Spectroscopy and stereochemistry of the optically active copper(II), cobalt(II) and nickel(II) complexes with Schiff bases N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(3-methylbenzylideneiminato) and N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(5-methylbenzylideneiminato)

Schiff bases obtained from N,N′-(1R,2R)-1,2-cyclohexanediamine and 2-hydroxy-3-methylbenzaldehyde, 2-hydroxy-5-methylbenzaldehyde, have been used as ligands for copper(II), cobalt(II) and nickel(II). The complexes were characterized with UV–Vis, circular dichroism (CD), infrared, diamagnetic and paramagnetic ¹H NMR spectroscopy. CD spectra revealed exciton coupled π→π* transitions. Assignments of LMCT and d–d transitions in CD spectra of Ni(II), Co(II) and Cu(II) complexes is proposed. CD data are characteristic for central ion tetrahedral distortion from the planarity and λ conformation of the cyclohexane ring. ¹H NMR of Ni(II) complexes exhibited significant coordination shifts of CHN and ring protons which are in the closest proximity to Ni(II). The ¹H NMR paramagnetic spectra of Co(II) complexes revealed the most upfield shifted resonance at −60 ppm assigned to CHN and −28 ppm to hydrogen atom at C(5′) of the phenyl ring. Results of spectral analyses suggest central ions in a distorted square-planar geometry with N₂O₂ chromofore group.     

On the structure of humulinone

Two structures have been proposed for humulinone (II and III in Fig. 1). The high resolution NMR spectrum of this and related substances points to the five-membered ring structure II.     

1, 4, 5, 6-Tetrahydro-ν-tetrazin-Derivate

1, 4, 5, 6-Tetrahydro-ν-tetrazin-Derivate The title compounds 2 and 13 are readily available from α-lithiated N-alkyl-nitrosoamines 1 (see Tables 1 and 2) which decompose at ? 73° to yield the N-oxides 2. The ESR. spectra of two derivatives 1 are recorded (Fig. 1), and tentative mechanisms are proposed for the head to head dimerizations ( la- 3- 4- 5- 2a and Scheme 1). Coupling of lithionitrosoamines with iodine (-6) and alternative decomposition routes of representatives of this class of organometallics with special substitution [equations (2)-(5)] are reported. The structures of the tetrazines are established by spectroscopic data [ESCA] (Fig. 2), IR., UV., ¹H- (cf. Fig. 9) and ¹³C-NMR., PE. (Scheme 2), by an X-ray analysis of 2a (Fig. 4-8 and Table 3), and by the chemical reactions. The crystal structure of 2a is a twisted boat with non planar terminal nitrogen atoms which reflects the electron repulsion in the 4-atom-6-electron N? N?N?N-system. Comparisons are made with 2-tetrazenes, the open chain analogues of 13 , wherever possible. Raney-Ni reductions of 2 or 13 gives diamines 14 to which is assigned the d, l-configuration through the ¹H-NMR. spectra of the aminals 7 and 15 . Neither the oxides 2 nor the tetrazines 13 undergo cycloaddition reactions [equation (6) and Section 4]. Compound 2a is dimerized to the bis (nitrosoamino)-2-tetrazene 18 by treatment with acid, Zn^II, Cu^I or iodomethane. 2a is oxidized at nitrogen to the ethylene diamine derivative 6a (through 20 , with H₂O₂), or at the CH₂-groups of the ring to give oxo-N-oxide 21 (with MnO₂ or the ring contracted oxo-tetrazoline-N-oxide 22 (with KMnO₄). Pyrolysis or photolysis of the dimethyl tetrahydrotetrazine 13a furnishes the trimer 26 of N-methylimine, but no diazetidine 27 . Silver and mercury complexes 29 are obtained from 13a , while Cr(CO)₅. THF does not furnish a complex as with azocompounds, but rather replaces N₂ in 13a by CO (→ 28). Oxidation with permanganate converts 13a into the oxalic acid derivative 30 with unchanged tetrazine structure.     

