(119/117/115)Sn low-abundance single-transition correlation spectroscopy (LASSY): sensitivity-enhanced homonuclear correlation experiments for Sn NMR

We report the implementation of our novel rare-spin homonuclear correlation experiment, namely, Low-Abundance Single-transition correlation SpectroscopY (LASSY), for (119/117/115)Sn NMR at natural abundance. Our pulse sequence results in diagonal suppressed COSY-style display and outperforms the optimal homonuclear correlation experiment for rare spins, which involves double quantum evolution (INADEQUATE CR). The new experiment maximizes efficiency both in respect of pulse transformations as well as relaxation effects, and gives rise to a simplified two-dimensional (2D) spectrum with considerably reduced crowding, exhibiting only one transition in each cross peak, instead of four. Performance optimization of LASSY is carried out in light of the relatively 'large' line widths typical of Sn NMR in solution state. The superior performance of the sequence is demonstrated on dimeric tetraorganodistannoxane samples.     

The detection and quantification of adulteration in olive oil by near-infrared spectroscopy and chemometrics.

A new procedure has been developed for the classification and quantification of the adulteration of pure olive oil by soya oil, sun flower oil, corn oil, walnut oil and hazelnut oil. The study was based on a chemometric analysis of the near-infrared (NIR) spectra of olive-oil mixtures containing different adulterants. The adulteration of olive oil was carefully carried out gravimetrically in a 4 mm quartz cuvette, starting with pure olive oil in the cuvette first. NIR spectra of the 525 adulterated mixtures were measured in the region of 12,000-4000 cm(-1). The spectra were subjected batch wise to multiplicative signal correction (MSC) before calculating the principal component (PCA) models. The MSC-corrected data were subjected to Savitzky-Golay smoothing and a mean normalization procedure before developing partial least-squares calibration (PLS) models. The results revealed that the models predicted the adulterants, corn oil, sun flower oil, soya oil, walnut oil and hazelnut oil involved in olive oil with error limits +/-0.57, +/-1.32, +/-0.96, +/-0.56 and +/-0.57% weight/weight, respectively. Furthermore, the PCA developed models were able to classify unknown adulterated olive oil mixtures with almost 100% certainty. Quantification of the adulterants was carried out using their respective PLS models within the same error limits as mentioned above.     

Quantitative determination of saccharides in dietary glyconutritional products by anion-exchange liquid chromatography with integrated pulsed amperometric detection

A new technique for the assay of carbohydrates is described in which separation and quantification of neutral saccharides, aminosaccharides, glycuronic acids, and disaccharides may be accomplished in less than 50 min of total run time. This method involves optimized anion-exchange liquid chromatography coupled with integrated pulse amperometric detection. Complex carbohydrates from various sources, including dietary supplements, were hydrolyzed in a dilute solution of trifluoroacetic acid, freeze-dried, and reconstituted in water containing 2-deoxygalactose as the internal standard. The solution was filtered and separated on CarboPac PA20 column. The eluted saccharides were detected by oxidation on a gold electrode with quadruple-pulsed integrated amperometry. The calibration plots for the saccharides were linear with an average correlation coefficient of 0.999. Method precision regarding peak retention time and resolution used in the peak identifications was verified. With this method, previously difficult-to-separate saccharides, such as galactosamine, glucosamine, and N-acetylglucosamine, were successfully resolved from the neutral saccharides rhamnose, arabinose, and galactose. Mannose was also resolved from xylose, and de-acetylation of aminosaccharides prior to separation was not necessary. This technique provides an accurate and efficient means to assay carbohydrates in dietary supplements, which new federal regulations will soon mandate.     

Assessment of functional changes in nanoparticle-exposed neuroendocrine cells with amperometry: exploring the generalizability of nanoparticle-vesicle matrix interactions

Using two of the most commonly synthesized noble metal nanoparticle preparations, citrate-reduced Au and Ag, the impacts of short-term accidental nanoparticle exposure are examined in primary culture murine adrenal medullary chromaffin cells. Transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Alamar Blue viability studies revealed that nanoparticles are taken up by cells but do not decrease cell viability within 48 hours of exposure. Carbon-fiber microelectrode amperometry (CFMA) examination of exocytosis in nanoparticle-exposed cells revealed that nanoparticle exposure does lead to decreased secretion of chemical messenger molecules, of up to 32.5% at 48 hours of Au exposure. The kinetics of intravesicular species liberation also slows after nanoparticle exposure, between 30 and 50% for Au and Ag, respectively. Repeated stimulation of exocytosis demonstrated that these effects persisted during subsequent stimulations, meaning that nanoparticles do not interfere directly with the vesicle recycling machinery but also that cellular function is unable to recover following vesicle content expulsion. By comparing these trends with parallel studies done using mast cells, it is clear that similar exocytosis perturbations occur across cell types following noble metal nanoparticle exposure, supporting a generalizable effect of nanoparticle-vesicle interactions.     

