Oxygen-17 hyperfine structures in the pure rotational spectra of SrO, SnO, BaO, HfO and ThO

Hyperfine structures arising from the couplings of the nuclear spin angular momentum of (17)O (I = 5/2) with the end over end rotation of several metal-containing diatomic monoxides have been observed using a Fourier transform microwave spectrometer. The molecules have been produced by reacting (17)O(2) with laser ablated metal atoms. The oxygen-17 nuclear quadrupole coupling constants have been determined for the title molecules and are interpreted in terms of a simple Townes-Dailey model. Also, the oxygen-17 nuclear spin-rotation constants have been determined and used to calculate the oxygen-17 shieldings for each molecule.     

Complete (1)H and (13)C assignments of the four major saponins from Dioscorea villosa (wild yam)

Complete (1)H and (13)C spectral assignments for the four major steroidal saponins isolated by methanolic extraction of the roots of Dioscorea villosa, collected in North Carolina, United States (in summer and autumn), are presented in this paper. The structures were determined by a combination of (1)H, (13)C and 2D NMR techniques and were found to be ((3beta,25R)-26-(beta-D-glucopyranosyloxy)-22-methoxyfurost-5-en-3-yl-O-beta-D-glucopyranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 4)-O-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (1) (or methyl parvifloside), ((3beta,25R)-26-(beta-D-glucopyranosyloxy)-22 methoxyfurost-5-en-3-yl-O-alpha-L-rhamnopyranosyl-(1 --> 2)-O-[beta-D-gluco- pyranosyl-(1 --> 4)]-beta-D-glucopyranoside (2) (or methyl protodeltonin), (3beta,25R)-spirost-5-en-3-yl-O-beta-D-glucopy ranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 4)-O-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (3) (or Zingiberensis saponin I) and (3beta,25R)-spirost-5-en-3-yl-O-alpha-L-rhamnopyranosyl-(1 --> 2)-O-[beta-Ds-glucopyranosyl -(1 --> 4)]-beta-D-glucopyranoside (4) (or deltonin).     

Analysis of isotope ratios in vitamin K1 (phylloquinone) from human plasma by gas chromatography/mass spectrometry

Vitamin K(1) is a fat-soluble vitamin required for the gamma-carboxylation of vitamin K-dependent proteins. Recent work has suggested an important role for vitamin K(1) in bone health beyond its more established function in the control and regulation of blood coagulation. However, current UK recommended intakes do not reflect this recent evidence. The use of stable isotopes provides a powerful tool to investigate vitamin K kinetics, turnover and absorption in man, although published methods have reported difficulties in the extraction and analysis of isotope ratios of vitamin K in human plasma. In this paper, we report a new methodology for the extraction and measurement of isotope ratios in vitamin K(1). Sample clean-up is achieved with liquid-liquid extraction, enzyme hydrolysis with lipase and cholesterol esterase, and solid-phase extraction. Isotopic analysis of the pentafluoropropionyl derivative of vitamin K(1) is performed by gas chromatography/mass spectrometry (GC/MS). The limit of quantitation is equivalent to at least 0.3 nmol/L and the method is demonstrated to be linear over a range of enrichments. This method provides a robust alternative to previous work requiring the use of semi-preparative high-performance liquid chromatography (HPLC).     

Liposome-Based Optochemical Nanosensors

 This paper describes the optochemical pH and oxygen sensing properties of dye-encapsulating and fluorescently labeled nano-sized unilamellar liposomes. To prepare the oxygen sensitive liposomes a lipid mixture consisting of dimyristoylphospatidylcholine, cholesterol, and dihexadecyl phosphate (molar ratio 5:4:1) all dissolved in dry isopropyl alcohol is injected into a sensing dye solution. The mixture is then sonicated with a liposome maker to form dye-encapsulating liposomes. A lipid mixture consisting of dimyristoylphospatidylcholine, N-(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (fluorescein DHPE), cholesterol, and dihexadecyl phosphate (molar ratio 20:1:16:4) is used to prepare the pH sensitive liposomes by the same sonication technique. Fluorescein labeled DHPE phospholipids are combined with DMPC phospholipids in a 1:20 ratio to incorporate the sensing dye directly into the bilayer membrane, virtually eliminating any instability due to dye leakage. Oxygen sensing liposomes are created by encapsulating the oxygen sensitive ruthenium tris(1,10)-phenanthroline complex [Ru(phen)₃]. The dye is believed to exist both in free solution within the liposome, and as an adherent on the inner membrane of the liposome. High uniformity of the liposomes is realized by extruding them back and forth through a 100 nm pore-size polycarbonate membrane. TEM images of the liposomes, stained with uranyl acetate, show that the liposomes are unilamellar, spherical in shape, maintain high structural integrity, and average 70 nm in diameter. The liposomes show high stability with respect to dye leaking at room temperature for 8 days, and high photostability when exposed to the excitation light. Individual liposomes are used to monitor the pH and oxygen level in their vicinity during the enzymatic oxidation of glucose by the enzyme glucose oxidase. The newly prepared environmentally sensitive liposomes can be applied for non-invasive pH and oxygen determination in tissues and single biological cells. Received June 8, 1998. Revision November 10, 1998.     

