Click-Functionalization of Silanized Carbon Nanotubes: From Inorganic Heterostructures to Biosensing Nanohybrids.

Here we present an approach to functionalize silanized single-walled carbon nanotubes (SWNTs) through copper-free click chemistry for the assembly of inorganic and biological nanohybrids. The nanotube functionalization route involves silanization and strain-promoted azide-alkyne cycloaddition reactions (SPACC). This was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and Fourier transform infra-red spectroscopy. Silane-azide-functionalized SWNTs were immobilized from solution onto patterned substrates through dielectrophoresis (DEP). We demonstrate the general applicability of our strategy for the functionalization of SWNTs with metal nanoparticles (gold nanoparticles), fluorescent dyes (Alexa Fluor 647) and biomolecules (aptamers). In this regard, dopamine-binding aptamers were conjugated to the functionalized SWNTs to perform real-time detection of dopamine at different concentrations. Additionally, the chemical route is shown to selectively functionalize individual nanotubes grown on the surface of silicon substrates, contributing towards future nano electronic device applications.

The 2'-deoxyribofuranoside of 3-phenyltetrahydropyrimido[4,5-c]pyridazin-7-one: a bicyclic nucleoside with sugar residues in N and S conformations, and its molecular recognition.

The title compound 3-phenyltetrahydropyrimido[4,5-c]pyridazine 2'-deoxyribonucleoside [systematic name: 6-(2-deoxy-ß-D-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-3-phenylpyrimido[4,5-c]pyridazin-7-one monohydrate, C17H18N4O4·H2O, 1] shows two conformations in the crystalline state and the two conformers (1a and 1b) adopt different sugar puckers. The sugar residue of 1a shows a C2'-endo S-type conformation, while 1b displays a C3'-endo N-type sugar pucker. Both conformers adopt similar anti conformations around the N-glycosylic bonds, with χ = -97.5 (3)° for conformer 1a and χ = -103.8 (3)° for conformer 1b. The extended crystalline network is stabilized by several intermolecular hydrogen bonds involving nucleoside and water molecules. The nucleobases and phenyl substituents of the two conformers (1a and 1b) are stacked and display a reverse alignment. A Hirshfeld surface analysis supports the hydrogen-bonding pattern, while curvedness surfaces visualize the stacking interactions of neighbouring molecules. The recognition face of nucleoside 1 for base-pair formation mimics that of 2'-deoxythymidine. Nucleoside 1 shows two pKa values: 1.8 for protonation and 11.2 for deprotonation. DNA oligonucleotides containing nucleoside 1 were synthesized and hybridized with complementary DNA strands. Nucleoside 1 forms a stable base pair with dA which is as stable as the canonical dA-dT pair. The bidentate 1-dA base pair is strengthened by a third hydrogen bond provided by the dA analogue 3-bromopyrazolo[3,4-d]pyrimidine-4,6-diamine 2'-deoxyribofuranoside (4). By this, duplex stability is increased and the suggested base-pairing patterns are supported.

Free-Sustaining Three-Dimensional S235 Steel-Based Porous Electrocatalyst for Highly Efficient and Durable Oxygen Evolution.

A novel oxygen evolution reaction (OER) catalyst (3 D S235-P steel) based on a steel S235 substrate was successfully prepared by facile one-step surface modification. The standard carbon-manganese steel was phosphorized superficially, which led to the formation of a unique 3 D interconnected nanoporous surface with a high specific area that facilitated the electrocatalytically initiated oxygen evolution reaction. The prepared 3 D S235-P steel exhibited enhanced electrocatalytic OER activities in the alkaline regime, as confirmed by a low overpotential (326 mV at a 10 mA cm-2 ) and a small Tafel slope of 68.7 mV dec-1 . Moreover, the catalyst was found to be stable under long-term usage conditions, functioning as an oxygen-evolving electrode at pH 13, as evidenced by the sufficient charge-to-oxygen conversion rate (faradaic efficiency: 82.11 and 88.34 % at 10 and 5 mA cm-2 , respectively). In addition, it turned out that the chosen surface modification delivered steel S235 as an OER electrocatalyst that was stable under neutral pH conditions. Our investigation revealed that the high catalytic activities likely stemmed from the generated Fe/(Mn) hydroxide/oxohydroxides generated during the OER process. Phosphorization treatment therefore not only is an efficient way to optimize the electrocatalytic performance of standard carbon-manganese steel but also enables for the development of low-costing and abundant steels in the field of energy conversion.

