Primary Nitrogen Atoms Research Articles

Crystal and molecular structure of the “asymmetric” ethylenediamine-N,N-di-3-propionic acid monohydrate

A new complexing agent the “asymmetric” ethylenediamine-N,N-di-3-propionic acid (as.EDDP) is obtained. The crystal structure of the new compound is determined by single-crystal X-ray diffraction. C8H16N2O4·H2O crystals are monoclinic; space group P21/c, a = 12.7416(4) A, b = 6.5470(2) A, c = 12.1908(4) A, β = 93.100(1)°, Z = 4, ρ x = 1.454 mg/m3, and R 1 (I > 2.0σ(I)) = 0.0326. In the solid form, the as.EDDP molecule has a double betaine structure: The intramolecular hydrogen bonds with the betaine proton of the tertiary nitrogen atom are formed with the participation of one oxygen atom of the carboxyl group of each 3-propionic fragment, which forms two N(1)-H(1N)-bonded six-membered H-cycles. The intermolecular hydrogen bonds are formed between the three hydrogen atoms of the protonated primary nitrogen atom and the oxygen atoms of the 3-propionic fragments of three other as.EDDP molecules. The water molecule participates in the formation of intermolecular hydrogen bonds with the oxygen atom of one carboxyl group of the molecule.

4-Aminopyridine Catalyzed Direct and Regioselective Acylation of N-Tosylhydrazide

An efficient and simple method for selective acylation of either one of two nitrogen atoms of tosylhydrazide was developed. The selectivity was drastically controlled by a catalytic amount of 4-aminopyridine or 4-(dimethylamino)pyridine with common acylating agents. The nitrogen atom masked with a tosyl group was acylated in the presence of 4-aminopyridine, whereas the primary nitrogen atom was acylated in the absence of 4-aminopyridine.

Amino Acid Binding to Copper(II) in (1,4,7-Triazacyclononane) (L-histidine)copper(II) Hexafluorophosphate Monohydrate

The synthesis, characterization, and single-crystal X-ray structure determination of [Cu(tacn)(L-His)](PF6)2 . H2O (tacn = 1,4,7-triazacyclononane, L-His = L-histidine) are reported. Spectroscopic studies indicated the formation of the square pyramidal copper(II) complex [Cu(tacn)(L-His)]2+. This was confirmed through structure determination, which also revealed that the distorted square-pyramidal copper(II) coordination sphere is comprised of three nitrogen donors from the tacn macrocycle plus one carboxylate oxygen atom and the primary nitrogen atom from L-histidine. The L-histidine ligand is zwitterionic, with the negative charge on the carboxylate balanced by protonation at one nitrogen atom on the imidazole ring. It binds to the copper centre, forming a five-membered chelate ring, common in amino acid coordination.

STUDY OF THE PROTONATION/DEPROTONATION SEQUENCE OF TWO POLYAMINES: BIS-[(2S)-2-PYRROLIDINYLMETHYL] ETHYLENEDIAMINE AND SPERMIDINE BY 1H AND 13C NUCLEAR MAGNETIC RESONANCE

ABSTRACT In this paper we describe the study of protonation/deprotonation of two polyamines: bis-[(2S)-2-pyrrolidinylmethyl]ethylenediamine (tetra) and spermidine (Spd). A new synthetic route was established for the synthesis of tetra, which structure was confirmed by IR, elemental analyzes, 1H-NMR, 13C-NMR(Pendant) and 2D-NMR (COSY, 13C-1H HETCOR and HMQC) spectra. The protonation/deprotonation sequence studies of tetra and Spd were determined by potentiometric and NMR methods. For the NMR studies, the tetra and Spd samples were dissolved in D2O and the pD adusted with NaOD. The protonation/deprotonation sequences of tetra and Spd were determined by means of the values and the variations of the hydrogen atom and 13C NMR chemical shifts as a function of hydrogen atom pD. The variation of δ 1H with pD clearly showed that the first protonation of tetra occurs at the pyrrolidine nitrogen atoms and the second protonation occurs at the ethylenediamine nitrogen atom. The analysis of the 13C-NMR spectra confirmed the results obtained by 1H-NMR, as a greater chemical shift variation was observed for C-6 (5.6 ppm), as compared to C-8 (1.8 ppm). In the study with Spd, the greater chemical shift variation was observed for C-2 (6.75 ppm) and C-5 (4.95 ppm), indicating that the deprotonation occurs first at the secondary nitrogen atoms and the second and third deprotonation steps occur at the primary nitrogen atoms.

