Properties of molten carboxylates part 5. A quantitative differential thermal analysis study of mesophase formation in the sytems lead(II)dodecanoate/lead(II) oxide and lead(II)dodecanoate/hendecane

Measurements have been made of the temperatures and enthalpy changes of phase transitions in the systems lead dodecanoate/lead oxide and lead dodecanoate/hendecane. The data have been discussed in terms of the R theory of amphiphylic mesophases. The concepts of the R theory are shown to be useful in the interpretation of phase transitions in molten carboxylate systems.     

Epoxides,cyclic sulfites,and sulfate from natural pentacyclic triterpenoids: theoretical calculations and chemical transformations

Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical (13)C and (1)H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and (3)J(H,H) coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and alpha- or beta-epoxide configurations together with 4-aza or 3-aza structures.     

Properties of molten carboxylates part 6. A quantiative differential thermal analysis study of phase transitions in some zinc and cadmium carboxylates

Quantitative DTA results are presented for the phase changes in some cadmium and zinc n-alkanoates. Cadmium carboxylates form liquid crystal phases. The total entropy of the solid-to-liquid transition is small indicating a high degree of aggregation in the isotropic liquid. The phases previously reported by Skoulios are shown to be due to the presence of basic carboxylates. The zinc carboxylates have solid—solid transformations but do not form liquid crystal phases. The entropies of fusion are of the same order as those in the lead salts showing only a small degree of aggregation in the liquid.     

Protection from inflammation, immunosuppression and carcinogenesis induced by UV radiation in mice by topical Pycnogenol

Pycnogenol is a standardized extract of the bark of the French maritime pine, Pinus pinaster Ait., that has multiple biological effects, including antioxidant, anti-inflammatory and anticarcinogenic properties. This study describes the effect of topical application of lotions containing Pycnogenol to Skh:hr hairless mice undergoing minimally inflammatory daily exposures to solar-simulated UV radiation (SSUV). We report that concentrations of Pycnogenol of 0.05-0.2% applied to the irradiated dorsal skin immediately after exposure resulted in dose-dependent reduction of the inflammatory sunburn reaction, measured as its edema component. When mice received three consecutive daily exposures of minimally edematous SSUV, their ability to raise a contact hypersensitivity (CHS) reaction was suppressed by 54%. Pycnogenol lotions applied postirradiation reduced this immunosuppression to 22% (0.05% Pycnogenol) and 13% (0.1% Pycnogenol). Furthermore, when CHS was suppressed by 71% with exogenous treatment with cis-urocanic acid, the putative epidermal mediator of photoimmunosuppression, 0.2% Pycnogenol lotion reduced the immunosuppression to 18%. Chronic exposure to SSUV on 5 days/week for 10 weeks induced skin tumors from 11 weeks in both control mice and in mice receiving daily applications of 0.05% Pycnogenol, but tumor appearance was significantly delayed until 20 weeks in mice receiving 0.2% Pycnogenol. Furthermore, whereas 100% of control mice had at least one tumor by 30 weeks, and mice treated with 0.05% Pycnogenol by 33 weeks, the maximum tumor prevalence in mice treated with 0.2% Pycnogenol was significantly reduced to 85%, with some mice remaining tumor free. Average tumor multiplicity was also significantly reduced by 0.2% Pycnogenol, from 5.2 in control mice to 3.5 at 35 weeks. Thus, topical Pycnogenol offered significant and dose-dependent protection from SSUV-induced acute inflammation, immunosuppression and carcinogenesis, when applied to the skin after daily irradiation. Pycnogenol, therefore, in addition to its recognized health benefits in other organs, appears to have potential in providing photoprotection for humans in a complementary role with sunscreens, having demonstrable activity when applied to the skin after, rather than before, UV exposure.     

Anomalous thermal hysteresis in the SmC* phase of 10FHBBBM7*, revealed by dielectric measurements

The SmC* phase of (R)-4-(1-methylheptyloxycarbonyl)phenyl 4'-(4-decyloxy-3-fluorobenzoyloxy)-benzoate, 10FHBBBM7*, shows an anomalous thermal hysteresis that is reflected in the values of the measured dielectric constant. When the cooling-heating cycle is repeated, a memory effect occurs. In this work, we present a detailed study and a tentative interpretation of this unusual effect.     

Belated recognition: Lise Meitner's role in the discovery of fission

Although physicist LiseMeitner is known for the first theoretical explanation of nuclear fission, the discovery itself is generally attributed only to her co-workers OttoHahn and FritzStrassmann. In fact, however,Meitner was essential to the discovery at every phase: she brought the uranium investigation to Berlin, led the Berlin group for four years, and, even after fleeing Germany, provided the critical direction which culminated in the identification of barium in December 1938. Recognition of LiseMeitner's contributions remedies a significant historical omission, and places the discovery itself in its proper scientific context.     

The Politics of Memory: Otto Hahn and the Third Reich

As President of the Kaiser Wilhelm Society and its successor, the Max Planck Society, from 1946 until 1960, Otto Hahn (1879–1968) sought to portray science under the Third Reich as a purely intellectual endeavor untainted by National Socialism. I outline Hahn’s activities from 1933 into the postwar years, focusing on the contrast between his personal stance during the National Socialist period, when he distinguished himself as an upright non-Nazi, and his postwar attitude, which was characterized by suppression and denial of Germany’s recent past. Particular examples include Hahn’s efforts to help Jewish friends; his testimony for colleagues involved in denazification and on trial in Nuremberg; his postwar relationships with émigré colleagues, including Lise Meitner; and his misrepresentation of his wartime work in the Kaiser Wilhelm Institute for Chemistry.     

Properties of molten carboxylates

Data are presented for the heats of phase changes and specific heats for the even chain length lead(II) carboxylates from hexanoate to octadecanoate. Structures are proposed by analogy to the properties of “fused” aqueous ampiphilic mesophases. Optical examination under a polarising microscope suggests the phase sequence

for the dodecanoate and lower chain length soaps. For tetradecanoate, and above, the V₂ phase is absent and the G phase melts directly to the liquid. The chain length dependence of the entropies of the crystal→G and G→V₂ or G→liquid transitions demonstrates that disordering of the hydrocarbon chain is a stepwise process. The entropy of the V₂→liquid transition is consistent with the melting of a globular solid and may indicate an average micelle size of 4 carboxylate molecules. This leads to a model of the isotropic liquid consistent with the viscosity data previously presented².     

The Search for Transuranium Elements and the Discovery of Nuclear Fission

The synthesis of new, artificial elements beyond uranium was at the cutting-edge of physical research in the 1930s, and nearly half a dozen transuranium elements were reported between 1934 and 1938. Nuclear physicists and radiochemists collaborated closely, but each field introduced fundamental assumptions that proved to be false: that nuclear changes would always be small, and that transuranium elements would resemble transition elements chemically. With its surprise ending in the discovery of nuclear fission, the misguided transuranium project can be viewed as an example of the illogical progress of scientific discovery. It is also an example of an interdisciplinary collaboration that was flawed yet crucial, for although chemists and physicists both contributed to the delay in discovering fission, their collaboration was essential in leading them to it in the end.     

Frustrated structure of an anticlinic-like smectic-C phase

We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB₈Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index of the material. The long-period modulation is temperature dependent and disappears for thin sample cells (< 5μm). The short-period modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure proposed for this phase. DB₈Cl presents a structure formed by dimers that can be viewed as flexible bent-core-like molecules, showing similarities with phases found in banana-like systems, but exhibiting a much more complex structure.