UV-resonant magnetoplasmonic properties of chemically synthesized indium nanoparticles.

In this article, we for the first time demonstrate magnetoplasmonic properties of metallic indium (In0) nanoparticles, one of the promising non-noble metals for UV plasmonics, by using magnetic circular dichroism (MCD) spectroscopy. In0 nanoparticles are synthesized by a kinetically controlled reduction of indium salts, followed by performing centrifugation-based size selection, giving nanoparticles of 37.5 ± 9.7 or 51.6 ± 8.4 nm in diameter. These In0 nanoparticles exhibit a single extinction peak in the UV region (<300 nm), which can be attributed to localised surface plasmon resonance (LSPR), and upon increasing the particle size, the peak is red-shifted and broadened. The MCD signatures are then typical for circular magnetoplasmonic modes of metal nanospheres, and on the basis of the MCD responses, the effective mass of an electron (m*) of indium is estimated. Interestingly, although the large-sized In0 nanoparticles (51.6 nm) have a broader LSPR linewidth, the magneto-optical (MO) activity is larger than that of the smaller one (37.5 nm), which is unlike the behaviour of Ag nanospheres with high-quality-factor plasmonic performance. This can probably be due not only to the formation of stiff semiconducting (In(OH)3) shell layers on the In0 cores (= In0@In(OH)3 core-shell morphology) but also to the effect of the dielectric function of In0 that can influence the light-helicity-dependent field-induced cyclotron shift.

Mixed-ligand strategy for synthesizing water-soluble chiral gold clusters with phosphine ligands.

Water-soluble chiral metal clusters have drawn much attention by virtue of their fascinating physicochemical properties and potential biomedical applications, but currently, phosphine-protected Au clusters with both chirality and water-solubility are still very limited. In this article, we demonstrate a mixed-ligand strategy for the facile synthesis of atomically precise, water-soluble chiral Au clusters protected by phosphine alone. The clusters are obtained by the reduction of aurate ions in the presence of a phosphine mixture consisting of highly hydrophilic monophosphine (i.e., triphenylphosphine trisulfonate; TPPTS) and hydrophobic chiral diphosphine (i.e., S-Segphos or S-BINAP), both of which are commercially available. The clusters are size/composition-separated via gel electrophoresis, and notably, heptanuclear cluster Au7(S-Segphos)3(TPPTS)2 exhibits a large chiroptical activity with the maximum anisotropy factor (g-factor) of 4.7 × 10-3, one of the largest values in such Au clusters. Quantum chemical calculations for model Au7 cluster species suggest two important factors to obtain large chiroptical activity: (i) more than two axially-chiral diphosphine ligands, and (ii) the absence of configurational isomer averaging. Consequently, despite the experimental use of a mixture containing both chiral and achiral phosphines, a large chiroptical activity can be created in Au clusters with high water-solubility.

Mixed-diphosphine-protected chiral undecagold clusters Au11(S,S-DIOP)4(rac-/R-/S-BINAP): effect of the handedness of BINAP on their chiroptical responses.

In this article, we report a preference of homochiral-type ligation of BINAP that produces SS-type ligand assembly onto the Au11 clusters protected by diphosphine S,S-DIOP. The Au11 clusters synthesized and isolated are Au11(S,S-DIOP)4(rac-/R-/S-BINAP), and their optical/chiroptical responses are characterized. Absorption spectra of these Au11 clusters are almost identical to each other, but their CD profiles are dependent on the handedness of BINAP. In Au11(S,S-DIOP)4(rac-BINAP), the yield of S-BINAP or R-BINAP coordination is roughly comparable, but we found a small but distinctive preference in the S-BINAP ligation; that is, homochiral-type (SS-type) ligand assembly formation. Quantum chemical calculations for simplified model clusters suggest equal contributions of S- and R-form BINAP coordination. The experimentally-observed preference of homochiral-type ligation can then be due to that of the whole ligand structures and assemblies involving interligand interactions. Chiral sorting and amplification processes through the assembly control of homochirality or heterochirality are of primary importance for the development of enantioselective reactions, so we anticipate this finding will contribute to further understanding of such processes based on various metal clusters with chiral ligands.

Strong chiroptical activity in Au25 clusters protected by mixed ligands of chiral phosphine and achiral thiolate.

