A color version of the Hinsberg test: permethylated cyclodextrin and crown-appended azophenol for highly selective sensing of amines

Azophenol dyes 1-5 having the permethylated cyclodextrin and/or crown moieties have been synthesized. Compounds 1 and 2 provide critical information for discrimination among 1°-3° amines by unique color changes. Addition of 1° and 2° amines to solutions of 1 or 2 in chloroform shifts the absorbance maximum of the initial solutions from 380 nm to ∼580 nm and ∼530 nm, respectively, but no change is observed with 3° amines. The high selectivity of 1 is mainly due to H-bonding between the ammonium H atoms of the amine and oxygen atoms of the crown-6. The selectivity of 1 possessing the β-cyclodextrin moiety toward amines was higher than that of 2 possessing the α-cyclodextrin moiety. On the other hand, chloroform solutions of 3 or 4, which lack the crown ether moiety, changed from yellow (380 nm) to pink (500 nm) with the addition of 1° and 2° amines, but with no selectivity. These results indicate that the crown unit in 1 or 2 plays an important role in discriminating among the types of amines.     

Self-assembly of amphiphiles with terthiophene and tripeptide segments into helical nanostructures

We previously reported a class of tripeptide amphiphiles known as peptide lipids that self-assemble into one-dimensional nanostructures with superhelical twisting. The pitch of this supramolecular twisting is controlled directly through sterics in the molecular structure of hydrophobic segments. In this work we study the supramolecular behavior of these nanoscale helices by substituting with a terthiophene conjugated segment of potential electronic interest and also through variations in the stereochemistry of the tripeptide. This terthiophene peptide lipid was shown to self-assemble into one-dimensional helical nanofibers with a regular diameter of 9±1 nm and helical pitch of 65±6 nm, and also found to form hierarchical double- and triple-stranded helices, which could be associated with terthiophene J-aggregate interactions among fibers. For stereochemical effects, we compared four diastereomers in the tripeptide sequence using l-glutamic acid and l- and d-alanine residues to probe their ability to control supramolecular organization. Interestingly, we found by atomic force microscopy that the LLD diastereomers formed cylindrical nanofibers without any twisting, whereas LDD diastereomeric segments self-assembled into helical nanofibers with a pitch of 40±6 nm. LDL diastereomeric segments formed, on the other hand, aggregates without any regular shape. We propose that these profound effects of chirality with amino acid sequence are related to changes in the β-sheet sub-structure within the nanofibers.     

Clockwise helical stacking of triphenylbenzene-based organogelator induced by peripheral chirality

We report on the synthesis and self-assembly of a new discotic organogelator based on π-conjugated triphenylbenzene with three peripheral chiral substituents. It is found that the introduction of chiral groups to the C₃-symmetric molecule led to a hexagonal columnar chiral stacking of the molecules in a clockwise direction in the organogel fibers. And the fluorescent emission of the gel decreased significantly compared to the monomer state at the same concentration, as a result of the aggregation of the nonplanar triphenylbenzene core in the gel phase.     

Double versus single helical structures of oligopyridine-dicarboxamide strands. Part 1: Effect of oligomer length

Oligoamides of 2,6-diaminopyridine and 2,6-pyridinedicarboxylic acid were previously shown to fold into single helical monomers and to hybridize into double helical dimers. A new series of these oligomers comprising 5 to 15 pyridine units, 4-decyloxy residues, and benzylcarbamate end groups were synthesized using a new convergent scheme that involves an early disymmetrization of the diamine and of the diacid. The hybridization of these compounds into double helices was studied by ¹H NMR spectroscopy in chloroform solutions at various temperatures. Somewhat unexpectedly, these studies revealed that dimerization increases with oligomer length up to a certain point, and then decreases down to undetectable levels for the longest strands. NMR studies show that both double helices and single helices become more stable when strand length increases. The measured values of enthalpy and entropy of hybridization for oligomers of various length show that the enthalpic gain constantly decreases with strand length. This can be interpreted as being the result of an increasing enthalpic price of the spring-like extension that the strand undergoes upon hybridization as its length increases. On the other hand, the entropic loss of hybridization also constantly decreases with strand length. Presumably, the helical preorganization of the monomers increases with strand length, which allows the longer strands to hybridize with a minimal loss of motional freedom, that is to say at a low entropic price. The competiton between these two factors results in a maximum of hybridization for the strands having an intermediate length.     

