32 research outputs found
Polymeric strontium ranelate nonahydrate
The title compound, poly[[μ-aqua-tetraaqua{μ-5-[bis(carboxylatomethyl)amino]-3-carboxylatomethyl-4-cyanothiophene-2-carboxylato}distrontium(II)] tetrahydrate], [Sr2(C12H6N2O8S)(H2O)5]·3.79H2O, crystallizes with nine- and eight-coordinated Sr2+ cations. They are bound to seven of the eight ranelate O atoms and five of the water molecules. The SrO8 and SrO9 polyhedra are interconnected by edge-sharing, forming hollow layers parallel to (011). The layers are, in turn, interconnected by ranelate anions, forming a metal–organic framework (MOF) structure with channels along the a axis. The four water molecules not coordinated to strontium are located in these channels and hydrogen bonded to each other and to the ranelates. Part of the water H atoms are disordered. The compound dehydrates very easily and 0.210 (4) water molecules out of nine were lost during crystal mounting causing additional disorder in the water structure
Design of Elastomer Structure to Facilitate Incorporation of Expanded Graphite in Silicones Without Compromising Electromechanical Integrity
Design of elastomer structure to facilitate incorporation of expanded graphite in silicones without compromising electromechanical integrity
Human insulin polymorphism upon ligand binding and pH variation: the case of 4-ethylresorcinol
Optical Chemical Sensor Using Intensity Ratiometric Fluorescence Signals for Fast and Reliable pH Determination
Optical
pH sensors enable noninvasive monitoring of pH, yet in
pure sensing terms, the potentiometric method of measuring pH is still
vastly superior. Here, we report a full spectrometer-based optical
pH sensor system consisting of sensor chemistry, hardware, and software
that for the first time is capable of challenging the performance
of an electrode-based pH meter in specific applications such as biopharmaceutical
process monitoring and in single-use bioproduction. A highly photostable
triangulenium fluorophore emitting at 590 nm was immobilized in an
organically modified silicon matrix that allows for fast time-response
by rapid diffusion of water in and out of the resulting composite
polymer deposited on a polycarbonate substrate. Fluctuations from
the fiber optical sensor hardware have been reduced by including a
highly photostable terrylene-based reference dye emitting at 660 nm,
thus enabling intensity-based ratiometric readouts. The dyes were
excited by 505 nm light from a light emitting diode. The sensor was
operational within a pH range of 4.6–7.6, and was characterized
and demonstrated to have properties that are comparable to those of
commercial pH electrodes considering time-response (t90 < 90 s), precision (0.03 pH-units), and drift
Hydrothermal Pretreatment of Date Palm (Phoenix dactylifera L.) Leaflets and Rachis to Enhance Enzymatic Digestibility and Bioethanol Potential
Date palm residues are one of the most promising lignocellulosic biomass for bioethanol production in the Middle East. In this study, leaflets and rachis were subjected to hydrothermal pretreatment to overcome the recalcitrance of the biomass for enzymatic conversion. Evident morphological, structural, and chemical changes were observed by scanning electron microscopy, X-ray diffraction, and infrared spectroscopy after pretreatment. High glucan (>90% for both leaflets and rachis) and xylan (>75% for leaflets and >79% for rachis) recovery were achieved. Under the optimal condition of hydrothermal pretreatment (210 ∘ C/10 min) highly digestible (glucan convertibility, 100% to leaflets, 78% to rachis) and fermentable (ethanol yield, 96% to leaflets, 80% to rachis) solid fractions were obtained. Fermentability test of the liquid fractions proved that no considerable inhibitors to Saccharomyces cerevisiae were produced in hydrothermal pretreatment. Given the high sugar recovery, enzymatic digestibility, and ethanol yield, production of bioethanol by hydrothermal pretreatment could be a promising way of valorization of date palm residues in this region
Tuning the pK(a) of a pH Responsive Fluorophore and the Consequences for Calibration of Optical Sensors Based on a Single Fluorophore but Multiple Receptors
Since
Sørensen and Bjerrum defined the pH scale, we have relied
on two methods for determining pH, the colorimetric or the electrochemical.
For pH electrodes, calibration is easy as a linear response is observed
in the interesting pH range from 1 to ∼12. For colorimetric
sensors, the response follows the sigmoidal Bjerrum diagram of an
acid–base equilibrium. Thus, calibration of colorimetric sensors
is more complex. Here, seven pH responsive fluorescent dyes based
on the same diazaoxatriangulenium (DAOTA) fluorophore linked to varying
receptor groups were prepared. Photoinduced electron transfer (PeT)
quenching from appended aniline or phenol receptors generated the
pH response of the DAOTA dyes, and the position of the pKa value of the dye was tuned using the Hammett relationship
as a guideline. The fluorescence intensity of the dyes in a sol–gel
matrix environment was measured as a function of pH in universal buffer,
and it was found that the dyes behave as perfect pH responsive probes
under these conditions. The response of optical pH sensors is nonlinear
and was found to be limited to 2–3 pH units for a precision
of 0.01 pH unit. As sensors with a broader sensitivity range can be
achieved by mixing multiple dyes with different pKa values, mixtures of dyes in solution were investigated,
and a broad range pH sensor with a precision of 0.006 pH units over
a range of 3.6 pH units was demonstrated. Further, approximating the
sensor response as linear was considered, and a limiting precision
for this approach was determined. As the responses of the pH responsive
DAOTA dyes were found to be ideally sigmoidal and as the six dyes
were shown to have pKa values scattered
over a range from ∼2 to ∼9, this allows for design of
a broad range optical pH sensor in the pH range from 1 to 10. This
hypothesis was tested using quaternary mixtures of the different DAOTA
dyes, and these were found to behave as a direct sum of the individual
components. Thus, while linear calibration is limited to a precision
of 0.02 in a range of 2–3 pH units, calibration using ideal
sigmoidal functions is possible in the range of 1–10 with a
precision better than 0.01, and as good as 0.002 pH units
Towards accurate structural characterization of metal centres in protein crystals: the structures of Ni and Cu T6 bovine insulin derivatives
Using synchrotron radiation (SR), the crystal structures of T(6) bovine insulin complexed with Ni(2+) and Cu(2+) were solved to 1.50 and 1.45 Å resolution, respectively. The level of detail around the metal centres in these structures was highly limited, and the coordination of water in Cu site II of the copper insulin derivative was deteriorated as a consequence of radiation damage. To provide more detail, X-ray absorption spectroscopy (XAS) was used to improve the information level about metal coordination in each derivative. The nickel derivative contains hexacoordinated Ni(2+) with trigonal symmetry, whereas the copper derivative contains tetragonally distorted hexacoordinated Cu(2+) as a result of the Jahn–Teller effect, with a significantly longer coordination distance for one of the three water molecules in the coordination sphere. That the copper centre is of type II was further confirmed by electron paramagnetic resonance (EPR). The coordination distances were refined from EXAFS with standard deviations within 0.01 Å. The insulin derivative containing Cu(2+) is sensitive towards photoreduction when exposed to SR. During the reduction of Cu(2+) to Cu(+), the coordination geometry of copper changes towards lower coordination numbers. Primary damage, i.e. photoreduction, was followed directly by XANES as a function of radiation dose, while secondary damage in the form of structural changes around the Cu atoms after exposure to different radiation doses was studied by crystallography using a laboratory diffractometer. Protection against photoreduction and subsequent radiation damage was carried out by solid embedment of Cu insulin in a saccharose matrix. At 100 K the photoreduction was suppressed by ∼15%, and it was suppressed by a further ∼30% on cooling the samples to 20 K