Synthesis of an analogue of the polyoxins: X-ray structure of starting carbohydrate and acetal migration accompanying acetolysis

An analogue of the polyoxins has been prepared from 1,5 - di - O - acetyl - 3 - C - (R) - ethoxycarbonylmethyl -5(R),1′(R) - N - formylepimino - 2,3 - O - isopropylidene - β - d - ribofuranose (13). The structure of 13 was determined by X-ray analysis. Intramolecular acetal migrations were observed during acetolysis under acid conditions.     

An economical and preparative orthogonal solid phase synthesis of fluorescein and rhodamine derivatized peptides: FRET substrates for the Staphylococcus aureus sortase SrtA transpeptidase reaction

An economical and preparative-scale orthogonal solid-phase method of incorporating carboxyrhodamine and carboxyfluorescein fluorescence resonance energy transfer (FRET) probes site-specifically into synthetic peptide substrates for the S. aureus Sortase transpeptidase SrtA has been developed.     

Tympanic membrane perforations in cats: configurations of losses with and without ear canal extensions

In cat, a small tympanic membrane (TM) perforation produces a low-frequency loss--in terms of sound pressure changes (deltaSP) in front of the TM re a 10-micronV round window cochlear microphonic (RW CM)--that varies inversely with frequency at a rate of 12dB/octave with a surgically shortened external auditory meatus (EAM). Losses were determined at the outer opening (deltaSP00) and at the TM (deltaSPTM) of four artificial EAM's of various lengths, volumes, and leakiness. In the low-frequency region, a leaky EAM produced a flat loss. In the midfrequency region, the flatness of losses was attributable to (1) the length of the EAM and (2) the location at which the loss was determined. EAM volume was not related to the configuration of the loss. Losses, under all conditions, were always identical in shape and magnitude for the open and closed systems. Clinically, hearing losses due to TM perforations are essentially frequency independent, especially in the low frequencies. The relation between voltage changes (deltaV) across the transducer and losses with different EAM's suggests that the discrepency between audiometric results and CM losses--at least in the high and midfrequencies--may be due to the use of precalibrated SPL's in clinical audiometry.     

Experiments on the stability of spherical and paraboloidal shells

This paper presents the experimental part of a study of the elastic stability of clamped and hinged spherical and paraboloidal shell caps subjected to external uniform pressure loading. Ninety-six poly-vinyl-chloride (PVC) shells of 15-in. base diameter and formed by thermovacuum process, were tested and their critical loads recorded. The effects of geometry, clamped and hinged boundary conditions, height/span and radius of curvature/thickness ratios on the critical pressure were investigated. The results are compared, where possible, with experimental data obtained by previous investigators.     

In-line ultrasonic monitoring of semi-solid magnesium die casting process

Ultrasonic velocity and attenuation measurements in AZ91D magnesium (Mg) alloy with dendritic, rosette and globular microstructures were performed at elevated temperatures using a non-contact laser-ultrasonic technique. It was found that the ultrasonic velocity in the globular microstructure and the ultrasonic attenuation in the dendritic microstructure are the highest among the three microstructures. An ultrasonic clad steel buffer rod sensor embedded in the die has been used to monitor the semi-solid die casting process in-line for the AZ91D Mg alloy. This probe monitored the completion of the die filling, the release of the pressure, the opening of the die, part detachment, solidification of the part, the averaged temperature of the die and the part.     

AknT is an activating protein for the glycosyltransferase AknS in L-aminodeoxysugar transfer to the aglycone of aclacinomycin A

During biosynthesis of the anthracycline antitumor agents daunomycin, adriamycin, and aclacinomycin, the polyketide-derived tetracyclic aglycone is enzymatically glycosylated at the C7-OH by dedicated glycosyltransferases (Gtfs) that transfer L-2,3,6-trideoxy-3-aminohexoses. In aclacinomycins, the first deoxyhexose is predicted to be transferred via AknS action, then subjected to further elongation to a trisaccharide by the subsequent Gtf, AknK. We report here that purified AknS has very low activity in the absence of the adjacently encoded AknT; however, at a 3:1 ratio, AknT stimulates AknS k(cat) by 40-fold up to 0.22 min(-1) for transfer of L-2-deoxyfucose (2-dF) to the aglycone aklavinone. It is likely that several other Gtfs that glycosylate polyketide aglycones also act as two-component catalytic systems. Incubations of purified AknS/AknT/AknK with two aglycones and two dTDP-2-deoxyhexoses produced previously uncharacterized anthracycline disaccharides.     

Fluorescent Photoinduced Electron Transfer (PET) Sensors for Anions; From Design to Potential Application

This mini review highlights the synthesis and photophysical evaluation of anion sensors, for nonaqueous solutions, that have been developed in our laboratories over the last few years. We have focused our research mainly on developing fluorescent photoinduced electron transfer (PET) sensors based on the fluorophore-spacer-anion receptor principle using several anthracene (emitting in the blue) and 1,8-naphthalimide (emitting in the green) fluorophores, with the aim of targeting biologically and industrially relevant anions such as acetates, phosphate and amino acids, as well as halides such as fluoride. The receptors and the fluorophore are separated by a short methyl or ethyl spacer, where the charge neutral anion receptors are either aliphatic or aromatic urea (or thiourea) moieties. For these, the anion recognition is through hydrogen bonding, yielding anion:receptor complexes. Such bonding gives rise to enhanced reduction potential in the receptor moieties which causes enhancement in the rate of PET quenching of the fluorophore excited state from the anion:receptor moiety. This design can be further elaborated on by incorporating either two fluorophores, or urea/thiourea receptors into the sensor structures, using anthracene as a fluorophore. For the latter design, the sensors were designed to achieve sensing of bis-anions, such as di-carboxylates or pyrophosphate, where the anion bridged the anthracene moiety. In the case of the naphthalimide based mono-receptor based PET sensors, it was discovered that in DMSO the sensors were also susceptible to deprotonation by anions such as F⁻ at high concentrations. This led to substantial changes in the absorption spectra of these sensors, where the solution changed colour from yellow/green to deep blue, which was clearly visible to the naked eye. Hence, some of the examples presented can act as dual fluorescent-colorimetric sensors for anions. Further investigations into this phenomenon led to the development of simple colorimetric sensors for fluorides, which upon exposure to air, were shown to fix carbon dioxide as bicarbonate.