N1 Atom Research Articles

Enzymatic C[sbnd]S bond cleavage: Mechanism for the conversion of methanesulfonate to sulfite by flavin-dependent MsuD monooxygenase

MsuD, a flavin-dependent monooxygenase, catalyzes the conversion of methanesulfonate (MS−) into formaldehyde and sulfite, playing a crucial role in the organic sulfur cycle. Using density functional calculations, we have demonstrated that the MsuD reaction uses mechanism A involving a FlN5-OO− intermediate. It mainly includes electron transfer from the N5 atom of deprotonated reduced flavin to O2, NO bond formation yielding FlN5-OO−, deprotonation of MS− methyl by FlN5-OO− forming FlN5-OOH and MS2− carbanion, and hydroxy rebound from FlN5-OOH to MS2− accompanying with immediate CS bond dissociation producing sulfite and formaldehyde. In contrast, mechanism B containing FlC4-OO− is ruled out due to the inaccessible hydroxy rebound from FlC4-OOH to MS2−, although the FlC4-OO− species, a common intermediate in the family of flavin-dependent monooxygenases, may also appear in MsuD. Our research provides insights into the enzymatic CS bond cleavage and confirms the potential of the flavin N5 site to facilitate various chemical reactions.

Studying the Interaction between Bendamustine and DNA Molecule with SERS Based on AuNPs/ZnCl2/NpAA Solid-State Substrate.

Bendamustine (BENDA) is a bifunctional alkylating agent with alkylating and purinergic antitumor activity, which exerts its anticancer effects by direct binding to DNA, but the detailed mechanism of BENDA-DNA interaction is poorly understood. In this paper, the interaction properties of the anticancer drug BENDA with calf thymus DNA (ctDNA) were systematically investigated based on surface-enhanced Raman spectroscopy (SERS) technique mainly using a novel homemade AuNPs/ZnCl2/NpAA (NpAA: nano porous anodic alumina) solid-state substrate and combined with ultraviolet-visible spectroscopy and molecular docking simulation to reveal the mechanism of their interactions. We experimentally compared and studied the SERS spectra of ctDNA, BENDA, and BENDA-ctDNA complexes with different molar concentrations (1:1, 2:1, 3:1), and summarized their important characteristic peak positions, their peak position differences, and hyperchromic/hypochromic effects. The results showed that the binding modes include covalent binding and hydrogen bonding, and the binding site of BENDA to DNA molecules is mainly the N7 atom of G base. The results of this study help to understand and elucidate the mechanism of BENDA at the single-molecule level, and provide guidance for the further development of effective new drugs with low toxicity and side effects.

Comparative study of antimicrobial potential and DNA/BSA binding affinity of silver(I) and gold(III) coordination compounds with 1,6-naphthyridine

In the present study, synthesis of silver(I) and gold(III) coordination compounds with 1,6-naphthyridine (1,6-naph), {[Ag(1,6-naph)(H2O)](BF4)}n (1) and [AuCl3(1,6-naph)] (2), was reported. The methods used for the structural characterization of a new compound 1 included IR, NMR (1H and 13C) and UV–Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction analysis. The crystallographic results showed that compound 1 represents silver(I) coordination polymer, in which 1,6-naph ligand acts as a bidentate bridging ligand connecting two Ag(I) ions via its N1 and N6 nitrogen atoms, while the third coordination site of the metal ion is occupied by the water oxygen atom, resulted in a T-shape geometry. Compounds 1 and 2 were evaluated in vitro for antimicrobial activity against five bacterial and two Candida species, while their cytotoxicity was tested on the normal human lung fibroblast cell line (MRC-5). Compound 1 has manifested a remarkable antifungal activity on both tested Candida strains (C. albicans and C. parapsilosis) with minimal inhibitory concentrations (MICs) of 1.43 and 11.38 µM (0.49 and 3.9 µg/mL), respectively, while no significant antimicrobial activity was observed for 2. Moreover, silver(I) coordination polymer 1 inhibits the hyphae formation of C. albicans at subinhibitory concentration. The binding affinity of both compounds 1 and 2 with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy, indicating their ability to interact with these biomolecules, with compound 2 being more reactive.

