Guanidinium Alkynesulfonates with Single‐Layer Stacking Motif: Interlayer Hydrogen Bonding Between Sulfonate Anions Changes the Orientation of the Organosulfonate R Group from “Alternate Side” to “Same Side”

Hydrolyses of HC?CSO₃SiMe₃ ( 1 ) and CH₃C?CSO₃SiMe₃ ( 2 ) lead to the formation of acetylenic sulfonic acids HC?CSO₃H?2.33 H₂O ( 3 ) and CH₃C?CSO₃H?1.88 H₂O ( 4 ). These acids were reacted with guanidinium carbonate to yield [⁺C(NH₂)₃][HC?CSO₃^?] ( 5 ) and [⁺C(NH₂)₃][CH₃C?CSO₃^?] ( 6 ). Compounds 1 – 6 were characterized by spectroscopic methods, and the X‐ray crystal structures of the guanidinium salts were determined. The X‐ray results of 5 show that the guanidinium cations and organosulfonate anions associate into 1D ribbons through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions, whereas association of these ions in 6 is achieved through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) and ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) interactions. The ribbons in 5 associate into 2D sheets through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{3\hfill \atop 6\hfill}}}$ (12) rings, whereas those in 6 are connected through ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) and ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{4\hfill \atop 6\hfill}}}$ (14) rings. Compound 6 exhibits a single‐layer stacking motif similar to that found in guanidinium alkane‐ and arenesulfonates, that is, the alkynyl groups alternate orientation from one ribbon to the next. The stacking motif in 5 is also single‐layer, but due to interlayer hydrogen bonding between sulfonate anions, the alkynyl groups of each sheet all point to the same side of the sheet.     

Unprecedented Electron‐Poor Octahedral Ta6 Clusters in a Solid‐State Compound: Synthesis,Characterisations and Theoretical Investigations of Cs2BaTa6Br15O3

The crystal structure of Cs₂BaTa₆Br₁₅O₃ has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta₆ clusters is similar to that of Cs₂LaTa₆Br₁₅O₃ exhibiting 14‐MEs per [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta₆ cluster in the solid state.     

The Electronic Structure of the Al3− Anion: Is it Aromatic?

Multiconfigurational high‐level electronic structure calculations show that the ${{\rm Al}{{- \hfill \atop 3\hfill}}}$ ring‐like cluster anion has three close low‐lying electronic states of different spin, all of them having strong multiconfigurational character. The aromaticity of the cluster has, therefore, been studied by means of total electron delocalization and normalized multicenter electron delocalization indices evaluated from the multiconfigurational wave functions of each state. The lowest‐lying singlet and triplet states are found to be highly aromatic, whereas the next lowest‐lying state, the quintet state, has much less, though non‐negligible, aromatic character.     

Polysulfide Chemistry in Sodium–Sulfur Batteries and Related Systems— A Computational Study by G3X(MP2) and PCM Calculations

The sodium–sulfur (NAS) battery is a candidate for energy storage and load leveling in power systems, by using the reversible reduction of elemental sulfur by sodium metal to give a liquid mixture of polysulfides (Na₂S_n) at approximately 320 °C. We investigated a large number of reactions possibly occurring in such sodium polysulfide melts by using density functional calculations at the G3X(MP2)/B3LYP/6‐31+G(2df,p) level of theory including polarizable continuum model (PCM) corrections for two polarizable phases, to obtain geometric and, for the first time, thermodynamic data for the liquid sodium–sulfur system. Novel reaction sequences for the electrochemical reduction of elemental sulfur are proposed on the basis of their Gibbs reaction energies. We suggest that the primary reduction product of S₈ is the radical anion ${{\rm S}{{{{\bullet}}- \hfill \atop 8\hfill}}}$ , which decomposes at the operating temperature of NAS batteries exergonically to the radicals ${{\rm S}{{{{\bullet}}- \hfill \atop 2\hfill}}}$ and ${{\rm S}{{{{\bullet}}- \hfill \atop 3\hfill}}}$ together with the neutral species S₆ and S₅, respectively. In addition, ${{\rm S}{{{{\bullet}}- \hfill \atop 8\hfill}}}$ is predicted to disproportionate exergonically to S₈ and ${{\rm S}{{2- \hfill \atop 8\hfill}}}$ followed by the dissociation of the latter into two ${{\rm S}{{{{\bullet}}- \hfill \atop 4\hfill}}}$ radical ions. By recombination reactions of these radicals various polysulfide dianions can in principle be formed. However, polysulfide dianions larger than ${{\rm S}{{2- \hfill \atop 4\hfill}}}$ are thermally unstable at 320 °C and smaller dianions as well as radical monoanions dominate in Na₂S_n (n=2–5) melts instead. The reverse reactions are predicted to take place when the NAS battery is charged. We show that ion pairs of the types ${{\rm NaS}{{{{\bullet}}\hfill \atop 2\hfill}}}$ , ${{\rm NaS}{{- \hfill \atop n\hfill}}}$ , and Na₂S_n can be expected at least for n=2 and 3 in NAS batteries, but are unlikely in aqueous sodium polysulfide except at high concentrations. The structures of such radicals and anions with up to nine sulfur atoms are reported, because they are predicted to play a key role in the electrochemical reduction process. A large number of isomerization, disproportionation, and sulfurization reactions of polysulfide mono‐ and dianions have been investigated in the gas phase and in a polarizable continuum, and numerous reaction enthalpies as well as Gibbs energies are reported.     

