Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds-II

At room temperature, three of the six polymorphic compounds described are not present in their highest melting-point form, owing to enantiotropy. These three are triphenyltin chloride (3 modifications), 1-(4,4-dimethyl-2-oxo-3-tetrahydrofuryl)thiourea (4 modifications), and 2-aminoethyl diphenylborinate (3 modifications). In the case of 4-amino-1-(2-phenylethyl)-1,2,4-triazoline-5-thione, in addition to the absolutely stable modificationI, a further six unstable crystal forms have been observed. The three modifications of,-dimethyl-[1,1-biphenyl]-4-methanol are also monotropic in character. 2,9-Dimethyl-1,10-phenanthroline, the three polymorphic forms of which are unstable, is a special case, since it absorbs water from the air and changes into a semi-hydrate.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—VII

For four of the polymorphic compounds described, the commercial product does not consist of the form with the highest melting point. A spontaneous enantiotropic transformation is observed for 2-benzoxazolethiol (three modifications). For 2-furancarboxylic acid (three modifications) and 4-methoxy-3-nitrobenzaldehyde (three modifications), the form with the lower melting point either melts inhomogeneously with crystallization of modificationI, or homogeneously without formation of the highest melting form. Monotropy is observed for 2-nitrophenylacetic acid (four modifications) and salicylic acid hydrazide (four modifications). A special case is 1,2,4-triazole-3-thiol (three modifications) which in the commercial product occurs mainly as the metastable modificationIII, which is monotropic, whereas there is enantiotropy between modificationsI andII.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—IV

Twenty-four polymorphic compounds which show between two and four modifications are cited. The compounds described in detail are tetrabutylammonium iodide, tetraheptylammonium bromide, tetraoctylammonium bromide, 3-(3,4,5-trimethoxyphenyl)-2-propenoic acid andl-tyrosine ethyl ester hydrochloride. For the remaining nineteen compounds, only the number of modifications found, and their melting points where possible, are given.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—I

Seven polymorphic compounds are described, for each of which at least one enantiotropic relationship can be shown. 2-Chloro-ethylamine hydrochloride is a classical example, with two highly reproducible transformation points. Compounds which do not normally occur in their highest-melting form include 3,4-dibenzyloxyphenylacetic acid (3 modifications), 2-chlorotriethylamine hydrochloride (2 modifications) and 3,5-dimethoxbenzamide (3 modifications).N-Benzylphthal-imide and 2-chloro-4-nitrobenzoic acid occur naturally as mixtures of two modifications, the lower-melting of which is metastable at room temperature and the higher-melting is stable, with transformation points between 10 and 20° C. Only 2,4-dinitrophenyl-2,4-dinitrobenzoate (4 modifications) occurs naturally as the pure highest-melting modification, which is stable at room temperature.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—VI

Four of the six polymorphic compounds described occur in an enantiotropic low temperature form in the commercial products. Only for two of them is the highest melting form the stable form at room temperature. Enantiotropy between the commercial form and the higher melting modifications was observed for aminoacetonitrile hydrochloride (3 modifications), 3,4-dinitrobenzoic acid (4 modifications), 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (3 modifications) and (2-furyl)oxoacetamide (3 modifications). 2-Biphenyl-5-phenyl-1,3,4-oxadiazole (5 modifications) and (+-)-4-chloromandelic acid (3 modifications) can be assumed to be monotropic, but exact information about the modifications was impossible to obtain.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—V

All the polymorphic compounds described are enantiotropic, so that in four cases, order-disorder or rotational transformation can be deduced on the basis of the relationships between enthalpy of transformation and enthalpy of fusion. The following compounds are of this type: (±)-1-azabicyclo- [2.2.2]-octan-3-ol (4 modifications), 5-norbornene-2,3-dicarboxylic anhydride (3 modifications), (l.R)-(–)-camphorquinone (3 modifications) and 2-bromoethylamine hydrobromide (3 modifications). For tris(acetylacetonato)aluminium(III) (3 modifications) and 2-(4-aminophenyl)-6-methylbenzothiazole (5 modifications), another type of transformation must be assumed.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—VIII

Five polymorphic organic compounds which exhibited from three to seven modifications were examined. Because of enantiotropy, the commercial forms of three of the compounds did not consist of the modification with the highest melting point: These were 4-hydroxy-3,5-dimethoxybenzoic acid (4 modifications), 3-pyridylacetic acid (4 modifications) and 2,4,5-triaminopyrimidine (4 modifications). In contrast, 2-amino-2-cyanoacetamide (3 modifications) and [([(4-methylphenyl)sulphonyl]oxy)imino]propanedinitrile (7 modifications) were present in the highest melting form in the commercial products. A further 32 compounds (most of which had only two modifications) were examined and are reported without detailed results; six of them were enantiotropic.     