Recent advances in assemblies of cyclodextrins and amphiphiles: construction and regulation

Cyclodextrins (CDs) had been regarded as destructors in molecular assembly systems for a long time until CD/surfactants were found to assemble into high order structure driven by hydrogen bonding between CDs. Thereafter, intensive researches have been conducted on construction and regulation of CD–amphiphile systems. Here, we summarized the recent progress on construction and regulation of CDs and amphiphiles assembly. The scope of amphiphiles have been extended from surfactants (ionic surfactants, zwitterion surfactants, nonionic surfactants, gemini surfactant, and so on), to nontypical amphiphiles (amines, aromatic molecules, alkanes, and so on). Owing to the abundant choices of guest amphiphiles and dynamic nature of host–guest inclusive interaction, numerous regulation methods (such as enzyme, light, pH, concentration, temperature, and so on) have been used in CD–amphiphile systems. Moreover, remarks and future perspectives are also discussed at the end of this review, which is expected to stimulate progress on both mechanism and application level.     

Tartradiamide formation by thermolysis of tartaric acid with alkylamines

The formation of N,N′-dialkyltartramides by microwave-assisted reactions and by conventional thermolysis was investigated. Thus, the thermolysis of l-tartaric acid with n-hexylamine at 200 °C showed that all the possible stereoisomers of N,N′-dihexyltartramide were formed albeit with partial racemization only. The same was observed for the microwave-assisted reaction.     

磺化双酞菁钴自组装膜结构的表面增强拉曼光谱

采用自组装的方法构建了双核磺化酞菁钴轴向配位有序排列的膜层结构. 结合双核磺化酞菁钴分子体系自身所具有的性质及其和桥联分子四巯基吡啶之间相互作用的信息, 对其自组装膜的表面增强拉曼光谱进行了分析, 探讨了其自组装行为, 合理地解释了本自组装体系的膜层结构. 研究结果表明, 双核磺化酞菁钴分子(Bi-CoPc)在这种自组装膜中是以与基底平面存在一定夹角的倾斜的方式排列的.     

Self-assembly of different single-chain bolaphospholipids and their miscibility with phospholipids or classical amphiphiles

A variety of bolalipids with a single long alkyl chain and two identical headgroups self-assemble in aqueous solutions into helical entangled nanofibers leading to the formation of a hydrogel. An increase in temperature usually leads to the break-up of the fiber structure into micellar aggregates. In this paper the question is addressed whether bolalipids of different lengths or different headgroup structures can form mixed fibers. Also, the stability of the fiber aggregation of bolalipids in mixtures with phospholipids forming lamellar bilayers is discussed. Here, the question whether single-chain bolalipids can be incorporated into phospholipid bilayers to stabilize bilayer membranes is important, as possibly lipid vesicles used for drug delivery can be improved. Finally, the stability of the fiber aggregate against solubilisation by common surfactants was studied. The paper addresses the question which type of aggregate structure dominates the self-assembly of bipolar and monopolar amphiphiles in aqueous suspension.     

A novel dinuclear double-stranded helical complexes of bis(terdentate) N4O2 donor ligand with silver(I) and zinc(II) d metal ions

Reaction of the hexadentate N₄O₂-donor ligand 6,6′-bis(3-hydrazonobutan-2-one)-2,2′-bipyridine (L) with Ag^(I) and Zn^(II) affords a dinuclear double stranded helicate species [Ag₂L₂]²⁺ (1a) and [Zn₂L₂]²⁺ (1b), in which partitioning of the ligand into two bis-tridentate pyridyl-ketoimine chelating units allow each ligand to bridge both metal centres. X-ray crystallography, ESI-MS and UV–Vis spectrophotometric titration experiments reveal that the complex (1a) retains its solid-state structure in solution. The crystal structure of (1a) provides the first example of dinuclear silver(I) complex in which both of the metal centres can be approximated as a seven coordinate distorted mono-capped trigonal prism in which the Ag?Ag close contact of 3.034(4) Å is taken into account and forms the cap. The counter-ions do not interact with metal centres but hydrogen bond to N–H protons of the hydrazonic arms from the separate strands. The adjacent helical units are cross-linked together via NH?O_keto hydrogen bonding to maintain the supramolecular structure.     

