Proton transfer and N(+)-H...S(-) hydrogen bonds in the crystal structure of 4-aminothiophenol

4-Aminothiophenol exists as 4-ammonio-1-benzenethiolate in the solid and liquid state. The crystal structure is characterised by a tetrahedral beta-As type network which is the driving force for the proton transfer.     

Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and 4', 6'-Di-O-benzyl Ethers

Synthesis of stereoisomers of 6′‐mono‐ and 4′,6′‐di‐O‐benzyl cryptofolione is described through a key intermediate 6 , which was prepared by coupling of iodobenzene 8 with chiral propargyl alcohol 9 under Cosford protocol conditions. Monobenzyl ether 4 is obtained via epoxide 6 opening with vinyl Grignard, followed by cross‐metathesis reaction with a vinyl lactone 11 . Whereas, dibenzyl ether 5 is prepared by epoxide 6 opening with chiral propargyl alcohol 7 followed by simple transformations and finally cis‐Wittig olefination.     

Total Synthesis of (+)‐Cryptocaryalactone and of a Diastereoisomer of (+)‐Strictifolione via Ring‐Closing Metathesis (RCM) and Olefin Cross‐Metathesis (CM)

Ring‐closing metathesis (RCM) and olefin cross‐metathesis (CM) reactions were used as the key steps for the synthesis of (+)‐cryptocaryalactone ( 1 ) and the first synthesis of the diastereoisomer 3 of (+)‐strictifolione, starting from the commercially available L ‐malic acid (=(2S)‐2‐hydroxybutanedioic acid).     

Acid cleavable surface enhanced raman tagging for protein detection

Dye conjugation is a common strategy improving the surface enhanced Raman detection sensitivity of biomolecules. Reported is a proof-of-concept study of a novel surface enhanced Raman spectroscopic tagging strategy termed as acid-cleavable SERS tag (ACST) method. Using Rhodamine B as the starting material, we prepared the first ACST prototype that consisted of, from the distal end, a SERS tag moiety (STM), an acid-cleavable linker, and a protein reactive moiety. Complete acid cleavage of the ACST tags was achieved at a very mild condition that is 1.5% trifluoroacetic acid (TFA) aqueous solution at room temperature. SERS detection of this ACST tagged protein was demonstrated using bovine serum albumin (BSA) as the model protein. While the SERS spectrum of intact ACST-BSA was entirely dominated by the fluorescent signal of STM, quality SERS spectra can be readily obtained with the acid cleaved ACST-BSA conjugates. Separation of the acid cleaved STM from protein further enhances the SERS sensitivity. Current SERS detection sensitivity, achieved with the acid cleaved ACST-BSA conjugate is ～5 nM in terms of the BSA concentration and ～1.5 nM in ACST content. The dynamic range of the cleaved ACST-BSA conjugate spans four orders of magnitudes from ～10 nM to ～100 μM in protein concentrations. Further improvement in the SERS sensitivity can be achieved with resonance Raman acquisition. This cleavable tagging strategy may also be used for elimination of protein interference in fluorescence based biomolecule detection.     

Some polishing experiments on copper in a hyperbolic cell

Some polishing experiments have been carried out on copper anodes in a hyperbolic cell designed by Gilmont and Walton, using orthophosphoric acid as the electrolyte. The results obtained have been compared to those obtained in similar experiments in a Hull cell. It has been found that very similar bands of different reflectivity and polishes are found to form in both the cells. These bands shift with time and a study of such displacements has been made. The results are briefly discussed.     

Relative importance of X...O=C vs. X...X halogen bonding as structural determinants in 4-halotriaroylbenzenes

The structures of 4-chloro- and 4-bromotribenzoylbenzene, as well as a solid solution prepared from these two components, are isomorphous and dominated by C-X...O=C interactions, whereas type-II I...I interactions are important in the 4-iodo derivative.     

Robust spatially resolved pressure measurements using MRI with novel buoyant advection-free preparations of stable microbubbles in polysaccharide gels

MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25 min. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-distearoyl-sn-glycero-3-phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44 bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar.     

Ultrasensitive detection of malondialdehyde with surface-enhanced Raman spectroscopy

Malondialdehyde (MDA) is a biomarker of lipid peroxidation that has been widely associated with food rancidity as well as many human diseases. Most current MDA detection methods involve MDA reaction with thiobarbituric acid (TBA), followed by UV-visible and/or fluorescence detection of high-performance liquid chromatography (HPLC)-separated TBA-MDA. Herein, we report the first proof-of-concept study of surface-enhanced Raman detection of a TBA-MDA adduct using silver nanoparticles as the SERS substrate and the 632.8 nm HeNe laser as a Raman excitation source. Current SERS detection limit of TBA-MDA is 0.45 nM, ~100 times higher than the 36 nM fluorescence sensitivity recently reported with the HPLC-purified TBA-MDA. Molecular specificity of the SERS technique was studied by comparing the SERS spectrum of TBA-MDA with those acquired with TBA adducts of other TBA-reactive compounds (TBARCs) that includes formaldehyde, acetaldehyde, butyraldehyde, trans-2-hexenal, and pyrimidine. Compared to TBA and TBA adducts with those TBARCs, the SERS activity of TBA-MDA adduct is significantly higher. The possibility of direct SERS detection of TBA-MDA in a reaction mixture (without HPLC separation) has also been investigated.     

Crystal structure prediction of aminols: advantages of a supramolecular synthon approach with experimental structures

The supramolecular synthon approach to crystal structure prediction (CSP) takes into account the complexities inherent in crystallization. The synthon is a kinetically favored unit, and through analysis of commonly occurring synthons in a group of related compounds, kinetic factors are implicitly invoked. The working assumption is that while the experimental structure need not be at the global minimum, it will appear somewhere in a list of computationally generated structures so that it can be suitably identified and ranked upward using synthon information. These ideas are illustrated with a set of aminophenols, or aminols. In the first stage, a training database is created of the 10 isomeric methylaminophenols. The crystal structures of these compounds were determined. The prototypes 2-, 3-, and 4-aminophenols were also included in the training database. Small and large synthons in these 13 crystal structures were then identified. Small synthons are of high topological but low geometrical value and are used in negative screens to eliminate computationally derived structures that are chemically unreasonable. Large synthons are more restrictive geometrically and are used in positive screens ranking upward predicted structures that contain these more well-defined patterns. In the second stage, these screens are applied to CSP of nine new aminols carried out in 14 space groups. In each space group, up to 10 lowest energy structures were analyzed with respect to their synthon content. The results are encouraging, and the predictions were classified as good, unclear, or bad. Two predictions were verified with actual crystal structure determinations.