Borate adsorption at Pt(111) in acidic medium

The adsorption/desorption process of borate was studied at Pt(111) in acidic solution by cyclic voltammetry. A so-called butterfly wave in the cyclic voltammogram of Pt(111) in HClO₄ shifted to negative direction upon the addition of boric acid with the disappearance of its sharp spikes. The shift in potential was found to be −57 mV with a tenfold increase of boric acid concentration. This illustrates that this anomalous wave is due to borate adsorption/desorption by a one-electron transfer process. The borate adsorption/desorption wave was observed to shift by −63 mV/pH. At pH>3, the anomalous wave splits forming two separate waves, depending on the pH and the scan rate. The appearance of two waves is assigned to the change in the adsorption mode of borate or the participation of OH in the adsorption process.     

Uncovering the Stoichiometry of Pyrococcus furiosus RNase P,a Multi‐Subunit Catalytic Ribonucleoprotein Complex,by Surface‐Induced Dissociation and Ion Mobility Mass Spectrometry

We demonstrate that surface‐induced dissociation (SID) coupled with ion mobility mass spectrometry (IM‐MS) is a powerful tool for determining the stoichiometry of a multi‐subunit ribonucleoprotein (RNP) complex assembled in a solution containing Mg²⁺. We investigated Pyrococcus furiosus (Pfu) RNase P, an archaeal RNP that catalyzes tRNA 5′ maturation. Previous step‐wise, Mg²⁺‐dependent reconstitutions of Pfu RNase P with its catalytic RNA subunit and two interacting protein cofactor pairs (RPP21⋅RPP29 and POP5⋅RPP30) revealed functional RNP intermediates en route to the RNase P enzyme, but provided no information on subunit stoichiometry. Our native MS studies with the proteins showed RPP21⋅RPP29 and (POP5⋅RPP30)₂ complexes, but indicated a 1:1 composition for all subunits when either one or both protein complexes bind the cognate RNA. These results highlight the utility of SID and IM‐MS in resolving conformational heterogeneity and yielding insights on RNP assembly.     

Facile synthesis of platinum nanoparticle-containing porous carbons,and their application to amperometric glucose biosensing

This study describes the facile synthesis of platinum nanoparticle-containing porous carbons (Pt/C) by carbonization of freeze-dried agarose gels containing potassium tetrachloroplatinate under a nitrogen atmosphere at 800 °C. By adjusting the ratio between agarose and platinate in the freeze-dried gels, the Pt content in the final Pt/C products could be systematically varied from 0–10 wt.%. Transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, Raman spectroscopy, and nitrogen physisorption measurements revealed that the Pt/C materials obtained by this method possess high surface areas (350–500 m² g⁻¹), narrow Pt nanoparticle size distributions (6 ± 3 nm) and nanocrystalline graphite –like carbon character. By immobilization of glucose oxidase on the surface of a 4 wt.% Pt/C electrocatalyst prepared by this route, a very sensitive amperometric glucose biosensor was obtained (response time <2 min, sensitivity 1.9 mA M⁻¹; and a linear response with glucose concentration up to 10 mM). The simplicity and versatility of the described synthetic method suggests its application to the preparation of carbon supported noble metal catalysts including palladium/C and gold/C.

This study describes the facile synthesis of platinum nanoparticle-containing porous carbons (Pt/C) by carbonization of freeze-dried agarose gels containing potassium tetrachloroplatinate. The Pt/C materials exhibited excellent electrocatalytic activities, as demonstrated by their successful integration into amperometric glucose biosensor

     

Polytypic phase transition in alkyl chain-functionalized valence tautomeric complexes

A novel series of valence tautomeric (VT) complexes, [Co(Cnbpy)(3,5-DTBQ)2] (Cnbpy = 4,4'-dialkyl-2,2'-bipyridine (alkyl = (C(n)H(2n+1)) where n = 0 (CoC0bpy), 1 (CoC1bpy), 5 (CoC5bpy), 9 (CoC9bpy) and 13 (CoC13bpy); 3,5-DTBQ = 3,5-di-tert-butylsemiquinonate or catecholate), including two previously reported complexes (CoC0bpy and CoC1bpy), were systematically prepared and their properties examined. Introduction of alkyl groups into VT chromophores leads to unexpected variations in the VT process, depending on the lengths of the alkyl chains. An even more interesting observation is that significant polytypic phase transitions with crystallographic symmetry changes accompanying the abrupt VT conversion are induced for the first time in CoC9bpy and CoC13bpy.     

