Atom Exchange Versus Reconstruction: (GexAs4−x)x− (x=2, 3) as Building Blocks for the Supertetrahedral Zintl Cluster [Au6(Ge3As)(Ge2As2)3]3−

The Zintl anion (Ge₂As₂)^2? represents an isostructural and isoelectronic binary counterpart of yellow arsenic, yet without being studied with the same intensity so far. Upon introducing [(PPh₃)AuMe] into the 1,2‐diaminoethane (en) solution of (Ge₂As₂)^2?, the heterometallic cluster anion [Au₆(Ge₃As)(Ge₂As₂)₃]^3? is obtained as its salt [K(crypt‐222)]₃[Au₆(Ge₃As)(Ge₂As₂)₃]?en?2 tol ( 1 ). The anion represents a rare example of a superpolyhedral Zintl cluster, and it comprises the largest number of Au atoms relative to main group (semi)metal atoms in such clusters. The overall supertetrahedral structure is based on a (non‐bonding) octahedron of six Au atoms that is face‐capped by four (Ge_xAs_4?x)^x? (x=2, 3) units. The Au atoms bind to four main group atoms in a rectangular manner, and this way hold the four units together to form this unprecedented architecture. The presence of one (Ge₃As)^3? unit besides three (Ge₂As₂)^2? units as a consequence of an exchange reaction in solution was verified by detailed quantum chemical (DFT) calculations, which ruled out all other compositions besides [Au₆(Ge₃As)(Ge₂As₂)₃]^3?. Reactions of the heavier homologues (Tt₂Pn₂)^2? (Tt=Sn, Pb; Pn=Sb, Bi) did not yield clusters corresponding to that in 1 , but dimers of ternary nine‐vertex clusters, {[AuTt₅Pn₃]₂}^4? (in 2 – 4 ; Tt/Pn=Sn/Sb, Sn/Bi, Pb/Sb), since the underlying pseudo‐tetrahedral units comprising heavier atoms do not tend to undergo the said exchange reactions as readily as (Ge₂As₂)^2?, according to the DFT calculations.     

Electrochemiluminescence Bioassays with a Water‐Soluble Luminol Derivative Can Outperform Fluorescence Assays

The most efficient and commonly used electrochemiluminescence (ECL) emitters are luminol, [Ru(bpy)₃]²⁺, and derivatives thereof. Luminol stands out due to its low excitation potential, but applications are limited by its insolubility under physiological conditions. The water‐soluble m‐carboxy luminol was synthesized in 15 % yield and exhibited high solubility under physiological conditions and afforded a four‐fold ECL signal increase (vs. luminol). Entrapment in DNA‐tagged liposomes enabled a DNA assay with a detection limit of 3.2 pmol L^?1, which is 150 times lower than the corresponding fluorescence approach. This remarkable sensitivity gain and the low excitation potential establish m‐carboxy luminol as a superior ECL probe with direct relevance to chemiluminescence and enzymatic bioanalytical approaches.     

On the Photophysical Properties of New Luminol Derivatives and their Synthetic Phthalimide Precursors

The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity.     

Changes in the Structural Dimensionality of Selenidostannates in Ionic Liquids: Formation,Structures, Stability,and Photoconductivity

In situ transformations of selenidostannate frameworks in ionic liquids (ILs) were initiated by treatment of the starting phase K₂[Sn₂Se₅] and the consecutive reaction products by means of temperature increase and/or amine addition. Along the reaction pathway, the framework dimensionalities of the five involved selenidostannate anions develop from 3D to 1D and back, both in top‐down and bottom‐up style. Addition of ethane‐1,2‐diamine (en) led to the reversion of the 2D→1D step from 2D‐{[Sn₂₄Se₅₆]^16?} to 1D‐{[Sn₆Se₁₄]^4?}. As rationalized by DFT investigations, the 2D anion is thermodynamically favored. Photoconductivity measurements reveal that all samples show Schottky contact behavior with absolute thresholds below 10 V. One of the samples exhibits conductive states within the energy range of visible photons.     

