Diamine Molecules Research Articles

Asymmmetric Diamino Functionalization of Nanotubes Assisted by BOC Protection and Their Epoxy Nanocomposites

AbstractHomogenous dispersion and strong interfacial bonding are prerequisites for taking full advantage of the mechanical properties of nanotubes in a composite. In order to simultaneously achieve both conditions, a highly efficient and mechanically non‐destructive functionalization of nanotubes is developed. With fluoronanotubes as the precursor, asymmetric diamine molecules, N‐BOC‐1,6‐diaminohexane, are used to replace fluorines on the wall of fluoronanotubes and construct covalent bonding to the surface of the nanotubes. A BOC de‐protection reaction is conducted and the resulting exposed amino groups create strong covalent bonds with the matrix in the course of epoxy ring‐opening etherification and curing chemical reactions. In comparison with the conventional functionalization based on symmetric diamine molecules, the functionalized nanotubes derived from the BOC‐protected diamine molecule are more dispersed within the epoxy matrix. Dynamic mechanical analysis shows that the functionalized nanotubes have better crosslinking with the matrix. The composites reinforced by the nanotubes demonstrate improvement in various mechanical properties. The Young’s Modulus, ultimate tensile strength, and storage modulus of composites loaded with 0.5 wt% functionalized nanotubes are enhanced by 30%, 25%, and 10%, respectively, compared with the neat epoxy. The increase of the glass transition temperature, as much as 10 °C, makes the composites suited for engineering applications under higher temperatures. The new functionalization method allows for an competitive enhancement in the composite performance in use of relatively low cost raw nanotubes at a small loading level. The reinforcement mechanism of the functionalized nanotubes in the epoxy resin is discussed.

P-Phenylenediamine and its dihydrate: two-dimensional isomorphism and mechanism of the dehydration process, and N—H...N and N—H...π interactions

p-Phenylenediamine can be obtained as the dihydrate, C(6)H(8)N(2) x 2 H(2)O, (I), and in its anhydrous form, C(6)H(8)N(2), (II). The asymmetric unit of (I) contains one half of the p-phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p-phenylenediamine molecules are arranged in layers stabilized by N-H...pi interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in-plane rotation of every fourth p-phenylenediamine molecule by ca 60 degrees. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.

Change in neuron aggregation and neurite fasciculation on EVAL membranes modified with different diamines

In this study, we modified poly(ethylene-co-vinyl alcohol) (EVAL) membranes by the covalent bonding of diamines via epoxidation of surface hydroxyl groups of EVAL to analyze the effect of immobilized diamines with different carbon chain length on the cultured cerebellar granule neurons. Morphological studies showed that neurons seeded on the diamine-immobilized EVAL membrane were able to survive and regenerate with formation of an extensive neuritic network. Furthermore, cultured neurons showed that the presence of diamine with different carbon chain length was able to effectively regulate the neuron adhesion, migration, aggregation, and neurite growth pattern, but mediated neuronal activity with equal efficacy. The short-chain amine stimulated neuron migration, aggregation, and neurite fasciculation, whereas the long carbon chain diamine maintained single neuron distribution with the defasciculated feature of the neurite. Although it is known that positively charged amine molecules can interact directly with cell surface proteoglycans to mediate cell attachment, this study further demonstrated that the terminal primary amine with different carbon chain length is involved in mediating cell-substrate interaction to further regulate neuron aggregation and neurite fasciculation. This indicates a delicate interaction of neuron with the immobilized diamine molecules on the EVAL membrane surface. This work is encouraging because the diamine- immobilized EVAL membranes can be applied for the establishment of different neural culture systems useful for future investigations of neuron biology under in vitro conditions.

Features of the synthesis of 1,1′-Phenylenebis(1H-tetrazoles) and their transformations in basic environment

Reactions of substituted 1,3- and 1,4-phenylenediamines with sodium azide and triethyl orthoformate in the presence of acetic acid led to the formation in high yields of the corresponding 1,12 -phenylenebis(1Htetrazoles). The presence of electron-acceptor groups in the molecules of the initial diamines reduces the yield of the target heterocycles. With 2-nitro-1,4-phenylenediamine the prevailing product was 2-nitro-4-(1H-tetrazol-1-yl)aniline. The obtained bistetrazoles in basic environment suffer an opening of one or both heterocycles forming cyanamides.

