Contribution to the Protonation of a Calix[4]arene: DFT Calculated Structure of Protonated p-tert -Butylcalix[4]arenetetrakis( N , N -diethylacetamide)

By using DFT calculations, the most probable structure of the p-tert-butylcalix[4]arenetetrakis(N,N-diethylacetamide) · H₃O⁺ complex species was derived. In this complex, the hydroxonium ion H₃O⁺ is predominantly bound by strong hydrogen bonds to three phenoxy oxygens of the ligand and partly to the remaining phenoxy oxygen atom by two somewhat weaker hydrogen bonds. Besides, the H₃O⁺ cation is also bound to two carbonyl oxygens of the mentioned ligand by further two weaker hydrogen bonds.     

Calix[4]arene-Based Triple-Stranded Metallohelicate in Water

The title complex is a triple-stranded metallohelicate organized by the self-assembly of 5,17-difunctionalized calix[4]arenes and metal cations with octahedral coordination geometry. Due to hydrophilic triethylene glycol chains on the lower rim of the calix[4]arene, the metallohelicate can encapsulate cationic guests in water. NMR and UV-vis titration experiments reveal that the metallohelicate captures a pyridinium guest with an alanine derivative to form a host-guest complex with a host-guest ratio of 1 : 1. CD spectroscopy confirms the bias of the P- and M-helical sense of the metallohelicate by the captured guest. The metallohelicate captures two molecules of dicationic N,N’-dimethyl-DABCO and monocationic N-methyl quinuclidine, exhibiting a positive allosteric effect. ¹H NMR titration experiments indicate that the bound guests are in close proximately to the aromatic rings of the ligands. Molecular mechanics calculations based on the UV-vis and NMR observations suggest that the first guest preorganizes the conformation of the metallohelicate to facilitate access of the second guest to the cavity.     

Aminolysis reaction of calix [ 4 ] arene esters and crystal structures and conformational behaviors of calix[4]arene amides

We first make use of aminolysis of calix[4]arene esters to synthesize calix[4]arene amides. When the two ethyl esters of the calix[4]arene esters are aminolysized, the 1, 3-amide derivative is formed selectively. The crystal structures of the calix-[4]arene with two butyl amide (3b) and four butyl amide moieties (4b) were determined. The intermolecular hydrogen bonds make 4b form two-dimensional net work insolid state. The 1H NMR spectra prove that 3b is of a pinched cone conformation, while 4b and tetraheptylamide-calix[4]arene (6b) take fast interconversion between two C2v isomers in solution and appear an apparent cone conformation at room temperature. As decreasing temperature, the interconversion rate decreases gradually and, finally, the interconversion process is frozen at Tc = -10℃, which makes both conformations of 4b and 6b the pinched cone structures. The hydrogen bond improves the interconversion barrier, and the large different values of the potential barrier between 6b and 4b (or 6b) may     

Chiral Calix[3]pyrrole Derivatives: Synthesis,Racemization Kinetics,and Ring Expansion to Calix[9]- and Calix[12]pyrrole Analogues

Chiral pyrrolic macrocycles continue to attract interest. However, their molecular design remains challenging. Here, we report a calixpyrrole-based chiral macrocyclic system, calix[1]furan[1]pyrrole[1]thiophene ( 1 ), synthesized from an oligoketone. Macrocycle 1 adopts a partial cone conformation in the solid state, and undergoes racemization via ring inversion. Molecular dynamics simulations revealed that inversion of the thiophene is the rate determining step. Pyrrole N-methylation suppressed racemization and permitted chiral resolution. Enantioselective N-methylation also occurred in the presence of a chiral ammonium salt, although the stereoselectivity is modest. A unique feature of 1 is that it acts as a useful synthetic precursor to yield several calix[n]furan[n]pyrrole[n]thiophene products (n=2–4), including a calix[12]pyrrole analogue that to our knowledge constitutes the largest calix[n]pyrrole-like species to be structurally characterized.     

