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Ab initio calculations have been carried out to determine the dissociation pathways for the hydrogen fluoride trimer and tetramer that are accessible with single photon excitation of an HF stretching vibration. This requires evaluation of the stabilities of the small HF clusters. Electron correlation effects are found to contribute 1.0 kcal to the stability of the trimer, compared to 0.5 kcal for the dimer. The equilibrium stabilities with respect to dissociation into monomers are 4.6 kcal for the dimer, 14 kcal for the trimer, and 25 kcal for the tetramer. With zero-point vibrational effects, single photon vibrational excitation is sufficient for dissociation of the trimer into three monomers. The orientational structural parameters of the trimer and tetramer, like those of the dimer are found to be well explained by dipole and quadrupole moment interactions. [ABSTRACT FROM AUTHOR]

We report the H I bond activation on free and confined silver tetramer clusters using the first principles approach. The objective of this study is to underscore the effect of confinement on the chemical reactivity of Ag 4 . All calculations were carried out under the density functional theory formalism using both atomic and plane wave basis sets. We have used armchair carbon nanotube as a model system for confinement. The results show that the interaction energy is increased inside nanotube, leading to enhanced bond stretching. The origin of such effect has been demonstrated using molecular orbital theory and electronic density of state analysis. [ABSTRACT FROM AUTHOR]

The novel columnar liquid crystals based on symmetric hairpin-shaped cholesterol tetramers bridged by rigid or hydrogen-bonding Schiff-base spacers were prepared by reacting cholesterol dimer with phenylenediamines or dihydrazides in yields of 70-85%. Structural characterisation of these new compounds had been achieved by infrared, nuclear magnetic resonance and mass spectrometry. Their mesomorphic properties were investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. They exhibited good hexagonal columnar mesophase with three molecules in a disc of the columnar hexagonal state. This study implied that the symmetric cholesterol tetramers with rigid cores or hydrogen-bonding cores prefer to columnar mesophase. [ABSTRACT FROM AUTHOR]

Hydrogen bonded interaction of pyrrole multimer and acetylene-pyrrole complexes were studied in N 2 and p -H 2 matrixes. DFT computations showed T-shaped geometry for the pyrrole dimer and cyclic complex for the trimer and tetramer were the most stable structures, stabilized by N H⋯π interactions. The experimental vibrational wavenumbers observed in N 2 and p -H 2 matrixes for the pyrrole multimers were correlated with the computed wavenumbers. Computations performed at MP2/aug-cc-pVDZ level of theory showed that C 2 H 2 and C 4 H 5 N forms 1:1 hydrogen-bonded complexes stabilized by C H⋯π interaction (Complex A), N H⋯π interaction (Complex B) and π⋯π interaction (Complex C), where the former complex is the global minimum and latter two complexes were the first and second local minima, respectively. Experimentally, 1:1 C 2 H 2 C 4 H 5 N complexes A (global minimum) and B (first local minimum) were identified from the shifts in the N H stretching, N H bending, C H bending region of pyrrole and C H asymmetric stretching and bending region of C 2 H 2 in N 2 and p -H 2 matrixes. Computations were also performed for the higher complexes and found two minima corresponding to the 1:2 C 2 H 2 C 4 H 5 N and three minima for the 2:1 C 2 H 2 C 4 H 5 N complexes. Experimentally the global minimum 1:2 and 2:1 C 2 H 2 C 4 H 5 N complexes were identified in N 2 and p -H 2 matrixes. [ABSTRACT FROM AUTHOR]

Three novel triphenylene tetramers with triazole bridges, rigid aromatic Schiff-bases and hydrogen-bonding spacers were designed and synthesized in yield of 73–78%. Their structures were confirmed by IR, NMR and MS. Their mesomorphic properties were studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. These novel triphenylene tetramers possessed the hexagonal columnar mesophase and exhibited excellent mesomorphic properties with melting points at 30–60 °C, which was first observed near room temperature for triphenylene tetramers. This study suggested that the mesomorphic properties of triphenylene oligomers could be tuned conveniently by the structures of spacers. [ABSTRACT FROM AUTHOR]

