8 research outputs found
Guest Exchange in a Robust Hydrogen-Bonded Organic Framework: Single-Crystal to Single-Crystal Exchange and Kinetic Studies
The salt 3,4-lutidinium
pamoate crystallizes as its hemihydrate,
forming a hydrogen-bonded organic framework with tetrahydrofuran (THF)
as a guest in channels in the structure (<b>1·THF</b>).
Extensive investigation has shown this framework to be highly robust:
the THF in the channels can be exchanged for 20 different compounds,
with 13 of these exchanges occurring in a single-crystal to single-crystal
manner. The THF can also be exchanged for the volatile solids pyrazine
or iodine, both via single-crystal to single-crystal transformations.
Stepwise exchange of solvents is also possible, with a sequence of
five exchanges occurring before the crystals begin to deteriorate.
Investigation of the kinetics of exchange in <b>1·THF</b> revealed that exchange occurs according to a deceleratory kinetic
model for contracting volume
A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene
A series of conformational polymorphs of hexakis(4-fluorophenoxy)cyclotriphosphazene
have been identified and characterized. Three of the four polymorphs
are previously unreported. Thermal analysis coupled with variable
temperature powder X-ray diffraction has shown that conversion between
polymorphs occurs at well-defined temperatures. The high temperature
form is metastable at room temperature and is never obtained from
solution. Two forms are observed in solution crystallization experiments,
a monoclinic form and a triclinic form. Slurry experiments revealed
that the triclinic form is the most stable at room temperature. The
fourth polymorph is observed only at low temperatures. Interconversion
between three of the polymorphs occurs in a single-crystal to single-crystal
manner
Selectivity Behavior of a Robust Porous Organic Salt Based on the Pamoate Ion
The
selectivity of a porous hydrogen-bonded framework, <b>1</b>,
toward various solvent mixtures has been investigated. Framework <b>1</b>, which is the hydrate of 3,4-lutidinium pamoate, crystallizes
as its THF solvate, <b>1·THF</b>. Solvent exchange can
take place either by exposing crystals of <b>1·THF</b> to
solvent vapors or by immersing the crystals in a solvent. Framework <b>1</b> shows preferential inclusion of particular solvents when
exposed to mixed solvent vapors, or to mixed solvents in the liquid
form. Analysis showed that solvents are included in the same ratios
when exposed to mixed solvents in the liquid or vapor phase, despite
the significant differences in mole ratios between the liquid and
vapor phases due to the different vapor pressures of the solvents
investigated. In some cases, when immersed in solvent mixtures containing
acetonitrile or acetone, <b>1·THF</b> recrystallizes as
an acetonitrile or acetone solvate of 3,4-lutidinium pamoate. The
crystal structures of these two new solvates are also reported
A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene
A series of conformational polymorphs of hexakis(4-fluorophenoxy)cyclotriphosphazene
have been identified and characterized. Three of the four polymorphs
are previously unreported. Thermal analysis coupled with variable
temperature powder X-ray diffraction has shown that conversion between
polymorphs occurs at well-defined temperatures. The high temperature
form is metastable at room temperature and is never obtained from
solution. Two forms are observed in solution crystallization experiments,
a monoclinic form and a triclinic form. Slurry experiments revealed
that the triclinic form is the most stable at room temperature. The
fourth polymorph is observed only at low temperatures. Interconversion
between three of the polymorphs occurs in a single-crystal to single-crystal
manner
Polymorphic Behavior of Two Organic Zwitterions: Two Rare Cases of No Observable Conversion between Polymorphs
The
solid-state behavior of two organic zwitterions, (<i>Z</i>)-3-carboxy-2-(4-cyanopyridin-1-ium-1-yl)-acrylate (<b>1</b>) and (<i>Z</i>)-1-(3-carboxy-1,1-dihydroxyprop-2-en-1-ide-2-yl)-pyridin-1-ium
(<b>2</b>), has been extensively investigated. Variation of
crystallization conditions resulted in the identification of two conformational
polymorphs of <b>1</b>, a kinetic and thermodynamic form. Three
polymorphs of <b>2</b>, where the formation of a particular
polymorph depends entirely on solvent of crystallization, were also
identified. The relationship between the polymorphs of both <b>1</b> and <b>2</b> has been extensively studied, and attempts
were made to interconvert between forms to determine their relative
stability. No interconversion between polymorphs is observed in either <b>1</b> or <b>2</b>. In the case of <b>1</b>, this is
likely due to restrictions on rotation of the carboxylic group in
the solid state, which is required for conversion between polymorphs
Iron(III) Protoporphyrin IX Complexes of the Antimalarial <i>Cinchona</i> Alkaloids Quinine and Quinidine
The antimalarial properties of the <i>Cinchona</i> alkaloids
quinine and quinidine have been known for decades. Surprisingly, 9-epiquinine
and 9-epiquinidine are almost inactive. A lack of definitive structural
information has precluded a clear understanding of the relationship
between molecular structure and biological activity. In the current
study, we have determined by single crystal X-ray diffraction the
structures of the complexes formed between quinine and quinidine and
iron(III) protoporphyrin IX (Fe(III)PPIX). Coordination of the alkaloid
to the Fe(III) center is a key feature of both complexes, and further
stability is provided by an intramolecular hydrogen bond formed between
a propionate side chain of Fe(III)PPIX and the protonated quinuclidine
nitrogen atom of either alkaloid. These interactions are believed
to be responsible for inhibiting the incorporation of Fe(III)PPIX
into crystalline hemozoin during its <i>in vivo</i> detoxification.
It is also possible to rationalize the greater activity of quinidine
compared to that of quinine
Solid-State Supramolecular Chemistry of a Benzylpyridine-Functionalized Zwitterion: Polymorphism, Interconversion, and Porosity
The
reaction between acetylenedicarboxylic acid and 4-benzylpyridine
yields two products: a salt and a zwitterion. The relationship between
these two products has been investigated, revealing that the salt
is the kinetic product of the reaction and the zwitterion is the thermodynamic
product. The zwitterion has four polymorphs and three solvates. Interconversion
between these forms has been studied and was shown to be solvent-mediated
when it occurs; conversion between most polymorphic forms cannot be
achieved using thermal methods. The temperature at which the reaction
to form the zwitterion is carried out and the solvent system used
are crucial in determining which polymorphic form crystallizes from
the reaction. In addition, polymorphic Form I is shown to be porous
to dioxane
Solid-State Supramolecular Chemistry of a Benzylpyridine-Functionalized Zwitterion: Polymorphism, Interconversion, and Porosity
The
reaction between acetylenedicarboxylic acid and 4-benzylpyridine
yields two products: a salt and a zwitterion. The relationship between
these two products has been investigated, revealing that the salt
is the kinetic product of the reaction and the zwitterion is the thermodynamic
product. The zwitterion has four polymorphs and three solvates. Interconversion
between these forms has been studied and was shown to be solvent-mediated
when it occurs; conversion between most polymorphic forms cannot be
achieved using thermal methods. The temperature at which the reaction
to form the zwitterion is carried out and the solvent system used
are crucial in determining which polymorphic form crystallizes from
the reaction. In addition, polymorphic Form I is shown to be porous
to dioxane