NH2 Function Research Articles

Parallel Chirality Inductions in Möbius Zn(II) Hexaphyrin Transformation Networks.

Networked chemical transformations are key features of biological systems, in which complex multicomponent interactions enable the emergence of sophisticated functions. Being interested in chirality induction phenomena with dynamic Möbius π-systems, we have designed a pair of Möbius [28]hexaphyrin ligands in order to investigate mixtures rather than isolated molecules. Thus, a hexaphyrin bearing a chiral amino arm was first optimized and found to bind a ZnOAc moiety, triggering an impressive quasi-quantitative chirality induction over the Möbius π-system. Second, this amino-type hexaphyrin was mixed with a second hexaphyrin bearing a chiral carboxylate arm, affording at first ill-defined coordination assemblies in the presence of zinc. In contrast, a social self-sorting behavior occurred upon the addition of two exogenous achiral effectors (AcO- and BuNH2), leading to a well-defined 1:1 mixture of two Möbius complexes featuring a sole Möbius twist configuration (parallel chirality inductions). We next successfully achieved compartmentalized switching, i.e., a single-component transformation from such a complex mixture. The BuNH2 effector was selectively protected with Boc2O, owing to a lower reactivity of the arm's NH2 function intramolecularly bound to zinc, and subsequent addition of BuNH2 restored the initial mixture, retaining parallel chirality inductions (five cycles). By changing the nature and twist configuration of only one of the two complexes, at initial state or by switching, this approach enables a "two-channel" tuning of the chiroptical properties of the ensemble. Such multiple dynamic chirality inductions, controlled by selective metal-ligand recognition and chemical reactivity, set down the basis for Möbius-type stereoselective transformation networks with new functions.

Recovery of vanadium with melamine in acidic medium

ABSTRACT Many hydro-metallurgical methods are developed to recover vanadium, while ammonium salt precipitation possesses the final step and it has threatened the environment. The key point is to find a new compound to replace ammonium salts without reducing vanadium recovery efficiency. Some compounds with –NH2 function groups have attracted our attention as they have similar function groups with ammonium salts. In this paper, the adsorption of vanadium with melamine is conducted. The results show that high adsorption efficiency can be achieved in a short time and melamine displays great performance in the recovery of all concentrations of vanadium. Response surface methodology (RSM) is used to optimize the reaction conditions and order the parameters: reaction temperature > concentration of vanadium > dosage of melamine > reaction time. 99.63% vanadium is adsorbed under optimized conditions: n(melamine)/n(V) = 0.6, reaction time of 60 min, 10 g/L vanadium solution and reaction temperature of 60°C. The successful application of melamine in the recovery of vanadium provides a new way for the utilization of melamine and also a glorious future for –NH2 compounds in the recovery heavy metals.

Studying the optical and thermal properties of Cs/ZnO and Cs/ZnO/GO hybrid nanocomposites

Green nanotechnology, defined as the synthesis or hybridization of nanomaterials with natural bioactive compounds, is a low-cost, eco-friendly, easy-to-manage and non-toxic technology. Nanocomposites have recently gained attention due to their unique characteristics and applications in the fabrication of microelectronic circuits, sensors, piezoelectric devices, optoelectronic components, fuel cells, corrosion surface passivation coatings, and catalysts. Accordingly, chitosan (Cs), a bioactive polymer, was hybridized with nanomaterials including ZnO and graphene oxide (GO) utilizing two easy, eco sustainable, and low-cost methods of preparation. All samples were analyzed using different analytical techniques. The FTIR and NMR results confirmed that the interaction between Cs, ZnO and GO occurs through the NH2 function group of Cs with ZnO and the O of the carboxyl group COOH of GO. Furthermore, the SEM data show the agglomeration generated by ZnO and GO on the Cs surface. According to the optical characterization of hybrid Cs/ZnO/GO, the one-pot preparation method achieves the lowest indirect and direct optical band gap values of 0.176 and 3.18 eV, respectively. Furthermore, it has a larger Eu = 5.46 eV value than the other samples, indicating a higher degree of disorder and high conductivity. Finally, the TGA results showed that hybridization of Cs with ZnO and Go improved the temperature decomposition and degradation of Cs by 79.9%. As a result, the one-pot approach for creating CS/ZnO/GO hybrid nanocomposite is effective for preparing Cs/ZnO/GO as an optoelectronic material.