A hydrogen-bonded cyclic tetramer is assembled with remarkably high effective molarities from a properly designed dinucleoside monomer. This self-assembled species exhibits an impressive thermodynamic and kinetic stability and is formed with high fidelities within a broad concentration range. [ABSTRACT FROM AUTHOR]

Proton transfer through hydrogen bonds plays a fundamental role in many physical, chemical and biological processes. Proton dynamics is susceptible to quantum tunnelling, which typically involves many hydrogen bonds simultaneously, leading to correlated many-body tunnelling. In contrast to the well-studied incoherent single-particle tunnelling, our understanding of many-body tunnelling is still in its infancy. Here we report the real-space observation of concerted proton tunnelling in a cyclic water tetramer using a cryogenic scanning tunnelling microscope. This is achieved by monitoring the reversible interconversion of the hydrogen-bonding chirality of the water tetramer with a chlorine-terminated scanning tunnelling microscope tip. We found that the presence of the Cl anion at the tip apex may either enhance or suppress the concerted tunnelling process, depending on the details of the coupling symmetry between the Cl ion and the protons. Our work opens up the possibility of controlling the quantum states of protons with atomic-scale precision. [ABSTRACT FROM AUTHOR]

The title compound, 3C6H4N4O2S2·2C3H7NO·4H2O, comprises three 2,2′-disulfanylidene-5,5′-biimidazolidinylidene-4,4′-dione molecules, two dimethylformamide molecules and four water molecules arranged around a crystallographic inversion centre. The non-H atoms within the 5,5′-biimidazolidinylidene molecule are coplanar and these molecules aggregate through N-H...S hydrogen-bonding interactions with cyclic motifs [graph set R22(8)], giving two-dimensional ribbon structures which are close to being parallel. The two independent water molecules associate to form centrosymmetric cyclic hydrogen-bonded (H2O)4 tetrameric units [graph set R44(8)]. The ribbon structures extend along the a axis and are linked through the water tetramers and the dimethylformamide molecules by a combination of two- and three-centre hydrogen bonds, giving an overall three-dimensional structure. [ABSTRACT FROM AUTHOR]

Highlights: [•] A tetraprotonated triethylenetetramine molecule is bonded with three water tetramers via H-bonds and vice versa. [•] A new 2D H-bonded supramolecular framework is formed with hexagon pores. [•] Two symmetry-operation related standing and lying style POMs present as template. [•] The standing and lying style POMs are wrapped between the layers, resulting in a 3D entity. [ABSTRACT FROM AUTHOR]

We have developed new helical oligomers using a combination of (1S,2S)-cyclopentane-1,2-diamine [(S,S)-CPDA] and 2,2-dimethylmalonic acid (DMM) residues as building blocks. In solution, the preferred secondary structure of the (S,S) tetramer 6 was a right-handed (P) helix, and that of the (R,R) tetramer ent-6 was a left-handed (M) helix. In the crystalline state, both 6 and the (S,S) pentamer 7 folded into (P) 11-helices, and ent-6 folded into an (M) 11-helix with hydrogen bonds that were oriented in alternating directions. [ABSTRACT FROM AUTHOR]

Abstract: The (tetrazol-5-yl)acetic acid crystal was characterized by the X-ray diffraction and FTIR spectroscopic methods. The analysis of the crystal structure reveals that the compound exists in the solid state as 1H-tautomer. The molecules are linked by two types of the intermolecular hydrogen bonds forming an infinite two-dimensional network in the (101) plane. Intramolecular NO hydrogen bonds are also formed in the crystal. The analysis of the FTIR spectra of the crystalline sample and its deuterated analogue, based on the B3LYP/6-311++G(2d,2p) frequency calculations of two model tetramers, has been performed in relation to the obtained crystal structure data. [Copyright &y& Elsevier]