Calix

Chiral calix[4]arene derivatives with four O-(N-acetyl-PhgOMe), (1), (Phg denotes R-phenylglycine), or O-(N-acetyl-LeuOMe) (2) strands have been synthesised. Both compounds exist in chloroform in stable cone conformations with a noncovalently organised cavity at the lower rim that is formed by circular interstrand amidic hydrogen bonds. Such organisation affects both the selectivity and extraction/transport properties of 1 and 2 toward metal cations. Calix[4]arene derivatives with one OCH2COPhgOMe strand (3), two OCH2COPhgOMe strands (5) and with 1,3-OMe-2,4-(O-CH2COPhgOMe) substituents (4) at the lower rim have also been prepared. For 3, a conformation stabilised by a circular hydrogen-bond arrangement is found in chloroform, while 4 exists as a time-averaged C2 conformation with two intramolecular NH ...OCH3 hydrogen bonds. Compound 5 has a unique hydrogen-bonding motif in solution and in the solid state with two three-centred NH-.. O and two OH...O hydrogen bonds at the lower rim. This motif keeps 5 in the flattened cone conformation in chloroform. The X-ray structure analysis of 1 revealed a molecular structure with C2 symmetry; this structure is organised in infinite chains by intra- and intermolecular H bonds. The solid-state and solution structures of the [1-Na]ClO4 complex are identical, C4 symmetric cone conformations.     

Dimeric Capsules Formed by Tetra‐CMPO Derivatives of (Thia)Calix[4]arenes

Thiacalix[4]arene 2 , calix[4]arene 3 a and its tetraether fixed in the cone conformation 3 b form homo‐ and heterodimeric capsules in apolar solvents, which are held together by a seam of NH???O=P hydrogen bonds between carbamoylmethyl phospine oxide functions attached to their wide rim. Their internal volume of ～370 ų requires the inclusion of a suitable guest. Although neutral molecules such as adamantane (derivatives) or tetraethylammonium cations form kinetically stable complexes (¹H‐ and ³¹P‐time scale), the included solvent is rapidly exchanged. The internal mobility of the included tetraethylammonium cation is distinctly higher (ΔG=42.5 and 49.7 kJ mol^?1 for 3 a and 3 b ) than that for similar capsules of tetraurea calix[4]arenes 1 . Mixtures of 1 with 2 , 3 a , or 3 b contain only the two homodimers but the heterodimerization occurs with the tetraloop tetraurea 6 , which cannot form homodimers. Two dimers with cationic guests ( 2? (C₅H₅)₂Co⁺ ?2 and 3 a? Et₃NH⁺ ? H₂O ?3 a ) were confirmed by single‐crystal X‐ray analysis.     

Extended Calixpyrroles: meso-Substituted Calix[6]pyrroles

A 1,3,5- alternate conformation of the pyrrole rings is adopted by the calix[6]pyrrole 1 in the crystal (see picture). Compound 1 was synthesized in a two-step process and although it crystallizes in the form of the adduct 1 ⋅3CH₃COCH₃⋅H₂O⋅CHCl₃, there are no solvent molecules in the cavity (cross section ca. 60Ų) of this macrocycle which possesses alternating dimethyl and diphenyl substitutents at the meso positions.     

Synthesis and Solid-State Conformation of a Calix[8]arene 1,5-Diquinone Derivative

The first example of a calix[8]quinone derivative, hexamethoxy-p-tert-butylcalix[8]-1,5-diquinone 5, has been synthesized from p-tert-butylcalix[8]arene 1by exploiting a protection-deprotection procedure. The structure of the 5·toluene inclusion compound has been determined by a single crystal X-ray diffraction study. The calix[8]arene molecule possesses a crystallographic inversion centre and assumes a ‘pseudo-chair-like’ conformation, with two opposite 3/4-cone moieties, which resembles the previously reported chair-like conformation of p-tert-butylcalix[8]arene. The 4 toluene molecules per unit cell occupy interstitial voids and are released in the temperature range of 30–160 °C.This revised version was published online in July 2005 with a corrected issue number.     

