The Osmotic Coefficient of Rod-like Polyelectrolytes: Computer Simulation, Analytical Theory, and Experiment

The osmotic coefficient of solutions of rod-like polyelectrolytes is considered by comparing current theoretical treatments and simulations to recent experimental data. The discussion is restricted to the case of monovalent counterions and dilute, salt-free solutions. The classical Poisson-Boltzmann solution of the cell model correctly predicts a strong decrease in the osmotic coefficient, but upon closer look systematically overestimates its value. The contribution of ion-ion-correlations are quantitatively studied by MD simulations and the recently proposed DHHC theory. However, our comparison with experimental data obtained on synthetic, stiff-chain polyelectrolytes shows that correlation effects can only partly explain the discrepancy. A quantitative understanding thus requires theoretical efforts beyond the restricted primitive model of electrolytes.Comment: 16 pages, 2 figure

Vibrational spectra of ferrocene, ferrocene-containing polymers and their oxidized compounds

Ferrocene-containing polymers are an important member in the class of redox- responsive polymers, changing e.g. their solubility or conformation upon external stimuli. We present a study of their vibrational spectra using inelastic neutron scattering, focusing on the central building block of these polymers, the organometallic ferrocene complex. The vibrational modes of a bulk ferrocene sample are compared to those of poly(vinylferrocene), poly(ferrocenyldimethylsilane) and poly(ferrocenylmethylsilane). In the former polymer, the ferrocene complex is laterally attached to the polymer chain and the vibrational spectrum shows a slight shift and broadening of the fingerprint modes in the range of 100-800 cm⁻¹ except for the ring-metal-ring stretching mode which was not detectable anymore. The latter two polymers, where the ferrocene complex is part of the polymer backbone, exhibit larger differences to the vibrational spectrum of bulk ferrocene. Moreover, several contributions to the spectra caused by methyl groups in these polymers could be identified. In order to study the influence of oxidation on ferrocene and redox-responsive polymers, we investigated the ionic compound ferrocenium triiodide and oxidized poly(vinylferrocene). It is observed that the weakening of the η⁵-complex bond by a missing electron leads to a significant shift of the fingerprint modes to lower frequencies

The spinal cord injury-induced immune deficiency syndrome: results of the SCIentinel study

Infections are prevalent after spinal cord injury (SCI), constitute the main cause of death and are a rehabilitation confounder associated with impaired recovery. We hypothesize that SCI causes an acquired lesion-dependent (neurogenic) immune suppression as an underlying mechanism to facilitate infections. The international prospective multicentre cohort study (SCIentinel; protocol registration DRKS00000122; n = 111 patients) was designed to distinguish neurogenic from general trauma-related effects on the immune system. Therefore, SCI patient groups differing by neurological level, i.e. high SCI [thoracic (Th)4 or higher]; low SCI (Th5 or lower) and severity (complete SCI; incomplete SCI), were compared with a reference group of vertebral fracture (VF) patients without SCI. The primary outcome was quantitative monocytic Human Leukocyte Antigen-DR expression (mHLA-DR, synonym MHC II), a validated marker for immune suppression in critically ill patients associated with infection susceptibility. mHLA-DR was assessed from Day 1 to 10 weeks after injury by applying standardized flow cytometry procedures. Secondary outcomes were leucocyte subpopulation counts, serum immunoglobulin levels and clinically defined infections. Linear mixed models with multiple imputation were applied to evaluate group differences of logarithmic-transformed parameters. Mean quantitative mHLA-DR [ln (antibodies/cell)] levels at the primary end point 84 h after injury indicated an immune suppressive state below the normative values of 9.62 in all groups, which further differed in its dimension by neurological level: high SCI [8.95 (98.3% confidence interval, CI: 8.63; 9.26), n = 41], low SCI [9.05 (98.3% CI: 8.73; 9.36), n = 29], and VF without SCI [9.25 (98.3% CI: 8.97; 9.53), n = 41, P = 0.003]. Post hoc analysis accounting for SCI severity revealed the strongest mHLA-DR decrease [8.79 (95% CI: 8.50; 9.08)] in the complete, high SCI group, further demonstrating delayed mHLA-DR recovery [9.08 (95% CI: 8.82; 9.38)] and showing a difference from the VF controls of -0.43 (95% CI: -0.66; -0.20) at 14 days. Complete, high SCI patients also revealed constantly lower serum immunoglobulin G [-0.27 (95% CI: -0.45; -0.10)] and immunoglobulin A [-0.25 (95% CI: -0.49; -0.01)] levels [ln (g/l × 1000)] up to 10 weeks after injury. Low mHLA-DR levels in the range of borderline immunoparalysis (below 9.21) were positively associated with the occurrence and earlier onset of infections, which is consistent with results from studies on stroke or major surgery. Spinal cord injured patients can acquire a secondary, neurogenic immune deficiency syndrome characterized by reduced mHLA-DR expression and relative hypogammaglobulinaemia (combined cellular and humoral immune deficiency). mHLA-DR expression provides a basis to stratify infection-risk in patients with SCI

Elektrisch leitfähige Kunststoffe: Der Weg zu einer neuen Materialklasse

Konventionelle gesättigte Polymere sind typische Isolatoren. Anders verhält es sich bei den konjugierten Polymeren: Liegen lange Ketten vor, die alternierend aus C-C-Doppel-und C-C-Einfachbindungen bestehen, könnte es prinzipiell zu einer Delokalisierung der π-Elektronen entlang des Polymerrückgrates kommen. Aufgrund der Peierls-Instabilität ist dies aber nicht der Fall. Vielmehr bedarf es zusätzlich der Dotierung. Metallähnliche intrinsische Leitfähigkeit bei organischen Polymeren ist Ausgangspunkt für breite Anwendungen