A Rotational BODIPY Nucleotide: An Environment‐Sensitive Fluorescence‐Lifetime Probe for DNA Interactions and Applications in Live‐Cell Microscopy

Fluorescent probes for detecting the physical properties of cellular structures have become valuable tools in life sciences. The fluorescence lifetime of molecular rotors can be used to report on variations in local molecular packing or viscosity. We used a nucleoside linked to a meso‐substituted BODIPY fluorescent molecular rotor ( dC^bdp ) to sense changes in DNA microenvironment both in vitro and in living cells. DNA incorporating dC^bdp can respond to interactions with DNA‐binding proteins and lipids by changes in the fluorescence lifetimes in the range 0.5–2.2 ns. We can directly visualize changes in the local environment of exogenous DNA during transfection of living cells. Relatively long fluorescence lifetimes and extensive contrast for detecting changes in the microenvironment together with good photostability and versatility for DNA synthesis make this probe suitable for analysis of DNA‐associated processes, cellular structures, and also DNA‐based nanomaterials.     

Light-actuated resorcin[4]arene cavitands

A light-actuated resorcin[4]arene cavitand equipped with two quinone (Q) and two opposite Ru(II)-based photosensitizing walls was synthesized and investigated. The cavitand is capable of switching from an open to a contracted conformation upon reduction of the two Q to the corresponding SQ radical anions by intramolecular photoinduced electron transfer in the presence of a sacrificial donor. The molecular switch was investigated by cyclic and rotating disc voltammetry, UV–Vis–NIR spectroelectrochemistry, transient absorption, NMR, and EPR spectroscopy. This study provides the basis for the development of future light-activated switches and molecular actuating nanodevices.     

Transitions to high tautomeric states can be induced in adenine by interactions with carboxylate and sodium ions: DFT calculation data

Twelve triple complexes of nine adenine tautomers with carboxylate ion of acetic acid CH₃COO⁻ and sodium ion Na⁺ of the CH₃COO⁻:Ade:Na⁺ type were studied by the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d,p) quantum chemical method. It was established that three rare adenine tautomers generate more stable complexes than the ground state one. The B3LYP/6-311++G(d,p) full optimization was applied to four most stable triple complexes in order to refine on their stability order. To evaluate contributions of each ligands for stabilization of these complexes, calculations of energies and dipole moments of respective binary complexes of the CH₃COO⁻:Ade and Ade:Na⁺ types were performed at the B3LYP/6-31++G(d,p) level of theory. At the same level, there were computed energies and dipole moments of isolated tautomers. Two of them, first calculated in this work, appeared to be zwitter-ions. Highly cooperative interplay of interactions of both ligands with adenine tautomers was observed in triple complexes. Preferable sites of coordination of Na⁺ with tautomers were ascertained. Biological importance of the results obtained is discussed.     

Morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) block copolymer

The morphology of a highly asymmetric double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) (PCL-b-PEO) block copolymer has been studied with in situ simultaneously small and wide-angle x-ray scattering as well as atomic force microscopy. The molecular masses Mn of the PCL and PEO blocks are 24,000 and 5800, respectively. X-ray scattering and rheological measurements indicate that no microphase separation occurs in the melt. Decreasing the temperature simultaneously triggers off a crystallization of PCL and microphase separation between the PCL and PEO blocks. Coupling and competition between microphase separation and crystallization results in a morphology of PEO spheres surrounded by PCL partially crystallized in lamella. Further decreasing temperature induces the crystallization of PEO spheres, which have a preferred orientation due to the confinements from hard PCL crystalline lamella and from soft amorphous PCL segments in different sides. The final morphology of this highly asymmetric block copolymer is similar to the granular morphology reported for syndiotactic polypropylene and other (co-) polymers. This implies a similar underlying mechanism of coupling and competition of various phase transitions, which is worth further exploration.     

Pyrazolo[1,5-a]pyrimidines. Identification of the privileged structure and combinatorial synthesis of 3-(hetero)arylpyrazolo[1,5-a]pyrimidine-6-carboxamides

The pyrazolo[1,5-a]pyrimidine class of compounds has been identified as a privileged structure for library synthesis on the basis of several key characteristics of the core molecule. A chemical set in excess of 400 compounds was synthesized to give 3,6,7-substituted pyrazolo[1,5-a]pyrimidinecarboxamides 9. To facilitate the rapid preparation of this library, a preparative strategy included the synthesis of activated p-nitrophenyl esters, followed by subsequent scavenging of the p-nitrophenol leaving group. Excess reagents were also removed using scavenging reagents that were found to be compatible with the synthetic methodology and that afforded target compounds in acceptable purity and yields.     

Anisotropic reorientation of 9-methylpurine and 7-methylpurine molecules in methanol solution studied by combining 13C and 14N nuclear spin relaxation data and quantum chemical calculations

Reorientation of 9-(trideuteromethyl)purine and 7-(trideuteromethyl)purine molecules in methanol-d4 solutions has been investigated on the basis of the interpretation of the nuclear spin relaxation rates of their 14N (or 1H) and 13C nuclei. The transverse quadrupole relaxation rates of 14N nuclei have been obtained from the line shape analysis of their 14N NMR spectra. Alternatively, the information on the longitudinal 14N relaxation rates has been obtained via the scalar relaxation of the second kind of protons coupled to 14N. The longitudinal dipolar relaxation rates of the protonated 13C nuclei in the investigated molecules have been determined by measuring their overall relaxation rates and NOE enhancement factors. The molecular geometries, scalar coupling constants, and EFG tensors needed for quantitative interpretation of the above data have been calculated theoretically [DFT B3LYP/6-311++G(2d,p) or B3PW91/6-311+G(df,pd)] including the impact of the solvent by using discrete solvation and the polarizable continuum model. The reorientation of the investigated purines has been described as rotational diffusion of an asymmetrical top. It has been found that to get a fully consistent interpretation of the relaxation data, effective C-H bond lengths being 3% longer than the calculated ones had to be used in analysis to compensate for the ground-state vibrations. The obtained rotational diffusion coefficients and orientations of the principal diffusion axes show that the investigated molecules reorient anisotropically and that the mode of their solvation is remarkably different, in spite of their structural similarity.     

Influence of the nature of the substituent in 3-(2-pyridyl)-1,2,4-triazole for complexation with Pd<Superscript>2+</Superscript>

The structure of four new palladium complexes [Pd(HL ² )Cl ₂ and Pd(L ^1–3 ) ₂ ] with 3-(2-pyridyl)-5-R-1,2,4-triazoles (R=H, CH₃, Ph respectively HL ¹ , HL ² , HL ³ ) was proposed based on IR, NMR, UV spectroscopy and MALDI mass spectrometry data analysis. It is found that the complexation of HL ² and HL ³ with Pd²⁺ ions results in a decrease of their fluorescence intensity and it is vice versa in case of HL ¹ . Furthermore, the influence of the substituent (R) in the 3-(2-pirydyl)-5-R-1,2,4-triazoles on the fluorescent and protolytic properties of HL ^1–3 was investigated.