The low-lying excited singlet states of the keto, enol, and keto−imine tautomers of cytosine have been investigated employing a combined density functional/multireference configuration interaction ...(DFT/MRCI) method. Unconstrained geometry optimizations have yielded out-of-plain distorted structures of the π → π* and n → π* excited states of all cytosine forms. For the keto tautomer, the DFT/MRCI adiabatic excitation energy of the π → π* state (4.06 eV including zero-point vibrational energy corrections) supports the resonant two-photon ionization (R2PI) spectrum (Nir et al. Phys. Chem. Chem. Phys. 2002, 5, 4780). On its S1 potential energy surface, a conical intersection between the 1ππ* state and the electronic ground state has been identified. The barrier height of the reaction along a constrained minimum energy path amounts to merely 0.2 eV above the origin and explains the break-off of the R2PI spectrum. The 1ππ* minimum of the enol tautomer is found at considerably higher excitation energies (4.50 eV). Because of significant geometry shifts with respect to the ground state, long vibrational progressions are expected, in accord with experimental observations. For the keto−imine tautomer, a crossing of the 1ππ* potential energy surface with the ground-state surface has been found, too. Its n → π* minimum (3.27 eV) is located well below the conical intersection between the π → π* and S0 states, but it will be difficult to observe because of its small transition moment. The identified conical intersections of the π → π* excited states of the keto cytosine tautomers are made responsible for the ultrafast decay to the electronic ground states and thus may explain their subpicoseconds lifetimes.
Ovaj rad istražuje korisnost i moguće probleme s kojima bi se nastavnici mogli susresti u matematičkim učionicama koje upotrebljavaju matematički softver. Nakon kratkoga pregleda raznih tipova ...matematičkoga softvera rad se koncentrira na dva matematička alata koji su prevedeni na hrvatski jezik i koji su u upotrebi u hrvatskim matematičkim učionicama. Navedene su prednosti i nedostaci ovih programa kao i njihove mogućnosti sa stajališta hrvatskih, ali i stranih znanstvenika koji su istraživali utjecaj tih programa na učenike i studente. Također je dana usporedba između dva matematička programa koji se koriste u Republici Hrvatskoj, a koja se odnosi na tehničke, ali i na praktične detalje.
Dyspraxia is often defined as a disorder or immaturity in the development of motor skills and organized, voluntary movements in the objective space. Considering speech as a motor activity of high ...specificity and complexity, dyspraxic disorders can also affect the control of oral-buccal-lingual movements and produce problems in oral expression. Developmental verbal dyspraxia is the developmental speech and language disorder that is manifested in the difficulty of programming sequential speech movements, and therefore the production of meaningful verbal messages and its accompanying nonverbal elements. It is diagnosed if the child has no detected peripheral organ damage, severe sensory disturbances, nor muscle weakness or dysfunction. Also, an intellectual functioning is within normal range ande receptive language skills are intact. Good results in the treatment of developmental dyspraxic disorders are achieved by using techniques of psychomotor reeducation method, a kind of developmental therapy that achieves reintegration of practognostical skills and psychomotor activity by using speech, body movements and tonic dialogue as authentic means of communication. This paper will describe certain types of exercises of general psychomotor re-education which can be used in the treatment of developmental verbal dyspraxia, as a supplement to speech and neuropsychological therapy.
In relation to drug release properties the lateral and rotational mobility of two drugs and one drug mimic in photopolymerized poly(ethylene glycol) diacrylate (PEGDA) networks were investigated by ...nuclear magnetic resonance as a function of the network cross-link density and temperature. The network mesh size affects the lateral diffusivity for all drugs, even if the mesh size is an order of magnitude larger than the drug molecular size. The rotational diffusional motion is only appreciably affected when the drug size and network mesh size are of the same order of magnitude. By complexing the drug to cyclodextrin (CD) it is found that in some cases, depending on network mesh size and complex size, the complex is absorbed by the PEGDA gel, but that the diffusion of the drug in the gel is not necessarily slower than in the absence of the CD. This is explained by a theoretical model.
The transport of oxygen through silicone-hydrogel (SiHy) materials is of great interest in bio-materials' applications. In this study O2 permeability of hydrogels made from UV-cured polyacrylamide ...containing different siloxane co-monomers were analyzed through the traditional coulometric flux method, as well as by 1H NMR T1 relaxometry. It was shown by coulometric flux methods that the crosslinked polyacrylamide with short, linear siloxane side chains (polydimethylsiloxane (PDMS)) has higher O2 permeability as well as O2 solubility, as calculated from the composite diffusivity, than that with branched siloxane (tris-(trimethylsiloxysilyl-) (TRIS)). On the other hand, based on direct measurement from NMR T1 analyses, a slightly higher O2 solubility was observed for the samples with branched siloxane as expected from its larger free volume. In order to understand the reason behind this discrepancy, a series of morphological studies using 29Si and 1H NMR T2 relaxometry, as well as small-angle X-ray scattering (SAXS) were undertaken. These results are discussed in the context of molecular dynamic simulations undertaken on the same systems which together strongly suggest that morphology plays a critical role in O2 permeability. It is proposed that samples made from the linear silicone, PDMS, has a more pronounced siloxane phase separation than its bulky counterpart, TRIS. Significantly percolating hydrophobic silicone domains with twice the siloxane content are found for the PDMS sample with reduced tortuosity of the hydrophilic domain's percolating path. The mobility in the linear siloxane was also much higher which can be attributed to the molecular structure and to fewer interfacial and topological constraints arising from the different domain structure. Hence, we propose a framework for O2 permeability in SiHys, emphasizing the importance of percolated hydrophobic domain in designing SiHy with optimized O2 permeability. The study demonstrates that while a simple permeability measurement can be used for materials' comparison, the use of multiple orthogonal techniques is critical for developing a more complete understanding of small molecule transport in heterogeneous materials.
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•O2 permeability in Si hydrogels with different Si monomers were analyzed by coulometrics and NMR relaxometry.•MD simulations were performed to understand the impact of microheterogeneity on O2 permeability.•Effects of branched and linear monomers on Si hydrogels' morphology were studied.•A new framework was proposed to explain the contribution of morphology to permeability of Si hydrogels.
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