Imine Units Research Articles

Enhancing the Biocompatibility and Biodegradability of Linear Poly(ethylene imine) through Controlled Oxidation

(Bio)degradable poly(ethylene imine-co-glycine)s (P(EI-co-Gly)) were synthesized through efficient and controlled oxidation of linear poly(ethylene imine) (LPEI) using hydrogen peroxide in a methanol/water mixture. Temperature, peroxide concentration, and reaction time were varied to adjust the degree of oxidation (DO). At low temperatures, the oxidation process was found to be well-controlled with almost 85% of ethylene imine units converted to the corresponding amide. Importantly, oxidation of more than 10% of the LPEI rendered the polymers water-soluble. The oxidation reaction and molecular structure of P(EI-co-Gly)s were studied in detail by various nuclear magnetic resonance (NMR) methods, infrared (IR) spectroscopy, and size exclusion chromatography (SEC). The introduction of backbone amide groups to the P(EI-co-Gly)s facilitated its (bio)degradation under acidic conditions or by proteases. Moreover, the P(EI-co-Gly)s exhibited negligible cytotoxicity, particularly relative to LPEI. The interaction ...

In vitro study of partially hydrolyzed poly(2-ethyl-2-oxazolines) as materials for biomedical applications.

Polymers based on 2-oxazoline, such as poly(2-ethyl-2-oxazolines) (PETOx), are considered to be a type of 'pseudopeptide' with the ability to form novel biomaterials. The hydrolysis of PETOx was carried out to evaluate its use in biomedical applications. In the present work, PETOx samples with a range of molar masses were prepared by living cationic polymerization. Hydrolysis was carried out at time intervals ranging from 15 to 180 min to prepare copolymers with different amounts of ethylene imine units. (1)H NMR spectroscopy was used to identify the structure of the hydrolyzed polymers. The dependence of in vitro cell viability on the degree of hydrolysis was determined using three different model cell lines, namely, mouse embryonic 3T3 fibroblasts, pancreatic βTC3 cells, and mouse lymphoid macrophages P388.D1. It was demonstrated that increasing the degree of hydrolysis decreased cell viability for all cell types. Fibroblast cells displayed the highest tolerance; additionally, the effect of polymer size showed no observable significance. Macrophage cells, immune system representatives, displayed the highest sensitivity to contact with hydrolyzed PETOx. The effect of polymer hydrolysis, polymer concentration and the incubation time on cell viability was experimentally observed. Confocal laser-scanning microscopy provided evidence of cellular uptake of pyrene-labeled (co)polymers.

Effect of HAuCl4concentration on electrochemical DNA sensing behaviors of Au/nanoSPAN nanocomposite

Sensing properties of Au nanomaterials are greatly influenced by their morphology, size, and structure. Studying influencing factors to achieve controllable morphology, size and electrochemical properties is profoundly significant for further analytical applications. In this work, various Au micro-nanostructures were fabricated by varying the concentrations of HAuCl4 through a three-step electrodeposition method, in which self-doped polyaniline nanofibers (nanoSPAN) served as a supported matrix to obtain Au/nanoSPAN nanocomposite. The obtained electrodes were characterized by scanning electron microscopy, energy disperse X-ray spectroscopy and cyclic voltammetry (CV). The sulfonic acid groups and the imine units on the surface of nanoSPAN ensured the nucleation and growth of Au micro-nanostructures. Compared with other morphologies, the hierarchical and homogeneously dispersed flower-like Au microspheres (obtained in 5.0 mM HAuCl4 solution) showed high electrochemical activity in a 0.5 M H2SO4 solution and the largest electroactive areas. The next-step DNA sensing results based on various Au/nanoSPAN nanocomposites using methylene blue as electrochemical probe showed that controlling the concentrations of HAuCl4 can influence the amount of immobilized ssDNA and its sensitivity.

