Crown Unit Research Articles

Engineering highly efficient Li+ responsive nanochannels via host–guest interaction and photochemistry regulation

Artificial nanochannels have seen great progress in energy storage, molecular filters, nanofluidic diodes, and biosensors. Precisely recognizing and transporting molecules or ions underpin the basis of artificial nanochannels. Here, we report highly efficient Li+ responsive nanochannels by design of functionalized porous anodic aluminum oxide (AAO) membranes. The 12-crown-4 unit was tethered to the synthesized spiropyran molecule, creating a smart Li+ responsive element, photochromic crowned spiropyran (CE-SP). The crown unit can specifically bind with Li+ while exempting the harassment of other metallic cations; and importantly, the spiropyran moiety possesses reversible photochemistry response, adding the flexibility to regulate ion transport behaviors. Upon the ultraviolet light stimulus, hydrophobic CE-SP molecules transform to positively charged crowned merocyanine (CE-MC), which can further convert to oxygen-negative ions in weak alkaline environment, thereby forming O--Li+ interaction. Such structural evolutions enable to deftly tune the surface charge and wettability of the nanochannels, and thus ingeniously manipulate Li+ recognition profiled by ionic current signal. Moreover, electrically-driven release of the captured Li+ can be realized in an amiable condition, showing controllable capture-to-release ability. Finite element simulation unveils the fundamental mechanisms of ion transport pertaining to Li+ recognition events in the nanoconfinement. This work thus paves a way to construct high-performance Li+-selective nanodevice, and holds promise for Li+-related electrochemistry energy research.

Structural Geology and Volcanism in Hululais Geothermal Area, Bengkulu, Indonesia

Hululais Prospect in Rejang Lebong, Bengkulu is one of the geothermal fields developed by Pertamina Geothermal Energy. The field is situated within the Bukit Barisan Mountain Range, an NW-SE volcanic arc of Sumatra, and located 8 km western from Musi Segment of Sumatra Fault Zone Zone. Based on field data from geological mapping, remote sensing analyses and borehole data these regional structures influence the occurrence of the NW-SE volcanic axis in Hululais Volcanic Complex (HVC). The Hululais Volcanic Complex (HVC) itself is a Quaternary volcanic complex which comprised of six crown units namely: (Bukit Resam, Suban Agung, Bukit Beriti, Bukit Gedang, Bukit Lumut and Bukit Pabuar) with its associated Hummocks and primary/secondary deposits. These NW-SE distributed of Subang Agung, Bukit Beriti and Bukit Gedang volcanic crowns can be grouped as Hululais Brigade. The manifestations distribution in Hululais also depict the influence of the NW-SE geological structure and its volcanic activity. This is validated by the presence of geothermal manifestation such as fumarole in the central of Hululais Volcanic Complex and hot spring in the medial – distal part of the field.

Survival and success rates of soft-milled cobalt-chromium-ceramic full-arch screw-retained implant-supported prostheses: a 2- to 7-year follow-up retrospective study.

To retrospectively assess implant and prosthesis survival and success and patient satisfaction in edentulous patients treated with soft-milled cobalt-chromium-ceramic full-arch screw-retained implant-supported prostheses (SCCSIPs) over a mean clinical follow-up period of 4years. Twenty-one edentulous patients, aged 47-80years, underwent restoration with 27 SCCSIPs (210 implants, 349 crown units). After definitive prosthesis insertion, patients participated in a yearly dental check-up recall program, including clinical and radiographic examinations. All supporting implants were examined for biological and technical complications, and the restorations were evaluated using modified California Dental Association (CDA) criteria. Life table and Kaplan-Meier survival analyses were performed. Patient satisfaction regarding chewing, esthetics, comfort, and phonetics was evaluated using a visual analog scale (VAS). After a mean of 4years, two implants (3.8%) failed, with no effect on prosthesis survival. The cumulative survival rate was 98.6% and 100% for implants and prostheses, respectively. The most frequent minor biological complication was soft tissue recession (11%). Porcelain fracture was the only major technical complication (0.6% of crown units), while the only minor technical complication was porcelain chipping (4% of crown units), which required only polishing. Overall, 66.7% of the prostheses were free of technical complications. Patient satisfaction was high to very high. Less satisfaction was noted with comfort due to soft tissue recession and food impaction. Within the limitations of this study, we conclude that the survival and success rates of SCCSIPs in edentulous patients were excellent. SCCSIPs should be considered when planning metal-ceramic implant-supported restorations.