We report the successful synthesis of a chiroptically active Au25 cluster protected by mixed ligands of chiral bidentate S-BINAP and achiral dodecanethiol (DDT), which can be formulated as [Au25(S-BINAP)4(DDT)5X4] (X = Cl or Br). The UV-vis absorption spectral pattern is similar to that of the well-known bi-icosahedral cluster [Au25(PPh3)10(SR)5X2]2+, so the obtained cluster should also have a similar bi-icosahedral structure assembled from two vertex-sharing icosahedral Au13 units. With a closer inspection of the optical absorption, interestingly, the lowest-energy peak is red-shifted as compared to that of [Au25(PPh3)10(SR)5X2]2+. Quantum chemical calculations for model bi-icosahedral Au25 structures suggest the reason of the red shift. On the other hand, the obtained Au25 cluster exhibits a weak CD signature in the lowest-energy transition region, whereas higher-energy transitions have very large chiroptical responses with a maximum g-factor of 1.7 × 10-3. The calculations also give implications for the origin of the CD response in the Au25 cluster. We then believe that bi-icosahedral Au25 clusters with chirality will be a good prototype for understanding the influence of constituent Au13 units on the chiroptical activity of their assembling structures.

Chirality in Au9 clusters protected by chiral/achiral mixed bidentate phosphine ligands: influence of the metal core and ligand array.

In this article, the chiroptical responses of Au9 clusters protected by chiral/achiral mixed bidentate phosphine ligands are reported. The mixed phosphine we use is (S)-BINAP/Xantphos in the molar ratio of 1/0 (= pure (S)-BINAP), 3/1, 1/1, or 0/1 (= pure Xantphos), where BINAP and Xantphos represent 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl and 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, respectively. Electronic absorption spectra of the clusters are similar between the samples with different molar diphosphine ratios, but the chiroptical activity or g-factor decreases nonlinearly with an increase in the fraction of Xantphos. Quantum chemical calculations and geometrical quantifications based on the Hausdorff chirality measure (HCM) for model Au9 cluster species suggest that (i) two types of metal core structures with pseudo-P- and M-chirality are found, and their appropriate contributions would cancel out the chiroptical response in the low-energy region; (ii) the origin of optical activity in pure (S)-BINAP-protected Au9 clusters can mainly be attributed to the metal core chirality, whereas that of other mixed-ligand protected clusters would be due to the chiral ligand arrangement. This work demonstrates that the modulation of chiroptical activity in Au9 clusters by chiral/achiral mixed-diphosphine ligation is controlled by the difference in the degree of chirality existing in the cluster core and/or the ligand array.

Parity As a Protective Biomarker Against Silent Brain Infarction in Community-Dwelling Older Adults: The Sefuri Study.

BACKGROUND: Although several studies have reported an association between parity and increased risk of stroke, this relationship remains controversial. AIMS: The present study aimed to determine whether parity is associated with silent brain infarction (SBI), independent of other confounders. METHODS: We analyzed the brain magnetic resonance imaging findings in 576 of community-dwelling older adults with a mean age of 72.1 years. All female participants were asked to provide information regarding the total number of live births, their age at the last parity, and their age at menopause. RESULTS: The prevalence of SBI and the number of infarcts per participant were higher in men than in women. Although all women who had given birth (0, 1-2, 3-4, or 5+ times) exhibited lower age-adjusted odds ratios (ORs) for SBI than men, a significant difference was observed between women with ≧5 births and men after adjustment for common vascular risk factors (OR: .348, 95% confidence interval [95% CI]: .123-.986). Among women who had given birth, the relationship between fertility and SBI was attenuated, but was enhanced after adjustment for age at the last parity (OR: .300, 95% CI: .102-.886). CONCLUSIONS: Our findings indicate that fertile women may be protected against SBI or cerebral small vessel disease via the biological effects associated with reproductive activity, and that high fertility may be a marker of protection against SBI. However, late childbearing may blunt protective effects of fertility against SBI.

Low-Grade Inflammation Is Associated with Apathy Indirectly via Deep White Matter Lesions in Community-Dwelling Older Adults: The Sefuri Study.

