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PubMed2007

Molecular dynamics study of the conformational dynamics and energetics of some large-ring cyclodextrins (CDn, n = 24, 25, 26, 27, 28, 29).

Molecular dynamics simulations in water solution were performed on six large-ring cyclodextrins (LR-CDs) with a degree of polymerization 24, 25, 26, 27, 28, and 29. The AMBER parm99 force field and explicit water molecules (TIP3P) were used in the simulations. The present research was aimed at further extending our knowledge on the structural dynamics and the energetics of this new class of compounds that may eventually provide chiral cavities suitable for formation of inclusion complexes with small molecules, and, accordingly, to serve as host structures for chiral recognition. The study focused on several representatives flanking CD26-the largest LR-CD for which X-ray data is available. Both the monitoring of the structural variations during the simulations as well as the analyses of energy balances are indicative for high flexibility of the macrorings. Slight differences of the overall preferred shapes were detected with diminishing the size of the macromolecules from CD29 to CD24. An elongated cavity (CD28) or a double parallel strand in different specific representations are the dominating motifs in the LR-CDs studied: with loops at the two ends (CD25, CD28, CD29), with a loop at one end (CD25), twisted (CD26, CD27) or twisted with an open portion in the middle (CD24), helical (CD24, CD25), or linking two loops from one of their sides (CD27). Two loops connected by an arc (CD28, CD29) and a cavity with the shape of an extended rectangular (CD24, CD28) appear preferentially during the conformational interconversions of the two larger CDs, whereas helical motifs are present in the smaller macrorings: an extended helix with ends linked by an arc (CD24), helical turn and helical portion (CD26, CD27). A triple propeller conformation or three symmetrical loops of almost equal size were also detected for CD26 and CD29, respectively. The present results further support the hypothesis for the existence of more than one cavity in large-ring cyclodextrins and suggest preferred conformations in water solution for the LR-CDs with degree of polymerization from 24 to 29.

Journal Article↗
PubMed1992

Patterns of GABAergic immunoreactivity define subdivisions of the mustached bat's medial geniculate body.

The anatomy and the spatial distribution of neurons and axonal endings (puncta) immunoreactive for glutamic acid decarboxylase (GAD) or gamma-aminobutyric acid (GABA) were studied in the medial geniculate body of the mustached bat (Pteronotus parnellii). The principal findings are that: 1) most GABAergic neurons are present in the dorsal and ventral divisions with few, if any, in the medial division; 2) only a small fraction, about 1% or less, of auditory thalamic neurons are immunopositive; 3) the density of immunoreactive puncta is independent on the number of GABAergic neurons in the thalamic divisions, with the ventral division having the largest number/unit area, the medial division about 75% of this value, and the dorsal division only about 50%; and 4) the form of the puncta was unique to each division, those in the ventral division being medium-sized and comparatively simple, those in the medial division predominantly large, coarse, and complex, while dorsal division ending were finer and more delicate. These patterns recapitulate, with some significant exceptions, those found in the rat and cat. The puncta could originate from several sources; while many may arise from intrinsic GABAergic Golgi type II local circuit neurons, these cells may not be the only or even the principal source. Thus, the dorsal division contains comparatively many immunopositive cells though fewer puncta than might be expected if the bulk of these were to arise from auditory thalamic interneurons. This suggests that other, extrinsic sources, such as the thalamic reticular nucleus, may be the source of such endings. A second point is that the form and density of the puncta is regionally specific within the medial geniculate complex. These local patterns might have a significant and regionally specific role in controlling the differential excitability of auditory thalamic neurons. The distribution of presumptive synaptic endings also has implications for the number and arrangement of glomeruli or synaptic nests. Thus, these circuit elements, which are common to the thalamic nuclei in other species, might play an important role in local synaptic circuits between different types of cells. If so, then the structural variations embodied in these patterns could subserve functional arrangements that differ among species. Such patterns might reflect concomitant physiological differences in the organization of local circuits within the microchiropteran medial geniculate body.

Animals↗
PubMed2005

Structure and properties of new ionic liquids based on alkyl- and alkenyltrifluoroborates.

