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1.
α-, β-, and γ-cyclodextrins (CDs) marketed by five different companies were characterized from the thermal and structural
point of view. Three αCD samples showed two-step DSC dehydration profiles and their XRD patterns were characteristic for αCD⋅6H2O form I, whereas one brand with an apparent three-step DSC dehydration behaviour was a mixture of αCD⋅6H2O form I and anhydrous αCD. The differences in the DSC profiles after dehydration and EGA onset decomposition temperatures
recorded for the five βCD brands were attributed to different manufacturing and purification processes. The five γCDs brands
showed a common thermal behaviour and very similar XRD patterns. The patterns did not match the idealized pattern of γCD⋅14.1H2O, indicating the occurrence of two different hydrated crystal structures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Thermal behaviors of trehalose dihydrate (T
h) and β-anhydrous trehalose (T
β) have been investigated by in-situ laboratory parallel-beam X-ray powder diffraction. Data indicate that both phases show
essentially the same volume expansion but expansion of the anhydrous form is markedly anisotropic due to the features of the
hydrogen-bond network. Under the present experimental conditions, dehydration starts at 66 °C and within the 75 < T < 114 °C the presence of the T
α anhydrous polymorphic form has been detected. 相似文献
3.
The intensities of the Fe L lines/bands l = L3M1, η = L2M1, α1,2 = L3M4,5, β1 = L2M4, and β3,4 = L1M2,3 were measured for pure Fe and Fe3O4 using a TAP crystal as the dispersing element. The energy of the exciting electrons, E0, was varied in the range 5 ≤ E0 ≤ 25 keV.
For pure Fe the following results were obtained. The net peak height ratio Ll/Lα remains relatively constant with varying
E0 at approximately 14%. The E0 dependence of Lη is similar to that of Ll, although Lη is less intense than Ll by a factor of 7. Lβ1/Lα decreases from 20% for E0 = 5 keV to about 5% for 25 keV. Lβ3,4 behaves like Lβ1 but is weaker by a factor of 15.
For Fe3O4 a much weaker intensity of Lα was observed which can be partially explained by its stronger absorption. Again, the E0 dependence of Ll and Lη is similar with Ll/Lα = 19% and Lη/Lα = 4%. Lβ1 and Lβ3,4 show a comparable E0 dependence. Lβ1/Lα decreases from 50% for E0 = 5 keV to 34% for 25 keV. Lβ3,4 is weaker than Lβ1 by a factor of about 25.
The observed E0 dependence of the different lines was used to estimate a set of mass absorption coefficients. Our value for Lα in Fe agrees
well with other data which were deduced from variable E0 measurements but differs considerably from data given by Heinrich and Henke. 相似文献
4.
The L spectra of the elements 14 ≤ Z ≤ 22 were reinvestigated. Because of the limited energy resolution of the multilayer
reflectors neither Ll and Lη nor Lα and Lβ1 could be resolved. Nevertheless, the line Lβ3,4 = L1M2,3 was observed for all elements Z ≥ 16, but not for 14Si and 15P. Exceptions to this are 18Ar and 22Ti. For 18Ar no suitable sample is available. In the case of 22Ti the Lβ3,4 line is overlapped by the O Kα line which has its origin in the oxide surface layer of the Ti standard. In all cases the
Lβ3,4 line was observed near to the expected position which was determined by means of the known electron binding energies.
The L spectrum of 21Sc was studied for various energies of the incident electrons, E0. These measurements show that Lβ3,4 is much more strongly absorbed in Sc than Ll,η and Lα,β1. From these measurements approximate mass absorption coefficients (m.a.c.) were deduced. The relative net peak height I(Lβ3,4)/I(Lα,β1) decreases from 15% at E0 = 4 keV to 4% at E0 = 20 keV, whereas I(Ll,η)/I(Lα,β1) remains nearly constant at 90%. The peak to background ratio of Ll,η is greater than that of Lα,β1. 相似文献
5.