Low-grade inflammation is implicated in the pathogenesis of atherosclerosis, metabolic syndrome, and apathy as a form of vascular depression. We analyzed the brain magnetic resonance imaging findings in 259 community-dwelling older adults (122 men and 137 women, with a mean age of 68.4 years). The serum concentrations of high-sensitivity C-reactive protein (hsCRP) were measured by a quantitative enzyme-linked immunosorbent assay. Logistic regression analysis revealed that the log10 hsCRP value and the presence of a metabolic syndrome were independently associated with confluent but not punctate deep white matter lesions (DWMLs). Path analysis based on structural equation modeling (SEM) indicated that the direct path from the log10 hsCRP to the DWMLs was significant (ß = 0.119, p = 0.039). The direct paths from the metabolic syndrome to the log10 hsCRP and to the DWMLs were also significant. The direct path from the DWMLs to apathy (ß = -0.165, p = 0.007) was significant, but the direct path from the log10 hsCRP to apathy was not significant. Inflammation (i.e., elevated serum hsCRP levels) was associated with DWMLs independent of common vascular risk factors, while DWMLs were associated with apathy. The present analysis with SEM revealed the more realistic scheme that low-grade inflammation was associated with apathy indirectly via DWMLs in community-dwelling older adults.

Organic nanoparticles based on Lewis-pair formation: observation of prototropically controlled dual fluorescence.

We successfully synthesize fluorescent organic nanoparticles of a Lewis-pair consisting of an amino-type hydrogen-bonding molecule (Lewis base) and a borinate derivative (Lewis acid). 2-(2'-Aminophenyl)benzothiazole (o-ABT) is chosen as the fluorophore. This molecule has a transferable proton in the amino group, but it does not exhibit ESIPT (excited-state intramolecular proton transfer) reaction in solution and thus shows a single normal emission solely from the enamine form. Organic nanoparticles are prepared by the reprecipitation method in which the fluorophore (o-ABT) in conjunction with a Lewis acid (diphenylborinic anhydride; DPBA) dissolved in a good solvent is rapidly injected into water under sonication. Interestingly, the nanoparticles produced exhibit a characteristic dual fluorescence that can be ascribed to the enamine and imine tautomers of o-ABT generated in the ground-state prototropy, which can be revealed by UV-vis absorption and excitation spectroscopy, IR spectroscopy and computational approaches. In the o-ABT/DPBA Lewis-pair nanoparticles, highly Stokes-shifted emission from the imine tautomer is enhanced in comparison with that from the molecularly dissolved state, suggesting that the present nanofabrication methodology based on Lewis acid-base chemistry (or N-B bonding interaction) plays a key role in tuning the fluorescence colour for the new type of organic nanoparticle.

Size dependence of magneto-optical activity in silver nanoparticles with dimensions between 10 and 60 nm studied by MCD spectroscopy.

Size-dependent magneto-optical activity in Ag nanoparticles with dimensions from 10 to 60 nm is demonstrated with magnetic circular dichroism (MCD) spectroscopy. The Ag nanoparticles are prepared on the basis of a seeded-growth strategy using sodium citrate and/or tannic acid as reducing agents in aqueous solution. The obtained nanoparticles are roughly spherical, but those larger than ∼28 nm have a slight diversity of shapes with quasi-spherical polyhedrons. They exhibit a derivative-like MCD response in the localized surface plasmon resonance (LSPR) region, which originates from two circular modes of surface magnetoplasmons. With an increase in the nanoparticle diameter, the bisignated MCD signal is strongly distorted and weakened. Such a distortion for large-sized Ag nanoparticles can be phenomenologically simulated on the basis of both spectral inhomogeneity and MCD signal lobe asymmetry. Then the maximum value of MCD amplitude (MCDmax), which is obtained by normalization of the amplitude to the LSPR peak absorbance, first increases with increasing particle diameter and then decreases with a maximum for the 23 nm nanoparticle. Interestingly, the MCDmax values are inversely correlated with the spectral bandwidth of LSPR extinction. This behaviour is discussed from a viewpoint of inhomogeneous effects of both spectral and size/shape distributions. We believe the present results will advance the design and application of optical devices based on magnetoplasmonics.

Plasmonic optical trapping of nanometer-sized J- /H- dye aggregates as explored by fluorescence microspectroscopy.

In the present study, we explored plasmonic optical trapping (POT) of nanometer-sized organic crystals, carbocyanine dye aggregates (JC-1). JC-1 dye forms both J- and H- aggregates in aqueous solution. POT behavior was analyzed using fluorescence microspectroscopy. POT of JC-1 aggregates was realized in an increase in their fluorescence intensity from the focus area upon plasmon excitation. Repeating on-and-off plasmonic excitation resulted in POT of JC-1 aggregates in a trap-and-release mode. Such POT of nanometer-sized dye aggregates lying in a Rayleigh scattering regime (< 100 nm) is important toward molecular manipulation. Furthermore, interestingly, we found that the J-aggregates were preferentially trapped than H-aggregates. It possibly indicates semi-selective optical trapping of nanoparticles on the basis of molecular alignments.