Infrared spectroscopic and thermal analytical investigations on the polymorphism of N-arylsulphonyl isothioureas

34 compounds containing the SO₂-N-C-N-moiety are investigated by means of infrared spectroscopy and differential scanning calorimetry to study problems of polymorphic species. There are arguments for different crystalline solids of 16 sulphonyl derivatives. The phenomenon of polymorphism can be discussed both in terms of different hydrogen bonding and conformational effects. Although two tautomers are thinkable for the compounds being investigated the sulphonylimino structure is assumed to yield the most stable state.     

Trends in Fourier transform infrared spectroscopic imaging

Fourier transform infrared (FTIR) spectroscopic imaging is a relatively new method that has received great attention as a new field of analytical chemistry. The greatest benefit of this technique lies in the high molecular sensitivity combined with a spatial resolution down to a few micrometers. Another advantage is the ability to probe samples under native conditions, which allows new insights into samples without the need for fixation, stains, or an additional marker. Advances in instrumentation have made FTIR spectroscopic imaging the tool of choice for an increasing number of applications. The main applications are in the bioanalytical chemistry of cells and tissue, polymers, and recently as well as in homeland security. This report gives a short overview of current developments and recent applications. Figure FTIR image of a polymer blend reveals the chemical composition. Online Abstract Figure (365 KB).     

Thermal and infrared spectroscopic characterization of historical mortars

The characterization of historical mortars was performed by thermal analysis (TG-DTG), simultaneous infrared spectroscopy (TG-FTIR) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The samples were taken from St. John Church (Tartu, Estonia), built in the 13th–14th centuries. The analyses are important for the restoration of the church.

In reality, mortar is a very difficult system, the lime is accompanied with different hydraulic components. TG-DTG analysis and FTIR methods can be used to identify various components of mortar and to observe the reactions associated with the controlled heating at 25–900°C in dynamic air and nitrogen atmosphere. The elemental composition of the acid-soluble components (ASC) was determined by using the ICP-AES techniques.     

Thermal,spectroscopic and structural studies of zinc(II) complex with nicotinamide

The zinc(II) complex with nicotinamide (ncam) was prepared and investigated by single-crystal X-ray diffraction, infrared spectrum (FTIR), conductivity and thermal analysis techniques. The formula of complex is [Zn(ncam)₂(H₂O)₄](NO₃)₂·2H₂O. The nicotinamide molecule has three following donor sites: pyridine ring nitrogen, aminonitrogen and carbonyl group oxygen. In this monomeric complex, the Zn(II) ion is six-coordinated by two pyridine ring N atoms and four water O atoms in a slightly distorted octahedral arrangement. In the crystal structure, intermolecular O-H…O and N-H…O hydrogen bonds link the molecules to form a supramolecular structure. The complex is stable up to 323 and above 360 K it dehydrates in one step losing six water molecules. The dehydration proceeds in the range of 360–438 K, and its enthalpy value is equal to 62.6±1.5 kJ mol⁻¹.     

Strategies for constructing the calibration set for a near infrared spectroscopic quantitation method

Three strategies for the construction of calibration sets have been tried, with the objective to develop and to validate a NIR quantitation method.The first two approaches consist of the use of two types of samples, named: samples of laboratory obtained by mixing the ingredients that compose the drug, and doped samples obtained by under- and over-dosed production samples. In order to improve the prediction results, production samples have been added to each calibration model. The ensuing models were validated with a view to determine their fitness for purpose. However, spectral differences between the laboratory samples and doped samples resulted in spurious predictions in quantifying samples of one type using the model developed from samples of the other.Such differences were studied in depth and a third procedure has been proposed, based on a calibration model constructed with an unique type of sample (laboratory sample) for later to correct it with a few doped samples. This corrected model has a good predictive ability on production samples.     