Rubidium Polyhydrides Under Pressure: Emergence of the Linear H3− Species

The structures of compressed rubidium polyhydrides, RbH_n with n>1, and their evolution under pressure are studied using density functional theory calculations. These phases, which start to stabilize at only P=2 GPa, consist of Rb⁺ cations and one or more of the following species: H^? anions, H₂ molecules, and ${{\rm H}{{- \hfill \atop 3\hfill}}}$ molecules. The latter motif, the simplest example of a three‐center four‐electron bond, is found in the most stable structures, RbH₅ and RbH₃, which metallize above 200 GPa. At the highest pressures studied, our evolutionary searches find an RbH₆ phase which contains polymeric (${{\rm H}{{- \hfill \atop 3\hfill}}}$ )_∞ chains that show signs of one‐dimensional liquid‐like behavior.     

A Copper–Formate Framework Showing a Simple to Helical Antiferroelectric Transition with Prominent Dielectric Anomalies and Anisotropic Thermal Expansion,and Antiferromagnetism

We present here the compound [NH₄][Cu(HCOO)₃], a new member of the [NH₄][M(HCOO)₃] family. The Jahn–Teller Cu²⁺ ion leads to a distorted 4⁹?6⁶ chiral Cu–formate framework. In the low‐temperature (LT) orthorhombic phase, the Cu²⁺ is in an elongated octahedron, and the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ions in the framework channel are off the channel axis. From 94 to 350 K the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ion gradually approaches the channel axis and the related modulation of the framework and the hydrogen‐bond system occurs. The LT phase is simple antiferroelectric (AFE). The material becomes hexagonal above 355 K. In the high‐temperature (HT) phase, the Cu²⁺ octahedron is compressed, and the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ions are arranged helically along the channel axis. Therefore, the phase transition is one from LT simple AFE to HT helical AFE. The temperature‐dependent structure evolution is accompanied by significant thermal and dielectric anomalies and anisotropic thermal expansion, due to the different status of the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ions and the framework modulations, and the structure–property relationship was established based on the extensive variable‐temperature single‐crystal structures. The material showed long range ordering of antiferromagnetism (AFM), with low dimensional character and a Néel temperature of 2.9 K. Therefore, within the material AFE and AFM orderings coexist in the low‐temperature region.     

Calixarene‐Based Surfactants: Conformational‐Dependent Solvation Shells for the Alkyl Chains

Thermodynamic parameters obtained from studying the micellization of amphiphilic p‐sulfonatocalix[n]arenes were correlated with the alkyl chain length and with the number of monomeric units (n) in the calix[n]arene structure. The micellization Gibbs free energy (Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) becomes more negative upon increasing the alkyl chain length of the p‐sulfonatocalix[4]arene. This is in agreement with the trend generally observed for other surfactants. However, the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ value for transferring one CH₂ group from the bulk aqueous medium to the micelle [Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH₂)] is lower than the value generally observed for single‐chain surfactants, suggesting the existence of intramolecular interactions between the alkyl chains of the free unimers. On the other hand, the critical micelle concentration (cmc; per alkyl chain unit) increased with the increasing number of monomeric units. These results are explained on the basis of the conformation adopted by the calixarene in the bulk solution. The calix[4]arene derivatives are preorganized into the cone conformation, which is favorable for the formation of globular aggregates. The calix[6]arene and calix[8]arene derivatives do not adopt cone conformations. Changing these conformations to the more favorable cone conformer in the aggregates implies an energetic cost that contributes to making Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ less efficient. In the case of the calix[6]arene derivative this energetic cost is enthalpic, whereas in the case of the octamer it is both enthalpic and entropic. Both the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH₂) value and the change in heat capacity (ΔC${{\rm p}{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) seem to indicate that for the cone calix[4]arene derivatives all alkyl chains are solvated by the same hydration shell, whereas in the case of the highly flexible calix[8]arene derivative each alkyl chain is individually hydrated.     

