N1 Atom Research Articles

Structural Insights into Pseudomonas aeruginosa Exotoxin A-Elongation Factor 2 Interactions: A Molecular Dynamics Study.

Exotoxin A (ETA) is an extracellular secreted toxin and a single-chain polypeptide with A and B fragments that is produced by Pseudomonas aeruginosa. It catalyzes the ADP-ribosylation of a post-translationally modified histidine (diphthamide) on eukaryotic elongation factor 2 (eEF2), which results in the inactivation of the latter and the inhibition of protein biosynthesis. Studies show that the imidazole ring of diphthamide plays an important role in the ADP-ribosylation catalyzed by the toxin. In this work, we employ different in silico molecular dynamics (MD) simulation approaches to understand the role of diphthamide versus unmodified histidine in eEF2 on the interaction with ETA. Crystal structures of the eEF2-ETA complexes with three different ligands NAD+, ADP-ribose, and βTAD were selected and compared in the diphthamide and histidine containing systems. The study shows that NAD+ bound to ETA remains very stable in comparison with other ligands, enabling the transfer of ADP-ribose to the N3 atom of the diphthamide imidazole ring in eEF2 during ribosylation. We also show that unmodified histidine in eEF2 has a negative impact on ETA binding and is not a suitable target for the attachment of ADP-ribose. Analyzing of radius of gyration and COM distances for NAD+, βTAD, and ADP-ribose complexes revealed that unmodified His affects the structure and destabilizes the complex with all different ligands throughout the MD simulations.

Uncovering Zn2+ as a cofactor of FAD-dependent Pseudomonas aeruginosa PAO1 d-2-hydroxyglutarate dehydrogenase

Pseudomonas aeruginosa couples the oxidation of d-2-hydroxyglutarate (D2HG) to l-serine biosynthesis for survival, using d-2-hydroxyglutarate dehydrogenase from P.aeruginosa (PaD2HGDH). Knockout of PaD2HGDH impedes P.aeruginosa growth, making PaD2HGDH a potential target for therapeutics. Previous studies showed that the enzyme's activity increased with Zn2+, Co2+, or Mn2+ but did not establish the enzyme's metal composition and whether the metal is an activator or a required cofactor for the enzyme, which we addressed in this study. Comparable to the human enzyme, PaD2HGDH showed only 15% flavin reduction with D2HG or d-malate. Upon purifying PaD2HGDH with 1mM Zn2+, the Zn2+:protein stoichiometry was 2:1, yielding an enzyme with ∼40s-1kcat for d-malate. Treatment with 1mM EDTA decreased the Zn2+:protein ratio to 1:1 without changing the kinetic parameters with d-malate. We observed complete enzyme inactivation for the metalloapoenzyme with 100mM EDTA treatment, suggesting that Zn2+ is essential for PaD2HGDH activity. The presence of Zn2+ increased the flavin N3 atom pKa value to 11.9, decreased the flavin ε450 at pH 7.4 from 13.5 to 11.8 mM-1cm-1, and yielded a charged transfer complex with a broad absorbance band >550nm, consistent with a Zn2+-hydrate species altering the electronic properties of the enzyme-bound FAD. The exogenous addition of Zn2+, Co2+, Cd2+, Mn2+, or Ni2+ to the metalloapoenzyme reactivated the enzyme in a sigmoidal pattern, consistent with an induced fit rapid-rearrangement mechanism. Collectively, our data demonstrate that PaD2HGDH is a Zn2+-dependent metallo flavoprotein, which requires Zn2+ as an essential cofactor for enzyme activity.

