Carboxylic Ring Research Articles

Investigation of the occurrence characteristics of organic components in high-sulfur waste residues (HSWR)

High-sulfur waste residues (HSWR) is a typical byproduct produced in the printing and dyeing industry that has hazardous properties, such as flammability and reactivity, etc. It is of great significance for the directional and harmless treatment of waste residues in the later stage on the research in-depth of the occurrence characteristics of each component in HSWR. In this paper, the combinatorial analysis method is employed to perform in-depth research on the phase composition, surface chemical situation of element, and the occurrence state of functional groups of the waste residue from multiple perspectives. The results show that the organic and inorganic components in HSWR are intricately interwoven, and exhibit significant thermal instability at high temperatures, with a maximum weight less of 86.66%. Carbon mainly exists in the states of C-H/C-OH/C-C, C-O/C-NH2, and C=O/C-N/C-S/CHx and constitutes the main chain of the carboxylic ring. Sulfur mainly occurs in three forms, namely, amorphous aggregated sulfur, sulfur-containing inorganic salts such as sulfate, and nitrogen-heterocyclic organic compounds containing sulfhydryl groups and methyl sulfur groups. These organic compounds constitute branch chains of the organic phase, and combine with metal cations through hydroxyl or carboxyl groups, and deposit on the surface of inorganic agglomerated sulfur. This wrapping structure increases the stability of volatile compounds in the slag and increases the difficulty of sulfur and chlorine removal. These findings provide a material basis for the later development of safe and effective HSWR disposal techniques.

Crystal structure of trans-di-aqua-(1,4,8,11-tetra-aza-undeca-ne)nickel(II) bis-(pyridine-2,6-di-carboxyl-ato)nickel(II).

The asymmetric unit of the title compound, trans-di-aqua-(1,4,8,11-tetra-aza-undecane-κ4 N 1,N 4,N 8,N 11)nickel(II) bis-(pyridine-2,6-di-carboxyl-ato-κ3 O 2,N,O 6)nickel(II) {[Ni(L)(H2O)2][Ni(pdc)2] where L = 1,4,8,11-tetra-aza-undecane (C7H20N4) and pdc = the dianion of pyridine-2,6-di-carb-oxy-lic acid (C7H3NO4 2-)} consists of an [Ni(L)(H2O)2]2+ complex cation and a [Ni(pdc)2]2- anion. The metal ion in the cation is coordinated by the four N atoms of the tetra-amine ligand and the mutually trans O atoms of the water mol-ecules in a tetra-gonally elongated octa-hedral geometry with the average equatorial Ni-N bond length slightly shorter than the average axial Ni-O bond [2.087 (4) versus 2.128 (4) Å]. The ligand L adopts its energetically favored conformation with five-membered and six-membered chelate rings in gauche and chair conformations, respectively. In the complex anion, the NiII ion is coordinated by the two tridentate pdc2- ligands via their carboxyl-ate and nitro-gen atom donors in a distorted octa-hedral trans-NiO4N2 geometry with nearly orthogonal orientation of the planes defining the carboxyl-ate rings and the average Ni-N bond length [1.965 (4) Å] shorter than the average Ni-O bond distance [2.113 (7) Å]. In the crystal, the NH donor groups of the tetra-amine, the carb-oxy-lic groups of the pdc2- anion and the coordinated water mol-ecules are involved in numerous N-H⋯O and O-H⋯O hydrogen bonds, leading to electroneutral sheets oriented parallel to the (001) plane.

Crystallographic investigation of the ubiquinone binding site of respiratory Complex II and its inhibitors

The quinone binding site (Q-site) of Mitochondrial Complex II (succinate-ubiquinone oxidoreductase) is the target for a number of inhibitors useful for elucidating the mechanism of the enzyme. Some of these have been developed as fungicides or pesticides, and species-specific Q-site inhibitors may be useful against human pathogens. We report structures of chicken Complex II with six different Q-site inhibitors bound, at resolutions 2.0–2.4 Å. These structures show the common interactions between the inhibitors and their binding site. In every case a carbonyl or hydroxyl oxygen of the inhibitor is H-bonded to Tyr58 in subunit SdhD and Trp173 in subunit SdhB. Two of the inhibitors H-bond Ser39 in subunit SdhC directly, while two others do so via a water molecule. There is a distinct cavity that accepts the 2-substituent of the carboxylate ring in flutolanil and related inhibitors. A hydrophobic “tail pocket” opens to receive a side-chain of intermediate-length inhibitors. Shorter inhibitors fit entirely within the main binding cleft, while the long hydrophobic side chains of ferulenol and atpenin A5 protrude out of the cleft into the bulk lipid region, as presumably does that of ubiquinone. Comparison of mitochondrial and Escherichia coli Complex II shows a rotation of the membrane-anchor subunits by 7° relative to the iron‑sulfur protein. This rotation alters the geometry of the Q-site and the H-bonding pattern of SdhB:His216 and SdhD:Asp57. This conformational difference, rather than any active-site mutation, may be responsible for the different inhibitor sensitivity of the bacterial enzyme.

