ABSTRACT
A critical step in the synthesis of the hydroxypyrrolidines, 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol, from the corresponding d-sugars is the synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses. Instead of applying homogeneous catalysis process with conventional inorganic acid catalysts like HCl and HClO4, it was found that heterogeneous catalysis using zeolites could be used for the one-pot synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses directly from d-sugars, MeOH and acetone at mild condition. The best catalyst was H-beta zeolite containing a Si/Al molar ratio of 150, where a yield of >83% was obtained. The overall yields of the five-step procedure to 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol were 57% and 50%, respectively. This synthetic procedure has several advantages such as competitive overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the zeolite catalyst can be easily recovered from the reaction mixture and reused with no loss of activity.
Subject(s)
Pyrrolidines/chemical synthesis , Zeolites/chemistry , Catalysis , Green Chemistry Technology , Molecular Structure , Pyrrolidines/chemistryABSTRACT
OBJECTIVES: Cariostatic effects of lasers have been well documented in the past few decades; however, the mechanisms remain unclear. Our previous study revealed the statistically significant effect of organic matrix (OM) in the laser-induced caries prevention. The aim of the present study is to further investigate the role of organic matters in the laser-induced porosity changes. METHODS: Enamel powder from five sound molars was randomly divided into two samples. One sample was treated with approximately 10% NaClO solution to remove OM and the other was left untreated. Both groups were then subjected to irradiation by an Er:YAG laser. The samples were characterized by thermogravimetric analysis (TGA) and N(2) physico-adsorption. RESULTS: TGA results confirmed that the NaClO treatment had at least partially removed the OM in enamel powder. The surface area and pore volume of normal enamel powder decreased significantly after laser treatment. In contrast, in the NaClO-treated enamel powder, laser treatment did not significantly decrease the surface area and the pore volume remained almost unchanged. The substantial difference between the normal enamel powder and the NaClO-treated enamel powder after laser treatment confirmed the laser-induced blocking of OM in the micro-diffusion pathway in enamel. CONCLUSION: The findings in this study seemed to substantiate the "organic blocking theory" as one of the mechanisms in the laser-induced caries prevention.
Subject(s)
Dental Enamel/chemistry , Laser Therapy , Tooth Demineralization/therapy , Dental Enamel/drug effects , Diffusion , Erbium , Hot Temperature , Humans , Hydrocarbons , Low-Level Light Therapy , Porosity , Sodium Hypochlorite/pharmacology , ThermogravimetryABSTRACT
AIM: We report a case of tuberculous choroidal granulomas in a patient with systemic lupus erythematosis (SLE) who developed miliary tuberculosis (TB) and bilateral granulomas while on immunosuppressive medication. METHODS: The case notes of this patient were reviewed. RESULTS: The patient was first seen for base-line ophthalmic screening before anti-tuberculous medication was started. The patient was subsequently followed up at 2 weeks, 4 weeks and 2 months with fundal examination and photography. One choroidal granuloma was found in the right eye while another peripheral lesion involved the left eye. Both resolved in response to anti-tuberculous medication over a 2-month period with resultant chorioretinal atrophy and scarring. CONCLUSION: This case demonstrates the need to screen immuno-suppressed SLE patients who have miliary TB for possible eye involvement.
Subject(s)
Choroid Diseases/etiology , Granuloma/etiology , Lupus Erythematosus, Systemic/complications , Tuberculosis, Miliary/etiology , Tuberculosis, Ocular/etiology , Adult , Antitubercular Agents/therapeutic use , Choroid Diseases/drug therapy , Cost-Benefit Analysis , Female , Fundus Oculi , Granuloma/drug therapy , Humans , Immunocompromised Host , Lupus Erythematosus, Systemic/immunology , Risk Factors , Tuberculosis, Miliary/drug therapy , Tuberculosis, Ocular/drug therapyABSTRACT
A 28-year-old Chinese woman presented with poor night vision since childhood. Ocular examination showed pigmentary retinopathy and systemic examination revealed sensorineural hearing loss. Family history showed a similar condition in her youngest sister. Ocular and systemic examination of her sister showed similar findings. This is presented as the first case report of Usher's syndrome in Singapore. A general discussion of Usher's syndrome is also presented.
Subject(s)
Hearing Loss, Sensorineural/diagnosis , Night Blindness/diagnosis , Retinitis Pigmentosa/diagnosis , Adult , Consanguinity , Diagnosis, Differential , Female , Hearing Loss, Sensorineural/genetics , Humans , Night Blindness/epidemiology , Night Blindness/genetics , Retinitis Pigmentosa/epidemiology , Retinitis Pigmentosa/genetics , Singapore/epidemiology , SyndromeABSTRACT
A novel technique, the temperature programmed decomposition (TPDE) of [Mo(CO)(6)], has been developed to examine surface acid/base properties. In particular, the nucleophility of different surface hydroxyl groups can be quantified with this method, and it is found that the activation energy for decarbonylation of the carbonyl complex correlates well with the field strength of the metal cations in the support. Activation energies are derived from the CO peak maxima in the TPDE spectra by means of the Redhead equation. TPDE is also used to probe surface-mediated reactions of metal carbonyls. The technique enables identification of intermediates formed during the thermal decomposition process. Comparison with simulated TPDE spectra provides evidence for cluster formation during decarbonylation. By quantifying the amounts of CO and H(2) generated during the TPDE reaction, the surface concentration of the adsorbed species and the oxidation state of the central atom can be deduced at any given temperature.
ABSTRACT
Bee stings of the eye are not uncommon. Quite a few clinical case reports have documented the various ocular reactions to the venom of the bee stings, which may range from mild conjunctivitis to sudden loss of vision. This report presents 2 patients who suffered bee stings to the cornea and their different outcomes. The properties of bee venom as well as the treatment of various possible complications are also discussed.
Subject(s)
Bees , Bites and Stings/complications , Corneal Edema/etiology , Uveitis/etiology , Adult , Animals , Anti-Bacterial Agents/therapeutic use , Corneal Edema/diagnosis , Corneal Edema/drug therapy , Humans , Male , Middle Aged , Uveitis/diagnosis , Uveitis/drug therapy , Visual AcuityABSTRACT
Two first cousins both suffering from insulin dependent diabetes mellitus since early childhood developed progressive optic atrophy from the age of 5 and 9 years respectively. They had similar ophthamological features which include optic atrophy with cupping, paracentral scotomata, and total achromatopsia. One patient also had stunted growth, delayed puberty and psychiatric disorder. Neither had diabetes insipidus and deafness. It is suggested that they may be a variant of DIDMOAD (Diabetes Insipidus, Juvenile Diabetes Mellitus, Optic Atrophy, Deafness).
Subject(s)
Diabetes Mellitus, Type 1/genetics , Diabetic Neuropathies/genetics , Optic Atrophy/genetics , Adolescent , Adult , Child , Child, Preschool , Follow-Up Studies , Humans , Male , Visual AcuityABSTRACT
Mixed metal oxides are discussed as possible substitutes for noble metals in automobile catalytic converters. The catalytic activity for CO oxidation of LaMnO3 and La0.5Sr0.5MnO3 catalysts was examined.The ability of these catalysts to provide lattice oxygen and to sustain the oxidation reaction, even in the absence of molecular oxygen, has been confirmed. Measurements were performed of the reversible oxygen uptake on the two catalysts.
