Stretching single polymer chains of donor-acceptor foldamers: toward the quantitative study on the extent of folding

Single-molecule force spectroscopy has proven to be an efficient tool for the quantitative characterization of flexible foldamers on the single-molecule level in this study. The extent of folding has been estimated quantitatively for the first time to the best of our knowledge, which is crucial for a better understanding of the ``folding-process'' on single-molecule level. Therefore, this study may provide a guidance to regulate folding for realizing rational control over the functions of bulk materials.

Raman and infra-red microspectroscopy: towards quantitative evaluation for clinical research by ratiometric analysis

Biomolecular structure elucidation is one of the major techniques for studying the basic processes of life. These processes get modulated, hindered or altered due to various causes like diseases, which is why biomolecular analysis and imaging play an important role in diagnosis, treatment prognosis and monitoring. Vibrational spectroscopy (IR and Raman), which is a molecular bond specific technique, can assist the researcher in chemical structure interpretation. Based on the combination with microscopy, vibrational microspectroscopy is currently emerging as an important tool for biomedical research, with a spatial resolution at the cellular and sub-cellular level. These techniques offer various advantages, enabling label-free, biomolecular fingerprinting in the native state. However, the complexity involved in deciphering the required information from a spectrum hampered their entry into the clinic. Today with the advent of automated algorithms, vibrational microspectroscopy excels in the field of spectropathology. However, researchers should be aware of how quantification based on absolute band intensities may be affected by instrumental parameters, sample thickness, water content, substrate backgrounds and other possible artefacts. In this review these practical issues and their effects on the quantification of biomolecules will be discussed in detail. In many cases ratiometric analysis can help to circumvent these problems and enable the quantitative study of biological samples, including ratiometric imaging in 1D, 2D and 3D. We provide an extensive overview from the recent scientific literature on IR and Raman band ratios used for studying biological systems and for disease diagnosis and treatment prognosis.

Studies on ultrasonic emulsification

An experimental setup suitable for a quantitative study of the ultrasonic emulsification is described. The methods of producing a well-defined sound field, of measuring the sound intensity, and of following the emulsion concentration are discussed critically. The good reproducibility resulting from the improved experimental techniques is examined.

Polyelectrolyte microcapsules for sustained delivery of water-soluble drugs

Polyelectrolyte capsules composed of weak polyelectrolytes are introduced as a simple and efficient system for spontaneous encapsulation of low molecular weight water-soluble drugs. Polyelectrolyte capsules were prepared by layer-by-layer (LbL) assembling of weak polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly (methacrylic acid) (PMA) on polystyrene sulfonate (PSS) doped CaCO3 particles followed by core removal with ethylene-diaminetetraacetic add (EDTA). The loading process was observed by confocal laser scanning microscopy (CLSM) using tetramethylrhodamineisothiocyanate labeled dextran (TRITC-dextran) as a fluorescent probe. The intensity of fluorescent probe inside the capsule decreased with increase in cross-linking time. Ciprofloxacin hydrochloride (a model water-soluble drug) was spontaneously deposited into PAH/PMA capsules and their morphological changes were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The quantitative study of drug loading was also elucidated which showed that drug loading increased with initial drug concentration, but decreased with increase in pH. The loaded drug was released in a sustained manner for 6 h, which could be further extended by cross-linking the capsule wall. The released drug showed significant antibacterial activity against E. coli. These findings indicate that such capsules can be potential carriers for water-soluble drugs in sustained/controlled drug delivery applications. (C) 2010 Elsevier B.V. All rights reserved.

Quantum phenomena in magnetic nano clusters

One of the fascinating fields of study in magnetism in recent years has been the study of quantum phenomena in nanosystems. While semiconductor structures have provided paradigms of nanosystems from the stand point of electronic phenomena the synthesis of high nuclearity transition metal complexes have provided examples of nano magnets. The range and diversity of the properties exhibited by these systems rivals its electronic counterparts. Qualitative understanding of these phenomena requires only a knowledge of basic physics, but quantitative study throws up many challenges that are similar to those encountered in the study of correlated electronic systems. In this article, a brief overview of the current trends in this area arc highlighted and some of the efforts of our group in developing a quantitative understanding of this field are outlined.

