Anion Recognition by Urea Derivatives of Anthraquinone: Dihydrogen Phosphate Ion Selective Neutral Receptors

Three urea derivatives of anthraquinone were synthesized and they showed a high selectivity for dihydrogen phosphate ions.     

2‐(1 H‐1,2,3‐Triazol‐4‐yl)‐Pyridine Ligands as Alternatives to 2,2′‐Bipyridines in Ruthenium(II) Complexes

The synthesis of a variety of 2‐(1H‐1,2,3‐triazol‐4‐yl)‐pyridines by click chemistry is demonstrated to provide straightforward access to mono‐functionalized ligands. The ring‐opening polymerization of ε‐caprolactone initiated by such a mono‐functionalized ligand highlights the synthetic potential of this class of bidentate ligands with respect to polymer chemistry or the attachment onto surfaces and nanoparticles. The coordination to Ru^II ions results in homoleptic and heteroleptic complexes with the resultant photophysical and electrochemical properties strongly dependent on the number of these ligands attached to the Ru^II core.     

LED‐Illuminated NMR Studies of Flavin‐Catalyzed Photooxidations Reveal Solvent Control of the Electron‐Transfer Mechanism

Mechanistic insights into chemical photocatalysis are mainly the domain of UV/Vis spectroscopy, because NMR spectroscopy has been limited by the type of illumination so far. An improved LED‐based illumination device can be used to obtain NMR reaction profiles of photocatalytic reactions under synthetic conditions and perform both photo‐CIDNP and intermediate studies. Flavin‐catalyzed photooxidations of alcohols show the potential of this setup. After identical initial photoreaction steps the stabilization of a downstream intermediate is the key to the further reaction mechanism and the reactivity. As a chemical photocatalyst flavin can act either as a one‐ or a two‐electron mediator when the stability of the zwitterionic radical pair is moldulated in different solvents. This demonstrates the importance of downstream intermediates and NMR‐accessible complementary information in photocatalytic reactions and suggests the control of photoorganic reactions by solvent effects.     

Synthesis and Solution Studies of Silver(I)‐Assembled Porphyrin Coordination Cages

The synthesis and the characterization of two porphyrin coordination cages are reported. The design of the cage formation is based on the coordination of silver(I) ions to the pyridyl units of 3‐pyridyl appended porphyrins. ¹H/¹⁰⁹Ag NMR spectroscopy, and diffusion‐ordered spectroscopy (DOSY) experiments demonstrate that both the free base porphyrin 2H‐TPyP and the Zn‐porphyrin Zn‐TPyP form the closed cages, [ Ag₄(2H‐TPyP)₂ ]⁴⁺ and [ Ag₄(Zn‐TPyP)₂ ]⁴⁺, respectively, upon addition of two equivalents of Ag⁺. The complexation processes are characterized in details by means of absorption and emission spectroscopy in diluted CH₂Cl₂ solutions. The data are discussed in the frame of the point‐dipole exciton coupling theory; the two porphyrin monomers, in fact, experience a rigid face‐to‐face geometry in the cages and a weak inter‐porphyrin exciton coupling. An intermediate species is observed, for Zn‐TPyP , in a porphyrin/Ag⁺ stoichiometric ratio of about 1:0.5 and is tentatively ascribed to an oblique open form. The occurrence of a photoinduced electron‐transfer reaction within the cages is excluded on the basis of the experimental outcomes and thermodynamic evaluations. Photophysical experiments evidence different reactivities of singlet and triplet excited states in the assemblies. A lower fluorescence quantum yield and triplet formation is discussed in relation to the constrained geometry of the complexes. Unusually long triplet excited state lifetimes are measured for the assemblies.     

Aggregation of 2‐Aminobenzimidazole—A Combined Experimental and Theoretical Investigation

An investigation of 2‐aminobenzimidazole was carried out by calculations at HF, MP2, and DFT levels of theory and also by UV and IR spectroscopy. The quantum chemical calculations predict a full shift of the equilibrium towards the amino form, but the absorption spectra in different solvents distinctly show a two‐component equilibrium system. Examination of possible equilibria in solution shows that an equilibrium between two dimeric forms of the amino tautomer of 2‐aminobenzimidazole explains the spectral observations.     

