Authors:Ravi Bhushan, Deepak Gupta, and Aishwarya Jain
A simple and sensitive method for separation and quantitative determination of antidiabetic drugs in pharmaceutical preparations has been established and validated. Commercial formulations of five antidiabetic drugs (metformin, pioglitazone, rosiglitazone, glibenclamide, and gliclazide) were chosen for the studies. The compounds were extracted, isolated, purified, recrystallized, and characterized by measurement of melting point,
, and IR. Quantitative determination was performed by HPLC, TLC, and column chromatography supplemented with UV spectrophotometry. Two of the combinations, metformin + pioglitazone and metformin + gliclazide, were separated by open-column chromatography. Detection was by UV spectrophotometry in HPLC and by use of iodine vapor in TLC.
Isomorphic substitution, accompanied by surface adsorption, of a trace cation into a crystalline host matrix from its saturated solution can be studied by a double radiotracer experiment. Recrystallization of the matrix and uptake of the trace cation are thus measured simultaneously. This paper gives the formulation of the radiotracer experiment and the precision with which mole fractions of the trace cation in both phases, may be derived from it. The final result is thus a set of coexisting mole fractions and their uncertainties as a function of time. As an illustration, the case of calcite as the host matrix and CdII as the trace cation is considered.
The characteristics of crystallization, melting and spherulitic growth of a random propylene copolymer (PRC) containing small amount of ethylene were studied in the presence of a selective Β-nucleating agent (calcium pimelate). It was established that the products of isothermal and non-isothermal crystallization are very rich in Β-modification but have mixed polymorphic composition. The formation of α-modification may be attributed to Βα-transition on the surface of growing Β-spherulites resulting in αΒ-twin-spherulites. During melting of PRC of Β-modification, the characteristics observed with Β-nucleated propylene homopolymers, namely, a Βα-recrystallization of recooled samples and separated melting of non-recooled samples (i.e. the melting memory effect), as well as a ΒΒ-recrystallization leading to a perfection of the structure within the Β-modification, are also demonstrated. The disturbance of regularity of the polymer chain highly reduces the tendency to Β-crystallization. In contrast to the observations with propylene homopolymers, the growth rate of α-modification (Gα) is higher than that of Β-modification (Gβ) and no critical crossover temperature can be found (T(Βα)=413 K) below whichGα>Gβ. The experimental results show that a partial disturbance of chain regularity by incorporation of comonomer units considerably reduces the tendency to Β-crystallization.
Authors:F. Giordano, A. Rossi, R. Bettini, A. Savioli, A. Gazzaniga, and Cs. Novák
The thermal behavior of binary mixtures of paracetamol and a polymeric excipient (microcrystalline cellulose, hydroxypropylmethylcellulose
and cross-linked poly(vinylpyrrolidone)) was investigated. The physical mixtures, ranging from 50 to 90% by mass of drug,
were submitted to a heating-cooling-heating program in the 35–180C temperature range. Solid-state analysis was performed
by means of differential scanning calorimetry (DSC), hot stage microscopy (HSM), micro-Fourier transformed infrared spectroscopy
(MFTIR), and scanning electron microscopy (SEM).
The polymeric excipients were found to address in a reproducible manner the recrystallization of molten paracetamol within
the binary mixture into Form II or Form III. The degree of crystallinity of paracetamol in the binary mixtures, evaluated
from fusion enthalpies during the first and second heating scans, was influenced by the composition of the mixture, the nature
of the excipient and the thermal history. In particular, DSC on mixtures with cross-linked poly(vinylpyrrolidone) and hydroxypropylmethylcellulose
with drug contents below 65 and75%, respectively, evidenced the presence only of amorphous paracetamol after the cooling phase.
Microcrystalline cellulose was very effective in directing the recrystallization of molten paracetamol as Form II.
The multiple melting behaviour of isothermally crystallized bulk poly(trimethylene
terephthalate) (PTT) observed using DSC has been correlated to the total depolarized
light intensity (DLI) of thin films using hot-stage polarized light optical
microscopy. The observation of partial melting, recrystallization and final
melting in the DSC is correlated to the observation of the partial decrease,
sudden increase and final decrease in DLI under the same heating conditions.
Integration of real-time visible spectra of the transmitted light was used
to separate the effects of retardation from pure birefringence of the colorful
spherulitic thin-film PTT samples. The correlation of the results from these
two methods has demonstrated clearly that the observed DSC multiple melting
behaviour of this particular polymer is the illustrated effect of a process
of continuous partial melting/recrystallization/final melting in the material
during thermal analysis. The observed thermal behaviour of these metastable
spherulitic materials is a complex function of their thermal history including
crystallization temperature and anneal conditions, including scanning rate
during thermal analysis.