Complexation and Separation of Trivalent Actinides and Lanthanides by a Novel DGA Derived from Macrocyclic Crown Ether: Synthesis, Extraction, and Spectroscopic and Density Functional Theory Studies.

A DGA-arm-grafted macrocyclic aza-crown ether ligand (Cr6DGA) was synthesized, and its solvent extraction behavior toward trivalent americium and europium in nitric acid medium was studied. The effects of various parameters such as the contact time, temperature, concentration of the extractant, and acidity on the extraction by Cr6DGA were investigated. It was found that in 3 mol/L HNO3, the SFEu/Am value was about 2. The complexation energies calculated by DFT showed that the Eu(III) complexes were more stable than the corresponding Am(III) complexes in gas, aqueous, and organic phases. Furthermore, the coordination study showed that the metal/ligand ratio of the extracted species was 1:2 by mass spectrometry (MS) analysis. The time-resolved laser-induced fluorescence spectra (TRLFS) further proved that the extracted species contained one water molecule, and so the composition of the extracted complexes may be [EuL2NO3(H2O)]2+ or [EuL2(NO3)2(H2O)]+. Finally, DFT calculations revealed that [EuL2(NO3)2(H2O)]+ is a more stable species and the binding energy of Eu(III) with the DGA unit is lower than that with the crown unit.

Buckyball-Based Spherical Display of Crown Ethers for De Novo Custom Design of Ion Transport Selectivity.

Searching for membrane-active synthetic analogues that are structurally simple yet functionally comparable to natural channel proteins has been of central research interest in the past four decades, yet custom design of the ion transport selectivity still remains a grand challenge. Here we report on a suite of buckyball-based molecular balls (MBs), enabling transmembrane ion transport selectivity to be custom designable. The modularly tunable MBm-Cn (m = 4-7; n = 6-12) structures consist of a C60-fullerene core, flexible alkyl linkers Cn (i.e., C6 for n-C6H12 group), and peripherally aligned benzo-3m-crown-m ethers (i.e., m = 4 for benzo-12-crown-4) as ion-transporting units. Screening a matrix of 16 such MBs, combinatorially derived from four different crown units and four different Cn linkers, intriguingly revealed that their transport selectivity well resembles the intrinsic ion binding affinity of the respective benzo-crown units present, making custom design of the transport selectivity possible. Specifically, MB4s, containing benzo-12-crown-4 units, all are Li+-selective in transmembrane ion transport, with the most active MB4-C10 exhibiting an EC50(Li+) value of 0.13 μM (corresponding to 0.13 mol % of the lipid present) while excluding all other monovalent alkali-metal ions. Likewise, the most Na+ selective MB5-C8 and K+ selective MB6-C8 demonstrate high Na+/K+ and K+/Na+ selectivity values of 13.7 and 7.8, respectively. For selectivity to Rb+ and Cs+ ions, the most active MB7-C8 displays exceptionally high transport efficiencies, with an EC50(Rb+) value of 105 nM (0.11 mol %) and an EC50(Cs+) value of 77 nM (0.079 mol %).

Molecular Tetrahedrons as Selective and Efficient Ion Transporters via a Two-Station Swing-Relay Mechanism

The traditional approach to utilizing an ion-relay mechanism for ion transport requires three or more ion-relay stations. Herein, we describe a novel strategy, incorporating a swing action to reali...

5,31-Diaza-2,8,15,18,21,28,34,41,44,47-decaoxaheptacyclo[46.4.0.04,32.06,30.09,14.022,27.035,40]dopentaconta-1(48),4,6(30),9(14),10,12,22(27),23,25,31,35(40),36,38,49,51-pentadecaene monohydrate

In the title compound, C40H40N2O10·H2O, each dual 17-crown-5 unit crystallizes with one solvent water molecule. The crown units are connected by a pyrazine ring. One oxo group in a crown moiety is disordered over two sites, with a refined occupancy ratio close to 1:1. The water molecule is linked to the crown unit by bifurcated O—H...O hydrogen bonds. In the crystal, molecules are linked by weak C—H...N and C—H...O interactions for the packing.

