High-temperature decomposition of the cellulose molecule: a stochastic molecular dynamics study

The kinetics and products of cellulose pyrolysis can be studied using large-scale molecular dynamics simulations at high temperatures, where the reaction rates are high enough to make the simulation times practical. We carried out molecular dynamics simulations employing the ReaxFF reactive force field to study the initial step of the thermal decomposition process. We gathered statistics of simulated reactive events at temperatures ranging from 1400 to 2200 K, considering cellulose molecules with different molecular weights and initial conformations. Our simulations suggest that, in gas-phase conditions at these high temperatures, the decomposition occurs primarily through random cleavage of the β(1 → 4)-glycosidic bonds, for which we obtained an activation energy of (171 ± 2) kJ mol^?1 and a frequency factor of \(\left( {1.07 \pm 0.12} \right) \times 10^{15}\) s^?1. We did not observe dependency of the kinetic parameters on the molecular weight or initial conformation. Some of the decomposition reactions involved the release of low-molecular-weight products. Excluding radicals, the most commonly observed species were glycolaldehyde, water, formaldehyde and formic acid. Many of our observations are supported by the existing experimental and theoretical knowledge. We did not, however, observe the formation of levoglucosan, which is the dominant product in conventional pyrolysis experiments at much lower temperatures. This is understandable, since the high temperatures can force the dominance of radical reactions over pericyclic reactions. Nevertheless, our results support further use of ReaxFF-based molecular dynamics simulations in the study of cellulose pyrolysis.     

Comparison of triple quadrupole,hybrid linear ion trap triple quadrupole,time‐of‐flight and LTQ‐Orbitrap mass spectrometers in drug discovery phase metabolite screening and identification in vitro – amitriptyline and verapamil as model compounds

Liquid chromatography in combination with mass spectrometry (LC/MS) is a superior analytical technique for metabolite profiling and identification studies performed in drug discovery and development laboratories. In the early phase of drug discovery the analytical approach should be both time‐ and cost‐effective, thus providing as much data as possible with only one visit to the laboratory, without the need for further experiments. Recent developments in mass spectrometers have created a situation where many different mass spectrometers are available for the task, each with their specific strengths and drawbacks. We compared the metabolite screening properties of four main types of mass spectrometers used in analytical laboratories, considering both the ability to detect the metabolites and provide structural information, as well as the issues related to time consumption in laboratory and thereafter in data processing. Human liver microsomal incubations with amitriptyline and verapamil were used as test samples, and early‐phase ‘one lab visit only’ approaches were used with all instruments. In total, 28 amitriptyline and 69 verapamil metabolites were found and tentatively identified. Time‐of‐flight mass spectrometry (TOFMS) was the only approach detecting all of them, shown to be the most suitable instrument for elucidating as comprehensive metabolite profile as possible leading also to lowest overall time consumption together with the LTQ‐Orbitrap approach. The latter however suffered from lower detection sensitivity and false negatives, and due to slow data acquisition rate required slower chromatography. Approaches with triple quadrupole mass spectrometry (QqQ) and hybrid linear ion trap triple quadrupole mass spectrometry (Q‐Trap) provided the highest amount of fragment ion data for structural elucidation, but, in addition to being unable to produce very high‐important accurate mass data, they suffered from many false negatives, and especially with the QqQ, from very high overall time consumption. Copyright © 2010 John Wiley & Sons, Ltd.     

Filler-nanocellulose substrate for printed electronics: experiments and model approach to structure and conductivity

Composites made of inorganic filler particles and cellulose nanofibres can be applied as substrates for printed electronics. We have studied the structural properties of these substrates both experimentally and with particle-level modeling approach. Our model describes the skeleton structure formed by pigment particles of varied shapes and size distributions. Nanocellulose is assumed to fill voids of the structure. The model simulations predict quite well the relative changes in measured density, porosity and roughness for kaolin and precipitated calcium carbonate (PCC) pigments. Measured roughness turns out to be higher for kaolin than for PCC. Yet, the measured conductivity of printed lines on kaolin surface is higher than the conductivity on the PCC surface. The simulations reveal a more open surface pore structure for PCC than for kaolin, which leads to stronger absorption of the silver ink, and thus explains the differences in the measured conductivities.     