Stability of small mesoporous silica nanoparticles in biological media

In this work, sub-50 nm pegylated mesoporous silica nanoparticles prepared with hydrothermal treatment are shown to have long-term stability in various media at both room and physiological temperature. Compared to bare mesoporous silica nanoparticles, the highly pegylated mesoporous silica nanoparticles show significantly improved biocompatibility and decreased macrophage uptake, making these nanoparticles viable for in vivo stealth drug delivery applications.     

1H Indirect detected 13C Low-Abundance Single-transition correlation Spectroscopy (HICLASS)-13C homonuclear correlation at natural abundance

A novel proton-detected (13)C homonuclear correlation experiment is reported at natural abundance, viz., (1)H Indirect detected (13)C Low-Abundance Single-transition correlation Spectroscopy (HICLASS). HICLASS is based on the evolution of (13)C single-quantum single transitions, followed by their mixing, and (1)H detection subsequent to heteronuclear transfer. Reduced relaxation losses during the evolution time and partial selectivity in the (1)H multiplet structure result in enhanced sensitivity of HICLASS. The superior performance of HICLASS is demonstrated for (1)H-detected (13)C correlation work.     

Total synthesis of the photoprotecting dipyrrolobenzoquinone (+)-terreusinone

The first synthesis of (+)-terreusinone 1, a dipyrrolobenzoquinone with a potent UV-A protecting capability, is described. Key transformations include a one-pot Larock indolization-Sonogashira coupling reaction and the hydroamination of an unsubstituted ortho-alkynylaniline catalyzed by a cationic gold(I) complex. The synthesis proceeds in eight steps from commercially available starting materials, confirming the structure and absolute configuration of the natural product.     

Ultrastable, redispersible, small, and highly organomodified mesoporous silica nanotherapeutics

Practical biomedical application of mesoporous silica nanoparticles is limited by poor particle dispersity and stability due to serious irreversible aggregation in biological media. To solve this problem, hydrothermally treated mesoporous silica nanoparticles of small size with dual-organosilane (hydrophilic and hydrophobic silane) surface modification have been synthesized. These highly organomodified mesoporous silica nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, N(2) adsorption-desorption, dynamic light scattering, zeta potential, and solid-state (29)Si NMR, and they prove to be very stable in simulated body fluid at physiological temperature. Additionally, they can be dried to a powdered solid and easily redispersed in biological media, maintaining their small size for a period of at least 15 days. Furthermore, this preparation method can be expanded to synthesize redispersible fluorescent and magnetic mesoporous silica nanoparticles. The highly stable and redispersible mesoporous silica NPs show minimal toxicity during in vitro cellular assays. Most importantly, two types of doxorubicin, water-soluble doxorubicin and poorly water-soluble doxorubicin, can be loaded into these highly stable mesoporous silica nanoparticles, and these drug-loaded nanoparticles can also be well-redispersed in aqueous solution. Enhanced cytotoxicity to cervical cancer (HeLa) cells was found upon treatment with water-soluble doxorubicin-loaded nanoparticles compared to free water-soluble doxorubicin. These results suggest that highly stable, redispersible, and small mesoporous silica nanoparticles are promising agents for in vivo biomedical applications.     

Acoustic characterization of echogenic liposomes: frequency-dependent attenuation and backscatter

Ultrasound contrast agents (UCAs) are used clinically to aid detection and diagnosis of abnormal blood flow or perfusion. Characterization of UCAs can aid in the optimization of ultrasound parameters for enhanced image contrast. In this study echogenic liposomes (ELIPs) were characterized acoustically by measuring the frequency-dependent attenuation and backscatter coefficients at frequencies between 3 and 30 MHz using a broadband pulse-echo technique. The experimental methods were initially validated by comparing the attenuation and backscatter coefficients measured from 50-μm and 100-μm polystyrene microspheres with theoretical values. The size distribution of the ELIPs was measured and found to be polydisperse, ranging in size from 40 nm to 6 μm in diameter, with the highest number observed at 65 nm. The ELIP attenuation coefficients ranged from 3.7 ± 1.0 to 8.0 ± 3.3 dB/cm between 3 and 25 MHz. The backscatter coefficients were 0.011 ± 0.006 (cm str)(-1) between 6 and 9 MHz and 0.023?±?0.006 (cm str)(-1) between 13 and 30 MHz. The measured scattering-to-attenuation ratio ranged from 8% to 22% between 6 and 25 MHz. Thus ELIPs can provide enhanced contrast over a broad range of frequencies and the scattering properties are suitable for various ultrasound imaging applications including diagnostic and intravascular ultrasound.