(Photo)physical Properties of New Molecular Glasses End-Capped with Thiophene Rings Composed of Diimide and Imine Units.

New symmetrical arylene bisimide derivatives formed by using electron-donating–electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N′-bis(5-aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5-thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69–0.90%.

A novel atom-economic synthesis of functionalized imidazolidines through copper(I)-catalyzed domino three-component coupling and cyclization reactions

An interesting approach to functionalized imidazolidines is described. These compounds are obtained in a copper(I)-catalyzed domino three-component coupling and cyclization reaction involving two formaldehyde-derived imine units and a terminal alkyne. Alternatively, imidazolidines can be obtained from propargylamines and formaldehyde-derived imines. This strategy provides a straightforward and atom-economic pathway to construct imidazolidines with high yields and benefits from readily available starting materials, convenient one-pot operations.

Linear Poly(ethylene imine)-Based Hydrogels for Effective Binding and Release of DNA

A series of copolymers containing both amine groups of linear poly(ethylene imine) (LPEI) and double bonds of poly(2-(3-butenyl)-2-oxazoline) (PButEnOx) was prepared. To this end, a poly(2-ethyl-2-oxazoline) (PEtOx) precursor was hydrolyzed to the respective LPEI and functionalized in an amidation reaction with butenyl groups resulting in the double bond containing poly(2-(3-butenyl-2-oxazoline)-co-ethylene imine) (P(ButEnOx-co-EI)). Hydrogels were obtained by cross-linking with dithiols under UV-irradiation resulting in networks with different properties in dependence of the content of double bonds. The developed method allows the exact control of the amount of ethylene imine units within the copolymer and, thus, within the resulting hydrogels. The gel structures were characterized by solid state NMR and infrared spectroscopy. In addition the water uptake behavior from the liquid and the gas phase was investigated. It was shown by an ethidium bromide assay (EBA) that the copolymers and the respective hydrogels were able to bind and release DNA. Furthermore, the influence of the ethylene imine content on this interaction was investigated.

A Tetracoordinated Phosphasalen Nickel(III) Complex

The oxidation of a Ni(II) complex bearing a tetradentate phosphasalen ligand, which differs from salen by the presence of an iminophosphorane (PN) in place of an imine unit, was easily achieved by addition of a silver salt. The site of this oxidation was investigated with a combination of techniques (NMR, EPR, UV/Vis spectroscopy, X-ray diffraction, magnetic measurements) as well as DFT calculations. All data are in agreement with a high-valent Ni(III) center concentrating the spin density. This markedly differs from precedents in the salen series for which oxidation on the metal was only observed at low temperature or in the presence of additional ligands or anions. Therefore, thanks to the good electron-donating properties of the phosphasalen ligand, [Ni(Psalen)](+) represents a rare example of a tetracoordinated high-valent nickel complex in presence of a phenoxide ligand.

A Tetracoordinated Phosphasalen Nickel(III) Complex

The oxidation of a NiII complex bearing a tetradentate phosphasalen ligand, which differs from salen by the presence of an iminophosphorane (PN) in place of an imine unit, was easily achieved by addition of a silver salt. The site of this oxidation was investigated with a combination of techniques (NMR, EPR, UV/Vis spectroscopy, X-ray diffraction, magnetic measurements) as well as DFT calculations. All data are in agreement with a high-valent NiIII center concentrating the spin density. This markedly differs from precedents in the salen series for which oxidation on the metal was only observed at low temperature or in the presence of additional ligands or anions. Therefore, thanks to the good electron-donating properties of the phosphasalen ligand, [Ni(Psalen)]+ represents a rare example of a tetracoordinated high-valent nickel complex in presence of a phenoxide ligand.

