Understanding Clusters toward the Design of Functional Molecules and Nanomaterials

Singh, N. Jiten,Lee, Eun Cheol,Choi, Young Cheol,Lee, Han Myoung,Kim, Kwang S. Chemical Society of Japan 2007 Bulletin of the Chemical Society of Japan Vol.80 No.8

<P>In this account, we highlight the theoretical investigations of various cluster systems comprising of water clusters, π-containing clusters, and metallic clusters. We illustrate how these investigations help us understand and design structures and properties of nanowires, novel functional ionophores/receptors, and nanomaterials. Many of these theoretically predicted systems have been experimentally realized and some of the predicted structures/properties are left for the future which of course could be promising challenges for experimentalists.</P>

De novo design approach based on nanorecognition toward development of functional molecules/materials and nanosensors/nanodevices

Singh, N. Jiten,Lee, Han Myoung,Suh, Seung Bum,Kim, Kwang S. International Union of Pure and Applied Chemistry 2007 Pure and Applied Chemistry Vol.79 No.6

<P>For the design of functional molecules and nanodevices, it is very useful to utilize nanorecognition (which is governed mainly by interaction forces such as hydrogen bonding, ionic interaction, π-H/π-π interactions, and metallic interactions) and nanodynamics (involving capture, transport, and release of electrons, photons, or protons). The manifestation of these interaction forces has led us to the design and realization of diverse ionophores/receptors, organic nanotubes, nanowires, molecular mechanical devices, molecular switches, enzyme mimetics, protein folding/unfolding, etc. In this review, we begin with a brief discussion of the interaction forces, followed by some of our representative applications. We discuss ionophores with chemo-sensing capability for biologically important cations and anions and explain how the understanding of hydrogen bonding and π-interactions has led to the design of self-assembled nanotubes from calix[4]hydroquinone (CHQ). The binding study of neutral and cationic transition metals with the redox system of hydroquinone (HQ) and quinone (Q) predicts what kind of nanostructures would form. Finally, we look into the conformational changes between stacked and edge-to-face conformers in π-benzoquinone-benzene complexes controlled by alternating electrochemical potential. The resulting flapping motion illustrates a promising pathway toward the design of mobile nanomechanical devices.</P>

Designing Ionophores and Molecular Nanotubes Based on Molecular Recognition

Singh, N. Jiten,Lee, Han Myoung,Hwang, In-Chul,Kim, Kwang S. Taylor Francis 2007 Supramolecular chemistry Vol.19 No.4

<P> In this mini-review we briefly describe intermolecular interactions ranging from hydrogen bonding to ionic interactions to aromatic interactions. Manifestation of these interaction forces is in the design and realization of various ionophores with chemo-sensing capability for biologically important cations and anions. We also explain how the understanding of hydrogen bonding and π-interactions has led to the design of self-assembled organic nanotubes. We further discuss the conformational changes between stacked and edge-to-face conformers in benzoquinone-benzene complexes, which are controlled by alternating electrochemical potential. The resulting flapping motion illustrates a promising pathway toward the design of nanomechanical devices.</P>

Comprehensive Energy Analysis for Various Types of π-Interaction

Singh, N. Jiten,Min, Seung Kyu,Kim, Dong Young,Kim, Kwang S. American Chemical Society 2009 Journal of chemical theory and computation Vol.5 No.3

Aromatic π–π interaction mediated by a metal atom: structure and ionization of the bis(η⁶-benzene)chromium–benzene cluster

Han, Songhee,Singh, N. Jiten,Kang, Tae Yeon,Choi, Kyo-Won,Choi, Sunyoung,Baek, Sun Jong,Kim, Kwang S.,Kim, Sang Kyu Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.27

<P>Aromatic π–π interaction in the presence of a metal atom has been investigated experimentally and theoretically with the model system of bis(η<SUP>6</SUP>-benzene)chromium–benzene cluster (Cr(Bz)<SUB>2</SUB>–Bz) in which a free solvating benzene is non-covalently attached to the benzene moiety of Cr(Bz)<SUB>2</SUB>. One-photon mass-analyzed threshold ionization (MATI) spectroscopy and first principles calculations are employed to identify the structure of Cr(Bz)<SUB>2</SUB>–Bz which adopts the parallel-displaced configuration. The decrease in ionization potential for Cr(Bz)<SUB>2</SUB>–Bz compared with Cr(Bz)<SUB>2</SUB>, resulting from the increase of the cation–π stabilization energy upon ionization, is consistent with the parallel-displaced structure of the cluster. Theoretical calculations give the detailed cluster structures with associated energetics, thus revealing the nature of π–π–metal or π–π–cation interactions at the molecular level.</P> <P>Graphic Abstract</P><P>The nature of the aromatic π–π interaction in the presence of a metal atom has been revealed by the combined study of ionization spectroscopy and first principles calculations for the model system of the Cr(C<SUB>6</SUB>H<SUB>6</SUB>)<SUB>2</SUB>–C<SUB>6</SUB>H<SUB>6</SUB> cluster. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b923929d'> </P>