5,11,17,23-Tetrakis[(p-carboxyphenyl)azo]-25,26,27,28-tetra-hydroxy Calix[4]arene: Crystal Structure and pH Sensing Properties

Treatment of 5,11,17,23‐tetrakis[(p‐carboxyphenyl)azo]‐25,26,27,28‐tetrahydroxy calix[4]arene ( 2 ) with HCl in DMF or NaOH in MeOH produced 5,11,17,23‐tetrakis[(p‐carboxyphenyl)azo]‐25,26,27,28‐tetrahydroxycalix[4]‐arene·4DMF (2·4DMF) and 5,11,17,23‐tetrakis[(p‐carboxyphenylsodium)azo]‐25,26,27,28‐tetrahydroxycalix[4]‐ arene ( 3 ), respectively, which were characterized by elemental analysis, IR, UV‐vis, ¹H NMR and ¹³C NMR. An X‐ray analysis of 2·4DMF revealed that its calix[4]arene core adopts a flattened cone conformation in which opposed phenyl groups take parallel or sharply inclined positions. The intra‐ and intermolecular hydrogen‐bonding interactions and the π···π interactions form a 2D hydrogen‐bonded wavelike network. Compound 2 had a unique reversible color change in a wide pH range from 1 to 13.5 and showed interesting pH sensing properties.     

Synthesis of New Calix[4]arenes Functionalizated by Acetylhydrazide Groups

A series of new calix[4]phenols, calix[4]resorcinols and calix[4]pyrogallols with acetylhydrazide substitutes has been␣synthesized with high yields by hydrazinolysis of ester group containing calix[4]arenes. The synthesized calix[4]phenols adopt the cone conformation while the calix[4]resorcinol and calix[4]pyrogallol derivatives prefer the boat conformation. The amide fragment of the hydrazide groups predominantly exists in the trans-conformation. The binding ability of synthesized calix[4]arenes toward transition and alkali metals by solvent extraction has been investigated.     

Calix[4]arenes with 1,2- and 1,3-upper rim tetrathiafulvalene bridges

Herein we report the synthesis of several calix[4]arene derivatives with tetrathiafulvalene bridges at the upper rim. Calix[4]arene-tetrathiafulvalene (TTF) conjugates 4a–d, fixed in cone conformation and comprising two smaller 1,2-bridges, were prepared by cyclisation of tetrakis-chloromethylated calix[4]arene 1 with 2,3-dithiolates of TTFs. Larger calix[4]arene-TTF macrocycles 14 and 15, also in cone conformation, contain 1,3-bridges and were synthesised by cyclisation of 2,6- and 2,7-dithiolates of TTFs with bis-bromomethylated calix[4]arene 7. Redox properties of new calix[4]arene-TTF conjugates were characterised using cyclic voltammetry.     

Cesium Complex of an Unsymmetrical Calix[4]crown-dibenzocrown-6

An unsymmetrical calix[4]-bis-crown ether having both conventional crown-6 and dibenzocrown-6 rings in a fixed 1,3-alternate conformation was synthesized with good yield by the reaction of a monocyclic calix[4]crown-6 with dibenzodimesylate in the presence of cesium carbonate. The cesium ion selectivity among alkali metal ions increased compared to symmetrical calix[4]-bis-crown-6. The solid state structureof the ligand-cesium complex illustrates a 1:2 complex ratio. On the contrary, insolution, e.g., extraction equilibrium and ¹H NMR experiment gave a 1:1 complex ratio. From the result of the chemical shift change upon metal ion complex, the cesium ion seems to prefer the dibenzocrown loop to the conventional crown-6 ring.     

