Recent advances on smart TiO2 nanotube platforms for sustainable drug delivery applications.

To address the limitations of traditional drug delivery, TiO2 nanotubes (TNTs) are recognized as a promising material for localized drug delivery systems. With regard to the excellent biocompatibility and physicochemical properties, TNTs prepared by a facile electrochemical anodizing process have been used to fabricate new drug-releasing implants for localized drug delivery. This review discusses the development of TNTs applied in localized drug delivery systems, focusing on several approaches to control drug release, including the regulation of the dimensions of TNTs, modification of internal chemical characteristics, adjusting pore openings by biopolymer coatings, and employing polymeric micelles as drug nanocarriers. Furthermore, rational strategies on external conditions-triggered stimuli-responsive drug release for localized drug delivery systems are highlighted. Finally, the review concludes with the recent advances on TNTs for controlled drug delivery and corresponding prospects in the future.

TiO2 nanotube platforms for smart drug delivery: a review.

Titania nanotube (TNT) arrays are recognized as promising materials for localized drug delivery implants because of their excellent properties and facile preparation process. This review highlights the concept of localized drug delivery systems based on TNTs, considering their outstanding biocompatibility in a series of ex vivo and in vivo studies. Considering the safety of TNT implants in the host body, studies of the biocompatibility present significant importance for the clinical application of TNT implants. Toward smart TNT platforms for sustainable drug delivery, several advanced approaches were presented in this review, including controlled release triggered by temperature, light, radiofrequency magnetism, and ultrasonic stimulation. Moreover, TNT implants used in medical therapy have been demonstrated by various examples including dentistry, orthopedic implants, cardiovascular stents, and so on. Finally, a future perspective of TNTs for clinical applications is provided.

Tetra-kis(µ-3,4-dimethoxy-phenyl-acetato)bis-[(3,4-dimethoxy-phenyl-acetato)(1,10-phenanthroline)dysprosium(III)].

The title centrosymmetric dinuclear dysprosium(III) complex, [Dy(2)(C(10)H(11)O(4))(6)(C(12)H(8)N(2))(2)] or [Dy(L)(3)phen](2), is comprised of six 3,4-dimethoxy-phenylacetate (L) anions, two 1,10-phenanthroline (phen) mol-ecules and two Dy(III) ions. The Dy(III) atom is nine-coordinated by seven O atoms from five L ligands and two N atoms from the phen mol-ecules. The L ligands are coordinated to the Dy(III) ion in three coordination modes: chelating, bridging and bridging-tridentate. C-H⋯O hydrogen bonding interactions consolidate the crystal packing.

Tetra-kis[µ-2-(3,4-dimeth-oxy-phen-yl)acetato]-κO:O';κO,O':O;κO:O,O'-bis-{[2-(3,4-dimeth-oxy-phen-yl)acetato-κO,O'](1,10-phenanthroline-κN,N')samarium(III)}.

In the centrosymmetric dinuclear title complex, [Sm(2)(C(10)H(11)O(4))(6)(C(12)H(8)N(2))(2)], the Sm(III) ion is nine-coordinated by seven O atoms of five 2-(3,4-dimeth-oxy-phen-yl)acetate (DMPA) ligands and two N atoms of one bis-chelating 1,10-phenanthroline (phen) ligand, forming a distorted tricapped trigonal-prismatic environment. The DMPA ligands coordinate in bis-chelate, bridging and bridging tridentate modes. An intra-molecular C-H⋯O hydrogen bond occurs. Inter-molecular C-H⋯O inter-actions are also present in the crystal.

Tetra-kis[µ-2-(3,4-dimeth-oxy-phen-yl)acetato]-κO,O:O;κO:O,O;κO:O-bis-{[2-(3,4-dimeth-oxy-phen-yl)acetato-κO,O](1,10-phenanthroline-κN,N')erbium(III)}.

In the dimeric centrosymmetric title complex, [Er(2)(C(10)H(11)O(4))(6)(C(12)H(8)N(2))(2)], the Er(III) ion is nine-coordinated by five 2-(3,4-dimeth-oxy-lphen-yl)acetic acid (DMPA) ligands via seven O atoms and two N atoms from a bis-chelating 1,10-phenanthroline (phen) ligand in a distorted tricapped trigonal-prismatic geometry. The DMPA ligands are coordinated to the Er(III) ion in bis-chelate, bridging and bridging tridentate modes. Relatively weak intra-molecular C-H⋯O inter-actions reinforce the stability of the mol-ecular structure. Inter-molecular C-H⋯O inter-actions are also observed.

Tetra-kis(µ(2)-3,4-dimethoxy-phenyl-acetato)-κO,O':O';κO:O:O';κO:O';κO:O'-bis-[(3,4-dimethoxy-phenyl-acetato-κO,O')(1,10-phenanthroline-κN,N)thulium(III)].

In the title centrosymmetric dinuclear complex, [Tm(2)(C(10)H(11)O(4))(6)(C(12)H(8)N(2))(2)], the unique Tm(III) ion is coordin-ated by five 3,4-dimethoxy-phenyl-acetate (DMPA) ligands and and a bis-chelating 1,10-phenanthroline (phen) ligand via seven O atoms and two N atoms, forming a distorted tricapped trigonal-prismatic environment. The DMPA ligands coordin-ate in the bis-chelate, bridging and bridging tridentate modes.

Bis(1-adamantylammonium) tetra-chloridocobaltate(II).

The Co(II) atom in the title salt, (C(10)H(18)N)(2)[CoCl(4)], exists in a tetra-hedral coordination geometry. The asymmetric unit has two cations that lie on different special positions of site symmetry m; the anion lies on another special position of site symmetry m.

Bis{(E)-2-meth-oxy-6-[(4-methyl-phen-yl)-imino-meth-yl]phenolato}zinc(II).

The title compound, [Zn(C(15)H(14)NO(2))(2)], contains a four-coordinate Zn atom located on a twofold rotation axis that exhibits a distorted tetra-hedral geometry by two phenolate O atoms and two azomethine N atoms of the Schiff base 2-methoxy-6-[(4-methyl-phen-yl)imino-meth-yl]phenolate ligands.

catena-Poly[[{2-meth-oxy-6-[(4-methyl-phen-yl)imino-meth-yl]phenolato}-cad-mium(II)]-di-µ(2)-chlorido-[dimethanol-cadmium(II)]-di-µ(2)-chlorido-[{2-meth-oxy-6-[(4-methyl-phen-yl)imino-meth-yl]-phenolato}cadmium(II)]-di-µ(2)-chlorido].

The structure of the title compound, [Cd(3)Cl(6)(C(15)H(15)NO(2))(2)(CH(4)O)(2)](n), is based on a layered zigzag polymeric chain along the c axis. The Cd(II) ions are linked by double chlorine bridges alternating between one CdCl(4)(CH(3)OH)(2) and two CdCl(4)(C(15)H(15)NO(2)) octa-hedral coordination units. Additional intrachain N-H⋯O and O-H⋯Cl hydrogen-bond interactions stabilize this arrangement.

Bis{6-meth-oxy-2-[(4-methyl-phen-yl)-iminio-meth-yl]phenolato-κO,O'}bis-(nitrato-κO,O')cadmium(II).

The Schiff base 6-meth-oxy-2-[(4-methyl-phen-yl)imino-meth-yl]-phenol (HL) forms a neutral complex with cadmium(II) nitrate, [Cd(NO(3))(2)(C(15)H(15)NO(2))(2)], in which the four O atoms of the two independent ligands are coordinated to the metal center and the protonated imine N atoms are involved in a hydrogen bond with the phenoxide group. Intra-molecular N-H⋯O hydrogen-bonding inter-actions stabilize the structure. Each organic ligand assumes a zwitterionic form, chelating to the metal atom through the two O atoms, while the two nitrate groups also exhibit chelating behavior, leading to a distorted octahedral coordination of the Cd atom.

Bis{2-methoxy-6-[(4-methyl-phen-yl)iminiometh-yl]-phenolato-κO}bis-(thio-cyanato-κN)zinc(II).

The Schiff base 2-[(4-methyl-phen-yl)imino-meth-yl]-6-methoxy-phenol (HL) forms a complex with a Zn(2+) atom and two independent thio-cyanate ions, [Zn(NCS)(2)(C(15)H(15)NO(2))(2)], in which two phenolate O atoms the two independent Schiff base ligands are coordinated to thee Zn(2+) atom. The protonated imine N atoms are involved in an intramolecular hydrogen bond with the phenoxide group. The Zn atom is also coordinated by two N atoms of two thio-cyanate ligands. The coordination environment of the Zn atom is distorted-tetra-hedral.

catena-Poly[[di-µ-chlorido-bis-{[6-methoxy-2-(4-methyl-phenyl-iminio-methyl)phenolato-κO,O']cadmium(II)}]-di-µ(2)-thio-cyanato-κN:S;κS:N].

The asymmetric unit of the title compound, [Cd(2)Cl(2)(NCS)(2)(C(15)H(15)NO(2))(2)](n), contains the Schiff base 2-[(4-methyl-phenyl-imino)meth-yl]-6-methoxy-phenol (HL) ligand, one thio-cyanate and one chloride ligand coordinated to a cadmium centre. The cadmium centers are linked to each other via two thio-cyanate and two chloride bridges alternately, resulting in centrosymmetric zigzag chains running parallel to the a axis. The Cd(II) coordination environment contains two Cl atoms, one thio-cyanate (SCN) S atom, one isothio-cyanate (NCS) N atom and two O atoms from the HL ligand. The Schiff base ligand is in the trans conformation.