Microalgal biomass has proven to be highly effective in the removal of heavy metals such as Pb
2+
and Cd
2+
. Moreover, there are treatments available to enhance the heavy metal removal capabilities. ...This study investigates the impact of alkaline pretreatment on
Nannochloropsis oculata
biomass on the biosorption of Pb
2+
and Cd
2+
.
Nannochloropsis oculata
was cultured in fed-batch reactors at 25 °C, with 166 μmol photons m
-2
s
-1
light intensity, in f/2 Guillard medium for 21 days. The biomass was treated with 0.2 M CaCl
2
and 0.2 M NaOH for 24 h with slow stirring. FTIR studies indicated that carboxyl functional groups were mainly responsible for binding Pb
2+
and Cd
2+
during biosorption. The maximum biosorption capacity of Pb
2+
was 227.86 mg g
-1
and 57.17 mg g
-1
for Cd
2+
in the untreated biomass. The treatment with CaCl
2
(Bs1) was more effective in the removal of Pb
2+
than NaOH treatment (Bs2), otherwise NaOH treatment (Bs2) was better in the absorption of Cd
2+
than CaCl
2
treatment (Bs1). The experimental results and biosorption isotherms suggest that the microalgae showed a greater affinity for the removal of Pb
2+
than for Cd
2+
in all of the experiments. Both biomass treatments had a negative effect on Pb
2+
and Cd
2+
biosorption. Furthermore, the equilibrium data align well with the Sips isotherm model in the Langmuir derivation, suggesting a complex monolayer biosorption process.
Graphical Abstract
This work reports on the synthesis and characterization of three tritopic receptors and their binding properties toward various anions, as their tetrabutylammonium salts, and three alkali ...metal–acetate salts by UV–vis, fluorescence, 1H, 7Li, 23Na, and 39K NMR in MeCN/dimethyl sulfoxide (DMSO) 9:1 (v/v). Molecular recognition studies showed that the receptors have good affinity for oxyanions. Furthermore, these compounds are capable of ion-pair recognition of the alkali metal–acetate salts studied through a cooperative mechanism. Additionally, molecular modeling at the density functional theory (DFT) level of some lithium and sodium acetate complexes illustrates the ion-pair binding capacity of receptors. The anion is recognized through strong hydrogen bonds of the NH– groups from the two urea sites, while the cation interacts with the oxygen atoms of the polyether spacer. This work demonstrates that these compounds are good receptors for anions and ion pairs.
Two bis-urea type receptors were synthesized containing a polyether bridge and two 4-nitrophenyl groups as chromogenic units, R1 and R2. Molecular recognition studies of receptors towards different ...tetraalkylammonium and alkali metal salts were carried out in DMSO by UV-Vis and
1
H-NMR spectroscopy. The receptors were found to have high affinity for diverse anions and ion-pairs, showing the highest affinities towards the tetramethylammonium and sodium salts. The cation binding ability of the receptors was evidenced by means
1
H NMR, mass spectrometric ESI
+
studies and the crystal structures of some precursors. Additionally, the molecular modelling at the DFT level of the tetramethylammonium acetate complexes illustrates the potential ion-pair binding ability of the receptors: the anion is recognized through strong hydrogen bonds from the NH─ groups from the two urea sites, while the cation is bound by a combination of cation─π, C-H···O and C-H···π interactions.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Kinetics of transesterification of the RNA model substrate 2-hydroxypropyl 4-nitrophenyl phosphate promoted by Mg2+ and Ca2+, the most common biological metals acting as cofactors for nuclease ...enzymes and ribozymes, as well as by Co(NH3)6 3+, Co(en)3 3+, Li+, and Na+ cations, often employed as mechanistic probes, was studied in 80% v/v (50 mol %) aqueous DMSO, a medium that allows one to discriminate easily specific base (OH–-catalyzed) and general base (buffer-catalyzed) reaction paths. All cations assist the specific base reaction, but only Mg2+ and Na+ assist the general base reaction. For Mg2+-assisted reactions, the solvent deuterium isotope effects are 1.23 and 0.25 for general base and specific base mechanisms, respectively. Rate constants for Mg2+-assisted general base reactions measured with different bases fit the Brønsted correlation with a slope of 0.38, significantly lower than the slope for the unassisted general base reaction (0.77). Transition state binding constants for catalysts in the specific base reaction (K ⧧ OH) both in aqueous DMSO and pure water correlate with their binding constants to 4-nitrophenyl phosphate dianion (K NPP) used as a minimalist transition state model. It was found that K ⧧ OH ≈ K NPP for “protic” catalysts (Co(NH3)6 3+, Co(en)3 3+, guanidinium), but K ⧧ OH ≫ K NPP for Mg2+ and Ca2+ acting as Lewis acids. It appears from results of this study that Mg2+ is unique in its ability to assist efficiently the general base-catalyzed transesterification often occurring in active sites of nuclease enzymes and ribozymes.
