A note on proof of Gordon's Conjecture

Kun Du 대한수학회 2018 대한수학회보 Vol.55 No.3

In this paper, we show a proof of Gordon's Conjecture by using Qiu's labels and two new labels.

Biomimetic Designing of Functional Silk Nanotopography Using Self-assembly

Kundu, Banani,Eltohamy, Mohamed,Yadavalli, Vamsi K.,Kundu, Subhas C.,Kim, Hae-Won American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.42

<P>In nature inorganic organic building units create multifunctional hierarchical architectures. Organic silk protein is particularly attractive in this respect because of its micro-nanoscale structural blocks that are attributed to sophisticated hierarchical assembly imparting flexibility and compressibility to designed biohybrid materials. In the present study, aqueous silk fibroin is assembled to form nano/microtopography on inorganic silica surface via a facile diffusion-limited aggregation process. This process is driven by electrostatic interaction and only possible at a specified aminated surface chemistry. The self-assembled topography depends on the age and concentration of protein solution as well as on the surface charge distribution of the template. The self-assembled silk trails closely resemble natural cypress leaf architecture, which is considered a structural analogue of neuronal cortex. This assembled surface significantly enhances anchorage of neuronal cell and cytoskeletal extensions, providing an effective nano/microtopographical cue for cellular recognition and guidance.</P>

Nrf2-Keap1 Signaling as a Potential Target for Chemoprevention of Inflammation-Associated Carcinogenesis

Kundu, Joydeb Kumar,Surh, Young-Joon Springer-Verlag 2010 Pharmaceutical research Vol.27 No.6

A cobalt(<small>II</small>) iminoiodane complex and its scandium adduct: mechanistic promiscuity in hydrogen atom abstraction reactions

Kundu, Subrata,Chernev, Petko,Engelmann, Xenia,Chung, Chan Siu,Dau, Holger,Bill, Eckhard,England, Jason,Nam, Wonwoo,Ray, Kallol The Royal Society of Chemistry 2016 Dalton Transactions Vol.45 No.37

<P>In addition to oxometal [Mn+=O] and imidometal [Mn+=NR] units, transient metal-iodosylarene [M(n- 2)+-O=IPh] and metal-iminoiodane [M(n- 2)+-N(R)=IPh] adducts are often invoked as a possible 'second oxidant' responsible for the oxo and imido group transfer reactivity. Although a few metal-iodosylarene adducts have been recently isolated and/or spectroscopically characterized, metal-iminoiodane adducts have remained elusive. Herein, we provide UV-Vis, EPR, NMR, XAS and DFT evidence supporting the formation of a metal-iminoiodane complex 2 and its scandium adduct 2-Sc. 2 and 2-Sc are reactive toward substrates in the hydrogen-atom and nitrene transfer reactions, which confirm their potential as active oxidants in metal-catalyzed oxidative transformations. Oxidation of para-substituted 2,6-di-tert-butylphenols by 2 and 2-Sc can occur by both coupled and uncoupled proton and electron transfer mechanisms; the exact mechanism depends on the nature of the para substituent.</P>

Alcohol and Temperature Induced Conformational Transitions in Ervatamin B: Sequential Unfolding of Domains

Kundu, Suman,Sundd, Monica,Jagannadham, Medicherla V. Korean Society for Biochemistry and Molecular Biol 2002 Journal of biochemistry and molecular biology Vol.35 No.2

The structural aspects of ervatamin B have been studied in different types of alcohol. This alcohol did not affect the structure or activity of ervatamin B under neutral conditions. At a low pH (3.0), different kinds of alcohol have different effects. Interestingly, at a certain concentration of non-fluorinated, aliphatic, monohydric alcohol, a conformational switch from the predominantly $\alpha$-helical to $\beta$-sheeted state is observed with a complete loss of tertiary structure and proteolytic activity. This is contrary to the observation that alcohol induces mostly the $\alpha$helical structure in proteins. The O-state of ervatamin B in 50% methanol at pH 3.0 has enhanced the stability towards GuHCl denaturation and shows a biphasic transition. This suggests the presence of two structural parts with different stabilities that unfold in steps. The thermal unfolding of ervatamin B in the O-state is also biphasic, which confirms the presence of two domains in the enzyme structure that unfold sequentially. The differential stabilization of the structural parts may also be a reflection of the differential stabilization of local conformations in methanol. Thermal unfolding of ervatamin B in the absence of alcohol is cooperative, both at neutral and low pH, and can be fitted to a two state model. However, at pH 2.0 the calorimetric profiles show two peaks, which indicates the presence of two structural domains in the enzyme with different thermal stabilities that are denatured more or less independently. With an increase in pH to 3.0 and 4.0, the shape of the DSC profiles change, and the two peaks converge to a predominant single peak. However, the ratio of van't Hoff enthalpy to calorimetric enthalpy is approximated to 2.0, indicating non-cooperativity in thermal unfolding.

