How mobile NMR can help with the conservation of paintings

The conservation of paintings is fundamental to ensure that future generations will have access to the ideas of the grand masters who created these art pieces. Many factors, such as humidity, temperature, light, and pollutants, pose a risk to the conservation of paintings. To help with painting conservation, it is essential to be able to noninvasively study how these factors affect paintings and to develop methods to investigate their effects on painting degradation. Hence, the use of mobile nuclear magnetic resonance (NMR) as a method of investigation of paintings is gaining increased attention in the world of Heritage Science. In this mini-review, we discuss how this method was used to better understand the stratigraphy of paintings and the effect different factors have on the painting integrity, to analyze the different cleaning techniques suitable for painting conservation, and to show how mobile NMR can be used to identify forgeries. It is also important to keep in mind its limitations and build upon this information to optimize it to extend its applicability to the study of paintings and other precious objects of cultural heritage.     

Highly effective and enantioselective Phospho-Aldol reaction of diphenyl phosphite with N-alkylated isatins catalyzed by quinine

Cinchona alkaloids were first successfully reported to promote enantioselective Phospho-Aldol reaction of diphenyl phosphite to a variety of N-alkylated isatin derivatives in good to excellent yields (up to 99%) and moderate to good enantioselectivities (up to 73% ee) almost in no time.     

Designing for sustainability with biocatalytic and chemoenzymatic cascade processes

Cascade reactions have been widely recognized to cut costs, decrease solvent usage, and reduce cycle times in chemical processes. Recently, biocatalytic cascades have altered how we design synthetic routes to complex molecules to achieve sustainable commercial processes for pharmaceutical, agricultural, and fine chemical industries. With advancements in protein engineering and an increase in the number of enzyme classes available to chemists, industrial and academic groups alike have endeavored to expand the scope of biocatalysis from single reactions to multi-enzyme cascades to rapidly build complex molecular structures. Recent reports have drawn inspiration from biosynthetic pathways and have applied engineered enzymes to in vitro enzymatic cascades. Furthermore, combining transition-metal catalysis and enzymes in one-pot chemoenzymatic cascades likewise serves to broaden the scope of biocatalysis, enabling traditional chemical reactions to be performed under mild aqueous conditions. In this article, we review recent biocatalytic and chemoenzymatic cascades from 2019 to 2021.     

NMR spectroscopic study of the Murex trunculus dyeing process

It is widely accepted that indigo dyes derived from Murex trunculus were used to produce the biblical dyes tekhelet and argaman. We describe a method of following the debromination of natural leucoindigos and their binding to wool using NMR spectroscopy. Debromination is observed prior to reaction with the wool and prior to oxidation. Binding to the wool is shown to occur prior to oxidation. NMR allows the dyeing process to be followed. This, in principle, could be used to correct problems during dyeing that would increase the reliability of the process.     

Modification of Cyclodextrins for Use as Artificial Enzymes

The magical powers of enzymes have been attributed to their ability to bind specific substrates and catalyze reactions of the bound substrate. Artificial enzymes synthetically mimic the binding and the catalytic site to produce molecules that are not only smaller in size but also potentially have similar activity to the real enzymes. The main objective of our research is to create artificial redox enzymes by using cyclodextrins as binding sites and attaching flavin derivatives as the catalytic site. We have developed a strategy to attach a catalytic site to cyclodextrin exclusively at the 2-, 3- or the 6-position. The evaluation of the artificial enzyme in which flavin is attached to the 2-position gives a 647-fold acceleration factor. Although this is modest compared to those of real enzymes (which can have acceleration factors of a trillion), the artificial enzymes allow us to understand the elements that contribute to the incredible catalytic power of enzymes.     

Electrochemical approaches for the detection of amyloid-β, tau,and α-synuclein

According to the World Health Organization, there are 47 million people worldwide who are afflicted with dementia today, and this is expected to rise to 132 million by 2050. Therefore, it is pertinent to develop efficient analytical methods such as electrochemical biosensors to study these disorders and diagnose them early. This review highlights some of the recent key developments in the use of electrochemical biosensors to study the biomarkers related to neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Especially, we focus on the applications of electrochemistry to analyze amyloid-β and tau related to Alzheimer's disease and α-synuclein related to Parkinson's disease.     

Computational design of rasagiline derivatives: Searching for enhanced antioxidant capability

A set of new rasagiline derivatives is presented. They were designed to be antioxidant compounds with the potential to be used for treating neurodegenerative disorders. They are expected to be multifunctional molecules that can help reduce oxidative stress, which is thought to contribute to neurodegenerative disorders. The CADMA-Chem computational protocol was used to produce rasagiline derivatives and to evaluate their likeliness as oral drugs and antioxidants. Three of them were identified as the most promising ones. They are proposed to be better free radical scavengers than rasagiline. In addition, they are expected to keep the parent's molecule neuroprotective capability. Hopefully, the results presented here would promote further experimental and theoretical investigations on these compounds.     