A new water soluble 26-membered macrocyclic pyridinophane functionalized by amide and carboxymethyl groups has been synthesized in a single step reaction and characterized by elemental analysis, mass ...spectrometry (FAB
+
), UV-vis, fluorescence, and
1
H NMR spectroscopy as well as single-crystal X-ray diffraction analysis. Its complexation properties with the nucleobases thymine and uracil have been explored in aqueous media by performing
1
H NMR titration experiments and potentiometric studies. The binding constants of the 1:1 host-guest complexes were determined as 10
3
M
− 1
by proton NMR and 10
2
-10
3
M
− 1
by potentiometry. Semiempirical molecular modelling studies have shown that the nucleobases are included within the cavity of the macrocyclic receptor and that the complexes are stabilized by hydrogen bonding.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This work reports on two thiourea-based receptors with pyridine and amine units including 1-naphthyl (MT1N) and 4-nytrophenyl (MT4N) as signaling units. For both compounds, their affinity and ...signaling ability toward various anions of different geometry and basicity in DMSO were studied using UV–vis, fluorescence, and 1H NMR techniques. Anion recognition studies revealed that both MT1N and MT4N have, in general, high affinities toward basic anions. In this regard, a higher acidity of the MT4N receptor was demonstrated. Furthermore, MT4N has a higher affinity for fluoride (log K 1 = 5.98) than for the other anions and can effectively detect it through colorimetric changes that can be monitored by the UV–vis technique. The interaction between receptors and anions mainly involves the hydrogens of the amino and thiourea groups of the former. Complementary single-crystal X-ray diffraction studies and molecular modeling at the DFT level were also performed.
In this work, we report on the synthesis of two new mono-alkylated tetrandrine derivatives with acridine and anthracene units, MAcT and MAnT. The compounds were fully characterized by physicochemical ...techniques and single-crystal X-ray diffraction analysis. In addition, both derivatives were studied as nucleotide receptors and double-stranded DNA binders in aqueous phosphate buffer at pH = 7.2 using UV–vis and fluorescence spectroscopy. According to the molecular recognition studies, MAcT and MAnT exhibit high affinity (K ∼ 105 M−1) and selectivity for ds-DNA, presumably in an intercalation mode. Finally, the anti-proliferative effects of the tetrandrine derivatives on different cancer cell lines were explored, revealing promising activities. Particularly, the mono-anthracene tetrandrine derivative MAnT showed an IC50 of 2.74 μg/mL on the HeLa cervical cancer cell line, representing a value 3.3 times smaller than that obtained for unsubstituted tetrandrine. Examination of the cytotoxic effects on the HeLa cell line by inverted microscopy suggests that the cell death mechanism consists basically in apoptosis. The molecular modelling of three ds-DNA-MAcT complexes, suggested that the macrocycles may use an intercalation binding mode towards DNA. MAcT is predicted to bind into the major groove of the ds-DNA providing non-covalent interactions such as electrostatic, van der Waals and hydrophobic interactions that lead to selectivity. Overall experimental data supports the mode of action of MAnT and MAcT as cytotoxic compounds against cancer cell lines via a DNA interaction mechanism.
In this work we report on the synthesis and characterization of two new tetrandrine-based receptors and their binding properties towards a series of nucleotides and ds-DNA, in aqueous at pH = 7.2, by UV–Vis and fluorescence spectroscopy. Both receptors exhibit high affinity (K ∼ 105 M−1) and sequence selectivity for ds-DNA, in an intercalation binding mode. These studies were accompanied with single-crystal X-ray diffraction analysis and molecular modelling. Additionally, the anti-proliferative studies of the derivatives on different cancer cell lines reveal promising activities of the compounds. Display omitted
•Two new tetrandrine-based receptors were synthesized and characterized.•The receptors exhibit high affinity and sequence selectivity for ds-DNA.•The receptors bind to the ds-DNA by an intercalation binding mode.•The mono-anthracene derivative efficiently suppresses HeLa cancer cells growth.