Photophysical characterization of isothiazologuanosine, a unique isomorphic and isofunctional fluorescent analogue of guanosine

Application of fluorescence techniques to investigate molecular interactions with nucleic acids is complicated by their poor emission, making the substitution of natural nucleobases by fluorescent nucleoside analogues (FNAs) a useful strategy. A breakthrough in fluorescent nucleoside analogues has been the development of thienoguanosine (thG) and isothiazologuanosine (tzG), two isosteric mimics of guanosine (G). Due to its N7 atom needed in Hoogsteen base pairs and enzyme recognition, tzG is also an isofunctional G surrogate. Herein, we integrated fluorescence spectroscopy measurements with quantum mechanical (QM) calculations to characterize the mechanisms underlying tzG photophysics in different solvents. In dioxane and ethyl acetate, tzG existed primarily as a H1 keto-amino tautomer with short fluorescence lifetime (τ ∼ 2 ns) and low quantum yield (ϕ ∼ 0.10). In buffer, the H1 tautomer (ϕ = 0.36, τ = 8.84 ns) coexisted with a weakly emissive H3 keto-amino tautomer. The two tautomers were also observed in methanol, but with a 30% decrease in ϕ and τ values for the major H1 tautomer. QM calculations suggested that the main non-radiative pathway of tzG-H1 involves NS bond loosening and is responsible for the more solvent-sensitive ϕ and τ values compared to thG. This pathway is much more efficient for tzG-H3, for which an additional pathway to a dark nπ* state and a large coupling with triplet states further explain its very low emission. This study lays the ground for rationally using tzG as a sensitive FNA.

The effect of initial temperature and external heat flux on the H2 and CO production by biomass gasification using molecular dynamics simulation

Biomass is a fuel produced from organic matter, and a renewable and sustainable energy source used to generate electricity or other forms of energy. From an environmental point of view, biomass includes all materials found in nature. This resource can be a suitable alternative to fossil resources. Biomass is based on carbon particles, H2, O2, N2, and many other atoms, such as alkali metals and heavy metals. In this research, the changes in the number of H2, carbon monoxide (CO) molecules created, and combustion efficiency (CE) inside the simulation box, using molecular dynamics (MD) simulation in the presence of 10 % platinum nanocatalyst with different initial temperatures (Temp) (1800, 1850, 1900 and 2000 K) and different external heat fluxes (EHF) (1, 2, 3 and 5 W/m2) were evaluated. The results show that as the Temp increased from 1800 to 2000 K, the number of H2 and CO molecules increased from 586 to 165 to 614 and 199, respectively. Besides, CE increased to 70% with the Temp increase to 2000 K. Furthermore, increasing the EHF from 1 to 5 W/m2, the number of H2 and CO molecules decreases from 589 to 170 to 603 and 180, respectively, and the CE increases to 69 % with the EHF increasing to 5 W/m2. It is expected that by examining the effects of system Temp and EHF, and the presence of nanocatalysts, the production of the number of H2 molecules will reach the highest efficiency.

A cationic Co(II) coordination polymer 1∞[Co(µ-L)(µ-Cl)(H2O)2]+ with the 4-amino-4H-1,2,4-triazole ligand: Structure, thermal behavior, and antimicrobial activity

