Natural abundance 13C - 13C coupling constants observed via double quantum coherence. Structural elucidation by the one- and the two-dimensional NMR experiements of velloziolone,a new seco-diterpene.

With the help of Natural Abundance ¹³C - ¹³C Coupling Constants, observed via double quantum coherence, the structural determination of VELLOZIOLONE (1), a new diterpene, has been carried out.     

15N-NMR spectroscopy. III. Neighboring residue effects in sequence polymers containing glycylglycine units

The tripeptides Phe-Gly-Gly, β-Ala-Gly-Gly, and ?-Aca-Gly-Gly as well as the peptide derivatives δ-isothiocyanatovaleroyl-Gly-Gly and ?-isothiocyanatocaproyl-Gly-Gly were synthesized by using known methods so that the peptide nitrogen between the two glycyl residues was isotopically enriched in ¹⁵N to a level of 0.8–0.9%. These monomer units were then used to produce the sequence polymers (Phe-Gly-Gly)_n, (β-Ala-Gly-Gly)_n, (δ-Ava-Gly-Gly)_n, and (?-Aca-Gly-Gly)_n. The 18.24 MHz ¹⁵N-NMR spectra of the oligo- and polypeptides were obtained by using trifluoroacetic acid as solvent, since the solutions have relatively low viscosity and exhibit a strong negative nuclear Overhauser enhancement of the ¹⁵N signals. For comparison, ¹⁵N-NMR spectra of the homopolymers (Gly)_n, (β-Ala)_n, (γ-Abu)_n, (δ-Ava)_n, and (?-Aca)_n were also recorded. The ¹⁵N signals from the ω-aminoacyl residues in the sequence polymers appear up to 11 ppm upfield of the signals observed for the homopolyamides. The ¹⁵N signals from the two glycyl residues are separated by 3–7 ppm. Comparison with the ¹³C-NMR spectra of the same polymers indicates that ¹⁵N-NMR is better suited for the characterization and sequence analysis of these types of polymers.     

Separation of potential flavoring compounds by high-performance liquid chromatography

High-performance liquid chromatography separated successively and quantitatively the food flavoring agents pyrimidines, purines and nucleosides, followed by nucleotides, then by polyphenols and finally by pyrazines with a reversed-phase octadecylsilica (μBondapak C₁₈) column and various proportions of methanol, water, acetic acid and tetrabutylammonium phosphate (PIC A). The polar solvent (solvent A) was water—acetic acid—PIC A (97.5:1.5:1.0) and the relatively non-polar solvent (solvent B) was methanol—acetic acid—PIC A (97.5:1.5:1.0). Purines, pyrimidines, and nucleosides were eluted with solvent A. Nucleotides were eluted with a mixture of solvents A and B (9:1). Polyphenols were separated with a gradient starting at 10% solvent B and finishing at 25% solvent B, and finally the pyrazines were removed successively from the column with a gradient starting at 25% solvent B and finishing at 45% solvent B. The resolution and reproducibility were excellent for more than 50 compounds. By this method beverages could be analyzed directly, without solvent extraction, for flavoring compounds.     

The conformation of 4-t-butylcycloheptanone

The 400 MHz ¹H NMR spectra of two deuterated derivatives of 4-t-butylcycloheptanone ($\text{2}$ and $\text{3}$) provided ²J_HH values for the α-methylene protons on each side of the carbonyl group. The interpretation of their magnitude shows clearly that the carbonyl group is located at position 1 of the twist-chair conformation while the t-butyl group is located at position 4e.     

Cyclization of methyl 6,7-epoxycitronellate to methylcyclopentane derivatives : Alkoxide induced conversion of γ-lactones to γ,δ-unsaturated acids

The reaction of sodium hydride or potassium t-butoxide with methyl epoxycitronellate (1) in dimethylformamide affords a mixture of cis,cis-puleganolide (2) and cis,trans-puleganolide (3) in high yield. When the cyclization is conducted at 110°, the isomeric 2-isopropenyl-5-methylcyclopentanecarboxylic acids (8a–d) become the major products. It is demonstrated that γ-lactones undergo alkoxide-induced elimination to afford γ,δ-unsaturated acids.     

Synthesis of a tetraazacyclotetradecadiene and a pentaazacyclotetradecatriene

Useful procedures for preparing a novel tetraazacyclotetradecadiene and a pentaazacyclotetradecatriene are reported. J. Heterocyclic Chem., 14, 1097 (1977)     

Factors affecting the combustion toxicity of polymeric materials

Fire gas toxicity is an essential component of any fire hazard analysis. However, fire toxicity, like flammability, is both scenario and material dependent. A number of different methods exist to assess the fire toxicity, but many of them fail to relate this to a particular fire scenario. Sample thickness alone, in a closed box test such as the NBS Smoke Chamber, is shown to change the fire scenario from well-ventilated to under-ventilated. Data from two flow-through tests, the static tube furnace (NF X 70-100) and the steady state tube furnace (the Purser furnace, BS 7990 and ISO TS 19700) show that there are different patterns of behaviour for different polymers (LDPE, polystyrene, rigid PVC and Nylon 6.6). The predicted toxicities show variation of up to two orders of magnitude with change in fire scenario. They also show change of at least one order of magnitude for different materials in the same fire scenario. Finally, they show that in many cases CO, which is often assumed to be the most, or even the only toxicologically significant fire gas, is of less importance than either HCl, or HCN, when present, and in some cases less important than organo-irritants. Nylon 6.6 shows the highest predicted toxicity, the greatest scenario dependence, and the least sensitivity to different apparatuses, while polystyrene shows the highest sensitivity to the different apparatuses, but the lowest to different fire scenarios. PVC shows high toxicity, mostly due to HCl in the fire effluent, under all fire conditions, and LDPE shows a more progressive increase in toxicity from well-ventilated flaming to both smouldering and under-ventilated flaming.     

Porphyrin bleaching and PDT-induced spectral changes are irradiance dependent in ALA-sensitized normal rat skin in vivo

Photobleaching kinetics of aminolevulinic acid-induced protoporphyrin IX (PpIX) were measured in the normal skin of rats in vivo using a technique in which fluorescence spectra were corrected for the effects of tissue optical properties in the emission spectral window through division by reflectance spectra acquired in the same geometry and wavelength interval and for changes in excitation wavelength optical properties using diffuse reflectance measured at the excitation wavelength. Loss of PpIX fluorescence was monitored during photodynamic therapy (PDT) performed using 514 nm irradiation. Bleaching in response to irradiances of 1, 5 and 100 mW cm-2 was evaluated. The results demonstrate an irradiance dependence to the rate of photobleaching vs irradiation fluence, with the lowest irradiance leading to the most efficient loss of fluorescence. The kinetics for the accumulation of the primary fluorescent photoproduct of PpIX also exhibit an irradiance dependence, with greater peak accumulation at higher irradiance. These findings are consistent with a predominantly oxygen-dependent photobleaching reaction mechanism in vivo, and they provide spectroscopic evidence that PDT delivered at low irradiance deposits greater photodynamic dose for a given irradiation fluence. We also observed an irradiance dependence to the appearance of a fluorescence emission peak near 620 nm, consistent with accumulation of uroporphyrin/coproporphyrin in response to mitochondrial damage.