Crystal Structures and Emitting Properties of Trifluoromethylaminoquinoline Derivatives: Thermal Single‐Crystal‐to‐Single‐Crystal Transformation of Polymorphic Crystals That Emit Different Colors

2,4‐Trifluoromethylquinoline (TFMAQ) derivatives that have amine ( 1 ), methylamine ( 2 ), phenylamine ( 3 ), and dimethylamine ( 4 ) substituents at the 7‐position of the quinoline ring were prepared and crystallized. Six crystals including the crystal polymorphs of 2 (crystal GB and YG) and 3 (crystal B and G) were obtained and characterized by X‐ray crystallography. In solution, TFMAQ derivatives emitted relatively strong fluorescence (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =418–469 nm and Φ_f(s)=0.23–0.60) depending on the solvent polarity. From Lippert–Mataga plots, Δμ values in the range of 7.8–14 D were obtained. In the crystalline state, TFMAQ derivatives emitted at longer wavelengths (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464–530 nm) with lower intensity (Φ_f(c)=0.01–0.28) than those in n‐hexane solution. The polymorphous crystals of 2 and 3 emitted different colors: 2 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =470 and 530 nm with Φ_f(c)=0.04 and approximately 0.01 for crystal GB and YG, respectively; and 3 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464 and 506 nm with Φ_f(c)=0.28 and approximately 0.28 for crystal B and G, respectively. In both crystal polymorphs of 2 and 3 , crystals GB and G showed emission color changes by heating/melting/cooling cycles that were representative. By following the color changes in heating at the temperature below the melting point with X‐ray diffraction measurements and X‐ray crystallography, the single‐crystal‐to‐single‐crystal transformations from crystal GB to YG for 2 and from crystal B to G for 3 were revealed.     

Design of a Solid‐State Electrochemiluminescence Biosensor for Detection of PML/RARα Fusion Gene Using Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$‐AuNPs Aggregations on Gold Electrode

A solid‐state electrochemiluminescence (ECL) biosensor based on special ferrocene‐labeled molecular beacon (Fc‐MB) for highly sensitive detection of promyelocytic leukemia/retinoic acid receptor alpha (PML/RARα) fusion gene was developed successfully using Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ /2‐(dibutylamino)ethanol (DBAE) as detecting pattern. Such a special sensor involves two main parts, an ECL substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Ruthenium (II) tris‐(bipyridine) and Au nanoparticles (Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ ‐AuNPs) onto the Au electrode (AuE) surface. The molecular beacon probe in which the ferrocene tag could effectively quench the ECL of the Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ acted as ECL intensity switch. The molecular beacon probe was designed with special base sequence, which could hybridize with its complementary target DNA. In the absence of a target, the hairpin structure of the probe forced the ferrocene (Fc) into close proximity with the ECL substrate, thus reducing ECL intensity. Target binding allowed the Fc away from the ECL substrate and resulted in an obvious increment in ECL intensity due to the decreased Fc quenching effect. The effect of the amount of Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ and the mixing procedure of Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ and AuNPs solution on the fabrication of ECL film had been investigated. As a result, the change of ECL intensity had a direct relationship with the logarithm of PML/RARα fusion gene concentration in the range of 0.05–500 pM with a detection limit of 7 fM, and the developed biosensor possessed good molecular recognizability in human serum. Thus, the approach holds promise for the early diagnostics and prognosis monitoring of APL and other diseases.     

