Fully oxygen-tolerant atom transfer radical polymerization triggered by sodium pyruvate

ATRP (atom transfer radical polymerization) is one of the most robust reversible deactivation radical polymerization (RDRP) systems. However, the limited oxygen tolerance of conventional ATRP impedes its practical use in an ambient atmosphere. In this work, we developed a fully oxygen-tolerant PICAR (photoinduced initiators for continuous activator regeneration) ATRP process occurring in both water and organic solvents in an open reaction vessel. Continuous regeneration of the oxidized form of the copper catalyst with sodium pyruvate through UV excitation allowed the chemical removal of oxygen from the reaction mixture while maintaining a well-controlled polymerization of N-isopropylacrylamide (NIPAM) or methyl acrylate (MA) monomers. The polymerizations of NIPAM were conducted with 250 ppm (with respect to the monomer) or lower concentrations of CuBr₂ and a tris[2-(dimethylamino)ethyl]amine ligand. The polymers were synthesized to nearly quantitative monomer conversions (>99%), high molecular weights (M_n > 270 000), and low dispersities (1.16 < Đ < 1.44) in less than 30 min under biologically relevant conditions. The reported method provided a well-controlled ATRP (Đ = 1.16) of MA in dimethyl sulfoxide despite oxygen diffusion from the atmosphere into the reaction system.

A novel photoinduced ATRP system enabling a well-controlled polymerization in both aqueous and organic solvents in an ambient atmosphere.     

A new, mild preparation of sulfonyl chlorides

A new method was developed for the preparation of sulfonyl chlorides from sulfonic acids under neutral conditions using 2,4,6-trichloro-1,3,5-triazine as chlorinating agent.     

The exponent of discrepancy is at most

We study discrepancy with arbitrary weights in the norm over the -dimensional unit cube. The exponent of discrepancy is defined as the smallest for which there exists a positive number such that for all and all there exist points with discrepancy at most . It is well known that . We improve the upper bound by showing that

This is done by using relations between discrepancy and integration in the average case setting with the Wiener sheet measure. Our proof is not constructive. The known constructive bound on the exponent is .

     

Structure determination of resorcinol rotamers by high-resolution UV spectroscopy.

The rotationally resolved S1<--S0 electronic origins of several deuterated resorcinol rotamers cooled in a molecular beam have been recorded. An automated assignment of the observed spectra has been performed using a genetic algorithm approach with an asymmetric rotor Hamiltonian. The structures of resorcinol A and resorcinol B were derived from the rotational constants of twenty deuterated species for both electronic states. The lifetimes of different resorcinol isotopomers in the S1 state are also reported. As is the case for phenol, these lifetimes mainly depend on the position of deuteration. A nearly perfect additivity of the zero-point energies after successive deuterations in resorcinol rotamers has been discovered and subsequently used in the full assignment of the previously reported low-resolution spectra of deuterated resorcinol A. An analogous spectrum is also predicted for the resorcinol B rotamer.     

The First Ring‐Enlargement of a 1‐Azabicyclo[1.1.0]butane to a 1‐Azabicyclo[2.1.1]hexane

The reactions of 3‐phenyl‐1‐azabicyclo[1.1.0]butane ( 4 ) with dimethyl dicyanofumarate ((E)‐ 8 ) and dimethyl dicyanomaleate ((Z)‐ 8 ) lead to the same mixture of cis‐ and trans‐4‐phenyl‐1‐azabicyclo[2.1.1]hexane 2,3‐dicarboxylates (cis‐ 11 and trans‐ 11 , resp.; Scheme 3). This result of a formal cycloaddition to the central C? N bond of 4 is interpreted by a stepwise reaction mechanism via a relatively stable zwitterionic intermediate 10 , which could be intercepted by morpholine to give a 1 : 1 : 1 adduct 12 , which undergoes a spontaneous elimination of HCN to yield the fumarate 13 (Scheme 4).     