Ruthenation of duplex and single-stranded d(CGGCCG) by organometallic anticancer complexes

We have studied the interaction of the organometallic anticancer ruthenium(II) complexes [(eta(6)-p-cymene)Ru(en)Cl][PF(6)] (1) and [(eta(6)-biphenyl)Ru(en)Cl][PF(6)] (2) (en=ethylenediamine) with the single-stranded (ss) DNA hexamer d(CGGCCG) (I) and the duplex d(CGGCCG)(2) (II) by HPLC, ESI-MS, and one- and two-dimensional (1)H and (15)N NMR spectroscopy. For ss-DNA, all three G's are readily ruthenated with [(eta(6)-arene)Ru(en)](2+), but for duplex DNA there is preferential ruthenation of G3 and G6, and no binding to G2 was detected. For monoruthenated duplexes, N7 ruthenation of G is accompanied by strong hydrogen bonding between G-O6 and en-NH for the p-cymene adducts. Intercalation of the non-coordinated phenyl ring between G3 and C4 or G6 and C5 was detected in the biphenyl adducts of mono- and diruthenated duplexes, together with weakening of the G-O6NH-en hydrogen bonding. The arene ligand plays a major role in distorting the duplex either through steric interactions (p-cymene) or through intercalation (biphenyl).     

尿嘧啶和5-氯尿嘧啶1S0→1S2跃迁动态结构的共振拉曼光谱

采用含时量子波包理论的简单模型对5-氯尿嘧啶和尿嘧啶的共振拉曼光谱开展了强度分析拟合, 获得了1(π, π*)激发态的几何结构变化动态特征. 结果表明, 尿嘧啶1S0→1S2跃迁的动态结构特征因5-位氯原子取代而改变. 5-氯尿嘧啶的动态结构特征主要沿C5=C6伸缩振动+C6H12 弯曲振动和N3H9/N1H7弯曲振动+N1C6伸缩振动反应坐标展开, 而尿嘧啶的动态结构特征主要沿嘧啶环的伸缩振动+C5H11/C6H12/N1H7弯曲振动和C4=O10伸缩振动反应坐标展开. π和π*轨道中氯原子的pz电子参与嘧啶环的p-π共轭作用导致了在1(π, π*)激发态上5-氯尿嘧啶的振动重组能更多地配分给嘧啶环的弯曲振动模式和C5=C6伸缩振动模式. 尿嘧啶在甲醇中的激发态动态结构特征与在水中的基本一致, 但波包沿C5H11/C6H12/N1H7弯曲振动+N1C6伸缩振动(υ12)和环呼吸振动(υ17)反应坐标的运动明显增强.     

Effect of Through‐Bond Interaction on Conformation and Structure in Rod‐Shaped Donor–Acceptor Systems. Part 2.

The crystal structures of seven N‐aryltropan‐3‐one (=8‐aryl‐8‐azabicyclo[3.2.1]octan‐3‐one) derivatives 1T1, 2T1, 2T2, 3T2, 5T2, 2T3 , and 3T3 are presented (Fig. 2 and Tables 1–5) and discussed together with the derivatives 1T2 and 4T2 published previously. The piperidine ring adopts a chair conformation. In all structures, the aryl group is in the axial position, with the plane through the aryl C‐atoms nearly perpendicular to the mirror plane of the piperidine ring. The through‐bond interaction between the piperidine ring N‐atom (one‐electron donor) and the substituted exocyclic C?C bond (acceptor) not only elongates the central C? C bonds of the piperidine ring but also increases the pyrimidalization at C(4) of the piperidine ring. Flattening of the C(2)–C(6) part of the piperidine ring decreases the through‐bond interaction.     