(2 RS,4 SR)-7-Bromo-2-(2-methylphenyl)-2,3,4,5-tetrahydro-1 H-naphtho[1,2- b]azepin-4-ol, C21H20BrNO, (I), and (2 RS,4 SR)-2-(3-methylthiophen-2-yl)-2,3,4,5-tetrahydro-1 H-naphtho[1,2- b]azepin-4-ol, C19H19NOS, (II), both crystallize with Z′ = 2 in the space groups P21/ c and Cc, respectively; compound (II) crystallizes as a nonmerohedral twin, with twin fractions 0.183 (2) and 0.817 (2). The molecules of (I) are linked by O-H...O and O-H...N hydrogen bonds to form a cyclic centrosymmetric R44(16) tetramer. The molecules of (II) are linked by O-H...O hydrogen bonds to form a C22(4) chain and these chains are weakly linked by a single C-H...π(thienyl) interaction to form a three-dimensional array. Comparisons are made with some related compounds. [ABSTRACT FROM AUTHOR]

Abstract: Single crystal X-ray structures of cocrystals, 1·2 and 1·3, derived from U-shaped ureadicarboxylic acid (1) with 2-aminopyrimidine (2) and melamine (3), respectively, were examined. Cocrystals were obtained as a 1:1 mixture of 1 and the corresponding base. Two molecules of 1 and two molecules of the base were combined together via intermolecular H-bonding creating a supramolecularly assembled cyclic heterotetramer motif of rhombus shape. In the case of cocrystal 1·3, the cyclic heterotetramers were connected via H-bonding by utilizing a remaining amino group of melamine resulting in the formation of a tape of cyclic heterotetramer. [Copyright &y& Elsevier]

Characteristic H-bonding patterns define secondary structure in proteins and nucleic acids. We show that similar patterns apply for α2-8 sialic acid (SiA) in H2O and that H-bonds define its structure. A 15N,13C α2-8 SiA tetramer, (SiA)4, was used as a model system for the polymer. At 263 K, we detected intra-residue through-H- bond J couplings between `5N and C8 for residues R-I- R-III of the tetramer, indicating H-bonds between the `5N's and the 08's of these residues. Additional J couplings between the 15N's and C2's of the adjacent residues confirm the putative H-bonds. NH groups showing this long-range correlation also experience slower 1H/2H exchange. Additionally, detection of couplings between H7 and C2 for R-II and R-III implies that the conformations of the linkers between these residues are different than in the monomers. These structural elements are consistent with two left-handed helical models: 2 residues/turn (24 helix) and 4 residues/turn (14 helix). To discriminate between models, we resorted to 1H,1H NOEs. The 24 helical model is in better agreement with the experimental data. We provide direct evidence of H- bonding for (SiA)4and show how H-bonds can be a determining factor for shaping its 3D structure. [ABSTRACT FROM AUTHOR]

Abstract: A tetrameric spin crossover (SCO) FeII complex was synthesized, and the structure and magnetic properties were studied. The tetrameric structure is constructed by four imidazole···Cl− hydrogen bonds centered at one Cl− ion. The compound showed an incomplete gradual SCO behavior due to intra-cluster “anticooperative-like“ interaction. [Copyright &y& Elsevier]

Direct attachment of two 2-ureido-4-[1H]-pyrimidinone (UPy) subunits to a 3,6-carbazolyl core gives rise to a highly viscous, supramolecular polymer. However, insertion of a methylene spacer between the UPy’s and the carbazole leads to a well-defined, cyclic tetramer, in a belt-shaped arrangement, as evidenced by MALDI-TOF, DOSY, and NOESY spectra. [ABSTRACT FROM AUTHOR]

The interaction between SA (streptavidin) and biotin is one of the strongest non-covalent interactions in Nature. SA is a widely used tool and a paradigm for protein–ligand interactions. We previously developed a SA mutant, termed Tr (traptavidin), possessing a 10-fold lower off-rate for biotin, with increased mechanical and thermal stability. In the present study, we determined the crystal structures of apo-Tr and biotin–Tr at 1.5 Å resolution. In apo-SA the loop (L3/4), near biotin's valeryl tail, is typically disordered and open, but closes upon biotin binding. In contrast, L3/4 was shut in both apo-Tr and biotin–Tr. The reduced flexibility of L3/4 and decreased conformational change on biotin binding provide an explanation for Tr's reduced biotin off- and on-rates. L3/4 includes Ser45, which forms a hydrogen bond to biotin consistently in Tr, but erratically in SA. Reduced breakage of the biotin–Ser45 hydrogen bond in Tr is likely to inhibit the initiating event in biotin's dissociation pathway. We generated a Tr with a single biotin-binding site rather than four, which showed a simi-larly low off-rate, demonstrating that Tr's low off-rate was governed by intrasubunit effects. Understanding the structural features of this tenacious interaction may assist the design of even stronger affinity tags and inhibitors. [ABSTRACT FROM AUTHOR]