Facile approach to synthesize highly fluorescent multicolor emissive carbon dots via surface functionalization for cellular imaging

Kundu, Aniruddha,Lee, Jungpyo,Park, Byeongho,Ray, Chaiti,Sankar, K. Vijaya,Kim, Wook Sung,Lee, Soo Hyun,Cho, Il-Joo,Jun, Seong Chan Elsevier 2018 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.513 No.-

<P><B>Abstract</B></P> <P>Luminescent nanomaterials are encouraging scaffolds for diverse applications such as chemical sensors and biosensors, imaging, drug delivery, diagnostics, catalysis, energy, photonics, medicine, and so on. Carbon dots (CDs) are a new class of luminescent carbonaceous nanomaterial that have appeared recently and reaped tremendous scientific interest. Herein, we have exploited a simple approach to prepare tuneable and highly fluorescent CDs via surface functionalization. The successful synthesis of CDs is manifested from several investigations like high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The CDs exhibit excellent water solubility and with increasing nitrogen content fluorescence quantum yield increases whereas cell toxicity decreases. The CD synthesized at high temperature (180 °C) shows very high quantum yield (more than 56%). The tuneable optical properties of CDs are systematically studied using UV-vis and fluorescence spectroscopy. The cell viability evaluation and <I>in vitro</I> imaging study reveals that the synthesized CDs can be employed as a potential fluorescent probe for bio-imaging without further modification.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Water Structure at the Lipid Multibilayer Surface: Anionic Versus Cationic Head Group Effects

Kundu, Achintya,Kwak, Kyungwon,Cho, Minhaeng American Chemical Society 2016 The Journal of physical chemistry B Vol.120 No.22

<P>Membrane water interface is a potential reaction site for many biochemical reactions. Therefore, a molecular level understanding of water structure and dynamics that strongly depend on the chemical structure of lipid is prerequisite for elucidating the role of water in biological reactions on membrane surface. Recently, we carried out femtosecond infrared pump probe studies of water structure and dynamics at multibilayer surfaces of zwitterionic phosphatidylcholine-analogue lipid (J. Phys. Chem. Lett. 2016, 7, 741). Here, to further elucidate the anionic and cationic headgroup effects on water, we study vibrational dynamics of water on lipid multibilayers formed by anionic phospho-glycerol lipid molecules as well as by cationic choline-derivatized lipid molecules. We observed two significantly different vibrational lifetime components (very fast 0.5 ps and slow 1.9 ps) of the OD stretch mode of HOD molecules at the negatively charged phospho-lipid multibilayer whereas only one vibrational lifetime component (1.6 ps) was observed at the positively charged choline-derivatized lipid multibilayer. From the detailed analyses about the vibrational energy and rotational relaxations of HOD molecules in lipid multibilayers composed of anionic lipid with phosphate and cationic lipid without phosphate, the role of phosphate group in structuring water molecules at phospholipid membrane interface is revealed.</P>

Optimization conditions for oxalic acid pretreatment of deacetylated yellow poplar for ethanol production

Kundu, Chandan,Lee, Jae-Won Elsevier 2015 Journal of industrial and engineering chemistry Vol.32 No.-

<P><B>Abstract</B></P> <P>The optimal conditions for pretreatment of deacetylated yellow poplar (<I>Liriodendron tulipifera</I> L.) with oxalic acid for ethanol production were evaluated. Yellow poplar was deacetylated by treatment with 0.8% NaOH for 80min at 60°C. The conditions for pretreatment of deacetylated yellow poplar for ethanol production via simultaneous saccharification and fermentation (SSF) were optimized using response surface methodology (RSM). All pretreatments were conducted using the same solid-to-liquid ratio (1:8) and reaction temperature (150°C). The combined severity factor (CSF) was used to determine the overall effect of pretreatment on ethanol production. Severe pretreatment conditions (long reaction time and high oxalic acid concentration) caused a decrease in the xylan content of deacetylated yellow poplar. The highest ethanol concentration obtained via SSF was 26.60g/L at CSF 1.95. Based on the RSM data, the optimal pretreatment conditions for SSF were as follows: reaction temperature, 150°C; reaction time, 45min; and oxalic acid concentration, 0.15M. Under these conditions, the highest degradation ratio was 33.72%, which implied that maximum dissolution of the chemical components of biomass occurred during pretreatment. The ethanol yield from the hydrolysate ranged from 0.29g/g to 0.49g/g. The highest ethanol concentration in the hydrolysate was obtained when pretreatment was carried out at 150°C for 30min with 0.1M oxalic acid.</P>

