Ultrafast Singlet–Singlet Energy Transfer between an Acceptor Electrostatically Attached to the Walls of an Organic Capsule and the Enclosed Donor

Ultrafast Forster resonance energy transfer (FRET) between a donor (coumarin dye) and a cationic acceptor (rhodamine 6G) situated within and on the exterior walls, respectively, of a bimolecular capsule made up of anionic octa-acid (OA) is studied by femtosecond up-conversion. 1D and 2D 1H NMR spectral analyses reveal that donors coumarin-1, coumarin-153, and coumarin-480 form a 1:2 complex (guest to host) and are enclosed within the OA capsule. NMR and emission spectra suggest that the cationic acceptor rhodamine 6G is attached to the anionic exterior walls of the OA capsule. The acceptor emission displays a rise component of 1–3 ps which corresponds to a donor–acceptor distance (RDA) of ∼13 Å and thus indicates the occurrence of ultrafast FRET between the donor and acceptor at close contact

Ultrafast FRET in Ionic Liquid-P123 Mixed Micelles: Region and Counterion Dependence

Ultrafast fluorescence resonance energy transfer (FRET) in a mixed micelle containing a room-temperature ionic liquid (RTIL) is studied by picosecond and femtosecond emission spectroscopy. The mixed micelle consists of a triblock copolymer, (PEO)20-(PPO)70-(PEO)20 (Pluronic P123), and a RTIL, 1-pentyl-3-methyl-imidazolium tetra-flouroborate, ([pmim][BF4]) or 1-pentyl-3-methyl-imidazolium bromide ([pmim][Br]). Coumarin 480 (C480) is used as the donor, and the acceptor is rhodamine 6G (R6G). Multiple time scales of FRET were detectedan ultrashort component of 1−3 ps and two relatively long components (300−400 ps and 2500−3500 ps). The different time scales are attributed to different donor−acceptor distances. It is proposed that the ionic acceptor (R6G) is localized in the polar corona region of the mixed micelle, while the neutral donor (C480) is distributed over both corona and hydrophobic core regions. The ultrafast (1−3 ps) components are assigned to FRET at a close contact of donor and acceptor. This occurs for the donor in the polar corona region in close proximity of the acceptor. The longer components (300−400 ps and 2500−3500 ps) arise from long-distance FRET from the donor at the core and the acceptor at the corona region. The relative contribution of the ultrafast component of FRET (∼3 ps) increases from 5% at λex = 375 nm to 30% at λex = 435 nm in the 0.3 M [pmim][BF4] mixed micelle and from 25 to 100% in the 0.9 M [pmim][BF4] mixed micelle. It is suggested that, at λex = 435 nm, mainly the donor molecules present at the corona are excited, causing ultrafast FRET due to a short donor−acceptor distance. At shorter λex, the donor (C480) molecule at the core regions is excited, giving rise to a very long 3400 ps component (RDA ∼ 50 Å). Thus, λex variation leads to excellent spatial resolution. The counterion dependence (Br− vs BF4−) is attributed to the difference in the local polarity and size of the two mixed micelles

Solvation Dynamics of a Protein in the Pre Molten Globule State

The nature of solvent molecules around proteins in native and different non-native states is crucial for understanding the protein folding problem. We have characterized two compact denatured states of glutaminyl-tRNA synthetase (GlnRS) under equilibrium conditions in the presence of a naturally occurring osmolyte, l-glutamate. The solvation dynamics of the compact denatured states and the fully unfolded state has been studied using a covalently attached probe, acrylodan, near the active site. The solvation dynamics progressively becomes faster as the protein goes from the native to the molten globule to the pre molten globule to the fully unfolded state. Anisotropy decay measurements suggest that the pre-molten-globule intermediate is more flexible than the molten globule although the secondary structure is largely similar. Dynamic light scattering studies reveal that both the compact denatured states are aggregated under the measurement conditions. The implications of solvation dynamics in aggregated compact denatured states have been discussed

Diverse Gene Cassettes in Class 1 Integrons of Facultative Oligotrophic Bacteria of River Mahananda, West Bengal, India