Alternative Strategy for Spectral Tuning of Flavin-Binding Fluorescent Proteins.

iLOV is an engineered flavin-binding fluorescent protein (FbFP) with applications for in vivo cellular imaging. To expand the range of applications of FbFPs for multicolor imaging and FRET-based biosensing, it is desirable to understand how to modify their absorption and emission wavelengths (i.e., through spectral tuning). There is particular interest in developing FbFPs that absorb and emit light at longer wavelengths, which has proven challenging thus far. Existing spectral tuning strategies that do not involve chemical modification of the flavin cofactor have focused on placing positively charged amino acids near flavin's C4a and N5 atoms. Guided by previously reported electrostatic spectral tunning maps (ESTMs) of the flavin cofactor and by quantum mechanical/molecular mechanical (QM/MM) calculations reported in this work, we suggest an alternative strategy: placing a negatively charged amino acid near flavin's N1 atom. We predict that a single-point mutant, iLOV-Q430E, has a slightly red-shifted absorption and fluorescence maximum wavelength relative to iLOV. To validate our theoretical prediction, we experimentally expressed and purified iLOV-Q430E and measured its spectral properties. We found that the Q430E mutation results in a slight change in absorption and a 4-8 nm red shift in the fluorescence relative to iLOV, in good agreement with the computational predictions. Molecular dynamics simulations showed that the carboxylate side chain of the glutamate in iLOV-Q430E points away from the flavin cofactor, which leads to a future expectation that further red shifting may be achieved by bringing the side chain closer to the cofactor.

Non-canonical base pairing

Non-canonical base pairs are planar hydrogen-bonded pairs of nucleobases, having hydrogen bonding patterns which differ from the patterns observed in Watson-Crick base pairs, as in the classic double-helical DNA. The structures of polynucleotide strands of both DNA and RNA molecules can be understood in terms of sugar-phosphate backbones consisting of phosphodiester-linked D 2’ deoxyribofuranose (D ribofuranose in RNA) sugar moieties, with purine or pyrimidine nucleobases covalently linked to them. Here, the N9 atoms of the purines, guanine and adenine, and the N1 atoms of the pyrimidines, cytosine and thymine (uracil in RNA), respectively, form glycosidic linkages with the C1’ atom of the sugars. These nucleobases can be schematically represented as triangles with one of their vertices linked to the sugar, and the three sides accounting for three edges through which they can form hydrogen bonds with other moieties, including with other nucleobases. As also explained in greater detail later in this article, the side opposite to the sugar-linked vertex is traditionally called the Watson-Crick edge, since they are involved in forming the Watson-Crick base pairs which constitute building blocks of double-helical DNA. The two sides adjacent to the sugar-linked vertex are referred to, respectively, as the Sugar and Hoogsteen (C-H for pyrimidines) edges. Each of the four different nucleobases is characterized by distinct edge-specific distribution patterns of their respective hydrogen bond donor and acceptor atoms, complementarity with which, in turn, define the hydrogen bonding patterns involved in base pairing. The double helical structures of DNA or RNA are generally known to have base pairs between complementary bases, Adenine: Thymine (Adenine: Uracil in RNA) or Guanine: Cytosine. They involve specific hydrogen bonding patterns corresponding to their respective Watson-Crick edges and are considered Canonical Base Pairs. At the same time, the helically twisted backbones in the double helical duplex DNA form two grooves, major and minor, through which the hydrogen bond donor and acceptor atoms corresponding respectively to the Hoogsteen and sugar edges are accessible for additional potential molecular recognition events. Experimental evidence reveals that the nucleotide bases are also capable of forming a wide variety of pairing between bases in various geometries, having hydrogen bonding patterns different from those observed in Canonical Base Pairs [Figure 1]. These base pairs, which are generally referred to as Non-Canonical Base Pairs, are held together by multiple hydrogen bonds and are mostly planar and stable. Most of these play very important roles in shaping the structure and function of different functional RNA molecules. In addition to their occurrences in several double-stranded stem regions, most of the loops and bulges that appear in single-stranded RNA secondary structures form recurrent 3D motifs, where non-canonical base pairs play a central role. Non-canonical base pairs also play crucial roles in mediating the tertiary contacts in RNA 3D structures.