Supramolecular templates for the synthesis of new nanostructured uranyl compounds: Crystal structure of [NH3(CH2)9NH3][(UO2)(SeO4)(SeO2OH)](NO3)

Crystals of a new uranyl selenate, [NH3(CH2)9NH3][(UO2)(SeO4)(SeO2OH)](NO3) (1), were prepared by isothermal evaporation from aqueous solution at room temperature. The crystal structure was solved by the direct method $$ P\bar 1 $$ , a = 10.7480(7), b = 13.8847(9), c = 14.6363(10) A, α = 109.9600(10)°, β = 103.212(2)°, γ = 90.4090(10)°, V = 1990.0(2) A3, Z= 4) and refined to R 1 = 0.0379 (wR 2 = 0.0636) for 8515 reflections with ¦Fo¦ ≥ 4σF. The structure is based on [(UO2)(SeO4)(SeO2OH)]-layers parallel to the (001) plane. In the structure of 1, there are two crystallographically independent 1,9-diammoniononane cations forming micelles in which the hydrocarbon chains are packed crosswise. The micelles are cylinders with an elliptical cross section and a rough surface. They are organized by the principle of hydrophilic and hydrophobic interactions. The cylinders are separated from each other by layers of triangular NO 3 − groups. Compound 1 is an example of organic-inorganic composites with a unidimensional organic substructure in which the protonated chain-like diamine molecules arranged crosswise form cylindrical supramolecular templates.

Photoconductivity in aligned CdSe nanorod arrays

The voltage dependence of the phototransport in colloidal CdSe nanorods (NRs) arrays was studied for different capping molecules and degree of NR alignment. The photocurrent was found to considerably enhance by exchanging the trioctylphosphine capping ligands by diamine molecules or upon annealing. The corresponding current-voltage characteristics were highly nonlinear, showing, in the aligned NR arrays, a notable decrease in the differential conductivity at a certain capping-molecule-dependent applied electrical field. This transition smears, however, when the degree of NR alignment is reduced. These findings are well described by an exciton field-ionization model, which also accounts for the correlation we observe between the photocurrent $I(V)$ curves and the voltage dependence of the fluorescence quenching in seeded-grown CdSe/CdS core/shell NR films.

Synergistic stabilization of emulsions by poly(oxypropylene)diamine and Laponite particles

Liquid paraffin–water emulsions were prepared which were stabilized by Laponite particles in situ modified with poly(oxypropylene)diamines in the absence of electrolytes. First, the characteristics of the Laponite dispersions in the presence of increasing concentrations of diamines were studied in detail. Infrared absorption spectra and zeta potential measurements confirm the adsorption of diamines on the Laponite particles. Adsorption isotherms further indicate highly affinitive L-type behaviors and the diamine molecules are deduced to lie with both end groups anchored on the particle surface and the poly(oxypropylene) chain exposed to the aqueous solution. Then, emulsions were prepared using the diamine-modified particles. Diamines and Laponite particles alone are ineffective emulsifiers, but a strong synergism is exhibited between them. Laser-induced fluorescent confocal micrographs and TEM observations demonstrate the arrangement of the particles on the emulsion surfaces and also reveal the stability mechanisms. The emulsion stability was also explored with optical microscopy and droplet size measurements. As the diamine concentration increases, the extent of emulsion creaming decreases and the droplet size correspondingly decreases. At a certain low diamine concentration, the extent of emulsion creaming decreases down to a minimum and the corresponding droplet size is the smallest. This optimal emulsion state is unchanged when the diamine concentration is further increased.

Synthesis and characterisation of lamellar ZnS nanosheets containing intercalated diamines

A solvothermal method has been used to prepare hybrid inorganic–organic composites with a lamellar structure in which layers of wurtzite ZnS are separated by intercalated diamine molecules. A hybrid composite prepared with diethylenetriamine has been isolated and characterised and its structure and properties compared with those of the composite prepared using ethylenediamine. Comparative structural and morphological studies of the two lamellar hybrid composites are described on the basis of powder XRD, electron and scanning probe microscopies and thermal analysis of the materials.