Light Dynamics of the Retinal‐Disease‐Relevant G90D Bovine Rhodopsin Mutant

The RHO gene encodes the G‐protein‐coupled receptor (GPCR) rhodopsin. Numerous mutations associated with impaired visual cycle have been reported; the G90D mutation leads to a constitutively active mutant form of rhodopsin that causes CSNB disease. We report on the structural investigation of the retinal configuration and conformation in the binding pocket in the dark and light‐activated state by solution and MAS‐NMR spectroscopy. We found two long‐lived dark states for the G90D mutant with the 11‐cis retinal bound as Schiff base in both populations. The second minor population in the dark state is attributed to a slight shift in conformation of the covalently bound 11‐cis retinal caused by the mutation‐induced distortion on the salt bridge formation in the binding pocket. Time‐resolved UV/Vis spectroscopy was used to monitor the functional dynamics of the G90D mutant rhodopsin for all relevant time scales of the photocycle. The G90D mutant retains its conformational heterogeneity during the photocycle.     

Spatially Heterogeneous Nature of Self‐Catalytic Reaction in Hetero‐Double Helix Formation of Helicene Oligomers

A 1:1 mixture of pseudoenantiomeric aminomethylenehelicene oligomers, (P)‐tetramer and (M)‐pentamer, in fluorobenzene show a self‐catalytic phenomenon in the formation of hetero‐double helices from random coils. This study visualizes the spatially heterogeneous nature of the self‐catalytic reaction in dilute solution. UV/Vis imaging analysis of the mixture at 70 °C, containing random coils, exhibits a homogeneous bright area. When the solution is cooled from 70 to 30 °C and held at that temperature, dark domains of approximately 1 mm in size appear, which move approximately at a rate of 1 mm min^?1. The dark domains indicate that weaker UV/Vis absorption results from the formation of hetero‐double helices, which is supported by circular dichroism (CD) imaging experiments. Then a homogeneous mixture is regenerated upon heating to 55 °C, as shown by CD imaging. Under self‐catalytic conditions, a homogeneous solution spontaneously changed to a heterogeneous solution in the process of hetero‐double‐helix formation.     

Perylene Bisimide Dimer Aggregates: Fundamental Insights into Self‐Assembly by NMR and UV/Vis Spectroscopy

A novel perylene bisimide (PBI) dye bearing one solubilizing dialkoxybenzyl and one bulky 2,5‐di‐tert‐butylphenyl substituent was synthesized and its aggregation behavior was analyzed by NMR and UV/Vis spectroscopy in various chloroform/methylcyclohexane (MCH) solvent mixtures. In the presence of no less than 10 vol % chloroform, exclusive self‐assembly of this PBI dye into π‐stacked dimers was unambiguously confirmed by means of both concentration‐dependent ¹H NMR and UV/Vis spectroscopic experiments. Based on ROESY NMR, a well‐defined π‐stacked dimer structure was determined and further corroborated by molecular modeling studies. By varying the solvent composition of chloroform and MCH, the solvent effects on the Gibbs free energy of PBI dimerization were elucidated and showed a pronounced nonlinearity between lower and higher MCH contents. This observation could be related to a further growth process of dimers into larger aggregates that occurs in the absence of chloroform, which is required to solvate the aromatic π surfaces. With the help of a single‐crystal structure analysis for a related PBI dye, a structural model could be derived for the extended aggregates that are still composed of defined π–π‐stacked PBI dimer entities.     

Highly Luminescent and Color‐Tunable Salicylate Ionic Liquids

High quantum yields of up to 40.5 % can be achieved in salicylate‐bearing ionic liquids. A range of these ionic liquids have been synthesized and their photoluminescent properties studied in detail. The differences noted can be related back to the structure of the ionic liquid cation and possible interionic interactions. It is found that shifts of emission, particularly in the pyridinium‐based ionic liquids, can be related to cation–anion pairing interactions. Facile and controlled emission color mixing is demonstrated through combining different ILs, with emission colors ranging from blue to yellow.     