A new series of low-melting, low-viscosity, hydrophilic ionic liquids, which comprise 1-ethyl-3-methylimidazolium ([EMI]+) and alkyl(alkenyl)trifluoroborate anions ([RBF3]-, R=n-C(m)H(2m+1) (m=1-5), CH2CH), were prepared and characterized. The phase-transition behavior, thermal stability, density, viscosity, conductivity, and surface tension of these salts were measured. The influence of the structural variations, such as changing the length and fluorination of the alkyl chain (R) in the anion [RBF3]-, on the above properties was extensively investigated. The low viscosity of these [RBF3]- salts suggests that a high degree of freedom and/or a somewhat flat-shaped feature in the anion make an important contribution to reducing the viscosity. The Walden products for each salt are not constant and vary with temperature, which suggests that the ions in these salts are not completely dissociated.

Journal Article↗
PubMed1985

Automated analysis and survival selection of anchorage-dependent cells under normal growth conditions.

An instrument is described that can automatically analyze and select for a subpopulation of anchorage-dependent cells in tissue culture. Cells that label with fluorescently tagged antibodies or demonstrate structural variations are saved from exposure to a destructive high-intensity argon laser beam. The surviving population may then be cloned. The cell selection may occur in a tissue culture plate or in a microflow incubator which is designed to maintain a constant flow of media at 37 degrees C across cells growing on a glass coverslip. This incubator sits on an inverted microscope which focuses the laser beam to a diameter as small as 1 micron. A high-speed computer-controlled two-dimensional stage moves the cells past the beam for analysis, the results of which determine the fate of each cell: whether it is to be destroyed by radiant energy or selected for survival and subsequent proliferation. Another selection strategy performed by the instrument involves growing the cells on a thin, blackened polyester film which can be cut by the argon laser beam. Cells selected for cloning are then circumscribed. The heat of cutting welds the circumscribed film to a plastic coverslip surface or tissue culture chamber bottom. Nonselected cells may be removed by pulling the unattached polyester sheet from the attachment surface. The selected cells remain on polyester film disks welded to the plastic. Selections may be done automatically under computer control or manually by operator direction of stage movements. This instrument extends the art of automated cell selection and analysis to normal cell lines that must maintain cell-substratum contact (anchorage dependence) for differentiated cell function, e.g., neurons, fibroblasts, or kidney cells.

Cell Adhesion↗
PubMed2026

Pangenome of Streptomyces sampsonii and Relatives Highlights Horizontal Gene Transfer and Secondary Metabolism in Environmental Adaptation and Ecological Significance.

Streptomyces sampsonii is a promising biocontrol bacterium, but its genomic basis of adaptation and secondary metabolism remains unclear. Here, we present a chromosome-level genome assembly of S. sampsonii (7.20 Mb, 6015 protein-coding genes) and perform comparative analyses with 95 related Streptomyces species. Phylogenomic and synteny analyses revealed its closest relationship with S. albidoflavus, while extensive structural variations distinguished more distant lineages. Pangenome analysis uncovered 84,178 gene clusters, with pan_shell and pan_cloud genes predominantly enriched in xenobiotic biodegradation, metabolism, and antibiotic biosynthesis, highlighting their roles in ecological adaptation and biocontrol potential. Biosynthetic gene cluster (BGC) analysis identified numerous NRPS, PKS, and terpene pathways, many of which belong to pan_shell and pan_cloud regions, suggesting dynamic evolutionary origins. We further detected 66,260 horizontally transferred (HGT) genes, including 438 in BGCs, underscoring HGT as a major driver of metabolic innovation. Together, these findings provide novel insights into the genomic diversity, adaptive capacity, and secondary metabolic potential of S. sampsonii and its close relatives.

BGCs↗
PubMed1996

Amino acid substitutions at position 97 in HLA-A2 segregate cytolysis from cytokine release in MART-1/Melan-A peptide AAGIGILTV-specific cytotoxic T lymphocytes.

