N2 Bond Research Articles

Geometric Restraint Drives On- and Off-pathway Catalysis by the Escherichia coli Menaquinol:Fumarate Reductase

Complex II superfamily members catalyze the kinetically difficult interconversion of succinate and fumarate. Due to the relative simplicity of complex II substrates and their similarity to other biologically abundant small molecules, substrate specificity presents a challenge in this system. In order to identify determinants for on-pathway catalysis, off-pathway catalysis, and enzyme inhibition, crystal structures of Escherichia coli menaquinol:fumarate reductase (QFR), a complex II superfamily member, were determined bound to the substrate, fumarate, and the inhibitors oxaloacetate, glutarate, and 3-nitropropionate. Optical difference spectroscopy and computational modeling support a model where QFR twists the dicarboxylate, activating it for catalysis. Orientation of the C2-C3 double bond of activated fumarate parallel to the C(4a)-N5 bond of FAD allows orbital overlap between the substrate and the cofactor, priming the substrate for nucleophilic attack. Off-pathway catalysis, such as the conversion of malate to oxaloacetate or the activation of the toxin 3-nitropropionate may occur when inhibitors bind with a similarly activated bond in the same position. Conversely, inhibitors that do not orient an activatable bond in this manner, such as glutarate and citrate, are excluded from catalysis and act as inhibitors of substrate binding. These results support a model where electronic interactions via geometric constraint and orbital steering underlie catalysis by QFR.

Functionalization of Hafnium Oxamidide Complexes Prepared from CO-Induced N2 Cleavage

Functionalization of the nitrogen atoms in the hafnocene oxamidide complexes [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf](2)(N(2)C(2)O(2)) and [(η(5)-C(5)Me(4)H)(2)Hf](2)(N(2)C(2)O(2)), prepared from CO-induced N(2) bond cleavage, was explored by cycloaddition and by formal 1,2-addition chemistry. The ansa-hafnocene variant, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf](2)(N(2)C(2)O(2)), undergoes facile cycloaddition with heterocumulenes such as (t)BuNCO and CO(2) to form new N-C and Hf-O bonds. Both products were crystallographically characterized, and the latter reaction demonstrates that an organic ligand can be synthesized from three abundant and often inert small molecules: N(2), CO, and CO(2). Treatment of [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf](2)(N(2)C(2)O(2)) with I(2) yielded the monomeric iodohafnocene isocyanate, Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Hf(I)(NCO), demonstrating that C-C bond formation is reversible. Alkylation of the oxamidide ligand in [(η(5)-C(5)Me(4)H)(2)Hf](2)(N(2)C(2)O(2)) was explored due to the high symmetry of the complex. A host of sequential 1,2-addition reactions with various alkyl halides was discovered and both N- and N,N'-alkylated products were obtained. Treatment with Brønsted acids such as HCl or ethanol liberates the free oxamides, H(R(1))NC(O)C(O)N(R(2))H, which are useful precursors for N,N'-diamines, N-heterocyclic carbenes, and other heterocycles. Oxamidide functionalization in [(η(5)-C(5)Me(4)H)(2)Hf](2)(N(2)C(2)O(2)) was also accomplished with silanes and terminal alkynes, resulting in additional N-Si and N-H bond formation, respectively.

Bisoxazoline–copper(I)-catalyzed aziridination of diazoacetate with imines — A DFT study

Density functional theory (DFT) has been used to study bisoxazoline–copper(I)-catalyzed aziridination of diazoacetate with syn-imines or anti-imines. All the intermediates and transition states were optimized completely at the B3LYP/6-31G(d) level. Calculation results confirm that Cu(I)-catalyzed aziridination goes mainly through the catalyst–diazoacetate complex (M1), the copper(I)–carbene intermediate (M2), the copper–carbene–imine complex (M3), and the catalyst–aziridine carboxylate complex (M4). For syn-imines, the reaction mode I (C3–N5 bond attacking the Cu–C1 bond of M2) is more dominant than the reaction mode II (C3–N5 bond attacking the carbene–carbon C1 of M2), and the attack from the si-surface of M2 is prior to the re-surface. For anti-imines, the reaction modes and attacks from the si- or re-surface coexist. The reactivity of syn-imines is stronger than anti-imines. The favorable reaction channel is CA2 → M1b → TS1b → M2 → syn-TS2b → syn-M3b → syn-TS3b → syn-M4b → syn-P2. The dominant product theoretically predicted is of (S,S)-chirality. On the whole, the solvent effect decreases the free energies of the species.