Fluctuation Bounds in the Exponential Bricklayers Process

This paper is the continuation of our earlier paper (Balázs et al. in Ann. Inst. Henri Poincaré Probab. Stat. 48(1):151–187, 2012), where we proved t ^1/3-order of current fluctuations across the characteristics in a class of one dimensional interacting systems with one conserved quantity. We also claimed two models with concave hydrodynamic flux which satisfied the assumptions which made our proof work. In the present note we show that the totally asymmetric exponential bricklayers process also satisfies these assumptions. Hence this is the first example with convex hydrodynamics of a model with t ^1/3-order current fluctuations across the characteristics. As such, it further supports the idea of universality regarding this scaling.     

Quantification of triacylglycerol regioisomers by ultra‐high‐performance liquid chromatography and ammonia negative ion atmospheric pressure chemical ionization tandem mass spectrometry

The regioisomer composition of triacylglycerols (TAGs) in various vegetable oils was determined with a new liquid chromatography/tandem mass spectrometry (LC/MS/MS method). A direct inlet ammonia negative ion chemical ionization (NICI) MS/MS method was improved by adapting it to LC negative ion (NI) atmospheric pressure chemical ionization (APCI) MS/MS system using ammonia as nebulizer gas. The method is based on the preferential formation of [M–H–RCOOH–100]^? ions during collision‐induced dissociation by loss of sn‐1/3 fatty acids from [M–H]^? ions. Calibration curves were created from nine reference TAGs: Ala/L/L, Gla/L/L, L/L/O, L/O/O, P/O/O, P/P/O, Po/Po/V, Po/Po/O, and C/O/O. The calibration curves were used to quantify the regioisomer compositions of selected TAGs in rapeseed oil, sunflower seed oil, palm oil, black currant seed oil, and sea buckthorn pulp oil. The method discriminates the different regioisomers and the results obtained by this method were in good agreement with previous results. This proves that this new method can be used for the determination of regiospecific distribution of fatty acids in TAGs. Copyright © 2009 John Wiley & Sons, Ltd.     

Layer-by-layer deposition of a polythiophene/Au nanoparticles multilayer with effective electrochemical properties

Multilayers consisting of a water soluble polythiophene derivative and Au nanoparticles have been deposited onto different electrode substrates by means of layer-by-layer deposition technique. The assembly of the films has been performed by taking advantage of the electrostatic interactions between the positively charged imidazolic moiety of the polythiophene chain and the negative charges of citrate ions surrounding Au nanoparticles, as well of the affinity of S to Au. The nanoparticles result stably grafted to the organic matrix. The resulting modified electrodes have been characterised through electrochemical, spectroelectrochemical and microscopic techniques. The results evidenced that a high number of individual nanoparticles is present inside the multilayer. The presence of nanoparticles is of chief importance for most effective charge percolation through the multilayer, as suggested by the responses to electroactive probe species in solution. The electrocatalytic performances of the modified electrodes have been tested with respect to the oxidation of ascorbic acid.

     

Investigation of the microstructure of metallocene-catalyzed norbornene–ethylene copolymers using NMR spectroscopy

Norbornene–ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with ¹H-NMR and ¹³C-NMR methods. From a Cosy ¹H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using ¹³C-¹H correlations, hmqc for one-bond correlations, and hmbc for two- or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy ¹H-NMR spectrum revealed a new crosspeak which, according to the corresponding ¹³C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1633–1638, 1998     

Solid state 13-C NMR spectroscopy with special reference to proteins and their derivatives. A comparison with vibrational spectroscopic methods

Possible applications of solid-state NMR in studies on polypeptides and proteins are presented. Several examples of 13-C CP/MAS NMR spectra are discussed in relation to model compounds and polypeptides from various sources. A comparison is made with vibrational spectroscopic methods. It is concluded that the CP/MAS NMR method is especially useful in elucidating secondary structures in the unperturbed state, and, thus, may also be useful in the study of various conditions involving the disturbance of biochemical equilibria (e.g. the skin disease psoriasis and β-fibrilloses). In these cases the NMR method is more elucidative than vibrational spectroscopy. However, owing to the fact that multiple spectral scans must be performed, it is very time consuming. It therefore appears that high resolution Fourier transform infra-red spectroscopy is a complementary method, but not as informative regarding structural details in secondary structures. Combining both methods together provides a powerful tool for structure analysis.