Probes for Narcotic Receptor Mediated Phenomena

The synthesis of a series of epoxy 5‐phenylmorphans is being explored in order to determine the conformational requirements of the phenolic ring in a phenylmorphan molecule that may be needed both for binding to a specific opioid receptor and for exhibiting opioid agonist or antagonist activity. Of the twelve possible ortho‐ and para‐bridged isomers (a–f) (Fig. 1), we now report the synthesis of the para‐d isomer, rac‐(3R,6aS,11aR)‐2‐methyl‐1,3,4,5,6,11a‐hexahydro‐2H‐3,6a‐methanobenzofuro[2,3‐c]azocin‐8‐ol ( 3 ). Compound 3 was synthesized via construction of the 5‐phenylazabicyclo[3.3.1]non‐3‐ene skeleton (Scheme 1) and subsequent closure of the epoxy bridge (Scheme 2). As determined by an X‐ray diffraction study, the epoxy bridge, restricting the phenyl‐ring rotation, fixed the dihedral angle between the least‐squares planes through the phenyl ring and atoms N(2), C(3), C(11a), and C(6a) of the piperidine ring (Fig. 2) at 43.0°, and the torsion angle C(12)? C(6a)? C(6b)? C(10a) at ?95.0°.     

红移型Cu(II)离子比率荧光探针的光物理性质

应用密度泛函理论(DFT)及含时密度泛函理论(TDDFT)方法研究了N-丁基-4,5-二[2-(苯胺基)乙胺基]-l,8萘酰亚胺红移型铜离子比率荧光探针的光物理性质. 通过探针分子与金属离子结合前后的几何构型优化, 结合自然键轨道分析, 揭示了探针分子对铜离子的识别作用. 通过激发态计算阐明了光诱导分子内电荷转移(ICT)机理. 研究结果表明, 由于Cu(II)离子络合导致萘胺脱氢, 带负电荷的胺基N原子与萘环形成C＝N双键,延长了共轭体系; N的非键电子向Cu(II)离子的空d轨道转移一个电子, 抑制了Cu(II)离子的顺磁效应所导致的荧光淬灭, 受光激发后, 共轭N与萘环之间发生n→π^*电子转移导致ICT效应和荧光红移.     

Synthesis,spectroscopic studies,and preliminary antibacterial assays of a palladium(II) complex with 2-mercaptothiazoline

In this article, synthesis of a palladium(II) complex with 2-mercaptothiazoline in aqueous solution is presented. Composition of the complex was defined as 1?:?2 (metal?:?ligand). Infrared and solid-state nuclear magnetic resonance indicate ligand coordination to Pd(II) through nitrogen of thiazole ring and sulfur of thiol. ESI–QTOF–mass spectrometric analysis shows primarily the dimeric form in solution. An antibiogram assay of the complex was performed by the disc diffusion method. The compound did not show antibacterial activity against the considered bacterial cells in the tested concentrations.     

Organometallic ruthenium(II) diamine anticancer complexes: arene-nucleobase stacking and stereospecific hydrogen-bonding in guanine adducts