Atomic-structure and charge redistribution modified by intrinsic strain in α-fe/TMN (TM=Ti/Zr/Hf/V/Nb/Ta) interfaces

Metal/ceramics interfaces, ubiquitous in functional materials, alloys, and coatings/films systems, provide excellent mechanical and chemical properties, mainly originating from atomic structures and charge distribution at the hetero-interfaces. In the present work, the α-Fe/TMN (TM = Ti/Zr/Hf/V/Nb/Ta) interfaces were chosen as the typical metal/ceramic candidates to explore the atomic structures and electronic properties at such types of heterostructures. After full optimization, the relaxed models kept the stacking sequence OT (on top) of FeN, producing a slight difference in interfacial distance ( Δz ). Furthermore, a significant charge transfer emerged in interfacial Fe and N atoms, indicative of the stronger bond strength across the interfaces obtained from the analysis of planar-averaged charge density difference, PDOS, charge density and difference, partial charge density and ELF . Moreover, the increasing gain of interfacial N1 atoms and enhanced overlap of Fe and TM1 atoms could account for the higher adhesion strength of Fe/TMN. Finally, the amount of charge transfer for interfacial Fe1 was tiny compared to that of inner Fe4 atoms based on the Bader charge analysis, indicative of insignificant variation of interfacial ionicity. However, the magnetic moment (in μ B ) of interfacial Fe1 changed significantly compared to Fe4 atoms, indicating the charge redistribution, which enhanced the hybridization of N1- p and TM1- d states. One can conclude that the enhanced interfacial bonding strength could be ascribed to the strengthened hybridization of interfacial Fe1- d and N1- p covalence. These findings are relevant for a better comprehension of these specific configurations and improving technological modification of such kind of metal/ceramic system. • The relaxed interfacial models kept the stacking sequence of Fe–N (on top) OT. • The significant charge transfer results in the stronger bond strength across the interfaces. • The enhanced overlap of interfacial atoms account for the higher adhesion strength. • The magnetic moment of interfacial Fe1 changed significantly in comparison to that of Fe4 atoms.

Constructing a built-in electric field in monolayer g-C3N4 by carbon and oxygen co-doping for enhanced photocatalytic oxidation of toluene to benzaldehyde activity

The sustainable production of benzaldehyde with mild reaction conditions is challenging. Recently, carbon and oxygen co-doped g-C3N4 was experimentally discovered to enhance the performance of g-C3N4 for photocatalytic selective oxidation of toluene into benzaldehyde in the experiment. However, the microscopic mechanism of C/O co-doped g-C3N4 (COCN) to improve photocatalytic activity remains unclear. In this study, the optoelectronic properties of the COCN were investigated using density functional theory. The results show that the C and O atoms preferentially substitute for the bridge N1 and edge N2 atoms, respectively. The direct bandgap of COCN is 2.36 eV, smaller than that of Pure and Single-doped g-C3N4, which exhibits stronger absorption in the visible light region. Especially, the HOMO and LUMO of COCN are more delocalized, since the COCN forms a built-in electric field that facilitates the separation of electron-hole pairs. Moreover, the band edge positions of COCN conform to the redox potential of the efficient photocatalytic oxidation of toluene into benzaldehyde, and the synergetic effect of C/O co-doping significantly promoted the adsorption of toluene on COCN surface. This study analyzes the microscopic mechanism of non-metallic atoms co-doping to improve photocatalytic efficiency and will provide theoretical strategies for the development of other efficient photocatalysts.

Slippage at the initiation of RNA synthesis by Qβ replicase results in a periodic polyG pattern.

The repetitive copying of template nucleotides due to transcriptional slippage has not been reported for RNA-directed RNA polymerases of positive-strand RNA phages. We unexpectedly observed that, with GTP as the only substrate, Qβ replicase, the RNA-directed RNA polymerase of bacteriophage Qβ, synthesizes by transcriptional slippage polyG strands, which on denaturing electrophoresis produce a ladder with at least three clusters of bolder bands. The ≈ 15-nt-long G15 , the major product of the shortest cluster, is tightly bound by the enzyme but can be released by the ribosomal protein S1, which, as a Qβ replicase subunit, normally promotes the release of a completed transcript. 7-deaza-GTP suppresses the polyG synthesis and abolishes the periodic pattern, suggesting that the N7 atom is needed for the initiation of RNA synthesis and the formation of the structure recognized by protein S1. The results provide new insights into the mechanism of RNA synthesis by the RNA-directed RNA polymerase of a single-stranded RNA phage.

