Dual-rotor strategy for organic cocrystals with enhanced near-infrared photothermal conversion.

Organic cocrystal engineering provides a promising route to promote the near-infrared (NIR) light harvesting and photothermal conversion (PTC) abilities of small organic molecules through the rich noncovalent bond interactions of D/A units. Besides, the single-bond rotatable groups known as "rotors" are considered to be conducive to the nonradiative transitions of the excited states of organic molecules. Herein, we propose a single-/double-bond dual-rotor strategy to construct D-A cocrystals for NIR PTC application. The results reveal that the cocrystal exhibits an ultra-broadband absorption from 300 nm to 2000 nm profiting from the strong π-π stacking and charge transfer interactions, and the weakened p-π interaction. More importantly, the PTC efficiency of cocrystals at 1064 nm in the NIR-II region can be largely enhanced by modulating the number of rotor groups and the F-substituents of D/A units. As is revealed by fs-TA spectroscopy, the superior NIR PTC performance can be attributed to the nonradiative decays of excited states induced by the free rotation of the single-bond rotor (-CH3) from the donors and the inactive double-bond rotor ([double bond, length as m-dash]C(C[triple bond, length as m-dash]N)2) being in the active form of [-C(C[triple bond, length as m-dash]N)2] in the excited states from the acceptors. This prototype displays a promising route to extend the functionalization of small organic molecules based on organic cocrystal engineering.

Anion-Counterion Strategy toward Organic Cocrystal Engineering for Near-Infrared Photothermal Conversion and Solar-Driven Water Evaporation.

An anion-counterion strategy is proposed to construct organic mono-radical charge-transfer cocrystals for near-infrared photothermal conversion and solar-driven water evaporation. Ionic compounds with halogen anions as the counterions serve as electron donors, providing the necessary electrons for efficient charge transfer with unchanged skeleton atoms and structures as well as the broad red-shifted absorption (200-2000 nm) and unprecedented photothermal conversion efficiency (~90.5 %@808 nm) for the cocrystals. Based on these cocrystals, an excellent solar-driven interfacial water evaporation rate up to 6.1±1.1 kg ⋅ m-2 ⋅ h-1 under 1 sun is recorded due to the comprehensive evaporation effect from the cocrystal loading in polyurethane foams and chimney addition, such performance is superior to the reported results on charge-transfer cocrystals or other materials for solar-driven interfacial evaporation. This prototype exhibits the great potential of cocrystals prepared by the one-step mechanochemistry method in practical large-scale seawater desalination applications.

Primary Structural Units "D+A-" Ion Pairs Dominating Near-Infrared Photothermal Conversion of Organic Ionic Cocrystals.

The specific stacking mode of D/A blocks is often considered to largely determine the physicochemical properties of cocrystals. However, this rule may fail when encountering a large degree of (integer or near-integer) charge transfer situations. Herein, we explore the extensive correlations between the possible smallest structural units, stacking modes, and near-infrared photothermal conversion (NIR-PTC) properties of F4TCNQ-based cocrystals with typical features of integer-charge-transfer. Surprisingly, these cocrystals with distinct stacking modes display analogous D-A interactions, broad red-shift absorption, ultrafast (1-3 ps) relaxation dynamics of excited states, and excellent NIR-PTC properties. This supports that the resulting "D+A-" ion pairs from integer-charge-transfer may serve as the primary structural units beneath the secondary stacking modes to dominate the property of cocrystals. The stacking modes play an important but only secondary role. This work provides new insights into the structure-dynamics-property correlations and modular design of organic cocrystals for PTC and other applications.

Boosting the Release of Leaving Group from Blebbistatin Derivative Photocages via Enhancing Intramolecular Charge Transfer and Stabilizing Cationic Intermediate.

Blebbistatin (Bleb) derivatives are a visible light photocage platform. During the photocleavage process, intramolecular charge transfer (ICT) and cationic intermediates play a decisive role. However, slow photolysis rate and low photolysis quantum yield are the main problems for Bleb's derivatives. Herein, by introducing a substituted OCH3 group at the para-position of the D ring, Bleb and Bleb derivatives with various leaving groups were synthesized and studied, and the photolysis performance was unveiled by steady-state spectra, photolysis rate experiments, photolysis quantum yield, and density functional theory calculations. Substituted OCH3 derivatives of Bleb may enhance the photolysis rate and increase the photolysis quantum yield because the electron-donating group can promote the ICT process and stabilize the cationic intermediate during the photolytic reaction. More generally, the insights gained from this structure-reactivity relationship may provide theoretical guidance and aid in the development of new highly efficient photoreactions.