New tetramer structures, based on 9-methylxanthine (Xa), 9-methylxanthine protonated at N7 (XaH+) and 9-methyluric acid (Ua), were investigated by high-level density functional calculations. We have found that homo- and heterotetrads (XaH+)4, (XaH+–Xa)2, (XaH+–Ua)2carrying positive charges can be formed by low barrier hydrogen bonds. Systems with zero charge [(Xa)4, (Xa–Ua)2, (Ua)4] were also constructed, investigated and compared to the guanine tetrad [(G)4]. It was shown that the new tetramers can bind cations and anions without the necessity of stacking interactions. Application of the calculated systems in higher-ordered structures (e.g.quadruplexes) is promising with or without intercalating ions. [ABSTRACT FROM AUTHOR]

Two kinds of water clusters, the unique dodecahedral (H2O)14cage and the truncated cubic (H2O)12cluster formed from both coordinated and lattice water molecules, are captured in three lanthanide complexes [Ln4(chtc)3(H2O)10]·9H2O (Ln = Tb 1, Yb 2, Dy 3, H4chtc = cyclohexane-1,2,4,5-tetracarboxylic acid). Compound 1exhibits the characteristic photoluminescence of the Tb3+ion in the visible region, while 2exhibits NIR luminescence properties. [ABSTRACT FROM AUTHOR]

initio calculations at the MP2/aug-cc-pVTZ level have been performed to study the cooperativity of hydrogen bonds in homoclusters (HNC-HNC-HNC and HNC-HNC-HNC-HNC) and heteroclusters (HN-HNC-HNC and HN-HNC-HNC-HNC). The cooperative energies in the HNC-HNC-HNC and HN-HNC-HNC trimers are -2.05 and -2.56 kcal/mol, respectively. The result shows that the cooperativity in the heterotrimer is larger than that in the homotrimer. A similar result also happens in the tetramers. The energy decomposition scheme indicates that orbital interaction is a major contribution to the cooperative energy of N···HN hydrogen bond, whereas the electrostatic and orbital interactions to that of C···HN hydrogen bond. The effect of HNC chain length on the strength of N···HN hydrogen bond has also been considered at the MP2/aug-cc-pVDZ level. It is indicated that the interaction energy of N···HN hydrogen bond trends to be a fixed value when the HNC number tends to be infinite, and the strength of N···HN hydrogen bond is regulated mainly through the electrostatic and polarization interactions although the charge transfer interaction also has an effect on it. [ABSTRACT FROM AUTHOR]

Self-assembly of four bis(pyridyl) ligands with longer flexible spacer: 1,4-bis(3-pyridylaminomethyl)benzene (L1), 1,4-bis(2-pyridylaminomethyl)benzene (L2), 1,3-bis(3-pyridylaminomethyl)benzene (L3) and 1,3-bis(2-pyridylaminomethyl)benzene (L4), and CuX (X = Br and I) leads to the formation of eight [CunXn]-based (X = Br and I; n = 1, 2, and 4) complexes, [Cu2I2L1(PPh3)4] (1), [Cu4Cl2Br2(L4)2(PPh3)6]·(CH3CN)2(2), [Cu2I2(L3)2] (3), {[Cu2Br2L2(PPh3)2]·(CH2Cl2)2}n(4), [CuIL1]n·nCH2Cl2(5), [CuIL1]n(6), [CuIL4]n(7) and [Cu2I2L4]n(8), which have been synthesized and characterized by elemental analysis, IR, TG, powder and single-crystal X-ray diffraction. Structural analyses show that the eight complexes possess an increasing dimensionality from 0D (1–3) to 1D (4) to 2D (5–8), in which 1and 2contain a CuX unit, 2–7contain a Cu2X2unit and 8contains a Cu4X4unit. Such evolvement indicates that the conformation of flexible bis(pyridyl) ligands and the participation of triphenylphosphine (PPh3) as a second ligand take an essential role in the framework formation of the Cu(i) complexes. Moreover, a pair of symmetry-related L3ligands in complex 3coordinate to the rhomboid Cu2I2dimer to form “handcuff-shaped” dinuclear structures, which are further joined together through intermolecular N–HI hydrogen bonds to furnish a 2D (4,4) layer. Although complexes 5and 6exhibit a similar 2D (4,4) layer constructed from L1ligand bridging [Cu2I2]nunits, the different packing fashion of the layers leads to the formation of 3D porous frameworks of 5and dense 3D frameworks of 6. The “twisted-boat” conformation of the Cu4I4tetramer unit in complex 8has not been reported so far. [ABSTRACT FROM AUTHOR]