Calix[4]Arenes in the partial cone conformation as ionophores in silver ion-selective electrodes

Two calix[4]arene derivatives, in the partial cone conformation, with sulfur-containing functionalities, were tested as neutral carrier ionophores in potentiometric silver-selective electrodes of conventional membrane and membrane-coated glassy carbon electrode types. Comparison with a calix[4]arene in the cone conformation was made. The membranes were prepared using either 2-nitrophenyl octyl ether or bis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p-chlorophenyl)borate as the lipophilic salt in a poly(vinyl chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec⁻¹) in the range 10⁻⁴–10⁻¹ M and excellent selectivity [log K_Ag,_MH+ < −1.5] of transition, alkali and heavy metal cations, including sodium, mercury(II) and lead(II) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(II) and lead (II) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix[4]arenes in the cone conformation.     

A,C-Bridged Calix[6]arene： Relationship between the Length of Bridge and Conformation

Three new A,C-diamide bridged p-tert-butylcalix[6]arenes were synthesized from p-tert-butylcalix[6]arenes by bridging ClCH2CONH(CH2)nNHCOCH2Cl(n=3,4,6) in acetonitrile using K2CO3 as a base in 17%-25% yields.It was found that the bridged calix[6]arenes with shorter bridges (n=2,3,4 in N′,N′-bischloroacetodiamines) adopt cone conformation, but the last one (n=6) adopts alternate conformation, i.e., accompanying the lengthening of bridge, the conformation of A,C-bridged calix[6]arenes changes from cone to alternate.     

杯[4]吡咯-阴离子体系相互作用的理论研究——杯[4]吡咯-卤素阴离子体系的密度泛函研究

用密度泛函B3LYP/LANL2DZ方法对自由杯[4]吡咯的最低能量构象和卤素阴离子-杯[4]吡咯复合物进行了计算研究.结果表明,杯[4]吡咯与卤素离子能通过彼此间的相互作用形成复合物,并且这种相互作用在本质上应为分子间的氢键相互作用;杯[4]吡咯与卤素阴离子形成的复合物在构型变化、电荷转移、前线轨道及其作用方式、成键布居以及能量和热力学参数等方面均按元素周期律有规律地变化,杯[4]吡咯与卤素阴离子间的相互作用沿元素周期依次减少.     

Vibrational spectra and structure of methyl-derivatives of imidazo[4,5-c]pyridine based on DFT quantum chemical calculations and XRD studies

The molecular structures, vibrational energy levels and potential energy distribution of 4-methyl-imidazo[4,5-c]pyridine (4MIPc) and 7-methyl-imidazo[4,5-c]pyridine (7MIPc) are derived from the quantum chemical calculations and compared to the experimental results obtained from the X-ray diffraction (XRD), IR and Raman studies. The B3LYP/6-311G(2d,2p) quantum model and PED contributions have been applied for the assignment of the vibrational modes. 4MIPc crystallizes in an orthorhombic structure, space group Pna2₁ and Z = 4 and 7MIPc crystallizes in a triclinic structure, space group P−1 and Z = 4. The almost planar conformation of the molecules and presence of the N–H?N hydrogen bonds formed with the pyridine and imidazole nitrogen atoms was found to be characteristic for the studied systems. The presence of hydrogen bonds is also confirmed by the results of IR studies.     

Synthesis of （p—Substituted phenyl）azo Calix[4] arenes

A novel method for the preparation of chromogenic calixarenes with azo groups was reported.p-Substituted(-NO2,-CH3,-Cl)amilines were diazotized with isoamyl nitrite in EtONa/EtOH under refluxing condition.Fifteen mono-,bis-,tris-and tetrakis(p-substituted phenyl)azo calix[4]arenes (including proximal and distal isomers) were obtainged respectively by diazo-coupling in different molar ratio to calix[4]arenes(1) under pH=7.5-9.0 in non-aqueous solution at 0-5℃.^1H NMR and ^13C NMR spectra of (p-substtituted phenyl)azo calix[4]-arenes indicated that they existed in cone conformation in solution.     