Somatic acupressure for the fatigue-sleep disturbance-depression symptom cluster in breast cancer survivors: A phase II randomized controlled trial.

OBJECTIVE: To evaluate the feasibility of the somatic acupressure (SA) for managing the fatigue-sleep disturbance-depression symptom cluster (FSDSC) among breast cancer (BC) survivors and its preliminary effects. METHODS: In this Phase II randomized controlled trial (RCT), 51 participants were randomised evenly into the true SA group, sham SA group, and usual care group. All the participants received usual care. The two SA groups performed additional true or sham self-acupressure daily for seven weeks. The primary outcomes related to the assessment of participants' recruitment and compliance with study questionnaires and interventions. Clinical outcomes assessed the preliminary effects of SA on fatigue, sleep disturbance, depression, and quality of life. Semi-structured interviews were undertaken to capture participants' experiences of participating in this study. The statistical effects of the intervention on the outcomes were modelled in repeated measures ANOVA and adjusted generalized estimating equations. RESULTS: Forty-five participants completed the SA intervention. No adverse events were reported. Over 85% of the participants could sustain for 25 days or more and 15 min or more per session, but the adherence to the intervention requirement was yet to improve. The group by time effect of the FSDSC and depression were significant (p < 0.05). Qualitative findings showed that participants positively viewed SA as a beneficial strategy for symptom management. CONCLUSIONS: The SA intervention protocol and the trial procedures were feasible. The results demonstrated signs of improvements in targeted outcomes, and a full-scale RCT is warranted to validate the effects of SA on the FSDSC.

Mechanochemistry toward Organic "Salt" via Integer-Charge-Transfer Cocrystal Strategy for Rapid, Efficient, and Scalable Near-Infrared Photothermal Conversion.

Invited for this month's cover is the group of Shun-Li Chen and Ming-De Li at the Shantou University. The image shows that one electron can be transferred easily from donor to acceptor unit to obtain integer-charge-transfer cocrystals for realizing high-efficient solar-harvesting and photothermal conversion. The Research Article itself is available at 10.1002/cssc.202300644.

Mechanochemistry toward Organic "Salt" via Integer-Charge-Transfer Cocrystal Strategy for Rapid, Efficient, and Scalable Near-Infrared Photothermal Conversion.

Inspired by the concept of ionic charge-transfer complexes for the Mott insulator, integer-charge-transfer (integer-CT) cocrystals are designed for NIR photo-thermal conversion (PTC). With amino-styryl-pyridinium dyes and F4TCNQ (7,7',8,8'-Tetracyano-2,3,5,6-tetrafluoroquinodimethane) serving as donor/acceptor (D/A) units, integer-CT cocrystals, including amorphous stacking "salt" and segregated stacking "ionic crystal", are synthesized by mechanochemistry and solution method, respectively. Surprisingly, the integer-CT cocrystals are self-assembled only through multiple D-A hydrogen bonds (C-H⋅⋅⋅X (X=N, F)). Strong charge-transfer interactions in cocrystals contribute to the strong light-harvesting ability at 200-1500 nm. Under 808 nm laser illumination, both the "salt" and "ionic crystal" display excellent PTC efficiency beneficial from ultrafast (∼2 ps) nonradiative decay of excited states. Thus integer-CT cocrystals are potential candidates for rapid, efficient, and scalable PTC platforms. Especially amorphous "salt" with good photo/thermal stability is highly desirable in practical large-scale solar-harvesting/conversion applications in water environment. This work verifies the validity of the integer-CT cocrystal strategy, and charts a promising path to synthesize amorphous PTC materials by mechanochemical method in one-step.

Ultrafast excited-state energy dissipation pathway of diethylamino hydroxybenzoyl hexyl benzoate (DHHB) via the nanoparticles.