Predicting adsorption behavior of Triacanthine anticancer drug with pure B12N12 nano-cage: A theoretical study

Predicting adsorption behavior of the Triacanthine (TRC) anticancer drug on the surface of B12N12 nano-cage was investigated using DFT and TD-DFT methods by B3LYP/6-311+G(d) level in the water solution. The adsorption energies of the TRC-B12N12 complexes (A-C) were shown that the adsorption process is exothermic. The UV/Vis absorption and IR spectra analysis were calculated to investigate the changes happening in adsorption of TRC over nano-cage. According to the results, the interaction of the TRC drug from the N9 atom on the B12N12 nano-cage (model A) has the most chemical stability rather than models B and C. Based on NBO analysis, the charge transfer process has happened between the TRC drug and B12N12 nano-cage. Recovery time, charge difference (ΔN), and ELF analysis were calculated. It was understood that the B12N12 nano-cage can be a good carrier for the delivery of TRC anticancer medicine.

2,6‐Di(1H‐tetrazol‐1‐yl)pyridine and its cupric chloride complex

Abstract2,6‐Di(1H‐tetrazol‐1‐yl)pyridine (DTP) was prepared by a four‐stage procedure, including step‐by‐step heterocyclization of both amino groups of 2,6‐diaminopyridine with triethyl orthoformate and sodium azide. According to quantum‐chemical calculations and single crystal X‐ray diffraction data, DTP crystallizes in the form of the thermodynamically most stable conformer and has an almost flat molecular geometry. DTP was found to react with CuCl2 ⋅ 2H2O in ethanol to give the [Cu(DTP)Cl2(H2O)]n complex, which is a 1D coordination polymer, formed at the expense of bridging DTP ligand via the tetrazole ring nitrogen atoms N4. Possible coordination cites in DTP molecule are discussed using the data of quantum chemical calculations. The pyridine ring nitrogen atom of DTP does not participate in the formation of either coordination or intermolecular hydrogen bonds. This is explained by the results of quantum chemical calculations showing that this atom is less basic than N3 and N4 atoms of DTP molecule.

Coumarin 337 in aqueous solution: interplay between excitation and hydration

Excitation of the C337, highly fluorescent dye in an aqueous solution was studied by the TD-DFT. Through the B3PW91/6-311++G(d, p)/IEFPCM theory level, we obtained the C337 vibronic absorption spectrum which exactly reproduces the experimental maximum. Significant differences are shown between the results of calculating the transition energies using the models of vertical and vibronic transitions. Upon excitation, the main shift of the electron density occurs from C10 to C4 neighboring atom. Thus, large-scale ICT not occur. The effect of excitation on the vibrational spectra of C337 was analyzed. A single C337 molecule and its five different hydration complexes with strongly bound water molecules have been analyzed. Various hydrate complexes of the dye have been studied, and the effect of hydration on its excitation vibrational properties has been elucidated. It was taken into account that a water molecule can attach to the nitrogen atom N1 ("A" type) and the C=O carbonyl ("B" type), and cyano C≡N ("C" type) groups of the dye.

Defect Engineering Modulated Iron Single Atoms with Assist of Layered Clay for Enhanced Advanced Oxidation Processes.

Single-atom catalysts (SACs) feature maximum atomic utilization efficiency; however, the loading amount, dispersibility, synthesis cost, and regulation of the electronic structure are factors that need to be considered in water treatment. In this study, kaolinite, a natural layered clay mineral, is applied as the support for g-C3 N4 and single Fe atoms (FeSA-NGK). The FeSA-NGK composite exhibits an impressive degradation performance toward the target pollutant (>98% degradation rate in 10min), and catalytic stability across consecutive runs (90% reactivity maintained after three runs in a fluidized-bed catalytic unit) under peroxymonosulfate (PMS)/visible light (Vis) synergetic system. The introduction of kaolinite promotes the loading amount of single Fe atoms (2.57wt.%), which is a 14.2% increase compared to using a bare catalyst without kaolinite, and improved the concentration of N vacancies, thereby optimizing the regulation of the electronic structure of the single Fe atoms. It is discovered that the single Fe atoms successfully occupied five coordinated N atoms and combined with a neighboring N vacancy. Consequently, this regulated the local electronic structure of single Fe atoms, which drives the electrons of N atoms to accumulate on the Fe centers. This study opens an avenue for the design of clay-based SACs for water purification.