Hydrothermal synthesis of two copper helical coordination polymers with acentric three-dimensional framework constructing from mixed pyridine carboxylates

Two copper helical coordination polymers, [Cu(2-pc)(3-pc)]_n1 and [Cu(2-pc)(4-pc)]_n2 (2-pc=2-pyridine carboxylate, 3-pc=3-pyridine carboxylate, 4-pc=4-pyridine carboxylate) have been hydrothermally synthesized directly from pyridine carboxylic acids and copper nitrate. The crystal structure were determined by single-crystal X-ray diffraction with the following data: compound 1, orthorhombic, P2₁2₁2₁, a=6.591(3) Å, b=8.692(5) Å, c=20.548(9) Å, V=1177.2(9) Å³, Z=4; compound 2, orthorhombic, Pna2₁, a=21.160(10) Å, b=9.095(5) Å, c=6.401(3) Å, V=1231.9(11) Å³, Z=4. The acentric three-dimensional (3D) framework of 1 is constructed from right-handed helical Cu(2-pc) chains and left-handed Cu(3-pc) helices. As for 2, Cu(2-pc) helical chains, in which left- and right-handed helices are coexisting, and Cu(4-pc) zigzag chains combined together to form acentric 3D architecture of 2 as well. Additionally, besides general spectral characterization, we first introduce generalized 2D correlation spectroscopy to explore the coordination polymers and ascertain the stretching vibration location of carboxylate groups of compounds 1 and 2.     

Synthesis and Structural Analysis of a Helical Coordination Polymer Formed by the Self-Assembly of a 2,2′-Bipyridine-Based exo-Ditopic Macrocyclic Ligand and Silver Cations

The overall topology of coordination polymers can be controlled by means of the coordination preferences of the metal center and the structure of the bridging ligand. This is demonstrated here by the synthesis of a single-stranded helical coordination polymer by the self-assembly of the exo-ditopic ligand 1 and silver ions.     

Tuning the helical twisting power of nematic liquid crystals induced by chiral 1, 2-propanediol derivatives using varied substituents

In this study,a novel series of chiral 1,2-propanediol derivatives with different electron-donating and electron-withdrawing groups were synthesized and characterized by FT-IR and ~1H NMR.The helical twisting properties of all the chiral dopants were investigated by doping the chiral dopants into a nematic liquid crystal host(SLC-1717).The results indicate that the donor-acceptor electron effect have a prominent influence on helical twisting property of the chiral nematic phase induced by the chiral dopants. Introducing electron-withdrawing groups into the terminal ends of chiral 1,2-propanediol can decrease the absolute values of the helical twisting power.In addition,the helix inversion temperatures of the induced chiral nematic phase are variational with the change of terminal groups.     

Syntheses,structures, and fluorescent properties of two helical complexes based on a long rigid N-heterocyclic ligand

A long N-heterocyclic ligand, 2,6-bis(3-(pyrid-3-yl)-1,2,4-triazolyl)pyridine (H₂bptp), and Zn(II)/Pb(II) yield {[Zn(bptp)(H₂O)]?·?2H₂O·CH₃CN} _n (1) and {[Pb(bptp)]?·?H₂O} _n (2). Single-crystal X-ray diffraction analysis reveals that 1 and 2 possess 2-D networks containing alternating left- and right-handed helical motifs. Topologically, 1 features a (4,4) topology, while 2 exhibits a (6,3) topology. The bptp^2? in 1 and 2 adopts syn-anti and syn-syn conformations, respectively. The results indicate that the long rigid N-heterocyclic ligand can adopt different conformations to coordinate with metals, beneficial to construction of helical structures with diverse topologies. The difference between the photoluminescence properties of the two complexes reveals that metal ions and coordination environment have significant influences on photoluminescence behavior.     

