Solvent-induced changes on the polarity of the triplet excited state of 2-chlorothioxanthone: From time-resolved absorption and resonance Raman spectroscopies

Solvent polarity has been known to influence the triplet state structure and reactivity. Here, we present our experimental and theoretical study on the effect of solvent on the lowest triplet excited state structure of 2-chlorothioxanthone (CTX). Time-resolved absorption (TA) spectroscopy has been employed to understand the triplet state electronic structure; whereas solvent-induced structural changes have been studied using time-resolved resonance Raman (TR3) spectroscopy. Both the DFT and TD-DFT calculations have been performed in the solution phase employing self-consistent reaction field implicit solvation model to support the experimental data. It has been observed that CO stretching frequencies of the excited triplet state are sensitive to the solvent polarity and increase with the increase in the solvent polarity. Both TA and TR3 studies reveal that specific solvent effect (H-bonding) is more pronounced in comparison to the nonspecific solvent effect. (C) 2013 Elsevier B.V. All rights reserved.

Solvent polarity and nanoscale morphology in bulk heterojunction organic solar cells: A case study

Organic bulk heterojunction solar cells were fabricated under identical experimental conditions, except by varying the solvent polarity used for spin coating the active layer components and their performance was evaluated systematically. Results showed that presence of nitrobenzene-chlorobenzene composition governs the morphology of active layer formed, which is due to the tuning of solvent polarity as well as the resulting solubility of the P3HT:PCBM blend. Trace amount of nitrobenzene favoured the formation of better organised P3HT domains, as evident from conductive AFM, tapping mode AFM and surface, and cross-sectional SEM analysis. The higher interfacial surface area thus generated produced cells with high efficiency. But, an increase in the nitrobenzene composition leads to a decrease in cell performance, which is due to the formation of an active layer with larger size polymer domain networks with poor charge separation possibility. (C) 2014 AIP Publishing LLC.

Comparative Study of Protein Unfolding in Aqueous Urea and Dimethyl Sulfoxide Solutions: Surface Polarity, Solvent Specificity, and Sequence of Secondary Structure Melting

Elucidation of possible pathways between folded (native) and unfolded states of a protein is a challenging task, as the intermediates are often hard to detect. Here, we alter the solvent environment in a controlled manner by choosing two different cosolvents of water, urea, and dimethyl sulfoxide (DMSO) and study unfolding of four different proteins to understand the respective sequence of melting by computer simulation methods. We indeed find interesting differences in the sequence of melting of alpha helices and beta sheets in these two solvents. For example, in 8 M urea solution, beta-sheet parts of a protein are found to unfold preferentially, followed by the unfolding of alpha helices. In contrast, 8 M DMSO solution unfolds alpha helices first, followed by the separation of beta sheets for the majority of proteins. Sequence of unfolding events in four different alpha/beta proteins and also in chicken villin head piece (HP-36) both in urea and DMSO solutions demonstrate that the unfolding pathways are determined jointly by relative exposure of polar and nonpolar residues of a protein and the mode of molecular action of a solvent on that protein.

Organic fragments from graphene oxide: Isolation, characterization and solvent effects

As-prepared graphene oxide (GO) contains oxidative debris which can be washed using basic solutions. We present the isolation and characterization of these debris. Dynamic light scattering (DLS) is used to monitor the separation of the debris in various solvents in the presence of different protic and aprotic alkylamino bases. The study reveals that the debris are rich in carbonyl functional groups and water is an essential component for separation and removal of the debris from GO under oxidative reaction conditions.

Substituent effect on fluorescence signaling of the cell permeable HSO4- receptors through single point to ratiometric response in green solvent