Abstract: For the first time, a 2D water sheet that contains both cyclic water hexamers around Al3+ in boat and chair conformations and cyclic water tetramers was crystallographically observed in an Anderson-type supramolecular complex, [Al(H2O)6][Al(OH)6Mo6O18]·10H2O 1, in which the element type of both the counter cation and the heteroatom of the polyanion are the same, that is Aluminum. The counter cation Al3+ is coordinated by six water molecules forming a nearly ideal octahedron. The octahedron is then hydrogen-bonded to its surrounding lattice water molecules producing a novel Al3+-containing 1D water chain composed of both boat- and chair-like water hexamers. More interestingly and importantly, the water chains further on join together through a parallelogram composed of four water molecules to yield a unique 2D water sheet. [Copyright &y& Elsevier]

Nucleosomes are highly dynamic macromolecular complexes that are assembled and disassembled in a modular fashion. One important way in which this dynamic process can be modulated is by the replacement of major histones with their variants, thereby affecting nucleosome structure and function. Here we use fluorescence resonance energy transfer between fluorophores attached to various defined locations within the nucleosome to dissect and compare the structural transitions of a H2A.Z containing and a canonical nucleosome in response to increasing ionic strength. We show that the peripheral regions of the DNA dissociate from the surface of the histone octamer at relatively low ionic strength, under conditions where the dimer-tetramer interaction remains unaffected. At around 550 mM NaCl, the (H2A–H2B) dimer dissociates from the (H3–H4)2 tetramer-DNA complex. Significantly, this latter transition is stabilized in nucleosomes that have been reconstituted with the essential histone variant H2A.Z. Our studies firmly establish fluorescence resonance energy transfer as a valid method to study nucleosome stability, and shed new light on the biological function of H2A.Z. [ABSTRACT FROM AUTHOR]

A highly constrained pseudo-tetrapeptide (OC252-324) further defines a new allosteric binding site located near the center of fructose-1,6-bisphosphatase. In a crystal structure, pairs of inhibitory molecules bind to opposite faces of the enzyme tetramer. Each ligand molecule is in contact with three of four subunits of the tetramer, hydrogen bonding with the side chain of Asp[sup 187] and the backbone carbonyl of residue 71, and electrostatically interacting with the backbone carbonyl of residue 51. The ligated complex adopts a quaternary structure between the canonical R- and T-states of fructose-1,6-bisphosphatase, and yet a dynamic loop essential for catalysis (residues 52-72) is in a conformation identical to that of the T-state enzyme. Inhibition by the pseudo-tetrapeptide is cooperative (Hill coefficient of 2), synergistic with both AMP and fructose 2,6-bisphosphate, noncompetitive with respect to Mg[sup 2+], and uncompetitive with respect to fructose 1,6-bisphosphate. The ligand dramatically lowers the concentration at which substrate inhibition dominates the kinetics of fructose-1,6-bisphosphatase. Elevated substrate concentrations employed in kinetic screens may have facilitated the discovery of this uncompetitive inhibitor. Moreover, the inhibitor could mimic an unknown natural effector of fructose-1,6-bisphosphatase, as it interacts strongly with a conserved residue of undetermined functional significance. [ABSTRACT FROM AUTHOR]

The article focuses on a research conducted by Xiangzhi Meng and colleagues and published in the "Nature Physics" journal which investigates about transfer of protons. It states that the researchers present evidence for correlated tunneling through means of experimental real-space image and controlled concerted tunneling of four protons within hydrogen-bonded water tetramers. It mentions that chirality and proton order go hand in hand.