CD8+ T lymphocytes recognize antigenic peptides presented by major histocompatibility complex (MHC) class I molecules. Individual peptide termini appear to be fixed at the C- and N-terminal ends. In contrast, central peptide side chains residues may point in different directions and exhibit limited flexibility, dependent on the MHC class I structural variation. For instance, position 97 in HLA-A201 has been shown to shift individual peptide species into different coordinations, one oriented towards the peptide N terminus, or more towards the C-terminal end. The conformational shape of such non-anchor peptide residues may affect the affinity of MHC/peptide/TCR interaction, resulting in quantitative, or qualitative different T cell effector functions. To characterize the impact of different amino acid residues occupying position 97 in HLA-A2 on peptide binding and presentation to CTL, we generated a panel of mutated HLA-A2 molecules containing either M, K, T, V, G, Q, W, P or H at position 97. The HLA-A0201 presented melanoma-associated MART-1/Melan-A derived peptide AAGIGILTV was employed to assess the impact of such position-97 mutations on HLA-A2 in peptide binding measured in an HLA-A2 reconstitution assay and presentation to AAGIGILTV-specific polyclonal or clonal T lymphocytes as measured by cytotoxicity, or interferon (IFN)-gamma and granulocyte/ macrophage colony-stimulating factor (GM-CSF) secretion. The high-affinity AAGIGILTV peptide bound to all position-97 mutants, albeit with differential efficiencies, and elicited specific release of IFN-gamma and GM-CSF by CTL. CTL responses were triggered only by the HLA-A2 wild type, by HLA-A2-H97 (histidine position 97 mutant), and HLA-A2-W97. The HLA-A2-M97 presenting molecule elicited enhanced cytokine release and CTL effector functions by polyclonal and by clonal effector T cells. These results indicate that MHC class I-bound peptides can trigger specific cytokine release by effector T cells independently of their ability to induce cytolysis. We conclude that relatively minor changes in the MHC class I peptide binding groove, including substitutions at position 97, can affect recognition by antigen-specific T cells. Mutant MHC class I molecules, such as those described here, may act as partial peptide antagonists and could be useful for inducing T lymphocytes with qualitatively different effector functions.

Amino Acid Sequence↗
PubMed2006

Distinct orientation of the alloreactive monoclonal CD8 T cell activation program by three different peptide/MHC complexes.

We have characterized three different programs of activation for alloreactive CD8 T cells expressing the BM3.3 TCR, their elicitation depending on the characteristics of the stimulating peptide/MHC complex. The high-affinity interaction between the TCR and the K(b)-associated endogenous peptide pBM1 (INFDFNTI) induced a complete differentiation program into effector cells correlated with sustained ERK activation. The K(bm8) variant elicited a partial activation program with delayed T cell proliferation, poor CTL activity and undetectable ERK phosphorylation; this resulted from a low-avidity interaction of TCR BM3.3 with a newly identified endogenous peptide, pBM8 (SQYYYNSL). Interestingly, mismatched pBM1/K(bm8) complexes induced a split response in BM3.3 T cells, with total reconstitution of T cell proliferation but defective generation of CTL activity that was correlated with strong but shortened ERK phosphorylation. Crystal structures highlight the molecular basis for the higher stability of pBM8/K(bm8) compared to pBM1/K(bm8) complexes that exist in two conformers. This study illustrates the importance of the stability of both peptide/MHC and peptide/MHC-TCR interactions for induction of sustained signaling required to induce optimal CTL effector functions. Subtle allelic structural variations, amplified by peptide selection, may thus orient distinct outcomes of alloreactive TCR-based therapies.

Animals↗
PubMed1989

Genetic studies of low-abundance human plasma proteins. X. Coagulation factor XIIIB variants in blacks.

Human coagulation factor XIIIV (F XIIIB) demonstrates genetically determined-structural variation with three common and several rare alleles. Population genetics studies reveal enormous intra and interracial group variation. In the present study, using isoelectric focusing and immunoblotting, we have determined for the first time the polymorphic occurrence of F XIIIB allelic forms in a native African population, namely Nigerian Blacks. In addition, F XIIIB data have been extended to various US Black populations. The characteristic feature of the black gene pool is the relative high frequency of the F XIIIB*2 allele, the highest being in Nigerians (0.723). The F XIIIB*6 allele is present at a polymorphic level in both the US and Nigerian Blacks and appears to be a unique black allele marker. The present technique has demonstrated several new alleles designated: F XIIIB*18, FXIIIB*22, F XIIIB*23 and F XIIIB*24. Among these new alleles the F XIIIB*23 exists at polymorphic level in both the US and Nigerian Blacks and is another unique Black allele marker of potential significance in population genetics studies.

Alleles↗
PubMed2004

Novel enantioselective strong cation exchangers based on sulfodipeptide selectors: evaluation for enantiomer separation of chiral bases by nonaqueous capillary electrochromatography.