We report a combined experimental and theoretical study on a Co(II) coordination polymer 1∞[Co(µ-L)(µ-Cl)(H2O)2]Cl based on 4-amino-4H-1,2,4-triazole (L). Single crystal X-ray diffraction showed that the Co(II) ions are coordinated by the N1 and N2 atoms of the bridging 4-amino-1,2,4-triazole ligand, two trans-oriented bridging Cl− ligands and two O atoms from coordinated water molecules in a distorted octahedral geometry. The ligand shows a bridging µ-κ1,κ1,(N,N) coordination with Cl–Cl–N–N–Co five membered rings in the polymeric strand. Intra and intermolecular N–H…O and O–H…Cl hydrogen bonding interactions stabilize the crystal structure. Hirshfeld surface analysis in combination with ATR–FTIR, and FT-Raman spectroscopy were carried out to study the multitude of non-covalent interactions. Geometry optimization using density functional theory (DFT) calculations on the monomolecular model [Co(L)2Cl2(H2O)2] on B3LYP/6–311++G(2d,2p) level gave good agreement with the metrics found in the crystal structure and also agreed quite well with the experimental IR and Raman data, thus allowing spectral assignments. Thermogravimetric (TGA) and Differential Scanning Calorimetric (DSC) experiments coupled with mass spectrometry (MS) under an argon atmosphere in the temperature range 25 to 950 °C showed thermal stability till about 100 °C. The compound showed inhibitory activity against the Gram-negative bacterium E. fergusonii, the Gram-positive bacteria S. aureus, E. feacalis, and B. cereus, and the yeast C. parapsilosis in agar diffusion experiments at a concentration of 1.25 and 2.50 mg/mL with inhibition zones of 10 to 20 mm in 24 h, but not against the Gram-negative E. coli and the yeast C. saké.

Density functional theory investigation of the coordination of Zn(II)-tetraphenylporphyrin with 1,2,3-triazole ligands

In this paper, we report density functional theory (DFT) studies to fully understand the coordination interactions between 1,4-disubstituted 1,2,3-triazole derivatives and the metal center of Zn(II)-porphyrins. Coordination through the most electron-rich N3 atom of the triazole heterocycle is more favorable. However, the energy difference between the N2- and N3-coordinated isomers is moderate and the less stable is likely also present in the solution. The binding of 1,4-disubstituted 1,2,3-triazole ligands to oxidized and reduced Zn(II)-porphyrins has been also investigated. Upon reduction, the binding interactions are extremely weak and the formation of the complex is not favorable anymore. In contrast, the binding energy is considerably increased upon oxidation of the Zn(II)-porphyrin moiety thus leading to more stable complexes. The calculations fully support experimental findings and explain the differences observed for the redox potentials of complexed and uncomplexed Zn(II)-porphyrin residues.

Discrete Cu-Metalloporous Polycarbazole as a Nanoelectromediator for Effective Electrocarboxylation of Benzyl Bromide with CO2

The electrochemical fixation of carbon dioxide (CO2) into organic halides is one of the most prominent strategies for mitigating atmospheric CO2 emission, along with the difficulties associated with the toxic and carcinogenic halogenated compounds. Cu-based nanomaterials have been explored for numerous applications in nanotechnology, including electrocatalysis, organic catalytic transformations, and photocatalysis. In this work, we have designed and developed a Cu-embedded carbazole-derived porous organic polymer (Cu@Cz-POP) nanohybrid by utilizing the Friedel–Crafts alkylation approach and employing 1,4-dimethoxybenzene as the cross-linking agent comprising unique characteristic features of the extended π-conjugated system along with an active metal center with tunable electrochemical properties. The Brunauer–Emmett–Teller surface area of the conjugated Cz-POP is found to be 1060 m2 g–1. The X-ray photoelectron spectroscopy (XPS) study demonstrates the formation of CuO nanoparticles in the polymeric framework. X-ray absorption fine structure analysis (EXAFS) also reveals the existence of CuO with a smaller fraction of Cu in the polymeric framework, which is corroborated with the XPS analysis. The Cu@Cz-POP nanohybrid is fabricated by drop-casting over a Ni foam, showing promising electrocatalytic activity toward electrocarboxylation of benzyl bromide in 0.1 M TBA·BF4/CH3CN with saturated CO2 medium with a current density of 120 mA cm–2 delivering 65% yield of phenylacetic acid (PAA) as the primary product along with traces of benzyl 2-phenylacetate (BPA) and 1,2-diphenylethane (DPE), and the turnover frequency is found to be 8.556 × 10–7 s–1. Density functional theory calculations demonstrate that CuO is adsorbed more favorably at the N1 nitrogen atom of Cz-POP. An electron transfer from the N1 atom and the aromatic rings of Cz-POP to the CuO center is observed and confirmed by the overlap of alpha orbitals.