Perlovich G. L. Hansen L. K. Bauer-Brandl A. 《Journal of Thermal Analysis and Calorimetry》2001,66(3):699-715
X-ray, DSC and solution calorimetric investigations were carried out for α-, β- and γ-modifications of glycine. Particular
attention was paid to kinetic and thermochemical aspects of γ- → α-phase transition. The temperature of this phase transition
turned out to be sensitive to a) conditions under which the crystals of the γ-modification were grown, b) tempering of crystals
c) form (geometry) of crystals. Kinetics of this phase transition of single crystals of γ-phase in rhomboedric form can be
described by the equation for two-dimension nuclei growth, whereas for crystals of triangle geometry the equation for three
dimension growth is valid. On the basis of energy parameters describing growth of α-form in γ- →α-phase transition, the kind
of structure defects, which are responsible for this phase transition, was estimated. Taking into account the Δsol
H
m, the absolute values of the lattice energies of the investigated polymorphs indescending order are follows: γ->α->β-modification.
The obtained results are discussed with respect to the peculiarity of the crystal lattice structures, particularly the network
of hydrogen bonds. The β-modification of glycine is monotropically related to the other forms, whereas γ-and α-polymorphs
are enantiotropically-related phases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
A new method was proposed for determining the most probable mechanism function of a solid phase reaction. According to Coats-Redfern's
integral equation Eβ→0 was calculated by extrapolating β to zero using a series of TG curves with different heating rates. Similarly, Eα→0 was calculated according to Ozawa's equation. The most probable mechanism function of the solid phase dehydration of manganese(II)
oxalate dihydrate was confirmed to be G(α)=(1-α)1/2 by comparing Eα→0 with Eβ→0.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
The heat required to release and vaporize bound H2O from crystalline α-lactose monohydrate and from lactose glass, as determined by differential scanning calorimetry is 12.3±0.7 and 10.8±0.5 kcal·mole−1 of H2O, respectively. Water vapor sorption by anhydrous α-lactose leads to the formation of the α-monohydrate. The isotherm, obtained gravimetrically for this process is Langmuir type. β-Lactose is completely non-hygroscopic below 97% relative humidity. Thereafter, it sorbs H2O rapidly to form a concentrated solution wherein the lactose is capable of mutarotation. Densites of lactose forms determined pycnometrically by helium displacement are: 1.535 g/cm3 for α-lactose·H2O; 1.547 g/cm3 for anhydrous α-lactose; and 1.576 g/cm3 for β-lactose. 相似文献
8.
A reinvestigation was undertaken in order to obtain reliable data of the relative intensities of the L spectra for the elements
24 ≤ Z ≤ 33. A TAP crystal with a periodicity of 25.757 ? was used as the dispersing element. With this crystal one is able
to resolve the lines/bands Ll = L3M1, Lη = L2M1, Lα1,2 = L3M4,5, Lβ1 = L2M4, and Lβ3,4 = L1M2,3. Among the investigated elements 33As is the only one for which the energy of the lines Lα1,2 and Lβ1 is below the L3 absorption edge. For all the other elements the lines Ll, Lη, and Lα1,2 are below the L3 edge, whereas Lβ1 and Lβ3,4 are above this edge. This difference leads to effects of differential absorption, where the absorption is stronger for decreasing
line energy. For the net peak height ratio β1/α we obtained results which are of the same order of magnitude as those given by White and Johnson (W&J) in their popular
tables. But for l/α and β3,4/β1 our results show an atomic number dependence which is completely different from those given by W&J. 相似文献
9.
