Calorimetric study on pure and KOH-doped argon clathrate hydrates

Pure and KOH (x=1.3×10^?3)-doped argon clathrate hydrates were synthesized in an adiabatic high-pressure calorimetric cell from one mole of water and 200 MPa of Ar gas. The heat capacities of the hydrates were measured from 12 to 130 K. No anomaly was found in the pure sample but a glass transition considered to be related to a proton-configurational mode of the host hydrogen-bonded lattice was observed for the first time at 55 K in the doped sample. Comparison with the results on pure and KOH-doped tetrahydrofuran clathrate hydrates indicated that the thermodynamic properties of a hydrogen-bonded system depend on the kind of guest molecule. The heat capacity of argon in the hydrate cages was adequately analyzed with the one-dimensional Pöschl-Teller potential as used in the Ar-β-quinol clathrate and the addivity of heat capacities of the guest and host was shown to be valid in the temperature range 12–130 K.     

Utilization of matrix-assisted laser desorption/ionization imaging mass spectrometry to search for cannabis in herb mixtures

Herb mixtures including cannabis among the other herbs have recently appeared. When cannabinoids from herb extracts are detected by chemical examinations such as gas chromatography/mass spectrometry, forensic analysts have to determine whether cannabis is actually in the mixture or the cannabinoids are spiked. Morphological examinations are time-consuming, since it is difficult to find several pieces of cannabis among a large number of herb pieces using a microscope. Here, we propose a procedure for efficiently searching for cannabis in herb mixtures using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI/IMS). Pieces of herb mixtures were spread on double-sided adhesive tape attached to a stainless steel plate. The pieces were then covered with a conductive sheet and pressed. After a solution containing a matrix reagent was sprayed, the distribution of cannabinoids in the sample was visualized by MALDI/IMS. Then, just the pieces with cannabinoids could be picked up selectively with tweezers and decolorized. Cystolith hairs and trichomes, which are characteristic of cannabis, were observed in most of these pieces using a biological microscope. This MALDI/IMS procedure enables cannabis to be found in herb mixtures without inefficient random sampling and microscopic morphological examination.     

Hydration properties and compressive strength development of Low Heat Cement

For Low Heat Cement (LHC), its hydration reaction properties and compressive strength development were studied by quasi-elastic neutron scattering (QENS) and compressive strength test. In the QENS experiments, the amount of hydration products was estimated and the hydration behavior of LHC was revealed in the early hydration times of 7 days. Simultaneously, we compared the compressive strength of a mortar specimen made from LHC with the amount of hydration products. It was found that the compressive strength is strictly proportional to the amount of hydration products in the range from 15 h to 7 days of hydration.     

Hierarchical structure and dynamics of an ionic liquid 1-octyl-3-methylimidazolium chloride

We have performed the heat capacity, neutron diffraction, and neutron quasielastic scattering measurements of an ionic liquid 1-octyl-3-methylimidazolium chloride (C8mimCl). The heat capacity data revealed that C8mimCl exhibits a glass transition with a large heat capacity jump at T(g) = 214 K, which is lower than T(g) of C4mimCl with a shorter alkyl-chain. In the neutron diffraction measurement for a deuterated analogue, d-C8mimCl, the peaks associated with the inter-domain, inter-ionic, and inter-alkyl-chain correlations appeared at (3, 11, and 14) nm(-1), respectively. The temperature dependence of these peaks indicates that the packing of the alkyl-chains becomes more compact and the domains become more vivid and larger as decreasing temperature. The quasielastic neutron scattering measurements using neutron spin echo and time-of-flight type instruments demonstrated that C8mimCl has faster relaxations probably owing to the alkyl-group and a slower relaxation owing to the ions. The latter relaxation, which is related to the glass transition, is of non-exponential as in the α relaxation of glass-forming molecular liquids. The relaxation of domains could not be observed in the present experiment but should have relaxation times longer than 100 ns. This is the first report to clarify temperature dependence of the hierarchical structure and relaxations simultaneously for a typical ionic liquid.     

The queue length in an <Emphasis Type="Italic">M</Emphasis>/<Emphasis Type="Italic">G</Emphasis>/1 batch arrival retrial queue

An M/G/1 retrial queue with batch arrivals is studied. The queue length K _μ is decomposed into the sum of two independent random variables. One corresponds to the queue length K _∞ of a standard M/G/1 batch arrival queue, and another is compound-Poisson distributed. In the case of the distribution of the batch size being light-tailed, the tail asymptotics of K _μ are investigated through the relation between K _∞ and its service times.     

Crystal structures and phase behaviour of acetaldehyde-d4: a study by high-resolution neutron powder diffraction and calorimetry

High-resolution neutron powder diffraction is particularly suited for structure solution and refinement of low-melting point organic crystals of moderate complexity. Here we present the ab initio structure solution and refinement of stable-phase and metastable-phase perdeuterated acetaldehyde (m.p.: 151 K). In the stable phase, the molecule crystallises in the space group P2₁/c (no. 14) with a=3.9069(1) Å, b=5.4224(1) Å, c=12.1868(1) Å, β=94.2970(2)° at 5 K, Z=4. In the metastable phase, the molecule crystallises in the space group Pna2₁ (no. 33) with a=5.1973(1) Å, b=6.9791(1) Å, c=6.9712(1) Å at 5 K, Z=4. The metastable to stable phase transition is characterised by heat capacity measurements.     