Synthesis,Characterization and Fluorescent Properties of Three One‐Dimensional Coordination Polymers Derived from Polypyridyl Ligands

Three one‐dimensional coordination polymers, [MnCl₂(4‐pyterpy)]∙2CHCl₃ ( 1 ), [Mn(NO₃)₂(4‐pyterpy)]∙CHCl₃ ( 2 ) and [Ag(NO₃)(3‐pyterpy)]∙H₂O ( 3 ) (4‐pyterpy = 4′‐(4‐pyridyl)‐2,2′:6′,2″‐terpyridine and 3‐pyterpy = 4′‐(3‐pyridyl)‐2,2′:6′,2″‐terpyridine) were synthesized and characterized by X‐ray diffraction. All three compounds exhibit a rare “head‐to‐tail” coordination of the multidentate ligand, but differ significantly in their polymer chain conformations. Additionally, the fluorescent properties of all three compounds were investigated and show a weak, ligand‐centered fluorescence at 416–418 nm.     

Sustainable photochemistry: solvent-free singlet oxygen-photooxygenation of organic substrates embedded in porphyrin-loaded polystyrene beads

A solvent-free photooxygenation process that uses organic substrates embedded in porphyrin-loaded polystyrene beads as solid support is described and applied for ene- and [4 + 2]-cycloaddition reactions involving singlet oxygen (1 delta g).     

Helfrich repulsion and dynamical phase separation of multicomponent lipid bilayers

Thermal fluctuations of surfactant bilayers in an aqueous solution produce an effective, long-range repulsion that can lead to a continuous unbinding transition. We report on an optical interferometry study of the thermal fluctuations of multicomponent bilayers close to the unbinding transition. We find that, in contrast to the case of single-component bilayers, the thermal fluctuation spectrum of multicomponent bilayers does not agree with a continuous unbinding transition but instead indicates the proximity of an unbinding tricritical point.     

Photoinduced electron-transfer reactions with quinolinic and trimellitic acid imides: experiments and spin density calculations(1)

The regioselectivity of photoinduced electron-transfer (PET) reactions of unsymmetrical phthalimides is controlled by the spin density distribution of the intermediate radical anions. ROHF ab initio calculations were found to be most suitable for atomic spin density analysis. Intramolecular PET reactions of quinolinic acid imides were studied with the potassium butyrate and hexanoate 1a,b and a cysteine derivative 3. The photocyclizations products 2a,b and 4 were formed with moderate regioselectivities (68:32, 57:43, and 81:19) showing preferential ortho cyclization. The intermolecular reaction of potassium propionate and potassium isobutyrate with N-methylquinolinic acid imide (5) yielded as addition products the dihydropyrrolo[3,4-b]pyridines 6a,b with slight ortho regioselectivity (55:45). In contrast to these low regioselectivities, the PET reaction of potassium propionate with the methyl ester of N-methyltrimellitic acid imide (9) yielded solely the para addition product 10. Likewise, the intramolecular photoreaction of the cysteine derivative 7 gave a 75:25 (para/meta) mixture of regioisomeric cyclization products 8. The regioselectivity originates from donor-acceptor interactions prior to electron transfer and differences in spin densities in the corresponding imide radical anions. The results of DFT and ab initio calculations for the radical anions of the quinolinic acid imide (11(*)(-)) and the methyl ester of trimellitic acid imide (12(*)(-))( )()were in agreement with the latter assumption: spin densities in 11(*)(-) were higher for the imido ortho carbon atoms (indicating preferential ortho coupling); for 12(*)(-) the spin densities were higher for the imido para carbon atoms (indicating preferential para coupling). These correlations became more significant when the additional spin densities at the carbonyl oxygen and the adjacent carbon atoms were taken into account. The cyclization selectivities for 2, 4, and 8 deviate from the intermolecular examples probably because of ground-state and solvent effects.