4-Aminophthalimide Derivatives as Environment-Sensitive Probes

The potential of 4-aminophthalimide (AP) and its derivatives as fluorescence probes for organized media is highlighted. The fluorescence response of AP, as measured from the position of the fluorescence maximum, fluorescence intensity and lifetime, is highly sensitive to the polarity of the medium. The sensitivity of the fluorescence parameters is further enhanced due to the involvement of the emitting intramolecular charge transfer state in hydrogen bonding interaction with the solvent molecules containing hydroxyl groups. It is shown that the microheterogeneous environments of organized media such as cyclodextrins and micelles can be very conveniently monitored using this probe. The results of the investigations carried out employing AP and its derivatives as fluorescence probe molecules in these media clearly suggest that a combination of the hydrophobic interaction with the host media and hydrogen bonding interaction with the solvent molecules determine the location of the fluorophore, which in all cases is found to be the interfacial region separating the nonpolar core of the micelle or the cyclodextrin cavity and the polar aqueous environment. Guidelines for the design of probes of this class of systems for the nonpolar core region of the micelles are provided and possible ways to increase the sensitivity of the fluorescence response of the systems are suggested.     

Experimental (vapour + liquid) equilibrium data of (methanol + water), (water + glycerol) and (methanol + glycerol) systems at atmospheric and sub-atmospheric pressures

Experimental (vapour + liquid) equilibrium results for the binary systems, (methanol + water) at the local atmospheric pressure of 95.3 kPa and at sub-atmospheric pressures of (15.19, 29.38, 42.66, 56.03, and 67.38) kPa, (water + glycerol) system at pressures (14.19, 29.38, 41.54, 54.72, 63.84, and 95.3) kPa and the (methanol + glycerol) system at pressures (32.02 and 45.3) kPa were obtained over the entire composition range using a Sweitoslwasky-type ebulliometer. The relationship of the liquid composition (x₁) as a function of temperature (T) was found to be well represented by the Wilson model. Computed vapour phase mole fractions, activity coefficients and the measured values along with optimum Wilson parameters are presented.     

Molecular beacon probes of photodamage in thymine and uracil oligonucleotides

Molecular beacons (MB) are becoming more common as sequence-selective detectors of nucleic acids. Although they can easily detect single-base mismatches, they have never been used to directly detect DNA or RNA damage. To measure the degree of ultraviolet (UV) light damage in oligonucleotides, we report a novel MB approach for general detection of photoproducts in UV-irradiated rU17 and dT17 oligonucleotides. With monochromatic UV light irradiation at ca 280 nm under anoxic conditions, the oligonucleotide absorption decays with a single-exponential time constant of 123+/-1 min for rU17 and with double-exponential time constants of 78+/-0.5 min (99%) and 180+/-5 min (0.05%) for dT17 oligonucleotides. Under the same conditions, the MB fluorescence decays more quickly, with single-exponential time constants of 19+/-2 and 26+/-3 min for rU17 and dT17, respectively. Similar kinetics were observed with broadband UV light irradiation of oligonucleotides. The differences in the UV damage kinetics of dT17 and rU17 and their detection by absorption and fluorescence techniques will be discussed in the context of differential instabilities introduced in the nucleic acid-MB duplex by the different photoproducts formed.     

Metabolite Dysregulation by Pranlukast in Mycobacterium tuberculosis

Mycobacterium tuberculosis has been infecting millions of people worldwide over the years, causing tuberculosis. Drugs targeting distinct cellular mechanisms including synthesis of the cell wall, lipids, proteins, and nucleic acids in Mtb are currently being used for the treatment of TB. Although extensive research is being carried out at the molecular level in the infected host and pathogen, the identification of suitable drug targets and drugs remains under explored. Pranlukast, an allosteric inhibitor of MtArgJ (Mtb ornithine acetyltransferase) has previously been shown to inhibit the survival and virulence of Mtb. The main objective of this study was to identify the altered metabolic pathways and biological processes associated with the differentially expressed metabolites by PRK in Mtb. Here in this study, metabolomics was carried out using an LC-MS/MS-based approach. Collectively, 50 metabolites were identified to be differentially expressed with a significant p-value through a global metabolomic approach using a high-resolution mass spectrometer. Metabolites downstream of argJ were downregulated in the arginine biosynthetic pathway following pranlukast treatment. Predicted human protein interactors of pranlukast-treated Mtb metabolome were identified in association with autophagy, inflammation, DNA repair, and other immune-related processes. Further metabolites including N-acetylglutamate, argininosuccinate, L-arginine, succinate, ergothioneine, and L-phenylalanine were validated by multiple reaction monitoring, a targeted mass spectrometry-based metabolomic approach. This study facilitates the understanding of pranlukast-mediated metabolic changes in Mtb and holds the potential to identify novel therapeutic approaches using metabolic pathways in Mtb.     

