The nature of the active site in heterogeneous metal catalysis

This tutorial review, of relevance for the surface science and heterogeneous catalysis communities, provides a molecular-level discussion of the nature of the active sites in metal catalysis. Fundamental concepts such as "Br?nsted-Evans-Polanyi relations" and "volcano curves" are introduced, and are used to establish a strict partitioning between the so-called "electronic" and "geometrical" effects. This partitioning is subsequently employed as the basis for defining the concept "degree of structure sensitivity" which can be used when analyzing the structure sensitivity of catalytic reactions.     

均相催化的醇和胺借氢反应

醇和胺的借氢反应是一种制备胺类化合物的绿色途径。本文介绍了借氢反应的概念,并重点介绍了均相催化的醇和胺之间借氢反应的起源、重要进展以及未来的发展趋势。     

"Polysiloxane-Pd" nanocomposites as recyclable chemoselective hydrogenation catalysts

Polysiloxane-encapsulated "Pd"-nanoclusters were generated by reduction of Pd(OAc)(2) with polymethylhydrosiloxane, which functions as a reducing agent as well as a capping material for production and stabilization of catalytically active "Pd"-nanoparticles. Chemoselective hydrogenation of functional conjugated alkenes was achieved by in-situ- or ex-situ-generated polysiloxane-stabilized "Pd"-nanoclusters under mild reaction conditions in high yields. Electron microscopy, UV-vis, and NMR studies of the reaction mixture during the catalytic transformation were performed and, in conjunction with catalyst poisoning experiments, demonstrated unequivocally the role of polysiloxane-encapsulated "Pd"-nanoclusters as the real catalytic species. The recyclability of the "Pd"-nanoclusters was established by reusing the solid left after the reaction.     

A study on the synthesis of calix[4 and 6]arenes using alternately arranged phloroglucinols and p-tert-butylphenols

A method for the synthesis of calix[4 and 6]arenes with two or three alternately arranged phloroglucinols and p-tert-butylphenols was studied using "3+1" and "5+1" approaches, compared to a simple one-pot synthesis based on a "1+1" approach. By using Yb(OTf)3 as a catalyst, each calix[4 and 6]arenes was afforded, in an overall yield of 20.7% and 11.8% in the "3+1" and "5+1" approaches, respectively, and 24.6% and 19.9% using a "1+1" approach with chlorobenzene and toluene as refluxing solvents, respectively.     

Water-soluble ionic liquids as novel stabilizers in suspension polymerization reactions: engineering polymer beads

Aqueous solutions of ionic liquids have been used as novel and environmentally friendly reaction media to synthesize and "control" the size of different cross-linked polymer beads by suspension polymerization reactions. It was found that the investigated ionic liquids can act as novel stabilizing agents of the suspensions as a result of their surface-active properties. The results have demonstrated that the average size of polymer beads can be varied from the macro- to the nanoscale and their surface area can also be "adjusted" by this synthetic approach. Furthermore, the use of a combination of ionic liquids and water for the synthesis of polymers, the simple isolation of the products formed in this polymerization procedure, as well as the recycling of the continuous medium for further reactions open up possibilities for the development of "new and green" polymerization processes.     

ARCHITECTURE OF LADDER,TUBULAR AND SIEVE-PLATE POLYMERS PREPARED BY STEPWISE COUPLING POLYMERIZATION

"Stepwise-coupling polymerization" (SCP) is a very useful approach for preparing microstructure-controllableordered network polymers, including soluble one-dimensional ladderlike polymers (LP) and tubular polymers (TP), and two-dimensional sieve-plate polymers. The novel reactive LPs are important precursors of micro-structure controllable polymerssuch as "fishbone-" or "rowboat-"like mesomorphic polymers and their metal complexes as well as tubular polymers (TPs).They are full of great potential for use as advanced materials.     

