Synchronization in a network of model neurons

We study the spatiotemporal dynamics of a network of coupled chaotic maps modelling neuronal activity, under variation of coupling strength ε and degree of randomness in coupling p. We find that at high coupling strengths (ε > εfixed) the unstable saddle point solution of the local chaotic maps gets stabilized. The range of coupling where this spatiotemporal fixed point gains stability is unchanged in the presence of randomness in the connections, namely εfixed is invariant under changes in p. As coupling gets weaker (ε < εfixed), the spatiotemporal fixed point loses stability, and one obtains chaos. In this regime, when the coupling connections are completely regular (p=0), the network becomes spatiotemporally chaotic. Interestingly however, in the presence of random links (p > 0) one obtains spatial synchronization in the network. We find that this range of synchronized chaos increases exponentially with the fraction of random links in the network. Further, in the space of fixed coupling strengths, the synchronization transition occurs at a finite value of p, a scenario quite distinct from the many examples of synchronization transitions at p→0. Further we show that the synchronization here is robust in the presence of parametric noise, namely in a network of nonidentical neuronal maps. Finally we check the generality of our observations in networks of neurons displaying both spiking and bursting dynamics

Algorithms for merging tick data and data analysis for Indian financial market

This paper discusses the problem of ‘merging’ financial tick data available from data sources such as Bloomberg, NSE, and Thomson Reuters etc. Different derivative securities are traded on the exchange with different frequencies in each unit of time such as second or minute in intraday trading , therefore, it is difficult to form ‘ordered pairs’, which are essential for any financial analysis, of tick data representing the simultaneous trades of the different derivative securities. Merging refers to the conversion of intraday tick data of different securities of varying frequencies, as provided by data sources, into the form in which the tick data of all traded derivative securities have same frequency, so that it is possible to form ordered pairs of data (in every unit time period) in such a way that the original nature of the data is preserved. The four merging algorithms: Truncation, Weighted mean, median and all-combinations algorithm are compared with Dropdown algorithm, which is being used widely by the trading firms. Using NSE intraday tick data for various trading days, it is found that ‘Truncation’ and ‘Weighted Mean’ algorithms are more efficient merging algorithms

Cocrystallization of nutraceuticals

Cocrystallization has emerged over the past decade as an attractive technique for modification of the physicochemical properties of compounds used as active pharmaceutical ingredients (APIs), complementing more traditional methods such as salt formation. Nutraceuticals, with associated health benefits and/or medicinal properties, are attractive as coformers due to their ready availability, known pharmacological profile, and natural origin, in addition to offering a dual therapy approach. Successful studies of favorably altering the physicochemical properties of APIs through cocrystallization with nutraceuticals are highlighted in this review. Many of the key functional groups commonly seen in nutraceuticals (e.g., acids, phenols) underpin robust supramolecular synthons in crystal engineering. This review assesses the structural data available to date across a diverse range of nutraceuticals, both in pure form and in multicomponent materials, and identifies the persistent supramolecular features present. This insight will ultimately enable predictive and controlled assembly of functional materials incorporating nutraceuticals together with APIs

Novel co-crystals of the nutraceutical sinapic acid

Sinapic acid (SA) is a nutraceutical with known anti-oxidant, anti-microbial, anti-inflammatory, anti-cancer, and anti-anxiety properties. Novel co-crystals of SA were prepared with co-formers belonging to the category of GRAS [isonicotinic acid (INC), nicotinamide (NIA)], non-GRAS [4-pyridinecarbonitrile (PYC)], and active pharmaceutical ingredients (APIs) [6-propyl-2-thiouracil (PTU)] list of compounds. Structural study based on the X-ray crystal structures revealed the intermolecular hydrogen-bonded interactions and molecular packing. The crystal structure of sinapic acid shows the anticipated acid-acid homodimer along with discrete hydrogen bonds between the acid carbonyl and the phenolic moiety. The robust acid-acid homodimer appears to be very stable and is retained in the structures of two co-crystals (SA[middle dot]NIA and SA[middle dot]PYC). In these cases, co-crystallization occurs via intermolecular phenol O-H[three dots, centered]Naromatic hydrogen bonds between the co-formers. In the SA[middle dot]PTU[middle dot]2MeCN co-crystal the acid-acid homodimer gives way to the anticipated acid-amide heterodimer, with the phenolic moiety of SA hydrogen-bonded to acetonitrile. Attempts at obtaining the desolvated co-crystal led to lattice breakdown, thus highlighting the importance of acetonitrile in the formation of the co-crystal. Among the co-crystals examined, SA[middle dot]INC (5 weeks), SA[middle dot]NIA (8 weeks) and SA[middle dot]PYC (5 weeks) were found to be stable under accelerated humidity conditions (40 [degree]C, 75% RH), whereas SA[middle dot]PTU[middle dot]2MeCN decomposed after one week into individual components due to solvent loss

