The Properties of Cu Ions in Zeolites CuY Studied by IR Spectroscopy

The properties of both Cu²⁺ and Cu⁺ ions in zeolite CuY were followed with NO and CO as probe molecules. Cu²⁺ was found to be located in S_II, S_II*, and S_III sites, whereas Cu⁺ was found in S_II and S_II* sites. The fine analysis of the spectra of Cu²⁺-NO and Cu⁺-CO adducts suggests that both in S_II and in S_II* sites two kinds of Cu cations exist. They differ in the positive charge, which may be related to the varying numbers of AlO₄⁻ in close proximity. The experiments of NO and CO adsorption and desorption evidenced that both Cu²⁺ and Cu⁺ sites of highest positive charge bind probe molecules most strongly but activate them to a lesser extent than the Cu sites of lowest positive charge. The experiments of reduction with hydrogen evidenced that the Cu ions of higher positive charge are first reduced by hydrogen. On the other hand, Cu sites of the lowest positive charge are first oxidized by oxygen. The experiments with CuNaY zeolites of various Cu contents suggest that the first introduced Cu (at low Cu contents) created Cu⁺, which was the most neutralized by framework oxygens. Such Cu cations are the most stabilized by framework oxygens.     

Numerical optimisation of chemotherapy dosage under antiangiogenic treatment in the presence of drug resistance

We consider a two-compartment model of chemotherapy resistant tumour growth under angiogenic signalling. Our model is based on the one proposed by Hahnfeldt et al. (1999), but we divide tumour cells into sensitive and resistant subpopulations. We study the influence of antiangiogenic treatment in combination with chemotherapy. The main goal is to investigate how sensitive are the theoretically optimal protocols to changes in parameters quantifying the interactions between tumour cells in the sensitive and resistant compartments, that is, the competition coefficients and mutation rates, and whether inclusion of an antiangiogenic treatment affects these results. Global existence and positivity of solutions and bifurcations (including bistability and hysteresis) with respect to the chemotherapy dose are studied. We assume that the antiangiogenic agents are supplied indefinitely and at a constant rate. Two optimisation problems are then considered. In the first problem a constant, indefinite chemotherapy dose is optimised to maximise the time needed for the tumour to reach a critical (fatal) volume. It is shown that maximum survival time is generally obtained for intermediate drug dose. Moreover, the competition coefficients have a more visible influence on survival time than the mutation rates. In the second problem, an optimal dosage over a short, 30-day time period, is found. A novel, explicit running penalty for drug resistance is included in the objective functional. It is concluded that, after an initial full-dose interval, an administration of intermediate dose is optimal over a broad range of parameters. Moreover, mutation rates play an important role in deciding which short-term protocol is optimal. These results are independent of whether antiangiogenic treatment is applied or not.     

The Effects of Ring Strain on Cyclic Tetraaryl[5]cumulenes

Cyclic tetraaryl[5]cumulenes ( 1 a–f ) have been synthesized and studied as a function of increasing ring strain. The magnitude of ring strain is approximated by the extent of bending of the cumulenic core as assessed by a combination of X-ray crystallographic analysis and DFT calculations. Trends are observed in ¹³C NMR, UV-vis, and Raman spectra associated with ring strain, but the effects are small. In particular, the experimental HOMO-LUMO gap is not appreciably affected by bending of the [5]cumulene framework from ca. 174° (λ_max=504 nm) in 1 a to ca. 178° (λ_max=494 nm) in 1 f .     

The structure of 11,12-bis[spiro(cyclopropyl)]-1,4,4a,5,8,8a,9a,10a-octahydro-1,4∶5,8-dimethano-9,10-anthraquinone

In the solid state the 21 Diels-Alder adduct between spiro[4.2]hepta-1,3-diene and p-benzoquinone has a planar cyclohexadione ring with a center of symmetry. Both planar and boat conformations have been observed in similar systems, and the relative stability of the two conformers is of interest. The adduct in the gas phase should contain a mirror plane perpendicular to the cyclohexadione ring; however, a data set collected on a crystal in a capillary resulted in a structure where some bond lengths related by this mirror plane differed by more than 4 in the solid state. Molecular mechanics, MOPAC, and the Cambridge Structural Data Base were used to investigate the factors influencing the conformation of the cyclohexadione ring and the asymmetry across the noncrystallographic mirror plane. The energy differences between the planar and nonplanar ring system is small, and the conformation is determined by crystal packing. No reason for the bond length asymmetry could be found, and a recollection of data on a crystal exposed to the environment led to a structure with statistically equivalent bond lengths.     

Side Methyl Groups Control the Conformation and Contribute to Symmetry Breaking of Isoprenoid Chromophores

Ab initio DFT computations reveal that the essential structural and photophysical features of the conjugated π‐electron system of retinal and carotenoids are dictated by “innocent” methyl substituents. These methyl groups shape the conformation and symmetry of the isoprenoid chromophores by causing a sigmoidal distortion of the polyene skeleton and increasing its flexibility, which facilitates fitting to their binding pockets in proteins. Comparison of in vacuo conformations of the chromophores with their native (protein‐bound) conformations showed, surprisingly, that the peripheral groups and interactions with the protein environment are much less significant than the methyl side groups in tuning their structural features. The methyl side groups also contribute to a loss of symmetry elements specific to linear polyenes. In effect, the symmetry‐imposed restrictions on the chromophore electronic properties are disabled, which is of tremendous relevance to their photophysics. This is evidenced by their non‐negligible permanent dipole moments and by the simulated and experimentally measured circular dichroism spectra, which necessarily reflect the chirality of the conjugated π‐electron system.     

Nepetanudone, a dimer of the α-pyrone 5,9-dehydronepetalactone

The title compound C₂₀H₂₄O₄ crystallizes in the orthorhombic space group P2₁2₁2, with a = 10.245(3), b = 17.103(3), c = 9.879(3) Å, D _c = 1.260 g cm ^–3, and Z = 4. Nepetanudone is postulated to be formed by a [4+4] cycloaddition of two 5,9-dehydronepetalactone moieties to give an asymmetric dimer in which each pair of atoms is magnetically nonequivalent. The compound was recovered from extracts of Nepeta nuda ssp. albiflora.