N-Heterocyclic compounds are widely spread in the biosphere, being constituents of alkaloids, cofactors, allelochemicals, and artificial substances. However, the fate of such compounds including a ...catabolism of hydroxylated pyridines is not yet fully understood. Arthrobacter sp. IN13 is capable of using 4-hydroxypyridine as a sole source of carbon and energy. Three substrate-inducible proteins were detected by comparing protein expression profiles, and peptide mass fingerprinting was performed using MS/MS. After partial sequencing of the genome, we were able to locate genes encoding 4-hydroxypyridine-inducible proteins and identify the kpi gene cluster consisting of 16 open reading frames. The recombinant expression of genes from this locus in Escherichia coli and Rhodococcus erytropolis SQ1 allowed an elucidation of the biochemical functions of the proteins. We report that in Arthrobacter sp. IN13, the initial hydroxylation of 4-hydroxypyridine is catalyzed by a flavin-dependent monooxygenase (KpiA). A product of the monooxygenase reaction is identified as 3,4-dihydroxypyridine, and a subsequent oxidative opening of the ring is performed by a hypothetical amidohydrolase (KpiC). The 3-(N-formyl)-formiminopyruvate formed in this reaction is further converted by KpiB hydrolase to 3-formylpyruvate. Thus, the degradation of 4-hydroxypyridine in Arthrobacter sp. IN13 was analyzed at genetic and biochemical levels, elucidating this catabolic pathway.
Tributyl phosphate (TBP) exhibit significant intensification effect toward the extraction of 4-hydroxypyridine by di(2-ethylhexyl) phosphoric acid in 1-octanol via a more tendency to form (1:1) type ...complexes.
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The efficient separation of amphoteric organic compounds from dilute solutions is of great importance in the industrial field. In the present work, the reactive extractions of 4-hydroxypyridine (4-HP) with tributyl phosphate (TBP), di(2-ethylhexyl) phosphoric acid (D2EHPA) and TBP + D2EHPA dissolved in 1-octanol were investigated, respectively. The influences of the initial concentrations of TBP, D2EHPA and TBP + D2EHPA on distribution ratio (D) were discussed, as well as the reactive extraction mechanism were proposed. The obvious intensification effect was observed when the mixture of TBP and D2EHPA was used as extractant. The best extraction conditions were found to be of the molar ratio of D2EHPA and TBP at 2:1 and the equilibrium aqueous pH at 3.50–4.50. D values increased with the increase of the total concentration of TBP and D2EHPA in 1-octanol. Especially, the analysis on the extraction mechanisms clearly indicate (i) TBP in 1-octanol shows negligible reactive extraction toward 4-HP, (ii) D2EHPA in 1-octanol exhibits moderate extraction effect by forming 4-HP:D2EHPA (1:1) and 4-HP:2D2EHPA (1:2) type complexes, while (iii) D2EHPA in TBP/1-octanol demonstrates the maximum distribution ratio with the 4-HP:D2EHPA (1:1) type complex domination. The discussion provides new insights on the mechanism and opens a new way for the intensified extraction of amphoteric organic compounds by using the mixture of multiple extractants in the diluent.
Influence of counterion on the mesomorphic behavior and photophysical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine Display omitted
•ILC pyridinium salts ...derived from 4-hydroxypyridine were prepared and studied.•N-3,4,5-tridodecyloxybenzyl-4-pyridone shows a monotropic Colh phase.•Bulkier counterions (BF4- or PF6-) destabilize the LC phase.•3,4,5-Tridodecyloxybenzyl pyridinium bromide salt shows two LC columnar phases.
A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56°C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br−) with other counterions (NO3-,BF4- and PF6-) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed.
The asymmetric unit of the title compound, ReCl(C
5
H
5
NO)
2
(CO)
3
·C
5
H
5
NO, contains one molecule of the complex
fac
-ReCl(4-pyOH)
2
(CO)
3
(where 4-pyOH represents 4-hydroxypyridine) and one ...molecule of pyridin-4(1
H
)-one (4-HpyO). In the molecule of the complex, the Re atom is coordinated to two N atoms of the two 4-pyOH ligands, three carbonyl C atoms, in a facial configuration, and the Cl atom. The resulting geometry is slightly distorted octahedral. In the crystal structure, both fragments are associated by hydrogen bonds; two 4-HpyO molecules bridge between two molecules of the complex using the O=C group as acceptor for two different HO– groups of coordinated 4-pyOH from two neighbouring metal complexes. The resulting square arrangements are extented into infinite chains by hydrogen bonds involving the N—H groups of the 4-HpyO molecule and the chloride ligands. The chains are further stabilized by π-stacking interactions.
