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The urea-formaldehyde (UF) reaction under strong alkaline condition was investigated by using quantitative analysis of 13C NMR. The main reaction products were methylolureas and oligomers linked by ether bonds at the beginning stage. With the reaction undergoing, the methylene linkages began to be formed and become predominant at the end point. The conversion of linear methylene ether bond to methylene linkage was also observed. These features were also observed previously for the reaction under acidic condition. It was found that the cyclic ether structure (uron) is much more stable than the linear ether bond, and its stability is second only to the methylene linkages among all the condensed structures. The formaldehyde was consumed in fast Cannizarro reaction under strong alkaline condition, producing considerable amount of methanol, which is the main negative aspect of this condition. With the exception of the differences caused by Cannizarro reaction, the UF production reactions under alkaline and acidic conditions are similar. The pH did not change the thermodynamic nature of the involved reactions, but only changed the competitive relationships of different reactions in kinetics. [ABSTRACT FROM AUTHOR]

ABSTRACT The acid-catalyzed urea-formaldehyde reactions were reexamined in detail by using quantum chemistry method and 13C-NMR determinations. Some issues in the synthesis theory that were not well understood previously have been addressed and clarified. The identified reaction mechanisms and calculated energy barriers suggest that the competitive formations of methylene and methylene ether linkages are kinetically affected by both reaction energy barriers and steric hindrance effect. The thermodynamic properties determine that the methylene linkages are dominant at the late condensation stage. The theoretical results well rationalized the observed different changing processes of resin structures with different F/U molar ratios. The previously proposed mechanism for transformation of methylene ether linkage to methylene linkage cannot explain the structural changes during condensation, and thus, other mechanisms were proposed. The calculated results for uron explained the fact that the formation of such structure is much slower than other structures under weak acidic condition. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44339. [ABSTRACT FROM AUTHOR]

Top spinning is one of the favorite sports among the minority communities of China hailing from the Yunnan province, such as Han, Va, Dai and others. Tops are made from the purple poplar tree and vary in shapes and weights from village to village. The top game can be contested individually or as a team and is a major attraction in the Spring Festival. The group in a team event is divided between the hitter and the setter. Rules of the game is detailed.

Base-catalyzed urea⁻formaldehyde condensation reactions were investigated by using a quantum chemistry method. It was found that monomethylolurea or N , N '-dimethylolurea can produce the methyleneurea intermediate (⁻HN⁻CO⁻N=CH₂) with the catalysis of base. The E1cb (unimolecular elimination of conjugate base) mechanism was identified for the formation of such an intermediate. The potential energy barrier was theoretically predicted to be 59.6 kJ/mol for the E1cb step, which is about half of that of previously proposed S N 2 (bimolecular nucleophilic substitution) mechanism. In the subsequentcondensation reactions, Michael addition reactions that lead to different condensed structures can occur between the methyleneurea intermediate and the anions produced from methylolureas under alkaline conditions. Based on the theoretical calculations on the kinetics and thermodynamics of the selected reactions, the competitive formations of methylene linkages, ether linkages and uron were discussed in combination with our previous experimental observations., Competing Interests: The authors declare no conflict of interest.

1,3-dimethylurea (DMU) was used to mimic urea and to model melamine-urea-formaldehyde (MUF) co-condensation reactions. The products of 1,3-dimethylurea-formaldehyde (DMUF), melamine-formaldehyde (MF), and melamine-1,3-dimethylurea-formaldehyde (MDMUF) reactions under alkaline and weak acidic conditions were compared by performing quantitative carbon-13 nuclear magnetic resonance ( 13 C-NMR) analysis. The effect of pH on the co-condensation reactions was clarified. With the presence of the methyl groups in DMU, the appearance or absence of the featured signal at 54⁻55 ppm can be used to identify the co-condensed methylene linkage ⁻N(⁻CH₃) ⁻CH₂⁻NH⁻. Under alkaline condition, MDMUF reactions produced primarily MF polymers and the featured signal at 54⁻55 ppm was absent. Even though the co-condensations concurrently occurred, undistinguishable and very minor condensed structures with ether linkage were formed. Differently, under weak acidic condition, the relative content of co-condensed methylene carbons accounts for over 40%, indicating the MDMUF co-condensation reactions were much more competitive than the self-condensations. The formation of reactive carbocation intermediate was proposed to rationalize the results.

