic structures or reaction intermediates, physical characterization of these species and determination of the competence of such moieties towards reactivity patterns found in the biochemical systems. 

Z. Zuo, G. Kwon, B. Stevenson, J. Diakur, L.l. Wiebe, Flutamide—Hydroxypropyl-beta-cyclodextrin complex Formulation, physical characterization, and absorption studies using the Caco-2 in vitro model, J. Pharm. Pharm. Scl. 3 (2000) 220-227. 

Finally, receptor modeling offers a useful theme around which to organize aerosol characterization studies. Large scale field studies are expensive, and they also tend to be diffuse. Data requirements for source resolution can be used to select the chemical and physical properties of the aerosol to be measured both at receptor sites and at sources. 

The advantage of using free radical inhibitors to facilitate the copolymerization of a bisbenzocyclobutene with a bismaleimide was first noted in a patent to Bartmann [78]. Subsequent to this, Corley in a series of patents described some detailed experiments on the copolymerization of bisbenzocyclobutenes with bismaleimides both with and without the addition of a free radical inhibitor [33, 34]. The structures of the bisbenzocyclobutenes used in this study are shown in Fig. 33. The bismaleimide component that was used was a mixture of three different bismaleimides in the molar ratio shown in Fig. 34. The individual bisbenzocyclobutenes were blended at elevated temperature with varying amounts of the bismaleimide composition. In some of the experiments, the free radical inhibitor phenothiazine was added at a 0.5 mole % level. The various monomer mixtures were then copolymerized using one of the cure schedules described in Table 14. The copolymers were then physically characterized using a variety of techniques. Table 14 shows the results obtained from copolymers... 

Niobium- and tantalum-containing mesoporous molecular sieves MCM-41 have been studied by X-ray powder diffraction, 29Si MAS NMR, electron spin resonance, nitrogen adsorption and UV-Vis spectroscopy and compared with niobium- and tantalum-containing silicalite-1. The results of the physical characterization indicate that it is possible to prepare niobium- and tantalum-containing MCM-41 and silicalite-1, where isolated Nb(V) or Ta(V) species are connected to framework defect sites via formation of Nb-O-Si and Ta-O-Si bonds. The results of this study allow the preparation of microporous and mesoporous molecular sieves with remarkable redox properties (as revealed by ESR), making them potential catalysts for oxidation reactions. 

Since the first synthesis of mesoporous materials MCM-41 at Mobile Coporation,1 most work carried out in this area has focused on the preparation, characterization and applications of silica-based compounds. Recently, the synthesis of metal oxide-based mesostructured materials has attracted research attention due to their catalytic, electric, magnetic and optical properties.2 5 Although metal sulfides have found widespread applications as semiconductors, electro-optical materials and catalysts, to just name a few, only a few attempts have been reported on the synthesis of metal sulfide-based mesostructured materials. Thus far, mesostructured tin sulfides have proven to be most synthetically accessible in aqueous solution at ambient temperatures.6-7 Physical property studies showed that such materials may have potential to be used as semiconducting liquid crystals in electro-optical displays and chemical sensing applications. In addition, mesostructured thiogermanates8-10 and zinc sulfide with textured mesoporosity after surfactant removal11 have been prepared under hydrothermal conditions. 

Table I lists some magnetic resonance methods that are applied in the physical characterization of BPCAs, and identifies the key physical parameters best studied by each technique. ...

As part of a more extensive study of cocrystals formed by isonicotinamide with carboxylic acids, 1 1 products containing the dicarboxylic fumaric or succinic acids [59]. In the structures of these particular cocrystals, the typical discrete dimeric synthon was not observed, but instead effectively infinite assemblies of one-dimensional chains were found instead. In a subsequent work, cocrystals of isonicotinamide containing mixed fumaric/succinic acids were prepared using both solid-state grinding and solution crystallization [60]. A full physical characterization of the products demonstrated that the products consisted of a single cocrystal phase, and were not simple physical mixtures of two cocrystal components. Such solid solutions were proposed as yet another method whereby one might obtain even finer control over the physical properties of cocrystal systems proposed as drug substances. 

In this chapter, we made an attempt to provide a comprehensive review of the current state-of-the-art on sources, chemical nature, and physical properties of organic aerosols. This review begins with an overview of few basic concepts on atmospheric aerosols, followed by a description of the major constituents of atmospheric aerosols. The sources, transformations, and removal processes of organic aerosols are outlined and followed by an overview of the major environmental and human health issues associated with organic aerosols. The chemical and physical characterization of organic aerosols is then reviewed and is finally followed by a list of uncertainties and suggestions that require further studies. 

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