Synthesis, structure, and magnetic properties of two 1-D helical coordination polymeric Cu(II) complexes

Two helical coordination polymeric copper(II) complexes bearing amino acid Schiff bases HL or HL′, which are condensed from 2-hydroxy-1-naphthaldehyde with 2-aminobenzoic acid or l-valine, respectively, have been prepared and characterised by X-ray crystallography. In [CuL]_n (1) the copper(II) atoms are bridged by syn-anti carboxylate groups giving infinite 1-D right-handed helical chains which are further connected by weak C-H?Cu interactions to build a 2-D network. While in [CuL′]_n (2) the carboxylate group acts as a rare monatomic bridge to connect the adjacent copper(II) atoms leading to the formation of a left-handed helical chain. Magnetic susceptibility measurements indicate that 1 exhibits weak ferromagnetic interactions whereas an antiferromagnetic coupling is established for 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data.     

Synthesis of helical [2.2]paracyclophanes containing carbocyclic and heterocyclic five-membered rings

The preparation of a [2.2]indenoparacyclophane-based diene is described. Diels-Alder cycloadditions of this diene with N-methylmaleimide, N-phenylmaleimide and maleic anhydride occurred in good yields and anti-diastereoselectively only under high pressure conditions. Heterohelicenophanes were prepared by dehydrogenation of the Diels-Alder products with 10% Pd/C catalyst. A new helicenophanequinone was obtained by the reaction between the diene and 1,4-naphthoquinone.     

Preparation and characterizations of helical mesoporous silica nanorods using CTAB and alcohols

Helical mesoporous silica nanorods were prepared using cetyltrimethylamrnonium bromide and achiral alcohols as the co-structure-directing agents.They were characterized using field-emission scanning electron microscopy,transmission electron microscopy,nitrogen sorptions,and small angle X-ray diffraction.The length of the silica nanorods increases with increasing the length of the alcohols.When n-heptanol and n-octanol were used,helical mesoporous silica nanorods with lamellar mesopores on the surfaces were obtained.     

Micelle formation induced by photo-Claisen rearrangement of poly(4-allyloxystyrene)-block-polystyrene

A novel micelle formation induced by the photo-Claisen rearrangement was attained using a poly(4-allyloxystyrene)-block-polystyrene (PASt-b-PSt) diblock copolymer. The photoreaction was performed in cyclohexane at room temperature without a catalyst. The conversion of the 4-allyloxystyrene units reached 90% by irradiation for 24 h. The photo-Claisen rearrangement of PASt-b-PSt into poly(3-allyl-4-hydroxystyrene)-block-PSt quantitatively proceeded up to a 20% conversion; however, the elimination of the allyl groups competitively occurred over the 20% conversion. The degrees of the photorearrangement and elimination showed good agreement in their material balance throughout the course of the reaction. Both of the photorearrangement and elimination finally reached ca. 50% degrees over 60% conversion. The light-scattering studies demonstrated that the PASt-b-PSt copolymer with a 36-nm hydrodynamic diameter as unimers formed micelles with a 98-nm diameter by irradiation.     

硫堇衍生化自组装膜修饰金电极的电化学性质及其对抗坏血酸的电催化氧化

将硫堇共价键合到自组装在金电极表面的半胱胺单分子层上,制成了衍生化自组装单分子膜修饰电极,并用电化学方法研究了它的电化学性质.循环伏安图显示其在pH＝7.7的磷酸盐缓冲液中,于－0.45～＋0.50V(vs.SCE)范围内有2对氧化还原峰.峰电位分别为E_pa¹＝214mV。E_pc¹＝82mV,E_pa2＝－75mV,E_pc2＝－160mV(vs.SCE).pH在5.0～9.0范围内,峰1有2个质子参与反应,峰2有1个质子参与反应.它的表面电子转移速率常数k_s＝0.02S^－1.此膜对抗坏血酸的氧化有催化作用,其氧化过电位较在裸金电极上降低了约250mV.催化电流与抗坏血酸的浓度在1.0×10^-6～4.0×10^-3mol/L范围内呈良好的线性关系.抗坏血酸催化氧化的异相速率常数为2.68×10^-3cm/s.