A novel comparative study for electrochemical urea biosensor design: Effect of different ferrite nanoparticles (MFe2O4, M: Cu, Co, Ni, Zn) in urease immobilized composite system

A new enzymatic electrochemical biosensor has been developed with the PANI/Nafion composite system containing ferrite nanoparticles with four different transition metals. The ferrite nanoparticles containing copper, cobalt, nickel, and zinc metals were synthesized by the co-precipitation method and their surfaces were modified with tetraethoxysilane and (3-aminopropyl) triethoxysilane to obtain –NH2 function in order to develop the purposed sensing system. The modified and unmodified ferrite nanoparticles were characterized by physically, chemically, and morphologically. Ferrite nanoparticles with suitable for enzyme immobilization were integrated on the GCE surface and covered with PANI/Nafion. According toelectrochemical measurements, it was determined that copper ferrite nanoparticles, which have the lowest bandgap value, significantly increased the biosensor performance. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to monitor biosensor production and evaluate its performance. A detection limit of 0.17 µM and a wide linear range of 0.5–45.0 µM were obtained for the urea detection with the DPV method with the sensing system (Nf/PANI/CuF/Urs). The biosensor has been successfully applied to soil and milk samples with high accuracy. In addition, it has been determined that the proposed method has good reproducibility, selectivity, and stability.

Nano-Ni-MOFs: High Active Catalysts on the Cascade Hydrogenation of Quinolines

The reduction of nitrogen-containing heterocyclic compounds in aqueous medium under mild condition is quite challenging. In view of metal–organic frameworks (MOFs) possess adjustable pore size and modifiable organic linkers, MOFs could be used in heterogeneous catalysis. Herein, Three Nano-Ni-MOFs, MOF-74-Ni, MOF-69-Ni, and Ni–NH2 (constructed from similar ligands and Ni2+ ions) are introduced for hydrogenating of azacyclo-compounds. As expected, Ni–NH2 shows outstanding activity of hydrogenation of quinoline under mild conditions, due to the moderate pore size and the modified –NH2 function group, which makes the substrate anchored on the surface of the framework facilitate the following catalysis process. Theoretical calculations identified that the –NH2 group at the catalyst facilitates the H2 heterolytic dissociation for the hydrogenation reactions. Compared to MOF-74-Ni and MOF-69-Ni, the catalyst of Ni–NH2 shows outstanding activity of hydrogenation of quinoline, due to the modified –NH2 function group which makes the substrate anchored on the surface of the framework facilitate the following catalysis process

ChemInform Abstract: Two‐Step Regioselective Synthesis of 3‐(Sulfonylamino)imidazo[1,2‐a]pyrimidines from 2‐Aminopyrimidines and N‐(2,2‐Dichloro‐2‐phenylethylidene)arensulfonamides.

AbstractReaction of various 2‐aminopyrimidines with imines (II) leads to addition of the ‐NH2 function to the azomethine group.

Hydrogen Bond Optimization via Molecular Design for the Fabrication of Crystalline Organometallic Wheel-and-Axle Compounds Based on Half-Sandwich Ru(II) Units

A new series of half-sandwich ruthenium(II) complexes containing p-aminobenzoic acids (4-aminobenzoic acid and 4-aminocynnamic acid) and different arene ligands (benzene, p-cymene, and indane) have been synthesized and fully characterized giving particular attention to the analysis of the generated crystalline supramolecular architectures. A careful design of the molecular building blocks allows a perfect match to be reached between hydrogen bond donors and acceptors thus leading to the construction of crystalline wheel-and-axle metal–organic (WAAMO) systems, where the wheels are the half-sandwich units [(arene)RuCl2] and the axles are based on the cyclic dimerization of the COOH functions of the aminobenzoic ligands. The R22(8) cyclic pattern is however conserved only in absence of hydrogen bond donor crystallization solvents, which, when present, tend to insert between the COOH group and a Cl–Ru moiety with formation of hydrates or solvates. Far more robust is the supramolecular synthon based on the coupling involving the Ru–NH2 function as donor and the RuCl2 group as acceptor, which has been found in five out of seven X-ray structures reported in this work. The porosity of the WAAMOs can be modulated acting on the steric requirements of the arene ligand and on the length of the covalent segment of the central supramolecular axle.