《Thermochimica Acta》2006,448(1):31-36
In this study, dehydration of sodium carbonate monohydrate (Na2CO3·H2O) (SCM) in microwave (MW) field with silicon carbide (SiC) as an indirect heating medium was investigated. SCM samples containing up to 3% free moisture were placed in the microwave oven. The heating experiments showed that SCM is a poor microwave energy absorber for up to 6 min of irradiation at an 800 W of microwave power. The heat for SCM calcination is provided by SiC which absorbs microwave. The monohydrate is then converted to anhydrous sodium carbonate on the SiC plate by calcining, i.e. by removing the crystal water through heating of the monohydrate temperatures of over 120 °C. The calcination results in a solid phase recrystallization of the monohydrate into anhydrate. In the microwave irradiation process, dehydration of SCM in terms of indirect heating can be accelerated by increasing the microwave field power. 相似文献
10.
G. Bruni V. Berbenni C. Milanese A. Girella P. Cofrancesco G. Bellazzi A. Marini 《Journal of Thermal Analysis and Calorimetry》2009,95(3):871-876
In this work the solid-state characterization of anhydrous D-mannitol has been performed: α and β modifications can be distinguished only by XRPD and FTIR as they show melting temperature
and enthalpy that are the same within the standard deviation. The understanding of the thermal behaviour of the δ form (obtained
by re-crystallization in acetone) has required XRPD experiments performed at variable temperature. This form during heating
undergoes a solid phase transition to α modification. By cooling a melted sample, under a wide range of experimental conditions,
a very fast crystallization occurs. Independently of the starting crystal form (β or δ form), the re-crystallization of D-mannitol from melt always leads to α form. 相似文献
11.
The nature of epitaxial intergrowth of black (β) and red (α) modifications of zinc diphosphide is studied. The intergrowth
of single crystals is shown to be caused by that the atoms-analogs form almost identical structural motifs in both structures.
The black modification grows on the (001) plane of the red one so that its b axis is parallel to the (110) plane of α-ZnP2. 相似文献
12.
Hiroko Mineki Yoshiyasu Kaimori Tsuneomi Kawasaki Arimasa Matsumoto Kenso Soai 《Tetrahedron: Asymmetry》2013,24(21-22):1365-1367
An achiral nucleobase cytosine forms an achiral monohydrate crystal (space group: P21/c) by crystallization from a water solution. It was found that the removal of crystal water under reduced pressure at room temperature afforded a chiral crystal of anhydrous cytosine (P212121). The crystal chirality of anhydrous cytosine corresponds to the enantiotopic crystal face of the achiral monohydrate; therefore, when the enantiotopic b1-face is exposed to the reduced pressure, dehydration occurred in the direction from the b1-face to provide [CD(+)310KBr]-cytosine crystal. In contrast, dehydration from the b2-face gave the opposite enantiomorphous [CD(?)310KBr]-cytosine crystal. The correlation between enantiotopic faces and the formed crystal chirality is opposite to that from dehydration by heating. The formed chiral cytosine crystals act as a chiral trigger for asymmetric autocatalysis with enantioenrichment amplification of pyrimidylalkanol. 相似文献
13.
Effects of dehydration temperatures on moisture absorption and dissolution behavior of theophylline. 总被引:1,自引:0,他引:1
Anhydrous theophylline was prepared by heating theophylline monohydrate at temperatures between 60 degrees C and 140 degrees C. The effects of dehydration temperatures on the moisture absorption and dissolution behavior of anhydrous theophylline were investigated in this study. The hydration rate of anhydrous theophylline at 95% relative humidity and 25 degrees C decreased with increasing dehydration temperatures. From the fitting analysis of solid-state reaction models, the hydration reaction was found to be governed by the phase boundary reaction model for samples prepared at lower dehydration temperatures (<100 degrees C) but the reaction obeyed the growth of nuclei reaction model when samples were dehydrated at higher temperatures. The dissolution rates of various anhydrous theophylline samples were measured by the rotating disk method. The calculated solubility of anhydrous theophylline prepared by heating was about 2.5 times higher than that of theophylline monohydrate. The phase transformation rate from the anhydrous form to the monohydrate during dissolution tests decreased with higher dehydration temperatures. It was found that the anhydrous theophylline prepared at different dehydration temperatures transformed to the monohydrate by way of different growth of hydrate nuclei mechanism. 相似文献
14.