Why Lewis acids accelerate the thermal Curtius rearrangement of benzoyl azide into phenyl isocyanate

The thermal Curtius rearrangement of benzoyl azide in the presence of Lewis acids has been studied by DFT (PBE/TZ2P) method. The complexation of Lewis acids (BF 3, AlCl 3, SbCl 5) with benzoyl azide leads to the formation of 1:1 and 1:2 stable complexes with interaction of catalysts with O and N atoms of carbonyl azide group. The potential energy surfaces of the catalytic rearrangement have been calculated for each complex and the relation between the complexes and the transition states on potential energy surface have been established by IRC calculation. The energy barriers for catalytic reactions are significantly lower in the most cases in comparison with an uncatalyzed reaction. The activation energy is decreasing in the range of Lewis acids AlCl 3 > SbCl 5 > BF 3 and it correlates with the decreasing of Lewis acids strength. The Mulliken bond population analysis has been done for three compounds RCON 3 (R = H, Me, Ph) and for their complexes, and for all corresponding transition states using the B3LYP/6-311G∗ approximation. The interaction of Lewis acids with carbonyl azide group causes the decreasing of N1 N2 bond strength and it helps the thermal Curtius rearrangement to proceed.

Crystal structure of (E)-4-chloro-2-(isopropyliminomethyl)phenol, C10H12ClNO

C10H12ClNO, monoclinic, C12/c1 (no. 15), a = 21.459(2) A, b = 5.6893(6) A, c = 17.760(2) A, ) = 105.137(2)°, V = 2093.1 A, Z = 8, Rgt(F) = 0.066, wRref(F) = 0.190, T = 298 K. Source of material All reagents and solvents were used as purchased without further purification. 5-chloro-2-hydroxybenzaldehyde (147 mg, 1 mmol), propan-2-amine (118 mg, 2 mmol) were dissolved in methanol (15 mL). The mixture was refluxd for a period of 8 h and, after cooling to room temperature, was filtered. The filtrate was kept still in air for one week. Large block-shaped crystals were precipitated. They were filtered and washed with ethanol and dried in a vacuum desiccator using anhydrous CaCl2 (yield 89 %). Experimental details All H atoms were positioned geometrically and refined as riding with d(C—H) = 0.93 0.98 A), Uiso(H) = 1.2 or 1.5 Ueq(C), respectively. The instability of isopropyl group and the poor quality of the crystals result in quite large residual values. Discussion Extended interest to the Schiff bases is caused by their use as startingmaterials in the synthesis of important drugs, such as antibiotics and antimalarial, antifungal, and antitumor substances [15], as components of rubber compounds [6], or as ligands for the complexation of metal ions [7-9]. The bond lengths and angles in the title crystal structure are in normal ranges. The C7=N1 bond length of 1.263(4) A conforms to the value of a double bond. The torsion angleN1–C7–C1–C6 is –178.94(3)°. In the crystal packing, the molecules are linked by several weak intermolecular C–H···O interactions. Z. Kristallogr. NCS 225 (2010) 567-568 / DOI 10.1524/ncrs.2010.0248 567 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: yellow block, size 0.13 × 0.21 × 0.32 mm Wavelength: Mo K* radiation (0.71073 A) -: 3.26 cm−1 Diffractometer, scan mode: Bruker SMART CCD, #/% 2+max: 53° N(hkl)measured, N(hkl)unique: 6601, 2155 Criterion for Iobs, N(hkl)gt: Iobs > 2 ((Iobs), 1755 N(param)refined: 121 Program: SHELXTL [10] Table 1. Data collection and handling. H(1) 8f 0.0753 0.3538 0.2691 0.129 H(3) 8f 0.1186 0.5580 0.1155 0.085 H(4) 8f 0.1912 0.3766 0.0593 0.083 H(6) 8f 0.2143 −0.1420 0.2160 0.068 H(7) 8f 0.1569 −0.1417 0.3181 0.067 H(8) 8f 0.1191 −0.1426 0.4202 0.081 H(9A) 8f 0.1246 0.2348 0.4733 0.151 H(9B) 8f 0.0784 0.0770 0.5069 0.151 H(9C) 8f 0.0496 0.2614 0.4415 0.151 H(10A) 8f −0.0130 −0.0494 0.3577 0.158 H(10B) 8f 0.0148 −0.2445 0.4197 0.158 H(10C) 8f 0.0227 −0.2676 0.3347 0.158 Table 2. Atomic coordinates and displacement parameters (in A). Atom Site x y z Uiso

