Search

Fluorosis is one of the factors which bring about mineralisation changes in a dentinal structure leading to dentin. The purpose of the present study was to compare and evaluate the dentinal tubular changes in fluorosed and nonfluorosed teeth subsequent to the application of citric acid,strontium acetate based sodium fluoride (SAF) using scanning electron microscopy (SEM). Dentin specimens from healthy fluorosed and nonfluorosed teeth were included in the study. Each of them was grouped into acid treated and SAF treatment groups. Using SEM, the photomicrographs (3500x) of dentin specimens were evaluated. Results showed while there was a significant difference in tubular width of partial occlusion ≤ 25%, being more in fluorosed group compared to nonfluorosed group after application SAF. Application of desensitising agents demonstrated higher number of dentinal tubular occlusion and diameter reduction in nonfluorosed dentin compared to fluorosed dentin. Summary: Root biomodification and desensitising agent procedure brings in definite difference between fluorosed and non-fluorosed dentin specimens.

Nanotechnology involving cellulosic substrates has generated a great attention owing to their exceptional physical and chemical properties. Self-assembled nanostructures obtained from carbohydrate polymers are of interest in the biomedical field for the biocompatibility and non-toxic nature. In the present study modification of nano-fibrillated cellulose (NFC) synthesised from the husk fibers of Areca catechu nuts (AHF) was studied by controlled regio-selective amidation with oleylamine (OA) and characterized. The modified system (MNFC) with more than 66% OA content showed self-assembly into unilamellar vesicles of 2-5μm diameters with a wall thickness of 300-600nm in tetrahydrofuran (THF) at 2.5mgmL-1. This result is attributed to the folding of MNFC into bilayers driven by long cis-unsaturated aliphatic chains in polar aprotic solvents stabilized by hydrogen bonded interactions within the fibrils. These giant vesicles formed can have applications in storage and delivery of drugs in topical applications.

An examination of the dependence of total flux from competing photodissociation channels on the photolysis field parameters and initial vibrational states for IBr and HI molecules reveals that, for a range of field attributes, considerable selectivity and yield may be obtained by using only the ground or the ground and the first excited vibrational states in the optimal linear combination constituting the field optimized initial state (FOIST). The new simplifications obviate the need for overtone excitations or multicolor photolysis fields making it easier to implement FOIST experimentally. Concrete specifications of field attributes for achieving selective control of IBr photodissociation products is provided. (C) 2000 [S0021-9606(00)01427-6].

The probability density profiles from the optimal superpositions of the field free vibrational eigenstates which maximize flux out of the desired photodissociation channels are examined for IBr and HI molecules. Analysis of the structure in these optimal superposition states obtained by applying the Rayleigh-Ritz variational procedure to the time integrated flux operator shows that the transfer of probability density to appropriate areas of the Franck-Condon region on the excited surfaces is responsible for selective flux maximization out of different channels. Localizing the wave packet on the more repulsive part of the higher curve facilitates fast diabatic exit out of the upper channel and transition to the less repulsive part promotes slow adiabatic exit out of the lower channel. This mechanism is further probed by utilizing time dependent wave packet dynamics to obtain absorption spectra and branching ratios using full Fourier transform of the autocorrelation functions for these field optimized initial states. The results corroborate the central role of altered spatial profile of the initial state in selective control of photodissociation. (C) 1999 [S0021-9606(99)00610-8].

A study is made of the kinetics and mechanism of the reaction of radiolytically produced hydrated electron (e-(aq)) with some triazine derivatives [1,3,5-triazine (T), 2,4,6-trimethoxy-1,3,5-triazine (TMT), 2,4-dioxohexahydro-1,3,5-triazine (DHT), 6-chloro N-ethyl N-(1-methylethyl)-1,3,5-triazine 2,4-diamine (atrazine, AT), and cyanuric acid (CA)] in aqueous medium using pulse and steady-state radiolysis techniques. The second-order rate constants were determined from the pseudo first-order decay of e(-)(aq) in the presence of triazines at 720 nm, and the values obtained with T, TMT, AT, and CA are in the order of 10(9) dm(3) mol(-1) s(-1) and that of DHT was 10(8) dm(3) mol(-1) s(-1) at pH 6. The transient absorption spectra from the reaction of e(-)(aq) with T and TMT are characterized by their lambda(max) at 310 nm, and those of DHT and CA are around 280 and 290 nm, respectively. However, a very weak and featureless absorption spectrum is obtained from AT. On the basis of the spectral evidence and on the quantitative electron transfer from the transient intermediates to the oxidant, methyl viologen (MV(2+)), the intermediate radicals are assigned to N-protonated electron adducts (with the unpaired spin density at carbon) of triazines. The degradation profiles, monitored as the disappearance of parent triazine concentrations as a function of dose, obtained with AT, TMT, CA, and DHT, highlight the potential use of e-(aq) in the degradation of triazines.

The validity of different sets of model potential energy curves and functional forms for nonadiabatic and optical coupling between them used to treat IBr photodissociation is ascertained by calculation of Raman excitation profiles using the time dependent wave packet method. Our results suggest that the additional three states in the six state model play only a marginal role in the photodynamics of IBr., © Elsevier