A comprehensive review on production of bio-surfactants by bio-degradation of waste carbohydrate feedstocks: an approach towards sustainable development.

The advancement of science and technology demands chemistry which is safer, smarter and green by nature. The sustainability of science thus requires well-behaved alternates that best suit the demand. Bio-surfactants are surface active compounds, established to affect surface chemistry. In general, microbial bio-surfactants are a group of structurally diverse molecules produced by different microbes. A large number of bio-surfactants are produced during hydrocarbon degradation by hydrocarbonoclistic microorganisms during their own growth on carbohydrates and the production rate is influenced by the rate of degradation of carbohydrates. The production of such biological surfactants is thus of greater importance. This write up is a dedicated review to update the existing knowledge of inexpensive carbohydrate sources as substrates, microorganisms and technologies of biosurfactant production. This is an economy friendly as well as sustainable approach which will facilitate achieving some sustainable development goals. The production is dependent on the fermentation strategies, different factors of the microbial culture broth and downstream processing; these all have been elaborately presented in this article.

Catechol oxidation promoted by bridging phenoxo moieties in a bis(µ-phenoxo)-bridged dicopper(ii) complex.

A dinuclear copper(ii) complex [Cu2(papy)2(CH3OH)2] has been synthesized by reaction of one equiv. of Cu(OAc)2·2H2O with one equiv. of the tetradentate tripodal ligand H2papy [N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] and has been characterized by various spectroscopic techniques and its solid state structure has been confirmed by X-ray crystal structure analysis. The single-crystal structure of the complex reveals that the two copper centers are hexa-coordinated and bridged by two O-atoms of the phenoxo moieties. The variable temperature magnetic susceptibility measurement of the complex reveals weak ferromagnetic interactions among the Cu(ii) ions with a J value of 1.1 cm-1. The catecholase activity of the complex has been investigated spectrophotometrically using 3,5-di-tert-butyl catechol as a model substrate in methanol solvent under aerobic conditions. The Michaelis-Menten kinetic treatment has been applied using different excess substrate concentrations. The parameters obtained from the catecholase activity by the complex are K M 2.97 × 10-4 M, V max 2 × 10-4 M s-1, and k cat 7.2 × 103 h-1. A reaction mechanism has been proposed based on experimental findings and theoretical calculations. The catechol substrate binds to dicopper(ii) centers and subsequently two electrons are transferred to the metal centers from the substrate. The bridging phenoxo moieties participate as a Brønsted base by accepting protons from catechol during the catalytic cycle and thereby facilitating the catechol oxidation process.

Green Synthesized Carbon Quantum Dots from Polianthes tuberose L. Petals for Copper (II) and Iron (II) Detection.

In this work carbon quantum dots (CQDs) are synthesized via a simple, low cost and as well as green way using tuberose (Polianthes tuberose L.) petals as the carbon source for the first time. We have not done any surface modification to the prepared CQDs although we directly employed this as fluorescent probe for the sensitive and selective detection of Fe2+ and Cu2+ ions. Both these ions drastically quench the emission intensity of the CQDs; in case of Cu2+ ions quenched CQDs EDTA results in regaining the fluorescence property but for Fe2+ ions quenched CQDs no such effect of EDTA is found. The limit of detection (LOD) is observed to be 200 nM in case of Cu2+ which is much lower than the safe limit provided by the WHO in drinking water. Hence the CQDs prepared in this simple and low cost method may find an important role in monitoring the water quality. The quantum yield of the CQDs prepared in our method is around 3%. Transmission electron microscope shows picture of nicely shaped CQDs with average size ~ 4 nm.

Review on Recent Advances in Metal Ions Sensing Using Different Fluorescent Probes.

Fluorescence probes serves as unique detection methods for its simplicity and low detection limit (LOD) and especially bioimaging ability. Research on the probes has already sprouted during the last decade with the help of its molecular recognition properties. This review spotlights recent progress in sensing and bioimaging biologically, environmentally and industrially important metal ions e.g. Zn2+, Cu2+, Hg2+, Ag+ etc. using suitable fluorescent chemosensors including carbon quantum dots (CQD).

Beating Darwin-Bragg losses in lab-based ultrafast x-ray experiments.

The use of low temperature thermal detectors for avoiding Darwin-Bragg losses in lab-based ultrafast experiments has begun. An outline of the background of this new development is offered, showing the relevant history and initiative taken by this work.

Probing deuterium isotope effect on structure and solvation dynamics of human serum albumin.