Organic Ion-Pair Charge-Transfer (IPCT) Nanoparticles: Synthesis and Photoinduced Electrochromism.

We report fabrication of photoinduced-electrochromic (or photochromic) organic nanoparticles that can be regarded as a new class of photoswitchable nanomaterials. Ion association between dicationic benzyl viologen (BzV2+) and tetraphenylborate anion (TPB-) in water produces organic ion-pair charge-transfer-type (IPCT) nanoparticles with a mean diameter of 15-20 nm. Electrostatic binding of BzV2+ with TPB- results in the prominent appearance of a new broad absorption band at 400-550 nm, which can be assign to the CT transition between these species. The IPCT nanoparticles show an interesting photoinduced electrochromic behavior caused by the electron transfer (ET) from TPB- to BzV2+, giving an intense blue-color dispersion. The feed charge stoichiometry (= [TPB-]/(2 × [BzV2+])) does not influence the kinetics of the photoinduced electrochromism, but it remarkably controls the reverse ET reaction (or retention time) in the nanoparticles; in the case of neutral stoichiometry, a very long-lived ET state can be observed, which is mainly due to decomposition of the oxidized TPB (sacrificial donor) and the resultant absence of the counterpart of benzyl viologen radical cations (BzV+•) for back ET reaction. On the other hand, the excess presence of TPB- does not cause the decomposition of oxidized TPB in the nanoparticle, making the reverse ET reaction faster, but a moderately long-lived ET state is still observable, which is probably originated from efficient electron diffusion or transport between molecules inside the nanoparticle.

NADPH Oxidase-Related Pathophysiology in Experimental Models of Stroke.

Several experimental studies have indicated that nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox) exert detrimental effects on ischemic brain tissue; Nox-knockout mice generally exhibit resistance to damage due to experimental stroke following middle cerebral artery occlusion (MCAO). Furthermore, our previous MCAO study indicated that infarct size and blood-brain barrier breakdown are enhanced in mice with pericyte-specific overexpression of Nox4, relative to levels observed in controls. However, it remains unclear whether Nox affects the stroke outcome directly by increasing oxidative stress at the site of ischemia, or indirectly by modifying physiological variables such as blood pressure or cerebral blood flow (CBF). Because of technical problems in the measurement of physiological variables and CBF, it is often difficult to address this issue in mouse models due to their small body size; in our previous study, we examined the effects of Nox activity on focal ischemic injury in a novel congenic rat strain: stroke-prone spontaneously hypertensive rats with loss-of-function in Nox. In this review, we summarize the current literature regarding the role of Nox in focal ischemic injury and discuss critical issues that should be considered when investigating Nox-related pathophysiology in animal models of stroke.

Chronic Kidney Disease and Subclinical Brain Infarction Increase the Risk of Vascular Cognitive Impairment: The Sefuri Study.

BACKGROUND AND PURPOSE: The purpose of this study was to determine the complex associations among chronic kidney disease (CKD), subclinical brain infarction (SBI), and cognitive impairment. METHODS: We used structural equation modeling (SEM) to examine the complex relationships among CKD, SBI, and cognitive function with Mini-Mental State Examination (MMSE; global function) and modified Stroop test (executive function) in a population-based cohort of 560 non-demented elderly subjects. RESULTS: Path analysis based on SEM revealed that the direct paths from estimated glomerular filtration rate (eGFR) to SBI and from SBI to executive function were significant (ß = -.10, P = .027, and ß = .16, P < .001, respectively). Furthermore, the direct path from eGFR to executive function was also significant (ß = -.12, P = .006), indicating that the effects of CKD on executive function are independent of SBI. The direct paths from age and education to global cognitive function were highly significant (ß = -.17 and .22, respectively, P < .001), whereas the direct path from eGFR to MMSE was not significant. CONCLUSIONS: Our findings indicate that CKD confers a risk of vascular cognitive impairment or executive dysfunction through mechanisms dependent and independent of SBI. Treating CKD may be a potential strategy to protect against vascular cognitive impairment or executive dysfunction in healthy elderly subjects.

Water-Soluble Phosphine-Protected Au11 Clusters: Synthesis, Electronic Structure, and Chiral Phase Transfer in a Synergistic Fashion.