钠和钾离子对磷酸二氢根拉曼光谱的影响

磷酸二氢根(H₂PO^-₄)溶液在生物缓冲、分子识别、晶体生长等方面有着重要的研究价值。 本文以KH₂PO₄(KDP)和NaH₂PO₄(NaDP)溶液为研究对象,利用原位微区拉曼光谱研究钠离子和钾离子对H₂PO^-₄溶液团簇聚合及化学键振动的影响,讨论单价阳离子(K⁺,Na⁺)的差异、溶液浓度对H₂PO^-₄拉曼位移变化和成核诱导时间的影响。 结果表明,拉曼位移变化、成核诱导时间随阳离子溶液电负性的增加、浓度的降低而增大。 在拉曼光谱中观察到P(OH)₂和PO₂振动峰在成核过程中发生偏移,表明由氢键作用导致的团簇构型逐渐稳定,化学键逐渐增强,深化溶液结晶过程中对溶液结构和化学键的理解。     

New Pentacoordinated Rhodium Species as Unexpected Products during the In Situ Generation of Dimeric Diphosphine‐Rhodium Neutral Catalysts

Dimeric rhodium complexes of the type [Rh(PP)(μ₂‐Cl)]₂ (PP=diphosphine) are often used as precatalysts and are generated “in situ” from the corresponding diolefin complexes by exchange of the diene with the desired diphosphine. Herein, we report that the “in situ” procedure also leads to unexpected monomeric pentacoordinated neutral complexes of the type [RhCl(PP)(diolefin)], for the first time herein characterized by NMR spectroscopy and X‐ray crystallography for the ligands 1,4‐bis(diphenylphosphino)propane (DPPP), 1,4‐bis(diphenylphosphino)butane (DPPB), and 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP). The pentacoordinated complexes are in equilibrium with the dimeric target compound [Rh(PP)(μ₂‐Cl)]₂. The equilibrium is influenced by the rhodium‐diolefin precursor, the solvent and the temperature. Based on the results of NMR and UV/Vis spectroscopic analysis (kinetics) it could be shown that the pentacoordinated complex [RhCl(PP)(diolefin)] may arise both from the “in situ”‐generated neutral complex [Rh(PP)(μ₂‐Cl)] by reaction with the free diolefin and, more surprisingly, directly from [Rh(diolefin)(μ₂‐Cl)]₂ and the diphosphine.     

Base‐Pairing Directed Folding of a Bimolecular G‐Quadruplex: New Insights into G‐Quadruplex‐Based DNAzymes

Base pairs, magic hands : An additional base‐pairing duplex is utilized to control the folding topologies of a bimolecular G‐quadruplex formed by two G‐rich single‐stranded DNAs (see picture), which is dependent on the position of base pairs. This study clearly reveals an important intrinsic role of additional base pairs in the G‐quadruplex structure, and also provides a clue to the formation mechanism of the G‐quadruplex‐based DNAzyme.

     

Lanthanide(III) Complexes of Bis‐semicarbazone and Bis‐imine‐Substituted Phenanthroline Ligands: Solid‐State Structures,Photophysical Properties,and Anion Sensing

Phenanthroline‐based hexadentate ligands L¹ and L² bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as La^III, Eu^III, Tb^III, Lu^III, and Y^III metal ions, were synthesized, and the crystal structures of [ML¹Cl₃] (M=La^III, Eu^III, Tb^III, Lu^III, or Y^III) complexes were determined. Solvent or water molecules act as coligands for the rare‐earth metals in addition to halide anions. The big Ln^III ion exhibits a coordination number (CN) of 10, whereas the corresponding Eu^III, Tb^III, Lu^III, and Y^III centers with smaller ionic radii show CN=9. Complexes of L², namely [ML²Cl₃] (M=Eu^III, Tb^III, Lu^III, or Y^III) ions could also be prepared. Only the complex of Eu^III showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine‐5′‐triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine‐5′‐diphosphate (ADP) and adenosine‐5′‐monophosphate (AMP) was found. ³¹P NMR spectroscopic studies revealed the formation of a [EuL²(ATP)] coordination species.     