Organometallic ruthenium(II) arene anticancer complexes of the type [(eta(6)-arene)Ru(II)(en)Cl][PF(6)] (en = ethylenediamine) specifically target guanine bases of DNA oligomers and form monofunctional adducts (Morris, R., et al. J. Med. Chem. 2001). We have determined the structures of monofunctional adducts of the "piano-stool" complexes [(eta(6)-Bip)Ru(II)(en)Cl][PF(6)] (1, Bip = biphenyl), [(eta(6)-THA)Ru(II)(en)Cl][PF(6)] (2, THA = 5,8,9,10-tetrahydroanthracene), and [(eta(6)-DHA)Ru(II)(en)Cl][PF(6)] (3, DHA = 9,10-dihydroanthracene) with guanine derivatives, in the solid state by X-ray crystallography, and in solution using 2D [(1)H,(1)H] NOESY and [(1)H,(15)N] HSQC NMR methods. Strong pi-pi arene-nucleobase stacking is present in the crystal structures of [(eta(6)-C(14)H(14))Ru(en)(9EtG-N7)][PF(6)](2).(MeOH) (6) and [(eta(6)-C(14)H(12))Ru(en)(9EtG-N7)][PF(6)](2).2(MeOH) (7) (9EtG = 9-ethylguanine). The anthracene outer ring (C) stacks over the purine base at distances of 3.45 A for 6 and 3.31 A for 7, with dihedral angles of 3.3 degrees and 3.1 degrees, respectively. In the crystal structure of [(eta(6)-biphenyl)Ru(en)(9EtG-N7)][PF(6)](2).(MeOH) (4), there is intermolecular stacking between the pendant phenyl ring and the purine six-membered ring at a distance of 4.0 A (dihedral angle 4.5 degrees). This stacking stabilizes a cyclic tetramer structure in the unit cell. The guanosine (Guo) adduct [(eta(6)-biphenyl)Ru(en)(Guo-N7)][PF(6)](2).3.75(H(2)O) (5) exhibits intramolecular stacking of the pendant phenyl ring with the purine five-membered ring (3.8 A, 23.8 degrees) and intermolecular stacking of the purine six-membered ring with an adjacent pendant phenyl ring (4.2 A, 23.0 degrees). These occur alternately giving a columnar-type structure. A syn orientation of arene and purine is present in the crystal structures 5, 6, and 7, while the orientation is anti for 4. However, in solution, a syn orientation predominates for all the biphenyl adducts 4, 5, and the guanosine 5'-monophosphate (5'-GMP) adduct 8 [(eta(6)-biphenyl)Ru(II)(en)(5'-GMP-N7)], as revealed by NMR NOE studies. The predominance of the syn orientation both in the solid state and in solution can be attributed to hydrophobic interactions between the arene and purine rings. There are significant reorientations and conformational changes of the arene ligands in [(eta(6)-arene)Ru(II)(en)(G-N7)] complexes in the solid state, with respect to those of the parent chloro-complexes [(eta(6)-arene)Ru(II)(en)Cl](+). The arene ligands have flexibility through rotation around the arene-Ru pi-bonds, propeller twisting for Bip, and hinge-bending for THA and DHA. Thus propeller twisting of Bip decreases by ca. 10 degrees so as to maximize intra- or intermolecular stacking with the purine ring, and stacking of THA and DHA with the purine is optimized when their tricyclic ring systems are bent by ca. 30 degrees, which involves increased bending of THA and a flattening of DHA. This flexibility makes simultaneous arene-base stacking and N7-covalent binding compatible. Strong stereospecific intramolecular H-bonding between an en NH proton oriented away from the arene (en NH(d)) and the C6 carbonyl of G (G O6) is present in the crystal structures of 4, 5, 6, and 7 (average N...O distance 2.8 A, N-H...O angle 163 degrees ). NMR studies of the 5'-GMP adduct 8 provided evidence that en NH(d) protons are involved in strong H-bonding with the 5'-phosphate and O6 of 5'-GMP. The strong H-bonding from G O6 to en NH(d) protons partly accounts for the high preference for binding of [(eta(6)-arene)Ru(II)en](2+) to G versus A (adenine). These studies suggest that simultaneous covalent coordination, intercalation, and stereospecific H-bonding can be incorporated into Ru(II) arene complexes to optimize their DNA recognition behavior, and as potential drug design features.     