Synthesis of atomically precise, water-soluble phosphine-protected gold clusters is still currently limited probably due to a stability issue. We here present the synthesis, magic-number isolation, and exploration of the electronic structures as well as the asymmetric conversion of triphenylphosphine monosulfonate (TPPS)-protected gold clusters. Electrospray ionization mass spectrometry and elemental analysis result in the primary formation of Au11(TPPS)9Cl undecagold cluster compound. Magnetic circular dichroism (MCD) spectroscopy clarifies that extremely weak transitions are present in the low-energy region unresolved in the UV-vis absorption, which can be due to the Faraday B-terms based on the magnetically allowed transitions in the cluster. Asymmetric conversion without changing the nuclearity is remarkable by the chiral phase transfer in a synergistic fashion, which yields a rather small anisotropy factor (g-factor) of at most (2.5-7.0) × 10(-5). Quantum chemical calculations for model undecagold cluster compounds are then used to evaluate the optical and chiroptical responses induced by the chiral phase transfer. On this basis, we find that the Au core distortion is ignorable, and the chiral ion-pairing causes a slight increase in the CD response of the Au11 cluster.

Organic nanoparticles of malachite green with enhanced far-red emission: size-dependence of particle rigidity.

In tracing the biological processes using fluorescent probes, it is desirable to shift the excitation/emission energy to a far-red/near-infrared (FR/NIR) region. In this study, we successfully synthesize FR fluorescent organic nanoparticles via ion-association between the malachite green (MG) cations and tetrakis(4-fluorophenyl)borate (TFPB) anions in the presence of a neutral stabilizing polymer. Binding of MG with TFPB results in the prominent appearance of an absorption band that can be assigned to an H-aggregate of MG. The fluorescence intensity as well as the fluorescence lifetime shows a significant increase with a decrease in the nanoparticle size. Since the MG dye is known as a local viscosity or environmental rigidity probe showing a rotational friction dependence of the excited state lifetime, we find that the rigidity of the organic nanoparticle is strongly size-dependent; that is, the smaller the size of the nanoparticle, the greater the rigidity of the nanoparticle. We also reveal that surface regions of the ion-based organic nanoparticles are more rigid than inner regions. The presence of H-aggregates that are almost non-fluorescent is the major origin of aggregation-caused quenching (ACQ) and still avoids the enhancement of the fluorescence quantum yield of the MG nanoparticles, so we develop a new approach to prevent H-aggregation inside the nanoparticle by incorporating photochemically inert, bulky phosphonium cations, which results in a 430-fold enhancement of its fluorescence yield. We believe that such a methodology will open up an avenue in the development of new types of fluorescent nanomaterials for many applications.

Leisure-Time Physical Inactivity Associated with Vascular Depression or Apathy in Community-Dwelling Elderly Subjects: The Sefuri Study.

BACKGROUND: Although physical inactivity is a major public health problem, the causative factors for physical inactivity per se are poorly understood. To address this issue, we investigated the relationship between deep white matter lesions (DWMLs) on magnetic resonance imaging, apathy, and physical activities using structural equation modeling (SEM). METHODS: We examined 317 community-dwelling elderly subjects (137 men and 180 women with a mean age of 64.5 years) without dementia or clinically apparent depression. Physical activity was assessed with a questionnaire consisting of 3 components (leisure-time, work, and sport activities). RESULTS: The mean score from the apathy scale (a visual analogue version of Starkstein's apathy scale) of the Grades 2-3 DWML group was 420 (95% confidence interval [CI] 379-461), which was lower (more apathetic) than the Grade 0 DWML group score of 478 (95% CI 463-492) after adjustment for education as a covariate. SEM showed that the direct paths from DWMLs or education to apathy were significant, and the direct path from apathy to leisure-time activity was highly significant (ß = .25, P < .001). The degree of apathetic behavior was negatively associated with sport activity in female subjects and positively associated with TV watching in male subjects. CONCLUSIONS: The results of the study show that DWMLs are one of the major factors that cause apathetic behavior and that apathy has significant negative effects on leisure-time physical activity in community-dwelling elderly subjects. Even a minor level of apathy without major depression would have a significant impact on activities of daily living and quality of life.

Early menopause and the risk of silent brain infarction in community-dwelling elderly subjects: the Sefuri brain MRI study.

