Optimizing the mechanical properties of cellulose nanopaper through surface energy and critical length scale considerations

Cellulose nanopaper exhibits outstanding stiffness, strength, and toughness that originate from the exceptional properties of constituent cellulose nanocrystals (CNCs). However, it remains challenging to link the nanoscale properties of rod-like CNCs and their structural arrangements to the macroscale performance of nanopaper in a predictive manner. Here we address this need by establishing an atomistically informed coarse-grained model for CNCs via a strain energy conservation paradigm and simulating CNC nanopaper properties mesoscopically. We predict how the mechanical properties of CNC nanopaper with nacre-inspired brick-and-mortar structure depend on CNC overlap length and interfacial energy. We show that the modulus and strength both increase with increasing overlap length, but saturate at different critical length scales where a transition from non-covalent interfacial sliding to CNCs fracture is the key influencing mechanism. Maximum toughness is achieved when the interface and CNC failure are tuned to occur at the same time through balanced failure. We propose strategies for maximizing nanopaper mechanical performance by tuning interfacial interactions of constitutive CNCs through surface modifications that improve shear transfer capability. Our model generates broadly applicable insights into factors governing the performance of self-assembling paper materials made from 1D nanostructures.     

Influence of oligonucleotide interaction on electronic properties of single walled carbon nanotubes

Raman spectroscopy is a powerful tool to study molecular systems. The influence of the non‐covalent interactions of two different lengths of oligonucleotides, 10‐base and 25‐base, composed of polyA, polyT, polyG and polyC, on the electronic structure of single‐walled carbon nanotubes (SWCNTs) is first studied by means of Raman spectroscopy. Then, the possible changes in their electronic structure with chemical attachment of the oligonucleotides are investigated. The Raman data indicates that polyA with 10‐base wraps the SWCNTs at increased incubation time, while polyA with 25‐base wraps quickly, but increasing the incubation time reduces the efficient wrapping, possibly due to the self‐stacking. The polyT‐10 does not wrap around the SWCNTs very effectively even at increased incubation times, but the polyT‐25 wraps them effectively in 30 mins, but increasing the time again decreases the wrapping significantly. While polyG shows similar pattern to the case for the polyA, the polyC shows much higher affinity for the SWCNTs under all studied conditions. The chemical attachment of the same oligonucleotides does not alter the electronic properties of the SWCNTs significantly. These results suggest that oligonucleotides can be used to bring the SWCNTs into higher structures through DNA hybridization without significantly altering their unique properties. Copyright © 2012 John Wiley & Sons, Ltd.     

Testing the accuracy of correlations for multicomponent mass transport of adsorbed gases in metal-organic frameworks: diffusion of H2/CH4 mixtures in CuBTC

Mass transport of chemical mixtures in nanoporous materials is important in applications such as membrane separations, but measuring diffusion of mixtures experimentally is challenging. Methods that can predict multicomponent diffusion coefficients from single-component data can be extremely useful if these methods are known to be accurate. We present the first test of a method of this kind for molecules adsorbed in a metal-organic framework (MOF). Specifically, we examine the method proposed by Skoulidas, Sholl, and Krishna (SSK) ( Langmuir, 2003, 19, 7977) by comparing predictions made with this method to molecular simulations of mixture transport of H 2/CH 4 mixtures in CuBTC. These calculations provide the first direct information on mixture transport of any species in a MOF. The predictions of the SSK approach are in good agreement with our direct simulations of binary diffusion, suggesting that this approach may be a powerful one for examining multicomponent diffusion in MOFs. We also use our molecular simulation data to test the ideal adsorbed solution theory method for predicting binary adsorption isotherms and a method for predicting mixture self-diffusion coefficients.     

(Amidomethyl)pyridine zirconium and hafnium complexes: Synthesis and structural characterization

A series of 2-formyl and 2-acetylpyridines was condensed with 2,6-diisopropylaniline to yield the corresponding imines. Their reaction with sodium borohydride gave the respective N-arylaminomethylpyridines. Treatment of the N-arylformimino- or -acetiminopyridines with trimethylaluminum followed by hydrolysis furnished a series of the respective substituted N-arylaminoethylpyridine derivatives. Their reaction with tetrabenzylzirconium or tetrakis(dimethylamido)zirconium or -hafnium gave the corresponding (chelate ligand)MX₃ systems in a variety of cases. Some of these gave very active ethene polymerization catalysts upon activation with methylalumoxane. Six of the neutral aminoalkylpyridines were characterized by X-ray diffraction, as were eight of the zirconium or hafnium complexes and two aluminum chelate complex systems.     

Transport and Reaction Characteristics of Reconstructed Polyolefin Particles

The 3D spatial structure of porous polyethylene particles was reconstructed from their X‐ray micro‐tomography images. Several polyolefin particles with an artificial granular structure were generated. Transport in reconstructed particles was calculated for the case of a monomer diffusing through both the pores and the polymer. The calculated degassing characteristics of reconstructed polyolefin particles can be compared to experiments. Monomer mass transport limitations are important not only in the early stage of particle growth, but also in fully‐developed polyolefin particles. The problems and limitations of the developed method are discussed. The method developed allows prediction of the effect of particle structure on mass transport limitations for real particle structures.

