Programmable assembly of colloidal particles using magnetic microwell templates

A substrate of thin micromagnets covered by a template of microwells is used to direct the assembly of superparamagnetic colloidal beads into two-dimensional arrays. It is confirmed that the magnetization of the micromagnets can direct beads to programmed locations on the substrate with assistance of externally applied magnetic fields. Empirical investigations on this topic were guided by mathematical models with the intent to elucidate the conditions that promote a single bead to be assembled in the desired microwells. To demonstrate that this technique is programmable, heterogeneous arrays of colored beads are produced.     

Quantum mechanical modeling of a transannular interaction in a bicyclic amidinium ion

A transannular donor-acceptor interaction in a bicyclic azaamidinium salt was modeled by quantum mechanical calculations using a supermolecule complex consisting of a formamidinium cation and an ammonia molecule. Molecular properties are reported at various geometries. These results are compared with the results of similar calculations on the bicyclic cation itself. The model calculations and the bicyclic cation calculations are in good agreement, but both fail to reproduce the experimentally known structure. Results from ab initio calculations on the model system are discussed, as are results from calculations which included iodide as counterion.     

The determination of chromium in water-soluble polymers by gas chromatography

Water-soluble polymers have found increasing use in the areas of water treatment, paper production and oil recovery, and the determination of heavy metals in such materials is important from an environmental standpoint. Heavy metal contamination could result from redox catalysts in the polymerization system, raw materials or stainless steel storage facilities.     

Computer-aided determination of relative stereochemistry and 3D models of complex organic molecules from 2D NMR spectra

A method for elucidation of the relative stereoconfiguration of natural product molecular structures and their 3D models based on NOE data and the application of a genetic algorithm is described. The method is applicable mainly for rigid polycyclic structures commonly encountered in natural products. It is demonstrated that the technique of simulated annealing cannot be easily used when dealing with low-weight fused ring molecules but the application of a genetic algorithm is proven successful. Examples of a typical genetic algorithm workflow and the optimization of the algorithmic parameters are discussed. The efficiency of the approach developed here is demonstrated on the complex natural products of both Taxol^® (C₄₇H₅₁NO₁₄) and brevetoxin B (C₅₀H₇₀O₁₄).     

Analyzer scan modes for hybrid mass spectrometers

The scan modes that can be used to obtain daughter ion, parent ion, and constant neutral-loss spectra on hybrid mass spectrometers are derived for instruments with a quadrupole combined with a magnetic and/or electric sector. All combinations of sector/quadrupole and quadrupole/sector instruments are discussed. The advantages or lack thereof of the various scans are presented with respect to operation, resolution and potential artifacts.     

Regioselective syntheses of 2-amino-4,5-dialkylthiophene-3-carboxylates and their conversion to 3,4-dihydro-4-oxothieno[2,3-d]pyrimidine-2-carboxylates

The synthesis of 3,4-dihydro-4-oxothieno[2,3-d]pyrimidine-2-carboxylates via acid catalyzed reactions of various 2-aminothiophene-3-carboxylates with activated nitriles is presented. The requisite thiophenes were prepared regioselectively by methods which represent improvements over previously published procedures.     

Infrared spectrum of D2O vibrationally decoupled in H2O ice Ic

The study of D₂O isolated in amorphous H₂O (ice Iv) has been extended to the determination of the bending mode frequency (1230 cm^?1) and to the measurement of the vibrational spectrum of the cubic ice phase (ice Ic). The vibrationally decoupled stretching frequencies (ν₁ = 2367 cm^?1 and ν₃ = 2444 cm^?1) for D₂O in the H₂O (Ic) have been obtained and an estimate of the exchange activation energy is given.     

A new procedure for regioselective synthesis of 8,9-dichloro-2,3,4,5-tetrahydro-1H-2-benzazepine (LY134046) and its 3-methyl analogue as inhibitors of phenylethanolamine N-methyltransferase (PNMT)

A regioselective synthesis of 8,9-dichloro-2,3,4,5-tetrahydro-1H-2-benzazepine (LY134046, 10 ) and its 3-methyl analogue 26 from 6,7-dichloro-3-hydroxyphthalide ( 16 ) is described. The key step involved 1,4-hydride addition to the α,β-unsaturated nitrile 17 to give the saturated nitrile 18 using sodium borohydride in 2-propanol. In the preparation of LY134046 10 , the COOH group in 18 was first esterified and then the nitrile function was selectively reduced with borane to yield the aminoester 20 . The aminoester 20 was then cyclized to the azepinone 21 which on reduction with borane provided LY134046 10 in an overall yield of 22%. The route is adaptable to the preparation of hitherto unknown 3-substituted-2-benzazepines as demonstrated by the preparation of the 3-methyl analogue 26 . In this case the nitrile 18 was reacted with an excess methylmagnesium iodide to give the ketoacid 22 . Esterification of 22 followed by reductive amination with sodium cyanoborohydride and ammonium acetate provided the aminoester 24 , which was then converted to the target benzazepine 26 as described earlier for the title compound. The reaction conditions and the reagents used throughout the sequence are fairly mild and many functional groups may be tolerated. The only limitation to this procedure is the availability of the corresponding hydroxyphthalide. A variation in the choice of reagent in the Grignard reaction of 18 should provide an access to a variety of 3-substituted-2-benzazepines.     

Large-scale millisecond intersubunit dynamics in the B subunit homopentamer of the toxin derived from Escherichia coli O157

We report here solution NMR relaxation measurements that show millisecond time-scale intersubunit dynamics in the homopentameric B subunit (VTB) of the toxin derived from Escherichia coli O157. These data are consistent with interconversion between an axially symmetric form and a low-abundance ( approximately 10%, 45 degrees C) higher energy form. The higher energy state is depopulated on binding of a novel bivalent analogue (P(k) dimer) of the natural carbohydrate acceptor globotriaosylceramide. The isothermal titration calorimetry isotherm for the binding of P(k) dimer to VTB is consistent with a five-site sequential binding model which assumes that cooperative effects arise through communication only between neighboring binding sites. The resulting thermodynamic parameters (K(a1) = 114 +/- 2.2 M(-1), K(a2) = 283 +/- 4.5 M(-1), DeltaH(1) degrees = -116.3 +/- 0.55 kJ/mol, and DeltaH(2) degrees = -50.3 +/- 0.11 kJ/mol) indicate favorable entropic cooperativity that has not previously been observed in multivalent systems.