Defects,flexoelectricity and RF communications: the ZBD story

ABSTRACT

The zenithal bistable display (ZBD) was the first liquid crystal device mode to be commercialised that uses nematic disclinations in a constructive fashion, to use the flexoelectric effect inherent to all liquid crystals but at the time was considered too weak an effect to be useful, and to transfer nano-replication methods to the LCD manufacturing environment. The genesis of the invention and spin-out company ZBD Displays Limited will be described, and the evolution of that company from licensing model, through fabless manufacturer to display provider and finally to a system provider for the retail sector. The story may be useful not just to those interested in the science behind a rather unusual LCD, but also those involved in taking technology from laboratory to manufacturing, from idea to commercial success.     

Sol-Gel Fabrication of Rare-Earth Doped Photonic Components

The use of sol-gel to fabricate silica-on-silicon waveguides, and particularly erbium-doped waveguide amplifiers, is reviewed. In particular, efforts to use sol-gel to improve molecular homogeneity in heavily Er-doped silica-based films is discussed. A variety of material studies carried out to investigate the gain limitations found in these materials is then presented. These include x-ray diffraction, ellipsometry and Rutherford backscattering. Excess heat treatment is used to force crystallisation of the films, and analysis of the resulting structure is used to infer properties of the glass before the additional heating. The use of erbium alkoxide precursors is shown to alter the erbium environment in the final glass, in comparison to the use of inorganic erbium salts.     

增强无机化学教学的趣味性策略的案例研究

针对无机化学的理论知识学习的"枯燥",提出无机化学教学趣味性的三大增强策略,一是设定情境,让"枯燥"的知识生动起来;二是善用比喻,让"困难"的知识有趣起来;三是自创"小诗",让"复杂"的知识幽默起来。通过实践,三大增强策略的效果很好,值得广泛推广。     

Thermal degradation of wood treated with guanidine compounds in air: Flammability study

Wood has been treated with guanidine phosphate, guanidine nitrate, guanidine carbonate and guanidine chloride to impart flame retardancy. The samples were subjected to differential thermal analysis (DTA) and thermogravimetry (TG) from ambient temperature to 800°C in air to study their thermal behaviors. From the resulting data, kinetic parameters for different stages of thermal degradation were obtained following the method of Broido. For the decomposition of wood and flame retardant wood, the activation energy was found to decrease from 116 to 54 kJ mol^–1; the char yield was found to increase from 5.6 to 34.9%, LOI from 18 to 41.5, which indicated that the flame retardancy of treated wood was improved. Effects of the different compounds on the degradation and flammability of wood have also been proposed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Some steps toward a central theory of ecosystem dynamics

Ecology is said by many to suffer for want of a central theory, such as Newton's laws of motion provide for classical mechanics or Schroedinger's wave equation provides for quantum physics. From among a plurality of contending laws to govern ecosystem behavior, the principle of increasing ascendency shows some early promise of being able to address the major questions asked of a theory of ecosystems, including, "How do organisms come to be distributed in time and space?, what accounts for the log-normal distribution of species numbers?, and how is the diversity of ecosystems related to their stability, resilience and persistence?" While some progress has been made in applying the concept of ascendency to the first issue, more work is needed to articulate exactly how it relates to the latter two. Accordingly, seven theoretical tasks are suggested that could help to establish these connections and to promote further consideration of the ascendency principle as the kernel of a theory of ecosystems.     

Kinetics of phenol hydrogenation over supported palladium catalyst

Kinetics of vapor phase hydrogenation of phenol to cyclohexanone over Pd/MgO system has been studied in a flow microreactor under normal atmospheric pressure. The reaction rate is found to be negative order with respect to the partial pressure of phenol and has increased from −0.5 to 0.5 with increasing temperature (473 to 563 K). The apparent activation energy (E_a) of the process is found to be close to 65 kJ per mol. On the basis of kinetic results a surface mechanism is proposed.     

Gel formation in free radical polymerization via chain transfer and terminal branching

Gel formation in free-radical polymerization via chain transfer to polymer, recombination termination, and terminal branching due to either chain transfer to monomer or disproportionation termination is investigated using the method of moments. It is found that no gel can possibly form in the systems consisting of initiation, propagation, and one of the above reactions. However, systems with the following combination of reactions are found to be capable of gelling. They are: chain transfer to polymer + recombination termination; chain transfer to polymer + terminal branching due to disproportionation termination; and terminal branching due to transfer to monomer + recombination termination. Systems with the following combination of reactions are incapable of gelling; transfer to polymer + terminal branching due to transfer to monomer; and terminal branching due to disproportionation termination + recombination termination. An examination of the gelation mechanisms reveals that the formation of multivinyl macromonomers during the course of polymerization is the reason that systems involving terminal branching gel. Sol/gel diagrams are generated to give critical kinetic parameters required for gelation. It is found that terminal branching does not always promote gelation due to the adverse effect on chain length through chain transfer to monomer and termination by disproportionation, reactions which generate terminal double bonds. © 1994 John Wiley & Sons, Inc.     