Synthesis and corrosion protection properties of poly(o-phenylenediamine) nanofibers

The present study shows a novel method for the synthesis of uniformly-shaped poly(othophenylediamine) (PoPD) nanofibers by chemical oxidative polymerization method for application towards smart corrosion resistance coatings. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) studies confirm morphology of PoPD with three dimensional (3D) networked dendritic superstructures having average diameter of 50–70nm and several hundred meters of length. UV–vis and FTIR spectral results shows the formation of PoPD nanofibers containing phenazine ring ladder-structure with benzenoid and quinoid imine units. Thermogravimetric analyses (TGA) of PoPD nanofibers possess good thermal stability. The anti-corrosion behavior of PoPD nanofibers on 316L SS was investigated in 3.5% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) measurements. The PoPD coated 316L SS exhibits higher corrosion potential when compared to uncoated specimen. EIS studies, clearly ascertain that PoPD nanofiber coatings exhibits excellent potential barrier to protect the 316L SS against corrosion in 3.5% NaCl.

New low band gap compounds comprised of naphthalene diimide and imine units

New arylene bisimide derivatives, both low molecular compounds and polymers consisting of a naphthalene diimide core and imine linkages were synthesized. The azomethine-diimides were prepared from N,N′-bis(4-amino-2,3,5,6-tetramethylphenyl)naphthalene-1,4,5,8-dicarboximide (DANDI) which was condensed with 4-pyridinecarboxaldehyde or 1,3-benzothiazole-2-carboxaldehyde or 2-thiophenecarboxaldehyde or 2,2′-bithiophene-5-carboxaldehyde. Poly(azomethine-naphthaleneimide)s were obtained by high temperature polycondensation of DANDI with 2,5-thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The materials do not show decomposition below 300°C. The azomethine-diimides exhibited glass-forming properties with glass transition temperatures in the range of 80–195°C. For the first time, to the best of our knowledge, amorphous molecular naphthalene diimide compounds were obtained. Optical properties of the prepared compounds were investigated by UV–vis and photoluminescence (PL) measurements. Most of the azomethine-diimides emitted green light with the highest intensity with emission maximum (λem) at ca. 519–535nm contrary to polymers which λem was at 450 and 485nm. All the compounds are electrochemically active and azomethine-diimides undergo quasi-reversible reduction and irreversible oxidation as evidenced by cyclic voltammetry (CV). In all studied molecules the electrochemically determined HOMO level is in the range of −5.5 to −5.13eV whereas the LUMO level is close to −4.0eV for azomethine-diimides and −3.8eV for polymers as determined by differential pulse voltammetry (DPV). The investigated compounds exhibited low electrochemical band gap (1.21–1.5eV) being promising for optoelectronic applications.

Synthesis, Reactivity Studies, Structural Aspects, and Solution Behavior of Half Sandwich Ruthenium(II)N,N′,N″-Triarylguanidinate Complexes