Addition of trimethylsilyl azide and of “mixed anhydrides” to the N-C(3) σ-bond in 3-substituted-1-azabicyclo[1.1.0]butanes

Trimethylsilyl azide adds smoothly to the highly strained N-C(3) σ-bond in 3-ethyl-1-azabicyclo[1.1.0]-butane ( 1 ) to afford an adduct, 2 , that reacts in situ with a variety of electrophilic reagents (i.e., ethyl chloroformate, p-toluenesulfonyl chloride, benzoyl chloride, acetyl chloride, and oxalyl chloride) to afford the corresponding N-substituted-3-azido-3-ethylazetidines 3–7 , respectively in 62–72% yield. Similarly, 1 reacts regiospecifically with “mixed anhydrides” (i.e., p-toluenesulfonyl acetate, methanesulfonyl acetate, and benzoyl trifluoromethanesulfonate) to afford the corresponding adducts, 8–10 , respectively) in 38–68% yield. Reaction of p-toluenesulfonyl azide with 1-aza-3-phenylbicyclo[1.1.0]butane ( 12 ) produces two products: N-(p-toluenesulfonyl-3-azido-3-phenylazetidine ( 13 , 15%) and a dimeric product, N-(N'-p-toluenesulfonyl-3′-phenyl-3′-azetidinyl)-3-azido-3-phenylazetidine ( 14 , 28%). Ethyl chloroformate adds to the N-C(3) σ-bond in 1-aza-3-(bromomethyl)bicyclo[1.1.0]butane ( 15 ) to afford N-carboethoxy-3-(bromomethyl)-3-chloroazetidine ( 16 ) in 73% yield.     

Formation of hydrogen-bonded complexes of 3,3′,5,5′-tetrabromo-2,2′-biphenol with MTBD and triethylamine

The complexes of 3,3′,5,5′-tetrabromo-2,2′-biphenol (TBBPh) with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) and triethylamine (TEA) were studied by FTIR spectroscopy. In chloroform and in acetonitrile a proton transfer from TBBPh to N-bases (MTBD, TEA) occurs. In chloroform solution the protonated N-base molecules are hydrogen-bonded to the deprotonated TBBPh molecules, whereas in acetonitrile the complexes dissociate. The intra- as well as intermolecular hydrogen bonds within the chains show large proton polarizability.     

Electrochemical detection of nitric oxide using polymer modified electrodes

Electrochemical sensors based on chemical surface modification are very attractive because they combine high sensitivity of amperometry with new dimensions of selectivity and stability provided by the surface modifier. This review shows a few strategies employed to facilitate the detection, determination and monitoring of nitric oxide using polymer modified electrodes. Conducting and nonconducting polymer films and composite films are considered. The most significant achievements reached in this field, during the last decade, are critically reviewed. The collected data are also presented in three tables.     

Selective and sensitive detection of nitrite based on NO sensing on a polymer-coated rotating disc electrode

A new effective way of nitrite detection in complex samples is presented. It is based on chemical conversion of nitrite to nitric monoxide (NO) in acidic aqueous solution containing hexacyanoferrate(II) as a reductor. NO is then detected on a poly-eugenol coated platinum electrode. When the electrode is rotating and the reduction medium is continuously purged with nitrogen, the addition of a nitrite-containing sample produces narrowed current spikes. The peak current is proportional to nitrite content in the sample over the range of 5.0–100 μM and detection limit is 0.6 μM. The method is simple and highly reproducible. Relative standard deviation of 10 repetitions is less than 4%. Practical utility of the proposed approach is demonstrated by nitrite determination in human saliva.     

Total Synthesis of Cryptophycins via a Chemoenzymatic Approach

A highly convergent synthesis of cryptophycins in their enantiomerically-pure forms was achieved. Our strategy consists of the synthesis of the two units 3 and 4 and linking them together to form the macrocyclic ring. The upper unit 3 was prepared from 10 in four steps, and the lower unit 4 was prepared from 20 in three steps. Enantioselective biocatalytic methodology was used to prepare the requisite chiral building blocks, (R)-11 and (R)-19. The stereochemical versatility of this synthetic approach is demonstrated by the synthesis of cryptophycin A and the four diastereomers of cryptophycin C.