The deuterium isotopic effect on the structure and solvation dynamics of the protein, human serum albumin (HSA), has been studied by using circular dichroism (CD), femtosecond up-conversion, FRET, and single-molecule spectroscopy. The CD spectra suggest that D(2)O affects the structure of HSA, leading to a 20% decrease in the helical structure. The FRET study indicates that the distance of C153 from the lone tryptophan residue of HSA is quite similar (≈21 Å) in H(2)O and D(2)O, and hence, the location of the probe in the protein remains the same in the two solvents. The single-molecule study suggests that coumarin 153 (C153) binds almost exclusively (>96%) to one site of HSA. Solvation dynamics of C153 in HSA is found to be markedly retarded in D(2)O compared with H(2)O. In H(2)O, the solvation of C153 bound to HSA is found to be biexponential with one component of 7 ps (30%) and a long component of 350 ps (70%). In D(2)O, we detected a short component of 4 ps (41%) and a long component of 950 ps (59%). Thus, the ultraslow component of the solvation dynamics of C153 bound to HSA in D(2)O (950 ps) is 2.5-fold slower than that in H(2)O (350 ps). The marked deuterium isotope effect has been ascribed to water molecules confined in the protein environment and to a lesser extent to the structural modification of protein by D(2)O.

Diffusion of organic dyes in immobilized and free catanionic vesicles.

Fluorescence correlation spectroscopy (FCS) has been used to study the motion of fluorescent dyes in a giant (diameter 20 000 nm = 20 µm) catanionic vesicle comprised of the surfactant sodium dodecyl sulfate (SDS) and dodecyltrimethyl ammonium bromide (DTAB). The diffusion in the anion (SDS) rich catanionic vesicle was studied both in bulk water and in an immobilized vesicle attached to a positively charged glass surface. In the case of the immobilized vesicle, the diffusion coefficients (D(t)) of R6G (rhodamine 6G), DCM (4-dicyanomethylene-2-methyl-6-p-dimethyl aminostyryl-4H-pyran), and C343 (coumarin 343) are found to be 1.5, 2.5, and 10 µm(2)/s, respectively, which are 280, 120, and 55 times slower compared to those for the same dyes in bulk water. The magnitude of D(t) is found to vary for different vesicles. This was attributed to the difference in size and shape of the immobilized vesicles. In bulk, R6G binds completely to the vesicle and exhibits extremely slow diffusion with D(t) = 0.5 ± 0.1 µm(2)/s (∼850 and 3 times slower compared to that of R6G in bulk water and within the immobilized vesicle). This is attributed to very slow overall diffusion of the very large size vesicles (20 µm = 20 000 nm). Both of the dye molecules (DCM and C343) show two different diffusion coefficients for the vesicles in bulk. In this case, the small D(t) (0.5 ± 0.1 µm(2)/s) corresponds to the diffusion of the vesicle as a whole and the large D(t) value (300 and 550 µm(2)/s for DCM and C343, respectively) corresponds to the free dye molecules in bulk water.

Study of diffusion of organic dyes in a triblock copolymer micelle and gel by fluorescence correlation spectroscopy.

Fluorescence correlation spectroscopy (FCS) has been used to study translational diffusion of three fluorescent dyes in a micelle and a gel. It was demonstrated that a highly hydrophobic dye, DCM, remains confined to a particular micelle during the passage of the micellar aggregation through the confocal volume. As a result, DCM exhibits slow diffusion of the large micellar aggregate with a diffusion coefficient (D(t)) approximately 25 times slower compared with that of water. In contrast, a hydrophilic probe (C343 or C480) occasionally diffuses out of the micelle into bulk water and displays a large D(t) (twofold smaller in F127 and approximately six times smaller in the P123 micelle compared with that in bulk water). In a gel, diffusion of the individual micelles is completely arrested and hence, the autocorrelation in FCS arises solely from the diffusion of the dye in the gel. In this case, all the three dyes exhibit extremely slow diffusion (300, 45, and 20 times slower than that in water for DCM, C480, and C343 in F127 gel, respectively). In a P123 and F127 gel, diffusion of DCM is respectively, seven and 29 times slower compared with that of the ionic probe C343. The relatively small value of red-edge excitation shift (REES) of the emission maximum, suggests that DCM is confined within the core of the triblock copolymer micelles and gels. The hydrophilic probes (C343 or C480) exhibit fast diffusion in the micelles and gels. However, their REES is very different. The large REES of C480 suggests that it is distributed over a large region of the micelle, whereas the low REES of C343 indicates that it is located primarily in the peripheral corona region.

