Anti-Arrhenius cleavage of covalent bonds in bottlebrush macromolecules on substrate

Spontaneous degradation of bottlebrush macromolecules on aqueous substrates was monitored by atomic force microscopy. Scission of C─C covalent bonds in the brush backbone occurred due to steric repulsion between the adsorbed side chains, which generated bond tension on the order of several nano-Newtons. Unlike conventional chemical reactions, the rate of bond scission was shown to decrease with temperature. This apparent anti-Arrhenius behavior was caused by a decrease in the surface energy of the underlying substrate upon heating, which results in a corresponding decrease of bond tension in the adsorbed macromolecules. Even though the tension dropped minimally from 2.16 to 1.89 nN, this was sufficient to overpower the increase in the thermal energy (k_BT) in the Arrhenius equation. The rate constant of the bond-scission reaction was measured as a function of temperature and surface energy. Fitting the experimental data by a perturbed Morse potential V = V₀(1 - e^-βx)² - fx, we determined the depth and width of the potential to be V₀ = 141 ± 19 kJ/mol and β^-1 = 0.18 ± 0.03 Å, respectively. Whereas the V₀ value is in reasonable agreement with the activation energy E_a = 80–220 kJ/mol of mechanical and thermal degradation of organic polymers, it is significantly lower than the dissociation energy of a C─C bond D_e = 350 kJ/mol. Moreover, the force constant K_x = 2β²V₀ = 1.45 ± 0.36 kN/m of a strained bottlebrush along its backbone is markedly larger than the force constant of a C─C bond K_l = 0.44 kN/m, which is attributed to additional stiffness due to deformation of the side chains.     

Serologic response to Epstein-Barr virus antigens in patients with systemic lupus erythematosus: a controlled study

Previous studies showed a link between systemic lupus erythematosus (SLE) and Epstein-Barr virus (EBV) infection. We sought to determine the features of serologic response to EBV in SLE patients and whether this response differs from those of systemic sclerosis (SSc) and primary antiphospholipid syndrome (PAPS) patients as well as healthy individuals. Sera from 198 consecutive SLE patients have been tested to detect IgG antibodies to EA/D, EBNA-1, VCA P18 and for comparison, cytomegalovirus (CMV) using commercially available ELISA kits (Trinity Biotech, USA). Forty-six SSc patients and 38 PAPS patients were enrolled as diseased control groups and sixty-five individuals as healthy controls. Significantly more SLE (54%, P?=?0.001, OR 5.77, 95% CI 2.8?C11.6), SSc (41.3%, P?=?0.005, OR 3.4, 95% CI 1.4?C8.2) and PAPS sera (36.8%, P?=?0.023, OR 2.86, 95% CI 1.14?C7.22) reacted against EA/D than healthy controls (16.9%). The mean age of anti-EA/D-positive SLE patients was significantly higher, and their disease duration was longer compared to anti-EA/D-negative SLE patients (41 ± 14 vs. 33.8 ± 10.8?years, P?<?0.001 and 100 ± 73 vs. 71 ± 62?months, P?=?0.003). In SLE patients, EA/D reactivity was associated with Raynaud??s phenomenon and the presence of any anti-ENA antibodies. Although it did not reach a statistical significance, anti-EBNA-1 reactivity was slightly lower in patients with SLE. The frequency of anti-CMV Ig G positivity was found significantly higher in SLE patients (100%) when compared to patients with SSc (95.7%), PAPS (94.7%) and healthy controls (95.4%) (P?=?0.035, P?=?0.025 and P?=?0.015 respectively). Our results support the proposed link between EBV and SLE. The finding that SSc and PAPS patients also have increased frequency of anti-EA/D response has revealed that this immune interaction may not be unique to patients with SLE, and there may be a common mechanism involving EBV in these autoimmune diseases.     

Intussusception in Adults

To review clinical, radiological and histopathological findings of adult intussusception and its management, 18 adult patients who had been treated surgically because of intussusception were reviewed. Of the patients, 5 (27.8%) had idiopathic intussusceptions, while the other 13 (72.2%) had a definable intraluminal pathology. The site of the intussusception was more common in the small bowel (83.3%) than the colon (16.7%). Ultrasonography and computed tomography were successful in demonstrating “target lesion” in 80% and 75% respectively. Patients with idiopathic intussusception were treated with simple reduction, while the others underwent segmental resection because of the possibility of malignant tumour. In contrast to intussusception in childhood, intussusception in adults usually has a definable lead point and resection of the involved bowel, rather than simple reduction, is indicated.