Two new 2-(2-aminophenyl)benzimidazole-based HSO4- ion selective receptors, 6-(4-nitrophenyl)-5,6-dihydrobenzo4,5]imidazo1,2-c]quinazoline (L1H) and 6-(4-methoxyphenyl)-5,6-dihydrobenzo4,5]imidazo1,2-c] quinazoline (L2H), and their 1 : 1 molecular complexes with HSO4- were prepared in a facile synthetic method and characterized by physicochemical and spectroscopic techniques along with the detailed structural analysis of L1H by single crystal X-ray crystallography. Both receptors (L1H and L2H) behave as highly selective chemosensor for HSO4- ions at biological pH in ethanol-water HEPES buffer (1/5) (v/v) medium over other anions such as F-, Cl-, Br-, I-, AcO-, H2PO4-, N-3(-) and ClO4-. Theoretical and experimental studies showed that the emission efficiency of the receptors (L1H and L2H) was tuned successfully through single point to ratiometric detection by employing the substituent effects. Using 3 sigma method the LOD for HSO4- ions were found to be 18.08 nM and 14.11 nM for L1H and L2H, respectively, within a very short responsive time (15-20 s) in 100 mM HEPES buffer (ethanol-water: 1/5, v/v). Comparison of the utility of the probes (L1H and L2H) as biomarkers for the detection of intracellular HSO4- ions concentrations under a fluorescence microscope has also been included and both probes showed no cytotoxic effect.

Stabilization of Co-3 - Oxoclusters in a pcu Net: Synthesis, Structure, Solvent Exchange (Single Crystal to Single Crystal) and Magnetic Studies

The solvothermal reaction of CoCl(2)4H(2)O and 4,4-sulfonyldibenzoic acid (H(2)SDBA) resulted in the formation of a three-dimensional coordination polymer Co-3(C14H8O6S)(3)(DMA)(2)(MeOH)].DMA (Ia) consisting of trinuclear Co-3 oxo-cluster units. The Co-3 trimeric units are connected by SDBA(2-) anions leading to a three dimensional structure with a pcu topology. The terminal methanol molecules could be exchanged in a single crystal to single crystal (SCSC) fashion by other similar solvent molecules (ethanol, acetonitrile, water, ethyleneglycol). Magnetic studies on the parent compound, Ia, indicate antiferromagnetic interactions between the central metal atoms.

A metal-free and a solvent-free synthesis of thio-amides and amides: an efficient Friedel-Crafts arylation of isothiocyanates and isocyanates

A rapid, metal-free and solvent-free (very low loading of solvent in few cases) reaction conditions for synthesizing thioamides and amides using a Bronsted super acid such as triflic acid has been developed. This method shows a broad substrate scope with a variety of electron-rich arenes including thiophene derivatives. The reaction works well for both aromatic as well as aliphatic isothiocyanates. Most of the thioamides are obtained in excellent yields in short reaction times and in most of the examples, a simple work up procedure has been developed which does not require further purification.

A bio-attuned ratiometric hydrogen sulfate ion selective receptor in aqueous solvent: structural proof of the H-bonded adduct

A new cell permeable quinazoline based receptor (1) selectively senses HSO4- ions of nanomolar region in 0.1 M HEPES buffer (ethanol-water: 1/5, v/v) at biological pH over other competitive ions through the proton transfer followed by hydrogen bond formation and subsequent anion coordination to yield the LHSO4]-LH+center dot 3H(2)O (2) ensemble, which has been crystallographically characterised to ensure the structure property relationship. This non-cytotoxic HSO4- ion selective biomarker has great potential to recognize the intercellular distribution of HSO4- ions in HeLa cells under fluorescence microscope.

High Proton Mobility, Solvent Induced Single Crystal to Single Crystal Structural Transformation, and Related Studies on a Family of Compounds Formed from Mn-3 Oxo-Clusters