Electrophilic arene hydroxylation and phenol O-H oxidations performed by an unsymmetric μ-η(1):η(1)-O2-peroxo dicopper(II) complex

Reactions of the unsymmetric dicopper(II) peroxide complex [Cu(II)(2)(μ-η(1):η(1)-O(2))(m-XYL(N3N4))](2+) (1?O(2), where m-XYL is a heptadentate N-based ligand), with phenolates and phenols are described. Complex 1?O(2) reacts with p-X-PhONa (X = MeO, Cl, H, or Me) at -90?°C performing tyrosinase-like ortho-hydroxylation of the aromatic ring to afford the corresponding catechol products. Mechanistic studies demonstrate that reactions occur through initial reversible formation of metastable association complexes [Cu(II)(2)(μ-η(1):η(1)-O(2))(p-X-PhO)(m-XYL(N3N4))](+) (1?O(2)?X-PhO) that then undergo ortho-hydroxylation of the aromatic ring by the peroxide moiety. Complex 1?O(2) also reacts with 4-X-substituted phenols p-X-PhOH (X = MeO, Me, F, H, or Cl) and with 2,4-di-tert-butylphenol at -90?°C causing rapid decay of 1?O(2) and affording biphenol coupling products, which is indicative that reactions occur through formation of phenoxyl radicals that then undergo radical C-C coupling. Spectroscopic UV/Vis monitoring and kinetic analysis show that reactions take place through reversible formation of ground-state association complexes [Cu(II)(2)(μ-η(1):η(1)-O(2))(X-PhOH)(m-XYL(N3N4))](2+) (1?O(2)?X-PhOH) that then evolve through an irreversible rate-determining step. Mechanistic studies indicate that 1?O(2) reacts with phenols through initial phenol binding to the Cu(2)O(2) core, followed by a proton-coupled electron transfer (PCET) at the rate-determining step. Results disclosed in this work provide experimental evidence that the unsymmetric 1?O(2) complex can mediate electrophilic arene hydroxylation and PCET reactions commonly associated with electrophilic Cu(2)O(2) cores, and strongly suggest that the ability to form substrate?Cu(2)O(2) association complexes may provide paths to overcome the inherent reactivity of the O(2)-binding mode. This work provides experimental evidence that the presence of a H(+) completely determines the fate of the association complex [Cu(II)(2)(μ-η(1):η(1)-O(2))(X-PhO(H))(m-XYL(N3N4))](n+) between a PCET and an arene hydroxylation reaction, and may provide clues to help understand enzymatic reactions at dicopper sites.     

Accurate calculation of N1s and C1s core electron binding energies of substituted pyridines. Correlation with basicity and with Hammett substituent constants

Substituent shifts of the energetics of four related ionization processes of pyridines and benzoic acids (Fig. 1) were investigated. The first process is core-electron ionization of gas-phase pyridines (Fig. 1A), while the second concerns gas-phase acid-base reaction between a substituted pyridine and a conjugated acid (Fig. 1B), and the third and fourth processes are the acid dissociation of substituted benzoic acids in aqueous solution (Fig. 1C) and in vacuum (Fig. 1D), respectively. Core-electron binding energies for the first process were calculated using density-functional theory with the scheme ΔE_KS (PW86x-PW91c/TZP+C_rel)//HF/6-31G*. Average absolute deviation of calculated core electron binding energy shifts at N atom in substituted pyridines from experiment was 0.08 eV. The shift at N coincides highly with that at a ring carbon atom. The four shifts corresponding to the four processes shown in Figs. 1A–D correlate strongly with one another, with numerical values fairly close to each other when expressed in unit of electron volts.     

Binuclear Copper(II) Complexes in which other copper(II) complexes are coordinated as bidentate ligands

Twelve new copper(II) complexes in which N,N′-bis-(2-pyridylmethyl)-oxamidatocopper(II) or N,N′-bis(2-pyridylethyl)-oxamidatocopper(II) coordinates as a bidentate ligand have been isolated and characterized. These complexes have a structure bridged by the oxamide group (including two tetranuclear complexes formed by olation of two binuclear complexes, of. Fig. 1), and possess Cu? Cu interaction resulting in a sub-normal magnetic moment at room temperature. In one of them, [Cu₂(PMoxd) (bipy)₂] (NO₃)₂ (cf. Fig. 2), each copper(II) ion has a five-coordinated environment.     