Crystal structure, Hirshfeld surface and DFT computations, along with molecular docking investigations of a new pyrazole as a tyrosine kinase inhibitor

In the present work we report the experimental and computational investigations of (2-aminophenyl)[4-(4-chlorophenyl)-1,3-diphenyl-1H-pyrazol-5-yl]methanone (C28H20ClN3O). X-ray diffraction (XRD) showed that the undertaken compound 3 crystallized in a monoclinic system, space group P21/n. The structure exhibited both inter- and intramolecular hydrogen bonding contacts of the type N—H···X (X= O, N, Cl) and C—H···O, which ensured the stabilization of the crystal then the molecular structure. Hirshfeld surface analysis (HSA) showed that other unconventional interactions such as H⋯H (48%) and C⋯H (28%) contributed as well in the molecular assembly. The energy of the HOMO and LUMO orbitals, the molecular electrostatic potential (MEP) and the absorption spectrum were generated using the density functional theory (DFT). The MEP map showed areas of the negative potential region around the electronegative atoms O1 and N3, while the maximum positive sites were around the hydrogen atoms of the amine group. The experimental and computed UV-Vis spectra showed the presence of π-π* and n-π* transitions. The computational results showed that the geometrical and electronic parameters were consistent and in accordance with the experimental data. The anticancer activity of the studied pyrazole was investigated in-silico via molecular docking (MD) towards EGFR tyrosine kinases (PDB ID: 1M17 and 2ITN). The outcomes suggest that the pyrazole 3 has significant interaction with the target receptors. Afterwards, drug properties were investigated by ADME/T analysis, which show that the examined pyrazole 3 has an excellent pharmacokinetic profile and no toxicity risks.

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.

Electrochemical Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy of Imidazole Ring Functionalized Monolayer on Smooth Gold Electrode.

The imidazole ring (Im) of histidine side chains plays a unique role in the function of proteins through covalent bonding with metal ions and hydrogen bonding interactions with adjusted biomolecules and water. At biological interfaces, these interactions are modified because of the presence of an electric field. Self-assembled monolayers (SAMs) with the functional Im group mimic the histidine side chain at electrified interfaces. In this study, we applied in-situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to probe the structure and hydrogen bonding of Im-functionalized SAM on smooth Au at the electrochemical interface. The self-assembly of molecules on the Au induced the proton shift from N1 atom (Tautomer-I), which is the dominant form of Im in the bulk sample, to N3 atom (Tautomer-II). The impact of electrode potential on the hydrogen bonding interaction strength of the Im ring was identified by SHINERS. Temperature-Raman measurements and density functional theory (DFT) analysis revealed the spectral marker for Im ring packing (mode near 1496–1480 cm−1) that allowed us to associate the confined and strongly hydrogen bonded interfacial Im groups with electrode polarization at −0.8 V. Reflection adsorption IR (RAIR) spectra of SAMs with and without Im revealed that the bulky ring prevented the formation of a strongly hydrogen bonded amide group network.

Structural basis for the transformation of the traditional medicine berberine by bacterial nitroreductase.