     

Ab initio and density functional computations of the vibrational spectrum, molecular geometry and some molecular properties of the antidepressant drug sertraline (Zoloft) hydrochloride

Sertraline hydrochloride is a highly potent and selective inhibitor of serotonin (5HT). It is a basic compound of pharmaceutical application for antidepressant treatment (brand name: Zoloft). Ab initio and density functional computations of the vibrational (IR) spectrum, the molecular geometry, the atomic charges and polarizabilities were carried out. The infrared spectrum of sertraline is recorded in the solid state. The observed IR wave numbers were analysed in light of the computed vibrational spectrum. On the basis of the comparison between calculated and experimental results and the comparison with related molecules, assignments of fundamental vibrational modes are examined. The X-ray geometry and experimental frequencies are compared with the results of our theoretical calculations.     

Electrochemical Analysis of Liposome-encapsulated Colistimethate Sodium

In this study, the neutral and cationic liposomal formulations of Colistimethate sodium (CMS), an antibiotic for multi-drug resistant gram-negative bacteria, were prepared and electrochemical quantification of CMS from these liposomes were achieved. This is the first study of the electrochemical detection of CMS released from liposomes. First, the electrochemical properties of CMS were analysed, then the encapsulation efficiency, and the release kinetic of CMS from liposomes were determined with Differential Pulse Voltammetry (DPV) measurements. In addition, Cyclic Voltammetry were applied to determine oxidation signal of CMS. A higher encapsulation efficiency was found in the cationic liposome compared to the neutral liposome. Moreover, CMS was controlled released from liposomes with zero-order drug release kinetics.     

Synthesis, IR spectral studies and quantum-chemical calculations on 1,2-dihydronaphto[1,2-e]oxazine-3-thiones and 3,4-dihydrobenzo[e][1,3]oxazine-2-thione

2-Hydroxy-1-naphthaldehyde (1) was reacted with substituted anilines to afford 1-(substituted phenyliminomethyl)naphthalen)-2-ols (2). The reduction of these imines by NaBH₄ gave 1-((substituted phenylaminomethyl)naphthalen)-2-ols (3) which were cyclized with thiophosgene to give corresponding 2-substituted phenyl-1,2-dihydronaphto[1,2-e]oxazine-3-thiones (4). 3-p-Tolyl-3,4-dihydrobenzo[e][1,3]oxazine-2-thione (8) was also obtained by the same way. The structures of these new compounds were determined by ¹H NMR, IR spectroscopic data and elemental analyses. AM1, PM3 and ab initio (at Hartree–Fock level with 3-21G basis set) methods were used to study the molecular geometry of the compounds. A complete infrared spectral analysis of the oxazines has been performed in this paper. Observed frequencies of the molecules were compared with calculated normal mode analysis which was carried out on the basis of RHF/3-21G method. Assignments of vibrational bands (in the range of 1760–400 cm⁻¹) have been performed by taking into account the results of the ab initio vibrational analysis. The mechanism of the cyclization reaction between (3a) and thiophosgene was studied by the semi-empirical AM1 and ab initio (RHF) calculations.     

Development of reactive phosphonated methacrylates

Five novel phosphonated mono‐ and dimethacrylate monomers have been synthesized by two different routes. Monomers 1 and 2 were synthesized by reactions of methacryloyl chloride with diethyl (2‐hydroxyphenyl) phosphonate or tetraethyl (2,5‐dihydroxy‐1,4‐phenylene) bisphosphonate; monomers 3 and 4 by reactions of α‐(chloromethyl)acryloyl chloride (CMAC) first with dimethyl (2‐hydroxyethyl) phosphonate and then with benzoic or formic acids. The reaction of CMAC with two moles of dimethyl (2‐hydroxyethyl) phosphonate gave monomer 5 . Thermal homopolymerization of monomers 1 , 3 , 4 , and 5 and copolymerization of monomer 1 with methyl methacrylate (MMA) were investigated using azobisisobutyronitrile (AIBN) at 60 °C. Glass transition temperatures were observed for poly‐ 1 , poly(MMA‐co‐ 1 ) (50:50), poly(MMA‐co‐ 1 ) (90:10), PMMA, poly‐ 3 , and poly‐ 5 at 52, 90, 99, 129, 50, and 70 °C, respectively. TGA analysis of these polymers indicated formation of char on combustion. Homo‐ and/or copolymerization behavior of the synthesized monomers with 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxy propyloxy) phenyl] propane (Bis‐GMA) were investigated with photodifferential scanning calorimetry. The maximum rate of polymerizations decreased in the following order: Bis‐GMA～ 3 > 1 > 4 > 5 . The conversions of monomers 1 , 3 , 4 , and 5 (73.9, 85.9, 98.2, and 62.2%) were very high compared with Bis‐GMA (40.5%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5737–5746, 2009