Constructing predictable supramolecular architectures using building blocks derived from versatile and ‘green’ synthetic routes

Doctor of PhilosophyDepartment of ChemistryChrister B. AakeröyA series of four bifunctional ligands based on β-diketonate moieties bearing methyl, chloro, bromo and iodo substituents and their corresponding Cu(II) complexes were synthesized and crystallographically characterized in order to explore the possibility of using relatively weak halogen…halogen contacts for the directed assembly of predictable architectures in coordination chemistry. The four ligands have characteristic O–H...O intramolecular hydrogen bonds, and the structures of the halogenated ligands contain extended 1-D architectures based on C-O...X halogen bonds, which can be explained on the basis of electrostatic considerations. The corresponding Cu(II) complexes show a constant coordination chemistry for all the ligands, wherein the metal ion sits in a slightly distorted square-planar pocket, without any coordinated or uncoordinated solvent molecules. Furthermore, the absence of halogen-bonds in the coordination complexes is due to the depleted charge on the potential halogen-bond acceptors. As a result, the halogen-bonds are unable to compete with the inherent close packing in the crystal lattice, and thus display a head to head close-packed motif for methyl, chloro, and bromo, substituted Cu(II) complexes. The enhanced polarizability of the iodine atom, produces a more electropositive surface which means that this structure cannot accommodate a linear head-to-head arrangement due to electrostatic repulsion, and thus a unique close-packed structure very different from the three iso-structural complexes is observed for the iodo substituted Cu(II) complex.(1) Oximes offer great opportunities in supramolecular chemistry (hydrogen-bond donors), as well as in coordination chemistry (strong coordinating ligands). Hence, we established a versatile and robust mechanochemical route to aldehyde/ketone–oxime conversions for a broad range of aldehydes(2) and ketones(3) via a simple mortar–pestle grinding method. The relative reactivity of aldehydes vs. ketones under these conditions was also explored, along with an examination of the possible connection between reactivity and electronic substituent effects. The growing interest in the oxime (RR′C═N–OH) functionality, and a lack of the systematic examinations of the structural chemistry of such compounds, prompted us to carry out analysis of intermolecular oxime···oxime interactions, and identify the hydrogen-bond patterns for four major categories of oximes (R′ = −H, −CH3, −NH2, −CN), based on all available structural data in the CSD, complemented by three new relevant crystal structures.(4) It was found that the oximes could be divided into four groups depending on which type of predominant oxime···oxime interactions they present in the solid-state: (i) O–H···N dimers (R22(6)), (ii) O–H···N catemers (C(3)), (iii) O–H···O catemers (C(2)), and (iv) oximes in which the R′ group accepts a hydrogen bond from the oxime moiety catemers (C(6)). In order to explore and establish a hierarchy between hydrogen (HB) and halogen (XB) bonds in supramolecular architectures, we designed and synthesized two ditopic HB/XB donors, and screened them with a series of 20 HB acceptors. IR was used as a preliminary and reliable tool to gather information on the presence/absence of HB/XB in the different cases. We were able to get the solved single-crystal data for three of the 40 reactions. In two out of two cases with symmetric ditopic acceptors, both HB and XB were present leading to 1-D infinite chains, which suggests that in a system of “equal opportunities”, both these interactions can be tolerant of each other. In the only case with asymmetric ditopic acceptor, the HB donor binds to the best acceptor, whereas XB donor binds to the second best acceptor. This selectivity can be rationalized on the basis of electrostatic considerations, where the HB donor was shown to have a higher molecular electrostatic potential than the XB donor. Finally, we designed and synthesized a versatile and dynamic metallomacrocycle based on the 2,2'-bipyridyl backbone capable of controlling the metal-metal distance within the macrocycle cavity. The macrocycle was synthesized by high-dilution method and characterized by several spectroscopic techniques (IR, NMR, Mass, UV-Visible). Also, the macrocycle:Cu(II) stoichiometric ratio was determined by Job’s continuous variation method using UV-Visible spectroscopy, and was found to be 1:2, respectively. (1) Aakeröy, C. B; Sinha, A. S.; Chopade, P. D.; Desper, J. Dalton Trans. 2011, 40, 12160. (2) Aakeröy, C. B.; Sinha, A. S.; Epa, K. N.; Spartz, C. L.; Desper, J. Chem. Commun. 2012, 48, 11289. (3) Aakeröy, C. B.; Sinha, A. S. RSC Adv. 2013, 3, 8168. (4) Aakeröy, C. B.; Sinha, A. S.; Epa, K. N.; Chopade, P. D.; Smith, M. M.; Desper, J. Cryst. Growth Des. 2013, 13, 2687