Ultrafine sanding paper: a simple tool for creating small particles.

A top-down approach, i.e., creating small particles by mechanical force starting from bulk materials, probably presents the most logical approach to particle size reduction and, therefore, top-down techniques are among the first to achieve small particles. A new solvent-free, amazingly simple approach is reported, suitable to achieve nanoparticles and sub-micro particles.

7-Cyclopropyl-2'-deoxytubercidin: a carbocyclic side-chain derivative of 7-deaza-2'-deoxyadenosine.

The title compound {systematic name: 4-amino-5-cyclopropyl-7-(2-deoxy-ß-D-erythro-pentofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine}, C14H18N4O3, exhibits an anti glycosylic bond conformation, with the torsion angle χ = -108.7 (2)°. The furanose group shows a twisted C1'-exo sugar pucker (S-type), with P = 120.0 (2)° and τm = 40.4 (1)°. The orientation of the exocyclic C4'-C5' bond is -ap (trans), with the torsion angle γ = -167.1 (2)°. The cyclopropyl substituent points away from the nucleobase (anti orientation). Within the three-dimensional extended crystal structure, the individual molecules are stacked and arranged into layers, which are highly ordered and stabilized by hydrogen bonding. The O atom of the exocyclic 5'-hydroxy group of the sugar residue acts as an acceptor, forming a bifurcated hydrogen bond to the amino groups of two different neighbouring molecules. By this means, four neighbouring molecules form a rhomboidal arrangement of two bifurcated hydrogen bonds involving two amino groups and two O5' atoms of the sugar residues.

Extraordinary thermal stability of an oligodeoxynucleotide octamer constructed from alternating 7-deaza-7-iodo guanine and 5-Iodocytosine base pairs - DNA duplex stabilization by halogen bonds?

A reinvestigation of the published X-ray crystal-structure analyses of 7-halogenated (Br, I) 8-aza-7-deaza-2'-deoxyguanosines Br(7) c(7) z(8) Gd ; 1a and I(7) c(7) z(8) Gd , 1b, as well as of the structurally related 7-deaza-7-iodo-2'-deoxy-ß-D-ribofuranosyladenine (ß-I(7) c(7) Ad ; 2=6e in Table 1) and its α-D-anomer (α-I(7) c(7) Ad ; 3) clearly revealed the existence of halogen bonds between corresponding halogen substituents and the adjacent N(3)-atoms of neighboring nucleoside molecules within the single crystals. These halogen bonds can be rationalized by the presence of a region of positive electrostatic potential, the σ-hole, on the outermost portion the halogen's surface, while the three unshared pairs of electrons produce a belt of negative electrostatic potential around the central part of the halogen substituent. The N(3) atoms of the halogenated nucleosides carry a partial negative charge. This novel type of bonding between nucleosides was tentatively used to explain the extraordinary high stability of oligodeoxynucleotides constructed from halogenated nucleotide building blocks.

Reversible adhesion switching of porous fibrillar adhesive pads by humidity.

We report reversible adhesion switching on porous fibrillar polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) adhesive pads by humidity changes. Adhesion at a relative humidity of 90% was more than nine times higher than at a relative humidity of 2%. On nonporous fibrillar adhesive pads of the same material, adhesion increased only by a factor of ~3.3. The switching performance remained unchanged in at least 10 successive high/low humidity cycles. Main origin of enhanced adhesion at high humidity is the humidity-induced decrease in the elastic modulus of the polar component P2VP rather than capillary force. The presence of spongelike continuous internal pore systems with walls consisting of P2VP significantly leveraged this effect. Fibrillar adhesive pads on which adhesion is switchable by humidity changes may be used for preconcentration of airborne particulates, pollutants, and germs combined with triggered surface cleaning.

1,7-Dideaza-2'-deoxy-6-nitronebularine: a pyrrolo[2,3-b]pyridine nucleoside with an intramolecular hydrogen bond stabilizing the syn conformation.

