The Binary System Tetradecanedioic Acid–Hexadecanedioic Acid: Polymorphism of the Components and Experimental Phase Diagram

Complementary techniques had to be applied to investigate the binary system tetradecanedioic acid (C₁₄H₂₆O₄)–hexadecanedioic acid (C₁₆H₃₀O₄), because all the forms observed have the same space group (P2₁/c; Z = 2). We studied the polymorphism of the two single compounds and of their mixtures by X‐ray powder diffraction, differential‐scanning calorimetry (DSC), infrared spectroscopy (IR), scanning electron microscopy (SEM), and thermo‐optical microscopy (TOM). The two diacids were found to be isopolymorphic. At low temperature, they crystallize in the same ordered C‐form, and, on heating, adopt the ordered C_h‐form, 1° below their melting point. In contrast to similar compounds (unbranched alkanes, alkanols, and fatty acids), the solid–solid and solid–liquid phase‐transition temperatures decrease with increasing chain length. At low temperature, a new monoclinic form, C_i, appears as a result of the disorder of composition in the mixed samples. There are two [C + C_i]‐type solid–solid domains. On heating, the solid domains are related to solid–liquid domains by a peritectic invariant for compositions rich in C₁₄H₂₆O₄, and by a eutectic invariant for compositions rich in C₁₆H₃₀O₄. At higher temperature, there appears a second peritectic invariant for compositions rich in C₁₄H₂₆O₄, together with a metatectic invariant for compositions rich in C₁₆H₃₀O₄. All the solid forms observed in this binary system are isostructural. Nevertheless, the equilibrium between them is complex near the melting point, and their miscibility in the solid state is reduced.     

Entropy Maximization for Markov and Semi-Markov Processes

The literature about maximum of entropy for Markov processes deals mainly with discrete-time Markov chains. Very few papers dealing with continuous-time jump Markov processes exist and none dealing with semi-Markov processes. It is the aim of this paper to contribute to fill this lack. We recall the basics concerning entropy for Markov and semi-Markov processes and we study several problems to give an overview of the possible directions of use of maximum entropy in connection with these processes. Numeric illustrations are presented, in particular in application to reliability.     

An Ω(n 5/4) lower bound on the randomized complexity of graph properties

A decision tree algorithm determines whether an input graph withn nodes has a property by examining the entries of the graph's adjacency matrix and branching according to the information already gained. All graph properties which are monotone (not destroyed by the addition of edges) and nontrivial (holds for somes but not all graphs) have been shown to require (n ²) queries in the worst case.In this paper, we investigate the power of randomness in recognizing these properties by considering randomized decision tree algorithms in which coins may be flipped to determine the next entry to be examined. The complexity of a randomized algorithm is the expected number of entries that are examined in the worst case. The randomized complexity of a property is the minimum complexity of any randomized decision tree algorithm which computes the property. We improve Yao's lower bound on the randomized complexity of any nontrivial monotone graph property from (n log^1/12 n) to (n ^5/4).     

Isolation and Characterization of Crystalline,Neutral Diborane(4) Radicals

Diaryldihalodiboranes(4) were reacted with bis(amidinato)‐ and bis(guanidinato)silylenes to generate the first neutral diborane‐centered radicals. These formally non‐aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid‐state structure determination, high‐resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4‐benzoquinone led to ring‐opening and B?O bond formation.     

Micro Raman spectroscopy used for the study of corrosion products on copper alloys: study of the chemical composition of artificial patinas used for restoration purposes

Studying the atmospheric corrosion of copper alloy artifacts is important to acquire a better knowledge about the condition of the object and its possible conservation and restoration. The nature of the formed product, e.g. sulfate, carbonate or chloride, depends on factors such as the amount of polluting elements or humidity but may also depend on the nature of the underlying aesthetic patina, applied by the artist. The composition of the patination solution and the method of patination will both influence the nature of this aesthetic patina, i.e. its chemical composition and morphology. However, although a lot of patination recipes exist, little is known about these patinas as far as composition, structure and ageing is concerned. Therefore, a combination of several surface analytical techniques is required for the complete characterization of patina layers. In this paper, Raman spectroscopy is used to study the characteristics of several patinas obtained on copper following different traditional recipes.     

