Stereochemistry in trivalent nitrogen compounds. 37. Effect of alkali metal coordination on amide configurational equilibria

Carbon-13 NMR spectroscopy indicates that amides bearing a triethyleneoxide substituent at nitrogen exist as a mixture of E and Z isomers; the change in isomer ratio upon addition of KSCN can be used to determine the association constant for chelation.     

Metal-peptide frameworks (MPFs): "bioinspired" metal organic frameworks

Chiral metal-organic frameworks (MOFs) have attracted a growing interest for their potential use in energy technologies, asymmetric catalysis, chiral separation, and on a more basic level, the creation of new topologies in inorganic materials. The current paper is the first report on a peptide-based MOF, a metal peptide framework (MPF), constructed from an oligovaline peptide family developed earlier by our group (Mantion, A.; et al. Macromol. Biosci. 2007, 7, 208). We have used a simple oligopeptide, Z-(L-Val)2-L-Glu(OH)-OH, to grow porous copper and calcium MPFs. The MPFs form thanks to the self-assembling properties of the peptide and specific metal-peptide and metal-ammonia interactions. They are stable up to ca. 250 degrees C and have some internal porosity, which makes them a promising prototype for the further development of MPFs.     

Isoindolo[2,1-a]indol-6-one--a new pyrolytic synthesis and some unexpected chemical properties

Isoindolo[2,1-a]indol-6-one 1 is formed by a sigmatropic shift-elimination-cyclisation cascade by flash vacuum pyrolysis (FVP) of methyl 2-(indol-1-yl)benzoate 7 at 950 degrees C. The dihydro compound 16 is easily obtained by catalytic reduction of 1, but the reaction is very sensitive to steric effects at the 11-position. Attempted ring-opening of 1 in basic methanol provides an equilibrium of isoindolo[2,1-a]indol-6-one 1 and the ester 19. Lithium aluminium hydride reduction of 1 provides the alcohol 22 which can be dehydrated to a mixture of 23 and 24 by FVP at 800-950 degrees C.     

Thermal chemistry of bicyclo[4.2.0]oct-2-enes

At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.     

Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple‐quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI‐type zeolites by desilication. The findings, subsequently generalized to FAU‐ and BEA‐type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends.     

Gd‐DTPA‐Dopamine‐Bisphytanyl Amphiphile: Synthesis,Characterisation and Relaxation Parameters of the Nanoassemblies and Their Potential as MRI Contrast Agents

Here, a new amphiphilic magnetic resonance imaging (MRI) contrast agent, a Gd^III‐chelated diethylenetriaminepentaacetic acid conjugated to two branched alkyl chains via a dopamine spacer, Gd‐DTPA‐dopamine‐bisphytanyl (Gd‐DTPA‐Dop‐Phy), which is readily capable of self‐assembling into liposomal nanoassemblies upon dispersion in an aqueous solution, is reported. In vitro relaxivities of the dispersions were found to be much higher than Magnevist, a commercially available contrast agent, at 0.47 T but comparable at 9.40 T. Analysis of variable temperature ¹⁷O NMR transverse relaxation measurements revealed the water exchange of the nanoassemblies to be faster than that previously reported for paramagnetic liposomes. Molecular reorientation dynamics were probed by ¹H NMRD profiles using a classical inner and outer sphere relaxation model and a Lipari–Szabo “model‐free” approach. High payloads of Gd^III ions in the liposomal nanoassemblies made solely from the Gd‐DTPA‐Dop‐Phy amphiphiles, in combination with slow molecular reorientation and fast water exchange makes this novel amphiphile a suitable candidate to be investigated as an advanced MRI contrast agent.     

Recovering incomplete data using Statistical Multiple Imputations (SMI): a case study in environmental chemistry

This paper presents a statistical technique that can be applied to environmental chemistry data where missing values and limit of detection levels prevent the application of statistics. A working example is taken from an environmental leaching study that was set up to determine if there were significant differences in levels of leached arsenic (As), chromium (Cr) and copper (Cu) between lysimeters containing preservative treated wood waste and those containing untreated wood. Fourteen lysimeters were setup and left in natural conditions for 21 weeks. The resultant leachate was analysed by ICP-OES to determine the As, Cr and Cu concentrations. However, due to the variation inherent in each lysimeter combined with the limits of detection offered by ICP-OES, the collected quantitative data was somewhat incomplete. Initial data analysis was hampered by the number of ‘missing values’ in the data. To recover the dataset, the statistical tool of Statistical Multiple Imputation (SMI) was applied, and the data was re-analysed successfully. It was demonstrated that using SMI did not affect the variance in the data, but facilitated analysis of the complete dataset.     

Multiple double cross-section transmission electron microscope sample preparation of specific sub-10 nm diameter Si nanowire devices

The ability to prepare multiple cross-section transmission electron microscope (XTEM) samples from one XTEM sample of specific sub-10 nm features was demonstrated. Sub-10 nm diameter Si nanowire (NW) devices were initially cross-sectioned using a dual-beam focused ion beam system in a direction running parallel to the device channel. From this XTEM sample, both low- and high-resolution transmission electron microscope (TEM) images were obtained from six separate, specific site Si NW devices. The XTEM sample was then re-sectioned in four separate locations in a direction perpendicular to the device channel: 90° from the original XTEM sample direction. Three of the four XTEM samples were successfully sectioned in the gate region of the device. From these three samples, low- and high-resolution TEM images of the Si NW were taken and measurements of the NW diameters were obtained. This technique demonstrated the ability to obtain high-resolution TEM images in directions 90° from one another of multiple, specific sub-10 nm features that were spaced 1.1 μm apart.