How can we avoid the lock-in problem in the substitution of hazardous chemicals used in consumer products?

A wide range of chemical substances is used in consumer products for various purposes, including plastic softeners, dyestuffs and colorants, flame retardants, impregnation agents, antioxidants and UV absorbers, preservation agents and biocides, and many others. Among these chemicals, there is a certain fraction of substances with hazardous properties such as persistence, bioaccumulation potential and toxicity (PBT properties) or the ability to interfere with the hormonal system (endocrine disrupting chemicals, EDCs). Large-scale screening exercises have shown that there may be several hundreds of chemicals with PBT properties among the several tens of thousands of substances on the market. There are some groups of chemicals that have raised particular concerns such as polybrominated diphenyl ethers (PBDEs) or long-chain poly and perfluorinated alkyl substances (PFASs). These substances have been regulated or are subject to voluntary phase-out programs; specifically, penta- and octabrominated BDEs are scheduled for elimination globally under the Stockholm Convention on Persistent Organic Pollutants; uses of perfluorooctane sulfonic acid (PFOS) are being restricted under the Stockholm Convention, and perfluorooctanoic acid (PFOA) and C11–C14 perfluorocarboxylic acids are regulated in the European Union as PBT substances and vPvB (very persistent, very bioaccumulative) substances, respectively. In addition, all long-chain PFASs (substances with seven or more perfluorinated carbons) are subject of voluntary phase-out programs conducted by major producers of fluoropolymers and fluorotelomer-based products. However, it has become evident that the replacements of these substances include chemically similar substances, i.e. brominated aromatic substances in the case of PBDEs and shorter-chain PFASs in the case of long-chain PFASs. These are two examples of a substitution process that leads to an incremental rather than a fundamental change in the structure of chemicals used in consumer products. Here we discuss the conditions for incremental and fundamental changes in the substitution process of chemicals

Resistance scaling at the Kosterlitz-Thouless transition

We study the linear resistance at the Kosterlitz-Thouless transition by Monte Carlo simulation of vortex dynamics. Finite size scaling analysis of our data show excellent agreement with scaling properties of the Kosterlitz-Thouless transition. We also compare our results for the linear resistance with experiments. By adjusting the vortex chemical potential to an optimum value, the resistance at temperatures above the transition temperature agrees well with experiments over many decades.Comment: 7 pages, 4 postscript figures included, LATEX, KTH-CMT-94-00

Experimental Evidence for Quantum Interference and Vibrationally Induced Decoherence in Single-Molecule Junctions

We analyze quantum interference and decoherence effects in single-molecule junctions both experimentally and theoretically by means of the mechanically controlled break junction technique and density-functional theory. We consider the case where interference is provided by overlapping quasi-degenerate states. Decoherence mechanisms arising from the electronic-vibrational coupling strongly affect the electrical current flowing through a single-molecule contact and can be controlled by temperature variation. Our findings underline the all-important relevance of vibrations for understanding charge transport through molecular junctions.Comment: 5 pages, 4 figure

Conditional human VEGF‐mediated vascularization in chicken embryos using a novel temperature‐inducible gene regulation (TIGR) system

Advanced heterologous transcription control systems for adjusting desired transgene expression are essential for gene function assignments, drug discovery, manufacturing of difficult to produce protein pharmaceuticals and precise dosing of gene‐based therapeutic interventions. Conversion of the Streptomyces albus heat shock response regulator (RheA) into an artificial eukaryotic transcription factor resulted in a vertebrate thermosensor (CTA; cold‐inducible transactivator), which is able to adjust transcription initiation from chimeric target promoters (PCTA) in a low‐temperature‐ inducible manner. Evaluation of the temperature‐dependent CTA-PCTA interaction using a tailored ELISA‐like cell‐free assay correlated increased affinity of CTA for PCTA with temperature downshift. The temperature‐inducible gene regulation (TIGR) system enabled tight repression in the chicken bursal B‐cell line DT40 at 41°C as well as precise titration of model product proteins up to maximum expression at or below 37°C. Implantation of microencapsulated DT40 cells engineered for TIGR‐controlled expression of the human vascular endothelial growth factor A (hVEGF121) provided low‐temperature‐induced VEGF‐mediated vascularization in chicken embryo