Papers by Koushik Goswami
Journal of Physics A: Mathematical and Theoretical
In this topical review, we give an overview of the structure and dynamics of a single polymer cha... more In this topical review, we give an overview of the structure and dynamics of a single polymer chain in active baths, Gaussian or non-Gaussian. The review begins with the discussion of single flexible or semiflexible linear polymer chains subjected to two noises, thermal and active. The active noise has either Gaussian or non-Gaussian distribution but has a memory, accounting for the persistent motion of the active bath particles. This finite persistence makes the reconfiguration dynamics of the chain slow as compared to the purely thermal case and the chain swells. The active noise also results superdiffusive or ballistic motion of the tagged monomer. We present all the calculations in details but mainly focus on the analytically exact or almost exact results on the topic, as obtained from our group in recent years. In addition, we briefly mention important works of other groups and include some of our new results. The review concludes with pointing out the implications of polymer c...
Physical Review E, 2020
We consider the problem of first-passage time for reaching a boundary of a particle which diffuse... more We consider the problem of first-passage time for reaching a boundary of a particle which diffuses in one dimension and is confined to the region x ∈ (0, L), with a diffusion coefficient that switches randomly between two states, having diffusivities that are different. Exact analytical expressions are found for the survival probability of the particle as a function of time. The survival probability has a multiexponential decay, and to characterize it, we use the average rate constant k, as well as the instantaneous rate r(t). Our approach can easily be extended to the case where the diffusion coefficient takes n different values. The model should be of interest to biological processes, in which a reactant searches for a target in a heterogeneous environment, making the diffusion coefficient a random function of time. The best example for this is a protein searching for a target site on the DNA.
Soft Matter, 2022
Theoretical investigation of the motion of an active particle in a dynamically disordered medium,... more Theoretical investigation of the motion of an active particle in a dynamically disordered medium, exploring how the interplay between activity and heterogeneity affects the dynamics.
CCDC 951987: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
CCDC 935966: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
CCDC 935965: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Dipyrromethane‐Based Receptor for Fluorometric Sensing of Hydrogenpyrophosphate
ChemistrySelect, 2021
Physical Review E, 2021
We study the dynamics of an overdamped Brownian particle subjected to Poissonian stochastic reset... more We study the dynamics of an overdamped Brownian particle subjected to Poissonian stochastic resetting in a nonthermal bath, characterized by a Poisson white noise and a Gaussian noise. Applying the renewal theory we find an exact analytical expression for the spatial distribution at the steady state. Unlike the single exponential distribution as observed in the case of a purely thermal bath, the distribution is double exponential. Relaxation of the transient spatial distributions to the stationary one, for the limiting cases of Poissonian rate, is investigated carefully. In addition, we study the first-arrival properties of the system in the presence of a delta-function sink with strength κ, where κ = 0 and κ = ∞ correspond to fully nonreactive and fully reactive sinks, respectively. We explore the effect of two competitive mechanisms: the diffusive spread in the presence of two noises and the increase in probability density around the initial position due to stochastic resetting. We show that there exists an optimal resetting rate, which minimizes the mean first-arrival time (MFAT) to the sink for a given value of the sink strength. We also explore the effect of the strength of the Poissonian noise on MFAT, in addition to sink strength. Our formalism generalizes the diffusion-limited reaction under resetting in a nonequilibrium bath and provides an efficient search strategy for a reactant to find a target site, relevant in a range of biophysical processes
Diffusion caused by two noises—active and thermal
Journal of Statistical Mechanics: Theory and Experiment, 2019
The diffusion of colloids inside an active system-e.g. within a living cell or the dynamics of ac... more The diffusion of colloids inside an active system-e.g. within a living cell or the dynamics of active particles itself (e.g. self-propelled particles) can be modeled through overdamped Langevin equation which contains an additional noise term apart from the usual white Gaussian noise, originating from the thermal environment. The second noise is referred to as `active noise' as it arises from activity such as chemical reactions. The probability distribution function (PDF or the propagator) in space-time along with moments provides essential information for understanding their dynamical behavior. Here we employ the phase-space path integral method to obtain the propagator, thereby moments and PDF for some possible models for such noise. At first, we discuss the diffusion of a free particle driven by active noise. We consider four different possible models for active noise, to capture the possible traits of such systems. We show that the PDF for systems driven by noises other than Gaussian noise largely deviates from normal distribution at short to intermediate time scales as a manifestation of out-of-equilibrium state, albeit converges to Gaussian distribution after a long time as a consequence of the central limit theorem. We extend our work to the case of a particle trapped in a harmonic potential and show that the system attains steady state at long time limit. Also, at short time scales, the nature of distribution is different for different noises, e.g. for particle driven by dichotomous noise, the probability is mostly concentrated near the boundaries whereas a long exponential tail is observed for a particle driven by Poissonian white noise.
