Interactions of 3, 3.5, 4, and 4.5 generations of poly(amido amine) dendrimer with cationic surfactants

The conductivity (κ), turbidity (τ), NMR, and Krafft temperature (T _K) studies have been carried out for hexadecylpyridinium bromide (HPyBr), hexadecylpyridinium chloride (HPyCl), and hexadecyltrimethylammonium bromide (HTAB) in the presence of 3G, 3.5G, 4G, and 4.5G generations of poly(amido amine) dendrimers (PAMAM) in aqueous phase. The cmc of all present surfactants were evaluated from κ and τ measurements, both in the presence as well as in the absence of PAMAM. The cmc values decrease in the presence of PAMAM in comparison to that in pure water, especially in the presence of amine terminated PAMAM. Krafft temperature values of pure surfactants also decrease in the presence of various generations of PAMAM. A comparison of all present results from different techniques indicates that HPyBr interacts more strongly with all generations of PAMAM rather than HPyCl and HTAB.     

Role of titanium oxidation states in polymerization activity of Ziegler-Natta catalyst: A density functional study

The role of titanium oxidation states in olefin polymerization activity for Ziegler-Natta (ZN) catalyst has been investigated using density functional calculations at B3LYP/LANL2DZ as well as extended LANL2DZ basis that includes diffuse and polarization functions for C, H and Cl. Using the simple [TiCl₂CH₃]ⁿ (n = +1, 0, −1) model catalyst systems, we could rationalize some of the well-known experimental facts with varying Ti oxidation states (+4, +3, +2) in the real ZN systems. Firstly, irrespective of Ti oxidation states, the activation barriers (E_act) for ethylene and syn propylene insertion in Ti-CH₃ bond are comparable in accordance with experimental and modeling studies. Secondly, it was observed that Ti(IV) catalyst has the lowest E_act which progressively increase in the order Ti(IV) < Ti(III) < Ti(II) high spin < Ti(II) low spin catalysts in line with experimental and several modeling results. The effect of solvation on olefin insertion barriers are seen more prominent in case of Ti(IV) systems compared to other oxidation states.     

The mechanism of photolysis of n-methyldihydroberberine salts and a sequence for transposition of ring D substituents

Photolysis of N-deuteriomethyl dihydroberberine salt (1b) gave 1-o-toluyl-3,4-dihydroisoquinoline (5b) with a deuterium atom incorporation; a mechanism involving a 1,7-hydrogen shift step is proposed. The keto-imine (5a) on irradiation followed by reduction furnished 11,12-dimethoxy tetrahydroberberine (9a).     

Frequency-dependent shape changes of colloidal clusters under transverse electric field

We have studied clustering of colloidal particles under the influence of an ac electric field as a function of frequency. The field was applied in a direction perpendicular to the confining walls. Two regimes are observed, a low frequency regime where the clusters are isotropic with a local triangular order, as reported earlier in the literature, and a new high-frequency regime where the clusters are highly elongated (anisotropic) with no local order. The crossover from one regime to the other occurs at a critical frequency, f(c). The threshold field for the cluster formation, E(th), increases with frequency in both the regimes. An increase in the particle size leads to a reduction in both E(th) and f(c). We present evidence to show that the elongated structures seen at high frequency are related to the field inhomogeneities at imperfections on the conducting surface. We also propose a possible mechanism based on hydrodynamic flow considerations to explain the formation of these clusters.     

Multiplexed optical barcoding of cells via photochemical programming of bioorthogonal host–guest recognition

Modern chemical and biological studies are undergoing a paradigm shift, where understanding the fate of individual cells, in an apparently homogeneous population, is becoming increasingly important. This has inculcated a growing demand for developing strategies that label individual cells with unique fluorescent signatures or barcodes so that their spatiotemporal trajectories can be mapped in real time. Among various approaches, light-regulated methods employing photocaged fluorophores have received particular attention, owing to their fine spatiotemporal control over labelling. However, their multiplexed use to barcode large numbers of cells for interrogating cellular libraries or complex tissues remains inherently challenging, due to the lack of multiple spectrally distinct photoactivated states in the currently available photocaged fluorophores. We report here an alternative multiplexable strategy based on optically controlled host–guest recognition in the cucurbit[7]uril (CB[7]) system that provides spatial control over the positioning of fluorophores to generate distinct barcodes in ‘user-defined’ cells. Using a combination of three spectrally distinct CB[7]-conjugated fluorophores and by sequentially performing cycles of photoactivation and fluorophore encoding, we demonstrate 10-color barcoding in microtubule-targeted fixed cells as well as 7-color barcoding in cell surface glycan targeted live MCF7 cells.

Barcoding provides abilities to learn about individual species within an apparently homogeneous population. We describe a light-mediated multiplexed cellular barcoding strategy through spatial programming of cucurbit[7]uril molecular recognition.     