Direct measurement of the energy thresholds to conformational isomerization in tryptamine: experiment and theory

The methods of stimulated emission pumping-hole filling spectroscopy (SEP-HFS) and stimulated emission pumping population transfer spectroscopy (SEP-PTS) were applied to the conformation-specific study of conformational isomerization in tryptamine [TRA, 3-(2-aminoethyl)indole]. These experimental methods employ stimulated emission pumping to selectively excite a fraction of the population of a single conformation of TRA to well-defined ground-state vibrational levels. This produces single conformations with well-defined internal energy, tunable over a range of energies from near the zero-point level to well above the lowest barriers to conformational isomerization. When the SEP step overcomes a barrier to isomerization, a fraction of the excited population isomerizes to form that product. By carrying out SEP excitation early in a supersonic expansion, these product molecules are subsequently cooled to their zero-point vibrational levels, where they can be detected downstream with a third tunable laser that probes the ground-state population of a particular product conformer via a unique ultraviolet transition using laser-induced fluorescence. The population transfer spectra (recorded by tuning the SEP dump laser while holding the pump and probe lasers fixed) exhibit sharp onsets that directly determine the energy thresholds for conformational isomerization in a given reactant-product conformer pair. In the absence of tunneling effects, the first observed transition in a given X-Y PTS constitutes an upper bound to the energy barrier to conformational isomerization, while the last transition not observed constitutes a lower bound. The bounds for isomerizing conformer A of tryptamine to B(688-748 cm(-1)), C(1)(860-1000 cm(-1)), C(2)(1219-1316 cm(-1)), D(1219-1282 cm(-1)), E(1219-1316 cm(-1)), and F(688-748 cm(-1)) are determined. In addition, thresholds for isomerizing from B to A(<1562 cm(-1)), B to F(562-688 cm(-1)), and out of C(2) to B(<747 cm(-1)) are also determined. The A-->B and B-->A transitions are used to place bounds on the relative energies of minima B relative to A, with B lying at least 126 cm(-1) above A. The corresponding barriers have been computed using both density functional and second-order many-body perturbation theory methods in order to establish the level of theory needed to reproduce experimental results. While most of the computed barriers match experiment well, the barriers for the A-F and B-F transitions are too high by almost a factor of 2. Possible reasons for this discrepancy are discussed.     

ACTIVATION OF THE HUMAN IMMUNODEFICIENCY VIRUS PROMOTER BY UVA RADIATION IN COMBINATION WITH PSORALENS OR ANGELICINS

Abstract— The effects of mono- and bifunctional furocoumarins plus UVA radiation (PUVA and related treatments) on the human immunodeficiency virus-1 (HIV-1) promoter were studied using HeLa cells stably transfected with the chloramphenicol acetyl transferase gene under the control of the HIV-1 promoter. The experiments were performed with three psoralens (5-methoxypsoralen, 5-MOP; 8-methoxypsoralen, 8-MOP; and 4′-aminomethyl-4,8,5′-trimethyl-psoralen, AMT) and four angelicins (angelicin; 4,5′-diniethylangclicin, 4,5′-DMA; 6,4′-dimethylangelicin, 6,4′-DMA; and 4,6,4′-trimethylangelicin, TMA). The drugs alone and UVA radiation alone showed no erect on the HIV promoter. However, when the cells were incubated with the furocoumarins at 0.1–40 μg/mL and then irradiated. the HIV promoter was activated in distinct fluence ranges, i.e. (1) no promoter activity was discernible at low fluences (e.g. at 0.1 μg/mL of 8-MOP up to 100 kJ/m²), (2) as the fluence was increased, the promoter activity increased to reach a maximum (10–50-fold with respect to the unexposcd samples), and (3) as the fluence was further increased, the promoter activity decreased. Similar (although shifted on the fluence scale) pattcrns were observed with either > 340-nm UVA radiation or with UVA radiation contaminated with a small amount of UVB radiation (typical for PUVA lamps). The effective fluences were inversely related to the drug concentration. Experiments with 5-MOP and 8-MOP indicated reciprocity of the drug concentration and radiation hence. The HIV promoter response patterns were similar for monofunctional angelicins and bifunctional psoralens. This indicated that the furocoumarin-DNA crosslinks are not a prerequisite for the promoter activation and that the monoadducts suffice to elicit the HIV promoter response. The HIV promoter-activating effectiveness of diKcrent drugs correlated with their photosensitizing potential. Thus, among psoralens the effectiveness order was AMT >. 5-MOP >8-MOP, and among angelicins: TMA > 6,4′-DMA > 4,5′-DMA > angelicin. The ektiveness did not vary substantially for 5-MOP, 8-MOP, 4,5′-DMA, and 6,4′-DMA. The combined drug and UVA radiation doses were higher than those that elicit cellular responses or those that may be received by the human white blood cells during cxtracorporeal PUVA therapy (photopheresis).     

Brocaenols A-C: novel polyketides from a marine derived Penicillium brocae

Chemical investigation of a Penicillium brocae, obtained from a tissue sample of a Fijian Zyzyya sp. sponge, yielded two known diketopiperazines and three novel cytotoxic polyketides, brocaenols A-C. The brocaenols contain an unusual enolized oxepine lactone ring system that to the best of our knowledge is unprecedented in the literature. The structures were elucidated by using 2D-NMR methods including an INADEQUATE experiment. The absolute stereochemistry of brocaenol A was established by using a modified Mosher method. The taxonomy of the producing fungus was elucidated by using both morphological and rDNA sequence analysis.