[(η(6)-C(10)H(14))RuCl(μ-Cl)](2) (η(6)-C(10)H(14) = η(6)-p-cymene) was subjected to a bridge-splitting reaction with N,N',N''-triarylguanidines, (ArNH)(2)C═NAr, in toluene at ambient temperature to afford [(η(6)-C(10)H(14))RuCl{κ(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (1), C(6)H(4)(OMe)-2 (2), C(6)H(4)Me-2 (3), and C(6)H(3)Me(2)-2,4 (4)) in high yield with a view aimed at understanding the influence of substituent(s) on the aryl rings of the guanidine upon the solid-state structure, solution behavior, and reactivity pattern of the products. Complexes 1-3 upon reaction with NaN(3) in ethanol at ambient temperature afforded [(η(6)-C(10)H(14))RuN(3){κ(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (5), C(6)H(4)(OMe)-2 (6), and C(6)H(4)Me-2 (7)) in high yield. [3 + 2] cycloaddition reaction of 5-7 with RO(O)C-C≡C-C(O)OR (R = Et (DEAD) and Me (DMAD)) (diethylacetylenedicarboxylate, DEAD; dimethylacetylenedicarboxylate, DMAD) in CH(2)Cl(2) at ambient temperature afforded [(η(6)-C(10)H(14))Ru{N(3)C(2)(C(O)OR)(2)}{κ(2)(N,N')((ArN)(2)C-N(H)Ar)}]·xH(2)O (x = 1, R = Et, Ar = C(6)H(4)Me-4 (8·H(2)O); x = 0, R = Me, Ar = C(6)H(4)(OMe)-2 (9), and C(6)H(4)Me-2 (10)) in moderate yield. The molecular structures of 1-6, 8·H(2)O, and 10 were determined by single crystal X-ray diffraction data. The ruthenium atom in the aforementioned complexes revealed pseudo octahedral "three legged piano stool" geometry. The guanidinate ligand in 2, 3, and 6 revealed syn-syn conformation and that in 4, and 10 revealed syn-anti conformation, and the conformational difference was rationalized on the basis of subtle differences in the stereochemistry of the coordinated nitrogen atoms caused by the aryl moiety in 3 and 4 or steric overload caused by the substituents around the ruthenium atom in 10. The bonding pattern of the CN(3) unit of the guanidinate ligand in the new complexes was explained by invoking n-π conjugation involving the interaction of the NHAr/N(coord)Ar lone pair with C═Nπ* orbital of the imine unit. Complexes 1, 2, 5, 6, 8·H(2)O, and 9 were shown to exist as a single isomer in solution as revealed by NMR data, and this was ascribed to a fast C-N(H)Ar bond rotation caused by a less bulky aryl moiety in these complexes. In contrast, 3 and 10 were shown to exist as a mixture of three and five isomers in about 1:1:1 and 1·0:1·2:2·7:3·5:6·9 ratios, respectively in solution as revealed by a VT (1)H NMR, (1)H-(1)H COSY in conjunction with DEPT-90 (13)C NMR data measured at 233 K in the case of 3. The multiple number of isomers in solution was ascribed to the restricted C-N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl substituent in 3 or the aforementioned restricted C-NH(o-tolyl) bond rotation as well as the restricted ruthenium-arene(centroid) bond rotation caused by the substituents around the ruthenium atom in 10.

Bio-functionalisation of polydimethylsiloxane with hyaluronic acid and hyaluronic acid – Collagen conjugate for neural interfacing

In this work, polydimethylsiloxane was activated with oxygen plasma and treated with silanes bearing ethylene imine units. Hyaluronic acid was then grafted covalently onto the aminated surfaces. The influence of silane structure on surface amination was assessed and the influence of the modification on surface physiochemical properties and protein adsorption of modified polydimethylsiloxane were investigated. Collagen type I was conjugated onto the modified polydimethylsiloxane to improve its cyto-compatibility for neural applications. In vitro cultivation of rat pheochromocytoma cells on the bioactive polydimethylsiloxane showed a significant increase in cell growth and differentiation. The potential applications of the bio-functionalized polydimethylsiloxane in cochlear implant electrode arrays were discussed.

Selective partial hydrolysis of amphiphilic copoly(2-oxazoline)s as basis for temperature and pH responsive micelles

The acidic and basic hydrolyses of gradient and diblock copolymers based on 2-methyl-2-oxazoline (MeOx) and 2-phenyl-2-oxazoline (PhOx) were investigated. Various reaction times were examined revealing polymers with varying ratios of PMeOx, PPhOx and poly(ethylene imine) (PEI). It could be shown that under acidic conditions, PMeOx as well as PPhOx are readily cleaved while under basic conditions PPhOx was almost not hydrolyzed leading to higher selectivity. However, partial degradation of the polymers occurred under basic conditions as evidenced by SEC. Thermal investigations of the polymers cleaved under acidic conditions revealed that most obtained copolymers exhibited a melting temperature due to the large PEI content. Self-assembly studies revealed that the partially hydrolyzed copolymers formed micelles at both ambient and elevated temperatures in acidic medium due to protonation of the ethylene imine units leading to good solubility. In contrast, the copolymers were insoluble at ambient temperature in water or basic medium, but self-assembled into spherical micelles at elevated temperatures as evidenced by transmission electron microscopy and dynamic light scattering. As such, these novel PEI–PPhOx copolymers exhibit thermoresponsive micellization behavior based on the crystallization induced phase separation of linear PEI at lower temperatures. Moreover, the copolymer consisting of 84 ethylene imine repeat units, 16 PPhOx groups also revealed pH responsive micellization due to increased solubility of the ethylene imine units upon protonation in acidic solution.