The organic UVA filter is popularized in sunscreen cosmetics due to the advantages of excellent light stability and high molar extinction coefficient. However, the poor water solubility of organic UV filters has been a common problem. Given that nanoparticles (NPs) can significantly improve the water solubility of organic chemicals. Meanwhile, the excited-state relaxation pathways of NPs might differ from their solution. Here, the NPs of diethylamino hydroxybenzoyl hexyl benzoate (DHHB), a popular organic UVA filter, were prepared by an advanced ultrasonic micro-flow reactor. The surfactant (sodium dodecyl sulfate) was selected as an effective stabilizer to prevent the self-aggregation of the NPs for DHHB. Femtosecond transient ultrafast spectroscopy (fs-TA) and theoretical calculations were utilized to trace and explain the excited-state evolution of DHHB in NPs suspension and its solution. The results reveal that the surfactant-stabilized NPs of DHHB reserve a similarly good performance of ultrafast excited-state relaxation. The stability characterization experiments demonstrate that the strategy of surfactant-stabilized NPs for sunscreen chemicals can maintain its stability and enhance the water solubility of DHHB compared with that of the solution phase. Therefore, the surfactant-stabilized NPs of organic UV filters are an effective method to improve water solubility and keep the stability from aggregation and photoexcitation.

Necrostatin-1 prevents skeletal muscle ischemia reperfusion injury by regulating Bok-mediated apoptosis.

BACKGROUND: Receptor interacting serine/threonine kinase 1 (RIPK1) mediates apoptosis by regulating the classic proapoptotic effectors Bcl-2-associated X protein (Bax) and Bcl-2 homologous antagonist/killer (Bak). Although Bcl-2-related ovarian killer (Bok) is structurally similar to Bak and Bax, it is unclear whether it mediates apoptosis in skeletal muscle ischemia reperfusion (IR) injury. We hypothesized that by regulating Bok-mediated apoptosis, inhibiting RIPK1 with necrostatin-1 would reduce skeletal muscle IR injury. METHODS: Rats were randomized into four groups: sham (SM), IR, IR treated with necrostatin-1 (NI), or vehicle dimethyl sulfoxide (DI). For the IR group, the right femoral artery was clamped for 4 hours and then reperfused for 4 hours, and for the NI and DI groups, necrostatin-1 (1.65 mg/kg) and the equal volume of dimethyl sulfoxide were intraperitoneally administered prior to IR induction. The structural damage of muscle tissue and protein expression of Bok, Bcl-2, and cleaved caspase-3 were investigated, and apoptotic cells were identified with terminal dUTP nick-end labeling (TUNEL) staining. In vitro, human skeletal muscle cells (HSMCs) were exposed to 6 hours of oxygen-glucose deprivation followed by normoxia for 6 hours to establish an oxygen-glucose deprivation/reoxygenation (OGD/R) model. To determine the role of Bok, cell viability, lactate dehydrogenase (LDH) release, and flow cytometry were examined to demonstrate the effects of necrostatin-1 and Bok knockdown on the OGD/R insult of HSMCs. RESULTS: Necrostatin-1 pretreatment markedly reduced IR-induced muscle damage and RIPK1, Bok, and cleaved caspase-3 expression, whereas upregualted Bcl-2 expression (p < 0.05). Furthermore, necrostatin-1 prevented mitochondrial damage and decreased TUNEL-positive muscle cells (p < 0.05). In vitro, HSMCs treated with necrostatin-1 showed reduced Bok expression, increased cell viability, and reduced LDH release in response to OGD/R (p < 0.05), and Bok knockdown significantly blunted the OGD/R insult in HSMCs. CONCLUSION: Necrostatin-1 prevents skeletal muscle from IR injury by regulating Bok-mediated apoptosis.

Probing catalytic reduction on the surface of Au nanoparticles by second-harmonic generation and two-photon luminescence.

The catalytic reduction of aromatic nitro compounds by metallic nanoparticles in the presence of sodium borohydride (NaBH4) has been widely studied as model reactions. However, the reaction mechanisms still need further investigations. For example, the origin of the induction time that has often been observed is still controversial. Here, we demonstrated that such catalytic reduction reactions on the surface of colloidal gold nanoparticles (AuNPs) may be inspected by the second-harmonic generation (SHG) and two-photon luminescence (TPL) emission from AuNPs. It was revealed that the SHG and TPL signals from AuNPs were sensitive to the substitution of citrate by active hydride species derived from the hydrolysis of NaBH4. Based on the UV-vis spectroscopy analyses and monitoring the SHG/TPL signals, the induction time in the catalytic reaction of 4-nitrothiophenol was revealed to originate from the hindered adsorption of hydride on the gold surface. This work demonstrated that SHG and TPL can provide a new approach for detecting active hydrides on the surface of metallic nanoparticles in colloids.

The effect of an evidence-based Tai chi intervention on the fatigue-sleep disturbance-depression symptom cluster in breast cancer patients: A preliminary randomised controlled trial.