The Cyclo‐β‐Tetrapeptide (β‐HPhe‐β‐HThr‐β‐HLys‐β‐HTrp): Synthesis,NMR Structure in Methanol Solution,and Affinity for Human Somatostatin Receptors

The known solid‐state structure (Fig. 1, top) of cyclo(β‐HAla)₄ was used to model the structure of the title compound 1 as a prospective somatostatin mimic (Fig. 1, bottom). The synthesis started with the N‐protected natural amino acids Boc‐Phe‐OH, Boc‐Trp‐OH, Boc‐Lys(2‐Cl‐Z)‐OH, and Boc‐Thr(OBn)‐OH, which were homologated to the corresponding β‐amino‐acid derivatives (Scheme 1) and coupled to the β‐tetrapeptide Boc‐β‐HTrp‐β‐HPhe‐β‐HThr(OBn)‐β‐HLys(2‐Cl‐Z)‐OMe ( 16 ); the (N‐Me)‐β‐HThr‐(N‐Me)‐β‐HPhe analog 17 was also prepared. C‐ and N‐terminal deprotection and cyclization through the pentafluorophenyl ester gave the insoluble β‐tetrapeptide with protected Thr and Lys side chains ( 18 ). Solubilization and debenzylation could only be effected in LiCl‐containing THF (ca. 10% yield; with ca. 55% recovery). HPLC Purification provided a sample of the title compound 1 , the structure of which, as determined by NMR‐spectroscopy (Fig. 2, left) was drastically different from the `theoretical' model (Fig. 1). There is a transannular H‐bond dividing the macrocyclic 16‐membered ring, thus forming a ten‐ and a twelve‐membered H‐bonded ring, the former mimicking, or actually being superimposable on, an α‐peptidic so‐called β‐turn. Still, the four side chains occupy equatorial positions on the ring, as planned, albeit with somewhat different geometry as compared to the `original'. The cyclo‐β‐tetrapeptide has micromolar affinities to the human somatostatin receptors (hsst 1 – 5). Thus, we have demonstrated for the first time that it is possible to mimic a natural peptide hormone with a small β‐peptide. Furthermore, we have discovered a simple way to construct the ubiquitous β‐turn motif with β‐peptides (which are known to be stable to mammalian peptidases).     

Platinum(II) and palladium(II) complexes with substituted pyrimidines

Summary Platinum(II) and Palladium(II) complexes with 2-mercaptopyrimidine, 2-thiocytosine (4-aminopyrimidine 2-thione), and isocytosine (2-amino-4-hydroxy pyrimidine) were prepared and characterised by elemental analysis, conductivity data, i.r.,¹H n.m.r. and¹³C n.M.r. spectral studies. 2-Mercaptopyrimidine and 2-thiocytosine are coordinated to the metal ion through N(3) and C₂S, thus forming a four-membered chelate ring. Isocytosine acts as a monodentate ligand and coordinates to the metal ion through N(1). All the complexes are non-electrolytes.     

New one-dimensional azido-bridged manganese(II) coordination polymers exhibiting alternating ferromagnetic-antiferromagnetic interactions: structural and magnetic studies

