Planar Geometry (planar + geometry)

Distribution by Scientific Domains


Selected Abstracts


Drawing Lithography: Three-Dimensional Fabrication of an Ultrahigh-Aspect-Ratio Microneedle

ADVANCED MATERIALS, Issue 4 2010
Kwang Lee
Drawing lithography is a novel fabrication technique in which a thermosetting polymer is directly drawn from a two-dimensional solid surface without the need for a mask and light irradiation (see figure). Drawing lithography differs from traditional lithography techniques, such as photolithography, in that it is based on the inherently planar geometries of a two-dimensional substrate in a three-dimensional microstructure. [source]


Experimental and modeling analysis of diffusive release from single-shell microcapsules

AICHE JOURNAL, Issue 11 2009
Enrique Muoz Tavera
Abstract There is much experimental and mathematical work that describes chemical transport from multilayered films of planar geometries. There is less so, however, for chemical transport from multilayered spheres, a common structure for controlled-release materials. Based on the Sturm,Liouville approach of Ramkrishna and Amundson (1974), explicit analytical solutions for the concentration profiles and release kinetics from spherical capsules are presented. Fluorescent dye-release studies using single-shelled microspheres called nanoparticle-assembled capsules were performed to validate the model for uniformly and nonuniformly sized capsules. The combined experiment-modeling approach allows optical microscopy images and release measurements to be readily analyzed for estimating diffusion coefficients in capsule core and shell walls. 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Evaluation of binding selectivities and affinities of platinum-based quadruplex interactive complexes by electrospray ionization mass spectrometry

BIOPOLYMERS, Issue 4 2009
Sarah E. Pierce
Abstract The quadruplex binding affinities and selectivities of two large ,-surface PtII phenanthroimidazole complexes, as well as a smaller ,-surface platinum bipyridine complex and a larger RuII complex, were evaluated by electrospray ionization mass spectrometry. Circular dichroism (CD) spectroscopy was used to determine the structures of various quadruplexes and to study the thermal denaturation of the quadruplexes in the absence and presence of the metal complexes. In addition, chemical probe reactions with glyoxal were used to monitor the changes in the quadruplex conformation because of association with the complexes. The platinum phenanthroimidazole complexes show increased affinity for several of the quadruplexes with elongated loops between guanine repeats. Quadruplexes with shorter loops exhibited insubstantial binding to the transition metal complexes. Similarly binding to duplex and single strand oligonucleotides was low overall. Although the ruthenium-based metal complex showed somewhat enhanced quadruplex binding, the PtII complexes had higher quadruplex affinities and selectivities that are attributed to their square planar geometries. The chemical probe reactions using glyoxal indicated increased reactivity when the platinum phenanthroimidazole complexes were bound to the quadruplexes, thus suggesting a conformational change that alters guanine accessibility. 2008 Wiley Periodicals, Inc. Biopolymers 91: 233,243, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]


Crystal structure of ,-phenoxo bridged dicopper complex: {N-[(2-hydroxylato-5-methyl)benzyl-(2,-hydroxylato-3,,5,-dimethylbenzyl)]ethyl amine dicopper(II)}

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2002
S. M. Malathy Sony
Abstract The title compound crystallizes in monoclinic space group C2/c with cell parameters a = 21.404(2), b = 13.962(1), c = 17.917(1), , = 124.394(2), V = 4418.3(6)3, Z = 8, Dcal = 1.193Mg/m3 and T = 293 K. The structure was solved by Patterson method and refined by full-matrix least-squares procedures to final R = 0.0882 using 5253 observed reflections. The tetra coordinated copper atom have a slight distorted square planar geometry with the Cu-Cu distance of 2.987(1). The two six membered rings containing copper atom assume distorted sofa conformation. C-H,, and C-H,O type of intermolecular interactions play a role in stabilizing the crystal packing in addition to van der Waals forces. [source]


Synthesis, Structural Diversity, and Ligand-Transfer Potential of (Carbene)copper(I) Complexes