A femtosecond study of the interaction of human serum albumin with a surfactant (SDS).

The interaction of a protein, human serum albumin (HSA) with a surfactant (sodium dodecyl sulfate, SDS) was studied by femtosecond up-conversion. HSA was labeled covalently with a probe (CPM, 7-dimethylamino-3-(4-maleimidophenyl)-4-methylcoumarin). Binding of SDS to HSA is found to accelerate the solvation dynamics approximately 1.3-fold. The solvation dynamics in HSA displays two time components: 30 ps (20 %) and 800 ps (80 %). When approximately 10 SDS molecules bind to HSA the components are 15 ps (40 %) and 800 ps (60 %). It is argued that SDS may increase the solvent exposure of the probe (CPM); it may also displace the buried water molecules in the immediate vicinity of CPM.

Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer.

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3 x 10(9) M(-1) s(-1)) of ET for C152 is about two times higher than that (3.8 x 10(9) M(-1) s(-1)) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.

Solvation dynamics in ionic liquid swollen p123 triblock copolymer micelle: a femtosecond excitation wavelength dependence study.

Femtosecond solvation dynamics of coumarin 480 (C480) in a mixed micelle is reported. The mixed micelle consists of a triblock copolymer (PEO)20-(PPO) 70-(PEO)20 (Pluronic P123) and an ionic liquid (IL), 1-pentyl-3-methylimidazolium tetrafluoroborate ([pmim][BF4]). At a low concentration (0.3 M), the sparingly water soluble IL ([pmim][BF4]) penetrates the hydrophobic PPO core of the P123 micelles. Thus emission maximum of C480 in the core (accessed at lambdaex=375 nm) in 0.3 M IL is red-shifted by 8 nm from that in its absence and the red edge excitation shift (REES) is large (19+/-1 nm). At a high concentration (0.9 M), the ionic liquid [pmim][BF4] invades both the core and corona region and the mixed micelle exhibits very small REES (3+/-1 nm). Anisotropy decay and solvation dynamics in different regions of the mixed micelle are studied by variation of excitation wavelength (lambda ex). In P123 micelle, the average rotational time () is 2800 ps in the core (at lambdaex=375 nm) and 1350 ps in the corona region (at lambdaex=435 nm). In 0.3 M [pmim][BF4], tau rot at the core of the mixed micelle decreases to 1950 ps while that in the corona remains unaffected. In 0.9 M IL, both the core and corona (lambda ex=375 and 435 nm) exhibit similar and short approximately 600 ps. In 0.3 M IL, solvation dynamics in the core region (lambdaex=375 nm) of P123 micelle is about 2 times faster than in its absence. In 0.3 M IL, solvation dynamics in the corona region (lambdaex=435 nm) is approximately 100 times faster than that in the core. In 0.9 M IL, the solvation dynamics in the core and in the corona is, respectively, approximately 9 times and 4 times faster than that in 0.3 M IL.

A femtosecond study of excitation wavelength dependence of a triblock copolymer-surfactant supramolecular assembly: (PEO)20-(PPO)70-(PEO)20 and CTAC.

Solvation dynamics and anisotropy decay of coumarin 480 (C480) in a supramolecular assembly containing a triblock copolymer, PEO20-PPO70-PEO20 (Pluronic P123) and a surfactant, CTAC (cetyl trimethylammonium chloride) are studied by femtosecond up-conversion. In a P123-CTAC complex, C480 displays a significant (22 nm) red edge excitation shift (REES) in the emission maximum as lambda ex increases from 335 to 445 nm. This suggests that the P123-CTAC aggregate is quite heterogeneous. The average rotational relaxation time (tau rot) of C480 in a P123-CTAC complex decreases by a factor of 2 from 2500 ps at lambda ex = 375 nm to 1200 ps at lambda ex = 435 nm. For lambda ex = 375 nm, the probe molecules in the buried core region of P123-CTAC are excited and the solvation dynamics displays three components, 2, 60, and 4000 ps. It is argued that insertion of CTAC in P123 micelle affects the polymer chain dynamics, and this leads to reduction of the 130 ps component of P123 micelle to 60 ps in P123-CTAC. For lambda ex = 435 nm, which selects the peripheral highly polar corona region, solvation dynamics in P123-CTAC and P123 are extremely fast with a major component of <0.3 ps ( approximately 80%) and a 2 ps ( approximately 20%) component.