Crown morphology of the mandibular first molars with distolingual roots

Background/purposeMost mandibular first molars have two roots. A major common variation of this tooth is the presence of a distolingual root, which is a common Mongoloid trait in certain populations. The aim of this article was to examine crown morphology in relation to the presence of the distolingual root. Materials and methodsUsing dental casts, the crown morphology of 141 mandibular first molars from 71 Taiwanese individuals was analyzed. Periapical radiographs were used to detect distolingual roots. The length and width of the crowns and the crown units (i.e., trigonid and talonid) were measured. Ten intercuspal distances and five cusp angles were examined. ResultsThe buccolingual dimension of the crown and its ratio to the mesiodistal dimension were significantly increased in molars with a distolingual root, compared to molars without a distolingual root. Mesiodistal crown dimensions were similar; however, the crown unit dimensions were different: molars with a distolingual root had a shorter mesiodistal trigonid dimension but a longer talonid dimension, compared to molars without a distolingual root. The intercuspal distances from the three buccal cusps to the distolingual cusp were significantly longer, however, the distance between the mesiobuccal cusp and mesiolingual cusp was significantly shorter in teeth with a distolingual root than in teeth without a distolingual root. A significantly wider mesiolingual angle and narrower distolingual angle were observed in molars with a distolingual root, compared to molars without a distolingual root. ConclusionThe presence of a distolingual root significantly increased the buccolingual dimension of the crown and the location of distolingual cusp is significantly closer to the lingual side.

2,8,15,18,21,24,31,37,44,47,50,53-Dodeca-oxahepta-cyclo-[52.4.0.0(4,35).0(6,33).0(9,14).0(25,30).0(38,43)]octa-penta-conta-1(54),4,6(33),9(14),10,12,25(30),26,28,34,38(43),39,41,55,57-penta-deca-ene di-chloro-methane disolvate.

In the title compound, C46H50O12·2CH2Cl2, each dual 20-crown-6 unit crystallizes with two di­chloro­methane solvent mol­ecules. The crown unit mol­ecule lies about an inversion centre located at the central benzene ring. The two crown ring groups adopt an anti conformation, stabilized by weak intra­molecular C—H⋯O inter­actions. In the crystal, the crown unit mol­ecules and the solvent mol­ecules are linked by C—H⋯O inter­actions into a three-dimensional network.

A Taco Complex Derived from a Bis-Crown Ether Capable of Executing Molecular Logic Operation through Reversible Complexation

As learned from natural systems, self-assembly and self-sorting help in interconnecting different molecular logic gates and thus achieve high-level logic functions. In this context, demonstration of important logic operations using changes in optical responses due to the formation of molecular assemblies is even more desirable for the construction of a molecular computer. Synthesis of an appropriate divalent as well as a luminescent crown ether based host 1 and paraquat derivatives, 2(PF(6))(2) and 3(PF(6))(2), as guests helped in demonstrating a reversible [3](taco complex) (1·{2(PF(6))(2)}(2) or 1·{3(PF(6))(2)}(2)) formation in nonpolar solvent. Detailed (1)H NMR studies revealed that two paraquat units were bound cooperatively by the two crown units in 1. Because of preorganization, the flexible host molecule 1 adopts a folded conformation, where each of two paraquat units remain sandwiched between the two aromatic units of each folded crown ether moiety in 1. Disassembly of the "taco" complex in the presence of KPF(6) and reassembly on subsequent addition of DB18C6 was initially demonstrated by (1)H NMR spectral studies, which were subsequently corroborated through luminescence spectral studies. Further, luminescence spectral responses as output signals with appropriate and two independent molecular inputs could be correlated to demonstrate basic logic operation like OR and YES gates, while the results of the three molecular inputs could be utilized to demonstrate important logic operation like an INHIBIT gate.

6,7-Bis(bromo-meth-yl)-2,11,18,21,24,27-hexa-oxatetra-cyclo-[26.4.0.0.0]dotriaconta-1(28),4,6,8,12(17),13,15,29,31-nona-ene dichloro-methane monosolvate.

The title 20-crown-6 unit, C28H30Br2O6·CH2Cl2, consisting of three benzo groups and triethyl­ene glycol was prepared from the reaction of 1,2,4,5-tetra­kis­(bromo­meth­yl)benzene and bis­phenol in the presence of sodium hydride. In the crystal, one O atom of the central ethyl­ene glycol in the triethyl­ene glycol unit exhibits an exo conformation as a result of intra­molecular C—H⋯O hydrogen bonds. The crown unit and the solvent mol­ecule are linked by weak C—H⋯O hydrogen bonds.