Our previous study showed that the male predominance of silent brain infarction (SBI) was largely because of higher prevalence of alcohol habit and smoking in men than in women. In the present study, we further conducted an analysis of brain magnetic resonance imaging findings to examine whether early menopause contributes to SBI in community-dwelling subjects. Women were queried as to the age and cause of menopause, the total number of children, and the age at giving birth to her last child. Among 306 female subjects aged 60 years or older, univariate analysis showed that early menopause (total or natural) was significantly associated with SBI but age at natural menopause, number of children, and age at the last parity were not. In the total of 715 subjects (283 men and 432 women with a mean age of 67.2 years), the forward stepwise method of logistic analysis revealed that natural early menopause (odds ratio [OR] 4.28, 95% confidence interval [CI] 1.07-17.11), in addition to age, hypertension, alcohol intake, and smoking, was a significant factor concerning SBI. Also in the subgroup of female subjects aged 60 years or older, natural early menopause was a significant factor concerning SBI (OR 4.35, 95% CI 1.05-18.08) adjusted for covariates. Although the prevalence of natural early menopause was low (3.3% of 306 female subjects), natural menopause before the age of 40 years may be a risk for SBI or small-vessel disease of the brain.

Dual task walking reveals cognitive dysfunction in community-dwelling elderly subjects: the Sefuri brain MRI study.

The aim of our study was to investigate the effects of subclinical brain lesions and cognitive function on gait performance with or without concurrent cognitive task in community-dwelling elderly subjects. Participants without dementia (92 men and 109 women with a mean age of 67.8 years) underwent brain magnetic resonance imaging, neuropsychologic tests, and gait measurements. Impaired gait velocity of the Timed Up and Go test was associated with deep white matter lesions (odds ratio [OR], 2.338; 95% confidence interval [CI], 1.120-4.880) and diabetes mellitus (OR, 2.725; 95% CI, 1.120-6.630) after adjusted for age, sex, education, and cognitive function tests. Impaired gait velocity of dual task walking was associated with age and the score of Rivermead Behavioral Memory Test (OR, .899/1 point higher; 95% CI, .813-.994), whereas deep white matter lesions were not significantly associated with dual task walking. The present study showed that gait represents not only physical functioning but also subclinical cognitive dysfunction particularly memory impairment in healthy elderly subjects.

Emergence of large chiroptical responses by ligand exchange cross-linking of monolayer-protected gold clusters with chiral dithiol.

We here present a study of cross-linking chemistry of optically inactive monothiol-protected gold clusters by chiral bidentate dithiol with two stereogenic centers, (2R,3R)-1,4-dimercapto-2,3-butanediol (L-dithiothreitol; L-DTT), and explore the impacts of the cross-linking on their chiroptical responses. The pristine protective ligand is racemic penicillamine (rac-Pen), and the products of the ligand exchange reactions include clusters containing both rac-Pen and L-DTT (partial exchange). Electrophoresis using polyacrylamide gel with a very low gel concentration (3%) can make the products separable into two components, each of which has the similar mean core diameter of 0.78 and 0.83 nm, so the difference in the relative mobility is mainly ascribed to the size of the cluster assembly. In addition, very large optical activity with the maximum anisotropy factors of about 1.0 × 10(-3) is found for the assemblies. In comparison with chiral 1,3-dithiol protection incapable of cross-linking between gold clusters, we propose that the observed optical activity is due to surface intrinsic handedness caused by a cyclic cross-linking with at least two L-DTT molecules.

Water-Soluble Chiral Ag29 Clusters Protected by Monothiol N-Acetyl-(S)-penicillamine Synthesized in One Pot.

Despite significant advances in atomically precise Au clusters with chirality, Ag clusters with the relevant features are still less explored. In this study, we report successful synthesis of chiral Ag29 clusters protected by water-soluble monothiol in one pot, which is carried out by reducing Ag ions in the presence of N-acetyl-(S)-penicillamine (S-NAP) and triphenylphosphine (TPP) at 10 °C, yielding the Ag29(S-NAP)24 cluster. The obtained cluster is isolable as a solid-state powder. Optical absorption of Ag29(S-NAP)24 is almost identical with that of Ag29(R-DHLA)12, where DHLA denotes α-dihydrolipoic acid, and magnetic circular dichroism (MCD) results support the similarity of their electronic structures. The anisotropy factor of Ag29(S-NAP)24 is comparable to or larger than that of Ag29(R-DHLA)12, suggesting that the surface shell structure of Ag29(S-NAP)24 is inherently chiral, as has been observed for Ag29(R-DHLA)12. Then the use of enantiopure NAP would preferentially lead to a one-handed atomic arrangement in the clusters.