Carboxymethylation of Cage Amines: Control of Alkylation by Metal Ion Coordination

Reactions between chloroacetate and both "free" and coordinated forms of the cage amine diaminosarcophagine (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) result in the introduction of between one and four pendent carboxymethyl substituents on the nitrogen atoms of the cage. While at least the first two steps in the reaction of the free ligand have been found to involve only the secondary nitrogen centers, in both the Cu(II) and Co(III) complexes alkylation occurs only at the primary (1,8) centers, the greater ease of achieving a higher degree of alkylation of the Cu(II) complex being attributed to the lower charge of this species causing a lesser reduction of the nucleophilicity of the uncoordinated primary nitrogen atoms. All the new ligands have been characterized by X-ray structure determinations of their Cu(II) or Co(III) complexes. In some cases, this has shown that the methods used to isolate the crystalline complexes result in lactamization of the ligand.

Alkali Metal and Ammonium Dif'Luoromono(Isonicotinoylhydrazinato)Cuprate(II) Trihydrate

Alkali metal and ammonium difluoromono(isonicotinoylhydrazinato)cuprate(II) trihydrates, M[CuF2(pyinhH)].3H2O (where M. = Li, Na, K, Rb and NH4 pyinhH2 = isonicotinoylhydrazine), have been synthesized and characterized. The complexes have anomalously low μeff values suggesting weak Cu-Cu interaction. ESR evidence suggests that all complexes have weakly interacting electrons in the dx2-y2 orbital. IR data suggest bonding of mononegative isonicotinoylhdrazine through the enolate oxygen atom and primary nitrogen atom, and terminal and bridging fluoride groups. All complexes are suggested to have square-pyramidal stereochemistry.

Reactions at the N2Ni(μ2-SR)2NiN2 Core in Dinuclear Nickel(II) Amine-Thiolate Complexes

A discrete dinickel complex with a central N2NiII(μ2-SR)2NiIIN2 core has been synthesized and investigated in the context of ligand binding and oxidation state changes. Reaction of the hexadentate amine-thiolate ligand N,N′-bis-[2-thio-3-aminomethyl-5-tert-butylbenzyl]propane-1,3-diamine (8) with Ni(ClO4)2 · 6 H2O in methanol affords [NiII28][ClO4]2 · 3 CH3OH (9), the structure of which has been determined by X-ray crystallography. Complex 9 contains a central N2Ni(μ2-SR)2NiN2 core with two approximately planar cis-N2S2Ni coordination polyhedra bridged at the thiolate sulfur atoms. The cis-N2S2Ni units differ in that one nickel atom forms a six-membered chelate ring with the two secondary amine nitrogen atoms of 8 whereas the other nickel atom is bound to the remaining primary nitrogen atoms. Complex 9 binds a variety of substrates. Binding of anions to the N2Ni(μ2-SR)2NiN2 core in 9 occurs selectively at the Ni atom bound to the secondary nitrogen atoms because of a slightly weaker ligand-field strength. This is demonstrated by X-ray structure determination of the isothiocyanate complex [NiII28(NCS)2] · MeOH (10) formed by the reaction of 9 with 2 equiv. of KSCN in methanol. Complex 10 is the first example of a complex with adjacent octahedral cis-N4S2Ni and planar cis-N2S2Ni sites. The overall dinuclear structure of the parent complex 9 is retained in 10, except for trans-axially bound isothiocyanate ions at Ni(1) and an as yet unexplained inversion of configuration at both secondary amine nitrogen atoms. In DMF solution both complexes undergo two successive reductions at potentials of –0.95 V and –1.53 V vs SCE, assigned to the formation of mixed-valent [NiINiII8]1+ and [NiI28]0 species, respectively. The similar electrochemical properties of 9 and 10 suggest that the trans-axially bound isothiocyanate ions in 10 are replaced by DMF molecules in DMF solution. Upon reduction, these solvent molecules decoordinate to produce an unsolvated [NiINiII8]1+ species with two planar N2S2Ni units.