Resorcinarene Bis-Thiacrowns: Prospective Host Molecules for Silver Encapsulation

Mixed-donor atom tetramethoxy resorcinarene bis-thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X-ray crystallography. It was found that the resorcinarene bis-thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host-guest complexes in solution. The solid state structures also revealed that the bis-thiacrowns form silver complexes in an unanticipated endo- and exo-cavity fashion within the same host molecule. Both the solution and solid state studies indicated the sulfur atoms to be the major contributing donor atoms in forming the binding interactions with silver cations.

Tweezer‐like Complexes of Crown Ethers with Divalent Metals: Probing Cation‐Size‐Dependent Conformations by Vibrational Spectroscopy in the Gas Phase

AbstractCrown ethers constitute central building blocks for the synthesis of molecular tweezers capable of trapping cationic species. In this study, isolated ternary complexes comprising two [18]crown‐6 (18c6) ether molecules and one divalent cation of varying size (Cu2+, Ca2+, Ba2+) are investigated by means of laser vibrational action spectroscopy and computations. In the ternary (18c6)2–Cu2+ complex, one of the crown units folds tightly around the cation, while the second crown ether unit binds peripherally. Such asymmetrical binding manifests itself as a bimodal splitting of the vibrational bands measured for the complex. The size of the cation in the Ca2+ and Ba2+ complexes leads to a progressively more symmetrical coordination of the two crown ether molecules with the metal. In particular, in the spectrum of the (18c6)2–Ba2+ complex, the two components of the vibrational bands are merged into single‐maximum envelopes. This is consistent with a C2 arrangement predicted by the computation, in which the cation coordinates with the two crown ether units in a fully symmetrical way.

Different metal-ion-induced dimeric self-assembling cavities based on thiacalix[4]benzocrown-4 isomers

To construct the self-assembly of metal-ion-induced well-ordered architectures based on calixcrowns, isomeric thiacalix[4]benzocrowns-4 1 and 2 with rigid and small crown units were employed as the new scaffolds. They all show remarkable selectivity for Ag(+) and their complexation ability towards Ag(+) results in two novel dimeric aggregates of calixcrowns, which were first evidenced by ESI-MS, (1)H and DOSY-NMR spectra. Ultimately, X-ray diffraction experiments confirmed unambiguously the existence of the two metal-ion-induced dimers in lower rim/lower rim mode, and showed that dimerization of calixcrown 1 or 2 in the presence of Ag(+) could form dimeric supramolecular cavity with a small inner room. Moreover, the positional isomerism of their crown units (o-benzocrown unit for ligand 1 and m-benzocrown unit for 2) led to a dramatic change in the configuration of the two dimeric cavities 1·Ag(+) and 2·Ag(+). For dimeric cavity 1·Ag(+), two silver centers seamed two thiacalix[4]crown molecules together and resided at the edge of the dimeric self-assembling cavity; for dimeric cavity 2·Ag(+), one Ag(+) stitched two thiacalixcrowns together and was encapsulated in the center of the self-assembling cavity, while the other Ag(+) is tied down to one end of the dimer. Consequently, as a result of the different construction of dimeric cavities 1·Ag(+) and 2·Ag(+) the extended structures of the complexes are also different. The neighbour self-assembling cavities 1·Ag(+) are mutually oriented side-by-side and form a 1-D rectilineal polymeric chain. While, the neighbour self-assembling cavities 2·Ag(+) arrange themselves in a typical head-to-tail fashion to form a zig-zag polymeric chain.

Helical Nanostructures of an Optically Active Metal‐Free Porphyrin with Four Optically Active Binaphthyl Moieties: Effect of Metal–Ligand Coordination on the Morphology