Pyrrole-based tetra-amide for hydrogen pyrophosphate (HP2O73−) and F− ions in sol-gel medium
Supramolecular Chemistry, 2017
Abstract A simple pyrrole-based tetra-amide 1 shows selective fluorescence sensing of HP2O73− ove... more Abstract A simple pyrrole-based tetra-amide 1 shows selective fluorescence sensing of HP2O73− over a series of other anions in CH3CN by exhibiting excimer emission at ~450 nm. In DMSO:CHCl3 (1:5 v/v), compound 1 forms gel that undergoes disintegration to sol in the presence of basic anions such as F−, AcO− and H2PO4−. However, the gel state of 1 under a particular condition is observed to be selective to F− over AcO− and H2PO4− anions. The recognition properties of the receptor have been studied by fluorescence, UV–vis and 1H NMR spectroscopic methods.
ChemInform Abstract: Syntheses of Spiro[cyclopent[3]ene-1,3′-indoles]s and Tetrahydrocyclohepta[b]indoles from 2,3-Disubstituted Indoles Through Sigmatropic Rearrangement
ChemInform, 2014
Pd-Catalyzed reaction of o-alkynylanilines (I) and (V) with 3,4-dichloro-1-butane (II) provides 3... more Pd-Catalyzed reaction of o-alkynylanilines (I) and (V) with 3,4-dichloro-1-butane (II) provides 3-(chlorobutenyl) substituted indoles (III) and (VI) in good yields.
Tetrahedron, 2012
D-Homotryptophan and its sulfur analogue have been synthesized by Sonogashira coupling between 3-... more D-Homotryptophan and its sulfur analogue have been synthesized by Sonogashira coupling between 3-iodoheteroarenes and ethynyloxazolidine followed by reduction of triple bond and oxidation of alcohol to acid. L-Homotryptophan and its oxygen analogue have been synthesized from silylated internal alkyne using Larock's heteroannulation as the key reaction. The alkynyloxazolidines were synthesized from L-serine and L-glutamic acid, respectively.
Tetrahedron, 2012
Synthesis of five-, six-, seven-, eight-, and nine-membered cyclic a-hydrazino acids from a commo... more Synthesis of five-, six-, seven-, eight-, and nine-membered cyclic a-hydrazino acids from a common starting material 'diethylmalonate' with 26, 16, 34, 13.5, and 13.33% overall yields is described. Sequential allylation or homoallylation and electrophilic amination followed by cyclization gave the desired rings. The methyl esters of eight-and nine-membered rings were synthesized by RCM and the corresponding free acids were generated after hydrolysis in the presence of 1 M BBr 3 solution in DCM.
Improved Synthesis of Cyclic α-Hydrazino Acids of Five- to Nine-Membered Rings and Optical Resolution of 5,6,7-Membered Ring Hydrazino Acids
Synthetic Communications, 2014
ABSTRACT Synthesis of cyclic α-hydrazino acids of 5, 6, 7, 8, and 9-membered rings has been descr... more ABSTRACT Synthesis of cyclic α-hydrazino acids of 5, 6, 7, 8, and 9-membered rings has been described. Di-tert-butyl or dibenzyl malonate was used as starting materials instead of diethyl malonate which was used in our first report. Deprotection of tert-butyl or benzyl ester of the final compounds was much easier than ethyl or methyl esters. Overall yield of these acids were 39, 50, 47, 52, 51 %, respectively. These acids were then converted to the diastereomers either via the formation of peptides with L-phenylalanine methyl ester or via the formation of esters (for 5 to 7-memebered rings) with L-2-phenylalaninol. All diastereomers were separated except 9-membered ring by flash chromatography. Hydrolysis of diastereomeric esters generated the optically pure 5, 6 and 7-membered cyclic α-hydrazino acids. In this process, both the enantiomers have been isolated and recovered the chiral auxiliary L-2-phenylalaninol. Absolute stereochemistry was determined from X-ray crystallographic analysis
Physical Chemistry Chemical Physics, 2012
European Journal of Organic Chemistry, 2013
A NaOH-mediated protocol was developed for the syntheses of a series of 2Ј-arylspiro[cyclopent[3]... more A NaOH-mediated protocol was developed for the syntheses of a series of 2Ј-arylspiro[cyclopent[3]ene-1,3Ј-indole]s and 6-alkyl-5,6,7,10-tetrahydrocyclohepta[b]indoles in good yields by cyclization through a sigmatropic rearrangement of suitable 2,3-disubstituted indoles. These precursors that contain a 4-chloro-2-butenyl side chain at the 3-position were obtained as a mixture of (E) and (Z) isomers through
European Journal of Organic Chemistry, 2013
Selenoisotryptophan and its higher homologues were synthesized by Sonogashira coupling of iodophe... more Selenoisotryptophan and its higher homologues were synthesized by Sonogashira coupling of iodophenyl methyl selenide and alkynyloxazolidines followed by iodocyclization as [a]
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Papers by Koushik Goswami