Characterization of the aggregates of N-alkyl-N-methylpyrrolidinium bromide surfactants in aqueous solution

We have characterized a new class of surfactant molecules using fluorescence spectroscopic and light-scattering techniques. Our results suggest that this homologous series of N-alkyl-N-methlypyrrolidinium bromide (CnMPB) surfactants with n = 10, 12, 14, 16, and 18 represents a bridge between the well-characterized alkyltrimethylammonium bromide (CnTAB) and dialkyldimethylammonium bromide (di-CnDAB) surfactant series. For the smaller members of the CnMPB series with n = 10, 12, and 14, our results are consistent with the formation of spherical micelles as the surfactant concentration is increased. With increasing alkyl chain length, we observe that the critical micelle concentration decreases and the aggregation number increases, typical of single-tail surfactants. For C16MPB, the formation of micelles at dilute concentrations (0.10 mM) is likely, followed by the coexistence of micelles and small unilamellar vesicles at higher concentrations up to 0.82 mM where only vesicles are present. For C18MPB, our data are consistent with the formation of vesicles only. We demonstrate in this study that the combination of spectroscopic and light-scattering methods is a powerful approach to reveal aspects of aggregate structure and morphology in aqueous CnMPB surfactant systems. In particular, the sensitivity of the fluorescence probe prodan to the polarity of its microenvironment enables the rich complexity of surfactant aggregates exhibited by this series of amphiphilic molecules to be detected.     

Stress Inhomogeneity in Powder Specimens Tested in the Jenike Shear Cell: Myth or Fact?

In the mechanical characterization of powders using the direct shear testers such as the Jenike shear cell, the existence of a uniform or well‐defined stress field in a powder specimen is assumed. This assumption has not been subjected to any serious scrutiny in the literature. In this study, the normal stress variation in a silica powder was locally determined by locating a pressure‐sensitive TekScan pad at the bottom section of a Jenike shear cell. A computer simulation of the consolidation and pre‐shearing stages of the Jenike test procedure was performed using the Discrete Element Method (DEM). The paper presents both experimental and computational evidence for the existence of a complex stress field in the powder specimen, thus clearly invalidating the long‐standing stress homogeneity assumption in the direct shear testing of powders. The implications of the stress inhomogeneity in terms of the accuracy of the material properties extracted from the Jenike test are also presented.     

Stability of DNA containing a structural water mimic in an A-T rich sequence

We describe here the synthesis and properties of A-T rich DNA containing covalently bound water mimics located in the DNA minor groove.     

Dissecting alkynes: full cleavage of polarized C≡C moiety via sequential bis-Michael addition/retro-Mannich cascade

The reaction of diaryl ketoalkynes with 1,2-diamino ethane leads to the full scission of the triple bond with the formation of acetophenone and imidazoline fragments. In this transformation, one of the alkyne carbons undergoes formal reduction with the formation of three C-H bonds, whereas the other carbon undergoes formal oxidation via the formation of three C-N bonds (one π and two σ). Computational analysis confirmed that the key fragmentation step proceeds via a six-membered TS in a concerted manner. Both amines are involved in the fragmentation: the N-H moiety of one amine transfers a proton to the developing negative charge at the enolate oxygen, while the other amine provides direct stereoelectronic assistance to the C-C bond cleavage via a hyperconjugative n(N) → σ*(C-C) interaction.     

Evaluation of Spinning Cone Column Distillation as a Strategy for Remediation of Smoke Taint in Juice and Wine

Where vineyard exposure to bushfire smoke cannot be avoided or prevented, grape and wine producers need strategies to transform smoke-affected juice and wine into saleable product. This study evaluated the potential for spinning cone column (SCC) distillation to be used for the remediation of ‘smoke taint’. Compositional analysis of ‘stripped wine’ and condensate collected during SCC treatment of two smoke-tainted red wines indicated limited, if any, removal of volatile phenols, while their non-volatile glycoconjugates were concentrated due to water and ethanol removal. Together with the removal of desirable volatile aroma compounds, this enhanced the perception of smoke-related sensory attributes; i.e., smoke taint intensified. Stripped wines also became increasingly sour and salty as ethanol (and water) were progressively removed. A preliminary juice remediation trial yielded more promising results. While clarification, heating, evaporation, deionization and fermentation processes applied to smoke-tainted white juice gave ≤3 µg/L changes in volatile phenol concentrations, SCC distillation of smoke-tainted red juice increased the volatile phenol content of condensate (in some cases by 3- to 4-fold). Deionization of the resulting condensate removed 75 µg/L of volatile phenols, but fermentation of reconstituted juice increased volatile phenol concentrations again, presumably due to yeast metabolism of glycoconjugate precursors. Research findings suggest SCC distillation alone cannot remediate smoke taint, but used in combination with adsorbents, SCC may offer a novel remediation strategy, especially for tainted juice.