Ultrasonic velocity and absorption on methylmetha acrylic resins

Ultrasonic velocity and absorption were studied in autocure and heatcure resin monomers at different temperatures. Ultrasonic velocity increased in the autocure sample while absorption was reduced. This is attributed to the presence of certain structural factors such as hydrogen bonding.     

Sequencing of T-superfamily conotoxins from <Emphasis Type="Italic">Conus virgo</Emphasis>: Pyroglutamic acid identification and disulfide arrangement by MALDI mass spectrometry

De novo mass spectrometric sequencing of two Conus peptides, Vi1359 and Vi1361, from the vermivorous cone snail Conus virgo, found off the southern Indian coast, is presented. The peptides, whose masses differ only by 2 Da, possess two disulfide bonds and an amidated C-terminus. Simple chemical modifications and enzymatic cleavage coupled with matrix assisted laser desorption ionization (MALDI) mass spectrometric analysis aided in establishing the sequences of Vi1359, ZCCITIPECCRI-NH(2), and Vi1361, ZCCPTMPECCRI-NH(2), which differ only at residues 4 and 6 (Z = pyroglutamic acid). The presence of the pyroglutamyl residue at the N-terminus was unambiguously identified by chemical hydrolysis of the cyclic amide, followed by esterification. The presence of Ile residues in both the peptides was confirmed from high-energy collision induced dissociation (CID) studies, using the observation of w(n)- and d(n)-ions as a diagnostic. Differential cysteine labeling, in conjunction with MALDI-MS/MS, permitted establishment of disulfide connectivity in both peptides as Cys2-Cys9 and Cys3-Cys10. The cysteine pattern clearly reveals that the peptides belong to the class of T-superfamily conotoxins, in particular the T-1 superfamily.     

Micellar induced regioselectivity in the two-step consecutive reaction of SO3(2-) with Br-(CH2CH2)n-Br (n=2-5)

High field (800 MHz) (1)H NMR was used to monitor the two-step consecutive reaction of excess SO(3)(2-) with symmetrical bifunctional alpha,omega-dibromoalkanes with butane (DBB), hexane (DBH), octane (DBO), and decane (DBD) chains in CTAB micelles at 25 degrees C. The first-order rate constant for the first substitution step for DBB and DBH is about 5 times faster than for the second, but the kinetics for DBO and DBD were not cleanly first-order. After 40 min, the solution contained about 80% of the intermediate bromoalkanesulfonate from DBB and DBH and the remainder is alkanedisulfonate and unreacted starting material. The same reactions were carried out in homogeneous MeOH/D(2)O solutions at 50 degrees C. The rate constants for all four alpha,omega-dibromoalkanes were first-order throughout the time course of the reaction and the same within +/-10%. However, because micellar solutions are organized on the nanoscale and bring together lipophilic and hydrophilic reactants into a small reaction volume at the micellar interface, they speed this substitution reaction considerably compared to reaction in MeOH/D(2)O. The CTAB micelles also induce a significant regioselectivity in product formation by speeding the first step of the consecutive reaction more than the second. The results are consistent with the bromoalkanesulfonate intermediates having a radial orientation within the micelles with the -CH(2)SO(3)(-) group in the interfacial region and the -CH(2)Br group directed into the micellar core such that the concentration of -CH(2)Br groups in the reactive zone, i.e., the micellar interface, is significantly reduced. These results provide the first example of self-assembled surfactant system altering the relative rates of the reaction steps of a consecutive reaction and, in doing so, enhancing monosubstitution of a symmetrically disubstituted species.     

Dictyostatin flexibility bridges conformations in solution and in the β-tubulin taxane binding site

Dictyostatin (DCT, 1) is a complex, flexible polyketide macrolide that demonstrates potent microtubule-polymerization activity. Both a solution structure (2a) and a possible binding mode for DCT (Conf-1) have been proposed by earlier NMR experiments. In the present study, the conformational landscape of DCT in DMSO-d(6) and methanol-d(4) was explored using extensive force-field-based conformational searches combined with geometric parameters derived from solution NMR data. The results portray a diversity of conformations for dictyostatin that illustrates the molecule's flexibility and excludes the previously suggested dominant solution conformation 2a. One conformation present in DMSO-d(6) with a 7% population (Conf-2, 0.6 kcal/mol above the global minimum at 298°) also satisfies the TR-NOESY NMR parameters of Canales et al. that characterize the taxane binding-site interaction between DCT and assembled microtubules in water. Application of several docking methods (Glide, Autodock, and RosettaLigand) has identified a low-energy binding model of the DCT/β-tubulin complex (Pose-2/Conf-2) that is gratifyingly compatible with the emerging DCT structure-activity data.     

PAA-derived gold nanorods for cellular targeting and photothermal therapy

A single-step LbL procedure to functionalize CTAB-capped GNRs via electrostatic self-assembly is reported. This approach allows for consistent biomolecule/GNR coupling using standard carboxyl-amine conjugation chemistry. The focus is on cancer-targeting biomolecule/GNR conjugates and selective photothermal destruction of cancer cells by GNR-mediated hyperthermia and NIR light. GNRs were conjugated to a single-chain antibody selective for colorectal carcinoma cells and used as probes to demonstrate photothermal therapy. Selective targeting and GNR uptake in antigen-expressing SW 1222 cells were observed using fluorescence microscopy. Selective photothermal therapy is demonstrated using SW 1222 cells, where >62% cell death was observed after cells are treated with targeted A33scFv-GNRs.     

A study of shallow water waves with Gardner’s equation

In this paper the dynamics of solitary waves governed by Gardner’s equation for shallow water waves is studied. The mapping method is employed to carry out the integration of the equation. Subsequently, the perturbed Gardner equation is studied, and the fixed point of the soliton width is obtained. This fixed point is then classified. The integration of the perturbed Gardner equation is also carried out with the aid of He’s semi-inverse variational principle. Finally, Gardner’s equation with full nonlinearity is solved with the aid of the solitary wave ansatz method.     

Polarized naphthalimide CH donors enhance Cl- binding within an aryl-triazole receptor

The dipolar character of 1,8-naphthalimide together with polarization of the C(4)-H and C(5)-H donors has been utilized in receptor 1 to effectively bind chloride alongside triazole and phenylene units. The Cl(-) binding strength of 1 shows that the naphthalimide provides greater anion stabilization than an unactivated phenylene, and DFT calculations show that its collinear donor array can be a "urea-like" analog for CH···anion interactions.     

Expeditious synthesis of N-bridged heterocycles via dipolar cycloaddition of pentafulvenes with 3-oxidopyridinium betaines

A new and highly versatile approach towards the synthesis of bicyclo[6.3.0]undecanes and bicyclo[5.3.0]decanes was accomplished. The methodology adopted involved [6+3] and [3+2] cycloaddition reactions of pentafulvenes with 3-oxidopyridinium betaines generated either by the action of a base on the pyridinium salt or thermally from pyridinium betaine dimer. These well-functionalized bicyclo[6.3.0]undecanes and bicyclo[5.3.0]decanes offer a wide range of synthetic options, which can be expected to translate into a variety of rapid and efficient synthesis of natural products.     

Confirmation of the absolute configuration of (−)-aurantioclavine

We confirm our previous assignment of the absolute configuration of (−)-aurantioclavine as 7R by crystallographically characterizing an advanced 3-bromoindole intermediate reported in our previous synthesis. This analysis also provides additional support for our model of enantioinduction in the palladium(II)-catalyzed oxidative kinetic resolution of secondary alcohols.