Plasma-enhanced synthesis of bactericidal quaternary ammonium thin layers on stainless steel and cellulose surfaces

We have investigated bottom-up chemical synthesis of quaternary ammonium (QA) groups exhibiting antibacterial properties on stainless steel (SS) and filter paper surfaces via nonequilibrium, low-pressure plasma-enhanced functionalization. Ethylenediamine (ED) plasma under suitable conditions generated films rich in secondary and tertiary amines. These functional structures were covalently attached to the SS surface by treating SS with O 2 and hexamethyldisiloxane plasma prior to ED plasma treatment. QA structures were formed by reaction of the plasma-deposited amines with hexyl bromide and subsequently with methyl iodide. Structural compositions were examined by electron spectroscopy for chemical analysis and Fourier transform infrared spectroscopy, and surface topography was investigated with atomic force microscopy and water contact angle measurements. Modified SS surfaces exhibited greater than a 99.9% decrease in Staphylococcus aureus counts and 98% in the case of Klebsiella pneumoniae. The porous filter paper surfaces with immobilized QA groups inactivated 98.7% and 96.8% of S. aureus and K. pneumoniae, respectively. This technique will open up a novel way for the synthesis of stable and very efficient bactericidal surfaces with potential applications in development of advanced medical devices and implants with antimicrobial surfaces.     

A new family of heteroleptic ruthenium(II) polypyridyl complexes for sensitization of nanocrystalline TiO2 films

Two new heteroleptic ruthenium(II) photosensitizers that contains 2,2';6,2'-terpyridine with extended π-conjugation with donor groups, a 4,4'-dicarboxylic acid-2,2'-bipyridine anchoring ligand and a thiocyanate ligand have been designed, synthesized and fully characterized by CHN, mass spectrometry, UV-vis and fluorescence spectroscopies and cyclic voltammetry. The new sensitizers have either 3,5-di-tert-butyl phenyl (m-BL-5) or triphenylamine (m-BL-6) groups, where the molar extinction coefficient of both the sensitizers is higher than the analogous ruthenium dyes. Both the sensitizers were tested in dye-sensitized solar cells using two different redox electrolytes.     

DFT study of core‐modified porphyrin isomers

B3LYP/6‐311+G** calculations were performed systematically on 1,2 (syn) and 1,3 (anti) tautomeric forms of oxa‐ and thia‐ core‐modified porphyrin isomers, which resulted in a total of 86 structures. The structural and energetic variation in all the isomers were analyzed. In corrphycene, hemiporphycene and porphycene the Z forms are more stable compared to the corresponding E forms in both the anti and syn oxa‐ and thiaporphyrin isomers. In contrast, in the syn isomeric forms of [3.0.1.0], [3.1.0.0] and [4.0.0.0] oxaporphyrins and in both syn and anti forms of thiaporphyrin isomers, Z forms are less stable. The HOMO and LUMO values are both negative and varied in a narrow zone, indicating no dramatic effect on the position of heteroatom substitution on the redox properties. The effect of geometric constraints due to the alteration of meso‐bridge length and the hetero atom disposition in the porphyrin core on the relative stabilities of the isomers is analyzed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Further shortening of the C-C single bond in substituted tetrahedranyl tetrahedrane systems: an energy decomposition analysis

The computational study explores the electronic fine tuning of the exocyclic C-C single bond length in tetrahedranyl tetrahedrane as a function of various substituents. The factors which determine the bond lengths and bond strengths are examined by using the EDA method.     

Photochemical E (trans)-->Z (cis) isomerization in substituted 1-naphthylacrylates.

Substituted naphthylacrylates, 1-3, not showing rotamerism have been synthesized with a view to study photochemical E (trans)-->Z (cis) isomerization. Photostationary state composition of the isomers upon direct excitation, triplet sensitized isomerization, quantum yield of isomerization, and steady state and time-resolved fluorescence behavior have been studied for these naphthylacrylates. The direct excitations of the compounds yield high Z (approximately 80%) isomer composition, whereas the triplet sensitization results in less Z (approximately 20%) isomer composition. This indicates that the singlet pathway is very efficient in converting the E isomer to the Z isomer. The naphthylacrylates 1 and 2 exhibit structured fluorescence at room temperature in hexane and upon changing the solvent to CH3CN; the structure of the fluorescence is lost, indicating that the singlet excited-state develops a polar character in a polar environment. The polar nature of the singlet excited state becomes more clear in the case of 3 from its fluorescence solvatochromism. The naphthylacrylates did not exhibit excitation wavelength-dependent fluorescence at room temperature suggesting that the ground state conformers (rotamers) are not involved. Fluorescence lifetimes measured for these compounds displayed biexponential behavior, which is explained using a two-state model.     

Permeability of Human Tooth Surfaces Studied In Vitro by Electrochemical Impedance Spectroscopy

Electrochemical Faradaic impedance spectroscopy was applied to evaluate dependence of the electrical resistance on human teeth. The experiments were performed using iodide anions as a redox probe to model permeability of teeth for fluoride upon an iontophoresis process. Tooth molars were used – as these are teeth most affected by tooth decay processes in vivo. Teeth compared included sound molars – with no evidence of pit and fissure decay, teeth with pits and fissures regarded ‘clinically’ as showing signs of decay, and teeth with crowns removed to present exposed dentin surfaces. A difference of more than an order of magnitude in electrical resistance was observed between sound molars and those regarded as showing evidence of tooth decay processes. Sound dentin, as expected from structural considerations demonstrated significantly lower resistance when compared to sound molars. Importantly, the difference in tooth resistance measured between carious and sound molars was shown to be much more representative of their structural integrity than comparison of digitally processed images of the teeth. The results support the utility of electrochemical Faradaic impedance spectroscopy for the development of understanding on how tooth electrical resistance may vary according to structural changes. This understanding may be useful to continued refinements in the use of electrical resistance measures as caries diagnostics and support generically the potential for iontophoretic processes in in‐office fluoride treatments of teeth.