The reaction between 4,4'-sulfonyldibenzoic acid (H(2)SDBA) and manganese under mild conditions resulted in the isolation of two new three-dimensional compounds, Mn-4(C14H8O6S)(4)(DMA)(2)]center dot 3DMA, I, and Mn-3(C14H8O6S)(3)(DMA)(2)(MeOH)]center dot DMA, IIa. Both structures have Mn-3 trimer oxo cluster units. While the Mn-3 oxoclusters are connected through octahedral manganese forming one-dimensional Mn-O-Mn chains in I, the Mn-3 units are isolated in IIa. The SDBA units connect the Mn-O-Mn chains and the Mn-3 clusters giving rise to the three-dimensional structure. Both compounds have coordinated and free solvent molecules. In IIa, two different solvent molecules are coordinated, of which one solvent can be reversibly exchanged by a variety of other similar solvents via a solvent-mediated single crystal to single crystal (SCSC) transformation. The free lattice DMA solvent molecules in I can be exchanged by water molecules resulting in hydrophilic channels. Proton conductivity studies on I reveals a high proton mobility with conductivity values of similar to 0.87 x 10(-3) Omega(-1) cm(-1) at 34 degrees C and 98% RH, which is comparable to some of the good proton conductivity values observed in inorganic coordination polymers. We have also shown structural transformation of I to IIa through a possible dissolution and recrystallization pathway. In addition, both I and IIa appear to transform to two other manganese compounds H3O]Mn-3(mu(3)-OH)(C14H8O6S)(3)(H2O)](DMF)(5) and H3O](2)Mn-7(mu 3-OH)(4)(C14H8O6S)(6)(H2O)(4)](H2O)(2)(DMF)(8) under suitable reaction conditions. We have partially substituted Co in place of Mn in the Mn-3 trimer clusters forming CoMn2(C14H8O6S)(3)(DMA)(2)(EtOH)]center dot DMA, III, a structure that is closely related to IIa. All the compounds reveal antiferromagnetic behavior. On heating, the cobalt substituted phase (compound III) forms a CoMn2O4 spinel phase with particle sizes in the nanometer range.

Effect of solvent; enhancing the wettability and engineering the porous structure of a calcium phosphate/agarose composite for drug delivery

Tissue engineering deals with the regeneration of tissues for bone repair, wound healing, drug delivery, etc., and a highly porous 3D artificial scaffold is required to accommodate the cells and direct their growth. We prepared 3D porous calcium phosphate ((hydroxyapatite/beta-tricalcium phosphate)/agarose, (HAp/beta-TCP)/agarose) composite scaffolds by sol-gel technique with water (WBS) and ethanol (EBS) as solvents. The crystalline phases of HAp and beta-TCP in the scaffolds were confirmed by X-ray diffraction (XRD) analysis. The EBS had reduced crystallinity and crystallite size compared to WBS. WBS and EBS revealed interconnected pores of 1 mu m and 100 nm, respectively. The swelling ratio was higher for EBS in water and phosphate buffered saline (PBS). An in vitro drug loading/release experiment was carried out on the scaffolds using gentamicin sulphate (GS) and amoxicillin (AMX). We observed initial burst release followed by sustained release from WBS and EBS. In addition, GS showed more extended release than AMX from both the scaffolds. GS and AMX loaded scaffolds showed greater efficacy against Pseudomonas than Bacillus species. WBS exhibited enhanced mechanical properties, wettability, drug loading and haemocompatibility compared to EBS. In vitro cell studies showed that over the scaffolds, MC3T3 cells attached and proliferated and there was a significant increase in live MC3T3 cells. Both scaffolds supported MC3T3 proliferation and mineralization in the absence of osteogenic differentiation supplements in media which proves the scaffolds are osteoconducive. Microporous scaffolds (WBS) could assist the bone in-growth, whereas the presence of nanopores (EBS) could enhance the degradation process. Hence, WBS and EBS could be used as scaffolds for tissue engineering and drug delivery. This is a cost effective technique to produce scaffolds of degradable 3D ceramic-polymer composites.

Optimization of solution-processed oligothiophene:fullerene based organic solar cells by using solvent additives

The optimization of solution-processed organic bulk-heterojunction solar cells with the acceptor-substituted quinquethiophene DCV5T-Bu-4 as donor in conjunction with PC61BM as acceptor is described. Power conversion efficiencies up to 3.0% and external quantum efficiencies up to 40% were obtained through the use of 1-chloronaphthalene as solvent additive in the fabrication of the photovoltaic devices. Furthermore, atomic force microscopy investigations of the photoactive layer gave insight into the distribution of donor and acceptor within the blend. The unique combination of solubility and thermal stability of DCV5T-Bu-4 also allows for fabrication of organic solar cells by vacuum deposition. Thus, we were able to perform a rare comparison of the device characteristics of the solution-processed DCV5T-Bu-4:PC61BM solar cell with its vacuum-processed DCV5T-Bu-4:C-60 counterpart. Interestingly in this case, the efficiencies of the small-molecule organic solar cells prepared by using solution techniques are approaching those fabricated by using vacuum technology. This result is significant as vacuum-processed devices typically display much better performances in photovoltaic cells. Keywords