Substituted 2,5 thiophene dicarboxaldehyde bisthiosemicarbazones and their copper(II) complexes: Synthesis, structure elucidation, HSA binding, biological activities and docking studies

Reaction of copper (II) acetate with 2,5 thiophenedicarboxaldehyde bisthiosemicarbazone (2,5 H2bttsc, 1H2L), 2,5 thiophenedicarboxaldehyde-N1-methyl bisthiosemicarbazone (2,5 H2bttsc-N1-Me, 2H2L) and 2,5 thiophenedicarboxaldehyde -N1-phenyl bisthiosemicarbazone (2,5 H2bttsc-N1-Ph, 3H2L) in 1:1 (M:L) molar ratio yielded complexes of stoichiometry, [Cu(L)] 1-3 (1L, 1; 2L 2; 3L 3). All the complexes are characterized using elemental analysis FTIR, Mass and ESR spectroscopy. The two distinct g values, g‖ = 2.40 (1), 2.15 (2), 2.20 (3) and g⊥ = 2.08 (1), 2.07 (2), 2.12 (3) indicate axial symmetry for the complexes. The greater g‖ value than g⊥, confirms the presence of free electrons in dx2-y2 ground term in square planar geometry. The ligands (1H2L - 3H2L) and their complexes (1–3) were tested for DPPH radical scavenging, ABTS radical scavenging, FRAP ferric reducing, and CUPRAC cupric reducing antioxidant capacity assays. In general, all the ligands and their metal complexes exhibited moderate antioxidant potential, however 3H2L has shown best Cu2+ reducing activity (7.34 μg TE/ml) and ABTS radicals scavenging activity (IC50, 16.95) amongst all. Ligands (1H2L - 3H2L) and their complexes (1–3) were also evaluated for anti-tuberculosis activity against M. tuberculosis H37RV strain. It has been observed that with the increase of hydrophobicity of ligand due to substituent present at N1 atom, anti-TB activity increased (H, MIC = 6.25 µg/ml < Me, MIC = 3.12 µg/ml < Ph, MIC = 1.6 µg/ml). Molecular modeling studies have shown considerable intermolecular interaction of these compounds with minimum binding energy −5.8 (1H2L), −5.8 (2H2L), −9.6 (3H2L), −6.9 (1), −6.6 (2) and −9.6 (3) Kcal/ mol, which also supports the experimental data. Pharmacokinetics (effective transport of molecule to their target sites) was studied using drug-protein binding study of molecules with human serum albumin (HSA) was performed using UV–vis and fluorescence spectroscopy. The ligand 2H2L and complex 2 showed strong binding interactions with HSA having binding constant values of 4.24 × 105 M−1 and 4.92 × 105 M−1 respectively.

Intramolecular Hydrogen Bonding in N6-Substituted 2-Chloroadenosines: Evidence from NMR Spectroscopy.

Two forms were found in the NMR spectra of N6-substituted 2-chloroadenosines. The proportion of the mini-form was 11-32% of the main form. It was characterized by a separate set of signals in COSY, 15N-HMBC and other NMR spectra. We assumed that the mini-form arises due to the formation of an intramolecular hydrogen bond between the N7 atom of purine and the N6-CH proton of the substituent. The 1H,15N-HMBC spectrum confirmed the presence of a hydrogen bond in the mini-form of the nucleoside and its absence in the main form. Compounds incapable of forming such a hydrogen bond were synthesized. In these compounds, either the N7 atom of the purine or the N6-CH proton of the substituent was absent. The mini-form was not found in the NMR spectra of these nucleosides, confirming the importance of the intramolecular hydrogen bond in its formation.

New nitrification inhibitors based on copper(II) complex compounds

The work presents the results of research aimed at the synthesis of new nitrification inhibitors based on complex compounds of Cu2+ with 4-amino-1,2,4-triazole (ATC) and dicyandiamide (DCD). The purpose of the conducted work is the synthesis of new nitrification inhibitors based on complex copper compounds followed with subsequent studies of their structure, properties and biological activity. Four compounds of different compositions were obtained. A number of physical and chemical properties of substances were established: thermal behavior, and solubility in the KAS-28 system (a saturated solution of urea and ammonium nitrate with a nitrogen content of 28%)–water. With the help of infrared spectroscopy, the presence of functional groups and bonds inherent in ligands was proven in the synthesized compounds. Possible ways of coordination of 4-amino-1,2,4-triazole (monodentately through the atom N1 or N2) and dicyandiamide (through the group C=NH or CN with equal probability) were proposed. The content of Cu2+ ions in the synthesized compounds was determined by iodometry. The biological activity of the synthesized substances in relation to soil bacteria was investigated by the potentiometric method. The dynamics of changes in NH4+ and NO3– ions in research samples containing the obtained substances and commonly used nitrification inhibitors (ATC and DCD) was established. All results were equated relative to the control. It was established that the substance with the probable empirical formula [Cu(ATC)2(DCD)1(H2O)1]SO4 had the highest biological activity.