Gallium Halides as Alternative Ligands to CO and N2 in Transition Metal Complexes: A Bonding Analysis

Quantum chemical calculations using gradient-corrected DFT at the BP86/TZ2P+ level have been carried out for the gallium halide complexes [Fe(CO)4(GaX)] (X = F−I) and for [Fe(CO)5] and [Fe(CO)]4(N2)]. The nature of the metal−ligand bond has been investigated with an energy decomposition analysis. The Fe−GaX bonds in [Fe(CO)4(GaX)] have rather high bond dissociation energies that are smaller than the BDE of [Fe(CO)5] but larger than the BDE of [Fe(CO)]4(N2)]. The axial isomer of [Fe(CO)4(GaF)] is predicted to be slightly more stable than the equatorial form, while the equatorial isomers of the heavier halogen systems [Fe(CO)4(GaX)] (X = Cl−I) are a bit lower in energy than the axial form. The energy difference between the two isomers is for all gallium complexes [Fe(CO)4(GaX)] smaller than 1.0 kcal/mol. The ratio of covalent bonding and electrostatic attraction in the (CO)4Fe−GaX bonds is very similar to the values that are calculated for the (CO)4Fe−CO and (CO)4Fe−N2 bonds. The analysis of the bonding sit...

ChemInform Abstract: Cyclization Reactions of Nucleoside Anomeric Radical with Olefin Tethered on Base: Factors that Induce Anomeric Stereochemistry.

Nucleoside anomeric radicals were formed through 1,5-translocation of vinyl radicals generated from the 2,2-dibromovinyl group tethered at the uracil 6-position (1, 2, and 4) by tin radical. The anomeric radicals attacked the resulting C-6 vinyl group in a 5-endo-trig manner to afford anomeric spiro nucleosides (11−13, 21, 23, and 24) with the 6,1‘-etheno bridge as the major cyclized products. The anomeric stereochemistry of the cyclization was found to be affected by the 2‘-substituent. To consider the structure of the intermediate anomeric radical, the reaction using α-6-(2,2-dibromovinyl)-2‘-deoxyuridine 9 was investigated. The same anomeric β/α-stereoselectivity as the counterpart of 2 showed that the nucleoside anomeric radical would have nearly a planar structure and the C1‘−N1 bond rotation in the radical is much faster than cyclization. The origin of the minor spiro nucleosides (14−20, 22, and 25−28) with the 6,1‘-ethano bridge has also been investigated and appeared to be (E)-6-(2-bromovinyl)urid...

DFT STUDY ON METAL CATIONIZATION AND O6-PROTONATION ON 2′-DEOXYGUANOSINE CONFIGURATION: CHANGES ON SUGAR PUCKERING AND STRENGTH OF THE N-GLYCOSIDIC BOND

Density functional theory (DFT) calculations were performed at the B3LYP/6-311++G (d, p) level to determine coordination geometries, absolute metal ion affinities, and free energies for all possible complexation stable products formed by monovalent metal cations including Li+ , Na+ , K+ with the nucleoside 2′-Deoxyguanosine. All computations indicate that the metal ion affinity (MIA) decreases on going from Li+ to Na+ and K+ for 2′-Deoxyguanosine. For example, the affinities for the metal ions described above are 75.2, 57.3, 43.4 kcal/mol, respectively. Furthermore, the influence of metal cationization and O6 protonation on the strength of the N-glycosidic bond, torsion angles and angle of pseudorotation (P) have been studied. With respect to the results, it has been found that metal binding significantly change the values of the phase angle of pseudorotation (P) in the sugar unit of these nucleosides but, O6 -protonation do not significantly change the values of the torsion angles and angle of pseudorotation (P). In all modified forms, the length of the C1'–N9 bond increases. The Mulliken population analysis and natural bond orbital (NBO) analysis on atomic charges have been carried out on the optimized geometries.