Femtosecond solvation dynamics in different regions of a bile salt aggregate: excitation wavelength dependence.

Solvation dynamics of coumarin 480 (C480) in the secondary aggregate of a bile salt (sodium deoxycholate, NaDC) is studied using femtosecond up-conversion. The secondary aggregate resembles a long (approximately 40 A) hollow cylinder with a central water-filled tunnel. Different regions of the aggregate are probed by variation of the excitation wavelength (lambdaex) from 375 to 435 nm. The emission maximum of C480 displays an 8 nm red shift as the lambdaex increases from 345 to 435 nm. The 8 nm red edge excitation shift (REES) suggests that the probe (C480) is distributed over regions of varied polarity. Excitation at a short wavelength (375 nm) preferentially selects the probe molecule in the buried locations and exhibits slow dynamics with a major (84%) slow component (3500 ps) and a small (16%) contribution of the ultrafast component (2.5 ps). Excitation at lambdaex=435 nm (red end) corresponds to the exposed sites where solvation dynamics is very fast with a major (73%) ultrafast component (

Ultrafast proton transfer of pyranine in a supramolecular assembly: PEO-PPO-PEO triblock copolymer and CTAC.

Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) is studied in a polymer-surfactant aggregate using femtosecond emission spectroscopy. The polymer-surfactant aggregate is a supramolecular assembly consisting of a triblock copolymer (PEO)(20)-(PPO)(70)-(PEO)(20) (P123) and a cationic surfactant, cetyltrimethylammonium chloride (CTAC). ESPT of the protonated species (HA) in HPTS leads to the formation of A(-). The dynamics of ESPT may be followed from the decay of the HA emission (at approximately 440 nm) and rise of the A(-) emission (at approximately 550 nm). Both steady-state and time-resolved studies suggest that ESPT of HPTS in P123-CTAC aggregate is much slower than that in bulk water, in P123 micelle, or in CTAC micelle. The ratio of the steady-state emission intensities (HA/A(-)) in P123-CTAC aggregate is 2.2. This ratio is approximately 50, 12, and 2 times higher than that respectively in water, in P123 micelle, and in CTAC micelle. Retardation of ESPT causes an increase in the rise time of the A(-) emission of HPTS. In P123-CTAC aggregate, A(-) displays three rise times: 30, 250, and 2400 ps. These rise times are longer than those in CTAC micelle (23, 250, and 1800 ps), in bulk water (0.3, 3, and 90 ps), and in P123 micelle (15 and 750 ps). The rate constants for initial proton transfer, recombination, and dissociation of the ion pair are estimated using a simple kinetic scheme. The slow fluorescence anisotropy decay of HPTS in P123-CTAC aggregate is analyzed in terms of the wobbling-in-cone model.

Femtosecond solvation dynamics in a neat ionic liquid and ionic liquid microemulsion: excitation wavelength dependence.

Solvation dynamics in a neat ionic liquid, 1-pentyl-3-methyl-imidazolium tetra-flouroborate ([pmim][BF4]) and its microemulsion in Triton X-100 (TX-100)/benzene is studied using femtosecond up-conversion. In both the neat ionic liquid and the microemulsion, the solvation dynamics is found to depend on excitation wavelength (lambda(ex)). The lambda(ex) dependence is attributed to structural heterogeneity in neat ionic liquid (IL) and in IL microemulsion. In neat IL, the heterogeneity arises from clustering of the pentyl groups which are surrounded by a network of cation and anions. Such a nanostructural organization is predicted in many recent simulations and observed recently in an X-ray diffraction study. In an IL microemulsion, the surfactant (TX-100) molecules aggregate in form of a nonpolar peripheral shell around the polar pool of IL. The micro-environment in such an assembly varies drastically over a short distance. The dynamic solvent shift (and average solvation time) in neat IL as well as in IL microemulsions decreases markedly as lambda(ex) increases from 375 to 435 nm. In a [pmim][BF4]/water/TX-100/benzene quaternary microemulsion, the solvation dynamics is slower than that in a microemulsion without water. This is ascribed to the smaller size of the water containing microemulsion. The anisotropy decay in an IL microemulsion is found to be faster than that in neat IL.

Excitation wavelength dependence of solvation dynamics in a supramolecular assembly: PEO-PPO-PEO triblock copolymer and SDS.

