The effect of a precursor on growth of forward masking

This study examined the effect of an on-frequency precursor on growth-of-masking (GOM) functions measured using an off-frequency masker. The signal was a 6-ms, 4-kHz tone. A GOM function was measured using a 40-ms, 2.8-kHz tone (the off-frequency masker). GOM functions were then measured with an on-frequency, fixed level precursor presented before the off-frequency masker. The precursor was 50 or 60 dB SPL, and 160 ms in duration. For the 60-dB SPL precursor, a 40-ms duration was also used. Two-line functions were fit to the GOM data to estimate the basilar membrane input-output function. The precursors reduced the gain of the input-output function, and this decrease was graded with precursor level. Both precursor durations had the same effect on gain. Changes in masking following a precursor were larger than would be predicted by additivity of masking. The observed decrease in gain may be consistent with activation of the medial olivocochlear reflex by the precursor.     

UV-DNA Damage in Mouse and Human Cells Induces the Expression of Tumor Necrosis Factor α

Ultraviolet light induces the expression of tumor necrosis factor α (TNFα) in many mammalian cells. We have examined the signal for this induction in a human DNA repair-deficient cell line carrying a transgene composed of the murine TNF regulatory sequences fused to the chloramphenicol acetyltransferase (CAT) structural gene. When compared by fluence, UVC was a more efficient inducer of CAT than was UVB, but they were equivalent inducers when compared by the frequency of cyclobutyl pyrimidine dimers produced by each source. Further, treatment of UV-irradiated cells with the prokaryotic DNA repair enzyme T4 endonuclease V in-creased the level of repair of dimers and concomitantly reduced CAT gene expression. Membrane-bound TNFα expression was increased by UV and reduced by repair of dimers. Finally, in the TNFcat transgene system, DNA damage directly to the cell with the transgene was required as cocultivation of unirradiated TNFcat cells with UV-irradiated cells did not increase CAT activity. These results show that DNA damage is a signal for the induction of TNFa gene expression in mouse and human cells.     

Trimethyl phosphate-acetylene interaction: a matrix-isolation infrared and ab initio study

Trimethyl phosphate (TMP) and acetylene were codeposited in nitrogen and argon matrices and adducts of these species were identified using infrared spectroscopy. Formation of the adducts was evidenced by shifts in the vibrational frequencies of the modes involving the TMP and acetylene submolecules. The structures of these adducts, energies and the vibrational frequencies were computed at the HF/6-31G** level. Both the experimental and computational studies indicated that two types of TMP-acetylene complexes were formed; one in which the hydrogen in acetylene was bonded to the phosphoryl oxygen and another in which the bonding was at the alkoxy oxygen of the phosphate. In addition to the primary hydrogen bonded interaction at the phosphoryl oxygen, this complex, also appeared to be stablilized by a secondary and weaker interaction involving a methyl hydrogen in TMP and the pi cloud in acetylene--a case of a H...pi interaction. The computed vibrational frequencies in the adducts agreed well with the observed frequencies for the modes involving the TMP submolecule, while the agreement was relatively poor for the modes involving the acetylene submolecule. The stabilization energies of these adducts, corrected for both zero-point energies and basis set superposition errors, were approximately 3 kcal/mol for the phosphoryl complex and, approximately 1 kcal/mol for the alkoxy complex.     

Delineation of the chemical pathways underlying nitric oxide-induced homologous recombination in mammalian cells

Inflammation is an important risk factor for cancer. During inflammation, macrophages secrete nitric oxide (NO*), which reacts with superoxide or oxygen to create ONOO- or N2O3, respectively. Although homologous recombination causes DNA sequence rearrangements that promote cancer, little was known about the ability of ONOO- and N2O3 to induce recombination in mammalian cells. Here, we show that ONOO- is a potent inducer of homologous recombination at an integrated direct repeat substrate, whereas N2O3 is relatively weakly recombinogenic. Furthermore, on a per lesion basis, ONOO(-)-induced oxidative base lesions and single-strand breaks are significantly more recombinogenic than N2O3-induced base deamination products, which did not induce detectable recombination between plasmids. Similar results were observed in mammalian cells from two different species. These results suggest that ONOO(-)-induced recombination may be an important mechanism underlying inflammation-induced cancer.     

Silica tungstic acid (STA) as a highly efficient and reusable catalyst for the synthesis of benzoxanthenes under solvent-free conditions in ultrasonication

An environmentally benign, ultrasound-promoted synthesis of biologically active benzoxanthene derivatives has been developed by silica-supported tungstic acid as an efficient catalyst under solvent-free conditions. The major advantages of the present protocol are operational simplicity, use of an inexpensive catalyst, bypassing the chromatographic purification, good yields, and short reaction times. The catalyst could be reused at least five consecutive cycles, without loss of its catalytic activity.     

Oxa bowls: synthesis of new tetraoxa-cages and their C-H.O-mediated solid-state architecture

We have envisioned a new family of oxa-bowls, and a general approach to these entities has been proposed through polycyclic frameworks having two converging olefinic double bonds. Ozonolysis of such molecules was envisaged to give all-cis-tetraaldehyde functionality, which could undergo intramolecular cascade acetalization to oxa-bowls having C(2)(v )()symmetry. Homohypostrophene 16a and its functionalized derivative 16b and hypostrophene 17 on ozonolysis furnished the oxa-cages 22a, 22b, and 23, respectively. Single-crystal X-ray analysis of 22a and 23 showed an interesting network of C-H.O interactions mainly involving the nonacidic cycloalkane hydrogen atoms. The molecule 22a exhibits an interesting tapelike C-H.O hydrogen bonding motif in its crystal structure. On the other hand, the molecule 23 revealed an undulated ribbonlike C-H. O motif. The "chain of rings" pattern of C-H.O interactions in 23 has been observed for the first time in the solid-state structure of oxa-bowls.     

Recent topics of radical-based carbon-carbon bond formations

Radical reactions have been a fascinating arena in organic chemistry for decades and the rapid progress in this field is the topic of this review. Generation of radicals through sustainable catalysis using photoredox catalysts and iron based catalysts have significantly expanded the scope of radical reactions for carbon–carbon and carbon-heteroatom bond formations in recent years. Selective transformations using silver salts and other single electron transfer oxidants have also played significant roles. Cascade reactions based on radical intermediates have even widened the potential of radical reactions for carbocyclic and heterocyclic constructions. The recent advances (2014–2017) in radical based methods for CC bond formations are discussed in this digest review.     

Dinuclear trivalent chromium,manganese, iron and cobalt complexes bridged by aromatic diamines

Summary Trivalent chromium, manganese, iron and cobalt salts react withm-phenylenediamine and acetylacetone to give complexes of the type [M(C₁₆H₁₈N₂O₂)X]: X = Cl, Br, NO₃ or NCS for M = chromium(III) and iron(III); X = Cl, Br, OAc or NCS for manganese(III); and X = OH for cobalt(III). Conductance measurements show the complexes to be nonelectrolytes. Molecular weights determined cryoscopically, show the iron complexes to be dinuclear. Magnetic measurements above 85 K reveal the presence of slight antiferromagnetic interactions. The complexes are dimeric five-coordinate square-pyramidal withm-phenylenediamine residues acting as bridges. The electronic spectra are interpreted in terms of the Normalised Spherical Harmonic Hamiltonian Theory and the DT/DQ values which indicate that chromium complexes are slightly distorted, whereas those of manganese are severely distorted.