Benzyl N-((S)-2-hydr-oxy-1-{N'-[(E)-2-methoxy-benzyl-idene]hydrazinecarbon-yl}eth-yl)carbamate from synchrotron data.

A U-shaped conformation is found in the title compound, C19H21N3O5, with the benzene rings lying to the same side of the mol­ecule; the dihedral angle between them is 10.83 (16)°. The dihedral angle formed between the hydrazinecarbonyl and carbamate residues is 68.42 (13)°. The carbonyl groups lie approximately at right angles to each other [O—C⋯C—O pseudo torsion angle of 107.7 (3)°], and the conformation about the C12=N3 bond [1.279 (4) Å] is E. An intra­molecular Ncb—H⋯Ohy (cb = carbmate and hy = hydr­oxy) hydrogen bond occurs, generating an S(6) loop. In the crystal, inter­molecular Oh—H⋯Oca (ca = carbon­yl) and Nhz—H⋯Oca (hz = hydrazine) hydrogen bonds lead to the formation of a supra­molecular chain, two mol­ecules thick, which propagates along the a axis; these are connected by C—H⋯Oca contacts.

Exploring water-soluble Pt(II) complexes of diethylenetriamine derivatives functionalized at the central nitrogen. Synthesis, characterization, and reaction with 5′-GMP

Abstract The aims of our program are to develop coordination complexes that can be used as selective probes, fluorescent agents and inorganic medicinal agents. In order to accomplish this, the design, synthesis, characterization and X-ray structure of new water-soluble monofunctional Pt(II) complexes with useful spectroscopic properties for assessing metal binding to biomolecules were investigated. Two diethylenetriamine (dien) derivatives, 2-(bis(2-aminoethyl)amino)acetic acid (acdien) and N′-[7-(acetamido)-4-(trifluoromethyl)coumarin]diethylenetriamine (atfcdien), were used. The latter was designed to allow the fluorophore group, 7-amino-4-(trifluoromethyl)coumarin (atfc), to be attached to metal centers through the dien moiety. 1H NMR spectroscopy and X-ray crystallography were employed to characterize the [Pt(atfcdien)Br][Pt(Me2SO)Br3] (8a) and [Pt(acdien)Br]Br (9a) complexes. 1H NMR and fluorescence spectroscopic methods were used to characterize the [Pt(atfcdien)Br]Br (8b) and [Pt(acdien)Br]Br (9a) complexes. 1H NMR studies of the monofunctional [Pt(acdien)Br]Br (9a) complex conducted to examine its interaction with guanosine 5′-monophosphate (5′-GMP) in D2O solutions revealed one downfield-shifted H8 and one downfield-shifted H1′ signal, consistent with 5′-GMP binding via N7 and fast rotation about the Pt–N7 bond.

Theoretical study on the singlet and triplet potential energy surfaces of NH (X3Σ−) + HCNO reaction