The ligand 2,6-bis(benzimidazol-2-yl)-4-hydroxypyridine (H
3
OBP) and its complexes, Co(HOBP)(H
2
OBP)·2H
2
O·2EtOH (1) and Ni(H
2
OBP)
2
Ni(H
3
OBP)(H
2
OBP)NO
3
·3H
2
O (2), have been synthesized ...and characterized by single-crystal X-ray crystallography, IR, UV-Vis, and fluorescence spectroscopies. Each metal center in two complexes is six-coordinated with N6 donor set in slightly distorted octahedral environment, which are further linked by extensive hydrogen bonds and π-π stacking to form multidimensional supramolecular network. Moreover, the interactions of complexes 1 and 2 with calf thymus DNA (CT-DNA) have been investigated by fluorescence spectroscopy, showing the apparent binding constant (K
app
) values of 4.31 × 10
5
M
−1
and 3.14 × 10
5
M
−1
for 1 and 2, respectively.
Synthesis and structures of six lanthanide complexes M(4-O-C
6H
4NH)
3(NO
3)
2(H
2O)
2NO
3 {M
=
La, Ce, Pr, Nd, Eu, Gd} is described. The metal ion in these complexes has a tricapped trigonal ...prismatic structure. The neodymium complex in the solid state has a configuration different from the rest of the complexes.
Preferential formation and X-ray structures of tris(4-hydroxypyridinium) nitrato complexes M(4-O-C
6H
4NH)
3(NO
3)
2(H
2O)
2NO
3 {M
=
La, Ce, Pr, Nd, Eu, Gd} in the simple reaction of 4-hydroxypyridine with the respective nitrates is described. All these compounds are isostructural and crystallize in the space group
P2
12
12
1. There are, however, minor differences in the hydrogen bonding features. The central metal ion in all these complexes has a coordination number of nine and the geometry may be described as tricapped trigonal prism. The neodinium complex has a chirality opposite to that of the rest of the structures. TGA data are also consistent with the solid state structures of these compounds.
Extractions of 4-Hydroxpyridine (4HP) from aqueous solutions using Di(2-ethylhexyl)phosphoric acid (D2EHPA) as extractant in 1-octanol and kerosene were studied. The factors that affected the ...distribution coefficient (D), such as equilibrium pH, the concentration of D2EHPA, and the type of diluents were discussed. The interaction mechanism between 4HP and D2EHPA was validated by infrared spectroscopic analysis. D increased with the increase of the concentration of D2EHPA and peak values appeared at equilibrium pH = 3.6-5.0. D in the polar diluent (1-octanol) was much higher than those in the non-polar diluent (kerosene). The extraction reaction was found to be a proton-transfer process and D2EHPA mainly reacted through its -OH with -N- of 4HP. The apparent reactive extraction equilibrium constants K
11
and K
12
were obtained by fitting the experimental data of extraction equilibrium. By comparing calculated D values from the proposed model with the experimental ones, the accuracy of the proposed model was examined.
4-Hydroxypyridine undergoes a smooth reaction with dialkyl acetylenedicarboxylates in the presence of triphenylphosphine (15 mol %) to produce the E/Z isomers of dialkyl ...2-(4-oxopyridin-1(4H)-yl)but-2-enedioates in high yields.
A composite oxide ZnAl
2
O
4
was prepared by microwave-assisted hydrothermal treatment, a precursor mixture of hydroxides obtained by precipitation of aluminium and zinc nitrates. Characterization by ...TEM, XRD and textural studies shows that ZnAl
2
O
4
is nanosized and is a micro/mesoporous material with large a surface area (140 m
2
/g). The gas phase catalytic methylation of 4-hydroxypyridine in the presence of the ZnAl
2
O
4
catalyst was performed in a continuous process at atmospheric pressure in the temperature range of 240–360 °C. A mixture of
O
- and
N
-alkylated products, namely 4-methoxypyridine and
N
-methyl-4-pyridone were obtained. The alkylation of 4-hydroxypyridine with methanol at 345 °C offered 87.6% selectivity towards
N
-methyl-4-pyridone with about 89% 4-hydroxypyridine conversion.
Within our current studies on the natural photodegradation of representative aquatic environmental contaminants, the visible light irradiation of the model compound 4-hydroxypyridine (4-OHP), in ...air-equilibrated aqueous solution and in the presence of riboflavin (Rf), has been studied employing stationary photolysis, polarographic detection of oxygen uptake, stationary and time-resolved fluorescence spectroscopy, and laser flash photolysis. The results indicate that 4-OHP — a compound inert towards the attack of singlet molecular oxygen (O
2(
1
Δ
g)) generated by Rose Bengal sensitization — quenches excited singlet and triplet states of Rf, with rate constants of
2.4×10
9
M
−1
s
−1
and
1.2×10
7
M
−1
s
−1
, respectively. The photodecomposition of Rf, a known process taking place from triplet Rf, has been found to depend on the concentration of dissolved 4-OHP: at ≥20
mM limited photodecomposition occurs due to the quenching of excited singlet Rf, while at ca. 5
mM triplet Rf is photogenerated and subsequently quenched either by oxygen, giving rise to O
2(
1
Δ
g), or by 4-OHP, yielding semireduced Rf through an electron transfer process. Superoxide dismutase inhibition of the oxygen uptake and flash photolysis data indicate that superoxide anion is generated, likely by the reaction of the anion radical from Rf with dissolved oxygen, also yielding neutral, ground state Rf. The final result is that both 4-OHP and Rf are photodegraded, probably through oxidation with superoxide anion.
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