Ribozymomimetic Chemical Synthesis of Peptide Bond Using Phosphorous Acid/Oxirane Mediators

A model system is created that mimics natural ribosome as well as the way of ribozyme action. It uses oxirane analogue as condensation reagent and H3PO3 as activator for the carboxyl group and as protecting reagent for the NH2 function. In order to demonstrate the ability of the H3PO3/oxirane system to mimic natural peptide bond synthesis on the ribosome as well as to mimic the ribozyme synthesis and hydrolysis of an inter biomonomeric bond, four model compounds containing an amide bond were synthesized using phosphorous acid/oxirane mediators.GRAPHICAL ABSTRACT

Interaction of microcrystalline chitosan with Ni(II) and Mn(II) ions in aqueous solution

AbstractThe protonation constant of the NH2 function was determined by the method of Katchalsky and Spitnik and by the SUPERQUAD fitting procedure. Samples with higher concentrations of chitosan indicated aggregations of polymer chains, which led to a loss in the effective concentration of the ligand (L). It followed, as a result of potentiometric titrations, that an excess of L of microcrystalline chitosan (MCCh) with a deacetylation degree of 0.90 was a complexing agent toward the metal (M), which was Ni(II) or Mn(II). Species ML and ML2 were accepted by SUPERQUAD for both of the M's, where coordination occurred via the amino nitrogen. For Ni(II), however, the hydroxyl oxygen may also have been an electron‐pair donor at lower excesses of MCCh and, by that, made possible the formation of five‐membered chelate rings in the hydroxyl deprotonated MLH‐1 species. The evaluated formation constants were compared with the values known until now for monomeric D‐glucosamine. Additional confirmation of the M–L interaction was determined by the spectrophotometric titration of a Ni(II)–MCCh solution. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2572–2577, 2005

Relationship between the structure of guanidines and N‐hydroxyguanidines, their binding to inducible nitric oxide synthase (iNOS) and their iNOS‐catalysed oxidation to NO

The binding of several alkyl- and aryl-guanidines and N-hydroxyguanidines to the oxygenase domain of inducible NO-synthase (iNOS(oxy)) was studied by UV/Vis difference spectroscopy. In a very general manner, monosubstituted guanidines exhibited affinities for iNOS(oxy) that were very close to those of the corresponding N-hydroxyguanidines. The highest affinities were observed for the natural substrates, L-arginine and N(omega)-hydroxy-L-arginine (K(d) at the microm level). The deletion of either the CO2H or the NH2 function of their amino acid moiety led to dramatic decreases in the affinity. However, alkylguanidines with a relatively small alkyl chain exhibited interesting affinities, the best being observed for a butyl chain (K(d) =20 microM). Arylguanidines also bound to iNOS(oxy), however, with lower affinities (K(d) > 250 microm). Many N-alkyl- and N-aryl-N'-hydroxyguanidines are oxidized by iNOS with formation of NO, whereas only few alkylguanidines led to significant production of NO under identical conditions, and all the arylguanidines tested to date were unable to lead to the production of NO. The k(cat) values of NO production from the oxidation by iNOS of the studied N-hydroxyguanidines were found to vary independently of their affinity for the protein. The k(cat) values determined for the two-step oxidation of alkylguanidines to NO were not clearly related to the K(d) of these substrates toward iNOS(oxy). However, there is a qualitative relationship between these k(cat) values and the apparent rate constants of dissociation of the complex between iNOS(oxy) and the corresponding N-alkyl-N'-hydroxyguanidine (k(off) (app)) that were determined by stopped-flow UV/Vis spectroscopy. These data indicate that a key factor for efficient oxidation of a guanidine by iNOS to NO is the ability of the corresponding N-hydroxyguanidine to bind to the active site without being too rapidly released before its further oxidation. This explains why 4,4,4-trifluorobutylguanidine is so far the best non-alpha-amino acid guanidine substrate of iNOS with formation of NO, because the k(off) (app) of the corresponding N-hydroxyguanidine is particularly low. This suggests that the rational design of guanidines as new NO donors upon in situ oxidation by NOSs should take into account both thermodynamic and kinetic characteristics of the interaction of the protein not only with the guanidine but also with the corresponding N-hydroxyguanidine.

