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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Atom transfer radical polymerization.

Metabolite profiling in biomarker discovery, enzyme substrate assignment, drug activity/specificity determination, and basic metabolic research requires new data preprocessing approaches to correlate specific metabolites to their biological origin. Here we introduce an LC/MS-based data analysis approach, XCMS, which incorporates novel nonlinear retention time alignment, matched filtration, peak detection, and peak matching. Without using internal standards, the method dynamically identifies hundreds of endogenous metabolites for use as standards, calculating a nonlinear retention time correction profile for each sample. Following retention time correction, the relative metabolite ion intensities are directly compared to identify changes in specific endogenous metabolites, such as potential biomarkers. The software is demonstrated using data sets from a previously reported enzyme knockout study and a large-scale study of plasma samples. XCMS is freely available under an open-source license at http://metlin...

XCMS: processing mass spectrometry data for metabolite profiling using nonlinear peak alignment, matching, and identification.

Electrolytes and interphases in Li-ion batteries and beyond.

Self-localized nonlinear excitations (solitons, polarons, and bipolarons) are fundamental and inherent features of quasi-one-dimensional conducting polymers. Their signatures are evident in many aspects of the physical and chemical properties of this growing class of novel materials. As a result, these polymers represent an opportunity for exploring the novel phenomena associated with topological solitons and their linear confinement which results from weakly lifting the ground-state degeneracy. The authors review the theoretical models that have been developed to describe the physics of polyacetylene and related conducting polymers and summarize the relevant experimental results obtained for these materials. An attempt is made to assess the validity of the soliton model of polyacetylene and its generalization to related systems in which the ground-state degeneracy has been lifted.

Solitons in conducting polymers

PLA is prepared by the ring opening polymerization (ROP) of lactide, the cyclic dimer of lactic acid. Commercial polylactides usually are synthesized from lactide monomers prepared from a single lactic acid enantiomer, and because the resulting polymers are stereoregular, they have high degrees of crystallinity. 2 The mechanical properties of crystalline polymers are stable to near the polymer melting point, and thus they have higher use temperatures than their amorphous analogues. For example, polymerization ofL-lactide gives a semicrystalline polymer with a melting transition near 180 °C andTg ∼ 67 °C,3 properties that make it useful for applications ranging from degradable packaging to surgical implants and matrices for drug delivery. 4 In contrast, the polymer derived fromrac-lactide, a 1:1 mixture ofDand L-lactide, yields amorphous polymers with glass transitions near room temperature. AlthoughL-lactide can be prepared with relatively high enantiopurity from corn fermentation, the requirement for an enantiopure monomer places restrictions on the polymer synthesis. As shown in Scheme 1, chiral catalysts have been employed to effect kinetic resolution of racemic lactide. Spassky et al. have reported kinetic resolutions of rac-lactide by employing a chiral Schiff’s base complex of aluminum, ( -)1.5 At low conversions high enantiomeric enrichment in the polymer is observed. 6 This finding is significant because the catalyst overrides the tendency for syndiotactic placements that are typically favored by chainend control. 7 At higher conversions the enantiomeric enrichment in the polymer decreases. The drop in selectivity can be attributed to the fact that the relative concentration of the “wrong” isomer increases in the monomer pool as the desired enantiomer is incorporated in the polylactide. In a recent report, Coates et al. effected the syndiotactic polymerization of meso-lactide by using the isopropoxide catalyst ( -)-2.8 Sincemeso-lactide possesses two stereocenters of opposite configuration, the concentration of D andL stereocenters remains constant and the intrinsic selectivity of the catalyst is not diminished by statistical depletion of the preferred stereocenter. An interesting effect of stereoregularity on lactide properties was first reported by Tsuji and co-workers. 9-11 As shown in Scheme 1,L-PLA and D-PLA form a stereocomplex that has a Tm 50 °C higher than theTm for the homochiral polymers. Preparation of this stereocomplex presently requires parallel ROP of Dand L-lactide with subsequent combination of the chiral polylactide chains. Despite its improved mechanical properties, practical applications of the stereocomplex are prohibited by the requirement that separate pools of enantiopure lactide monomers must be polymerized to enantiopure polymers. If the same material could be prepared from the rac-lactide, it is conceivable that applications of the stereocomplex could be realized. Spassky’s and Coates’ results in stereoselective ROP of lactides suggests a strategy for the direct preparation of the polylactide stereocomplex fromrac-lactide. Specifically, the racemic catalyst, rac-2, should lead to parallel syntheses of isotactic D-PLA and L-PLA chains since ( -)-2 preferentially polymerizes D-lactide and (+)-2 preferentially polymerizesL-lactide. In contrast to kinetic resolution ofrac-lactide with (-)-1, theD:L ratio in the monomer pool should remain constant at high conversion since polymerization by the racemic catalyst will remove D and L isomers at equal rates. Thus, the high enantioselectivity that is realized at low conversion in kinetic resolutions using chiral 1 should be maintained at high conversion with rac-1 to give a 1:1 mixture of isotactic chains (Scheme 2). Polymerization ofrac-lactide withrac-2 yields nearly monodisperse chains ( Mw/Mn ) 1.05) consistent with a “living” polymerization and the absence of transesterification. This is supported by the linear relationship between the monomer conversion to polymer andMn. More importantly, the1H NMR spectrum (Figure 1a) is consistent with formation of chains