Both the singlet and triplet potential energy surfaces (PESs) of the NH (X3Σ−) + HCNO reaction have been investigated at the BMC-CCSD level based on the UB3LYP/6-311++G(d, p) structures. The results show that the title reaction is more favorable through the singlet potential energy surface than the triplet one. For the singlet potential energy surface of the NH (X3Σ−) + HCNO reaction, the most feasible association of NH (X3Σ−) with HCNO is found to be a non-barrier nitrogen-to-carbon attack forming the adduct a (trans-HNCHNO), which can isomerize to the adduct b (cis-HNCHNO). The most feasible channel is that the 1, 3-H shift with N2–H2 and C–N1 bonds cleavage associated with the N1–H2 bond formation of adduct a leads to the product P 1 (HCN + HNO). Moreover, P 2 (HNC + HNO) should be the competitive product. The other products, including P 3 (NH2 + NCO) and P 4 (N2H2 + CO), are minor products. The product P 1 can be obtained through two competitive channels Path 1: R → a → P 1 and Path 3: R → b → d → P 1 , whereas the product P 2 can be formed through Path 2: R → b → d → P 2 . At high temperatures, the nitrogen-to-nitrogen approach may become feasible. For the triplet potential energy surface of the NH (X3Σ−) + HCNO reaction, the Path 10: R → 3 a → 3 a 1 → P 1 should be the most feasible pathway due to the less reaction steps and lower barriers. These conclusions will have impacts on further experimental investigations.

Thermal decomposition mechanism and quantum chemical investigation of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO)

The thermal decomposition mechanism of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) compound was studied by means of differential scanning calorimetry (DSC), thermogravimetry and derivative thermogravimetry (TG-DTG), and the coupled simultaneous techniques of in situ thermolysis cell with rapid scan Fourier transform infrared spectroscopy (in situ thermolysis/RSFTIR). The thermal decomposition mechanism is proposed. The quantum chemical calculation on HNTO was carried out at B3LYP level with 6-31G+(d) basis set. The results show that HNTO has two exothermic decomposition reaction stages: nitryl group break first away from HNTO molecule, then hydrazine group break almost simultaneously away with carbonyl group, accompanying azole ring breaking in the first stage, and the reciprocity of fragments generated from the decomposition reaction is appeared in the second one. The C–N bond strength sequence in the pentabasic ring (shown in Scheme 1) can be obtained from the quantum chemical calculation as: C3–N4 > N2–C3 > N4–C5 > N1–C5. The weakest bond in NTO− is N7–C3. N11–N4 bond strength is almost equal to N4–C5. The theoretic calculation is in agreement with that of the thermal decomposition experiment. Open image in new window Scheme 1 Scheme of HNTO

Structural Perturbations Induced by the α-Anomer of the Aflatoxin B1Formamidopyrimidine Adduct in Duplex and Single-Strand DNA

The guanine N7 adduct of aflatoxin B1exo-8,9-epoxide hydrolyzes to form the formamidopyrimidine (AFB-FAPY) adduct, which interconverts between α and β anomers. The β anomer is highly mutagenic in Escherichia coli, producing G → T transversions; it thermally stabilizes the DNA duplex. The AFB-α-FAPY adduct blocks replication; it destabilizes the DNA duplex. Herein, the structure of the AFB-α-FAPY adduct has been elucidated in 5′-d(C1T2A3T4X5A6T7T8C9A10)-3′·5′-d(T11G12A13A14T15C16A17T18A19G20)-3′ (X = AFB-α-FAPY) using molecular dynamics calculations restrained by NMR-derived distances and torsion angles. The AFB moiety intercalates on the 5′ face of the pyrimidine moiety at the damaged nucleotide between base pairs T4·A17 and X5·C16, placing the FAPY C5−N5 bond in the Ra axial conformation. Large perturbations of the ε and ζ backbone torsion angles are observed, and the base stacking register of the duplex is perturbed. The deoxyribose orientation shifts to become parallel to the FAPY base and displaced toward the minor groove. Intrastrand stacking between the AFB moiety and the 5′ neighbor thymine remains, but strong interstrand stacking is not observed. A hydrogen bond between the formyl group and the exocyclic amine of the 3′-neighbor adenine stabilizes the E conformation of the formamide moiety. NMR studies reveal a similar 5′-intercalation of the AFB moiety for the AFB-α-FAPY adduct in the tetramer 5′-d(C1T2X3A4)-3′, involving the Ra axial conformation of the FAPY C5−N5 bond and the E conformation of the formamide moiety. Since in duplex DNA the AFB moiety of the AFB-β-FAPY adduct also intercalates on the 5′ side of the pyrimidine moiety at the damaged nucleotide, we conclude that favorable 5′-stacking leads to the Ra conformational preference about the C5−N5 bond; the same conformational preference about this bond is also observed at the nucleoside and base levels. The structural distortions and the less favorable stacking interactions induced by the AFB-α-FAPY adduct explain its lower stability as compared to the AFB-β-FAPY adduct in duplex DNA. In this DNA sequence, hydrogen bonding between the formyl oxygen and the exocyclic amine of the 3′-neighboring adenine stabilizing the E configuration of the formamide moiety is also observed for the AFB-β-FAPY adduct, and suggests that the identity of the 3′-neighbor nucleotide modulates the stability and biological processing of AFB adducts.