PURPOSE: To explore the potential effects of Tai chi on the fatigue-sleep disturbance-depression symptom cluster (FSDSC) among breast cancer (BC) patients. METHODS: This study was conducted as a preliminary randomized controlled trial among 72 BC patients (36 Tai chi and 36 control participants). All the participants were provided with routine care, while participants in the Tai chi group received an additional 8-week Tai chi intervention. Participants' fatigue, sleep disturbance and depression were assessed by the Brief Fatigue Inventory, the Pittsburgh Sleep Quality Index, and the Hospital Anxiety and Depression Scale-Depression. Participants' quality of life (QoL) was assessed by the Functional Assessment of Cancer Therapy-Breast. Both covariates-unadjusted and adjusted GEE models were run to assess the effects of Tai chi intervention on the FSDSC and QoL and the relevant impacts of the covariates. RESULTS: Sixty-nine participants completed this study. In the unadjusted GEE model, compared with the control group and baseline, participants in the Tai chi group showed significant reductions in fatigue (p < 0.001), sleep disturbance (p < 0.001) and depression (p = 0.006), as well as a significant improvement in QoL (p = 0.032) at immediately post-intervention and four-week follow-up. The positive regression coefficients of the adjusted GEE model showed fatigue, sleep disturbance and depression can have impacts on each other (all at p < 0.05). CONCLUSION: Tai chi as an adjuvant intervention to routine care could relieve the symptom cluster of fatigue, sleep disturbance and depression and improve QoL among BC patients.

Near-Infrared Light Triggered a High Temperature Utilizing Donor-Acceptor Cocrystals.

Developing a suitable initiation for the energetic materials that respond to a low-power near-infrared laser can aid in replacing the current expensive and bulky laser-initiation systems. Here, we report on a system of molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystals that manifest ultrabroad absorption (200-2500 nm) characteristics as well as noteworthy very fast self-assembly behaviors. The very narrow highest occupied molecular orbital-lowest unoccupied molecular orbital gap enables N,N,N',N'-tetramethyl-p-phenylenediamine and tetrahalo-1,4-benzoquinones (TMPD-TXBQ) cocrystals to have a great light-harvesting ability in the near-infrared range. When irradiated with a low-power hand-held 808 nm laser with an input energy of only 40 mJ or a power density of 260 mW·cm-2, these TMPD-TXBQ cocrystals immediately undergo an efficient photothermal conversion followed by a dramatic exothermic thermal polymerization reaction due to the face-to-face D-A-D-A stacking in these cocystals to achieve a temperature as high as 318.9 °C. This temperature is high enough for a thermal initiation of most common energetic materials, and thus this TMPD-TXBQ cocrystal can potentially act as a near-infrared laser initiator that is compact, lightweight, and cost-effective.

[Features of intestinal flora in children with food protein-induced proctocolitis based on high-throughput sequencing]. / åŸºäºŽé«˜é€šé‡æµ‹åºæŠ€æœ¯åˆ†æžé£Ÿç‰©è›‹ç™½è¯±å¯¼æ€§ç›´è‚ ç»“è‚ ç‚Žæ‚£å„¿è‚ é“èŒç¾¤ç‰¹å¾.

OBJECTIVES: To study the features of intestinal flora in children with food protein-induced proctocolitis (FPIP) by high-throughput sequencing. METHODS: A total of 31 children, aged <6 months, who experienced FPIP after exclusive breastfeeding and attended the outpatient service of the Third Affiliated Hospital of Zunyi Medical University from October 2018 to February 2021 were enrolled as the FPIP group. Thirty-one healthy infants were enrolled as the control group. Fecal samples were collected to extract DNA for PCR amplification. High-throughput sequencing was used to perform a bioinformatics analysis of 16S rDNA V3-V4 fragments in fecal samples. RESULTS: The diversity analysis of intestinal flora showed that compared with the control group, the FPIP group had a lower Shannon index for diversity (P>0.05) and a significantly higher Chao index for abundance (P<0.01). At the phylum level, the intestinal flora in both groups were composed of Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes. Compared with the control group, the FPIP group had a significant reduction in the composition ratio of Actinobacteria (P<0.001) and a significant increase in the composition ratio of Proteobacteria (P<0.05). At the genus level, the intestinal flora in the FPIP group were mainly composed of Escherichia, Clostridium, Enterococcus, Klebsiella, and Bifidobacterium, and the intestinal flora in the control group were mainly composed of Bifidobacterium and Streptococcus. Compared with the control group, the FPIP group had a significant reduction in the composition ratio of Bifidobacterium and Ruminococcus (P<0.05) and significant increases in the composition ratios of Clostridium and Shigella (P<0.05). CONCLUSIONS: Compared with the control group, the FPIP group has a reduction in the diversity of intestinal flora and an increase in their abundance, and there are certain differences in several bacterial genera. These results suggest that changes in the composition of intestinal flora at genus level may play an important role in the development and progression of FPIP.