Strong cation exchange (SCX)-type chiral stationary phases (CSPs) based on beta-amino sulfonic acid-terminated dipeptide derivatives as chiral selectors, immobilized on thiol-modified silica particles (3.5 microm), were synthesized and applied to enantiomer separations of chiral bases by nonaqueous capillary electrochromatography (CEC). The effect of structural variations of the sulfodipeptide selectors on the separation factors alpha was investigated. These studies included variation of the acid-terminal amino sulfonic acid residue, variation of the configurations, i.e., comparison of the diastereomeric (S,S)- and (R,S)-configurations of the sulfodipeptides, and finally comparison of sulfodipeptide selectors with corresponding beta-amino sulfonic acid analogs. In general, the capillary columns (100 microm ID) packed with the new SCX-type CSPs showed enantioselectivity for an elaborated set of chiral basic drugs in CEC acting by an enantioselective cation-exchange retention mechanism. N-[N-(4-Allyloxy-3,5-dichlorobenzoyl)-leucyl]-2-amino-3,3-dimethylbutane sulfonic acid, in particular with (R,S)-configuration, turned out to be a more effective SCX-type selector than a more rigid analog based on N-[N-(4-Allyloxy-3,5-dichlorobenzoyl)-leucyl]-2-pyrrolidinemethane sulfonic acid. Both of the former diastereomers were capable to baseline-resolve the enantiomers of ca. 40% of the tested basic chiral solutes including sympathomimetics and beta-blockers, while for the latter SCX-type CSPs only 10-20% of the selected solutes afforded resolutions > 1.5.

Adrenergic beta-Antagonists↗
PubMed2007

Genetic analysis of human complement factor H polymorphisms.

Human complement factor H (factor H) is polymorphic, with five previously reported FH alleles and three previously reported HF alleles (HF*A, HF*B, and HF*Q0). The relationship between the FH and HF alleles is not clear, and the genetic basis of factor H phenotypes has not yet been identified. In this study, nucleotide sequence analysis of complementary DNA (cDNA) from individuals with each HF phenotype identified seven mutated sites in the factor H gene. However, in four cases, the same cDNA sequence was observed in individuals with two different HF phenotypes. Western blotting and 2-DE also showed that a 160 kDa protein corresponding to factor H was expressed in individuals with HF phenotypes. In addition, factor H cross-reacting 45 and 42 kDa polypeptides were detected in individuals with HF A, HF B, or HF AB phenotypes, but not in individuals with the HF Q0 (a null allele) phenotype. Thus, HF phenotype did not correlate well with factor H gene or protein structural variation. Evidence is provided to support the hypothesis that the HF phenotypes do not correspond to polymorphism in factor H, but instead correspond to polymorphism in factor H-related protein 1. A novel PCR-RFLP method was developed and used to detect four polymorphisms (G257A, G1492A, A2089G, and G2881T) in the factor H gene in 54 unrelated Japanese individuals. This method could be useful for studies on genetic disease associated with these mutations.

Alleles↗
PubMedDate not supplied

Bilirubin chemistry, ionization and solubilization by bile salts.

Bilirubin is a linear tetrapyrrole whose conformation is affected by internal hydrogen bonds formed between the carboxyl side chains and dipyrromethenone rings. Structural variations include: constitutional isomerism of the vinyl or carboxyethyl side chains, geometric isomerism of the methene bridges, tautomerism of the lactam groups, conformational rotations about the central methylene bridge and ionization of one or both carboxyl groups. Aggregation of the dianion into dimers and multimers may occur. The pKa' values of the two carboxyl groups are affected greatly by the environment and may differ widely in micellar solutions like bile. Solubility of bilirubin in water is less than 1 nM at pH = 7 and about 0.1 microM at pH = 8. Nonetheless, it dissolves poorly in most lipid solvents, except for asymmetrical chloroalkanes. Hydrogen bond-breaking solvents, especially dimethyl sulfoxide, are most effective in solubilizing bilirubin. In bile salt solutions, solubility of bilirubin is well above the concentrations of unconjugated bilirubin found in normal human gallbladder bile, and is impaired by lecithin but unaffected by cholesterol. At physiological pH in bile salt solutions, bilirubin is predominantly in its monoanion form that binds readily to the micelles. In such solutions, addition of physiological concentrations of calcium precipitates calcium bilirubinate, leaving residual bilirubin concentrations of up to 15 microM in 50 mM taurocholate or close to the maximum bilirubin concentrations in normal bile. Studies in which disodium bilirubinate is dissolved in bile salt solutions and pH is adjusted to the physiological range reveal that metastable supersaturation with bilirubin may occur and that a mesophase may also form in the presence of lecithin, akin to that seen with cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile Acids and Salts↗
PubMed1982

Immunoglobulin V region variants in hybridoma cells. II. Recombination between V genes.