Species and acoustic diversity of bats in a palaeotropical wet evergreen forest in southern India

The Western Ghats of India is among the top 25 biodiversity hotspots in the world. About 43% of the reported 117 bat species in India are found in this region, but few quantitative studies of bat echolocation calls and diversity have been carried out here thus far. A quantitative study of bat diversity was therefore conducted using standard techniques, including mist-netting, acoustical and roost surveys in the wet evergreen forests of Kudremukh National Park in the Western Ghats of Karnataka. A total of 106 bats were caught over 108 sampling nights, representing 17 species, 3 belonging to Megachiroptera and 14 to Microchiroptera. Acoustical and roost surveys added three more species, two from Microchiroptera and one from Megachiroptera. Of these 20 species, 4 belonged to the family Pteropodidae, 10 to Vespertilionidae, 3 to Rhinolophidae, 2 to Megadermatidae and 1 to Hipposideridae. We recorded the echolocation calls of 13 of the 16 microchiropteran species, of which the calls of 4 species (Pipistrellus coromandra, Pipistrellus affinis, Pipistrellus ceylonicus and Harpiocephalus harpia) have been recorded for the first time. Discriminant function analyses of the calls of 11 species provided 91.7% correct classification of individuals to their respective species, indicating that the echolocation calls could be used successfully for non-invasive acoustic surveys and monitoring of bat species in the future.

An experimental study on acoustic emission energy as a quantitative measure of size independent specific fracture energy of concrete beams

Notched three point bend specimens (TPB) were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and during the fracture process acoustic emissions (AE) were simultaneously monitored. It was observed that AE energy could be related to fracture energy. An experimental study was done to understand the behavior of AE energy with parameters of concrete like its strength and size. In this study, AE energy was used as a quantitative measure of size independent specific fracture energy of concrete beams and the concepts of boundary effect and local fracture energy were used to obtain size independent AE energy from which size independent fracture energy was obtained. (C) 2010 Elsevier Ltd. All rights reserved.

A laser flash photolysis study of pivalothiophenone triplets: steric and electronic effects in thione photoreaction kinetics

Upon laser pulse excitation (Aex = 532 nm) into the lowest-lying '(n,a*) band system, pivalothiophenones in benzene solutions give rise to short-lived triplets (Ama: = 325-335 nm, em: = (1 1-15) X lo3 M-' cm-I) with quantitative intersystem crossing efficiencies. The triplet yields decrease slightly (by 10-30%) upon changing A, to 308 nm (Le., upon excitation into S2). Kinetic data are presented for intrinsic triplet lifetimes, self-quenching, and quenching by oxygen, di-tert-butylnitroxy radical, and various reagents capable of interacting with the triplets via energy, electron, or hydrogen-atom transfer and by biradical formation (possibly leading to cycloaddition). The mechanisms of the quenching processes are discussed. Relative to rigid aromatic thiones, namely, xanthione and thiocoumarin, the interaction of pivalothiophenone triplets with most of the quenchers are kinetically inefficient. This is interpreted primarily as a manifestation of the steric crowding at positions a to the thiocarbonyl group.

Study of turbid media with light: Recovery of mechanical and optical properties from boundary measurement of intensity autocorrelation of light

We discuss the inverse problem associated with the propagation of the field autocorrelation of light through a highly scattering object like tissue. In the first part of the work, we reconstructed the optical absorption coefficient mu(u) and particle diffusion coefficient D-B from simulated measurements which are integrals of a quantity computed from the measured intensity and intensity autocorrelation g(2)(tau) at the boundary. In the second part we recover the mean square displacement (MSD) distribution of particles in an inhomogeneous object from the sampled g(2)(tau) measure on the boundary. From the MSD, we compute the storage and loss moduli distributions in the object. We have devised computationally easy methods to construct the sensitivity matrices which are used in the iterative reconstruction algorithms for recovering these parameters from the measurements. The results of the reconstruction of mu(a), D-B, MSD and the viscoelastic parameters, which are presented, show reasonable good position and quantitative accuracy.