HELVETICA CHIMICA ACTA, Issue 6 2009
Galmari Venkatachalam
Abstract Copper(I) complexes comprising different N-heterocyclic carbene ligands were prepared via in situ deprotonation and metallation. Depending on the wingtip groups on the carbene ligand (alkyl vs. aryl, chelating or monodentate), a variety of different structural motifs were identified, such as a trigonal planar geometry (alkyl wingtips) and an unprecedented see-saw-type structure (pyridinyl wingtip groups). While aryl wingtip groups increase the stability of the complexes, alkyl substituents induce rapid demetallation in the presence of moisture. The reactivity of these complexes was used to establish a carbene-transfer protocol, which is illustrated by the formation of new cyclic thiourea compounds (transfer to sulfur) and new (carbene)ruthenium(II) complexes (transfer to ruthenium). This suggests that (carbene)copper(I) complexes could become valuable alternatives to (carbene)silver(I) complexes for synthesizing (carbene)metal systems via transmetallation. [source]


Synthesis and spectral studies of diorganotin heterocyclic dithiocarbamate complexes and crystal structures of (2- F -Bz)2Sn(Cl) S2CN(CH2CH2)2NEt and (3- Cl -Bz)2Sn [S2CN(CH2CH2)2NEt]2 , 0.5HN(CH2CH2)2NH

HETEROATOM CHEMISTRY, Issue 4 2005
Shengcai Xue
Some new diorganotin(IV) complexes of heterocyclic dithiocarbamate having general formula R2Sn(Cl)S2CNR'2 and R2Sn(S2CNR'2)2 [R = 2-F-Bz, 3-Cl-Bz; NR'2 = N(CH2CH2)2NMe, N(CH2CH2)2NEt, and N(CH2CH2)2NBz] have been prepared, respectively. Elemental analyses, IR, and NMR spectral data characterized all compounds. The crystal structures of (2-F-Bz)2Sn(Cl)S2CN(CH2CH2)2NEt 2 and (3-Cl-Bz)2Sn[S2CN(CH2CH2)2NEt]2 , 0.5 HN(CH2CH2)2NH 5 were determined by single crystal X-ray diffractometer. In the crystal of complex 2, the tin atom is rendered five-coordination in a trigonal bipyramidal configuration by coordinating with S atoms of dithiocarbamate groups. For complex 5, the central Sn atom exists in a skew-trapezoidal planar geometry defined by two asymmetrically coordinated dithiocarbamate ligands and two 3-chlorobenzyl groups. 2005 Wiley Periodicals, Inc. 16:271,277, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20096 [source]


Planarity of acetamides, thioacetamides, and selenoacetamides: Crystal structure of N,N -dimethylselenoacetamide

HETEROATOM CHEMISTRY, Issue 4 2002
Shuqiang Niu
The planarity of acetamides 1a,3a, thioacetamides 4a,6a, and selenoacetamides 7a,9a, R1R2NC(=E)CH3 where E = O, S, Se, and R1, R2 = H or CH3, was investigated using theoretical calculations at the density functional theory (DFT) level. The calculations showed that the methyl substitution on nitrogen and the change from the amide moiety (NCO) to NCS or NCSe group increased the double bond character of the NC bond. In other words, the planarity of these compounds (1a,9a) increases in the order NH2 < NHCH3 < N(CH3)2 and O < S < Se. The calculations of bending energy suggest that the planar geometry represents the lowest energy conformation for all compounds investigated in this work. N,N-Dimethyl-selenoacetamide (9a), (CH3)2NC(Se) CH3, has the largest bending energy of 10.37 kcal/mol, which suggests that it possesses the greatest planarity among the compounds 1a,9a. However, the solid phase molecular structure of 9a was found to be slightly nonplanar by X-ray crystallography. The slight nonplanarity observed experimentally is very likely the consequence of intermolecular interactions arising within the crystal packing. 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:380,386, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10056 [source]


Substituted 1,3,2,4-benzodithiadiazines: Novel derivatives, by-products, and intermediates,

