Triplet NOAH supersequences optimised for small molecule structure characterisation

A series of NMR supersequences are presented for the time-efficient structure characterisation of small molecules in the solution state. These triplet sequences provide HMBC, HSQC, and one homonuclear correlation experiment of choice according to the NMR by Ordered Acquisition using ¹H detection principle. The experiments are demonstrated to be compatible with non-uniform sampling schemes and may be acquired and processed under full automation.     

Expansion of Magnetic Aromaticity Criteria to Multilayer Structures: Magnetic Response and Spherical Aromaticity of Matryoshka-Like Cluster [Sn@Cu12@Sn20]12−

Structural characterization of the discrete [Sn@Cu₁₂@Sn₂₀]¹²⁻ cluster exposed a fascinating architecture composed of three concentric structural layers in which an endohedral Sn atom is enclosed in a Cu₁₂ icosahedron, which in turn is embedded in an Sn₂₀ dodecahedron. Herein, the possibility of sustaining aromatic behavior for this prototypical multilayered species was evaluated, in order to extend this concept to more complex clusters on the basis of magnetic response and bonding analysis by the AdNDP approach. This revealed characteristic features of spherical aromatics, given by the ability to sustain the shielding cone property, similar to archetypal aromatics. The favorable bonding pattern in the [Sn@Cu₁₂@Sn₂₀]¹²⁻ cluster fulfills the 2(N+1)² Hirsch rule for aromaticity; thus, the cluster could be regarded as a first member of aromatic multilayered structures. The set of four 13c–2e aromatic bonds that was identified in the internal SnCu₁₂ structure results in spherical aromatic character of this multilayered cluster. This insight builds a bridge between the traditional concept of Hückel's aromaticity and the aromaticity of complex and stable 3D systems that may be explored on the basis of magnetic response and bonding analysis. It also may open a way to novel findings in bottled clusters displaying aromatic behavior in multilayer structures, which are of great interest for inorganic nano- and material sciences due to their unprecedented stability.     

On the existence of a generalized solution of a nonlinear evolution system of equations in a domain unbounded in time

We consider a mixed problem with Dirichlet homogeneous boundary conditions and nonzero initial conditions for a nonlinear coupled evolution system of equations in a domain unbounded in time. The conditions of existence of a generalized solution are obtained. It is shown that no solution of the problem exists at a negative initial value of the energy integral.     

Specific photodynamics in thymine clusters: the role of hydrogen bonding

A photoionization detected IR study of thymine and 1-methylthymine monohydrates and of their homodimers was carried out to shed some light on the structure of the thymine clusters whose complex photodynamics has recently been the subject of great interest. Under supersonic jet conditions, thymine forms doubly H-bonded cyclic clusters with water or another base preferentially via its N1-H group and the adjacent carbonyl group. This hydrate is of no biological relevance since the N1-H group is the sugar binding site in thymidine. On the other hand, 1-methylthymine forms the donor H-bonds only via the N3-H group. Hence, properties of the N1-H and the N3-H bound clusters of thymine can be studied using thymine and 1-methylthymine molecules, respectively. No biologically relevant conformations of the dimers and hydrates of thymine, contrary to those of 1-methylthymine, are observed under supersonic jet conditions. Thymine homodimer, which extensively fragments upon UV ionization by formation of a protonated monomer, exhibits two N1-H···O═C2 hydrogen bonds. The photodynamics of hydrated thymines is found to be extremely sensitive to the hydration site: ranging from an ultrafast relaxation in less than 100 fs up to formation of a dark state with the lifetime on the microsecond time scale.     

The Tail Wags the Dog: The Far Periphery of the Coordination Environment Manipulates the Photophysical Properties of Heteroleptic Cu(I) Complexes

In this work we show, using the example of a series of [Cu(Xantphos)(N^N)]⁺ complexes (N^N being substituted 5-phenyl-bipyridine) with different peripheral N^N ligands, that substituents distant from the main action zone can have a significant effect on the physicochemical properties of the system. By using the C≡C bond on the periphery of the coordination environment, three hybrid molecular systems with −Si(CH₃)₃, −Au(PR₃), and −C₂HN₃(CH₂)C₁₀H₇ fragments were produced. The Cu(I) complexes thus obtained demonstrate complicated emission behaviour, which was investigated by spectroscopic, electrochemical, and computational methods in order to understand the mechanism of energy transfer. It was found that the −Si(CH₃)₃ fragment connected to the peripheral C≡C bond changes luminescence to long-lived intra-ligand phosphorescence, in contrast to MLCT phosphorescence or TADF. The obtained results can be used for the design of new materials based on Cu(I) complexes with controlled optoelectronic properties on the molecular level, as well as for the production of hybrid systems.     

