In quest of strong neutral organic bases and superbases—supramolecular systems containing four pyridine subunits

It is shown by a reliable DFT method that supramolecular structures 1 and 2, constructed using pyridine as an essential building block, act as powerful neutral organic superbases in the gas phase and in acetonitrile due to cationic resonance and hydrogen bonding in the conjugate acids amplified by the NMe₂ groups placed at strategic positions on the molecular backbone.     

Finite 2-groups all of whose nonabelian subgroups are generated with involutions

In this note we determine finite nonabelian 2-groups G all of whose nonabelian subgroups are generated by involutions and show that such groups must be quasi-dihedral. This solves the problem Nr. 1595 for p = 2 in [1].     

Finite quaternion-free 2-groups

We present an elementary proof of the classification theorem for finite nonmodular quaternion-free 2-groups. This proof does not involve the structure theory of powerful 2-groups. Such a new proof is also necessary, since there are several gaps in the original proof given in [5].     

Effect of nano cadmium sulfide on combustion and thermal decomposition of polystryene and poly(methyl methacrylate)

Cadmium sulfide nano particles, both hollow spheres (CdS‐HS) and rods (CdS‐NR), were synthesized by ultrasonic and solvothermal processes, respectively, and characterized by XRD and SEM. The effect of the two kinds of nano particles on flammability was investigated using the cone calorimeter and microscale combustion calorimeter. The incorporation of small amount of CdS nano particles (1 wt.%, 3 wt.%, 5 wt.%) leads to a reduction in the peak heat release rate (PHRR) compared to pristine PS; CdS‐NR is more efficient in reducing the PHRR. CdS nano particles are less effective in reducing the PHRR of PMMA. Thermal stability of PS/CdS and PMMA/CdS nanocomposites was studied by TGA. The TGA results show that the addition of the nano particles mainly increases thermal stability of PS and PMMA at high temperatures. Copyright © 2014 John Wiley & Sons, Ltd.     

Finite 2-groups with exactly one nonmetacyclic maximal subgroup

We determine here the structure of the title groups. All such groups G will be given in terms of generators and relations, and many important subgroups of these groups will be described. Let d(G) be the minimal number of generators of G. We have here d(G) ≤ 3 and if d(G) = 3, then G′ is elementary abelian of order at most 4. Suppose d(G) = 2. Then G′ is abelian of rank ≤ 2 and G/G′ is abelian of type (2, 2^m), m ≥ 2. If G′ has no cyclic subgroup of index 2, then m = 2. If G′ is noncyclic and G/Φ(G ₀) has no normal elementary abelian subgroup of order 8, then G′ has a cyclic subgroup of index 2 and m = 2. But the most important result is that for all such groups (with d(G) = 2) we have G = AB, for suitable cyclic subgroups A and B. Conversely, if G = AB is a finite nonmetacyclic 2-group, where A and B are cyclic, then G has exactly one nonmetacyclic maximal subgroup. Hence, in this paper the nonmetacyclic 2-groups which are products of two cyclic subgroups are completely determined. This solves a long-standing problem studied from 1953 to 1956 by B. Huppert, N. Itô and A. Ohara. Note that if G = AB is a finite p-group, p > 2, where A and B are cyclic, then G is necessarily metacyclic (Huppert [4]). Hence, we have solved here problem Nr. 776 from Berkovich [1].     

Derivation of the model of elastic curved rods from three-dimensional micropolar elasticity

In this paper we derive a model of curved elastic rods from the threedimensional linearized micropolar elasticity. Derivation is based on the asymptotic expansion method with respect to the thickness of the rod. The method is used without any a priori assumption on the scaling of the unknowns. The leading term, displacement and microrotation, is identified as the unique solution of a certain one-dimensional problem. Appropriate convergence results are proved.      

Gas-phase dissociation reactions of protonated saxitoxin and neosaxitoxin

The aim of this study was to investigate the behavior of the protonated paralytic shellfish poisons saxitoxin (STX) and neosaxitoxin (NEO) in the gas-phase after ion activation using different tandem mass spectrometry techniques. STX and NEO belong to a group of neurotoxins produced by several strains of marine dinoflagellates. Their chemical structures are based on a tetrahydropurine skeleton to which a 5-membered ring is fused. STX and NEO only vary in their substituent at N-1, with STX carrying hydrogen and NEO having a hydroxyl group at this position. The collision-induced dissociation (CID) spectra exhibited an unusually rich variety and abundance of species due to the large number of functional groups within the small skeletal structures. Starting with triple-quadrupole CID spectra as templates, linked ion-trap MSn data were added to provide tentative dissociation schemes. Subsequent high-resolution FTICR experiments gave exact mass data for product ions formed via infrared multiphoton dissociation (IRMPD) from which elemental formulas were derived. Calculations of proton affinities of STX and NEO suggested that protonation took place at the guanidinium group in the pyrimidine ring for both molecules. Most of the observed parallel and consecutive fragmentations could be rationalized through neutral losses of H2O, NH3, CO, CO2, CH2O and different isocyanate, ketenimine and diimine species, many of which were similar for STX and NEO. Several exceptions, however, were noted and differences could be readily correlated with reactions involving NEO's additional hydroxyl group. A few interesting variations between CID and IRMPD spectra are also highlighted in this paper.     

Acidities of azoles in the gas phase and in DMSO: an ab initio and DFT study

Acidity of azoles, a very important family of biological molecules with useful pharmacological applications, is examined in the gas phase and in DMSO. The gas phase proton affinities of the corresponding conjugate bases are calculated by the G3 computational scheme and used as a measure of acidity. A good accordance with available experimental data is obtained. It is confirmed that acidity increases with the number of nitrogen atoms in the five-membered ring. The calculated deprotonation energies are interpreted by the triadic formula. It turns out that acidity of azoles is a result of the final state effect and the relaxation energy contribution. It is shown, by using NICS(1) values, that azoles are aromatic compounds and that their aromatic character increases with the number of N atoms. It is also found that aromaticity slightly increases upon deprotonation. Acidity of azoles in DMSO is considered using the isodensity polarized continuum model (IPCM) at the DFT-B3LYP level. A good agreement with accessible experimental results is obtained again. In other cases pK_a values are theoretically predicted and it was found that pentaazole is the most acidic compound with pK_a?=?2. A very good linear relation between theoretical pK_a values and calculated proton affinities of conjugate bases is obtained implying that the trend of changes in the gas phase and in the DMSO solutions is the same.