The title compound [systematic name: 1-(2-deoxy-ß-D-erythro-pentofuranosyl)-4-nitro-1H-pyrrolo[2,3-b]pyridine], C12H13N3O5, forms an intramolecular hydrogen bond between the pyridine N atom as acceptor and the 5'-hydroxy group of the sugar residue as donor. Consequently, the N-glycosylic bond exhibits a syn conformation, with a χ torsion angle of 61.6 (2)°, and the pentofuranosyl residue adopts a C2'-endo envelope conformation (²E, S-type), with P = 162.1 (1)° and τm = 36.2 (1)°. The orientation of the exocyclic C4'-C5' bond is +sc (gauche, gauche), with a torsion angle γ = 49.1 (2)°. The title nucleoside forms an ordered and stacked three-dimensional network. The pyrrole ring of one layer faces the pyridine ring of an adjacent layer. Additionally, intermolecular O-H∙∙∙O and C-H∙∙∙O hydrogen bonds stabilize the crystal structure.

5-Ethynyl-2'-deoxycytidine: a DNA building block with a 'clickable' side chain.

The title compound [systematic name: 4-amino-1-(2-deoxy-ß-D-erythro-pentofuranosyl)-5-ethynylpyrimidin-2(1H)-one], C(11)H(13)N(3)O(4), shows two conformations in the crystalline state. The N-glycosylic bonds of both conformers adopt similar conformations, with χ = -149.2 (1)° for conformer (I-1) and -151.4 (1)° for conformer (I-2), both in the anti range. The sugar residue of (I-1) shows a C2'-endo envelope conformation ((2)E, S-type), with P = 164.7 (1)° and τ(m) = 36.9 (1)°, while (I-2) shows a major C3'-exo sugar pucker (C3'-exo-C2'-endo, (3)T(2), S-type), with P = 189.2 (1)° and τ(m) = 33.3 (1)°. Both conformers participate in the formation of a layered three-dimensional crystal structure with a chain-like arrangement of the conformers. The ethynyl groups do not participate in hydrogen bonding, but are arranged in proximal positions.

A 2'-deoxycytidine long-linker click adduct forming two conformers in the asymmetric unit.

The title compound {systematic name: 4-amino-1-(2-deoxy-ß-D-erythro-pentofuranosyl)-5-[6-(1-benzyl-1H-1,2,3-triazol-4-yl)hex-1-ynyl]pyrimidin-2(1H)-one}, C(24)H(28)N(6)O(4), shows two conformations in the crystalline state, viz. (I-1) and (I-2). The pyrimidine groups and side chains of the two conformers are almost superimposable, while the greatest differences between them are observed for the sugar groups. The N-glycosylic bonds of both conformers adopt similar anti conformations, with χ = -168.02 (12)° for conformer (I-1) and χ = -159.08 (12)° for conformer (I-2). The sugar residue of (I-1) shows an N-type (C3'-endo) conformation, with P = 33.1 (2)° and τ(m) = 29.5 (1)°, while the conformation of the 2'-deoxyribofuranosyl group of (I-2) is S-type (C3'-exo), with P = 204.5 (2)° and τ(m) = 33.8 (1)°. Both conformers participate in hydrogen-bond formation and exhibit identical patterns resulting in three-dimensional networks. Intermolecular hydrogen bonds are formed with neighbouring molecules of different and identical conformations (N-H...N, N-H... O, O-H...N and O-H...O).

1,N6-etheno-2'-deoxytubercidin hemihydrate.

The title compound [systematic name: 7-(2-deoxy-ß-D-erythro-pentofuranosyl)-7H-imidazo[1,2-c]pyrrolo[2,3-d]pyrimidine hemihydrate], 2C(13)H(14)N(4)O(3)·H(2)O or (I)·0.5H(2)O, shows two similar conformations in the asymmetric unit. These two conformers are connected through one water molecule by hydrogen bonds. The N-glycosylic bonds of both conformers show an almost identical anti conformation with χ = -107.7 (2)° for conformer (I-1) and -107.0 (2)° for conformer (I-2). The sugar moiety adopts an unusual N-type (C3'-endo) sugar pucker for 2'-deoxyribonucleosides, with P = 36.8 (2)° and τ(m) = 40.6 (1)° for conformer (I-1), and P = 34.5 (2)° and τ(m) = 41.4 (1)° for conformer (I-2). Both conformers and the solvent molecule participate in the formation of a three-dimensional pattern with a `chain'-like arrangement of the conformers. The structure is stabilized by intermolecular O-H...O and O-H...N hydrogen bonds, together with weak C-H...O contacts.