Nature of anion-templated π⁺–π⁺ interactions

Geronimo, Inacrist,Jiten Singh, N.,Kim, Kwang S. Royal Society of Chemistry 2011 Physical chemistry chemical physics Vol.13 No.25

<P>Interaction between positively charged aromatic groups (π<SUP>+</SUP>–π<SUP>+</SUP>) is characterized by anti-parallel, displaced-stacked structures in the presence of counteranions. Binding energies of pyridinium, <I>N</I>-methylpyridinium and <I>N</I>-methylimidazolium dimers are much larger than that of benzene–pyridine (π–π) and pyridinium–benzene (π<SUP>+</SUP>–π). Stabilization is attributed to attractive electrostatic interaction with significant dispersion contribution.</P> <P>Graphic Abstract</P><P>Anion-templated π<SUP>+</SUP>–π<SUP>+</SUP> interaction is demonstrated as a major driving force for crystal growth and assembly. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cp20348g'> </P>

Unique Sandwich Stacking of Pyrene-Adenine-Pyrene for Selective and Ratiometric Fluorescent Sensing of ATP at Physiological pH

Xu, Zhaochao,Singh, N. Jiten,Lim, Jeesun,Pan, Jie,Kim, Ha Na,Park, Sungsu,Kim, Kwang S.,Yoon, Juyoung American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.42

<P>A pincer-like benzene-bridged sensor 1 with a pyrene excimer as a signal source and imidazolium as a phosphate anion receptor was synthesized and investigated for ATP sensing. A unique switch of excimer vs monomer pyrene fluorescence of 1 is observed in the presence of ATP due to the charcteristic sandwich pi-pi stacking of pyrene-adenine-pyrene. On the other hand, four other bases of nucleoside triphosphates such as GTP, CTP, UTP, and TTP can interact only from the outside with the already stabilized stacked pyrene-pyrene dimer of 1, resulting in excimer fluorescence quenching. The fluorescent intensity ratio of monomer-to-excimer for 1 upon binding with ATP (I(375)/I(487)) is much larger than that upon binding with ADP and AMP. This difference is large enough to discriminate ATP from ADP and AMP. As one of the biological applications, sensor 1 is successfully applied to the ATP staining experiments. Sensor 1 is also applied to monitor the hydrolysis of ATP and ADP by apyrase. The results indicate that 1 is a useful fluorescent sensor for investigations of ATP-relevant biological processes.</P>

A Calix[4]imidazolium[2]pyridine as an Anion Receptor

Chellappan, Kavitha,Singh, N. Jiten,Hwang, In-Chul,Lee, Jung Woo,Kim, Kwang S. WILEY-VCH Verlag 2005 Angewandte Chemie Vol.117 No.19

<B>Graphic Abstract</B> <P>Ein effektives makrocyclisches Ionophor für F<SUP>−</SUP>-Ionen, das aus einer Anordnung positiv geladener Imidazoliumeinheiten besteht, wurde hergestellt. Das Calix[4]imidazolium[2]pyridin-Kation bildet mit F<SUP>−</SUP>-Ionen einen 1:1-Komplex, wie Bindungsstudien mithilfe der <SUP>1</SUP>H-NMR-Spektroskopie, die Kristallstrukturbestimmung (siehe Bild) und Dichtefunktionalrechnungen belegen. <img src='wiley_img/00448249-2005-117-19-ANGE200500119-content.gif' alt='wiley_img/00448249-2005-117-19-ANGE200500119-content'> </P>

ORiginal Article : Intra-Abdominal Pressure in the Early Phase of Severe Acute Pancreatitis: Canary in a Coal Mine? Results from a Rigorous Validation Protocol

( Vimal Bhandari ),( Jiten Jaipuria ),( Mohit Singh ),( Avneet Singh Chawla ) The Editorial Office of Gut and Liver 2013 Gut and Liver Vol.7 No.6

