Dissociation quotients of succinic acid in aqueous sodium chloride media to 225°C

The first and second molal dissociation quotients of succinic acid were measured potentiometrically with a hydrogen-electrode, concentration cell. These measurements were carried out from 0 to 225°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The dissociation quotients from this and two other studies were combined and treated with empirical equations to yield the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: log K_1a=–4.210±0.003; H _1a ⁰ =2.9±0.2 kJ-mol^–1; S _1a ⁰ =–71±1 J-mol^–1-K^–1; and C _p1a ⁰ =–98±3 J-mol^–1-K^–1; and for the second acid dissociation equilibrium at 25°C: log K_2a=–5.638±0.001; H _2a ⁰ = –0.5±0.1 kJ-mol^–1; S _2a ⁰ =–109.7±0.4 J-mol^–1-K^–1; and C _p2a ⁰ = –215±8 J-mol^–1-K^–1.     

Detection of unexploded ordnance by PGNAA based borehole-logging

The performance of a borehole-logging system, based on prompt-gamma-neutron-activation-analysis (PGNAA), for explosive detection was studied by Monte-Carlo simulations. The prompt gamma of nitrogen, which is a constituent of common explosive, was used to identify the unexploded ordnance (UXO). Our results show that the minimum counting time depends on the soil moisture, the cladding thickness and the explosive composition. In conjunction with the standard detection by magnetometry, the PGNAA is a promising analytical technique for definitive identification of deep buried UXOs.     

Influence of dietary menhaden oil upon carcinogenesis and various cutaneous responses to ultraviolet radiation

Abstract Recent reports suggest that eicosapentaenoic acid (EPA) inhibits growth of transplanted tumors and the formation of various chemically induced cancers in animals. Menhaden oil is a source of polyunsaturated lipid with a high content of EPA, an omega-3 fatty acid. We sought to explore the effects of menhaden oil on photocarcinogenesis by employing the hairless mouse/UV-carcinogenesis model. Five groups of 40 SKH-Hr-1 mice received (a) a semipurined equicaloric diet containing either 0.75% corn oil, 4% corn oil. 4% menhaden oil or 12% menhaden oil and (b) an escalating regimen of UV radiation to a cumulative dose of 70 J/cm². Additional animals were employed to further examine the role of menhaden oil in acute cutaneous responses to UV, i.e., erythema, edema, and ornithine decarboxylase (ODC) induction. After a 2-week feeding period UV-induced ODC activity in mice receiving 12 or 20% menhaden oil was 3 to 13-fold lower than that of corn oil fed animals. Further studies showed that edema was also markedly decreased. Animals receiving menhaden oil required twice the level of irradiance to evoke a comparable erythema as that which occurred in corn oil fed animals. Menhaden oil exerted significant influence upon carcinogenic expression, as manifested in significantly longer tumor latent periods and lower tumor multiplicities when compared to corn oil fed animals. Although the mechanism(s) of these menhaden oil effects remains unknown, it is clear that this unique lipid has a pronounced influence upon cutaneous photoresponses. 15th Annual Meeting of the American Society for Photobiology, Bal Harbor, FL, June, 1987.     

Total Synthesis and Structural Revision of the Antibiotic Tetrapeptide GE81112A

The total synthesis of the naturally occurring antibiotic GE81112A, a densely functionalized tetrapeptide, is reported. Comparison of spectral data with those of the natural product and the lack of biological activity of the synthesized compound led us to revise the published configuration of the 3‐hydroxypipecolic acid moiety. This hypothesis was fully validated by the synthesis of the corresponding epimer.     

Time-dependent photoionization of azulene: competition between ionization and relaxation in highly excited states

Pump-probe photoionization has been used to map the relaxation processes taking place from highly vibrationally excited levels of the S(2) state of azulene, populated directly or via internal conversion from the S(4) state. Photoelectron spectra obtained by 1+2(') two-color time-resolved photoelectron imaging are invariant (apart from in intensity) to the pump-probe time delay and to the pump wavelength. This reveals a photoionization process which is driven by an unstable electronic state (e.g., doubly excited state) lying below the ionization potential. This state is postulated to be populated by a probe transition from S(2) and to rapidly relax via an Auger-like process onto highly vibrationally excited Rydberg states. This accounts for the time invariance of the photoelectron spectrum. The intensity of the photoelectron spectrum is proportional to the population in S(2). An exponential energy gap law is used to describe the internal conversion rate from S(2) to S(0). The vibronic coupling strength is found to be larger than 60+/-5 microeV.