Raman spectroscopic insights into the glass transition of poly(methyl methacrylate).

Poly(methyl methacrylate) (PMMA) is a very versatile polymer which is used as a glass substitute or as an economical alternative to polycarbonate for many types of important applications, due to its particular physical properties. In this study we deal with the Raman spectroscopic characterization of the glass transition of PMMA, the value of the glass transition temperature being generally a decisive parameter for determining the application of polymers. The information obtained by two-dimensional correlation spectroscopy (2DCOS) analysis and perturbation-correlation moving-windows spectroscopy (PCMW2D) analysis of the temperature dependent depolarized Raman spectra enabled us to recognize that the glass transition of PMMA is ruled by intermolecular interactions which influence the vibrational modes of the molecular groups associated with ν(C[double bond, length as m-dash]O), δa(C-H) of α-CH3 and/or O-CH3, ν(C-O-C), ν(C-COO), and ν(C-C-O). This information was employed for the temperature dependent study of the Raman shift and of the full width at half maximum of the Raman peaks obtained through anisotropic and isotropic Raman spectra, of the depolarization ratio, of the Raman spectroscopic noncoincidence effect, and of the Raman peak intensities represented by Arrhenius-type plots, all results supporting the outcomes of this work. The comparison with results obtained by differential scanning calorimetry and with published results in molecular dynamics studies was also part of this work. As the main result, one can highlight the peak associated with the ν(C-O-C) stretching mode at around 812 cm-1 as the one which presents the better outcome for explaining the glass transition from the molecular point of view.

Vibrational entropy of disorder in Cu3Au with different degrees of short-range order.

L12 ordered Cu3Au and fcc-disordered samples with different degrees of short-range order were synthesised by annealing and/or quenching experiments. Low-temperature heat capacities were determined by relaxation calorimetry. From these data the vibrational entropy of disorder was derived. The calorimetric results show that the vibrational entropy does not depend on the degree of short-range order. The calorimetric investigations were complemented by density functional calculations with different functionals simulating various atomic configurations by super cells of different size. Using super cells containing 32 atoms, the computed entropies show only small variations with the change of short-range order in good agreement with the calorimetric results. Using, however, super cells with only 8 atoms, the results depend strongly on the chosen atomic configuration at variance with the calorimetric data. This result is important for investigating substances with larger molecules (e.g., silicate solid solutions) because such investigations are typically limited on super cells containing only a few sites on which substitution takes place.

Chronic treatment with lithium does not improve neuromuscular phenotype in a mouse model of severe spinal muscular atrophy.

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by defective levels of the survival motor neuron (SMN) protein. SMA causes spinal motoneuron (MN) loss, and progressive muscle weakness and paralysis. Currently, there is no effective therapy to cure this disease. Although different strategies focused on increasing the expression of functional SMN protein have been assayed, numerous SMN-independent therapeutic approaches have been demonstrated to have potential effectiveness in improving the SMA phenotype in mouse models and clinical trials. Recent works have shown that compounds which inhibit GSK-3ß activity are effective in promoting MN survival and ameliorating lifespan in models of MN diseases including SMA. Taking into account the reported neuroprotective actions of lithium (Li) through the inhibition of GSK-3ß in different studies, we tested here its potential efficiency as a therapeutic agent in a mouse model of severe SMA (SMNΔ7 mice). We show that the chronic treatment with Li initiated before the appearance of disease symptoms, although inhibited GSK-3ß, did not improve the median survival, motor behavior, and spinal MN loss linked to SMA. Li administration did not either ameliorate the microglial and astroglial reaction in the spinal cord or the depletion of glutamatergic synapses on MNs observed in SMNΔ7 animals. Moreover, Li treatment did not mitigate muscle atrophy or calcitonin gene-related peptide (CGRP) downregulation in the neuromuscular junctions linked to the disease. However, a significant reduction in apoptotic cell death found in the skeletal muscle of SMA mice was observed after Li treatment.

Preoperative expectations and postoperative quality of life in liver transplant survivors.

OBJECTIVE: To assess normalization in the lives of liver transplant patients and the impact of preoperative expectations on postoperative quality of life (QOL). DESIGN: A semistructured interview, 2 QOL questionnaires, and chart reviews of medical histories. SETTING: Internal medicine department at Innsbruck university hospital, Austria. PARTICIPANTS: Fifty-five patients (32 men, 23 women) with liver transplants. INTERVENTIONS: The Sickness Impact Profile (SIP) and Functional Assessment of Cancer Therapy-General. RESULTS: Patients' preoperative expectations of a normal life style posttransplantation were predominantly optimistic (60%), but postoperatively only 40% thought that their expectations had been realized. The patients' SIP values showed significant impairments in nearly every area of life when compared with the values of a healthy control group. Only "complications during the hospitalized phase" had a statistically significant impact among the sociodemographic and clinical parameters on postoperative QOL. The lowest QOL scores were found among patients whose expectations of a return to normal life style had not been realized. CONCLUSION: Unmet life-style expectations after liver transplantation may lead to increased stress, which affects QOL long term. This finding is of clinical relevance; therapeutic measures, particularly professional pretransplant counseling, are indicated.