23 research outputs found
MAu<sub>2</sub>GeS<sub>4</sub>‑Chalcogel (M = Co, Ni): Heterogeneous Intra- and Intermolecular Hydroamination Catalysts
High surface area
macroporous chalcogenide aerogels (chalcogels) MAu<sub>2</sub>GeS<sub>4</sub> (M = Co, Ni) were prepared from K<sub>2</sub>Au<sub>2</sub>GeS<sub>4</sub> precursor and CoÂ(OAc)<sub>2</sub> or NiCl<sub>2</sub> by one-pot sol–gel metathesis reactions in aqueous media.
The MAu<sub>2</sub>GeS<sub>4</sub>-chalcogels were screened for catalytic
intramolecular hydroamination of 4-pentyn-1-amine substrate at different
temperatures. 87% and 58% conversion was achieved at 100 °C,
using CoAu<sub>2</sub>GeS<sub>4</sub>- and NiAu<sub>2</sub>GeS<sub>4</sub>-chalcogels respectively, and the reaction kinetics follows
the first order. It was established that the catalytic performance
of the aerogels is associated with the M<sup>2+</sup> centers present
in the structure. Intermolecular hydroamination of aniline with 1-R-4-ethynylbenzene
(R = −H, −OCH<sub>3</sub>, −Br, −F) was
carried out at 100 °C using CoAu<sub>2</sub>GeS<sub>4</sub>-chalcogel
catalyst, due to its promising catalytic performance. The CoAu<sub>2</sub>GeS<sub>4</sub>-chalcogel regioselectively converted the pair
of substrates to respective Markovnikov products, (<i>E</i>)-1-(4-R-phenyl)-<i>N</i>-phenylethan-1-imine, with 38%
to 60% conversion
Predicting Fuel Ignition Quality Using <sup>1</sup>H NMR Spectroscopy and Multiple Linear Regression
An improved model for the prediction
of ignition quality of hydrocarbon
fuels has been developed using <sup>1</sup>H nuclear magnetic resonance
(NMR) spectroscopy and multiple linear regression (MLR) modeling.
Cetane number (CN) and derived cetane number (DCN) of 71 pure hydrocarbons
and 54 hydrocarbon blends were utilized as a data set to study the
relationship between ignition quality and molecular structure. CN
and DCN are functional equivalents and collectively referred to as
D/CN, herein. The effect of molecular weight and weight percent of
structural parameters such as paraffinic CH<sub>3</sub> groups, paraffinic
CH<sub>2</sub> groups, paraffinic CH groups, olefinic CH–CH<sub>2</sub> groups, naphthenic CH–CH<sub>2</sub> groups, and aromatic
C–CH groups on D/CN was studied. A particular emphasis on the
effect of branching (i.e., methyl substitution) on the D/CN was studied,
and a new parameter denoted as the branching index (BI) was introduced
to quantify this effect. A new formula was developed to calculate
the BI of hydrocarbon fuels using <sup>1</sup>H NMR spectroscopy.
Multiple linear regression (MLR) modeling was used to develop an empirical
relationship between D/CN and the eight structural parameters. This
was then used to predict the DCN of many hydrocarbon fuels. The developed
model has a high correlation coefficient (<i>R</i><sup>2</sup> = 0.97) and was validated with experimentally measured DCN of twenty-two
real fuel mixtures (e.g., gasolines and diesels) and fifty-nine blends
of known composition, and the predicted values matched well with the
experimental data
Dynamics and Mechanism of Intercalation/De-Intercalation of Rhodamine B during the Polymorphic Transformation of the CdAl Layered Double Hydroxide to the Brucite-like Cadmium Hydroxide
We studied the kinetics
of intercalation of a fluorescent probe
(rhodamine B (RhB)) during the formation of hierarchal microspheres
of cadmium–aluminum layered double hydroxide (CdAlA LDH) and
its de-intercalation upon transformation from the LDH phase into the
cadmium hydroxide β phase (CdÂ(OH)<sub>2</sub>) using a reaction-diffusion
framework (RDF) where the hydroxide anions diffuse into an agar gel
matrix containing the proper salts–fluorescent probe mixture.
