Restriction of the conrotatory motion in photo-induced 6π electrocyclic reaction: formation of the excited state of the closed-ring isomer in the cyclization.

The electrocyclic reaction dynamics of a photochromic dithiazolylarylene derivative, 2,3-dithiazolylbenzothiophene (DTA) was investigated by using time-resolved transient absorption and fluorescence spectroscopies. The closed-ring isomer of DTA undergoes cycloreversion through the conical intersection mediating the potential energy surfaces of the excited and ground states, which is in agreement with the Woodward-Hoffmann rules for the electrocyclic reactions of 6π electron systems. On the other hand, a large portion of the open-ring isomer undergoes cyclization along the distinct reaction scheme, in which the cyclization takes place in the excited state manifold leading to the formation of the excited state of the closed-ring isomer. The suppression of the geometrical motion of DTA due to the intramolecular interaction could open a new efficient reaction pathway resulting in the formation of the electronically excited state of the product.

Cycloreversion Reaction of a Diarylethene Derivative at Higher Excited States Attained by Two-Color, Two-Photon Femtosecond Pulsed Excitation.

Two-color, two-pulse femtosecond pulsed excitation was applied to the elucidation of the dynamics and mechanism of cycloreversion reaction of a diarylethene derivative in the higher excited states. Transient absorption spectroscopy under one-photon visible excitation revealed that the 1B state produced by the excitation undergoes the internal conversion into the 2A state with a time constant of 200 fs. Geometrical rearrangement of the 2A state takes place concomitantly with the vibrational cooling with a time constant of 3 ps. The resultant 2A state undergoes the transition into the conical intersection point in competition with nonradiative as well as radiative deactivation into the ground state with a time constant of 12 ps. The second pulse excitation of the 2A state, especially the geometrically relaxed 2A state, led to the significant enhancement of the cycloreversion reaction through the large reaction quantum yield of ca. 50-90% in the higher excited state (Sn state), while the excitation of the 1B state, leading to the Sn' state, did not induce such enhancement. By integrating with the excitation wavelength dependence of the second pump laser pulse, we discussed the chemical reactivity of diarylethene derivatives in terms of the symmetry of the electronic states.

Palliation of malignant upper gastrointestinal obstruction with self-expandable metal stent.

OBJECTIVE: To assess the technical success, ability to eat, complications and clinical outcomes of patients with self-expandable metal stent (SEMS) placed for malignant upper gastrointestinal (GI) obstruction. MATERIALS AND METHODS: Data was collected retrospectively on patients who underwent SEMS placement for palliation of malignant upper GI obstruction by reviewing hospital charts from June 1998 to May 2011. Main outcome measurements were technical success, gastric outlet obstruction scoring system (GOOSS) score before and after treatment, complications, and survival. RESULTS: A total of 82 patients underwent SEMS placement with malignant upper GI obstruction. The initial SEMS placement was successful in 77 patients (93.9%). The mean GOOSS score was 0.56 before stenting and 1.92 (p < 0.001) after treatment. Complications arose in 12 patients (14.6%): stent migration in 1 patient (1.2%), perforation in 1 (1.2%), and obstruction of stent due to tumor ingrowth in 10 (12.2%). The median survival time after stenting was 52 days (6-445). CONCLUSION: SEMS placement is an effective and safe treatment for palliation of malignant upper GI obstruction. It provides lasting relief in dysphagia and improves the QOL of patients.

Case report: trouble-shooting for difficult cases of common bile duct stones with endoscopic treatment.

A case of basket catheter impaction was experienced during treatment for a common bile duct (CBD) stone. In cases of large CBD stones, mechanical basket lithotripsy or extracorporeal shock wave lithotripsy (ESWL) is usually carried out. However, once basket catheter impaction occurs, ESWL should be performed in the remaining basket catheter, which is passed through the patient's nose, and further ESWL basket lithotripsy must be carried out at a later time. On one occasion, a mechanical lithotripter was inserted along-side the conventional basket catheter through the incised papilla. This procedure is a safe and useful method for the clearance of CBD stones that cannot be removed with standard endoscopic procedures due to an impacted basket catheter.

Current status of endoscopic management for nonvariceal upper gastrointestinal bleeding.

Endoscopic hemostasis is widely performed for nonvariceal upper gastrointestinal (UGI) bleeding. As the aged Japanese population rapidly increases, the number of patients experiencing complications increases. The aim of this study was to evaluate the recent results of endoscopic hemostasis for nonvariceal UGI bleeding. A retrospective analysis of patients who underwent endoscopic procedures for nonvariceal UGI bleeding was performed. We performed 223 endoscopic procedures on 217 patients between January 1995 and July 2000, and 238 endoscopic procedures on 236 patients between January 2006 and September 2009 at the Kyoto Second Red Cross Hospital. We divided the patients into the 1995-2000 group and the 2006-2009 group. Patient characteristics, hemostasis methods chosen, rates of temporary hemostasis and rebleeding, and mortality were analyzed. There were many serious and actively bleeding cases in the 2006-2009 group (P < 0.001). The endoclip method and intravenous proton pump inhibitor were mainly used in the 2006-2009 group compared with the drug-injection method and intravenous H2 receptor antagonist in the 1995-2000 group (P < 0.001). Through these treatments, the two groups were able to obtain similar treatment outcomes. Through the progress of endoscopic management we obtained similar satisfactory results in the 2006-2009 group, which had multiple complicated cases, compared to the 1995-2000 group.