7-Amino-1-(2-deoxy-ß-erythro-pentofuranosyl)-1H-1,2,3-triazolo[4,5-d]pyrimidine: an 8-azaadenine nucleoside with the nucleobase in a syn conformation.

The title compound, C(9)H(12)N(6)O(3), shows a syn-glycosylic bond orientation [χ = 64.17 (16)°]. The 2'-deoxyfuranosyl moiety exhibits an unusual C1'-exo-O4'-endo ((1)T(0); S-type) sugar pucker, with P = 111.5 (1)° and τ(m) = 40.3 (1)°. The conformation at the exocyclic C4'-C5' bond is +sc (gauche), with γ = 64.4 (1)°. The two-dimensional hydrogen-bonded network is built from intermolecular N-H...O and O-H...N hydrogen bonds. An intramolecular bifurcated hydrogen bond, with an amino N-H group as hydrogen-bond donor and the ring and hydroxymethyl O atoms of the sugar moiety as acceptors, constrains the overall conformation of the nucleoside.

2-Amino-8-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)imidazo[1,2-a][1,3,5]triazin-4(8H)-one monohydrate, a 2'-deoxyguanosine analogue with an altered Watson-Crick recognition site.

The title compound, C(10)H(12)FN(5)O(4).H(2)O, shows an anti glycosyl orientation [chi = -123.1 (2) degrees]. The 2-deoxy-2-fluoroarabinofuranosyl moiety exhibits a major C2'-endo sugar puckering (S-type, C2'-endo-C1'-exo, (2)T(1)), with P = 156.9 (2) degrees and tau(m) = 36.8 (1) degrees , while in solution a predominantly N conformation of the sugar moiety is observed. The conformation around the exocyclic C4'-C5' bond is -sc (trans, gauche), with gamma = -78.3 (2) degrees. Both nucleoside and solvent molecules participate in the formation of a three-dimensional hydrogen-bonding pattern via intermolecular N-H...O and O-H...O hydrogen bonds; the N atoms of the heterocyclic moiety and the F substituent do not take part in hydrogen bonding.

2'-Deoxy-5-propynyluridine: a nucleoside with two conformations in the asymmetric unit.

The title compound, 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-5-(prop-1-ynyl)pyrimidin-2,4(1H,3H)-dione, C(12)H(14)N(2)O(5), shows two conformations in the crystalline state: conformer 1 adopts a C2'-endo (close to (2)E; S-type) sugar pucker and an anti nucleobase orientation [chi = -134.04 (19) degrees], while conformer 2 shows an S sugar pucker (twisted C2'-endo-C3'-exo), which is accompanied by a different anti base orientation [chi = -162.79 (17) degrees]. Both molecules show a +sc (gauche, gauche) conformation at the exocyclic C4'-C5' bond and a coplanar orientation of the propynyl group with respect to the pyrimidine ring. The extended structure is a three-dimensional hydrogen-bond network involving intermolecular N-H...O and O-H...O hydrogen bonds. Only O atoms function as H-atom acceptor sites.

A toyocamycin analogue with the sugar moiety in a syn conformation.

The title compound [systematic name: 4-amino-5-cyano-1-(beta-D-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine hemihydrate], C(12)H(13)N(5)O(4).0.5H(2)O, is a regioisomer of toyocamycin with the ribofuranosyl residue attached to the pyrimidine moiety of the heterocycle. This analogue exhibits a syn glycosylic bond conformation with a chi torsion angle of 57.51 (17) degrees. The ribofuranose moiety shows an envelope C2'-endo ((2)E) sugar conformation (S-type), with P = 161.6 (2) degrees and tau(m) = 41.3 (1) degrees. The conformation at the exocyclic C4'-C5' bond is +sc (gauche, gauche), with a gamma torsion angle of 54.4 (2) degrees. The crystal packing is stabilized by intermolecular O-H...O, N-H...N and O-H...N hydrogen bonds; water molecules, located on crystallographic twofold axes, participate in interactions. An intramolecular O-H...N hydrogen bond stabilizes the syn conformation of the nucleoside.

The N(1)-(2'-deoxyribofuranoside) of 3-iodo-5-nitroindole: a universal nucleoside forming nitro-iodo interactions.