Stereoselective polymerization of a racemic monomer with a racemic catalyst: Direct preparation of the polylactic acid stereocomplex from racemic lactide

Surface-initiated atom transfer radical polymerization on gold at ambient temperature

We report the bulk polymerization of ethylglycolide (3,6-diethyl-1,4-dioxane-2,5-dione), isobutylglycolide (3,6-diisobutyl-1,4-dioxane-2,5-dione), and hexylglycolide (3,6-dihexyl-1,4-dioxane-2,5-dione) to high molecular weight polymers. The glycolides were prepared by two routes:  the reaction of 2-bromoacyl bromides and α-hydroxy acids and the acid-catalyzed oligomerization of 2-hydroxy acids followed by thermal depolymerization of the oligomers in the presence of ZnO. Both methods gave the substituted glycolides as a mixture of diastereomers. The monomers were melt-polymerized using Sn(2-ethylhexanoate)2, SnO, SnBr2, SnBr4, PbO, and Ph4Sn with alcohol initiators. The polymerization rates depend on the steric bulk of the monomer, and the kinetic data for polymerizations using Sn(2-ethylhexanoate)2 can be fit to an equilibrium model. High molecular weight poly(ethylglycolide), poly(isobutylglycolide), and poly(hexylglycolide) have Tg's of 12, 22, and −37 °C, respectively. These polymers are amorphous and ...

Preparation and Characterization of Substituted Polylactides

Gain-of-function mutations in isocitrate dehydrogenase (IDH) in human cancers result in the production of d-2-hydroxyglutarate (d-2HG), an oncometabolite that promotes tumorigenesis through epigenetic alterations. The cancer cell–intrinsic effects of d-2HG are well understood, but its tumor cell–nonautonomous roles remain poorly explored. We compared the oncometabolite d-2HG with its enantiomer, l-2HG, and found that tumor-derived d-2HG was taken up by CD8+ T cells and altered their metabolism and antitumor functions in an acute and reversible fashion. We identified the glycolytic enzyme lactate dehydrogenase (LDH) as a molecular target of d-2HG. d-2HG and inhibition of LDH drive a metabolic program and immune CD8+ T cell signature marked by decreased cytotoxicity and impaired interferon-γ signaling that was recapitulated in clinical samples from human patients with IDH1 mutant gliomas. Description Oncometabolite targets T cells Cancer-causing mutations in isocitrate dehydrogenase cause accumulation of the metabolite d-2-hydroxyglutarate (d-2HG). Notarangelo et al. showed that such high concentrations of d-2HG could act as a direct inhibitor of lactate dehydrogenase in mouse T cells (see the Perspective by Nathan). Inhibition of this metabolic enzyme altered glucose metabolism in the T cells and inhibited their proliferation, cytokine production, and ability to kill target cells. The authors propose that in addition to its known cell-autonomous cancer-promoting effects, d-2HG may also have immunosuppressive activity. —LBR Excess metabolite from cancer cells may hinder antitumor immunity.

Oncometabolite d-2HG alters T cell metabolism to impair CD8+ T cell function

Poly(phenyllactide): synthesis, characterization, and hydrolytic degradation.

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