C13 Atoms Research Articles

The effect of hospital urine components on the degradation of ciprofloxacin during UV/chlorine disinfection process: Kinetics, pathways, and toxicity evaluation

UV/chlorine as an advanced oxidation process (AOPs) has been employed to treat contaminants. However, current research has primarily focused on drinking water and sewage treatment. This paper investigated the degradation of ciprofloxacin (CIP) by UV/chlorine treatment in hospital urine components that contain a higher concentration of iodine (I−). The results indicated that the characteristic ions (HCO3−, SO42−, and NH4+) and I− in hospital urine inhibited CIP removal. In contrast, the characteristic ion, Cl− ion promoted this degradation reaction. Surprisingly, microgram levels of I− strongly inhibited CIP degradation. The characteristic ions can reduce the contribution of hydroxyl radicals (HO•) and reactive chlorine species (RCS). I− can decrease the contribution rate of HO• while slightly increasing the contribution of other radical oxidation in phosphate buffer solution (PBS) ascribed to the formation of HOI and reactive iodine species (RIS). Three degradation pathways have been proposed based on the main transformation products: hydroxylation, electron transfer, and halogen substitution. The piperazine ring of CIP was the main reactive group, and the N2, C10, C16, and C13 atoms were identified as reaction sites. Preliminary toxicity analysis suggested that the toxicity of hospital hydrolyzed urine containing iodine was higher than that of PBS.

Quantum computation in a solid state diamond C12 with a chain of C13 atoms

Quantum computation in a solid state diamond C12 with a chain of C13 atoms

Transformation of sclareol under ritter reaction conditions

Sclareol under the mild conditions of Ritter reaction is converted into N,N′-[(8R,13)-labdan-14(15)-ene-8,13-diyl]diacetamides stereoisomeric at the C13 atom possessing the unrearranged skeleton of the initial diol. One of the minor reaction products is the N-[(8α,13)-epoxylabdan-14-yl]acetamide whose formation requires the intermediate cyclization of the sclareol. Under more severe conditions and at the reversed order of the reagents addition the prevailing components of the reaction mixture are cyclized and rearranged N-[(8α,14)-epoxy-16(13→14)-abeo-labdan-13-yl]acetamides stereoisomeric at the C13 atom, and minor compounds, (8α,13)-epoxy-16(13→14)-abeo-labdan-12(13)-ene and (8α,14)-epoxy-16(13→4)-abeo-labdan-12(13)-ene.

(-)-Sclareol Conversion in Ritter's Reaction Conditions

The main products of sclareol (1) Ritter’s reaction in mild conditions are (8R,13R)-Labd-14(15)-en-8,13-diacetamide (2) (8R,13S)-Labd-14(15)-en-8,13-diacetamide (3) stereoisomeric on C13 atom and having unrearranged native diol skeleton. We present in the current communication the results of sclareol converting (1) into nitrogen-containing labdanes in the Ritter’s reaction conditions.

The highly conserved KEOPS/EKC complex is essential for a universal tRNA modification, t6A

The highly conserved Kinase, Endopeptidase and Other Proteins of small Size (KEOPS)/Endopeptidase-like and Kinase associated to transcribed Chromatin (EKC) protein complex has been implicated in transcription, telomere maintenance and chromosome segregation, but its exact function remains unknown. The complex consists of five proteins, Kinase-Associated Endopeptidase (Kae1), a highly conserved protein present in bacteria, archaea and eukaryotes, a kinase (Bud32) and three additional small polypeptides. We showed that the complex is required for a universal tRNA modification, threonyl carbamoyl adenosine (t6A), found in all tRNAs that pair with ANN codons in mRNA. We also showed that the bacterial ortholog of Kae1, YgjD, is required for t6A modification of Escherichia coli tRNAs. The ATPase activity of Kae1 and the kinase activity of Bud32 are required for the modification. The yeast protein Sua5 has been reported previously to be required for t6A synthesis. Using yeast extracts, we established an in vitro system for the synthesis of t6A that requires Sua5, Kae1, threonine, bicarbonate and ATP. It remains to be determined whether all reported defects of KEOPS/EKC mutants can be attributed to the lack of t6A, or whether the complex has multiple functions.