Xenophilic complexes bearing a Tp(R) Ligand, [Tp(R)M--M'Ln] [Tp(R) = Tp(iPr2), Tp(#) (Tp(Me2,4-Br)); M=Ni, Co, Fe, Mn; M'Ln = Co(CO)4, Co(CO)3(PPh3), RuCp(CO)2]: the two metal centers are held together not by covalent interaction but by electrostatic attraction

A series of dinuclear complexes, [Tp(R)M--M'L(n)] [Tp(iPr(2) )M--Co(CO)(4) (1; M=Ni, Co, Fe, Mn); Tp(#)M--Co(CO)(4) (1'; M=Ni, Co); Tp(#)Ni--RuCp(CO)(2) (3')] (Tp(iPr(2) )=hydrotris(3,5-diisopropylpyrazolyl)borato; Tp(#) (Tp(Me(2),4-Br))=hydrotris(3,5-dimethyl-4-bromopyrazolyl)borato), has been prepared by treatment of the cationic complexes [Tp(iPr(2) )M(NCMe)(3)]PF(6) or the halo complexes [Tp(#)M--X] with the appropriate metalates. Spectroscopic and crystallographic characterization of 1-3' reveals that the tetrahedral, high-spin Tp(R)M fragment and the coordinatively saturated carbonyl-metal fragment (M'L(n)) are connected only by a metal-metal interaction and, thus, the dinuclear complexes belong to a unique class of xenophilic complexes. The metal-metal interaction in the xenophilic complexes is polarized, as revealed by their nu(CO) vibrations and structural features, which fall between those of reference complexes: covalently bonded species [R--M'L(n)] and ionic species [M'L(n)](-). Unrestricted DFT calculations for the model complexes [Tp(H(2) )Ni--Co(CO)(4)], [Tp(H(2) )Ni--Co(CO)(3)(PH(3))], and [Tp(H(2) )Ni--RuCp(CO)(2)] prove that the two metal centers are held together not by covalent interactions, but by electrostatic attractions. In other words, the obtained xenophilic complexes can be regarded as carbonylmetalates, in which the cationic counterpart interacts with the metal center rather than the oxygen atom of the carbonyl ligand. The xenophilic complexes show divergent reactivity dependent on the properties of donor molecules. Hard (N and O donors) and soft donors (P and C donors) attack the Tp(R)M part and the ML(n) moiety, respectively. The selectivity has been interpreted in terms of the hard-soft theory, and the reactions of the high-spin species 1-3' with singlet donor molecules should involve a spin-crossover process.     

New dimension in nano-imaging: breaking through the diffraction limit with scanning near-field optical microscopy

In recent years scanning near-field optical microscopy (SNOM) has developed into a powerful surface analytical technique for observing specimens with lateral resolution equal to or even better than 100 nm. A large number of applications, from material science to biology, have been reported. In this paper, two different kinds of near-field optical microscopy, aperture and scattering-type SNOM, are reviewed together with recent studies in surface analysis and biology. Here, near-field optical techniques are discussed in comparison with related methods, such as scanning probe and standard optical microscopy, with respect to their specific advantages and fields of application.     

Intermolecular π‐stacking and F...F interactions of fluorine‐substituted meso‐alkynylporphyrin

Two C2‐symmetric meso‐alkynylporphyrins, namely 5,15‐bis[(4‐butyl‐2,3,5,6‐tetrafluorophenyl)ethynyl]‐10,20‐dipropylporphyrin, C₅₀H₄₂F₈N₄, (I), and 5,15‐bis[(4‐butylphenyl)ethynyl]‐10,20‐dipropylporphyrin, C₅₀H₅₀N₄, (II), show remarkable π–π stacking that forms columns of porphyrin centers. The tetrafluorophenylene moieties in (I) show intermolecular interactions with each other through the F atoms, forming one‐dimensional ribbons. No significant π–π interactions are observed in the plane of the phenylene and tetrafluorophenylene moieties in either (I) or (II). The molecules of both compounds lie about inversion centers.     

Fully and partially fluorinated flavone derivatives

In the crystal structures of the fully and partially fluorinated flavone derivatives 5,6,7,8‐tetrafluoro‐2‐(2,3,4,5,6‐pentafluorophenyl)‐4H‐1‐benzopyran‐4‐one, C₁₅HF₉O₂, (I), and 5,6,7,8‐tetrafluoro‐2‐phenyl‐4H‐1‐benzopyran‐4‐one, C₁₅H₆F₄O₂, (II), the pentafluorophenyl group and the pyranone moiety in (I) are twisted due to repulsion of the F substituents, and a CO(δ⁻)...π(δ⁺) intermolecular interaction is observed between the carbonyl O atom and the pentafluorophenyl group. In (II), on the other hand, the phenyl group and the pyranone moiety are almost coplanar, and arene–perfluoroarene interactions are observed in the head‐to‐tail intermolecular columnar stacking between the phenyl group and the tetrafluorophenylene moiety.     

Noncovalent Modification of Cycloparaphenylene by Catenane Formation Using an Active Metal Template Strategy**

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π-conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π-conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2′-bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post-modification. Following the AMT strategy, the [9]CPP-bipyridine catenane was successfully synthesized through Ni-mediated aryl-aryl coupling. Catalytic C−H borylation/cross-coupling and metal complexation of the bipyridine macrocycle moiety, an effective post-functionalization method, were also demonstrated with the [9]CPP-bipyridine catenane. Single-crystal X-ray structural analysis revealed that the [9]CPP-bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions.