Interfacial regions governing internal cavities of dendrimers. Studies of poly(alkyl aryl ether) dendrimers constituted with linkers of varying alkyl chain length

This report deals with a study of the properties of internal cavities of dendritic macromolecules that are capable of encapsulating and mediating photoreactions of guest molecules. The internal cavity structures of dendrimers are determined by the interfacial regions between the aqueous exterior and hydrocarbon like interior constituted by the linkers that connect symmetrically sited branch points constituting the dendrimer and head groups that cap the dendrimers. Phloroglucinol-based poly(alkyl aryl ether) dendrimers constituted with a homologous series of alkyl linkers were undertaken for the current study. Twelve dendrimers within first, second, and third generations, having ethyl, n-propyl, n-butyl, and n-pentyl groups as the linkers and hydroxyl groups at peripheries in each generation, were synthesized. Encapsulation of pyrene and coumarins by aqueous basic solutions of dendrimers were monitored by UV-vis and fluorescence spectroscopies, which showed that a lower generation dendrimer with an optimal alkyl linker presented better encapsulation abilities than a higher generation dendrimer. Norrish type I photoreaction of dibenzyl ketone was carried out within the above series of dendrimers to probe their abilities to hold guests and reactive intermediate radical pairs within themselves. The extent of cage effect from the series of third generation dendrimers was observed to be higher with dendrimers having an n-pentyl group as the linker.     

Crystal structure of N-m-tolyl phthalimide

N-m-tolyl phthalimide, C₁₅NO₂H₁₁ crystallizes in the space group Cc with unit cell dimensions,a=8·54(1),b=19·89(2),c = 7·59(1)A, β=114·53(1)° andZ=4.V=1173(2)A³,D _m =1·35(1),D _c = 1·344 mg.m⁻³,M _r =237 λCoK_a=1·7903A. The structure was solved byMULTAN and refined to an R-factor of 0·116 for 632 counter reflections. The molecules are held together by van der Waal’s forces. The angle between the tolyl plane and the plane through the phthalimide group is 53·4(4)°. Contribution No. 607.     

New hybrid inorganic-organic polymers as supports for heterogeneous catalysis: a novel Pd(0) metalated cyclophosphazene-containing polymer as an efficient heterogeneous catalyst for the Heck reaction

[reaction: see text] A new Pd(0) complex of a pendant cyclophosphazene-containing cross-linked polymer is found to be an effective heterogeneous catalyst for the Heck arylation reaction. The catalyst is robust and can be recycled without significant loss of activity.     

Exhibition of low hyperfine coupling constant for copper(II) in magnesium rubidium sulphate hexahydrate

Single crystal EPR studies of Cu(II) incorporated in magnesium rubidium sulphate hexahydrate are carried out at RT and 77 K. Since the hyperfine lines are not resolved at RT, single crystal rotations have been carried out at 77 K. The spin Hamiltonian parameters calculated from the 77 K spectra are: g₁₁=2.133, g₂₂=2.137, g₃₃=2.327, A₁₁=0.01, A₂₂=1.44 and . The impurity ion occupies an interstitial position in this crystal lattice, which is not very common for copper ion. In addition, the low hyperfine coupling constant is explained by considering an admixture of dx²-y² ground state with dz² excited state. Bonding parameters, κ=0.254, , α²=0.706, α=0.8406 have also been calculated. The present study has helped to understand the static nature of JT, for which the present system is an example.     

Click reaction on in situ generated β-azidostyrenes from cinnamic acid using CAN-NaN3: synthesis of N-styryl triazoles

N-Styryl triazoles are synthesized in one-pot starting with azido styrene obtained in situ from cinnamic acids and various acetylenes.     

Assembly of a dinuclear silver complex containing an Ag2S2 motif from a phosphorus-supported trishydrazone ligand. P=S→Ag(I) coordination

The reaction of the phosphorus trihydrazide, (S)P[N(Me)-NH(2)](3) (1) with quinoline-2-carboxaldehyde (C(9)H(6)N-2-CHO) in a 1:3 ratio afforded a trishydrazone, (S)P[N(Me)-N=CH-2-C(9)H(6)N](3) (2). Crystals of 2 were grown in three different solvent media affording an unsolvated (2, monoclinic, P2(1)/n) and two solvated (2·3H(2)O, trigonal, R3 and 2·2CH(3)OH, triclinic, P ?1) crystal forms. Each of these, while possessing an essentially similar molecular structure, adopt different crystal packing giving rise to supramolecular structures mediated by a variety of weak interactions: O-H-N, O-H-O, C-H-N, C-H-O, C-H-S, C-H-π, π-π, N-π and S-π. The reaction of 2 with Ag(ClO(4))(2)·6H(2)O in methanol afforded a dinuclear cationic cage [Ag{(S)P[N(Me)-N=CH-2-C(9)H(6)N](3)}·ClO(4)](2) (3). The molecular structure of 3 reveals a dimeric structure consisting of two Ag(I) ions that are held together by two ligands. Only two arms of the tris hydrazone ligand are involved in coordination while an unprecedented P=S→Ag(I) coordination is seen. This results in the formation of an Ag(2)S(2) dimer that is encapsulated by two trishydrazone ligands. Both compounds 2 and 3 are photoluminescent.     

Practical synthesis of 2-keto-3-deoxy-D-glycero-D-galactononulosonic acid (KDN)

Reaction of propargylmagnesium bromide with 2,3;5,6-di-O-isopropylidene-D-mannonolactone followed by highly stereoselective reduction of the so-formed lactol with sodium borohydride gives a syn-diol from which practical syntheses of 2-keto-3-deoxy-D-glycero-D-galactononulosonic acid (KDN) and various partially protected derivatives have been achieved all of which feature the oxidative unmasking of the α-keto acid moiety from the alkyne.     

Light-induced enantiospecific 4π ring closure of axially chiral 2-pyridones: enthalpic and entropic effects promoted by H-bonding

Nonbiaryl axially chiral 2-pyridones were synthesized and employed for light-induced electrocyclic 4π ring closure leading to bicyclo-β-lactam photoproducts in solution. The enantioselectivity in the photoproducts varied from 22 to 95% depending on the reaction temperature and the ability of the axially chiral chromophore to form intramolecular and/or intermolecular H-bonds with the solvent. On the basis of the differential activation parameters, entropic control of the enantiospecificity was observed for 2-pyridones lacking the ability to form H-bonds. Conversely, enthalpy played a significant role for 2-pyridones having the ability to form H-bonds.