Solvent effects and photophysical studies of a new class of acridine(1,8)dione dyes

Spectroscopic properties of a new family of acridinedione dyes are reported. The absorption and fluorescence spectra of the different substituted acridinediones have been recorded in different solvents and the difference in the dipole moment between ground and excited state has been obtained by solvatochromic shift method. The value of the Onsager cavity radius was calculated from the total surface area using software PCMODEL. Fluorescence quantum yield and fluorescence lifetime were determined. Radiative and non-radiative constants have been calculated. The triplet-triplet absorption maxima and triplet lifetime show variation depending on the substitution.     

The Weierstrass Transform for a Class of Generalized Functions

The classical theory of the Weierstrass transform is extended to a generalized function space which is the dual of a testing function space consisting of purely entire functions with certain growth conditions developed by Kenneth B. Howell. An inversion formula and characterizations for this transform are obtained. A comparative study with the existing literature is also undertaken.     

Synthesis,characterization and properties of novel highly oxygen permeable amphiphilic membranes

The objective of this research was to develop new strategies for the synthesis of novel optically clear highly oxygen permeable membranes exhibiting appropriate water uptake and mechanical properties for possible ophthalmic applications. Thus a series of bicontinuous amphiphilic conetworks containing well‐defined poly‐ (ethylene glycol) and polydimethylsiloxane segments crosslinked by three novel crosslinking/modifying agents were synthesized, characterized, and evaluated. This paper concerns the design and synthesis of the crosslinking/modifying agents (see Fig. 2 ), and their use for the synthesis of clear, highly oxygen permeable amphiphilic membranes. Select membranes exhibit outstanding oxygen permeabilities (>200 barrers) far superior to contemporary commercial soft contact lenses, together with mechanical properties and water uptake appropriate for extended wear soft contact lens application. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 308–316, 2007     

Synthesis,characterization, and crosslinking of methacrylate‐telechelic PDMAAm‐b‐PDMS‐b‐PDMAAm copolymers

The synthesis and molecular characterization of a new amphiphilic conetwork (APCN) designed for silicone hydrogel use is described. The synthesis strategy, outlined in Scheme 1 , calls for the preparation, by the RAFT technique, of a new methacrylate‐telechelic amphiphilic pentablock, MA‐PHEA‐b‐PDMAAM‐b‐PDMS‐b‐PDMAAm‐b‐PHEA‐MA, and its crosslinking to the target APCN. The sketch shows the architecture of the APCN (dotted lines, PDMAAm; solid lines, PDMS; clusters, MA‐based crosslinking sites; see Fig. 3 ). All six synthesis steps proceed smoothly and efficiently, and the products are optically clear, colorless membranes exhibiting properties appropriate for ophthalmic use. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4284–4290, 2007     

Study of the Mode and Efficiency of DNA Binding in the Damage Induced by Photoactivated Water Soluble Porphyrins

We have investigated the DNA binding interactions and in vitro photoactivated DNA damage induced by a neutral water soluble porphyrin derivative 5,10,15,20‐tetrakis(2,4,6‐trihydroxyphenyl)porphyrin (TTHPP) and its zinc derivative 5,10,15,20‐tetrakis(2,4,6‐trihydroxyphenyl)porphyrinato zinc(II) (Zn‐TTHPP) upon visible light irradiation through various spectroscopic techniques and employing repair endonucleases. These porphyrin derivatives exhibited high affinity toward DNA through groove binding interactions as evidenced through the UV–vis absorption, emission, circular dichroism spectral and viscosity changes. Interestingly, the free base porphyrin derivative, TTHPP generated efficient singlet oxygen mediated DNA damage sensitive to formamidopyrimidine‐DNA glycosylase (Fpg protein), when compared with its metal derivative and to the well‐known photosensitizer, hematoporphyrin. These results provide direct evidence for the role of DNA binding mode as well as extent of interactions with DNA in the efficiency of photoactivated DNA damage induced by the neutral porphyrins, which are believed to be the ideal candidates for photodynamic therapeutic applications.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Vinyl polymerization

1:1 Poly (styrene-co-ethylmethacrylate) (PSEM) was prepared by bulk polymerization and fractionated using methylethyl ketone/petroleum ether system. IR and NMR analyses of the copolymer substantiated the composition kinetically expected. As the composition heterogeneity of the compolymer was narrow, the characterization of the copolymer was effected in a single solvent by light scattering as well as viscosity measurements at 35° C. The molecular weight dependence of [η], the limiting viscosity number;\(\left( {\bar r^2 } \right)w^{_2^1 } \), therms end to end distance and A₂ the second virial coefficient were established. The solvent ethylacetate was found to be thermodynamically more ideal for PSEM, than for polyethylmethacrylate. In an attempt to evaluate K, the Flory’s constant, application of various methods appeared to give almost similar values. In order to explain the low value ofΦ, the Flory’s universal parameter, rough estimates of\(\left( {\bar r_0 ^2 } \right)^{_2^1 } \), the unperturbedrms end to end distance;b, the statistical chain element;q, the persistence length and\({{\bar r_0 ^2 } \mathord{\left/ {\vphantom {{\bar r_0 ^2 } {l\bar r_{\max .} }}} \right. \kern-\nulldelimiterspace} {l\bar r_{\max .} }}\), the semiflexibility parameter were also made.