The mouse hybridoma line B1-8.delta 1 secretes a monoclonal IgD, lambda 1 anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibody with defined idiotypic determinants. Two spontaneous V-region variants (B1-8.V1/V2) with altered idiotope pattern were selected and the structural variation was located to the variable region of the heavy chain. The amino acid sequences of the B1-8. delta 1 and variant heavy chain V regions were determined. The variant VH regions are identical. Wild-type and variant VH regions differ in 10 positions. Single amino acid exchanges are found in the first and second framework at positions 20 and 43. The majority of replacements (eight substitutions) is clustered in the second complementary-determining region (CDR 2). There are no differences in CDR 1 and CRD 3 and the JH region. The variant, which at first glance appears to have undergone a series of point mutations, arose by recombination, possibly gene conversion, between the rearranged VDJ gene of the wild-type (B1-8.delta 1) and a neighbouring germ line VH gene encoding all of the substitutions.

Amino Acid Sequence↗
PubMed1988

Multiple RNAs expressed from the int-2 gene in mouse embryonal carcinoma cell lines encode a protein with homology to fibroblast growth factors.

Mouse embryonal carcinoma cell lines that differ in their patterns of expression of the potential oncogene int-2 have been exploited in a structural analysis of the multiple RNA transcripts characteristic of this gene. Ribonuclease protection experiments indicate that four major classes of int-2 RNA initiate at heterogeneous cap sites within two distinct promoter regions, P1 and P2, spanning approximately 50 and 150 bp respectively. The more downstream promoter P2 is located in a region of the DNA that constitutes an intron in RNA transcripts that initiate at the upstream promoter P1. Otherwise, all four RNA structures share the same splice donor and acceptor sites that define the boundaries of the second and third exons. Further complexity arises through usage of two distinct polyadenylation signals, both variants of the normal consensus, that are separated by 1100 bp. Despite these structural variations, the results suggest that all four major classes of RNA encode the same protein product which shows significant homology to the family of heparin-binding proteins typified by basic fibroblast growth factor (FGF).

Animals↗
PubMed1988

Antibody engineering for the analysis of affinity maturation of an anti-hapten response.

The influence of structural variation, previously observed in a panel of V186.2 VH/V lambda 1-expressing anti-NP antibodies from the secondary response, on the affinity of these antibodies was examined by site-specific mutagenesis and recombinant antibody construction. A tryptophan----leucine exchange at position 33 in the VH segment of all but one of the high-affinity antibodies is the most frequently observed somatic mutation and by itself leads to a 10-fold higher affinity; all other somatic exchanges are irrelevant for affinity selection. In the single case of a high-affinity antibody without this common exchange, high affinity is mediated by a combination of mutations (including a one-codon deletion) in VH and the particular D-JH rearrangement carried by this antibody. The data indicate that the pattern of somatic diversification through hypermutation is shaped by affinity selection, but that only a single point mutation is available in the VH and the VL gene of lambda 1 chain-bearing anti-NP antibodies which by itself leads to an increase of hapten-binding affinity. Based on the analysis of two secondary response antibodies from which somatic mutations in VH and VL have been eliminated, it is also concluded that the recruitment of B cell clones into the pathway of hypermutation involves a mechanism which is not based upon affinity differences towards the antigen.

Amino Acid Sequence↗
PubMed1994

Structure of PvuII endonuclease with cognate DNA.

We have determined the structure of PvuII endonuclease complexed with cognate DNA by X-ray crystallography. The DNA substrate is bound with a single homodimeric protein, each subunit of which reveals three structural regions. The catalytic region strongly resembles structures of other restriction endonucleases, even though these regions have dissimilar primary sequences. Comparison of the active site with those of EcoRV and EcoRI endonucleases reveals a conserved triplet sequence close to the reactive phosphodiester group and a conserved acidic pair that may represent the ligands for the catalytic cofactor Mg2+. The DNA duplex is not significantly bent and maintains a B-DNA-like conformation. The subunit interface region of the homodimeric protein consists of a pseudo-three-helix bundle. Direct contacts between the protein and the base pairs of the PvuII recognition site occur exclusively in the major groove through two antiparallel beta strands from the sequence recognition region of the protein. Water-mediated contacts are made in the minor grooves to central bases of the site. If restriction enzymes do share a common ancestor, as has been proposed, their catalytic regions have been very strongly conserved, while their subunit interfaces and DNA sequence recognition regions have undergone remarkable structural variation.