The bacterial nitroreductases (NRs) NfsB and NfsA are conserved homodimeric FMN-dependent flavoproteins that are responsible for the reduction of nitroaromatic substrates. Berberine (BBR) is a plant-derived isoquinoline alkaloid with a large conjugated ring system that is widely used in the treatment of various diseases. It was recently found that the gut microbiota convert BBR into dihydroberberine (dhBBR, the absorbable form) mediated by bacterial NRs. The molecular basis for the transformation of BBR by the gut microbiota remains unclear. Here, kinetic studies showed that NfsB from Escherichia coli (EcNfsB), rather than EcNfsA, is responsible for the conversion of BBR to dhBBR in spite of a low reaction rate. The crystal structure of the EcNfsB-BBR complex showed that BBR binds into the active pocket at the dimer interface, and its large conjugated plane stacks above the plane of the FMN cofactor in a nearly parallel orientation. BBR is mainly stabilized by π-stacking interactions with both neighboring aromatic residues and FMN. Structure-based mutagenesis studies further revealed that the highly conserved Phe70 and Phe199 are important residues for the conversion of BBR. The structure revealed that the C6 atom of BBR (which receives the hydride) is ∼7.5 Å from the N5 atom of FMN (which donates the hydride), which is too distant for hydride transfer. Notably, several well ordered water molecules make hydrogen-bond/van der Waals contacts with the N1 atom of BBR in the active site, which probably donate protons in conjunction with electron transfer from FMN. The structure-function studies revealed the mechanism for the recognition and binding of BBR by bacterial NRs and may help to understand the conversion of BBR by the gut microbiota.

5‐Amino‐2‐isopropenyltetrazole and its Cupric Chloride Complex: Synthesis, Structure and Magnetism

AbstractA new tetrazole ligand, 5‐amino‐2‐isopropenyltetrazole, was prepared by regioselective alkylation of 5‐aminotetrazole with allyl bromide in sulfuric acid followed by dehydrobromination of intermediate 5‐amino‐2‐(1‐bromopropan‐2‐yl)tetrazole. 5‐Amino‐2‐isopropenyltetrazole (L) was found to react with copper(II) chloride to generate complex [CuL2Cl2]n. The ligand and its complex were characterized by single crystal X‐ray and thermal analyses. Complex [CuL2Cl2]n presents 1D coordination polymer, formed at the expense of double chlorido bridges between neighbouring octahedral coordinated CuII cations. Tetrazole ligand acts as monodentate ligand coordinated by CuII cations via the heteroring N4 atoms only. Magnetic studies revealed that the copper(II) ions were weakly antiferromagnetically coupled. Natural bond orbital analysis was performed to explain the structural peculiarities of the ligand. Its basicity and the relative stability of the protonated forms were investigated using MO calculations.

Ferrocenoyl-adenines: substituent effects on regioselective acylation.

A series of N6-substituted adenine–ferrocene conjugates was prepared and the reaction mechanism underlying the synthesis was explored. The SN2-like reaction between ferrocenoyl chloride and adenine anions is a regioselective process in which the product ratio (N7/N9-ferrocenoyl isomers) is governed by the steric property of the substituent at the N6-position. Steric effects were evaluated by using Charton (empirical) and Sterimol (computational) parameters. The bulky substituents may shield the proximal N7 region of space, which prevents the approach of an electrophile towards the N7 atom. As a consequence, the formation of N7-isomer is a kinetically less feasible process, i.e., the corresponding transition state structure increases in relative energy (compared to the formation of the N9-isomer). In cases where the steric hindrance is negligible, the electronic effect of the N6-substituent is prevailing. That was supported by calculations of Fukui functions and molecular orbital coefficients. Both descriptors indicated that the N7 atom was more nucleophilic than its N9-counterpart in all adenine anion derivatives. We demonstrated that selected substituents may shift the acylation of purines from a regioselective to a regiospecific mode.

Coordination Sites for Sodium and Potassium Ions in Nucleophilic Adeninate Contact ion-Pairs: A Molecular-Wide and Electron Density-Based (MOWED) Perspective.