Five Mn(II)[bond]azido coordination polymers of formula [Mn(L)(N(3))(2)](n) have been synthesized and crystallographically characterized, and their magnetic properties studied, where L's are the bidentate Schiff bases obtained from the condensation of pyridine-2-carbaldehyde with aniline (1) and its derivatives p-toluidine (2), m-toluidine (3), p-chloroaniline (4), and m-chloroaniline (5). All the complexes consist of the zigzag Mn(II)[bond]azido chains in which the Mn(II) ions are alternately bridged by two end-to-end (EE) and two end-on (EO) azido ligands, the cis-octahedral coordination being completed by the two nitrogen atoms of the Schiff base ligands. Compound 2 is unique in that the Mn[bond](EE-N(3))(2)[bond]Mn ring adopts an unusual twist conformation with the two linear azido bridges crossing each other. By contrast, the rings in the other compounds take the usual chair conformation with the two azido bridges parallel. The double EO bridging fragments in the complexes are similar with the bridging angles (Mn[bond]N[bond]Mn) ranging from 99.6 degrees to 104.0 degrees. Magnetic analyses reveal that alternating ferro- and antiferromagnetic interactions are mediated through the alternating EO and EE azido bridges with the J(F) and J(AF) parameters in the ranges of 4.1-8.0 and -11.8 to -15.4 cm(-1), respectively. Finally, the magnetostructural correlations are investigated. The present complexes follow the general trend that the ferromagnetic interaction through the double EO bridge increases with the Mn[bond]N[bond]Mn bridging angle, while the antiferromagnetic interaction through the double EE bridge is dependent on the distortion of the Mn[bond](N(3))(2)[bond]Mn ring from planarity toward the chair conformation and the Mn[bond]N[bond]N angle.     

Potentiometric and spectrophotometric study of a new dipodal ligand N,N'-bis{2-[(2-hydroxybenzylidine)amino]ethyl}malonamide with Co(II), Ni(II), Cu(II) and Zn(II)

A new dipodal ligand, N,N'-bis{2-[(2-hydroxybenzylidine)amino]ethyl}malonamide (BHAEM) was synthesized by Schiff base condensation of N,N'-bis(2-aminoethyl)malonamide with two equivalent of salicylaldehyde and characterized on the basis of elemental analyses and various spectral (UV-vis, IR, (1)H NMR and (13)C NMR) data. The complexation reaction of the ligand with H(+), Co(II), Ni(II), Cu(II) and Zn(II) in solution was investigated by spectrophotometric and potentiometric method. Two protonation constants of BHAEM assigned for two hydroxyl groups of aromatic ring were determined and its hydrolysis mechanism was proposed through potentiometric result. In presence of metal ions, BHAEM shows different coordination properties. All metal ions form ML type complex where the ligand coordinates to the metal ion through two N-amine and two O-phenolate groups. In addition, Ni(II) and Cu(II) form additional complex species of the type MLH(-1) and MLH(-2), respectively due to ionization of amide protons. The molecular geometry of BHAEM was examined theoretically using the molecular mechanics MM3 force field followed by semi-empirical PM3 method and various spectral data UV-vis, IR and (1)H NMR were calculated from the energy-minimized structure applying semi-empirical ZINDO, PM3 and TNDO/2 method, respectively and compared with the experimental data. The probable structure of metal complexes in solution were proposed through calculated minimum strain energy by applying molecular mechanics MM(+) force field coupled with molecular dynamics simulation. Further the proposed structure of Cu(BHAEM) was refined through semi-empirical AM1/d method.     

Iron complexes of N-confused pyriporphyrin: NMR studies

Insertion of iron(II) into 6,11,16,21-tetraaryl-3-aza-m-benziporphyrin (N-confused pyriporphyrin, (PyPH)H) yielded the high-spin iron(II) complex, (PyPH)Fe(II)Br. The coordination of iron(II) to the perimeter nitrogen atom of (PyPH)Fe(II)Br resulted in the formation of the diiron species. Oxidation and oxygenation of (PyPH)Fe(II)Br were followed by 1H NMR spectroscopy. The addition of Br2 to the solution of (PyPH)Fe(II)Br in the absence of dioxygen results in a one-electron oxidation yielding the high-spin iron(III) N-confused pyriporphyrin [(PyPH)Fe(III)Br]+ which preserves the side-on interaction between the inverted pyridine ring and metal ion. The reaction of (PyPH)Fe(II)Br with dioxygen ends up with the formation of a five-coordinate species (PyPO)Fe(III)Br] ((PyPOH)H = 3-aza-22-hydroxy-m-benziporphyrin, PyPO = the corresponding dianion) which is formed by oxygenation at the C(22) position. Coordination of a metal ion by 3-aza-22-hydroxy-benziporphyrin imposes a steric constraint on the geometry of the ligand. The halide ligand of (PyPO)Fe(III)Br coordinates on one of the two inequivalent faces of the macrocycle, leading to two distinct species: syn and anti. The (1)H NMR spectra of paramagnetic iron(II) and iron(III) N-confused pyriporphyrin complexes have been examined. The characteristic patterns of pyrrole and pyridine resonances have been found to be diagnostic of the ground electronic state of iron and the donor nature of the C(22)H and N(3) centers. The enormous downfield H(22) paramagnetic shift, determined for the iron(II) N-confused pyriporphyrin, provides a distinct resonance in a peculiar spectroscopic window (350-800 ppm) for a series of axial ligands which can be considered as a diagnostic sign of an agostic Fe(II)...{C(22)-H} interaction. Coordination of the pyridine moiety via the perimeter N(3) atom is reflected unambiguously by the H(2/4) resonance at 201 ppm.     