Authors:A. Fave, M. Bouchaour, A. Kaminski, S. Begrger, A. Ould-Abbas, and N. Chabane Sari
The fabrication of solar cells based on the transfer of a thin silicon film on a foreign substrate is an attractive way to
realise cheap and efficient photovoltaic devices. The aim of this work is to realise a
thin mono-crystalline silicon film on a double porous silicon layer in order to detach and transfer it on mullite. The first
step is the fabrication of a double porous silicon layer by electrochemical
anodisation using two different current densities. The low current leads to a low porosity layer and during annealing, the
recrystallisation of this layer allows epitaxial growth. The second current leads
to a high porosity which permits the transfer on to a low cost substrate. Liquid Phase Epitaxy (LPE) performed with indium
(or In+Ga) in the temperature range of 950–1050C leads to almost homogeneous
layers. Growth rate is about 0.35 μm min−1. Crystallinity of the grown epilayer is similar on porous silicon and on single crystal silicon. In this paper, we focus
on the realisation of porous silicon
sacrificial layer and subsequent LPE growth.
Raw and thermally treated sepiolites from the Mantoudi area, Euboea, Greece, were investigated by means of X-ray diffraction
(XRD) in combination with thermo-gravimetric analysis (TG/DTG) and differential thermal analysis (DTA), as well as Fourier
transform (FTIR) spectroscopy, in order to study the collapse of the sepiolite structure with increasing temperature. The
main mineral constituent (>95%) is a well crystallized sepiolite. Quartz and dolomite occur in minor amounts. Calcination
of the samples was carried out up to 350, 720 and 820°C, for 2 h, and ‘sepiolite dihydrite’, ‘sepiolite anhydrite’ and ‘enstatite’
were formed, respectively, as magnesium co-ordinated water and octahedrically co-ordinated hydroxyl groups, are removed and
the dehydroxylated phase recrystallize to enstatite (MgSiO3). These structural and textural changes play an important role to the properties and uses of the studied sepiolites.
Authors:Gabriel de Araujo, Dalva de Faria, Márcio Zaim, Flávio de Souza Carvalho, Fabio de Andrade, and Jivaldo Matos
Tibolone polymorphic forms I (monoclinic) and II (triclinic) have been prepared by recrystallization from acetone and toluene,
respectively, and characterized by different techniques sensitive to changes in solid state, such as polarized light microscopy,
X-ray powder diffractometry, thermal analysis (TG/DTG/DSC), and vibrational spectroscopy (FTIR and Raman microscopy). The
nonisothermal decomposition kinetics of the obtained polymorphs were studied using thermogravimetry. The activation energies
were calculated through the Ozawa’s method for the first step of decomposition, the triclinic form showed a lower Ea (91 kJ mol−1) than the monoclinic one (95 kJ mol−1). Furthermore, Raman microscopy and DSC at low heating rates were used to identify and follow the thermal decomposition of
the triclinic form, showing the existence of three thermal events before the first mass loss.
Authors:Buchi Reddy Vaddula, Swathi Yalla, and Michael A. Gonzalez
A simple and rapid one-step continuous-flow synthesis route has been developed for the preparation of chromene derivatives from the reaction of aromatic aldehydes, α-cyanomethylene compounds, and naphthols. In this contribution, a one-step continuous-flow protocol in a ThalesNano H-Cube Pro™ has been developed for the preparation of these chromene derivatives. This arises from the multicomponent one-step reaction of aromatic aldehydes, α-cyanomethylene compounds, and naphthols. This flow protocol was optimized in 2-methyltetrahydrofuran, which is a more environmentfriendly solvent. The faster residence times (<2 min) coupled with elevated pressure (∼25 bar) results in an efficient, safer, faster, and modular reaction. Results obtained illustrate that this base-catalyzed reaction affords the respective chromene derivative products in very high yields. The products can then be easily purified by recrystallization, if desired.
High hydrostatic pressure (HHP) has been investigated as an alternative to thermal processing for food preservation. HHP has
been known to affect high molecular weight polymers causing phase change. Starch is gelatinized at a pressure on the order
of 600–700 MPa, at 25 °C. Gelatinized starch recrystallizes during storage affecting the texture and shelf life of food products.
The effect of HHP processing on the crystallization of starches from different botanical origins during storage at 4 and 23 °C
was investigated. Crystallization kinetics of HHP treated wheat and corn starch gels were compared using DSC. The effect of
crystallization on structure was evaluated in terms of storage modulus. The rate of retrogradation depended on the storage
temperature (23 °C and 4 °C) and the botanical origin of the starch. The least crystallization was observed in HHP treated
wheat starch stored at 23 °C. The storage modulus increased with crystallization of starch.