In this framework, we achieved the stabilization of the CdAlA LDH,
which is known to be thermodynamically unstable and transforms into
CdÂ(OH)<sub>2</sub> and AlÂ(OH)<sub>3</sub> in a short period. RDF is
advantageous as it allows with ease the extraction of the cosynthesized
polymorphs and their characterization using X-ray diffraction (XRD),
differential scanning calorimetry (DSC), thermal gravimetric analysis
(TGA), solid-state nuclear magnetic resonance (SSNMR), Fourier transform
infrared (FT-IR), and energy dispersive X-ray (EDX). The kinetics
of inter/de-intercalation is studied using <i>in situ</i> steady-state fluorescence measurements. The existence of RhB between
the LDH layers and its expel during the transition into the β
phase are examined via fluorescence microscopy, XRD, and SSNMR. The
activation energies of intercalation and de-intercalation of RhB are
determined and show dependence on the cationic ratio of the corresponding
LDH. We find that the energies of de-intercalation are systematically
higher than those of intercalation, indicating that the dyes are stabilized
due to the probe–brucite sheets interactions. SSNMR is used
to shed light on the mechanism of intercalation and stabilization
of RhB inside the layers of the LDH
TG/DTG, FT-ICR Mass Spectrometry, and NMR Spectroscopy Study of Heavy Fuel Oil
There is an increasing interest in
the comprehensive study of heavy
fuel oil (HFO) due to its growing use in furnaces, boilers, marines,
and recently in gas turbines. In this work, the thermal combustion
characteristics and chemical composition of HFO were investigated
using a range of techniques. Thermogravimetric analysis (TGA) was
conducted to study the nonisothermal HFO combustion behavior. Chemical
characterization of HFO was accomplished using various standard methods
in addition to direct infusion atmospheric pressure chemical ionization
Fourier transform ion cyclotron resonance mass spectrometry (APCI-FTICR
MS), high resolution <sup>1</sup>H nuclear magnetic resonance (NMR), <sup>13</sup>C NMR, and two-dimensional heteronuclear multiple bond correlation
(HMBC) spectroscopy. By analyzing thermogravimetry and differential
thermogravimetry (TG/DTG) results, three different reaction regions
were identified in the combustion of HFO with air, specifically, low
temperature oxidation region (LTO), fuel deposition (FD), and high
temperature oxidation (HTO) region. At the high end of the LTO region,
a mass transfer resistance (skin effect) was evident. Kinetic analysis
in LTO and HTO regions was conducted using two different kinetic models
to calculate the apparent activation energy. In both models, HTO activation
energies are higher than those for LTO. The FT-ICR MS technique resolved
thousands of aromatic and sulfur containing compounds in the HFO sample
and provided compositional details for individual molecules of three
major class species. The major classes of compounds included species
with one sulfur atom (S<sub>1</sub>), with two sulfur atoms (S<sub>2</sub>), and purely hydrocarbons (HC). The DBE (double bond equivalent)
abundance plots established for S<sub>1</sub> and HC provided additional
information on their distributions in the HFO sample. The <sup>1</sup>H NMR and <sup>13</sup>C NMR results revealed that nearly 59% of
the <sup>1</sup>H nuclei were distributed as paraffinic CH<sub>2</sub> and 5% were in aromatic groups. Nearly 21% of <sup>13</sup>C nuclei
were distributed in aromatic groups, indicating that most paraffinic
CH<sub>2</sub> groups are attached to aromatic rings. A negligible
amount of olefins was present, and an appreciable quantity of monoaromatic
and polyaromatic content was observed. Molecular connectivity between
the hydrogen and carbon atoms using HMBC spectra was utilized to propose
several plausible skeletal structures in HFO
Anti-cancer agents in Saudi Arabian herbals revealed by automated high-content imaging
<div><p>Natural products have been used for medical applications since ancient times. Commonly, natural products are structurally complex chemical compounds that efficiently interact with their biological targets, making them useful drug candidates in cancer therapy. Here, we used cell-based phenotypic profiling and image-based high-content screening to study the mode of action and potential cellular targets of plants historically used in Saudi Arabia’s traditional medicine. We compared the cytological profiles of fractions taken from <i>Juniperus phoenicea</i> (Arar), <i>Anastatica hierochuntica</i> (Kaff Maryam), and <i>Citrullus colocynthis</i> (Hanzal) with a set of reference compounds with established modes of action. Cluster analyses of the cytological profiles of the tested compounds suggested that these plants contain possible topoisomerase inhibitors that could be effective in cancer treatment. Using histone H2AX phosphorylation as a marker for DNA damage, we discovered that some of the compounds induced double-strand DNA breaks. Furthermore, chemical analysis of the active fraction isolated from <i>Juniperus phoenicea</i> revealed possible anti-cancer compounds. Our results demonstrate the usefulness of cell-based phenotypic screening of natural products to reveal their biological activities.</p></div
The effect of plant fractions on mitochondrial superoxide production and cell-membrane permeability.
<p><b>A)</b> HeLa cells were treated with plant fractions for 24 h. An increase in the MitoSox signal was detected and correlated with the increasing concentration of the plant fraction. <b>B)</b> HeLa cells were treated with different concentrations of plant fractions for 24 h and then subjected to a cell membrane permeability test. Fluorescence readouts were normalized against an in-plate control. Each sample was tested in quadruplicate. Data are presented as means ± SD.</p
Cytological profiling heat map.
<p>Automated HCS was used to assess compound-related perturbations of human cells using a full set of cellular markers. To assign possible biological targets to the test compounds, we compared the resulting cytological profiles to profiles retrieved from reference compounds with known modes of action. Some of the plant fraction extracts closely matched FDA-approved anticancer drugs and clustered with topoisomerase inhibitors. Individual features are presented on the x-axis and individual compounds are presented on the y-axis.</p
The cytotoxic effect of plant fractions on HeLa cells.
<p>A-B) Cells were treated with various concentrations of plant extracts for 24 h or 48 h, stained with Hoechst, and assessed using HCS. The cells exhibited cytotoxicity, which is indicator of induced apoptosis or necrosis. C) The distribution of cells during the cell cycle: G2/M, S, G0/G1 and low phases after a 24-h treatment with plant fractions. Data shown are means ± SD.</p
Plant fractions induced an apoptotic effect on HeLa cells.
<p>HeLa cells were treated with several concentrations (1.56, 3.12, 6.25, 12.5, 25, and 50 μg/ml) of plant fractions for 24 h or 48 h. A, B) Automated HCS was used to measure the activity of caspase-9 and C, D) p53. The fluorescence readout was normalized against an in-plate control. Each sample was tested in quadruplicate. Data are presented as means ± SD.</p
Assesment of the double-strand breaks in the DNA.
<p>HeLa cells were treated with different concentrations of SPE fractions to detect the expression of γ-H2AX. Data are presented as means ± SD.</p