Diterpenoid steviol derivatives regulate the growth of winter wheat and improve its frost resistance

411 One of the priority fields of studies in the modern plant growing is the regulation mechanisms of the plant growth and resistance provided by different chemical compounds with a wide range of activity. Diterpenoids constitute a large family of natural com pounds with various types of biological activity and geometry of linked hydrocarbon cycles. Among tetracy clic compounds, one should mention kauren derivatives, including steviol 1, a diterpenoid compound. Now it is clear that steviol is a precursor of gibberellic acid (which represents a wide known plant growth regulator) and is involved in the biosynthesis of this acid due to three struc tural features: (a) a cis bond of the B and C cycles, (b) a car boxyl group at the C4 atom, which is included in the enzy matic biosynthesis at the initial stage, and (c) a hydroxyl group at the C13 atom, which is included in the enzymatic biosynthesis at the final stage [1].

Crystal Structures of Trypanosoma brucei Sterol 14α-Demethylase and Implications for Selective Treatment of Human Infections

Sterol 14alpha-demethylase (14DM, the CYP51 family of cytochrome P450) is an essential enzyme in sterol biosynthesis in eukaryotes. It serves as a major drug target for fungal diseases and can potentially become a target for treatment of human infections with protozoa. Here we present 1.9 A resolution crystal structures of 14DM from the protozoan pathogen Trypanosoma brucei, ligand-free and complexed with a strong chemically selected inhibitor N-1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadi-azol-2-yl)benzamide that we previously found to produce potent antiparasitic effects in Trypanosomatidae. This is the first structure of a eukaryotic microsomal 14DM that acts on sterol biosynthesis, and it differs profoundly from that of the water-soluble CYP51 family member from Mycobacterium tuberculosis, both in organization of the active site cavity and in the substrate access channel location. Inhibitor binding does not cause large scale conformational rearrangements, yet induces unanticipated local alterations in the active site, including formation of a hydrogen bond network that connects, via the inhibitor amide group fragment, two remote functionally essential protein segments and alters the heme environment. The inhibitor binding mode provides a possible explanation for both its functionally irreversible effect on the enzyme activity and its selectivity toward the 14DM from human pathogens versus the human 14DM ortholog. The structures shed new light on 14DM functional conservation and open an excellent opportunity for directed design of novel antiparasitic drugs.

Mechanism of photoisomerization of the rhodopsin chromophore

This work is devoted to the problem connected with rhodopsin activation. Electrostatic forces involved in photoisomerization of retinal are considered. It is suggested that the repulsion force and rotating moment between electric dipole moments of methyl groups on the C5 and C13 atoms of retinal can promote isomerization upon light absorption because the pi-pi* transition is accompanied by a decrease in the potential barrier for torsional rotations around the C11-C12 bond.

Temperature response of C13 atoms in amorphized 6H–SiC

Implantation of C2+13 ions was employed to produce a concentration profile in 6H–SiC at 140K. In situ study of C13-implanted species was performed using the resonant reaction of C13(p,γ)N14 at Ep=1.748MeV. Significant C13 diffusion in the amorphized SiC does not occur up to 1130K. The presence of Au implants (1.9at.%) does not affect the C13 behavior. High-energy H+ irradiation also does not promote the C13 diffusion. The results suggest that C atoms are readily trapped locally in the SiC structure during disordering, which is important in understanding the amorphization and recrystallization processes in SiC.

Structural Basis of Leukotriene B4 12-Hydroxydehydrogenase/15-Oxo-prostaglandin 13-Reductase Catalytic Mechanism and a Possible Src Homology 3 Domain Binding Loop

The bifunctional leukotriene B(4) 12-hydroxydehydrogenase/15-oxo-prostaglandin 13-reductase (LTB(4) 12-HD/PGR) is an essential enzyme for eicosanoid inactivation. It is involved in the metabolism of the E and F series of 15-oxo-prostaglandins (15-oxo-PGs), leukotriene B(4) (LTB(4)), and 15-oxo-lipoxin A(4) (15-oxo-LXA(4)). Some nonsteroidal anti-inflammatory drugs (NSAIDs), which primarily act as cyclooxygenase inhibitors also inhibit LTB(4) 12-HD/PGR activity. Here we report the crystal structure of the LTB(4) 12-HD/PGR, the binary complex structure with NADP(+), and the ternary complex structure with NADP(+) and 15-oxo-PGE(2). In the ternary complex, both in the crystalline form and in solution, the enolate anion intermediate accumulates as a brown chromophore. PGE(2) contains two chains, but only the omega-chain of 15-oxo-PGE(2) was defined in the electron density map in the ternary complex structure. The omega-chain was identified at the hydrophobic pore on the dimer interface. The structure showed that the 15-oxo group forms hydrogen bonds with the 2'-hydroxyl group of nicotine amide ribose of NADP(+) and a bound water molecule to stabilize the enolate intermediate during the reductase reaction. The electron-deficient C13 atom of the conjugated enolate may be directly attacked by a hydride from the NADPH nicotine amide in a stereospecific manner. The moderate recognition of 15-oxo-PGE(2) is consistent with a broad substrate specificity of LTB(4) 12-HD/PGR. The structure also implies that a Src homology domain 3 may interact with the left-handed proline-rich helix at the dimer interface and regulate LTB(4) 12-HD/PGR activity by disruption of the substrate binding pore to accommodate the omega-chain.