Dihydrofolate reductase from soybean seedlings: A fluorescence and circular dichroism study

The fluorescence emission spectrum of soybean dihydrofolate reductase suggests that the emitting tryptophan residues are situated in a hydrophobic microenvironment. The dissociation constants determined from fluorescence and circular dichroism data reveal that the soybean enzyme has a lower affinity for substrates and substrate analogs than that determined for dihydrofolate reductases isolated from other sources. The binding of methotrexate to the soybean enzyme does not affect the binding of NADPH. Similarly, the binding of NADPH has no effect on subsequent methotrexate binding. Polarimetric study indicates that the enzyme has a low (ca. 5%) α-helical content. Addition of dihydrofolate to the soybean enzyme results in the generation of a positive ellipticity band at 298 nm with a molar ellipticity, [θ], of 186,000, whereas the binding of folate induces a negative ellipticity band at 280 nm with [θ] of −181,000. The qualitative and quantitative differences in the circular dichroism of the enzyme-dihydrofolate and enzyme-folate complexes indicate that the mode of binding of these ligands may be different. The formation of an enzyme-NADPH complex is accompanied by a negative Cotton effect at 270 nm. These studies indicate that the binding of substrates or inhibitors causes significant conformational changes in the enzyme and also leads to the formation of a number of spectroscopically identifiable complexes.

Transferability of Multipole Charge Density Parameters for Supramolecular Synthons: A New Tool for Quantitative Crystal Engineering

The modularity of the supramolecular synthon is used to obtain transferability of charge density derived multipolar parameters for structural fragments, thus creating an opportunity to derive charge density maps for new compounds. On the basis of high resolution X-ray diffraction data obtained at 100 K for three compounds methoxybenzoic acid, acetanilide, and 4-methyl-benzoic acid, multipole parameters for O-H center dot center dot center dot O carboxylic acid dimer and N-H center dot center dot center dot O amide infinite chain synthon fragments have been derived. The robustness associated with these supramolecular synthons has been used to model charge density derived multipolar parameters for 4-(acetylamino)benzoic acid and 4-methylacetanilide. The study provides pointers to the design and fabrication of a synthon library of high resolution X-ray diffraction data sets. It has been demonstrated that the derived charge density features can be exploited in both intra- and intermolecular space for any organic compound based on transferability of multipole parameters. The supramolecular synthon based fragments approach (SBFA) has been compared with experimental charge density data to check the reliability of use of this methodology for transferring charge density derived multipole parameters.

Analysis of a conformation-specific epitope of the alpha subunit of human chorionic gonadotropin: Study using monoclonal antibody probes

Monoclonal antibodies (MAbs) have been used extensively for identification of sequence-specific epitopes using either the ELISA or/and IRMA methods, However, attempts to use MAbs for identification of conformation-specific epitopes have been very few as they are considered very labile. We have investigated the stability of conformation-specific epitopes of human chorionic gonadotropin (hCG) using a quantitative solid-phase radioimmnunoassay (SPRIA) technique. Several epitopes are stable to mild modification (chemical and proteolytic) conditions, and epitopes show differential stability for these modifications. Based on these observations, a monoclonal antibody (MAb 16) for an a-subunit-specific epitope of hCG has been used to monitor changes at the epitopic site (identified as epitope 16) on modification of hCG, using SPRIA with immobilized MAb 16. Modifications of amino groups, hydroxyl group of tyrosine as well as carboxyl group of Asp/Glu all bring about sufficient changes in the epitope integrity. Peptide bond hydrolysis at lysine residues damages the epitope, but not at arginine residues, Hydrolysis at tyrosine does not affect the epitope, though modification of the side-chain of tyrosine inactivates the epitope. Destruction of the epitope occurs on reduction of the disulphide bonds. Partial retention of the epitope activity is seen on modification of carboxyl or the epsilon-amino groups of lysine. Based on these results four to six amino acids have been identified to be at the epitopic site, and the data suggest that two peptide segments are brought together by the disulphide bond Cys10-Cys60 to form the epitope.