Molecular hybridization based design and synthesis of new benzo[5,6]chromeno[2,3-b]-quinolin-13(14H)-one analogs as cholinesterase inhibitors

A Series of new tacrine analogs were designed, synthesized, characterized by respective spectral data and evaluated for cholinesterase inhibitory activity to be useful in Alzheimer’s disease. Most of the synthesized compounds showed good in vitro inhibitory activities toward acetyl cholinesterase (AChE) and butyrylcholinesterase (BuChE) enzymes. Among the compounds, 6i, 6o and 6r with increased saturated carboxylic ring size attached to the pyridine moiety and having 3,4-dihydroxy, 3,4,5-trimethoxy substituents on the aromatic ring attached at the stereogenic center have shown equal potency to that of tacrine with IC50values 0.65 ± 0.06, 1.32 ± 0.02 and 0.85 ± 0.05, 1.65 ± 0.12 and 0.92 ± 0.03, 1.91 ± 0.12 μM against AChE and BuChE, respectively. Standard drug tacrine exhibited IC50 values of 0.47 ± 0.02 and 0.65 ± 0.08, while Donepezil showed IC50 0.71 ± 0.06 and 0.31 ± 0.04 μM against AChE and BuChE, respectively. Docking studies of all the molecules disclosed close hydrogen bond interactions with the binding site.

Ion and inhibitor binding of the double-ring ion selectivity filter of the mitochondrial calcium uniporter

The calcium (Ca2+) uniporter of mitochondria is a holocomplex consisting of the Ca2+-conducting channel, known as mitochondrial calcium uniporter (MCU), and several accessory and regulatory components. A previous electrophysiology study found that the uniporter has high Ca2+ selectivity and conductance and this depends critically on the conserved amino acid sequence motif, DXXE (Asp-X-X-Glu) of MCU. A recent NMR structure of the MCU channel from Caenorhabditis elegans revealed that the DXXE forms two parallel carboxylate rings at the channel entrance that seem to serve as the ion selectivity filter, although direct ion interaction of this structural motif has not been addressed. Here, we use a paramagnetic probe, manganese (Mn2+), to investigate ion and inhibitor binding of this putative selectivity filter. Our paramagnetic NMR data show that mutants with a single carboxylate ring, NXXE (Asn-X-X-Glu) and DXXQ (Asp-X-X-Gln), each can bind Mn2+ specifically, whereas in the WT the two rings bind Mn2+ cooperatively, resulting in ∼1,000-fold higher apparent affinity. Ca2+ can specifically displace the bound Mn2+ at the DXXE site in the channel. Furthermore, titrating the sample with the known channel inhibitor ruthenium 360 (Ru360) can displace Mn2+ binding from the solvent-accessible Asp site but not the inner Glu site. The NMR titration data, together with structural analysis of the DXXE motif and molecular dynamics simulation, indicate that the double carboxylate rings at the apex of the MCU pore constitute the ion selectivity filter and that Ru360 directly blocks ion entry into the filter by binding to the outer carboxylate ring.

Pore Architecture and Ion Selectivity Filter of the Mitochondrial Calcium Uniporter

The calcium uniporter of mitochondria is a holocomplex consisting of the calcium-conducting channel, known as the MCU channel, and a score of regulatory proteins. Previous electrophysiology study found that a preeminent property of the uniporter is the high calcium selectivity and conductance and this has been shown to critically depend on the highly conserved amino acid sequence motif, DXXE, in the MCU channel. Our recent NMR data of the MCU channel indicate that the DXXE forms two parallel carboxylate rings at the channel entrance that appear to serve as the ion selectivity filter. We used paramagnetic probes to show that mutants with a single carboxylate ring can bind divalent cation specifically, while in the wild type, the two rings bind the ion cooperatively, resulting in drastically higher apparent affinity. Our new data, together with structural analysis of the DXXE motif, indicate that the double carboxylate rings at the apex of the MCU pore constitute the ion selectivity filter of the channel and that Ru360 directly blocks ion entry into the filter.

Architecture of the mitochondrial calcium uniporter.

Mitochondria from multiple, eukaryotic clades uptake and buffer large amounts of calcium (Ca2+) via an inner membrane transporter called the uniporter. Early studies demonstrated that this transport requires a mitochondrial membrane potential and that the uniporter is itself Ca2+ activated, and blocked by ruthenium red or Ru3601. Later, electrophysiological studies demonstrated that the uniporter is an ion channel with remarkably high conductance and selectivity2. Ca2+ entry into mitochondria is also known to activate the TCA cycle and appears to be critical for matching ATP production in mitochondria with its cytosolic demand3. MCU (mitochondrial calcium uniporter) is the pore forming and Ca2+ conducting subunit of the uniporter, but its primary sequence does not resemble any calcium channel known to date. Here, we report the structure of the core region of MCU, determined using nuclear magnetic resonance (NMR) and electron microscopy (EM). MCU is a homo-oligomer with the second transmembrane helix forming a hydrophilic pore across the membrane. The channel assembly represents a new solution of ion channel architecture and is stabilized by a coiled coil motif protruding in the mitochondrial matrix. The critical DxxE motif forms the pore entrance featuring two carboxylate rings, which appear to be the selectivity filter based on the ring dimensions and functional mutagenesis. To our knowledge, this is one of the largest structures characterized by NMR, which provides a structural blueprint for understanding the function of this channel.