Tricyclo[7.3.1.02,7]tridecanes with an Amino Group at the Bridging Carbon. Synthesis and Stereochemistry.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Tricyclo[7.3.1.02,7]tridecanes with an amino group at the bridging carbon. Synthesis and stereochemistry

Hydroamination of tricyclo[7.3.1.02,7]tridec-2(7)-en-13-one according to Leukart reaction furnished (tricyclo[7.3.1.02,7]tridec-2(7)-en-13-yl)methanamides stereoisomeric at C13 atom. The corresponding epoxides were prepared therefrom. The unsaturated and epoxidized methanamides were hydrolyzed into amines that were converted into Schiff bases.The configurations of substances were established.

Structural/Physicochemical Properties of Corycavidine, a Key Intermetabolite in the Biosynthesis of Isoquinoline Alkaloids, Elucidated by X-Ray Crystallography, Solution Conformation and Thermal Behavior Analyses, and Energy Calculations

Abstract The conformational/physicochemical features of corycavidine (1), 5,7,8,15-tetrahydro-3,4-dimethoxy-6,15-dimethyl-[1,3]benzodioxolo[5,6-e] [2]benzazecin-14(6H)-one, an important protopine-type alkaloid that serves as the key intermetabolite in the biosynthesis of isoquinoline alkaloids, were examined by X-ray crystallography, 1H NMR spectroscopy, as well as thermal analysis and energy calculations. Two stable conformations of 1, as proposed by energy calculations, were also observed in both the crystalline and solution states. Racemization of optically active 1, which was caused by heating of the crystal, was analyzed by differential-scanning calorimetry. By taking advantage of the H-2H replacement reaction at the C13 atom of 1, the rate of racemization in the C2H3O2H/NaO2H solution was measured as a function of the temperature; the energy barrier between both enantiomers was estimated to be 4.7 kcal mol-1. The crystallization of racemic 1 led to two different crystal forms, i.e., the racemic crystal and the conglomerate crystal (1 : 1 mixture of both enantiomeric crystals). This was probably due to the low energy difference between both crystals. These physicochemical behaviors are important for understanding the in vivo nonenzymatic racemization of 1 and its related alkaloids during metabolic processes.

Structure and conformation of 2β,3β-epoxyestr-5(10)-en-1,4,17-trione, spectroscopic and X-ray crystallographic studies

Colourless single crystals were isolated as by-product during the synthesis of steroidal A-ring substituted 1,4-quinones (and epoxyquinols), as synthetic products with antibiotic and antitumor properties. Its structure was proposed by comparing IR, UV, 1H and 13C NMR spectra to the ones of quinone 2 and independently determined by an X-ray analysis, as 2β,3β-epoxyestr-5(10)-en-1,4,17-trione. Crystals belong to the monoclinic system with space group P2 1 : a=6.767(3) A ̊ , b=7.097(5) A ̊ , c=15.748(5) A ̊ , β=97.070(5)°, V=750.6(8) A ̊ 3, Z=2, D x=1.329 Mg m −3, μ( Mo K α)=0.093 mm −1. The structure was solved by direct methods and refined to a final R=0.064 for 1729 reflections with I>2 σ( I). The steroidal skeleton with chiral centre at C13 possesses the S configuration defining β-orientation of O2 atom bridging C2 and C3 atoms and β-oriented methyl group bonded to C13 atom. The best plane through the ring A and epoxy ring plane form an angle of 89.6(2)°. Conformational analysis of the steroid rings are performed by calculating the ring puckering parameters and asymmetry factors. The conformation of the A ring is screw-boat 1S 6, ring B half-chair 4H 3, ring C chair 1C 4, and the five-membered D ring is half-chair 2H 1 conformation. The crystal structure is stabilised by the weak C–H⋯O hydrogen bonds and van der Waals interaction.