Cross-polarisation applied to the study of liquid crsytalline ordering

Cross polarisation is extensively used in solid state NMR for enhancing signals of nuclei with low gyromagnetic ratio. However, the use of the method for providing quantitative structural and dynamics information is limited. This arises due to the fact that the mechanism which is responsible for cross polarisation namely, the dipolar interaction, has a long range and is also anisotropic. In nematic liquid crystals these limitations are easily overcome since molecules orient in a magnetic field. The uniaxial ordering of the molecules essentially removes problems associated with the angular dependence of the interactions encountered in powdered solids. The molecular motion averages out intermolecular dipolar interaction, while retaining partially averaged intramolecular interaction. In this article the use of cross polarisation for obtaining heteronuclear dipolar couplings and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment were considered and their utility illustrated. A method for obtaining proton-proton dipolar couplings, by utilizing cross polarisation from the dipolar reservoir, is also presented.

Coordination-driven self-assembly of 2D-metallamacrocycles using a shape-selective Pt(2)(II)-organometallic 90 degrees acceptor: design, synthesis and sensing study

Synthesis of a series of two-dimensional metallamacrocycles via coordination-driven self-assembly of a shape-selective Pt(2)(II)-molecular building unit incorporating carbazole-ethynyl functionality is described. An equimolar (1 : 1) combination of a Pt(2)(II)-organometallic 90 degrees acceptor, 1, with rigid linear ditopic donors (L(a) and L(b)) afforded [4 + 4] self-assembled octanuclear molecular squares, 2 and 3, in quantitative yields, respectively [L(a) = 4,4'-bipyridine; L(b) = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar treatment of 1 with an amide-based unsymmetrical flexible ditopic donor, L(c), resulted in the formation of a [2 + 2] self-sorted molecular rhomboid (4a) as a single product [L(c) = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboid, triangle and square) due to the different connectivity of L(c), the formation of a single and symmetrical molecular rhomboid (4a) as the only product is an interesting observation. All the self-assembled macrocycles (2, 3 and 4a) were fully characterized by multinuclear NMR ((1)H and (31)P) and ESI-MS analysis. Further structural insights about the size and shape of the macrocycles were obtained through energy minimization using density functional theory (DFT) calculations. Decoration of the starting carbazole building unit with Pt-ethynyl functionality enriches the assemblies to be more p-electron rich and luminescent in nature. Macrocycles 2 and 3 could sense the presence of electron deficient nitroaromatics in solution by quenching of the initial intensity upon gradual addition of picric acid (PA). They exhibited the largest quenching response with high selectivity for nitroaromatics compared to several other electron deficient aromatics tested.

Coordination-Driven Self-Assembly of 2D-Metallamacrocycles Using a New Carbazole-Based Dipyridyl Donor: Synthesis, Characterization, and C-60 Binding Study

A new carbazole-based 90 degrees dipyridyl donor 3,6-di(4-pyridylethynyl)carbazole (L) containing carbazole-ethynyl functionality is synthesized in reasonable yield using the Sonagashira coupling reaction. Multinuclear NMR, electrospray ionization-mass spectrometry (ESI-MS), including single crystal X-ray diffraction analysis characterized this 90 degrees building unit. The stoichiometry combination of L with several Pd(II)/Pt(II)-based 90 degrees acceptors (1a-1d) yielded 2 + 2] self-assembled metallacycles (2a-2d) under mild conditions in quantitative yields 1a = cis-(dppf)Pd(OTf)(2); 1b = cis-(dppf)Pt(OTf)(2); 1c = cis-(tmen)Pd(NO3)(2); 1d = 3,6-bis{trans-Pt(C C) (PEt3)(2)(NO3))carbazole]. All these macrocycles were characterized by various spectroscopic techniques, and the molecular structure of 2a was unambiguously determined by single crystal X-ray diffraction analysis. Incorporation of ethynyl functionality to the carbazole backbone causes the resulted macrocycles (2a-2d) to be pi-electron rich and thereby exhibit strong emission characteristics. The macrocycle 2a has a large internal concave aromatic surface. The fluorescence quenching study suggests that 2a forms a similar to 1:1 complex with C-60 with a high association constant of K-sv = 1.0 X 10(5) M-1.