Highly Transparent and Refractive Polyimides with Controlled Molecular Structure by Chlorine Side Groups

Transparent polyimides (PIs) that have a high refractive index and low birefringence as well as good thermal and mechanical stability were synthesized by the judicious introduction of di- and tetrachlorinated aromatic diamines with aromatic/aliphatic dianhydrides. All the PI films, except for the PI derived from aromatic dianhydride and dichlorinated diamine (BPDA/2DCDB and BPDA/3DCDB), exhibited high optical transparency over the entire visible region. In particular, tetrachlorinated, fully aromatic polyimide (BPDA/TCDB) with a highly distorted conformation of the main chain exhibited excellent optical transparency in the visible range that was comparable to highly fluorinated aromatic PIs. This was attributed to the effective suppression of intra- and intermolecular charge transfer (CT) interactions by steric hindrance between the five-membered imide rings and chlorine atoms attached directly to the adjacent benzene rings as well as between chlorine atoms in the diamine molecules. A high transmittance o...

Amplifying the molecular sieving capability of polyimide membranes via coupling of diamine networking and molecular architecture

The integration of molecular design with diamine modification generates synergistic effects for enhancing and fine tuning the molecular sieving potential of polyimide membranes. Polymer free volume and rigidity represent crucial conformational parameters that influence the effectiveness of diamine modification for elevating the H2/CO2 permselectivity of polyimide membranes. Experimental and molecular dynamics simulation results suggest that polyimides with higher intrinsic free volume and rigidity are ideal for diamine treatment, yielding greater increment in H2/CO2 selectivity. A series of copoly(4,4′-diphenyleneoxide/1,5-naphthalene-2,2′-bis(3,4-dicarboxylphenyl) hexafluoropropane diimide) (6FDA-ODA/NDA) membranes are modified with 1,3-diaminopropane (PDA). Polyimides with higher free volume intensify the methanol swelling effect which facilitates the transport and subsequent reaction of the diamine molecules. Gel content analyses of the PDA-modified films prove that the penetration depth of the diamine molecules and the extent of crosslinking are higher for polyimides with greater NDA content. 6FDA-NDA has the highest free volume and rigidity, thus exhibiting impressive improvement in ideal H2/CO2 selectivity from 1.8 to 120 after PDA modification. Conversely, 6FDA-ODA which is deficient in terms of free volume and rigidity, demonstrates a much lower increment in H2/CO2 selectivity from 2.5 to 8.2. The inherent heterogeneity of the PDA-modified polyimide films results in thickness-dependent gas permeability and selectivity. The potential of merging macromolecular tailoring with diamine networking to enhance the H2/CO2 separation performance of polyimide membranes is evident.

Theoretical studies on proton affinities of H 2N–(CH 2) n–NH 2 ( n = 2−10) diamines at gas phase. Good correlation with protonation constants in solution

A theoretical study on complete protonation of a series of diamine molecules with general formula H 2N–(CH 2) n –NH 2 ( n = 2−10, L2−L10) has been reported. The gas-phase protonation energies were computed using density functional theory (DFT) calculations. The standard 6-31G ∗ and 6-311++G ∗∗ basis sets were used in all calculations. Three species, L, HL + and H 2L 2+ can be considered in protonation steps of diamine molecules. Among these, the HL + is involved in both the first, L + H + → HL +, and second, HL + + H + → H 2L 2+, steps. Two different structures were considered for latter species: (I) a linear-like structure (II) a cyclic structure due to intramolecular hydrogen bonding. The trends for variations of calculated PA 1 in the series of these molecules, is very similar to that of their measured protonation constants when we consider the linear structure for all species. Furthermore, for latter structures there are good correlations between the calculated proton macroaffinities in the gas-phase with corresponding protonation constants in solution. The latter observation has led us to predict the stepwise protonation constants for L7 and L9.