Near infrared spectroscopic imaging assessment of cartilage composition: Validation with mid infrared imaging spectroscopy

Disease or injury to articular cartilage results in loss of extracellular matrix components which can lead to the development of osteoarthritis (OA). To better understand the process of disease development, there is a need for evaluation of changes in cartilage composition without the requirement of extensive sample preparation. Near infrared (NIR) spectroscopy is a chemical investigative technique based on molecular vibrations that is increasingly used as an assessment tool for studying cartilage composition. However, the assignment of specific molecular vibrations to absorbance bands in the NIR spectrum of cartilage, which arise from overtones and combinations of primary absorbances in the mid infrared (MIR) spectral region, has been challenging. In contrast, MIR spectroscopic assessment of cartilage is well-established, with many studies validating the assignment of specific bands present in MIR spectra to specific molecular vibrations. In the current study, NIR imaging spectroscopic data were obtained for compositional analysis of tissues that served as an in vitro model of OA. MIR spectroscopic data obtained from the identical tissue regions were used as the gold-standard for collagen and proteoglycan (PG) content. MIR spectroscopy in transmittance mode typically requires a much shorter pathlength through the sample (≤10 microns thick) compared to NIR spectroscopy (millimeters). Thus, this study first addressed the linearity of small absorbance bands in the MIR region with increasing tissue thickness, suitable for obtaining a signal in both the MIR and NIR regions. It was found that the linearity of specific, small MIR absorbance bands attributable to the collagen and PG components of cartilage (at 1336 and 856 cm⁻¹, respectively) are maintained through a thickness of 60 μm, which was also suitable for NIR data collection. MIR and NIR spectral data were then collected from 60 μm thick samples of cartilage degraded with chondroitinase ABC as a model of OA. Partial least squares (PLS) regression using NIR spectra as input predicted the MIR-determined compositional parameters of PG/collagen within 6% of actual values. These results indicate that NIR spectral data can be used to assess molecular changes that occur with cartilage degradation, and further, the data provide a foundation for future clinical studies where NIR fiber optic probes can be used to assess the progression of cartilage degradation.     

Thermal hazard analysis of cumene hydroperoxide using calorimetry and spectroscopy

Organic peroxides have been widely used in industries and are known to be self-reactive chemicals. In this paper, thermal and infrared spectroscopic analyses were carried out to obtain a better understanding of the thermally hazardous behavior of cumene hydroperoxide (CHP) with cumene solvent. The temperature and heat flow profiles of different concentrations of CHP at scanning and isothermal conditions were measured with a small scale reaction calorimeter. Furthermore, probe type in situ infrared spectroscopic measurements were performed and the reaction mechanism will be discussed in regards to both energy release and product identification.     

Regression models based on new local strategies for near infrared spectroscopic data

In this work, a comparative study of two novel algorithms to perform sample selection in local regression based on Partial Least Squares Regression (PLS) is presented. These methodologies were applied for Near Infrared Spectroscopy (NIRS) quantification of five major constituents in corn seeds and are compared and contrasted with global PLS calibrations. Validation results show a significant improvement in the prediction quality when local models implemented by the proposed algorithms are applied to large data bases.     

Thermal decomposition of humboldtine: A high resolution thermogravimetric and hot stage Raman spectroscopic study

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. Humboldtine as the natural iron(II) oxalate mineral is a classic example. Thermogravimetry coupled to evolved gas mass spectrometry shows dehydration takes place in two steps at 130 and 141°C. Loss of the oxalate as carbon dioxide occurs at 312 and 332°C. Dehydration is readily followed by Raman microscopy in combination with a thermal stage and is observed by the loss of intensity of the OH stretching vibration at 3318 cm^-1. The application of infrared emission spectroscopy supports the results of the TG-MS. Three Raman bands are observed at 1470, 1465 and 1432 cm^-1 attributed the CO symmetric stretching mode. The observation of the three bands supports the concept of multiple iron(II) oxalate phases. The significance of this work rests with the ability of Raman spectroscopy to identify iron(II) oxalate which often occurs as a film on a host rock.This revised version was published online in November 2005 with corrections to the Cover Date.     