HETEROATOM CHEMISTRY, Issue 7 2001
Alexander Yu.
The synthesis of the title compounds 1 by 1:1 condensation of ArNSNSiMe3 2 with SCl2 followed by intramolecular ortho-cyclization of each [ArNSNSCl] intermediate is complicated by further reaction of 1 with SCl2 to give Herz salts 3. With the 2:SCl2 ratio of 2:1, the formation of by-products 3 is reduced and novel compounds 1 are accessible. With ortho-I containing starting material 2j, the parent compound 1s is obtained as the result of an unexpected I, not H, substitution. The rate of the 1 + SCl2 reaction depends upon a substituent's position, and the minor 8-R isomers 1l,p (R = Br, I) are isolated for the first time from mixtures with the major 6-R isomers due to reduced reactivity toward SCl2. The synthesized compounds 1,3 are characterized by multinuclear (including nitrogen) NMR and X-ray crystallography. According to the X-ray diffraction data, 1j (6-Br) and 1k (7-Br) derivatives are planar, whereas 1i (5-Br) and 1l (8-Br) are bent along the S1N4 line by ,5 and ,4, respectively, and the 1r (7-OCH3) derivative is planar in contrast to the known 5-OCH3 isomer, which possesses a significantly folded heterocycle. The distortion of the planar geometry of some compounds 1 is interpreted in terms of a pseudo-Jahn-Teller effect as the result of ,-highest occupied molecular orbital (HOMO) ,*-(LUMO) lowest unoccupied molecular orbital + 1 mixing in a planar conformation. The 2p compound is the first structurally defined Ar,N = S = N,SiMe3 azathiene. The compound Ar,N = S = N,S,NH-Ar 6 modeling the aforementioned intermediate has been isolated and structurally characterized. We describe the attempts to synthesize compounds 1 from 2-aminobenzenethiols and (SN)4 and from salts 3 and Me3SiN3, and we discuss the reaction pathways. 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:563,576, 2001 [source]


The lattice Boltzmann method and the finite volume method applied to conduction,radiation problems with heat flux boundary conditions

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2009
Bittagopal Mondal
Abstract This article deals with the implementation of the lattice Boltzmann method (LBM) in conjunction with the finite volume method (FVM) for the solution of conduction,radiation problems with heat flux and temperature boundary conditions. Problems in 1-D planar and 2-D rectangular geometries have been considered. The radiating,conducting participating medium is absorbing, emitting and scattering. In the 1-D planar geometry, the south boundary is subjected to constant heat flux, while in the 2-D geometry the south and/or the north boundary is at constant heat flux condition. The remaining boundaries are at prescribed temperatures. The energy equation is solved using the LBM and the radiative information for the same is computed using the FVM. In the direct method, by prescribing temperatures at the boundaries, the temperature profile and heat flux are calculated. The computed heat flux values are imposed at the boundaries to establish the correctness of the numerical code in the inverse method. Effects of various parameters such as the extinction coefficient, the scattering albedo, the conduction,radiation parameter, the boundary emissivity and the total heat flux and boundary temperatures are studied on the distributions of temperature, radiative and conductive heat fluxes. The results of the LBM in conjunction with the FVM have been found to compare very well with those available in the literature. Copyright 2008 John Wiley & Sons, Ltd. [source]


Theoretical studies on the role of ,-electron delocalization in determining the conformation of N-benzylideneaniline with three types of LMO basis sets

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2006
Peng Bao
Abstract To understand the role of ,-electron delocalization in determining the conformation of the NBA (Ph,NCH,Ph) molecule, the following three LMO (localized molecular orbital) basis sets are constructed: a LFMO (highly localized fragment molecular orbital), an NBO (natural bond orbital), and a special NBO (NBO-II) basis sets, and their localization degrees are evaluated with our suggesting index DL. Afterward, the vertical resonance energy ,EV is obtained from the Morokuma's energy partition over each of three LMO basis sets. ,EV = ,EH (one electron energy) + ,Etwo (two electron energy), and ,Etwo = ,ECou (Coulomb) + ,Eex (exchange) + ,Eec (or ,,En) (electron correction). ,EH is always stabilizing, and ,ECou is destabilizing for all time. In the case of the LFMO basis set, ,ECou is so great that ,Etwo > |,EH|. Therefore, ,EV is always destabilizing, and is least destabilizing at about the , = 90 geometry. Of the three calculation methods such as HF, DFT, and MPn (n = 2, 3, and 4), the MPn method provides ,EV with the greatest value. In the case of the NBO basis set, on the contrary, ,EV is stabilizing due to ,ECou being less destabilizing, and it is most stabilizing at a planar geometry. The LFMO basis set has the highest localization degree, and it is most appropriate for the energy partition. In the NBA molecule, ,-electron delocalization is destabilization, and it has a tendency to distort the NBA molecular away from its planar geometry as far as possible. 2006 Wiley Periodicals, Inc. J Comput Chem 27: 809,824, 2006 [source]


IR/Raman spectroscopy and DFT calculations of cyclic di-amino acid peptides.

JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2009
Part III: comparison of solid state, solution structures of cyclo(L -Ser- L -Ser)
Abstract B3-LYP/cc-pVDZ calculations of the gas-phase structure and vibrational spectra of the isolated molecule cyclo(L -Ser- L -Ser), a cyclic di-amino acid peptide (CDAP), were carried out by assuming C2 symmetry. It is predicted that the minimum-energy structure is a boat conformation for the diketopiperazine (DKP) ring with both L -seryl side chains being folded slightly above the ring. An additional structure of higher energy (15.16 kJ mol,1) has been calculated for a DKP ring with a planar geometry, although in this case two fundamental vibrations have been calculated with imaginary wavenumbers. The reported X-ray crystallographic structure of cyclo(L -Ser- L -Ser), shows that the DKP ring displays a near-planar conformation, with both the two L -seryl side chains being folded above the ring. It is hypothesized that the crystal packing forces constrain the DKP ring in a planar conformation and it is probable that the lower energy boat conformation may prevail in the aqueous environment. Raman scattering and Fourier-transform infrared (FT-IR) spectra of solid state and aqueous solution samples of cyclo(L -Ser- L -Ser) are reported and discussed. Vibrational band assignments have been made on the basis of comparisons with the calculated vibrational spectra and band wavenumber shifts upon deuteration of labile protons. The experimental Raman and IR results for solid-state samples show characteristic amide I vibrations which are split (Raman: 1661 and 1687 cm,1, IR: 1666 and 1680 cm,1), possibly due to interactions between molecules in a crystallographic unit cell. The cis amide I band is differentiated by its deuterium shift of ,30 cm,1, which is larger than that previously reported for trans amide I deuterium shifts. A cis amide II mode has been assigned to a Raman band located at 1520 cm,1. The occurrence of this cis amide II mode at a wavenumber above 1500 cm,1 concurs with results of previously examined CDAP molecules with low molecular weight substituents on the C, atoms, and is also indicative of a relatively unstrained DKP ring. Copyright 2009 John Wiley & Sons, Ltd. [source]


Design of a miniaturized planar antenna for FCC-UWB communication systems

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2008
L. Lizzi
Abstract In this letter, the design of a planar antenna compliant with FCC requirements for ultra-wideband (UWB) transmission systems is described. With reference to a planar geometry on a dielectric substrate, the shape of the antenna is described by means of a spline-based representation and it is determined by means of an optimization process aimed at finding the optimal descriptive parameters that allow to fit the user-defined electrical and dimensional requirements. The reliability and effectiveness of the antenna prototype are assessed through simulations as well as experimental measurements. Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1975,1978, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23519 [source]


The role of Kelvin,Helmholtz instability in dusty and partially ionized outflows

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
Mohsen Shadmehri
ABSTRACT We investigate the linear theory of Kelvin,Helmholtz instability at the interface between a partially ionized dusty outflow and the ambient material analytically. We model the interaction as a multifluid system in a planar geometry. The unstable modes are independent from the charge polarity of the dust particles. Although our results show a stabilizing effect for charged dust particles, the growth time-scale of the growing modes gradually becomes independent of the mass or charge of the dust particles when the magnetic-field strength increases. We show that growth time-scale decreases with increasing the magnetic field. Also, as the mass of the dust particles increases, the growth time-scale of the unstable mode increases. [source]


Diamminesilver(I) bis(2-amino-5-nitrobenzoato-,2O1,O1,)silver(I): a two-dimensional supramolecular sheet with a short intersheet distance containing a rare four-coordinate planar silver(I) centre

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010
Di Sun
The asymmetric unit of the title compound, [Ag(NH3)2][Ag(C7H5N2O4)2], comprises half an [Ag(NH3)2]+ cation and half an [Ag(anbz)2], anion (anbz is 2-amino-5-nitrobenzoate). Both AgI ions are located on inversion centres. The cation has a linear coordination geometry with two symmetry-related ammine ligands. The AgI cation in the anionic part shows a rare four-coordinate planar geometry completed by two chelating symmetry-related anbz ligands. Intra- and intermolecular N,H...O hydrogen bonds create a slightly undulating two-dimensional supramolecular sheet. Adjacent sheets are only ca 3.3, apart. Ag...O, Ag...N and ,,, stacking interactions consolidate the packing of the molecules in the solid state. [source]


Pseudomerohedrally twinned monoclinic structure of unfolded `free' nonactin: comparative analysis of its large conformational change upon encapsulation of alkali metal ions