Interactions of a Cationic Mercury(II) Thiolate Complex [Hg(Tab)2](PF6)2 with N-Donor Ligands

Reactions of [Hg(Tab)(2)](PF(6))(2) (1) with phen, 2,2'-bipy, py, N-Meim, N-(i)Prim, en, eten, tmen, dap, and dpt gave rise to a family of cationic mercury(II) thiolate complexes, [Hg(Tab)(2)(L)](PF(6))(2).S (2, L = phen, S = 2MeOH; 3, L = 2,2'-bipy, S = DMF), [Hg(Tab)(2)(L)(2)](PF(6))(2) (4, L = py; 5, L = N-Meim), [Hg(Tab)(2)(N-(i)Prim)](PF(6))(2) (6), [Hg(Tab)(2)(L)](PF(6))(2).0.5MeCN (7, L = en; 8, L = eten), and [Hg(Tab)(2)(L)](PF(6))(2) (9, L = tmen; 10, L = dap; 11, L = dpt). These complexes were characterized by elemental analysis, IR spectra, UV-vis spectra, (1)H NMR, and single-crystal X-ray crystallography. The Hg atom in [Hg(Tab)(2)](2+) dications of 2-5 is further coordinated either by two N atoms from one phen or 2,2'-bipy ligand or by two N atoms from two py or N-Meim ligands, affording a distorted seesaw-shaped coordination geometry. In 6, the Hg atom of the [Hg(Tab)(2)](2+) dication is coordinated by one N atom of the N-(i)Prim ligand, forming a T-shaped coordination geometry, and these [Hg(Tab)(2)(N-(i)Prim)](2+) dications are further coordinated to another S atom of Tab from the adjacent unit, giving a chain structure. The Hg atoms in [Hg(Tab)(2)](2+) dications of 7-11 are chelated by two N atoms from one diamine molecule such as en in 7, eten in 8, tmen in 9, or dap in 10 or by two N atoms from the triamine molecule dpt in 11, forming a distorted seesaw-shaped coordination geometry. In all of these structures, the original trans configuration of the [Hg(Tab)(2)](2+) dication of 1 is changed via rotation and/or switching of the two Tab species along the S-Hg-S line together with the rotation of the phenyl groups of the Tab ligands. The results may provide interesting insight into mimicking of the interactions of the Hg(Cys)(2) linear species in Hg-MerR and Hg-MT with various N-donor ligands encountered in nature and its potential changes in the structural chemistry (bond length, angles, configurations, etc.).

Heterojunction Photovoltaics Using Printed Colloidal Quantum Dots as a Photosensitive Layer

We demonstrate a bilayer photovoltaic device consisting of a heterojunction between colloidal cadmium selenide (CdSe) quantum dots (QDs) and a wide band gap organic hole-transporting thin film of N,N'-diphenyl-N,N'-bis(3-methylphenyl)[1,1'-biphenyl]-4,4'-diamine (TPD) molecules. The active light-absorbing film of QDs is nondestructively printed onto TPD using microcontact stamping. Indium-tin-oxide (ITO) provides the top contact. The resulting device structure can accommodate different size QDs, produces an exceptionally large open circuit voltage (0.8 V) for an architecture with symmetric electrodes, and yields an internal quantum efficiency of 10% at the first QD absorption peak.

Semi Empirical Approach to the Charge Transport Characteristics of Molecular Junctions

The idea of using molecules and molecular structures as functional electronic device, promises to substantially decrease the size and improve the performance of electronic devices. In this paper, nonequilibrium Green's function formalism (NEGF) combined with extended Huckel theory (EHT), a semiempirical approach is used to study the electron transport phenomenon in single molecular junction systems. Benzene diamine molecule is studied to investigate the bonding of amine group to gold electrodes and the electron transport across the junction. The results are compared with that of benzene dithiol molecule with thiol end groups. Furthermore, the influence of charging and torsion angle on the transport characteristics is emphasized.

Allosteric binding of amino alcohols and diamines by dimeric zinc biladienone

A zinc complex of biladienone forms a dimer in toluene and dichloromethane. Binding of two molecules of amino alcohols and diamines to the dimer occurs cooperatively, with the first binding constant being two orders or three orders of magnitude smaller than the second binding constant. Simple amines such as butylamine did not show such cooperative binding. We suggest the mechanism of cooperative binding, where the amino or hydroxyl group in amino alcohols or diamines prevents the dimer dissociation to result in the less tight binding for the first guest, while the binding of the second ligand caused dimer dissociation to release strain in the intermediate complex.