The dynamic properties of plasticized epoxies over a wide frequency range

Summary The dynamic mechanical properties of a class of plasticized epoxies were investigated over a wide temperature range by means of a Rheovibron Viscoelastometer. Master curves for storage and loss moduli were produced by means of the frequency-temperature superposition principle, as well as for relaxation modulus by a conversion formula. The effect of plasticizer percentage on the said parameters, as well as the loss peaks, corresponding to and relaxations was investigated.     

Arsenic Curiosa and Humanity

Despite its undoubted toxicity, arsenic is a much-used element, finding applications in agriculture, industry, and medicine. Arsenic as a poison has a prominent role in plays and novels as well as in real life. In medicine, arsenic was so widely used in the 19th century as a cure-all that it has been termed a therapeutic mule. Some arsenic compounds are still used in the treatment of parasitic disease. Moreover, in a striking development for a material regarded as a carcinogen, arsenous trioxide (brand name, Trisenox) was recently approved for treatment of leukemia. Arsenic has had a profound overall impact on human lives.     

Certified reference materials chlorobiphenyls (IUPAC nos 28, 52, 101, 118, 153 and 180) in dried sewage sludge — CRM 392

Summary Six chlorinated biphenyls — CB IUPAC nos 28, 52, 101, 118, 153 and 180 — have been certified in a dried sewage sludge of a mainly residential area. After a thorough preparation the material has been studied for the within- and between bottle homogeneity as well as for its long term stability. The certification of the CBs in the dried sludge has been performed with 18 well trained laboratories, applying different methods of extraction, clean-up and chromatographic separation. ECD has been used as final detection and MS to verify the peak identities. All methods for the homogeneity and stability studies as well as those used for the certification campaign are described. CB 138 could not be certified as it co-eluted with CB 183. The major precautions followed by the participants to ensure traceability of the results to the basic units are also discussed. They highlight the level of quality control requested from certifying laboratories. The certified values were obtained after a technical discussion of the methods followed and of each of the individual results. They are given together with the indicative value for CB 138+CB 163.     

Chromene "lock", thiol "key", and mercury(II) ion "hand": a single molecular machine recognition system

A regenerative, molecular machine-like "ON-OFF-ON" chemosensor based on a chromene molecule with the pyran ring "OFF-ON-OFF" cycle is reported for the first time. It behaves as a molecular lock that requires a thiol "key" to open the lock and a mercury(II) ion "hand" that unlatches the key for unsheathing the key to close the lock.     

Spacer effect of appended moieties for molecular recognition in doubly-sodium anthranilate modified γ-cyclodextrin

-Cyclodextrin with two sodium anthranilate moieties (1) has been prepared as a sensor for detecting organic compounds including terpenoids and steroids. Compound1 shows a pure monomer fluorescence whose intensity is increased or decreased upon addition of the guest species examined. In this system, the sodium anthranilate moieties act either as a spacer, which enables the cyclodextrin to form a 1:1 host-guest complex by narrowing the -cyclodextrin cavity, or as a hydrophobic cap.1 recognizes steroids with much higher sensitivity than terpenoids, in which the appended moieties act as a hydrophobic cap for terpenoids and a spacer for steroids, respectively.     

Fluorescence studies on native and bound to trifluraline soy bean Lb"a" in the enhanced N2 fixation.