Understanding the different cross-membrane transport kinetics of two charged molecules on the DOPG lipid surface with second harmonic generation and MD simulation.

A clear physical picture of the dynamic behavior of molecules on the surface of the lipid membrane is highly desired and has attracted great attention from researchers. In this study, a step forward in this direction based on previous studies was presented with second harmonic generation (SHG) and molecular dynamic (MD) simulation. Specifically, details on the orientation flipping and cross-membrane transport of two charged molecules, 4-(4-diethylaminostyry)-1-methyl-pyridinium iodide (D289) and malachite green (MG), on the surface of 2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG) lipids were presented. Firstly, the orientation flipping of the two molecules on the surface of lipids before their cross-membrane transport was confirmed by the MD simulation. Then, the concentration dependent rate of the cross membrane transport for MG/D289 was analyzed. It was found that a simplified model could satisfactorily interpret the faster cross-membrane transport of MG under higher bulk concentrations. A different concentration dependent dynamics was observed with D289 and the reason behind it was also discussed. With this investigation, the surface structures and dynamics of D289 and MG on the DOPG lipid surface were clearly presented.

Revealing the mechanisms of vesicle formation with multiple spectral methods.

The investigation of the self-assembly of amphiphilic molecules and the formation of micelles/vesicles has attracted significant attention. However, in situ and real-time methods for such studies are rare. Here, a surface-sensitive second harmonic generation (SHG) technique was applied to study the formation of vesicles in solutions of an anti-cancer drug, doxorubicin (DOX), and a generally used surfactant (sodium bis (2-ethylhexyl) sulfosuccinate, AOT). With the aid of two-photon fluorescence (TPF), Rayleigh scattering and TEM, we revealed the structural evolution of the aggregated micelles/vesicles. It was found that AOT and DOX molecules rapidly aggregated and formed micelles in the solution. The residual DOX then acted as a "glue" that induced the aggregating/growing of the micelles and the transformation from aggregates to vesicles. The existence of lipid films, which was considered as the necessary intermediate state for vesicle formation, was excluded via the SHG observations, indicating that hollow shells may be directly transformed from solid aggregated micelles in the self-assembly formation of complex vesicles. The combined spectroscopic methods were also used to investigate the formation of vesicles from a commonly used lipid (i.e., 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt, DOPG) from its stacked bilayers. The swelling, curving and sealing of the DOPG bilayers for vesicle formation was monitored and clear dynamics were revealed. This work shows that the vesicle formation mechanism varies with the initial state of the surfactant/lipid molecules. It not only demonstrates the capability of the combined spectroscopic methods in investigating the aggregated systems but also provides new insight for understanding the formation of vesicles.

Evaluating the cross-membrane dynamics of a charged molecule on lipid films with different surface curvature.

Does the curvature of a phospholipid membrane influence the permeability of the lipid bilayers? This is a question of great importance yet hard to answer. In this work the permeability of a positively charged rod like probing molecule (D289 dye) on the bilayers of DOPG lipid vesicles was investigated using angle resolved second harmonic generation method. It was revealed that the permeability of D289 on the surface of small vesicles with âˆ¼ 100 nm diameter was notably lower than that on giant vesicles with âˆ¼ 1000 nm diameter. With the increasing of temperature or the introducing of dimethyl sulfoxide (DMSO) in the solutions, the D289 permeability of the lipid bilayers was notably enhanced as expected, on both the small and the giant vesicles. Still, the D289 permeability of the lipid film with more curvature is lower than the relatively flat film in all these cases. This work demonstrated a general protocol for the investigating of surface permeability of lipid films with various curvature.

Photocatalytic redox on the surface of colloidal silver nanoparticles revealed by second harmonic generation and two-photon luminescence.