(5RS)‐6H‐Spiro[pyrazolo[1,5‐c]quinazoline‐5,4′‐thiochroman]: efficient synthesis under mild conditions,molecular structure and supramolecular assembly

Pyrazolo[1,5‐c]quinazolines are fused‐quinazoline derivatives which have been reported as potential agents against neurological disorders. The normal synthesis routes to these compounds require harsh reaction conditions, long reaction times or multistep sequences. The title compound, C₁₈H₁₅N₃S, has been prepared under very mild conditions by condensation of thiochroman‐4‐one with 5‐(2‐aminophenyl)‐1H‐pyrazole, which had itself been prepared by the reaction of hydrazine hydrate with 4‐hydroxyquinoline mediated by a brief period of microwave heating. Within the molecule in the crystal structure, the reduced pyrimidine ring adopts an envelope conformation, whereas the thiane ring adopts a half‐chair conformation. Molecules are linked into sheets by a combination of one N—H...S hydrogen bond and two independent C—H...π(arene) hydrogen bonds, which utilize the same aryl ring as the acceptor, with one C—H bond donating to each face of the ring. Comparisons are made with some related compounds.     

Synthesis and Molecular Structures of Tetrasilyl Ethers of Calix[4]arenes

The tetrasilyl ethers calix[4]areneOSiMe₂R (R = Me, H, vinyl, allyl) were prepared by salt elimination; the calix[4]arene was deprotonated with sodium hydride and subsequently reacted with chlorosilanes ClSiMe₂R. In general, DMF was chosen as solvent in order to steer the reactions in terms of a preference for the cone‐conformation of the products. In the case of calix[4]areneOSiMe₃ both, partial‐cone‐ and cone‐conformers, were synthesised. All products were characterised by NMR (¹H, ¹³C, ²⁹Si) spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction.     

Stereoselective Synthesis and Structure of New Types of Calix[4]resorcinarenes. Complexation of Tetrakis(O,O‐Phosphorus)Bridged‐Calix[4]resorcinarenes with Heavy Metal Atoms

The acid‐catalyzed (with HCl) condensation reactions of resorcinol ( 1 ) with 1‐naphthaldehyde ( 2 ) and isobutyraldehyde ( 3 ) furnished the tetrameric macrocyclic compounds 4 and 6 . Detailed NMR‐investigations of the acetylated tetrameric species 5 surprisingly support a structure not in agreement with the expected all‐cis conformation. The chair conformation (C_2h symmetry) of the acetylated derivative 5 was established through a crystal X‐ray diffraction study. The naphthyl substituents are arranged in trans position above and below the plane made up by the resorcinol units. The reaction of resorcinol 1 with isobutyraldehyde, in accord with expectation, led to the calix[4]resorcinaren ( 6 ). The ¹H NMR spectra of compound 6 and 7 appeared at room temperature as broad signals, indicating a conformation of C_2v symmetry. The reaction of the C‐methyl‐tetrakis‐P‐(chlorodioxaphosphocin)‐calix[4]resorcinarenes ( 8 ) and ( 10 ) with suitable N‐trimethylsilyl organic amines were conducted in tetrahydrofuran suspension, furnishing the P–N‐substituted calix[4]resorcinarenes ( 9 ) and ( 11 ). While in the complexation of C‐methyl‐tetrabromotetrakis‐P‐(dimethylaminodioxaphosphocin)‐calix[4]resorcinarene ( 13 ) with (tht)AuCl (tht = tetrahydrothiophene) the expected, neutral tetra‐substituted complex 15 was formed, the reaction of 13 with moist acetonitrile led to the anionic atomic framework 14 . X‐ray structure determinations of the complexes 14 and 15 show that both possess the cone conformation. In the gold complex 15 , the Au–Cl groups form a loose aggregate, with three Au…Cl contacts of 316–340 pm; one of the groups points towards the centre of the cone. The copper(I) complex 14 displays crystallographic mirror symmetry, with a central Cu₄Cl₅ unit involving tetrahedrally coordinated copper.