The adeninate anion (Ade−) is a useful nucleophile used in the synthesis of many prodrugs (including those for HIV AIDS treatment). It exists as a contact ion-pair (CIP) with Na+ and K+ (M+) but the site of coordination is not obvious from spectroscopic data. Herein, a molecular-wide and electron density-based (MOWED) computational approach implemented in the implicit solvation model showed a strong preference for bidentate ion coordination at the N3 and N9 atoms. The N3N9-CIP has (i) the strongest inter-ionic interaction, by −30 kcal mol−1, with a significant (10–15%) covalent contribution, (ii) the most stabilized bonding framework for Ade−, and (iii) displays the largest ion-induced polarization of Ade−, rendering the N3 and N9 the most negative and, hence, most nucleophilic atoms. Alkylation of the adeninate anion at these two positions can therefore be readily explained when the metal coordinated complex is considered as the nucleophile. The addition of explicit DMSO solvent molecules did not change the trend in most nucleophilic N-atoms of Ade− for the in-plane M-Ade complexes in M-Ade-(DMSO)4 molecular systems. MOWED-based studies of the strength and nature of interactions between DMSO solvent molecules and counter ions and Ade− revealed an interesting and unexpected chemistry of intermolecular chemical bonding.

Plasma‐Assisted Coupling Reactions of Dinitrogen and Carbon Dioxide Mediated by Monometallic YB1–4−⋅Anions: Carbon−Nitrogen Bond Formation

Transition-metal catalyzed coupling to form C-N bonds is significant in chemical science. However, the inert nature of N2 and CO2 renders their coupling quite challenging. Herein, we report the activation of dinitrogen in the mild plasma atmosphere by the gas-phase monometallic YB1-4 - anions and further coupling of CO2 to form C-N bonds by using mass spectrometry and theoretical calculation. The observed product anions are NCNBO- and N(BO)2 - , accompanied by the formation of neutral products YO and YB0-2 NC, respectively. We can tune the reactivity and the type of products by manipulating the number of B atoms. The B atoms in YB1-4 N2 - act as electron donors in CO2 reduction reactions, and the carbon atom originating from CO2 serves as an electron reservoir. This is the first example of gas-phase monometallic anions, which are capable to realize the functionalization of N2 with CO2 through C-N bond formation and N-N and C-O bond cleavage.

Synthesis, structure and characterisation of late transition metal complexes with 2-(tetrazol-1-yl)pyridine

Complexes [MII(2-pytz)Cl2] (M(II) = Pt, Pd; 2-pytz = 2-(tetrazol-1-yl)pyridine) were synthesised via direct interaction of the corresponding metal chlorides (K2PtCl4 or PdCl2) with 2-pytz under ambient conditions. RuCl3 does not react with 2-pytz under reflux in the protic media, while under reflux in N, N-dimethylformamide in the presence of LiCl, decomposition of the tetrazole cycle occurred leading to the formation of Ru(III)-coordinated N, N-dimethyl-N ′-(pyridin-2-yl)formimidamide derivative Li[RuIII(Py — N =C — NMe2)2Cl2]. The complex [Ru(2-pytz)(DMSO)3Cl2] ⋅ MeOH, where DMSO is dimethyl sulfoxide, was synthesised by reacting a specially prepared precursor cis-[Ru(DMSO)4Cl2] with 2-pytz in methanol under reflux conditions. The complex [Ru(2-pytz)(DMSO)2Cl2] was synthesised by reacting cis-[Ru(DMSO)4Cl2] with 2-pytz in ethanol under reflux conditions. The resulting complexes were characterised by elemental analyses, electrospray ionisation mass-spectrometry with detection of positive and negative ions, infrared spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and simultaneous thermal analysis. The structures of complexes [Pd(2-pytz)Cl2] and [Ru(2-pytz)(DMSO)3Cl2] ⋅ MeOH were investigated by single-crystal X-ray analysis. In the former, 2-pytz shows a N,N-chelating coordination via the pyridine ring N and the tetrazole ring N2 atoms. In the latter, 2-pytz coordinates as a monodentate ligand via the tetrazole ring N4 atom. According to 1H NMR spectroscopy data, in complex [Ru(2-pytz)(DMSO)2Cl2], 2-pytz coordinates as a N, N-chelating ligand via the pyridine ring N and the tetrazole ring N2 atoms.