Olefin polymerisation catalysts: when perfection is not enough

Despite decades of thorough mechanistic investigations, it is still hard to predict the activity of a novel olefin polymerisation catalyst, even when the precursor is a well-defined molecular entity. In the present study, we highlight the crucial importance of activation entropy on the polymerisation rate and how weak interactions of the catalytic species with electron donating species in the reaction pool can ultimately lower the activation free energy.

Oral complications of head and neck radiotherapy: prevalence and management

AIM

The aim of the study was to evaluate the short-term and long-term toxicity caused by radiation treatment in the head and neck with the technique of intensity-modulated radiotherapy (IMRT).

METHODS

We selected 20 patients, 18 men and 2 women aged between 21 and 71 years, undergoing radiation therapy (IMRT) in head and neck. Patients were visited during radiotherapy and followed for six months after the end of the therapy. We assessed the presence of: mucositis, xerostomia, dysgeusia, dysphagia, pain, trismus and, in the case of late-onset complications, radiation cavities.

RESULTS

Acute toxicity: in 20 patients, 18 reported mucositis, 19 xerostomia, 17, dysgeusia, 15 dysphagia, 18 had pain and 3 patients had trismus. Tardive toxicity: in 14 patients, 5 reported mucositis, 11 xerostomia, 6 dysgeusia, 2 dysphagia, 3 had pain, 4 trismus and in 4 patients were found radiation cavities.

CONCLUSION

Acute complications with higher prevalence were xerostomia (19 of 20 patients), dysgeusia of 2nd grade (11 patients of 20), mucositis of 1st grade and pain of 1st grade (10 patients of 20). Among the late complications it was noted a maintenance of the high prevalence of xerostomia (11 patients of 14) and an increase in prevalence of trismus (4 patients of 14) against a reduction of all other complications. The presence of radiation cavities in 4 patients of 14 was also recorded.

Combined orthodontic-surgical approach in the treatment of impacted maxillary canines: three clinical cases

Impaction of maxillary canine is a relatively frequent orthodontic anomaly which could represent fuctional and aesthetic problems for patients. Nowadays, the conventional technique to impacted canines consists of a combined orthodontic and surgical approach, aimed to guide cuspids at the center of the alveolar ridge in a stable position and surrounded by healthy hard and soft tissues. This article presents three cases studies with different combined surgical-orthodontic approaches for the treatment of infraosseous impacted canines. An impacted maxillary canine could be guided, after adequate space is created orthodontically, to the center of the ridge through an orthodontic traction directly applied to the crown of impacted cuspid. Several surgical techniques have been proposed to expose the crown of impacted tooth. Location (buccal or palatal side) of impactation and depth influence surgical approach in order to obtain best aesthetic and functional results.

Prenatal diagnosis of heterozygosity for biotinidase deficiency by enzymatic and molecular analyses

Biotinidase deficiency is characterized by neurological and cutaneous abnormalities that can be prevented or ameliorated by oral biotin therapy. A child with biotinidase deficiency went undiagnosed for a long period and has irreversible neurological deficits despite biotin treatment. This child is homozygous for the most common mutation (G98:d7i3) found in symptomatic children with the disorder. The parents insisted on having prenatal diagnosis in a subsequent pregnancy to alleviate their anxiety about having another affected child. Mutation analysis of DNA obtained directly from amniotic fluid and from cultured amniocytes revealed that the fetus was heterozygous for the mutation. Maternal cell contamination of the amniocytes was excluded by genotype analysis. Biotinidase activity in extracts of cultured amniocytes revealed 40 per cent of mean normal activity. At birth, the infant was confirmed to be heterozygous by serum enzyme analysis. This is the first report of the use of molecular analysis for the prenatal diagnosis for biotinidase deficiency.

Mechanism of intestinal formation of deoxycholic acid from cholic acid in humans: evidence for a 3-oxo-delta 4-steroid intermediate

12 alpha-Hydroxy-3-oxo-4-cholenoic acid coupled to an adenosine nucleotide has been shown to be a metabolite of cholic acid in the intestinal anaerobic bacteria, Eubacterium species VPI 12708 (1987. J. Biol. Chem. 262: 4701-4707) and it has been suggested that this may be an intermediate in the conversion of cholic acid into deoxycholic acid. The possibility that the intestinal conversion of cholic acid into deoxycholic acid involves a 3-oxo-delta 4-steroid as an intermediate has been studied in the present work by use of [3 beta-3H]- and [5-3H]-labeled cholic acid. Whole cells as well as cell extracts of Eubacterium sp. VPI 12708 catalyzed conversion of [3 beta-3H] + [24-14C]cholic acid into deoxycholic acid with loss of about 50% of 3H label. When unlabeled chenodeoxycholic acid (20 microM) was added along with [3 beta-3] + [24-14C]cholic acid, then approximately 85% of the [3 beta-3H]-labeled was lost from deoxycholic acid. After administration of the same mixture to two healthy volunteers, deoxycholic acid could be isolated that had lost 81 and 84%, respectively, of the 3H label. Conversion of a mixture of [5-3H]- and [24-14C]labeled cholic acid by the above intestinal bacteria or cell extracts led to loss of 79-94 of the [5-3H] label.(ABSTRACT TRUNCATED AT 250 WORDS)