Carbon Dots: The Newest Member of the Carbon Nanomaterials Family

Carbon nanomaterials have been extensively researched in the past few years owing to their interesting properties. The massive research efforts resulted in the emergence of carbon dots, which belong to the carbon nanomaterials family. Carbon dots (C‐dots) have garnered the attention of researchers mainly due to their convenient availability from organic as well as inorganic materials and also due to the novel properties they exhibit. C‐Dots have been said to overcome the era of quantum dots, referring to their levels of toxicity and biocompatibility. In this review, we focus on the discovery of C‐dots, their structure and composition, surface passivation to enhance their optical properties, the various synthetic methods used, their applications in different areas, and future perspectives. Emphasis has been given to greener approaches for the synthesis of C‐dots in order to make them cost effective as well as to improve their biocompatibility.     

New Falling Film Reactor for Melt Polycondensation Process

Summary: A grid falling film tower (GFFT) has been invented as an ideal polycondensation reactor. In this reactor, polymer melt flows through multi-layers grids from top to bottom to form falling film owing to gravity without agitation and shear; large gas-liquid interfacial area is generated; the grids are perpendicular between adjacent layers to ensure film renewal and to achieve uniformly flowing. The fluid flow in this reactor has little back-mixing and dead zone, which is near to plug flow. All melts are under the state of thin film which avoids the negative effect of hydrostatic head on the mass transfer impetus. Furthermore, the GFFT has wide operation flexibility as well as adjustable configuration parameters to meet different demands. A pilot scale GFFT with the height of 4.0 meters has been applied to polyester polycondensation process. The intrinsic viscosity of polyethylene terephthalate increased from 0.45 dl/g to 0.8–0.9 dl/g successfully. GFFT is supposed to be an universal apparatus for many devolatilization processes.     

An untargeted metabolomics approach to contaminant analysis: pinpointing potential unknown compounds

This study deals with an automated data analysis strategy to pinpoint potential unknown compounds in full scan mass spectrometry (MS) experiments. Three examples of an untargeted metabolomics approach to contaminant analysis are given. By comparing a plant-oil based hormone cocktail to 90 plant oil samples ca. 25 compounds specific to the hormone cocktail could be detected. Five of these compounds were confirmed as steroid hormones. A comparison of a drink water sample from a farm to distillated water showed the presence of contaminants specific to this drink water sample. A grass sample, which was known to give a false positive result in a DR-CALUX bioassay, was unexpectedly shown to contain an abnormal level of chrysene, which was obviously not eliminated during clean-up.     

Cyclodextrin Molecular Reactors

The ability of cyclodextrins to form inclusion complexes with hydrophobic species in aqueous solution makes them well-suited to the development of molecular reactors, to be used as miniature reaction vessels in order to control the outcomes of chemical transformations at the molecular level. In this manner, reaction rates can be increased and products may be obtained that are different to those normally accessible from reactions in free solution. Examples used to illustrate these effects include: the application of cyclodextrins to control the regioselectivity of bromination of aromatic substrates with pyridinium dichlorobromate: the use of a metallocyclodextrin to increase the rate of hydrolysis of a phosphate triester by almost five orders of magnitude; the development of modified cyclodextrins to increase the rates and reverse the regioselectivity of nitrile oxide cycloadditions ; and the use of a cyclodextrin dimer to change the ratio of formation of indigoid dyes by a factor of more than 3500.     

Fluorocarbons in the global environment: a review of the important interactions with atmospheric chemistry and physics

Fluorocarbon impact on ozone depletion is reviewed together with the efficacy of the Montreal Protocol in acting to correct the imbalance between stratospheric ozone production and destruction. The Protocol is also helping to reduce global warming: CFCs are shown to be currently the largest fluorocarbon contributors to climate change. Relative contributions to climate change from CFCs and their HFC substitutes are discussed, together with the consequences of control of minor greenhouse gases on an environmental impact which is dominated by carbon dioxide emissions. Both the potencies of the materials for environmental change and their concentrations in the atmosphere are important and are considered here.Trifluoroacetic acid, a minor product of atmospheric decomposition of some HCFCs and HFCs and of the pyrolysis of fluoropolymers, has been shown to be uniformly distributed in seawater to a depth of over 4000 m and so is natural, although the actual source has yet to be identified.The Montreal Protocol is only one example of action to reduce undesirable impact from fluorocarbons. Other, less universal, actions include abatement of fluoroform greenhouse gas emissions from HCFC manufacturing, process changes to eliminate trifluoromethylsulfur pentafluoride emissions from electrochemical fluorination and ceasing manufacture of perfluorooctanyl sulfonate compounds due to their persistence in human tissue.     

Mechanopolymerchemie

Although many methods can be employed to transfer energy to a chemical reaction, mechanical energy has not been widely used: It is difficult to apply mechanical forces high enough to lead to breaking bonds to small molecules. Work is the product of force and displacement but when the distances are small, very high forces are needed to obtain sufficient energy to break a bond. The situation is different in polymers, where the path length can be high. Here, bond cleavage, cycloreversions and isomerisations can be observed when mechanical energy is supplied, both in solution and solid systems. Mechanical energy can lead to different mechanistic pathways than those observed under thermal conditions or irradiation. Practical applications of the mechanochemistry of polymers are only just emerging and range from a better understanding of polymer decomposition under force to the development of strain sensors using mechanochromic polymers.