The Conformation of Cycloartenol Investigated by NMR and Molecular Mechanics

Cycloartenol ( 4 ), a natural plant sterol, was shown to be an effective membrane reinforcer; this was attributed to its conformation. We now present a conformational analysis of 4 by molecular modeling and NMR. Molecular modeling suggests that two conformations I and II coexist, differing mainly at the level of ring C, and of nearly equal energy, I and II each having ring A and B in a chair and half-chair conformation, respectively, with ring C 1,3-diplanar in I (solid-state structure as determined by X-ray crystallography) and in chair conformation in II . A complete assignment of the ¹H- and ¹³C-NMR spectra of 4 and the entire coupling network in rings A and B is determined by various modern NMR techniques. The conformation of rings A and B thus determined is in agreement with conformations I and II . Low-temperature NMR experiments show a fast equilibrium between two conformations, presumably I and II . It is concluded, therefore, that the cyclopropane ring of 4 produces a flexibility at the level of ring C which may be important for the membrane properties.     

Microscopic understanding of preferential exclusion of compatible solute ectoine: direct interaction and hydration alteration

Ectoine, a zwitterionic compatible solute (CS), acts as an effective stabilizer of protein function. Using molecular dynamics simulation, solvent spatial distributions around both met-enkephalin (M-Enk) and chymotrypsin inhibitor 2 (CI2) were investigated at the molecular level in ectoine aqueous solution. An unexpected finding was that ectoine exhibits preferential binding, as an overall tendency, around both peptides. However, with the aid of the surficial Kirkwood-Buff parameter, it was clearly shown that the preferential exclusion of ectoine from the peptide surface was weaker in the smaller M-Enk than in the larger CI2. It is concluded that a denser and more structured hydration layer, such as that developed on the surface of CI2, is an important factor in the exclusion of ectoine.     

Design of a Hyperpolarized Molecular Probe for Detection of Aminopeptidase N Activity

Aminopeptidase N (APN) is an important enzyme that is involved in tumor angiogenesis. Detection of APN activity can thus lead to early diagnosis and elucidation of tumor development. Although some molecular probes for APN have been developed, the detection of APN activity in opaque biological samples remains a challenge. To this end, we designed a hyperpolarized NMR probe [1‐¹³C]Ala‐NH₂ which satisfies the prerequisites for APN detection, namely, sufficient retention of the hyperpolarized state, a high reactivity to APN, and an APN‐induced chemical shift change. The [1‐¹³C]Ala‐NH₂ probe allowed sensitive detection of APN activity using ¹³C NMR spectroscopy.     

An iminocoumarin-Cu(II) ensemble-based chemodosimeter toward thiols

An 'ensemble'-based fluoregenic chemodosimeter 1-Cu(II) for detection of thiols is reported. Complex 1-Cu(II) sensitively senses thiols followed by hydrolysis to give a marked fluorescence enhancement over other amino acids at pH 7.4 under aqueous media. Confocal microscopic imaging of complex 1-Cu(II) is also herewith demonstrated for cellular thiol detection in HepG2 cells.     

Simultaneous capillary electrophoretic separation and detection of P(V) and As(V) As heteropoly-blue complexes

A capillary electrophoretic (CE) method was developed for the simultaneous determination of P(V) and As(V). A Mo(VI)-ascorbic acid reagent reacted with a mixture of trace amounts of P(V) and As(V) to form the corresponding heteropoly-blue complexes in 0.05 M acetate buffer (pH 3.5). When 0.05 M malonate buffer was used as a migration buffer, the peaks due to their migrations were well separated in the electropherogram, and the pre-column complex-formation reaction was applied to the simultaneous CE determination of P(V) and As(V) with direct UV detection at 220 nm. With the proposed method, the calibration curves were linear in the concentration range of 5 x 10(-7) - 1 x 10(-4) M, with a detection limit of 1 x 10(-7) M (a signal-to-noise ratio of 3). Interference from foreign ions was also discussed.     

Enhancement of visibility of fringes and exposure time for moiré topography

The aperture filtering of lenses for the purpose of moiré topography is described. By replacing the circular iris of a lens with a rectangular one whose long side is parallel with the bars of the grating, both the visibility of the fringes and the exposure condition are greatly enhanced. Using this technique, it becomes possible to take pictures of moiré fringes on a moving, living human body.