Background/Aims: Intra-abdominal hypertension (IAH) is being increasingly reported in patients with severe acute pancreatitis (SAP) with worsened outcomes. The present study was undertaken to evaluate intra-abdominal pressure (IAP) as a marker of severity in the entire spectrum of acute pancreatitis and to ascertain the relationship between IAP and development of complications in patients with SAP. Methods: IAP was measured via the transvesical route by measurements performed at admission, once after control-ling pain and then every 4 hours. Data were collected on the length of the hospital stay, the development of systemic inflammatory response syndrome (SIRS), multiorgan failure, the extent of necrosis, the presence of infection, pleural ef-fusion, and mortality. Results: In total, 40 patients were en-rolled and followed up for 30 days. The development of IAH was exclusively associated with SAP with an APACHE II score ≥8 and/or persistent SIRS, identifying all patients who were going to develop abdominal compartment syndrome (ACS). The presence of ACS was associated with a significantly in-creased extent of pancreatic necrosis, multiple organ failure, and mortality. The mean admission IAP value did not differ significantly from the value obtained after pain control or the maximum IAP measured in the first 5 days. Conclusions: IAH is reliable marker of severe disease, and patients who mani-fest organ failure, persistent SIRS, or an Acute Physiology and Chronic health Evaluation II score ≥8 should be offered IAP surveillance. Severe pancreatitis is not a homogenous entity. (Gut Liver 2013;7:731-738)

Hydrogen-Release Mechanisms in Lithium Amidoboranes

Kim, Dong Young,Singh, N. Jiten,Lee, Han Myoung,Kim, Kwang S. WILEY-VCH Verlag 2009 Chemistry Vol.15 No.22

<P>Hydrogen storage: In lithium amidoboranes an initial molecule of H<SUB>2</SUB> is released by the formation of LiH, followed by a redox reaction of the dihydrogen bond formed between LiH<SUP>δ−</SUP> and NH<SUP>δ+</SUP>. In this dehydrogenation process, an intermolecular N&n.bond;B bond forms through the catalytic effect of a Li cation. After releasing the first molecule of H<SUB>2</SUB>, a Li cation binds to a nitrogen atom, lowering the energy barrier for the second H<SUB>2</SUB> loss per lithium amidoborane dimer (see figure). <img src='wiley_img/09476539-2009-15-22-CHEM200900092-content.gif' alt='wiley_img/09476539-2009-15-22-CHEM200900092-content'> </P><P>Alkali-metal amidoboranes have been recently highlighted as materials that satisfy many of the criteria required to make hydrogen-storage media. It is, therefore, crucial for us to understand the dehydrogenation mechanism of these materials for further development towards making successful hydrogen-storage media. In the present study, we attempt to shed light on the mechanisms involved in the loss of one molar equivalent of H<SUB>2</SUB> from solid lithium amidoboranes by using high-level ab initio calculations of monomeric and dimeric compounds in the gas phase. In the lithium amidoborane dimer, H<SUB>2</SUB> is released by the formation of LiH, which is followed by a redox reaction of the dihydrogen bond formed between the strongly basic H<SUP>−</SUP> in LiH and H<SUP>δ+</SUP> bonded to N. In the dehydrogenation process, the Li cation catalyzes the intermolecular N&n.bond;B bond formation; this could lead to new pathways for N&n.bond;B polymerization. After the release of the first molecule of H<SUB>2</SUB>, a Li cation binds to a nitrogen atom, resulting in a lowering of the energy barrier for the second dehydrogenation process per dimer. These results will be useful for the design of future hydrogen-storage media.</P> <B>Graphic Abstract</B> <P>Hydrogen storage: In lithium amidoboranes an initial molecule of H<SUB>2</SUB> is released by the formation of LiH, followed by a redox reaction of the dihydrogen bond formed between LiH<SUP>δ−</SUP> and NH<SUP>δ+</SUP>. In this dehydrogenation process, an intermolecular N&n.bond;B bond forms through the catalytic effect of a Li cation. After releasing the first molecule of H<SUB>2</SUB>, a Li cation binds to a nitrogen atom, lowering the energy barrier for the second H<SUB>2</SUB> loss per lithium amidoborane dimer (see figure). <img src='wiley_img/09476539-2009-15-22-CHEM200900092-content.gif' alt='wiley_img/09476539-2009-15-22-CHEM200900092-content'> </P>