Authors:R. Bettini, G. Bertolini, E. Frigo, A. Rossi, I. Casini, I. Pasquali, and F. Giordano
The aim of this work was to study the solubility in supercritical CO2 of the hydrated phase of three model drugs, namely theophylline, carbamazepine, and diclofenac sodium, in comparison with
the respective anhydrous form. Possible solid-state modifications, stemming from the interaction with supercritical CO2, were investigated by differential scanning calorimetry, thermogravimetric analysis, hot stage microscopy, Fourier Transform
infrared spectroscopy and Karl-Fischer titrimetry. It was found that all three pharmaceutical hydrates exhibited higher solubility
in supercritical CO2 than the relevant anhydrous phases. In the case of theophylline monohydrate, the instability of the crystal phase at the
experimental temperature adopted has been evidenced. Diclofenac sodium tetrahydrate represents a peculiar case of chemical
interaction with the acid supercritical fluid, mediated by crystal water.
1 Introduction Natural gas hydrates are crystalline solids composed of water and gas. The gas molecules are trapped in water cavities that are composed of hydrogen-bonded water molecules [ 1 ]. Typical natural gas composition includes methane
The problem of interaction
between organic and water moieties (neutral or ionized water molecular species)
is of particular interest in chemistry in view of its implications to physico-chemical
behavior of chemical and biological systems. Hydration patterns which result
from interaction between hydrophilic and hydrophobic species are non trivial
in chemistry. The key issue is that water molecules are able to aggregate
in extremely large variety of structural modes. Tetrahedral geometry of intermolecular
bonding around water molecule is analogous in geometrical terms to that of
intramolecular geometry of carbon atom, known as a source of infinite number
of organic structures.
In general, space filling with hydrogen bonded water molecules
is rather low. It may be illustrated in the following way: volume of neonium
atoms is comparable to that of water molecules whilst having atomic mass just
10% higher than molecular mass of water. Thus, liquid neonium and liquid water
would have similar densities if molecular packing is of comparable efficiency.
The real values are much different, however. Liquid neonium at its boiling
temperature has density of 1.20 g cm–3 ,
thus displaying significantly denser packing that that of water molecules.
It certainly means that solid or liquid water has a ‘porous’ structure
and may lead to molecular inclusion of foreign (guest) species in the intermolecular
space of water framework. This property is not that simple, however, since
inclusion of foreign (guest) species is, as a rule, associated with rearrangement
of the host framework structure . Anyway, inefficient packing of the mono-component
host solid phases may be considered as a prerequisite for its pronounced clathration
Routine tests by TG and DSC with the common heating rates of 10‡C min−1 show large batch-to-batch variations for certain hydrate compounds. By additional measurements and changing to a gradient of 1‡C min−1 most differences are wiped out giving almost uniform characters.
Authors:Alex Neves Junior, Romildo Dias Toledo Filho, Eduardo de Moraes Rego Fairbairn, and Jo Dweck
Thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis have helped to understand and to study the behavior of cementitious materials during their hydration stages. Among these applications, there
distribution [ 3 ], which mainly depend on packing density of fresh paste and filling effect of hydration products. Water requirement for normal consistency, which consists of filling water, chemically combined water, absorption water, and free water, has a
Authors:Jiří Kučerík, Petra Bursáková, Alena Průšová, Lucie Grebíková, and Gabriele Ellen Schaumann
) are fulvic acids (FA) and humic acids (HA); FA are fractions of NOM soluble at all pH values, while HA are soluble only in alkaline solutions [ 2 ].
Hydration is the crucial factor playing role in biological function of molecules in both living
Authors:Nabajyoti Saikia, Shigeru Kato, and Toshinori Kojima
of the main phases of normal Portland cement clinker, plays an important role in the early stage of hydration process, and it is believed to be the responsible species for the setting and hardening behaviours of cement. The ionic substitution of this
The hydration of the cement minerals C 3 S (3CaO·SiO 2 ), C 2 S (2CaO·SiO 2 ), C 3 A (3CaO·Al 2 O 3 ) and C 4 AF (4CaO·Al 2 O 3 ·Fe 2 O 3 ) is an exothermal chemical process. At early ages, the generated heat can