Developing Intense Blue and Magenta Colors in α‐LiZnBO3: The Role of 3d‐Metal Substitution and Coordination

We describe the synthesis, crystal structures, and optical absorption spectra/colors of 3d‐transition‐metal‐substituted α‐LiZnBO₃ derivatives: α‐LiZn_1?xM^II_xBO₃ (M^II=Co^II (0<x<0.50), Ni^II (0<x≤0.05), Cu^II (0<x≤0.10)) and α‐Li_1+xZn_1?2xM^III_xBO₃ (M^III=Mn^III (0<x≤0.10), Fe^III (0<x≤0.25)). The crystal structure of the host α‐LiZnBO₃, which is both disordered and distorted with respect to Li and Zn occupancies and coordination geometries, is largely retained in the derivatives, which gives rise to unique colors (blue for Co^II, magenta for Ni^II, violet for Cu^II) that could be of significance for the development of new, inexpensive, and environmentally friendly pigment materials, particularly in the case of the blue pigments. Accordingly, this work identifies distorted tetrahedral MO₄ (M=Co, Ni, Cu) structural units, with a long M?O bond that results in trigonal bipyramidal geometry, as new chromophores for blue, magenta, and violet colors in a α‐LiZnBO₃ host. From the L*a*b* color coordinates, we found that Co‐substituted compounds have an intense blue color that is stronger than that of CoAl₂O₄ and YIn_0.90Mn_0.10O₃. The near‐infrared (NIR) reflectance spectral studies indicate that these compounds exhibit a moderate IR reflectivity that could be significant for applications as “cool pigments”.     

Cs4K2CuSi2O8: Synthese,Kristallstruktur, UV‐Vis‐IR‐Daten

Cs₄K₂CuSi₂O₈: Synthesis, Crystal Structure, UV‐Vis‐IR Data Cs₄K₂CuSi₂O₈ may be obtained via a redox reaction of KCuO₂ in the presence of Cs₂O and SiO₂ with the container material (Cu) at 450 °C as blue single crystals which are sensitive to moisture. Powder samples were obtained by annealing intimate mixtures of the binary oxides under an inert gas atmosphere (Ar) in sealed Ag containers at 500 °C. The crystal structure contains isolated trimeric anions of [O₂SiO₂CuO₂SiO₂]^6–. Cu²⁺ in square‐planar coordination share trans‐edges with [SiO₄] tetrahedra. Spectroscopic investigations focus on the bonding situation of the [CuO₄] unit (AOM) and characteristic vibrational modes of the silicate.     

Modular Synthesis of Linear Bis‐ and Tris‐monodentate Fused [6]Polynorbornane‐Based Ligands and their Assembly into Coordination Cages

A modular approach has been developed for the synthesis of rigid linear di‐ and tritopic ligands based on a fused [6]polynorbornane scaffold. The design provides up to three sites for installing functionality, including both “ends” and a “central” position with the advantage that each region can be independently addressed during synthesis. To illustrate the utility of the approach, both pyridyl and picolyl units were incorporated to provide six new ligands, with centers and ends either matched or mismatched. Indeed, both [M₂L₄] cages with endohedral functionality and [M₃L₄] complexes were cleanly produced from these ligands with assembled structures confirmed by using ¹H NMR spectroscopy, HRMS, and molecular modelling.     

Cooling,Spectroscopy and Non‐Sticking of trans‐Stilbene and Nile Red

We create and study trans‐Stilbene and Nile Red in a cryogenic (7 K) cell with a low density helium buffer gas. No molecule–helium cluster formation is observed, indicating limited atom–molecule sticking in this system. We place an upper limit of 5 % on the population of clustered He–trans‐Stilbene, consistent with a measured He–molecule collisional residence time of less than 1 μs. With its very low energy torsional modes, trans‐Stilbene is less rigid than any molecule previously buffer‐gas‐cooled into the Kelvin regime. We also report cooling and gas phase visible spectroscopy of Nile Red, a much larger molecule. Our data suggest that buffer gas cooling will be feasible for a variety of small biological molecules.