Confirms that a stable tetramer, isoguanosine (isoG) self-assembles via complementary hydrogen bonds. Characterization of isoG self-association by vapor phase osmometry; Indications that isoG 2 self-associates in organic solvents; Stoichiometry and structure of the isoG-K+ complex.

The crystal structure of the title complex, trans-dichloridotetrakis[1-phenyl-3-(1 H-1,2,4-triazol-1-yl-κ N4)propan-1-one]copper(II) hexahydrate, [CuCl2(C11H11N3O)4]·6H2O, is isomorphous with that of the corresponding nickel and cobalt compounds. The complex has crystallographic inversion symmetry with the CuII atom on an inversion centre. Each CuII atom is six-coordinated by one N atom from each of the four 1-phenyl-3-(1 H-1,2,4-triazol-1-yl)propan-1-one ligands in the equatorial plane and by two chloride ligands in axial positions. The structure includes a centrosymmetric irregular up-up-down-down (uudd) water tetramer cluster and O-H...Cl hydrogen bonds. Intermolecular C-H...Cl hydrogen bonds exist between adjacent molecules, resulting in a three-dimensional supramolecular network. [ABSTRACT FROM AUTHOR]

A new design strategy to produce a supramolecular elastomer with self‐healing and dielectric properties by synthesizing an aniline tetramer (AT)‐functionalized supramolecular elastomer (SE‐AT) is demonstrated. The termination of AT in the supramolecular system not only shortens linear amide molecular chain to decrease glass transition temperature but also destroys the crystallization to achieve amorphous structure. The SE‐AT provides two kinds of noncovalent bonding including π–π stacking and the hydrogen bond, which makes the material more easily healed. The SE‐AT20% can heal mechanical properties within 24 h at room temperature without any external stimulus. The dielectric constant shows a continuous increase overall with increasing AT content. The material exhibits good electro‐mechanical properties, which is attributed to a simultaneous increase in dielectric constant and decrease in modulus. The maximum actuated strain significantly increases with the increasing AT content and the SE‐AT20% reaches 10% at 1 V µm−1. Moreover, SE‐AT exhibits the ability to regain actuated strain on the location of the mechanical damage after self‐healing. A new design strategy to produce a self‐healing dielectric elastomer by synthesizing an aniline tetramer(AT)‐functionalized supramolecular elastomer (SE‐AT) is demonstrated. The SE‐AT exhibits an excellent self‐healing capability at room temperature and outstanding electro‐mechanical property at low electric field. Moreover, SE‐AT exhibits the ability to regain actuated strain at electric fields after self‐healing. [ABSTRACT FROM AUTHOR]

The article discusses the study which shows the synthesis, structural analysis and self-organization of a tetrameric Januas type DNA base G^C heterocyles. The study uses several approaches including electrospray ionization mass spectrometry (ESI-MS), variable temperature nuclear magnetic resonance (NMR) spectroscopy, and diffusion-ordered spectroscopy (DOSY). It is found that the self-complementary G^C heterocycle assembly into hydrogen (H)-bonded tetrameric structures.

The title compound, [Pd4(C8H11N2O2)4Cl4]·9H2O, is a cyclic tetra­mer. The PdII atom shows distorted square-planar coordination arising from chelation by the phenolate O atom and the pyridoxamine ligand; the metal atom is also linked to the pyridyl N atom from an adjacent ligand and a Cl atom. A twofold axis, which is parallel to the c axis, is located at the center of a tetramer. The crystal packing is stabilized by hydrogen bonding among neighboring complex mol­ecules via the solvent water mol­ecules. [ABSTRACT FROM AUTHOR]

The stability of quadruple hydrogen bonding in the cyclic tetramer of a metallo-porphyrin before and after a covalent fixation was investigated. According to competition and energy-transfer experiments, the exchange reaction between the cyclic tetramers of the metallo-porphyrin was fully suppressed by the covalent fixation. This spontaneous cyclization-covalent fixation strategy based on olefin metathesis can open the way to the use of cyclic assemblies in a solid phase. [ABSTRACT FROM AUTHOR]