Reversible photochemical control of cholesteric liquid crystals with a diamine-based diarylethene chiroptical switch

Upon addition of a chiral dopant to a nematic liquid crystal, amplification of molecular chirality can occur and consequently a cholesteric liquid crystal is formed. A major challenge in materials science consists in designing efficient chiral dopants that allow for control over chiral amplification by use of an external trigger, for example by irradiation with light, and thereby achieving the control of the dynamic and responsive structure of cholesteric liquid crystals. Here, a chiral photochromic switch bearing two chiral imine units connected viaphenyl spacers was synthesized and characterized in solution, where it can be photo-chemically converted from a colourless ring-opened form 1o to a coloured ring-closed form 1c, reversibly. We show that a small amount of 1o used as a dopant induces the formation of a stable cholesteric liquid crystal. The retention of the photochromic properties of 1, when used as a chiral dopant, allows for reversible photocontrol over the period of the cholesteric helix, and shows the highest values of helical twisting power achieved so far with diarylethene-based photoswitchable dopants.

Multi-colored electrochromic polymer with enhanced optical contrast

A new π-conjugated monomer was synthesized which contains an electron-donating unit 3,4-ethylenedioxythiophene and electron withdrawing quinoxaline-based heterocycle to examine the effects of imine unit on the optoelectronic and redox properties of the resulting polymer. Electroactivity of monomer and electrochemical redox behavior of its polymer were investigated by cyclic voltammetry. An irreversible anodic wave at +0.85 V vs Ag wire reference electrode corresponding to the monomer oxidation was observed. Spectroelectrochemical analysis revealed that the neutral polymer has an absorbance at 820 nm. The band gap of the polymer was determined as 1.0 eV from the onset of the π–π∗ transition. The polymer shows multi-colored electrochromic behavior with five distinct states: brick red (−0.3 V), orange (+0.4 V), brown (+0.7 V), green (+0.85 V), gray (+1.2 V). The polymer revealed 34% optical contrast at 460 nm and an excellent optical contrast of 99% in the NIR region.

ChemInform Abstract: Synthesis of Mesomeric Betaines Containing a Pyrrolo- or Imidazotriaziniumolate System and Their Cycloaddition with Acetylenic Dipolarophiles Leading to Triazocinone Derivatives.

Abstract A series of 2-substituted mesomeric betaines containing a cyclic azomethine imine unit were synthesized and their cycloaddition with acetylenic dipolarophiles were examined. Unexpectedly the cycloaddition of the betaines with electron-deficient dipolarophiles gave ring-expanding adducts having a triazocinone structure. With electron-rich dipolarophiles such as ynamines, the reactions proceeded more readily leading regioselectively to the same type of triazocinones in almost quantitative yields. In particular in the case of an imidazobetaine and an ynamine the cycloaddition took place at room temperature to afford the initial cycloadducts exclusively and in excellent yields. The isolated tricyclic precursors were found to rearrange quantitatively to the final products on heating to 60°C.