Characterization of amorphous solid derived from crystal

Amorphous solid of tri-O-methyl-β-cyclodextrin was produced by grinding its crystalline sample with a rod-milling machine at room temeprature. Structural and thermal characterizations of the sample during amorphizing process were done by X-ray powder diffraction and differential scanning calorimeter. The glass transition for a fully amorphized sample was found to occur at essentially the same temperature as that for a liquid-quenched glass. The heat capacities of the non-crystalline solids realized by grinding and liquid quenching and of the crystalline solid were measured by a low temperature adiabatic calorimeter. Excess enthalpies of the ground amorphous solid and liquid quenched glass over that of the hypothetical equilibrium liquid were determined calorimetrically. Similar and dissimilar thermal behavior of both non-crystalline solids were compared.     

Solid state amorphization and glass transition of tri-O-methyl-β-cyclodextrin

Amorphous solid of tri-O-methyl--cyclodextrin was formed by grinding the crystalline sample with a vibrating mill at room temperature. The amorphising process was examined by X-ray powder diffraction technique and differential scanning calorimetry (DSC). The Bragg peaks disappeared and the enthalpy of crystallization became constant for the sample ground for 25 min, indicating the apparent completion of the amorphization. A glass transition of the ground amorphous solid was found by DSC. The glass transition temperature T_g moved from 58°C to 79°C with grinding. The saturated T_g of the ground sample was the same as that of the liquid-quenched glass. No significant difference between the ground and liquid-quenched amorphous solids was found in the X-ray diffraction patterns. Infrared spectra of both amorphous solids, however, showed a definite difference for the band at 1194 cm^–1 assigned to the rocking of the CH₃ groups which are located at the molecular periphery.

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Zusammenfassung Amorphes festes Tri-O-methyl--cyclodextrin wurde bei Raumtemperatur durch Mahlen einer kristallinen Probe in einer Vibrationsmühle hergestellt. Der Amorphisierungsprozeß wurde mittels Röntgenpulverdiffraktion und DSC verfolgt. Die Braggschen Peaks verschwanden und die Kristallisierungsenthalpie nahm nach einem Mahldauer von 25 min einen konstanten Wert an, was auf die augenscheinliche Beendigung des Amorphisierungsprozesses hinweist. Mittels DSC wurde ein Glasumwandlungspunkt des gemahlenen amorphen Feststoffes gefunden. Die Glasumwandlungstemperatur T_g stieg durch das Mahlen von 58°C auf 79°C. Der Sättigungswert T_g der gemahlenen Probe war der gleiche wie für flüssigkeitsabgeschrecktes Glas. In den Röntgendiffraktogrammen konnte zwischen den gemahlenen und den flüssigkeitsabgeschreckten amorphen Feststoffen keinen Unterschied feststellen. Die IR-Spektren von beiden amorphen Feststoffen zeigen einen signifikanten Unterschied für die Bande bei 1194 cm^–1, der Nickschwingung der CH₃-Gruppen am Molekülrand.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday

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Contribution No. 35 from the Microcalorimetry Research Centre.

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The authors thank the research group of Professor Yoshinobu Nakai, Faculty of Pharmaceutical Science, Chiba University, for their kind advice for the grinding-amorphization method. The authors are deeply indebted to Mr. Tetsuo Yamamoto for his X-ray diffraction experiments and Mr. Shin-ichi Ishikawa for his IR experiments.     

Spurt and instability in a two-layer Johnson-Segalman liquid

The Johnson-Segalman model is an example of a model that exhibits a nonmonotone curve for the shear stress in terms of shear rate. There are many works based on such models for an explanation of the spurt phenomenon but they have concerned the one-dimensional problem. This paper concerns a model problem, taking a one-dimensionally stable spurted solution, viewed in two dimensions. A two-layer arrangement between walls in parallel shear, with a thin layer in the higher shear rate and the bulk of the fluid in the lower shear rate, is examined for linear stability in two dimensions. The spectrum is computed numerically for normal mode solutions. Instabilities with dominant growth rates for short waves are found. Thus, the one-dimensionally stable solutions of this model are actually two-dimensionally unstable.This research was sponsored by ONR Grant No. N00014-92-J-1664 and NSF Grant CTS-9307238.     

Synthesis and Properties of Carbocyclic 5′- Nor Oligodeoxynucleotides as Potential Antisense Molecules

We have synthesized carbocyclic 5'-nor oligodeoxynucleotides with a shortened overall chain length lacking the 5'-methylene. Their hybridization properties with DNA and RNA were investigated by UV and CD melting curves. These oligomers formed unstable duplexes with DNA, but formed stable duplexes with RNA selectively. In addition, these oligomers were very stable against nucleases.