Hydration mechanism of polysaccharides: A comparative study

AbstractWater sorption was studied at 20 °C on films composed of different natural polymers. Three polysaccharides were investigated: chitosan, cellulose, and alginate. The major differences between these polymers, from a structural point of view, lay in the substitution of an OH group by an NH2 function for chitosan and by an ionic COO−Na+ group for alginate. An analysis of the experimental water sorption isotherms, expressed as the number of water molecules sorbed per repeating unit in the amorphous phase, associated with an analysis of the enthalpy profile related to the water sorption allowed us to propose a water sorption mechanism in two steps for all the polymers: water sorption on polymer‐specific sites in the first step and water clustering around the first sorbed water molecules in the second step. It was determined that two water molecules interacted with the polymer chains for cellulose and chitosan, whereas four water molecules were bonded to alginate chains. The specific sorption sites were identified as OH groups for cellulose, OH and NH2 groups for chitosan, and ionic and OH groups for alginate. A systematic reduction of the half‐sorption time was observed in the activity range corresponding to this first sorption step, and it was explained by a water plasticization effect. On the other hand, an increase in the half‐sorption time was observed in the second sorption step, at a high activity (>0.8), for chitosan and alginate. A modelization associating the Guggenheim–Anderson–de Boer model and the clustering theory, applied to our systems, allowed us to relate the occurrence of this last phenomenon to the formation of water clusters containing more than two water molecules. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 48–58, 2005

Amide from dinitrogen by in situ cleavage and partial hydrogenation promoted by a transient zero-valent thorium synthon.

Amide from dinitrogen by in situ cleavage and partial hydrogenation promoted by a transient zero-valent thorium synthon.

The substrate binding site of human liver cytochrome P450 2C9: an NMR study.

Purified recombinant human liver cytochrome P450 2C9 was produced, from expression of the corresponding cDNA in yeast, in quantities large enough for UV-visible and 1H NMR experiments. Its interaction with several substrates (tienilic acid and two derivatives, lauric acid and diclofenac) and with a specific inhibitor, sulfaphenazole, was studied by UV-visible and 1H NMR spectroscopy. At 27 degrees C, all those substrates led to an almost complete conversion of CYP 2C9 to high-spin (S = 5/2) CYP 2C9-substrate complexes characterized by a Soret peak at 390 nm; their KD values varied between 1 and 42 microM. On the contrary, sulfaphenazole led to a low-spin (S = 1/2) CYP 2C9 complex upon binding of its NH2 group to CYP 2C9 iron. Interactions of the five substrates with the enzyme were studied by paramagnetic relaxation effects of CYP 2C9-iron(III) on the 1H NMR spectrum of each substrate. Distances between the heme iron atom and substrate protons were calculated from the NMR data, and the orientation of the substrate relative to iron was determined from those distances. Finally, a model for substrate positioning in the CYP 2C9 active site was constructed by molecular modeling studies under the constraint of the iron-proton distances. It points out two structural characteristics for a compound to be selectively recognized by CYP 2C9: (i) the presence of an anionic site able to establish an ionic bond with a putative cationic residue of the protein and (ii) the presence of an hydrophobic zone between the substrate hydroxylation site and the anionic site. Sulfaphenazole was easily included in that model; its very high affinity for CYP 2C9 is due to a third structural feature, the presence of its NH2 function which binds to CYP 2C9 iron.

Nucleosides. Part LV. Efficient synthesis of arabinoguanosine building blocks

AbstractFrom guanosine (1) as starting molecule, protected arabinoguanosine derivatives such as phosphoramidite precursors and arabinoguanosine (18) itself were prepared in high yields. Inversion of the configuration at C(2′) was achieved by introduction of the (trifluoromethyl)sulfonyl residue and subsequent displacement by nucleophiles like acetate, bromide, and azide. The guanine moiety was protected at the amide function by the 2‐(4‐nitrophenyl)ethyl (npe) group on O6 and at the NH2 function by the 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) group.

Structural requirements for inhibitors of poly(ADP-ribose) Polymerase

The purpose of this study was to examine the structure/activity relationships of a series of substituted benzamides as poly(ADP-ribose) polymerase inhibitors. The experimental approach has involved the use of in vitro and in vivo assays in order to gather information either on the intrinsic activity of the benzamides or on the effect of various pharmacodynamic parameters on the activity in vivo. Although some discrepancies between the data obtained in vivo and in vitro were found in this study, results seem to indicate that most powerful inhibitors were characterized by acylation of the -NH2 function in the 3 position or by substitution in this same position with hydroxy or methoxy groups. The best inhibitors were not cytotoxic under these experimental conditions. Computed calculations of molecular electrostatic potential of these molecules were also performed and a good correlation was found between the similarity index and the experimental inhibitory activity.

Benzamidoximes: configuration, conformation, and reactivity. Molecular orbital calculations

MO-SCF-FORCE calculations on benzamidoxime confirm the amino-oxime tautomer as being the more stable and explain the anomalous chemical behaviour of the NH2 function.