Lattice model for polymer hydration: collapse of poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) (PNIPAM) in dilute aqueous solution undergoes a collapse transition from coil to globule on increasing temperature. Such coil-to-globule collapse is usually considered analogous to the cold renaturation of small globular proteins. In this paper we propose a theoretical approach that is able to reproduce, in a semi-quantitative way, the unusual behavior of PNIPAM, and the observed thermodynamic properties. The procedure is based on two main steps: (i) the characterization of single monomer hydration thermodynamics, interpreted by a balance between the removal of monomer-monomer interactions and the addition of water-monomer interactions, and (ii) a simplified analysis of a lattice self-avoiding walk (SAW) model, which allows to account for the configurational entropy in a controlled way, and hence to relate the microscopic interactions to the “macroscopic” behavior of the polymer chain. The results show that the temperature dependence and magnitude of the interaction parameters that best fit experimental data validate a recently proposed qualitative interpretation of the mechanism of collapse transition for PNIPAM. The latter result turns out to be relevant to support the analogy with the cold renaturation of small globular proteins, and to clarify some important aspects of protein thermodynamics.     

Synthesis and Structure Determination of 1, 4, 7, 11, 14, 17, 21, 24, 27-Nonaoxatriacontan-8, 10, 18, 20, 28, 30-Esaone

The title compound crystallizes in the trigonal space group R-3, with unit-cell parameters: a = 23.261(4), c = 9.537(2) Å; λ(MoKα) = 0.71073 Å, V = 4469(2) Å³, and Z = 6. The structure has been solved by direct methods using X-ray diffraction techniques. The final reliability index for the computed structure is 0.0826 for 929 observed reflections and 121 refined parameters. Crown ether adopts an almost circular shape and macrocycles are piled up in a columnar arrangement forming tubular nanochannels. The channels are filled with guest CDCl₃ molecules, characterised by rotational disorder.     

Working Memory Decline in Alzheimer’s Disease Is Detected by Complexity Analysis of Multimodal EEG-fNIRS

Alzheimer’s disease (AD) is characterized by working memory (WM) failures that can be assessed at early stages through administering clinical tests. Ecological neuroimaging, such as Electroencephalography (EEG) and functional Near Infrared Spectroscopy (fNIRS), may be employed during these tests to support AD early diagnosis within clinical settings. Multimodal EEG-fNIRS could measure brain activity along with neurovascular coupling (NC) and detect their modifications associated with AD. Data analysis procedures based on signal complexity are suitable to estimate electrical and hemodynamic brain activity or their mutual information (NC) during non-structured experimental paradigms. In this study, sample entropy of whole-head EEG and frontal/prefrontal cortex fNIRS was evaluated to assess brain activity in early AD and healthy controls (HC) during WM tasks (i.e., Rey–Osterrieth complex figure and Raven’s progressive matrices). Moreover, conditional entropy between EEG and fNIRS was evaluated as indicative of NC. The findings demonstrated the capability of complexity analysis of multimodal EEG-fNIRS to detect WM decline in AD. Furthermore, a multivariate data-driven analysis, performed on these entropy metrics and based on the General Linear Model, allowed classifying AD and HC with an AUC up to 0.88. EEG-fNIRS may represent a powerful tool for the clinical evaluation of WM decline in early AD.     

First synthesis of thiazepino[3,4-a]isoquinolines,a facile new synthetic route to diazepino[3,4-a]isoquinolines and assessment of their dopamine and σ receptor affinities

Heterocycles that bear the novel 5,6,14,14a-tetrahydro-8H-benzo[6,7][1,4]thiazepino[3,4-a]isoquinoline and the 5,6,14,14a-tetrahydro-8H-13l2-benzo[6,7][1,4]diazepino[3,4-a]isoquinoline frameworks were synthesized in a facile manner. These tetrahydroprotoberberine (THPB)-inspired scaffolds demonstrate selective affinity for the σ₁R in contrast to the naturally occurring THPB congeners that show D₁R and σ₂R selectivity.     

Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

In recent years, a number of authors have studied entropy generation in Wells turbines. This is potentially a very interesting topic, as it can provide important insights into the irreversibilities of the system, as well as a methodology for identifying, and possibly minimizing, the main sources of loss. Unfortunately, the approach used in these studies contains some crude simplifications that lead to a severe underestimation of entropy generation and, more importantly, to misleading conclusions. This paper contains a re-examination of the mechanisms for entropy generation in fluid flow, with a particular emphasis on RANS equations. An appropriate methodology for estimating entropy generation in isolated airfoils and Wells turbines is presented. Results are verified for different flow conditions, and a comparison with theoretical values is presented.     

Hydrogenative Catalysis with Three-Coordinate Zinc Complexes Supported with PN Ligands is Enhanced Compared to PNP Analogs

This work details the synthesis, characterization, and catalytic activity of reactive low-coordinate organozinc complexes. The complexes activate hydrogen and they appear to be more active in hydrogenation of ketones and imines than their tridentate pincer analogs. This is thought, in part, to be due to the lack of trailing third phosphorus arm present in previous work. DFT computations reveal a sigma-bond metathesis mechanism is comparable to an alternative aromatization/dearomatization metal-ligand cooperative mechanism.     

Computation of the eigenvalues of Fredholm–Stieltjes integral equations

The Rayleigh–Ritz and the inverse iteration methods are used in order to compute the eigenvalues of Fredholm–Stieltjes integral equations, i.e. Fredholm equations with respect to suitable Stieltjes-type measures. Some applications to the so-called ‘charged’ (in German ‘belastete’) integral equation, and particularly the problem of computing the eigenvalues of a string charged by a finite number of cursors are given.     

Luminescent iridium(III) complexes with N^C^N-coordinated terdentate ligands: dual tuning of the emission energy and application to organic light-emitting devices

A family of complexes (1a-3a and 1b-3b) was prepared, having the structure Ir(N^C^N)(N^C)Cl. Here, N^C(∧)N represents a terdentate, cyclometallating ligand derived from 1,3-di(2-pyridyl)benzene incorporating CH(3) (1a,b), F (2a,b), or CF(3) (3a,b) substituents at the 4 and 6 positions of the benzene ring, and N^C is 2-phenylpyridine (series a) or 2-(2,4-difluorophenyl)pyridine (series b). The complexes are formed using a stepwise procedure that relies on the initial introduction of the terdentate ligand to form a dichloro-bridged iridium dimer, followed by cleavage with the N^C ligand. (1)H NMR spectroscopy reveals that the isomer that is exclusively formed in each case is that in which the pyridyl ring of the N^C ligand is trans to the cyclometallating aryl ring of the N^C^N ligand. This conclusion is unequivocally confirmed by X-ray diffraction analysis for two of the complexes (1b and 3a). All of the complexes are highly luminescent in degassed solution at room temperature, emitting in the green (1a,b), blue-green (2a,b), and orange-red (3a,b) regions. The bidentate ligand offers independent fine-tuning of the emission energy: for each pair, the "b" complex is blue-shifted relative to the analogous "a" complex. These trends in the excited-state energies are rationalized in terms of the relative magnitudes of the effects of the substituents on the highest occupied and lowest unoccupied orbitals, convincingly supported by time-dependent density functional theory (TD-DFT) calculations. Luminescence quantum yields are high, up to 0.7 in solution and close to unity in a PMMA matrix for the green-emitting complexes. Organic light emitting devices (OLEDs) employing this family of complexes as phosphorescent emitters have been prepared. They display high efficiencies, at least comparable, and in some cases superior, to similar devices using the well-known tris-bidentate complexes such as fac-Ir(ppy)(3). The combination of terdentate and bidentate ligands is seen to offer a versatile approach to tuning of the photophysical properties of iridium-based emitters for such applications.