E. Cengiz V. Aylıkcı N. Kaya G. Apaydın E. Tıraşoğlu 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(1):89-96
In this study, the chemical effects on σKi
(i = α, β), σLα cross sections, Kβ/Kα X-ray intensity ratios and vacancy transfer probabilities from K to L (η
KL) for pure Nb and Nb compounds were investigated. The samples were excited by 59.5 keV γ-rays from 241Am and 5.96 keV photon energy from a 55Fe annular radioactive sources. K and L X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution
of 150 eV at 5.9 keV. While it was observed that the chemical bonding had an effect on the σKβ, σLα cross sections and Kβ/Kα X-ray intensity ratios for compounds, it was almost negligible for σKα cross section because Kα transitions (2P3/2,1/2→1S1/2) occurred in inner shells. It is well known that interactions between central element atom and ligands come into existence
in valence state, so outer energy levels are sensitive to the chemical environment. The experimental values of σKα cross section and η
KL are in good agreement with theoretically calculated and other experimental values of pure niobium, but the experimental values
of the σKβ, σLα cross sections and Kβ/Kα X-ray intensity ratios have differences for some compounds because valence electrons have different bond distances and binding
energies in different compounds. 相似文献
15.
Kinetics and mechanism of condensation of amino acids and amines of different structure and their derivatives with pyridoxal
were studied. It was established that the amino acid with secondary amino group, proline, adds to pyridoxal with the formation
of amino alcohol. α-Amino acids in the course of condensation with pyridoxal form amino alcohols which transform to Schiff
bases. The latter compounds by elimination of the α-hydrogen atom or CO2 from the amino acid fragment and the subsequent hydrolysis of the quinoid structure form the final products. β- And ɛ-amino
acids react with pyridoxal to form Schiff bases which are stable to chemical transformations. The possibility was shown of
their conversion to the quinoid structure. It was established that the guanidine structure of the molecule of L-arginine unlike
its α-NH2 group did not take part in the condensation with pyridoxal. The quantitative evaluation of the condensation rates of triptamine,
Ltriptofane, and its methyl ester in the stage of dehydration of their amino alcohols was carried out. 相似文献
16.
Y. Duan J. Li X. Yang X. -M. Cao L. Hu Z. -Y. Wang Y. -W. Liu C. -X. Wang 《Journal of Thermal Analysis and Calorimetry》2008,94(1):169-174
The thermal decomposition of strontium acetate hemihydrate has been studied by TG-DTA/DSC and TG coupled with Fourier transform
infrared spectroscopy (FTIR) under non-isothermal conditions in nitrogen gas from ambient temperature to 600°C. The TG-DTA/DSC
experiments indicate the decomposition goes mainly through two steps: the dehydration and the subsequent decomposition of
anhydrous strontium acetate into strontium carbonate. TG-FTIR analysis of the evolved products from the non-oxidative thermal
degradation indicates mainly the release of water, acetone and carbon dioxide. The model-free isoconversional methods are
employed to calculate the E
a of both steps at different conversion α from 0.1 to 0.9 with increment of 0.05. The relative constant apparent E
a values during dehydration (0.5<α<0.9) of strontium acetate hemihydrate and decomposition of anhydrous strontium acetate (0.5<α<0.9)
suggest that the simplex reactions involved in the corresponding thermal events. The most probable kinetic models during dehydration
and decomposition have been estimated by means of the master plots method. 相似文献
17.
La2Mo2O9 (LMO) was synthesized at lower temperature 973 K (LT-phase) by ceramic route. Differential thermal analysis (DTA) scan of
LT-phase of LMO showed α→β transition at 843 K during heating and β→α conversion via a metastable γ-phase during cooling.