Natural bond orbital analysis of some para-substituted N-nitrosoacetanilide biological molecules

Theoretical study of several para-substituted N-nitrosoacetanilide biological molecules has been performed using density functional B3LYP method with 6-31G(d,p) basis set. Geometries obtained from DFT calculation were used to perform natural bond orbital analysis. The p characters of two nitrogen natural hybrid orbital (NHO) σN3–N2 bond orbitals increase with increasing σp values of the para substituent group on the benzene, which results in a lengthening of the N3–N2 bond. The p characters of oxygen NHO σO1–N2 and nitrogen NHO σO1–N2 bond orbitals decrease with increasing σp values of the para substituent group on the benzene, which results in a shortening of the N2=O1 bond. It is also noted that decreased occupancy of the localized σN3–N2 orbital in the idealized Lewis structure, or increased occupancy of \( \sigma_{\rm N3-N2}^{\ast}\) of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are also related with the resulting p character of the corresponding nitrogen NHO of σN3–N2 bond orbital.

Natural bond orbital population analysis of para-substituted O-nitrosyl carboxylate compounds

Theoretical study of several para-substituted O-nitrosyl carboxylate compounds has been performed using density functional B3LYP method with 6-31G(d,p) basis set. Geometries obtained from DFT calculation were used to perform natural bond orbital analysis. It is noted that weakness in the O3–N2 sigma bond is due to \( n_{{{\text{O}}_{1} }} \to \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} \) delocalization and is responsible for the longer O3–N2 bond lengths in para-substituted O-nitrosyl carboxylate compounds. It is also noted that decreased occupancy of the localized \( \sigma_{{{\text{O}}_{3} --{\text{N}}_{2} }} \) orbital in the idealized Lewis structure, or increased occupancy of \( \sigma_{{{\text{O}}_{3} - {\text{N}}_{2} }}^{*} \) of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital of \( \sigma_{{{\text{O}}_{3} --{\text{N}}_{2} }} \) bond orbital. In addition, the charge transfer energy decreases with the increase of the Hammett constants of substituent groups and the partial charges distribution on the skeletal atoms may approve anticipating that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intra- and intermolecular interaction.

Restricting the versatile metal-binding behaviour of adenine by using deaza-purine ligands in mixed-ligand copper(II) complexes

In order to deepen our understanding of the versatile behaviour of adenine (Hade) as ligand, we have synthesized four novel ternary copper(II) complexes having two deazaadenine ligands, namely 4-azabenzimidazole (H4abim) or 7-azaindole (H7azain) as N1,N6-dideazaadenine or N1,N6,N7-trideazaadenine, respectively. The related compounds were studied by thermal, spectral and single crystal X-ray diffraction methods. In [Cu(NBzIDA)(H4abim)] n ( 1) the recognition between H4abim and the ( N-benzyliminodiacetate)-copper(II) chelate only displays the formation of the Cu–N7(purine-like) bond, in contrast to Hade behaviour in [Cu(NBzIDA-like)(Hade)(H 2O)]·H 2O (Cu–N3(Hade) bond reinforced by N9–H···O(IDA-like) interaction). In [Cu(EIDA)(H7azain)(H 2O)] ( 2, EIDA = N-ethyliminodiacetate ligand), [Cu(NBzIDA)(H7azain)(H 2O)] ( 3) and [Cu(μ 2-SO 4)(H7azain) 2(H 2O) 2] n ( 4), H7azain binds Cu(II) centre by the Cu–N3(purine-like) bond, reinforced by a N9–H···O(IDA-like or sulfate) intra-molecular interligand interaction.