Unusual fluorescent photoswitching of imidazole derivatives: the role of molecular conformation and twist angle controlled organic solid state fluorescence

Kundu, Anu,Karthikeyan, Subramanian,Sagara, Yoshimitsu,Moon, Dohyun,Anthony, Savarimuthu Philip The Royal Society of Chemistry 2018 Physical Chemistry Chemical Physics Vol.20 No.43

<P>Molecular photoswitching, light induced reversible color/fluorescence modulation, has mostly been realized in organic molecules <I>via E</I>/<I>Z</I> isomerization of azobenzenes and stilbenes and ring opening/closing reactions of spiropyrans and diarylethenes. We report here new fluorescent molecular photoswitches based on triphenylamine (TPA)-imidazole derivatives, <I>N</I>-phenyl-<I>N</I>-(4-(1,4,5-triphenyl-1<I>H</I>-imidazol-2-yl)phenyl)benzenamine (NTPB) and <I>N</I>-phenyl-<I>N</I>-(4-(1-phenyl-1<I>H</I>-phenanthro[9,10-<I>d</I>]imidazol-2-yl)phenyl)benzenamine (NPPB), that exhibited light induced reversible fluorescence switching <I>via</I> conformational change from a twisted molecular structure to more planar. NTPB and NPPB in CHCl3 showed red shift of absorption and fluorescence upon UV light irradiation whereas white light exposure reversed both absorption as well as fluorescence. The role of the TPA-imidazole twisted molecular structure in photoswitching was established based on structure property, computational and photophysical studies. The isobestic point observed in time dependent fluorescence change under UV light irradiation clearly demonstrated the presence of two different conformational isomers. Interestingly, polymorphism and torsion angle (<I>τ</I>) dependent fluorescence of NTPB and NPPB in the solid state also supported the role of the twisted molecular structure of TPA-imidazole in fluorescence switching/tuning. Interestingly, NTPB showed fluorescence photoswitching in the solid state also whereas rigid phenanthrene based NPPB did not show fluorescence photoswitching. Thus the present studies provide structural insight for designing a new type of fluorescent organic molecular photoswitches based on conformational modulation that could be of potential interest in optoelectronic devices.</P>

Epigallocatechin Gallate Inhibits Phorbol Ester-Induced Activation of NF- B and CREB in Mouse Skin: Role of p38 MAPK

KUNDU, J. K.,SURH, Y.-J. Wiley (Blackwell Publishing) 2007 Annals of the New York Academy of Sciences Vol.1095 No.1

<P>The modulation of intracellular signaling network involved in an inappropriate expression of cyclooxygenase-2 (COX-2) is a pragmatic approach for chemoprevention with a wide variety of dietary phytochemicals. Epigallocatechin gallate (EGCG), a major green tea polyphenol, is one of the most extensively investigated chemopreventive agents. Our previous study revealed that EGCG inhibited expression of COX-2 and activation of mitogen-activated protein kinases (MAPKs) in mouse skin stimulated with a prototype tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA). This study was aimed at identifying transcription factors as molecular targets of EGCG in downregulating COX-2 expression. We found that EGCG inhibited TPA-induced DNA binding of NF-kappaB and CREB in mouse skin in vivo. EGCG also suppressed TPA-induced phosphorylation and subsequent degradation of IkappaBalpha, and prevented nuclear translocation of p65. We also examined whether extracellular signal-regulated protein kinase (ERK) and p38 MAPK, which are known to regulate activation of NF-kappaB, can also modulate CREB DNA binding. Pretreatment with U0126 and SB203580, pharmacological inhibitors of ERK and p38 MAPK, respectively, showed that SB203580, but not U0126, attenuated TPA-induced CREB DNA binding in mouse skin. Taken together, EGCG inhibited TPA-induced DNA binding of NF-kappaB and CREB by blocking activation of p38 MAPK, which may provide a molecular basis of COX-2 inhibition by EGCG in mouse skin in vivo.</P>