Molecular and Electronic Structures of Macrocyclic Compounds Formed at Template Synthesis in the M(II)-Thiocarbohydrazide-Diacetyl Triple Systems: A Quantum-Chemical Analysis by DFT Methods.

Using density functional theory (DFT) B3PW91/TZVP, M06/TZVP, and OPBE/TZVP chemistry models and the Gaussian09 program, a quantum-chemical calculation of geometric and thermodynamic parameters of Ni(II), Cu(II), and Zn(II) macrotetracyclic chelates, with (NNNN)-coordination of ligand donor centers arising during template synthesis between the indicated ions of 3d elements, thiocarbohydrazide H2N-HN-C(=S)-NH-NH2 and diacetyl Me-C(=O)-C(=O)-Me, in gelatin-immobilized matrix implants was performed. The key bond lengths and bond angles in these coordination compounds are provided, and it is noted that in all these complexes the MN4 chelate sites, the grouping of N4 atoms bonded to the M atom, and the five-membered and six-membered metal chelate rings are practically coplanar. NBO analysis of these compounds was carried out, on the basis of which it was shown that all these complexes, in full accordance with theoretical expectations, are low-spin complexes. The standard thermodynamic characteristics of the template reactions for the formation of the above complexes are also presented. Good agreement between the data obtained using the above DFT levels is noted.

Symmetric Electronic Structures of Active Sites to Boost Bifunctional Oxygen Electrocatalysis by MN4+4 Sites Directly from Initial Covalent Organic Polymers

AbstractTransition metal‐nitrogen‐carbon (M‐N‐C) catalysts with CoN4 centers have attracted great attention as a potential alternative to precious metal catalysts for bifunctional oxygen electrocatalysis. However, the asymmetric charge environment of the active site of MN4 obtained by conventional pyrolysis strategy makes the unbalanced adsorption of oxygen molecules, which restricts the activities of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a series of well‐defined quasi‐phthalocyanine conjugated 2D covalent organic polymer (COPBTC‐M) is developed with MN4+4 active sites through a pyrolysis‐free strategy. Compared to CoN4 site, the additional subcentral N4 atoms in MN4+4 site in COPBTC‐Co catalyst balance the charge environment and form a symmetric charge distribution, which changes the antibonding orbital of the active metal and regulate the oxygen species adsorption, thus improving the activity of the bifunctional oxygen electrocatalysis. In Silico screening demonstrates that cobalt has the best ORR and OER activity for COPBTC‐M with MN4+4 sites, which can be attributed to the fewer anti‐bonding orbital below the Fermi level, which weakens the oxygen species adsorption. Both theoretical and experimental results verify that the COPBTC‐Co possesses unique CoN4+4 active sites and the harmonious coordinating environment can lead to superior bifunctional oxygen catalytic activity with a high bifunctional oxygen catalytic activity (ΔE [Ej10 – E1/2] = 0.76 V), which is comparable with the benchmark Pt/C‐IrO2 pairs. Accordingly, the as‐assembled Zn–air battery exhibits a maximum power density of 157.7 mW cm −2 with stable operation for &gt;100 cycles under an electric density of 10 mA cm −2. This study provides a characteristic understanding of the intrinsic active species toward MNx centers and could inspire new avenues for designation of advanced bifunctional electrocatalysts that catalyze ORR and OER processes simultaneously.

Selective Photocatalytic Reduction of CO2 to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride.