The triblock copolymer (PEO)20-(PPO)70-(PEO)20 (P123) forms a supramolecular aggregate with sodium dodecyl sulfate (SDS). The solvation dynamics and anisotropy decay of coumarin 480 (C480) in different regions of a P123-SDS aggregate are studied through variation of the excitation wavelength (lambdaex) using femtosecond upconversion. In a P123 micelle, because of the drastic differences in polarity between the hydrophilic corona region (PEO block) and the hydrophobic PPO core, C480 exhibits a pronounced red edge excitation shift (REES) of emission maximum by 24 nm. In the P123-SDS aggregate, SDS penetrates the core of the P123 micelle. This increases the polarity of the core and reduces the difference in the polarity between the core and the corona region. In a P123-SDS aggregate, the REES is much smaller (5 nm) which suggests a reduced difference between the core and the corona. Solvation dynamics in a P123 micelle displays a bulklike ultrafast component (<0.3 and 1 ps) in the PEO corona region, a 200 ps component arising from dynamics of polymer segments, and a very long component (5000 or 3000 ps) due to the highly restricted PPO core. In a P123-SDS aggregate, at lambdaex = 375 and 405 nm, the solvation dynamics is found to be faster than that in P123 micelle. In this case, the component (3000 ps) arising from the core region is faster than that (5000 ps) in P123 micelle. In both P123 micelle and P123-SDS aggregate, the relative contribution of the core region decreases and that of the corona region increases with an increase in lambdaex. At lambdaex = 435 nm, which probes the hydrophilic corona, the solvation dynamics for both P123 micelle and P123-SDS aggregate are almost similar.

Ultrafast fluorescence resonance energy transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer: excitation wavelength dependence.

Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to rhodamine 6G (R6G) is studied in the micelle and the gel phase of a triblock copolymer, (PEO)20-(PPO)70-(PEO)20 (Pluronic P123 (P123)) by picosecond and femtosecond emission spectroscopy. The time constants of FRET were obtained from the rise time of the acceptor (R6G) emission. In a P123 micelle, FRET occurs in multiple time scales: 2.5, 100, and 1700 ps. In the gel phase, three rise components are observed: 3, 150, and 2600 ps. According to a simple Förster model, the ultrafast (2.5 and 3 ps) components of FRET correspond to donor-acceptor distance RDA=13 +/- 2 A. The ultrafast FRET occurs between a donor and an acceptor residing at close contact at the corona (PEO) region of a P123 micelle. With increase in the excitation wavelength (lambdaex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET ( approximately 3 ps) increases from 13% to 100% in P123 micelle and from 1% to 100% in P123 gel. It is suggested that at lambdaex = 435 nm, mainly the highly polar peripheral region is probed where FRET is very fast due to close proximity of the donor and the acceptor. The 100 and 150 ps components correspond to RDA = 25 +/- 2 A and are ascribed to FRET from C480 deep inside the micelle to an acceptor (R6G) in the peripheral region. The very long component of FRET (1700 ps in micelle and 2600 ps component in gel) may arise from diffusion of the donor from outside the micelle to the interior followed by fast FRET.

Ultrafast fluorescence resonance energy transfer in a reverse micelle: excitation wavelength dependence.

Fluorescence resonance energy transfer (FRET) from coumarin 480 (C480) to fluorescein 548 (F548) in a sodium dioctyl sulfosuccinate (AOT) reverse micelle is studied by picosecond and femtosecond emission spectroscopy. In bulk water, at the low concentration of the donor (C480) and the acceptor (F548), no FRET is observed. However, when the donor (C480) and the acceptor (F548) are confined in a AOT reverse micelle very fast FRET is observed. The time constants of FRET were obtained from the rise time of the emission of the acceptor (F548). In a AOT microemulsion, FRET is found to occur in multiple time scales--3, 200, and 2700 ps. The 3 ps component is assigned to FRET in the water pool of the reverse micelle with a donor-acceptor distance, 16 A. The 200 ps component corresponds to a donor-acceptor distance of 30 A and is ascribed to the negatively charged acceptor inside the water pool and the neutral donor inside the alkyl chains of AOT. The very long 2700 ps component may arise due to FRET from a donor outside the micelle to an acceptor inside the water pool and also from diffusion of the donor from bulk heptane to the reverse micelle. With increase in the excitation wavelength from 375 to 405 nm the relative contribution of the FRET due to C480 in the AOT reverse micelle (the 3 and 200 ps components) increases.