Copper(I)‐Catalyzed Amination of Halogenopyridines with Polyamines

Cu^I‐Catalyzed amination of 2‐bromo‐, and 2‐, 3‐, and 4‐iodopyridines with tri‐ and tetraamines aimed at the synthesis of N,N′‐diheteroaryl derivatives was studied. A strong dependence of the product yields on the nature of starting compounds and the ligand used was observed. The increase in the number of ethene‐1,2‐diamine fragments in the polyamine structure led to the increase in the yields of polyheteroarylated compounds, whereas propane‐1,3‐diamine fragments favored the formation of monopyridinyl derivatives and promoted the heteroarylation of the secondary amino groups. 2‐Iodopyridine, as a more reactive compound, readily formed N,N‐diarylated products. The best yields of the target N,N′‐dipyridin‐2‐yl derivatives were 76% in the case of the triamine and 68% in the case of the tetraamine. A comparison of Cu^I‐ and Pd⁰‐mediated heteroarylation of polyamines was also presented.     

Synthesis of 2,5,7‐Triaryl‐4,7(6,7)‐dihydropyrazolo[1,5‐a]pyrimidine‐3‐carbonitriles by Reaction of 5(3)‐Amino‐3(5)‐aryl‐1H‐pyrazole‐4‐carbonitriles with Chalcones

The reaction of 5(3)‐amino‐3(5)‐aryl‐1H‐pyrazole‐4‐carbonitriles with 1,3‐diaryl‐2‐propen‐1‐ones (chalcones) in refluxing DMF leads to 2,5,7‐triaryl‐4,7(6,7)‐dihydropyrazolo[1,5‐a]pyrimidine‐3‐carbonitriles. In DMSO solution, the latter exist in equilibrium of two tautomeric 4,7‐dihydropyrazolo[1,5‐a]pyrimidines and 6,7‐dihydropyrazolo[1,5‐a]pyrimidines in various ratios, depending on the nature of aryl substituents in chalcone building blocks.     

Amination of 5-Spiro-Substituted 3-Hydroxy-1,5-dihydro-2H-pyrrol-2-ones

The 3-hydroxy-1,5-dihydro-2H-pyrrol-2-one motif is a valuable scaffold in drug discovery. The replacement of the 3-oxy fragment in 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones-based compounds with a 3-amino one (3-amino analogs of 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones, 3-amino-1,5-dihydro-2H-pyrrol-2-ones) can play a crucial role in their biological effect. Thus, approaches to 3-amino-1,5-dihydro-2H-pyrrol-2-ones are of significant interest. We developed an approach to 5-spiro-substituted 3-amino-1,5-dihydro-2H-pyrrol-2-ones that could not be obtained using previously reported approaches (reactions of 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones with amines). The developed approach is based on the thermal decomposition of 1,3-disubstituted urea derivatives of 5-spiro-substituted 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones, which were prepared via their reaction with carbodiimides.     

Phase relations in the Fe-P system at high pressures and temperatures from ab initio computations

ABSTRACT

Based on the first-principles calculations within the density functional theory and crystal structure prediction algorithms iron phosphide phases stable under pressure of the Earth’s core and temperatures up to 4000?K were determined. A new low-temperature modification FeP-P2₁/c stable above ～75?GPa was predicted. Fe₂P with the allabogdanite structure has been established to be stable in the low-temperature region at ambient conditions. At 750?K it transforms into the barringerite structure. The transition from Fe₃P with schreibersite structure to Fe₃P-Cmcm was observed at 27?GPa, and the phase transition boundary is nearly isobaric. Fe₂P and FeP are thermodynamically stable at the Earth’s inner core pressures and 0?K according to the obtained results, whereas Fe₃P stabilizes with respect to decomposition to Fe?+?Fe₂P at high temperatures above ～3200?K.