Artificial photosynthesis is a promising strategy for converting carbon dioxide (CO2 ) and water (H2 O) into fuels and value-added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C3 N4 nanotubes (PCN) to form the photocatalyst Ag1 @PCN with Ag-N3 coordination for CO2 photoreduction using H2 O as the reductant. The as-synthesized Ag1 @PCN exhibits a high CO production rate of 0.32 μmol h-1 (mass of catalyst: 2 mg), a high selectivity (>94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal-support interactions (Ag-N3 ) favor *CO2 adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C3 N4 and Ag single atoms, thereby accounting for the enhanced CO2 photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal-support interactions in enhancing the photoactivity and CO selectivity of CO2 photoreduction.

Synthesis of &amp;lt;I&amp;gt;N&amp;lt;/I&amp;gt;&amp;apos;-(2,3-dihydroxybenzylidene)-4-methylbenzohydrazide: Spectroscopic Characterization and X-ray Structure Determination

p-Toluic hydrazide was used for synthetizing a new Schiff base <I>N</I>'-(2,3-dihydroxybenzylidene)-4-methylbenzohydrazide (I). The prepared compound was characterized by elemental analysis, infrared and ¹H and ¹³C NMR spectroscopy techniques, and the structure of compound (I) was determined by single-crystal X-ray diffraction study. The compound (C₁₅H₁₄N₂O₃) crystallises in the monoclinic space group <I>P</I>2₁/<i>n</i> with the following unit cell parameters: <i>a</i> = 11.7820 (6) Å, <i>b</i> = 8.5278 (4) Å, <i>c</i> = 13.6054 (7) Å, <i>β</i> = 109.346 (5)°, <I>V </I>= 1289.81 (12) ų, <I>Z</I> = 4, <I>R</I>₁ = 0.071 and <i>wR</i>₂ = 0.197. The X-ray structure shows that the compound (I) adopts an <I>E</I> configuration with respect to the double bond C7=N1. The carbonyl oxygen atom O3 and the nitrogen atom N1 of the hydrazide moiety are in a <i>syn</i> conformation with respect to C8—N2 bond. The crystal packing of compound (I) is stabilized by intramolecular O(phenol)–H•••N(carbohydrazide) which results in an <I>S</I>(6) ring motif and intermolecular O(phenol)–H•••O(carbohydrazide) hydrogen bonds which form chains. The carbonohydrazide moiety C=N–N–C(O)–N–N=C fragment is almost coplanar with the two benzene rings with dihedral angles of their mean planes of 10.35° [C1—C6] and 7.99° [C9—C14], respectively. The dihedral angle between the mean planes of the phenyl rings is 2.46°.

Electrostatic Interactions in the Formation of DNA Complexes with Cis- and Trans-Isomers of Azobenzene-Containing Surfactants in Solutions with Di- and Trivalent Metal Ions.

The effect of the presence of divalent and trivalent metal ions in solutions upon DNA packaging induced by the photosensitive azobenzene-containing surfactant is considered. It has been shown that the addition of divalent and trivalent metal ions does not affect the DNA-surfactant interaction for both the cis- and the trans-isomers of the surfactant. At the same time, the ionic strength of the solution, which is provided by a certain concentration of the salt, has a huge impact. It affects the association of surfactant molecules with each other and their binding to DNA. It has been shown by computer simulation that cobalt hexamine is attracted to the N7 atom of guanine in the major groove of DNA and does not penetrate into grooves near the AT base pairs.

Insights on adsorption properties of a DNA base, guanine on nano metal cages (Ag24/Au24/Cu24): DFT, SERS, NCI and solvent effects

A detailed theoretical study was implemented on 2-amino-1,7-dihydropurin-6-one's (ADO). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) simulations were accomplished to explain the adsorption performance of the ADO drug molecule on metal nanocages. Adsorption energy og ADO was calculated to be -53.90, -50.67 and -63.56 kcal/mol for Ag, Au and Cu cages, respectively. ADO interacts with Ag/Cu through the N5, N4 and N6 atoms with a perpendicular orientation and Au-ADO, the interaction is through O, N3H13 and NH2 groups with a perpendicular orientation. Reactivity computations were used to find the electron density in NMC-containing ADO complexes. The intermolecular interaction forces were found by the establishment of numerous bond critical point, monitored by ring critical points at the midpoint of interaction state. The ADO molecule will also be examined as part of the computational study to ascertain its bioactivity and docking studies. We can get accurate estimates of the atomic contact energies for drug delivery using the docking process.