Tautomerism and Atropisomerism in Free‐Base (meso)‐Strapped Porphyrins: Static and Dynamic Aspects

We report herein some outstanding examples of atropisomerism and tautomerism in five (meso‐)strapped porphyrins. Porphyrins S0 – S4 have been synthesised, characterised and studied in detail by spectroscopic and spectrometric techniques, and their isomeric purity verified by HPLC analysis. In particular, they exhibit perfectly well‐defined NMR spectra that display distinct patterns depending on their average symmetry at room temperature: C_2v, D_2d, C_2h, C_2v, and D_2h for S0 – S4 , respectively. NH tautomerism was evidenced by variable‐low‐temperature ¹H NMR experiments in [D₂]dichloromethane performed on S0 (Δ${G{{{\ne}\hfill \atop {\rm 298K}\hfill}}}$ =48±1 kJ mol^?1) and S1 (Δ${G{{{\ne}\hfill \atop {\rm 298K}\hfill}}}$ =55±3 kJ mol^?1), which has led to an understanding of the average spectra observed for the five porphyrins at room temperature. On the other hand, S2 and S3 are stable atropisomers at room temperature, easily separated and characterised, as a result of restricted rotation of their strapped bridges due to their high rotational barrier energies. Upon heating to 82 °C, they slowly equilibrate to a thermodynamic ratio of 64:36 in favour of the more stable S2 isomer. This atropisomerisation process was evidenced by ¹H NMR spectroscopy and monitored by HPLC, from which high rotational energy barriers of 115.2 (Δ${G{{{\ne}\hfill \atop {\rm S2}\rightarrow {\rm S3}\hfill}}}$ ) and 116.9 kJ mol^?1 (Δ${G{{{\ne}\hfill \atop {\rm S2}\rightarrow {\rm S3}\hfill}}}$ ) were deduced.     

Tuning the Photocatalytic Activity of CdS Nanocrystals through Intermolecular Interactions in Ionic‐Liquid Solvent Systems

Synthetic solvent systems for the fine‐tuned preparation of CdS nanocrystallites, active in visible‐light photocatalytic hydrogen production, were studied. To control crystallite size and spectral properties, the CdS crystals were synthesised by using different solvent systems, containing a series of tetrabutylammonium amino carboxylate ionic liquids as the crystal‐growth control agents. Six samples of CdS, all with similar physical and spectral properties, exhibited greatly varying photocatalytic activity, with the most active sample outperforming the least active one by almost 60 %. To rationalise this effect, the intermolecular interactions of the synthesis solvent system with the growing CdS nanocrystallites were characterised by using the Reichart betaine dye and the ${E{{{\rm N}\hfill \atop {\rm T}\hfill}}}$ polarity scale. A correlation was observed between the ${E{{{\rm N}\hfill \atop {\rm T}\hfill}}}$ values of the solvent system and the photocatalytic activity of the CdS nanocrystallite, suggesting that the hydrogen‐bond‐donating ability and/or dipolarity/polarisability interactions of the solvent system led to the preferential formation of active surfaces/surface sites on the CdS crystals.     

A Bis(pyridine N‐oxide) Analogue of DOTA: Relaxometric Properties of the GdIII Complex and Efficient Sensitization of Visible and NIR‐Emitting Lanthanide(III) Cations Including PrIII and HoIII

We report the synthesis of a cyclen‐based ligand (4,10‐bis[(1‐oxidopyridin‐2‐yl)methyl]‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid= L1 ) containing two acetate and two 2‐methylpyridine N‐oxide arms anchored on the nitrogen atoms of the cyclen platform, which has been designed for stable complexation of lanthanide(III) ions in aqueous solution. Relaxometric studies suggest that the thermodynamic stability and kinetic inertness of the Gd^III complex may be sufficient for biological applications. A detailed structural study of the complexes by ¹H NMR spectroscopy and DFT calculations indicates that they adopt an anti‐Δ(λλλλ) conformation in aqueous solution, that is, an anti‐square antiprismatic (anti‐SAP) isomeric form, as demonstrated by analysis of the ¹H NMR paramagnetic shifts induced by Yb^III. The water‐exchange rate of the Gd^III complex is ${k{{298\hfill \atop {\rm ex}\hfill}}}$ =6.7×10⁶ s^?1, about a quarter of that for the mono‐oxidopyridine analogue, but still about 50 % higher than the ${k{{298\hfill \atop {\rm ex}\hfill}}}$ of GdDOTA (DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid). The 2‐methylpyridine N‐oxide chromophores can be used to sensitize a wide range of Ln^III ions emitting in both the visible (Eu^III and Tb^III) and NIR (Pr^III, Nd^III, Ho^III, Yb^III) spectral regions. The emission quantum yield determined for the Yb^III complex (${Q{{{\rm L}\hfill \atop {\rm Yb}\hfill}}}$ =7.3(1)×10^?3) is among the highest ever reported for complexes of this metal ion in aqueous solution. The sensitization ability of the ligand, together with the spectroscopic and relaxometric properties of its complexes, constitute a useful step forward on the way to efficient dual probes for optical imaging (OI) and MRI.     