Variable geometry of nickel(II) complexes with N1-isopropyl-2-methyl-1,2-propanediamine(L). Crystal structures of [NiL2]Br2·3H2O, [NiL2Br]Br and [NiL2(NCS)2] and solid-state thermochromism in [NiL2]Br2·3H2O

The complexes NiL2X2·nH2O (L =N1-isopropyl-2-methylpropane-1,2-diamine; n= O, X = Cl, NCS or Br; n= 3, X = Br) have been prepared and the crystal structures of [NiL2]Br2·3H2O 2, [NiL2Br]Br 3 and [NiL2(NCS)2]4 determined. The metal co-ordination in complex 2 is square planar (N4 chromophore), whereas in 3 it is a distorted trigonal bipyramid with one of the bromine atoms and the two primary nitrogen atoms defining the basal plane, the secondary nitrogen atoms being in axial positions. Complex 4 is trans octahedral with a N6 chromophore. The geometry of NiL2Cl21 is proposed to be five-co-ordinate as in 3. Complex 2 on heating, undergoes an irreversible exothermic isomerisation after dehydration transforming into 3, a unique example of a change from square-planar to trigonal-bipyramidal nickel(II), accompanied by a yellow to green thermochromism in the solid state.

On the mechanism of protonation of triamines

The protonation behaviour of several triamines having the general formula H2N[CH2]mNH[CH2]nNH2 with m⩽n has been studied by 13C and 1H n.m.r. techniques. In all cases, in the first two protonation steps, only primary amino-groups are involved. The protonation of the secondary amino-group starts only after the protonation of the primary ones is complete.In the case of symmetrical triamines, in the first step, the proton is shared by the two primary nitrogens to an equal extent. Unsymmetrical triamines having m < 3 are initially protonated on the primary nitrogen atom attached to the longer aliphatic chain. However the unsymmetrical triamine spermidine, having m= 3 and n= 4. behaves like the symmetrical ones.

Determination of rate constants for the reaction of diglycidyl ether epoxy groups with aniline

1. A study has been made of the relative reactivities of the epoxy groups of the diglycidylic esters of resorcin, hydroquinone, pyrocatechol, and bisphenol A in reactions with the primary nitrogen atom of aniline in butanol solution. 2. In each of these esters, the second epoxy group reacts more rapidly with the aniline than the first. The rate constants for first epoxy group addition were essentially the same in the case of the resorcin, hydroquinone, and bisphenol A ethers. The corresponding rate constant for the pyrocatechol ether was considerably higher. 3. It is suggested that the kinetics of these reactions may be effected by the establishment of various types of hydrogen bonding in these systems.

Thermodynamic and electronic and electron spin resonance spectroscopic investigation of the co-ordinating properties of 4-azaoctane-1,8-diamine (spermidine) in aqueous solution

The reason for the exchange of copper(II)-containing proteins with spermidine (4NH-od), according to a non-immunogenic mechanism for retardation of tumour growth, has been explored from a thermodynamic standpoint. Of the two complexes found in aqueous solution at physiological pH, [Cu(H-4NH-od)]3+ and [Cu(4NH-od)]2+, only the latter has the possibility of exchange. Its relatively high stability constant arises from a favourable enthalpy contribution, due to the full co-ordination of the three nitrogen atoms in a tetragonally distorted octahedral structure. This complex contains one seven-membered chelate ring fused to another six-membered ring. In the protonated spermidine complex the primary nitrogen atom of the tetramethylene chain is protonated. The spectroscopic (electronic and e.s.r.) properties of these two complexes have been determined. The protonation behaviour of spermidine has been also studied thermodynamically and the successive enthalpy and entropy values are explained on the basis of a tautomeric process which exists in symmetrical triamines.

Eine neue Cyclolestersynthese zum Aufbau von Ergot-Peptidalkaloiden 82. Mitt. �ber Mutterkornalkaloide

Starting from acylated dipeptides of the general formula G the so-called cyclol esters D are stereospecifically formed in good yields after treatment with a base in polar aprotic solvents. These compounds D are key intermediates for the synthesis of ergot alkaloids of the peptide type. Extension of the scope of this reaction i.e. cyclisation of corresponding acylated dipeptides, the terminal proline being replaced by another amino acid bearing a primary nitrogen atom, could not be verified.