<div><p>Background</p><p>In this study a large random collection (n = 2188) of facultative oligotrophic bacteria, from 90 water samples gathered in three consecutive years (2007–2009) from three different sampling sites of River Mahananda in Siliguri, West Bengal, India, were investigated for the presence of class 1 integrons and sequences of the amplification products.</p><p>Methodology/Principal Findings</p><p>Replica plating method was employed for determining the antibiotic resistance profile of the randomly assorted facultative oligotrophic isolates. Genomic DNA from each isolate was analyzed by PCR for the presence of class 1 integron. Amplicons were cloned and sequenced. Numerical taxonomy and 16S rRNA gene sequence analyses were done to ascertain putative genera of the class 1 integron bearing isolates. Out of 2188 isolates, 1667 (76.19%) were antibiotic-resistant comprising of both single-antibiotic resistance (SAR) and multiple-antibiotic resistant (MAR), and 521 (23.81%) were sensitive to all twelve different antibiotics used in this study. Ninety out of 2188 isolates produced amplicon(s) of varying sizes from 0.15 to 3.45 KB. Chi-square (χ²) test revealed that the possession of class 1 integron in sensitive, SAR and MAR is not equally probable at the 1% level of significance. Diverse antibiotic-resistance gene cassettes, <i>aadA1, aadA2, aadA4, aadA5, dfrA1, dfrA5, dfrA7, dfrA12, dfrA16, dfrA17, dfrA28, dfrA30, dfr-IIe, blaIMP-9, aacA4, Ac-6′-Ib, oxa1, oxa10</i> and <i>arr2</i> were detected in 64 isolates. The novel cassettes encoding proteins unrelated to any known antibiotic resistance gene function were identified in 26 isolates. Antibiotic-sensitive isolates have a greater propensity to carry gene cassettes unrelated to known antibiotic-resistance genes. The integron-positive isolates under the class <i>Betaproteobacteria</i> comprised of only two genera, <i>Comamonas</i> and <i>Acidovorax</i> of family <i>Comamonadaceae,</i> while isolates under class <i>Gammaproteobacteria</i> fell under the families, <i>Moraxellaceae</i>, <i>Pseudomonadaceae</i>, <i>Aeromonadaceae</i> and <i>Enterobacteriaceae</i>.</p><p>Conclusions</p><p>Oligotrophic bacteria are good sources of novel genes as well as potential reservoirs of antibiotic resistance gene casettes.</p></div

Dendogram based on similarity matrices computed from phenotypic characters and 1D-SDS-PAGE.

<p>SDS PAGE anlaysis was done using total protein extracted from bacteria possessing class 1 integrons. MB12 and MB13 were excluded from this analysis. Numbers corresponding to the isolates are: 1, OB 05; 2, OB 12; 3, MB 03; 4, MB 05; 5, MB 08; 6, MB 09; 7, MB 16; 8, MB 19; 9, MB 20; 10, MB 21; 11, MB 22; 12, MB 23; 13, MB 24; 14, MB 25; 15, MB 26; 16, MB 27; 17, MB 28; 18, MB 29; 19, MB 30; 20, MB 31; 21, MB 32; 22, MB 33; 23, MB 34B; 24, MB 35; 25, MB 36; 26, MB 37A; 27, MB 38; 28, MB 39; 29, MB 40; 30, MB 41; 31, MB 42; 32, MB 43; 33, MB 44; 34, MB 45; 35, MB 46; 36, MB 47; 37, MB 48; 38, MB 49; 39, MB 50; 40, MB 51; 41, MB 52; 42, MB 53; 43, MB54; 44, MB 55; 45, MB 56; 46, MB 57; 47, MB 58; 48, MB 59; 49, MB 60; 50, MB 61; 51, MB 62; 52, MB 63; 53, MB 64; 54, MB 65; 55, MB 66; 56, MB 67; 57, MB 68; 58, MB 69; 59, MB 70; 60, MB 71; 61, MB 72; 62, MB 73; 63, MB 74; 64, MB 75; 65, MB 76; 66, MB 77; 67, MB 78; 68, MB 79; 69, MB 80; 70, MB 81; 71, MB 82; 72, MB 83; 73, MR 01; 74, MR 02; 75, MR 03; 76, MR 04; 77, SR 19; 78, NV 66; 79, OD 05; 80, OD 08; 81, OD 10; 82, OC 16; 83, OC 24; 84, OC 74; 85, OC 75; 86, OC 78; 87, OD 21; 88, OD 24.</p

Isolates bearing gene cassettes unrelated to antibiotic resistance.

a<p>Resistance index;</p>b<p>gene sequence identical to that isolate.</p

Comparative analyses of MAR, SAR and sensitive facultative oligotrophs.

<p>Water samples were collected from three different sampling sites (SS) from the River Mahananda in three consecutive years (2007–2009).</p

Geographical Map showing sampling sites (SS).

<p>The map was constructed using ArcGIS software. SSI, Champasari; SSII, Mahananda Bridge at Siliguri; and SSIII, Fulbari.</p

Isolates bearing gene cassettes related to antibiotic resistance or bearing no cassettes (empty class 1 integron).

a<p>Resistance index (RI); ^b gene sequence identical to that isolate.</p><p>TMP, trimethoprim; STR, streptomycin; KAN, kanamycin; SPEC, spectinomycin.</p

Putatively assigned genera (on the basis of partial 16S rRNA gene sequences) of integron carrying isolates.

<p>Un.B, Unclassified bacterium; Isolates exhibiting similar phenotype: a, <i>Acidovorax</i> sp.; b, <i>Acinetobacter</i> sp.; c, <i>Shigella</i> sp.; d, <i>Klebsiella</i> sp.; e, <i>Enterobacter</i> sp.; f, <i>Proteus</i> sp.; g, <i>Salmonella</i> sp.; h, <i>Providencia</i> sp.; i, <i>Serratia</i> sp.; j and k, <i>Citrobacter</i>.; l–n, Unknown bacterium; o, <i>Escherichia</i> sp.; p and q, <i>Aeromonas</i> sp.; r, <i>Pseudomonas</i> sp.; <i>A. johnsonii, Acinetobacter johnsonii</i>; <i>B. siliguriense, Brevibacterium siliguirense; K. pneumoniae, Klebsiella pneumoniae</i>; rDNA, ribosomal deoxyribonucleic acid.</p