SPECTROSCOPIC INVESTIGATION OF DIHYDRONICOTINAMIDES-I: CONFORMATION, ABSORPTION, AND FLUORESCENCE

Abstract— The 1(N)-(2,6-dichlorobenzyl)-1,4-dihydronicotinamide (I), N-methyl- and N,N-dimethyl-1(N)-(2,6-dichlorobenzyl)-1,4-dihydronicotinamide (II and III), respectively), and 1(N)-(2,6-dichloro-benzyl)-2-aminomethyl-1,4-dihydronicotinic acid lactame (IV) were synthesized as model compounds for natural coenzymes, and systematically studied by 1H NMR, UV/V1S absorption and fluorescence spectroscopy. The absorption at ∼ 340 nm argues for an effective conjugation between dihydropyridine and carboxamide π-system, and rules out any severely twisted conformation. For the natural coenzymes NADH and NMNH, as well as for I and II (with no or only one N-amide substituent), 1H NMR definitively establishes a transoid conformation in solution, with the carbonyl O close to 2-H of the dihydropyridine ring. N,N-dimethyl substitution effectively inverts the carboxamide orientation into the cisoid form. The 1H NMR data (as well as molar extinctions) for the fused-ring derivatives IV and V, with a fixed cisoid and transoid structure, respectively, provide final proof for the conformational assignment.
Absorption maxima are shifted to lower energies with increasing solvent polarity. In solvents which can act as hydrogen bond acceptors to the carboxamide N-H, absorption shows a general blue-shift of ∼ 10 nm. H-bond donor solvents do not affect absorption maxima but enhance molar extinction. Fluorescence maxima show a similar dependence on solvent polarity but no specific hydrogen-bonding effect. Fluorescence quantum yields appear increased tenfold in solvents donating H-bonds to the carboxamide C=O group. These results are interpreted in terms of the vinylogous amide resonance between C=O function and ring-N lone pair being the electronic interaction dominating in the ground state of dihydronicotinamides.     

Sorption of Co(II) onto chelating pyrocatechol violet–Amberlite XAD-16 resin

In this study, a chelating resin was synthesized by covalently linking pyrocatechol violet (PV) with the benzene ring of Amberlite XAD-16 through an azo (–N=N–) spacer group and the resulting resin was characterized by infrared (IR) spectra. It has been used for the sorption of Co(II) in aqueous solutions at batch system by flame atomic absorption spectrometry (FAAS). Co(II) ions were extracted quantitatively in acidic nitric media at pH 4.15–5.10. The sorption capacity of modified resin was 99.36 mg g^?1 of resin. The influences of pH of aqueous solutions, the amount of PV-XAD-16 resin, and the electrolyte salt concentration on the sorption of Co(II) ions were examined. The proposed separation-enrichment method was applied for the atomic absorption spectrometric determinations of Co(II) in river water with satisfactory results (recovery greater than 96.77%, relative standard deviation lower than 5%).