Crystal structure of catena-poly[diaquabis(4-formylpyridinethiosemicarbazone- N,S)cadmium(II)] sulfate hydrate, [Cd(H2O)2(C7H8N3S)2][SO4] · H2O

C56H88Cd4N32O28S12, monoclinic, C12/c1 (no. 15), a = 13.6879(6) A, b = 18.6173(8) A, c = 18.2470(7) A, . = 90.392(1)°, V = 4649.8 A, Z = 2, Rgt(F) = 0.050, wRref(F ) = 0.159, T = 296 K. Source of material 4-Formylpyridine thiosemicarbazone (0.186 g, 1 mmol) was dissolved in ethanol (15 ml) and refluxed with CdSO4.·.H2O (0.226.g, 1 mmol) dissolved in 10 ml of hot water. The product that separated out was collected, washed with ether and dried in vacuo. Single crystals of the title complex were obtained by vapour diffusion of diethyl ether into a DMF solution. Experimental details Hydrogen atomswere positioned geometrically and refined using a riding model, with d(C—H) = 0.85 0.97A and withUiso(H) = 1.2 Ueq(C) [1.5 Ueq(C) for the methyl group]. The solvent molecule H2Owas found to be disordered over two sites with 0.50 occupancy. Discussion Heterocyclic thiosemicarbazones have attracted considerable interest in chemistry and in biology [1], since these compounds have remarkable coordination properties [2-5], antiviral [6], antibacterial [7], antimalarial [8], antifungal [9], and antitumoral activities [10]. The chemistry of copper complexes with these ligands is one of the interesting themes of current research due to their interesting structural [11], electrochemical [12], spectrophotometric [13], and magnetic properties [14] and also because of their relevance to the active sites of several metalloenzymes [15,16]. The crystal structure of the title complex is a chain polymer. The Cd(II) ion is coordinated by the four ligands, 4-formylpyridine thiosemicarbazone (L), and two aqua to form a distorted octahedral environment. The ligand L behaves as a bridging ligand through the N atom of the pyridyl ring and S atom of thiosemicarbazone moity. Two N atoms and two O atoms comprise the equatorial plane with the Cd1—O1, Cd1—O2 and Cd1—N2 bond distances being 2.357(6) A, 2.362(7) A and 2.353(5) A, respectively. The apical positions are occupied by two S atoms from two other ligands (L), the Cd2—S2 bond distance is 2.664(2)A (x+1/2,y−1/2,z; −x+3/2,−y−1/2,−z), which are slightly longer than the corresponding values found in the reported complexes CdI2(C9H11N3OS)2 with d(Cd—S) of 2.588(1) A and 2.580 (1) A) [17] and C14H22CdCl2N10O10S2 d(Cd—S) of 2.573 (1) A and 2.563 (1) A [18]. The C6=N2 bond distance (1.277(8) A) in the tilte complex is the same as those found in free ligand (1.279 A) [19], but is shorter than that in the reported complex (1.293 A) C14H22CdCl2N10O10S2 [18]. However, the C7=S1 bond distance 1.717(6)A is longer than that observed in free ligand (1.677 A) [19], but is the same within experimental error to that found in the reported complex (1.711.A) [18]. The crystal packing of the complex is stabilized through strong intermolecular hydrogen bonds. Z. Kristallogr. NCS 224 (2009) 205-207 / DOI 10.1524/ncrs.2009.0092 205 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: yellow prism, size 0.08 × 0.15 × 0.20 mm Wavelength: Mo K0 radiation (0.71073 A) &: 12.62 cm−1 Diffractometer, scan mode: Bruker SMART APEX CCD, +/1 2max: 52° N(hkl)measured, N(hkl)unique: 28659, 4560 Criterion for Iobs, N(hkl)gt: Iobs > 2 !(Iobs), 3364 N(param)refined: 306 Programs: SHELXS-97 [20], SHELXL-97 [21], SHELXTL [22], ORTEP-III [23], PLATON [24] Table 1. Data collection and handling.