The title compound [systematic name: 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3-iodo-5-nitro-1H-indole], C(13)H(13)IN(2)O(5), exhibits an anti glycosylic bond conformation with a chi torsion angle of -114.9 (3) degrees . The furanose moiety shows a twisted C2'-endo sugar pucker (S-type), with P = 141.3 degrees and tau(m) = 40.3 degrees . The orientation of the exocyclic C4'-C5' bond is +ap (gauche, trans), with a gamma torsion angle of 177.4 (2) degrees . The extended crystal structure is stabilized by hydrogen bonding and I...O contacts, as well as by stacking interactions. The O atoms of the nitro group act as acceptors, forming bifurcated hydrogen bonds within the ac plane. Additionally, the iodo substituent forms an interplanar contact with an O atom of the nitro group, and another contact with the O atom of the 5'-hydroxy group of the sugar moiety within the ac plane is observed. These contacts can be considered as the structure-determining factors for the molecular packing in the crystal structure.

A commonly used spin label: S-(2,2,5,5-tetramethyl-1-oxyl-delta3-pyrrolin-3-ylmethyl) methanethiosulfonate.

The title compound, C(10)H(18)NO(3)S(2), which finds application as a spin label, has triclinic (P\overline{1}) symmetry at 100 (2) K with two independent molecules in the asymmetric unit. Both molecules are very similar with respect to bond lengths and angles, but molecule 2 shows disordering of its side chain. The pyrroline rings differ slightly with respect to the position of the NO group, which in both cases are sterically shielded by the surrounding methyl groups. The crystal structure of the title compound represents the first example of a 2,2,5,5-tetramethyl-1-oxyl-Delta(3)-pyrroline derivative with a side chain at the double bond which is linked to it through an sp(3)-hybridized C atom. In the solid state, the side chain adopts a conformation with the methyl group above/below the pyrroline ring and a H atom directed towards a C atom of the double bond. The disordered side chain of molecule 2 represents a second conformation with low potential energy. Both molecules exhibit planar chirality, but in the solid state both pairs of stereoisomers are present. These four stereoisomers are stacked one behind the other in four different columns, denoted A, A', B and B', the angle between the vectors of the N-O bonds in columns A and B being 80.38 (8) degrees .

7-Deaza-2'-deoxyinosine: a nucleoside showing ambiguous base-pairing properties against the four canonical DNA constituents.

The title compound [systematic name: 7-(2-deoxy-beta-D-erythro-pentofuranosyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one], C(11)H(13)N(3)O(4), represents an acid-stable derivative of 2'-deoxyinosine. It exhibits an anti glycosylic bond conformation, with a chi torsion angle of 113.30 (15) degrees . The furanose moiety adopts an S-type sugar pucker (4)T(3), with P = 221.8 (1) degrees and tau(m) = 40.4 (1) degrees . The conformation at the exocyclic C4'-C5' bond of the furanose ring is ap (trans), with gamma = 167.14 (10) degrees . The extended structure forms a three-dimensional hydrogen-bond network involving O-H...O, N-H...O and C-H...O hydrogen bonds. The title compound forms an uncommon hydrogen bond between a CH group of the pyrrole system and the ring O atom of the sugar moiety of a neighbouring molecule.

7-Fluorotubercidin: a halogenated derivative of a naturally occurring nucleoside antimetabolite.

The title compound [systematic name: 4-amino-5-fluoro-7-(beta-D-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine], C(11)H(13)FN(4)O(4), exhibits an anti glycosylic bond conformation, with a chi torsion angle of -124.7 (3) degrees. The furanose moiety shows a twisted C2'-endo sugar pucker (S-type), with P = 169.8 (3) degrees and tau(m) = 38.7 (2) degrees. The orientation of the exocyclic C4'-C5' bond is +sc (gauche, gauche), with a gamma torsion angle of 59.3 (3) degrees. The nucleobases are stacked head-to-head. The extended crystal structure is a three-dimensional hydrogen-bond network involving O-H...O, O-H...N and N-H...O hydrogen bonds. The crystal structure of the title nucleoside demonstrates that the C-C bonds nearest the F atom of the pyrrole system are significantly shortened by the electronegative halogen atom.

O2,1'-anhydro-(beta-D-psicofuranosyl)thymine and 1-(1',4'-O-anhydro-beta-D-psicofuranosyl)thymine: the crystal structures versus the 1H NMR and ab initio data.

The crystal structures of the title compounds 1 and 2 have been determined. Relation between the stereochemistry of both nucleosides in the crystal state and the (1)H NMR data in solution as well as the ab initio calculations is discussed.