ABSTRACT
The 'Sergeants-and-Soldiers' principle has been examined in a series of m-phenylene ethynylene oligomers containing both chiral and achiral side chains. Circular dichroism (CD) spectroscopy was used to examine the twist sense bias of the helical conformation in the polar solvent acetonitrile. A non-linear dependence of the CD signal on the amount of chiral side chains was observed revealing cooperative interactions among the side chains through the backbone. On the other hand, the experiments indicate that in acetonitrile a full bias of the helicity cannot be accomplished by chiral side chains alone. Nevertheless, the folded oligomers are highly ordered since the placement of a single chiral side chain at the beginning of an oligomer results in the induction of a strong twist sense bias into the ordered helical conformation.
ABSTRACT
Circular dichroism spectroscopy has been used to study the self-assembly of two series of m-phenylene ethynylene oligomers in highly polar solvents. The helical conformation of shorter oligomer lengths was found to be stabilized in aqueous acetonitrile solutions, while longer oligomers began to interact intermolecularly. The intermolecular aggregation of the oligomers in aqueous solutions revealed a chain length dependent association that required the presence of a stable helical conformation. Evidence for intermolecular interactions is provided by Sergeants and Soldiers experiments in which the twist sense bias of a chiral oligomer is transferred to an achiral oligomer.
ABSTRACT
Tissue adhesive are commonly used in ophthalmology to seal small corneal perforations. We report a case of inadvertent instillation of cyanoacrylate adhesive (Histoacryl) in the anterior chamber resulting in polymerization of the glue on the corneal endothelial surface, with iridocorneal and iridolenticular adhesion.
Subject(s)
Corneal Diseases/chemically induced , Enbucrilate/adverse effects , Endothelium, Corneal/drug effects , Iris Diseases/chemically induced , Iris/drug effects , Lens Capsule, Crystalline/drug effects , Anterior Chamber/drug effects , Corneal Diseases/surgery , Enbucrilate/administration & dosage , Endothelium, Corneal/pathology , Humans , Iris/pathology , Iris/surgery , Iris Diseases/surgery , Keratoplasty, Penetrating , Lens Capsule, Crystalline/pathology , Lens Capsule, Crystalline/surgery , Male , Middle Aged , Polymers , Surgical Wound Dehiscence/therapyABSTRACT
Conversion from extracapsular cataract surgery to small-incision phacoemulsification is inevitably associated with a learning curve. Retrospective analysis of one surgeon's learning curve was carried out on the first 50 consecutive operations using small-incision phacoemulsification. Parameters were evaluated, including postoperative acuity and astigmatism at eight days, three weeks, three months, and six months. A comparison of the results of the first 25 operations and the subsequent 25 showed statistically significant differences only in acuity at eight days and cylinder at three months. The most frequent complication was corneal edema lasting at least one week. With careful preparation, proper patient selection, and meticulous technique, the learning curve for converting from extracapsular surgery to small-incision phacoemulsification does not necessarily increase the complication rate.