The redox of silver on the surface of Ag nanoparticles (AgNPs) has received extensive attention because of its significant impact on the biological, physical and chemical properties of AgNPs and their applications. Here we demonstrate that the surface redox reaction of AgNPs in colloids may be investigated by the second harmonic generation (SHG) and two-photon luminescence (TPL) emission from the AgNPs. It was revealed that the oxidation of silver on the surface of AgNPs was accelerated upon femtosecond laser excitation, accompanied by a decrease in the SHG and TPL emissions from the AgNPs. The photon-induced reduction of oxidized silver on AgNPs and the formation of surface defects were also revealed by the changes in the SHG and TPL emissions. Size and morphology changes have not been detected by dynamic light scattering and TEM measurements. The changes in the UV-vis extinction spectra were also very weak compared with previous reports. However, the occurrence of redox reactions on the Ag surface upon femtosecond laser irradiation has been confirmed by multiple control experiments. This work demonstrates that SHG and TPL can sensitively probe the subtle structural change on the surface of AgNPs.

Drastically modulating the structure, fluorescence, and functionality of doxorubicin in lipid membrane by interfacial density control.

In this work, we report on the observation of a drastic modulation of the fluorescence emission of an anticancer drug, doxorubicin, at the lipid interface during the variation of its molecular density at the interface. The emission efficiency of doxorubicin in the lipid membrane was modulated in the range of less than 10% to above 300% that in the aqueous solution. The corresponding changes in the structure and functionality of doxorubicin on the lipid surface were analyzed with the aid of second harmonic generation and theoretical calculation. It was observed that doxorubicin molecules aggregated on the lipid membrane at a relatively high interfacial density. However, this aggregation may not cause interfacial domain large enough to alter the permeability of the lipid bilayer. At an even higher doxorubicin density, the domain of the aggregated doxorubicin molecules induced a cross-membrane transportation.

Surface curvature-dependent adsorption and aggregation of fluorescein isothiocyanate on gold nanoparticles.

The interaction between metallic nanoparticles and fluorescent molecules and its influence on the optical properties of the particles/molecules have been intensively investigated because of their biology and sensing applications. Here, we studied the adsorption and aggregation of a commonly used dye, fluorescein isothiocyanate (FITC), on gold nanoparticles of various diameters. It was observed that the adsorption of FITC on relatively large gold nanoparticles (≥15 nm in diameter) induced quenching in the two-photon fluorescence (TPF) emission from the FITC molecules, while smaller-sized gold nanoparticles (1.6 nm) had no such effect. This difference was interpreted by the fluorescence resonance energy transfer (FRET) between the FITC molecules and the larger gold nanoparticles. At the same time, it was observed that the ratio of TPF quenching was notably higher than the ratio of the FITC molecules chemically adsorbed on the large gold particles. This unexpected observation revealed that the aggregation-induced fluorescence quenching also contributed significantly to the attenuation of the TPF emission. Time-dependent TPF attenuation during the interaction of FITC and the larger gold nanoparticles was recorded and used to confirm this interpretation. With this experimental evidence, a clear picture of the interaction of the FITC molecules on the gold surface was presented: FITC molecules chemically adsorbed on the small gold nanoparticles. However, the relatively larger surface curvature hindered the aggregation of the FITC molecules on the small gold nanoparticles. On the surface of the larger gold nanoparticles, both adsorption and aggregation occured. The influence of the surface curvature on the interfacial structure of the adsorbed molecules on nanoparticles was discussed.

Particle adsorption at the oil-water interface studied with second harmonic generation.

In this work, energetics of the adsorption of polystyrene nanoparticles at the hexadecane-water interface was studied with second harmonic generation. The adsorption of positively and negatively charged nanoparticles at the oil-water interface induced a decrease and an increase in the SHG emission from the interface, respectively. This change in the SHG emission, which is similar to that upon the adsorption of ionic surfactants at the hexadecane-water interface, which we reported previously, was then used as an indicator of particle adsorption at the interface. The adsorption free energies of the particles with a diameter of 20 nm at the hexadecane-water interface were found to be -14.7 ± 0.5 kcal mol-1, -14.4 ± 0.4 kcal mol-1 and -15.1 ± 0.3 kcal mol-1 for the amidine, carboxyl and sulfate latex beads, respectively. This result implied that the van der Waals interaction between the oil phase and the polystyrene particles is capable of driving negatively charged particles to the negatively charged hexadecane-water interface. The principle of like dissolves like played a major role in the adsorption of polystyrene particles from the aqueous phase to the oil-water interface. The origin of the SHG emission from the oil-water interface was also discussed.