The differences in the tryptophan (Trp) fluorescence of native (control) Lb"a" and experimental substance isolated from nodules of the Williams' soy beans variety treated with trifluraline at a concentration of 2.1 x 10(-10) M have been studied. A positively charged environment has been proved for the tryptophans of the native Lb"a" and a negative one for the tryptophans of the experimental Lb"a". The difference in the tryptophan emission spectra at lambdaex = 280 and 300 nm may be assigned to conformational alterations occurring in the experimental Lb"a". This is also confirmed by the greater energy transfer from tyrosine to tryptophan in the experimental Lb"a"--30% compared to the 10% in the native Lb"a". The value of the constant of acrylamide quenching (Ksv = 2.77 M(-1)) shows that the tryptophans are buried more deeply in the experimental Lb"a" than in the native Lb"a" (Ksv = 4 M(-1)). They are substantially lower than Ksv of the standard compound N-Ac-Trp-NH2 (16.30 M(-1)). The activation energy (Ea) of the thermal quenching of tryptophan fluorescence is higher for the experimental Lb"a" (37 kJ mol(-1)) as compared to the standard compound N-Ac-Trp-NH2 (24 kJ mol(-1)) and the native Lb "a" (32 kJ mol(-1)). The dissociation constant of the complex of trifluraline with Lb "a" (6.32 x 10(-11) M) has been determined as well as the stoichiometric ratio trifluraline/Lb"a" (1:1). The estimated nitrogenase activity (microM/gfrw h) and the total Lb (mg/gfrw) for trifluraline are higher as compared to those for the control.     

Gas-liquid chromatography of isopropylidene-glucose and glucose as their trimethylsilyl derivatives

Summary This paper describes the gas chromatographic separation of the mixture of di- and mono-O-isopropylidene-D-glucose and D-glucose as their trimethylsilyl derivatives. The use of OV-101 as liquid phase provides a complete separation for the all components in the mixture. Quantative analysis was performed using xylitol as the internal standard for di- and mono-O-isopropylidene-D-glucose, and sorbitol as the internal standard for -and -glucose.     

Correction: A caged imidazopyrazinone for selective bioluminescence detection of labile extracellular copper(ii)

Correction for ‘A caged imidazopyrazinone for selective bioluminescence detection of labile extracellular copper(ii)’ by Justin J. O’Sullivan et al., Chem. Sci., 2022, https://doi.org/10.1039/D1SC07177G.

The authors regret that a key organisation was omitted from the Acknowledgements section of their article. The correct Acknowledgement should read as follows:This work was supported by the National Institute of Health (NIH MIRA 5R35GM133684-02 and NIH {"type":"entrez-nucleotide","attrs":{"text":"DK104770","term_id":"187499553","term_text":"DK104770"}}DK104770), the National Science Foundation (NSF CAREER 2048265). We also thank the Hartwell Foundation for their generous support for M. C. H. as a Hartwell Individual Biomedical Investigator, as well as the UC Davis CAMPOS Program and the University of California’s Presidential Postdoctoral Fellowship Program for their support of M. C. H. as a CAMPOS Faculty Fellow and former UC President’s Postdoctoral Fellow, respectively. This work was also supported in part by gift funds from the UC Davis Comprehensive Cancer Center. We thank Dr’s Gary and Kathy Luker (University of Michigan) for gifting MDA-MB-231 cell lines stably expressing secreted nanoluciferase. We also thank Joseph AbouAyash and Adam Hillaire for their support in the synthesis of precursors and the entire Heffern lab group for their support.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Frequency response analysis of a closed diffusion cell with two resonators

This paper deals with frequency response (FR) analysis of a closed diffusion cell system with two resonators, that is both the LHS and RHS volumes are modulated. The analysis is made for a homogeneous particle described by a single effective diffusivity as well as a biporous pellet described by macropore and micropore diffusions. It is shown that if the perturbation of the volume of the reservoir #2 is lagged behind that of the reservoir #1 by 3/2, the pressure response in reservoir #1 is significantly enhanced with larger amplitude as well as phase angle. When the perturbations of the two reservoirs are out of phase, the heat effect is reduced and can become insignificant when the two perturbations are completely out of phase ( = ). Under such a condition, the pressure difference between the two reservoirs could be doubled. In the case of biporous pellets, it is shown that the FR behaviours obtained for micropore diffusion control and macropore diffusion control are well distinguished. In the former case, the FR system reduces to a traditional batch adsorber one while in the latter case, the FR behaviour is the same as for a two resonator system with homogeneous particles. This difference can be used for the discrimination of micropore and macropore diffusion processes.     