Scaling behavior of permeability and conductivity anisotropy near the percolation threshold

We use the finite-size scaling method to estimate the critical exponent that characterizes the scaling behavior of conductivity and permeability anisotropy near the percolation thresholdp _c . Here is defined by the scaling lawk _l /k _t –1(p–p _c ), wherek _t andk _t are the conductivity or permeability of the system in the direction of the macroscopic potential gradient and perpendicular to this direction, respectively. The results are (d=2)0.819±0.011 and (d=3)0.518±0.001. We interpret these results in terms of the structure of percolation clusters and their chemical distance. We also compare our results with the predictions of a scaling theory for due to Straley, and propose that (d=2)=t- _B , wheret is the critical exponent of the conductivity or permeability of the system, and _B is the critical exponent of the backbone of percolation clusters.     

Partial volume effect compensation for improved reliability of quantitative blood-brain barrier permeability

INTRODUCTION: Blood-brain barrier (BBB) plays an important role in the pathophysiology of many central nervous system disorders. In the past, a number of laboratory techniques have been proposed to quantify permeability coefficient, k(i), an important index of barrier function. Recently, MRI has been used to estimate k(i) based on the unidirectional tracer kinetics model in one compartment as proposed by Patlak et al. and has been found to be in good agreement with the gold standard quantitative autoradiography technique. Rapid data acquisition, a prerequisite of this MRI-based technique, causes a compromise in spatial resolution resulting in partial volume (PV) averaging, an effect that is seldom explicitly compensated for in quantitative neuroimaging studies. This may have profound effect on the reliability of estimates obtained using quantitative methods. Existing PV compensation techniques that use complex statistical algorithms perform corrections on stationary images. In this proof-of-principle study, the effect of PV averaging on BBB permeability coefficient has been evaluated using a simulation model, and a postprocessing technique that makes use of dynamic information has been proposed for PV compensation in order to improve the reliability of this quantitative method. MATERIALS AND METHODS: A computer simulation model is presented, which evaluates the effect of PV averaging on permeability coefficient estimates. Beginning with a known k(i), a PV compensation technique is proposed, which aims at correcting calculated k(i) to obtain the original estimate. The application of the PV compensation technique is demonstrated in a rat stroke brain model. Magnetic resonance imaging experiments were performed in Wistar rats (n=2) on a 4.7-T scanner. After acquiring localizer, T2-weighted and diffusion-weighted images, a rapid T1 mapping protocol was implemented to acquire one pre-gadolinium-diethylenetriaminepentaacetic acid baseline data set followed by a series of postinjection data sets. The data were postprocessed without and with application of PV compensation technique to obtain a k(i) estimate. RESULTS AND DISCUSSION: The issue of PV averaging as a result of limited spatial resolution is often not addressed in quantitative MRI studies. In this work, simulation experiments have provided useful insight into the PV effects on permeability coefficient estimate. The findings of the simulation experiments agree well with the results obtained from MR experiments. Results from the MR experiments suggest that it may be important to perform PV compensation in order to improve the reliability of permeability coefficient estimates. Future work involves classification of tissue component into gray and white matter and CSF to improve the accuracy of the compensation technique and to investigate repeatability of the technique in a larger group of animals.     

Localization transition of biased random walks on random networks

We study random walks on large random graphs that are biased towards a randomly chosen but fixed target node. We show that a critical bias strength bc exists such that most walks find the target within a finite time when b > bc. For b < bc, a finite fraction of walks drift off to infinity before hitting the target. The phase transition at b=bc is a critical point in the sense that quantities such as the return probability P(t) show power laws, but finite-size behavior is complex and does not obey the usual finite-size scaling ansatz. By extending rigorous results for biased walks on Galton-Watson trees, we give the exact analytical value for bc and verify it by large scale simulations.     

Synthetic pharmaceutical peptides characterization by chromatography principles and method development

As per the United States Food and Drug Administration, any polymer/chain composed of 40 or fewer amino acids is called a peptide, where more than 40 amino acids are considered proteins. On many occasions, there is a change in the source of manufacturing of the peptide active pharmaceutical ingredient, where one has to prove the sameness of that product with the existing formulation by considering several aspects like the presence of impurities/degradation products, the extent of aggregations, and so forth. For the same, several chromatographic characterization techniques such as reversed-phase high-performance liquid chromatography-ultraviolet/high-resolution mass spectrometry, supercritical fluid chromatography, size-exclusion chromatography, ion-exchange chromatography, and so forth, are widely used in the pharmaceutical industry. It is well known that the method development of peptide molecules is often challenging as many variables are to be kept in mind which can affect the separation, recovery, and stability of the molecule. The present review focuses on the basics of peptide degradation and method development by using various chromatographic techniques for characterization. It also covers a deep insight of method development parameters and variables to be considered which might directly or indirectly affect the chromatographic separation and recovery and also provides a guide on the selection of chromatographic parameters.     

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.