Misuse of topical corticosteroids on the face: A cross-sectional study among dermatology outpatients

Background: Topical corticosteroids (TC) are being misused widely on the face without a prescription from the dermatologist. Aim: To evaluate the misuse of TC-containing preparations on the face and the adverse effects due to its application. Materials and Methods: A questionnaire-based analysis was done among patients attending the dermatology outpatient department of a tertiary care hospital between March 2014 and March 2015. Patients with various facial dermatoses were asked about their current use of topical preparations and on further followup questioning, those who revealed the use of TCs (25g or more) continuously or intermittently for a minimum duration of four weeks were included in the study and observed for local adverse effects. Results: A total of 410 patients were observed, 306 were females (74.6%) and 104 were males (25.3%). One hundred and seventy-eight patients (43.4%) used topical steroids alone, 124 (30.2%) used creams containing TC, hydroquinone, and tretinoin, 108 (26.3%) used creams containing a combination of TC, antibiotic, and/or antifungal. One hundred and seventy-six patients (42.9%) bought TC or TC containing creams over the counter on their own, without the prescription of a dermatologist, 35 (8.5%) were recommended TC by a beautician (beauty parlors), 82 (20%) by their friends, family members, or neighbors, 75 (18.2%) by a non-dermatologist practitioner, and 42 (10.2%) by a dermatologist. Limitations: The sample size was small. Conclusion: Dispensing of TCs must be regulated in India; they should only be issued against a doctor's prescription

A versatile and green mechanochemical route for aldehyde-oxime conversions

A robust, facile and solvent-free mechanochemical path for aldehyde–oxime transformations using hydroxylamine and NaOH is explored; the method is suitable for aromatic and aliphatic aldehydes decorated with a range of substituents

The Impact of Halogen Substituents on the Synthesis and Structure of Co-Crystals of Pyridine Amides

Strategies for co-crystal synthesis tend to employ either hydrogen- or halogen-bonds between different molecules. However, when both interactions are present, the structural influence that they may exert on the resulting assembly is difficult to predict a priori. To shed some light on this supramolecular challenge, we attempted to co-crystallize ten aliphatic dicarboxylic acids (co-formers) with three groups of target molecules; N-(pyridin-2-yl)picolinamides (2Pyr-X), N-(pyridin-2-yl)nicotinamides (3Pyr-X), N-(pyridin-2-yl)isonicotinamides (4Pyr-X); X=Cl/ Br/ I. The structural outcomes were compared with co-crystals prepared from the non-halogenated targets. As expected, none of the reactions with 2Pyr-X produced co-crystals due to the presence of a very stable intramolecular N-H···N hydrogen bond. In the 3Pyr series, all six structures obtained showed the same synthons, –COOH···N(py) and –COOH···N(py)-NH, that were found in the non-halogenated parent 3Pyr and were additionally accompanied by structure directing X···O(OH) interactions (X=Br/I). The co-crystals of the unhalogenated parent 4Pyr co-crystals assembled via intermolecular –COOH···N(py) and –COOH···N(py)-NH synthons. Three of the analogues 4Pyr-X co-crystals displayed only COOH···N(py) and –COOH···N(py)-NH interactions. The three co-crystals of 4Pyr-X with fumaric acid (for which no analogues structures with 4Pyr are known) formed –COOH···N(py)-NH and –NH···O=C hydrogen bonds and showed no structure-directing halogen bonds. In three co-crystals of 4Pyr-I in which –COOH···N(py)-NH hydrogen bond was present, a halogen-bond based –I···N(py) synthon replaced the –COOH···N(py) motif observed in the parent structures. The structural influence of the halogen atoms increased in the order of Cl < Br < I, as the size of σ-holes increased. Finally, it is noteworthy that isostructurality among structures of the homomeric targets was not translated to structural similarities between their respective co-crystals