Copper‐Catalyzed Cycloaddition of Sulfonyl Azides with Alkynes to Synthesize N‐Sulfonyltriazoles ‘on Water’ at Room Temperature

AbstractWe have developed a green and practical method for the Huisgen cycloaddition of water‐insoluble sulfonyl azides with alkynes ‘on water’ at room temperature under catalysis of the inexpensive catalyst system CuX/PhSMe, and addition of the ligand (thioanisole) greatly inhibited cleavage of the N1N2 bond in the 5‐cuprated N‐sulfonyltriazole intermediates to amides and improved the yields of N‐sulfonyltriazoles.

Deamination of the Radical Cation of the Base Moiety of 2′‐Deoxycytidine: A Theoretical Study

Five pathways leading to the deamination of cytosine (to uracil) after formation of its deprotonated radical cation are investigated in the gas phase, at the UB3LYP/6-311G(d,p) level of theory, and in bulk aqueous solvent. The most favorable pathway involves hydrogen-atom transfer from a water molecule to the N3 nitrogen of the deprotonated radical cation, followed by addition of the resulting hydroxyl radical to the C4 carbon of the cytosine derivative. Following protonation of the amino group (N4), the C4--N4 bond is broken with elimination of the NH3+(. ) and formation of a protonated uracil. The rate-determining step of this mechanism is hydrogen-atom transfer from a water molecule to the cytosine derivative. The associated free energy barrier is 70.2 kJ mol(-1).

The structure and chemical bonding in the N2CuX and N2···XCu (X = F, Cl, Br) systems studied by means of the molecular orbital and Quantum Chemical Topology methods

Ab initio studies carried out at the MP2(full)/6-311+G(2df) and MP2(full)/aug-cc-pVTZ-PP computational levels reveals that dinitrogen (N(2)) and cuprous halides (CuX, X = F, Cl, Br) form three types of systems with the side-on and end-on coordination of N(2): N[triple bond]N-CuX (C(infinity v)), N(2)-CuX (C(2v)) stabilized by the donor-acceptor bonds and weak van der Waals complexes N(2)...XCu (C(2v)) with dominant dispersive forces. An electron density transfer between the N(2) and CuX depends on type of the N(2) coordination and a comparison of the NPA charges yields the [N[triple bond]N](delta+)-[CuX](delta-) and [N(2)](delta-)-[CuX](delta+) formula. According to the NBO analysis, the Cu-N coordinate bonds are governed by predominant LP(N2)-->sigma*(Cu-X) "2e-delocalization" in the most stable N[triple bond]N-CuX systems, meanwhile back donation LP(Cu)-->pi*(N-N) prevails in less stable N(2)-CuX molecules. A topological analysis of the electron density (AIM) presents single BCP between the Cu and N nuclei in the N[triple bond]N-CuX, two BCPs corresponding to two donor-acceptor Cu-N bonds in the N(2)-CuX and single BCP between electron density maximum of the N[triple bond]N bond and halogen nucleus in the van der Waals complexes N(2)...XCu. In all systems values of the Laplacian nabla(2)rho(r)(r(BCP)) are positive and they decrease following a trend of the complex stability i.e. N[triple bond]N-CuX (C(infinity v)) > N(2)-CuX (C(2v)) > N(2)...XCu (C(2v)). A topological analysis of the electron localization function (ELF) reveals strongly ionic bond in isolated CuF and a contribution of covalent character in the Cu-Cl and Cu-Br bonds. The donor-acceptor bonds Cu-N are characterized by bonding disynaptic basins V(Cu,N) with attractors localized at positions corresponding to slightly distorted lone pairs V(N) in isolated N(2). In the N[triple bond]N-CuX systems, there were no creation of any new bonding attractors in regions where classically the donor-acceptor bonds are expected and there is no sign of typical covalent bond Cu-N with the bonding pair. Calculations carried out for the N[triple bond]N-CuX reveal small polarization of the electron density in the N[triple bond]N bond, which is reflected by the bond polarity index being in range of 0.14 (F) to 0.11 (Cl).