The reactions of di-hydroxymethylurea with phenol under alkaline (pH = 10), weak (pH = 6) and strong acidic (pH = 2) conditions were investigated via the 13 C-NMR method. Based on the proposed reaction mechanisms, the variations of the structures of different condensed products were analyzed and the competitive relationship between self- and co-condensation reactions was elucidated. The required experimental conditions for co-condensations were clearly pointed out. The main conclusions include: (1) the self-condensation between urea formaldehyde (UF) or phenol formaldehyde (PF) monomers were dominant while the co-condensations were very limited under alkaline conditions. This is because the intermediates produced from urea, methylolurea and phenol are less reactive in co-condensations with respect to self-condensations; (2) under weak acidic conditions, the self-condensations occurred exclusively among the UF monomers. The co-condensation structures were not observed; and (3) the co-condensations became much more competitive under strong acidic conditions as the relative content of the co-condensed methylenic carbon accounts for 53.3%. This result can be rationalized by the high reactivity of the methylolphenol carbocation intermediate toward urea and methylolurea. The revealed reaction selectivity and mechanisms may also be applied to the synthesis of those more complex co-condensed adhesives based on natural phenolic and amino compounds.

Objective: To investigate the surgical techniques and appropriate perioperative management for ensuring successful orthotopic liver transplantation (ROLT) in rats., Methods: Based on the double-cuff technique of Kamada, we modified the surgical techniques of separation, perfusion and cold preservation of the donor liver, shearing and anastomosis of the suprahepatic vena cava with optimized postoperative infusion protocols and animal care., Results: Two hundred and seventy rats underwent ROLT and a learning curve of the success rate was built to reflect the improvement of techniques. The learning curve showed steep improvements over the exploration stage, breakthrough stage and maturation stage, and the success rates increased sharply over time (0%, 71.1%, and 94.5%, respectively) until finally reaching over 90%. The shearing and anastomosis of the suprahepatic vena cava remained the most critical and difficult techniques in ROLT modeling., Conclusion: Proficient microsurgical techniques and meticulous nursing can reduce postoperative complications, enhance operational success rate and extend the survival time after ROLT.

Objective: To investigate the expression and clinical significance of Nusap1 in hepatical carcinoma., Methods: The expression of Nusap1 protein in 61 specimens of hepatical carcinoma was examined by immunohistochemistry. Based on the levels of Nusap1 expression, the 61 specimens were divided into a high Nusap1 expression group and a low Nusap1 expression group. The correlation between Nusap1 expression with clinicopathologic features and prognosis of hepatical carcinoma was analyzed., Results: The rate of high Nusap1 expression was 54.1% in hepatical carcinoma. The rate of high Nusap1 expression was 21.3% in noncarcinoma, with significant difference between the 2 groups (P<0.01).Nusap1 overexpression had significant correlation with histological differentiation, tumor size, liver cirrhosis, lymphatic metastasis, tumor thrombi and early recurrence (P<0.05), but not with sex, age, AFP level, tumor number, TNM classification and tumor encapsulation (P>0.05). Survival analysis suggested that the 6 month and 12 month noncarcinoma survival rate was significantly lower in the high Nusap1 expression group [33.3% (11/33), 17.9% (5/33)] than that in the low Nusap1 expression group [89.3% (25/28), 53.6% (15/28); P<0.005]., Conclusion: Nusap1 is overexpressed in hepatical carcinoma and is a valuable prognostic factor for hepatical carcinoma.