Single Crystal to Single Crystal (SC‐to‐SC) Transformation from a Nonporous to Porous Metal–Organic Framework and Its Application Potential in Gas Adsorption and Suzuki Coupling Reaction through Postmodification

A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH₂ groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m² g^?1. The material also possesses good CO₂ (8 wt %) and H₂ (1.87 wt %) adsorption capabilities.     

Substituent electronic effects on the persistence and absorption spectra of (Z)-o-xylylenols. A nanosecond laser flash photolysis study

[reaction: see text] A systematic investigation on a broad set of aldehydes reveals that the lifetimes of (Z)-photoenols can be modulated by variation of the substituents. We have found that the lifetimes of (Z)-enols (in benzene) can be varied by more than 1 order of magnitude with a judicious choice of the substituents that exert mesomeric and inductive effects as, for example, in the case of pentamethylbenzaldehyde (tau = 35 ns) and dicyanomesitaldehyde (tau = 760 ns). This study thus points to the fact that the electronic factors in conjunction with hydrogen bonding stabilization can considerably broaden the uni- as well as bimolecular chemistry based on photoenolization. Further, we have shown that the photoenols exhibit dramatic shifts in their absorption properties with variation of the substituents; although the photoenols have long been considered to be colored, their absorption properties have not been heretofore comprehensively examined.     

Thermochromism in nickel(II) complexes: thermal, solid state H NMR and single crystal X-ray analysis of bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate

The complex bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate undergoes a first-order thermochromic phase transition at ca. 476 K, changing its color from orange to red. The room temperature X-ray crystal structure determination showed that the nickel ion possesses a square-planar geometry with two five membered chelate rings, in the δλ conformation, forming the NiN₄ chromophore. The broad-line ¹H NMR indicates the onset of a dynamic disorder of diamine chelate rings at the phase transition temperature region, while T₁ measurement of ¹H affords the activation energy of the puckering metal chelate rings to be 26 kJ mol⁻¹. The electronic spectrum revealed that a weakening of ligand field around the nickel is associated with the phase transition.     

Unprecedented low Cu-N(azide)-Cu angles in end-on double azido bridged copper(II) complex

A rare asymmetric end-on double azido-bridged copper(II) complex has been synthesized and characterized structurally and magnetically. The Cu-N(azide)-Cu angle in this complex is calculated to be 89.1 degrees. This is unusually low in comparison to the same angle in other end-on azido-bridged binuclear complexes reported so far. Though a strong ferromagnetic interaction between the metal centers is expected in the complex, the coupling has actually been found to be antiferromagnetic, instead.     

Spherical shape complementarity as an overriding motif in the molecular recognition of noncharged organic guests by p-sulfonatocalix[4]arene: complexation of bicyclic azoalkanes

[reaction: see text] The complexation of p-sulfonatocalix[4]arene (CX4) with 2,3-diazabicyclo[2.2.1]hept-2-ene (1), 2,3-diazabicyclo[2.2.2]oct-2-ene (2), 2,3-diazabicyclo[3.2.2]non-2-ene (3), 1-methyl-4-isopropyl-2,3-diazabicyclo[2.2.2]oct-2-ene (4), and 1-phenyl-2,3-diazabicyclo[2.2.2]oct-2-ene (5) was studied in D2O at pD 7.4 by 1H NMR spectroscopy. The formation of deep inclusion complexes was indicated by large upfield 1H NMR shifts of the guest protons (up to 2.6 ppm), which were also used to assign, in combination with 2D ROESY spectra, a preferential inclusion of the isopropyl group of 4 and a dominant inclusion of the azo bicyclic residue for 5. The bicyclic azoalkanes 1-3 showed exceptionally high binding constants on the order of 1000 M(-1), 1-2 orders of magnitude larger than for previously investigated noncharged organic guest molecules. The strong binding was attributed to the spherical shape complementarity between the guest and the conical cavity offered by CX4. Interestingly, although the derivatives 4 and 5 are more hydrophobic, they showed a 2-3 times weaker binding, which was again attributed to the deviation from spherical shape in these bridgehead-substituted derivatives. The preferential inclusion of the hydrophilic but spherical bicyclic residue of 5 rather than the hydrophobic aromatic phenyl group provides a unique observation in aqueous host-guest chemistry and corroborates the pronounced spherical shape affinity of CX4.     

Identification of archaeal proteins that affect the exosome function in vitro

Background  

The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors.     

Anomalous excited-state dynamics of lucifer yellow CH in solvents of high polarity: evidence for an intramolecular proton transfer

The photophysics of the fluorescent probe Lucifer yellow CH has been investigated using fluorescence spectroscopic and computational techniques. The nonradiative rate is found to pass through a minimum in solvents of intermediate empirical polarity. This apparently anomalous behavior is rationalized by considering the possibility of predominance of different kinds of nonradiative processes, viz. intersystem crossing (ISC) and excited-state proton transfer (ESPT), in solvents of low and high empirical polarity, respectively. The feasibility of the proton transfer is examined by the structure determined by the density functional theory (DFT) calculations. The predicted energy levels based on the time-dependent density functional theory (TD-DFT) method in the gas phase identifies the energy gap between the S(1) and nearest triplet state to be close enough to facilitate ISC. Photophysical investigation in solvent mixtures and in deuterated solvents clearly indicates the predominance of the solvent-mediated intramolecular proton transfer in the excited state of the fluorophore in protic solvents.