This was also confirmed by thermo-dilatometry and impedance spectroscopy. La2Mo1.95V0.05O9-δ (LMVO), La1.96Sr0.04Mo2O9-δ (LSMO) and La1.96Sr0.04Mo1.95V0.05O9-δ (LSMVO) were prepared in a similar way. These compounds exhibited α→β transition on heating with shift in transition temperature,
but the existence of γ-phase during cooling disappeared. Substitution increased the ionic conductivity of α-phase and reduced
that of β-phase. 相似文献
18.
Cold crystallization and multiple melting behavior of poly(l-lactide) in homogeneous and in multiphasic epoxy blends 总被引:1,自引:0,他引:1
M. Itxaso Calafel Pedro M. Remiro M. Milagros Cortázar M. Elena Calahorra 《Colloid and polymer science》2010,288(3):283-296
Cold crystallization and melting of poly(l-lactide) (PLLA) blended with an uncured or with an amino-cured epoxy resin (diglycidyl ether of bisphenol-A [DGEBA]) were
investigated. It was found that the uncured PLLA/DGEBA blends were miscible, as they exhibited a single composition-dependent
glass transition temperature (T
g). Melting point depression measurements indicated the existence of some type of interaction between the blend components,
which was confirmed by Fourier transform infrared spectroscopy. Depending on the crystallization conditions and on the blend
composition, a mixture of α and α′ crystals have been detected in PLLA and in uncured DGEBA/PLLA blends when crystallized
from the glassy state. At high DGEBA contents, preferably imperfect α crystals are formed. On the contrary, at low DGEBA contents,
the α′ form predominates and an exotherm associated to the α′–α transformation appears on the differential scanning calorimetry
(DSC) scan before the main melting peak. Upon curing, the system transforms from a homogeneous mixture with a single refractive
index into an opaque multiphasic one, as revealed by the existence of two T
gs in the DSC scans. These cross-linked immiscible blends displayed a single crystallization exotherm which scarcely changed
with composition, and PLLA cold crystallized mainly into the α′ form from an almost pure PLLA phase; subsequently, the α′
crystals transform into the α form just before melting during the DSC scan. 相似文献
19.
A. Valor S. Kycia E. Reguera F. Sánchez-Sinencio 《Journal of solid state chemistry》2003,172(2):471-479
In the present work, an X-ray diffraction (XRD) and thermal study of calcium undecanoate is presented. The measured high-resolution XRD powder pattern of the synthesized salt at room temperature, using synchrotron radiation, showed that the salt is a mixture of monohydrated and anhydrous calcium undecanoate. Calcium undecanoate monohydrate proved to have a monoclinic cell with a symmetry described by the P21/a space group. The structure dehydrates at about 100°C. After dehydration, the salt undergoes a phase transformation which results in a thermotropic mesophase. Further heating of the salt leads to decomposition and melting. Ketones are the probable products of decomposition at 400°C. 相似文献
20.
α-[Mn(O2CMe)2]: a two-dimensional coordination polymer of the anhydrous manganese acetate polymorphs
Jian Lin Lei Yuan Dong-Wei Guo Gao Zhang Shi-Yan Yao Yun-Qi Tian 《Structural chemistry》2009,20(3):505-508
Abstract Two polymorphs of crystalline anhydrous manganese acetate, α-[Mn(O2CMe)2] (1) and β-[Mn(O2CMe)2] (2), were prepared under temperature-controlled solvothermal dehydration. X-ray single-crystal (and powder) diffractions revealed
that compound 1 crystallizes in monoclinic (a = 9.763(4), b = 4.972(2), c = 6.122(3) ?, β = 102.878(5)°, V = 289.7(2) ?3, Z = 4) space group P2/c. Although it was early prepared, its single crystal structure is firstly determined and known as a two-dimensional (2D) layer
structure; whereas, compound 2 demonstrates a three-dimensional diamondoid (dia-e) structure that people in its early X-ray single-crystal study was not aware of.
Graphical Abstract Anhydrous α-[Mn(O2CMe)2] was discovered in 1967, which two-dimensional layer structure is firstly determined by the X-ray single-crystal analysis.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献