1,3-Diphosphapropenes for novel chemistry of metal complexes

2-Methyl-3,3-diphenyl-1-(2,4,6-tri-t-butylphenyl)-1,3-diphosphapropene was obtained as a chelate ligand for palladium(II) and platinum(II) complexes. Sulfurization of 2-methyl-1,3-diphosphapropene mainly gave 3-thioxo-1,3-diphosphapropene which bears a PC-PS skeleton and was used as a ligand of transition-metal complexes. A doubly-sulfurized product of the 1,3-diphosphapropene, 1,3-dithioxo-1,3-diphosphapropene, was isolated and characterized. The palladium(II) complexes containing the ligated 1,3-diphosphapropenes were used for catalytic reactions such as cross-couplings and direct conversion of allyl alcohol to allylaniline.     

Optimal control in a dissipative system: vibrational excitation of CO/Cu(100) by IR pulses

The question as to whether state-selective population of molecular vibrational levels by shaped infrared laser pulses is possible in a condensed phase environment is of central importance for such diverse fields as time-resolved spectroscopy, quantum computing, or "vibrationally mediated chemistry." This question is addressed here for a model system, representing carbon monoxide adsorbed on a Cu(100) surface. Three of the six vibrational modes are considered explicitly, namely, the CO stretch vibration, the CO-surface vibration, and a frustrated translation. Optimized infrared pulses for state-selective excitation of "bright" and "dark" vibrational levels are designed by optimal control theory in the framework of a Markovian open-system density matrix approach, with energy flow to substrate electrons and phonons, phase relaxation, and finite temperature accounted for. The pulses are analyzed by their Husimi "quasiprobability" distribution in time-energy space.     

Soft nanotechnology with soft nanoparticles

The last decade of research in the physical sciences has seen a dramatic increase in the study of nanoscale materials. Today, "nanoscience" has emerged as a multidisciplinary effort, wherein obtaining a fundamental understanding of the optical, electrical, magnetic, and mechanical properties of nanostructures promises to deliver the next generation of functional materials for a wide range of applications. While this range of efforts is extremely broad, much of the work has focused on "hard" materials, such as Buckyballs, carbon nanotubes, metals, semiconductors, and organic or inorganic dielectrics. Meanwhile, the soft materials of current interest typically include conducting or emissive polymers for "plastic electronics" applications. Despite the continued interest in these established areas of nanoscience, new classes of soft nanomaterials are being developed from more traditional polymeric constructs. Specifically, nanostructured hydrogels are emerging as a promising group of materials for multiple biotechnology applications as the need for advanced materials in the post-genomic era grows. This review will present some of the recent advances in the marriage between water-swellable networks and nanoscience.     

Host-guest sensory system of sodium anthranilate-modifiedβ-cyclodextrin: Molecular recognition properties

Sodium anthranilate-modified-cyclodextrin (1) has been prepared as a sensor for detecting organic compounds including terpenoids and steroids.1 shows a pure monomer fluorescence whose intensity is increased or decreased upon addition of the guest species examined. In this system, the sodium anthranilate moiety acts either as a spacer, which enables the cyclodextrin to form a 11 guest complex by narrowing the-cyclodextrin cavity or acts as a hydrophobic cap.1 shows a higher sensitivity for terpenoids than for steroids, but has a higher selective molecular recognition ablity for steroids than for terpenoids.     

The Application of Scientific Methodology to a Contemporary Sports Journal

Often neglected as a foundation for scientific inquiry are contemporary sports journals and the articles contained within them. It is common to encounter authoritative assertions by various authors that are in truth ordinary suppositions infrequently based on tenable scientific data. This article outlines a model for transforming an ordinary factual statement, taken from a recent sporting journal, into an educational experience that includes experimental design, supporting documentation, methods of experimental verification, and the scientific method as a whole.