The Role of Tyr-His-Trp Triad and Water Molecule Near the N1-Atom of 2-Hydroperoxycoelenterazine in Bioluminescence of Hydromedusan Photoproteins: Structural and Mutagenesis Study.

Hydromedusan photoproteins responsible for the bioluminescence of a variety of marine jellyfish and hydroids are a unique biochemical system recognized as a stable enzyme-substrate complex consisting of apoprotein and preoxygenated coelenterazine, which is tightly bound in the protein inner cavity. The binding of calcium ions to the photoprotein molecule is only required to initiate the light emission reaction. Although numerous experimental and theoretical studies on the bioluminescence of these photoproteins were performed, many features of their functioning are yet unclear. In particular, which ionic state of dioxetanone intermediate decomposes to yield a coelenteramide in an excited state and the role of the water molecule residing in a proximity to the N1 atom of 2-hydroperoxycoelenterazine in the bioluminescence reaction are still under discussion. With the aim to elucidate the function of this water molecule as well as to pinpoint the amino acid residues presumably involved in the protonation of the primarily formed dioxetanone anion, we constructed a set of single and double obelin and aequorin mutants with substitutions of His, Trp, Tyr, and Ser to residues with different properties of side chains and investigated their bioluminescence properties (specific activity, bioluminescence spectra, stopped-flow kinetics, and fluorescence spectra of Ca2+-discharged photoproteins). Moreover, we determined the spatial structure of the obelin mutant with a substitution of His64, the key residue of the presumable proton transfer, to Phe. On the ground of the bioluminescence properties of the obelin and aequorin mutants as well as the spatial structures of the obelin mutants with the replacements of His64 and Tyr138, the conclusion was made that, in fact, His residue of the Tyr-His-Trp triad and the water molecule perform the "catalytic function" by transferring the proton from solvent to the dioxetanone anion to generate its neutral ionic state in complex with water, as only the decomposition of this form of dioxetanone can provide the highest light output in the light-emitting reaction of the hydromedusan photoproteins.

Synthesis and Characterization of Metals Complexes with Uracil and Uracil Derivatives (A Review)

Previous studies on the synthesis and characterization of metal chelates with uracil by elemental analysis, conductivity, IR, UV-Vis, NMR spectroscopy, and thermal analysis were covered in this review article. Reviewing these studies, we found that uracil can be coordinated through the electron pair on the N1, N3, O2, or O4 atoms. If the uracil was a mono-dentate ligand, it will be coordinated by one of the following atoms: N1, N3 or O2. But if the uracil was bi-dentate ligand, it will be coordinated by atoms N1 and O2, N3 and O2 or N3 and O4. However, when uracil forms complexes in the form of polymers, coordination occurs through the following atoms: N1 and N3 or N1 and O4.

Modified quantum mechanical approach for the estimation of single-electron reduction potential of nitroaromatic compounds in aqueous medium

The midpoint single-electron reduction potential of nitroaromatic compounds in aqueous medium at pH 7.0 (potential of ArNO2/ArNO2 · – couple, E m7) frequently determines their therapeutic and/or toxic properties. However, its estimation remains a complex problem. We propose a modified method of E m7 estimation by quantum mechanical calculations, based on the use of the dielectric continuum model together with a certain number of H2O molecules at the vicinity of nitro group. The optimal number of H2O molecules corresponds to a minimal difference between the experimentally determined and calculated values of E m7, and/or the most negative value of calculated E m7. This enabled us to calculate the E m7 values for a number of ArNO2 (n = 19) with the average deviation of 0.027 V from the experimentally determined ones. Apart from nitrobenzene derivatives, the application of this approach for the representatives of nitropyridines, nitrofurans, nitrothiophenes, and nitrothiazoles was demonstrated. In this case, nitroimidazole derivatives are an exception, evidently due to a strong proton accepting properties of N3 atom of their free radicals.