Characterizing Methyl‐Bearing Side Chain Contacts and Dynamics Mediating Amyloid β Protofibril Interactions Using 13Cmethyl‐DEST and Lifetime Line Broadening

Many details pertaining to the formation and interactions of protein aggregates associated with neurodegenerative diseases are invisible to conventional biophysical techniques. We recently introduced ¹⁵N dark‐state exchange saturation transfer (DEST) and ¹⁵N lifetime line‐broadening to study solution backbone dynamics and position‐specific binding probabilities for amyloid β (Aβ) monomers in exchange with large (2–80 MDa) protofibrillar Aβ aggregates. Here we use ¹³C_methyl DEST and lifetime line‐broadening to probe the interactions and dynamics of methyl‐bearing side chains in the Aβ‐protofibril‐bound state. We show that all methyl groups of Aβ40 populate direct‐contact bound states with a very fast effective transverse relaxation rate, indicative of side‐chain‐mediated direct binding to the protofibril surface. The data are consistent with position‐specific enhancements of ¹³C_methyl‐${R{{{\rm tethered}\hfill \atop 2\hfill}}}$ values in tethered states, providing further insights into the structural ensemble of the protofibril‐bound state.     

Nanosilver‐Decorated TiO2 Nanofibers Coated with a SiO2 Layer for Enhanced Light Scattering and Localized Surface Plasmons in Dye‐Sensitized Solar Cells

Enhanced harvesting of visible light is vital to the development of highly efficient dye‐sensitized solar cells (DSSCs). Nanosilver‐decorated TiO₂ nanofibers (Ag@TiO₂ NFs) were synthesized by depositing chemically reduced Ag ions onto the surface of electrospun TiO₂ nanofibers (TiO₂ NFs). The prepared Ag@TiO₂ NFs were coated with SiO₂ (SiO₂@Ag@TiO₂ NFs) by using PVP as coupling agent for protecting corrosion of Ag nanoparticle by I^?/${{\rm I}{{- \hfill \atop 3\hfill}}}$ solution. The fabricated SiO₂@Ag@TiO₂ NFs demonstrated a synergistic effect of light scattering and surface plasmons, leading to an enhanced light absorption. Moreover, an anode consisting of SiO₂@Ag@TiO₂ NFs incorporating TiO₂ nanoparticles (NPs) increased light harvesting without substantially sacrificing dye attachment. The power conversion efficiency increased from 6.8 to 8.7 % for a thick film (10 μm), that is, 28 %. These results suggest that SiO₂@Ag@TiO₂ NFs are promising materials for enhanced light absorption in dye‐sensitized solar cells.     

Catalytic Dinitrogen Reduction at the Molybdenum Center Promoted by a Bulky Tetradentate Phosphine Ligand

Stoichiometric reduction of N₂ at a Mo center stabilized by a bulky tetradentate phosphine ligand (${{\rm PP}{{{\rm Cy}\hfill \atop 3\hfill}}}$ ) allowed isolation of Mo–imidoamine and Mo–imido complexes. Both complexes as well as the Mo^II precursor are equally suitable catalysts for the synthesis of NTMS₃ (TMS=trimethylsilyl) from N₂, TMSCl, and electron sources. Mechanistic studies prove the involvement of a TMS radical at least in one of the catalytic steps.     