Selective intercalation of o-phenylene diamine into molybdenum oxide layers

o-Phenylene diamine molecules were intercalated into molybdenum oxide layers by an in situ co-precipitation method. The structure and composition of the intercalated material were studied by X-ray diffraction (XRD), infrared spectroscopy (IR) and elemental analysis. XRD data evidenced a layered structure with a spacing of 18 Å, which corresponds to an organic–inorganic hybrid-layered structure. IR and UV–vis spectra indicated the polymerization of o-phenylene between the molybdenum oxide layers. It was also observed that compared with aniline molecules, o-phenylene diamine molecules can be selectively intercalated into molybdenum oxide layers. We provide evidence that affinity for o-phenylene diamine to form intermolecular polymers is the reason for its selective intercalation. The polymer chain structure of o-phenylene diamine makes it a preferential guest species compared with aniline. We believe that this opens a new way to create organic–inorganic hybrid structures.

Hydrogen bonding in the perhydrate and hydrates of 1,4-diazabicyclo[2.2.2]octane (DABCO)

The crystal structures of the bis(perhydrate), the monohydrate, and the hexahydrate of 1,4-diazabicyclo[2.2.2]octane (DABCO) were determined by single-crystal X-ray diffraction to investigate the hydrogen bonding architectures. The bis(perhydrate) revealed helical chains of hydrogen peroxide molecules forming a 3-D network by interaction with the diamine. In the monohydrate, water and diamine molecules are alternately linked. In the hexahydrate, cyclic water aggregates create cavities which are occupied by DABCO molecules doubly hydrogen-bonded to the water framework of the cage.

Effects of acid- and diamine-modified MWNTs on the mechanical properties and crystallization behavior of polyamide 6

The acid- and diamine-modified multi-walled carbon nanotubes were characterized by XPS, apparent density test and SEM. Their effects on the mechanical properties and crystallization behavior of polyamide 6 (PA6) were comparatively investigated via SEM, DMA, tensile test and DSC. It was revealed that acid treatment could effectively induce polar oxygen-containing groups on the surface of MWNTs, which was beneficial for MWNTs to combine with polar PA6 matrix. However, the interactions such as the hydrogen bonds among the acid-modified MWNTs caused a compact stacking morphology, resulting in a worse dispersion in PA6 matrix. Further diamine modification on the acid-modified MWNTs could graft diamine molecules onto the surface of MWNTs, which weakened the interactions among the MWNTs and thus resulted in a less compact stacking morphology compared with acid-modified MWNTs. Therefore, a better dispersion and a stronger interfacial adhesion of MWNTs in PA6 matrix could be obtained with diamine-modified MWNTs. The storage modulus, glass transition temperature, yield strength, Young's modulus and crystallization temperature of PA6 were found to be improved significantly by the incorporation of diamine-modified MWNTs.

Nanostructured Crystals: Unique Hybrid Semiconductors Exhibiting Nearly Zero and Tunable Uniaxial Thermal Expansion Behavior

A unique family of II−VI based nanostructured inorganic−organic hybrid semiconductors exhibit nearly zero uniaxial thermal expansion in the temperature range of 95−295 K. Both their optoelectronic and thermal expansion properties are systematically tunable. The diamine molecules show a strong negative thermal expansion effect, and the extent of such an effect increases as the length of the organic molecules increases.

Gene Delivery Properties of End-Modified Poly(β-amino ester)s

Here, we present the synthesis of a library of end-modified poly(beta-amino ester)s and assess their utility as gene delivery vehicles. Polymers were synthesized using a rapid, two-step approach that involves initial preparation of an acrylate-terminated polymer followed by a postpolymerization amine-capping step to generate end-functionalized polymers. Using a highly efficient poly(beta-amino ester), C32, we show that the terminal amine can greatly affect and improve polymer properties relevant to gene delivery. Specifically, the in vitro transfection levels can be increased by 30% and the optimal polymer:DNA ratio lowered 5-fold by conjugation of the appropriate end group. The most effective modifications were made by grafting primary diamine molecules to the chain termini. The added charge and hydrophobicity of some derivatives enhanced DNA binding and resulted in the formation of polymer-DNA complexes less than 100 nm in diameter. In addition, cellular uptake was improved 5-fold over unmodified C32. The end-modified poly(beta-amino ester)s presented here are some of the most effective gene-delivery polycations, superior to polyethylenimine and previously reported poly(beta-amino ester)s. These results show that the end-modification of poly(beta-amino ester)s is a general strategy to alter functionality and improve the delivery performance of these materials.