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Density-functional theory with scalar-relativistic pseudopotential and a generalized gradient correction is used to calculate the neutral and cationic Bi(n) clusters (2< or =n< or =24), with the aim to elucidate their structural evolution, relative stability, and magnetic property. The structures of neutral Bi clusters are found to be similar to that of other group-V elemental clusters, with the extensively studied sizes of n=4 and 8 having a tetrahedron and wedgelike structure, respectively. Generally, larger Bi clusters consist of a combination of several stable units of Bi(4), Bi(6), and Bi(8), and they have a tendency to form an amorphous structure with the increase of cluster sizes. The curves of second order energy difference exhibit strong odd-even alternations for both neutral and cationic Bi clusters, indicating that even-atom (odd-atom) sizes are relatively stable in neutral clusters (cationic clusters). The calculated magnetic moments are 1micro (B) for odd-atom clusters and zero for even-atom clusters. We propose that the difference in magnetism between experiment and theory can be greatly improved by considering the orbital contribution. The calculated fragmentation behavior agrees well with the experiment, and for each cationic cluster the dissociation into Bi(4) or Bi(7) (+) subclusters confirms the special stability of Bi(4) and Bi(7) (+). Moreover, the bond orders and the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital show that small Bi clusters would prefer semiconductor characters to metallicity.

Pretargeted imaging has emerged as ap romising approach to advance nuclear imaging of malignant tumors. Herein, we combine the enzyme-mediated fluorogenic reaction and in situ self-assembly with the inverse electron demand Diels-Alder (IEDDA) reaction to develop an activatable pretargeted strategy for multimodality imaging. The transcyclooctene (TCO) bearing small-molecule probe, P-FFGd-TCO,can be activated by alkaline phosphatase and in situ selfassembles into nanoaggregates (FMNPs-TCO)retained on the membranes,p ermitting to (1) amplify near-infrared (NIR) fluorescence (FL) and magnetic resonance imaging (MRI) signals,and (2) enrich TCOs to promote IEDDAligation. The Gallium-68 ( 68 Ga) labeled tetrazine can readily conjugate the tumor-retained FMNPs-TCO to enhance radioactivity uptake in tumors.S trong NIR FL, MRI, and positron emission tomography (PET) signals are concomitantly achieved,allowing for pretargeted multimodality imaging of ALP activity in HeLa tumor-bearing mice.

Reactions of two platinum(II) complexes, cis-[Pt(NH3)2(H2O)2]2+ (Pt1) and cis-[Pt(en)(H2O)2]2+ (Pt2), with several sulfur-containing peptides, have been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The species produced in the reactions were detected with ESI-MS, and MS/MS analysis was performed to probe structural information. Collision-induced dissociation revealed different dissociation pathways for the main reaction products of the two platinum(II) complexes with the same peptides. The major difference is the prominent loss of ammonia ligand for complexes of Pt1 due to the strong trans effect of sulfur, whereas the loss of ethylenediamine (en) ligand from Pt2 complexes is less favored, reflecting the chelating effect of the bidentate ligand. Despite the differences in dissociation patterns, Pt1 and Pt2, in general, form structurally similar complexes with the same peptides. In the reactions with Met-Arg-Phe-Ala they both produce a N,S-chelate ring through the N-terminal NH2 and sulfur of the Met residue, and in the reactions with Ac-Met-Ala-Ser they bind to the sulfur of Met and deprotonate an amide nitrogen upstream from the anchor site. Both of them are able to promote hydrolysis of the peptides. In reactions with glutathione they both form four-membered Pt2S2 rings and Pt-S-Pt bonding through the bridging thiolate ligand, although the reaction rate is much slower for Pt2 due to steric hindrance of the en ligand.

Tumor-targeted and stimuli-activatable nanosensitizers are highly desirable for cancer theranostics. However, designing smart nanosensitizers with multiple imaging signals and synergistic therapeutic activities switched on is challenging. Herein, we report tumortargeted and redox-activatable nanosensitizers (1-NPs) for sono-photodynamic immunotherapy of tumors by molecular co-assembly and redox-controlled disassembly. 1-NPs show a high longitudinal relaxivity (r 1 = 18.7 � 0.3 mM À 1 s À 1 ), but "off" dual fluorescence (FL) emission (at 547 and 672 nm), "off" sono-photodynamic therapy and indoleamine 2,3-dioxygenase 1 (IDO1) inhibition activities. Upon reduction by glutathione (GSH), 1-NPs rapidly disassemble and remotely release small molecules 2-Gd, Zn-PPA-SH and NLG919, concurrently switching on (1) dual FL emission, (2) sonophotodynamic therapy and (3) IDO1 inhibition activities. After systemic injection, 1-NPs are effective for bimodal FL and magnetic resonance (MR) imagingguided sono-photodynamic immunotherapy of orthotropic breast and brain tumors in mice under combined ultrasound (US) and 671-nm laser irradiation.

Enzyme-triggered macrocyclization and in situ self-assembly of small molecules into nanoparticles has shown promise to design activatable probes for molecular imaging. However, controlling macrocyclization and self-assembly to concurrently augment positron emission tomography (PET) and photoacoustic (PA) signals for bimodality imaging is challenging. Herein, we report the engineering of a triazole-IR780 fluorophore as a versatile macrocyclization scaffold for controlling in situ selfassembly and design a caspase-3-activatable PA/PET bimodal probe ([ 18 F]-IR780-1) for in vivo imaging of tumor apoptosis. By leveraging the high-sensitivity whole-body imaging signals offered by PET with the high-resolution imaging signals offered by PA, [ 18 F]-IR780-1 can provide a promising tool for the early evaluation of antitumor efficacy, helpful for optimizing the therapeutic protocol for patients. This scaffold may be adopted to design other activatable bimodal probes for in vivo imaging.

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Smart near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probes have shown promise for preoperative and intraoperative imaging of tumors. In this paper, we report an enzyme-activatable probe (P-CyFF-68 Ga) and its cold probe (P-CyFF-Ga) using an enzyme-induced fluorogenic reaction and in situ coassembly strategy and demonstrate the utility for NIR FL/PET bimodality imaging of enzymatic activity. P-CyFF-68 Ga and P-CyFF-Ga can be converted into dephosphorylated CyFF-68 Ga and CyFF-Ga in response to alkaline phosphatase (ALP) and subsequently coassemble into fluorescent and radioactive nanoparticles (NP-68 Ga). The ALPtriggered in situ formed NP-68 Ga is prone to anchoring on the ALP-positive HeLa cell membrane, permitting the concurrent enrichment of NIR FL and radioactivity. The enhancements in NIR FL and radioactivity enables high sensitivity and deep-tissue imaging of ALP activity, consequently facilitating the delineation of HeLa tumor foci from the normal tissues in vivo.