1,721,103 research outputs found
Thermal and structural characterization of cyclomaltononaose (delta-cyclodextrin), cyclomaltodecaose (epsilon-cyclodextrin) and cyclomaltotetradecaose (iota-cyclodextrin)
No full textThermal behavior of cyclomaltononaose (delta-cyclodextrin, delta-CD), cyclomaltodecaose (epsilon-cyclodextrin, epsilon-CD) and cyclomaltotetradecaose (iota-cyclodextrin, iota-CD) and the solid-state phase transitions associated with the respective dehydration and rehydration processes were investigated. delta-CD, epsilon-CD and iota-CD in their amorphous and crystalline states were tested by differential scanning calorimetry (DSC), thermogravimetry (TG) and hot stage microscopy (HSM). X-ray powder diffraction (XRD) patterns both experimental and computer generated from single crystal data were used to support thermal data and to follow the solid-state phase transitions associated with thermal dehydration and rehydration of each cyclodextrin (CD). Thermal events associated with dehydration of delta-CD, epsilon-CD and iota-CD were evaluated and tentatively interpreted on the basis of water arrangements observed in the crystal lattice. Dehydrated delta-CD reverted to the starting 13.75H2O hydrate under high relative humidity (RH) conditions (100% RH) at room temperature (RT), while transformed into a 7H2O hydrate at 30–35% RH. Physicochemical characterization based on thermal behavior, which can be related to water arrangements observed in the respective crystals, permits to distinguish between delta-CD, epsilon-CD and iota-CD, as well as between the amorphous and crystalline states of each CD. The results can be useful for demonstrating the formation of a true inclusion complex of delta-CD, which occurs in two crystalline hydration states, with a guest drug
Thermal and structural characterization of commercial a-, b, and g-cyclodextrins
No full textalfa-, beta-, and gamma-cyclodextrins (CDs) marketed by five different companies were characterized from the thermal and structural point of view. Three aCD samples showed two-step DSC dehydration profiles and their XRD patterns were characteristic for alfaCD·6H2O form I, whereas one brand with an apparent three-step DSC dehydration behaviour was a mixture of alfaCD·6H2O form I and anhydrous alfaCD. The differences in the DSC profiles after dehydration and EGA onset decomposition temperatures
recorded for the five betaCD brands were attributed to different manufacturing and purification processes. The five gammaCDs brands showed a common thermal behaviour and very similar XRD patterns. The patterns did not match the idealized pattern of gammaCD·14.1H2O, indicating the occurrence of two different hydrated crystal structures
DSC study of crystallinity changes of naproxen in ground mixtures with linear maltooligomers
No full textDifferential scanning calorimetry has been applied to the analysis of cogrinding-induced crystallinity changes of naproxen in binary mixtures with linear maltooligomers. Factors which play a role in the amorphization process were the mixture composition, the duration of mechanical treatment and the degree of polymerization of the carrier. Maltopentaose was about as active as amorphous hydroxypropyl alpha- and beta-cyclodextrin MS 0.6, while maltotetraose displayed practically the same amorphizing capacity as native alpha- and beta-cyclodextrin. The melting peak temperature of naproxen was substantially unaltered by cogrinding with maltooligomers, while it considerably dropped in coground mixtures with cyclodextrin derivatives. This might be due to formation of a true inclusion complex in the solid state
Caratterizzazione termoanalitica e strutturale di modificazioni polimorfe e pseudopolimorfe del complesso molecolare tetroxoprim-sulfametrolo
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Trimethoprim-sulfadimidine 1:2 molecular complex monohydrate
No full textTrimethoprim [5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4diamine, TMP] interacts with one sulfadimidine [4-amino-N-(4,6-dimethyl-2-pyrimidinyl)benzenesulfonamide, SDMD] molecule through two hydrogen bonds forming an eight membered ring, as in the 1:1 methanolate complex, with no proton transfer from the imino sulfonamide N atom to the pyrimidine N atom of the partner. Association with the second sulfadimidine molecule (SDMD') occurs through an interaction involving the same pyrimidine N atom of TMP (which therefore acts as a double acceptor) and the NH imino group of the sulfonamide. The water molecule bridges the sulfonamido O atom and the p-aminophenyl group of SDMD' of two molecular complex units
Thermoanalytical characterization of pseudopolymorphs of sulphadimidine and sulphadimidine-trimethoprim molecular complexes
No full textIn recrystallization experiments of sulphadimidine from water, dioxane and their mixtures aimed at preparing the unstable
hydrate, a non-stoichiometric solvate with dioxane and a pseudopolymorph with similar X-ray powder diffraction and infrared absorption properties but different thermal behaviour (DSC, TG) were isolated. In co-crystallization experiments of trimethoprim and sulphadimidine, a monohydrate of the respective 1 : 2 molecular complex and a methanol solvate of the equimolecular complex were obtained from aqueous ethanol and anhydrous methanol, respectively. The thermal stability of both pseudopolymorphic complexes is re ̄ected by the high DSC and TG onset temperatures of solvent escape from the crystal lattice (Te=163 °C and Te = 144 °C, respectively, for water and methanol) and is consistent with the important role of water in the hydrated crystal packing and the very strong hydrogen-bonding interaction of methanol with a sulphonamido oxygen atom in the methanol solvate crystal
Thermal behaviour of crystalline and non-crystalline forms of triacetyl alfa-, beta-, and gamma-cyclodextrins.
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Large-ring cyclodextrins: physical chemical characterization and potential use in drug delivery
No full textInvestigation of physico-chemical properties of delta-, epsilon- and iota-cyclodextrins by means of thermal analysis (DSC and TG) supported by X-Ray powder diffraction has been done. Studies on dehydration-rehydration behaviour demonstrated that dehydrated delta-cyclodextrin may transform under controlled humidity conditions to a heptahydrate and dehydrated epsilon-cyclodextrin to an amorphous form, while the dehydrated iota-cyclodextrin reverted to the starting nonhydrate crystal form
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