AbstractAn optically active metal‐free porphyrin (1) with four chiral binaphthyl units attached at the meso‐phenyl substituents through crown ether moieties has been designed, synthesized, and characterized. Its self‐assembly behavior in the absence and presence of K+ was comparatively investigated by electronic absorption and circular dichroism (CD) spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atom force microscopy (AFM), and energy‐dispersive X‐ray (EDX) spectroscopy. In the absence of K+, metal‐free porphyrin self‐assembles into nanoparticles depending mainly on the van der Waals interaction among neighboring metal‐free molecules. In the presence of K+, additionally formed metal–ligand K–Ocrown coordination bonds between K+ and crown units of (R)‐ and (S)‐1 molecules, together with chiral discrimination of chiral side chains and intermolecular van der Waals interactions, induce a right‐handed and left‐handed helical arrangement in a stack of (R)‐ and (S)‐1 molecules, respectively, with an ordered “head‐to‐tail” internal molecular arrangement. This then further hierarchically self‐assembles into highly ordered fibrous nanostructures with a helicity opposite to that of the original porphyrin stack. This clearly reveals the effect of the metal–ligand coordination bonding interaction on the morphology and handedness of self‐assembled nanostructures.

A linear regression method for tree canopy height estimation using airborne lidar data

Tree canopy height is one of the most fundamental measurements in forest inventory and is a critical variable in the quantitative assessment of tree (or stand) volume, forest biomass, carbon stocks, growth, and site productivity. In this study, we analyzed two traditional methods for tree canopy height estimation and designed a new linear regression method for improved tree canopy height estimation using airborne light detection and ranging (lidar) data. Examples of two typical crown shapes were used, and theoretical analysis was performed on simulated datasets with varying crown shape, unit penetrability, and laser-missed canopy layer(s). The final result derived from the simulated lidar data illustrates that the linear regression method can improve canopy height estimation. This method was also applied to lidar data covering a tall pine forest in Idaho, USA. An average error of 0.51 m was obtained from a comparison of the lidar-derived tree canopy heights and 79 field measurements. This error was also compared with the estimation error resulting from the use of two traditional methods. Results indicate our method produced more accurate tree canopy height estimates, with a mean error and root mean square error (RMSE) ranging between 25% and 50% lower than those from the two traditional methods.

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.

Crown Ethers as Building Blocks for Carbohydrate Receptors

Acyclic receptors containing neutral hydrogen bonding sites, such as amino-pyridine groups and a crown unit, perform effective recognition of neutral sugar molecules through multiple interactions. Receptor 1 has been shown to be a particularly effective and highly selective receptor for beta-glucopyranoside.

Size relationships among permanent mandibular molars in Aboriginal Australians and Papua New Guinea Highlanders

Size relationships among crown units of permanent mandibular molars were investigated in two Sahul-Pacific samples: Aboriginal Australians (Yuendumu) and Papua New Guinea Highlanders (Wabag). Measurements of first, second, and third molars (M1, M2, and M3), including overall mesiodistal and buccolingual diameters as well as the mesiodistal and buccolingual diameters of the trigonid and talonid, were obtained from dental casts using a sliding caliper. Molar reduction was noted in talonid dimensions within both samples, but the trigonid mesiodistal diameter was not reduced in M2 or M3 compared with M1, indicating that the later-developing crown unit (talonid) was more reduced than the early-developing unit (trigonid). M2 was most reduced in size mesiodistally of the three molars, but its buccolingual diameter was not reduced. M3 was the most reduced tooth in trigonid buccolingual diameter. The percentage sexual dimorphism values were greater for the size of the talonid than for the trigonid, indicating that male values exceeded those for females by a greater amount in the later-developing crown unit. Crown dimensions were larger generally in the Aboriginal Australians from Yuendumu than in the Papua New Guinea Highlanders from Wabag, with differences being more evident in M2 and M3 than M1, especially in talonid dimensions. The trigonid, which develops early both phylogenetically and ontogenetically, tended to be relatively stable in size, whereas the later-forming talonid displayed size reduction when comparisons were made both within and between groups.

Sexual dimorphism in crown units of mandibular deciduous and permanent molars in Australian Aborigines

Sexual differences in the crown units of mandibular molars were investigated in Australian Aborigines. The first and second deciduous molars (dm1 and dm2), and first to third permanent molars (M1, M2 and M3) were measured on dental casts using a sliding caliper. Measurements of tooth crowns included overall mesiodistal and buccolingual diameters, as well as the mesiodistal and buccolingual diameters of the trigonid and talonid. Percentage dimorphism values were greater in the talonid dimensions than the trigonid, indicating that sex differences tend to be larger in the later-developing crown units. Sex differences in mesiodistal diameters increased from dm1 to M2 but decreased for M3, the tooth that showed the least dimorphism of all the molars. This result seems to be due to the marked variability in size of the M3 between individuals.