A biosynthetically-inspired synthesis of the tetrahydrofuran core of obtusallenes II and IV

[reaction: see text] Sharpless asymmetric dihydroxylation was regioselective for the trans olefin in an E vs Z vs terminal triene substrate. To test a biosynthetic hypothesis, the resulting diol underwent diastereoselective bromoetherification to provide the des-chloro core of marine natural products obtusallenes II and IV. Alternatively, anionic chloride ring-opening of a Z-beta,gamma-unsaturated epoxide gave separable regioisomeric halohydrins. Bromoetherification gave the fully elaborated core of obtusallenes II and IV with all of the relative stereochemistry correctly set.     

Formation and Structural Characterization of Metal Complexes derived from Thiosalicylic Acid

The formation and structural aspects of some metal complexes of thiosalicylic acid (TSA) were studied. The μ‐bridging tetra‐coordinated Ru complex, [Ru(C₆H₄(CO₂)(μ‐S)(H₂O)]₂ ( 1 ) was formed by hydrothermal reaction of TSA with RuCl₃. The complexes [M(dtdb)(phen)(H₂O)]_n ( 2 – 4 ) (M = Zn^II, Co^II, Ni^II, dtdb = 2,2′‐dithiodibenzoate anion, phen = 1,10‐phenanthroline) were obtained by the slow diffusion technique and the in situ S–S bond formation was confirmed by elemental, spectral and X‐ray analysis. Reaction of TSA with CuCl₂ and 2,2′‐bipyridine (bipy) under the slow diffusion technique yielded the dimer [Cu(tdb)(bipy)] ( 5 ) (tdb = thiodibenzoic acid), where the in situ generation of 2,2′‐thiodibenzoic acid was observed.     

Antiresonant guiding optofluidic biosensor

We propose a novel optofluidic biosensor in which detection is based on a shift in the transmission spectrum due to the contrast in refractive index between the carrier fluid and the target biomaterial. The sensor can function using focused illumination without the need for fiber or waveguide coupled input/output signals. We study the spectral response of the sensor using 2D full-wave time-harmonic field analysis and perform parametric analysis of detection sensitivity as a function of material and device parameters. Our analysis demonstrates that detectible shifts in the transmission spectrum can be achieved with nanoscale accumulation of biomaterial within the sensor. We show that the transmission minima and detection sensitivity can be estimated using analytical expressions based on a 1D antiresonant waveguide model.     

Kinetic and Mechanistic Investigations on Some N,N‐Chelated Pt(II) Oxalate Complexes with Some “S” Containing Biorelevant Ligands at Physiological Condition

The substitution of the chelating oxalate group by a group of nucleophiles, viz. thiourea (L₁), 2‐thiouracil (L₂), diethyldithiocarbamate (L₃), dl ‐penicillamine (L₄), and thiosemicarbazide (L₅) was studied under pseudo–first‐order conditions as a function of concentration and temperature using UV–vis spectrophotometry and stopped‐flow technique. π‐Accepting effects are often used to account for the unusual high lability of Pt(bipy) complexes. The complexes [Pt(dach)(oxalate)] (1) (dach = cis‐1,2‐diaminocyclohexane) and [Pt(bipy)(oxalate)] (2) (bipy = 2,2'‐bipyridine) and substituted products were isolated and characterized by FTIR and ESI‐MS spectroscopic analysis. The negative entropies of activation support a strong contribution from bond making in the transition state of the substitution processes.     

Substitution Reaction of the Hydroxopentaaquarhodium(III) Ion with l-Glutamine,Glycine and l-Histidine in Aqueous Medium: A Kinetic and Mechanistic Approach

The title reactions have been studied spectrophotometrically. A two step consecutive mechanism for the amino acids was found which differs from that of the dipeptides, which follow two parallel paths under identical reaction conditions. In the case of amino acids the first step is ligand dependent, but the second step is a ligand independent chelation step, whereas for dipeptides two parallel ligand dependent paths are observed. A comparison between these closely related systems and the unique findings in their mechanistic behavior is discussed in detail.     

The stereochemical course of bromoetherification of enynes

Enynes undergo stereoselective syn intramolecular bromoetherification; the stereochemical course of the reaction was elucidated by X-ray crystallographic studies and by stereospecific synthesis of authentic bromoallenes.     

Comprehensive mathematical simulation of functional magnetic resonance imaging time series including motion-related image distortion and spin saturation effect

There has been vast interest in determining the feasibility of functional magnetic resonance imaging (fMRI) as an accurate method of imaging brain function for patient evaluations. The assessment of fMRI as an accurate tool for activation localization largely depends on the software used to process the time series data. The performance evaluation of different analysis tools is not reliable unless truths in motion and activation are known. Lack of valid truths has been the limiting factor for comparisons of different algorithms. Until now, currently available phantom data do not include comprehensive accounts of head motion. While most fMRI studies assume no interslice motion during the time series acquisition in fMRI data acquired using a multislice and single-shot echo-planar imaging sequence, each slice is subject to a different set of motion parameters. In this study, in addition to known three-dimensional motion parameters applied to each slice, included in the time series computation are geometric distortion from field inhomogeneity and spin saturation effect as a result of out-of-plane head motion. We investigated the effect of these head motion-related artifacts and present a validation of the mapping slice-to-volume (MSV) algorithm for motion correction and activation detection against the known truths. MSV was evaluated, and showed better performance in comparison with other widely used fMRI data processing software, which corrects for head motion with a volume-to-volume realignment method. Furthermore, improvement in signal detection was observed with the implementation of the geometric distortion correction and spin saturation effect compensation features in MSV.     

Self-Forming Norbornene-Tetrazine Hydrogels with Independently Tunable Properties

Although photopolymerization reactions are commonly used to form hydrogels, these strategies rely on light and may not be suitable for delivering therapeutics in a minimally invasive manner. Here, hyaluronic acid (HA) macromers are modified with norbornene (Nor) or tetrazine (Tet) and upon mixing click into covalently crosslinked Nor-Tet hydrogels via a Diels–Alder reaction. By incorporating a high degree of Nor and Tet substitution, Nor-Tet hydrogels with a broad range in elastic moduli (5 to 30 kPa) and fast gelation times (1 to 5 min) are achieved. By pre-coupling methacrylated HANor macromers with thiolated peptides via a Michael addition reaction, Nor-Tet hydrogels are peptide-functionalized without affecting their physical properties. Mesenchymal stem cells (MSCs) on RGD-functionalized Nor-Tet hydrogels adhere and exhibit stiffness-dependent differences in matrix mechanosensing. Fluid properties of Nor-Tet hydrogel solutions allow for injections through narrow syringe needles and can locally deliver viable cells and peptides. Substituting HA with enzymatically degradable gelatin also results in cell-responsive Nor-Tet hydrogels, and MSCs encapsulated in Nor-Tet hydrogels preferentially differentiate into adipocytes or osteoblasts, based on 3D cellular spreading regulated by stable (HA) and degradable (gelatin) macromers.