Enantiodivergent Approach to Trifluoromethylated Amines: A Concise Route to Both Enantiomeric Analogues of Calcimimetic NPS R‐568

AbstractReported herein is a straightforward and enantiodivergent synthesis of both enantiomers of trifluoromethylated analogues of calcimimetic NPS R‐569 in a highly estereoselective manner. The synthesis features a diastereoselective synthesis of the N‐(isopropylsulfinyl)imine unit by the “DAG methodology” and a diastereoselective addition of Ruppert–Prakash's reagent to the imine as the key steps. No protecting groups were necessary, permitting an atom economic synthesis in only six steps. Further addition reactions of the CF3 anion to different N‐(isopropylsulfinyl)imines were performed to demonstrate the suitability of the sulfinyl substituent to balance perfectly reactivity and diastereoselectivity.

Weak intra- and intermolecular interactions in a binaphthol imine: an experimental charge-density study on (±)-8′-benzhydrylideneamino-1,1′-binaphthyl-2-ol

The charge density in (+/-)-8'-benzhydrylideneamino-1,1'-binaphthyl-2-ol (1) has been studied experimentally using Mo Kalpha X-ray diffraction at 100 K, and by theory using density-functional thoery (DFT) calculations at the B3LYP/6-311++G** level. The nature of the weak intramolecular peri-C...N, CH...pi, H...H and C(pi)...C(pi) interactions has been examined by topological analysis using the Quantum Theory of Atoms in Molecules (QTAIM) approach. An analysis of the density rho(r), the Laplacian of the density inverted Delta(2)rho(r(b)) and other topological properties at the bond-critical points were used to classify these interactions. The study confirms the presence of the intramolecular CH...pi interaction in (1), which was previously suspected on geometrical grounds. An analysis of the ellipticity profiles along the bond paths unambiguously shows the pi-delocalization between the imine unit and one N-phenyl group. The weak intermolecular interactions in the crystal of (1) were examined experimentally and theoretically through the pairwise interactions of the seven independent dimeric pairs of (1) responsible for the set of unique intermolecular interactions, and also through examination of the Hirshfeld surface d(norm) property. The theoretical dimeric-pair calculations used the BLYP-D functional which supplements the exchange-correlational functional with an empirical dispersion term to provide a more accurate determination of the energies for the weak intermolecular interactions.

Fluorescent chemosensor for Cu2+ ion based on iminoanthryl appended calix[4]arene

Calix[4]arene based podands 1a of cone conformation and 1b of 1,3-alternate conformation possessing imine units and bearing anthracene moieties have been synthesized by a 1 + 2 Schiff base condensation in good yields and examined for their cation recognition abilities towards cations such as lithium, sodium, potassium, nickel, cadmium, copper, zinc, lead, silver and mercury ions by UV–vis and fluorescence spectroscopy. The calix[4]arene derivative 1b shows a selective fluorescence enhancement in presence of Cu2+ ions among the various metal ions tested (Li+, Na+, K+, Ni2+, Cd2+, Cu2+, Zn2+, Pb2+, Ag+ and Hg2+ ions). The colour of the solution changes from colourless to light yellow in the presence of Cu2+ ions. The stoichiometry of the complex formed between 1b and Cu2+ was found to be 1:1 as established by Job’s plot.

Atmospheric condensed‐phase reactions of glyoxal with methylamine

Glyoxal reacts with methylamine in drying cloud droplet/aerosol surrogates to form high molecular mass oligomers along with smaller amounts of 1,3‐dimethylimidazole and light‐absorbing compounds. The patterns observed by high‐resolution time‐of‐flight aerosol mass spectrometry indicate that oligomers form from repeated imine units. The reactions are 1st order in each reactant: rate‐limiting imine formation is followed by rapid dimer and oligomer formation. While excess methylamine evaporates from the droplet, half the glyoxal does not, due to self‐oligomerization reactions that occur in the absence of methylamine. Glyoxal irreversibly traps volatile amine compounds in the aerosol phase, converting them into oligomers. This is the first reported mechanism for the formation of stable secondary organic aerosol (SOA) material from methylamine, a substance with only one carbon, and could produce as much as 11 Tg SOA yr−1 globally if glyoxal reacts exclusively by this pathway.