Amino Acid Sequence↗
PubMed1995

Structural effect of galactose residue in synthetic glycoconjugates on interaction with rat hepatocytes.

N-p-Vinylbenzyl-O-beta-D-galactopyranosyl-(1,4)-D-gluconamide++ + (PVLA) has been used as an asialoglycoprotein model polymer. Rat hepatocytes expressing asialoglycoprotein receptors are capable of binding to hydrophobic plastic dishes coated with PVLA. PVLA, water-soluble polystyrene derivatives bearing galactose residues preferentially adsorb to plastic plates made of polystyrene rather than those of poly(methyl methacrylate). Hence, we modified chitosan beads with linear chains composed of a long alkyl or phenyl moiety to study the effect of structural variations of adsorbed PVLA, and investigated the extent of hepatocyte attachment to the hydrophobic beads coated with PVLA. The attachment was independent of the amount of immobilized PVLA; rather, it was dependent on the hydrophobicity of the beads with PVLA. To simplify the surface of the hydrophobic beads with PVLA, galactopyranoses were covalently linked to chitosan beads via hydrophobic spacer arms, and hepatocyte attachment was compared among the prepared beads. The beads with spacer arms containing phenylalanine and a phthalic moiety showed increased hepatocyte attachment, which was elicited by galactose residues on the beads. These results suggest that rotational restriction or stiffness and hydrophobicity due to the phenyl moiety are essential to enhance the specificity of terminal galactose in PVLA. This analysis contributes to the design and optimization of an artificial ligand for cellular receptors recognizing sugar moieties.

Animals↗
PubMed1989

The role of Asp-49 and other conserved amino acids in phospholipases A2 and their importance for enzymatic activity.

The role of aspartic acid-49 (Asp-49) in the active site of porcine pancreatic phospholipase A2 was studied by recombinant DNA techniques: two mutant proteins were constructed containing either glutamic acid (Glu) or lysine (Lys) at position 49. Enzymatic characterization indicated that the presence of Asp-49 is essential for effective hydrolysis of phospholipids. Conversion of Asp-49 to either Glu or Lys strongly reduces the binding of Ca2+ ions, in particular for the lysine mutant, but the affinity for substrate analogues is hardly affected. Extensive purification of naturally occurring Lys-49 phospholipase A2 from the venom of Agkistrodon piscivorus piscivorus yielded a protein that was nearly inactive. Inhibition studies showed that this residual activity was due to a small amount of contaminating enzyme and that the Lys-49 homologue itself has no enzymatic activity. Our results indicate that Asp-49 is essential for the catalytic action of phospholipase A2. The importance of Asp-49 was further evaluated by comparison of the primary sequences of 53 phospholipases A2 and phospholipase homologues showing that substitutions at position 49 are accompanied by structural variations of otherwise conserved residues. The occurrence of several nonconserved substitutions appeared to be a general characteristic of nonactive phospholipase A2 homologues.

Amino Acid Sequence↗
PubMed2001

Polymorphism of rac-5,6-diisobutyryloxy-2-methylamino-1,2,3,4-tetrahydro-naphthalene hydrochloride (CHF 1035). I. Thermal, spectroscopic, and X-ray diffraction properties.

The polymorphism of rac-5,6-diisobutyryloxy-2-methylamino-1,2,3,4-tetrahydro-naphthalene hydrochloride (CHF 1035) was investigated. Three different crystal forms (Form I, Form II, and Form III) were obtained by recrystallization procedures from common organic solvents. The polymorphs were characterized by Raman and carbon-13 nuclear magnetic resonance ((13)C NMR) spectroscopy, in solution and in solid state (cross polarization-magic angle spinning), powder X-ray diffractometry, and thermal methods (differential scanning calorimetry, hot stage microscopy, and thermogravimetry). Moreover, the diffraction patterns of Form I, collected at controlled temperatures, gave evidence of the presence of two reversible structural rearrangements at approximately 60 and approximately 75 degrees C. These structural variations were confirmed by the results obtained by differential scanning calorimetry and hot stage microscopy techniques. The analysis of the Raman spectra allowed the identification of peculiar absorption bands for each polymorph. Form III was the stable crystal form at room temperature as determined by the basis of slurry conversion method.

Calorimetry, Differential Scanning↗