Near‐infrared spectroscopic studies on the cure behaviors of the CAE/DGEBA blend system initiated by a thermal latent catalyst

The latent properties and cure behaviors of an epoxy blend system based on cycloaliphatic epoxy (CAE) and diglycidyl ether of bisphenol A (DGEBA) epoxy containing N‐benzylpyrazinium hexafluoroantimonate (BPH) as a thermal latent initiator were investigated with near‐infrared (N‐IR) spectroscopy. The assignments of the latent properties and cure kinetics were performed by the measurements of the N‐IR reflectance for epoxide and hydroxyl functional groups at different temperatures and compositions. As a result, this system showed more than one type of reaction, and BPH was an excellent thermal latent catalyst without any coinitiator. The cure behaviors were identified by the changes in the absorption intensity of the hydroxyl groups at 7100 cm⁻¹ with different composition ratios. Moreover, characteristic N‐IR band assignments were used to evaluate the reactive kinetics and were shown to be an appropriate method for studying the cure behaviors of the CAE/DGEBA blend system containing a thermal latent catalyst. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 326–331, 2001     

Photoacoustic infrared spectroscopy and thermophysical properties of syncrude cokes

This paper presents and interprets photoacoustic (PA) infrared spectra and four different thermophysical properties (thermal conductivity, thermal diffusivity, volumetric specific heat and thermal effusivity) for four sets of hydrocarbon cokes. A total of 12 samples, with varying histories, were analyzed. These cokes are a by-product of the upgrading of bitumen to Syncrude Sweet Blend (a blend of hydrotreated components), and were obtained from several locations in the thermal cokers operated by Syncrude Canada Ltd. in Fort McMurray, Alberta, Canada. PA infrared spectroscopy provides detailed information on the amount and type of residual aromatic hydrocarbons in cokes; aliphatic hydrocarbons are sometimes detected in smaller quantities. Three of the thermophysical properties (thermal conductivity, diffusivity and effusivity) display systematic differences among the cokes. On the other hand, volumetric specific heat hardly varies, a phenomenon that accounts for the observed proportionality between thermal diffusivity and conductivity. Analogous relationships exist between thermal effusivity and both thermal conductivity and thermal diffusivity for these cokes. The magnitudes of these three thermophysical properties tend to increase as aromatics contents, determined by PA spectroscopy, decrease.This revised version was published online in November 2005 with corrections to the Cover Date.     

FTIR-Microscopic investigations of micro-phases and micro-phase-transitions in organic substances

From visual inspection by light microscopy it is likely that structural modifications are coexisting in microdomains of e.g.a-oxofuran acetamide, salicylic acid hydrazide and benzotriazole-5-carbonic acid methyl ester. An isolation of these phases is, however, not easy and a direct analysisin situ requires a non-destructive method of molecular specific microanalysis. Using FTIR-microscopy the samples prepared as thin film by cooling from the molten stage on an Al-mirror could be characterized as heterogeneous (lateral resolution 20m). The IR-spectra of the different microphases could be recorded for the first timein situ. Any conventional sample preparation technique (KBr-disk or dissolution) would destroy the important information about the microphase composition. A mere comparison of the micro-FTIR-spectra shows clearly the difference between the microphases. By using step scanning and image processing devices also invisible microphases can be detected (FTIR-microprobe). FTIR-microscopy can be successfully used to investigate temperatureinduced microphase transitions. Examples for D,L-norleucine, oxeladin citrate and 2-chloro-ethane-amine hydrochloride are given also.     

Quantitative chemical composition of thin films with infrared spectroscopic ellipsometry: application to hydrated oxide films on aluminium

A method to quantify the composition of thin films using infrared spectroscopic ellipsometry (IRSE), supplemented by visible spectroscopic ellipsometry (VISSE), is proposed. Because ellipsometry measures the thickness and optical constants of a surface layer simultaneously, the absorption coefficient of the film as a function of wavelength can be obtained. Using values of the absorption coefficients for the pure components of the film, the percentages (mol.% or wt.%) of each component in the film can be calculated. The method is demonstrated in a study of the hydration of oxide films on electropolished aluminium and the anodically formed barrier oxide film. The IRSE technique shows that hydration of the films by immersion in boiling water results in the conversion of aluminium oxide to pseudoboehmite. Copyright © 2003 John Wiley & Sons, Ltd.