Nickel(II) complexes of whole set of the simple ethylenediaminetetracarboxylate ligands: DFT study of complexes invoking molecular orbital and configurational analysis

The whole set of the nickel(II) complexes with no derivatized edta-type hexadentate ligands has been investigated from their structural and electronic properties. Two more complexes have been prepared in order to complete the whole set: trans(O5)-[Ni(ED3AP)]2- and trans(O5O6)-[Ni(EDA3P)]2- complexes. trans(O5) geometry has been verified crystallographically and trans(O5O6) geometry of the second complex has been predicted by the DFT theory and spectral analysis. Mutual dependance has been established between: the number of the five-membered carboxylate rings, octahedral/tetrahedral deviation of metal-ligand/nitrogen-neighbour-atom angles and charge-transfer energies (CTE) calculated by the Morokuma’s energetic decomposition analysis; energy of the absorption bands and HOMO–LUMO gap.

Proton-pair disorder in dimers of aromatic carboxylic acids: vibrational spectra of benzoic acid at low temperatures

The resolved multiplet structure of carboxylic ring bands observed for benzoic acid and d 5-deuterated benzoic acid by IR and Raman spectroscopy at low temperatures is not in agreement with previous assignments. The temperature dependence of half-widths of some other vibrational bands reveals that more than one mechanism for proton-pair disorder has to be taken into account.

An infrared linear dichroism study of carboxylic acids oriented in stretched polyethylene

Polarized IR spectra of four carboxylic acids have been recorded using the stretched polymer method. Benzoic, propanoic and propynoic acids form cyclic dimers in polyethylene, while formic acid forms an α type polymer. The transition moment directions of 23 vibrations of benzoic acid dimer are given and the carboxylic ring in-plane vibrations of the studied acids are discussed in the light of the obtained results.

ChemInform Abstract: POLARIZED INFRARED SPECTRA OF HYDROGEN‐BONDED SYSTEMS BY THE STRETCHED‐POLYMER METHOD. 2. TRANSITION MOMENT DIRECTIONS OF THE VIBRATIONS OF NORMAL AND DEUTERATED ACETIC ACID DIMERS

Transition moment directions of the vibrations of dimers of CH/sub 3/COOH, CH/sub 3/COOD, CD/sub 3/COOH, and CD/sub 3/COOD have been measured by using the stretched-polymer orientation method. O-H, C-O, and C=O stretching vibrations are directed almost parallel to the respective bonds. The OCO bending is observed to be directed above 30/sup 0/ from the long axis of the dimers. The rocking OCO vibration is directed almost parallel to the long axis of the dimers in each species. The OH (OD) bending is the only vibration which shows noticeable differences in the directions of transition moments between different isotopic forms. The obtained results are compared to theoretical directions for carboxylic ring in-plane vibrations calculated by the fixed partial charge model using the formic acid dimer as a model system.

Polarized infrared spectra of hydrogen-bonded systems by the stretched-polymer method. 2. Transition moment directions of the vibrations of normal and deuterated acetic acid dimers

Transition moment directions of the vibrations of dimers of CH/sub 3/COOH, CH/sub 3/COOD, CD/sub 3/COOH, and CD/sub 3/COOD have been measured by using the stretched-polymer orientation method. O-H, C-O, and C=O stretching vibrations are directed almost parallel to the respective bonds. The OCO bending is observed to be directed above 30/sup 0/ from the long axis of the dimers. The rocking OCO vibration is directed almost parallel to the long axis of the dimers in each species. The OH (OD) bending is the only vibration which shows noticeable differences in the directions of transition moments between different isotopic forms. The obtained results are compared to theoretical directions for carboxylic ring in-plane vibrations calculated by the fixed partial charge model using the formic acid dimer as a model system.

A Study of the Inhibiting Action of Benzene Thiols and Related Compounds on the Corrosion of Zinc in Acidic Media

Abstract The effect of benzenethiol and its methyl, amino, and carboxylic ring substituted derivatives, benzylthiol and thioglycollic acid on the electrochemical and corrosion behavior of zinc in CH3COOH, H2SO4, and HCl solutions was studied using the galvanostatic technique. In CH3COOH, compounds which function by an adsorption mechanism were found to have inhibitive effects on the corrosion of zinc, while those functioning by surface chelation were ineffective. In H2SO4 and HCl, with the exception of o-methylbenzenethiol (H2SO4 and HCl) and benzylthiol (H2SO4), all investigated compounds were found to accelerate zinc dissolution. Adsorption of the inhibitors followed the Langmuir isotherm, and the mechanism of both the hydrogen evolution reaction and zinc dissolution were found to be the same in the uninhibited and inhibited states.