A First‐Principles Study on the Interaction between Alkyl Radicals and Graphene

The interaction between alkyl radicals and graphene was studied by means of dispersion‐corrected density functional theory. The results indicate that isolated alkyl radicals are not likely to be attached onto perfect graphene. It was found that the covalent binding energies are low, and because of the large entropic contribution, Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ is positive for methyl, ethyl, isopropyl, and tert‐butyl radicals. Although the alkylation may proceed by moderate heating, the desorption barriers are low. For the removal of the methyl and tert‐butyl radicals covalently bonded to graphene, 15.3 and 2.4 kcal mol^?1 are needed, respectively. When alkyl radicals are agglomerated, the binding energies are increased. For the addition in the ortho position and on opposite sides of the sheet, the graphene–CH₃ binding energy is increased by 20 kcal mol^?1, whereas for the para addition on the same side of the sheet, the increment is 9.4 kcal mol^?1. In both cases, the agglomeration turns the Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ <0. For the ethyl radical, the ortho addition on opposite sides of the sheet has a negative Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ , whereas for isopropyl and tert‐butyl radicals the reactions are endergonic. The attachment of the four alkyl radicals under consideration onto the zigzag edges is exergonic. The noncovalent adsorption energies computed for ethyl, isopropyl, and tert‐butyl radicals are significantly larger than the graphene–alkyl‐radical covalent binding energies. Thus, physisorption is favored over chemisorption. As for the Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ for the adsorption of isolated alkyl radicals, only the tert‐butyl radical is likely to be exergonic. For the phenalenyl radical we were not able to locate a local minimum for the chemisorbed structure since it moves to the physisorbed structure. An important conclusion of this work is that the consideration of entropic effects is essential to investigate the interaction between graphene and free radicals.     

A Solid‐State Electrochemiluminescence Sensor for Label‐Free Analysis of Leukemia Cells

A novel electrochemiluminescence (ECL) method for label‐free detection of cancer cells was proposed for the first time by capturing negatively charged Jurkat cells onto Ru(bpy′)${{{2+\hfill \atop 3\hfill}}}$ ‐immobilized indium tin oxide (ITO) electrode via electrostatic interaction. The ECL sensor exhibited excellent sensitivity, good stability and a linear response to Jurkat cells in the concentration range from 1×10³ to 2×10⁵ cells/mL, with a detection limit of 730 cells/mL. Furthermore, the method was successfully applied in the study of cell growth and cell apoptosis, which was supported by fluorescent images analysis. The proposed protocol is simple, rapid, inexpensive and universally targetable for tumors, offering a novel platform for the development of an ECL biosensor for cell detection.     

Electrografting of Diazonium‐Functionalized Polyoxometalates: Synthesis,Immobilisation and Electron‐Transfer Characterisation from Glassy Carbon

Polyoxometalates (POMs) are attractive candidates for the rational design of multi‐level charge‐storage materials because they display reversible multi‐step reduction processes in a narrow range of potentials. The functionalization of POMs allows for their integration in hybrid complementary metal oxide semiconductor (CMOS)/molecular devices, provided that fine control of their immobilisation on various substrates can be achieved. Owing to the wide applicability of the diazonium route to surface modification, a functionalized Keggin‐type POM [PW₁₁O₃₉{Ge(p‐C₆H₄‐C?C‐C₆H₄‐${{\rm N}{{+\hfill \atop 2\hfill}}}$ )}]^3? bearing a pending diazonium group was prepared and subsequently covalently anchored onto a glassy carbon electrode. Electron transfer with the immobilised POM was thoroughly investigated and compared to that of the free POM in solution.     

Solar Fuels: Photoelectrosynthesis of CO from CO2 at p‐Type Si using Fe Porphyrin Electrocatalysts

Photoelectrocatalytic conversion of CO₂ to CO can be driven at a boron‐doped, hydrogen terminated, p‐type silicon electrode using a meso‐tetraphenylporphyrin Fe^III chloride in the presence of CF₃CH₂OH as a proton source and 0.1 M [NBu₄][BF₄]/MeCN/5 % DMF (v/v) as the electrolyte. Under illumination with polychromatic light, the photoelectrocatalysis operates with a photovoltage of about 650 mV positive of that for the dark reaction. Carbon monoxide is produced with a current efficiency >90 % and with a high selectivity over H₂ formation. Photoelectrochemical current densities of 3 mA cm^?2 at ?1.1 V versus SCE are typical, and 175 turnovers have been attained over a 6 h period. Cyclic voltammetric data are consistent with a turnover frequency of ${k{{{\rm Si}\hfill \atop {\rm obs}\hfill}}}$ =0.24×10⁴ s^?1 for the photoelectrocatalysis at p‐type Si at ?1.2 V versus SCE this compares with ${k{{{\rm C}\hfill \atop {\rm obs}\hfill}}}$ =1.03×10⁴ s^?1 for the electrocatalysis in the dark on vitreous carbon at a potential of ?1.85 V versus SCE.