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009
Ilia A. Guzei
The title compound, C40H64O12, crystallizes in a pseudomerohedrally twinned primitive monoclinic cell with similar contributions of the two twin components. There are two symmetry-independent half-molecules of nonactin in the asymmetric unit. Each molecule has a pseudo- S4 symmetry and resides on a crystallographic twofold axis; the axes pass through the molecular center of mass and are perpendicular to the plane of the macrocycle. The literature description of the room-temperature structure of nonactin as an order,disorder structure in an orthorhombic unit cell is corrected. We report a low-temperature high-precision ordered structure of `free' nonactin that allowed for the first time precise determination of its bond distances and angles. It possesses an unfolded and more planar geometry than its complexes with encapsulated Na+, K+, Cs+, Ca2+ or NH4+ cations that exhibit more isometric overall conformations. [source]


,-Amino boronates as cyanoborane complexes: crystal structure and inhibition properties for the serine proteases: ,-chymotrypsin and trypsin

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2006
Amal Shibli
Abstract The first examples of ,-amino boronate complexes stabilized by amino cyanoborane complexation were tested as trypsin and chymotrypsin inhibitors, and they showed moderate inhibition. The structure of compound 1 that contains two different boron atoms reveals that the geometry around the boron atom in the cyano group is tetrahedral, whereas a trigonal planar geometry exists around the boron atom attached to two oxygen atoms and a carbon atom. Copyright 2006 John Wiley & Sons, Ltd. [source]


Electronic Structure and Bonding in Neutral and Dianionic Boradiphospholes: R,BC2P2R2 (R=H, tBu, R,=H, Ph)

CHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009
Dandamudi Usharani
Abstract Classical and non-classical isomers of both neutral and dianionic BC2P2H3 species, which are isolobal to Cp+ and Cp,, are studied at both B3LYP/6-311++G(d,p) and G3B3 levels of theory. The global minimum structure given by B3LYP/6-311++G(d,p) for BC2P2H3 is based on a vinylcyclopropenyl-type structure, whereas BC2P2H32, has a planar aromatic cyclopentadienyl-ion-like structure. However, at the G3B3 level, there are three low-energy isomers for BC2P2H3: 1),tricyclopentane, 2),nido and 3),vinylcyclopropenyl-type structures, all within 1.7,kcal,mol,1 of each other. On the contrary, for the dianionic species the cyclic planar structure is still the minimum. In comparison to the isolobal Cp+ and HnCnP5,n+ isomers, BC2P2H3 shows a competition between ,-delocalised vinylcyclopropenyl- and cluster-type structures (nido and tricyclopentane). Substitution of H on C by tBu, and H on B by Ph, in BC2P2H3 increases the energy difference between the low-lying isomers, giving the lowest energy structure as a tricyclopentane type. Similar substitution in BC2P2H32, merely favours different positional isomers of the cyclic planar geometry, as observed in 1),isoelectronic neutral heterodiphospholes EtBu2C2P2 (E=S, Se, Te), 2),monoanionic heterophospholyl rings EtBu2C2P2 (E=P,, As,, Sb,) and 3),polyphospholyl rings anions tBu5,nCnP5,n (n=0,5). The principal factors that affect the stability of three-, four-, and five-membered ring and acyclic geometrical and positional isomers of neutral and dianionic BC2P2H3 isomers appear to be: 1),relative bond strengths, 2),availability of electrons for the empty 2p boron orbital and 3),steric effects of the tBu groups in the HBC2P2tBu2 systems. [source]


Structure of Pyridazine in the S1 State: Experiment and Theory

CHEMPHYSCHEM, Issue 11 2008
Doo-Sik Ahn
Abstract The molecular structure of pyridazine in the first electronically excited state (S1) is deduced from the combined use of resonance-enhanced two-photon ionization and mass-analyzed threshold ionization spectroscopic methods. The equation-of-motion coupled-cluster single and double (EOM,CCSD) calculation gives the distorted planar geometry for the most stable structure of the S1 pyridazine. The symmetry constraint of C2v is relaxed to that of Cs, and consequently many in-plane vibrational modes are found to be optically active in both S1,S0 and D0,S1 excitation spectra, being appropriately assigned from the comparison of their frequencies with ab initio values. This indicates that the S1,S0 excitation is partially localized, and provides an alternative explanation for the long-standing spectroscopic puzzle in S1 pyridazine. [source]