Polymorphic forms of lupane triterpenoid betulonic aldehyde (betulonal)

The lupane triterpenoid betulonic aldehyde [also known as betulonal; systematic name: lup‐20(29)‐en‐28‐al‐3‐one, C₃₀H₄₆O₂] is a product of betulin oxidation. Crystals were obtained from hexane [form (I)] and dimethyl sulfoxide [form (II)] solutions. Forms (I) and (II) are both orthorhombic. The molecular geometric parameters in the two forms are similar, but the structures are different with respect to the crystal packing. Polymorph (I) contains two independent molecules in the asymmetric unit, while polymorph (II) contains only one molecule, which has a disordered aldehyde group [the disorder ratio is 0.769 (4):0.231 (4)]. In each molecule, the six‐membered rings have chair conformations, whereas the cyclopentane ring in each molecule adopts an envelope conformation. All the rings in the lupane nucleus are trans‐fused. The extended structures of both polymorphs are stabilized by weak intermolecular C—H...O and van der Waals interactions. Weak intramolecular C—H...O interactions are also observed.     

Nondislocation origin of GaAs nanoindentation pop-in event

The present Letter demonstrates a pop-in event that is caused by a nanoindentation-induced phase transformation in GaAs, and not accompanied by any dislocation nucleation. Our computer simulations reveal the appearance of the new phase, documented by the structural correlation functions and visualization of the atomic positions. This challenges the orthodox view that the initial pop-in event reflects nucleation of dislocations or their movement, and has a bearing on materials where dislocation activity is not present.     

Barrier Dispersion-Based Coatings Containing Natural and Paraffin Waxes

Petroleum, synthetic, and natural waxes have been used as hydrophobic bases for dispersions intended for use as barrier coatings for packaging paper. Oil-in-water dispersions with alkaline pH were prepared by a two-step homogenization procedure containing paraffin wax, with various characteristics, the Fischer–Tropsch synthesis product or beeswax. The size of the dispersed particles determined by dynamic light scattering depended on the type of hydrophobic base used and was in the range of 350–440 nm. The ability of dispersion particles in aggregation driven by electrostatic attraction, evaluated by Zeta potential analysis by electrophoretic light scattering, was from −26 to −50 mV. Static multiply light scattering was used for 30 days of stability assessment and helped to select the dispersion with a Sarawax SX70 wax base as the most stable. Dispersions were further used for coating the backing of kraft paper by the Meyer rod method. Coated paper with an applied coating of 6 g/m² had very good hydrophobic properties (Cobb60 < 4 g/m²), sufficient strength properties, and air permeation, which enabled its application as a packaging material. The dispersions based on Sarawax SX70 wax were evaluated as the best coating for Mondi ProVantage Kraftliner 125 g/m² backing paper. Good hydrophobic properties and strength properties indicate the possibility of using the SX70-based wax dispersion coating as a replacement for PFAS coatings in some applications.     

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals

This paper presents results of the photoacoustic (PA) spectral studies of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. This is the first attempt of the quantitative evaluation of the surface quality of the samples from the photoacoustic experimental spectra.     

Contents to volume 19

Miscellanea

Contents to volume 19     

The hydrogen‐bonding network in deacetyl­cephalothin

The structural analysis of deacetyl­cephalothin [systematic name: (6R,7R)‐3‐hydroxy­methyl‐8‐oxo‐7‐(2‐thio­phen‐2‐yl­acetyl­amino)‐5‐thia‐1‐aza­bicyclo­[4.2.0]oct‐2‐ene‐2‐carboxylic acid], C₁₄H₁₄N₂O₅S₂, shows that the geometry of the central bicyclic moiety is close to the geometry exhibited by other biologically active cephalosporin antibiotics. The mol­ecules are arranged in a helical chain running parallel to the 2₁ axis via a strong O—H⋯O hydrogen bond. The main helices are zipped together via N—H⋯O inter­actions, forming infinite layers. The supramolecular architecture is stabilized by O—H⋯S and C—H⋯O hydrogen bonds.     

Competitive Algorithms for Relaxed List Update and Multilevel Caching

We study relaxed list update problem (RLUP), in which access requests are made to items stored in a list. The cost to access the jth item x_j is c_j, where c_i ≤ c_{i + 1} for all i. After the access, x_j can be repeatedly swapped, at no cost, with any item that precedes it in the list. This problem was introduced by Aggarwal et al. (1987, “Proc. 19th Symp. Theory of Computing,” pp. 305–313) as a model for the management of hierarchical memory that consists of a number of caches of increasing size and access time. They also proved that a version of LRU is C-competitive, for some C, for a restricted class of cost functions. We give an efficient offline algorithm that computes the optimal strategy for RLUP. We also show an elegant characterization of work functions for RLUP. We prove that move-to-front (MTF) is optimally competitive for RLUP with any cost function. An interesting feature of the proof is that it does not involve any estimates on the competitive ratio. Finally, we give a lower bound on the competitive ratio of online algorithms for RLUP.     

Effect of structural disorder on magnetic frustrations in the Fe80Nb6B14 amorphous alloy

The paper presents measurements of magnetic frustrations for the Fe₈₀Nb₆B₁₄ amorphous alloy preliminary annealed for 1 h at temperatures ranging from 300 to 770 K in comparison with other parameters characterizing structural relaxation. It was shown that annealing out of free volume and internal stresses cause a reduction in number of frustrated states observed in the range 400>T>50 K. In the range 2<T<50 K additional frustrations due to iron clusters or nanograins were detected.     

Preparation and Oxidative-Chlorination Splitting of Nitro Derivatives OF 1,4-Dithiino[2,3-C:5,6-C′]Diquinoline as a Source of 4-Substituted 5- and 8-Nitro-3-Quinolinesulfonic Acid Derivatives

Abstract

Treatment of 1,4-dithiino[2,3-c:5,6-c′]diquinoline (a thioquinanthrene) (1a) with an excess of nitrating mixture (0 °C, 14 days) led to a mixture of mono- and dinitrothioquinanthrene 7-oxides 2b–e and 2f–h. This mixture was: (i) reduced to a mixture of mono- and dinitrothioquinanthrenes 1b– e, or (ii) oxidatively chlorinated with a gaseous chlorine/80% acetic acid/hydrochloric acid system to a mixture of 4-chloro-3-chlorosulfonylquinoline 3a and its 5- and 8-nitroderivatives 3b and 3d. Sulfochlorides 3a– d were independently synthesized from 3,4′-diquinolinyl sulfides 4 and converted to the respective 4-dimethylamino-3-quinoline-N,N-dimethylsulfonamides 9a–d.     

Numerical analysis of absorption and transmission photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies, of a series of silicon samples with differently prepared surfaces, in two PA experimental configurations, so-called, absorption and transmission ones. The PA amplitude spectra of the samples indicated existence of the damaged surface layers. In the paper, the two layer mathematical models of a sample with a damaged surface layer that were used for numerical interpretation of the amplitude PA spectra of the investigated samples, are presented and discussed.